Proposed selenium standard under attack
The U.S. EPA’s proposed standard for selenium discharges to rivers and streams has come under attack by aquatic biologists and U.S. Department of Interior (DOI) experts, including the author of a key study that is the basis of the new regulation. But EPA officials contend that the proposals—which were welcomed by power companies, mining officials, and California farmers—adequately reflect the study’s conclusions and will give selenium regulations a firmer scientific basis to protect sensitive fish.
The current controversy is the latest in more than a decade of arguments over selenium that have pitted DOI scientists against industry scientists and EPA. The dispute began shortly after EPA set a chronic water quality standard of 5 parts per billion (ppb) in 1987. Biologists from the U.S. Fish and Wildlife Service (FWS) and the U.S. Geological Survey (USGS) argued that this standard should be cut in half to protect fish and birds. However, industries that discharge selenium said that the standard was overprotective and burdened operators with excessive compliance costs (Environ. Sci. Technol. 1998, 32, 350A; 2003, 37, 274A–275A).
Selenium is a naturally occurring element and an essential micronutrient, but it can accumulate to harmful levels in fish and birds at the top of the food chain. The effects of extreme selenium poisoning were vividly demonstrated in the 1980s, when the metal deformed and killed hundreds of fish and birds at California’s Kesterson National Wildlife Refuge. In most cases, it is chronic exposure to relatively low doses in adults that leads to developmental effects in bird and fish embryos. Some studies show that dietary selenium levels only a few times higher than normal may cause such developmental problems.
The toxic element concentrates in waters as a byproduct of mining. And it is in the water used to irrigate fields over much of the U.S. Southwest. The metal also leaches out of piles of coal ash at power plants. The 2003 discovery of high selenium concentrations in West Virginia rivers downstream of mountaintop mining operations temporarily jeopardized this controversial activity.
However, adverse effects in the field are hard to find, contends Peter Chapman with EVS Environment Consultants in Vancouver, Canada, which advises coal mining interests. “There is nothing catastrophic happening to fish populations, even in the areas most affected by coal mining,” he says. It is difficult to apply laboratory findings to wild populations when many are limited by habitat competition rather than by selenium-mediated effects, Chapman adds.
Like mercury, selenium has a complex aquatic cycle, and diet is thought to be the main exposure route, according to aquatic toxicologists. Consequently, EPA’s current chronic criterion for selenium, 5 ppb in water, is often not closely related to the amount of selenium in fish. To improve the standard’s toxicological basis and sidestep the controversy, EPA contractors finished a draft guidance in March 2002 that expressed the chronic criterion as a whole-body fish tissue concentration of 7.9 ppm dry weight.
The 2002 draft value pleased industry but infuriated DOI scientists. Aquatic toxicologists agree with the approach but not the value. FWS used its powers under the Endangered Species Act to block publication of the draft, which remained in limbo until February 2004, when the White House Council on Environmental Quality became concerned about the delay. As a result, FWS dropped its publication block. Meanwhile, 5 DOI scientists submitted a detailed critique of the 2002 7.9-ppm draft regulation to EPA in June.
Nevertheless, the new draft released in December is quite similar to its 2002 predecessor. Both identify the most sensitive species as bluegill (Lepomis macrochirus), a staple of recreational warm-water fishing. EPA’s value was derived from a study by U.S. Forest Service aquatic toxicologist Dennis Lemley that combined selenium exposure with a temperature drop to simulate the natural stress on fish during the winter (Aquat. Toxicol. 2003, 27, 133–158).
Lemley originally supported a 7.9-ppm standard, but he changed his mind and joined the June 2004 critique of the proposal. At a residue level of 7.9 ppm, 40% of the fish died, he warned. A more appropriate residue level would be 5.85 ppm, he wrote. This is because EPA’s standard is supposed to be based on the amount in selenium in fish tissue that would kill 20% of the exposed fish. The agency’s contractor misinterpreted the study, Lemley writes, because he misunderstood how many fish were used. The study started out with 210 fish – that’s the total the contractor used. But Lemley removed fish over the course of the study. This error made it appear that, at a given selenium tissue level, a smaller percentage of fish had died than actually did.
Charles Delos, EPA’s selenium proposal manager, says that the 2004 proposal accounts for this by identifying 7.9 ppm as the critical value that protects fish but calls for additional monitoring if tissue concentrations reach 5.85 ppm in the fall. DOI scientists stopped talking to the press after EPA released its proposal, but FWS Division of Environmental Quality chief Everett Wilson says that his agency is still considering whether the researchers’ concerns have been adequately addressed by the December draft.
“Using 7.9 as a blanket approach is wrong and will not protect species,” argues fish biologist Vincent Palace with the Canadian Office of Fisheries and Oceans in Winnipeg. Palace’s three-year study of the impacts of selenium from coal mining in Alberta, currently in press in Environmental Toxicology and Chemistry, finds that rainbow trout appear to be very sensitive to developmental effects at levels below 7.9 ppm.
Others take an opposite view. “The Lemley study is well done, but it’s difficult to interpret the mortality results, and it’s not the kind of study previously used,” says aquatic toxicologist William Adams, with international mining giant Rio Tinto in Murray, Utah. “The overwintering stress doesn’t apply in the south. How should Florida, Louisiana, or any of those states interpret it?”
ES&T could not verify that overwintering stress is an issue in southern states, but one state scientist spoke out strongly against the December proposal. “This 5.85 monitoring requirement is just confusing,” says the scientist, who requested anonymity. “If we get a 5.85 and then see levels going up, do we do something or do we have to wait until 7.9? We should use 5.85 because that’s protective,” he says. Delos does say that in principle action could be taken before fish tissue levels reach 7.9 ppm, but he says the details have not yet been worked out.
EPA is taking comments on the proposal until April 18. Meanwhile, the agency is funding USGS to develop a separate aquatic standard for California that would protect wildlife as well as fish.
