Assessment of polycyclic aromatic hydrocarbon exposure in the waters of Prince William Sound after the Exxon Valdez oil spill:: 1989-2005

The synthesis of all reported TPAH concentrations measured in water samples and those estimated from caged and indigenous, intertidal mussels from Exxon and government studies provides an effective means to assess acute and long-term exposure of and ecological risk to offshore and nearshore water-column organisms. Measured TPAH concentrations in more than 2000 water samples and estimated water TPAH concentrations based on PAH concentrations in more than 2700 mussel samples were incorporated into this synthesis. Concentrations of PAH in the upper water column at scattered locations in the spill zone were elevated in the first few weeks after the spill to levels that probably were high enough to cause harm to some individual marine organisms; however, only nine (9) of the 1288 water samples taken along the spill path in PWS in 1989 contained more than 10 ppb TPAH, the State of Alaska's water-quality standard for total aromatic hydrocarbons. TPAH concentrations in shallow water adjacent to oiled shorelines were elevated, but, by the time herring spawned along the shore several weeks after the spill, and when herring larvae and juvenile pink salmon were abundant in coastal waters 2 to 3 months after the spill, average concentrations in the water column were less than 0.5 ppb, lower than concentrations known to cause harm to sensitive early life stages of these species. Water column concentrations of TPAH resulting from the spill returned to background levels by 1990, ranging from 0.001 to 0.1 ppb TPAH. On a larger, population-level and ecologically significant scale, TPAH levels in the water column declined rapidly in the spill area and, after the first few weeks, were not high enough to cause population-level harm to even sensitive early life stages of marine organisms, including herring and salmon. TPAH concentrations measured in spill-zone water samples in 2005 do not indicate any detectable release into the water column of buried oil residues known to still exist at several locations in PWS. The findings from this synthesis are consistent with those from other spills and with other measures of exposure determined in other Exxon Valdez related studies. © 2006 Elsevier Ltd. All rights reserved.