The monitoring programs used to determine if sediments and mussels can be used interchangeably to assess environmental condition were: Mussel Watch (MW, National Status and Trends (NS&T), NOAA), Gulfwatch (GW, Gulf of Maine Council), National Coastal Assessment (NCA, US EPA), National Coastal Condition Assessment (NCCA, US EPA), and newly available sediment data from the EcoSystem Indicator Partnership (ESIP). Mussel Watch, Gulfwatch, NCA and NCCA are high profile, long-term, well organized national and regional mussel and/ or sediment monitoring programs. Sediment contaminant data generated by Eastern Charlotte Waterways (ECW) Inc, from funding by the Gulf of Maine Council on the Marine Environment’s EcoSystem Indicator Partnership, were used for sites in the Canadian portion of the GOM; sediments were collected by ECW and analyzed by RPC (http://www.rpc.ca/english/index.html). All the data source programs have quality assurance measures (details can be found at the URLs listed below).

NOAA’s NS&T Mussel Watch (NOAA MW) https://en.wikipedia.org/wiki/Mussel_Watch_Program https://products.coastalscience.noaa.gov/nsandt_data/data.aspx

Gulf of Maine Council’s Gulfwatch (GOMC GW) http://www.gulfofmaine.org/2/gulfwatch-homepage/ https://gulfofmaine.org/public/gulfwatch-contaminants-monitoring/data-reports/ The Canadian portion of Gulfwatch also has published QA documentation (Sowles et al., 1997).

EPA’s National Coastal Assessment (EPA NCA) & National Coastal Condition Assessment (NCCA) https://archive.epa.gov/emap/archive-emap/web/html/about.html https://www.epa.gov/national-aquatic-resource-surveys/ncca https://www.epa.gov/national-aquatic-resource-surveys/data-national-aquatic-resource- surveys

EcoSystem Indictor Partnership (ESiP) http://www.gulfofmaine.org/2/esip-homepage/ Eastern Charlotte Waterways Inc. (D. Killorn, pers comm). Sediments were collected by ECW and analyzed through a subcontract to RPC. Data with accompanying QA data were obtained from Donald Killorn, ECW (pers comm).

This dataset is associated with the following publication: Elskus, A., L. LeBlanc, J. Latimer, D. Page, G. Harding, and P. Wells. Monitoring chemical contaminants in the Gulf of Maine, using sediments and mussels (Mytilus edulis): An evaluation. MARINE POLLUTION BULLETIN. Elsevier Science Ltd, New York, NY, USA, 153: 110956, (2020).