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.