A large amount of coal slurry — a watery mix of coal dust, rock and chemicals, including the chemical crude MCHM — spilled from a preparation plant into a tributary of the Kanawha River in Charleston, W.Va., on Tuesday. Local officials said the impact of the spill is “significant.”

Local officials estimated it to be more than 100,000 gallons, according to the West Virginia Gazette. That is 10 times the volume of an MCHM spill that tainted water for hundreds of thousands in the area last month.

Emergency officials and environmental inspectors told the Charleston Gazette that roughly 6 miles of Fields Creek had been blackened and that a smaller amount of the slurry made it into the Kanawha River near the town of Chesapeake.

"There has been a significant environmental impact," Harold Ward, acting director of the state Department of Environmental Protection's Division of Mining and Reclamation, told the paper.

The plant, Patriot Coal, said that levels of MCHM were low and that it is “fully cooperating” with the investigation into the spill.

But environmental groups say MCHM isn’t the only problem with slurry pollution across coal country, and that other contaminants in the coal slurry can be harmful.

“The rock, coal and clays contain a wide range of heavy metals including arsenic, lead, cadmium, chromium, iron, manganese, aluminum and nickel,” according to the Sludge Safety Project, an environmental group. In areas that have experienced slurry contamination, people have suffered “kidney and liver disease, serious diarrhea, skin rashes, tooth loss and several different cancers,” the SSP said on its website.

Coal slurry pollution has also been blamed for rendering water undrinkable.

Davitt McAteer, former head of the federal Mine Safety and Health Administration, told Al Jazeera that it was hard to say exactly what lies in this particular coal slurry but that there are “unwanted, potentially risky elements” in raw coal.

Coal processing is performed to remove as many harmful impurities as possible, including selenium and arsenic, to prevent their release into the atmosphere when coal is burned.

“Those impurities can be severe. Those impurities are what you are taking out, and you’re having these impurities congregate in the impoundment,” said McAteer, referring to a reservoir of slurry that can be kept above ground or below ground.

The coal slurry that spilled Tuesday morning was reportedly on its way from the processing plant to the impoundment.

Environmental groups charge that exposure to coal slurry, and the mix of chemicals it contains, can result in negative health effects.

The slurry spilled into Fields Creek from the Kanawha Eagle preparation plant near Winifrede sometime between midnight Monday and 5:30 a.m. Tuesday when a valve inside a slurry line ruptured. There are not any public water intakes immediately downstream from the plant, said state DEP spokesman Thomas Aluise in a release.

However, Aluise told Al Jazeera that two water intakes are “somewhat nearby.”

“It's possible depending on the level of water contamination the groundwater could become contaminated from the spill,” he added.

West Virginia American Water said it does not expect the slurry spill to affect its treatment plant on the Elk River.

"Our employees are working on behalf of our customers with local and state officials to gather additional information," West Virginia American Water spokeswoman Laura Jordan said in a release. "We have been in contact with the West Virginia Bureau for Public Health, which concurs that they do not anticipate any impact to our plant on the Elk River."

Crews were working to contain the spill Tuesday, Aluise said.

West Virginia American Water told the DEP that the plant uses Flomin 110-C, a frothing chemical that contains crude MCHM. Inspectors with the DEP collected water samples from the creek on Tuesday for testing to be conducted by ALS Laboratory in South Charleston, Aluise said.

Aluise said enforcement is pending against the company.

Patriot Coal told Al Jazeera in a statement that “containment activities” are currently its top priority. “All pumping related to the slurry line was promptly discontinued and the discharge ceased," the company said. "Cleanup activities are underway and will continue until state regulatory officials determine the spill is remediated."

Also Tuesday, Gov. Earl Ray Tomblin's administration said it will test water in some West Virginia homes for the chemical that spilled last month. Tomblin has said he does not intend to test the water in the households of all 300,000 affected West Virginians but would consider representative sampling.

Al Jazeera and The Associated Press. Wilson Dizard contributed to this report.