EDCs comprise a diverse group of compounds displaying a broad array of molecular structures and physiochemical properties. They include natural steroidal hormones such as 17b-estradiol, estrone and estriol, synthetic hormones such as 17a-ethinyl estradiol found in birth control formulations and many other industrial chemicals such as chlorinated pesticides, polychlorinated biphenyls phthalate esters and alkylphenols.
The endocrine system regulates development, growth, reproduction, and behavior through an intricate system of hormones (Richardson 2004). Exposure to various hormonally active compounds can result in decreased androgen production (demasculinization) or increased estrogen production (feminization) in the males of many aquatic species (Milnes, Bermudez et al. 2006) As the fish endocrine system shares many similarities with those of higher vertebrates including humans, fish have been used to monitor exposure to EDCs in aquatic environments (Zeng, Shan et al. 2005). EDCs have been shown to affect the form and function of reproductive systems skewing male-female ratios in fish.
Vitellogenesis is a critical part of the reproductive process. It involves the synthesis of a large molecular weight protein precursor, vitellogenin (VTG), in the liver. VTG transported through the blood circulation to the ovary is thus sequestered by growing oocytes and proteolytically cleaved into the major yolk protein components (Soverchia, Ruggeri et al. 2005). Effluent from sewage-treatment containing estrogenic disrupting chemicals, or mixtures of EDC chemicals, stimulates vitellogenin synthesis in male fish (Sumpter 1995). Elevated plasma levels of vitellogenin have been observed in male fish exposed to EDC concentrations as low as 1 to 10 nanograms per liter in aquatic environments.
EDCs disrupt gonadal differentiation and can result in the simultaneous presence of ovarian and testicular tissue in the same gonad creating a condition referred to as intersex (Milnes, Bermudez et al. 2006). This intersex phenomenon of feminized males is characterized by the occurrence of oocytes scattered throughout the testis or within distinct regions of ovarian tissue that are well delineated from testicular tissue (Nolan, Jobling et al. 2001).
Examples of wild fish populations exhibiting intersex gonads include flounder taken from Tokyo Bay (Hashimoto, Bessho et al. 2000); rainbow trout (Tyler and Routledge, 1998), gudgeon (Gobio gobio) (vanAerle, Nolan et al. 2001) collected from rivers in the UK polluted with estrogenic sewage treatment effluent; wild barbell from polluted portions of the Po River in Italy (Vigano, Arillo et al. 2001), and lake whitefish (Coregonus clupeaformis) collected from the St. Lawrence River in Quebec, Canada (Mikaelian, Lafontaine et al. 2001).
Studies show that reproductive effects from anthropogenic 17b-estradiol are dependent of the time and concentration of exposures in zebrafish. Some of these effects are reversible while others are permanent and those that occur in early life stages are brought about by low concentrations (Brion, Tyler et al. 2004). Fathead minnows (Pimephales promelas) exposed to an environmentally relevant concentration of ethinylestradiol for short intervals in fish early life-stages showed vitellogenic and gonadal responses where 60% of the male fish studied had feminizing transformations (vanAerle, Pounds et al. 2002)
Endocrine disrupting chemicals can also substantially affect gamete production and fertility. General decreases in spermatogenesis and ejaculated sperm counts have been observed in several species, including goldfish treated with 17b-estradiol (Schoenfuss, Levitt et al. 2002), adult zebrafish after 24 days of laboratory exposure to 17-b-ethynylestradiol (VandenBelt, Verheyen et al. 2001), adult Japanese medaka exposed to 4-tert-octylphenol (Gronen, Denslow et al. 1999), swordtails (Xiphophorus helleri) exposed to nonylphenol (Kwak, Bae et al. 2001), and adult and sexually developing juvenile guppies exposed to vinclozolin and p; p’-DDE (Baatrup and Junge 2001); (Bayley, Nielsen et al. 1999)). Van den Belt et al. (2002) noted that spermatogenesis recovered when fish were removed to clean water.
Endocrine hormones are correlated with the mating displays of guppies and the secretion of pheromones in goldfish, but various EDCs can alter the performance of these reproductive behaviors. In adult male guppies exposed to EDCs, the number of sexual displays directed toward females were significantly reduced (Baatrup and Junge 2001).
Many natural and synthetic EDCs are continuously released in the aquatic environment when sewage treatment plants (STPs) are unsuccessful in completely removing them (Ternes, Stumpf et al. 1999). Other EDCs enter the environment from agricultural runoff from fields treated with manure as fertilizer (Pedersen, Soliman et al. 2005). The removal of EDCs from STP effluent is very complex and currently not well understood (Servos, Bennie et al. 2005). STPs systems designed for nitrification and denitrification may appreciably eliminate natural and synthetic estrogens (Andersen, Siegrist et al. 2003). However, storm events frequently overwhelm STPs and untreated sewage is often released into surface waters. Furthermore, municipal effluents may contain a wide variety of other industrial and domestic EDCs such as alkylphenols, bisphenol-A, as well as many pharmaceuticals. The environmental impact of the complex mixtures in effluents remains poorly understood.(Servos, Bennie et al. 2005)
Recent studies show the potential for EDCs to be easily distributed in the environment and their physicochemical properties can enable them to accumulate in river sediments (Kuster, Alda et al. 2004) Recent data suggest that hormones in readily measured quantities can be transported considerable distances from the source of pollution. Significant levels of estrogens were detected over a 100-km section of the Lower Jordan River below a major sewage treatment facility (Barel-Cohen, Shore et al. 2006). Detectable levels of estrogens were observed downstream from an STP effluent discharge near Bordeaux, France along the Jalle d’Eysines River (Labadie and Budzinski 2005). The effects of EDCs on fish and wildlife have been well-documented (Milnes, Bermudez et al. 2006). Environmental impacts may be profound at levels as low as ~1 ng l-1 in aquatic species (Hansen, Dizer et al. 1998).
Many municipalities utilize surface water as a source of drinking water. Drinking water supplies downstream from effluent discharges containing EDCs clearly raises concerns over the removal of these compounds by common drinking water treatment processes. Conventional treatment regimes may have low removal of many EDC. Therefore, knowledge of source concentrations is essential for devising efficient drinking water treatment to avoid drinking water contamination by EDCs. Ozonation, activated carbon, and bank filtration have shown potential for removing EDCs (Richardson 2004) (Westerhoff, Yoon et al. 2005).
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