Some pollutants attach to suspended particles in the water, and subsequently settle out to the bottom sediment.
Why are they of concern?
Through complex chemical, physical and biological interactions, these contaminants may move to other parts of lakes, streams, and other water bodies. At elevated concentrations, contaminated sediments can contribute to fish advisories, habitat impairments and restrictions on dredging.
Contaminated sediments may also pose an unacceptable risk to aquatic organisms, wildlife and humans. Contaminants that build up in the food chain are of particular concern, especially mercury, polychlorinated biphenyls (PCBs), dioxins and organochlorine pesticides. Polycyclic aromatic hydrocarbons (PAHs) are widely found in urban areas. They are of particular concern in stormwater pond sediments and many Superfund sites. Endocrine disrupting compounds and other emerging contaminants, like flame retardants, are also being detected in Minnesota sediments. See the sidebar links for sediment studies conducted in Minnesota.
The Minnesota Pollution Control Agency is responsible for the assessment, management and cleanup of contaminated sediment sites in Minnesota. The goals are to restore water to unimpaired use and to achieve applicable water quality standards.
The MPCA does not have sediment quality standards. Sediment quality targets (SQTs) can be used as benchmark values for making comparisons to surficial sediment chemistry measurements. For more information, refer to the MPCA’s guidance document: Guidance for the Use and Application of Sediment Quality Targets for the Protection of Sediment-dwelling Organisms in Minnesota