In this study, started in 1977, clinical and serologic evaluations of workers involved in composting of wastewater treatment plant sludge by the aerated pile method was initiated to evaluate the potential health effects of exposure to Aspergillus fumigatus and other viable and nonviable components of sludge. A health study consisting of analysis of blood specimens for liver and kidney function parameters, determination of serum and urine bile acid concentrations, physical examinations, interviews, and air and water monitoring was conducted of residents exposed to carbon tetrachloride and other toxic chemicals in drinking water as a result of contamination of domestic wells by a nearby hazardous waste dump. A study was undertaken to determine if evidence of exposure to hexachlorocyclopentadiene (HEX), hexachlorobicycloheptadiene (HEX-BCH), heptachlorobicycloheptane, and chlordene could be detected by urine analysis of workers exposed to chlorinated insecticide substances discharged to the sewer by a pesticide formulator. In order to assess the potential for health risks associated with the spray irrigation of wastewater, a clinical and virus serologic evaluation of workers and wastewater and air monitoring for viruses, pathogenic bacteria, and volatile organic chemicals was conducted. A field ecosystem study was carried out to evaluate the effects of land application of heat dried municipal wastewater treatment plant sludge (Milorganite) on vegetation, insects and meadow voles. The potential health effects associated with sludge incineration and pyrolysis are also presented.