Cadmium and Lead in Dry and Wet Zone Rice - Vegetable Cropping Systems

Abstract

High input agriculture could lead to accumulation of heavy metals in soils. This research is undertaken to compare the total concentration of Cd and Pb in selected rice-vegetable cultivations of wet and dry zones of Sri Lanka, and to develop relationships between heavy metal concentrations and soil properties. Soils were collected from mid country wet zone (WM3b) and low country dry zone (D Llb). Important soil properties, total Cd and Pb were determined using standard methods. Geometric mean values for WM3b were Cd 0.84 mg/kg, Pb 10.1 mg/kg and for DLlb were Cd 0.45 mg/kg and Pb 8.1 mg/kg. Significantly higher (P<0.05) Cd concentration was observed in wet zone than that of dry zone but the difference in Pb for two zones were not significant. The obtained Pb values did not exceed the lower limit of the European Union set standards. Few soils exceeded lower limit of Cd (1 mg/kg) with less than 6.5 soil pH indicating the possible environmental threat. Among the tested soil properties, organic matter (OM) showed a significant positive correlation with total Cd concentration in soil (r=0.54; p=0.006). There was no significant correlation between other properties with total Cd or Pb in soil. Weak relationships between soil properties and heavy metal concentrations indicated anthropogenic metal contamination due to use of fertilizers and agrochemicals in rice-vegetable systems. This study emphasizes importance of investigating sources of heavy metals and bioavailability of heavy metals of agricultural soils in Sri Lanka.