Risk Based Evaluation of Pesticide Movement in Right Bank Soils of the Walawa Basin in Southern Sri Lanka

Abstract

Embilipitiya, located in the Right Bank of Walawa basin is under heavy agriculture and therefore agrochemical usage is very high. Paddy and banana are the most common crops cultivated in this area. The commonly used pesticides in Embilipitiya were identified through a survey and they were propanil, MCPA, carbofuran, and dimethoate. These pesticides are highly water soluble and a risk assessment for movement of these pesticides in soils is Important for better soil and water management. Using two simple indices, Retardation factor (RF) and Attenuation factor (AF), the leaching potential and vulnerability for ground water contamination of these major pesticides were assessed. According to RF, carbofuran followed by dimethoate (estimated 1.0<RF<2.0 for both pesticides) and based on AF carbofuran (2.Sxl0'l<AF<1.0) have great risks for ground water contamination in many places in this area. Hence the ranking of commonly used pesticides in the Walawa basin according their risk levels can be done as carbofuran > propaniF dimethoate> MCPA’diazinon