Assessment of risks on US Pacific Coast otters feeding on bivalves and associated tributyltin

Potential risks to US Pacific Coast sea otters were assessed using tributyltin (TBT) bivalve data and sea otter food ingestion rates and body weights. TBT toxicity data (e.g. no observed adverse effects levels and lowest observed adverse effects levels) for a surrogate wildlife species were used after applying an uncertainty factor using Environmental Protection Agency guidance. The toxicological effectsʹ endpoints were based on immune suppression effects. Potential risk to sea otters was considered using hazard quotients to determine whether the estimated dose exceeded the toxic dose. Populations of sea otters were evaluated as well as individuals that frequented marinas. Risks are not predicted for greater than 99% of the sea otter populations which feed on prey in coastal waters. If we assume that the few individual otters seen in marinas of California and Alaska are feeding on bivalves living in marinas, and if we make conservative assumptions about the percent of marina bivalves in their diet, risks are not predicted for three of the four immune suppression effect endpoints.