Degradation of Benthos BUI 6 Overview

Not Impaired

Why was this BUI originally listed as impaired?

• Benthos communities have been negatively affected by pollution and sediment contamination in the Detroit River for decades.
• Pollution discharges from the heavily urbanized and industrialized shorelines of the river have contributed to the significant ecological degradation of the river benthos community.
• Pollutants such as mercury and polychlorinated biphenyls (PCBs) have accumulated in the sediment and modified the quantity and quality of benthic communities over time.

This BUI will be considered to be ‘not impaired’ when….

The benthic community composition is temporally and spatially identified as non-impaired based on an objective and quantitative community analysis and/or a comparison to appropriate reference sites within the river; AND

…when benthic organisms analyzed for persistent, bioaccumulative substances (e.g., PCBs and mercury) are below thresholds required to protect fish and wildlife.

What was done?

• Environmental researchers conducted a series of intensive investigations into Detroit River sediment quality and benthic health in 1980, 1999, 2001, 2008, 2009, and 2013.
• Sediment contaminants have declined steadily from 1999-2013.
• Since 1999, the majority of study sites (81/82 or 99%) had sediment contaminant levels that were below levels considered highly polluted and likely to affect benthos.
• Sediment contaminants found in the majority of Detroit River sites were not significantly different from reference sites (i.e., sites that have not been exposed to or have been exposed to only small amounts of contaminants within the Detroit River).
• None of the sites sampled exceeded Canadian guidelines for PCBs in tissues and only one site exceeded guidelines for methyl mercury. This indicates low bioaccumulation potential.
• 36/37 (97%) of sites sampled in 2013 had benthos communities that are unlikely to be impaired.

When did the status change?

• The status changed to not impaired in December 2020

The bi-national connection: What is the U.S. doing?

• American agencies are working towards sediment remediation to improve the quality of the benthos
• Check out the Detroit River Sediment Remediation Collaborative to learn more about what our American partners are doing for the river

Where can I learn more?

Detroit River Canadian Remedial Action Plan: Stage 2 Report (2010): pages 68-76.

Factsheet – Re-designation of the Degradation of Benthos Beneficial Use Impairment

Assessment of Benthos (BUI #6) in the Detroit River Canadian Area of Concern