Page 396 - The Toxicology of Fishes

376 The Toxicology of Fishes

(Terman et al., 1999b). Intracellular lipopigment accumulation, indicative of adverse cytological effects,
means that the biomarkers could be signifying exposure and adverse effect. Moreover, both the cyto-
logical and biochemical changes proved reversible, subsiding upon withdrawal of BaP exposure (Au et
al., 2004). Hepatic EROD activity and lipopigments may therefore be useful to indicate recent exposure
of the fish to BaP and PAHs.
Proliferation of the smooth and rough ER systems was repeatedly demonstrated in the hepatocytes of
fish exposed to xenobiotic compounds (Au et al., 1999, 2004; Braunbeck and Appelbaum, 1998; Lemaire
et al., 1992). A dose–response relationship was not obvious between ER proliferation and levels of BaP
(Au et al.,1999). Earlier correlation studies demonstrated inconsistent relationship between biochemical
and hepatic ER changes in response to toxicants. Catfish exposed to the PAH 3-methylcholanthrene
(3-MC) (Schoor and Couch 1979) and barbell and mullet exposed to PCBs (Hugla and Thome, 1999;
Klaunig et al., 1979) showed good correlation between proliferation of ER system with an increase in
EROD/MFO activities. In contrast, subsequent studies on rainbow trout exposed to 3-MC (Kontir et al.,
1984) and speckled trout exposed to chlorinated diphenyl ethers (Chui et al., 1985) showed no corre-
sponding changes in ER with increased EROD/MFO activities.

Linkage of Biological Responses to
Environmental Pollutants in Water and Sediment

Over the past 15 years, numerous field and laboratory studies have been conducted from all over the world
to link biological responses (i.e., molecular, biochemical, histopathological, immunological, physiological)
in fish to environmental pollutants (ANZECC, 1992; Au, 2004; Payne et al., 2003; Stagg et al., 1998),
with an attempt to estimate exposure to and effects of environmental contaminants. A variety of biological
responses, at different levels of organization, are candidate biomarkers or bioindicators for pollution
monitoring. According to Peakall (1992), biomarkers are measures of suborganismal responses (i.e.,
molecular, biochemical, physiological, or histological response) in organisms that can demonstrate expo-
sure to or the effects of environmental contaminants. In general, molecular responses will first occur when
an organism is subject to stress. This is followed by a variety of homeostatic mechanisms in biological
systems that enable the organism to restore to original conditions or to an altered state of equilibrium that
is consistent with life. Biological responses at a higher biological organization (i.e., population, community,
and ecosystem responses) occur if these mechanisms fail to restore to normal conditions.
Many of the molecular biomarkers used in environmental monitoring are measured from liver tissue
of fish. One example is the CYP1A biomarker. The induction of the fish liver cytochrome P450 system,
especially the enzyme 7-ethoxyresorufin-O-deethylase (EROD), has been commonly used as a biochem-
ical biomarker for exposure to PAHs, PCBs, and petroleum hydrocarbons (Ahokas et al., 1976; Au,
2004; Au and Wu, 2001; Au et al., 1999; Behrens and Segner, 2005; Beyer et al., 1994; Bucheli and
Font 1995; Collier et al., 1995; Holdway et al., 1995; Livingstone et al., 1997; Wu et al., 2003).
CYP1A/EROD induction is sensitive to low levels of contamination exposure and could be more sensitive
than direct measures of contaminant residuals (Collier et al., 1995); however, dose–response studies
reveale CYP1A induction reaches maximal levels after exposure to moderate levels of contaminants
(Banka et al., 1997; Fent et al., 1998; Wu et al., 2003). In addition, response time for EROD to PAHs
appeared to be highly variable; for example, hepatic EROD activities in the Solea ovata subsided to
background levels 7 days after an intraperitoneal injection of BaP (Au et al., 1999), while EROD activities
in the dietary BaP-treated grouper fish subsided at week 4 of exposure and throughout the depuration
period (Au, 2004). In contrast, sustained EROD activity was found in rainbow trout fed with 2,3,4,7,8-
pentachlorodibenzofuran during the 31-day exposure period as well as the 180-day depuration period
(Muir et al., 1990). The difference in response time was probably attributable to different half-lives of
these compounds or the route of exposure in fish. Generally, induction of hepatic EROD activity is
sensitive to a wide range of xenobiotics; the increase tends to be transient and subsides shortly after
exposure is terminated. Importantly, a good relationship has been established between hepatic EROD
induction and lipopigment accumulation, a harmful biological effect. The ecological relevance and