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Sediment Management:
Deciding When To Intervene 2 2 A • JANUARY 1, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
Identification of cleanup options for contaminated sediment requires a solid mix of pragmatism and sound science. GAIL K R A N T Z B E R G , J O H N H. H A R T I G , AND M I C H A E L A. Z A R U L L
D
iverse government and private sectors in the Great Lakes Basin have reached a consensus that contaminated sediment is an important element of many of the ecological impairments in the Great Lakes. Contaminant uptake and movement through the food chain have resulted in consumption advisories and in tumors and other deformities in fish and wildlife. The contamination impairs fish and wildlife habitat and raises human health concerns regarding drinking water and swimming. Moreover, high levels of phosphorus in polluted sediment can make nutrient control and elimination of nuisance algal blooms problematic. In devising sediment management strategies, decisions need to be made bearing in mind the relationship between contaminated sediment and the renewal of environmental quality, which goes far beyond setting numerical chemical cleanup criteria, as these strategies are not based on the need to fully recover natural ecosystem processes. Unfortunately, few, if any, simple or proven methods have become available to predict ecosystem recovery based on sediment cleanup. What is needed is a pragmatic means of interpreting comprehensive sediment bioassessment data that leads to the selection of ecosystem-based and cost-effective options for management of contaminated sediment. Toward this end, a variety of analysis tools—for example, multivariate statistical methods, graphical plotting techniques, and steady-state bioaccumulation models—are available that can be used to evaluate and manage contaminated sediments. Multivariate statistical methods are useful for characterizing distinct community assemblages in the Great Lakes. Such statistical techniques enable an assessment of the similarity of reference community assemblages to those found in suspected or known contaminated sediment sites. Local support for cleanup efforts also needs to be fostered. An evaluation of both short-term adverse effects and long-term beneficial results of contaminated sediment management should be undertaken. It is imperative that source control be achieved to a level that will not recontaminate an area that has been cleaned up. Used in this context to support management decisions, modeling also permits an integrated assessment of various source control and sediment cleanup options. Assessment elements Substantial progress in developing bioassessment frameworks has occurred recently, and in many cases, large data sets now contain the necessary components for selecting a sediment management strategy. At the same time, there is a growing convergence of opinion about what central data categories are needed in order to carry out a scientific determination of the extent and severity of a contaminated sediment deposit. Knowledge of chemistry alone is insufficient; five basic components compose the foundation of a comprehensive sediment assessment: JANUARY 1, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 2 3 A
• benthic community structure; • laboratory bioassays for evaluating the toxicity of in-place pollutants; • bioaccumulation and biomagnification information, including estimates of tissue concentrations in both invertebrates and vertebrates in the food web; • knowledge of site stability, including fate and transport; the potential for mobility with disturbance over long time periods; and the bioavailability over a range of sediments, sediment pore waters, organismal microenvironments, and overlying water chemistries (pH, redox, and hardness); and • physico-chemical sediment properties. Although often overlooked as a central element, bioaccumulation can be used to interpret observed toxicity, exposure duration, pathways, and routes of exposure by which contaminants in sediment can reach fish and fish-eating birds and mammals, including humans. Contaminants like PCBs can be present at concentrations in sediment that are not toxic to benthic invertebrates but that can result in fish consumption advisories for humans and impaired reproduction in fish-eating wildlife like mink and bald eagles.
FIGURE 1
Predicting the likelihood of ecosystem impairment by contaminated sediment A distribution of hypothetical study (test) sites within the ordination axes of the reference sites provides clues about possible ecosystem impairment. The axes are defined through mulitivariate statistical methods and are described by the physical, chemical, and geographical characteristics of reference sediment sites. The farther the test site falls from the central ellipse, the more likely it is that the sediment diverges significantly from the reference conditions, thereby suggesting the influence of sediment contaminants.
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In applying an ecosystem approach to sediment assessment and management, an analysis of the likelihood for sediment to adversely affect the system would look beyond benthos and further consider die nature and extent of fish tumors and abnormalities and the risk to human health from sediment contamination, and wildlife risk from sediment contamination. A way to interpret data Equally important to the collection of data is that sufficient attention be placed on thorough and comprehensive data interpretation. Decisions to clean up contaminated sediment depend on a large number of variables—sediment bioassessment, economics, legal and regulatory frameworks, available technology, funding, and other factors. Sound science must be included as an important element. By using scientifically sound, ecologically relevant methods of data interpretation, the information from an intensive sediment assessment can finally be integrated to make the science-based judgment about whether to intervene (remediate contaminated sediment) or pursue source control and recovery as the preferred remedial options. Also, the sampling design used should enable one to determine whether contaminant sources are historic or current, and facilitate the identification of any potentially responsible party to the contaminant deposit. Although scientific frameworks for evaluating the ecological significance of contaminants in sediment are either lacking or not widely used or communicated, it is possible to suggest the beginnings of a pragmatic data interpretation framework. This data interpretationframeworkwould use the best science and lead to the selection of cost-effective options for management of contaminated sediment, which would result in ecosystem-based improvements (see Table 1). For example, a recent approach used in the Great Lakes could be implemented consistently across jurisdictions to determine the significance or severity of benthic community structure data or laboratory toxicity results. Using this method, a reference site database is used to predict the structure of the benthic invertebrate community or the response of bioassay species for a test site in the absence of impairment. The test site's potential for a certain faunal community or bioassay end point can be based on variables that are least affected by anthropogenic impacts for instance, geographic location, particle size distribution, and major elements. The distribution of the reference sites provides the range of expected variation in unimpaired communities. The actually observed community at the test site can then be compared to this normal variabilitv The greater the departure from the reference sites as measured in multivariate space the greater the certainty that biota at the test site are responding to contaminants A Great Lakes study (i) assembled a database from 312 locations across all the lakes and analyzed the data to establish reference conditions. Information from each site included the responses of four benthic macroinvertebrate species used in lab-
oratory bioassays, benthic invertebrate community structure, and selected environmental variables from the same site. Assessment proceeds as follows: Using multivariate statistical methods and the assembled database, distinct community assemblages can be characterized in the Great Lakes. In addition, the invertebrate community at any test site in the Great Lakes can be predicted (average error rate, 12%) from the measurement of 12 habitat attributes (latitude, longitude, depth, alkalinity, pH, TN, TOC, K20, CaO, MgO, MnO, and Si02). Assessment of the (impaired/ not impaired) condition of the invertebrates found at a test site then involves comparing them with invertebrates found at reference sites to which the test site is predicted as belonging. The reference communities can be plotted graphically as a site "cloud" in ordination space. By plotting a test site with the reference sites' cloud (see Figure 1), the similarity to the reference sites can be determined by using probability ellipses for the reference sites only and examining the position of the test site relative to the reference site ellipses. A site is defined as "equivalent to reference" if it is within
die 90% probability ellipse; "possibly different" if between the 90 and 99% ellipses; "different" if between the 99 and 99.9% ellipses; and "very different" if outside the 99.9% ellipse (i.e., less than a 1 in 1000 chance of error). If it is concluded that the effects of bioaccumulative substances are driving the proposed sediment management action, a Natural Resource Damage Assessment can be performed. This technique, used predominantly in the United States, evaluates injuries to resources. Actions mat could restore the ecosystem functions and compensate the public for injuries to their natural resources caused by contaminants are also considered. In the injury assessment process, selected species and end points are evaluated. Target concentrations of trace contaminants (general organic chemicals) in the sediment are then calculated. Bald eagles and fish-eating birds may be selected for evaluation because they are at the top of the food chain and are highly exposed to bioaccumulative contaminants. Sport fish are often selected for analysis because of fish consumption advisories and because the public values having access to waters from which they can eat the fish
TABLE 1
Data interpretation tools A matrix of data interpretation tools relating to different ecological threats associated with contaminants in sediment can be used for making a sediment management decision aimed at rehabilitating an aquatic ecosystem. The term "use impairment" derives from Annex 2 of the Great Lakes Water Quality Agreement. Sample references
Use impairment
Assessment element
Data interpretation tools
Restrictions on fish and wildlife consumption
Bioaccumulation
Equilibrium partitioning, comparison to guidelines
(2,3)
Degradation o f f i s h and wildlife populations
Community structure, bioaccumulation
Food w e b model, weight of evidence
(2,3)
Fish tumors or other deformities
Bioaccumulation, chemistry
Reference frequencies
(4)
Bird or animal deformities or reproduction problems
Bioaccumulation, community structure
Food web model, comparison to reference conditions, weight of evidence
(5)
Degradation of benthos
Community structure, toxicity (bioassays)
Comparison to reference conditions
(5,6)
Restrictions on dredging activities (no open water disposal)
Chemistry, toxicity (bioassays), stability*
Comparison to guidelines and/or reference conditions
(7,8)
Eutrophication or undesirable algae
Chemistry, stability
Modeling
(9)
Degradation of aesthetics
Chemistry, stability
Comparison to reference conditions
(10)
Added costs to agriculture or industry (to pretreat or avoid contaminated water)
Chemistry, stability
Comparison to reference conditions
(11)
Degraded phytoplankton and
Bioaccumulation, chemistry, stability
Comparison to reference conditions, target nutrient loads
(12)
Chemistry, bioaccumulation, toxicity, benthos, stability
Comparison to reference conditions, weight of evidence
(13)
zooplankton populations Loss o f f i s h and wildlife habitat
•Physical sediment characteristics, quiescent •versus energetic site characteristics, etc.
JANUARY 1, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 2 5 A
FIGURE 2 The logic of sediment decision making In seeking to intervene beyond source control, a logical flow of elements, as well as sequencing of sediment assessment, interpretation, and management decisions, can be laid out and followed.
Steady-state bioaccumulation models are then used to calculate a No Observable Adverse Effect Level (NOAEL) in the specifically selected species of predators by using NOAEL values obtained from the control species (species with recognized toxicological effects, as cited in the literature), and site-specific information is used to estimate what would result in the corresponding NOAEL in top predators. The end point for sport fish could be tissue concentrations low enough to warrant removal of consumption advisories for a particular chemical such 3s PCBs. Siiespecific information would also be used to estimate sediment concentrations corresponding to target tissue concentrations in sport fish. Modeling is another effective tool in sediment management decision making. To consolidate local support for a cleanup effort, an evaluation mat compares short-term adverse impacts with long-term beneficial outcomes must be undertaken. This is especially true for high-energy environments, such as sites frequently disturbed by storm action, which have a greater potential for contaminant losses as a result of intervention. Once data from each of the assessment elements are interpreted, integration of the results will be required to resolve different apparent outcomes. For example, it is not unusual for benthic community structure to be found to be very different from reference conditions, yet for laboratory bioassays to find no departure from predicted end points. It is also not unusual for the reverse to be found, in which benthic community structure is deemed impaired but no measurable toxicity or bioaccumulation is detected. For illustrative purposes only (see Table 2), it is possible to demonstrate a potential means of in-
TABLE 2
Resolving differences in assessment outcomes A matrix of sample information—provided by comparisons of chemical, laboratory, field, and bioaccumulation results—and possible explanations of the outcomes can be used by decision makers to resolve apparently conflicting assessment outcome results. Except for "Contaminants above chemical criteria", + indicates that the data interpretation technique demonstrated ecologically significant degradation. A + for chemistry means that the contaminant exceeds a guideline, standard, or criteria. Benthic community structure
Contaminants above chemical criteria
Laboratory toxicity
+ +
+ +
+
+
+
+
-
Bioaccumulation
+ +
Conclusive evidence for pollution-induced degradation
+
-
Conclusive evidence for pollution-induced degradation; unlikely due to persistent bioaccumulative substances
-
-
Contaminants not sufficiently bioavailable to cause effects
+
+
-
Possible conclusions
Strong evidence for pollution-induced degradation; benthos may have developed tolerance. Alternatively, substantial change in chemical bioavailability due to handling for toxicity test (less likely)
Laboratory false positive, possibly due to change in bioavailability due to sediment handling. Aternatively, and less likely, due to an unknown chemical
+
-
Impairment could be due to water column effects
+
Although bioavailable, contaminants are not affecting the system; potential food web effects
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tegrating the data and interpreting apparent disparities. The ultimate conclusion based on various lines of evidence requires professional judgment and thorough investigation. Arriving at conclusions Although sediment remediation, removal of a mass of contaminants, and reduction of risk are important indicators of incremental progress toward ecosystem recovery, the ultimate success of sediment management activities should be judged by gains in ecosystem quality. These include, for example, elimination offish consumption advisories, restoration of fish and wildlife populations, and restoration of benthos. Considerable work has been undertaken to identify the extent and severity of sediment contamination, as well as enviionmental impairment in the nearshore zones of the Great Lakes, particularly in the Areas of Concern identified in the 1987 revision to the Canada-United States Great Lakes Water Quality Agreement. In many cases, information needed to make connections between contamination and impairment has been collected by assessing chemistry; benthic community structure and composition; laboratory toxicity; contaminant bioaccumulation and biomagnification; and sediment and site stability. If contaminated sediment is not causing or contributing to any environmental impairments and site stability is clearly known to be high, then regardless of sediment chemistry, no sediment management actions are recommended beyond routine monitoring (and pollution prevention). However, if the data that link contaminated sediment to environmental impairment or site stability cannot be ensured, an intensive assessment of the quantitative relationships between contaminated sediment and ecosystem end-points impairment should be undertaken (see Figure 2). A central tenet of rehabilitating sediment quality and renewing ecosystem health is that control of contaminants at their source remains the primary imperative for action. Only through the cessation of contaminant inputs from sources can other sediment management actions, such as sediment removal, in situ treatment, or capping, be economically viable, ecologically successful, and sustainable. Sediment management aimed at rehabilitating the environment should extend beyond source control and involve active intervention, where the weight of evidence of biological data demonstrates that action other than natural recovery is ncccsscirv Data interpretation tools (see Table 1) can help decision making regarding whether the scientific evidence warrants consideration of taking action beyond source control. However, the following additional elements require consideration in arriving at any final management strategy: • Engineering factors; (e.g., technical feasibility, contaminant reduction; and permanence of remedial options like capping, in situ treatment, and dredging and disposal); • Economic factors (e.g., cost-effectiveness and economic benefits); • Social factors (e.g., public acceptance, partners'
opinions, adherence to public use goals, and conflicting actions); and • Long-term monitoring considerations (e.g., containments and capping). That there are few, if any, simple or proven methods to predict ecosystems recovery based on sediment cleanup is in part due to a paucity of cases in which remediation has been followed by postproject monitoring. Therefore, the concept of ecological benefit forecasting (predicting ecological benefits) is an important management need, which if accomplished, would be a substantial step forward. Acknowledgments We thank the participants in the December 1998 Binational Sediment Workshop, and particularly the members of the IJC Water Quality Board's Sediment Priority Action Committee (SedPAC), for sharing their techniques and experiences with the authors. References (1) Reynoldson, T. B.; Day, K. E. Biological Guidelines for the Assessment of Sediment Quality in the Laurentian Great Lakes; NWRI Report No. 98-232; Environment Canada: Burlington, Ontario, 1998. (2) Risk Assessment Guidance for Superfund. Volume 1. Human Health Evaluation Manual. Part A. (Interim Final); EPA/540/1-89/002; Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, U.S. Government Printing Office: Washington, DC, 1989. (3) Beltran, R.; Richardson, W. The Green Bay/Fox River Mass Balance Study Management Summary: Preliminary Management Study; U.S. Environmental Protection Agency, U.S. Government Printing Office: Washington, DC, 1992. (4) Baumann, R C. /. Aquatic Ecosys. Health 1192,11 ,27-133. (5) Jaagumagi, R.; Persaud, D. An Integrated Approach to the Evaluation and Management of Contaminated Sediment; Ontario Ministry of Environment: Toronto, 1996. (6) Reynoldson, T. B., et al. /. N. Am. Benthic Soc. 1997, 16, 833-852. (7) Persaud, D.; laagumagi, R.; Hayton, A. Guidelines for the Protection and Management of Aquatic Sediment Quality in Ontario; Ontario Ministry of Environment and Energy: Toronto, 1993. (8) Evaluation of Material Proposed for Discharge to Waters of the U.S.B. Testing Manual (Inland Testing Manual); EPA823-B-98-004; Office of Water, U.S. Environmental Protection Agency, U.S. Government Printing Office: Washington, DC, 1998. (9) The Lake Model-Implementation Guidance Section 95.6: Management of Point Source Phosphorus Discharges to Lakes, Ponds, and Impoundments; DEP 391-2000-010; Pennsylvania Department of Environmental Protection: Meadville, PA, 1998. (10) Heidtke.T. M.; Tauriainen, E. An Aesthetic Quality Index for the Rouge River; Department of Civil and Enviionmental Engineering, Wayne State University: Detroit, MI, 1996. (11) Ontario Ministry of Environment and Michigan Department of Natural Resources. The St. Clair River Area of Concern: Environmental Conditions and Problem Definitions— Remedial Action Plan Stage 1 Report; Ontario Ministry of Environment and Energy: Sarnia, Ontario, 1991. (12) Bierman, V I.; Dolan, D. M.; Kasprzk, R. Environ. Sci. Techno! 1983, 18 (1), 23-31. (13) Minns, C. K.; Kelso, J. R. M.; Randall, R. G. Can.J. Fish. Aquat. Sci. 1996, 53 (Suppl. 1), 403-414.
Gail Krantzberg is Great Lakes strategic coordinator in the Ontario Ministry ofEnvironment in Toronto; John H. Hartig is river navigatorfor the Greater Detroit American Heritage River Initiative; and Michael A. Zarull is a limnologist and a program manager in the National Water Research Institite, Lakes Research Branch, Canada Centre for Inland Waters in Burlington, Ontario. JANUARY 1,2000/ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 2 7 A
