Page 1007 - The Toxicology of Fishes

Estrogenic Effects of Treated Sewage Effluent on Fish in English Rivers 987

It is worth emphasizing that care has to be taken when ascribing species sensitivities to natural (and
synthetic) estrogens, because the stage of the reproductive cycle at the time of exposure may affect
the magnitude of the response (Billard et al., 1981). The effects of estradiol-17β in the medaka can
illustrate this. Iwamatsu and coworkers (1999) found that exposure of medaka early life stages to 1
µg/L estradiol-17β (for 20 days from fertilization to 10 days post-hatch [dph]) induced gonadal
feminization, but ten times this amount of estradiol-17β was required to cause sex reversal in adult
medaka. Together, these laboratories studies strongly support the contention that natural steroid estro-
gens present in STW effluents are contributing to the altered patterns of gonadal development seen in
wild fish in U.K. rivers. High concentrations of estradiol-17β (1 to 10 µg/L) have also been shown to
inhibit both sexual behavior and the development of secondary sexual characteristics in fish, including
goldfish (Carassius auratus) (Bjerselius et al., 2001) and guppy (Poecilia reticulata) (Bayley et al.,
1999), but whether the lower levels of steroidal estrogens present in English rivers have discernible
effects on fish behavior and secondary sexual characteristics has not been studied and indeed will be
more difficult to quantify.
Ethinylestradiol is the most potent inducer of vitellogenesis reported to date, and exposure of male
rainbow trout to concentrations in the water of only 0.1 µg/L and above causes a rapid and pronounced
synthesis of VTG (3-week exposures) (Purdom et al., 1994; Sheahan et al., 1994). In male adult
fathead minnow exposed to ethinylestradiol for 3 weeks, the least effective concentration for VTG
induction was similarly less than 1 µg/L (our own unpublished data). The potency of ethinylestradiol
exceeds that of natural steroid estrogens in vivo. For VTG induction in fish, ethinylestradiol is between
20 and 50 times more potent than estradiol-17β (Thorpe et al., 2001, 2003), and for induction of
intersex it is up to 100-fold more potent (Metcalfe et al., 2001). The greater potency of ethinylestradiol
compared with natural steroid estrogens is likely to be due to the 17α-ethinyl group that increases its
longevity by reducing the rate of metabolism at C-16 and C-17 (Guengerich, 1990) and its capacity
to bioaccumulate (10,000 times in bile in rainbow trout after only a 3-week exposure) (Larsson et al.,
1999). In the rainbow trout, maximal rates of VTG synthesis have been shown to occur at concentra-
tions of ethinylestradiol at, or below, a concentration of 10 µg/L (Purdom et al., 1994; Thorpe et al.,
2001, 2003).
Less is known about the reproductive consequences of exposure of oviparous animals to ethinylestra-
diol; however, it is known that a single dose of 2 µg/L ethinylestradiol in water can significantly retard
the growth and development of the testes in maturing male trout (Jobling et al., 1996). In a study on
the fathead minnow, exposure to 10 µg/L ethinylestradiol for only a brief period during the period of
sexual differentiation (10 to 15 dph) has been shown to result in feminization of the gonadal duct
(formation of an ovarian cavity) in 60% of the male population (Figure 25.12) (van Aerle et al., 2002).
Furthermore, exposure of mature fathead minnows to ethinylestradiol at a concentration of 10 µg/L for
a period of 4 weeks resulted in a reduction in the number of eggs oviposited (Lange et al., 2001). Recent
studies have shown that exposure to low microgram-per-liter concentrations of ethinyloestradiol impact
negatively on reproductive output in zebrafish (Hill and Janz, 2003). Importantly, exposure of zebrafish
for long periods to only 5 µg/L has been shown to result in reproductive failure in the population (Nash
et al., 2004). Thus, although the concentrations of ethinylestradiol in English rivers are likely to be very
low (low micrograms per liter or less) (Desbrow et al., 1998; Rodgers-Gray et al., 2001), the extreme
potency of this synthetic estrogen, together with its capacity to bioaccumulate, means that, even at these
concentrations, it could be a major contributor to the estrogenic responses observed in fish exposed to
domestic effluents in U.K. rivers.

Alkylphenolic Chemicals

Concentrations in Effluents and Rivers
Alkylphenol polyethoxylates (APEOs) are nonionic surfactants that have been used for over 40 years,
primarily in the manufacture of plastics, elastomers, agricultural chemicals, paper (pulping and de-
inking), and industrial detergent formulations. APEOs are one of the largest volume surfactants in