Where does all that waste go?! The effect of estrogens and endocrine-disrupting compounds on fish reproduction

Have you ever wondered where things go after they’re flushed down the toilet? If you’re a kindred spirit, maybe you’ve written several term papers on waste water treatment. More likely, you’ve probably truly never given the process much thought or aren’t exactly dying to admit that you’ve spent time pondering the transport and fate of toilet waste. One of the most common misconceptions about biological waste is that it goes to a wastewater treatment plant and every single contaminant in the waste is filtered out. Unfortunately, this isn’t always the case. In humans, chemicals that contain estrogen (e.g., birth control) are metabolized in the body, however, a small amount of un-metabolized estrogens are excreted in urine or feces (Racz & Goel 2010). While it is true that wastewater treatment plants are able to remove almost one hundred percent of the estrogen in urine and feces, some cities still have combined sewers (i.e., underground pipes that store excess waste and precipitation until it is treated) in which it is possible for untreated wastewater to overflow into nearby waterways during periods of high precipitation. This means that untreated waste containing estrogen compounds enters streams directly (EPA 2017; Racz & Goel 2010). Unfortunately, these estrogens can have detrimental physiological impacts on fish reproduction. Additionally, naturally-occurring chemicals and man-made chemicals such as pesticides enter streams as runoff from agricultural fields and contain endocrine-disrupting compounds (EDCs) that mimic sex hormones, having similar negative physiological impacts on fish reproduction (Arcand-Hoy & Benson 1998).

Untreated wastewater being deposited into a stream from a combined sewer overflow (CSO) after a period of heavy precipitation (Image drawn by Krystal Pocock).

A fish being affected by the untreated wastewater from the combined sewer overflow (Image drawn by Krystal Pocock).


Endocrine-disrupting compounds can have detrimental effects on reproductive development during early life stages in fishes (e.g., larval, juvenile) (Arcand-Hoy & Benson 1998). Exposure to EDCs at the larval or juvenile stage can interfere with the determination (i.e., development) of sex organs and can even cause hermaphroditism, which occurs when an individual organism has both female and male sex organs (Arcand-Hoy & Benson 1998; Mill et al., 2011). While chemically-induced hermaphroditism does not always cause reproductive decline in fishes, there is evidence that hermaphroditism reduces the hatchability of eggs, the number of successful eggs, and swimming success (Hill Jr. and Janz 2003). Additionally, exposure to EDCs during the larval or juvenile stages can cause fishes to reach reproductive maturity earlier or later than expected, which can result in reduced lifetime reproductive output. Furthermore, male fishes exposed to estrogens or endocrine disrupting compounds later in life can experience feminization of the testes, which can negatively interfere with reproductive efforts. The processes by which these transformations occur in the body are complex, however, they have serious implications for fish reproduction (Arcand-Hoy & Benson 1998). In the future, proper management of wastewater and the phasing-out of CSO systems can help minimize the amount of estrogen-laden wastewater entering streams. Applying fertilizers and pesticides when there is little to no chance of precipitation will also help minimize the contamination of streams with endocrine-disrupting compounds.

Arcand-Hoy LD, Benson WH (1998) Fish reproduction: an ecologically relevant indicator of endocrine disruption. Environmental Toxicology and Chemistry 17(1):49-57.

Hill Jr. RL, Janz DM (2003) Developmental estrogenic exposure in zebrafish (Danio rerio): I. Effects on sex ratio and breeding success. Aquatic Toxcology 63(4):417-429.

Racz L, Goel K (2010) Fate and removal of estrogens in municipal wastewater. Journal of Environmental Monitoring 12:58-70.

EPA (2017) What are combined sewer overflows (CSOs)? Webpage. Retrieved from https://www3.epa.gov/region1/eco/uep/cso.html on 22 April 2019.

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