COMPORTAMENTO E ECOTOXICOLOGIA DE PESTICIDAS EM SOLOS DO CERRADO

Abstract

Intensive and often unreasonable use of pesticides can result in environmental problems such as contamination of water, soil, air and food, and the possibility of adverse effects on non-target organisms. The pesticides behavior in soil is strongly influenced by its chemical and physical characteristics, as well as by the climatic conditions and pesticides physo-chemical properties. This environmental dynamic can significantly influence pesticides environmental concentrations and, consequently, the intensity of pesticides effects on non-target organisms. So, it is important to study the pesticide-soil-environment interactions in tropical soils. One experiment evaluated the sorption-desorption and leaching of the mesotrione herbicide in a Quartzarênico Neossolo with different rates of liquid swine manure. A second experiment evaluated the imidacloprid effects on the avoidance behavior and reproduction of earthworms (Eisenia Andrei) and collembolans (Folsomia candida) in soils with contrasting texture of the Brazilian Cerrado (dystrophic red latosol and typical ortic quartzarenic neosol). For the mesotrione behavior tests, soils (0-10, 10-20 and 20-30 cm) with no application and 01, 05 and 12 years use of liquid swine manure LSM were used. Sorption Kf values ranged from 0.08 to 3.14, and the highest values were found in the treatments with 01 year of LSM application. Desorption Kf values ranged from 1.28 to 5.26. The highest leaching occurred in the soil without LSM addition, where 13.43% of the applied herbicide leached along the column, mainly related to the higher pH value of this soil, showing that mesotrione has leaching potential. In the soil with 1 year of LSM application, the lowest mesotrione leaching occurred. Concerning imidacloprid ecotoxicology assays avoidance behavior was observed for the collembolans, being more expressive (up to 75% of avoidance) in the clayey soil. In the sandy soil, only in the two highest concentrations tested avoidance was observed (up to 63% avoidance). In the earthworms assay, avoidance behavior above 80% in both soils was observed, in all tested concentrations, demonstrating the loss of habitat function in both soils and evidencing the ecotoxicity of imidacloprid for these organisms. On the other hand, the EC50 values obtained in the clay soil were 0.255 mg kg-1, whereas for the sandy soil, this value was lower, 0.015 mg kg-1, showing a higher sensitivity of the organisms to the second soil tested. The strong difference between the soils can be explained by soil properties, indicating a low herbicide retention capacity and a higher pesticide availability in the sandy soil. It was concluded that soil pH was a determinant factor in the mesotione behavior, that the LSM addition favored herbicide sorption, reducing its mobility. Also, imidacloprid is highly toxic to soil invertebrates, causing avoidance and reproduction inhibition of these organisms.