Biosolids contain small amounts of heavy metals, or “inorganic trace elements,” as do natural soils, manures and commercial fertilizers. These trace elements enter the municipal wastewater recycling plant from several sources. The EPA thoroughly studied the potential risks from these trace elements and set strict maximum levels in biosolids to ensure protection of public health and the environment. Because of required industrial pretreatment and the risk-based standards for biosolids recycling, the risks posed by trace elements in biosolids are minimal.
Many of the regulated elements in biosolids are beneficial in correct amounts. Chromium, copper, iron, manganese, selenium, and zinc are micronutrients for plants, animals and humans (look at the contents of a multi-vitamin tablet). It is the presence of these micronutrients that accounts for the greater effectiveness of biosolids as fertilizer when compared to traditional chemical fertilizers. However, if the concentration of these elements were to get too high, they could be harmful to people, plants or animals. There are several steps taken to prevent this from happening.
- Government limits: In order to protect human health and the environment, the EPA and DEQ set limits on the amount of trace elements allowed in biosolids. These levels are based on more than 20 years of research and scientific risk assessments and routine reviews of how trace elements affect soils, plants and animals.
- Pretreatment requirements: Rigorous pretreatment programs control the amount of pollutants entering wastewater recycling facilities. Laws regulate industries to make sure that they dispose of their pollutants safely. This means that pollutants are removed from the waste stream before they ever reach the sewer, ensuring that biosolids contain only small quantities that the EPA and DEQ have determined pose no risk.
- Testing & Monitoring: Biosolids are routinely tested by the wastewater recycling facilities and the biosolids applicators to make sure they comply with all regulatory requirements.
Trace elements in biosolids can enrich soils upon repeated land application. The potential for excessive soil accumulation of potentially deleterious trace elements in biosolids was addressed by Federal regulations found in the U.S. EPA Standards for the Use or Disposal of Sewage Sludge (Title 40 of the Code of Federal Regulation, Part 503).