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.

• Issue Paper on the Environmental Chemistry of Metals (PDF)(113 pp, 2 MB, January 25, 2005)