JACKSON, Miss. (AP) -- The Mississippi Department of Environmental Quality has fined DuPont Co.'s DeLisle plant $117,000 after pollution control equipment broke down, allowing a smokestack to emit too much during a March 2011 test.

DuPont Co., based in Wilmington, Del., makes titanium dioxide, a whitening agent used in paint, paper and plastics, at the Harrison County plant. More than 800 employees and contractors work at the complex, which is Mississippi's largest single releaser of toxic chemicals.

As part of its process, the plant burns coal in two boilers, according to 2011 MDEQ documents. DuPont spokesman Duane Wilson said equipment failed on a smokestack that vents a silo holding coal ash.

The environmental regulator found that the smoke coming from the stack was 60 percent opaque, when it was limited to 40 percent under the terms of DuPont's environmental permits. Wilson wrote in an email that the smokestack only exceeded legal limits on March 2, 2011, the day of the test.

MDEQ spokesman Robbie Wilbur wrote in an email that opacity levels began to increase in the weeks before the test, although they didn't exceed permit limits.

Wilson said that the unit was shut down immediately and a baghouse capturing dust and particulate pollution was replaced later that month. He said the filter captures "non-hazardous particulate matter." The Environmental Protection Agency regulates particulate pollution because it can get into human lungs, causing or aggravating respiratory problems.

DuPont was also fined for failing to submit paperwork regarding a construction project and another smokestack test in late 2011. Wilson said those problems were "administrative errors."

"None of the three citations had any adverse impacts," he said. The company agreed to pay the fine in July 2012 and mailed the check Aug. 2

The DuPont plant is traditionally Mississippi's biggest polluter. In 2010, it released almost 18 million pounds of substances covered in the federal Toxic Release Inventory. That was more than a quarter of all such hazardous substances that are emitted to air, water or land or injected underground in all of Mississippi.

DuPont's air emissions have fallen sharply over the last two decades. Wilson puts the reduction at 53 percent since 1991, although federal records show an even greater reduction.

Wilson said DuPont is "committed to operating the DeLisle plant in compliance with all regulations."