STUDY OF THE FATES AND EFFECTS OF THE EXXON-VALDEZ OIL-SPILL ON BENTHIC SEDIMENTS IN 2 BAYS IN PRINCE-WILLIAM-SOUND, ALASKA - 1 - STUDY DESIGN, CHEMISTRY, AND SOURCE FINGERPRINTING

This study was conducted to assess the subtidal effects of the Exxon V aldez oil spill in a large embayment in Prince William Sound, AK. A st ratified random-sampling design was used to compare stations in an oil ed bay, the Bay of Isles, with stations in Drier Bay, a bay that recei ved little impact from the spill. The study included sediment chemistr y, benthic ecology, and bioaccumulation elements. Only the results on chemistry of the oil in the bottom sediments are reported here. Analys es of sediment samples revealed four types of polycyclic aromatic hydr ocarbons (PAH) in the two bays: (1) Alaska North Slope (ANS) crude oil attributable to the spill, (2) natural oil seep-derived background, ( 3) pyrogenic, and (4) diagenetic. The Bay of Isles subtidal sediments contained significantly higher levels of weathered ANS-PAH attributabl e to the spill than did Drier Bay. However, the levels of ANS-PAH in t he Bay of Isles were generally lower than those of the petrogenic back ground PAH naturally present in the subtidal sediments of the sound. T his natural petrogenic background PAH component increased in concentra tion with increasing depth zone (and increasing sediment clay content) for each bay. Drier Bay, a location of past cannery and mining activi ty, had significantly greater concentrations of pyrogenic PAH than did the Bay of Isles. All sediment PAH concentrations were well below the effects range-low (ER-L) sediment toxicity threshold value of 4000 ng /g for total PAH. The highest sediment total PAH concentration (1500 n g/g) occurred in Drier Bay, and the highest sediment ANS (spill)-PAH c oncentration (201 ng/g) occurred in the Bay of Isles. There is no evid ence far large-scale offshore transport of Exxon Valdez crude to the s ubtidal sediments.