RESUMO
This study combined laboratory based microcosm systems as well as field experiments to evaluate the mobility of atrazine on a Ultisol under humid tropical conditions in Brazil. Results from sorption experiments fit to the Freundlich isotherm model [K(f) 0.99 mg kg(-1)/(mg l(-1))(1/n)], and indicate a low sorption capacity for atrazine in this soil and consequently large potential for movement by leaching and runoff. Microcosm systems using (14)C-atrazine to trace the fate of the applied herbicide, showed that 0.33% of the atrazine was volatilized, 0.25% mineralized and 6.89% was recorded in the leachate. After 60 d in the microcosms, 75% of the (14)C remained in the upper 5 cm soil layer indicating atrazine or its metabolites remained close to the soil surface. In field experiments, after 60 d, only 5% of the atrazine applied was recovered in the upper soil layers. In the field experiments atrazine was detected at a depth of 50 cm indicating leaching. Simulating tropical rain in field experiments resulted in 2.1% loss of atrazine in runoff of which 0.5% was adsorbed onto transported soil particles and 1.6% was in solution. Atrazine runoff was greatest two days after herbicide application and decreased 10 fold after 15 d. The use of atrazine on Ultisols, in the humid tropics, constitutes a threat to water quality, causing surface water and ground water pollution.
Assuntos
Atrazina/química , Herbicidas/química , Poluentes do Solo/química , Adsorção , Atrazina/análise , Brasil , Herbicidas/análise , Umidade , Solo/análise , Poluentes do Solo/análise , Movimentos da ÁguaRESUMO
14C-terbuthylazine was applied to three Brazilian soils in closed aerated laboratory microcosms, both under standardized and under natural Brazilian climate conditions. Volatilization from soil to air, leaching from soil to percolate water, and transport from upper to deeper soil layers were higher in sandy soil than in clay soil and in organic soil. Mineralization of 14C-terbuthylazine to 14CO2 was higher in sandy soil than in clay and organic soils under standardized climatic conditions, whereas it was higher in organic soil than in sandy soil under Brazilian summer conditions. Under natural Brazilian summer conditions, leaching as well as vertical transport within the soil were enhanced as compared to standardized climate conditions comprising lower precipitation rates; volatilization was strongly reduced under high irrigation conditions.
Assuntos
Clima , Herbicidas/análise , Poluentes do Solo/análise , Triazinas/análise , Brasil , Radioisótopos de Carbono/análise , Monitoramento Ambiental , Herbicidas/química , Minerais , Chuva , Triazinas/química , Volatilização , Movimentos da ÁguaRESUMO
The herbicide atrazine is the most commonly detected pesticide in groundwater world-wide. A new microcosm test-system was used to determine the fate of 14C-atrazine in a Brazilian oxisol. 14C Ring-labelled atrazine was applied in a mixture with the commercial product Gesaprim 500 (Novartis) at a rate of 3 kg ha-1. During two months, about 1% of the initially applied amount was lost by volatilization. The mineralization of the pesticide, measured directly using 14CO2 evolved from the applied pesticide, was between 0.09% and 0.16%, whereas less than 0.2% was leached. The distribution of radioactivity in the soil profile showed that most of the radioactivity remained in the top soil down to a 3 cm depth. The radioactivity in the upper 3 cm of the column was adsorbed perferably in fulvic acid (FA) and human fractions.
Assuntos
Atrazina/metabolismo , Ecossistema , Herbicidas/metabolismo , Poluentes do Solo/metabolismo , Atrazina/farmacocinética , Biodegradação Ambiental , Brasil , Radioisótopos de Carbono , Herbicidas/farmacocinética , VolatilizaçãoRESUMO
The genetic modified Pseudomonas fluorescens Br 12, resistant to kanamycin and rifampycin, was used to follow the cotransport of the organochlorine acaricide dicofol through a nonsterilized soil column. P. fluorescens was found to bioaccumulate dicofol with the highest bioconcentration factor of 279 within 30 min. Separate soil column experiments where applied P. fluorescens or [14C]dicofol were submitted to heavy rain simulation did not reveal any correlation between the distribution patterns of P. fluorescens and [14C]dicofol in the leachate fractions (r = 0.3). Similar experiments with P. fluorescens that previously had bioaccumulated [14C]dicofol demonstrated a high correlation of these bacteria and radioactivity in the leachate fractions (r = 0.8). The total recovery of radioactivity in the leachate, when [14C]dicofol was previously bioaccumulated in bacteria, was more than two times higher (4.5%) than the total recovery of radioactivity in the leachate when [14C] dicofol was directly applied in the soil (2%). This indicates cotransport by Pseudomonas. Fractionation and analysis of soil columns indicated that most of the bioaccumulated dicofol was rapidly released and adsorbed in soil, while bacteria moved down by leaching.
Assuntos
Dicofol/farmacocinética , Inseticidas/farmacocinética , Pseudomonas fluorescens/fisiologia , Poluentes do Solo/farmacocinética , Radioisótopos de Carbono/farmacocinéticaRESUMO
The organochlorine Thiodan CE inhibited growth and nitrogenase activity of Azospirillum lipoferum. The active ingredient, Endosulfan, was nonspecifically bound to proteins and mainly adsorbed to the cell envelope with small amounts transported into cytosol. The involvement of the external membrane and cyst formation in protection against hazardous substances is discussed.
RESUMO
Diferenças na carga celular entre populaçöes de epimastigotas e de tripomastigotas foram comparadas nas cepas Y, CL e Colombiana do T. cruzi. As populaçöes de tripomastigotas mostraram-se mais homogêneas quanto à carga celular do que os epimastigotas. Esta maior homogeneidade de cargas näo foi decorrente da seleçäo de sub-populaçöes de tripomastigotas por açäo do sitema imunológico do hospedeiro, mas talvez esta se deva à capa superficial formada por componentes sangüíneos dos hospedeiros