Development and mapping of seleniferous soils in northwestern India

Abstract

Periodic surveys were undertaken to identify and characterize Se-contaminated soils in northwestern India. Total Se content varied from 0.023 to 4.91mgkg−1 in 0–15cm surface soil and 0.64–515.0mgkg−1 in samples of vegetation. Selenium-contaminated land occupying an area of 865ha was classified into different categories based on total Se content of soils as moderately contaminated (0.5–2.0mg Sekg−1) and highly contaminated (>2.0mg Sekg−1). The normal soils contained <0.5mg Sekg−1. The soil map was prepared using village level cadastral maps. Se-contaminated soils were silty loam to silty clay loam in texture and tested pH 7.9–8.8, electrical conductivity 0.3–0.7dSm−1, calcium carbonate 0.1–4.1% and organic carbon 0.4–1.0%. Selenium was present throughout the soil profile up to 2m depth; 0–15cm surface soil layer contained 1.5 to 6.0 times more Se than in subsurface layers.Selenium content in rock samples collected from lower and upper Shiwalik sub-Himalayan ranges varied from 1864 to 2754 and 11 to 847μgkg−1, respectively. The sediments transported through seasonal rivulets linking the Shiwalik ranges to affected sites contained 0.57–2.89mg Sekg−1. The underground water containing 2.5–69.5μg SeL−1 used for irrigating transplanted rice grown in Se-contaminated area resulted in a net Se addition in soil up to 881gha−1y−1; possibly further aggravating the Se-toxicity problem. Presence of substantial amount of Se in rock samples and sediments of seasonal rivulets suggests that Se-rich materials are being transported from Shiwalik hills and deposited in regions where seasonal rivulets end up.