Sorption of carbofuran and diuron pesticides in 43 tropical soils of Sri Lanka

To better understand the environmental fate of pesticides in Sri Lankan soils, we studied the sorption behavior of two commonly used pesticides (carbofuran and diuron) in 43 surface soils representing a range of soil physicochemical properties from dry and wet zones of Sri Lanka. For carbofuran, the K-d (L/kg) values varied from 0.11 to 4.1 (mean, 0.83; median, 0.62) and K-oc ranged from 7.3 to 120.6 (mean, 41.65; median, 36.1), whereas for diuron K-d values varied from 0.5 to 75 (mean, 9.6; median, 5.15) and K-oc ranged from 55.3 to 962 (mean, 407; median, 328). A comparison of sorption data on these tropical soils with published studies (mostly European and north American soils) showed that the ranges of sorption coefficients from Sri Lankan soils were within the wide range of K-oc values reported in the literature. However, these values for both pesticides in soils from dry zones of Sri Lanka were consistently higher (up to twotimes) than those from the wet zone. The wide range of K-oc values in Sri Lankan soils may be due to the possible difference in the nature of soil organic carbon, which needs to be further investigated.