Transferability of heavy metal(loid)s from karstic soils with high geochemical background to peanut seeds

Globally distributed karstic soils are characterized by the high accumulation of heavy metal(loid)s, such as Cd. Biogeochemistries and transferability of metal(loid)s in such soils are notably different from that in soils of anthropogenic pollution as evidenced by increasing studies about rice and maize. To solve the question about metal(loid) background and transferability in the system of karstic soils and crops with underground fruits, we designedly collected 246 paired soil-peanut seed samples in a world-famous karstic region in Southwestern China covering an area of 98,700 km². The concentrations of eight regulatory metal(loid)s (Cd, As, Cr, Cu, Hg, Ni, Pb, and Zn) in soil samples exceeded current standards to different degrees, demonstrating a typical high background. However, the transferability of metal(loid)s from soils to peanut seeds is quite low, resulting in a low exceedance rate of metal(loid)s (Cd, 12.2% and Pb, 1.2%) in seeds ("seed metal(loid)s"), in accordance with the results that metal(loid)s in soils mostly distributed in the inert/residual fractions. Based on the distinct response characteristics of peanut seed metal(loid)s to soil status from rice/maize grain metals, a model was further developed for effectively predicting the concentration of Cd in peanut seeds. Collectively, this study provides a basis for the assessment of soil environmental quality and safety zoning of upland field in karst areas.