Utah continues to climb on a national list that ranks U.S. states by the prevalence of environmental hazards, but that rise has more to do with a single company than the state as a whole.

Salt Lake City-based Kennecott Utah Copper’s emissions of potentially harmful materials — toxic heavy metals such as lead and zinc in particular — rose by nearly 20 percent in 2016, according to the national Toxic Release Inventory (TRI), issued by the U.S. Environmental Protection Agency.

A spokesman for mining, smelting, and refining company said the increase was due to its mining of a vein of ore last year that was especially heavy with lead, considered an emission under TRI’s definition. The copper mine and its related operations account for more than 90 percent of all TRI-listed emissions in Utah.

So when Kennecott’s emissions go up, Utah as a whole also jumps up the list of “most toxic” states. The Beehive state currently ranks as the TRI’s third-largest for toxic releases. It ranked fourth in 2015, and 17th in 2005.

Kennecott has long led the TRI’s list of top-polluting companies nationwide, surpassed only by a similar but larger mining operation in Alaska.

The Toxic Release Inventory, maintained and updated regularly by the EPA, requires industries to report their emissions of certain substances that pose a potential risk to human health or to the environment. The materials in question are diverse and difficult to classify as a whole — ranging from heavy metals such as lead and zinc to gaseous chemical pollutants such as chlorine. All three of those are common hazardous materials in Utah, according to the TRI.

Materials on the TRI are said to be “released” when the company that produced or processed them emits them into the air or water, or disposes of them in a landfill or similar holding facility.

Kennecott’s reported releases are predominantly metals-laden waste rock that is deposited in Bingham Canyon or in the company’s tailings piles near Magna. Lead, which is known to cause developmental delays in young children who consume or inhale it, accounted for more than three-fourths of the company’s reported emissions last year.

The TRI has been criticized for over-representing the potential hazards of mining operations, in part because emissions are reported by weight, as opposed to toxicity, which would be difficult to compare directly. A mine, which has heavy waste products like lead, ranks higher on the TRI than a chemical refinery, for example, which might have mostly gaseous emissions.

And the TRI can’t tell you whether you have, in fact, been exposed to these materials, said April Nowak, a regional TRI coordinator for the EPA. The list is intended as public disclosure of potential environmental hazards.

Meanwhile, the increase in Kennecott’s emissions appears to be a temporary blip. Both the company and the state of Utah overall have remained relatively steady in their production of hazardous materials, against a backdrop of such emissions decreasing across the nation as a whole.

But this past year, Kennecott miners ran into a vein of ore that contained significant higher levels of useful metals such as copper, but also of potentially harmful heavy metals, such as lead, that the mine disposed of as waste product. So even though the mine’s output actually decreased slightly in 2016, the company reported an increase in emissions to the TRI.

“Naturally occurring concentrations of metals were nearly double” what Kennecott usually extracts, said Kyle Bennet, a spokesman for Kennecott, a subsidiary of the London-based global mining conglomerate Rio Tinto. “We actually moved less material last year, so it is just the concentration that increased.”