Behavior of atrazine and malathion pesticides in soil: Sorption and degradation processes

The objective of this study is to evaluate the sorption characteristics of two pesticides; Atrazine and Malathion by fitting the sorption data to linear and non-linear isotherm equations and to characterize the degradation of Atrazine and Malathion under laboratory conditions. The sorption of Atrazine and Malathion in soil was studied using a batch experiment technique. Solutions with different initial Atrazine or Malathion concentrations (Ci) of 0 to 600 μg L-1 in 50 μM L-1 CaCl2 were used in duplicate. Pesticide residues in solutions were extracted with acetone: hexane using ratio of 3:2 (v/v) by Microwave-Ass is ted Extraction technique (MAE). The sorption data were fitted in some mathematical models to obtain the sorption parameters of pesticides i.e., Linear, Freundlich, Langmuir and Exponential isotherm models. The present results indicate that the three isotherms including Freundlich, Langmuir and Exponential (proposed model) have similar accuracy in predicting the sorption process, but the proposed (Exponential) isotherm is better because it has high R2 and less SSE. Also, Atrazine has higher affinity for binding to soil particles than Malathion. Measured degradation rate averaged about 0.0102 day-1 for Atrazine and 0.1053 day-1 for Malathion. The half-life was accounted as 68.1 and 6.6 days for Atrazine and Malathion, respectively. Therefore, Atrazine is more stable in soil than Malathion. About 78% of Atrazine was remained in soil at 25 days after application, while 8% only of Malathion was remained in soil at the same period. The findings from this study emphasize on the need for care when using persistent pesticides to control weeds in soil. © 2010 Asian Network for Scientific Information.