Marine sediments are the ultimate receptor of contaminants in effluent from urban, agricultural, industrial and recreational activities, both at sea and on shore. Because of past industrial and ship activities, non-point source input,...
moreMarine sediments are the ultimate receptor of contaminants in effluent from urban, agricultural, industrial and recreational activities, both at sea and on shore. Because of past industrial and ship activities, non-point source input, etc., sediments at many sites have some level of impact from anthropogenic compounds. As marine sediment and coastal sites fall under increasing scrutiny, the number of sites for which ecological risk assessment, and potentially, management, will be deemed necessary is bound to increase. Contaminated sediment sites must be ranked and prioritized, and cost-effective management strategies must be developed. It is assumed that the management process will seek to balance two parallel goals: (a) minimizing contaminant risk to the environment and human health and (b) minimizing cost.
The Office of Naval Research (ONR) funded a project to identify problems, remediation approaches, technology gaps and needs relative to managing contaminated sediments in an integrated, cost-effective way. The goal was to examine what aspects of contaminated sediment assessment and management were successful, and what barriers existed for streamlining contaminated sediment management. As stated above, sediment management is complex, potentially contentious and often regional in its approach. However, seven major themes emerged as essential to better sediment management:
• A need for better integration of sediment R&D and “user” (e.g., site managers, policy makers, etc.) communities
• A need for better use of site data for risk assessment, communication and negotiation in support of decision making
• A need for clear and standardized methods for separating site-specific contaminant levels from regional background and off-site levels
• A need to better evaluate the impacts of innovative in-place and ex situ management technologies
• A need to evaluate pathways of contaminant mobility and attenuation in dynamic, near-shore sediments
• A need to standardize methods for evaluating soils and groundwaters to protect downstream sediment communities
• A need to evaluate the role of sediments in the TMDL process
1.2 THE CONCEPTUAL SITE MODEL
A conceptual site model (CSM) is critical for determining the most cost effective and efficient manner of protecting human health and the environment in environmental and remediation investigations. The CSM is a three-dimensional description of a site and its environment that represents what is known (or suspected) about the contaminant source area(s), as well as, the physical, chemical, and biological processes that affect contaminant transport from the source(s) through site environmental media to potential environmental receptors. The CSM identifies assumptions used in site characterization, documents the relevant exposure pathways at the site, provides a template to conduct the exposure pathway evaluation and identifies relevant receptors and endpoints for evaluation. CSM development is an on-going, iterative process that should be initiated as early as possible in the investigative process. The CSM should be as simple or as complex as required to meet site objective(s) but the overall site remediation strategy and risk-based considerations should guide the development of the CSM. Refinements to the CSM can drive re-optimization of remedial design and/or operation. The CSM is also an important communication tool to facilitate the decision-making processes at the site.
1.3 ECOLOGICAL ASSESSMENT TOOLS
Assessment or measurement tools are a fundamental part of the formulation of an ecological risk assessment. Contaminated sediments are particularly complex media to measure and assess. This brief chapter summarizes the currently available measurement methods and considers those tools with specific chemical considerations. The tool descriptions provided herein should provide an outline for the risk assessor in assessing the fate and effects of a particular substance in the sediment, and the potential for bioaccumulation, bioconcentration, and/or biotransformation. Tissue residue analysis and an introduction to bioaccumulation modeling are also addressed.
1.4 CHARACTERIZING THE SPATIAL EXTENT OF SEDIMENT CONTAMINATION AT IMPACTED SITES
Once sediment contamination has been discovered at a site, characterization of the full nature and spatial extent of contamination – that is, the extent of its vertical as well as lateral distribution – is often required to make appropriate and cost-effective, risk management-based decisions for the site. A logical, step-wise approach should be followed for characterizing the spatial extent of sediment contamination. This chapter briefly summarizes a step-wise and iterative approach – the Data Quality Objectives (or DQO) Process – that may be used to develop a resource-effective sampling and analysis plan for adequately characterizing the spatial extent of biologically relevant sediment contamination at an impacted site. A general example of application of the DQO process for characterizing the spatial extent of biologically relevant sediment contamination within a dynamic riverine environment is also included. Finally, the roles that site-specific information, the conceptual site model, and statistical considerations collectively play in developing a sampling and analysis plan consistent with the DQOs are also briefly discussed.
1.5 THE USE OF FIELD SCREENING OR RAPID SEDIMENT CHARACTERIZATION (RSC) TOOLS FOR SEDIMENT ASSESSMENTS
The primary goals of a sampling and analysis plan for an Ecological Risk Assessment (ERA) or a sediment site assessment are to identify potential contaminant sources and to delineate areas of contamination. However, traditional sampling and analysis approaches do not always provide all the information necessary to support the risk assessment process in a cost- and time-effective manner. Site assessments performed in the marine environment are often hindered due to the complexity and heterogeneity of marine ecosystems. One measure that can be implemented at various stages of the assessment or ERA process at sediment sites is the use of field screening or rapid sediment characterization (RSC) technologies. These are field transportable screening tools that provide measurements of chemical, biological or physical parameters on a real-time or near real-time basis. When used appropriately, these tools can streamline many aspects of the assessment process. The tools can be used to delineate areas of concern, to fill in information gaps and to assure that expensive, certified analyses have the greatest possible impact.
This paper provides information about several of the rapid sediment characterization technologies that can be used at marine sediment sites. Potential applications of RSC tools are described to illustrate the use of applying rapid sediment characterization tools to different stages of the ERA process. Finally, important considerations are described for the evaluation, selection and application of RSC tools for the assessment process.
1.6 EVALUATING REFERENCE AREA CONDITIONS IN SEDIMENT ASSESSMENTS
Reference areas can be used to make comparisons among biological, chemical or physical sediment data that might be collected from an area under study. Lack of appropriate criteria for selecting the reference area may result in an inappropriate location being selected, and inappropriate sediment remedial actions being taken. Identification of the reference site may depend on the remedial goals and options, historical and existing conditions at the site, as well as the critical physical, chemical and biological parameters that are being evaluated. A proper approach to assessing and selecting a reference area is a key element of the overall sediment assessment process. Currently, there is no definitive approach to selecting a reference area; however, criteria can be established that would permit a more systematic process for making this selection. Important considerations for selecting reference areas are discussed as well as where these areas may find application in sediment assessments.
1.7 APPLICATION OF SEDIMENT TOXICITY TESTING IN SITE REMEDIATION ACTIVITIES
Sediment toxicity tests have become an integral component of environmental assessments. Toxicity testing is a feature of many regulatory programs in the U.S. (e.g., CWA, FIFRA, TSCA, CERCLA/SARA, RCRA, MPRSA). Numerous sediment bioassays have been developed for a variety of purposes. Most of these bioassays have been designed to assess the toxicity of sediments to make regulatory-based decisions (e.g., identifying acceptable disposal alternatives for dredged material; determining cleanup levels; or evaluating the effectiveness of the cleanup remedy). Since sediments serve as the ultimate repository for many environmental contaminants, the use of sediment bioassay as a tool in site assessment and site remediation/management activities logically follows. However, sediment toxicity tests should not be applied without proper consideration of the strengths and weaknesses of the individual procedures. This chapter provides an overview of the general types sediment toxicity testing procedures currently available. A discussion of the strengths and weaknesses of individual procedures in context of the potential application to site assessment, remediation/management, and post-remediation/management monitoring is also included. While testing procedures exist for evaluating the potential for exposure and/or uptake of contaminants (e.g., biomarker and bioaccumulation tests), the scope of this review is limited solely to toxicity testing procedures.
1.8 BIOAVAILABILITY OF CONTAMINANTS IN SOIL AND SEDIMENT SYSTEMS
The bioavailability of a contaminant defines the relationship between the absolute concentration of a chemical in a specific environmental matrix and the level of chemical that actually enters the receptor, potent...
