The Effect of Exposure to Synthetic Estrogen on Fish Populations
In a world full of pharmaceutical drugs and hormone replacement, pharmacists and toxicologists alike squabble with the implications of improper chemical disposal. Fewer professionals fully analyze how these chemicals are making it into the aquatic environment in ways other than improper disposal and to the extent in which synthetic reproductive hormones may affect other populations after serving their prescribed purpose. With a growing population, the use of prescriptions drugs including hormone replacements like synthetic estrogen and androgen are increasing as well. Ethinyl Estradiol is a synthetic estrogen that is used in nearly all hormonal birth control methods, including the patch, vaginal ring, and hundreds of variations of the pill. This form of synthetic estrogen is present in aquatic environments around the globe and research shows that it may be threatening future populations by affecting the reproductive ability of many fish species.
In 2011, approximately 31% of women of reproductive age (15-44 years) in the United States used hormonal birth control containing synthetic estrogen (Jones). Therefore, of the roughly 61,488,000 women in the country in that year, an estimated 19,061,280 women were on hormonal birth control (United States Census Bureau). Unfortunately, not all the active hormones in the medication were metabolized by this population. In fact, the human body excretes approximately 68% of the synthetic estrogen used to manufacture birth control, which then travels on to municipal wastewater treatment centers (Fears). Currently, there are no regulatory requirements governing how much synthetic estrogen these wastewater treatment sites can release into the environment, therefore, these concentrations of natural and synthetic estrogen remain unmonitored (Stiffler). Due to the lack of regulatory requirements and compliance inspections, the amount of estrogen that existing wastewater treatment practices can filter out or chemically break down is unknown; however, environmental testing has found that synthetic estrogens are making it into the wastewater and the amount of wastewater in the environment is attainable (Kidd). According to Kristen Keteles, an environmental toxicologist for the United States Environmental Protection Agency (EPA), some aquatic fluxes and pools in the western United States are 90% wastewater! The EPA hypothesizes that the high concentrations of wastewater are the result of an increasing human population and decreasing precipitation in the area due to climate change (Keteles).
Ethinyl estradiol, the prominent synthetic estrogen used in most hormonal birth control, is one of the most potent estrogens found in the rivers and streams receiving wastewater from treatment plants (Kidd). Exposure to this and other estrogens, increases the likelihood of death in male fish and decreases the reproductive ability of both sexes of adult fish exposed as juveniles according to the EPA. Studies analyzed by the EPA also show that synthetic estrogen not only affects directly exposed fish, but it also affects the next generation if the exposed fish are reproductively successful. Fish of the second generation were found to be less likely to be reproductively successfull if they were born to two parents that had been exposed to synthetic estrogens when compared to those spawned of parents that had not been exposed (Keteles). In an agreeing study, Battelle Marine Sciences Laboratory (BMSL) in western Washington state, conducted an experiment using adult trout and discovered that trout that had been exposed to synthetic estrogen for two months were half as fertile as those that had not been exposed (Stiffler). Throughout their studies, BMSL found that trout exposed to synthetic estrogen, even at a lower concentration than found in the local wildlife habitats, still showed diminished fertility (Stiffler).
Similarly, at the University of New Brunswick in Canada scientists analyzed the effects of natural and synthetic estrogen on the fathead minnow population in entire lakes over seven years. This study found a decrease in population size over the course of the study in all lakes exposed to estrogen. The population of fathead minnow in one of three lakes in fact collapsed over the course of the study. The collapse of the population was attributed to the reproductive failure of the population which was seen at that site for two years after the estrogen induction had ended. The observed decline in reproductive success was thought to be the result of feminization of male fathead minnow and altered development of the females due to the high vitellogenin production in the sampled fish from each site (see fig. 1). This study found that many male fish downstream of municipal water treatment plants are producing vitellogenin, a protein only produced in the presence of estrogen. This protein is necessary to produce female gametes which can be found developing in the testes of many male fathead minnow exposed to estrogen polluted waters (Kidd).
Fig 1. Mean +/- SE vitellogenin (VTG) concentration (µg/g wet bodyweight) in male (Lower) and female (Upper) Fathead minnow in three experimental sites, Lake 260, 114 and 442 from 1999 to 2003. Collapse of the population in lake 260 prevented sampling in 2004 and 2005 perceivably due to the high VTG concentrations.
This data corresponds to that found by the United States Department of Fish and Wildlife which depicted that at least 60% of the male smallmouth bass surveyed in nineteen areas thought to be pristine wetlands, had female eggs developing in their testes as well (Konkel). The phenomenon of males gaining female characteristics is an endocrine system disruption that is also referred to as intersexuality. Thirty-seven species of fish around the world were discovered in the ten-year span from 2006 to 2016 showing this type of disruption (Konkel).
In addition to disruption in the endocrine system of the male fish, females also suffer from delayed maturation after exposure to synthetic estrogens. Females with higher than normal amounts of vitellogenin protein were found to have delayed ovarian development, which may further impair the reproduction of fish populations (Kidd). Most fish species express the genes for more estrogen receptors than humans do, three vs. two estrogen receptors, leading to a potentially greater uptake of the chemical (Norris 338). Increased estrogen uptake paired with many fish species’ inability to rid themselves of synthetic hormones, generates concern for the future of many aquatic populations (Stiffler).
The concern for these populations is driving research for the implementation of more advanced filtration systems to remove synthetic estrogen and other chemicals (Stiffler). Another innovative solution, which one large wastewater treatment plant in Ontario, Canada adopted, is to change from a carbon-based treatment process to a nitrogen-based treatment process. The nitrogen-based treatment breaks down the endocrine system disrupting chemicals more effectively as depicted by the reduction from 70-100% to less than 10% incidence in fish intersexuality downstream from the plant after the upgrade in Canada (Hicks).
To upgrade all facilities to a the nitrogen-based treatment method would be extremely expensive; however, it does appear to be a highly effective means of combatting intersexuality in fish, in turn protecting future generations of aquatic populations. With the use of hormone replacement and contraception increasing in conjunction with the human population, this urgent issue is unlikely to sideline without intervention. Without such intervention, as the concentration of synthetic estrogen in the environment increases, the likelihood of fish population downfalls, as seen in Canada, will continue to grow. Improvement of wastewater treatment practices and an increase in regulatory requirements governing the amount of each chemical that the municipal water treatment plants can legally release into the environment is crucial for the healthy future of the fishes and aquatic biomes.
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- United States Census Bureau. Current Population Survey – March 2011 Detailed Tables. United States. 2011. PDF file.