This potentially good news for individual Eurasian perch (Perca fluviatilis) exposed to the anti-anxiety drug Oxazepam is not necessarily beneficial for the ecosystem as a whole – it could have knock-on results for other species.
“A therapeutic effect leading to increased survival of one species may generate a proportional increase in mortality of that species’ prey, which may have cascading ecological consequences," said Tomas Brodin of Umeâ University.
“A new, conceptual view of ecotoxicological testing should include the possibility that a substance can improve the health of an organism and make individuals affected by contamination more competitive than non-affected individuals.”
The team believes that exposure to other pharmaceuticals such as antibiotics, painkillers, anti-inflammatory drugs, hormones and antidepressants in surface waters could also be therapeutic. "Our conceptual view of a pollutant has, up until now, blocked us from testing for similar effects at environmentally relevant concentrations," said Mr Brodin.
Brodin and colleagues found that two-year old Eurasian perch exposed to the benzodiazepine Oxazepam at a concentration of around 1 µg per litre of water for seven days in the lab were bolder, more active and showed a higher survival rate.
Sewage treatment plants do not currently remove pharmaceuticals such as benzodiazepines; treated wastewater effluence may contain levels of Oxazepam as high as 1.9 µg per litre while effluence-dominated surface waters may contain 0.6 µg per litre. The lethal level for long-term exposure is likely to be in the high milligrammes per litre range.
Previously, the team had found that Oxazepam makes fish bolder and more active and, as a result, more efficient at foraging for food. The chemical bioconcentrates, reaching a level in perch muscle six times higher than in the surrounding water.
Perch fry hatched from roe exposed to Oxazepam for 24 hours between three and six days after the eggs were laid also showed a higher survival rate in tests 30 days after their exposure.
“To our knowledge, this is the first paper providing empirical evidence from exposure assays that such a therapeutic effect can improve health at concentrations comparable to those measured in treated wastewater effluents,” Jonatan Klaminder of Umeâ University told EnvironmentalResearchWeb.
Traditional ecotoxicological tests, which are searching for chemicals’ detrimental effects, are likely to miss health benefits; pharmaceuticals are beneficial at concentrations much lower than the levels at which they become poisonous. What’s more, researchers discard any trials in which the animals in the control group are not in good condition, in order to assess the harm caused by the chemical accurately. But in the wild, particularly after the harsh Swedish winter, perch may not be in the best of health; as many as 92 per cent of wild fry may not survive their first week. And fish that are more stressed may experience greater therapeutic effects from pharmaceuticals.
“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," said Mr Klaminder.
“Pharmaceuticals, which are designed to improve health, are a new group of contaminants that do not necessarily fit into the traditional view. I think there is a ‘bandwagon effect’ within the research community where the old test and the traditional view of a contaminant is routinely used without reflection about the conceptual flaw implicit in the methods.”
Klaminder hopes the study will “serve as a ‘mind opener’ for the research community and set the stage for a new era of ecotoxicological research where therapeutic effects are more systematically screened in assays and where [the] eventual ecological consequences spawning from these are more often discussed”.
Now the team will investigate to what extent the therapeutic effects from bioactive compounds could have cascading ecological effects in contaminated waters.