Risk Assessment, Monitoring, and Management of Contaminated Marine Sediments

Sediments are a sink and a source for contaminants discharged directly or indirectly (e.g., via rivers, estuaries) into marine waters such as the Salish Sea. Contaminants in sediments, although less bioavailable than in the water column, can adversely affect benthic infauna and epifauna and, if released to overlying waters (e.g., by extreme events such as storms in shallow waters), can affect water column fauna. Determining the risk posed by contaminated sediments requires more than simply measuring total concentrations of contaminants in sediments, although such can serve for subsequent monitoring. Such measurements provide no information on bioavailability, provide simple binary decision-points related to hazard not risk, and ignore uncertainty. Biological assessments are also necessary, for instance determining sediment toxicity and the status of resident benthic communities. The latter assessments are the most realistic, but are confounded by increasing human-related natural variability (e.g., due to climate change, invasive species). Thus, risk assessment of contaminated sediments requires both chemical and biological measurements, which should be interpreted in the context of ecosystem services (i.e., the benefits people obtain from ecosystems), not in the context of protection of individual or even all species. They should also be interpreted relative to other, non-chemical stressors. Management of contaminated sediments requires not doing more harm than good; in general, when appropriate, monitored natural recovery is the preferred option. Other management options include capping, in situ treatment, dredging and disposal. All management options have constraints; none is useful without effective source control, and none should be undertaken based solely on perception, political, and/or bureaucratic reasons. Such decisions require a rational, technically defensible basis