Aquatic sediments are often the ultimate repository of discharged contaminants. According to an estimate by the U.S. Environmental Protection Agency (U.S. EPA), approximately 10% or 1.2 billion cubic yards of the sediment underlying the country’s surface water is sufficiently contaminated with toxic pollutants to pose potential risks to fish and to humans and wildlife that eat fish (U.S. EPA, 1998). Contaminated sediments can pose a threat to human health when pollutants in sediments accumulate in edible aquatic organisms (U.S. EPA 1998 and references therein).
Highlighted in the 2016 Workshop Report, developing in situ remedial strategies is important for all contaminants in sediments, but especially for the emerging contaminants. Much of the recent work on amendments for in situ remediation of sediments has focused on adsorption by carbon or other substrates (e.g., organoclays, apatite). There remains continued interest from the regulatory community and public in approaches that remove the mass of the contaminants through treatment. These new technologies should meet the following criteria for in-placement management: reduce exposures through a combination of chemical adsorption, degradation and transformation; have low impact on native biota; have long-term effectiveness; be competitively priced from a life cycle perspective that considers all benefits and costs, and should be applicable to complex mixtures of contaminants.
Monitoring costs represent a significant and increasing burden for contaminated site management. The development and demonstration of innovative and lower-cost monitoring techniques should result in cost effective monitoring. Development of methods that provide more temporal and spatial data will reduce uncertainty in assessing long term monitoring (LTM) goals. Sample compositing strategies should be rigorously evaluated and demonstrated for potential broader application in sediment, in particular with respect to advantages for LTM. Sediment-specific methods for determining the numbers of samples per composite and the number of composites per test condition as determined by a statistical power analysis should be evaluated. Trade-off analysis and optimization of the increased field sampling costs of these methods versus the lower analytical costs would help to guide practitioners in the application.
At many sites, monitoring for reduction in biological endpoints such as fish can drive a substantial fraction of the monitoring cost. Such monitoring can be very labor intensive, complex and costly. In addition, it is often performed at time intervals that have no basis to the known or unknown recovery rate of the site. Alternative monitoring methods that utilize lower cost bioavailability measures such as passive samplers or laboratory exposures as initial proxies for recovery could be used in an adaptive framework to guide decisions on when fish sampling or other complex monitoring events should take place.