DERIVATION OF SHELLFISH HARVEST REOPENING CRITERIA FOLLOWING THE NEW CARISSA OIL SPILL IN COOS BAY, OREGON

Abstract

Oil spills in Alaska, California, Maine, and other states have raised concerns regarding potential contamination of fish and shellfish, and have led to temporary closures of seafood harvests while health risks are assessed. Lacking standardized protocols, these assessments are generally ad hoc, site-specific efforts, with significant differences in risk evaluation criteria. This article describes the response of a state health agency to shellfish contamination following an oil spill on the Oregon coast, and discusses some of the factors that can complicate the evaluation of potential health risks from consumption of oil-contaminated shellfish. On 4 February 1999, the Japanese-owned cargo ship M/V New Carissa, carrying an estimated 400,000 gallons of light diesel and heavy fuel oil, ran aground 2 miles north of Coos Bay, Oregon. Damage to the ship?s hull from the grounding and pounding surf caused the release of an estimated 25,000 to 70,000 gallons of oil. Concern for potential contamination of local recreational shellfish and commercial oyster beds prompted the Oregon Department of Agriculture (ODA) to close shellfish harvesting in Coos and Douglas counties. ODA requested assistance from the Oregon Health Division in the derivation of risk-based criteria for reopening the shellfish harvest. Criteria were developed for the primary contaminants of concern, polycyclic aromatic hydrocarbons (PAHs) expressed as total benzo[a]pyrene (BaP) equivalents. "Safe (<10 µg/kg) and "unsafe" (>45 µg/kg) BaP equivalent levels were derived based on upper end (32.5 g/d) and average (7.5 g/d) estimates of shellfish consumption, respectively. Composite samples of oysters, clams, and mussels (15?20 per composite) were collected from target areas and analyzed for PAHs by gas chromatography/mass spectroscopy (GC/MS). Carcinogenic PAHs were converted to total BaP equivalents (wet weight) and compared with criteria. Two oyster samples, collected from a slough off of Coos Bay, contained 33.9 and 34.5 µg/kg BaP equivalents; all other samples had less than 10 µg/kg BaP equivalents. An evaluation of the PAH profiles in the two higher oyster samples indicated a primary source other than the New Carissa oil. Because shellfish sample BaP equivalents attributable to the New Carissa oil spill did not exceed 10 µg/kg, shellfish harvesting was reopened on 4 March 1999. This study revealed some of the inherent difficulties in attempting to quantify health risks from contaminated shellfish following an oil spill and demonstrated the clear need for standardized protocols for responding to such events.