Trace Elements and Oil-Related Contaminants in Sediment, Bivalves, and Eelgrass from Padilla and Fidalgo Bays, Skagit County, Washington.
Padilla Bay is a tidal estuary in Puget Sound, Washington, with extensive eelgrass beds and mudflats. It is an important natural resource which provides habitat for a wealth of wildlife and aquatic life including salmon, dungeness crab, shorebirds, peregrine falcons, bald eagles, and it is a staging area for the black brant. Potential contaminant threats to Padilla Bay include spills and emissions from two large oil refineries, runoff from agricultural lands, and active and inactive landfills. The purpose of this study was to document existing contaminant concerns and provide background information on contaminant levels in the event of an oil spill.
Methods: Thirty three sediment samples were collected from Padilla, Fidalgo, and Samish Bays. These sites were selected to examine the different possible sources of pollution. Bivalve and eelgrass samples were also collected from eight sites in Padilla, Fidalgo, and Samish Bays. Sediment, bivalve, and eelgrass samples were analyzed for organochlorines (OC), aliphatic hydrocarbons (AH), polycyclic aromatic hydrocarbons (PAH), and trace elements. Percent moisture was determined for all samples, percent lipids for bivalve samples, and percent total volatile solids for sediment samples.
Results and Discussion: Overall, the results from this study indicated that the occurrences of elevated contaminant residues from sediment in Padilla Bay were few and localized. Nickel was found at about half of the sites. Zinc concentrations were elevated at two sites and chromium concentrations were elevated at one site. Sediment from the mouth of Joe Leary Slough contained concentrations of total PAHs an order of magnitude higher than other sites in this study and exceeded the effects levels. The potential source of elevated PAHs may include: nonpoint source runoff for Interstate 5 and the upstream town of Burlington, improper disposal of waste motor oils from an upstream migrant labor camp, and/or burning of wood and yard waste at the Inman Landfill located about one mile inland from the Padilla Bay shoreline. Several trace elements (arsenic, chromium, iron, manganese, lead, and zinc) were higher in softshell clams and eelgrass from the sites closest to the refinery piers and pipelines used to transfer crude oil from tankers to the refineries on March Point and to the associated discharge outfalls. Several trace element residues were also higher in Littleneck clams and eelgrass from the sites closest to the March Point Landfill, suggesting that leachate from the March Point Landfill is contributing contaminants to Padilla Bay. Concentrations of aliphatic hydrocarbons (AHs) in eelgrass and bivalves were relatively consistent between sites, however, total AHs in sediment at Telegraph Slough were much higher than at other sites. For the most part, organochlorines were not detected in sediment or bivalve samples. Two sediment samples did contain traces of p,p'DDE typical for sediments in agricultural areas.
Potential sources and the extent of contamination of nickel should be examined since nickel residues exceeded known biological effects levels and may be impacting aquatic biota.
Potential sources and extent of contamination of PAHs at Joe Leary Slough should be examined as these contaminants occurred above biologically based effect levels and may be causing impacts to biota.
Existing evidence indicates that march Point Landfill leachate is contributing contaminants to Padilla Bay and it has been demonstrated to cause impacts to biota. Further remediations strongly advised for the landfill.
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