Estrogens, including naturally occurring steroids and synthetic estrogens from a birth control pill, are common fresh water pollutants in densely inhabited areas, despite chemical treatment carried out in wastewater treatment plants.
A fascinating research came out few years ago suggesting that fish populations downstream of wastewater works are undergoing sex change. That is, male fish were observed to produce eggs and little or no functional sperm, posing an immediate risk to wild fish populations.
Such findings stirred up the issue of water pollution, and predicted a decline of fish populations in these areas in the near future. In contrast to the original expectations though, certain fish species now seem to have adapted to such way of life, and maintain their populations nonetheless.
A new research published in BMC Biology last month suggests that wild roach populations in Southern England are fairly self-sustained, even though a proportion of male fish are feminized and have reduced reproductive success.
Wild roach is quite often found in river stretches polluted with wastewater, as is the case in Southern England, which “has some of the highest proportions of wastewater treatment works effluent in rivers known globally”. Up to 10% of male roaches can be feminized in these areas; however, the effect on intra-population breeding is revealed to be relatively insignificant.
DNA microsatellite analysis identified distinct subpopulations of roach in isolated river stretches, which were contained in highly contaminated areas and did not experience much migration over multiple generations. As such, roach populations seem to be capable of self-maintenance, and show no immediate prospect of extinction, in spite of a high number of feminized males.
Attempts to reduce the amount of estrogen in wastewaters incur significant costs and could mean increased carbon footprint due to tertiary treatment in wastewater treatment plants, putting pressure on researchers to understand and manage the consequences of estrogen pollution on fresh water fish.
In theory, exposure to natural or synthetic hormones, could wipe out the males completely in some species, making them reliant on external estrogen to reproduce. Moreover, estrogen pollution may be responsible for secondary health effects and overall survival rate of certain fish (for example, synthetic estrogens have been recently reported to disrupt heart development), triggering an adverse cascade in fresh water ecosystems.
While the wild roach might have found a way around a shortage of males in the population, fresh water pollution remains a pressing issue, especially considering a predicted doubling of estrogen in some ecosystems by 2050 due to population growth and climate change.