Wheat tends to accumulate higher levels of cadmium in the grains than rice under a wide range of soil pH and Cd concentrations: A field study on rice-wheat rotation farmland

Dietary intake is a predominant pathway of human exposure to environmental Cadmium (Cd), but wheat (Triticum aestivum L.) has not received enough concerns for its risk of Cd contamination. A field survey of Cdcontaminated rice-wheat rotation farmlands in China provided detailed comparison of Cd accumulation capacity by rice and wheat grains. The results indicated that Cd-BCF of wheat grains (median values 0.42) were obviously higher than those of rice grains (median values 0.12) under wide soil Cd levels and pH ranges. Soil Cd levels rather than pH played a vital role on Cd accumulation by wheat grains, and high wheat grain Cd concentrations (0.12-0.13 mg kg-1) were even observed in mildly alkaline soil that normally have low Cd mobility. Dietary Cd exposure risks were assessed by the crop Cd exposure models considering different soil Cd content, pH and dietary structures of residents. The results indicated that the intake of wheat grains contributed 56.1-86.5% of total crop Cd exposure, with an increase in its contribution with the increase of soil pH. Residents favoring wheat would have a significant Cd exposure risk if consuming crops from soils with Cd levels above 0.41 mg kg-1, which was considerably lower than the current soil Cd risk screening value for alkaline soils (0.6 mg kg-1). Our findings indicate a high Cd accumulation capacity of wheat grains and consequent risk of dietary Cd exposure, which deserves further exploration on the correlation among soil Cd screening value, grain Cd limit value and its dietary exposure risk.