Page 948 - The Toxicology of Fishes
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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.
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