Wastewater effluent impacts: endoctrine disrupters

Endocrine Disruptors

Environmental contaminants can affect the reproduction of fish and wildlife through a wide variety of mechanisms. Recently, concern has arisen about chemicals that can bind to the estrogen receptor, thereby regulating the activity of estrogen-responsive genes. Estrogens play a critical role in controlling reproductive processes in fish. One of the functions of natural estrogens in fish is to stimulate the liver to produce vitellogenin, a large phospholipoprotein, which is released into the blood stream and sequestered by developing oocytes for production of egg yolk. In maturing female fish, vitellogenin is a

Major constituent of the blood proteins whereas in male fish it is not normally present in any appreciable amount. However, if male fish are exposed to estrogens, vitellogenin can be produced at similar levels to that found in maturing females. Although the implications of this induction on reproductive function are not fully understood, the presence of vitellogenin has been used as a sensitive indicator of exposure of fish to exogenous estrogens.

Sewage effluents appear to have the potential to cause endocrine disruption in fish. Studies in the early 1980’s in the River Lea, UK, reported a low incidence of intersex in the roach (Rutilus rutilus) exposed to sewage effluents. Follow-up studies have demonstrated that the effluents were strongly estrogenic with many of the exposures resulting in plasma vitellogenin levels in fish being elevated to the levels expected in gravid females (Purdom et al. 1994). This response has been observed in fish collected immediately downstream of many sewage treatment plants in the UK and the response persists in some cases several kilometers downstream of the outfalls (Harries et al. 1997). This response has also recently been reported in wild fish at North American sites (Folmar et al. 1996).

There are many compounds which are capable of  binding to estrogen receptor and causing estrogenic responses, e.g., alkylphenol polyethoxylates, bisphenolics, phthalates, p,p’-DDE (White et al. 1994; Soto et al. 1995; Jobling et al. 1996; Routledge and Sumpter 1996). Municipal effluents are complex mixtures which contain a variety of contaminants which may be capable of endocrine disruption. There is also growing evidence that non-ionic surfactants in detergents can act as estrogen mimics (Jobling and Sumpter 1993). Measurable quantities of nonylphenol ethoxylates and their degradation products have been found in a variety of MWWEs and sludge in southern Ontario, Quebec and Atlantic Canada, and in surface waters in the Great Lakes Basin (Bennie et al. 1996, 1997; Lee et al. 1997). Exposure of rainbow trout to several alkylphenolics resulted in the synthesis of vitellogenin and inhibition of testicular growth (Jobling et al. 1996). Nonylphenol has recently been shown to cause intersex in Medaka (Gray and Metcalfe 1997). Alkylphenol polyethoxylates and several degradation products which are estrogenic are expected to partition to sewage sludge and aquatic sediments and be persistent in the environment (White et al. 1994; Jobling and Sumpter 1993). Although elevated vitellogenin production may be caused by several estrogenic compounds in effluent, the majority of the response in a sewage effluent has recently been isolated into a single chromatographic fraction (Routledge et al. 1995). This suggests that the response is largely due to a single chemical or group of very similar chemicals, at least for the effluent studied.  Following a toxicity identification evaluation approach, Desbrow et al. (1996), were able to isolate and identify natural and synthetic estrogens in the bioactive fractions (e.g., 17a -ethynylestradiol, 17b -estradiol and estrone). Although these chemicals are found at very low concentrations, they were at levels (low ng/L) which would explain the vitellogenin induction observed in fish (Desbrow et al. 1996). Schweinfurth et al. (1996) reported similar low levels of 17a -ethynylestradiol in surface waters.  Although this work strongly suggests that natural and synthetic estrogens are likely responsible for the estrogenic responses observed near sewage outfalls, the levels of nonylphenols in municipal effluents which receive textile or other industrial effluent inputs may be high enough to explain the responses at these sites.  Blackburn and Waldock (1995) measured concentrations of nonylphenol (24-53m g/L) downstream of a wool scouring plant, discharging through a municipal treatment plant, which were sufficiently high to explain the observed effects (Harries et al. 1997).

In Canada, the extent of estrogenic effects attributable to sewage effluents has not been established. Although some chemical characterization of effluents has recently been undertaken (Bennie et al. 1996, 1997; Lee et al. 1997), the causal relationship between the chemical constituents, such as nonylphenols and synthetic estrogens, and possible estrogenic effects has not been established. There are potentially several responsible chemicals and their toxicity and bioavailability are dependent on the characteristics of the effluent and the receiving environment. A comprehensive toxicity (estrogenicity) analysis of MWWE coupled with a detailed survey of the physiological status of fish from receiving waters is required to fully evaluate the extent and potential impact of endocrine disrupting compounds in the Canadian environment.

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