7 August 2002 14:55 EST

by Damaris E. Christensen, BioMedNet News

[caption and credit]

A new study suggests that low concentrations of pharmaceuticals now widely found in the sewage, ground water, surface water, and even tap water of the United States could have "significant effects" - especially in combination - "on the critters that live in the water."

So concludes Colleen Flaherty of the University of Wisconsin, Madison, who studies daphnia (a kind of zooplankton) in particular. They "play a key ecological role in freshwater," she said. "They are eaten by fish and they eat algae."

When Flaherty looked into the possible effects on the daphnia of common cholesterol-lowering drugs, antibiotics, and antidepressants, she found that low concentrations of each - about 10 parts per billion - stunted their growth and resulted in more male offspring in the first brood exposed to the contaminants, a sign of environmental stress. However, if all of the offspring of a single daphnia were exposed to these contaminants over their entire life span, they generally seemed to adapt to the pollution, Flaherty observed.

The effects of combinations of the drugs, however, were a different story. Consider, for example, a mixture of clofibric acid (a metabolite of cholesterol-lowering drugs) at 36 ppb and fluoxetine (an antidepressant) at 100 ppb. In "a pharmaceutical cocktail of these two drugs that had almost no effect on their own," she said, "darn near everything died - up to 90%." Lower doses led to deformities in about a third of the offspring, she reported yesterday at the annual meeting of the Ecological Society of America in Tucson.

"There are definitely synergistic and antagonistic effects," Flaherty said. "I hope [these results] will encourage scientists to do more complex testing to evaluate risk for an organism or an ecosystem."

"Real world exposure is rarely if ever to a single toxicant," said Christian Daughton of the National Exposure Research Laboratory in Las Vegas, a division of the US Envoronmental Protection Agency. A recent federal study found at least 82 drugs, hormones, and other organic compounds polluting national waterways; among the 139 sites surveyed, the average number of contaminants per stream was 7.

These pollutants can come from a number of sources. Hormones and antibiotics from animal feed will appear in the animals' wastes and can then leach into nearby waterways. Similarly, when people take drugs, the chemicals' metabolites show up in sewage systems. If drugs are thrown away, they may dissolve as rainwater seeps through landfills.

Studies like Flaherty's suggest that the resultant pollutant combinations could harm aquatic animals and ecosystems, Daughton said. He cautions, however, that the doses tested by most researchers, including Flaherty, are higher than those commonly found in the natural environment. "The question is, what do these concentrations mean with respect to the real world?" he asked. "And that answer is still unknown."

Another unknown answer and emerging field of research regards the effects, if any, of these waterborne contaminants on human beings. "To say that there will be human consequences [to this kind of pollution] is jumping the gun," said John Trant of the University of Maryland Biotechnology Institute in Baltimore. "But there are a lot of red flags out there."

Picture caption and credit:
Daphnia. Image courtesy Water and Land Resources Division, King County, Washington

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