ANNAPOLIS, MD (February 22, 2002) – The Maryland Department of the Environment is continuing the temporary closure to shellfish harvesting for parts of the Potomac River and tributaries issued last week. Yesterday’s water sampling of the Potomac River in Southern Maryland confirmed that the bloom of Dinophysis acuminata, a potentially harmful algae, continues. Cell counts of approximately 40,000 cells per liter of water were found at Swan Point in the Potomac River and up to 46,000 in the Wicomico River, a tributary to this section of the Potomac River.
Following analysis of 12 samples taken yesterday in the Potomac River and in the Wicomico and St. Mary’s River tributaries, MDE has determined that the cell counts remain too high and widespread to remove the shellfish harvesting restrictions.
Last Friday, Maryland Department of the Environment announced the detection of the algae at high concentrations and temporarily closed Potomac River shellfish waters upstream of the mouth of the Potomac, including the Maryland tributaries that empty into that part of the river. The closure will remain in effect until weekly monitoring shows the algae have decreased to acceptable background levels. The Maryland Natural Resources Police will enforce the closure.
The harvesting closure has no impact on recreational activities on the river.
Dinophysis acuminata’s cells can contain a toxin that can accumulate in oysters and, if ingested, cause diarrhetic shellfish poisoning that is not fatal in humans, but can result in gastro-intestinal illness and vomiting. The symptoms usually pass in about three days. The risk to public health is expected to be low because oysters feed very little at current water temperatures and would not accumulate high levels of the algae's toxin.
As a reminder, small children, pregnant women and individuals with compromised immune systems may be more sensitive to the effects of toxins and should never consume raw shellfish. Unlike most bacteria found in shellfish, the toxin contained in Dinophysis acuminata cannot be destroyed by cooking.
There are no specific thresholds or critical values for the number of cells that pose a health risk. More common to northern regions of the world, Dinophysis acuminata had previously been detected in Maryland waters at very low concentrations, typically well below 1,000 cells per liter of water. Cell counts were detected last week at levels high enough to warrant concern -- ranging from 6,000 to 44,000 cells per liter of water. The samples were taken as part of the Chesapeake Bay routine monitoring program. The presence of the algae also led Virginia officials to close Virginia’s Potomac River tributaries to shellfish harvesting, including the Little Wicomico River.
For more information on shellfish harvesting waters, visit the MDE website at: http://mde.maryland.gov/health/shellfish.html
For more information on the algae, visit the DNR web site at: www.dnr.state.md.us/bay/hab/dinophysis.html