A new state study shows perfluorochemical levels continue to decrease in Washington County residents whose drinking water was contaminated by 3M-related pollution.

The Minnesota Department of Health study of area residents found PFC levels generally have fallen since a public health intervention program launched 10 years ago. It was the third time blood samples have shown PFC level declines, though study participants still had levels higher than the national average.

The latest data, released Jan. 12, included blood samples of 149 residents of Oakdale, Lake Elmo and Cottage Grove whose drinking water was contaminated by PFCs prior to 2006 and who have continued to live in the area. Specifically, 79 participants live in Oakdale, 56 in Lake Elmo and 14 in Cottage Grove.

Biomonitoring program coordinator Jessica Nelson said the study results “are confirmation that all the efforts to reduce the (PFC levels) are working.

“The trend seems very strong and clear in that long-term group.”.

The Health Department began studying the east-metro PFC levels after the chemicals produced for decades by 3M for a variety of its manufactured products were found to have polluted drinking water sources in three areas of Washington County - near the company’s Cottage Grove plant, at an approved dump site along the Cottage Grove-Woodbury border and at Washington County landfill. The company stopped producing PFCs in 2002 and was involved in the remediation.

Remediation included the installation of large carbon filtration units at a city water treatment facility in Oakdale and residential filtration systems provided to Cottage Grove residents whose private wells were affected. Lake Elmo residents on private wells either were connected to city water service after the contamination was discovered or received residential water filters.

The latest study, based on blood samples taken in 2014, also included 156 Oakdale residents who moved to the area after 2006. They had PFC levels similar to the national average, according to the Health Department.

Scientists tested for eight PFCs. Three variations of the chemical are most common and were found in the blood of almost all study participants. However, those chemical levels dropped in most people over the past six years, by between 34 and 59 percent.

PFC levels remained flat or increased slightly in a small number of people, though it did not concern state scientists. Some variation in the levels is expected and likely attributed to different sources of exposure some people had beyond just drinking water, said Nelson, an environmental epidemiologist.

While officials have set health-based limits for recommended maximum PFC levels in the human body, Nelson said there still is no conclusive evidence connecting increased PFC exposure to any particular illness.

“It continues to be the case that we really need more research to know if some of these relationships are cause and effect,” she said.

The future of the east-metro biomonitoring study is unclear. Funding for the study runs out in June 2017. Nelson said a science advisory panel that reviews the study results, and state lawmakers, will decide whether to continue.

“We will keep talking to them about these results and if there are next steps that are needed,” she said.

Sen. Katie Sieben, DFL-Cottage Grove, who sponsored past legislation to fund the biomonitoring, said it is important the program continues.

“There are still elevated levels and as the science becomes more clear that there are health impacts of exposure, it is critical to continue to monitor levels in people’s bodies,” Sieben said.

In addition to blood samples, the Health Department has tested private wells for PFC levels. Some 1,500 private wells in Washington County have been sampled, and about 500 are sampled on a regular basis, the department said.