Ecological risks associated with the application of sewage sludge to non-agricultural ecosystems

The Clean Water Act of 1977 directed EPA to establish standards for use and disposal of sewage sludge (biosolids). The application of biosolids to non-agricultural lands is becoming increasingly important as a method of waste disposal. Ecological endpoints at the population, community, and/or ecosystem level have not previously been emphasized in the development of regulatory standards for municipal sewage sludge. This risk assessment focuses on terrestrial endpoints in four ecosystem types to which substantial quantities of sludge have been applied or are expected to be applied in the future: northwest Douglas-fir forest, southeastern loblolly pine plantation, eastern deciduous forest, and semi-arid rangeland. Conceptual models suitable for all ecosystems were developed that depict the links among assessment endpoints. Estimates of risks to wildlife from contaminants and simulations of impacts of nitrogen in sewage sludge on the structure and function of forest communities are presented in detail elsewhere at this conference. This project overview integrates these two assessment components and adds contaminant risks to plants, soil invertebrates, and microbial processes and risk of leaching and erosion altered by biosolids application. Management practices and empirical measures of bioavailability are considered for each ecosystem. Concentrations of constitutents of sewage sludge used for the analysesmore » have been obtained from the 1988 USEPA National Sewage Sludge Survey. Existing regulatory standards that are primarily human health-based are also evaluated for the adequacy of protection of ecological systems and populations. Predicted impacts of sewage sludge applications are presented, even if they may be regarded as benefits rather than risks.« less