Page 906 - The Toxicology of Fishes

886 The Toxicology of Fishes

10000

r 2 = 0.95
1000
FACs in Bile

100

10
1 10 100 1000 10000 100000
PAHs in Sediment (ng/g dry wt.)
FIGURE 22.4 Relationship between levels of fluorescent aromatic compounds in bile of oyster toadfish and concentrations
of polycyclic aromatic hydrocarbons (PAHs) in sediment of the Elizabeth River. (From Collier, T.K. et al., Environ. Sci.,
2, 161–177, 1993. With permission.)

William Sound after the Exxon Valdez spill are very dissimilar to those of fish exposed to contaminants
from urban sites (Figure 22.3). The source of contamination suggested from the HPLC chromatogram
can often be substantiated by examining the relative proportions of PAH metabolites determined by gas
chromatography–mass spectrophotometer (GC–MS) analysis of bile (Krahn et al., 1987, 1993). Bile of
fish exposed to PAHs from urban sites typically contains high proportions of four- to six-ring PAHs from
pyrogenic sources, whereas the bile of fish exposed to crude oil contains much larger proportions of
metabolites of alkylated naphthalenes, phenanthrenes, and dibenzothiophenes than bile from urban fish.
Laboratory studies have shown that biliary fluorescent aromatic compound (FAC) levels increase in
a dose-dependent manner with exposure to PAHs, and field studies have demonstrated strong and
consistent correlations between biliary FAC concentrations in fish and sediment PAH concentrations at
sites where the animals are collected (Figure 22.4). Biliary FAC concentrations, however, reflect relatively
short-term exposure to PAHs. Concentrations typically increase very quickly with exposure, within a
day, but decline to baseline levels within about 2 to 4 weeks of exposure (Anulacion et al., 1995; Collier
and Varanasi, 1991).

CYP1A Activity
One of the earliest changes associated with exposure to contaminants is induction of cytochrome P450-
associated enzymes (CYP) in the liver, especially CYP1A, which is largely responsible for metabolism
of PAHs and a variety of other toxic compounds (Buhler and Williams, 1989; Goksøyr and Forlin, 1992).
Although several methods are available to assess induction of CYP1A in fish, the most common methods
are catalytic assays to measure the functional activity of the enzyme—for example, aryl hydrocarbon
hydroxylase (AHH) and ethoxyresorufin-O-deethylase (EROD) activities—and immunoquantitation of
the CYP1A protein directly by methods such as an enzyme-linked immunosorbent assay (ELISA). Three
of these measures (AHH activity, EROD activity, and CYP1A quantitation by ELISA) were evaluated
in Puget Sound flatfish species during a year-long field study (Collier et al., 1995). Each measure could
detect significant between-site differences that were consistent with PAH concentrations in sediment
where the fish were collected, but AHH activity measured by a standardized protocol showed the least
amount of unexplained variability and was the measure most sensitive to site differences. For this reason,
in our studies, we have primarily used measurement of hepatic AHH activity for monitoring of CYP1A
induction in fish. We believe that this method is particularly useful for analysis of trends in contaminant
exposure in fish (Collier et al., 1998a). Because CYP1A is inducible by a wide variety of organic chemical