release of the report seemed stalled. In a letter to EPA Administrator Carol Browner and Shalala, the National Fisheries Institute castigated EPA, saying, "This report will unnecessarily raise public fears about consuming fish and seafood." The institute's criticism was joined by several senators. Then in late February when EPA decided to formally issue the report as a draft, a spokesperson with the Edison Electric Institute, a utility-funded trade association, said, "The Seychelles study is not showing a toxic effect from fish consumption, and this important new data should be included in the report. EPA should not release a mercury study that is not based on the best available science." The Seychelles' study follows mother-infant pairs whose fish
consumption averages 12 meals a week. The average level of mercury in the mothers' hair was about 10 ppm but, according to an NIEHS statement, the study found no impairment in children whose mothers' hair contained as much as 36 ppm of mercury, three times EPA's safe level of 11 ppm. Harvey defended EPA's decision to release the report without the Seychelles data: "First, it is only partly available. The full results from the Seychelles study will follow the children's development to age five. What we have now is a partial analysis of the data to age two, and we don't know when the full results will be available." Meanwhile, for mothers with mercury levels comparable to EPA's recommended level, there would be no observable de-
velopmental effect, which is what the preliminary data show, he added. Shalala's recommendation to put off a decision until 1998 is based on NIEHS's view of how to handle the uncertainty in previous epidemiological studies, Harvey said. "We have used an existing EPA methodology to account for this uncertainty, and we are comfortable with it. NIEHS is not." EPA's report charts a clear path back from ingestion of methylmercury, a powerful neurotoxin, by fish to power plant emissions, added Steve Page, EPA Office of Air and Radiation communications director. It will have significant ramifications for utility industry regulation and advice concerning fish consumption. —REBECCA RENNER
Toxicity of aquatic mixtures yielding to new theoretical approach Researchers in the United States and the Netherlands are developing tests to predict the toxicity of complex chemical mixtures in the aquatic environment. Building on new research on the classification of chemical compounds by their "mode" of toxic action and a recently developed analytical procedure that estimates total bioconcentration, such tests could provide more information than do current empirical methods that determine toxicity by placing living organisms directly into effluent. Determining the toxicity of a complex chemical mixture is not straightforward because the toxicities of individual chemicals are not simply additive when combined. The total toxicity of a mixture may be less or more than the sum of its parts, depending on the chemicals in the mix. Toxicologists have long known that chemicals that influence an organism in the same way—have the same "mode of action"—are additive. But until recently they have not known which chemicals shared the same mode of action, or even how many different modes of action there are. Quantitative structure-activity relationship (QSAR) studies are providing that information by classifying chemicals with similar structural features and similar
modes of action, according to toxicologist Steve Bradbury of the EPA Environmental Research Laboratory in Duluth, Minn. Research at Duluth indicates that, in the aquatic environment, "a large range of chemical structures and classes can be classified into some five or six mode-of-action groups," he said. By first identifying the mode of action for each group, aquatic toxicologists hope to construct a framework of knowledge that will allow them to predict the toxicity of mixtures containing many groups. Although tests to predict the toxicity of mixtures still require
Additive toxicity A new analytical method estimates the toxicity of chemical mixtures in the aqueous phase by simulating bioconcentration in aquatic organisms. The "baseline toxicity" is the cumulative concentration of all compounds (three in this example) when the chemicals have the same toxic effect, or mode of action.
Source: Environ. Sci. Techno!., 1995,29,728.
considerable work, recent research is probing mixtures dominated by one mode-of-action group: narcotic chemicals. The toxicity of narcotic chemicals, often termed baseline or nonspecific toxicity, acts as a reversible general anesthetic. This group often dominates the toxicity of aquatic mixtures because it includes many industrial chemicals that were not designed to be biologically active, including chlorinated benzenes, toluenes, and alkanes. In standard biological toxicity tests of aquatic species, the effects of mixtures of narcotic chemicals are completely additive for endpoints such as mortality, inhibition of reproduction, and growth, according to Joop Hermens at the Research Institute of Toxicology, Utrecht University, the Netherlands. However, moving from the toxicity of mixtures in the lab to the toxicity of mixtures in the environment is a difficult step because from the moment a mixture enters the environment, its composition changes. No single rule or factor can be applied to convert the mixture toxicity determined in the lab to effects in the environment. Toxicologists at the Research Institute of Toxicology, Utrecht University, have devised an ana-
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lytical procedure to estimate exposure in the aquatic environment. They account for bioconcentration in the environment by measuring the concentration of each chemical onto a hydrophobic substrate, which serves as a surrogate for bioconcentration in the environment (Environ. Set Technol. 1995,29, 726, 734). By analyzing the chemicals on the substrate and not the mixture itself, they account for some of the changes in the effluent composition that occur in the environment. Because narcotic chemicals dominate the toxicity of the mixtures being analyzed, the toxicologists need only measure the total molar concentration extracted during this concentration process to determine the total mixture toxicity The results of such analyses must be treated with some caution, according to Hermens. The procedure measures only the nonspecific toxicity of mixtures; chemicals with more specific modes of actions (for example, mixtures of polychlorinated biphenyls [PCBs] and dioxins) must be treated in another way. But despite these limitations, this approach is a breakthrough, according to Bradbury. "The Utrecht group is using the modeof-action idea to sort out this one toxicological group. It's a pattern for handling other groups." Most aquatic toxicologists agree that the QSAR-based approach for determining the toxicity of mixtures requires further development before it can be put to practical application. Mixture effects are, to a limited extent, already incorporated into regulations, and there are indications that such approaches will be increasingly used. In the Netherlands, the government applies an extra "application factor" of 100 to individual standards to deal with combined exposure. Although this is a first step, Hermens says, the factor does not have a sound scientific basis and is still controversial. Instead, he believes that because regulation of chemicals usually is based on standard bioassays, the theoretical work on mode-of-action groups forms the basis for including mixture effects in regulations. —REBECCA RENNER
NEWS
TECHNOLOGY
NOAA project attempts to rebuild coral reefs Widespread deterioration of coral reefs and a recent project to rebuild damaged ones was addressed at a symposium of the American Association for the Advancement of Science at its annual meeting Feb. 11. Marine biologists estimate that up to 10% of the world's coral reefs have been altered beyond recovery and another 30% will reach that status within 10 to 20 years. A new research project that attempts to reconstruct damaged reefs, although not a cure-all, may offer a tool to help preserve these elaborate ecosystems. Siltation and eutrophication from erosion and sewage, overharvesting of aquatic species, and physical destruction from shipwrecks and dynamiting by fishermen are the chief forces destroying the world's coral reefs and the species that inhabit them, said marine biologists at the meeting. In turn, the damage makes corals and other reef organisms more susceptible to infectious pathogens, noted Esther Peters, a biologist with the consulting firm TetraTech, and an expert in histopathological changes in coral. Coral reefs are also hit by long-term, global factors, such as increased ultraviolet light caused by depletion of the stratospheric ozone layer, speakers emphasized, which results in coral bleaching through expulsion of symbiotic algae. The decline of coral reefs may
increase, according to recent data presented by James Thomas of the Smithsonian Institution. Thomas said reef species have a much higher level of endemism than previously thought. Because they are restricted, endemic species are particularly susceptible to extinction by catastrophic local events, noted Marjorie ReakaKudla of the University of Maryland, who added that only 10% of reef species may be known. A pioneering project by the National Oceanic and Atmospheric Administration (NOAA) in the Florida Keys addresses one of the more severe impacts on reefs: gross destruction by shipwrecks. The project was conducted on a larger scale and with greater technological support than previous efforts, and it appears to have been successful, according to project director Charles M. Wahle. At two sites of 1989 ship groundings off Key Largo, 4000 square meters of reef had been destroyed by the groundings and subsequent salvage operations. The reconstruction used barges as floating work stations, tethered over the reefs to prevent additional damage. Unstable coral rubble piles were removed and craters in the reefs filled in. At one site, both the shallow, six-foot depth and large crater size presented major challenges, Wahle said. There, 10-ton custom-made concrete blocks with embedded fossil coral from upland quarries
A construction barge works at reef restoration site in the Florida Keys.
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