Accumulation, fractionation and health risk assessment of fluoride and heavy metals in soil-crop systems in northwest China.

Untreated industrial sewage and domestic wastewater irrigation has led to agricultural soil-crop system contamination by heavy metals and fluoride in Dongdagou and Xidagou stream basins, Baiyin city, China. A total of 36 pairs of soil and wheat samples (roots, stalks, leaves, husks, and grains) and 42 pairs of soil and maize samples (roots, stalk1, stalk2, stalk3, leaves, husks, corncobs and grains) were collected from Dongdagou and Xidagou stream basins to examine the accumulation, fractionation, correlation of heavy metals and F in soil-crop systems. Risks posed by heavy metals and F in this system to human health was also assessed. The total contents of F and heavy metals (Cd, Cu, Pb, Mn Zn, Cr and Ni), as well as the fraction distribution in soil, were determined. The total contents of F and heavy metals in crop tissues were also determined. The results indicated that the average contents of Cd, Cu, Pb, Mn Zn, F and Cr in Dongdagou and Xidagou stream basins exceeded the soil background value. Heavy metals and F more easily accumulated in the male inflorescence of maize. Correlation analysis showed that content of water soluble F positively were correlated with the contents of Cd, Cu, Pb, Mn Zn, Cr and Ni in exchangeable and carbonate fractions (P < 0.05). Stepwise discriminant analysis showed that the combined stresses of soil total Cu and Ni accounts for 100% effect on water soluble F accumulation in soil and crop roots. The hazard index indicated that noncancerous risk is likely to occur through maize grains and wheat grains consumption by children and adults.

Accumulation, fractionation, and risk assessment of mercury and arsenic in the soil-wheat system from the wastewater-irrigated soil in Baiyin, northwest China.

Wastewater irrigation can increase metal concentrations in soil and wheat, thereby posing metal-associated health risk via food ingestion. We investigated levels of mercury (Hg) and arsenic (As) in roots, husks, stems, leaves, and grains of wheat and their fractionations in farmland soil from Baiyin City, an industrial and mining city, northwest China. Results show that the mean concentrations of Hg in soils from Dongdagou and Xidagou stream in Baiyin were 8.5 times and three times higher than local soil background values, respectively. Those of As were 4.5 times and 1.6 times higher, respectively. Most Hg and As were mainly accumulated in wheat leaves. The spatial distributions of As in soils and grains exhibit a very similar pattern, which suggest that As pollution in soils might be predicted by its level in wheat grains. Residual fractions for Hg (RES-Hg) and As (RES-As) are the highest compared to other fractions, indicating weak mobility of Hg and As in soil. The crop oral intake hazard quotients of both Hg and As for children were approximately two times higher than that for adults, indicating that children have higher exposure risks to Hg- and As-contaminated wheat. The crop oral intake was the main route of exposure causing non-carcinogenic and carcinogenic risk for local residents.