Public Health Concerns About Chemical Constituents in Treated Wastewater and Sludge

There are many chemical constituents that enter the municipal waste stream that are of potential concern for human health. These substances include organic chemicals, inorganic trace elements (such as cadmium and lead), and nitrogen. Conventional agricultural practices, such as the use of commercial fertilizers, also have the potential to introduce additional chemical constituents to soil. However, this report is not attempting a comparison between public health effects of conventional agricultural inputs and those derived from municipal wastewater or sludge. The degree to which constituents from municipal wastewater present a risk to human health depend on their concentration in reclaimed water and treated sludge and the fate and transfer of these chemicals from the wastewater/sludge sources to human receptors via various exposure pathways. The chemical composition of sewage and the degree to which chemical concentrations are reduced in effluent and sludge by secondary and advanced treatment were discussed in Chapters 2 and 3. The degree to which chemical concentrations of these con-taminants in reclaimed wastewater and sludge are further reduced through natural processes in the environment and their availability to food plants were the subjects of Chapter 4. Trans-mission of toxic contaminants to humans from agricultural use of reclaimed wastewater and sludge is covered in this chapter. The U.S. Environmental Protection Agency (EPA) identified Priority Pollutants in regulations that deal with municipal and industrial wastewater (EPA, 1984) due to their toxicity to humans and the aquatic environment. These Priority Pollutants are divided into four classes: (1) heavy metals (oftentimes referred to as trace elements or trace metals) and cyanide, (2) volatile organic compounds, (3) semivolatile organic compounds, and (4) pesticides and poly-chlorinated biphenyls (PCBs). In addition, nontoxic organic compounds in wastewater can be transformed into potentially toxic chlorinated organic compounds, such as trihalomethanes, when chlorine is used for disinfection purposes (National Research Council, 1980). For the purpose of this review, non-metallic trace elements, such as selenium, are grouped together with the heavy metals under the more general designation of "trace elements." The following discussion first considers the fate of organic compounds from sludge and wastewater applications to soil. The uptake of these chemicals into plants and animals that go into the human food chain is then examined. Finally, the potential for adverse health effects from trace elements in sludge and wastewater via these same pathways is evaluated.