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PW16 Ecological Risk Assessment (General)
(PW261) The Rule of Five: A Novel Weight of Evidence Approach to Derive a Site Specific Cleanup Goal.
Charters, D1, Greenberg, M1, 2, 1 U.S. EPA Environmental Response Team, Edison, NJ, USA2 Wright State University, Dayton, OH, USA
ABSTRACT- Weight of evidence evaluation has generally been used to determine the degree of risk (e.g., high, medium, or low risk) associated with a site. The weight of evidence, while potentially assisting in the prioritization of the site for remedial attention, does not assist in the establishment of a risk-based cleanup goal. Ecological risk assessment guidance for Superfund states that a preliminary remedial goal (PRG) should be selected within the risk range or between the no observed and low observed effect levels (NOAEL and LOAEL). The Rule of Five, or the establishment of a geometric progression of five nodes between the NOAEL and LOAEL, establishes a rationale and a set of guidelines for weighing lines of evidence within the risk range in determining a PRG. The initial point from which the PRG is derived is based on the assessment endpoint (AE). If the AE is based on survival of the surrogate receptor, then the initial point is the second point above the NOAEL. If the AE is based on growth or reproduction the starting point is the third node above the NOAEL. The measurement endpoints (MEs) are weighted according to their relevance to the AE. MEs that are closely linked to the AEs and technically valid are designated as discriminatory and, depending on the results, will move the PRG either one node up (towards the LOAEL) or down (towards the NOAEL). A ME with lesser relationship to the AE, or for which uncertainties are large will move the PRG node in the appropriate direction. A study or ME which does not provide discriminatory results is termed equivocal and does not move the PRG within the risk range. The weighing of the lines of evidence and the movement about the nodes in this fashion provide a logical and appropriately conservative approach which results in a scientifically-based PRG.
Key words: cleanup goal, preliminary remedial goal, weight of evidence, ecological risk assessment
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