Submitted to: Sustainable Land Application Conference
Publication Type: Abstract Only
Publication Acceptance Date: 9/1/2003
Publication Date: 1/4/2004
Citation: Chaney, R.L., Reeves, P.G., Kukier, U., Ryan, J.A., Green, C.E. 2004. Food chain transfer and bioavailability of Cd and other elements in plants grown on biosolids amended soils [abstract]. In: Proceedings of the Sustainable Land Application Conference, Buena Vista, Florida, January 4-8, 2004. p. 22.
Technical Abstract: Applications of biosolids, livestock manures, composts and many byproducts add trace elements to amended soils. These elements may comprise risk thru ingestion of the amendments or the amended soil, or thru crop accumulation of elements. Exposures of humans, livestock and wildlife to trace elements in applied amendments and soils have been evaluated for potential risks. Processes of soils and plants limit risk from applied elements: 1) Many elements are so insoluble or adsorbed so strongly in soil or in roots that the element is not bioaccumulated in plant shoots to levels which comprise risk to consumers. Indeed, many elements are so insoluble in amended soils that soil ingestion does not comprise risk from the element (e.g., Ti, Si, Zr, Au, Ag, V, Hg); 2) If an element is absorbed and translocated to shoots, and substantial yield reduction occurs from phytotoxicity before the crop would comprise risk during lifetime ingestion by livestock or wildlife, consumers are protected by the phytotoxicity of the element (e.g., Zn, Cu, Ni, Mn, As and F); these are regulated to prevent phytotoxicity; 3) Other elements may enter the feed-chain or food-chain (by plant uptake or soil ingestion) but do not comprise risk if limited by regulations (Pb, Co, Mo, Se, Cd). Co is a theoretical risk to ruminants because plants tolerate higher Co than cattle can tolerate in their diets. Similarly, high bioaccumulation of Se and Mo is possible in alkaline soils and have harmed livestock and wildlife. Because of industrial pretreatment and reduced use of Pb levels in biosolids do not comprise risk in the environment. Indeed, high phosphate and Fe oxides in biosolids used to amend Pb rich soils reduce soil Pb bioavailability substantially. Cd has been the subject of concern and extensive research for over 30 years. For most biosolids, manures and byproducts, Zn is present at 100-fold the level of Cd or greater; co-contaminating Zn can inhibit plant Cd uptake, reduce plant yield with low plant Cd levels, and reduce the bioavailability of crop Cd to animals. Thus, soil Cd has caused human Cd disease only where flooded rice was grown by subsistence farm families for decades. Polished rice is deficient in Fe, Zn and Ca for human health, and deficiency of these elements promotes intestinal Cd absorption. Further, grain Zn is not increased above background even in highly Zn contaminated soils. If soil amendments contain Cd without Zn, they comprise risk thru most crops; such Cd-rich unusual amendments should not be applied to cropland. Because of effective pretreatment, US biosolids are low in Cd and Cd:Zn, and do not comprise Cd risk. Further, high Cd adsorption by biosolids-amended soils, especially biosolids rich in Fe and Mn, can strongly reduce the phytoavailability of amended soil-Cd. We recently completed pot tests of lettuce uptake of Cd from long-term biosolids amended and control field plot-soils which showed much lower Cd uptake slopes with increasing cumulative applied rates of Fe-rich biosolids. Such strong metal sorption by biosolids amended soils substantially reduces potential Cd uptake and allows their use in metal remediation. Iron in surface applied fluid anaerobic biosolids may also comprise risk to cattle thru either Fe-induced Cu deficiency, or Fe-toxicity (observed when a fluid biosolids containing 11% Fe (DW) was surface applied on pasture). But, fluid biosolids with 4% Fe, dewatered and composted biosolids did not cause Fe toxicity in further studies. Thus, for some high Fe surface applied anaerobic biosolids, Fe should be regulated to prevent risk to ruminants. Surface applied fluid biosolids or manures may cause higher exposure of ruminant livestock to Cu than occurs with "normal" soil Cu. Because Zn and soil or manure organic matter are also ingested, Cu has low bioavailability. Season long grazing tests found no Cu toxicity to