Bioaccumulation of Lead by Indian Mustard in a Loamy Sand Soil Artificially Contaminated with Lead: Impact on Plant Growth and Uptake of Metal

Abstract

In a screen-house study, the effects of artificially contaminating the soil with lead (Pb) at levels ranging from 0 to 1500 mg kg−1 soil on the growth and uptake of Pb and micronutrients by Indian mustard [Brassica juncea (L.) Czern.] grown on a loamy sand soil (Typic Ustorthent) were investigated. The crop was grown for 60 days with adequate basal fertilization of nitrogen, phosphorus, and potassium, and dry matter was recorded. The plants were analyzed for total Pb and micronutrients, and the soil was analyzed for diethylenetriaminepentaacetic acid (DTPA)-extractable Pb. The DTPA-extractable Pb measured before sowing of Indian mustard increased consistently and significantly with increase in rates of Pb application to soil. It increased from 0.65 mg kg−1 in the control to 199.8 mg kg−1 in soil treated with 1500 mg Pb kg−1 soil. Significant reduction in the dry-matter yield of Indian mustard occurred with Pb applications of 500 mg kg−1 soil and greater. The concentration as well as uptake of Pb by Indian mustard increased significantly over control at all rates of its application. It increased from 9.4 μg pot−1 in the control to 220.6 μg pot−1 at Pb application of 1500 mg kg−1 soil. Applications of Pb to the soil decreased the concentration of micronutrients in plants, but a significant reduction occurred only for iron at rates greater than 500 mg Pb kg−1 soil. However, the uptake of iron, manganese, and copper registered a significant decline at Pb application of 500 mg kg−1 and greater and that of zinc at 750 mg kg−1 and greater. In a Typic Ustorthent soil, a DTPA-extractable Pb level of 59.5 mg kg−1 and plant content of 44.2 μg Pb g−1 dry matter was found to be the upper threshold levels of Pb for Indian mustard. This study suggests that once the soil is contaminated by Pb, it remains available in the soil for a long time, and such soils, if ingested with food crops, may be a significant source of Pb toxicity to both humans and grazing animals.