Missing bugs: Pesticides linked to decline in worms, flies and mollusks in Charlotte's streams
New research from the U.S. Geological Survey links certain pesticides we spray on our lawns to declining health for aquatic life in nearby creeks and streams.
Researchers analyzed more than 400 streams around the country, including several around Charlotte, in the study examining the effects of pesticide runoff.
"We’re talking about chemicals that are applied to control pests in both agricultural and urban settings. Some of them control insects, some weeds, some mildew or mold, but these all fit under the general category of pesticides," said Lisa Nowell, the study's lead author.
Her team zeroed in on animals that often live at the bottom of streams called invertebrates. Those are animals that don’t have backbones, like worms, mayflies and mollusks.
"It’s a very critical part of the food web in and around the stream," Nowell said. "They graze on algae and detritus in the stream. They’re also a major food supply for fish, and both invertebrates themselves and the fish can be food for wildlife and fish-eating birds."
Previous research has shown pesticides are toxic to aquatic life in the lab, and researchers know many streams are polluted with pesticides — but could they show pesticides harm aquatic life in the real world?
To find out, Nowell’s team took samples from hundreds of streams — some in polluted urban areas, others pristine — and they surveyed the invertebrates in the water. Their initial results were perhaps unsurprising.
"We do see a strong association between occurrence of pesticides and degradation in the invertebrate community, and that’s just an association. That doesn’t mean cause and effect," Nowell said.
Then her team went a step further with statistical models, and dosing invertebrates from healthy streams with pesticide levels from unhealthier streams.
"In these experiments, which we did with three insecticides — fipronil, bifenthrin, and imidacloprid — we did see the same kinds of effects in the laboratory that we were observing in the field," Nowell said.
That strengthened their conclusion that these chemicals were likely having a direct negative impact on the little stream-dwelling invertebrates.
You can hear their complete conversation here.
Nick de la Canal: And were there maybe one or two pesticides or insecticides that seemed especially high or impactful in streams near Charlotte or in the Southeast?
Lisa Nowell: In the Southeast, yes. It was unique actually. It was the only region where fipronil was the dominant insecticide.
De la Canal: This is used I believe in products that target ants and cockroaches —
Nowell: Ants, termites, yes, fire ants.
De la Canal: Termites and fleas.
Nowell: Yes, fleas as well. Yes, and as you know I’m sure, better than I, the Southeast has the highest density of some of these populations of fire ants and termites for example, so it’s reasonable that you probably have high fipronil application rates.
De la Canal: So looking at these findings, if a homeowner or a business owner is trying to get rid of say fire ants or termites in their yards, should these insecticides be off the table, in your view? Or is there any kind of middle ground here?
Nowell: I mean I don’t want to speak for the U.S. Geological Survey on that. I think — I will say that I think pesticides are applied for a function — for a certain reason. And ideally, they should stay where you apply them, and so you don’t want to apply pesticides before it rains, for example. And there’s very good evidence that having vegetation on the edge of the stream will slow any transport of chemicals into the streams, so there are things I can speak to, but I can’t answer your question about whether they should be used or not.
De la Canal: Sure. But maybe there are ways to apply it in a more careful way — like you said, ways so that there isn’t as much runoff, maybe there’s some ways we can protect the streams’ banks. Yeah.
Nowell: I think that’s a reasonable inference from this, yes.