All those antibacterial soaps we use are washing into Minnesota’s lakes and rivers, where they’re building up as toxins, University of Minnesota researchers have found.

Levels of triclosan, the active ingredient in household products ranging from soap to cosmetics have increased in rivers and ponds as people have used more of it over the past several decades, according to a study made public Tuesday, Jan. 22, and published in the journal Environmental Science and Technology.

“The big significance is that it’s a common household product that’s being found well beyond its point of use — the home,” said William Arnold, a civil engineering professor in the University of Minnesota’s College of Science and Engineering and the author of the study. “It’s a compound that we know is biologically active and we know its levels are accumulating in the environment.”

In one lake, triclosan and its derivatives — seven chemicals into which triclosan breaks down in the environment — made up more than 60 percent of its mass of dioxins, Arnold said.

The effects of triclosan and its derivatives on water ecology aren’t fully understood, although triclosan kills algae and can work its way up the food chain like other pollutants.

Elsewhere, studies gathered by the Proceedings of the National Academy of Sciences have found the chemical can hinder cell growth in mammals and slow swimming in fathead minnows. Widespread use of the chemical has prompted some consumer groups and public health officials to worry about whether its increasing use could lead to resistant bacteria — particularly since it’s no more effective at killing germs than washing with plain old soap.

In 2000, the American Medical Association concluded, in part, “there is little evidence to support the use of antimicrobials in consumer products such as topical hand lotions and soaps.”

Such activity has placed a spotlight on triclosan, prompting the Environmental Protection Agency to review its status. In the spring, after a Canadian Medical Association request for a ban in household products, the Canadian government determined triclosan was harmful enough to the environment to warrant regulation.

In August, Johnson & Johnson said it will phase out triclosan and a host of other chemicals that could be harmful to people or the environment. For several years, a number of consumer and environmental groups, including the Environmental Working Group, have pressured the companies to remove the chemical, which might or might not be listed in ingredient labels. (Whether disclosure is required depends on the agency regulating the product.)

In Minnesota, Arnold and a team of graduate students took core samples of sediments in eight bodies of water: Lake Pepin, Lake St. Croix, Lake Winona near Alexandria, East Lake Gemini in St. John, Lake Shagawa in Ely, Duluth Harbor, a Lake Superior site several miles offshore and Little Wilson Lake.

Little Wilson, which is in the Superior National Forest, was the control for the group. It receives no wastewater and contains no triclosan. All the other bodies of water receive, directly or indirectly, treated outflow from sewage treatment plants. All contained triclosan.

The chemical was invented in 1964, and Arnold said dated sediment core samples showed the chemical and its derivatives didn’t exist before its invention. In other words, triclosan is an entirely human-caused pollutant.

Wastewater treatment facilities don’t specifically attempt to remove triclosan, but standard treatment — either chlorination or ultraviolet light — destroys most of it. But not all of it, or its derivatives, some of which are created in the treatment process.

Arnold’s study, which began in 2010 and was backed by state and federal funds, was the first to measure levels of triclosan and all seven derivatives, which include four dioxins.

Arnold said increases in triclosan and its derivatives correlated directly with increased consumer use over time in six of the seven lakes where they were found. (In one lake, Shagawa, the numbers didn’t correlate, although Arnold said he suspects sediment might have been stirred up, so the core sample wasn’t an accurate calendar of the past.)

“Triclosan is very much a bellwether for our overall contamination of household chemicals,” said Heiko Schoenfuss, a biology professor at St. Cloud State University who has studied the chemical in the environment but isn’t directly affiliated with Arnold’s study.

He said Arnold’s research has significance beyond triclosan.

Schoenfuss said triclosan is an example of how aquatic environments are affected by the things we do in our homes.

“These are chemicals that mainly are put into our sinks and down our drains and toilets,” he said. “We have direct control over that.”

Dave Orrick can be reached at 651-228-5512. Follow him at twitter.com/OutdoorsNow.