Cadmium exposure via diet and its implication on the derivation of health-based soil screening values in China

The cadmium (Cd) intake rates via diet of adults from different regions in China were between 0.160 and 0.557 μg/(kg BW·day), which were less than the provisional tolerable monthly intake (0.833 μg/(kg BW·day)) issued by Food and Agriculture Organization/World Health Organization in 2010, but higher than the one (0.365 μg/(kg BW·day)) issued by the European Food Safety Authority in 2011, to protect children, vegetarians and people living in heavily contaminated regions, and the intake rate of children (1.007 μg/(kg BW·day)) at the national scale was higher than the values recommended by the above institutes and those of adults. Vegetables were the critical contributors, followed by rice, flour, meats and aquatic products. Cd concentration in vegetable was the most sensitive factor in calculating the intake rate, followed by its contents in rice and aquatic products, and the intake rate of flour, indicating that more attention should be given to these parameters in future total diet surveys. When dietary exposure was incorporated, the derived national screening value of Cd under commercial scenario was reduced from 825 to 458 mg/kg, while the values of the north, south, Beijing and Shanghai were reduced to 627, 365, 693 and 489 mg/kg, respectively, indicating that the hazard would be underestimated if dietary exposure was not taken into account, especially for the south. The great variance between the screening values was due to the varied Cd intake rates, which indicated that deriving a screening value for each specific area based on its corresponding exposure characteristics was more appropriate. The national screening level for the residential scenario derived theoretically based on the dietary exposure characteristics of children was a negative value, meaning that the dietary intake rate was above the tolerable value. The method used in the United Kingdom to derive soil guideline values when non-soil exposure accounted for more than half of the maximum tolerable daily intake dose may be an appropriate estimate, but the exact ratio assigned to soil exposure should be assessed comprehensively based on a more sophisticated dietary exposure survey and the corresponding economic implications.