Page 948 - The Toxicology of Fishes

928 The Toxicology of Fishes

Although many of the desired components were studied, some parts of the assessment puzzle are
incomplete. When data were incomplete, findings were compared with results of concurrent laboratory
studies or with previously published results.

Measurements of Potential for Exposure
The potential for exposure was documented by measuring hydrocarbon concentrations in water. Several
agencies and individuals recorded visual observations of surface oiling, but these observations often varied.
There seemed to be less controversy over hydrocarbon concentrations measured in the water column.
Exxon-funded scientists reported that polynuclear aromatic hydrocarbons (PAHs) in surface water (depth
up to 5 cm) from oiled sites averaged 0.9 µg/L in late April and early May 1989 (Neff and Stubblefield,
1995). Similarly, Trustee Council-funded scientists reported that PAH concentrations at a depth of 1 m
were 0.5 to 1.0 µg/L in mid-April, but at those depths PAHs were detectable only near heavily oiled
beaches by early May (Short and Harris, 1996). Both studies reported no significant PAH residues in the
water column by 1991. Fish tissues—including eggs—rapidly metabolize petroleum hydrocarbons (Collier
and Varanasi, 1991; Thomas et al., 1997); therefore, analysis of these samples usually does not provide
an accurate assessment of cumulative exposure over a period of several days. Exposure to sessile life
stages such as eggs can be better estimated by determining hydrocarbon concentrations in mussels sampled
from the same areas as eggs. In PWS, mussels were selected as a good model for previous hydrocarbon
exposure (Hose et al., 1996) because they do not readily metabolize petroleum hydrocarbons.
The primary controversy over the measured hydrocarbon concentrations in water was the potential
significance of the findings. The water-soluble fraction* of crude oil is toxic to Pacific herring embryonic
development at 0.1 to 1.0 mg/L (Cameron and Smith 1980; Kocan et al., 1996a; Smith and Cameron,
1979). Based in part on these reports, Exxon-funded scientists concluded that “it is likely that the safety
factor (ratio of effects concentration to environmental concentration) for marine organisms in PWS
following the spill was in excess of 100 and possibly as high as 10,000 during April and May 1989”
(Neff and Stubblefield, 1995). In contrast, evidence provided by Trustee Council-funded scientists from
field and laboratory studies supported the conclusion that hydrocarbon levels in PWS were indeed
significant (see the The Effects of Exposure section, below) (Carls et al., 1999; Marty et al., 1997). The
reason for this difference is that earlier studies determined toxicity based on the concentration of the
water-soluble fraction of crude oil, but the PAH component of crude oil is more toxic on a molar basis
(Lee and Page, 1997).

Measurements of Actual Exposure
Actual exposure was determined by measuring hydrocarbons or their metabolites in fish tissues. Exxon-
funded scientists identified hydrocarbons in eggs from highly contaminated sites (Pearson et al., 1995).
Trustee Council-funded scientists did not measure hydrocarbon concentrations in eggs; instead, they
determined the hydrocarbon concentrations in nearby mussels. Actual hydrocarbon exposure to Pacific
herring juveniles was not reported, but exposure was reported in adults. Tissue PAH concentrations in
1989 were higher in adults from oiled sites than in adults from reference sites, but site-related differences
were no longer significant in 1990 (Marty et al., 1999). Corroborative evidence that Pacific herring were
exposed to Exxon Valdez oil includes contaminated or possibly contaminated bile in two of two herring
examined in 1989 (Haynes et al., 1995).

The Effects of Exposure
The effects of the oil on Pacific herring were documented in several studies. In 1989, developing eggs
were removed from reference sites and from sites that were thought to have been exposed to oil in
PWS; they were incubated in the laboratory and examined for abnormalities less than 24 hours after

* Water-soluble fraction vs. polynuclear aromatic hydrocarbons: Primary components of the water-soluble fraction of crude oil
include low-molecular-weight compounds such as mono- and bicyclic hydrocarbons. Polynuclear aromatic hydrocarbons have
relatively higher molecular weights and include naphthalenes, phenanthrenes, dibenzothiophenes, fluorenes, and chrysenes.