Releasedin 1962, Rachel Carson’s book Silent Spring marked aturning point in increasing public awareness that the largely unregulated use of pesticides could have severe and long-lasting consequences for wildlife (Carson, 1962). We now know that pesticides, such as dichlorodiphenyltrichloroethane (DDT), have caused eggshell thinning in birds, altered fecundity and fertility in Œsh, and developmental abnormalities in most taxa studied to date (Colborn et al., 1993). EDCs are comprised of adiverse group of industrial and agricultural chemicals, as well as several naturally occurring ones (Table 7.1). Many EDCs behave like estrogen and interact with the estrogen receptor. Anumber of EDCs found in sewage treatment ef«uent have been shown to feminize male Œsh living downstream (Tyler and Jobling, 2008), and indeed a number of ef«uent chemicals share a similar structural relationship with the phenolic ring of estrogen. Tens of thousands of man-made chemicals including plasticizers, industrial compounds, personal care products, pharmaceuticals, and avarietyof others regularly make their way into aquatic systems. Following decades of Œeld research and laboratory investigations, our knowledge and detection of EDC-induced dysfunction have increased dramatically (Pait and Nelson, 2002, Hoffmann et al., 2006, 2008, Hook et al., 2006, Samuelsson et al., 2006, Chandrasekar et al., 2011, Webb and Doroshov, 2011), and studies of EDC exposures are now experiencing aparadigm shift driven by several important discoveries: (1) EDC effects can manifest in decidedly different ways, often permanently, depending on whether the animal is exposed as an embryo, larva, or adult; (2) the effects of EDC exposure in embryos can be delayed,
FIGURE 7.1 Environmental contaminants can disrupt normal endocrine function through a variety of pathways. Common targets of contaminant-induced dysfunction include the gonad, thyroid, brain, and clearance of steroid hormones by the liver. Other factors such as diet, stress, temperature, and photoperiod can also modulate endocrine function. (Drawing courtesy of David Basti.)
TABLE 7.1 Effects of Endocrine-Disrupting Contaminants in Fish
and not manifest until adulthood; and (3) high-dose exposures do not necessarily predict low-dose effects, and dose response curves that are not linear, or non-monotonic, are not uncommon in studies of EDC-induced dysfunction (Sumpter and Johnson, 2005).