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.