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Date of Award

Summer 2023

Document Type

Masters Thesis

Department or Program Affiliation

Marine and Estuarine Science Program, Environmental Science Department

Degree Name

Master of Science (MS)


Environmental Sciences

First Advisor

Van Alstyne, Kathryn Lyn, 1962-

Second Advisor

Sofield, Ruth M.

Third Advisor

Bingham, Brian L., 1960-


Seafood, including fish, shellfish, and seaweed, are an important source of nutrients that could meet some of the increasing demand for food globally. In addition to nutrients, chemical contaminants can also be acquired from the environment by primary producers. Seaweeds take up a variety of inorganic and organic contaminants, including metals, that may pose risks to human health. Through trophic transfer, organisms can accumulate elevated levels of contaminants from consuming lower trophic-level organisms. Since particulate organic matter, including seaweed detritus, is a food source for filter-feeding bivalves, contaminants present in seaweed could transfer to shellfish via ingestion. The purpose of my work was to investigate: 1) if seaweeds used in local co-culture operations are accumulating metals, 2) if there is evidence for the transfer of metals from seaweeds to shellfish, and 3) which of these metals are in high enough concentrations to pose human health risks. Given that seaweeds hyperaccumulate metals and bivalves consume particulate matter, we hypothesize that it is possible for the bivalves in co-culture systems with seaweed to have higher metal concentrations than would otherwise be expected and increase risk to human consumers. We conducted both laboratory-based bioaccumulation and feeding experiments, as well as field studies at two sites in the Puget Sound. Results of the bioaccumulation experiment showed that kelp can hyperaccumulate at least three metals (cadmium [Cd], chromium [Cr], and zinc [Zn]). Bioconcentration factors (BCF; L/kg) for Cd, Cr, and Zn were 4.97, 7.32, and 49.5, respectively, indicating that hyperaccumulation occurred (BCF>1). Results of the oyster feeding experiment did not demonstrate transfer of metals from kelp to shellfish, however, questions about ingestion of the kelp disallow us from concluding that the metals cannot be transferred from seaweed to oysters. Evidence that metals are being transferred to shellfish in the types of co-culture operations that currently exist in Washington State, at this point, is not well substantiated. Results of the field studies indicate elevated levels of Cd and copper (Cu) at the IMTA facility in oysters, but no human health-based exceedances in seaweeds or mussels at either site. These risks can be mitigated by reducing consumption rates. To be protective of human health, a new consumption rate was calculated to be 140 g wet weight per week based on the concentrations of Cd exceeding the screening level. Further work needs to be done to provide a better understanding of the uptake of kelp particulates by oysters and whether this could result in a transfer of metals.




Aquaculture, IMTA, Bioaccumulation Factor, Metals, Shellfish, Seaweed, Trophic Transfer


Western Washington University

OCLC Number


Subject – LCSH

Aquaculture--Washington (State); Shellfish--Washington (State); Marine algae--Washington (State); Environmental toxicology--Washington (State); Metals

Geographic Coverage

Washington (State)




masters theses




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