In what may be the nation's most extensive study of its kind, a survey of 118 test wells scattered around Minnesota has found that about a third of them contain measurable levels of antibiotics, detergents, or other consumer chemicals known as "contaminants of emerging concern."
The chemicals, apparently coming from landfills, septic systems and sewage treatment systems, have been found in surface waters in recent years, and some scientists have looked at their effects on fish and other animals. But this new survey, published online Monday by the U.S. Geological Survey, is the most extensive evidence yet that the chemicals are also making their way into both shallow and deep aquifers in Minnesota.
Groundwater is the source of drinking water for three-fourths of Minnesotans.
The study (PDF), conducted between late 2009 and mid-2012 by the USGS and the Minnesota Pollution Control Agency, found no chemicals in excess of drinking water quality standards.
But for four of the most common chemicals it found -- the antibiotic azithromycin, the antihistamine diphenhydramine, the flame-retardant tributyl phosphate and the animal antibiotic lincomycin - neither the state nor the federal government maintains any health-based water quality standards.
"Our use of these chemicals in our everyday lives is releasing them into our environment. Our question as a society is, 'What do we think about that?'"
The chemicals come from a variety of consumer and industrial products - prescription and over-the-counter medicines, lotions, detergents, plastic-making ingredients and more.
"Our use of these chemicals in our everyday lives is releasing them at low levels into our environment," said Mindy Erickson, groundwater specialist for the USGS. "Our question as a society is, 'What do we think about that?'"
Erickson said the groundwater study, which will continue, was prompted several years ago by scientists finding the chemicals in rivers and lakes in Minnesota, sometimes bodies of water that were otherwise considered pristine.
The 118 wells tested are among those the MPCA monitors regularly, and they were chosen because of their assumed vulnerability to this kind of contamination, said Sharon Kroening, research scientist at the MPCA. Some were in the Twin Cities area, some near St. Cloud and others in north central, northwestern and southeastern Minnesota.
The report suggests the chemicals are finding their way into groundwater from a variety of sources.
For example, the chemical found most often in the study was sulfamethoxazole, a common antibiotic. The scientists found it in more than 10 percent of the samples, mostly in areas where septic systems are prevalent. Although the concentrations were well below the levels considered dangerous, "the detections nonetheless indicate that this antibiotic is present in domestic wastewater, is mobile in groundwater, and that shallow aquifers in Minnesota are vulnerable to anthropogenic contamination," the study said.
On the other hand, another chemical, bisphenol A, used in making hard plastic bottles and other consumer products, was present mostly in wells near closed landfills.
In all, the authors suggest, sources of the chemicals are likely a combination of domestic, commercial and industrial wastewater systems, stormwater runoff, leaking municipal sewer lines and agricultural runoff.
"Do you need one that has a fragrance?"
The Minnesota Department of Health has been studying contaminants of emerging concern for several years, using money from the state's sales-tax-supported Clean Water Fund and gradually expanding the list of chemicals of concern.
The new groundwater information could generate a closer health department look, particularly at the four commonly found contaminants that scientists know little about, said Helen Goeden, a toxicologist for the department.
Goeden said she didn't consider the new report cause for alarm, but it should make people more aware. "People are complacent about their drinking water. Reports like this help inform."
One line of prevention is consumers making better choices, she said. That may not apply to prescription medications, for example, but "with lotions, detergents and so on, do you need one that has a fragrance?"
Other avenues, Kroening said, involve programs to dispose of products properly and to get manufacturers to make products differently.
Another approach for dealing with the chemicals is for wastewater treatment plants to be upgraded to remove contaminants of emerging concern.
Erickson said she believed the study was the broadest one in the nation to look at the chemicals in groundwater. In the end, the USGS and the MPCA will look at water samples over five years, hoping to learn more, not simply about the presence of the chemicals but about how mobile they are in any given place.
You can learn more about contaminants of emerging concern, including a list of those the Minnesota Department of Health is considering for evaluation.