Fate of Contaminants of Emerging Concern in Oyster Tissue: Biomagnification or Depuration

Project Background
oyster-cultivationMany towns on Cape Cod, MA are incorporating shellfish propagation into wastewater management plans, as a way of removing nitrogen from coastal waters. Although the ability of oysters to improve water quality is well documented, there have been few studies to investigate the impact on the oysters of being grown in polluted waters.

These same nutrient impacted waters also carry other potentially harmful contaminants associated with wastewater-impacted ground water and run-off. These contaminants are broadly classified as contaminants of emerging concern (CECs) and encompass a variety of contaminants including pharmaceuticals, personal care products, household cleansers and detergents. The fate and persistence of many of these compounds in the environment is not as well understood, nor is their potential for bioaccumulation and trophic transfer.

cecs-in-cc-estuariesThe Center for Coastal Studies’ (CCS) research on CECs was the first known research to document these contaminants in the coastal waters of Cape Cod (Table 1). Further research by CCS found some of these same CECs in oyster tissue.

Given all the toxicological unknowns associated with the presence of CECs in the marine environment, this study investigated the fate of CECs in oyster tissue. We anticipate that this research will provide critical information on whether CECs are depurated, or cleansed, from the tissue of oysters grown in waters compromised by wastewater and then harvested for public consumption.

Project Design
This study used oysters (Crassostrea virginica) to examine bioaccumulation of CECs.  Oysters are known to filter large volumes of water.  Although this makes them attractive as an alternative method of improving water quality in degraded areas, it also has the potential to expose them to high concentrations of anthropogenic contaminants.  Therefore, the ability of oysters to bioaccumulate these contaminants has implications for wastewater management and ecological rehabilitation methods that incorporate oysters in mitigation efforts to address water quality standards.  Two coastal ponds in Falmouth, Massachusetts were used as the study sites to investigate bioaccumulation and depuration of contaminants from oysters.

little-and-green-pondLittle Pond: Little Pond is significantly impaired by nitrogen enrichment, primarily from septic system effluent and surface run-off2. In at attempt to address the excessive nitrogen levels in the Pond, the Town of Falmouth has been testing the ability of oyster aquaculture to reduce nutrient pollution.  Oyster seed are grown in floating mesh bags during the summer months.  In the fall they are relayed to other estuaries for further growth and eventually for recreational and commercial harvest.

Green Pond: One of the sites used for the grow out of oysters relayed from Little Pond.  Oysters are available for commercial and recreational the following season.

Methods
Little Pond: Oysters were collected for analysis of tissue concentrations of CECs from Little Pond just before they were relayed to the grow-out sites (October 2016).  One month prior to the relay, a POCIS (Polar Organic Chemical Integrative Sampler) and a SPMD (Semipermeable Membrane Device) were deployed in Little Pond to measure time-integrated water concentrations of hydrophilic (pharmaceuticals, personal care products) and hydrophobic (flame retardants, PCBs, PFOS) compounds, respectively.

Green Pond: At set intervals (3 weeks, 6 weeks, 12 weeks, 24 weeks) after the oysters are relayed to their grow-out sites, they will be collected for analysis of tissue concentrations of CECs.  A comparison between the initial concentrations of CECs in the oyster tissue to the concentrations measured at each harvest interval will provide information on depuration rates.   A POCIS and SPMD were also deployed in Green Pond for the first month after the oysters were transferred to provide information on time-integrated water concentrations of CECs in Green Pond.

The data from the passive samplers will be compared to concentrations of CECs in oyster tissues to investigate exposure and bioavailability.

Corresponding water quality data (temperature, salinity, dissolved oxygen, pH, nitrate/nitrite, ammonia, silicate, ortho-phosphate, total nitrogen, total phosphorus, chlorophyll, and turbidity) were collected from Little Pond and Green Pond beginning in July and for the duration that the oysters are grown in each location.

spmd-pocis-oysters

Summary
The eastern oyster, Crassostrea virginica, is a sessile organism, filters large volumes of water, and is able to survive in a wide range of ecologic conditions from pristine to highly eutrophic.  These characteristics make them an ideal organism to use to improve water quality.  However, these same characteristics make them susceptible to potential uptake and bioaccumulation of other contaminants that are typically associated with wastewater, run-off or areas of degraded water quality. Although the Massachusetts Division of Marine Fisheries requires a 6-month depuration period for the purging of pathogens from shellfish taken from prohibited areas and a 3-month period for conditional areas before harvesting is allowed, depuration of CECs is not required and therefore not monitored.  Given the interest in growing and harvesting shellfish as a technique to remove nitrogen from coastal waters that are known to be compromised by wastewater, and then allowing harvesting of these shellfish for public consumption, this research is essential.  The results of this project will facilitate understanding of the links and make possible the development of concrete strategies to address and minimize impacts of pollution on Massachusetts’ coastal waters and potentially on human health.

Acknowledgements
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This project was funded by the Massachusetts Environmental Trust.  Thanks to the Town of Falmouth for help with logistics and planning and for donation of oysters, and to the Cape Cod Commission, and Cape Cod Cooperative Extension for support, guidance, data sharing and analysis