Submitted to: Proceedings Annual Conference US Composting Council
Publication Type: Proceedings
Publication Acceptance Date: December 12, 2001
Publication Date: December 12, 2001
Heavy metals and xenobiotics such as dioxins can limit acceptance of composts in markets. Research results and progress in understandings of risks, and development of regulations on such chemicals in composts and biosolids will be summarized. Beneficial use of composts/biosolids plus limestone to remediate metal killed ecosystems will also be summarized. Exciting progress has been made which confirms that Cd in composts has no significant risk to humans or the environment. Further, modern high quality composts and biosolids cause little increase in crop Cd even at the 1000 t/ha used in regulation development. We had hypothesized that the lack of Zn movement to grain, coupled with malnutrition of zinc, iron and calcium in subsistence rice consumers, caused much greater Cd absorption than other foods allowing soil Cd to cause disease after 30- 50 years. ARS conducted feeding tests with rats fed sunflower or rice with 109Cd and about 0.6 mg Cd/kg grain using a factorial experimental design: diet Zn, Fe, and Ca were provided at marginal or adequate levels. With multiple deficient treatment (low Zn, low Fe, low Ca), 2.7% of rice 109Cd but only 0.78% of sunflower 109Cd were absorbed to the kidney and liver of the test rats; with adequate supply, 0.35% of rice 109Cd and 0.22% of sunflower kernel 109Cd were absorbed to liver and kidney. Study confirms the very low food-chain transfer, bioavailability and risk of compost- applied Cd. Research has indicated that garden foods other than peel of carrot do not accumulate soil dioxins. A critical research finding in the last year is that dioxin residues in pentachlorophenol-treated wood is an important source of dioxins in meat products. It's critical to exclude PCP-treated wood from compost feedstocks.