Page 1003 - The Toxicology of Fishes

Estrogenic Effects of Treated Sewage Effluent on Fish in English Rivers 983

Fertilization success (proportion of eggs that gave rise to live hatchlings)

Histologically “Males” with “Males” with “Males” with
normal ovarian a few more than
males cavity only oocytes in half gonad
testis as ovarian
tissue
Intersex Fish

FIGURE 25.10 Relationship between the degree of sexual disruption and reproductive performance (proportion of eggs
that gave rise to live hatchlings) in wild roach (Rutilus rutilus) sampled from the River Arun. Intersex fish were grouped
into three classes according to the degree of severity of the intersex condition: feminized ducts only, gonads containing
some oocytes, and 50% or more of the gonad female. Asterisks represent significant differences between intersex fish and
males (∗∗∗p < 0.001).

responsible for adverse effects observed in the field is difficult. Testimony to this is the fact that there
are very few examples where an adverse effect in any aquatic wildlife species has been conclusively
linked to a specific chemical. In the United Kingdom, the search for the causative agents in STW effluents
and rivers responsible for VTG induction and feminization of male fish (intersexuality) has focused on
estrogens because of the estrogen-dependent nature of the responses seen. Effluents, however, may
potentially contain a wide variety of estrogens, including steroidal estrogens, phytoestrogens, mycoestro-
gens, and manmade estrogen mimics. Indeed, it has now been established that a wide variety of synthetic
chemicals are capable of mimicking estrogens, and they are structurally diverse. These chemicals include
alkylphenolic chemicals, many of which result from the breakdown of non-ionic surfactants (Jobling
and Sumpter, 1993; Nimrod and Benson, 1996); plasticizers, such as bisphenol-A (Brotons et al., 1995;
Krishnan et al., 1993; Sohoni et al., 2001) and some phthalates (Jobling et al., 1995; Harries et al.,
1997); and certain pesticides and herbicides and their products of metabolism and environmental deg-
radation (Soto et al., 1995; Tyler et al., 2000), many of which are likely to enter sewage treatment works.
Most of these estrogen mimics are weakly biologically active compared with steroidal estrogens (Tyler
et al., 1998) and may only cause endocrine modulation in wildlife if: (1) they circulate in the environment
at high concentrations, (2) their breakdown is slow or they bioaccumulate, or (3) they are in widespread
regular use and are entering the environment almost constantly. All of these criteria, however, are true
for certain manmade chemicals, such as alkylphenols (see below).
A toxicity identification evaluation (TIE) approach has been used successfully to identify the causative
agents in English STW effluents for some of the estrogenic effects in fish (Desbrow et al., 1998; Rodgers-
Gray et al., 2000, 2001). In the work of Desbrow and colleagues, effluent from seven English sewage
treatment works receiving primarily domestic inputs were analyzed for estrogenic contaminants: South-
End-on Sea, where the effluent had only primary treatment before being discharged into the marine
environment; Harpenden, Rye Meads, and Deephams sewage treatment works in the catchment of the
River Lea; Horsham sewage treatment works, which discharges into the River Arun (all of these effluents
were known previously to be estrogenic); Billing sewage treatment works, which discharges into the