Potential Polychlorinated Biphenyl Residues in Animal Products from Application of Contaminated Sewage Sludge to Land1
- George F. Fries2
Laboratory studies and field observations involving polychlorinated biphenyls (PCB's) and related compounds were used in making an assessment of residues in animal products from the application of sewage sludge to agricultural land. Animals can become exposed to PCB's applied to land by three routes: direct ingestion of sewage sludge that adheres to plants during sludge application, ingestion of plants indirectly contaminated by uptake or volatilization from the soil, and ingestion of contaminated soil when grazing. The last route has the greatest realistic potential for producing residues in animal products from a given rate of long-term application of PCB-contaminated sludge to land. Feeding experiments with PCB's indicate that the steady-state milk-fat concentrations are about five times the diet concentrations (dry basis) in dairy cattle and that the steady-state body-fat concentration will be similar in non-lactating animals. Soil consumption by grazing dairy cows can be as high as 14% of dry-matter intake when the amount of available forage is low and no supplemental feed is used. This could cause milk-fat residues of 0.7 ppm for each ppm of PCB in surface soil. There is little root absorption and translocation of PCB's to the aerial parts of plants. Plants can become contaminated by volatilization of PCB's from soil and redeposition on the plants if the residue occurs at the soil surface. Field experience with other halogenated hydrocarbons suggest that volatilization and redeposilion of PCB's will be less important in determining rates of PCB-containing sludge that can be applied to land than direct animal ingestion of sludge or contaminated soil.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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