PFOS: Contaminants Found in Lake Calhoun
As part of an ongoing effort to sample for perfluorochemicals (PFCs) in different settings in Minnesota, the Minnesota Pollution Control Agency (MPCA) recently discovered Perfluorooctane Sulfonate (PFOS) in fish tissue in Lake Calhoun. Low levels of PFOS were found in Lake Calhoun water in 2005.
PFOS is one of a class of hundreds of fluorinated compounds (based on an underlying 8 carbon molecule) that are extremely stable in the environment and were used in consumer and industrial manufacturing until it was phased out of production. Products derived from PFOS were used world-wide by a variety of industries beginning in the 1950s. PFOS was manufactured in the United States solely by 3M until it was phased out of production beginning in 2000.
Detection of PFOS in Lake Calhoun represents the first finding of PFCs at above health-based levels from a location that is not associated with several east metro waste disposal areas. These sources have apparently led to a wide area of groundwater impact and some surface water impact in Washington County. There are no currently known sources of PFCs in the area of the Minneapolis Chain of Lakes.
Potential Product and Process Sources of PFOS
PFOS and related perfluorochemicals (PFCs) were used in the following products/processes:
- Surface treatments for fabric, carpet, upholstery, and paper products
- Fire-fighting foams
- Semi-conductor manufacture
- Chromium Plating (a mist suppressant)
- Non-stick coatings
- Photographic and lithographic processes
The stability of these compounds in the environment both contributed to their utility as surface treatments (they are durable) and to their persistence in the natural environment (they don’t degrade under normal environmental conditions). PFCs have been detected at parts-per-billion levels (ppb) in environmental media (e.g. animal tissue, water, soils) world-wide. Research has also shown them to “bio-accumulate” in fish and mammal tissues, or persist at higher levels than found in the environment. The bio-accumulation has triggered recent health concerns regarding PFCs. The wide distribution and bio-accumulation of these compounds led, in part, to 3M ceasing production of PFOS and voluntarily withdrawing related products (such as Scotchgard™ ) from the marketplace. While environmental stability and bio-accumulation alone do not indicate a health risk, but they do indicate there is a concern for long-term exposure from PFOs.
Research by 3M and others has not shown significant risk from concentrations found in the natural environment, animal tissues, or in exposed workers at 3M. Research on much higher exposures has shown that accumulation poses cancer risks in laboratory animals.
The U.S. Environmental Protection Agency (EPA) began researching PFCs in 1999. It developed “Significant New Use Rules” (SNUR) in 2000 and 2002 to prevent PFOS from being manufactured or imported in the future. Some exceptions exist for specialized uses (e.g., semi-conductors, aviation fluids). However, widespread use in most consumer products (i.e., fabrics) has been discontinued.The EPA is currently developing a comprehensive risk assessment of PFOS.
In addition, the Minnesota Department of Health has developed drinking water guidelines of 0.3 ppb for PFOS in drinking water. This standard is considered “cautious” by the Minnesota Pollution Control Agency (MPCA) and represents a conservative approach while definitive toxicology data are being developed. This standard applies to direct human consumption of water and not to ecological receptors (fish and wildlife or human consumption of fish).
The pathways for PFCs to enter the environment are not completely understood, but they are probably as complex as the variety of industries and services that used the products. Industrial waste water discharge, urban runoff, and solid waste disposal practices are among the likely pathways. Since these chemicals are present in many products, the MPCA and EPA likely will take a closer look at PFCs at various types of facilities and sites in the near future.
Actions by State Organizations
Expanded fish sampling is planned and may include Lake Minnetonka. The MPCA plans to sample water flowing into and out of 31 waste water treatment plants. Groundwater and leachate (soluble particles from soil, landfill, etc. found in the water) will be tested at numerous active landfills.
It is important to recognize that past environmental sampling generally did not search for PFCs so a historical database is not available to study trends. The appearance of PFCs in the environment is probably not new, given the presence of PFCs in consumer products for more than 50 years. More attention to these compounds reflects people’s increased concern about PFCs, sampling procedures, and the availability of new analytical methods for detection.
Additional human risk assessment, environmental fate, and ecological risk assessment research is currently underway. More information is available from the website links below. We can expect to see new guidelines and standards at the state and national levels in the near future.