Preston Winter was cleaning out his late grandfather's garage in Floodwood, Minn., when he found four plastic jugs of mercury.

Sixty-four pounds of mercury, to be exact. Enough to fill 30,000 thermometers.

His grandfather apparently had stored the jugs 13 years ago, when he was thinking about mining gold. Figuring he might make a few bucks, Winter, 23, posted a photo on Craigslist and offered the batch for $650 -- not realizing that mercury is a highly toxic metal subject to tight legal restrictions.

On Thursday, officials announced that a state hazardous waste specialist, acting on a tip from someone browsing the online site, went to Winter's home and picked up the mercury after the state Pollution Control Agency (PCA) paid $300 for it.

It was the largest amount of mercury that officials recall ever getting from one house, although large amounts sometimes are collected at industrial sites.

"Industry spends millions of dollars to cut back emissions of less mercury than we recovered here," said Jeff Connell, a PCA enforcement manager.

The action removed a hazard and saved Winter from unknowingly making an illegal sale to an unauthorized buyer.

"This material could have ended up in a dumpster from a person cleaning out a garage, so the mere fact that [Winter] bothered to take a picture and offered to sell it -- well, we're lucky,'' said Carl Herbrandson, a toxicologist with the Minnesota Department of Health. "This is dangerous stuff."

Even a broken thermometer in a school classroom results in mobilizing an emergency response cleanup team -- and sometimes evacuating the school, Connell said.

Mercury can damage kidneys and the nervous system and is especially toxic to fetuses and young children.

In 2005, two teenagers stole 22 pounds of mercury from an industrial site in Rosemount, tracking it through homes and allowing 14 other children to play with it. In all, 38 people were evacuated from their houses for several weeks, and total cleanup cost was about $500,000, officials said.

Mercury occurs naturally, but the state has issued health advisories to limit consumption of some contaminated fish in Minnesota because of emissions from mining and coal-fired power plans.

Mercury sometimes is used in gold refining to help separate the gold from rock. The mercury is released as a dangerous vapor in the smelting process.

The mercury in Floodwood was picked up March 30 by Heidi Ringhofer, director of solid waste services at Western Lake Superior Sanitary District in Duluth.

Last year, her agency collected 231 pounds of mercury from hazardous household waste in eight northeastern counties, she said.

"It comes in original packaging, like in this case, or in mayonnaise jars or food jars -- labeled or unlabeled," Ringhofer said. "It's in basements and attics and garages and all over. But this is the first time we've pulled it off Craigslist."

Warren Wolfe • 612-673-7253