Submitted to: Annual Conference of the US Composting Council
Publication Type: Abstract Only
Publication Acceptance Date: 1/12/2006
Publication Date: 1/23/2006
Citation: Chaney, R.L., Kim, H.H., Davis, A.P. 2006. The significance of heavy metals, trace elements and toxic organic compounds in compost products [abstract]. Annual Conference of the US Composting Council. On disk. Interpretive Summary: .
Technical Abstract: All composts contain essential trace elements and non-essential metals which should be considered in evaluation of product production, sale and use. Manure from poultry and swine and some dairy cattle may contain as high Zn, Cu, and As as biosolids, but the manures seldom contain high levels of Fe, Mn or Al which could bind metals and reduce their phytoavailability. Risks from metals consider the potential for transfer from use of compost in crop or livestock production, and the very low potential risk of compost metals have become evident after many years of research. Metals are a risk to crops only when soils are very low pH, and compost tends to raise soil pH when applied. Food-chain transfer concerns have not been found for composts of typical manure, biosolids, or other feedstocks. This has occurred because Cd uptake and bioavailability is quite inhibited by the simultaneous presence of over 100-times more Zn in composts. Arsenic has low food-chain transfer potential. Phosphate rich composts are an important soil amendment to reduce risks from Pb in urban soils. And composts have been shown to be highly effective soil amendments to remediate severely contaminated disturbed soils. Composters will need to continue evaluating feedstocks for contamination to protect their compost products. CCA- or Pentachlorophenol-treated wood are not acceptable in composting; CCA wood adds As and Cu which can limit compost use, and PCP treated wood contains dioxins and furans which would prohibit compost use. Composting of unseparated MSW is still not recommended because glass, plastics, and particles of metals make products unacceptable to consumers. Pre-separated MSW (compostable fraction) is as acceptable as yard debris and other traditional compostable feedstocks but these sources are low in nutrient content. Combining carbon rich feedstocks and manure or other nutrient rich feedstocks makes more beneficial products. And higher levels of Fe, Mn and Al in composts help reduce potential for runoff or leaching of phosphate. Composters with high phosphate feedstocks will need to deal with limits on phosphate; we have found addition of Fe and Al oxides effective to reduce water solubility of P without making it unavailable to plants. Including high Fe and Mn byproducts among feedstocks is an effective solution to limits on phosphate risk from soil amendments. Composting has proven an effective method to limit risks from toxic organic compounds. Prohibition of use or disposal of PCBs, chlorinated pesticides or dioxins keep these out of compost feedstocks. Many compounds which survive anaerobic stabilization (e.g., phthalates, detergents) are readily biodegraded during composting. The rare case of Copyralid persisting thru composting has required change in use of this herbicide to protect compost quality. Copyralid remains a problem because manure can be indirectly contaminated by feeds or bedding materials which were treated with this herbicide; use of Copyralid on lawn is not the only problem use of Copyralid. Mature composts of many feedstocks remain valuable soil amendments for agriculture and horticulture and soil remediation.