Pesticide Leaching Potential in a Shallow Unconfined Aquifer

Contamination of soil and groundwater by pesticide leaching has become a serious threat to subsurface environment. Hazards of the leaching potential of various pesticides were studied in a shallow unconfined aquifer located in Northwest Bangladesh. Pesticide leaching potential was quantified using a one-dimensional advective-dispersive transport equation for a non-conservative chemical that follows first order decay and linear adsorption in soils. Leaching potential index (LPI) was calculated for sixty-nine sites in the study area to evaluate the relative vulnerability to pesticide leaching and to prioritize sites for soil sampling. The numerical ranks of computed LPI were grouped by quantiles into very high, high, moderate, low and very low categories and based on these rankings, the most vulnerable site was selected. Six soil samples were collected from this site at different depths (0.0, 1.5, 3.0, 4.5, 6.0, and 7.5m). The soil-water from the collected samples was extracted following the standard procedure and tested using GC and HPLC for pesticide residues. Results showed no trace of known pesticide residues in the soil-water but few unknown peaks were detected indicating the use of some unknown chemicals in the study area.