Derivation of human health risk-based thresholds for lead in soils promote the production of safer wheat and rice

A reliable and accurate soil threshold helps prevent excessive dietary Pb intake risks to consumers of locally grown wheat and rice crops. Based on a three-year investigation of 206 wheat fields and 358 rice fields throughout China, this study aimed to improve the soil protection guidelines by investigating Pb accumulation in soil-wheat and soil-rice systems and by assessing Pb exposure risks through the soil-grain-human pathway. A site-specific bioconcentration factor (BCF, ratio of Pb concentration in plant to that in soil) was calculated and used to assess grain Pb intake risks instead of a generic BCF value to reduce data uncertainty. In addition to soil pH, cation-exchange capacity exerted a major influence on the Pb BCF variations in wheat, whereas the organic carbon dynamics affected the BCF variations in rice. Once normalized BCF against those soil variables, the distributions of BCF were log-normal in nature. Optimizing the pH and cation-exchange capacity of wheat soils would help protect 49.8% of local adults from excessive Pb dietary intake. The scenario soil thresholds linked to soil variables and grain Pb intake risks were then derived and validated by independent data from field surveys and published articles. Poor production practices in the wheat fields under study included using soils with low fertility. [Display omitted] •Normalizing the bioconcentration data reduces the soil threshold uncertainty.•Optimum soil scenario protects 49.8% of wheat production from excessive Pb uptake.•Poor rice production practices included soils with low pH and organic carbon.•Derivation of a soil threshold requires reliable Pb soil-crop relationships.•Soil threshold links to health risk assessment were independently validated.