An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Science Advisor Programs

Issue Paper on the Environmental Chemistry of Metals

EPA has identified three types of regulatory risk assessments where information regarding speciation of metals is useful and desirable:

  • National hazard/risk ranking and characterization
  • Site-specific assessments
  • National Regulatory Assessments

National hazard or risk ranking assessments are typically used by EPA for broad priority setting. An example of this type of assessment is the Hazard Ranking System (HRS) used to determine the eligibility of a contaminated site for inclusion on the National Priorities List.

Site-specific assessments are performed to determine if a site requires remediation and, if so, what the type and extent of remediation should be. A Superfund risk assessment is an example of this type of assessment.

The National Regulatory Assessment is typically used for standard setting. Development of ambient water quality criteria is an example of this type of assessment.

These three examples will be used to illustrate the concepts of metal chemistry developed in this paper.

You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.