A man examining a gravel road in Wilton, Iowa Jon Henessee/Alamy

When Doug Hoag delivers seed to farmers in Iowa’s Muscatine County, he rumbles over miles and miles of dirt road. Hoag used to put 45,000 miles on his truck before its thick tires would fail. Now he’s lucky to get 30,000. Driving her car on the roads, Hoag’s wife, Sandi, got three flats in one week. Other drivers and truckers complain that the roads also crack their windshields.

What’s to blame? Bits of metal, some as big as fingers.

For the past five years, the county’s engineers have been adding slag, a byproduct of steel manufacturing, to its rural roadways in place of limestone gravel. At one-fifth of the cost, slag is much cheaper than gravel. But unlike gravel, slag doesn’t settle as well into the roadbed. It stays loose and is more difficult to drive on, says Hoag. And beyond all that, the metals it contains—and the dust that vehicles kick up when they drive on it—has become a health concern.

“We’ve got to get it stopped,” says Hoag, who formed the Citizens Slag Committee with other concerned neighbors. “Residents don’t want it, the costs that they’re looking at aren’t correct, and it’s extremely toxic.”

Doug Hoag and Daryl Sywassink made a presentation before the Muscatine County Board of Supervisors on residents' concerns regarding the use of steel slag on gravel roads. Meredith Ecklund/Muscatine Journal

A study conducted by Iowa state toxicologist Stuart Schmitz in 2008 for the Iowa Department of Public Health found small amounts of manganese, about 3,900 milligrams per kilogram, in slag that was later used on roads. Manganese is a potent neurotoxin, and many pediatricians and toxicologists suggest there may be no safe level of exposure during early brain development. Further, a more recent analysis of slag showed manganese levels five times higher than Schmitz’s 2008 findings. The initial report also did not detect cadmium, a heavy metal that can make bones brittle and cause kidney problems, which was found at worrisome levels (3,660 milligrams per kilogram) in the more recent analysis. Different additives or materials used at the steel manufacturing plant may account for the differences in the two analyses.

Those living and driving along slag-laden roadways, especially children who play and ride bikes on the roads, are at risk, says Ed Askew, the author of the recent report. A local chemistry consultant and a member of Hoag’s committee, Askew began looking into the county’s slag when a group of farmers approached him in 2017. The following October, he obtained samples from Swedish-based SSAB, the steel plant that provides slag to Harsco Metals and Minerals, the U.K. company that processes and sells the slag to Muscatine County. After testing the material, Askew concluded that the slag “is harmful to children” and “can be harmful to adults.”

Askew’s concerns, and subsequent presentations to Muscatine’s Board of Supervisors, prompted the county’s moratorium on the use of slag last June. But unless an upcoming investigation by the Iowa Department of Public Health finds that concentrations of the metal are unsafe, the practice could start up again. Hoag’s group wants more than just a temporary hold; they want to get the stuff off the road for good.

The 2008 report assumed that the slag stays put on the road, but Askew found otherwise. People can inhale dust kicked up from vehicles, and that dust can settle onto pastureland and yards and be tracked into homes. Askew focused on the threat of ingesting the heavy metals (since children and toddlers have a habit of putting everything in their mouths), but inhaling manganese is also a serious health concern. (NRDC is currently helping communities of Chicago’s South Side fight manganese pollution that has been blowing into their homes and yards from nearby factories.)

As Iowans learned more about slag, they began speaking out. In the past year, more than 700 people have signed a petition protesting slag’s use on roadways. As one farmer told the Des Moines Register in January, “No one should be poisoned by a county road.”

Jean Forbes of West Liberty, Iowa, brought a display panel to the Muscatine County Board of Supervisors meeting last month, showing examples of the pieces of debris she’s found on the road near her home. Meredith Ecklund/Muscatine Journal

Slag isn’t a potential problem just for Iowa. According to a representative of the National Slag Association, the states that most predominantly use slag on their roads include Wisconsin, Michigan, Ohio, and Pennsylvania—states in the old Iron Belt, where slag is most readily available.

“Everybody and their mother uses it,” says Nathan Mather, chairman of the Muscatine County Board of Supervisors. “Until this started, there’s never been any indication that it was in any way unsafe.” (A 1978 research paper on potential health concerns from the toxic components of slag identifies both cadmium and manganese.)

Each state has its own ways of regulating slag, and until 2014, Iowa considered it a solid waste. That meant when the state started applying slag to roads in 2006, state agencies managed its use and tested it periodically for potential safety issues. But after legislators took slag off Iowa’s solid waste list, it received very little scrutiny—until now.

State toxicologist Schmitz plans to test the slag on Muscatine County’s roads later this year, after any remaining snow and ice melt away. According to a health department spokesperson, this will mark the first time the agency has done testing to see what’s in the dirt along roadways.

In addition to checking the concentrations of heavy metals, Schmitz plans to measure the size of the slag particles. If metal concentrations prove high and the particle sizes are small, air testing may be needed, because smaller particles more easily become airborne. “If there are health concerns, we want to know,” says Schmitz. By pointing out potentially serious issues his department might be unaware of, he says, “the people who live in those areas are a great help to us.”

If the slag proves dangerous, the county is ready to remediate, says Mather. SSAB also plans to submit its own slag report to Muscatine County. In the meantime, members of the Citizens Slag Committee will continue to keep their eyes on the road—and what may be coming off it.

“Look at the long-term environmental burden. Look at what’s gotten on people’s property,” says Askew. “Metals don’t go away.”