Endocrine-Disrupting Chemicals and Their Environmental Impacts - Organic Pollutants: An Ecotoxicological Perspective - page 266

population genetic structure. Finally, we provide an analysis on the lessons learned
from endocrine disruption in the context of ecotoxicology more broadly.

15.2 tHe emergence of endocrIne

dISruPtIon aS a reSearcH tHeme

Endocrine disruption as a research theme emerged at the Wingspread Conference in
1991 and through the publications that resulted from this meeting (Colborn and Clement
1992; Colborn et al. 1993). Knowledge that chemicals can modify hormonal systems,
however, was known for many years prior to this, and as early as in the 1930s, Cook
and associates noted that injection of certain “estrus producing compounds” initiated a
sex change in the plumage of Brown Leghorn chickens (Cook et al . 1933). Dodds and
associates, in a series of papers, also in the 1930s (Dodds 1937a, 1937b; Dodds et al .
1937, 1938) similarly identified various synthetic compounds that had estrogenic activ-
ity. Furthermore, natural estrogens in plants (so-called phytoestrogens) were suspected
of causing reproductive disturbances in sheep feeding on clover-rich pastures 25 years
before the Wingspread Conference (Coop and Clark 1966).

15.3 modeS of actIon of endocrIne-
dISruPtIng cHemIcaLS
To date, most EDCs that have been identified work by mimicking endogenous hormones.
These chemicals can act as agonists or antagonists of hormone receptors to either gener-
ate or block hormone-mediated responses. Other mechanisms identified include inhibit-
ing or inducing enzymes associated with hormone synthesis, metabolism, or excretion.
Less well-characterized effect pathways include reacting directly or indirectly with
endogenous hormones or altering hormone receptor numbers or affinities.
The most commonly reported EDCs in the environment are estrogenic in
nature (McLachlan and Arnold 1996), and feminization in exposed males has been
reported in a wide range of wildlife species. The most comprehensively researched
case on the feminization of wildlife is for the intersex (the simultaneous presence
of both males and female sex cells within a single gonad) condition in fish living
in U.K. rivers, described later in this chapter. There is a wide body of literature on
the subject of environmental estrogens, including whole journal issues and special
reports dedicated to the subject and to which we would refer the reader for in-
depth analyses (e.g., Pure and Applied Chemistry , 1998 volume 70 [9]; Pure and
Applied Chemistry , 2003 volume 75 [11-12]; Ecotoxicology, 2007 volume 16 [1];
EPA Special Report on Environmental Endocrine Disruption 1997; Molecular and
Cellular, Endocrinology , 2005 volume 244 [1-2]; Water Quality Research Journal
Canada, 2001 volume 36 [2]). The list of known estrogenic chemicals spans phar-
maceuticals, various classes of pesticides, plasticizers, resins, and many more, and
this list has increased considerably with the systematic screening of chemicals for
this activity (see the following text).
Chemicals with antiestrogenic chemicals have been known to exist for 50
years (Lerner et al. 1958, in Wakeling 2000). These chemicals exert their effects