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Is Delaware Bay seafood safe to eat?

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After an oil spill in the marine environment, a number of actions must be considered regarding the safety of seafood from the affected location. Each spill is a unique combination of conditions and events. Seafood is only at risk of contamination from a spill if it is exposed to the oil. Once exposed to oil, an organism becomes contaminated only to the extent that it takes up and retains petroleum compounds.

In some cases, there may be an initial, temporary de facto closure if the U.S. Coast Guard establishes a safety zone restricting access in areas of active oil recovery. Fishermen also may voluntarily avoid working in oiled areas to prevent oiling their gear and catch. This initial period after a spill can provide an opportunity to evaluate spill conditions and conduct limited testing to determine whether a precautionary closure or other immediate restrictions on seafood harvest are warranted.

Decision Process for Managing Seafood Safety after an Oil Spill

Managing Seafood Safety Chart

 

Because oil spills are dynamic, conditions should be monitored and risks to seafood must be re-evaluated until the threat abates. Determining whether seafood has been contaminated can take substantial time. Developing and implementing sampling plans, conducting sensory and/or chemical testing, and evaluating results may require weeks or longer. Monitoring continues and the risk assessment process is repeated as necessary.

If it is determined that seafood is tainted or is contaminated to a level posing a potential health risk, the next step is to select the most appropriate seafood management action(s). These may include: (1) seafood advisories, (2) increased inspections of harvested seafood or gear, (3) harvest closures, and (4) fishing gear restrictions.

In Delaware, the authority to manage seafood to protect human health resides with the Division of Public Health, the Department of Natural Resources and Environmental Control, and the Food and Drug Administration. After an oil spill, these state and federal organizations would evaluate the situation as described for any product in commercial channels. Recreational fishermen should follow local fish consumption advisories. In Delaware, you can access fish consumption advisories on this DNREC Web page.

Oil types and properties strongly influence whether seafood is exposed and contaminated. Crude oils and the refined products derived from them are complex and variable mixtures of hydrocarbons of different molecular weights and structures. They can contain hundreds of different compounds. Oils have been grouped into types with similar properties to help predict their behavior at spills. This same approach can be used to characterize the relative risk of contamination of seafood by oil type. These are generalities that can be used to initially screen an incident to evaluate the potential for seafood contamination.

Since the Athos 1 spill was a heavy crude oil spill, here is some general information to assess the potential for seafood contamination by this grade of oil. Very little of this oil is lost by evaporation and will form persistent residues. It is very viscous to semisolid and will not readily disperse or mix into the water column. There is a low risk of finfish contamination because of low water-soluble fraction and little natural mixing in the water. There is moderate to high risk of shellfish contamination where shoreline oiling is heavy. It can also coat fishing gear and intertidal species.


Summary

Wild finfish are unlikely to become contaminated or tainted because they typically are either not exposed or are exposed only briefly to the spilled oil and because they rapidly eliminate petroleum compounds taken up. If nearshore sediments are contaminated, species that spawn in nearshore and shallow waters are more likely to be exposed to spilled oil than pelagic and benthic species.

Shellfish are more likely than finfish to become contaminated from spilled oil because they are more vulnerable to exposure and less efficient at metabolizing petroleum compounds once exposed. Shellfish are generally less mobile and have more contact with sediments, which can become contaminated and serve as a long-term source of exposure.

Among crustaceans, species that burrow are at the highest risk of exposure at spills where bottom sediments are contaminated, followed by species that utilize nearshore and estuarine benthic habitats.

Bivalves are at high risk of contamination because they are sessile, filter-and deposit feed, and occur in substrates in shallow tidal and intertidal areas that are more likely to become contaminated.

It is generally accepted that uptake and elimination rates both increase with temperature, though study results are somewhat contradictory.

PAHs (polyaromatic hydrocarbons) tend to accumulate to higher concentrations in lipid-rich tissues and organisms. Seasonal differences in tissue lipid content associated with spawning may influence uptake and elimination rates of PAHs in some marine species.

Chronic exposure to hydrocarbons in water and sediments may reduce elimination capacity.

Source: Yender, R., J. Michel, and C. Lord. 2002. Managing Seafood Safety after an Oil Spill. Seattle: Hazardous Materials Response Division, Office of Response and Restoration, NOAA, 72 pp.
A pdf of the report is available at http://response.restoration.noaa.gov/oilaids/pdfs/seafood2.pdf

Additional Fisheries Links
http://www.dnrec.state.de.us/fw/fisheries.htm

Fish Consumption Advisories
http://www.dnrec.state.de.us/fw/advisory.htm

Statewide Clamming Maps
http://www.dnrec.state.de.us/fw/clamclose.htm

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