Page 994 - The Toxicology of Fishes

974 The Toxicology of Fishes

(Flammarion et al., 2000), roach (Minier et al., 2000), and eels (Anguilla anguilla) (R. Billard, pers.
commun.); Sweden—rainbow trout (Larsson et al., 1999); Denmark—brown trout (Salmo trutta) (Bjer-
regaard et al., 2006); Portugal—common carp (Cyprinus carpio) (Diniz et al., 2005); Switzer-
land—brown trout (Salmo trutta) (Vermeirssen et al., 2005); and The Netherlands—bream (Abramis
brama) (Vethaak et al., 2005). Studies exposing fish to effluents from sewage treatment works handling
a mixture of both domestic and industrial influent have been carried out in the United States—common
carp (Folmar et al., 1996); Norway—rainbow trout (Knudsen et al., 1997); The Netherlands—bream
(Vethaak et al., 2005); United Kingdom—rainbow trout and common carp (Tyler et al., 2005); and
China—medaka (Oryzias latipes) (Ma et al., 2005). In all of these studies, estrogenic responses (VTG
induction) in exposed fish were demonstrated, although the magnitude of responses varied widely. The
differences in the estrogenic potency of these effluent discharges probably depends on the influents
received by the treatment works, the level and type of treatment that takes place in the sewage treatment
works (Choi et al., 2006; Kirk et al., 2001; Liney et al., 2005), and the level of influent/effluent dilution.
A study on the Chelmsford sewage treatment work effluent in the United Kingdom showed that the
estrogenic potency of this effluent varies on a seasonal basis; in the winter (November) a 1 in 2 dilution
of the effluent induced a vitellogenic response in rainbow trout (exposed for 3 weeks), whereas in the
summer (August) a 1 in 4 dilution resulted in VTG induction (Harries et al., 1999). Little seasonal
variation occurs in the composition of the Chelmsford STW influent (it is primarily domestic in origin);
therefore, the higher estrogenic potency of the effluent in the summer is likely to be a consequence of
the lower level of dilution of the influent in the treatment works or of the effluent discharged. At this
point in the discussion, it should be emphasized that the vitellogenic responses in caged fish that have
been used to assess the estrogenic potency of STW effluent discharges in all of the studies mentioned
above have been relatively short term (2 or 3 weeks in duration). In a study that exposed juvenile roach
to the Chelmsford STW effluent, it was established that longer term exposures resulted in vitellogenic
responses at lower effluent concentrations; an effluent concentration of 37.9 ± 2.3% induced a vitellogenic
responses after 1 month, but only a 9.4 ± 0.9% effluent concentration did so after 4 months (Rodgers-
Gray et al., 2000). This finding has important implications when assessing the possible impacts of treated
sewage effluents in wild fish that can spend much, even most, of their lives exposed to these treated
effluents in U.K. rivers.
Almost all treated sewage effluents studied in the United Kingdom have been found to be estrogenic,
albeit to varying degrees, but this is not so in some other countries. In a study by Nichols and coworkers
(1999) in central Michigan, no induction of plasma VTG occurred when caged fathead minnows
(Pimephales promelas) were exposed to effluents from wastewater treatment plants handling both
municipal and industrial influents. Similarly, common carp exposed to effluent from large sewage
treatment works in Nevada did not show any consistent elevation in plasma VTG (Snyder et al., 2004).
The reasons for the lack of an estrogenic response in fathead minnows at these sites in Michigan may
relate to a higher efficiency of treatment of the influent or a greater dilution of the effluent compared
with U.K. sewage treatment works. A report that documented the estrogenic activity of wastewater as
it passed through five different sewage treatment works in the United Kingdom showed that where there
was tertiary treatment more than 90% of the estrogenic activity of the influent was removed (Kirk et
al., 2001). In a more recent study of the effluents from 17 sewage treatment works across Norway,
Sweden, Finland, The Netherlands, Belgium, Germany, France, and Switzerland, it was also found that
the nature of the treatment employed in each plant was an important factor determining its effectiveness
at reducing the estrogenicity of the effluent (Johnson et al., 2005).

Estrogenic Activity in English Rivers
The widespread nature of estrogenic STW effluent in England and Wales prompted a series of investi-
gations to determine whether the estrogenic activity in the STW effluent persisted in rivers downstream
from point source discharges. Six rivers throughout England (namely, the Lea, Arun, and Kent Stour in
southern England; the Chelmer and Essex Stour in eastern England; and the Aire in northern England)
were studied at sites downstream of STW discharges (Harries et al., 1995, 1997) (Figure 25.3). The