PUBLIC HEALTH ASSESSMENT

LOWER DUWAMISH WATERWAY
SEATTLE, KING COUNTY, WASHINGTON

APPENDIX F: CONTAMINANT SCREENING PROCESS

The information in this section lays out how the contaminants of concern were chosen from alarge set of different contaminants in fish/shellfish and sediment. In general, a contaminant'smaximum fish concentration or 95^th percentile sediment concentration is compared to a screeningvalue (comparison value), and if the contaminant's concentration is greater than that value, thenit is considered further. The health comparison values used in this public health assessmentinclude screening values in fish from EPA guidance, environmental media evaluation guides(EMEGs), cancer risk evaluation guides (CREGs), reference dose media evaluation guides(RMEGs), EPA Region IX Preliminary Remedial Goals (PRGs), and Model Toxics Control Act(MTCA) cleanup values for soil.

EMEGs are calculated from ATSDR chronic Minimum Risk Levels (MRLs) using exposureparameters such as ingestion rate and body weight. EMEGs currently exist only for soil, water,and air. The MRL represents an estimate of daily human exposure to a contaminant below whichnoncancer adverse health effects are unlikely to occur. Comparison values were calculated usingchronic Reference Doses (RfDs) for chemicals that did not have chronic MRLs. These values arecalled Reference Media Evaluation Guide (RMEGs). RfDs represent an estimate of daily humanexposure to a contaminant below which non-cancer adverse health effects are unlikely. PRGs andMTCA cleanup values are determined using a similar methodology. Cancer Risk EvaluationGuides (CREGs) are estimated contaminant concentrations based on the probability that 1additional cancer case may occur in excess of the number that will be expected to occur among 1million people (assuming they have been exposed to the contaminant for a lifetime).

EPA's "Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories"suggests screening values to use when evaluating contaminant data in fish from water bodieswhere subsistence fishers consume fish. These values are calculated assuming a fish consumptionrate of 142.4 g/day, a body weight of 70 kg, and a 70 year lifetime. Values were calculated usingthe most current oral RfD's and cancer potency factors in EPA's IRIS database. For contaminantsthat did not have recommended screening values listed by EPA, a similar methodology was usedto derive screening values using MRLs and RfDs and CSFs (see equations below ). Thisscreening method ensured consideration of contaminants that may be of concern for fishconsumers, especially higher consumption groups such as tribal and API populations. Theequations below show how comparison values were calculated for both noncancer and cancerendpoints associated with consumption of fish. A complete list of contaminants in fish/shellfishand sediment and their respective comparison valuesare provided in this Appendix.

Figure F1. Fish contaminant screening process for Lower Duwamish Waterway fish, Seattle, Washington

Figure F1. Sediment contaminant screening process for Lower Duwamish Waterway fish, Seattle, Washington

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