domain: chim.othe chim sde

text:
Clément Lozano

Justina Givens

Didier Stien

Sabine Matallana-Surget

Philippe Lebaron

Bioaccumulation and toxicological effects of UV-filters on marine species

Keywords:

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

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 Table 1.
Introduction

UV-filters are recent anthropogenic pollutants encountered in the marine environment. Several studies have reported their occurrence in diverse ecosystems (Rainieri et al. 2016). Marine biota has not dealt with these compounds in their evolutionary life history. Therefore, questions have been raised as to how aquatic organisms are coping with emerging contaminants such as sunscreens. In the last decade, research has been carried out and received some attention. Benzophenone-3 (BP3) and ethylexyl methoxycinnamate (EMC), also known as oxybenzone and octinoxate, respectively, have been banned in Hawaii and Key West, Florida because of their detrimental effects to coral [START_REF] Downs | Toxicopathological Effects of the Sunscreen UV Filter, Oxybenzone (Benzophenone-3), on Coral Planulae and Cultured Primary Cells and Its Environmental Contamination in Hawaii and the U.S. Virgin Islands[END_REF] among other marine organisms [START_REF] Paredes | Ecotoxicological evaluation of four UV filters using marine organisms from different trophic levels Isochrysis galbana, Mytilus galloprovincialis, Paracentrotus lividus, and Siriella armata[END_REF]. The Republic of Palau and U.S Virgin Islands have also banned these two UV-filters, but they also included octocrylene (OC).

Species richness is higher in the shallow seas compared to below 100m [START_REF] Costello | Marine Biodiversity , Biogeography , Deep-Sea Gradients , and Conservation[END_REF] and species in the coastal waters are subjected to anthropogenic impacts to a greater degree.

Coastal waters allow for different ecosystems that support a wide variety of biodiversity. The shallow waters allow for thriving flora which provide shelter for different species and nursery grounds for juveniles, allowing fish populations to increase in yield. This natural wealth helps the economy that being tourism and fisheries, that are prolific sectors important for the socio-economic health. For these reasons, it is essential to explore the impact of emerging contaminants on marine biota. This chapter will review the toxicity of both organic and inorganic UV-filters and their bioaccumulation on marine species. Critical analysis and scientific trends are presented as well as the main challenges and needs related to ecotoxicological studies.

Current trends of UV-filters

The first paper to report on the toxicity of sunscreen agents with reference to marine life was [START_REF] Danovaro | Sunscreen products increase virus production through prophage induction in marine bacterioplankton[END_REF] They observed an increase in viral abundance with the addition of sunscreen that altered the ratio between the viral phage and the marine bacterial host. No papers were published following this in terms of sunscreens until Danovaro and colleagues published another paper in 2008 showing that changes in the viral:bacterial ratio due to the presence of sunscreen, induced coral bleaching. The authors included three brands of sunscreen and tested single molecules to target the cause.

Studies on mineral UV-filters, especially nanoparticles, are heavily weighted in terms of effort compared to the organic UV-filters. As mineral UV-filters can be found in a variety of manufactured products, some researchers did not focus on sunscreen components per se. Although the toxicity of ZnO nanoparticles dedicated for industrial or cosmetic use has been shown to be similar [START_REF] Spisni | Release and toxicity comparison between industrial-and sunscreen-derived nano-ZnO particles[END_REF]. Therefore, any studies found with ZnO or TiO 2 mineral UV-filters were included in this review.

Nanoparticle research for mineral UV-filters began to gain traction in 2011, whilst organic UV-filters were just being explored (Figure 1). There is an unbalance regarding the choice of UV-filter that has been examined in the literature. There are 60 UV-filters that are permitted in sunscreens worldwide [START_REF] Pirotta | The encyclopedia of allowed sunfilters in the world[END_REF] yet only 15 appear in literature regarding the toxicity on marine biota. Furthermore, only nine of them appear in more than one paper with BP3 and nanoparticles dominating (Figure 2). Homosalate (HS) is not examined as single molecule, yet it is commonly found in sunscreens.

The same pattern is also observed for in vivo bioaccumulation studies with more studies performed on mineral nanoparticles and an underrepresented range of organic UV-filters. However, mineral UVfilters have not been targeted for in situ bioaccumulation studies, which calls attention to a gap in the research. Perhaps this is because minerals such as zinc oxide (ZnO) and titanium dioxide (TiO 2 ) are naturally occurring which presents a difficulty to distinguish between natural and manufactured occurring levels [START_REF] Montaño | Current status and future direction for examining engineered nanoparticles in natural systems[END_REF]. The analytical methods for these minerals require more effort to identify and quantify.

This review shows that there is a preference on the model, that being algae and coral. Marine fish have not been well represented in the toxicity studies except in recent papers that saw the use of clownfish [START_REF] Barone | Acute toxicity testing of TiO 2 -based vs. oxybenzone-based sunscreens on clownfish (Amphiprion ocellaris)[END_REF], gilt-head bream (Ziarrusta et al. 2018), sole flatfish [START_REF] Araújo | Effects of UV filter 4-methylbenzylidene camphor during early development of Solea senegalensis Kaup, 1858[END_REF] and medaka [START_REF] Cong | The embryotoxicity of ZnO nanoparticles to marine medaka, Oryzias melastigma[END_REF] as models (Figure 2). The impacts on marine bacteria are often overlooked yet they are a major contributor to the oceans total biomass [START_REF] Bar-On | The biomass distribution on Earth[END_REF]. They are also key players in nutrient cycling and important symbionts to larger species. Zooplankton were examined by a few papers but mostly using the brine shrimp as a model [START_REF] Ates | Comparative evaluation of impact of Zn and ZnO nanoparticles on brine shrimp (Artemia salina) larvae: Effects of particle size and solubility on toxicity[END_REF][START_REF] Bhuvaneshwari | Toxicity and trophic transfer of P25 TiO 2 NPs from Dunaliella salina to Artemia salina : Effect of dietary and waterborne exposure[END_REF][START_REF] Clemente | Minimal levels of ultraviolet light enhance the toxicity of TiO 2 nanoparticles to two representative organisms of aquatic systems[END_REF][START_REF] Li | Comparative toxicity of nano ZnO and bulk ZnO towards marine algae Tetraselmis suecica and Phaeodactylum tricornutum[END_REF][START_REF] Lu | TiO 2 nanoparticles in the marine environment : Impact on the toxicity of phenanthrene and Cd 2+ to marine zooplankton Artemia salina ☆[END_REF][START_REF] Miglietta | Characterization of Nanoparticles in Seawater for Toxicity Assessment Towards Aquatic Organisms[END_REF]). These pelagic suspension feeders are also exposed to contaminants as they sieve through the water column collecting food. As the seafloor is the "sink" for contaminants, it is surprising that only two papers to date examined the effects of contaminated sediments for UV-filters; ZnO on the ragworm, the peppery furrow shell [START_REF] Buffet | Fate of isotopically labeled zinc oxide nanoparticles in sediment and effects on two endobenthic species, the clam Scrobicularia plana and the ragworm Hediste diversicolor[END_REF] and TiO 2 on the lugworm [START_REF] Galloway | Sublethal toxicity of nano-titanium dioxide and carbon nanotubes in a sediment dwelling marine polychaete[END_REF].

Figure 2. Number of marine species and their feeding mode for each UV-filter examined to date.

Abbreviations: 4-MBC, 4-Methylbenzylidene camphor; BM, Butyl methoxydibenzoylmethane; BP1, Benzophenone-1; BP2, Benzophenone-2; BP3, Benzophenone-3; BP4, Benzophenone-4; BP8, Benzophenone-8; DT, Drometrizole trisiloxane; TDSA, Terephtalidene dicamphor sulfonic acid ; EMC, Ethylhexyl methoxycinnamate; ET, Ethylhexyl triazone; OC, Octocrylene; OD-PABA, Ethylhexyl dimethyl PABA.

There have been 350 published papers on the ingestion of plastics to marine fauna in 2015 and it continues to escalate [START_REF] Provencher | Quantifying ingested debris in marine megafauna: A review and recommendations for standardization[END_REF]. Comparatively, there have only been 20 published papers for in situ bioaccumulation of organic UV-filters to date. This may highlight that there is a greater concern regarding marine plastics but also that we are at the beginning stages of understanding sunscreens as an emerging pollutant. UV-filter's presence in marine biota has been detected across the globe but there are still uncertainties for many waters (Figure 3). The next step is to address if UV-filters are true persistent organic pollutants. It was only after the longterm use of DDT (dichlorodiphenyltrichloroethane) that the true environmental impacts were detected, and a worldwide ban was actioned by the Stockholm Convention on persistent organic pollutants. To understand the future impacts of UV-filters, the following should be explored more thorough; biomonitoring focused on marine megafauna, in vivo testing, examining the contaminations passed on through generations and chronic toxicity assessments.

Toxicity of sunscreens

Common endpoints that were used to measure the toxicity effects of UV-filters were observed in this literature review. Oxidative stress causes free radicals resulting in damage to the cell by reactive oxygen species (ROS) and other reactive intermediates. This was mostly measured by assessing antioxidative enzymes, which is a common endpoint for mussels [START_REF] Barmo | In vivo effects of n-TiO 2 on digestive gland and immune function of the marine bivalve Mytilus galloprovincialis[END_REF][START_REF] Ciacci | Immunomodulation by Different Types of N-Oxides in the Hemocytes of the Marine Bivalve Mytilus galloprovincialis[END_REF][START_REF] D'agata | Enhanced toxicity of "bulk" titanium dioxide compared to "fresh" and "aged" nano-TiO 2 in marine mussels (Mytilus galloprovincialis)[END_REF][START_REF] Giraldo | Ecotoxicological Evaluation of the UV Filters Ethylhexyl Dimethyl p-Aminobenzoic Acid and Octocrylene Using Marine Organisms Isochrysis galbana, Mytilus galloprovincialis and Paracentrotus lividus[END_REF][START_REF] Hanna | Impact of Engineered Zinc Oxide Nanoparticles on the Individual Performance of Mytilus galloprovincialis[END_REF][START_REF] Huang | Hemocyte responses of the thick shell mussel Mytilus coruscus exposed to nano-TiO 2 and seawater acidification[END_REF][START_REF] Libralato | Embryotoxicity of TiO 2 nanoparticles to Mytilus galloprovincialis ( Lmk )[END_REF][START_REF] Wang | Significance of physicochemical and uptake kinetics in controlling the toxicity of metallic nanomaterials to aquatic organisms *[END_REF] and algae (M. [START_REF] Bhuvaneshwari | Toxicity and trophic transfer of P25 TiO 2 NPs from Dunaliella salina to Artemia salina : Effect of dietary and waterborne exposure[END_REF][START_REF] Giraldo | Ecotoxicological Evaluation of the UV Filters Ethylhexyl Dimethyl p-Aminobenzoic Acid and Octocrylene Using Marine Organisms Isochrysis galbana, Mytilus galloprovincialis and Paracentrotus lividus[END_REF][START_REF] Miller | TiO 2 nanoparticles are phototoxic to marine phytoplankton[END_REF][START_REF] Paredes | Ecotoxicological evaluation of four UV filters using marine organisms from different trophic levels Isochrysis galbana, Mytilus galloprovincialis, Paracentrotus lividus, and Siriella armata[END_REF]M. Sendra et al. 2017;[START_REF] Seoane | Flow cytometric assay to assess short-term effects of personal care products on the marine microalga Tetraselmis suecica[END_REF][START_REF] Thiagarajan | Chemosphere Diminishing bioavailability and toxicity of P25 TiO 2 NPs during continuous exposure to marine algae Chlorella sp[END_REF][START_REF] Wong | Temperature-dependent toxicities of nano zinc oxide to marine diatom, amphipod and fish in relation to its aggregation size and ion dissolution[END_REF][START_REF] Xia | Interaction of TiO 2 nanoparticles with the marine microalga Nitzschia closterium : Growth inhibition , oxidative stress and internalization[END_REF]. Growth inhibition was also a repetitive parameter for mineral UVfilters that was applied to different organisms such as bacteria, amphipods, bivalves but mostly for algae [START_REF] Deng | Biological effects of TiO 2 and CeO 2 nanoparticles on the growth, photosynthetic activity, and cellular components of a marine diatom Phaeodactylum tricornutum[END_REF][START_REF] Fabrega | Sequestration of Zinc from Zinc Oxide Nanoparticles and Life Cycle Effects in the Sediment Dweller Amphipod Corophium volutator[END_REF][START_REF] Li | Comparative toxicity of nano ZnO and bulk ZnO towards marine algae Tetraselmis suecica and Phaeodactylum tricornutum[END_REF]Manzo et al. 2013(a); Sendra et al. 2017;Wang et al. 2016;[START_REF] Xia | Interaction of TiO 2 nanoparticles with the marine microalga Nitzschia closterium : Growth inhibition , oxidative stress and internalization[END_REF]. Crustaceans saw mortality as a common endpoint [START_REF] Paredes | Ecotoxicological evaluation of four UV filters using marine organisms from different trophic levels Isochrysis galbana, Mytilus galloprovincialis, Paracentrotus lividus, and Siriella armata[END_REF][START_REF] Wong | Toxicities of nano zinc oxide to five marine organisms : influences of aggregate size and ion solubility[END_REF]Wong and Leung, 2013) and corals saw endpoints such as bleaching, polyp retraction, mortality [START_REF] Downs | Toxicopathological Effects of the Sunscreen UV Filter, Oxybenzone (Benzophenone-3), on Coral Planulae and Cultured Primary Cells and Its Environmental Contamination in Hawaii and the U.S. Virgin Islands[END_REF][START_REF] Downs | Toxicological effects of the sunscreen UV filter, benzophenone-2, on planulae and in vitro cells of the coral, Stylophora pistillata[END_REF]He et al. 2019) and metabolic alterations [START_REF] Stien | Metabolomics Reveal That Octocrylene Accumulates in Pocillopora damicornis Tissues as Fatty Acid Conjugates and Triggers Coral Cell Mitochondrial Dysfunction[END_REF]. DNA damage was studied on bivalves, lugworm, coral and algae [START_REF] D'agata | Enhanced toxicity of "bulk" titanium dioxide compared to "fresh" and "aged" nano-TiO 2 in marine mussels (Mytilus galloprovincialis)[END_REF][START_REF] Downs | Toxicopathological Effects of the Sunscreen UV Filter, Oxybenzone (Benzophenone-3), on Coral Planulae and Cultured Primary Cells and Its Environmental Contamination in Hawaii and the U.S. Virgin Islands[END_REF][START_REF] Galloway | Sublethal toxicity of nano-titanium dioxide and carbon nanotubes in a sediment dwelling marine polychaete[END_REF][START_REF] Jovanović | Effects of titanium dioxide (TiO 2 ) nanoparticles on caribbean reef-building coral (Montastraea faveolata)[END_REF][START_REF] Wang | Trophic transfer of TiO 2 nanoparticles from marine microalga (Nitzschia closterium) to scallop (Chlamys farreri) and related toxicity[END_REF]. Mortality, behavioral and morphological abnormalities were the most studied parameters for Fish [START_REF] Araújo | Effects of UV filter 4-methylbenzylidene camphor during early development of Solea senegalensis Kaup, 1858[END_REF][START_REF] Barone | Acute toxicity testing of TiO 2 -based vs. oxybenzone-based sunscreens on clownfish (Amphiprion ocellaris)[END_REF][START_REF] Cong | The embryotoxicity of ZnO nanoparticles to marine medaka, Oryzias melastigma[END_REF]. Table 1 summarizes the extent of toxicity for UV-filters across different studies.

4-Methylbenzilydene camphor

4-Methylbenzilydene camphor (4-MBC) is one of the most studied UV-filters in marine environments.

Coral bleaching effects have been demonstrated with exposure concentrations of 33 µg/L [START_REF] Danovaro | Sunscreens cause coral bleaching by promoting viral infections[END_REF], as well as developmental disruptive effects in sea urchin larvae at 0.8 µg/L [START_REF] Torres | Screening the toxicity of selected personal care products using embryo bioassays: 4-MBC, propylparaben and triclocarban[END_REF], an environmentally relevant concentration [START_REF] Sánchez Rodríguez | Occurrence of eight UV filters in beaches of Gran Canaria (Canary Islands). An approach to environmental risk assessment[END_REF][START_REF] Román | Dispersive solid-phase extraction based on oleic acid-coated magnetic nanoparticles followed by gas chromatography-mass spectrometry for UVfilter determination in water samples[END_REF].

Its toxicity was also shown for fish [START_REF] Araújo | Effects of UV filter 4-methylbenzylidene camphor during early development of Solea senegalensis Kaup, 1858[END_REF] and copepod [START_REF] Chen | Multigenerational effects of 4-methylbenzylidene camphor ( 4-MBC ) on the survival , development and reproduction of the marine copepod Tigriopus japonicus[END_REF]) at 25 and 10 µg/L, respectively.

Benzophenones

Benzophenone derivatives are by far the most studied compounds, with the greatest diversity of parameters studied. Among the compounds investigated: BP1, BP2, BP3, BP4 and BP8; BP4 is the only one that showed no toxicity with different organisms (algae, mussels, sea urchins, crustaceans, fish and coral) (Paredeles et al. 2015;He et al. 2019;[START_REF] Barone | Acute toxicity testing of TiO 2 -based vs. oxybenzone-based sunscreens on clownfish (Amphiprion ocellaris)[END_REF]. BP3, which is commonly used in cosmetics, induced bleaching in coral species such as Seriatopora caliendrum, Styolphora pistillata and Acropora sp. [START_REF] Danovaro | Sunscreens cause coral bleaching by promoting viral infections[END_REF]He et al. 2019;[START_REF] Downs | Toxicopathological Effects of the Sunscreen UV Filter, Oxybenzone (Benzophenone-3), on Coral Planulae and Cultured Primary Cells and Its Environmental Contamination in Hawaii and the U.S. Virgin Islands[END_REF]

Octocrylene

OC was detected in sea water at concentrations up to 7 µg/L [START_REF] Tsui | Occurrence, distribution and ecological risk assessment of multiple classes of UV filters in surface waters from different countries[END_REF][START_REF] Langford | Environmental occurrence and risk of organic UV filters and stabilizers in multiple matrices in Norway[END_REF].

Several studies have highlighted detrimental effects against several marine species from 40 µg/L. Its effect on coral species appeared to be nuanced [START_REF] Danovaro | Sunscreens cause coral bleaching by promoting viral infections[END_REF][START_REF] Fel | Photochemical response of the scleractinian coral Stylophora pistillata to some sunscreen ingredients[END_REF]. However, He et al. (2019) demonstrated that it induced polyp's retraction at 1 mg/L and increased mortality in P. damicornis if combined with EMC. A recent metabolomic study showed that P. damicornis accumulated OC in fatty acid-conjugated forms from 5 µg/L and is associated with mitochondrial dysfunctions at 50 µg/L, whereas polyps were only retracted at 300 µg/L [START_REF] Stien | Metabolomics Reveal That Octocrylene Accumulates in Pocillopora damicornis Tissues as Fatty Acid Conjugates and Triggers Coral Cell Mitochondrial Dysfunction[END_REF]). This study showed that usual ecotoxicological parameters such as mortality or polyps state may result in an underestimation of a compound toxicity.

Other organic UV-filters

Some chemicals, such as TDSA, BM, DT, ES and ET have undergone very little investigation on marine organisms, with only one or two studies on coral species [START_REF] Danovaro | Sunscreens cause coral bleaching by promoting viral infections[END_REF][START_REF] Fel | Photochemical response of the scleractinian coral Stylophora pistillata to some sunscreen ingredients[END_REF] with the papers concluding no major threat to cause harm for the single molecule toxicity. The toxicity of approximately 45 globally authorized sunscreen UV-filters have not been assessed on marine biota. Therefore, it is difficult to draw conclusions about their effects and the risk associated with their use.

Inorganic UV-filters

Mineral UV-filters have been broadly advertised as eco-friendly in the public market. Nevertheless, several recent studies on ZnO and TiO 2 reported their toxicity on marine biota (see Table 2 for full reference list). Corinaldesi and colleagues (2018) presented severe bleaching to stoney coral due to exposure of zinc nanoparticles at 6.3 mg/L over 48 hours. Alterations in the surrounding microbial abundance for the stoney coral were also presented after exposure to mineral UV-filters at the same concentration. Digestive and immune systems of bivalves were affected by mineral UV-filter [START_REF] Buffet | Fate of isotopically labeled zinc oxide nanoparticles in sediment and effects on two endobenthic species, the clam Scrobicularia plana and the ragworm Hediste diversicolor[END_REF][START_REF] D'agata | Enhanced toxicity of "bulk" titanium dioxide compared to "fresh" and "aged" nano-TiO 2 in marine mussels (Mytilus galloprovincialis)[END_REF]Canesi et al. 2010(a); Xia et al. 2017). Because of their feeding strategy, these organisms are subjected to nanoparticle ingestion.

Mineral UV-filters can display different sizes and shapes. These characteristics are potentially influenced by abiotic variables that can affect their toxicity. Wong and Leung (2013) proposed that temperature sequentially affects the toxicity by influencing the size of ZnO aggregates. [START_REF] Miao | Zinc oxide-engineered nanoparticles: Dissolution and toxicity to marine phytoplankton[END_REF] demonstrated that the dissolution rate, influenced by the pH and the nanoparticles shape, altered the toxicity of ZnO on the algae Thalassiosira pseudonana. D'Agata and colleagues (2014) observed that bulk TiO 2 was more toxic causing DNA damage compared to TiO 2 nanoparticles in mussels, even if the nanoparticles are more likely to be accumulated. [START_REF] Hazeem | Cumulative effect of zinc oxide and titanium oxide nanoparticles on growth and chlorophyll a content of Picochlorum sp[END_REF] looked at chronic exposures of ZnO and only showed growth inhibition at the early growth stages of Picochlorum sp. due to aggregation and sedimentation occurring at the later stages. Conversely, some authors highlighted that smaller particles are more toxic for example [START_REF] Xia | Interaction of TiO 2 nanoparticles with the marine microalga Nitzschia closterium : Growth inhibition , oxidative stress and internalization[END_REF] demonstrated a growth inhibition at lower concentrations for Nitzschia closterium algae with EC 50 values of 88.8 mg/L for 21 nm TiO 2 nanoparticles but 118.8 mg/L for 60 nm particle size. The shape is another characteristic that should be considered as [START_REF] Peng | Effect of morphology of ZnO nanostructures on their toxicity to marine algae[END_REF] demonstrated that rod shaped ZnO particles were more toxic than sphere shaped particles to marine algae when also measuring the growth inhibition.

Two crystalline forms are commonly used in mineral sunscreens, rutile and anatase. [START_REF] Doyle | Acute exposure to TiO 2 nanoparticles produces minimal apparent effects on oyster, Crassostrea virginica (Gmelin), hemocytes[END_REF] demonstrated minimal differences between the bulk anatase and bulk rutile crystalline forms for TiO 2 , when looking at the hemocyte responses from the Atlantic oyster, Crassostrea virginica. This feature is yet to be explored for nanoparticles. As described above, the characteristics of mineral filters can strongly influence ecotoxicology studies. The literature revealed a lack of detail on the characteristics of the filters studied. Some authors provided information on the anatase/rutile percentage, diameter and shape of the particles [START_REF] Miller | Impacts of Metal Oxide Nanoparticles on Marine Phytoplankton[END_REF], while others did not specify on the nanoparticle nature [START_REF] Barmo | In vivo effects of n-TiO 2 on digestive gland and immune function of the marine bivalve Mytilus galloprovincialis[END_REF][START_REF] Guan | Neurotoxic impact of acute TiO 2 nanoparticle exposure on a benthic marine bivalve mollusk , Tegillarca granosa[END_REF]. Ciacci and colleagues (2012) confirmed the size distribution using transmission electron microscope and noted that they were different to the declared 42nm size at purchase. These results highlight the difficulty of comparing toxicity studies for mineral filters.

Combination study

Emollients and emulsifiers make up typically 20% of the sunscreen ingredients as with other components of sunscreen such as sensory enhancers, boosting ingredients and rheology modifiers [START_REF] Osterwalder | Global state of sunscreens[END_REF]. The toxicity of these compounds has not been thoroughly explored. [START_REF] Danovaro | Sunscreen products increase virus production through prophage induction in marine bacterioplankton[END_REF] indicated that sunscreens can alter carbon, nitrogen and phosphate biogeochemical cycling in the Ocean. Further studies demonstrated that commercial sunscreen increased the nutrient content in seawater [START_REF] Rodríguez-Romero | Sunscreens as a New Source of Metals and Nutrients to Coastal Waters[END_REF][START_REF] Tovar-Sánchez | Sunscreen Products as Emerging Pollutants to Coastal Waters[END_REF]. [START_REF] Danovaro | Sunscreens cause coral bleaching by promoting viral infections[END_REF] showed that excipients like butylparaben preservatives which are commonly found in sunscreens and other cosmetic products caused coral bleaching by encouraging viruses and resulted in a 70-90% zooxanthellae release. Furthermore, sunscreens have also been shown to be a source of hydrogen peroxide production (Sánchez-Quiles and Tovar-Sánchez, 2014; Sendra et al. 2017). Toxicities can vary depending on the sunscreen formulation. For example, spray sunscreens have a greater bioavailability according to Tovar-Sánchez and colleagues (2013) as they demonstrated a higher toxicity in growth inhibition to phytoplankton compared to a cream. Only a few papers investigated the toxicity of a complete formulation instead of a single UV-filter [START_REF] Barone | Acute toxicity testing of TiO 2 -based vs. oxybenzone-based sunscreens on clownfish (Amphiprion ocellaris)[END_REF][START_REF] Danovaro | Sunscreens cause coral bleaching by promoting viral infections[END_REF][START_REF] Danovaro | Sunscreen products increase virus production through prophage induction in marine bacterioplankton[END_REF][START_REF] Mccoshum | Direct and indirect effects of sunscreen exposure for reef biota[END_REF][START_REF] Fastelli | Exposure of key marine species to sunscreens : Changing ecotoxicity as a possible indirect effect of global warming[END_REF]. Toxicities were seen to be greater in the formulation compared to a single molecule. For example, Sendra et al. (2017) showed that commercial sunscreens with TiO 2 nanoparticles were more toxic to micro algae compared TiO 2 nanoparticles alone due to greater H 2 O 2 production. ZnO and TiO 2 nanoparticles have been shown to negatively impact marine algae growth to a greater extent when they are combined [START_REF] Hazeem | Cumulative effect of zinc oxide and titanium oxide nanoparticles on growth and chlorophyll a content of Picochlorum sp[END_REF].

Laboratory assays are performed in controlled environments and not all environmental variables can be considered. Variation in abiotic parameters such as temperature, salinity, nutrient content, organic matter and UV radiation strongly shape the fate of chemicals in marine biota. For example, oxygen content [START_REF] Wang | Significance of physicochemical and uptake kinetics in controlling the toxicity of metallic nanomaterials to aquatic organisms *[END_REF]) and UV radiations [START_REF] Miller | TiO 2 nanoparticles are phototoxic to marine phytoplankton[END_REF]Sendra et al. 2017(a)) can influence the toxicity of TiO 2 . As UV-filter's transformation products could pose a greater risk than the native compound, a better understanding of their release and formation is needed. Literature data indicate that the following compounds remain stable under direct light exposure in experimental conditions: BP3 [START_REF] Liu | Photostability of the UV filter benzophenone-3 and its effect on the photodegradation of benzotriazole in water[END_REF][START_REF] Rodil | Photostability and phytotoxicity of selected sunscreen agents and their degradation mixtures in water[END_REF], OC [START_REF] Herzog | Photostability of UV absorber systems in sunscreens[END_REF][START_REF] Rodil | Photostability and phytotoxicity of selected sunscreen agents and their degradation mixtures in water[END_REF], bisethylhexyloxyphenol methoxyphenyl triazine (BEMT) [START_REF] Herzog | Photostability of UV absorber systems in sunscreens[END_REF]) and 4-MBC [START_REF] Rodil | Photostability and phytotoxicity of selected sunscreen agents and their degradation mixtures in water[END_REF]. On the other hand, EMC [START_REF] Jentzsch | Photodegradation of the UV filter ethylhexyl methoxycinnamate under ultraviolet light: Identification and in silico assessment of photo-transformation products in the context of grey water reuse[END_REF][START_REF] Macmanus-Spencer | Aqueous photolysis of the organic ultraviolet filter chemical octyl methoxycinnamate[END_REF], Isoamyl pmethoxycinnamate (IMC) [START_REF] Macmanus-Spencer | Aqueous photolysis of the organic ultraviolet filter chemical octyl methoxycinnamate[END_REF], ethylhexyl dimethyl PABA (OD-PABA) [START_REF] Rodil | Photostability and phytotoxicity of selected sunscreen agents and their degradation mixtures in water[END_REF], Ethylhexyl triazone (ET) [START_REF] Damiani | Assessment of the photo-degradation of UV-filters and radical-induced peroxidation in cosmetic sunscreen formulations[END_REF][START_REF] Herzog | Photostability of UV absorber systems in sunscreens[END_REF], butyl methoxydibenzoylmethane (BM) [START_REF] Damiani | Assessment of the photo-degradation of UV-filters and radical-induced peroxidation in cosmetic sunscreen formulations[END_REF][START_REF] Herzog | Photostability of UV absorber systems in sunscreens[END_REF]) demonstrate a lower photostability. In addition, the impact of organic matter on the fate of UV-filters was demonstrated, acting as photosensitizer through its triplet-excited states. Hence, we can distinguish between a direct and indirect photodegradation process [START_REF] Li | Photochemical transformation of sunscreen agent benzophenone-3 and its metabolite in surface freshwater and seawater[END_REF]. The involvement of biotic factors on the fate of UV-filters in marine environments is poorly documented.

Standardized toxicity studies

Today, there are no guidelines or standards specifically set for UV-filters for marine organisms. The Organization for Economic Co-operation and Development (OECD) has developed guidelines for toxicity testing on fish (OECD test guideline N°203, Fish, Acute toxicity Testing), although they recommend the use of the following marine species: Pagrus major, Dicentrarchus labrax and Cyprinodon variegatus. From an overall perspective, these guidelines are not specifically designed for marine organisms, let alone for the testing of highly hydrophobic chemicals such as UV-filters.

Standards that are globally harmonized would facilitate comparisons between studies by normalizing toxicological endpoints, exposure media, materials, tested concentrations and exposition times. In the literature, exposure concentrations vary greatly among the different studies ranging from a wide range (0.32 -5000 µg/L, [START_REF] Torres | Screening the toxicity of selected personal care products using embryo bioassays: 4-MBC, propylparaben and triclocarban[END_REF] to conservative ones (0.5-10 µg/L, [START_REF] Chen | Multigenerational effects of 4-methylbenzylidene camphor ( 4-MBC ) on the survival , development and reproduction of the marine copepod Tigriopus japonicus[END_REF]. It is noteworthy to underline that some authors measured the exposure concentration with methods that are hardly comparable between studies, due to the UV-filter's physicochemical properties. In addition, with similar organisms, exposure time is a parameter displaying variation from several hours [START_REF] Downs | Toxicological effects of the sunscreen UV filter, benzophenone-2, on planulae and in vitro cells of the coral, Stylophora pistillata[END_REF][START_REF] Seoane | Flow cytometric assay to assess short-term effects of personal care products on the marine microalga Tetraselmis suecica[END_REF] to several days (He et al. 2018;[START_REF] Stien | Metabolomics Reveal That Octocrylene Accumulates in Pocillopora damicornis Tissues as Fatty Acid Conjugates and Triggers Coral Cell Mitochondrial Dysfunction[END_REF]. Hydrophobic UVfilters tend to adhere to plastic and glass. Materials used for toxicity studies differ, some authors used PTFE (Teflon) [START_REF] Downs | Toxicopathological Effects of the Sunscreen UV Filter, Oxybenzone (Benzophenone-3), on Coral Planulae and Cultured Primary Cells and Its Environmental Contamination in Hawaii and the U.S. Virgin Islands[END_REF]Sendra et al. 2017) or glass [START_REF] Kusk | Effect of 2,4-dihydroxybenzophenone (BP1) on early life-stage development of the marine copepod Acartia tonsa at different temperatures and salinities[END_REF]He et al. 2019(a)), while it is not mentioned in most studies. Experimental studies performed in our group have highlighted that some UV-filters such as BP3 can evaporate during extraction process resulting in underestimated concentrations. This point emphasizes a need for standardization of analytical methods.

Bioaccumulation of UV-filters

Bioaccumulation may be a better indicative measure of the spread of UV-filters in the Ocean. These studies are pivotal to better understand to which extent marine organisms are exposed to UV-filters. Two types of studies can be distinguished: those that measure the concentration of different compounds from organisms collected in situ and those that expose the organism to a given concentration in vivo, in order to measure the bioaccumulation fraction.

Organic UV-filters are poorly soluble compounds, characterized by a high octanol-water partition coefficient (Log K ow ) [START_REF] Apel | Environmental occurrence and hazard of organic UV stabilizers and UV filters in the sediment of European North and Baltic Seas[END_REF][START_REF] Fagervold | Occurrence and Environmental Distribution of 5 UV Filters During the Summer Season in Different Water Bodies[END_REF]. These hydrophobic properties result in bioaccumulation of UV-filters in marine species. Interestingly, this literature analysis reveals the lack of studies for most UV-filters. Indeed, only a few were targeted in bioaccumulation analyses with 14 sunscreen UV-filters, the others being benzotriazole derivatives. A positive point that can be drawn from the literature is that studies are approaching a worldwide coverage, including the North & South Atlantic Ocean, the Pacific Ocean and the Mediterranean Sea.

In situ

Accumulation of UV-filters in mussels has been shown in different environments: Atlantic [START_REF] Castro | Occurrence, profile and spatial distribution of UV-filters and musk fragrances in mussels from Portuguese coastline[END_REF], Mediterranean Sea [START_REF] Bachelot | Organic UV filter concentrations in marine mussels from French coastal regions[END_REF] and Pacific [START_REF] Nakata | Asia-Pacific mussel watch for emerging pollutants: Distribution of synthetic musks and benzotriazole UV stabilizers in Asian and US coastal waters[END_REF] with concentrations up to 3,992 ng/g dw for OC and 1,765 ng/g dw for EMC [START_REF] Picot Groz | Detection of emerging contaminants (UV filters, UV stabilizers and musks) in marine mussels from Portuguese coast by QuEChERS extraction and GC-MS/MS[END_REF]. UV-filter prevalence in marine organisms is becoming a health concern as they are detected in seafood. Mussels, clam, mackerel, tuna, salmon and cod were shown to accumulate multiple UV-filters [START_REF] Cunha | Co-occurrence of musk fragrances and UV-filters in seafood and macroalgae collected in European hotspots[END_REF][START_REF] Langford | Environmental occurrence and risk of organic UV filters and stabilizers in multiple matrices in Norway[END_REF]. Cunha and coworkers (2018) highlighted the presence of nine UV-filters in shrimp, pangasius and salmon collected in an aquaculture farm. In 2019, Rodil et al. assessed the occurrence at 5 timepoints throughout a year, of multiple emerging pollutants, including BP3, EMC, OD-PABA, OC and 4-MBC, in bivalves. If they do not highlight a clear temporality in UV-filters abundance, they identified UV-filters as the most abundant persistent pollutants, behind polycyclic aromatic hydrocarbons.

The fate of sunscreen agents in species of higher trophic level has been poorly documented. To date, three studies were carried out on dolphins, which are the first assessments of UVF in marine mammals. Dolphins have been identified to accumulate organic pollutants and are good candidates as sentinel species for Ocean health, due to biomagnification [START_REF] Bossart | Marine mammals as sentinel species for oceans and human health[END_REF][START_REF] Tanabe | Global contamination by persistent organochlorines and their ecotoxicological impact on marine mammals[END_REF].

Benzotriazole UV stabilizers were identified in blubbers of finless porpoises in Japan with a bioaccumulation factor as high as 33,300, which is ten times higher than those reported for small fish [START_REF] Nakata | Detection of benzotriazole UV stabilizers in the blubber of marine mammals by gas chromatography-high resolution mass spectrometry (GC-HRMS)[END_REF]. [START_REF] Alonso | Toxic heritage: Maternal transfer of pyrethroid insecticides and sunscreen agents in dolphins from Brazil[END_REF] demonstrated maternal transfer of UV-filters in Franciscana Dolphin, demonstrating that 4-MBC, EMC, OD-PABA and OC can be considered as transplacental contaminants. These results suggest that UV-filters biomagnify through the marine food web. Further analyses are needed to better apprehend the biomagnification of these emerging pollutants.

In vivo

In vivo bioaccumulation studies are scarce, with only 5 and 12 studies on organic and mineral UVfilters, respectively. All studies carried out with organic UV-filters demonstrated bioaccumulation, regardless of the molecule and the organism studied (Table 4,5). Exposed concentrations ranged from 1 to 1000 µg/L, for organic UV-filters, with three modes of contamination: waterborne (WB), sediment exposure (SE) or dietary (D), the latter imitating trophic transfer mechanisms. Only one study has investigated bioaccumulation using contaminated sediment [START_REF] Buffet | Fate of isotopically labeled zinc oxide nanoparticles in sediment and effects on two endobenthic species, the clam Scrobicularia plana and the ragworm Hediste diversicolor[END_REF], although it is the medium containing the higher concentrations of UV-filter [START_REF] Fagervold | Occurrence and Environmental Distribution of 5 UV Filters During the Summer Season in Different Water Bodies[END_REF][START_REF] Mitchelmore | Science of the Total Environment Occurrence and distribution of UVfi lters and other anthropogenic contaminants in coastal surface water , sediment , and coral tissue from Hawaii[END_REF] . [START_REF] Vidal-Liñán | Bioaccumulation of UV filters in Mytilus galloprovincialis mussel[END_REF] exposed mussels to different UV-filters at 1 µg/L, which is the lowest concentration noticed in bioaccumulation studies, via the WB route for 14 days. OD-PABA and BP3 underwent the least bioaccumulation with 15.5 ng/g and 67 ng/g dw while OC and 4-MBC were found at 559.5 ng/g and 801 ng/g dw, respectively. As previously mentioned, [START_REF] Stien | Metabolomics Reveal That Octocrylene Accumulates in Pocillopora damicornis Tissues as Fatty Acid Conjugates and Triggers Coral Cell Mitochondrial Dysfunction[END_REF] demonstrated that Pocillopora damicornis accumulated and metabolized OC under fatty acid conjugated forms. This study raised the importance of conducting metabolomic studies to ensure that the effects and concentration of anthropogenic contaminants are not underestimated. Regarding the accumulation of mineral filters, there are no studies with bulk filters. In addition, the characteristics of the nanoparticles used are rarely mentioned. Both ZnO and TiO 2 have been demonstrated to encounter assimilation by several organisms such as turbot, oysters or algae [START_REF] Trevisan | Gills are an initial target of zinc oxide nanoparticles in oysters Crassostrea gigas, leading to mitochondrial disruption and oxidative stress[END_REF]Wang et al., 2016;[START_REF] Wang | Trophic transfer of TiO 2 nanoparticles from marine microalga (Nitzschia closterium) to scallop (Chlamys farreri) and related toxicity[END_REF]. Bhuvaneshwari and co-workers (2018) differentiated two different mechanisms: accumulation and uptake. The first is the stable assimilation of the compound while the second is used if the organism can excrete the contaminate over time. Abbreviations: dw, dry weight; ww, wet weight; WB, waterborne; D, dietary; SE, sediment exposure. Species mentioned alongside the dietary "D" were previously exposed to UVF before being used as feed.

Conclusion

This review provides an analysis of the UV-filter toxicity and bioaccumulation studies conducted up to August 2019. This analysis has allowed us to identify the progress made so far, and what remains to be explored. We have highlighted a disparity in the studies. Although, the number of published papers is increasing from year to year, the majority of compounds authorized for cosmetic use have not been studied, while 4-MBC, BPs or OC are at the core of several investigations. In addition, a trend on the models studied has been identified, particularly for organic filters, for which no sedimentary organisms have been studied, though sediments are the most concerned biotopes. It should also be noted that there are no standardized methods specifically designed to comparatively assess the toxicity of these chemicals and marine species. Bioaccumulation studies have shown that these compounds biomagnify through trophic levels. In addition, it is important to note that no in situ bioaccumulation studies have been conducted for inorganic filters. Intensive research is therefore needed to better understand the effect of UV-filters, in order to adapt the regulations with a science-based approach.

Figure 1 .

 1 Figure 1. Cumulative published papers .................................................................................................. Figure 2. An overview the toxicity studies. ............................................................................................. Figure 3. An overview of FAO fishing areas where UV-filter bioaccumulation has been reported to date. .........................................................................................................................................................

  Summary of organic UV-filter toxicity studies. ........................................................................ Table 2. Summary of inorganic UV-filter toxicity studies. ..................................................................... Table 3. In situ summary of UV-filter bioaccumulation studies. ........................................................... Table 4. Summary of In vivo studies reporting the bioaccumulation of organic UV-filters. ..................

Figure 1 .

 1 Figure 1. Cumulative number of publications for UV-filter, sunscreen and marine biota related searches from Google Scholar, Web of Science and NCBI databases. Toxicity of UV-filters (A) and bioaccumulation (B) in marine biota.

Figure 3 .

 3 Photo/hetero/mixotrophic (algae) Heterotrophic (bacteria) Sum of Papers

Table 5 .

 5 Summary of In vivo studies reporting the bioaccumulation of inorganic UV-filters. ...............

	Abbreviation list of UV-filters
	Abbreviation INCI	INN/USAN name	CAS #
	4-MBC	4-Methylbenzylidene camphor	Enzacamene	36861-47-9
	BEMT	bis-Ethylhexyloxyphenol		187393-00-6
		methoxyphenyl triazine	Bemotrizinol
	BM	Butyl methoxydibenzoylmethane	Avobenzone	70356-09-1
	BP1	Benzophenone-1	2,4-Dihydroxybenzophenone	131-56-6
	BP2	Benzophenone-2	2,2',4,4'-	131-57-5
			Tetrahydroxybenzophenone
	BP3	Benzophenone-3	Oxybenzone	131-57-7
	BP4	Benzophenone-4	Sulisobenzone	4065-45-6
	BP6	Benzophenone-6	2,2'-Dihydroxy-4,4'-	131-54-4
			dimethoxybenzophenone
	BP8	Benzophenone-8	Dioxybenzone	131-53-3
	DHHB	Diethylamino hydroxybenzoyl hexyl		302776-68-7
		benzoate	-
	DT	Drometrizole trisiloxane	-	155633-54-8
	EMC	Ethylhexyl methoxycinnamate	Octinoxate	5466-77-3
	ES	Ethylhexyl salicylate	Octisalate	118-60-5
	ET	Ethylhexyl triazone	Ethylhexyl triazone	88122-99-0
	HS	Homosolate	-	118-56-9
	IMC	Isoamyl p-methoxycinnamate	Amiloxate	71617-10-2
	MBBT	Methylene bis-benzotriazolyl	Bisoctrizole	103597-45-1
		tetramethylbutylphenol
	OC	Octocrylene	Octocrilene	6197-30-4
	OD-PABA	Ethylhexyl dimethyl PABA	Octyldimethyl PABA,	21245-02-3
			Padimate O
	PABA	PABA	Aminobenzoic acid	150-13-0
	TDSA	Terephtalidene dicamphor sulfonic	Ecamsule	90457-82-2
		acid

Table 1 .

 1 Summary of organic UV-filter toxicity studies.

	UV-filter	Species Model [Common name]	Endpoint	Tested conc. range	Toxic Effects [Conc with toxic effect]	Reference
	4-Methylbenzilidene	Acropora pulchra	bleaching	50 μl/L	95% bleaching rate over 62	Danovaro et al.
	camphor (4-MBC)	[Staghorn coral]			hours [50 µg/L]	2008
		Acropora sp.	bleaching	33 μl/L	63% bleaching rate over 48	Danovaro et al.
		[Stoney coral]			hours [33 µg/L]	2008
		Isochrysis galbana [Unicellular algae]	growth rate	N/A	EC 50 = 171.45 µg/L over 72h	Paredes et al.
		Mytilus	morphologies		changes in D-larvae, EC50 =
		galloprovincialis			587.17 µg/L over 48h
		[Mediterranean
		Mussel]
		Paracentrotus lividus	larval length	0.32-5000 µg/L 5% decrease in larval length [2	Torres et al. 2016
		[Purple sea urchin]			µg/L]
			morphological	0.32-5000 µg/L 20% of deformed larvae [0.8
			abnormalities		µg/L]
			larval growth	N/A	EC50 = 854 µg/L over 48h	Paredes et al.
		Senegalese sole	enzymatic activity 25-216 µg/L	increase of AChe activity [85	Araújo et al. 2018
		[Sole flatfish]			µg/L]
			enzymatic activity		decrease in LDH activity [25
					µg/L]
			swimming	68-360 µg/L	decrease in swimming distance
			behavior		[360 µg/L]
			mortality	235-935 µg/L 40 +/-18% mortality at 48hpf;
					85+/-5% mortality at 72hpf [935
					µg/L]
			growth	68-360 µg/L	decreased length [360 µg/L]
			hatching success 235-935 µg/L decrease of 40% in hatching
					rates [447 µg/L]
		Siriella armata	mortality	N/A	EC50 = 192.63 µg/L over 96h	Paredes et al.
		[Crustacea]
		Tigriopus japonicus	mortality	10-5000 µg/L 100% mortality over 72h [1000	Chen et al. 2018
		[Copepod]			µg/L]
			survival	0.5-10 μg/L	52% survival rate [10 µg/L]
	Benzophenone-1 (BP1)	Acartia tonsa	DT½ values	0.051-2 mg/L 89-296 (h) (time elapsed until	Kusk et al. 2011
		[Copepod]			50% of the organisms had
					developed into copepodites)
					[concentrations were pooled]
			hatching success		70-95% hatching success
					(depending on environment)
			survival success		64-92% survival success
					(depending on environment)
			mortality	0.5-10 mg/L	LC 50 = 2.6 mg/L at 24 and 48h
			larval development		EC 50 = 1.5 mg/L with 15% salinity
					EC 50 = 0.59 mg/L with 25%
					salinity
		Pocillopora damicornis	mortality	0.1-1000 μg/L mortality on the nubbin = 100%	He et al. 2019
		[Cauliflower coral]			on day 7 [1000 µg/L]
			bleaching rate		33% bleaching on the
					nubbin [1000 µg/L]
		Seriatopora	mortality		no mortality on the larvae
		caliendrum
		[Stoney coral]	mortality		100% mortality on the nubbin
					[1000 µg/L]
			bleaching rate		57% white, 25% pale brown for
					the larvae [1000 µg/L]
			bleaching rate		33% bleaching for the nubbin
					[1000 µg/L]
	Benzophenone-2 (BP2)	Stylophora pistillata	chlorophyll	2.46 µg-246	photoinduced toxicity -coral	Downs et al. 2014
		[Hood coral]	fluorescence	mg/L	bleaching [2.46 µg/L]
			DNA abasic		increase of DNA lesions
			lesions		(greater toxicity if exposed to
					light) [24.6 µg/L]

[START_REF] Beel | Biotransformation of the UV-filter sulisobenzone: Challenges for the identification of transformation products[END_REF]

highlighted the biodegradation of BP4 in contact with activated sludge of municipal wastewater treatment plant.

[START_REF] Badia-Fabregat | Degradation of UV filters in sewage sludge and 4-MBC in liquid medium by the ligninolytic fungus Trametes versicolor[END_REF]

have demonstrated fungus mediated degradation of 4-MBC. Microcosms experiments showed the biodegradation of BP3

(Liu et al. 2012;[START_REF] Volpe | Biodegradation of UV-filters in marine sediments[END_REF]

.

[START_REF] Volpe | Biodegradation of UV-filters in marine sediments[END_REF]

demonstrated that 4-MBC was stable whereas OD-PABA was biodegraded in marine sediments.

Table 2 .

 2 Summary of inorganic UV-filter toxicity studies.

	UV-filter	Species Model [Common name]	Endpoint	Tested conc. range	Toxic Effects [Conc with toxic effect]	Reference
	TiO2 (nanoparticles)	Acropora sp.	abundance of	6.3 mg/L	increase of zooxanthellae	Corinaldesi et al.
		[Stoney coral]	zooxanthellae		released into seawater from	2018
					coral. (24 + 48h)
			damaged		increase of damaged
			zooxanthellae		zooxanthellae (24 + 48h)
			bleaching		slight color loss in 6-7% (no
					visual bleaching)
			microbial		reduced number of prokaryotes
			enrichment		and viruses in the surrounding
					seawater of the exposed coral.
		Alexandrium [Dinoflagellate] tamarens	growth	2 -320 mg/L	recovery observed depending EC 50 = 140.09 mg/L (13 days) EC 50 = 85.08 mg/L (4 days)	Li et al. 2019
					on the exposure conc.
					(increase in antioxidative
					enzymes and toxins)
		Amphidinium	enzymatic	1 -10 mg/L	high H2O2 produced at first	Sendra et al. 2017
		carterae	activity		12h, combined with UV.
		[Unicellular algae]			Sunscreen products produced
					a higher concentration of H2O2
					[10 mg/L]
			cell density		reduced cell density (combined
					UV) [1 mg/L]
		Arenicola marina	DNA damage	1-3 g/kg	13% DNA damage [2 g/kg]	Galloway et al.
		[Lugworm]				2010
			cytotoxicity		reduced lysosomal stability [2
			effects		g/kg]
		Artemia salina	synergistic effect 5, 400 mg/L	nTiO2 increased the toxicity	Lu et al. 2018
		[Brine shrimp]			Cd 2+ by 57.5% [5 mg/L]
			% mortality	0.1-10 mg/L	increase in mortality (48h)	Bhuvaneshwari et
					LC 50 = 4.21 mg/L	al. 2018
			mobility	1-80 mg/L	EC 50 = 4 mg/L (48h) exposed to UV exposure.	Clemente et al. 2014
					5-80 mg/L (anatase)
					1-20 mg/L (anatase/rutile)
			growth rate	0.06, 0.6 mg/L	no effect (96h) (anatase and
					anatase/rutile mix) exposed to
					UV + visible light.
		Chaetoceros gracilis	enzymatic	1 -10 mg/L	high H2O2 produced at first	Sendra et al. 2017
		[Unicellular algae]	activity		12h, combined with UV.
					Sunscreen products produced
					a higher concentration of H2O2
					[10 mg/L]
			cell density		reduced cell density (combined
					UV) [1 mg/L]
		Chlamys farreri	oxidative stress 1 mg/L	SOD & CAT responses were	Xia et al. 2017
		[Marine scallop]			triggered in the gill and
					digestive gland over 14 days [1
					mg/L]
			enzymatic		increased AChE [>14 days]
			activity
			enzymatic		histopathological alterations of
			activity		the gill and digestive gland
					[>14 days]
			LMS	1 mg/L	increased lysosomal	Wang et al. 2017
					membrane destabilization but

Table 3 .

 3 In situ summary of UV-filter bioaccumulation studies.

	Reference	Organism model	Sunscreen	Concentration range	Location
			components
			(abbreviations)
	Alonso et al. 2015	Dolphin	EMC	ND-250 ng/g lw	South Atlantic
		(Pontoporia blainvillei & Sotalia guianensis)	4-MBC	ND-855 ng/g lw	Ocean
			OC	ND-11,130 ng/g lw
			OD-PABA	ND-1385 ng/g lw
	Bachelot et al. 2012	Mussels	EMC	3-256 ng/g dw	French Atlantic,
		(Mytilus edulis & Mytilus galloprocincialis)	OC	1-200 ng/g dw	Mediterranean Sea
			OD-PABA	ND
	Barbosa et al. 2018	Gilt-head bream,	ES	5-12 μg/kg ww	North Sea,
		mackerel, salmon, cod, monkfish and mussels.	HS	>LOD-10 μg/kg ww	Atlantic Ocean, Mediterranean Sea
		(Seafood species, wild	BP6	20-110 μg/kg ww
		and farmed origins.)	OC	4-28 μg/kg ww
			BP1	9-27 μg/kg ww
			4MBC	ND (detected after steaming)
			DHHB	ND (detected after steaming)
	Castro et al. 2018	Mussels	ES	ND-59.2 ng/g dw	North Atlantic Ocean
		(Mytilus galloprovincialis & Mytilus edulis)	BP3	ND-622.1 ng/g dw
			4MBC	ND-88.3 ng/g dw
			IMC	ND-43.1 ng/g dw
			EMC	ND-181.8 ng/g dw
	Cunha et al. 2015	Mussels, mullet, clam &	BP1	ND	North Atlantic
		flounder	BP3	ND -<MQL (ng/g dw)	Ocean, North Sea, Mediterranean Sea
			OD-PABA	ND
			HS	ND
			DHMB	ND -<MQL (ng/g dw)
			IMC	ND
			OC	ND -<LOQ (ng/g dw)
			EMC	ND -<LOQ (ng/g dw)
			ES	ND
			DHHB	ND
			4-MBC	ND
	Cunha et al. 2018	Mackerel, tuna, salmon,	BP1	ND-98.9 µg/kg dw	Mediterranean Sea,
		seabream, cod, monkfish, crab, shrimp, octopus,	BP3	ND-98.7 µg/kg dw	North Sea, North Atlantic
		plaice, hake, mussel &	ES	ND-72.1 µg/kg dw	Ocean, Pacific
		sardine (Seafood species, wild,	4-MBC	ND-56.2 µg/kg dw	Ocean
		farmed and industrial origins)	EMC	ND-74.4 µg/kg dw
			IMC	ND-66.7 µg/kg dw
			DHMB	ND-90.7 µg/kg dw
			OD-PABA	ND
			OC	ND-103.3 µg/kg dw
			DHHB	ND
	Gago-Ferrero et al.	Dolphin	OC	89-782 ng/g lw	South Atlantic
	2013	(Pontoporia blainvillei)			Ocean
	Horricks et al. 2019	Lionfish	4MBC	2.11 µg/kg ww	Caribbean Sea
		(Pterois volitans)
			EMC	ND or below LOD
			BP3	0.12-2.90 µg/kg ww

Table 4 .

 4 Summary of In vivo studies reporting the bioaccumulation of organic UV-filters.

	Organic UV filter	Species Model [Common name]	Exposed conc	Exposure time [exposition route]	Measured conc	Reference
	EMC	Tetraselmis suecica	100 µg/L	6h [WB]	12.7 µg/L	Gomez et al. 2012
		[Algae] Mytilus galloprovincialis	11.9 µg/L	48h [D -T. suecica]	38 ng/g dw
	OC	[Mussel]	11.6 µg/L	48h	>33 ng/g dw
	BP3	Pocillopora damicornis & Seriatopora caliendrum	10-1000 μg/L	7 days [WB]	1.42-67.51 ng/g dw	He et al. 2019
	BP1	[Coral]	10-1000 μg/L		1.02-53.08 ng/g dw
	BP8		10 and 100 μg/L		0.94-37.76 ng/g dw
	OC	Pocillopora damicornis	5-1000 µg/L	7 days [WB]	OC-fatty acid	Stien et al. 2019
		[Coral]			conjugates detected
	ES				bioaccumulation under
					fatty-acid conjugated
					form
	4-MBC BP3	Mytilus galloprovincialis [Mussel]	1 µg/L	14 days [WB]	801 ng/g dw 67 ng/g dw	Vidal-Liñán et al. 2018
	BP4				520 ng/g dw
	OC				559.5 ng/g dw
	OD-PABA				13.5 ng/g dw
					9-160 ng/g (note; up to
		Sparus aurata			20 by products were	Ziarrusta et al.
	BP3	[Gilt-head bream]	50 ng/ml	14 days [WB]	detected.)	2018

Table 5 .

 5 Summary of In vivo studies reporting the bioaccumulation of inorganic UV-filters.

	Mineral UV filter	Species Model [Common name]	Exposed conc	Exposure time [exposition route]	Measured conc	Reference
	nZnO	Artemia salina (larvae) [[Brine shrimp]	100 mg/L	24h [WB]	135 µg/g (Zn) or 735 µg/g ZnO	Ates et al. 2013
					220 µg/g (Zn) or 1301
			100 mg/L	96h	µg/g ZnO
		Artemia salina			0.001 mg/g dw	Bhuvaneshwari et
	nTiO2	[Brine shrimp]	1-7 ng/g dw	48h [D -D. salina]	(accumulated)	al. 2018
					0.5 mg/g dw
			10 mg/L	[WB]	(accumulated)
			1-7 ng/g dw	[D -D. salina]	0.12 mg/g dw (uptake)
			10 mg/L	[WB]	15 mg/g dw (uptake)
		Thalassiosira weissflogii				Bielmyer-Fraser et
	nZnO	[Centric diatoms]	0.1mg/L	7 days [WB]	1x10-9 µgZn/cell	al. 2014
	nZnO	Scrobicularia plana [Clam]	3 mg/kg	16 days [SE]	5.4 µg/g ww	Buffet et al. 2012
		Nereis diversicolor
		[Rag worm]	3 mg/kg	[SE]	3.7 µg/g ww
	nZnO	Mytilus galloprovincialis [Mussel]	2 mg/L	2 weeks [WB]	350-400 µg/L dw	Hanna et al. 2013
		Thalassiosira weissflogii [Algae]	168 µg/L	7 days [WB]	17 µg/g dry wt	Jarvis et al. 2013
		Acartia tonsa	200,000	7 days [D -T.	toxic effects were
		[Copepod]	cells/mL/d	weissflogii]	observed
		Orbicella faveolata	0.1, 10 mg/L			Jovanović and
		[Star coral]		17 days [WB]	6.19, 16.58 mg/L	Guzmán, 2014
		Ruditapes philippinarum
		[Clam]
			1, 10 µg/L	7 days [WB]	130 µg/g dw (Zn)	Marisa et al. 2016
		Mytilus galloprovincialis [Mussel]	10 mg/L	4 days [WB]	880 µg/g dw (Zn)	Montes et al. 2012
		Crassostrea Gigas [Oyster]	4 mg/L	24h [WB]	0.55 mg/kg (gills)	Trevisan et al. 2014
					0.28 mg/kg (digestive
				24h	gland)
	nTiO2	Perinereis aibuhitensis [Clamworm]	10, 50, 100 mg/L 24h [WB]	32.7-59.3 µg/g dw	Wang et al. 2016(b)
		Scophthalmus maximus	32.7 -59.3 µg/g	24h [D -	toxic effects were
		(juvenile) [Turbot]	dw	clamworms]	observed
		Nitzschia closterium [Algae]	1 mg/L	24h [WB]	ingestion occurred	Wang et al., 2017
		Chlamys farreri
		[Scallop]		14 days [D]	4.44-50.18 mg/kg dw
				14 days [WB]	2.5-65 mg/kg dw


German Montes-Hernandez
email: german.montes-hernandez@univ-grenoble-alpes.fr

François Renard

Anne-Line Auzende

Nathaniel Findling

Dr German Montes

Amorphous Calcium-Magnesium Carbonate (ACMC) Accelerates Dolomitization at Room Temperature under Abiotic Conditions

Keywords: Disordered dolomite, Mg-carbonate, Amorphous carbonate, Time-resolved Raman spectroscopy, Mineral nucleation and growth

HAL is

Introduction

Dolomite, CaMg(CO3)2, precipitation kinetics and formation mechanism have been widely studied and controversial claims have been reported in the past two centuries [START_REF] Warren | Dolomite: occurrence, evolution and economically important associations[END_REF]. Abiotic precipitation of dolomite at ambient temperature (~25°C) is virtually impossible within typical laboratory experimental time scales [START_REF] Deelman | Breaking Ostwald's rule[END_REF][START_REF] Pimentel | The formation of the dolomite-analogue norsethite: Reaction pathway and cation ordering[END_REF][START_REF] Hänchen | Precipitation in the Mg-carbonate system-effects of temperature and CO2 pressure[END_REF][START_REF] Xu | Testing the cation-hydration effect on the crystallization of Ca-Mg-CO3 systems[END_REF]. This difficulty is interpreted to originate from the strongly bonded solvation shells of magnesium ions into aqueous media [START_REF] Deelman | Breaking Ostwald's rule[END_REF]. Dehydration of Mg ions is significantly facilitated by bacterial activity, including exopolymeric substances, and organic functionalized surfaces [START_REF] Vasconcelos | Microbial mediation as a possible mechanism for natural dolomite formation at low temperatures[END_REF][START_REF] Warthmann | Bacterially induced dolomite precipitation in anoxic culture experiments[END_REF]. Therefore, several studies have claimed that dolomite may precipitate in bio-assisted systems at ambient laboratory conditions [START_REF] Vasconcelos | Microbial mediation as a possible mechanism for natural dolomite formation at low temperatures[END_REF][START_REF] Warthmann | Bacterially induced dolomite precipitation in anoxic culture experiments[END_REF][START_REF] Sanchez-Roman | Presence of sulfate does not inhibit low-temperature dolomite minerals[END_REF](9)(10)(11)(12). Therefore, both textural and crystallographic characterization, reaction mechanism, and kinetics studies of dolomite precipitation at ambient/low temperature remain exciting scientific challenges for geochemists and mineralogists (13-17).

In addition, the effect of Mg hydration might not be the only factor of inhibition of dolomite formation at room temperature. Recent studies claimed that a more intrinsic crystallization barrier and the influence of fluid chemistry (e.g., relative size of the cations in solution) may prevent the formation of long-range ordered crystallographic structures in dolomite at ambient conditions [START_REF] Pimentel | The formation of the dolomite-analogue norsethite: Reaction pathway and cation ordering[END_REF][START_REF] Hänchen | Precipitation in the Mg-carbonate system-effects of temperature and CO2 pressure[END_REF][START_REF] Xu | Testing the cation-hydration effect on the crystallization of Ca-Mg-CO3 systems[END_REF]. Lippmann [START_REF] Lippmann | Sedimentary carbonate minerals[END_REF] described specific superstructures, called ordering-reflections, in the X-ray diffraction patterns of dolomite that were related to the regular alternation of monolayers of Ca and Mg oriented perpendicular to the c-axis of dolomite crystals. This organization indicates an equal Mg and Ca composition in the structure at the crystal scale. In natural dolomites, structural imperfections are frequently measured and, sometimes, nanometer sized crystallites with shortrange order may be expected [START_REF] Warren | Dolomite: occurrence, evolution and economically important associations[END_REF]. In this last case, the term disordered dolomite (also called protodolomite) is used because the superstructures ordering reflections, corresponding to the peaks (101), (015) and ( 021)) in X-ray diffraction patterns, are not detected (13,[START_REF] Montes-Hernandez | Precipitation of ordered dolomite via simultaneous dissolution of calcite and magnesite : New experimental insights into an old precipitation enigma[END_REF].

The present study demonstrates that an amorphous calcium-magnesium carbonate phase (ACMC) accelerates the dolomitization process at room temperature under abiotic conditions. Herein, an ACMC phase was instantaneously precipitated by using concentrated ionic solutions (HCO3 -/CO3 2- solution -Mg 2+ /Ca 2+ solution interactions). Then, the persistence time or lifetime (i.e. the duration until ACMC starts transforming) and transformation of ACMC into new minerals in the interacting solutions were monitored in real-time by using dynamic Raman spectroscopy [START_REF] Montes-Hernandez | Time-resolved in situ Raman spectroscopy of the nucleation and growth of siderite, magnesite and calcite and their precursors[END_REF]. We also investigated the effect of the Mg molar fraction with respect to Ca in solution. This parameter controls the amount of Mg that can be incorporated into the carbonate crystal lattice and the nature of transient carbonate phases, allowing to the precipitation of calcite (Mg/(Mg+Ca) = 0), low Mgcalcite (Mg/(Mg+Ca)<10%), high Mg-calcite (10%<Mg/(Mg+Ca)<45%), disordered dolomite (45%<Mg/(Mg+Ca)≤55%) and high Ca-magnesite (Mg/(Mg+Ca)>60%), as reported in the literature (e.g. [START_REF] Long | Biogenic and synthetic high magnesium calcite -A review[END_REF][START_REF] Yu | High-Magnesium Calcite Mesocrystals: Formation in Aqueous Solution under Ambient Conditions[END_REF][START_REF] Landers | High-Magnesian Calcite Mesocrystals: A Coordination Chemistry Approach[END_REF][START_REF] Yang | A study on the influence of sodium carbonate concentration on the synthesis of high Mg calcites[END_REF][START_REF] Romaneck | Inorganic synthesis of Fe-Ca-Mg carbonates at low temperature[END_REF].

High Mg-calcite and disordered dolomite precipitation at room temperature is frequently related to bio-mineralization processes, as observed in corals, seashells and many other invertebrates or observed in laboratory experiments under biotic conditions [START_REF] Huang | Aerobically incubated bacterial biomass-promoted formation of disordered dolomite and implication for dolomite formation[END_REF][START_REF] Long | Biogenic and synthetic high magnesium calcite -A review[END_REF]. The present experimental study demonstrates that disordered dolomite, CaMg(CO3)2, can precipitate at low temperature when ideal Mg/Ca ratio, high-carbonate alkalinity (HCO3 -/CO3 2-coexistence) and high ionicconcentration are reached in abiotic or biotic systems. Herein, the formation of an amorphous phase plays a significant role to produce disordered dolomite

Materials and Methods

Disordered dolomite CaMg(CO3)2 formation at room temperature

The conditions to precipitate disordered dolomite at room temperature (27-31°C) were the following: 100 mL of NaHCO3 (1M) and 100 mL of Na2CO3 (1M) were placed into a Hastelloy C22 reactor (Parr, total internal volume of 600 mL) coupled with a Raman probe immerged into solution/suspension in order to monitor in real-time precipitating carbonate particles and aqueous carbonate species. This experimental setup was reported previously in Montes-Hernandez group [START_REF] Montes-Hernandez | Time-resolved in situ Raman spectroscopy of the nucleation and growth of siderite, magnesite and calcite and their precursors[END_REF]. Raman spectra were collected with a Raman RXN1, Kaiser Optical Systems with an exposure time of three seconds and averaged over three scans.

The carbonate speciation in initial solution was verified by Raman spectroscopy before the injection of Ca-Mg solution (HCO3 -peaking at 1016 cm -1 and CO3 -2 peaking at 1066 cm -1 ; see Fig. S1-A). This carbonate alkaline solution was immediately dispersed by mechanical agitation (400 rpm) before 200 ml of a Ca-Mg solution (Mg molar fraction of 0.75 and Mg concentration of 0.375M) were injected for about 1-2 minutes with a syringe. Following this injection step, the carbonate speciation and precipitated particles (i.e. transformation of amorphous calciummagnesium carbonate ACMC into carbonate crystalline phases) were monitored by Raman spectroscopy for three to seven days, with an acquisition frequency of one Raman spectra every minute during the first three hours and every five or ten minutes in the remaining time.

Selected Raman peaks corresponding to identified mineral phases (see Table S1) were fitted by using simple or combined Gaussian model in order to estimate both the full wide half maximum (FWHM) and integrated peak area as a function of time (Movie S1). This calculation provided the peak decomposition necessary to propose relevant reaction mechanisms and to quantify the kinetics of precipitation of disordered dolomite (MgCa(CO3)2).

Role of Mg molar fraction

The persistence time of amorphous calcium magnesium carbonate (ACMC) and its transformation into crystalline carbonate phases in the interacting solutions were measured as a function of Mg molar fraction (Mg molar fraction = (VMg/(VMg+VCa)) that was varied between 0 and 1 (experiments 5-11 in Table 1). Herein, the persistence time, also called lifetime, is defined as the duration over which ACMC is the only precipitate phase present in the suspension before starting to transform into crystalline carbonate phases. We define the nucleation time of each crystalline phase as the time where this mineral is detected by Raman spectroscopy. These experiments were performed following the same protocol described in section 2.1, except for the added volume of Ca and Mg solutions that was adjusted for each investigated Mg molar fraction. Table 1 summarizes all precipitation experiments performed in this study; each experiment was repeated at least twice to verify reproducibility of the results.

Ex situ characterization of precipitates

At the end of each experiment, the solid product was recovered by centrifugation and washed twice with ultrapure water, and once with ethanol. Then, it was dried under a laminar flow of air at 20°C for 48 h. The dry solid products were stored in plastic flasks for subsequent characterization of selected samples by Field Emission Gun Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and powder X-ray diffraction (XRD).

Powder XRD spectra were acquired using a Siemens D5000 diffractometer in Bragg-Brentano geometry, equipped with a theta-theta goniometer with a rotating sample holder. Diffraction patterns were collected using Cu kα1 (kα1=1.5406 Ǻ) and Cu kα2 (kα2=1.5444 Ǻ) radiations in the range 2 = 10 -70°, with a step size of 0.04° and a counting time of six seconds per step. For highresolution imaging, the solid products were dispersed by ultrasonic treatment in absolute ethanol for five minutes. Two droplets of the suspension were then deposited directly on an aluminum support and coated with gold-platinum. The powder was imaged using a Zeiss Ultra 55 FESEM with a maximum spatial resolution of approximately 1 nm at 15kV. In addition, recovered solid products from experiments 1 and 2 (Table 1) were shaken in ethanol for a short time in order to separate the aggregates without any additional treatment. One droplet of the suspension was deposited on a perforated carbon foil and placed on a conventional copper micro-grid for further observations with a JEOL 2100F Transmission Electron Microscope (TEM) operating at 200 kV, equipped with a field emission gun and a high-resolution pole piece achieving a point-to-point resolution of 1.8 Å. Chemical analyses in selected points on the sample were performed by Electron Dispersive Spectroscopy (EDS).

Results

Precipitation of disordered dolomite at room temperature: Reaction mechanism and kinetics

Concentrated ionic solutions were chosen to produce an amorphous calcium-magnesium carbonate (ACMC) phase. Our in-situ Raman spectroscopy data confirmed the instantaneous formation of ACMC when alkaline carbonate solution (HCO3 -/CO3 -2 =1) was mixed with Mg-Ca solution (Mg molar fraction = 0.75), as displayed for three experiments in Fig. S1-B. The precipitated ACMC (Ca0.5Mg0.5CO3.nH2O) is characterized by a broad Raman peak at 1085 cm -1 , shifted 6 cm -1 away and broader with respect to the peak of amorphous calcium carbonate (ACC: CaCO3.nH2O) at 1079 cm -1 (this study), close to the value of 1080 cm -1 reported in other studies (e.g. [START_REF] Wehrmeister | Amorphous, nanocrystalline and crystalline calcium carbonates in biological materials[END_REF][START_REF] Wang | Raman spectroscopic characterization of the magnesium content in amorphous calcium carbonates[END_REF]. Timeresolved Raman spectroscopy shows that ACMC starts transforming into crystalline phases after about 2.5 h of reaction. Nesquehonite (MgCO3.3H2O) is the first detected phase, with a peak at 1099 cm -1 and a nucleation time of 2.5 h, followed by monohydrocalcite (CaCO3.H2O), with a peak at 1067 cm -1 and a nucleation time of 3.3 h (Fig. 1). All phases detected in the time-resolved Raman spectroscopy measurements are summarized in Table S1 and their Raman feature assignation is supported by previous studies that used systematically ex-situ Raman spectroscopy onto powdered samples. Nesquehonite and monohydrocalcite are transient phases, i.e. their slow concurrent dissolution allows the continuous precipitation of disordered dolomite with a Raman peak at 1094 cm -1 (Fig. 2). Broad feature of the main peak and low Raman signal in lattice mode at 300 cm -1 suggest the presence of nanosized crystals, as confirmed by FESEM images that reveal crystallites with size in the range 20 to 80 nm and forming irregular aggregates (Fig. S2). Herein, we suggest that this phase is a disordered dolomite, i.e. short-range order forming nanosized crystallites, because the superstructures ordering reflections ((101), (015) and (021)) are not detected in our laboratory X-ray powdered diffraction, despite an ideal atomic composition (Mg/Ca=1) (Fig. S3).

The movie S1 displays the time evolution of the peaks of the main mineral phases during experiment 2 (Table 1), leading to the formation of disordered dolomite, including the evolution of ACMC, nesquehonite, and monohydrocalcite. The surface areas of the peaks corresponding to these four phases evolve as a function of time and are used here as proxies to measure the relative concentrations of these components in the suspension (Fig. S4).

From these time-resolved Raman measurements and spectra analyses (Figs. 1, 2 and S4), the following reactions are proposed, which summarize the mechanism for disordered dolomite formation: Nesquehonite formation 2Ca0.5Mg0.5CO3.nH2O + 3H2O → MgCO3.3H2O +CaCO3.nH2O + nH2O

(1)

Monohydrocalcite formation

CaCO3.nH2O + H2O → CaCO3.H2O + nH2O

Formation of disordered dolomite via concurrent dissolution of transient phases

MgCO3.3H2O + CaCO3.H2O → CaMg(CO3)2 + 4H2O (3)
Data show that the concurrent slow dissolution of nesquehonite and monohydrocalcite nourish the precipitation of disordered dolomite. However, disordered dolomite nucleation formed during the first hours (nucleation time = 3.2h), as detected by fitting the Raman spectra (see Movie S1 and Fig. S4). These results imply that nesquehonite and monohydrocalcite play a critical retarding effect on the formation of disordered dolomite as discussed below.

The precipitation of disordered dolomite from direct transformation of ACMC could also occur as:

2Ca0.5Mg0.5CO3.nH2O → CaMg(CO3)2 + 2nH2O (4)
This more simple reaction mechanism was detected by time-resolved Raman spectroscopy (Fig. 3, experiment 1 in Table 1), but with a low experimental reproducibility (once over four total experiments performed under identical conditions, experiments 1 to 4 in Table 1). In this particular case, the lifetime of ACMC was larger and equal to 10 hours, as shown on Fig. 3. Herein, the particle size distribution of disordered dolomite was more homogeneous with an average size of 20 nm (see FESEM images in Fig. S2 for experiment 1). We assumed that, in this particular case, ACMC reached an ideal Mg/Ca ~ 1 ratio and then its direct transformation into disordered dolomite could take place, as demonstrated by the Raman data (Fig. 3). However, this chemical event might be strongly sensitive to small fluctuations of room temperature, fluid chemistry, mechanical agitation and time of mixture of ionic solutions because it happened only once over the four experiments performed under the same conditions (experiments 1-4 in Table 1).

In natural open systems oversaturated with respect to dolomite, fluid chemistry and temperature fluctuations could inhibit dolomite formation and the precipitated transient phases could remain persistent and stable for long durations (e.g. [START_REF] Rodriguez-Blanco | The role of Mg in the crystallization of monohydrocalcite[END_REF][START_REF] Rodriguez-Blanco | A route for the direct crystallization of dolomite[END_REF]. Such observations may provide an explanation why dolomite is absent in natural systems presently oversaturated with respect to dolomite.

Role of Mg molar fraction

At the investigated carbonate alkaline conditions (HCO3 -/CO3 2-= 1, 0.5 M for each specie, and pH~pKa2~10.3), both the concentration of Mg and its molar fraction with respect to Ca play a critical role on the lifetime of ACMC. When the Mg molar fraction is larger than 0.5, the ACMC lifetime increases substantially (Fig. 4). The reaction mechanism, i.e. the nature of transient crystalline phases and final recovered products, is also strongly dependent on the concentration of Mg (see Table 1). For example, when the Mg molar fraction is less or equal than 0. despite the difference in pH and Mg concentration [START_REF] Rodriguez-Blanco | The role of pH and Mg on the stability and crystallization of amorphous calcium carbonate[END_REF]. At higher Mg molar fraction (e.g. 0.5 and 0.6), high Mg-calcite mesocrystals (MgxCa1-xCO3 with 0.1<x<0.45) form and the vaterite phase is not detected (see Table 1). Mg-calcite mesocrystals are micrometric porous aggregates constituted of oriented nano-crystals and that form cauliflower and peanut-like morphologies (Fig. S6). These peculiar morphologies and the process of aggregation of nanocrystals have been reported in previous studies (e.g. [START_REF] Yu | High-Magnesium Calcite Mesocrystals: Formation in Aqueous Solution under Ambient Conditions[END_REF][START_REF] Landers | High-Magnesian Calcite Mesocrystals: A Coordination Chemistry Approach[END_REF]. In some studies, high-Mg calcite with peculiar morphologies and with Mg content into crystal lattice (<45%) was misinterpreted as disordered dolomite (e.g. 15-16). Therefore, Mg-calcite mesocrystals are not necessary made of disordered dolomite, except when the Mg/Ca ratio of the crystal lattice is close to 1.

At a Mg molar fraction of 0.75 and under abiotic conditions, we observed the formation of disordered dolomite (CaMg(CO3)2), as discussed in section 3.1. In complement, X-ray data (Fig. 5) show the (104) reflection in the solid products recovered at the end of experiments that used different initial Mg molar fraction (see also Table 1. In addition, from Rietveld refinements of XRD patterns, the Table 2 summarizes the mineral composition and Mg content into calcite crystal lattice. In general, our results are in agreement with studies that have investigated the influence of Mg molar fraction on the lifetime of ACC and ACMC phases and their transformation into crystalline phases (e.g. [START_REF] Rodriguez-Blanco | The role of Mg in the crystallization of monohydrocalcite[END_REF][START_REF] Rodriguez-Blanco | A route for the direct crystallization of dolomite[END_REF][START_REF] Rodriguez-Blanco | The role of pH and Mg on the stability and crystallization of amorphous calcium carbonate[END_REF]. In addition to already published studies, our study reports specific experimental conditions that allow the synthesis of disordered dolomite by controlling exclusively the Mg molar content (0.75) and the carbonate alkalinity (HCO3 -/CO3 2-=1, pH~pKa2~10.3) at room temperature (experiments 1-4 in Table 1).

Finally, for Mg molar fraction of 0.9 (experiment 10 in Table 1), the lifetime of ACMC was prolonged to about 4.5 hours and a more complex reaction mechanism was monitored by timeresolved Raman spectroscopy (Fig. 6). In this experiment, monohydrocalcite (CaCO3•H2O) was detected as a transient phase before the formation of disordered dolomite and high Ca-Magnesite was measured by X-ray diffraction in the product recovered after the experiment (Fig. 5 and Table 2). Dypingite (Mg5(CO3)4(OH)2•5H2O) was also detected, and this hydrated carbonate co-existed with disordered dolomite and Ca-magnesite until the end of experiment (Fig. 6). These results demonstrate that the Mg molar fraction controlled the lifetime of ACMC in the interacting solutions, the reaction mechanism, the kinetics, and the amount of Mg incorporated into the carbonate.

Discussion and concluding remarks

Dolomite is a critical mineral that incorporates large volumes of carbon dioxide into a solid form in many geological environments [START_REF] Warren | Dolomite: occurrence, evolution and economically important associations[END_REF]. Primary dolomite formation (Mg 2+ + Ca 2+ + 2CO3 2- →CaMg(CO3)2) at low temperature (20-35°C) and secondary dolomite formation (2CaCO3 + Mg 2+ → CaMg(CO3)2 + Ca 2+ ) at higher temperature (diagenetic or hydrothermal, 60-300°C) have been proposed to explain dolomitization processes in natural environments [START_REF] Warren | Dolomite: occurrence, evolution and economically important associations[END_REF]. Primary dolomite formation has led to controversial claims because ordered dolomite could not be synthesized in laboratory under abiotic conditions and only disordered dolomite and high Mg-calcite are generally observed in environments oversaturated with respect to dolomite [START_REF] Deelman | Breaking Ostwald's rule[END_REF](15)[START_REF] Huang | Aerobically incubated bacterial biomass-promoted formation of disordered dolomite and implication for dolomite formation[END_REF][START_REF] Qiu | High salinity facilitates dolomite precipitation mediated by Haloferax volcaniiDS52[END_REF]. Bio-assisted primary dolomite formation, and/or formation mediated by living organisms, have been proposed. In such cases, cellular and intracellular surfaces and exopolymeric substances can overcome the kinetic barrier to nucleate dolomite (e.g. 6-12). Functionalized organic molecules/surfaces can also decrease the Mg hydration barrier and catalyze dolomite formation at low temperature (e.g. 31).

However, the reaction mechanism responsible for dolomite formation (e.g., role of transient amorphous or crystalline phases) and clear proofs or explanations concerning the dolomite superstructures ordering reflections in the X-ray diffraction patterns have been ambiguously

provided [START_REF] Vasconcelos | Microbial mediation as a possible mechanism for natural dolomite formation at low temperatures[END_REF]12). Based on the present study and on recent mechanisms proposed to explain mineral nucleation (e.g. 32-36), we infer that primary dolomite, as initially defined (Mg 2+ + Ca 2+ + 2CO3 2- →CaMg(CO3)2), has a very low probability to form at room temperature in abiotic or biotic systems, i.e. through heterogeneous nucleation (pre-existence of reactive surfaces) and a non- Another critical point concerning the so-called primary dolomite is the existence of superstructures ordering reflections in X-ray diffraction patterns (e.g. ( 101), ( 015) and (021), Fig. S3). Herein, some factors can perturb their unambiguous detection. For example, when dolomite crystal size is larger than 100 nm and coexisting crystalline phases have a low concentration, X-ray powder diffraction or electron diffraction in TEM allow a clear identification of superstructure ordering reflections. Conversely, if dolomite crystal size is of the order or smaller than 20 nm (Fig. S7), the detection of superstructure ordering reflections is more challenging in X-ray diffraction patterns and by electron diffraction in TEM when nanoparticles are aggregated, despite the ideal Mg content (Ca/Mg ~1) in the structure lattice (Fig. S3). In such case, disordered dolomite, i.e. short-range ordered crystallographic structures, is assumed and in general, longer range ordering is reached with an increase of temperature (corresponding to an increase of average size of dolomite crystals) as already demonstrated in a previous study (13). We claim that the detection limit of laboratory 1). The lifetime of ACMC and positions of crystalline phases are indicated.

classical
Figure 2. Time-lapse Raman spectroscopy monitoring of the formation of disordered dolomite from ACMC in experiment 2 (Table 1). Left: evolution of the two transient phases, nesquehonite and monohydrocalcite. Right: time-lapse evolution of the main peaks. 1). Right: time-lapse evolution of the main peaks. ACMC in experiment 10 (Table 1). Monohydrocalcite is a transient phase (Mg molar fraction of 0.9) and dypingite (hydrated Mg carbonate mineral: Mg5(CO3)4(OH)2.5H2O) coexist with disordered dolomite until the end of experiment.

  2, vaterite polymorph is the main transient phase before the formation of low Mg-calcite (MgxCa1-xCO3 with x<0.1) (Fig. S5). Here, three reaction steps are clearly identified: (1) ACC formation with a lifetime of 3 minutes; (2) concurrent transformation of ACC into vaterite and Mg-calcite; and (3) slow transformation of vaterite into low Mg-calcite via coupled dissolution-crystallization process. This reaction mechanism is in agreement with results obtained from in-situ time-resolved synchrotronbased wide-angle X-ray scattering (WAXS) and energy dispersive X-ray diffraction (ED-XRD),

  nucleation mechanism is therefore expected. The present study demonstrates that transient amorphous or crystalline phases play a significant role in the formation of disordered dolomite. Such transient phases can decrease the energy barrier under ideal fluid chemistry conditions (e.g. direct transformation of ACMC into disordered dolomite), but, they can also retard dolomite precipitation (e.g. via concurrent dissolution of nesquehonite and monohydrocalcite) as demonstrated in the present study (Figs. 1, 2, 3 and movie S1). Crystalline phases (e.g. dypingite, monohydrocalcite, aragonite) can produce an inhibiting effect in laboratory experiments or in some natural dolomitic environments (1). From the present experimental study, we conclude that ACMC accelerates dolomitization in a short interval of Mg molar content (0.6-0.75) at low temperature and the revealed reaction mechanism could exist in natural dolomitic environments such as lagoons, evaporitic settings, or caves.

Figure 3 .

 3 Figure 3. Left: Time-lapse Raman spectroscopy monitoring of the formation of disordered dolomite

Figure 4 .

 4 Figure 4. Lifetime of ACMC determined from time-resolved Raman measurements as a function

Figure 5 .

 5 Figure 5. X-ray diffraction data showing the (104) reflection for calcite, dolomite and magnesite

29

 29

Figure 6 .

 6 Figure 6. Time-lapse Raman spectroscopy monitoring of the formation of disordered dolomite from

Table 1 .

 1 X-ray diffraction data when nanoparticles exist (the peaks are broader and have lower intensity and the low intensity of superstructure ordering reflections) and the difficulty to synthesize dolomite in laboratory experiments have led to contradictory interpretations on the formation of dolomite at low temperature. In this perspective, the formation of disordered dolomite at low temperature in abiotic systems can be achieved at room temperature. A future challenge would be to determine whether a regular alternation of monolayers of Ca and Mg (perpendicular to the c-axis) may exist in nanosized dolomitic crystals, that would require to develop specific analytical and imaging methods, such as energy filtered transmission electron microscopy combined with electron energy List of experiments with time-lapse Raman spectroscopy for precipitation of disordered dolomite at room temperature and influence of Mg molar ratio. A constant carbonate alkalinity of HCO3 -/CO3 2-=1 (0.5M) and a total cationic (Mg-Ca) concentration of 0.5M were imposed.

	loss spectroscopy.

* these phases were also characterized by powder X-ray diffraction

Table 2 .

 2 Mineral carbonate composition and Mg content in lattice structure identified from Rietveld refinement of X-ray diffraction patterns. In experiment 10, aragonite, dypingite and eteilite were also detected.

	Exp.	Mg molar	Calcite	Low Mg-	High Mg-	Disordered	High Ca-
		fraction		Calcite	Calcite	Dolomite	Magnesite
	5	0	CaCO3	none	none	none	None
	6	0.05	CaCO3	none	none	none	none
	7	0.20	CaCO3	Mg0.05Ca0.95CO3	none	none	none
	8	0.50	none	none	Mg0.15Ca0.85CO3	none	none
					Mg0.23Ca0.77CO3
	9	0.6	none	none	Mg0.35Ca0.65CO3	none	none
	1	0.75	none	none	none	Mg0.49Ca0.51CO3	none
	10	0.9 x	none	Mg0.07Ca0.93CO3	none	Mg0.45Ca0.55CO3	Mg0.68Ca0.32CO3

Figure 1. Time-lapse Raman spectroscopy monitoring of amorphous calcium-magnesium carbonate (ACMC) transformation into crystalline phases during the first four hours of experiment 2 (Table

Acknowledgements

The authors acknowledge funding from the French National Centre for Scientific Research (CNRS).

Appendix A. Supplementary data

Supplementary material [START_REF] Warren | Dolomite: occurrence, evolution and economically important associations[END_REF]

Amorphous calcium-magnesium carbonate (ACMC) accelerates dolomitization at room temperature under abiotic conditions

By German Montes-Hernandez, François Renard, Anne-Line Auzende, Nathaniel Findling

Table of Contents Graphic

Synopsis: The present study reports on specific abiotic conditions that allows the precipitation of disordered dolomite, high Mg-calcite and high Ca-magnesite at room temperature over time scales of hours to days. Here we show that an amorphous calcium magnesium carbonate (ACMC) phase accelerates dolomitization at room temperature.