José Augusto Monteiro

Castro Lima

Jérôme Labanowski

Marília Camotti Bastos

Osmar Renato Zanella

Damian Prestes

Jocelina Paranhos

Rosa De Vargas

Leslie Mondamert

Eugenie Granado

Tales Tiecher
email: tales.tiecher@ufgrs.br

Mohsin Zafar

José Augusto Monteiro De Castro Lima

Alexandre Troian

Thibaut Le Guet

Danilo Rheinheimer

Santos

"Modern agriculture" transfers many pesticides to watercourses: a case study of a representative rural catchment of southern Brazil

Keywords: Environmental monitoring, Polar Organic Chemical Integrative Sampler, Water Contamination

come

Introduction

In southern Brazil there are more than 850 thousand family farms. In this region, 20 million hectares are occupied by more than 2.3 million people working exclusively in rural activities in and producing about 80 x 106 Mg of soybean, corn, rice and wheat in 2017, representing 36% of Brazilian national production (IBGE, 2019). Even if soybeans as the main crop, there is a great diversity of production, including fruits and vegetables. Indeed, more than 90% of swine and poultry meat, approximately 50% of milk and almost 100% of tobacco are produced in this macro-region.

Approximately 143 Mg of active ingredients of pesticides are dispersed in a rural environment densely populated, even small towns which surrounded by crops. This macro-region has one of the most important surface water reserves of South America, except to Amazon catchment. Furthermore, it has one of the largest aquifers in the world, Guarani Aquifer, which also involves part of Paraguay, Argentina and Uruguay.

The transformation of natural biomes such as Pampa and Atlantic Forest in southern Brazil into cropfields tremendously decreases the infiltration of rainwater which results in increasing runoff and soil losses. The intensive land use combined with high intensity rainstorms make this region one of the global erosion hotspots [START_REF] Borrelli | An assessment of the global impact of 21st century land use change on soil erosion[END_REF]. Results obtained by using the fingerprinting approach to investigate sediment origin in south Brazil revealed that about 90% of sediments present in Guaporé River (state of Rio Grande do Sul) come from cropfields, and the remaining from stream channels and unpaved roads [START_REF] Tiecher | Quantifying land use contributions to suspended sediment in a large cultivated catchment of Southern Brazil (Guaporé River, Rio Grande do Sul)[END_REF]. Accordingly, to these authors, this occurs because of the high connectivity of erosive processes from hillslopes to the stream network in Guaporé River catchment, were there is a lack of mechanical runoff control strategies and absence of crop rotation. The main agricultural use is based in mono-cropping system of soybean in upper part and tobacco in middle/lower part of this catchment. There is also intensive integrated crop-livestock systems for milk production that results in lower soil cover by plant residues. Moreover, this region presents a rapid displacing of soil water by new rainfall events [START_REF] Robinet | Impacts of forest conversion and agriculture practices on water pathways in Southern Brazil[END_REF]. Accordingly, this scenario may result in high transfer the soluble and colloidal pesticides to the watercourses. In southern Brazil, there is a great diversity of soil type and agricultural production systems. There are reports in the literature of studies that have focused on specific molecules in irrigated rice cultivation areas and the effect of pesticides used in rice fields on the oxidative stress of fish in a rice-fish system (Clasen et al., 2012;2018). Water and fish contamination in catchments with a predominance of tobacco cultivation [START_REF] Bortoluzzi | Contaminação de águas superficiais por agrotóxicos em função do uso do solo numa microbacia hidrográfica de Agudo, RS[END_REF][START_REF] Becker | Pesticide contamination of water alters the metabolism of juvenile silver catfish, Rhamdia quelen[END_REF], as well as glyphosate contamination in areas with predominance of soy/corn/wheat cultivation under no-tillage has also been studied (Fernandes et al., 2019). However, the impact of pesticide contamination on more complex catchments with contrasting cultivation systems, such as the Guaporé River catchment, needs to be better understood in order to more holistically assess the effect of contamination generated by agricultural activities on aquatic systems. It is also important to evaluate a more diverse number of molecules and sampling strategies to generate information that can be used for river basin monitoring programs.

In 2018, 5.3 x 105 Mg of active ingredients of pesticides were applied in Brazil (IBAMA, 2019). However, global estimates indicate that only 1% of applied amount reaches the target organisms. The remaining 99% of pesticides remains in the soil, water, and atmosphere, being eventually absorbed by non-target organisms [START_REF] Zhang | Global pesticide consumption and pollution: with China as a focus[END_REF]. The transport of pesticides from crops to other environmental compartments is mostly done by water through preferential flow and/or surface runoff. As a result, pesticides, especially polar and highly soluble ones, are found in surface and ground waters [START_REF] Masiá | Screening of currently used pesticides in water, sediments and biota of the Guadalquivir River Watershed (Spain)[END_REF].

The occurrence of pesticides in the aquatic environment has been reported worldwide (Fernandes et al., 2019;[START_REF] Schreiner | Pesticide mixtures in streams of several European countries and the USA[END_REF][START_REF] Michel | Fipronil and two of its transformation products in water and European eel from the river Elbe[END_REF][START_REF] Masiá | Screening of currently used pesticides in water, sediments and biota of the Guadalquivir River Watershed (Spain)[END_REF]Rabietet al., 2010;[START_REF] Bortoluzzi | Contaminação de águas superficiais por agrotóxicos em função do uso do solo numa microbacia hidrográfica de Agudo, RS[END_REF]2007). However, they are often found at concentrations below 1 µg L-1, requiring the use of sensitive methods and equipment that achieve low detection limits [START_REF] Terzopoulou | Active and passive sampling for the assessment of hydrophilic organic contaminants in a river watershed-ecotoxicological risk assessment[END_REF]. Most analytical methods and grab water sampling techniques have limited ability to provide holistic assessment of exposure to pesticides [START_REF] Petty | A holistic passive integrative sampling approach for assessing the presence and potential impacts of waterborne environmental contaminants[END_REF]. The monitoring of the Morcille stream (France) over a year, confirmed that discrete sampling was not suitable for the accurate measurement of the level of exposure to pesticides in surface waters, stating that grab sampling largely underestimated pesticide concentrations and fluxes transiting through the stream [START_REF] Rabiet | Assessing pesticide concentrations and fluxes in the stream of a small vineyard catchment--effect of sampling frequency[END_REF].

An alternative is to employ passive sampling devices like the Polar Organic Chemical Integrative Sampler (POCIS). Theory and modelling about passive samplers have been largely described elsewhere [START_REF] Alvarez | Comparison of a novel passive sampler to standard water-column sampling for organic contaminants associated with wastewater effluents entering a New Jersey stream[END_REF][START_REF] Huckins | Lipid-Containing Semipermeable Membrane Devices for Monitoring Organic Contaminants in Water[END_REF][START_REF] Stuer-Lauridsen | Review of passive accumulation devices for monitoring organic micropollutants in the aquatic environment[END_REF][START_REF] Vrana | Passive sampling techniques for monitoring pollutants in water[END_REF][START_REF] Morin | Chemical calibration, performance, validation and applications of the polar organic chemical integrative sampler (POCIS) in aquatic environments[END_REF][START_REF] Ibrahim | Polar organic chemical integrative sampler (POCIS) uptake rates for 17 polar pesticides and degradation products: laboratory calibration[END_REF][START_REF] Bayen | Application of Polar Organic Chemical Integrative Sampler (POCIS) to monitor emerging contaminants in tropical waters[END_REF]. There is evidence that the accumulation of target compounds by POCIS is a dynamic process, with adsorption and desorption on the sorbent occurring in response to ambient levels of the target compounds in water [START_REF] Metcalfe | Monitoring for contaminants of emerging concern in drinking water using POCIS passive samplers[END_REF]. Hence, the POCIS is a passive sampling technology that has been developed to accumulate trace levels of pesticides to provide time-integrated average concentrations for individual compounds in water. [START_REF] Metcalfe | Pesticides related to land use in catchments of the Great Lakes basin[END_REF], using POCIS for monitoring the pesticides in several catchments in the Great Lakes in Ontario, make evident the relationship between frequency and concentration of many pesticides (2,4-D, atrazine, carbendazim, tebuconazole and imidacloprid, especially) in watercourses and proportion of cropfields (soybean, corn and wheat). The POCIS was more adequate than active sampling for pesticides present in very low concentration. [START_REF] Challis | Inputs, source apportionment, and transboundary transport of pesticides and other polar organic contaminants along the lower Red River, Manitoba, Canada[END_REF], also in Canada (Red River -Lake Winnipeg), showed that using POCIS was possible to estimate the main sources of pesticides (i.e., atrazine from the United States and neonicotinoid both from Canadian and the United States agriculture fields) and signaled the time-scale concerning application and detection in surface water. [START_REF] Guibal | Two sampling strategies for an overview of pesticide contamination in an agriculture-extensive headwater stream[END_REF], working in headwaters in two small catchments in France, aware to difficulty for monitoring the pesticides frequency and concentration fluctuation using active or passive sampling. They identified the three possible types of behavior (active >, = and < POCIS) when compared grab and passive sampling in relation to pesticides concentration. We know that the time of concentration of agriculture hillslope catchment is very fast (fromminutes to some hours) and the peaks of pesticides concentration occurs only after a few days of the application time in the cropfields [START_REF] Liess | Determination of insecticide contamination in agricultural headwater streams[END_REF] and after, the pesticides concentration may be not detected in the water column. However, the use of POCIS allows the accumulation of compounds that persist at low concentrations in surface waters [START_REF] Terzopoulou | Active and passive sampling for the assessment of hydrophilic organic contaminants in a river watershed-ecotoxicological risk assessment[END_REF][START_REF] Metre | Complex mixtures of Pesticides in Midwest U.S. streams indicated by POCIS time-integrating samplers[END_REF]. Moreover, it enables to decrease the high variability remaining when using grab sampling.

In this study, we compared the active and passive water sampling to evaluate the pesticides concentration in Guaporé River (Rio Grande do Sul State, Brazil) and its tributaries in order to understand the role of soil use and management on degree of contamination of surface water in the region

Materials and Methods

Catchment Description

The Guaporé River catchment is located in the south of Brazil, Rio Grande do Sul Statebetween plane coordinates 420. 900 -366.400 mE and 6.874.286 -6.772.536 mS, zone 22S. The Guaporé River, which is the main watercourse, is 153 km long and drains an area of 2,490 km 2 . The average monthly flow rate was 31.3 m 3 s -1 in 2012 and 2013 [START_REF] Scotto | Fluxos de fósforo em uma bacia hidrográfica sob cultivo intensivo no sul do Brasil. Dissertação (Mestrado em Ciência do Solo)[END_REF]. Sediment production in 2012 amounted to 390.2 Mg km 2 year 1 , and the average from 2000 to 2010 was estimated at 140 Mg km 2 year 1 , with runoff coefficient of up to 31% [START_REF] Didoné | Impact of no-tillage agricultural systems on sediment yield in two large catchments in Southern Brazil[END_REF].

The average annual temperature is 17.9 °C and average annual minimum and maximum temperatures are 12.6 and 24.7 °C, respectively (Cfa Köppen system). Average annual rainfall varies between 1,550 and 1,700 mm, but the annual minimum and maximum rainfall is 950 to 2,500 mm, respectively [START_REF] Brasil | Projeto RADAMBRASIL[END_REF]. In this catchment, in previous studies conducted revealed that the rain events have high erosion potential (8,800 MJ mm ha-1 h-1 yr-1) [START_REF] Didoné | Impact of no-tillage agricultural systems on sediment yield in two large catchments in Southern Brazil[END_REF] with greater occurrence from July to November [START_REF] Meteorologia | Estações Automáticas[END_REF]. The main soil classes, in the FAO Classification, are Acrisols (14.8%), Ferralsols (33.8%), Luvisols (24.9%), Regosols (3.1%) and Nitosols (23.3%).

In the upper third of the catchment, where the relief is nearly level to gently sloping and predominated by Ferralsols, the farmers are practicing the no-tillage system from past two decades. There is a very direct relationship between soybean (Glycine max L. Merr.) ultivation, livestock/swine, and poultry production in the catchment in spring/summer. The animals reside in marginal noncultivated areas, generally and along the watercourse. The farmers use high doses of herbicides and fungicides to soybean production, including the 2,4-D for resistant plant to glyphosate. The Nitosols covers almost 100% of the surface of Marau River tributary sub-catchment. In this area family agriculture integrated to livestock, especially, production of corn silage in spring and summer and winter grasslands forage to milk production. In addition, almost all farmers have also swine and poultry production activities. In the Marau River tributary there are 2.9 and 9.7 times corn and corn silage and -1.3 times soybean density production (Mg km -2 ) than in the source of Guaporé River.

In the other two-thirds (middle and lower) of the catchment, land use is more diverse and conventional soil management predominates in shallow soils with rocky surface (Luvisols, Acrisols and Regosols). The cultivated surface is imbricated in landscape and the family farmers have less than 10 hectares. In this region there are 1.3 and 1.6 times corn and corn silage and -4.2 times soybean density production than in the upper third of the catchment. This region has the biggest density of tobacco (Nicotiana tabacum L.) and erva-mate (Ilex paraguariensis St. Hill) production of Brazil. There is also integrated poultry and pig farming systems as well as dairy farming. The main land use in this area is cropland (60.0%), natural forest (30.1%), pastureland (5.6%), forestry (3.1%), urban areas (0.6%) and water bodies (0.4%) (Figure 1)

Sampling Sites

Were selected 18 sampling sites, located in the Guaporé River (G1, G2, G3, G4, G5, G6, G7, G8, G9 and G10), Marau Stream Tributary (M1, M2, M3 and M4), Lajeado Carazinho Stream Tributary (LC1, LC2 and LC3) and Carazinho Sream Tributary (C1). Descriptions of each site and locations are shown in Table 1 andFigure 1, respectively.

Active Water Sampling

The water sampling was performed between 11 and 13 December 2014, after a high precipitation event (89 mm -INMET, 2019). The soybean was in the V3 stage, the corn was in R1 stage and the first leaf of flue cured tobacco was harvest. The bottles were cleaned with neutral detergent and HNO3 10% for 12 h and after with osmotic water and methanol. One liter of water was stored in an amber bottle, maintained at 4 °C in thermic boxes, and transported to Pesticides Residues Analysis Laboratory of Federal University of the Santa Maria, in Brazil.

Passive Sampling -Polar Organic Chemical Integrative Sampler

The samplers were made of 316 stainless steel with the following dimensions: 102 × 54 × 3 mm (outside diameter, inside diameter and thickness); containing five 7 mm holes, two on the central axis, 6 mm from the inner edge and three in the shape of an equilateral triangle with 67.5 mm sides. SUPOR® Polyethersulfone filtering membrane with 0.1 μm pores and 90 mm diameter [START_REF] Petty | Device for sequestration and concentration of polar organic chemicals from water[END_REF] was used. The sorbent consisted of 200 mg of OASIS® HLB resin (30 μm particle diameter) with hydrophilic and lipophilic balance.205 Such devices were installed at the sampling sites in June 2015, fixed to be submerged during 15 days and protected by an iron box with an aluminum screen to allow water flow and act as a physical barrier against branches and stones. After fourteen days of exposure, the POCIS were collected, cleaned, packaged wrapped with aluminum foil, arranged in plastic bags in a cooler with ice and transported to the laboratory. In this period less than 1/5 of the total agricultural surface is cultivated with wheat, barley and winter grasslands forage. There is a very low rate of pesticide application, comparatively to spring/summer season.

Analytical Procedure

In the laboratory, the pesticides present in water samples were extracted on Solid Phase Extraction using 200 mg of adsorbing Strata X cartridge. The pesticides determination was performed in an Ultra High-Performance Liquid Chromatography, tandem mass spectrometry Acquity UPLC® pump with the triple quadruple Xevo TQ® (Waters). The mass spectrometer was operating in Selected Reaction Monitoring using an electrospray source positive ionization. 79 pesticides were monitored: 2,4-D, atrazine, azoxystrobin,bentazone,bispyribac sodium,bitertanol,boscalid,bromoconazole,buprofezin,carbaryl,carbendazim,carbofuran,carboxin,cianazin,chlorimuron,chlorpropham,diazinon,dichlofluanid,difenoconazole,dimethoate,epoxiconazole,fenpropathrin,fenpropimorph,fenarimol,fenthion,fipronil,fluquiconazol,fluroxypyr,flutolanil,imazalil,imidacloprid,iprovalicarb,linuron,malathion,mecarbam,mepronil,metalaxyl,metconazole,methiocarb sulfone,methiocarb sulfoxide,mevinphos,myclobutanil,monocrotophos,monolinuron,oxamyl,paraoxonethyl,pendimethalin,pyraclostrobin,pyrazophos,pyrridiphention,pyrimethanil,pyrimicarbe,profenofos,propiconazole,propyzamide,propoxur,quinclorac,quinoxyfen,simazine,tebuconazole,terbufos,tetraconazole,thiacloprid,thiamethoxam,thiodicarbe,tolclofosmethyl,triadimefon,triadimenol,triazofos,trichlorfon,trifloxystrobin,triflumizole,and vamidothion. The POCIS adsorbent material was transferred to cartridges with the aid of ultrapure water, then dried first under vacuum in a SPE manifold with N2 flow Elution of the cartridges was done on a Thermo Scientific™ Dionex™ AutoTrace™ 150 Solid-Phase Extraction system with methanol. The extracts were evaporated under N2 flow and then reconstituted in 500 µL of a methanol: water (10:90, v/v) mixture. This method has been successfully used for elution of POCIS in a previous study. For quantification purposes, the standard curve method was used with all the pesticides under examination at concentrations of 0, 5, 10, 15 The analysis was carried out on an ultrahighperformance liquid chromatography (UHPLC) system (Thermo) with an electrospray source coupled to a quadrupole-time-of-flight mass spectrometer (Q-TOF) (Brucker). Three injections of 20 µL in positive and negative mode for each extract were done. Data processing and treatment were done using Compass Data Analysis 4.2 and Target Analysis software. The presence of each compound was confirmed according to three criteria: the exact mass and the mass spectrum of the compound compared with the exact mass and the mass spectrum of a certified standard solution of this compound, and the retention time determined in the analytical conditions The concentration of pesticides adsorbed in POCIS resin was carried out by adjusting the linear model used between the concentration of the standards and the peak area of each injection for each compound detected. Detection limits were calculated from the standard derivation of calibration curves. Due to variability for each compound, an over evaluated value of 1 µg L-1 was considered. A total of 23 compounds were analyzed, namely: 2,4-D, atrazine, boscalid, carbendazim, chlorotoluron, chlorpyriphos-éthyl, deethyl-atrazine, dicamba, epoxiconazole, imidacloprid, iodosulfuron-methyl-sodium, isoproturon, MCPA, mesotrione, mesosulfuron-methyl, metconazole, nicosulfuron, prochloraz, prosulfuron, prothioconazole, simazine, tebuconazole, thifensulfuron-methyl. To evaluate the time average concentration of waters, Rs value from literature were use [ Fauvelle et al. 2104 (2,4-D = 0.08), Mazella et al. 2010 (atrazine = 0.24; deethylatrazine = 0.17; simazine = 0.21), [START_REF] Ahrens | Characterization of five passive sampling devices for monitoring of pesticides in water[END_REF] (carbendazim = 0.22; epoxiconazole = 0.17; imidacloprid = 0.18; thifensulfuron-methyl = 0.02; mesosulfuron-methyl = 0.06), Belles et al. 2013 (tebuconazole = 0.19; prosulfuron = 0.12) and Mazella et al. 2007 (nicosulfuron = 0.04)]. All data regarding to development of analytical methods are available in supporting material.

Potential Ecological Risk

The predicted no effect concentration of each pesticide was calculated by dividing the concentration obtained in the literature responsible for causing some physiological damage or death of the standard species by an evaluation factor (EMEA, 2006). In this study, we assess the potential ecological risk for two species: (i) Daphinia magna, which is a crustacean used worldwide in ecotoxicological tests because of its sensitivity to environmental changes, and (ii) silver catfish (Rhamdia quelen), a fish commonly found in rivers in the southern region of Brazil. For Daphnia magna M. the critical concentrations found in the literature were: 2,4-D = 25.0 mg L -1 [START_REF] Toussaint | A comparison of standard acute toxicity tests with rapid-screening toxicity tests[END_REF]; atrazine and deethyl-atrazine = 50.4 mg L -1 [START_REF] Moreira | A comparative study of the acute toxicity of the herbicide atrazine to cladocerans Daphnia magna, Ceriodaphnia silvestrii and Macrothrix flabelligera[END_REF]; simazine = 4.2 mg L -1 [START_REF] Arufe | Comparative toxic effects of formulated simazine on Vibrio fischeri and gilthead seabream (Sparus aurata L.) larvae[END_REF]; carbendazim = 0.005 mg L-1 [START_REF] Silva | Ecotoxicity and genotoxicity of a binary combination of triclosan and carbendazim to Daphnia magna[END_REF]; tebuconazole = 40.1 mg L-1 (Sancho et al., 2008); and imidacloprid = 96.0 mg L-1 [START_REF] Loureiro | Toxicity of three binary mixtures to Daphnia magna: Comparing chemical modes of action and deviations from conceptual models[END_REF]. For silver catfish the critical concentrations found in the literature were: 2,4-D = 0.20 mg L -1 [START_REF] Glusczak | Acute effects of glyphosate herbicide on metabolic and enzymatic parameters of silver catfish (Rhamdia quelen)[END_REF]; atrazine and deethyl-atrazine = 10.2 mg L-1; simazine = 8.9 mg L-1; tebuconazole = 4.8 mg L - 1 [START_REF] Kreutz | Acute toxicity test of agricultural pesticides on silver catfish (Rhamdia quelen) fingerlings[END_REF]; carbendazim = 1.5 mg L-1 [START_REF] Sridhar | Carbendazim induced histopathological and histochemical changes in liver tissues of common carp Cyprinus carpio[END_REF]; imidacloprid = 78.0 mg L -1 [START_REF] Tyor | Effects of imidacloprid on viability and hatchability of embryos of the common carp (Cyprinus carpio L.)[END_REF]. The evaluation factor values were set at 1000, according to the suggestion of the European Commission Technical Guidance Document and Guidelines for the Implementation of REACH (2006). The potential ecological risk (RQi) for each pesticide studied and potential ecological risk mix (RQmix) was quantified using the ratio between the measured environmental concentration and the predicted no effect concentration [START_REF] Stehle | Pesticide authorization in the EU-environment unprotected[END_REF][START_REF] De Agudo | Ecological risk assessment of pesticide mixtures in the alluvial aquifers of central Italy: Toward more realistic scenarios for risk mitigation[END_REF]Kienzler et al., 2019Nie et al., 2015;Yao et al., 2017, Backhaus andFaust, 2012). The common risk ranking criteria are as follows: 0.01 <RQ <0. 1 is considered low risk, 0.1 <RQ <1 is considered medium risk, and RQ> 1 is considered high risk [START_REF] Hernando | Environmental risk assessment of pharmaceutical residues in wastewater effluents, surface waters and sediments[END_REF].

Statistical treatment

The Kolmogorov-Smirnov and Lilliefors tests were used to assess whether the concentrations of pesticides exhibited a normal distribution. As the results did not show normal distribution, the median was used as a measure of position, and the upper and lower quartiles, interquartile range, and maximum and minimum values as dispersion measures. The hypothesis that the systems of land use and management practiced in the northern and southern regions of the catchment contribute differently to the contamination of aquatic ecosystems by pesticides was statistically evaluated by the Mann-Whitney U nonparametric test. 3. Results and discussion 3.1 Grab Water Sampling None of the water samples collected from the National Forest contained pesticide residues. However, all others 17 water samples were contaminated with at least one pesticide. Of the 79 monitored pesticides, 11 were detected in the water samples (atrazine, simazine, propoxur, imidacloprid, carbendazim, azoxystrobin, thiamethoxam, fipronil, propiconazole, tebuconazole and carbofuran) (Figure 2). The two representative triazines pesticides (atrazine and simazine) were detected, respectively, in 94 and 89% of samples collected in Guaporé River and its tributaries (Table 2). It shows that this pesticides class (high log Kow 2.3-2.7 and low solubility 3.5-5.0 mg L-1 - [START_REF] Lewis | An international database for pesticide risk assessments and management[END_REF] are systematic transferred to the superficial watercourses in Brazilian agroecosystems [START_REF] Armas | Diagnóstico espaço-temporal da ocorrência de herbicidas nas águas superficiais e sedimentos do rio Corumbataí e principais afluentes[END_REF][START_REF] Azevedo | Triazines in the Tropical Lagoon System of Mundaú-Manguaba, NE-Brazil[END_REF][START_REF] Moreira | Contaminação de águas superficiais e de chuva por agrotóxicos em uma região do estado do Mato Grosso[END_REF], and can be persist in the water and aquatic biota [START_REF] Jablonowski | Persistence of 14Clabeled atrazine and its residues in a field lysimeter soil after 22 years[END_REF][START_REF] Bohn | Determination of atrazine and degradation products in Luxembourgish drinking water: origin and fate of potential endocrinedisrupting pesticides[END_REF]. These herbicides are, respectively, 3 and 6 most used in southern of Brazil [START_REF] Renováveis | Boletins anuais de produção, importação, exportação e vendas de agrotóxicos no Brasil[END_REF]. The 2,4-D was not detected despite its indiscriminate use (only surpassed by glyphosate) in Brazil and southern Brazil (57.4 and 14.8 Mg in 2017, respectively), due to its physicochemical properties (low Kow -0.82; high solubility 24.3 g L-1 and low half life time 4.4 days - [START_REF] Lewis | An international database for pesticide risk assessments and management[END_REF]. The 2,4-D transfer in the fluvial network is conditioned to the time of application and intensity of rainfall, which change the speed and flow of rivers. The active sampling is more adequate to detect this type of pesticides [START_REF] Silva | The Potential of POCIS and SPMD Passive Samplers to Measure Pesticides in California Surface Waters[END_REF]. The water of Guaporé River and its tributaries contain many insecticides (carbamates: propoxur and carbofuran; nicotinoids: imidacloprid and thiamethoxam; and pyrazole: fipronil). The neonicotinoids were detected in about 50% of water samples, and confirm previous data published with superficial water monitored near to the Guaporé catchment [START_REF] Bortoluzzi | Contaminação de águas superficiais por agrotóxicos em função do uso do solo numa microbacia hidrográfica de Agudo, RS[END_REF]2007;Sequinatto et al., 2013). The neonicotinoids pesticides use increased in the last two decades in about 120 countries in order to replace the organophosphates and carbamates insecticides (Jeschke et al., 2011), in contrast of interdiction in European Union after 2018. The systemic pesticides replace the contact pesticides with very active periods within the plant and acts against sucking insects, but also against beneficial insects such as bees. In southern Brazil the imidacloprid consummation increased eight times between 2009 and 2017 (IBAMA, 2019), and it has a very high potential for increased consumption because organophosphate is still seven times more consumed than neonicotinoids. Indeed, in 78% of water samples we detected propoxur insecticide, which is recommended to use in animals' production. Moreover the Guaporé catchment represents the highest concentration of swine and poultry in Brazil (FEE, 2019). Its low capacity of adsorption to colloids (Koc = 30 mL g-1 and log Kow = 0.14), high solubility (1800 g L -1 ), and high half life-time (180 days) make the propoxur very disperse in surface watercourse. The fungicides were detected in 11 monitored sites, especially those used in soybean production, such as the carbendazim (moderate Koc = 225 L kg-1, low Kow = 1.48, and high half life time = 350 days). While Singh et al. (2016) warned that this insecticide was banned in developed countries (Australia and most European countries), in Brazil its consumption is still extremely high (3.7 Mg in 2017 -IBAMA, 2019). The highest pesticides concentration and variability between monitored sites were observed for pesticides with the highest frequency of occurrence in Guaporé River and its tributaries (Figure 2). The medians concentration of atrazine and simazine were the highest among the pesticides monitored (680 and 190 ng L-1) and have also the highest spatial variability interquartile range (IQR of 1,000 and 150 ng L -1 ), and with 75% of concentration higher than 380 and 90 ng L -1 , respectively. For carbendazim, propoxur, imidacloprid and thiamethoxam analyses showed that 75% of the concentration was lower than 80, 60, 50 and 15 ng L -1 for, respectively. According to Brazilian legislation [START_REF] Brasil | Resolução do CONAMA nº 357[END_REF] the water from all monitored sites in Guaporé River catchment have been classified as "Special Class" and can be consumed by humans after a disinfection treatment. This classification allows the presence of glyphosate (65 µg L -1 ), alachlor (20 µg L -1 ), metolachlor (10 µg L -1 ), 2,4-D (4 µg L -1 ), atrazine (2 µg L -1 ) and simazine (2 µg L -1 ). Comparing pesticides concentrations obtained by grab sampling with the values allowed by the Brazilian legislation all sites could be used as a source of water for a drinking water treatment station. However, this egislation is very permissive when compared with other countries, for example France law. In France the quality limits for raw water of any origin used for the production of water, intended for human consumption, are limited to 2 µg L -1 for individual concentrations and 5 µg L -1 for the sum of pesticides. Based on this, if these values were compared with the France legislation, the grab samples satisfied these criteria. Nevertheless, POCIS sampling exhibited that pesticides concentrations values are largely above restrictive limits of French law.

Passive Sampling -Polar Organic Chemical Integrative Sampler

The use of POCIS enabled the detection of 2,4-D, atrazine, deethyl-atrazine, simazine, carbendazim, tebuconazole, epoxiconazole, imidacloprid, mesotrione, nicosulfuron, thifensulfuron-methyl, mesosulfuron-methyl and prosulfuron in the waters of the Guaporé River and its tributaries (Table 2 and Figure 3). All the sampling sites showed the presence of at least four of the 23 pesticides monitored, except in the National Forest site.

The uses of POCIS indicate that the pesticides, even months after their use, were transferred and detected in river ecosystems, in periods with low concentration. Therefore, the use of POCIS could avoid the problem of false negatives common in times of low pesticide use in agricultural fields, periods of low rainfall intensity and/or high rate. The POCIS exposed for 14 days provided the accumulation of the pesticides present in the water of the Guaporé River and its tributaries to such an extent that it enabled its quantification active sampling. These results have been evidenced in several studies evaluating the occurrence of organic contaminants such as pesticides, polychlorinated biphenyls, flame retardants and pharmaceuticals [START_REF] Alvarez | Comparison of a novel passive sampler to standard water-column sampling for organic contaminants associated with wastewater effluents entering a New Jersey stream[END_REF][START_REF] Dalton | Atrazine contamination at the watershed scale and environmental factors affecting sampling rates of the polar organic chemical integrative sampler (POCIS)[END_REF][START_REF] Schopfer | The Use of Passive Samplers to Reveal Industrial and Agricultural Pollution Trends in Swiss Rivers[END_REF][START_REF] Bueno | POCIS passive samplers as a monitoring tool for pharmaceutical residues and their transformation products in marine environment[END_REF][START_REF] Gonzalez-Rey | Occurrence of pharmaceutical compounds and pesticides in aquatic systems[END_REF]. This displays the relevance of this tool for assessing the water quality compared to the traditional sampling system. The frequency of quantification of atrazine, deethyl-atrazine, azoxystrobin, epoxiconazole, imidacloprid, simazine and tebuconazole in the waters was systematically enhanced with the use of POCIS [START_REF] Poulier | Can POCIS be used in Water Framework Directive (2000/60/EC) monitoring networks? A study focusing on pesticides in a French agricultural watershed[END_REF]. These results suggest that the contamination of Brazilian waters is being underestimated when using "active" grab water sampling. Among the herbicides, triazines (atrazine, deethyl-atrazine and simazine) and aryloxyalkanoic acid (2,4-D) chemical groups were detected in 94 to 100% of the sampled sites, respectively (Table 2). After glyphosate (IBAMA, 2019), the 2,4-D, atrazine and simazine are the most widely used pesticides in southern of Brazil and in the Guaporé River catchment,. Fernandes et al. (2019) showed that epilithic biofilms occurring in Guaporé River catchment were impregnated by glyphosate (10 to 305 μg kg-1) and your metabolite AMPA (50 to 670 μg kg-1) and are strongly influenced by the amount of herbicide applications. In general, the use of these compounds begins in June with the preparation of areas for the sowing of wheat and extends through January with the end of the corn and soybean planting season. The highest application volume is concentrated between the months of October and January, including for the others spring/summer cultures like tobacco and bean (Phaseolos vulgaris L.). Between January and June, the use of insecticides and fungicides are higher than the herbicide periods of vegetative and reproductive development of soybean and corn. The POCIS captured mesotrione, nicosulfuron, thifensulfuronmethyl, mesosulfuron-methyl and prosulfuron only in the Marau tributary sites and upstream of the Lageado Carazinho tributary. These herbicides were recommended and used in corn and grasslands forage production. The POCIS was also effective in detecting some fungicides in the Guaporé River network. Fungicides of the benzimidazole and triazole groups (in descendant order, carbendazim, tebuconazole and epoxiconazole) are those with the highest occurrence (Figure 3 and Table 2). However, anilide, imidazolecarboxamide and triazolinethione groups were not detected. Imidacloprid was detected in 75% of the sampling sites of the Guaporé River and its tributaries (Table 2). Conversely, chlorpyrifos (organophosphate) was not detected in the water of any of the sampling sites. This most likely happened due to its high octanol-water partition coefficient (Kow = 4.7), which ensures higher retention of these compounds in nonpolar matrices, reducing its concentration in solution and consequently reducing its exposure to the POCIS and its detection in water samples. Therefore, chlorpyrifos was not sequestered in the POCIS because of the reduced exposure time of the POCIS in the field, since it is commonly used by farmers [START_REF] Renováveis | Boletins anuais de produção, importação, exportação e vendas de agrotóxicos no Brasil[END_REF]. The uptake of less polar compounds (log Kow > 3.7) is strongly influenced by the exposure time of the POCIS [START_REF] Silva | The Potential of POCIS and SPMD Passive Samplers to Measure Pesticides in California Surface Waters[END_REF]. This characteristic, in addition to affecting the availability of the concentration in solution, also affects the diffusion of these pesticides between the two phases: from membranes with 0.1 µm porosity to the adsorbent. In the box-plots (Figure 4), the median location in the interquartile range of the pesticides confirms the results obtained by the Kolmogorov-Smirnov & Lilliefors test, that the data is unlikely to present normal distribution. Therefore, they are presented with the median, quartiles, minimum and maximum values. The herbicide class showed a higher concentration in the Guaporé River waters. 2,4-D stands out for two reasons, such as: (i) exhibited greater spatial variability between monitored points denoted in the IQR of 41,786 ng L-1; and (ii) the value of the first quartile was similar or higher than the values of the third quartile of other compounds analyzed in this study. Atrazine had a median of 1,905 ng L-1, an IQR of 2,857 ng L-1, and 75% of the observations were at concentrations below 655 ng L-1, five times less than the values found for 2,4-D. The lowest values found were of simazine, which presented median, IQR and first quartile values approximately 3 times lower than those of atrazine. The metabolite deethyl-atrazine showed similar behavior to simazine, but with higher amount accumulated in the POCIS sorbent. Among the fungicides, the variability between compounds and between the sampling sites was lower compared to the herbicides (Figure 4). For the median, IQR and first quartile values, the highest concentrations of fungicide present in the waters of the Guaporé River and its tributaries were (in downward order): carbendazim, tebuconazole and epoxiconazole. Contrary to the herbicides, 75% of the values for these three fungicides are below 994; 368; and 109 ng L-1. The interquartile range of carbendazim was 792 ng L-1, approximately 2.5 and 9.4 times than those of tebuconazole and epoxiconazole, respectively. Imidacloprid, the only representative of the insecticide class concentrated by the POCIS, was present in 75% of the sampled sites with concentrations below 786 ng L-1, whose median was 548 ng L-1 and the maximum concentration was 1,429 ng L-1 in the Guaporé River catchment. Although the use of the POCIS shows promise in improving the contaminant detection system in river waters, there are gaps of knowledge that must be overcome in order to obtain more realistic values of the concentration in the water derived from the amount sequestered, as well as for comparative purposes in each study and between studies. One of the issues is the lack of a method to satisfactorily correct in situ exposure conditions (water flow rates, temperature, pH, incrustation, etc.), which are known to affect the uptake rates of more polar compounds [START_REF] Harman | Field comparison of passive sampling and biological approaches for measuring exposure to PAH and alkylphenols from offshore produced water discharges[END_REF]2012). Another factor is related to the variability in the retention of pesticides in the membranes that protect the adsorbent. The study of [START_REF] Lissalde | Polar organic chemical integrative samplers for pesticides monitoring: Impacts of field exposure conditions[END_REF] showed that depending on the speed of water (3 to 13 cm s -1 ) between the sampled rivers and the tested compound, the accumulation in the membrane may vary from 3 to 60% of the total concentration sequestered by the membrane/adsorbent. For more nonpolar compounds (log Kow > 3), these limitations were overcome using performance reference compounds. This was possible due to its dissipation following first order kinetics to the uptake kinetics and could therefore be used to estimate the sampling rates of target compounds in situ [START_REF] Harman | Field comparison of passive sampling and biological approaches for measuring exposure to PAH and alkylphenols from offshore produced water discharges[END_REF]2012;[START_REF] Booij | Calibrating the uptake kinetics of semipermeable membrane devices using exosure standars[END_REF]. For the more polar compounds such limitations persist, there is a relationship between the flow rate and the reference compounds desorption, especially for speeds higher than 4 cm s-1 [START_REF] Lissalde | Polar organic chemical integrative samplers for pesticides monitoring: Impacts of field exposure conditions[END_REF]. However, the concentrations of 2,4-D, atrazine, carbendazim, simazine, imidacloprid and tebuconazole were higher than the highest concentrations [START_REF] Metre | Complex mixtures of Pesticides in Midwest U.S. streams indicated by POCIS time-integrating samplers[END_REF] reported in previous studies, except for deethyl-atrazine, which presented lower concentrations than those found by [START_REF] Lissalde | Polar organic chemical integrative samplers for pesticides monitoring: Impacts of field exposure conditions[END_REF]. If the interfering factors presented by [START_REF] Harman | Field comparison of passive sampling and biological approaches for measuring exposure to PAH and alkylphenols from offshore produced water discharges[END_REF] are minimized, the higher intensity in pesticide use in southern of Brazil, associated with reduced adsorption of soil and water conservation practices will be the main differing factors among the reviewed studies. This hypothesis is based on soil and climate characteristics (high levels of soil organic matter and 2:1 clay mineral; and temperate climate) of the studied regions. Thus, reduced rates of physicochemical degradation of pesticides in the soil were expected, resulting in a higher pesticide load on water resources. In regard of deethyl-atrazine, [START_REF] Lissalde | Polar organic chemical integrative samplers for pesticides monitoring: Impacts of field exposure conditions[END_REF] presented neither justification for the high values found in comparison to other compounds or other studies, nor did they present sufficiently relevant environmental conditions to justify such behavior*

Potential ecological risk

The surface water, generally, most of the sampling sites displayed low to medium ecological risk potential for the crustaceans Daphinia magnum and silver catfish by individual pesticides (Table 3). The 2,4-D and carbendazim concentrations could represented a huge risk of contamination than other pesticides, for silver catfish and crustaceans, respectively (RQ >>> 1 - [START_REF] Hernando | Environmental risk assessment of pharmaceutical residues in wastewater effluents, surface waters and sediments[END_REF][START_REF] Zeng | Risk assessment of an organochlorine Adv[END_REF]. The access of these two pesticides can induce DNA damage and immobility and death to crustacean, respectively. Indeed, the 2,4-D can increase hepatic glycogen and reduce muscle glycogen [START_REF] Glusczak | Acute effects of glyphosate herbicide on metabolic and enzymatic parameters of silver catfish (Rhamdia quelen)[END_REF] and carbendazim can cause the death of silver catfish [START_REF] Sridhar | Carbendazim induced histopathological and histochemical changes in liver tissues of common carp Cyprinus carpio[END_REF]. The cumulative potential risk (RQmix) for both species were null for watercourse in National Forest, and very low in the two tributaries monitored in middle/lower region ofthe catchment for crustaceans. In contrast, both Guaporé River and Marau tributary (upper region), the water represents a high ecological risk for the crustaceans and in all monitored site for silver catfish because of the high 2,4-D concentration. [START_REF] Becker | Pesticide contamination of water alters the metabolism of juvenile silver catfish, Rhamdia quelen[END_REF], using juvenile silver catfish maintained in cage for 30 days in a high (high concentration in imidacloprid and clomazone) and low contaminated watercourse next to Guaporé catchment, showed that the plasma glucose and hepatic glycogen levels of fishes were lowered, but it increased the plasma K+ levels, values of hepatic glycogen, muscle lactate and protein of the kidney when exposed to water at the high than at low anthropic activity. Generally speaking, sites with forests maintain a very low level of risk. For all other sites, the use of carbendazim exposes daphnia to a very high risk. For fish, the risk is associated with the presence of 2,4 D. However, as each species responds differently to a given molecule, it means that the ecosystem as a whole is threatened by the presence of pesticides in the water in Guaporé catchment due to the high anthropogenic pressure in the agricultural land.

Effect of agricultural use and management systems

It is known that in upper region prevail the transgenic soybean production in contrast to more diversified plant production in the middle/lower region (corn, tobacco, bean, etc.). In consequence, the type, doses and period of pesticides application are different in these regions. However, no differences in the diversity and concentration of pesticides between the upper and middle/lower region of the Guaporé River catchment using grab sampling (Table 4). Punctual pulses of pesticides application are indeed detectable only at short period soon after its application. Moreover, the presence of natural barriers in the landscape will also be responsible for a decrease of pesticide transfer to river, because it reduces runoff connectivity to stream network. These combined phenomena may maintain the concentrations of pesticides in watercourses at levels that cannot be distinguished between the upper and the middle/lower region of the catchment. Figure 5 presents the results of POCIS comparative analysis between the upper and middle/lower regions of the catchment by Mann Whitney U test for each contaminant. No differences at p <0.06 were found between the regions for 2,4-D, atrazine, deethyl-atrazine, simazine, epoxiconazole and imidacloprid. However, we found that the distributions of the values of carbendazim, tebuconazole and epoxiconazole are statistically different between the regions. Nevertheless, the waters of the Guaporé River and its tributaries in the middle/lower region had the highest median concentrations for all herbicides (2,4-D, atrazine, deethyl-atrazine, and simazine) and lower concentrations for all fungicides (carbendazim, epoxiconazole and tebuconazole) (Figure 5). The variability of the median concentration between the two macro-regions was 30 to 120% for herbicides and 67 to 270% for fungicides. The highest values found of atrazine and simazine in the Guaporé River and its tributaries in the middle/lower region of the catchment are consistent with higher corn density (124 and 258% for grains and silage, respectively), compared to the upper region, where soybean predominates (300% more density). In general, herbicides (2,4-D, atrazine, deethylatrazine and simazine) are more mobile in the environment [START_REF] Lewis | An international database for pesticide risk assessments and management[END_REF] and have higher concentrations in the waters of the river network compared to fungicides (carbendazim, epoxiconazole and tebuconazole). This is due to the lower capacity of these herbicides to be adsorbed by colloids (low Koc and low Kow values), and therefore remain soluble in water and are easily transported during the occurrence of rainfall events of low to high intensity. They may even percolate into the soil profile and contaminate subsurface waters. [START_REF] Robinet | Impacts of forest conversion and agriculture practices on water pathways in Southern Brazil[END_REF], in a small subcatchment in a Guaporé River catchment, showed that although the event rainfall is the main component for the surface runoff, and that the soil water is quickly displaced with new rainfall events in agriculture catchment, signifying a contribution of deep groundwater to the streamflow. Furthermore, the presence of five other herbicides (mesotrione, nicosulfuron, thifensulfuron-methyl, mesosulfuron-methyl and prosulfuron) detected in the catchment was coherent with corn density. For example, Marau tributary and source of Guaporé River regions are neighboring, have even soil type, even relief, even soil management system, but differ sensibly in the soybean/maize ratio (191 and 870% more grain and silage corn density in Marau tributary) (FEE, 2019). In the upper region, the highest values of fungicides in the Guaporé River and its tributaries can be explained by conditions of agricultural use and management of the land. Soybean is the main crop in the spring/summer period, which preceded monitoring. The absence of crop rotation and the use of transgenic plants in 100% of the farms significantly increased the incidence of fungal disease and, consequently, the quantity and frequency of fungicide applications. The discriminant function analysis was also used to verify which pesticides improve the discrimination of the established groups according to the predominant land use and soil management systems. The eigenvalues and standardized coefficients for canonical variables are shown in Table 5. The calculated variance on the first and second axis was 100%, with eigenvalue of 7.7. Four variables were maintained in the model. However, only carbendazim (partial λ = 0.19, F = 42.2 and p = 0.0001), imidacloprid (partial λ = 0.53, F = 8.9 and p = 0.0138) followed by deethylatrazine (partial λ = 0.68, F = 4.5 and p = 0.0593) showed significant contributions (Table 5), and therefore, they confirm that the concentrations of these pesticides in the two regions were different. The values of tolerance (R2) and 1-R2 represent the correlation of the given variable with all other variables included in the model [START_REF] Hair | Análise multivariada dos dados. 6rd[END_REF]. Thus, the most informative variable is carbendazim (R2 = 0.14). Samples from the upper region were well separated from middle/lower region samples along axis 1, the average probability of uncertainty in the classification of the points was 0.31% and 0.00% in the upper and middle/lower regions, respectively. These results also indicate that the molecules that most contributed to differentiate the regions were carbendazim, deethylatrazine, imidacloprid and 2,4-D and, therefore, future studies on the impact of agricultural activities on pesticide contamination in southern Brazil should focus on these molecules. In the upper region, 100% of the crops are conducted under no-tillage. However, these cropfields present conservationist efficacy compromised by the removal of physical barriers to surface water runoff, low addition of plant biomass, and insufficient soil cover. In this context there is an increase in the susceptibility of contaminant transfer from terrestrial ecosystems to the aquatic ecosystem. Even if no-tillage reduces soil losses by more than 70%, water losses are practically similar to other soil cultivation systems [START_REF] Londero | Impact of broad-based terraces on water and sediment losses in no-till (paired zero-order) catchments in southern Brazil[END_REF]. In this sense, several authors have emphasized the importance of resuming the adoption of terraces and increasing the density of soil cover for environmental conservation purposes [START_REF] Cogo | Perdas de solo e água por erosão hídrica influenciadas por métodos de preparo, classes de declive e níveis de fertilidade do solo[END_REF][START_REF] Didoné | Measuring and modelling soil erosion and sediment yields in a large cultivated catchment under no-till of Southern Brazil[END_REF][START_REF] Merten | No-till surface runoff and soil losses in southern Brazil[END_REF]. The distance between the crops and the river is very narrow (width riparian forest lower than 15 m). There is a high connectivity of erosive processes and the limited deposition of sediment in floodplains [START_REF] Rheinheimer | Flow Regularization and power dissipation in watershed in the center west region of Rio Grande do Sul state, Brazil[END_REF]. The least polar and highly persistent and reactive pesticides in the soil, such as tebuconazole and epoxiconazole, present in practically all monitored sites tend to be occasionally transported to water during rainfall events of high or low intensity. Longer distance and lower connectivity of crops with the river network are necessary conditions to maintain the quality of surface water, reducing the deposition of sediments and the water flow that drive the pesticides transport, both adsorbed and in solution, respectively. Catchment-scale connectivity is still a complex process of understanding and difficult to measure [START_REF] Michaelides | Connectivity as a concept for characterising hydrological behaviour Definitions of Connectivity[END_REF][START_REF] Fryirs | Connectivity in catchment sediment cascades: a fresh look at the sediment delivery problem[END_REF][START_REF] Koiter | Investigating the role of connectivity and scale in assessing the sources of sediment in an agricultural watershed in the Canadian prairies using sediment source fingerprinting[END_REF]. However, it is known that in the middle/lower Guaporé catchment before reaching the water sources, the eroded sediments pass through successive processes of deposition and remobilization over time (Minella et al., 2014). Moreover, the small cultivated surface was imbricated in the landscape, and the watercourses were bordered by a great width riparian forest (60 to > 100 m), resulting an efficient barrier to sediment [START_REF] Tiecher | Quantifying land use contributions to suspended sediment in a large cultivated catchment of Southern Brazil (Guaporé River, Rio Grande do Sul)[END_REF] and pesticides transfer to the surface water [START_REF] Bortoluzzi | Investigation of the occurrence of pesticide residues in rural wells and surface[END_REF], even of more accidently relief and conventional soil management. 4. Conclusions Agriculture is a major sector of the Brazilian economy. One the main priority of the Brazilian agricultural policy is to create conditions to increase production and improve the productivity of family farming. Consequently, the use of pesticides is widely favored to allow "modern intensive agriculture" also in rural areas. The results obtained in this study demonstrate that there is a high ecological risk of contamination with pesticides, indicating that the current agricultural production systems are contaminating the waters of the Guaporé River water and its tributaries, and highlighting that the current soil conservation practices are insufficient, even in the regions of the catchment where the use of no-till system predominates. The present work shows that the use of pesticides in rural catchments leads to the contamination of surrounding water resources. Thus, a very large variety of compounds was found in Guaporé River and its tributaries by grab or passive (POCIS) sampling, including 2,4-D, atrazine, simazine, deethyl-atrazine, carbendazim, epoxiconazole, tebuconazole and imidacloprid. Furthermore, the sampling by POCIS highlighted that a discriminant role of land use (type of culture, slope of soils) on the pesticide contamination. Thus, flat areas grown with high soybean density in a no-till system had higher levels of fungicide. However, streams near fields with various agricultural plantations had a higher concentration of herbicides. The presence of five herbicides used in maize, grassland and fodder production was linked to areas of integrated crop and livestock systems. In addition, the highest 2,4-D contamination was found in areas of intensive soybean and winter grain production. Facing the economic, social, sanitary and environmental issues, reconciling growth and sustainability in Brazil's agricultural development model is more than ever needed to maintain agriculture and to preserve water resources.

Fig. 1 .

 1 Fig. 1.Characteristics of area and location of the sampling sites in the Guaporé River and its tributaries (RS -Brazil).

Fig. 4 .

 4 Fig. 4. Boxplot of the pesticide concentrations detected in the Guaporé River catchment. Median concentrations, interquartile amplitude (1 st and 3 rd quartile), and minimum and maximum values obtained using POCIS (n = 16).

Fig. 5 .

 5 Fig. 5. Boxplot of the pesticide concentrations in the two regions of the catchment and results of the Mann-Whitney U test with Polar Organic Chemical Integrative Sampler.

Table 1

 1 Catchment area, land use and slope class at the different sampling sites in the Guaporé River and its tributaries.

	Upper Region

Table 2

 2 Frequency of pesticide detection (%) in Guaporé River and its tributaries using grab and passive (Polar Organic Chemical Integrative Sampler) water sampling

	Active ingredient	Frequency of detection (%) Grab sampling	POCIS
	Herbicides
	2,4-D	0	100
	Atrazine	94	100
	Deethyl-atrazine	NA	100
	Simazine	89	94
	Mesotrione	NA	31
	Thifensulfuron-methyl	NA	31
	Nicosulfuron	NA	25
	Mesosulfuron-methyl	0	19
	Prosulfuron	NA	12
	Fungicide
	Carbendazim	56	100
	Azoxystrobin	33	NA
	Propiconazole	17	NA
	Tebuconazole	11	75
	Epoxiconazole	0	50
	Insecticide
	Imidacloprid	67	75
	Propoxur	78	NA
	Thiamethoxam	33	NA
	Fipronil	28	NA
	Carbofuran	6	NA
	NA = not analyzed

Table 5

 5 Results of the discriminant function analysis for regions, upper and middle/lower in Guaporé River catchment.

		Wilks' Lambda Partial Lambda	F-Remove 1,10	p-level	Tolerance
	Pesticides						1-(R 2 )
			Variables in the model (F 4,10=19,256)
	Carbendazim	0.600	0.192		42.217	0.0001	0.8563
	Deethil-atrazine	0.167	0.689		4.527	0.0593	0.4332
	Imidacloprid	0.217	0.529		8.887	0.0138	0.8003
	2,4-D	0.140	0.823		2.149	0.1734	0.3367
			Variables currently not in the model (Df for all F-tests: 1.9)
	Atrazine	0.115	0.996		0.028	0.870903	0.6203
	Simazine	0.114	0.992		0.067	0.802	0.6777
	Epoxiconazole	0.114	0.996		0.030	0.867	0.7593
	Tebuconazole	0.114	0.997		0.020	0.890	0.4954
			Chi-Square Tests with Successive Roots Removed
	Discriminant	Eigenvalue Cum. Prop Canonicals Roots Wilks' Lambda Chi-Sqr.	p-level
	Function 01	7.702	1.000	0.941	0.115	23.800	8,8 x 10 -5

Acknowledgments

Coordination for the Improvement of Higher Education Personnel (CAPES). Brazilian National Council for Scientific and Technological Development (CNPq). Project "Mais Água" of FINEP/FEPAGRO/SEAPA-RS.

Table 3

Potential ecological risk for Daphinia magnum (M.) and Rhamdia quelen (Teleostei) by pesticides detected in Guaporé River and its tributaries.

Site

Daphinia magnum (M.) Rhamdia quelen (Teleostei)