Course:CONS200/2023WT1/Birth Control Impacts on Fish Populations

From UBC Wiki

Hormones found in birth control pills have been seen to alter the genes in fish, as well as change their behaviour. Birth control hormones enter wastewater through the urine of those who take birth control, flushing or excreting are often not filtered out by wastewater treatment plants– they can even be found in drinking water[1]. These hormones include a synthetic estrogen called ethinylestradiol (EE2) which has proven to have negative impacts on regeneration, swimming behaviour, and nervous system development of certain fish species [1]. There have been genetic balance changes in fish, problems have been developed in procreation, and in some cases, these fish have had a harder time catching food. Another impact of birth control hormones is “feminization,” which refers to male fish who have been affected by the excess amount of estrogen and experience genetic modification, such as developing female reproductive organs (Lang, 2010).  If this problem continues, it can affect the entire ecosystem and completely wipe out the fish population. However, recovery is possible for fish populations; a study in an Ontario experimental lake showed that after four years without hormones in the water, the fish population returned to normal[2].  

This image shows an example of what the birth control pills look like in their packaging

Hormones found in Birth Control

The birth control pill is one of many forms of birth control. Other forms of birth control include the birth control shot, NuvaRing, contraceptive patch, Nexplanon etc. The focus is on how birth control pills affect fish as the male fish population has been affected mostly by the hormones found in birth control pills [3]. The birth control pill contains different hormones which are originally used to prevent ovulation. This pill is and has always been intended for human use only. It is an artificial pill that is made of two hormones called estrogen and progestin. The National Library of Medicine states that birth control pills “are either combined estrogen-progesterone (also called combined oral contraceptive pill - COC) or progesterone-only pill (POP).” [4]. The pill was created to prevent ovulation however over time it has been used to help with other issues such as, “reducing the pain of ovulation, reduced risk of pelvic inflammatory disease (PID), reduced fibrocystic breast changes, reduced risk of ectopic pregnancy, may reduce acne” (“Birth Control: Pros and Cons of Hormonal Methods.”). Another example of how it has been used is for PCOS (Polycystic ovary syndrome) as PCOS causes hormones to be imbalanced and some birth control pills help with balancing them out.

According to the Microchemical Journal [5], “the estrogens 17-β-estradiol (E2) and 17-α-ethinylestradiol (EE2) are reported as being the highly disrupting agents, being recently included in an EU watch list regarding emerging aquatic pollutants''. These estrogens are used to help stop a woman's egg from fully developing each month. Estrogen is a hormone found in most birth control pills as it stops a woman's egg from fully developing which is the most common use of the birth control pill.

Clinical Key[6] has also discussed that “one particular synthetic estrogen has been singled out for purportedly detrimental effects on the environment: ethinyl-estradiol, or EE2, a synthetic estrogen used in birth control pills, patches, rings, and injectables.”. In the Clinical Key article about birth control hormones in water, there is one particular synthetic estrogen that has been singled out for its detrimental effects on the environment, this synthetic estrogen is the same one mentioned in the Microchemical Journal, EE2. This is “a synthetic estrogen used in birth control pills, patches, rings, and injectables''  (Moore et al., n.d.).

Effect of hormones on ecosystems

As previously mentioned above, the hormones “estrogens 17-β-estradiol (E2) and 17-α-ethinylestradiol (EE2) have been identified as being the highly disrupting agents, being recently included in an EU watch list regarding emerging aquatic pollutants''[7]. Unfortunately, current wastewater treatment plants are often inadequate in fully removing these hormones, leading to their gathering in our aquatic environments. These chemicals that humans are using actually have a large impact on our environment and ecosystems. These hormones originate from humans, in particular, the use of pharmaceuticals, such as the birth control pill, that are making their way into our waterways.

The impact of these hormones on our ecosystem is profound and multifaceted. The exposure to these hormones can disrupt the systems of fish, affecting crucial processes such as reproduction. These hormones produced in birth control are negatively affecting our fish population, “They act on the hypothalamus–pituitary–gonad axis, lead to oocyte maturation in female and sperm motility in male fish.”[8]. Not only are they affecting the sex of the fish, but also affecting and altering the gender ratio and reproductive behaviours.  “Adverse effects have been demonstrated for 17α-ethinylestradiol (EE2) on fish reproduction, leading to population declines, the occurrence of intersex gonads and skewed sex ratio, all of which are of high ecological importance. Furthermore, the synthetic androgen trenbolone affected sex determination even at 9.2 ng/L and decreased fecundity in fish ”[8] Water Waste treatment plants not being able to fully get rid of hormones used by humans is leading our fish populations to drastically alter. These inabilities of wastewater treatment plants to effectively remove hormones from human waste is a serious concern. It leads to alterations in the fish population and have wider implications for our aquatic ecosystems. For instance, the skewed sex ratio could cause the natural selection process within the fish population, leading to long term changes.

Effect of hormones on fish biology

Many compounds such as pharmaceuticals and endocrine disrupting chemicals are not removed during the wastewater treatment process, causing these chemicals to still be in their active form when entering bodies of water.  Endocrine disrupting chemicals have been known to affect marine organisms both physiologically and behaviourally when they are exposed. A main exposure comes from 17a-ethinylestradiol, which is commonly found in birth control pills. This exposure has led to feminization of males and has altered the reproduction capabilities of both male and female fish. Additionally, it has been found that exposure to EE2 can also cause change in mating preferences in fish, decreasing proper mating opportunities which can lead to population collapse.[9]

Harmful synthetic hormones

Endocrine-disrupting chemicals, also referred to as EDC’s are chemicals that can interfere with the function of the endocrine system in humans as well as wildlife, by interfering and changing the normal effects of their hormones. EDC’s include many different chemical groups, both natural and synthetic, and 17a-ethinylestradiol is the synthetic estrogen with a higher disrupting potency. Ethinylestradiol is a main component of oral birth control, and is another synthetic hormone.[10]

Hormone effects on Male and Female Fish

Wastewater released into fish habitats has been found to produce vitellogenin in male fish species, which is a protein typically produced by females and not males. There has also been research that shows male fish reproduction has been altered, as some have begun to produce eggs.[8] These changes seen in male fish are led back to the presence of estrogenic substances, often synthetic estrogen found in human oral contraceptives.[2] Similarly to the effects on male fish, female fish may experience a change in behaviour and mating preferences. The hormones in order to reproduce can also be affected, as the synthetic estrogen found in birth control pills are not meant for fish biology, and can be very harmful.[8] 

The effects on species populations

Due to the changes seen in the reproductive system of both male and female fish, it is foreseen that with the continuation of this effect, fish species population will experience an extensive decrease. Not only will fish no longer have the behaviour and incentive to mate in order to reproduce, but the biological changes have made it impossible for them to reproduce in some cases.[2] The entire food circle will be affected, which not only affects the marine life in the ocean or freshwater areas, but humans and other animals who rely on these fish species.

A Canadian study has also shown that the synthetic estrogen found in the urine of women who take birth control has had effects on fish. This is due to the sewage treatment plants not being able to completely break down the estrogen. The urine has had many side effects on the fish but one of the most notable ones is that male fish can produce eggs. The female fish have also been more stimulated by the extra hormones and have produced eggs at the wrong time of year [11]. Depending on environmental conditions the eggs that are laid pose many challenges. It is normal for fish to lay eggs in spring however with the extra hormones the eggs have laid in conditions that they will not survive[12]. Not only due to the weather, however, some many ponds and lakes are drying up fast due to global warming [12]. This causes large populations of eggs that are laid there to die as where they are laid does not have any water or has very little water. The extra hormones that the fish are exposed to have a large impact on many aspects of fish's lives, even before they are born. 

Zebrafish (Danio rerio) and EE2 experiments

Zebrafish (Danio rerio)

Zebrafish are a small fish species in the minnow family Cyprinidae. They are native to freshwater river basins in South Asia and India, especially the Ganges and Brahmaputra river systems. They are small in size (around 40 mm) and are identifiable by their black and white lateral stripes. Zebrafish are popular aquarium fish and are easily bred into different strains. They are considered a species of least concern on the IUCN Red List and are typically very abundant in the areas they inhabit. [13]

Significance in experimental design

Zebrafish are considered the most important and most common model fish species for genetic, behavioural, biomedical, and toxicological laboratory experiments.[14] Several traits of the fish contribute to its popular use in laboratories. Zebrafish are inexpensive and easy to breed, and can safely be kept in large amounts per tank. In captivity, female zebrafish can spawn as often as every 4-7 days, producing several hundreds of eggs each time, making the fish good candidates for genetic/selection experiments [14] [13]. The eggs are relatively large, are transparent, and develop externally to the parent fish, allowing researchers to monitor every developmental stage of the fish from birth.[13]  Zebrafish are vertebrates, unlike many other model organisms, and are therefore considered a good model for human research.

Many fish species are affected by birth control hormones, but the effect of EE2 on zebrafish has been studied extensively through laboratory experiments. One such lab experiment found that EE2 concentrations affected hair cell regeneration and axonal nerve regeneration, and altered genes in the central nervous system. [5] Another study looked at courtship behaviour, and found that male fish affected by EE2 had significantly altered courtship behaviour and swimming patterns and were often feminized. When these males paired with females unaffected by EE2, their reproductive behaviour changed and the fish did not produce as many offspring.[4] Several other studies discovered that EE2 also lowers immunity to microbial infection, lowers sperm production, causes lesions in gills and liver, causes early hatching, disrupts embryo development, and reduces survival rates of offpsring. [15][16][17][5]

These zebrafish experiments have been instrumental in providing evidence for the dangers of EDCs in surface water to ecosystems, especially fish populations.

Recovery of fish populations

Once fish have been exposed to chemicals like EE2, there is still a chance of recovering the populations. A small scale experiment found that zebrafish recovered almost completely after 40 days of discontinued exposure to EE2. Once they were no longer exposed to the chemicals, the feminization reversed, the sex ratio returned to normal, and the growth of reproductive systems in males was no longer inhibited. [18]

Ontario Experimental Lakes Area study
This graph charts the population size of fathead minnows in the Ontario experimental after the addition and removal of EE2. The pink area represents the years during which EE2 was present in the lake.

A large-scale whole-lake experiment [19]showed similar results and demonstrated two key findings: first, that exposure to EE2 can cause wild fish populations to collapse, and second, that it is possible for fish populations to fully recover once they are no longer exposed to EE2. The experiment was done in an experimental lake in Northwestern Ontario, and lasted over ten years. After EE2 was added to the experimental lake, stocked with fathead minnows, the fish population steeply declined. The fish showed abnormalities in reproductive organs and increased vitellogenin (a nutrient linked with feminization of male fish).[17] Once EE2 was no longer being added to the lake, these effects were almost completely reversed within three years. After three years, the fish population began to rapidly increase and the sex ratio returned to normal. [19]

Removal of EDCs from wastewater

The main sources of EE2 are from wastewater treatment plant output into bodies of water.  EE2 has been found in surface waters across 32 countries as a result of wastewater output [9]. Other sources include runoff from livestock, pharmacy, and hospital wastewater, though these are less significant. Researchers generally agree that wastewater treatment plant  regulation is the most practical and efficient solution to EE2 pollution. [9]

Several methods are used to remove endocrine disrupting chemicals (EDCs) like EE2 from water. The most commonly used methods include coagulation, flocculation, precipitation, and activated sludge techniques; These methods are chemical and biological processes which separate pollutant particles from water.[9] [20] Although these are the conventional methods, they are not as effective as more advanced techniques of EDC removal such as physical filtering through membranes or carbon filters, or advanced chemical processes like ozonation. These processes can be complex and expensive and are not as commonly used.[20] One promising solution is the use of functionalized biochar, a method which utilises charcoal-like material to absorb pollutants from water. A recent study found that the use of functionalized biochar removed around 100% of an EDC mixture which included EE2. [20]

Once EDCs are released into the water, they are difficult to remove, and recovery of the affected ecosystems is under-researched. A few recovery methods exist– one involves using EE2 degrading bacteria to reduce the amount of the chemicals. [21]This approach has proven successful in the Macao region of China, in the southeastern mangrove populations. Added bacterial communities were effective at reducing EE2 concentrations in the water in areas where wastewater treatment plants. More research is required to determine if supplementing these bacterial communities could help recover polluted water on a larger scale in vulnerable areas. [21]

Regulation of EDCs

Though it is well established that the effect of EE2 on fish communities is harmful and has long term effects on ecosystems, there is very little legislation regarding wastewater treatment of EDCs. The EU’s Environmental Quality Standards list places limits on concentrations of pollutants in water, but EE2 is not yet included (though it is projected to be included in the future). [20] The government of British Columbia has similar recommended guidelines for maximum concentrations of EE2, but no official legislation. The United States’ EPA has banned the use of EDCs in pesticides, but lacks regulation on EE2 and water treatment.[22] Generally, before any legislation or regulations can be made on EDC removal in wastewater treatment plants, more information about the effectiveness and innovation of different treatment processes is needed. [20]


In conclusion, the birth control pill has a significant effect on the diverse fish population and our aquatic ecosystems. There is a growing concern for the environmental impact of these synthetic estrogens. Without the proper wastewater treatment it significantly disrupts the reproductive systems of fish. The effects these hormones have on fish such as, the feminization of male fish, skewed sex ratios and altered reproductive behaviour. There have been studies that showcase these changes and there are also solutions that have been hypothesized to prevent any further damage to the aquatic ecosystem and the fish populations.




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