Modeling of Bentazone Leaching in Soils with Low Organic Matter Content.

The aim of this study was to estimate bentazone's potential to leach to groundwater in the Arenosols developed from sand, Luvisols developed from loamy sand or sandy loam, and Luvisols or Cambisols developed from loess, and to identify the major factors influencing bentazone's fate in the soils. Potato and maize cultivations were simulated using the FOCUS PELMO 5.5.3 pesticide leaching model. The amount of bentazone reaching groundwater was highly sensitive to degradation parameters, water-holding capacity, evapotranspiration, organic carbon content, and pH. The highest bentazone concentrations in percolate were noted in Arenosols. The risk of bentazone concentration exceeding 0.1 µg/L was low only in Arenosols with high organic carbon content (3.0% for topsoil or higher). In Luvisols developed from loamy sand or sandy loam, the estimated bentazone concentrations in percolate were highly dependent on the climate. In Luvisols or Cambisols developed from loess, concentrations of >0.1 µg/L were the least likely due to the high water-holding capacity and high organic carbon content of these soils. The study also revealed that the FOCUS Hamburg scenario, representing the coarsest soils in the European Union with relatively low organic carbon content, does not reflect the leaching potential of Arenosols and Luvisols.

Estimating sorption of monovalent acidic herbicides at different pH levels using a single sorption coefficient.

BACKGROUND: Monovalent acidic pesticide sorption can be determined for any soil pH if the dissociation constant of the compound is known, and sorption coefficients are available for at least two different pH values, measured in a wide enough range to enable estimating both neutral and anionic form coefficients. Sorption estimates have also been made from a single sorption coefficient available, assuming a non-compound specific value of the anionic form sorption coefficient or considering a generic ratio between sorption coefficients of the two forms. A compound-specific procedure for adjustment of parameters of the equation for estimating sorption of monovalent acidic herbicides at different pH levels, from a single sorption coefficient, is proposed and evaluated. RESULTS: The quality of fits was good for sorption of all three herbicides studied, especially for 2,4-D and flumetsulam at pH above 5, even for diverse soils and experimental procedures and conditions. The best fits resulted in the following ratios of theoretical maximum organic-carbon sorption coefficients for neutral and anionic forms (Kocn':Koca'): 440:1 for 2,4-D; 132:1 for flumetsulam; and 55:1 for sulfentrazone. CONCLUSION: The ratios of theoretical maximum sorption coefficients for neutral and anionic forms (Kocn':Koca') are compound-specific, thus this procedure should also be applied to pH-sorption datasets for other acidic pesticides to provide the respective ratio between the theoretical maximum sorption coefficients, instead of using generic assigned values. More calibration research is recommended and validation of this approach is required to demonstrate applicability of the method. © 2020 Society of Chemical Industry.

Environmental Behavior of Chlorpyrifos and Endosulfan in a Tropical Soil in Central Brazil.

The environmental behavior of chlorpyrifos and endosulfan in soil was studied in the central-western region of Brazil by means of a field experiment. Sorption was evaluated in laboratory batch experiments. Chlorpyrifos and endosulfan were applied to experimental plots on uncultivated soil and the following processes were studied: leaching, runoff, and dissipation in top soil. Field dissipation of chlorpyrifos and endosulfan was more rapid than reported in temperate climates. Despite the high Koc of the studied pesticides, the two endosulfan isomers and endosulfan sulfate as well as chlorpyrifos were detected in percolated water. In runoff water and sediment, both endosulfan isomers and endosulfan sulfate were detected throughout the period of study. Observed losses of endosulfan by leaching (below a depth of 50 cm) and runoff were 0.0013 and 1.04% of the applied amount, whereas chlorpyrifos losses were 0.003 and 0.032%, respectively. Leaching of these highly adsorbed pesticides was attributed to preferential flow.

Leaching of seven pesticides currently used in cotton crop in Mato Grosso State-Brazil.

This study aimed to evaluate the leaching of pesticides and the applicability of the Attenuation Factor (AF) Model to predict their leaching. The leaching of carbofuran, carbendazim, diuron, metolachlor, alpha and beta endosulfan and chlorpyrifos was studied in an Oxisol using a field experiment lysimeter located in Dom Aquino-Mato Grosso. The samples of percolated water were collected by rain event and analyzed. Chemical and physical soil attributes were determined before pesticide application to the plots. The results showed that carbofuran was the pesticide that presented a higher leaching rate in the studied soil, so was the one representing the highest contamination potential. From the total carbofuran applied in the soil surface, around 6% leached below 50 cm. The other pesticides showed lower mobility in the studied soil. The calculated values to AF were 7.06E-12 (carbendazim), 5.08E-03 (carbofuran), 3.12E-17 (diuron), 6.66E-345 (alpha-endosulfan), 1.47E-162 (beta-endosulfan), 1.50E-06 (metolachlor), 3.51E-155 (chlorpyrifos). AF Model was useful to classify the pesticides' potential for contamination; however, that model underestimated pesticide leaching.

Acetamiprid, carbendazim, diuron and thiamethoxam sorption in two Brazilian tropical soils.

Sorption of acetamiprid ((E)-N1-[(6-chloro-3-pyridyl)methyl]-N2-cyano-N1-methylacetamidine), carbendazim (methyl benzimidazol-2-ylcarbamate), diuron (N-(3,4-dichlorophenyl)-N, N-dimethyl urea) and thiamethoxam (3-(2-chloro-thiazol-5-ylmethyl)-5-methyl-[1,3,5]oxadiazinan-4-ylidene-N-nitroamine) was evaluated in two Brazilian tropical soils, Oxisol and Entisol, from Primavera do Leste region, Mato Grosso State, Brazil. To describe the sorption process, batch experiments were carried out. Linear and Freundlich isotherm models were used to calculate the K(d) and K(f) coefficients from experimental data. The K(d) values were utilized to calculate the partition coefficient normalized to soil organic carbon (K(oc)). For the pesticides acetamiprid, carbendazim, diuron and thiamenthoxan the K(oc) (mL g(- 1)) values ranged in both soils from 98 - 3235, 1024 - 2644, 145 - 2631 and 104 - 2877, respectively. From the studied pesticides, only carbendazim presented correlation (r(2) = 0.82 and p < 0.01) with soil organic carbon (OC) content. Acetamiprid and thiamethoxam showed low sorption coefficients, representing a high risk of surface and ground water contamination.

Review of potential environmental impacts of transgenic glyphosate-resistant soybean in Brazil.

Transgenic glyphosate-resistant soybeans (GRS) have been commercialized and grown extensively in the Western Hemisphere, including Brazil. Worldwide, several studies have shown that previous and potential effects of glyphosate on contamination of soil, water, and air are minimal, compared to those caused by the herbicides that they replace when GRS are adopted. In the USA and Argentina, the advent of glyphosate-resistant soybeans resulted in a significant shift to reduced- and no-tillage practices, thereby significantly reducing environmental degradation by agriculture. Similar shifts in tillage practiced with GRS might be expected in Brazil. Transgenes encoding glyphosate resistance in soybeans are highly unlikely to be a risk to wild plant species in Brazil. Soybean is almost completely self-pollinated and is a non-native species in Brazil, without wild relatives, making introgression of transgenes from GRS virtually impossible. Probably the highest agricultural risk in adopting GRS in Brazil is related to weed resistance. Weed species in GRS fields have shifted in Brazil to those that can more successfully withstand glyphosate or to those that avoid the time of its application. These include Chamaesyce hirta (erva-de-Santa-Luzia), Commelina benghalensis (trapoeraba), Spermacoce latifolia (erva-quente), Richardia brasiliensis (poaia-branca), and Ipomoea spp. (corda-de-viola). Four weed species, Conyza bonariensis, Conyza Canadensis (buva), Lolium multiflorum (azevem), and Euphorbia heterophylla (amendoim bravo), have evolved resistance to glyphosate in GRS in Brazil and have great potential to become problems.

Sorption and leaching potential of acidic herbicides in Brazilian soils.

Leaching of acidic herbicides (2,4-D, flumetsulam, and sulfentrazone) in soils was estimated by comparing the original and modified AF (Attenuation Factor) models for multi-layered soils (AFi). The original AFi model was modified to include the concept of pH-dependence for Kd (sorption coefficient) based on pesticide dissociation and changes in the accessibility of soil organic functional groups able to interact with the pesticide. The original and modified models, considering soil and herbicide properties, were applied to assess the leaching potential of selected herbicides in three Brazilian soils. The pH-dependent Kd values estimated for all three herbicides were observed to be always higher than pH-independent Kd values calculated using average Koc data, and therefore the original AFi model overestimated the overall leaching potential for the soils studied.

Sorption, degradation, and leaching of tebuthiuron and diuron in soil columns.

A study in small outdoor lysimeters was carried out to determine the leaching of the herbicides tebuthiuron and diuron in different soil types, using undisturbed soil columns. Soil sorption and degradation for both herbicides were also studied in the laboratory. The multi-layered AF (Attenuation Factor) model was evaluated for predicting the herbicides leaching in undisturbed soil columns. Tebuthiuron leached in greater amounts than diuron in both soils. Sorption was well represented by linear and Freundlich equations, however parameters from the linear equations were used in the AF model. In general, both herbicides presented very low sorption, with diuron presenting lower values of sorption coefficient than tebuthiuron in the two soils. Chromatographic data indicated rapid late degradation of diuron and tebuthiuron in both soil types at two different depths. Simple exponential equation was not able to represent degradation, thus a bi-exponential equation was used, and some model adjusting was needed. Average measured amounts of each herbicide were compared with amounts predicted by the multi-layered-soil AF model. The AF model was able to predict leaching amounts in the sandy soil, especially for diuron, however it did not perform well in the clayey soil.

Lixiviação dos herbicidas Tebutiuron e Diuron em colunas de solo / Tebuthiuron and diuron leaching in soil columns

Desenvolveu-se estudo em lisímetro para determinar a lixiviação dos herbicidas Tebutiuron e Diuron em colunas de solos com diferentes texturas coletados em área típica de recarga do Aquífero Guarani em Ribeirão Preto, São Paulo (Brasil). O método analítico utilizado para determinação dos resíduos desses produtos na água foi a cromatografia a líquido de alta eficiência (CLAE), após extração por agitação com diclorometano:isopropanol (9:1). Os resultados mostraram maior lixiviação de ambos produtos em Neossolo, sendo a do Tebutiuron mais acentuada. Esse resultado sugere que o teor de carbono orgânico, além da associação entre a baixa capacidade asortiva do Tebutiuron e sua longa persistência podem ser os responsáveis pela diferença. Os herbicidas estudados podem apresentar potencial de risco de contaminação do lençol freático da região da microbacia do Córrego do Espraiado, embora dificilmente alcançando a zona saturada do Aquífero Guarani (situada, bem abaixo do perfil estudado neste trabalho)

Soil sorption of acidic pesticides: modeling pH effects.

A model of acidic pesticide sorption in soils was developed from theoretical modeling and experimental data, which initially considered a combination of a strongly acidic pesticide and a variable-charge soil with high clay content. Contribution of 2,4-D [(2,4-dichlorophenoxy) acetic acid] anionic-form sorption was small when compared with molecular sorption. Dissociation of 2,4-D was not sufficient to explain the variation in Kd as a function of pH. Accessibility of soil organic functional groups able to interact with the pesticide (conformational changes) as a function of organic matter dissociation was proposed to explain the observed differences in sorption. Experimental 2,4-D sorption data and K(oc) values from literature for flumetsulam [N-(2,6-difluorophenyl)-5-methyl [1,2,4] triazolo [1,5-a] pyrimidine-2-sulfonamide] and sulfentrazone [N-[2,4-dichloro-5-[4-(difluromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl] phenyl] methanesulfonamide] in several soils fit the model.

Pesticide leaching potential assessment in multilayered soils

O modelo "Attenuation Factor" (AF) generalizado para solos em multi-camadas foi utilizado para estimar os potenciais de lixiviaçäo de pesticidas näo-i nicos e näo-ionizáveis em solos brasileiros. O modelo aplicado considera as propriedades dos pesticidas e dos solos, assim como a taxa de recarga líquida. O transporte advectivo dos pesticidas e dos solos, assim como a taxa de recarga líquida. O transporte advectivo dos pesticidas e o de primeira ordem dos pesticidas foram assumidos como premissas. Os pesticidas com os maiores potenciais de lixiviaçäo foram Tebutiuron e Hexazinone, os quais apresentaramvalores de tempo de meai-vida (t1/2) maiores que 90 dias e oeficiente de sorçäo (Koc) menores que 80 mL/G. Para todos os pesticidas, nos três solos, os valores de AF aumentaram com a profundidade pelo decréscimo no tempo de percurso (tr) do pesticida. Tal fato se deve ao menor tempo de percurso da água e ao menor fator de retardo (FR). em Neossolo Quartzarêncio )areia quartzosa). o tempo de percursäo mais curto, devido ao menor valor de capacidade de campo 9FC0 resultou em AF mais alto e maior potencial de lixiviaçäo. Os resultados permitem estimar que cerca de 54 por cento de Tebutiuron e 13 por cento de Hexazinone aplicados na superfície do solo passariam através dos primeiros 120 cm do Neossolo Quatzarênico.

Screening method for assessing pesticides leaching potential

Métodos de seleçäo säo necessários para determinar quais pesticidas deveriam receber maior atençäo com respeito aos problemas ambientais. Vários autores têm proposto métodos de seleçäo para verificar se determinado pesticida é potencialmente lixiviável para águas subterrâneas. O índice "Grounwater Ubiquity Score" 9GUS) desenvolvido por Gustafson tem sido usado como a primeira etapa ema bordagem de aproximaçöes sucessivas para especificar quais produtos deveriam merecer estudos mais demorados e caros de lixivialidade. Entretanto, o índice GUS é empiricamente baseado e apresenta o problema da previsäo de valores negativos para pesticidas com meia-vida curta e/ou grande coeficiente denominado íncdice LIX, täo simples com o índice GUS porém possibilitando mais rápida e melhor viasualizaçäo e interpretaçäo dos resultados.

Análise de risco de contaminaçäo das águas subterrâneas superficiais da regiäo de Petrolina (PE) e Juazeiro (BA) / Ground and surface water of the regions Petrolina (PE) and Juazeiro (BA)

Analisou-se o potencial de contaminaçäo das águas subterrâneas e superficiais do Submédio do Rio Säo Francisco por pesticidas aplicados nas culturas de manga e uva, mediante critérios da Environmental Protection Agency, do índice de GUS e critérios propostos por Goss. Todos os critérios utilizados levam em consideraçäo as propriedades dos produtos aplicados, näo demandado custos elevados nem muito tempo para o levantamento das informaçöes e para a avaliaçäo do potencial de contaminaçäo. Os resultados obtidos reforçam a importância de disponibilizar informaçöes sobre as propriedades físico-químicas dos pesticidas, principalmente o coeficiente de adsorçäo, cujo valor permite a previsäo da mobilidade do composto no solo. Este fator, integrado ao conhecimento do tempo de degradaçäo do produto até a metade de sua concentraçäo inicial (meia-vida) no solo, fornece informaçöes sobre a sua influência no potencial de contaminaçäo das águas. Os resultados deste trabalho propiciam o conhecimento dos pesticidas com maior potencial de contaminaçäo dos recursos hídricos, os quais devem ser priorizados no monitoramento "in loco"

Ocorrência do herbicida Tebuthiuron na água subterrânea da microbacia do Córrego Espraiado, Ribeiräo Preto - SP / Ocurrence of the herbicide Tebuthiuron in groundwater of Espraiado Catchment Ribeiräo Preto - SP (Brazil)

Pretendeu-se mostrar que o herbicida Tebuthiuron, selecionado entre outros usados na cultura de cana-de-açäcar, oferece risco de contaminaçäo para a água subterrânea em funçäo de suas características físico-químicas, principalmente, quando aplicado em áreas de recarga direta de aquíferos consideradas de alta vulnerabilidade natural. Assim, efetuou-se monitoramento do referido herbicida no período compreendido entre 1995 e 1999, coletando amostras de água de poço semi-artesiano, com 53 metros de profundidade, localizado na microbacia do Córrego Espraiado, município de Ribeiräo Preto/SP, Brasil, no qual tem sido frequente o uso do produto em questäo. Para efeito de testemunha da amostra de água foi considerado um poço semi-artesiano de profundidade semelhante, localizado cerca de três quilômetros de distância do poço objeto de monitoramento. Os resultados obtidos mostraram que o Tebuthiuron está presente em todas as amostras analisadas, embora em concentraçöes abaixo do nível crítico para padräo de potabilidade, conforme os limites mais restritivos estabelecidos pela Organizaçäo Mundial de Saúde (para os pesticidas em uso é de 0,1 ug/L por pesticida e de 0,5ug/L para pesticidas totais). Mesmo com os baixos valores de concentraçäo encontrados fica evidente que o Tebuthiuron está atingindo a água subterrânea podendo aumentar sua concentraçäo pela existência de condiçöes ambientais favoráveis à preservaçäo da molécula em profundidade (tais como baixa temperatura, baixa atividade biológica e ausência de luz). Caso o nível crítico seja atingido, o risco de contaminaçäo poderia ser minimizado por meio da substituiçäo do Telbuthiron por outro herbicida com menor mobilidade no perfil do solo

Avaliaçäo do potencial de lixiviaçäo de pesticidas em latossolo da regiäo de Guaíra, SP / Assessing leaching potential of pesticides in oxisol from Guaíra region, state of Säo Paulo, Brazil

Os potenciais de lixiviaçäo de dezenove pesticidas nos primeiros 60 cm de latossolo da regiäo de Guaíra, Estado de Säo Paulo, foram estimados mediante fator deatenuaçäo (AF). O modelo aplicado considerou propriedades do pesticida e do solo, assim como a taxa de recarga hídrica líquida. Os pesticidas com maior potencial de lixiviaçäo foram manocrotofós>carbofuranmetalaxil>aldicarb>metolactor>metamidofós. Para todos os pesticidas estudados naquele latossolo, o tratamento da lixiviaçäo devido à volatilizaçäo foi muito pequeno quando comparado com o retardamento devido à sorçäo:Todos os pesticidas que apresentaram os mais altos potenciais delixiviaçäo foram os mais solúveis em água, com valores do coeficiente de partiçäo (Koc) iguais ou menores que 200 mL/g. Além disso, a meia-vida da maioria destes pesticidas excedeu 30 dias. Os resultados obtidos permitiram estimar que 15,2 por cento do Monocrotofós, 5,7 por cento do Carbofuran e 2,5 por cento do Metalaxil que atinge a superfície do solo ultrapassariam os primeiros 60 cm do perfil do solo, sendo que cerca de 8 mg para cada 100g de Monocrotofós aplicados na superfície do solo passariam através dos primeiros 3m. Com base nos baixos valores de AF calculdados, o potencial de lixiviaçäo dos pesticidas que tem sido usados em áreas agrícolas de Guaíra (SP) sobre latossolos apresenta-se baixo, assim como o consequente risco de contaminaçäo da água subterrânea

Uso de agrotóxicos nas diferentes regiöes brasileiras: subsídios para a geomedicina / The use of pesticides in differents brazilian regions: geomedicine

A geomedicina pode ser definida como a ciência que estuda a influência de fatores ambientais sobre a distribuiçäo de problemas de saúde de seres humanos e animais. O uso de agrotóxicos figura entre os fatores ambientais de interesse para a geomedicina no Brasil, dada a diferenciaçäo marcante na aplicaçäo de agrotóxicos de acordo com a agricultura e o ambiente característicos de cada regiäo do país. Em geral o risco de contaminaçäo é maior para as águas subterrâneas nas regiöes de ocorrência de solos com horizonte B latossólico, predominantes nos Estados de Säo Paulo, Paraná e Rio Grande do Sul, especialmente nas áreas de recarga do Aquífero Guarani, na Bacia Sedimentar do Paraná. Já o risco de contaminaçäo das águas superficiais é maior nas regiöes de ocorrência de solos com horizonte B textural, uma vez que estes normalmente apresentam baixo potencial de lixiviaçäo, estando mais susceptíveis aos processos de transporte superficial, tanto de agroquímicos quanto de partículas via erosäo. Algumas culturas agrícolas merecem atençäo especial devido à elevada quantidade de agrotóxicos nelas aplicados como resultado de sua grande amplitude espacial, como é o caso da soja, de citrus e de cana-de-açúcar. Outras culturas, apesar de ocuparem áreas menores, destacam-se pelo uso intensivo de agrotóxicos por unidade de área cultivada, como as culturas de tomate e batata. Conforme a distribuiçäo destas culturas, o uso associado de agrotóxicos e as características dos ambientes (especialmente os solos) pode-se delinear alguns padröes de contaminaçäo. A situaçäo atual da contaminaçäo no pais demanda enfoque em escala adequada, em âmbito nacional, considerando a regionalizaçäo dos riscos