Wastewater lowers fish egg production more than thought.
Thorpe, KL, G Maack, R Benstead and CR Tyler. 2009. Estrogenic wastewater treatment works effluents reduce egg production in fish. Environmental Science and Technology doi:10.1021/es803103c.
A British study shows that wastewater released from sewage treatment plants has a bigger impact than prior research suggests on egg production – and the long-term reproductive health – of fish living in the treated water.
This study was unique in that it looked at real effluents with their mixtures of different types and amounts of hormones. The authors showed that common methods used to assess the level of hormonal disruption may underestimate true reproductive impairment caused by estrogenic compounds.
In this study, the exposures altered egg production more than would be predicted by two standard measures of estrogen action: the amount of the egg protein vitellogenin produced by male fish when exposed to estrogens and estrogen-like substances and egg production after exposure to the potent, natural estrogen ethinylestradiol (EE).
Previous studies have shown that exposure to individual estrogen hormones commonly found in wastewater effluents can negatively impact fish reproduction by affecting offspring survival and reversing sex in the adults. In the wild, researchers find fish that have both male and female sex organs and male fish that have more female-like ducts and reproductive tissue. These changes more than likely hamper reproduction.
The study's authors monitored egg production in mating pairs of fathead minnows – a widely used species in toxicology studies. The fish were held for three weeks in effluents (full strength or diluted to 25 or 50 percent) collected from three different treatment facilities. Eggs were collected daily and compared to the pair's egg production prior to exposure.
The hormones present in the effluents affected the animals by reducing egg production while the fish were exposed to full strength samples from two of the effluents tested. Cumulative egg production dropped by 28 and 32 percent in breeding pairs exposed to 50 and 100 percent concentrations of effluent 1. Egg production dropped by 44 percent in the breeding pairs exposed to the full strength of the other effluent. The reductions were greater than that measured from EE expsosure.
Generally, the higher the level of estrogens in the effluents, the fewer eggs the pairs produced. The egg reductions coincided with the amount of estrogens in the samples. Reduced egg numbers like these can contribute to long-term reproduction problems.
