LA PLATA, MD (February 15, 2002) - The presence of a potentially harmful algae in the lower Potomac River has led the Maryland Department of the Environment (MDE) to take action to safeguard public health and safety.
Dinophysis acuminata has bloomed on the river adjacent to oyster bars near Cedar and Swan Points in the Potomac River in Charles County. For that reason, MDE has ordered shellfish waters in the Potomac River impacted by this bloom temporarily closed. The effected waters are all Maryland shellfish waters upstream of the mouth of the Potomac, including the Maryland tributaries that empty into this part of the river. The closure will remain in effect until weekly monitoring shows that the algae has decreased to much lower levels.
This harvesting closure has no impact on recreational activities on the river. Maryland Natural Resources Police will enforce the closure until further notice. Virginia officials have been informed of Maryland's findings and actions taken today.
The algae's cells contain a toxin that can accumulate in oysters and 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.
The algae is more common in northern regions of the world. It was detected in cell counts high enough to warrant concern yesterday when Maryland Department of Natural Resources staffers reviewed water samples taken as part of the Chesapeake Bay monitoring program. Dinophysis acuminata had been previously detected in Maryland waters at very low concentrations, typically well below 1000 cells per liter of water. Samples taken on Tuesday ranged from 6,000 to 14,000 cells per liter of water.
MDE and Academy of Natural Sciences biologists conducted additional sampling today from Nanjemoy Creek to Ragged Point to confirm the presence of the algae. Surface and bottom samples ranged from approximately 7,000 to 44,000 cells per liter, resulting in the decision to close the river to shellfish harvesting. There are no specific thresholds or critical values for the number of cells that pose a health risk.
Algae with similar toxins have been known to Canadian and Nova Scotian scientists since 1990 where it has impacted their mussels industry. The micro-organism prefers ocean water with high saline (salt) content and colder water temperatures. It is believed to be coming into Maryland as colder, saltier Atlantic Ocean waters mix with the freshwater of the Chesapeake Bay. Low rainfall and water flow has resulted in record high salinities in this portion of the Potomac River, which may be contributing to this problem.
For more information on the algae, go to DNR's web site at: www.dnr.state.md.us/bay/hab/dinophysis.html