Atrazine degradation in soil: effects of adjuvants and a comparison of three mathematical models

Abstract

There are few reports on the effects of spray adjuvants on pesticide persistence. The role of three adjuvants used with atrazine on the herbicide's degradation in soil was examined. Three mathematical models were used to describe pesticide disappearance from soil: pseudo-first-order kinetics, the non-linear Gustafson-Holden model and the biexponential function. A mixture of atrazine with Atpolan 80 EC significantly inhibited herbicide soil degradation (DT50 = 78 days), while Adpros 85 SL and Break-Thru S 240 (DT50 = 25 and 24 days respectively) had little effect (DT50 = 22 days, atrazine alone). These results suggest that adjuvant can be a factor in field persistence. DT50 values obtained using the Gustafson-Holden and biexponential models were similar. Only the biexponential model requires an iterative method. A significant effect of one adjuvant on atrazine persistence in soil was observed. The biexponential model best described the disappearance of atrazine in the soil, as indicated by the values of R(2) and RMS and the relative concentration of the herbicide in the soil.