Submitted to: Great Lakes By-Product Management Association
Publication Type: Abstract Only
Publication Acceptance Date: April 25, 2004
Publication Date: December 2, 2004
Citation: Chaney, R.L. 2004. Use and abuse of part 503 requirements: improved risk assessment for contaminants in non-biosolids by-products. Great Lakes By-Product Management Association.
In development of the Clean Water Act, Section 503, limits for trace elements, the Pathway Risk Assessment evaluated potential risk from 14 Pathways for applied elements to cause adverse effects in the environment. Trace element limits for biosolids which may be beneficially used as a fertilizer and soil conditioner in agriculture and horticulture were based on phytoavailable metals in amended soils, and bioavailable metals in ingested biosolids or soil-biosolids mixtures. Biosolids are different from livestock manure and many other byproducts in their content of amorphous oxides of Fe and Mn, and high level of sorbed phosphate, which increase metal adsorption capacity. The amorphous Fe and Mn oxides provide persistent increased Cd, Zn, Pb and P adsorption capacity based on finding stronger adsorption and lower plant uptake slopes for long-term biosolids amended soils compared with unamended control soils. The level of amorphous Fe oxides was especially valuable in reducing biosolids Cd, Zn and Pb phytoavailability. Additionally, Fe and Mn can serve as fertilizers in addition to increasing metal adsorption. Because these biosolids adsorption surfaces strongly affect the phyto- and bio-availability of metals in biosolids, the 503 limits should not be applied to other byproducts without consideration of the metal adsorption specific to that byproduct. Some Fe and Mn rich byproducts may be valuable for reducing the phyto- and bio-availability of trace elements in byproduct blends. Processing of byproducts or blends may convert some byproduct Fe and Mn into more amorphous forms to increase the metal adsorption ability of a byproduct blend. Composting did not increase the fraction of oxalate extractable Fe and Mn in biosolids or manure mixed with crystalline Fe oxides. It will be important to maintain a balance between Fe and Mn to avoid Fe-induced Mn deficiency which has been observed when alkaline Fe rich biosolids were applied to low Mn Coastal Plain soils. In our continuing evaluation of beneficial reuse of foundry sand, we have examined data for a number of elements not yet regulated in biosolids, but which have been a concern for states asked to permit a range of byproducts in which some trace elements were present at higher levels than in typical US soils. Most trace elements not regulated under 503 have very limited plant uptake or bioavailability due to their chemical properties. Evidence of potential food-chain transfer or risk for trace elements in other byproducts can often be derived from the literature and serve as the basis for adaptation of the 503 limits to additional soil amendments.