“…Moreover, many studies point out that there is high risk of the environmental contamination of some pesticides, such as, α and β-endosulfan, diuron and metolachlor (Weaver et al, 2012;Kennedy et al, 2001; Barrett and Jaward, 2012). In addition, literature indicates that in tropical regions with cotton industry several pesticides have been detected in surface water and among the innumerous factors that affect pesticides runoff, the agricultural management system is a very important one (Carbo et al, 2008;Casara et al, 2012). Hence, it is necessary to study the influence of the management systems in the dynamics of the pesticides in the environment The present study, therefore, aimed to adjust a model by combination of the pesticide concentration model, reported by OECD (1999), with Runoff Curve Number (RCN) developed by the USDA Natural Resources Conservation Service (SCS-USDA), and the water balance in soil surface (WB) describe by Pruski et al (1997) to estimate the concentrations of α-and βendosulfan, diuron and metolachlor in runoff.…”