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TOXICITY TESTING, RISK ASSESSMENT, AND OPTIONS FOR DREDGED MATRIAL MANAGEMENT
Citation:
Munns Jr., W R., W J. Berry, AND T Dewitt. TOXICITY TESTING, RISK ASSESSMENT, AND OPTIONS FOR DREDGED MATRIAL MANAGEMENT. Presented at MIT Conference on Options for Dredged Material Disposal Management, Cambridge, MA, December 3, 2000.
Description:
The U.S. Environmental Protection Agency (U.S. EPA), in conjunction with the U.S. Army Corps of Engineers (U.S. ACE), has lead responsibility for developing guidelines that provide environmental criteria for evaluating proposed discharges of dredged material into U.S. waters. To comply with these guidelines, proposed discharges must: a) present the least environmentally damaging, practicable management alternative; b) comply with established legal standards; 3) not result in significant degradation of the aquatic environment; and 4) utilize all practicable means to minimize adverse environmental impacts. In the "Inland Testing Manual" (ITM) and the "Green Book", the U.S. EPA and U.S. ACE described a testing and analysis protocol to be used to evaluate whether guideline criteria are met for dredged material disposal in inland waters and open ocean waters, respectively.
The evaluation programs described in the ITM and Green Book were designed to support informed management decisions about the placement of dredged sediments. They specify a tiered testing and evaluation approach that includes performance of bioassays to assess toxicity of the dredged sediments to species inhabiting the disposal site. Both water column and bedded sediment toxicity tests are incorporated, and sediment bioaccumulation tests are specified when bioaccumulative chemicals are present in the dredged material at sufficiently high levels. Early tier toxicity tests focus on acute responses, whereas later tier testing (when required) can employ longer test exposures and sublethal endpoints. In all cases, the toxicity of dredged material proposed for disposal is evaluated against toxicity measured in a suitable reference sediment. As part of this talk, we will the describe toxicity tests currently used in dredged material evaluations, and will suggest ways to improve the battery of tests.
Although current U.S. evaluation protocols incorporate both exposure (sediment chemistry and bioaccumulation) and effects (toxicity) components, and therefore reflect to some degree the toxicological risks associated with disposal activities, the focus of analysis activities is limited to the sediments of each dredging project separately. Thus cumulative risks to water column and benthic organisms at and near the designated disposal site are difficult to assess. An alternate approach is to focus attention on the disposal site, with the goal of understanding more directly the risks of multiple disposal events to receiving ecosystems. Here we review an application of ecological risk assessment that allows specification of disposal site receptors and assessment endpoints, recognition of variation in exposure conditions (including the discharge sequence of sediments from different projects), and consideration of the temporal and spatial components of risk. When expanded to include other disposal options (upland, wetland), this approach to assessing risks to receiving ecosystems can provide the basis for holistic management of dredged material disposal. This presentation does not necessarily reflect the position or the policy of the U.S. EPA, and no official endorsement should be inferred.