Page 907 - The Toxicology of Fishes

The Effects of Polycyclic Aromatic Hydrocarbons in Fish from Puget Sound, Washington 887

120 Threshold = 290 ppb

DNA adducts (nmol/mol bases) 80 CI: 6–1380 ppb
100

60

40

20

0
1 10 100 1000 10000 100000
Total PAHs (ppb)
FIGURE 22.5 Relationship between levels of PAH-like hepatic DNA adducts in 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.)

contaminants, however, this measure should not be presumed to be diagnostic of PAH exposure in field
situations, unless PAHs are the only likely organic contaminant present, such as following oil spills
(Collier et al., 1996).

DNA Adducts
Covalent binding of carcinogenic PAHs to DNA (DNA adducts) in liver, an initial molecular step in the
chemical hepatocarcinogenesis model (Farber and Sarma, 1987), is observed in several species of fish
exposed to benzo(a)pyrene (BaP) and related PAHs (Collier et al., 1993; Ericson et al., 1999; Sikka et
al., 1991; Varanasi et al., 1989c). A very sensitive technique for determining levels of DNA adducts in
fish tissues is the P-postlabeling (PPL) method, which was developed in Dr. Kurt Randerath’s laboratory
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in the early 1980s (Gupta et al., 1982) and has evolved substantially since then (Reichert et al., 1999).
Currently, the P-postlabeling technique is the most sensitive method for the detection of a wide range
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of bulky, hydrophobic compounds bound to DNA. For hydrophobic, aromatic DNA adducts, such as
PAH–DNA adducts, this method can detect 1 adduct in 109 to 1010 (Gupta, 1985; Reddy and Randerath,
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1986). The versatility and high sensitivity of the assay has led to the broad use of the P-postlabeling
assay in studies with mammals and fish for assessing exposure to environmental genotoxins (Balch et
al., 1995; Dunn et al., 1987; Liu et al., 1991; Poginsky et al., 1990; Ray et al., 1991; Stein et al., 1992;
van der Oost et al., 1994; Varanasi et al., 1989d) and to specific genotoxic compounds, such as BaP and
7H-dibenzo(c,g)carbazole (Ericson et al., 1999; Randerath et al., 1984; Schurdak et al., 1987; Sikka et
al., 1991; Stein et al., 1993; Varanasi et al., 1989c; Watson et al., 1998).
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In 1987, we initiated studies using the P-postlabeling assay to evaluate exposure of marine fish to
environmental carcinogens. These studies have shown that the levels of hepatic DNA adducts in wild
fish positively correlate with the concentrations of PAHs present in marine sediments (Collier et al.,
1993; Stein et al., 1992) (Figure 22.5). Moreover, laboratory studies with model PAHs and sediment
extracts have shown that PAH–DNA adducts formed are persistent and have chromatographic character-
istics similar to DNA adducts detected in wild fish (French et al., 1996; Stein et al., 1993; Varanasi et
al., 1989d) (Figure 22.6). The study by French et al. (1996) of English sole exposed to a gradient of
contaminated sediments showed that the levels of hepatic DNA adducts increased in both a time- and a
dose-dependent manner. These findings suggest that the levels of hepatic DNA adducts found in fish
tissues could function as indices of cumulative exposure to potentially genotoxic environmental contam-
inants, such as carcinogenic PAHs. The use of DNA adducts as an exposure index has several important
features. First, it is a quantifiable measure of the biologically effective dose reaching a critical target site