Assessment of the impact of diuron to water bodies in the Walawa area

Abstract

Use of pesticides has significantly increased global food production and it is indispensable in modernagriculture to control weeds, insects, other pests and diseases. As the population increases the use ofpesticides also increases. The impact of these pesticides to the environment is not well understood forSri Lankan conditions Hence the sorption pattern of a non ionic pesticide, diuron {3-(3,4-dichlorophenyl)-l, l-dimethylurea; C9H IICI,KO} which is used as a herbicide to control weeds andmosses mainly in sugarcane, was studIed for-14 soil series in the right bank of the Walawa basin in SriLanka.

Information was collected from fanners in Walawa areas on crops, historical cropping patterns, typeof pesticides used, pesticides handling knowledge etc. The survey revealed that pesticides use ismalpracticed by fanners. The distribution of crop types in the area during last three years shows thatPaddy, which is scattered through out the area, is the most prominent crop. The average area underpaddy cultivation is approximately 9800 ha. Banana was the second highest grown crop that is inabout 4200 ha. Sugarcane, which covers about 2500 ha, is the prominent monoculture in the Walawabasin.

Adsorption of di uron to the collected surface (0-1 Ocrn) soi Is of the 14 soi I series in the Wa lawa basinwere measured using High Performance Liquid Chromatographic method. The Moraketiya seriesshowed the highest sorption among them. It also gives the highest Kd value of the selected soils andSiyambala series exhibited the lowest adsorption and Kd. The organic carbon content was highest inKachigalara series and it was lowest in the Walawa series. The measured Kd values were used topredict the risk of this pesticide to ground and surface water in the Walawa area using a simplemanagement model called Pesticide Impact Rating Index, PIRI which resulted a moderate risk forthe contamination of water bodies in the area.