April 28, 2004

Research uncovers hazards of popular pesticide

by K.C. Jaehnig

(PRONOUNCERS: Lydy is "LIE-dee;" pyrethroids is "pie-REE-throids")

CARBONDALE, Ill. -- A popular class of agricultural pesticides widely used in California's produce belt appears lethal to certain midges and amphipods (the aquatic version of pillbugs) -- two species that live at the bottom of the area's rivers, creeks and irrigation canals, scientists have found.

Pyrethroids, which also provide the knock-down power in bug sprays and the active ingredient in pet flea collars, turned up in 75 percent of the sediment samples researchers Michael J. Lydy, Donald P. Weston and Jing You took from 42 sites in a 10-county area of California's Central Valley, an area that produces more than half the fruits, vegetables and nuts Americans eat every day. Ten-day toxicity tests on these samples showed pyrethroid concentrations high enough to conclude that they played a major part in the deaths of 40 percent of the midges and nearly 70 percent of the amphipods.

"Prior to our study, scientists in area water-monitoring programs were seeing that if they placed aquatic invertebrates in their sediment samples, the animals would die, but they didn't know why -- they'd attribute it to organophosphates or organochlorines (two pesticide ingredients being phased out because of environmental concerns), or they'd put it down to 'unknown causes,'" said Lydy, an environmental toxicologist with Southern Illinois University Carbondale's Illinois Fisheries and Aquaculture Center.

"Where our study is unique is that we looked at the toxicity and tried to figure out what was actually causing it. We detected organochlorines (such as DDT and chlordane) in the sediments but at concentrations not high enough to cause the toxicity we noted, whereas concentrations of pyrethroids were high enough to account for that toxicity.

"There's been an assumption that pyrethroids were safe because they were 'locked up' in the sediment and so couldn't cause any harm. We found that wasn't true. Pyrethroids are the most likely cause for the 'unknown' toxicity of sediments in California. What we're doing now (in follow-up studies) is proving it. We're one of the very few labs with the ability to measure pyrethroids in sediments."

Why all the fuss about a few dead water critters? The EPA has identified three sediment species with three different habitats as aquatic "canaries in the mineshaft" -- living sentinels that alert us all is not right with watery environments, Lydy said, and the midges and amphipods are two of the three. In addition, because other species eat them, their fate could eventually affect us.

Even if pyrethroids turn out to be little better than the pesticide compounds they replaced, Lydy doesn't expect them to go away any time soon.

"Farmers don't have another class of compounds waiting in the wings," he said.

"I'm realistic. You can't ban them without giving farmers another choice, so you have to find some way of making them work better under the conditions in which they're being used. 'Best Management Practices,' such as introducing buffer strips and wetlands, may reduce pesticide loads in aquatic systems, which would reduce the risk to non-target species."

Results of this study appeared in the April 8 online version of the American Chemical Society's journal Environmental Science & Technology and will be published later in hard copy.