Submitted to: Society of Environmental Toxicology and Chemistry Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/10/2001
Publication Date: 11/18/2002
Citation: Interpretive Summary:
Technical Abstract: Biosolids are a complex mixture which usually contain 100-times more Zn than Cd, and both inorganic and organic Cd adsorbents. Experiments were conducted to test the effect of persistent inorganic adsorbents in biosolids on phytoavailability of soil Cd to lettuce, and the role of subsistence rice diets in inducing Zn-Fe-Ca malnutrition which increased bioavailability of food Cd. In long term field plots, and in pot studies using soils from the field plots, high Fe biosolids limited Cd phytoavailability and caused a plateau response with only small increase in lettuce Cd. Other experiments tested the role of Zn in lettuce and spinach on bioavailability of Cd when adequate levels of all nutrients were provided; increased plant Zn reduced plant Cd absorption. Separate research examined the role of Zn-Fe-Ca malnutrition of subsistence rice consumers on absorption of Cd from polished rice or from sunflower kernels. These studies showed that up to 20-fold higher Cd absorption to kidney + liver occurred in rats consuming Zn-Fe-Ca marginal diets which did not reduce growth rates. Prolonged Cd turnover in the duodenum of marginal Zn-Fe-Ca animals allowed Cd from a single test meal to be absorbed into the blood weeks after feeding. Remarkably, rice grown in Cd+Zn contaminated paddy soils has high grain Cd but no increase in grain Zn. This body of research indicates that for modern regulated biosolids, low Cd and low Cd:Zn inhibit food-chain transfer and bioavailability of Cd, preventing Cd risk to consumers, regardless of the fraction of diet grown on biosolids amended soils, except for rice or tobacco. Soil Cd should be considered to comprise risk only thru rice or tobacco, or when high Cd:Zn ratios occur.