Page 1000 - The Toxicology of Fishes

980 The Toxicology of Fishes

Controls
Upstream
Downstream
Log (Intersex index + 1) (Rutilus rutilus)

Roach

Adjusted population equivalents
FIGURE 25.7 Correlation between intersex in roach (Rutilus rutilus) and the strength of effluent discharged into the rivers
where the fish were caught. The degree of sexual disruption is presented as the logarithm of the intersex index, where the
intersex index is a measure of the degree of sexual disruption (the degree of feminization of the testis—that is, the proportion
of the testis occupied by oocytes and whether the gonad contains an ovarian cavity; see Jobling et al., 1998, for further
details of the index). The concentration, or strength, of the effluent in the river at each sampling site was approximated by
adjusting the population equivalent (a measure of the strength of the influent entering the sewage treatment works, where
one population equivalent is the amount of biodegradable organic load that has a biochemical oxygen demand of 60 g of
oxygen per day) to allow for the degree of dilution of the effluent in the river. The average dilution factor of the effluent
in the river at the capture sites were calculated using hydrometric data of monthly river flows and actual sewage flows over
a period of several years and for a time period encompassing the life spans of the fish captured wherever possible. Controls
are fish sampled from waters that do not receive treated sewage effluent. Data points for upstream and downstream are fish
sampled above and below major sewage treatment works outfalls, respectively. (Adapted from Jobling, S. et al., Environ.
Sci. Technol., 32, 2498–2506, 1998.)

to the number of intersex fish (Jobling et al., 1998); (2) sewage effluent discharges in the United Kingdom
are predominantly estrogenic (Harries et al., 1997, 1999; Purdom et al., 1994; Rodgers-Gray et al., 2000,
2001) and anti-androgenic (see below); and (3) the male and intersex fish contained VTG in the plasma
(Jobling et al., 1998; van Aerle et al., 2001), which provided strong evidence that some of the populations
of wild roach were being exposed, and responding to, (feminizing) estrogenic contaminants. In the original
field study on wild roach, there was a direct association (positive correlation) between the proportion of
intersex fish and the concentration of the effluent at the different sampling sites (Jobling et al., 1998)
(Figure 25.7). In summary, the results from the field studies on wild cyprinid fish in English rivers provided
very strong evidence that it was the exposure to STW effluent (and the estrogenic chemicals therein) that
caused the disruption in reproductive development (Jobling et al., 1998; van Aerle et al., 2001).
Mesocosm studies exposing roach to treated effluent from the Chelmsford and Great Billings STW
have established that disruption in the development of the gonadal duct occurs as a consequence of
exposure to treated sewage effluent during the period of sexual differentiation (Liney et al., 2005;
Rodgers-Gray et al., 2001) (Figure 25.8). As yet, in our mesocosm studies we have not been able to
induce altered sex cell development in fish. The reasons for this might be that the effluent used for the
exposures did not contain a sufficient concentration of the causative agent or we have yet to expose the
appropriate life stage or to expose the fish for long enough to cause this effect. Expanding on this, in
some of our unpublished studies on wild roach living in U.K. rivers receiving treated sewage effluent
we have shown a positive correlation between age of the fish (length of exposure) and the severity of
the intersex condition. Furthermore, in an analysis of datasets from all of the wild roach caught over