ADAIR COUNTY, Iowa — A semi-trailer fire at a rest stop on I-80 Tuesday led to a lactic acid spill near Adair.

The Iowa Department of Natural Resources says it is investigating after approximately 550 gallons of lactic acid spilled in the incident. The semi was hauling poly totes of the substance when the driver noticed the tires on the trailer were smoking. The driver pulled over at the I-80 eastbound rest stop, about three miles east of Adair, and tried to put the fire out but was unable to.

When the Adair Fire Department arrived at the rest stop the majority of the trailer and its contents were engulfed by flame.

Iowa Department Transportation crews tried to capture the lactic acid and water mixture by placing sand in the area, but the substance flowed in the storm drains, off the concrete, and onto farmland. The mixture made it about 200 feet into the field where it entered a tile intake that outlets into a tributary of the South Fork Middle River.

The DNR said an environmental clean-up company arrived around 8:00 p.m. to start cleaning the area. A neutralizing agent is being used to sanitize the area and any contaminated soil will be excavated and treated on-site. The rest stop will remain closed while the clean-up is completed.

No dead fish have been seen in the river but the DNR advises those downstream of the spill to avoid the area and remove cattle if needed.