—by Marilyn Davis

Living in tanks in the basement of the Life Science II building are some modern equivalents of the canary in the coal mine.

They're tiny freshwater invertebrates—bright-red midge larvae, threadlike aquatic worms, and shrimp-like amphipods—that dwell at the bottom of streams and ponds. These modest creatures, a key link in the aquatic food chain, may look insignificant. But if they're not thriving, it's a warning sign that all is not well with an ecosystem and bigger problems may be on the way.

Our streams and lakes absorb a constant incoming chemical stew, from farm-field runoff to factory effluent to the life-saving medications we take and excrete. Although most polluting compounds are present at very low concentrations in water, little is known about their storage in bottom sediment or about how that affects organisms and ecosystems.

Along with various fish and tadpole species, the midges, worms, and amphipods serve as aquatic "guinea pigs" for environmental toxicologist Michael Lydy and his students. Working with contaminated sediments from water systems, Lydy's team seeks to determine what pollutants and combinations of pollutants account for toxic effects. With colleagues in California, they have been the first to uncover risks from a group of widely used pesticides—and to push for solutions to the problem.

Lydy, a zoology professor affiliated with SIUC's Fisheries and Illinois Aquaculture Center, has done toxicology studies involving heavy metals, explosives, pharmaceuticals, herbicides, and other pollutants. For instance, he and SIUC zoologist Richard Halbrook have shown how PCBs (polychlorinated biphenyls, a class of industrial compounds) in lake sediment at Crab Orchard National Wildlife Refuge are accumulating up the food chain—moving from emerging insects to tree swallows, and from gizzard shad to great blue herons.

In another project, Lydy and SIUC zoologist James Garvey have discovered that young male sturgeon with elevated exposures to PCBs and first-generation pesticides like DDT (which, though banned, persists in the environment) develop sexually more like females, impairing their reproductive ability. Working with pallid sturgeon in the Mississippi River below St. Louis, Lydy says, "We're finding ovaries in 8 to 12 percent of male sturgeon." That's bad news for an already-endangered species.

On a more positive note, Lydy's lab has found that channel catfish cope quite well with TNT residues, breaking them down rapidly instead of accumulating the chemical in their flesh. That's good news for fishermen who eat their catch.

Lydy's lab also has found that the popular antibiotic Cipro appears to be relatively benign in aquatic environments, thanks partly to low concentrations. It's an open question, however, whether microbes in streams are developing "superbug" resistance to the antibiotic, which could pose problems.

Pesticides, however, are the major focus of Lydy's recent work, particularly a third-generation class of insecticides called pyrethroids. Farmers use them to control insect pests, but we consumers use them too—on our lawns, in our houses, on our pets—to kill everything from grubs to fleas. There are seven kinds of pyrethroids, and the typical can of bugkiller contains at least two, notes doctoral student Andrew Trimble.

It turns out that pyrethroids (pronounced pie-REE-throids) can decimate certain invertebrates that are indicators of water quality. Surprisingly, suburban homeowners are bigger offenders in this environmental scenario than farmers are, at least in the region he's studied, Lydy says.

Lydy's work with pyrethroids, done in conjunction with the University of California, Berkeley, has focused on California's Central Valley, home to farmland and urban areas alike. The research is slated to expand across the country soon.

Pyrethroids break down quickly in water or air, but they will bind tightly to sediment, where they stay intact for months. That's why Lydy's testing focuses on bottom-dwelling invertebrates.

The three species used for aquatic sediment testing are standards in environmental toxicology. They cover the waterfront in terms of getting a good picture of toxicity, Lydy explains: "They reside in different niches within the sediment. They have different exposure routes, they're eating different things, and the bioavailability of a contaminant (how much is actually available to be taken up by organisms) is going to be different for each."

The tiny amphipods, crustaceans that are related to pill bugs, graze on the surface of the sediment. The midge larvae live just under the surface, where they filter nutrients from the sediment. And the worms tunnel headfirst down through the sediment, essentially "digesting" it directly.

These lifestyle differences lead to different sensitivities in these species, Trimble says. "The [aquatic] worms are very useful for long-term, high-concentration exposure studies. Hyalella azteca (the amphipod species) would be useless for that, because you'd kill every one of them in a matter of hours." But with low concentrations, that same sensitivity makes Hyalella a model test species.

Lydy, postdoctoral fellow Jing You, and UC Berkeley biologist Don Weston began their pyrethroid investigations by collecting sediment from streams, irrigation canals, and ponds in 10 agricultural counties in the Central Valley. Lab tests exposing amphipods and midges to the sediment showed that one-third of the samples were toxic to one or both of these species—in some cases killing off every individual.

When Lydy and You tested the samples for the presence of 26 different pesticides, they found pyrethroids in three-quarters of them. Levels were high enough to account for 70 percent of the amphipod deaths and 40 percent of the midge deaths, the research team calculated.

"Pesticide manufacturers argue that pyrethroids bind so tightly to sediment that they're not bioavailable to organisms," Lydy says. "We've found that they are bioavailable, they are taken up by invertebrates, and they're incredibly toxic. Less than one part per billion will kill [Hyalella]. That's like taking a drop of water and putting it into a swimming pool."

The team went on to find that suburban drainages in part of the Central Valley had even bigger toxicity problems with pyrethroids. In this study, they collected sediment from creeks that drained a typical subdivision in Roseville, Calif.

"We had Hyalella living in a stream prior to the subdivision being built," Lydy says. "It was built, and then they were gone. If you go above the subdivision, the Hyalella are fine."

Lab testing showed that the sediment samples were high in pyrethroids. In fact, more than 90 percent of the samples were lethal to Hyalella.

The drive for a perfect lawn is the main culprit in suburban contamination. Manufacturers' decision to market fertilizer, herbicide, and pesticide in one multipurpose package means that many homeowners and gardening services are applying bugkiller to residential lawns needlessly, or much more often than they need to.

Regrettably, many homeowners also think that the more insecticide you apply, the better, Lydy says. And it's common for homeowners to wash off their spreaders in driveways, where the runoff flows directly into storm drains. Pyrethroid runoff is less of a problem in agricultural areas because farmers are well educated about how much insecticide to apply, Lydy says. They don't overuse the product; they know that's an extra cost with no benefit.

"There really was no concern about pyrethroids before Don's and my work," Lydy says. "California knew they had a problem with toxic sediments, but they didn't know the cause of the toxicity. Don and I were the first to say that the controlling problem is pyrethroids. We explained [the majority] of that unexplained toxicity, and now we have a new grant to explore the remaining toxicity issues, looking at other classes of compounds."

It's a measure of Lydy's professional reputation that two of his current graduate students, Trimble and master's student Amanda Harwood, hold prestigious STAR fellowships from the Environmental Protection Agency. Several other graduate students, an undergraduate research assistant, a visiting student from Finland, and two postdoctoral fellows round out the team.

His lab is unusual among environmental toxicology labs in the scope of its research, Lydy says. It is particularly known for its chemistry expertise: the ability to isolate and identify pollutants present in toxic sediment and to improve analytical techniques.

Lydy and his students also run dose/response tests with species to determine levels and causes of toxicity. They analyze susceptible animals to find out how a given chemical has its effects. They monitor field sites for reductions in species. They study how contaminants move in the environment and to what extent they're bioavailable. Finally, they're researching ways to reduce contaminant discharge into streams from suburbs and farms.

The lab's greatest challenge and greatest strength is teasing out which chemicals in a mix are doing the most damage, and how chemicals interact to harm organisms. Sometimes two toxic chemicals act synergistically, boosting toxicity far above what you'd expect by simply adding together the hazards of the individual compounds. Sometimes a benign compound will increase a second compound's toxicity, a phenomenon called potentiation. And sometimes, if you're lucky, two chemicals in combination will reduce or neutralize each other's toxicity.

To take one example, Trimble has used Hyalella to investigate the toxicity of second-generation organophosphate insecticides in combination with atrazine, a ubiquitous herbicide. By itself, atrazine has little to no toxicity to Hyalella in the concentrations he's using. But its presence makes organophosphates more toxic to the species, he's found. (Such potentiation may underlie Gulf War Syndrome, Trimble says, in which no chemical agent by itself has been shown to be the smoking gun.) He is now testing the effects of pyrethroid mixtures on Hyalella.

When Trimble analyzed sediment samples from California streams containing various pesticide residues—not just pyrethroids, but also older pesticides—he found that pyrethroids topped the list in their toxicity to invertebrates. One called bifenthrin, used for termite control and lawn care, appears to be the most problematic, information that might help manufacturers reformulate their products or regulators set limits.

If even 1 percent of the bifenthrin a single homeowner put on the lawn on a Saturday afternoon washed down a storm drain, it would take at least half a million gallons of water to render it harmless to Hyalella, the research team reported in late 2005. "And that's just one application by one person," Lydy says.

Part of Trimble's STAR project will address how pyrethroids move in the environment. Do they preferentially bind to coarse sediment? Fine? Super-fine? Do they prefer sediment with a high or low organic matter content? The answers will improve toxicologists' sample-collection protocols so that they don't miss pyrethroid residues.

Amanda Harwood, the other STAR Fellow, is investigating exactly how pyrethroids affect the test species, an area of research called toxicokinetics. "It's one thing to do toxicity testing and see how many animals die," she says. "It's more interesting to see how the organism processes the chemical." Understanding how the pollutant does its damage could help mitigation efforts down the line.

Harwood's research also is adding another useful technique to what's called Toxicity Identification Evaluation, or TIE: the initial screening of toxic sediment or water samples to begin pinpointing the toxic agent or agents. It's time-consuming and expensive to extract and identify chemical compounds from samples, Harwood explains. Thus, faced with unknown toxicity in water or sediment, scientists rely first on TIE procedures—quick, easy tests to help narrow their search for the suspects.

In tests exposing midge larvae to pyrethroid-contaminated sediment, Harwood found that raising the temperature of her samples decreases mortality. This is an unusual result, Lydy says. "For most chemicals, if you increase the temperature of your samples by 10 degrees, you see an increase in toxicity. That's because the organism respires more at a higher temperature and takes in more of the toxic chemical."

Pyrethroids, he explains, are nearly unique among toxic compounds in doing the opposite. The TIE procedure, then, would be to expose larvae to toxic sediment at two different temperatures, then see if fewer of them die off at the higher temperature. If so, the sediment should be tested for pyrethroids. If not, this potential cause of toxicity can be ruled out.

Harwood's ongoing toxicokinetics work will allow her to determine why deaths from pyrethroids decrease with higher temperatures. That will shed more light on these chemicals' mechanism of action.

Identifying the source of toxic sediments in the Illinois River downstream from Chicago, a new project for Lydy's team, will rely initially on TIE procedures. Mussels and other invertebrates once abundant in this stretch of river have been disappearing, and the Illinois Department of Natural Resources wants to know what is killing them. It could be one or a combination of any number of things, from pesticides to heavy metals.

And because the pyrethroid problem is unlikely to be unique to California, Lydy's team will soon begin another new project, analyzing sediment samples from a number of cities across the country. If problems turn up, they'll seek grant funding to do more extensive testing.

Lydy and his team stress that their research isn't aimed at banning chemicals or eliminating pesticide use. "We're saying, apply pesticides in a manner where you're going to minimize the impact on non-target species," Lydy says.

How to do that with pyrethroids? Lydy, Weston, and several colleagues will evaluate the results of various strategies—so-called "best management practices"—to reduce the amount of pyrethroids entering streams from farm fields.

Planting vegetation in drainage ditches as buffers to sediment movement is one option. Diverting runoff into managed wetlands is another. The team also will investigate using a special material on farmland that causes sediment to settle out before it reaches creeks or streams.

These experiments will be carried out on test fields in several California counties. The team hopes to dramatically reduce the toxicity of sediment downstream from the fields. Again using Hyalella, Lydy will test the success of these efforts.

But it's in the suburbs that mitigation practices could make the biggest difference, Lydy says. Educating homeowners and lawn services will be key. Already, thanks to Weston and Lydy's research, California is requiring pesticide manufacturers to re-register their pyrethroid formulations for both agricultural and residential use and to adopt new labeling requirements for products containing pyrethroids.

Consumers can help by using as little bugkiller on their lawns and gardens as possible, following package directions precisely, making sure they (or their lawn services) don't apply pesticide when it's likely to rain, and not rinsing off spreaders on concrete.

This is one environmental problem the average person has the power to affect—starting today.

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