Pharmaceutical products and household chemicals in rivers and streams may be affecting how fish mate and spawn, scientists warn, even when the substances are not present at levels high enough to cause visible damage.
Scientists have found that chemicals in rivers affect fish mating behaviors. Laboratory studies, reported at the November 7-11 meeting of the Society of Environmental Toxicology and Chemistry
in Portland, Ore., and are part of a growing effort to determine how pollution affects fish behavior.
We have known that pharmaceutical drugs and chemicals that are flushed
down toilets and drains have long been reported in urban waste water and the streams into which it flows. "Subtle effects are the issue," says Melissa Schultz, a chemist at the College of Wooster in Ohio. "It's easy to tell if a fish suffers from obvious anatomical changes such as being intersex or not having mature secondary sexual characteristics," she says. But determining effects on mating behavior "takes more meticulous work."
There has been speculation that antibacterial soaps
might be unsafe. Dr. Schultz has been studying the effects of low concentrations of triclosan
— antibacterial agents commonly added to soaps, disinfectants and increasingly to household products such as toys, bedding, socks and rubbish bags. Her team placed adult fathead minnows
) — fish commonly used in aquatic toxicity studies — in aquaria containing various mixtures of chemicals at levels they have found in the environment.
In the wild, fathead minnows establish nests, which males usually defend from rivals. But in Schultz's laboratory tests, exposed males were less interested than controls in trying to drive off artificial "bait" minnows placed near their nests.
A second study by environmental toxicologist Dalma Martinović, from the University of St. Thomas in St. Paul, Minn., found equally disturbing effects in zebrafish (Danio rerio) housed in tanks containing low concentrations of ibuprofen. Martinović found a significant reduction in courtship behaviour in males exposed to ibuprofen, she says. And water collected from the aquaria of ibuprofen-exposed females elicited less of a reaction in male fish than water from the tanks of females that had not been exposed to the drug.