Fish Consumption Advice For Mississippi River, Chain Of Lakes In Minneapolis
Fish in Minnesota
The Minnesota Department of Health issued new advice for people who eat fish caught in Lake Calhoun in Minneapolis and parts of the Mississippi River south of Minneapolis after the chemical perfluorooctane sulfonate was found in fish taken from those waters.
The new advice is based on analysis of recently completed fish sampling by the Minnesota Pollution Control Agency (PCA), as well as revisions by MDH in its health risk analysis of perfluorochemicals (PFCs) made earlier this year.
PFOS appears to be the compound from the PFC family that accumulates most abundantly in fish. It has been measured in fillets of certain fish at levels of health concern for people who eat these fish too often.
MDH recommends that people who eat bluegill sunfish from Lake Calhoun and several connected lakes limit their consumption to one meal per month. Because bluegill are known to move between connected lakes, the advice is being extended to bluegill taken from any of the upper chain of lakes connected to Calhoun: Brownie, Cedar, Lake of the Isles and Harriet.
In Pools 2 through 6 of the Mississippi River, PFOS has been found in bluegill, carp, channel catfish, smallmouth bass, largemouth bass, white bass, northern pike, and walleye. Depending on the size and species of fish, advice may range from one meal per week (four meals per month) to one meal per month. In many cases, species that have PFOS also have other contaminants, such as mercury or polychlorinated biphenols (PCBs). The department bases its advice on whichever contaminant requires the most protective advice.
A river pool refers to that section of the river between dams. For example, Pool 2 of the Mississippi River is between the Ford Dam in St. Paul and the Hastings Dam, including some backwater lakes and connecting channels. Pool 3 refers to the section between the Hastings Dam and the Red Wing dam. Pool 6 ends 14 miles south of Winona at the Flambeau dam.
For women who are or may become pregnant and children under 15, the department may issue more restrictive guidelines based on the presence of mercury in the fish, because a developing nervous system is more sensitive to mercury exposure. For details of recommendations for these special populations, see the Fish Consumption Advisory on the MDH Website.
The new advice comes following continued investigation by MDH, the Minnesota Pollution Control Agency (PCA) and the Department of Natural Resources (DNR) and others into the extent of contamination of area waters (surface and ground) with PFCs. Health officials last year provided revised advice on eating bluegills from Pool 2 of the Mississippi River after PFOS was found in fish tissue. These data were gathered as part of an investigation of PFC releases from the 3M Cottage Grove facility.
In this most recent round of sampling, scientists looked at fish from the Mississippi River Pools 3 through 5a, the St. Croix River and Lake Calhoun. PFOS was not detected in any of the fish fillets sampled from the St. Croix River. Lake Calhoun was selected for fish sampling because it was one of the lakes previously tested for the presence of PFCs as part of research by the University of Minnesota. That research found relatively higher levels of PFOS in urban lakes than in remote lakes such as in Voyageurs National Park, where very low levels were found.
The PCA is investigating what the possible source or sources for the PFOS and other PFCs in Calhoun might be. MDH, PCA and DNR staff intend to sample more waters and fish species this summer. A high priority will be to sample panfish.
A variety of health effects occur in laboratory animals exposed to high doses of PFOS, the PFC that accumulates in fish. The most sensitive effects (i.e., effects observed at the lowest dose causing adverse effects) are decreased high-density lipoprotein (HDL or good cholesterol) and changes in thyroid hormone levels in some animals. Special cleaning and cooking precautions used to reduce contaminants like PCBs that concentrate in fat are not effective with PFOS.
Health officials said that despite the presence of PFCs in some city lakes, swimmers are encouraged to keep swimming for its health benefits. Exposure to the chemicals through swimming is very low. The chemicals are poorly absorbed through the skin, and incidental ingestion of surface water while swimming would not likely expose someone to significant doses.
The toxicity of PFCs is the subject of active research. MDH continually reviews ongoing research on PFOS and other perfluorochemicals to ensure that Minnesota's health guidelines for contaminants in fish and water remain protective of people's health. As new studies and science become available, the guidelines may be revised to reflect additional information.
"With the fishing season coming up, this is a good time for all of us to remember that fish are good to eat," said Pat McCann, an environmental health researcher for MDH, "but we should make wise choices about which fish we eat and how often." She advises checking out the statewide Safe Eating Guidelines or site-specific advice for tested waters.
Health experts, including MDH, recommend eating one to two meals of fish per week. Fish are a good low-fat source of protein and contain many vitamins and minerals. Eating fish may help protect adults against cardiovascular disease. Pregnant women and women who may become pregnant should also eat fish because eating fish promotes eye and brain development in fetuses.