Minnesota hauled in 64 pounds of toxic mercury — all because of an advertisement on Craigslist and a tip from someone who saw it.

A Floodwood, Minn., man placed the online ad almost a month ago, after finding four plastic bottles of mercury while going through his late grandfather’s garage.

But an online shopper who saw it on the website contacted the Western Lake Superior Sanitary District, which in turn alerted the Minnesota Pollution Control Agency. The state agency then bought the toxic material at a reduced price rather than start a time-consuming regulatory compliance investigation.

“We felt we needed to move fast,” MPCA enforcement manager Jeff Connell said Thursday, May 17.

The action, he said, prevented the mercury — apparently the largest such discovery in recent state history — from falling into the wrong hands or harming the environment.

Mercury is a natural element, but people release more of it into the environment than is released through natural processes.

In Minnesota, the largest amounts come from coal-burning power plants, taconite processes and similar operations. It’s also in some thermometers, light bulbs and thermostats, but the state has pushed hard to limit those sources.

Elemental mercury is toxic to the kidneys and the nervous system, with dangerous pathways including long-term exposure to small amounts of spilled mercury. In the environment, it can be converted into methylmercury, which accumulates in the tissues of fish and can be consumed by people.

In the recent case, the MPCA said the man was selling the mercury for $650. To get it off the market quickly and disposed of properly, the agency chose to buy it, negotiating a $300 price and directing the sanitary district to use a state grant to make the purchase within hours.

District staff picked it up at the seller’s northeastern Minnesota home, photographed it and examined the entire area for any mercury contamination. None was found.

“This would be easily over 30,000 thermometers of mercury in this one purchase for $300,” Connell said.

The MPCA said the seller had inherited the mercury, along with unused mining equipment, from his grandfather, who had intended to get into gold mining. The mercury was in four sealed bottles and in its original packaging.

Mercury is not illegal to own in Minnesota, but state laws regulate its sale and purchase. In this case, the person trying to sell it will not face any penalties, the agency said.

That, Connell said, is because he hadn’t actually sold it yet and didn’t realize doing so would be breaking the law, Connell added.

Staff from state agencies said the cache, as well as other smaller ones discovered in recent years, likely will lead to heightened educational outreach efforts directed at long-forgotten hazardous materials still stored in garages or basements.

When just a few ounces of mercury are spilled, for example, it can set off a major hazardous materials response. The cleanup and response to 12 pounds of stolen and spilled mercury in Rosemount several years ago cost a half-million dollars.

Dennis Lien can be reached at 651-228-5588. Follow him at twitter.com/DennisLienPP.