Page 633 - The Toxicology of Fishes

Toxicity Resistance 613

TCDD LCegg50 (pg/g wet weight) 100000

1000

10
LT BT FH-S RT FM CC LH JM WS NP ZF FH-R
Fish Species Tested
FIGURE 13.8 Variation in response to TCDD (LC 50 and 95% confidence intervals) in early life stages of fish species (see
Figure 13.2) redrawn to include estimated responses of a reference population (white bar) and a tolerant population (New
Bedford Harbor, Massachusetts, gray bar) of Fundulus heteroclitus (i.e., 193 to 275,964 pg/g dioxin equivalents, respectively,
using values from Nacci et al., 2002a, and Van den Berg et al., 1998).

Harbor are heavily exposed to PCBs, including some of the most toxic (dioxin-like) congeners (Black
et al., 1998a; Lake et al., 1995). New Bedford Harbor mummichog exhibited levels of specific PCB
congeners that were lethal to reference fish when the latter were exposed via injection (Black et al.,
1998a) or diet (Gutjahr-Gobell et al., 1999). As a result, Black et al. (1998b) suggested that New Bedford
Harbor fish may also exhibit abnormally high mortality in the field; however, a series of studies confirmed
that, despite extreme tissue PCB concentrations and modeled predictions of contaminant risks (Munns
et al., 1997), New Bedford Harbor mummichogs are reproductively prolific (Nacci et al., 2002d), have
high condition indices (Nacci et al., 2001b), and have nearly normal levels of stored vitamin A (Nacci
et al., 2001). Vitamin A is considered a sensitive indicator of DLC toxicity in many vertebrate species
(Fletcher et al., 2001). Complementary studies suggest that demographic compensation (e.g., increased
reproductive effort) and migration (i.e., from less-contaminated populations) do not play important roles
in supporting a persistent population in New Bedford Harbor (Nacci et al., 2002b,d, 2007); therefore,
tolerance to PCBs was proposed to explain NBH mummichog population persistence.
In subsequent studies with New Bedford Harbor mummichog, Nacci et al. (1999) reported that the
acute toxicity of PCB 126 (one of the most toxic DLCs) was approximately 100-fold higher in progeny
of reference fish than in progeny of New Bedford Harbor fish. The significance of the difference in
sensitivity between populations within a single fish species is revealed when compared to sensitivity
variation among fish species for TCDD (Figure 13.2). When LC values are transformed into toxic
50
equivalency values that reflect sensitivity to TCDD (using values from Nacci et al., 2002a, and Van den
Berg et al., 1998), the intraspecies range for this single fish species (mummichog) exceeds the interspecies
sensitivity range among tested freshwater fish (Figure 13.8).
Tolerance to DLCs was observed in F and F generations of New Bedford Harbor mummichog and
2
1
therefore appears to involve genetic adaptation (Nacci et al., 1999, 2002a). Further, concentrations of PCB
126 producing early-life-stage lethality in hybrid embryos (i.e., New Bedford Harbor × reference mum-
michog) were intermediate in sensitivity between the parental populations, and sensitivities to PCB 126
were similar in hybrids whether of maternal or paternal origins from New Bedford Harbor, suggesting
minimal contributions from non-inherited maternal effects (Nacci et al., 1999). Laboratory exposures were
transformed into estimates of tissue concentrations and compared to concentrations measured in eggs from
New Bedford Harbor mummichog to estimate effects of field exposures (estimated from chemical mea-
surements of sediment cores (Nacci et al., 2002d). These results confirmed that mummichog embryos