Janitha A. Liyanage, Ransilu C. Watawala, and Ananda P. Mallawatantri. Dept of Chemistry, Univ of Kelaniya, Kelaniya, Sri Lanka
The contamination of ground water by leaching of pesticides used in agriculture is a major concern in many countries. The potential of contamination is governed by many soil, pesticide and environmental factors and the critical one is the rate at which pesticides degrade in soil. To avoid the potential hazard of pesticides on the environment, especially on the ground water contamination potential of pesticides and also to study the efficacy of the pesticide to control target pests, it is of great interest to study the fate, the microbial degradation of commonly used pesticides, like carbofuran, in Sri Lankan soils. Degradation rate of 14C ring labelled carbofuran in selected Sri Lankan soils were studied by adding 0.1 µ Ci/10g soil of carbofuran to red yellow podzolic, alluvials and regosols soils and incubated in 75% of maximum water holding capacity and 28 0 C of temperature for 13 hours light and 11 hours dark conditions. Liberated 14CO2 was collected after 0, 1, 3, 5, 7, 14, 28, 36, 42, 58 and 100 days to an alkaline solution and the activity of the solution was measured using a Liquid Scintillation Counter. Carbofuran has a mineralization rate of 12.5% in regosols, 7.5% in alluvials and lower rates in other soil after 20 days. After 40 days it increases over 20% in regosols and in other soils it was less than 15%. After 58 days the mineralization was over 60% in regosols soils but less than 50% in other soils. During the whole period the mineralization was less than 10% in red yellow podzolic soils. The degradation rate of carbofuran is much lower in red yellow podzolic soils, which has the highest organic carbon content than the other soils. It indicates that the microbial degradation is less than the chemical or other degradation methods in soils of Sri Lanka.