International Dredging Review

International Dredging Review

Several presentations at the recent meeting of the Society of Environmental Toxicology and Chemistry (SETAC) focused on assessing the ecological impacts of dredged materials.

The 27th annual SETAC meeting held November 5 through 9 in Montréal Québec is one of the largest North American conferences where scientists and environmental professionals present recent research on a variety of toxicological issues. Several topics were highlighted at this year’s meeting including new issues that reflected the meeting’s theme “Global Environment and Sustainability.” Bioavailability effects and fate of metals endocrine disruptors and sediment contamination and remediation were just some of the research discussed.

Studies related to dredging activities included those assessing toxicity of specific contaminants as well as broader assessment of dredged materials for use in specific disposal areas. Following are synopses of some of the presentations.

Development and Application of Wildlife Benchmarks to Support Evaluation of Dredged Material for Beneficial Use in Ecological Restoration by M. Ciarlo C. Papageorgis P. Derrick and J. McKee. Focuses on the framework developed to evaluate the suitability of dredged material for wetland and upland habitat restoration at the Poplar Island Environmental Restoration Project (PIERP) Chesapeake Bay Maryland. The impetus for this study is at the heart of concerns over dredged materials from several locales. Specifically what are the potential risks to wildlife via exposure to placed dredged materials and how does pre-placement chemistry of sediments influence post-placement chemistry of substrates? Because metals were identified as chemicals of interest additional data from the dredged sediments were collected using sequential extraction procedures (SEP) and diethylene triamine pentaacetic acid (DTPA) extraction. Bioaccumulation was evaluated using 28-day bioassays with Echinochloa crusgalli as well as collecting field specimens of Spartina sp. The study determined that sufficient data were available to calculate dose benchmarks for some metals and these benchmarks can be useful. However benchmarks may be overly conservative and site-specific data including SEP and DTPA can be valuable.

Assessment of Suitability of Placed Dredged Material for Ecological Restoration of Upland and Wetland Vegetation by M. Ciarlo C. Papageorgis C. Leasure P. Derrick and J. McKee. This presentation provided additional information on the previously-described PIERP investigation and provided more information on the bioassays. In pretests Echinochloa crusgalli (millet) proved to be most tolerant of salt and was therefore chosen for the definitive studies. Germination and growth of E. crusgalli in the dredged material was lower than in the reference and control sediments and nutrient addition did not improve performance. Sequential extraction procedures (SEP) showed that most metals in the soil were non-mobile forms that were unlikely to be bioavailable.

Management of Chromium Contamination in Dredged Sediments and in Excavated Soils by R.A. Brown S. Peterson and B.A. Rabe. Chromium in dredged material can be problematic for disposal of that material. The various processes of transport and transformation of hexavalent and trivalent were discussed. Hexavalent chromium which may originate from pigments plating tanning wood preservation and chemical synthesis industries is much more toxic than trivalent chromium. It is often found at low concentrations in dredged sediments but at higher concentrations in excavated soils because of air-borne deposition. Suggested chromium-mitigation measures includes reduction of Cr+6 to Cr+3 the less toxic form through addition of iron and carbon sources such as plant fiber and gypsum and buffering the soil to a pH of 6 to 10.

Bioaccumulation and Toxicity of Petroleum Hydrocarbons in Urban Harbor Sediments by A. McElroy R. Brownawell and C. Reddy. Many harbor sediments fail toxicity studies (e.g. with polychaetes or amphipods) but the cause of toxicity is often difficult to identify because these sediments at urbanized ports and estuaries are frequently contaminated with complex and variable mixtures of aliphatic hydrocarbons referred to as a Unresolved Complex Mixture (UCM). This presentation discussed UCM components of sediments from the New York/New Jersey Harbor where sediment is close to 0.1% by weight. Bioaccumulation modeling suggested that sediment organisms should accumulate levels of UCM sufficient to cause acute mortality; such accumulation does often not occur. Possible reasons for this lack of expected bioaccumulation were reviewed and toxicity mechanisms were discussed.

Contaminant Inventory Estimates and Historical Dredging Impacts in the Lower Passaic River by J. Atmadja A. Accardi-Dey and E.A. Garvey. The historical dredging and subsequent abandonment of the navigation channel of the Lower Passaic River may have created a situation that led to rapid accumulation of sediment which is highly contaminated with several pollutants including metals PAHs pesticides and dioxins. Results of an inventory of sediment contaminants along a 6-mile section of the Lower Passaic River were presented. Quantified contaminants include mercury 2378-TCDD DDT and PCBs. Small “hot spots” in the river probably do not exist however “hot regions” do exist on a larger scale of one mile or more and extending from bank to bank. Estimates of the volume of contaminated sediment in the Lower Passaic River range from 2.8 to 8.0 million cubic yards with an average depth ranging from 4.6 to 13 feet.

Preliminary Investigation of Sorbent Materials for Whole Sediment Toxicity Identification Evaluation of Dredge Materials by J.L Balaam Y.T. Allen D.A. Sheahan and J.E. Thain. Toxicity Identification Evaluations (TIEs) have been used for many years to positively identify causative agents of toxicity in effluents and more recently sediment extracts. TIEs on intact whole sediment remain in the early phases of development. Methods that have been developed by the USEPA include the use of organic carbon and sorbent resins to remove certain groups of contaminants. This presentation examined the scavenging efficiencies of different sorbents (e.g. zeolites TENAX and silicone rubber) on metals and organic chemicals found in dredged materials. Test variables included surface area of the media experimental conditions test species and sediment characteristics. It is hoped that using TIE-based methods may provide a framework for evaluating sediments prior to removal and making recommendations for disposal and/or reuse of the dredged materials.

Many more presentations were given that focus on a variety of aspects of sediment contamination chemical assessment toxicological evaluation and bioaccumulation. Much of the research will be published in Environmental Toxicology and Chemistry the primary research journal of SETAC or other scientific journals. To see all of the presentations at the 2006 SETAC meeting visit http://montreal.