Submitted to: Proceedings of the Composting in the Southeast Workshop
Publication Type: Proceedings
Publication Acceptance Date: 8/1/2002
Publication Date: 10/7/2002
Citation: Interpretive Summary: This paper comprises a review of progress in improving our understanding of the risks of metals in land-applied manures, biosolids, byproducts, and composts of such materials. In particular, the paper describes the strategy for preparation of composted organic residuals in combination with adsorbent Fe and Mn byproducts, and mixing with alkaline byproducts, for use as fertilizer and soil conditioner. This combination has been shown to reduce the plant availability of soil metals so strongly that such composts can provide immediate and complete remediation of metal toxic sites such as Superfund sites surrounding metal smelters or metal mine wastes. High pH improves adsorption and precipitation/occlusion of metals in such mixtures, and additions of Fe and Mn oxides can increase the metal adsorption capacity of the compost substantially. Research has shown that the inorganic absorbent materials in biosolids and amended soils is key to holding applied metals in forms which do not comprise risk to the environment or to food-chains. Because of the simultaneous presence of Zn, the Cd in the Tailor-Made Composts has very low bioavailability to animals. And such composts are very effective in reducing bioavailability of soil Pb to protect both children who live near smelters or mine wastes, and urban children exposed to Pb contaminated soils. Thus this paper summarizes a new strategy for management of many kinds of organic residues and inorganic byproducts to produce valuable fertilizers and soil remediation amendments at low cost. Last, the presence of high levels of Fe in the compost limits phosphate leaching from amended soils, offering another benefit to users.
Technical Abstract: This paper summarizes information on risk assessment for metals (Cd, Pb, As, Zn, Cu, Hg) in compost products used in agriculture or horticulture, and progress in research to develop and demonstrate the use of Tailor-Made Composts to remediate metal phytotoxic soils. Research has increasingly illustrated the role of inorganic absorption surfaces in composts and biosolids in adsorption of metals in the amendment and in amended soil. In general, hydrous oxides of Fe and Mn with high surface area can persist in amended soils, and limit solubility, phytoavailability, and bioavailability of soil metals including Zn, Cd, Ni, Cu, and Pb. And such products can be used as effective Zn, Cu, Fe and Mn fertilizers if Fe and Mn are balanced for plant nutrition during addition of absorbents to composts. Further, high Fe additions to organic products can help limit P leaching and runoff, of increasing importance in soil management. The ability of a Fe and Mn rich compost, biosolids, or manure to absorb or precipitate soil metals and correct the severe infertility of metal contaminated mine wastes or smelter contaminated land can provide comprehensive remediation of a metal phytotoxic site if sufficient limestone or alkaline byproduct is added to make and keep the site calcareous. The combination of alkalinity, sorption, and plant nutrients reduce solubility of Zn, Cd, Pb, Ni, and Cu, preventing phytotoxicity and reducing bioavailability of soil metals to animals which ingest soil. Highly effective revegetation of long dead smelter or mine waste killed ecosystems was achieved at numerous locations using the "Tailor-Made" approach.