O objetivo deste trabalho foi determinar os níveis de ocorrência de pesticidas em água, tendo em vista preservar a água de contaminação por esses produtos na região de Guaíra, SP. A hipótese foi que o uso intensivo de pesticidas nessa região propiciaria a contaminação das águas superficiais e subterrâneas por seus resíduos. Para a caracterização das propriedades, das características e da dinâmica da água do solo, foi selecionada a Fazenda Macaúba por possuir relevo e solos característicos da região. Aproximadamente 80% da área da fazenda é constituída por Latossolo Vermelho distroférrico típico (LVdf), profundo. As áreas cultivadas apresentam um horizonte superficial (Ap) completamente desprovido de sua estrutura natural e, abaixo deste, um horizonte compactado, ambos frutos das práticas agrícolas. Durante dois anos e meio realizou-se o monitoramento do Ribeirão do Jardim que abastece a cidade de Guaíra, bem como de um de seus afluentes e da água subterrânea proveniente do Aqüífero Guarani, à procura de pesticidas. A água superficial foi coletada de 21em 21 dias e a subterrânea, no início e no final do período monitorado (dois anos e meio). Os produtos monitorados, trifluralina, endosulfan, lambda cialotrina, dicofol (4,4 diclorobenzofenona), captan, metil paration, clorotalonil e clorpirifós, foram selecionados a partir de um levantamento dos pesticidas utilizados em quatro áreas agrícolas localizadas na bacia do Ribeirão do Jardim e em razão da efetividade de um método de análise de resíduos múltiplos para sua quantificação. Os resultados analíticos indicaram que não houve contaminação da água subterrânea, mas que ocasionalmente houve contaminação direta das águas de superfície. A não-contaminação da água subterrânea deve-se principalmente às características dos Latossolos, como sua grande espessura, sua textura argilosa e sua grande capacidade de armazenamento de água.
Pretendeu-se mostrar que o herbicida Tebuthiuron, selecionado entre outros usados na cultura de cana-de-açúcar, oferece risco de contaminação para a água subterrânea em função de suas características físico-químicas, principalmente, quando aplicado em áreas de recarga direta de aqüíferos 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 Ribeirão Preto/SP, Brasil, no qual tem sido freqüente o uso do produto em questão. 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 concentrações abaixo do nível crítico para padrão de potabilidade, conforme os limites mais restritivos estabelecidos pela Organização Mundial de Saúde (para os pesticidas em uso é de 0,1 µg/L por pesticida e de 0,5 µg/L para pesticidas totais). Mesmo com os baixos valores de concentração encontrados fica evidente que o Tebuthiuron está atingindo a água subterrânea podendo aumentar sua concentração pela existência de condições ambientais favoráveis à preservação da molécula em profundidade (tais como baixa temperatura, baixa atividade biológica e ausência de luz). Caso o nível crítico seja atingido, o risco de contaminação poderia ser minimizado por meio da substituição do Tebuthiuron por outro herbicida com menor mobilidade no perfil do solo. OCCURRENCE OF THE HERBICIDE TEBUTHIURON IN GROUNDWATER OF ESPRAIADO CATCHMENT RIBEIRAO PRETO - SP (BRASIL) Abstract The herbicide Tebuthiuron, selected among others utilized in sugar-cane crop, shows groundwater contamination risk due to its physicochemical properties, mainly, when applied in direct recharge areas of aquifers considered of high natural vulnerability. In this context, the monitoring of this herbicide in the period of 1995 through 1999 was realized, by collecting water samples of aquifers 53 m depht, located in Espraiado catchment, Ribeirao Preto/SP (Brazil) in which the product has been extensively used. For blank assays it was utilized water samples collected similarly 3 Km away from the monitoring area. The results obtained showed that Tebuthiuron is present in all analyzed samples. Although in lower concentrations of the critical level for drinkable water, following the restrictive limits established by World Health Organization (for pesticides in use is 0,1 µg/L by pesticide and of 0,5 µg/L for total pesticides). Even if the low concentration values found it is evident that the Tebuthiuron affects the groundwater, and could enhance its concentration by favorable ambiental conditions for molecule preservation in deep water (such as low temperature, low biological activity and absence of light). The present scenary reflects contamination risk in case of reaching the critical level, which could only be minimized by the substitution of Thebuthiuron for other herbicide with lower soil mobility.
Comportamento do herbiCida hexazinone em área de reCarga do aqüífero guarani Cultivada Com Cana-de-açúCar Sonia C. n. queiroz,* vera l. ferracini, marco a. f. gomes e maria a. rosa Laboratório de Resíduos e Contaminantes, Embrapa Meio Ambiente, CP 69, 13820-000 Jaguariúna-SP, Brasil Recebido em 27/3/08; aceito em 29/9/08; publicado na web em 2/2/09 THE BEHAVIOR OF HEXAZINONE HERBICIDE IN RECHARGE ZONE OF GUARANI AQUIFER WITH SUGARCANE CULTIVATED AREA. São Paulo state (Brazil) has an important area of sugarcane production, mainly for obtaining alcohol and sugar, where there is an intensive use of pesticides. An important recharge zone of Guarani aquifer, with supplies water for the local population, is located at Ribeirão Preto city, so the local behavior of pesticides must be investigated. The GUS index was obtained by using the paramenters Koc and half-life for hezazinone herbicide, determinated in representative soil of this region. This study has demonstrated that there is potential risks of hexazinone leaching to ground water, indicating that this herbicide must be monitored in ground water.
This study was undertaken to evaluate the degradation and mobility of the herbicide tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N'-dimethylurea) in soil under field conditions, and its potential for leaching and groundwater contamination. A watershed, Espraiado, located over a recharge area in Brazil, was chosen for soil and water studies. At Espraiado, water samples were collected from seven wells at intervals of three months from March 2004 to June 2006 and analyzed for tebuthiuron. Other samples were taken from city wells located outside of the recharge area. To assess the potential movement to the aquifer, tebuthiuron was also applied to trial plots at the recommended label rate of 1.0 kg/ha a.i. in May of 2004, with and without sugarcane coverage, on sandy soil. Soil samples were collected during the years of 2004 and 2005, at depths intervals of 20 cm from soil surface down to 120 cm and analyzed for tebuthiuron at zero, 3, 30, 60, 90, 120, 150, 180, 240, and 300 days after application. There was no clear effect of sugarcane coverage on the tebuthiuron degradation in soils, but it moved faster into the soil where there was no cover. After 180 days there were no measurable residues in the soil, and tebuthiuron was not found below 40 cm depth in any time. Tebuthiuron had a half-life of 20 days under those conditions. No tebuthiuron residue was found in ground water samples at any sampling time.
The region of Ribeirão Preto City, located in Southeast of Brazil, São Paulo State, is an important sugarcane, soybean, and corn producing area with a high level of pesticides utilization. This region is also an important recharge area for groundwater supply of the Guarany aquifer. Since the past ten years atrazine, simazine, ametryn, tebuthiuron, diuron, 2,4-D, picloram, and hexazinone are the main herbicides used in this area. In order to study a possible leaching of some of these herbicides into the aquifer, surface, and groundwater samples were collected in a watershed during the years of 1996 to 2003, from different locations. To detect and quantify the herbicides a GC-MS (gas chromatograph/mass spectrometry) method was used. The response of the herbicides analyzed was linear over the concentration range of 0.02 to 2.0 microg/L. Analysis of groundwater revealed that the herbicides tebuthiuron, diuron, atrazine, simazine, and ametryn were not present in the samples. In the surface water collected in 1997, ametryn was present in two out of nine locations with concentrations ranging from 0.17 and 0.23 microg/L, which is above the allowable 0.1 microg/L according to the European safety level. The leaching potential of tebuthiuron, diuron, atrazine, simazine, 2,4-D, picloram, and hexazinone has been evaluated using CMLS-94, "Chemical Movement in Layered Soil," as simulation model. No leaching into the depth of the water table at 40 m was found.
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