ENVIRONMENTAL NEWS Growing acceptance of soil contaminant bioavailability kicks off national meeting
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his month officials from EPA, the National Institutes of Environmental Health Sciences and the think tank National Environmental Policy Institute (NEPI) are gathering to discuss the scientific and policy issues concerning the bioavailability of contaminants in soil. The conference follows a flurry of meetings and workshops on bioavailability held this year, all pointing to a growing acceptance among remediation specialists that the reduced bioavailability of contaminants in soils over time is a real phenomethat should be considered in regulatory cleanup decisions said University of Texas environmental engineer Ray Loehr a former head of EPA's Science Advisorv Board whose dprade-loncr resparch on bioavailability has bppn at forefront of studies in this field Interest in the reduced bioavailability of contaminants is being fueled by scientific advances and the ascendancy of risk-based cleanup strategies, according to NEPI deputy project director Gregory Planicka. Some states have adopted new riskbased cleanup regulations that are designed to incorporate bioavailability, he said. NEPI has been promoting the importance of bioavailability in assessing hazardous waste cleanups at Superfund and other sites for several years. The growing acceptance of bioavailability has not been lost on EPA officials. "Capitol Hill, the private sector, and the states all want to know about bioavailability," said Peter Grevatt, science advisor for EPA's Office of Solid Waste and Emergency Response. That is why EPA program offices held talks earlier this year to develop an agency perspective on the issue, said Grevatt, who is
In this sediment sample, more than 100 times more PAHs are sorbed on black carbonaceous organic particles than on silica particles. This knowledge improves bioavailability predictions and management decisions. (Courtesy Richard Luthy, Carnegie Mellon University)
part of a work group developing guidance for the agency on bioavailability. Initially, bioavailability was the darling of industries faced with contaminant liability. It has been gaining acceptance among scientists and regulators involved in remediation as a result of increasing evidence for its occurrence and the shift to risk-based cleanups that explicitly ask, when is a site clean enough?, added Loehr. But while there has been a lot of progress in understanding bioavailability, at present, there is almost no way to measure it in the field. None of the proposed methods based on extraction or toxicity would survive the tiny of public interest groims or the rigors of beine incorDorated into the regulatorv process said Gillette head of Cornell's bioavailability research program With the exrention of lead there is not a sinplp validated mpthod for measnrinp bioavailabilitv Gil Iptte said Discussions on bioavailability can be confusing because different groups use the term to mean different things, observed Grevatt.
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Engineers use bioavailability to describe the amount of soil contamination that can be cleaned up by bioremediation. Toxicologists use it to describe the amount of contamination that gets into an organism, which is the meaning that EPA currendy attributes to the term. In addition, a new buzz word, "environmentally acceptable endpoints," is increasingly being used, especially by industry groups such as die Gas Research Institute in Chicago, 111. Industry groups use environmentally acceptable endpoints to describe a risk-based approach that involves determining cleanup levels that would protect specific organisms, for example, earthworms or birds that feed on them. Bioavailability is a major part of the environmentally acceptable endpoints approach because it plays a significant role in such a risk-based analysis. Among remediation specialists, opinion is divided over how soon it might be possible to account for bioavailability. The factors that control the bioavailability of metals are much better understood tiian those that affect organic contaminants, said Martin Alexander, an environmental toxicologist at Cornell University. Many researchers believe that a relatively cheap, rapid in vitro test for determining bioavailability is just around the corner for lead where bioavailability is best understood For some heavy organic contaminants such as polycyclic aromatic hydrocarbons (PAHs), wood preservatives, and some soils, measures of bioavailability are also in the pipeline, according to Loehr. "We are getting awfully close to a protocol that will allow some judgements," he said. Loehr's research group at the University
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of Texas-Austin, which is one of many looking for a way to apply bioavailability to cleanup decisions, is trying to correlate soil characteristics with the results of soil extraction experiments. For some organic compounds, such as DDT and some PAHs, and for some soils, there is a correlation between the extraction tests and bioavailability, said Alexander. In these cases, the fraction of contaminants easily extracted is a good approximation of the bioavailability fraction. But in other cases, he said, the picture is not so simple because organisms are able to use contaminants that are not readily extracted Bacteria for example excrete a substance that ca.fl mobilize contaminants and earthworms can access an even greater proportion than bacteria he said "We don't know the mechanisms and we don't have ennncrh i n f o r m a t i o n to predict which o r g a n i s m s ar-npcc t r i e
m o s t " h e said Alexander's p r o n n is r u r r e n t l y dpvplnning a t r m r i t v tpqt to measiT hinavailabil'ti
A major new research direction being pursued in the United States and in Europe, Gillette said, involves the use of ultramicroscopic techniques designed specifically to study the molecular-scale locations where organic compounds accumulate. "Until recently, we have largely relied on macroscopic measurements to infer microscopic phenomena. But we need a better understanding, and for that, we need to locate these compounds precisely on environmental samples " added Richard Luthv a civil engineer at Carnegie Mellon University who organized last month's National Research Council meeting to develop a research stratppv for u n d e r s t a n d i n g sequestration bioavailability
Interest in bioavailability is growing at EPA. At the most recent Superfund Basic Research Program meeting, 50-60% of the research concerns voiced by staff were about bioavailability, according to Cornell's Gillette. Existing risk assessment guidance for the Superfund program supports the use of bioavailability in risk assessment and decision making. But EPA officials are cautious. Grevatt reeled off a list of issues
that must be considered if reduced bioavailability is to be a factor in determining soil cleanups. These include the uses and future uses of the site, the organism that can access the greatest amount of contaminant and the pathway by which this exposure occurs. It also is important to remember that the toxicity assigned to a contaminant is based on laboratory testing, he said. This means that the relative bioavailability of the contaminant be-
tween the laboratory and the field is crucial for risk assessment. Efforts to incorporate bioavailability into risk assessments are furthest along for lead, Grevatt said, and these provide some pointers for the future. For other metals, particularly arsenic, there have been some important advances, and there has been progress with some PAHs—all driven by industry groups interested in expediting the cleanup process. REBECCA RENNER
Congress fits controversial riders into budget Congress approved $7.56 billion for EPA's 1999 fiscal year budget, handing the agency funding similar to what it received last year. The budget is about $197 million over last year's level, and includes $650 million for the science and technology programs, of which $47 million is set aside for particulate matter (PM) research. A separate $2.1 billion is provided for the Superfund program, and $110 million is provided for programs to reduce greenhouse gases The budget process this year entailed weeks of political haggling, with Congress originally writing into the budget bills as many as 56 provisions affecting environmental policy, environmental groups said. Several affecting EPA were softened. For example, a move by the House of Representatives to ban the use of dredging to remove contaminated sediments was dropped. The law now suggests that EPA wait for the results of a National Academy of Sciences (NAS) report before it •inn roves
the dredging of sediments Congress also advised the NAS
to complete mercurv emissions by April and reauested that EPA hold off until
the report is final Efforts to fix the Superfund program were finally dropped, including a proposal to reinstate the corporate tax on the oil, gas, and chemical industries that goes into the Superfund cleanup account, and a provision that would provide limited liability exemptions to small polluters. President Clinton signed into
law a delay in the deadline for phasing out the pesticide methyl bromide, which scientists say worsens the ozone hole. The new deadline is 2005, the same date set under the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. The new provision allows U.S. farmers to seek an exemption once 2005 has passed, environmental groups said. Congress also commended EPA for working with the NAS report reviewing EPA's PM research program, most likely in an effort to nudge EPA officials to continue to follow the academy's suggestions, said one budget staffer (ES&T, May 1998, p. 209A)) But it funded EPA's PM research programs at just $2 million more than last year's $49 million. As much as $2 million were earmarked for research into studying the causes mechanisms and underlying health and environmental effects of Pftesteria Last year Congress approved $15 million for Pftesteria research Congress approved a total of $110 million for programs designed to reduce greenhouse gases: $99.5 million in the EPA budget and an additional $10 million in the omnibus budget bill. Clinton had requested $205 million for climate change activities. To reflect its lack of support for the international agreement to reduce greenhouse gases, Congress initially wrote a provision that would prevent EPA from implementing any program that might be construed as implementing the Kyoto Protocol on
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