In the United States, about 60% of biosolids—solid residues produced by wastewater treatment—are applied to land as an agricultural amendment.  The biosolids supplement the nitrogen and phosphorous as well as the organic carbon in the soil and help crops grow.  EPA regulates land application of sewage sludge (biosolids).

In 2002, the National Research Council of the National Academy of Science issued a report: "Biosolids Applied to Land: Advancing Standards and Practices” (NRC, 2002).  The report recommended additional scientific work to reduce uncertainties about the potential for adverse effects from exposure to biosolids. EPA researchers are addressing some of these uncertainties by evaluating whether chemicals in biosolids degrade when biosolids are applied to agricultural soils or if the chemicals persist.

The biosolids are treated using methods similar to those commonly used in sewage-treatment plants, and then the biosolids are spread on fields. EPA researchers take samples from these fields to determine the persistence of endocrine disrupting chemicals.

One EPA study examined fields in North Carolina after an application of biosolids and tested for the presence of nonyl- and octylphenols; there are some concerns these substances are endocrine disrupting chemicals and are toxic to wildlife and aquatic species. EPA researchers found that these chemicals were present in the soil after application and did not degrade after 98 days when the study concluded.

More research is needed to determine if these concentrations of nonyl- and octylphenols in the soil might be a potential risk to people or the environment. EPA researchers are continuing their studies in a different geographic location to determine whether persistence is affected by weather, soil, and local conditions. They are also assessing fields over a longer time period and expanding the chemicals measured.

The research will be used to better understand the impacts of using biosolids, provide guidance on safer ways (time and mechanisms) to apply biosolids and develop innovative solutions to reduce the concentrations of endocrine disrupting chemicals in biosolids.