Municipal sewage sludge application on Ohio farms: health effects.

A 3-year prospective epidemiologic study was conducted on 47 farms receiving annual applications of treated sludge (average of 2-10 dry metric tons/ha/year) and 46 control farms in three geographic areas of Ohio. On the sludge-receiving farms 164 persons (78 families) and on the control farms 130 persons (53 families) participated by cooperating with monthly questionnaires concerning their health and their animals' health, annual tuberculin testing, and quarterly blood sampling for serological testing. The estimated risks of respiratory illness, digestive illness, or general symptoms were not significantly different between sludge farm and control farm residents. Similarly, there were no observed differences between disease occurrence in domestic animals on sludge and on control farms. No conversions from negative to positive tine test results occurred after sludge had been applied to the farms. The frequency of serological conversions (fourfold or greater rise in antibody) to a series of 23 test viruses and the frequency of associated illnesses were similar among persons on sludge and control farms. The absence of observed human or animal health effects resulting from sludge application in this study of Ohio farms was associated with low sludge application rates which were in accordance with Ohio and U.S. Environmental Protection Agency guidelines. Caution should be exercised in using these data to predict health risks associated with sludges containing higher levels of disease agents and with higher sludge application rates and larger acreages treated per farm than used in this study.

Municipal sewage sludge application on Ohio farms: tissue metal residues and infections.

Transmission of infectious agents and translocation of Cd, Cu, Pb, and Zn from anaerobically digested sludge to the tissues of farm animals grazing on pastures to which sludge was applied (2-10 metric tons per hectare) were studied on eight farms. No significant health risk associated with the possible presence in sludge of Salmonella spp., or of common animal parasites including Nematodirus spp., Strongylus spp., Strongyloides spp., Trichuris spp., Eimeria spp., Ascaris spp., and Ancylostomum spp. was noted. Caudal fold as well as cervical tuberculin testing indicated no conversions from negative to positive following exposure of cattle to sludge. Significantly higher fecal Cd concentrations were detected in samples collected from cattle soon after being placed on sludge-treated pastures compared to preexposure values in the same animals. Significant Cd and Pb accumulations were found in the kidneys of calves grazing sludge-treated pastures compared to control calves. Although older cows grazing sludge-treated pastures had significantly higher blood Pb levels, no metal accumulation was observed in other tissues. Statistically significant accumulations of Cd and Pb in the kidney of calves grazing these pastures for a relatively short period suggest that caution should be exercised to avoid prolonged grazing of cattle on pastures receiving heavy sludge applications, especially with sludges containing high concentrations of heavy metals.

Reduced cadmium body burden in cadmium-exposed calves fed supplemental zinc.

The objectives of this study were to evaluate the use of practical supplemental dietary zinc to modify the cadmium content in edible bovine tissues and to identify copper interactions with cadmium and zinc. The effect of supplemental zinc (200 or 600 micrograms/g) on the concentrations of cadmium, zinc, and copper in liver, kidney cortex, muscle, and blood of calves fed 50 micrograms/g cadmium for 60 days was evaluated. Blood samples were collected before and eight times after starting to feed cadmium or cadmium plus zinc. Liver, kidney, and muscle samples were collected when calves were slaughtered (baseline, at beginning of experimental feeding; cadmium-fed, at end of 60 days feeding). The cadmium concentrations of all sample types collected were markedly increased by the feeding of cadmium. Feeding 600 micrograms/g supplemental zinc significantly increased the zinc concentrations of liver, kidney cortex, and blood and decreased the cadmium accumulation in these organs as well as muscle. The copper concentrations of muscle or blood were not altered by feeding cadmium with or without zinc but those of liver and kidney cortex were significantly increased by higher dietary levels of zinc and cadmium. The potential use of dietary zinc salts in reducing cadmium body burden in food animals suspected or known to have high cadmium intakes is suggested.