Richard J. Wenning is the Practice Director for Environmental Management & Risk Services at The Weinberg Group, San Francisco.

Riwe@weinberggroup.com

This is the first column of a new feature in Contaminated Soil Sediment & Water devoted to current developments in characterization and assessment, remediation technologies, and regulatory issues confronting the management of contaminated sediments and dredged materials. This column, written either by myself or an invited expert, will highlight the technical and regulatory challenges facing port authorities, industrial dischargers, POTWs, resource conservationists, and environmental agencies charged with the protection of aquatic environments.

The challenges posed by assessment, remediation, and management of sediment in the U.S. are not trivial. According to the United States Environmental Protection Agency’s (USEPA) Contaminated Sediment Management Strategy (April, 1998), as much as 10% of the sediment underlying surface waters in the United States contains chemicals at concentrations that may adversely effect fish and wildlife. And, the consumption of contaminated fish from affected waterways may pose a health risk to fishermen. Assuming the USEPA estimate (approximately 1.2 billion cubic yards in the top 5 cm) is reasonable and further assuming that sediment material 2 to 3 feet deep is the practical management scale, as much as 20 trillion cubic yards of sediment requires some form of management at the present time. According to the Sediment Management Work Group (SMWG; www.smwg.org), an ad hoc technical work group dedicated to resolving science and management issues in this arena, sediment management in the U.S. would likely exceed $5 trillion at a median cost for environmental dredging of $250/cubic yard if removal was the only management option.

Two recent symposia suggest that the management of contaminated sediment and dredged material is poised for national debate with potentially far-reaching consequences in the U.S. It may well become one of the biggest environmental challenges facing USEPA and the next President.

SETAC Sediment Criteria Debate

At the 21st annual meeting of the Society of Environmental Toxicology & Chemistry (SETAC) held in November, Dr. Peter M. Chapman (EVS Consultants) and Dr. Wes Birge (University of Kentucky) hosted a debate on the merits of setting a single, unified approach for the use of sediment quality values (SQVs). According to the premise put before some 150 participants, the use of SQVs should never be elevated beyond their use as a screening-level tool to determine whether chemical conditions in sediment warrant further study prior to implementing a management decision.

There was no consensus on the use of SQVs, and considerable concern about the scientific validity of various current approaches, particularly those proposed for metals and high Koc, nonionic organic chemicals. While several members of the regulatory community spoke to the need for specific numerical guidelines rather than a screening-level approach, members of the regulated community urged flexibility and site-specific consideration. It was evident from the discussion that the numeric values that comprise an SQV scheme can have fundamentally different management purposes in navigation channels, at CERLA sites, in harbors and estuaries, lakes, offshore from POTWs, and in rivers and streams.

Perhaps even more contentious than numeric criteria is the debate among experts on what constitutes a “screening-level” sediment assessment. Regulatory agencies and scientists in both the U.S. and Europe have proposed several different sediment assessment schemes. The different schemes generally have a common management framework, such as that illustrated in a National Academy of Sciences review[1] of cleanup strategies and technologies for addressing contaminated sediments in ports and waterways (Figure 1).

The definition of “screening-level” varies depending upon the management context, which may be focused on: dredging and disposal; ecological risk assessment; contaminated site investigation; natural resource damage assessment; or, baseline evaluation. At the core of the debate is the definition of measurement parameters, which require considerations of seasonality, sample size, sedimentology, target analytes, biological sampling, and sediment effects testing.

MIT Sediment Assessment Debate

The SETAC debate continued less than one month later during the one-day risk assessment and sediment toxicity workshop conducted as part of the Conference on Dredged Material Management hosted by the Massachusetts Institute of Technology (MIT) Department of Environmental Engineering in early December. 

At issue in the debate among 50 participants and an invited panel of ecology, biology, and ecotoxicology experts was contrasting biological testing results with either a numeric- or effects-based SQV scheme. To some extent this relates to the continuing debate among ecological risk assessors as to how close we should be getting to comparing impaired or altered aquatic ecosystems to natural, or undisturbed, conditions in terms of chemistry, ecology and biology. If the environment and human use of the environment are constantly evolving, then the key questions in this debate are whether biological responses to chemical contaminants or population level changes in ecological communities represent adverse events or an adaption to changed conditions. Adaptation, as opposed to acclimation, may not have energetic costs to the organisms involved (though organisms not able to adapt may be excluded from such environments).

The question also relates to how SQVs should be used and when (or if) SQVs should be used to overrule biological testing results. Unfortunately there is a reluctant acknowledgement among ecotoxicology and risk assessment experts that it is almost impossible to account for, let alone distinguish the causes of, observed toxicity to test species based upon sediment chemistry data. Indeed, the debate at MIT started by asking whether the word “toxicity” was appropriate when discussing sediment testing. In the context of so many confounding environmental factors such as salinity, sediment chemistry, and chemical mixtures, some experts believe SQVs should reflect either a range of numeric values or a classification scheme based on grades of contamination, reflecting the uncertainties inherent in the sediment assessment process.

Research conducted over the past few years at Battelle by Dr Jack Word (MEC Analytical Systems Inc.) and others has identified a series of questions that address the potential for confounding factors to influence the outcome of sediment tests. According to Dr. Word, there are four categories of confounding factors in sediment tests: persistent sediment features such as grain size and total organic carbon; non-persistent features such as ammonia and salinity; exposure and behavioral coincidence between test organisms and the contaminants in pore water and the sediment - water interface; and, factors attributable to differences among laboratories involved in conducting and reporting the results of sediment tests.

Experts will readily acknowledge that risk assessment of a single chemical in sediment is a poor approach to managing contaminated sediments in the aquatic environment. Yet, the debate is equally fierce regarding the approach to evaluating mixtures of chemicals. Considerable effort is underway at USEPA environmental laboratories to develop SQVs for chemical mixtures and classes of chemicals such as those proposed by Swartz et al. for polyaromatic hydrocarbons (PAHs). The ongoing debate focuses on the fact that all PAH mixtures are not the same. While toxic equivalency factors based on additive dose-response models may be appropriate for narcotic chemicals, not all PAHs are toxic due to narcosis, and some individual PAHs impose significant toxic effects regardless of their presence in a mixture. In contrast to the scheme developed for the dioxins, the utility and relevance of SQVs for PAH mixtures remains much in doubt.

A Forum to Resolve this Debate?

The next stage in this continuing debate is likely to occur next year, if the funding effort currently underway is successful. Dr. Peter M. Chapman, others and myself plan to convene a workshop to facilitate an "objective" analysis of the management issues raised this past Fall at SETAC and at MIT. The workshop will provide guidance for national and international development and usage of SQVs where presently there is no guidance and very different decisions are being made depending on the individuals and jurisdictions involved. Not only is there no surety that the environment is being protected in all cases, there appears to be certainty that, in many cases, both science and common sense have been set aside in favor of questionable numeric SQVs and management schemes.

The key questions encompassing the current debate include: how SQVs should be used to evaluate sediment contamination; the role of SQVs in sediment assessments; the differences between screening-level and more detailed assessments; and, the minimum requirements and tools for conducting a contaminated sediment evaluation.

We invite anyone interested in resolving these issues to contact Dr. Peter M. Chapman (pchapman@attglobal.net) or Richard Wenning (riwe@weinberggroup.com) with recommendations for the workshop.

[1] National Academy of Sciences, 1997. Contaminated Sediments in Ports and Waterways: Cleanup Strategies and Technologies, National Academy Press, Washington, D.C.

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