Elevated cadmium concentrations in potato tubers due to irrigation with river water contaminated by mining in Potosi, Bolivia

Risk of cadmium (Cd) in the human food chain in Cd-contaminated areas is often limited by phytotoxicity from zinc (Zn) that is associated with the Cd contamination. A semiarid area, 60 km downstream of a tin mine in Bolivia, was surveyed where irrigation with Cd-contaminated river water (65-240 mu g Cd L-1) has increased median soil Cd to 20 mg kg(-1) while median soil Zn was only about 260 mg kg(-1). Cadmium concentrations in potato tubers increased from background values (0.05 mg kg(-1) dry wt.) in soils irrigated with spring water to a median value of 1.2 mg kg(-1) dry wt. in the affected area. Median concentration of Cd in soil solutions was 27 mu g L-1 and exceeded the corresponding value of Zn almost twofold. Soil-extractable chloride ranged from 40 to 1600 mg Cl- kg(-1) and was positively correlated with soil total Cd. Increasing soil solution Cl- decreased the solid-liquid distribution coefficient of Cd in soil. Soil total Cd explained 64% of the variation of tuber Cd concentration while only 3% of the variation was explained by soil extractable Cl- (n = 49). The estimated dietary Cd intake from potato consumption by the local population is about 100 mu g d(-1) which exceeds the WHO recommended total daily intake. It is concluded that the food chain risk of Cd in the irrigation water of the semiarid area is aggravated by the association with Cl- and, potentially, by the relatively large Cd/Zn ratio.