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(SPOKANE, Wash.) — Snails play a vital role in the ecological health of the Inland Northwest because they form the base of the region’s food chain for game fish. Now, Gonzaga University biology Professor Hugh Lefcort has discovered that snails in the polluted Coeur d’Alene River Basin actually benefit from small amounts of heavy metals pollution. Paradoxically, the findings indicate that snails – and, by extension, game fish – may be threatened by a complete cleanup of the Bunker Hill Superfund site in North Idaho.
Professor Lefcort working afield in the Coeur d'Alene River Basin
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“We have discovered that a small amount of heavy metal pollution — such as lead, zinc and cadmium — has a positive effect,” Lefcort said, pointing to his article published earlier this month in the journal EcoHealth (Volume 5, pages 10-17, 2008). It’s titled: “Hormetic Effects of Heavy Metals in Aquatic Snails: Is a Little Bit of Pollution Good?”
The site is one legacy of more than a century of mining in Idaho’s Silver Valley. Once one of the world’s most productive sources of silver, the area is now among the nation’s worst uncontrolled hazardous waste locations. The Environmental Protection Agency’s Superfund status is reserved for sites the federal government aims to completely clean up to protect the environment and public health.
Lefcort said his research could cause the EPA to reassess its approach to the cleanup.
“All government regulations of pollution are based on the theory that if a large amount of pollution has a large effect then half as much pollution should have roughly half as much effect, and so on,” Lefcort said. “Our findings that a small amount of pollution is better than no pollution turn all that regulation on its head.”
Lefcort, who has published numerous studies documenting the negative impact of heavy metals on the health of snails, began noticing something unusual in his experiments a few years ago. He spotted anecdotal indicators of a scientific anomaly known as the hormetic effect. Hormesis describes the stimulatory or beneficial effects associated with a low dose of a toxic or potentially toxic substance or stress.
“We noticed a persistent and heretofore unexplainable trend of a positive effect on growth and reproduction at low doses of metals,” Lefcort noted. “For example, we had anecdotal evidence that low levels of heavy metals were causing increased snail growth and recruitment (Lefcort et al., 1999, 2002). We discerned that high levels of metals killed snails but low levels left snails unaffected while killing their susceptible helminth parasites” (Lefcort et al., 2002).
To test for hormetic effects, Lefcort and students Zachary Freedman, Sherman House and Mathew Pendleton repeated a version of an earlier experiment but expanded the low-dose treatment and increased the sample size. The researchers also explored whether metals had a hormetic effect on algae.
“I figured that if you have been exposed to something for that long, then maybe you no longer are impacted. Or, maybe you have actually become dependent on it,” Lefcort said. “We found that snails from these lakes actually do better with a little bit of pollution than they do in clean habitats. A small amount of metals make them grow bigger and reproduce more.”
Lefcort raised snails from two separate sites in outdoor mini-ecosystems. One mini-ecosystem was comprised of snails and soil from the Silver Valley Superfund site contaminated with lead, zinc and cadmium. This site is located within the Lateral Lakes region at the western end of the Coeur d’Alene River in North Idaho, between the Silver Valley and Lake Coeur d’Alene. The snails in this population (Physella columbiana) have evolved for 120 years amid heavy metal contaminants.
The snails in the other ecosystem (Lymnaea palustris) were not exposed to heavy metal contaminants. (The second site was a reference pond, Favour Pond, located 40 kilometers from the polluted sites and is not impacted with heavy metals.) Both sites had large colonies of reproducing snails.
Lefcort discovered the first population of snails, those exposed to small amounts of metals, exhibited more reproduction and growth than snails not exposed to metals. Lefcort found that the naturally occurring Oscillatoria algae also exhibited a hormetic effect from heavy metals. However, the snails not exposed to heavy metals (Lymnaea palustris) displayed no evidence of hormesis.
The findings conclude that large doses of heavy metals negatively impacted all three species (Physella Columbiana, Lymnaea palustris and Oscillatoria algae). Overall, there was an inverse correlation between the levels of cadmium, lead and zinc in snails’ tissues and the number of snails recruited into each population.
Snails with lower levels of heavy metals recruited more snails into their populations than snails with higher levels of heavy metals contaminants. A positive impact or benefit to snails was found only in those with the lowest levels of metal contaminants.
As a result of the study, Lefcort and others could not reject the hypothesis that a small amount of heavy metals pollution may benefit the environment, and raised the question: Will the EPA’s efforts to clean up the area cause the snails to suffer and result in major change to the area’s ecosystem?
“This work is important because the eventual goal of the Environmental Protection Agency is to clean up this area. If they do this then the snails may suffer,” Lefcort said. “This will cause the snail’s fish predators to suffer, and then the fishermen who catch those fish. A cleanup may actually hurt the tourism industry.”
For more information, contact Hugh Lefcort at (509) 323-6706 or via e-mail.
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