Endocrine-Disrupting Chemicals and Their Environmental Impacts - Organic Pollutants: An Ecotoxicological Perspective - page 283

30 µg/L (Sheldon and Hites 1978; Fatoki and Ogunfowokan 1993) in the Western
world, which is below the no-effect level for wildlife species studied, but concentra-
tions in developing countries are often significantly higher. In Nigeria, for example,
DBP concentrations have been reported to be as high as to 1472 mg/L in river water
(Fatoki and Ogunfowokan 1993).
15.6.9 n a T u r a l edc s
All the foregoing examples, with the exception of some of the steroidal estrogens,
are synthetic chemicals. Naturally occurring estrogens produced by fungi (myco-
estrogens) and plants (phytoestrogens) can also have endocrine-disrupting effects.
We described one example of this earlier, where exposure to high level of phy-
toestrogens affects the reproductive biology of sheep (Adams 1998). Phyto- and
mycoestrogens enter the aquatic environment, and although detailed studies are
lacking, concentrations recorded range between 4 to 157 ng/L (Stumpf et al. 1996;
Erbs et al. 2007). Their effects in wildlife are largely unstudied when compared to
that for other EDCs, but controlled exposures to phytoestrogens have been shown to
induce estrogenic responses, including induction of VTG synthesis in fish (Pelissero
et al. 1991; Pelissero et al. 1993) and infertility and liver disease in captive cheetahs
(Setchell et al. 1987).
Although the likelihood for biologically harm has not been assessed fully, for most
EDCs the exposure concentrations in ambient environments (away from hotspots of
chemical discharges) would suggest that they are insufficient to do so. Exceptions
to this include the case studies detailed in the previous section. It should, however,
also be emphasized that most studies on the effects of EDCs under controlled labo-
ratory conditions have not considered long-term chronic exposures encompassing
full life cycles, and some wildlife species are exposed lifelong to some of the EDCs
described earlier.
15.7 effectS of mIxtureS
Wildlife, especially organisms living in and/or closely associated with the aquatic
environment, are often exposed to highly complex mixtures of EDCs, and this com-
plicates identification of the causality of the physiological disruptions seen. As an
example, although steroid estrogens and alkylphenolic chemicals have been identi-
fied as major contributors to the feminization of wild fish, many other estrogenic (and
antiandrogenic) chemicals occur in WWTW effluents, including plasticizers such as
phthalates, bisphenols, and various pesticides and herbicides, which could poten-
tially contribute to the feminized effects. Individually, these chemicals are unlikely
to play a significant role in the disruption of sex in wild fish, given their relatively
lower estrogenic potency compared with steroidal estrogens, but as part of a mixture
they may contribute to a more significant effect. Exposure studies that replicate envi-
ronmentally relevant mixtures of EDCs are lacking, but simple environmental mix-
tures of akylphenolic chemicals, pesticides, and plasticizers have been shown to be
additive in their estrogenic effects, both in vitro (Silva et al . 2002) and in vivo in fish
(Thorpe et al . 2001, 2003, 2006; Brian et al . 2005). Indeed, it has also been shown