Tiemélé Juliette Vievard

Laurent-Simon Amoikon

Aminata Nadjoua

Christine Coulibaly

Mónica Gisel Devouge-Boyer

Moussan Francine Arellano-Sánchez

Dede Théodore Désirée Aké, N'

Mélanie Djeni

Mignot

Tiemele Laurent

Simon Amoikon

Aminata Nadjoua Coulibaly

Christine Devouge-Boyer

Monica Arellano

Gisel Sanchez

Aké Francine

Theodore N'

Dede Djeni

Mélanie Mignot
email: melanie.mignot@insa-rouen.frtls.amoikon@gmail.com

Extraction and quantification of pesticides and metals in palm wines by HS-SPME/GC-MS and ICP-AES/MS

Keywords: palm wine, pesticides, metals, headspace solid-phase microextraction, gas chromatography, mass spectrometry, induced coupled plasma mass spectrometry

Introduction

Palms are believed to be among the oldest flowing plant in the world [START_REF] Redhead | Utilization of Tropical Foods: Trees[END_REF]. The oil palm (Elaeis guineensis Jacq.) is one of the major cultivated crops among the economically important palm species. Their growth is so vigorous that they are considered as a "weed" in neglected or abandoned farms. Different parts of the palm tree can be used for various purposes, but one important commercial activity associated with the tree is production of wine from the sap by the local populations [START_REF] Yaméogo | Uses and commercialization of Borassus akeassii Bayton, Ouédraogo, Guinko non-wood timber products in South-Western Burkina Faso, West Africa[END_REF]). Yet the oil palm in West Africa is highly valued for palm wine production, and could allow farmers to supplement and diversify their incomes. As an example, in western Ivory Coast, the resumption of wild oil palm in old cocoa farms played an important role in the 1990s, when farmers faced collapsing cocoa prices and inheritance conflicts, which resulted in the abandonment of many cocoa plantations where the density of oil palms trees grew rapidly. Thus, the felling of palm trees made it possible to produce palm wine for sale and for own consumption, thus generating income, reducing risks and creating jobs and new intergenerational and institutional arrangements (Ruf, 2014).

Palm wine is the collective name for a group of alcoholic beverages produced by the natural fermentation of the sap obtained from various tropical plants of the Palmae family [START_REF] Okafor | Microbiology and Biochemistry of Oil-Palm Wine[END_REF], such as Elaeis guineensis, Raphia hookeri, Phoenix dactylifera, B. aethiopum and Cocos nucifera [START_REF] Mollet | Sustainable Exploitation of Borassus aethiopum, Elaeis guineensis and Raphia hookeri for the Extraction of Palm Wine in Côte d'Ivoire. Environment[END_REF][START_REF] Sambou | Palm wine harvesting by the Bassari threatens Borassus aethiopum populations in north-western Guinea[END_REF][START_REF] Stringini | Yeast diversity during tapping and fermentation of palm wine from Cameroon[END_REF]; [START_REF] Ziadi | Microbiological analysis and screening of lactic acid bacteria from Tunisian date palm sap[END_REF]. It is mainly consumed by more than 10 million people in West Africa [START_REF] Battcock | Fermented Fruits and Vegetables: A Global Perspective[END_REF] but it is also available in Asia, India and Mexico [START_REF] Chandrasekhar | A Review on palm wine[END_REF]. A study by [START_REF] Fatoye | Substance use amongst secondary school students in rural and urban communities in south western Nigeria[END_REF] on alcoholic drinks (beer, locally fermented wine and locally distilled gins) in West Africa showed it as the most commonly used alcoholic beverages. It serves a variety of purposes, notably in traditional namings and marriage ceremonies, medicine (cure of low sperm count and poor sight), traditional incantation and also acts as catalyst for extraction of juice from herbs and roots for medical application.

Generally, the palm sap for palm wine production is obtained through a process known as tapping, operated in open-air, and involving a series of operations on live standing or felled or cut down tree, such as perforation of the trunk, insertion of a tube in the hole and collection of the sap in a container which can be a gourd, clay pot, plastic container, glass bottle or calabash as previously reported [START_REF] Ouoba | The microbiology of Bandji, palm wine of Borassus akeassii from Burkina Faso: Identification and genotypic diversity of yeasts, lactic acid and acetic acid bacteria[END_REF]. The tapping process between 2 and 8 weeks and palm wine is collected twice a day (early in the morning and in the evening) and either immediately consumed on fields or stored for later sale.

Despite the enormous economic, medicinal and socio-cultural importance attached to the production of palm wine in rural African society, the consumption of this drink is becoming increasingly problematic because of two major facts. Indeed, it becomes fearful on the one hand, and this is a recurring observation, to frequent the palm wine from cabarets. This fear is generated by the fact that crooked sellers tend to sell an adulterated version of the drink, resulting from the adulteration of the original palm wine by using water (generally of low quality with a distinct possibility of contamination with undesirable elements such as metals) and artificial sweetness, which sometimes result in diarrhea, abdominal pains, and other stomach problems [START_REF] Ukhun | Some mineral profile of fresh and bottled palm wine-A comparative study[END_REF]. In other hand, as palm trees mostly grow concomitantly in cocoa farms in rural areas, the second problem and hence the quieter comes from the potential contamination of this drink during tapping process by pesticides or their residues used in the agrochemical treatments of cocoa fields in which the sap extraction process takes place. Indeed, in an attempt to reduce the incidence of insect pests and diseases on cocoa farms, a large number of pesticides are usually applied on farms. These pesticides are hazardous in very low concentrations and cause immense damage to the ecosystem. In most developing countries like Ivory Coast, consequences are often severe because approved pesticides are not used and recommended frequencies of pesticides application by government agencies for crops are not followed. Farmers however misuse, overuse and apply pesticides indiscriminately with disregard to safety measures and regulations on chemical use as reported by [START_REF] Konradsen | Acute pesticide poisoning: a global public health problem[END_REF] and [START_REF] Sam | Effectiveness of an educational program to promote pesticide safety among pesticide handlers of South India[END_REF]. In consequence, the drink produced can be contaminated at multiple steps in the tapping process by plant material treated with pesticides, particularly leaves used to cover containers containing the drink in the palm wine processing environment, or insects when flying into bowls. According to the National Pesticide Information Center (2011), an increase in the use of agrochemicals has been observed over the past fifty years making humans more exposed to heavy metals, pesticides and insecticides. Heavy metals and pesticides have carcinogenic, mutagenic and teratogenic potential and exposure can cause irreversible damage to humans, including death, and are therefore considered a serious public health problem particularly in sub-Saharan countries. Although many studies have revealed that pesticides and heavy metals poses threats to the environment, and farmers themselves, their potential presence in palm wine and the risks associated have to be determined.

Several methods are available for extraction and quantification of pesticides and metals from complex matrices. For pesticides, liquid extraction with solvents, such as dichloromethane, acetone [START_REF] Gambacorta | Pesticide residues in tomato grown in open field[END_REF], and ethyl acetate (Munawar and Waqas Hameed, 2013) has been used. Pesticide residues have also been extracted from apple juice using a solid phase extraction (SPE) method [START_REF] Han | Application of graphene for the SPE clean-up of organophosphorus pesticides residues from apple juices[END_REF]; Velkoska-Markovska and Petanovska-Ilievska, 2013), from berry fruits using an Envi-Carb cartridge [START_REF] Yang | Multiresidue method for determination of 88 pesticides in berry fruits using solid-phase extraction and gas chromatography-mass spectrometry: Determination of 88 pesticides in berries using SPE and GC-MS[END_REF] and using an HS-SPME method, a fast, automatable, and inexpensive method, including in mangoes from Brazil (Filho, Dos Santos, and De Paula Pereira 2010), in water samples from Argentina (Bonansea, Amé, and Wunderlin 2013) and in wines from Italy [START_REF] Vitali | Determination of pesticide residues in wine by SPME and GC/MS for consumer risk assessment[END_REF]. In general, the analysis of pesticides is done using gas [START_REF] Han | Application of graphene for the SPE clean-up of organophosphorus pesticides residues from apple juices[END_REF][START_REF] Yang | Multiresidue method for determination of 88 pesticides in berry fruits using solid-phase extraction and gas chromatography-mass spectrometry: Determination of 88 pesticides in berries using SPE and GC-MS[END_REF] or liquid (Velkoska-Markovska and Petanovska-Ilievska, 2013) chromatography, depending on the polarity, volatility and decomposition risk of the compounds. For the detector, the electron capture detector is commonly used to quantify organochlorines, while the nitrogen-phosphorus detector is used for organophosphates. Mass spectrometry offers the advantage of being able to identify and quantify a wide range of molecules, without being limited to a single class of pesticides [START_REF] Bonansea | Determination of priority pesticides in water samples combining SPE and SPME coupled to GC-MS. A case study: Suquía River basin[END_REF]. Metals are commonly analyzed by ICP-AES/MS in pharmaceutical compounds [START_REF] Lewen | A rapid ICP-MS screen for heavy metals in pharmaceutical compounds[END_REF], textile materials [START_REF] Rezić | ICP-OES determination of metals present in textile materials[END_REF], or wines and alcoholic beverages (Płotka-Wasylka et al., 2018), due to sensitivity, low limit of detection and speed of analysis. Prior to analysis, samples are mineralized to remove organic matter and ensure quantitative dissolution of metals in the case of solid matrices. Most of the time, acids or acid mixtures are used for this step [START_REF] Lewen | A rapid ICP-MS screen for heavy metals in pharmaceutical compounds[END_REF]: nitric acid, hydrochloric acid, sulfuric acid, or mixtures, with aqua regia being the most famous. Due to the low detection levels required by regulatory agencies, efficient sample preparation and trace-level detection are important aspects in an analytical method.

This research was therefore conducted to determine the concentration of heavy metals and pesticides using optimized methods and then raise awareness of the possible health risk while consuming this beverage.

Materials and methods

Chemicals

Ultrapure water (resistivity 18.2 MW•cm), obtained from a Milli-Q system (Millipore, Bedford, MA, USA), sodium sulfate (GPR Rectapur, VWR Chemicals, Belgium), ethanol (99%, Fisher Scientific, UK), (+) limonene (97%, Accros Organics, USA) decane (99%, Sigma-Aldrich, USA), L-ascorbic acid (99%, VWR Chemicals, Belgium), calcium chloride (98%, VWR Chemicals, Belgium), potassium chloride (99%, Carlo Erba, Italia), magnesium nitrate (98%, Sigma-Aldrich, USA), and sodium chloride (99.5%, Acros Organics, USA), were used for the preparation of the simulative palm wine. For the mineralizations, nitric acid (68%, trace analysis grade, Fisher Scientific, UK) and hydrogen peroxide (30%, VWR Chemicals, Belgium) were employed. Acetone (pesticides residue grade, Fisher Scientific, UK) and methanol (HPLC grade, Fisher Scientific, UK) were used for the preparation of the stock solutions of pesticides.

The pesticides standard consisted in six stock solutions. Two solutions were purchased from Restek (USA): an OrganoPhosphorus Pesticides (OPPs) solution in acetone containing acephate (200 µg mL -1 ), azinphos methyl (400 µg mL -1 ), chlorpyrifos (100 µg mL -1 ), demeton-S-methyl (200 µg mL -1 ), dichlorvos (500 µg mL -1 ), dimethoate (200 µg mL -1 ), ethion (200 µg mL -1 ), malathion (200 µg mL -1 ), methamidophos (500 µg mL -1 ), methidathion (200 µg mL -1 ), omethoate (1,000 µg mL -1 ), pirimiphos methyl (100 µg mL -1 ), profenofos (200 µg mL -1 ), prothiofos (200 µg mL -1 ), pyrazophos (500 µg mL -1 ), and tolclofos-methyl (100 µg mL -1 ), and an organohalide pesticides solution in methanol containing aldrin, alachlor, atrazine, γ-BHC (lindane), cis-chlordane, trans-chlordane, dieldrin, endrin, heptachlor, heptachlor epoxide (isomer B), hexachlorobenzene, hexachlorocyclopentadiene, methoxychlor, cis-nonachlor, trans-nonachlor, and simazine, at 200 µg mL -1 each. Two solutions were purchased from Fisher Scientific (France): an OrganoChloride Pesticides (OCPs) solution in acetone containing aldrin, α, β and δ-BHC, dieldrin, α and β-endosulfan, endosulfan sulfate, endrin, endrin aldehyde, endrin ketone, lindane, heptachlor, heptachlor epoxide (isomer B), methoxychlor, p,p'-DDD, p,p'-DDE, and p,p'-DDT at 200 µg mL -1 each, and a terbutylazine solution in acetone at 100 µg mL -1 . A methyl parathion solution in acetone at 1000 µg mL -1 , and a diazinon solution in methanol at 100 µg mL -1 were purchased from Merck (Germany).

The stock solution containing all pesticides was prepared in pure acetone and before each serie of analyses. The pesticides standard solutions at different levels were prepared by spiking with the stock solution into 3 mL of the simulative palm wine contained in a 20 mL sealed glass vial.

Calibration curves were prepared from dilutions of the stock solution. The concentration of pesticides ranged from 0.25 µg L -1 for pirimidiphos methyl and tolclofos-metyl to 1000 µg L -1 for simazine.

A metal solution (VWR Chemicals, Leuven, Belgium) containing aluminum, silver, arsenic, boron, barium, calcium, cadmium, cerium, cobalt, chromium, copper, dysprosium, erbium, europium, iron, gadolinium, holmium, potassium, lanthanum, lithium, lutetium, magnesium, manganese, sodium, neodymium, nickel, phosphorus, lead, rubidium, selenium, samarium, strontium, thallium, thulium, vanadium, and zinc, at 10 mg L -1 each, was used. Three monoelement solutions containing bismuth at 10 mg L -1 (Spex CertiPrep, USA), molybdenum (Spex CertiPrep, USA) and tin at 1000 mg L -1 (Fisher Scientific, France) were used for preparing the stock solutions. Calibration curves were prepared from dilutions of the stock solution. The concentration of metals ranged from 0.05 µg L -1 to 100 µg L -1 for all metals except for rubidium which ranged from 0.05 to 2 mg L -1 and for phosphorus which ranged from 0.5 to 20 mg L -1 .

Samples

This study was carried out on different palm wines produced in four cities in Ivory Coast (Abidjan, Aboisso, Hiré and Toumodi). Four samples of each city were collected from local producers (P) and four from resellers (R), who could eventually modify the composition of the palm wines. Thirty two palm wines were analyzed (3 replicates) for determination of pesticides and metals. Samples were stored in a freezer at -18°C. Before analysis, samples were kept at 4°C during two hours in a fridge and thirty minutes at room temperature. The palm wines presented particles naturally present. To estimate the real concentrations to which the population is exposed, it was decided to let the samples as naturally present and consumed.

Consequently, no filtration nor centrifugation was done, and the samples were mixed before analysis in triplicate.

Instrumentation

GC-MS

Analyses of palm wine were performed using a GC-MS QP-2020 NX (Shimadzu, Germany) equipped with an auto-sampler AOC-6000 (automatic injection). Different GC conditions for analyzing pesticides were tested; to find a good compromise between the analysis time and the resolution. As final GC conditions, a ZB5MS+ (5% polysilarylene and 95% dimethylpolysiloxane, 30 m x 0.25 mm x 0.25 μm, Phenomenex) column was used to separate pesticides; helium was used as carrier gas (1 mL/min); injection was splitless and at 260°C. The oven temperature was programmed as follows: initially maintained at 40°C (held for 5 min), then increased to 180°C (held for 2 min) at a rate of 10°C/min, a second increase was used to 280°C (held for 2 min) at a rate of 5°C/min. The optimal analysis time was 43 minutes.

The MS transfer line was kept at 250°C. The mass spectrometer, equipped with a quadrupole mass filter, was in the electron impact ionization mode (70 eV) with an ion source temperature of 200°C. Chromatograms were acquired in Single Ion Monitoring (SIM) scaning mode. The m/z associated with pesticides are specified in Table S1. All compounds could be separated excepted cis and trans chlordane. These isomers were identified on the same peak. Moreover, MS was not able to identify with certainty the three BHC (hexachlorocyclohexane), the three isomers were identified as BHC on chromatograms.

ICP-AES and ICP-MS

Extraction and mineralization of samples were performed with a Milestone ETHOS 1 microwave digestion system equipped with a temperature sensor. TFM reactors were used with a maximum pressure of 100 bar. ICP-AES measurements were performed on an iCAP 6300 series instrument (Thermo Fisher Scientific) using the axial view. The quantification of phosphorus and rubidium was performed at 178 nm and 780 nm, respectively. Detection of lithium, boron, chromium, iron, manganese, cobalt, nickel, copper, zinc, strontium, molybdenum, silver, cadmium, tin, barium, lead, and bismuth was performed on an iCAP RQ ICP-MS instrument (Thermo Fisher Scientific) fitted with a collision cell. Two different measurement modes were used: standard mode (STD) and kinetic energy discrimination mode (KED). In the KED mode, Helium gas was injected in the collision cell and an energy discrimination barrier was applied in order to remove unwanted polyatomic interferences. Data processing was performed using ThermoFisher Scientific Qtegra software.

As example, optimized conditions for the plasma and nebulizer for ICP-AES and ICP-MS are given in Table S2.

Method optimization

The simulative palm wine

Because of the low volume of palm wine samples, a surrogate matrix (simulative palm wine) was developed to determine HS-SPME/GC-MS optimal conditions before application on real samples.

For this purpose, a palm wine sample was analyzed by GC-MS to determine the main constituents. It was found that palm wine contained around 88 % (m/m) of water, 2 % (m/m) of ethanol, and 10 % (m/m) of sucrose. Based on a previous study on palm wines (Simon Amoikon et al., 2020), the aromatic profile was recreated using 4 mg L -1 of limonene and 10 mg L -1 of decane, main compounds found in real palm wines. Calcium (5 mg L -1 ), potassium (280 mg L -1 ), magnesium (7 mg L -1 ) and sodium (4 mg L -1 ) concentrations were determined in the palm wine sample by ICP-AES. According to [START_REF] Cunningham | Nutritional value of palm wine fromHyphaene coriacea andPhoenix reclinata (Arecaceae)[END_REF], vitamin C (60 mg L -1 ) is generally added. Finally, the simulative palm wine was doped to achieve the concentrations generally found in such samples.

Optimization of the HS-SPME procedure

Experimental parameters were evaluated to determine the optimal conditions for the analysis of pesticides in palm wines. Three fiber types were tested: 100 μm polydimethylsiloxane (PDMS), 85 μm polyacrylate (PA), and 50/30 μm DVB/Carbon WR/PDMS (Restek USA).

Fibers were conditioned at 230°C during 30 min before each analysis, according to the manufacturer's recommendations. Three milliliters of the simulative palm wine were placed in a 20 mL sealed headspace glass vial (3 replicates). After extraction, the fiber was automatically retracted and transferred to the GC injector at 260 °C for a desorption time of 3 min.

In order to optimize the extraction efficiency, an experimental design (Table S3) with 45 trials was implemented (Ellistat software, Chavanod, France) on a 100 μm PDMS fiber. Some Data processing was performed using the GC-Solution software.

Method validation

Analysis of palm wine by HS/SPME-GC/MS

For the study of pesticides in complex matrix, an HS-SPME extraction technique was used. As final conditions after optimization, a 20 mL vial was filled with 3 mL of each palm wine samples (3 replicates) and 7.5 % (m/m) of sodium sulfate. Extraction was done in the headspace vial kept at 52.5°C. A DVB/C-WR/PDMS fiber was used for all extractions because it allowed the determination of many pesticides with good repeatability (see results and discussions -fiber coating). The palm wine samples were equilibrated for 11.25 min and extracted for 50 min under continuous stirring (437.5 rpm). The fiber was automatically transferred to the GC injector at 260 °C for desorption time of 3 min. The method performance was evaluated in terms of linearity, limit of detection, limit of quantification, accuracy, and precision (repeatability).

The concentration of three stock solutions ranged from 0.5-2.5 μg L -1 (for Tolclofos-methyl and Dichlorvos, respectively) to 5-25 μg L -1 (for Tolclofos-methyl and Dichlorvos, respectively). These three stock solutions were each injected three times in order to study the repeatability (represented by a relative standard deviation (RSD)). To study the linearity, calibration curves with 3-5 points were established. LOD and LOQ were estimated as concentrations of pesticides which allowed a signal-to-noise ratio (S/N) of 3 and 10, respectively. Additionally, samples were spiked with stock solutions (to obtain three samples with concentrations from 0.5-2.5 μg L -1 (for Tolclofos-methyl and Dichlorvos, respectively) to 5-25 μg L -1 (for Tolclofos-methyl and Dichlorvos, respectively) three times and relative recoveries were determined.

Analysis of palm wine by ICP/AES and ICP/MS

In accordance to the French standard « » for the determination of metals in drinking water, ICP-MS is the reference technique and is used after mineralization. No standard exists for palm wine, and it consists of 88% water, so the same methodology was followed and can be assimilated to drinking water.

A volume of 2 mL of palm wine was digested with 2 mL of nitric acid and 1 mL of hydrogen peroxide in a microwave system: from room temperature, 30 ºC, to 180 ºC, 20 minutes at 180 ºC. After the mineralization, the digest was diluted up to 50 mL with ultrapure water. A blank was analyzed in the same conditions.

Samples were analyzed with ICP-AES for the determination of phosphorus and rubidium, and with ICP-MS for the determination of the other metals. To study the linearity, calibration curves with 5 points were established.

LOD and LOQ were obtained for the palm wine samples using equations 1 and 2, where BEC is the background equivalent concentration (μg L -1 ), it represents the blank intensity divided by the angular coefficient of the analytical curve and RSDblank is the relative standard deviation of the blank (n=10). Finally, the extraction temperature was set at 52.5°C. Increasing the temperature allows reducing the extraction time, which increases the concentration of semi-volatiles in the vial headspace [START_REF] Bianchin | Screening of volatile compounds in honey using a new sampling strategy combining multiple extraction temperatures in a single assay by HS-SPME-GC-MS[END_REF]. Pesticides were mostly obtained with high peak areas for an extraction temperature of 52.5°C. Lowers peak areas were obtained with a temperature of 37.5°C (comparison of trials 4 and 8 in Table S3, parameters were set at the optimized values, except for extraction temperature), especially for chlorpyrifos (peak areas of 889083 and 3829688 for temperatures of 37.5°C and 52.5°C, respectively), ethion (peak areas of 18863 and 2459896 for temperatures of 37.5°C and 52.5°C, respectively), and tolclofos methyl (peak areas of 6788178 and 21189553 for temperatures of 37.5°C and 52.5°C, respectively.

Equilibrium time was set at 11.25 min. Equilibrium time depends on the chemical nature and physico-chemical parameters of pesticides. The optimum equilibration time was selected as the time ensuring the highest peak area for the majority of pesticides (all other parameters being constant), with a reasonable time. Finally, 11.25 min was selected for equilibration time.

The highest extraction time tested with the experimental design was 60 min. A higher extraction efficiency was observed for a higher exposure time between the SPME fiber and the sample headspace [START_REF] Ho | Solid phase microextraction associated with microwave assisted extraction of organochlorine pesticides in medicinal plants[END_REF]), but a longer exposure could also damage the fiber and/or the pesticides. The extraction time of 50 min was a compromise between extraction efficiency and fiber lifetime and/or pesticides stability. This extraction time was compared with a lower time of 30 min (trials 6 and 8). All other parameters were constant at the optimized values. Pesticides were mostly obtained with high peak areas with an extraction time of 50 minutes. Ethion (peak areas of 744276 and 2459886 for times of 30 min and 50 min, respectively), and prothiofos (peak areas of 1725649 and 3690958 for times of 30 min and 50 min, respectively) were more extracted with the higher extraction time. However, malathion was more extracted with the lower extraction time (peak areas of 502458 and 198595 for times of 30 min and 50 min, respectively).

Stirring and salinity of the sample allows the diffusion layer to reach the equilibrium faster [START_REF] Ho | Solid phase microextraction associated with microwave assisted extraction of organochlorine pesticides in medicinal plants[END_REF]. Stirring of 437.5 rpm and 7.5% (m/m) of Na2SO4 allowed to reduce the analysis time, by promotion of the pesticides from the liquid phase to the gas phase. [START_REF]International Code of Oenological Practices, Annex: Maximum Acceptable Limits[END_REF] dieldrin, (25) endrin, (26) β-endosulfan, (27) cis-nonachlor, (28) p,p'-DDD, (29) ethion, [START_REF] Rodrigues | Development of a headspace solidphase microextraction/gas chromatography-mass spectrometry method for determination of organophosphorus pesticide residues in cow milk[END_REF] endrin aldehyde, (31) endosulfan sulfate, (32) p,p'-DDT, (33) endrin ketone, (34) methoxychlor.

Hexachlorobenzene was not represented because its area was too important.

The three SPME fibers allowed the extraction of all pesticides as it can be observed from Table S4, except for the endrin aldehyde, which was not extracted by the PA fiber. The detector was saturated and no longer able to give an area for hexachlorobenzene using the DVB/Carbon WR/PDMS fiber. Some pesticides had low peak areas no matter the fiber, such as simazine, atrazine, malathion, β-endosulfan, endrin aldehyde, endosulfan sulfate or endrin ketone.

Twenty-eight pesticides were extracted with higher area with the PDMS fiber, 5 with the DVB/Carbon WR/PDMS fiber and 2 with the PA fiber. A lot of pesticides were extracted with an important area with PDMS and DVB/Carbon WR/PDMS fibers, such as aldrin (peak area of 8228026 for the PDMS fiber and 8021739 for the DVB/Carbon WR/PDMS fiber), diazinon (peak area of 2886678 for the PDMS fiber and 2577749 for the DVB/Carbon WR/PDMS fiber), or heptachlor (peak area of 11522371 for the PDMS fiber and 10058902 for the DVB/Carbon WR/PDMS fiber).

However, as shown in Table S4, the DVB/Carbon WR/PDMS fiber exhibited the lowest RSDs for 25 pesticides (RSDs between 0.7 and 18%) and offered 22 RSDs under 10%. Only 14 and 1 RSDs were under 10% for the PDMS and PA fibers, respectively. The best repeatability was achieved with the DVB/Carbon WR/PDMS fiber. Therefore, this fiber was selected for the analysis of palm wines. Initially, a linear calibration model was developed for all pesticides. This type of calibration is the most used to obtain an analytical result from the measurement of the signal. According to [START_REF] Balsini | Development of multi-response optimization and quadratic calibration curve for determination of ten pesticides in complex sample matrices using QuEChERS dispersive liquid-liquid microextraction followed by gas chromatography[END_REF], pesticides may have a quadratic behavior. In this study, 12 pesticides (aldrin, chlordane, α-endosulfan, endrin heptachlor, heptachlor epoxide, parathion methyl, pirimidiphos methyl, prothiofos, p,p-DDD, and simazine), followed a quadratic calibration curve and 23 of them had a linear behavior. The analytical results were listed in All calibration curves had correlation coefficients between 0.9963 and 1, therefore, the quantification of pesticides in palm wines was acceptable.

LODs and LOQs

The obtained LODs ranged between 0.002 and 27.6 μg L -1 , for trans-nonachlor and simazine, respectively, and LOQs ranges between 0.01 and 92.05 for p,p'-DDE and simazine, respectively.

For such compounds, some comparisons can be done with literature. For example, for the Dichlorvos, LOD with the optimized method was 0.11 μg L -1 , Sakamoto and Tsutsumi found a LOD of 0.05 μg L -1 in water sample with a 85 μm PA fiber, and Rodrigues et al found a LOD of 3.8 μg L -1 in cow milk sample with a 65 μm PDMS/DVB fiber. Tsoukali et al obtained higher

LODs from whole blood and with a 85 μm PA fiber, as for the Malathion (0.36 μg L -1 for palm wine sample and 45 μg L -1 for whole blood sample) or Parathion methyl (0.01 μg L -1 for palm wine sample and 50 μg L -1 for whole blood sample). Rodrigues et al obtained higher LOQs with a LOQ of 6.50 μg L -1 for Ethion (LOQ of 0.62 μg L -1 for optimized method). The developed method offered better performances for those compounds. As the pesticides were not at the same concentration in the stock solution, spiking was at three 400 levels and for each level the pesticides were not at the same concentration. For the first level, 401 the concentrations were between 0.5 (for chlorpyrifos and pirimiphos methyl for example) and 402 2.5 μg L -1 (for dichlorvos for example), between 2.5 and 12.5 μg L -1 for the second level, and 403 between 5 and 25 μg L -1 for the final level. Some pesticides were not detected at these 404 concentrations, such as simazine or atrazine, because its LOD were higher than the range of 405 concentrations. Their RSDs and relative recoveries were calculated thanks to higher 406 concentrations (between 100 and 1000 μg L -1 ). Some others were not detected at one concentration of the range tested, such as methoxychlor (replicate 1) or trans and cis-nonachlor (replicate 2), their RSDs and relative recoveries were calculated from another concentrations (at 1 μg L -1 instead of 2 μg L -1 and at 100 μg L -1 instead of 5 μg L -1 , respectively for methoxychlor, and for trans-nonachlor, and cis-nonachlor).

Relative standard deviation

Atrazine, cis-nonachlor, trans-nonachlor, ethion, methoxychlor, and simazine had RSDs higher than 20% for two replicates. Moreover, for these pesticides the calibration curve was only realized with 3 points, except for ethion (with 4 points), so they were identifiable but not quantifiable for this study.

The RSDs obtained, for the other pesticides, were between 3.9 and 26.8% for BHC and p,p'-DDT, respectively, at 1 ug L -1 for the replicate 1, between 0.7 and 23.2% for terbuthylazine and β-endosulfan, respectively, at 5 ug L -1 for the replicate 2, and between 0.3 and 18.2% for aldrin (at 20 μg L -1 ) and chlordane (at 20 μg L -1 ), respectively, for the replicate 3. The results are shown in Very good recoveries were obtained for all pesticides at level 3 (75% for hexachlorobenzene and 110% for chlorpyrifos) and level 2 (from 82% for malathion to 115% for diazinon). At level 1, the relative recoveries ranged from 72 to 120% (72% for endrin aldehyde and 120% for p,p'-DDT at 1 μg L -1 , respectively) except for BHC and chlorpyrifos, which showed the applicability of the developed method.

Pesticides in palm wine samples

Thirty-two palm wines were analyzed following the optimized HS-SPME-GC/MS method.

Seven pesticides (dichlorvos, endrin ketone, parathion methyl, p,p-DDD, p,p-DDE, p,p-DDT, and pirimidiphos methyl) were identified in 10 palm wine samples (AP1, AP2, AR3, BP4, HR4, TP1, TP2, TR1, TR2, and TR3) as presented in Table 3. Pesticides were found in palm wines from the 4 cities, in 3 samples from Abidjan, 1 from Aboisso, 1 from Hiré, and 5 from Toumodi, with concentrations from 0.26 to 164.7 μg L -1 for pirimiphos methyl in AP2 and dichlorvos in AR3, respectively. p,p'-DDT was identified in 5 palm wines, in 4 from Toumodi in low concentrations (from 0.503 for TP1 to 0.669 μg L -1 ). This study is among the first to detect these pesticides in alcoholic beverages.

In AP1, AP2, BP4, HR4, TP1, TP2, TR1, and TR3 palm wine samples, pesticides were quantified at concentrations close to LOQs. EML of pesticides in bunches of grapes are used because in France, the European Maximal Limits (EML) for wine does not exist. Parathion methyl was detected at 0.521 μg L -1 in AP1, which is a concentration below the EML, as well as a level below the concentration found in wines from different European countries, such as Spain or Portugal (Table 3). In AR3 and TR2, dichlorvos was detected at 164.7 and 38.4 µg L - 1 , respectively. As no study has detected this pesticide in alcoholic beverages, results were compared with the concentration of ethion and malathion (organophosphorus pesticides as dichlorvos) in wines from Brazil. Ethion was detected at concentrations between 0.29 and 0.32 μg L -1 and malathion at 4.4 μg L -1 . Dichlorvos was found at a level above the EML and concentrations found in wines from Brazil (Table 3). First, barium, boron, chromium, copper, iron, lead, manganese, phosphorus, rubidium, strontium, and zinc were found in all palm wine samples. The International Organization of Vine and Wine (OIV) recognized maximum limits for only a few elements in wine (Pb, Cd, Cu, Na, Zn, Ag, As, F, Br, F, and B). The levels of the other metals in palm wine, which is composed by 88% of water, can be compared with metal limits of drinking water. The higher concentrations for the most wine samples were found for phosphorus, rubidium, copper and iron, from 22.2 mg L -1 (BR3) to 303.9 mg L -1 (AR2) for phosphorus, from 1.5 mg L -1 (BR1) to 7.6 mg L -1 (AP2) for rubidium, from 155.6 (BP4) to 1046.9 μg L -1 (AP2, this concentration was above the OIV maximal limit of 1000 μg L -1 ) for copper and from 116.4 (TP4) to 2453.5 μg L - 1 (TR3) for iron. Manganese was mostly identified in samples from Aboisso, mainly in BR1 (641.6 μg L -1 ) and BR2 (1001.3 μg L -1 ) palm wines, at levels above the European maximal limits for drinking water.

Then, six metals (cadmium, chromium, copper, iron, manganese, and nickel) were detected in different samples at levels above the European maximal limits for drinking water or above the OIV maximal limits for wine. Cadmium was detected in TP3 (13.8 μg L -1 ) at level above limits of 10 μg L -1 , and chromium in TP3 (51.4 μg L -1 ), AR4 (52.2 μg L -1 ), HR2 (313.4 μg L -1 ), and HR3 (197.9 μg L -1 ) at level above limits of 50 μg L -1 .

Iron was at level above limits of 200 μg L -1 in 24 samples (AP2, AP3, AP4, AR1, AR2, AR3, AR4, BP1, BP2, BP3, BP4, BR1, BR2, BR3, BR4, HP1, HP2, HP3, HP4, HR1, HR2, HR3 ,HR4, TP1, TP2, TP3, TP4, TR1, TR2, TR3, and TR4), from 242.2 (HP3) to 2453.5 μg L -1 (TR3), and nickel at level of 20 μg L -1 in 28 samples too (AP1, AP2, AP3, AP4, AR1, AR2, AR3, AR4, BP1, BP2, BP3, BR1, BR2, BR3, BR4, HP1, HP2, HP3, HP4, HR1, HR2, HR3, HR4, TP1, TP2, TP3, TP4, TR1, TR2, TR3, and TR4), from 28.9 (AP4) to 699.8 μg L -1 (BR2).

Zinc, which was detected at a range of concentrations between 28.6 and 589.9 μg L -1 , was also found in wines from different European countries, such as Italy or France (Table 4), at similar and higher levels (for example, between 289 and 967 μg L -1 for Italian wines). As for Italian and French wines, zinc was not detected at levels above the OIV maximal limits for wine.

Moreover, cadmium was detected in one sample (TP3) at concentration above the OIV maximal limit of 10 μg L -1 . However, its concentration in Italian and French wines was not at levels above the limits.

Metals, like copper, iron, and zinc, are essential for human at low concentrations. However, at important concentrations, they can pose a real danger. For example, drinking water contaminated by cadmium and lead can cause renal failure or chromium and nickel can induce hair loss (Singh Sankhla et al., 2016).

Finally, the palm wine TP3 from Toumodi was the most polluted sample with metals at levels above European and OIV maximal limits (cadmium, chromium, iron, manganese and nickel),

given Table 4.

Conclusion

In this study, the concentration of pesticides and metals in palm wines from Ivory Coast using HS-SPME/GC-MS and ICP-AES/MS were determined. SPME conditions (equilibrium time, extraction time and temperature, stirring, and salinity) were optimized thanks to an experimental design with 45 trials. The developed method used a DVB/C-WR/PDMS fiber and the palm wine samples were equilibrated for 11.25 min and extracted for 50 min under continuous stirring (437.5 rpm) at 52.5°C. The method was validated in terms of linearity, repeatability, LOD, LOQ, and accuracy, and allowed the identification of 35 pesticides and the quantification of 29 in 32 palm wine samples. Additionally, 7 pesticides were identified but dichlorvos was the only one identified in 2 samples at levels above the European maximal limits.

In a second step, ICP-AES and ICP-MS were used to study the presence of 19 metals in palm wine samples. Barium, boron, chromium, copper, iron, lead, manganese, rubidium, strontium, and zinc explored were identified in all samples of palm wine. Moreover, 6 metals (cadmium, chromium, copper, iron, manganese, and nickel) were detected in different samples at levels above the European maximal limits for drinking water or above the OIV maximal limits for wine.

Finally, pesticides (dichlorvos, endrin ketone, parathion methyl, p,p-DDD, p,p-DDE, p,p-DDT, and pirimidiphos methyl) were found in palm wines from the 4 cities, in 3 samples from Abidjan, 1 from Aboisso, 1 from Hiré, and 5 from Toumodi. In addition, one of the palm wine samples from Toumodi was the most polluted sample with metals (cadmium, chromium, iron, manganese and nickel) at levels above European or OIV maximal limits.

Maximal limits for metals have been only defined for boron, cadmium, copper, lead and zinc.

As shown in this article, samples may contain pesticides and metals in high concentrations. This beverage is largely consumed by local population. It would be important to develop more studies on the composition of palm wine and maximal limits especially for pesticides in wines, in order to be aware of the potential danger of its consumption.

List of abbreviations

  parameters were tested, according to the literature for pesticides extraction by HS-SPME.Extraction temperature between 30 and 60°C[START_REF] Cincotta | Determination of Sesquiterpenes in Wines by HS-SPME Coupled with GC-MS[END_REF], equilibrium time between 5 and 30 min (Bernardi et al. 2015, Pellati et al. 2013), and extraction time between 20 and 60 min (Pellati et al., 2013) were investigated. Moreover, stirring was studied between 250 and 500 rpm (Filho et al., 2010, Bernardi et al. 2015), and salinity (sodium sulfate) between 5 and 15 % (m/m) (Vitali et al., 1998, Zhu et al., 2009) of the sample. According to Zhu et al (2009), who worked on the determination of OPPs in textiles using SPME coupled with GC/MS, OPPs were more extracted with sodium sulfate than with sodium chloride.

3 . 1

 31 Determination of pesticides in palm wines 3.1.1 Determination of SPME conditions Different parameters were tested in order to develop a HS/SPME-GC/MS method with the optimized extraction efficiency. Fiber coating, extraction temperature, equilibrium time, extraction time, stirring, and salinity were studied. 3.1.1.1 Extraction temperature, equilibrium and extraction time, stirring and salinity Five parameters have been explored in this study on a 100 μm PDMS fiber: extraction temperature, equilibrium and extraction time, stirring and salinity. Among the 45 trials of the experimental design, one offered the highest peak area for 7/12 extracted pesticides of the OPPs solution (azinphos methyl, chlorpyrifos, ethion, methidathion, pirimiphos methyl, profenofos and tolclofos methyl). This method had a long extraction time and according to the exploitation of the experimental design, the extraction time was the parameter that influences the most the extraction efficiency.

Finally,

  SPME optimized parameters for this study were: an extraction temperature of 52.5°C, an equilibrium time of 11.25 min, an extraction time of 50 min, stirring of 437.5 rpm, and salinity of 7.5% of Na2SO4. 3.1.1.2 Fiber coating Three SPME fiber coatings were used to extract the pesticides in the simulative palm wine solution: a 100 μm polydimethylsiloxane (PDMS), a 85 μm polyacrylate (PA), and a 50/30 μm DVB/Carbon WR/PDMS. Compounds were spiked between 2.5 to 12.5 μg L -1 triplicate. SPME optimized parameters (see 3.1.1.1 Extraction temperature, equilibrium and extraction time, stirring and salinity) were used.

Fig. 1 .

 1 Fig.1. Comparison of three SPME fiber coatings for the extraction of 35 pesticides. Peaks: (1) dichlorvos, (2) BHC, (3) simazine, (4) BHC, (5) atrazine, (6) lindane, (7) terbuthylazine, (8) diazinon, (9) BHC, (10) parathion methyl, (11) tolclofos methyl, (12), alachlor, (13) heptachlor, (14) pirimiphos methyl, (15) malathion, (16) chlorpyrifos, (17) aldrin, (18) heptachlor epoxide,

3. 1 . 2

 12 Analysis of palm wine samples 3.1.2.1 Method validation 3.1.2.1.1 Quadratic or linear behavior of calibration curves

392 a range of concentrations 393 b

 393 at the concentration of 0.5 μg L -1 394 c at the concentration of 1 μg L -1 395 d at the concentration of 100 μg L -1 396 e at the concentration of 500 μg L -1 397 f at the concentration of 1000 μg L -1 398 399

c

  Sala et al., 1997 d dos Anjos & de Andrade, 2015 3.2 Determination of metals in palm wines Thirty-two palm wine samples were mineralized and analyzed by ICP-AES and ICP-MS. The results are shown in Figure 2.

Fig. 2 .

 2 Fig. 2. Metals concentration in 32 palm wine samples, determined by ICP-AES and ICP-MS

  : Gas Chromatography coupled with Mass Spectrometry HS-SPME: Headspace Solid-Phase Microextraction ICP-AES: Inductively Coupled Plasma -Atomic Emission Spectrometry ICP-MS: Inductively Coupled Plasma -Mass Spectrometry KED: Kinetic Energy Discrimination mode Monica Arellano Gisel Sanchez wrote the paper Aké Francine collected the samples Tiemele Laurent Simon Amoikon wrote the paper, gave samples Aminata Nadjoua Coulibaly, wrote the paper, collected the samples Mélanie Mignot oversight the study, reviewed the paper

Table 1 (

 1 linear (L) or quadratic (Q) behavior, LODs, and LOQs).

Table 1

 1 Quadratic or linear behavior, LODs, and LOQs of pesticides in this study and results from the

	literature
	No. Pesticides	Behavior a	Range (μg L -1 )	R 2	LOQs (μg L -1 )	LODs (μg L -1 )	LODs from the literature (μg L -1 )	LOQs 1 ) from the literatur e (μg L -	Fiber used from literature
	1	Dichlorvos L	1.25-250	0.9999 1.25	0.11	0.05		85 μm PA [27]
								3.80	11.4	65 μm PDMS/DVB [25
	2	BHC	L	1-100	0.9998 0.31	0.09
	3	Hexachlor obenzène	L	0.5-5	0.9971 0.10	0.03
	4	Simazine Q	100-1000	1	92.1	27.6	0.10		85 μm PA [27]
	5	BHC	L	0.5-100 0.9999 0.20	0.10
	6	Atrazine	L	10-1000 0.9993 10.0	3.00
	7	Lindane	L	2-200	0.9999 0.11	0.03
	8	Terbuthyla zine	L	1-100	0.9999 1.00	0.30
	9	Diazinon L	5-100	0.9998 0.58	0.17	3.00		85 μm PA [33]
								0.01		85 μm PA [27]
	10 BHC	L	0.5-100 0.9999 0.75	0.22
	11	Parathion methyl	Q	0.5-10	0.9991 0.02	0.01	50.0		85 μm PA [33]
	12	Tolclofos-methyl	L	0.25-5	0.9993 0.13	0.04	0.01		85 μm PA [27]
	13 Alachlor	L	1-100	0.9999 0.53	0.16
	14 Heptachlor Q	1-200	0.9994 0.01	0.003

Table 2

 2 Repeatabilities and recoveries of pesticides

			Replicate 1 (0.5-2.5	Replicate 2 (2.5-12.5	Replicate 3 (5-25
			μg L -1 ) a		μg L -1 ) a		μg L -1 ) a
	No.	Pesticides	RSD	Relative	RSD	Relative	RSD	Relative
			(%) (n	recovery	(%) (n	recovery	(%) (n	recovery
			= 3)	(%)	= 3)	(%)	= 3)	(%)
	1	Dichlorvos	14.5	116	5.8	95	1	100
	2	BHC	10.8	51	11.1	97	3.6	107
	3	Hexachlorobenzene 7.9	114	1.4	100	2.5 b	75 b
	4	Simazine	6.2 d	102 d	36.5 e	88 e	59.3 f	100 f
	5	BHC	3.9	80	0.9	102	3.7	103
	6	Atrazine	11.2 d	115 d	31.8 e	98 e	41.7 f	117 f
	7	Lindane	22.1	73	12.2	100	2.7	103
	8	Terbuthylazine	18.7	94	0.7	98	1.1	102
	9	Diazinon	14.7 d	95 d	11.6	115	6.1	85
	10	BHC	22	96	6.9	96	3.1	92
	11	Parathion methyl	7.2	110	3.8	99	2.7	102
	12	Tolclofos-methyl	15.8	103	15.5	97	5.4	101

Table 2

 2

	. RSDs were mostly under 20% for replicates 1 and 2, respectively for 23/31
	and 25/31 pesticides, and under 10% for replicate 3 for 25/31 pesticides. Little variation of peak
	areas used to calculate RSDs for low concentrations could have an important effect, so RSDs
	were lower for concentrations of the replicate 3. The first BHC (RSD of 3.9% for replicate 1,
	0.9% for replicate 2, and 3.7% for replicate 3) and parathion methyl (RSD of 7.2% for replicate
	1, 3.8% for replicate 2, and 2.7% for replicate 3) were pesticides with the lower RSDs for all
	replicates.
	3.1.2.1.4 Relative recovery

Table 3

 3 Pesticides concentrations in palm wines, European Maximal Limits of pesticides in bunches of grapes and palm oil and comparison with other studies

		European
		Maximal Limits	Concentrations (μg L -1 )
		(ug/kg)
														Differe
														nt
														countri
	Pestici des	Bunc hes of grape s a	Pal m oil a	AP 1	A P2	AR 3	BP 4	HR 4	TP 1	TP 2	TR 1	TR 2	TR 3	al, es (Brazil , Portug	Spa in	Bra zil
														Argent
														ina,
														Chile)
	Dichlor vos	10	10			164 .7						38. 4
	Parathi on methyl	10	20	0.5 21										2.80 b 3-4 c
	Pirimip hos methyl	10	10		0. 26
	p,p'-DDE	50	50				0.6 45
	p,p'-DDD	50	50						0.6 09
	p,p'-DDT	50	50					0.5 75	0.5 03	0.6 69		0.6 71	0.6 69
	Endrin ketone	-	-								0.5 29
																0.2
	Ethion 10	20													9-0.3
																2 d
	Malath ion	20	20													4.4

Table 4

 4 KED, or STD mode, LODs and LOQs of metals in palm wines, European and OIV Maximal Limits of metal in drinking water and wine, and comparison with other studies

					Europ
					ean
	Metals	Mo de	LOQ (µg L -1 )	LOD (µg L -1 )	Maxi mal Limit s in drinki ng water	OIV Maxi mal Limit s (µg L -1 )	Concentr ations in French wines (mg L -1 ) a	Concentr ations in Italian wines (mg L -1 ) a	Concentr ations in Italian wines (µg L -1 ) b	This study (µg L -1 ) or (mg L -1 ) c
					(μg L -
					1 )
	Barium	KE D	1.5	0.45	-	-				3.65-132.4
	Bismuth	ST D	17	5.1	-	-				18.5-146.3
	Boron	ST D	4	1.2	1500	8000 0			1995-9489	55.7-614.4
	Cadmiu m	ST D	0.75	0.23	5	10	ND-0.0002	0.0012-0.0016	0.17-3.7	0.36-13.8
	Chromi um	KE D	5	1.5	50	-	0.006-0.09	0.02-0.05		5.86-313.4
	Cobalt	ST D	0.5	0.15	-	-	0.004-0.005	0.003-0.006		0.52-7.35
	Copper	KE D	3	0.9	2000 1000 ND-0.48	0.001-1.34	14-456	155.6-1046.9
	Iron	KE D	16.5	4.95	200	-	0.81-2.51	1.35-27.8		116.4-2453.5
	Lead	KE D	8.5	2.5	10	150	0.006-0.023	0.01-0.35	3-59	0.38-135.4
	Lithium	ST D	0.25	0.08	-	-				0.33-18.0
	Mangan ese	KE D	1	0.3	50	-	0.63-0.96	0.67-2.5		33.2-1001.3
	Molybd enum	KE D	1.3	0.38	-	-				1.36-69.0
	Nickel	KE D	9.3	2.9	20	-	ND-0.052	0.015-0.21		12.9-699.8
	Phospho rus	-	450	140	-	-				22.2-303.8 c

Acknowledgements

The authors would like to thank Marie Laget who helped for the analyses of metals by ICP-AES. This work has been partially supported by University of Rouen Normandy, INSA Rouen Normandy, the Centre National de la Recherche Scientifique (CNRS), European Regional Development Fund (ERDF) N° HN0001343, Labex SynOrg (ANR-11-LABX-0029), Carnot Institute I2C, the graduate school for research XL-Chem (ANR-18-EURE-0020 XL CHEM) and by Region Normandie. HS-SPME GC/MS has been financed by RIN 2019 FSP-CHEM 18P03656 and ICP/MS though Bioenairgy project (FEDER N° HN0001343). This work was also supported by International Foundation For Science (IFS) project E_037779.


Pratik Vadher
email: pratik-vinubhai.vadher@univ-rennes1.fr

Giulia Sacco
email: giulia.sacco@univ-rennes1.fr

Denys Nikolayev
email: denys.nikolayev@deniq.com

Higher Spatial Harmonic Leaky Wave Antenna Design Based on Meandering Microstrips

Keywords: LWA, K-Band, higher spatial order, scanning rate, meandering microstrip antenna

A Leaky Wave Antenna (LWA) design with high scanning rate (the ratio of beam scanning range and bandwidth) is proposed in this work. The antenna is based on a periodic meandering microstrip line operating in K-Band with continuous beam scanning from backward-to-forward direction in the elevation plane. The height of the transverse lines is varied periodically in the unit cell to increase the electrical length. Hence, the antenna operates in higher spatial order which increases the scanning rate. The final antenna shows a scanning range in the elevation plane from -40°to 45°in the frequency range from 20.6 GHz to 24.6 GHz corresponding to a scanning rate of 21.25 °GHz -1 . The antenna performance is compared with conventional meandering leaky wave antenna design to demonstrate notable increase in the scanning rate with very less impact on gain while also maintaining low profile.

I. INTRODUCTION

Leaky Wave Antennas (LWAs) have frequency-dependent beam steering capability due to dispersion of the guiding media [START_REF] Volakis | Antenna Engineering Handbook[END_REF], [START_REF] Walter | Traveling Wave Antennas[END_REF]. Thanks to the easiness of fabrication, simple structure, low profile and low cost, microstrip based LWAs have received significant interest in the literature [START_REF] Menzel | A New Travelling Wave Antenna in Microstrip[END_REF][START_REF] Oliner | The Nature of the Leakage from Higher Modes on Microstrip Line[END_REF][START_REF] Caloz | CRLH metamaterial leaky-wave and resonant antennas[END_REF][START_REF] Paulotto | Full-wave modal dispersion analysis and broadside optimization for a class of microstrip CRLH leaky-wave antennas[END_REF][START_REF] Casares-Miranda | Highgain active composite right/left-handed leaky-wave antenna[END_REF][START_REF] Ma | Dispersion Characteristics Analysis of One Dimensional Multiple Periodic Structures and Their Applications to Antennas[END_REF][START_REF] Jiang | Backward-to-forward wide-angle fast beam-scanning leaky-wave antenna with consistent gain[END_REF][START_REF] Rahmani | Backward to forward scanning periodic leaky-wave antenna with wide scanning range[END_REF][START_REF] Cheng | An approximate circuit model to analyze microstrip rampart line in osb suppressing[END_REF][START_REF] Vadher | On-body V-band leaky-wave antenna for navigation and safety applications[END_REF][START_REF] Wang | A periodic meandering microstrip line leaky-wave antenna with consistent gain and wide-angle beam scanning[END_REF].

Microstrip LWAs generally operate in a fundamental spatial harmonic [START_REF] Menzel | A New Travelling Wave Antenna in Microstrip[END_REF][START_REF] Oliner | The Nature of the Leakage from Higher Modes on Microstrip Line[END_REF][START_REF] Caloz | CRLH metamaterial leaky-wave and resonant antennas[END_REF][START_REF] Paulotto | Full-wave modal dispersion analysis and broadside optimization for a class of microstrip CRLH leaky-wave antennas[END_REF][START_REF] Casares-Miranda | Highgain active composite right/left-handed leaky-wave antenna[END_REF] or in a spatial harmonic of n = -1 [START_REF] Jiang | Backward-to-forward wide-angle fast beam-scanning leaky-wave antenna with consistent gain[END_REF][START_REF] Rahmani | Backward to forward scanning periodic leaky-wave antenna with wide scanning range[END_REF][START_REF] Cheng | An approximate circuit model to analyze microstrip rampart line in osb suppressing[END_REF][START_REF] Vadher | On-body V-band leaky-wave antenna for navigation and safety applications[END_REF][START_REF] Wang | A periodic meandering microstrip line leaky-wave antenna with consistent gain and wide-angle beam scanning[END_REF][START_REF] Lyu | Periodic leaky-wave antenna based on complementary pair of radiation elements[END_REF][START_REF] Günes | Microstrip tapered traveling wave antenna for wide range of beam scanning in X-and Kubands[END_REF][START_REF] Yu | A dual-beam leaky-wave antenna based on squarely modulated reactance surface[END_REF]. Certain designs operating in higher spatial order of n = -2 based on Substrate integrated waveguides (SIWs) have also been proposed [START_REF] Guan | Scanning rate enhancement of leaky-wave antennas using slowwave substrate integrated waveguide structure[END_REF], [START_REF] Rahimi | Higher-order space harmonics in substrate integrated waveguide leaky-wave antennas[END_REF]. In the present work, a new meandering microstrip design that operates in the spatial order of n = -2 is discussed. The consequence of operating in a higher spatial order results in faster scanning rate. A comparison with conventional simple meandering microstrip LWAs design [START_REF] Cheng | An approximate circuit model to analyze microstrip rampart line in osb suppressing[END_REF][START_REF] Vadher | On-body V-band leaky-wave antenna for navigation and safety applications[END_REF][START_REF] Wang | A periodic meandering microstrip line leaky-wave antenna with consistent gain and wide-angle beam scanning[END_REF] is also made to show the increase in scanning rate.

II. ANTENNA STRUCTURE AND CONCEPT OF OPERATION

The design of the proposed LWA is shown in Fig. 1. The antenna operates in fundamental transverse electromagnetic (TEM) (EH 0 ) mode. The wave propagating along the microstrip line in the longitudinal direction (+Y-axis) can be classified by propagating constant γ [START_REF] Volakis | Antenna Engineering Handbook[END_REF], [START_REF] Jackson | Leaky-Wave Antennas[END_REF]. where α denotes the attenuation constant and β denotes the phase constant.

γ = β -jα (1)
Since the antenna is periodic, unit cell simulation as performed in [START_REF] Dong | Composite right/left-handed substrate integrated waveguide and Half mode substrate integrated waveguide leaky-wave structures[END_REF], [START_REF] Lai | Left-Handed Metamaterials for Microwave Engineering Applications[END_REF], is used to analyze the propagation and radiation characteristics of the guiding medium.

Fig. 2 and Table I report the dimensions of the unit cell for the proposed antenna design based on Rogers 3003 (ε r = 3 and tan δ = 0.001). The following subsections highlight the rationale and subsequently the analysis of the optimised unit cell.

A. Operation in higher spatial order

Due to the periodicity (p) of the structure, there exists an infinite number of space harmonics exist according to Bloch-Floquet theorem [START_REF] Jackson | Leaky-Wave Antennas[END_REF], [START_REF] Collin | Field Theory of Guided Waves[END_REF], [START_REF] Collin | Antenna Theory. Part 2[END_REF] propagating through the periodic meandering microstrip line. The phase constant of the n th space harmonic β n satisfies

β n p = β 0 p + 2nπ (2)
where n = -∞ to +∞. Fig. 3 shows the Brillouin diagram [START_REF] Volakis | Antenna Engineering Handbook[END_REF], [START_REF] Jackson | Leaky-Wave Antennas[END_REF] for the conventional unit cell design [START_REF] Cheng | An approximate circuit model to analyze microstrip rampart line in osb suppressing[END_REF][START_REF] Vadher | On-body V-band leaky-wave antenna for navigation and safety applications[END_REF][START_REF] Wang | A periodic meandering microstrip line leaky-wave antenna with consistent gain and wide-angle beam scanning[END_REF] in comparison to the proposed unit cell. The antenna radiates only when it operates in the fast wave region (β n p < k 0 p) [START_REF] Jackson | Leaky-Wave Antennas[END_REF].

To enhance the scanning rate, the proposed structure operates in the spatial harmonic n = -2. This is achieved by adding transverse line segments of varying length of δ 0 and δ 1 (Fig. 2) and consequently the electrical path length of the unit cell. Fig. 3 (a) and(b) show the conventional and proposed unit cell designs for K-band operation, together with the associated Brillouin diagrams. For the latter, the radiation associated to the second spatial harmonic (β -2 ) occurs in the desired K-band frequency range.

B. Behaviour of leaky wave antenna

Table. I shows the design and dimensions of unit cell operating in a spatial harmonic of n = -2. The corresponding dispersion diagram is depicted in Fig. 4.

The antenna designed with this unit cell will radiate a narrow fan beam with the following characteristics.

The main beam direction θ m is given by [START_REF] Rahimi | Higher-order space harmonics in substrate integrated waveguide leaky-wave antennas[END_REF], [START_REF] Collin | Antenna Theory. Part 2[END_REF], [START_REF] Ishimaru | Electromagnetic Wave Propagation, Radiation, and Scattering: From Fundamentals to Applications[END_REF]

θ m = sin -1 (β -2 /k 0 ). (3)
where k 0 is the free space wave number Qualitatively, large attenuation constant α results in a large leakage rate producing a short effective aperture, which will generally cause in a large beamwidth (∆θ). Moreover, a narrow beam is due to low value of α resulting in long effective aperture. [START_REF] Volakis | Antenna Engineering Handbook[END_REF], [START_REF] Paulotto | A novel technique for open-stopband suppression in 1-D periodic printed leakywave antennas[END_REF].

A LWA operating in higher spatial order is designed with a substrate of height equal to 0.254 mm. 10 unit cells operating in n = -2 are cascaded to form the antenna as shown in Fig. 1 to obtain gain over 10 dB throughout the scanning range. The final antenna dimensions (excluding the connector) are 58 mm (length) × 10 mm (width) × 0.254 mm (height) hence making it quite compact.

III. K-BAND LEAKY WAVE ANTENNA

A. Feed design and matching for the leaky wave antenna

In order to calculate the input impedance of antenna, the bloch impedance (Z s ) is obtained from the unit cell simulation using the same method as used in [START_REF] Paulotto | A novel technique for open-stopband suppression in 1-D periodic printed leakywave antennas[END_REF], [START_REF] Sarkar | 60 GHz Compact Larger Beam Scanning Range PCB Leaky-Wave Antenna Using HMSIW for Millimeter-Wave Applications[END_REF]. The value of Z s for the structure is close to 44 Ω in the the operating frequency range. Full-wave simulation of the LWA is performed in Ansys HFSS with a 2.92 mm end-launch Southwest connector that has impedance of Z 0 = 50 Ω as shown in Fig. 5. The losses due to dielectric (α d ) is also accounted. The antenna array radiates a fan beam in the H-plane (Y-Z plane) that changes the angle of maximum radiation (θ m ) from backward (-Y) to forward direction (+Y).

B. Scanning rate enhancement of the proposed leaky wave antenna

To show the boost in scanning rate, a conventional LWA operating with spatial harmonic n = -1 (brillouin diagram described in Fig. 3(a)) with 10 unit cell cascaded with a periodicity of p 1 = 5 mm, is compared with the proposed antenna. The proposed antenna has a periodicity of p = 5.8 mm. As can be seen from the Fig. 6a and6b, the proposed antenna scans a significantly large space (-40°t o 45°) than the conventional design (-15°to 14°) for a similar operating frequency bandwidth of 4 GHz.

Although, there is an increase in electrical length of the antenna which enables operation in higher spatial harmonic, there is also an increase in physical length from p 1 = 5 mm to p = 5.8 mm

C. Performance of the proposed leaky wave antenna

The gain of the proposed antenna is nearly 10 dB throughout the operating frequency range shown in Fig. 6b.

Table II shows the comparison with other LWAs in the similar operating frequency range. Notable increase in scanning rate is observed as compared to existing designs while also maintaining low profile.

IV. CONCLUSION

A novel microstrip based LWA operating in higher spatial harmonic of n = -2 is designed to enhance the scanning rate and expand the scanning range for a given operating frequency. A comparison with the previous existing design operating in n = -1 is also made showing that scanning rate of antenna can be increased by operating in higher spatial harmonic. The antenna is self-matched as well in operating frequency range presenting an impedance of 50 Ω except for the range where OSB exists. Hence there is no need of additional matching circuit. Since the antenna is made up of simple meandered microstrip design with a single layer, it is easy to manufacture, robust and low profile.

Synthesis of the unit cell, elimination of open stop band (OSB) and measurements are out of the scope of this paper and will be expanded in future work.

Fig. 1 :Fig. 2 :

 12 Fig. 1: Proposed LWA with 10 unit cells.

Fig. 3 :

 3 Fig. 3: (a) Brillouin diagram for the conventional unit cell operating in space harmonic of n = -1. and (b) for the proposed unit cell operating in space harmonic of n = -2. f b1 = 22.6 GHz and f b = 22.6 GHz are the frequencies where radiation in broadside direction takes place. Here p 1 = 5 mm, W 1 = 2.8 mm and p = 5.8 mm, W = 3.01 mm.

Fig. 4 :

 4 Fig. 4: Dispersion diagram extracted from driven-mode unit cell simulation. The antenna scans from backward direction (-Y-axis) to positive direction (+ Y-axis) predicted by the ratio of β and k 0 . The ratio of α and k 0 predicts the beamwidth of the radiation pattern.

Fig. 5 :

 5 Fig. 5: Full Wave simulated fan-beam at f = 20 GHz. The gain of the antenna is shown and the scale is in dB.

Fig. 6 :

 6 Fig. 6: Variation in the angle of maximum radiation in the H-plane (Y-Z plane) for (a) conventional meandering microstrip LWA operating in spatial harmonic n = -1 and (b) proposed meandering microstrip LWA operating in spatial harmonic of n = -2. f b and f b1 shown in Fig. 3 are the frequencies at which broadside radiation takes place. Both the antennae are linearly polarized in the H-plane .

TABLE II COMPARISON

 II WITH OTHER K-BAND AND KA-BAND SCANNING LWAS

	Ref	Antenna Type	Frequency BW	Scanning Range	Gain (dB)	Rel. Permittivity	Scanning Rate
						(εr)	(°/GHz)
	[10]	Microstrip with metallized	20-29 GHz	95 °(-50 °to 45 °)	Approx. 10	6.15	10.55
		vias
	[27]	SIW	26-43 GHz	70 °(-40 °to 30 °)	13.4-15	3.0	3.04
	[12]	Microstrip	37-57 GHz	95 °(-45 °to 50 °)	10.8-13.8	3.0	4.75
	This Work	Microstrip	20.6-24.6 GHz	85 °(-40 °to 45 °)	9.8-13	3.0	21.25

ACKNOWLEDGMENT

This study was supported by the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie N • 899546 grant through the REACH-IT project and by the European Union's Horizon Europe research and innovation program through the Marie Skłodowska-Curie IN-SIGHT project N • 101063966.


Christine Voiron-Canicio
email: christine.voiron@unice.fr

Sophie Liziard
email: sophie_liziard@hotmail.com

INTERACTIONS BETWEEN COASTAL URBAN DYNAMICS AND AGRICULTURAL AREAS OF THE COTE D'AZUR: STAKES AND PROCESSES

On the Côte d'Azur, agricultural areas are major components of the landscape's beauty and contribute to tourism and residential development. However, the desire to take advantage of environmental assets leads to an intense urbanisation of agricultural areas and a degradation of the local landscape. This paper analyses the land use changes observed over the last 40 years, of a strip stretching 10 km from the coast. Urbanisation has been progressing inland, to the detriment of agricultural areas. The objective is to understand the processes at stake and to think about the future territorial evolutions, with a particular attention paid to systemic interactions and the spatial dynamics resulting from them.

Introduction

For many decades, Mediterranean coasts have been subjected to a process of littoralisation, which acts with more or less intensity depending on the regions. The densification of human occupation comes along with an increasing artificialisation whose environmental damages are well known. Urban sprawl, to the detriment of agricultural and natural areas, is the topic of several studies. However, few studies have focused on the spatial dynamics resulting from the interactions between agriculture, urbanisation, landscape and distance from the shore. These dynamics have become complex, particularly in the coastal regions with a high attractivity. Their understanding is fundamental for a sustainable planning and development of coastal regions. This paper studies the linked dynamics of agricultural and built-up areas, over the last forty years on the Côte d'Azur. The complex evolution of this region prefigures the dynamics of numerous coastal regions subjected to a strong land pressure. The objective is to understand the processes at stake and to think about the future territorial evolutions, with a particular attention paid to systemic interactions and the spatial dynamics resulting from them.

Evolution of agricultural areas and built-up surfaces on the Côte d'Azur

The image of the Côte d'Azur is strongly linked to certain agricultural specialisations, principally flowers, but also citrus fruits and olive trees [START_REF] Boyer | L'invention de la Côte d'Azur, l'hiver dans le Midi[END_REF]. Flowers, along with palm trees and exotic vegetation, are inseparable from the symbolic landscapes of Côte d'Azur. At the beginning of the last century, this region was covered with fields of flowers. Around Grasse and Vence, scented flowers were cultivated to make perfume. The coastal plain of Vallauris and Antibes was covered with orange tree flowers which were intended for the perfumeries of Grasse. The coast and the first hills located between Antibes and Nice were specialised in cut flowers. Rose and carnations were sent all over the world. The 1950s marked the peak of horticulture on the Côte d'Azur: the turnover of horticulture equaled the turnover of tourism at that time. As time has gone by, horticultural areas, as citrus fruits, vines and vegetables ones have been gradually replaced by urbanisation growth. This evolution has accelerated since 1975. Thus, between 1979 and 2000, the municipalities located less than 10 km from the coast lost 70 % of their vegetables surfaces, and 35% of their surfaces of vines and flowers. Only 50 ha of vines with a guarantee of origin remained. Surfaces in olive trees showed a higher level of resistance, with only a 15% diminution.

The result of this evolution is illustrated in figure 1A, which represents the state of land use in 2000, on a 10 km strip from the shore. Artificial surfaces spread along the coast and then widely penetrate inland, except in the eastern part because of the constraints of relief. Natural areas cover the major part of the hinterland. Agricultural areas are located between both, mainly in the Siagne valley in the northwest of Cannes, in the Var valley to the west of Nice, in the Nice hills and in the Menton hinterland. The coastal strip located between Cannes and Nice possesses almost no agricultural areas any more. On this portion of the coast, formerly highly agricultural, the creation of residential zones resulted in the disappearance of horticulture. Figure 1B shows agricultural areas which were urbanised between 1975 and 2000. The hills around Nice and the Var valley were the most extensively affected by the artificialisation of agricultural areas. The agricultural plots in the close hinterland from Vence to Grasse were not spared. All in all, more than 31 000 ha, or almost half of the agricultural areas of 1975, became artificial spaces during this period. New agricultural areas were scarce and couldn't compensate for the lost surfaces.

The decrease of agricultural areas in the Mediterranean coastal regions, resulting from the combined action of tourism and urbanisation, is described in numerous studies [START_REF] Diact | Construire ensemble un développement équilibré du littoral, Etude prospective[END_REF][START_REF] Bleu | Méditerranée, les perspectives du Plan Bleu sur l'environnement et le développement[END_REF][START_REF] Cnasea ; Daligaux | La périurbanisation en Provence : visages d'hier et d'aujourd'hui, interrogations pour demain[END_REF]. Rarer are the analyses which emphasise the spatial aspects of these processes. Such is the case of the study led by the Plan Bleu on the Suivi de l'évolution du littoral à partir des données LACOAST (2000), where the analysis of land use is carried out according to the distance from the coast. The distance is taken into account by means of five strips of 2 km wide, parallel to the coastline. On graphs 1 and 2, the percentages taken by each of the three classes within each strip are represented in the middle of the strips and linked. It may suggest a regular gradient, while in fact it is a mean value per strip.

Graph. 1. Land use of the Alpes-Maritimes coast according to the distance from the shore (1975)(1976)(1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)

Fig. 1. Land use of the Alpes-Maritimes coast in 2000 and evolution of agricultural areas on the Alpes-Maritimes coast between 1975 and 2000

Artificial surfaces constitute the major type of occupation on the 0-2 km strip, with more than 60% of land. This part quickly decreases in the following strips but never falls below 20%. Between 1975 and 1990, the part of artificial surfaces increases in the five strips and more particularly near the shore. It is in the 0 and 2 km strip where agriculture is the least present. The decrease of agricultural surfaces is particularly strong on the first two strips, then it reduces. It is interesting to draw a parallel between this evolution and the one of artificial surfaces. The growth of artificial surfaces in the first 6 kilometers is clearly made at the expense of the agricultural areas. We have prolonged the analysis by carrying out the same treatment with the data Corine Land Cover 1990 and 2000 (graph 2). The artificialisation has taken place on the whole area of study, but the 0-2 km strip seems to have reached a threshold of saturation. It is currently between 6 and 8 km from the coast that artificialisation has the strongest intensity. The proportion of agricultural and natural surfaces declined slightly in the first 2 kilometers and a little more on the last kilometers.

Graph. 2. Land use of the Alpes-Maritimes coast according to the distance to the shore (1990-2000)

During the period 1999-2006, treatments were carried out on the database, Land Use PACA (CRIGE PACA). The represented minimal surface is from 2.5 to 5 hectares while it is 25 ha for the data LACOAST and Corine Land Cover. Because of this difference of resolution, the obtained values must be compared with caution to the previous ones. It seems nevertheless that the tendency, although very slow, remains negative for the evolution of agricultural and natural areas, and positive for artificial surfaces.

Understanding the processes

The relationships which connect coastal agricultural areas and artificial areas are narrow. As time passed, they changed nature and became more complex. Three periods characterise these interrelations.

-Firstly, tourism and urbanisation development goes together with coastal agriculture. The need engendered by the economy of holiday resorts, population growth, plains planning and coastal rivers embanking encouraged the extension of vegetable and floral cultivation. Until the middle of the XXth century, urbanisation and agriculture grew on the coast in a concomitant way and without conflict because space was available.

-From the 1970s, horticulture underwent foreign competition, and the farmers in trouble stopped their activity all the more easily as real estate developers solicited them. Population growth accelerates and built-up areas spread. Along the coast, built-up areas combined little by little and once the interstitial spaces were filled, urban sprawling went inland. The "Loi Littoral" was promulgated in 1986 to contain the coastal urbanisation and to protect natural areas.

-With the end of the 90s starts the third period. The conflicts of uses increased with the rarefaction of available areas and caused the accelerated disappearance of farmlands. Authorities, at the national level and in a lesser measure, at the local level, became aware of the misdeeds of this evolution. New laws were promulgated at the beginning of the 2000s to limit the urban sprawling. In the Alpes-Maritimes, the objective for the "Directive Territoriale d'Aménagement" (DTA), developed in 2003, was to clarify the fundamental orientations in territorial planning. For the coast, it attempted especially to determine the modalities of enforcement of the "Loi Littoral". The attention is mainly focused on the urbanisation control and the preservation of natural sites. As regards farmlands, the DTA simply recognises that agricultural activities are in periurban context and that "besides their economic function, they play a role in the landscapes protection, the urban sprawl control and the natural risks prevention". It also defines geographical areas where agricultural activities must be protected.

In a geographical context, a set of factors contributes to the decrease of coastal agricultural areas. Agricultural areas of the coastal strip accumulate a double handicap. On one hand, as all periurban farmlands, they undergo the effects of the continuous urbanisation spread. On the other hand, they belong to an extremely attractive region where available areas for housing are scarce. Farmlands are potential land reserves. Land speculation increases the price of agricultural land to record levels. Today, the average price exceeds 300,000 euro/ha, which is prohibitive for farmers who wish to settle down or to purchase new land. The strong land pressure moves towards the close hinterland. The coastal subsystem reaches an advanced stage of littoralisation which appears through phenomena of saturation and diseconomies of built-up areas. The availability and the price of land, more affordable in the hinterland, encourages more and more city-dwellers to live there. The closer hinterland is henceforth included in the dynamics of the coastal subsystem and its spatial and functional structures have seen profound transformations [START_REF] Ch | L'espace dans la modélisation des interactions nature-société, Acte du colloque international « Interactions nature-société, analyse et modèles[END_REF]. In view of this situation, local authorities and the State have neglected, by indifference or due to a lack of clear-sightedness, the destiny of the Côte d'Azur agriculture, unlike in the nearby Ligurie where for more than 20 years, the town councils of the Riviera have had a strict policy of preservation of agricultural and natural sites. By a limited number of granted building permits, they succeeded in containing urbanisation and keeping agricultural activity on the Ligurie coast. Moreover, agricultural areas on French coasts have not benefited from the same protective measures as the natural areas. The "Loi Littoral" was promulgated at the same time as the "Loi Montagne". For the latter one, the conservation of agricultural activities is one of the first objectives. As a consequence, legal measures are taken while the "Loi Littoral" only recommends "the preservation or the development of agricultural activities". Finally, the "Loi Littoral" had perverse effects [START_REF] Cnasea ; Daligaux | La périurbanisation en Provence : visages d'hier et d'aujourd'hui, interrogations pour demain[END_REF]. By slowing down the artificialisation of the coast, it repelled the land pressure on the farmlands of the coastal zone and the hinterland. The individual strategy of the farmers is added to these factors (Jouve A-M., Napoléone C., 2003, pp. 143-171.). The uncultivated areas are relatively numerous while there is need for farmland. This paradox is explained by the fact that certain farmers are tempted to sell their lands to promoters who anticipate the changes of zoning, purchase this land and leave them uncultivated. Finally, spatial factors, which act at the scale of land plots, contribute to the processes of territorial transformations. Thus, conflicts of neighborhood appear when agricultural lands are enclosed in residential areas. The measures taken to limit the use of pesticides are more and more drastic when residential areas are close to cultivated lands. Farmers prefer to sell their land and reinstall their farm in less urbanised areas, as for example the department of Var bordering the Alpes-Maritimes. The decrease of agriculture presents spatial dynamics in connection with urbanisation processes. These processes take place gradually from built-up areas, so the farmland which adjoins or is near to them have a large propensity to disappear. Thereby, spatial surroundings of agricultural areas, in terms of land use, act on their sensibility to urbanisation [START_REF] Liziard | Enjeux et Dynamiques des Zones Agricoles Côtières face au Processus de Littoralisation (Alpes-Maritimes) : Une Analyse par la Sensibilité à l'Urbanisation[END_REF]. Farming areas with a certain unity on wide surfaces have a better resistance to urban sprawl than the isolated or small-sized agricultural areas. As the extension of residential areas is oriented by road networks, the farmland located nearby, with a good accessibility, are therefore subject to a preferential urbanisation. The disappearance of specific agricultural areas between 1975 and 2000 also shows the pursuit of particular advantages: on the valley beds, flat places are ideal for the installation of large-scale infrastructures; the ridge lines, hills and low hillsides offer a panoramic view and pleasant surroundings. Thus, the agricultural areas urbanisation refers to spatial factors not only corresponding to the search of practicality in the activities localisation, but also to the want to live in rural surroundings and near coastal urban areas.

Prospective and discussion

In spite of the slowing down of farmland artificialisation process observed, agricultural areas continue to decrease inexorably. Risks of disappearance are different according to agricultural specialisations. The symbolic floral cultures of the Côte d'Azur are, with vegetable farming, the most threatened. These cultures, generally under greenhouses or under low shelters, are considered as unaesthetic. On the contrary, landscapes of vineyards and olive groves are more valued. Consequently, these latter landscapes are the object of more attention in town planning documents than the first ones. Spaces with stakes are henceforth situated in the valley bed, on hillsides and summits of hills offering a clear view. If the observed tendencies continue, the emerging scenario is the one of a more and more urbanised coastal zone where the remaining agriculture would be residual. Some agricultural spots would be the subjects of protection: vines with a protected designation of origin, olive trees and cultivations recognised as homegrown. The rest of the agricultural areas would be gradually transformed into wasteland. During the renewing of town planning documents, the most suitable uncultivated plots of land for construction and the most accessible would eventually be classified as buildable land. The steeper sloping plots of land, affected by secondary vegetation, would change to the category of natural areas. The photo of the figure 2 illustrates the current process.

Fig. 2. Landscape of the Nice hills, in 2003

Landscape degradation would be irreversible, quite particularly on hills overlooking the coastal plain. The variety of traditional rural landscapes would be first substituted by a disorder resulting from the neglected cultures, then by a stratified landscape characterised by residential buildings on the summit of hills and the highest hillsides and forested areas in the middle-slope, and finally, an urbanisation combining activities and housing in the valley beds.

Is it possible to stop this evolution? Is there any desire to do so?

The laws promulgated in the last few years gave to local authorities some new tools to control this decrease of agricultural areas. Town councils and Prefectures of regions can ask for the classification of farming areas in "Zone Agricole Protégée" (ZAP) because of the quality of their production or their geographical situation (periurban zone, erosion sensitive areas, land with typical agriculture). The "agricultural vocation" is set up as "easement in the public interest" what allows for it to take from unforeseen fluctuations in the land-law. In 2001, the « Etablissement Public Foncier de Provence-Alpes-Côte d'Azur" was created in order to carry out land transactions and protect agricultural areas. A law passed in 2005 confers to the departmental authorities the right to delineate "perimeters of protection and development of periurban agricultural and natural areas", (PAEN). Thus, legal arsenal more effective than previously given to local authorities, some of them have chosen to use it. The Alpes-Maritimes General Council decided to buy land which will be protected by means of PAEN. In the Var plain, an "Opération d'Intérêt National" was enacted in March 2008. The OIN project presents a double objective of protection and development of the Var plain under the label "Eco Vallée".

The realisation of the environmental utility of agricultural areas is still limited. Nevertheless, their functions are essential in Mediterranean zones. They play the role of firewall, slow down landslides, restrains floods. ICZM policies are not very interested in coastal agricultural areas. They focus on polluting farm waste and don't pay enough attention to the protection of Mediterranean agricultural landscapes. The "Conservatoire du Littoral" sometimes purchases agricultural areas which are abandoned because of land pressure or urbanisation threats. Then, an activity of vineyards is reinstalled there because this is a way to keep the balance of nature at the lowest cost. But until now, no purchase of this type has been completed on the Côte d'Azur.

The landscaped patrimonial value of coastal agriculture is still not acknowledged enough on the Côte d'Azur, unlike what we can observe in certain coastal areas of the Var department. The most pleasant coastal landscapes combine a view of the sea, Mediterranean cultivations and wooded areas. On the peninsula of Saint Tropez, the classification of the site and a strict application of the "Loi Littoral" enables the containing of urbanisation and the spread of vineyard areas in combination with selfcatering cottages.

However, many people think that the fate of coastal agriculture is sealed. Legal measures have come too late and they are insufficient to confront the intensity of the land pressure exerted on agricultural areas. For the economist Claude Napoléone, an important part of the Mediterranean non-built-up coasts belongs henceforth to banks and pension funds which make long-term investments. According to him, only drastic measures of lands protection coupled with a policy of urban densification and the creation of a "Conservatoire des espaces agricoles" on the same type as the "Conservatoire du Littoral", could overcome the phenomenon.

Conclusion

To sum up these complex relationships between coastal landscapes, agriculture and urban areas, two conceptual systemic graphs have been built (Fig. 3). The first one is related to the period 1900-1970. Since the 19 th century, agricultural areas have always been major components of the regional attractiveness. These assets have contributed to the development of tourism and of the residential function. Until the seventies, urbanisation extended without encroaching on the agricultural activities because clear space was available on the coast. Afterwards, the links between agricultural and urban areas, as well as those between the coastal zone and the closer hinterland, became more complex. During the period 1970-2008, several laws and local territorial policies have tried to protect the sensitive coastal areas and to slow down the urban sprawl. As the agricultural lands did not get the same protection, the urban pressure has been moving towards them. Agricultural areas located on the coast, are more desired if they are flat, with a good accessibility to the metropolitan area, with a pleasant environment and a view of the sea. Nevertheless, the available space has become scarcer on the coastal territory, so urbanisation has been progressing inland to the detriment of the agricultural areas. The logic of these littoral spatial dynamics reaches disturbing limits. The desire to take advantage of environmental assets leads to an intense urbanisation of the agricultural areas. The consequence of such an evolution is a degradation of the local landscape which plays a major role in the coastal attractiveness. Henceforth, territorial stakes lie in the recognition of the landscaped patrimony represented by the agricultural areas of the Côte d'Azur and in the protection of the agricultural lands of the coast as those of the closer hinterland.

Fig. 3 .

 3 Fig. 3. Causal diagrams of coastal spatial dynamics