Concern grows about the impacts of hormones on aquatic ecosystems

12 June 2014

For quite  a few years now the threat of hormones and oestrogen mimicking compounds (EDCs) – entering our rivers, lakes and dams in sewage effluents – has been growing.  The topic is generally swept under some or other carpet as the implications for wastewater treatment needs (read “increased rates and taxes”) rendered it unpopular.  The scientific evidence suggests that there is cause for concern, especially in water-stressed countries.  The frightening concept of “feminized fish populations”, whispered about more frequently that many will realise – first appeared in the 1990s (see report about English sole).

These so-called “feminized” fish, first found in the late 1990s, are thought to be victims of human hormones and hormone-mimicking chemicals — flushed into the water from sewage-treatment plants, factories, storm-water drains and runoff from roads — that had made their reproductive systems go haywire. Now a King County study has found that those chemicals, which come from sources as varied as birth-control pills and plastic bottles, detergent and makeup, are more widespread in the region’s water than previously known.  The chemicals were found at very low levels, but some scientists worry that even in tiny amounts, they could mess with the sensitive reproductive systems of animals that already have plenty of challenges.

Back in 2007, impacts on lobsters were found to be somewhat different, affecting their moulting process and making them more susceptible to disease.  The controversial video entitled “The Disappearing Male” initiated a debate that was a small version of those nowadays typical of climate change.  The Bottom-Line here is that less-sophisticated wastewater treatment increases the risk of EDC build-up in our water resources.

Research findings just published in the Journal of Applied Ecology provides confirmation of what many aquatic scientists believe to be true:

Synthetic oestrogens in wastewater from contraceptive pills can have effects on fish reproduction and survival that worsen over several generations, new research has found. The study suggests that some fish populations may not be able to recover from levels of oestrogen pollution found in many freshwater environments. 

Summarized in Science for Environmental Policy:

Freshwater ecosystems are increasingly under threat from both climate change and expanding human populations. Climate change has led to lower levels of rainfall in many parts of the world, reducing freshwater stream flows, while growing populations will consume increasing amounts of freshwater and generate more polluted wastewater. This has led to many rivers and streams becoming dominated by processed sewage effluent.

Sewage effluent contains a complex mixture of chemicals, including pharmaceuticals, which are not completely removed during treatment. Among these are steroidal oestrogens, such as 17α-ethinylestradiol (EE2), from human birth control pills, that have been shown to negatively affect fish reproduction. However, oestrogens may also influence populations of fish through mechanisms other than reproduction, such as reducing survival, and have cumulative effects only seen over multiple generations.

The researchers in this study examined the effects of EE2 exposure on populations of fathead minnow (Pimephales promelas) fish, over multiple generations. They used concentrations of EE2 in the range commonly found in the environment as a result of wastewater effluents, from approximately 3 to approximately 11 nanograms per litre (ng L-1). They also included near-zero control treatments, and complemented experiments in outdoor water tanks representing near-natural conditions with experiments in laboratory aquaria.

EE2 was found to increase the chance of death in male fish by a factor of 1.7 for each 1 ng L-1 of EE2 added. No males survived longer than 126 days when exposed to 11 ng L-1. Females were less affected, with around 50% surviving over the same time scale. In the wild, fathead minnows have a lifespan of between one and three years.

Additionally, exposing the first generation during their reproductive season reduced the number of eggs, embryos and juvenile fish produced at all EE2 concentrations tested. Exposure of the second generation to EE2 early in life resulted in almost no eggs or larvae being produced. Even at the lowest concentration, survival of the third generation was also reduced even though the parents were transferred to unpolluted water for five months before reproduction.

These results show that exposure to EE2 at real-world levels can disrupt fathead minnow population dynamics by affecting reproduction over multiple generations, suggesting that fish populations may not be able to recover following oestrogen exposure.

While this research is based on North American data and species, the findings are relevant to all fish with high reproductive rates and relatively short lifespans in environments contaminated with relevant oestrogen levels, say the researchers.

Overall, the authors of the study conclude that this work suggests that there may be an ecological benefit to upgrading wastewater treatment plants to remove oestrogen-like pollutants. They also suggest a number of possible actions to reduce harm from oestrogens in freshwater ecosystems.  These include conserving breeding and rearing habitats in unpolluted areas and maintaining connections between and within rivers and streams.

Similar findings have recently emerged for several estuaries on the Basque coastline.

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