From: Editor, ENN
Published August 8, 2014 08:13 AM

Can water-polluting drugs have a positive effect on fish?

Many studies have shown that personal care products, like toothpaste, shampoo, and other drugs that we use and get into our wastewater have negatively affected fish populations, disrupting their endocrine systems. But can there be any positive effects?

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A new study shows that one anti-anxiety drug that made its way into a lake in Sweden has in fact, positively affected the Eurasian perch population, making them bolder, less social, and more active than unexposed fish, ultimately reducing their mortality rates.

The results indicate implications for existing standard ecotoxicological tests, which predominantly focus on harmful effects of water contaminants and ignore the potential benefits.

Lead author of the paper, Dr Jonatan Klaminder, said: "Ecotoxicological tests were designed with traditional toxic contaminants in mind, such as heavy metals and dioxins, which have historically been the major apparent threat against aquatic organisms in surface waters.

"Pharmaceuticals, which are designed to improve health, are a new group of contaminants that do not necessarily fit into the traditional view."

In the study, the researchers retrieved two-year-old Eurasian perch from a lake in Sweden as well as fish eggs from a separate population of perch and randomly exposed them to high and low concentrations of Oxazepam.

Oxazepam is commonly used to treat anxiety and insomnia in humans and regularly contaminates surface waters via treated wastewater effluent. 

Results showed that mortality rates were high among hatched fry — corresponding to mortality rates found among perch fry in natural populations — and relatively high among the two-year-old perch, but were significantly reduced by Oxazepam exposure in comparison to the control group of fish who were not exposed.

In the hatched fry, mortality was lower in the high concentration treatment than in the control and low concentration treatments. In the two-year-old perch, mortality was lower in both the low and high concentrations compared to the control.

Co-author of the study Tomas Brodin, who was the ecologist in the research team, said: "Even though our study focused on one single pharmaceutical contaminant, it is possible that similar effects could be induced by exposure to a whole range of pharmaceuticals that find their way into surface waters, such as antibiotics, painkillers, anti-inflammatory drugs, hormones and antidepressants. Our conceptual view of a pollutant has, up until now, blocked us from testing for similar effects at environmentally relevant concentrations."

The study is published in Environmental Research Letters.

Read more at The Institute of Physics.

Fish image via Shutterstock.

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