KANSAS CITY, Mo. (AP) – A company whose factory in northwest Missouri gave farmers fertilizer that critics say contained a cancer-causing chemical disputed the claims Thursday and defended its environmental record.

Prime Tanning Corp., of Hartland, Maine, issued a statement in response to a lawsuit filed Wednesday accusing it of knowingly distributing sludge containing hexavalent chromium as free fertilizer to farmers in four counties. The metal, also known as chromium 6, is a known carcinogen.

The company’s St. Joseph plant was purchased this year by National Beef Leathers, a subsidiary of Kansas City-based National Beef Packing Co. that also was named in the lawsuit. On Thursday, National Beef Leathers said it would stop distributing the sludge while it conducts its own investigation.

Environmental activist Erin Brockovich told a crowd in Cameron on Wednesday night that hexavalent chromium may be linked to what some area residents believe is a high number of brain tumors in the region.

State and federal agencies have tested several areas in and around Cameron in the last year in response to concerns about brain tumors, but not for chromium 6. The lawsuit and Brockovich’s meeting were the first time hexavalent chromium in fertilizer had been publicly identified as a possible cause.

“Based on our preliminary investigation, we believe there is no basis for the claims made in the litigation,” said Grover Elliott, vice president and chief financial officer of Prime Tanning Co. “We look forward to cooperating fully with state and federal agencies in their review and investigation.”

The lawsuit, filed by two northwest Missouri residents, accuses Prime Tanning of not telling the state that the sludge left over from tanning processes at the plant contained hexavalent chromium. Prime Tanning’s statement does not address that allegation, and the company said it would answer no other questions.

More tests will be conducted to determine how widespread the use of the fertilizer was, but an environmental investigator at Wednesday’s meeting said it has been distributed since 1983 primarily in Andrew, Buchanan, DeKalb and Clinton counties.

National Beef Leathers said the due diligence it conducted before buying the Prime Tanning plant did not uncover any irregularities with the application of the sludge.

Elliott said in a statement that application of the sludge “is an environmentally responsible practice that is done in accordance with all Missouri laws and regulations.”

The Missouri Department of Agriculture is not involved in regulating fertilizer. Enforcement of the state’s laws governing fertilizer is the responsibility of the Missouri Agricultural Experiment Station at the University of Missouri. Joe Slater, head of the station’s fertilizer/ag lime service, was out of the office Thursday and unavailable for comment.

The Missouri Department of Natural Resources, which has been leading the investigation into the tumor complaints, did not return phone calls Thursday.

The U.S. Environmental Protection Agency has been assisting in that investigation. Spokesman Chris Whitley said no one had suggested before Wednesday that the agency investigate the fertilizer or the possible presence of high levels of hexavalent chromium. He said the EPA has asked the law firm that filed the lawsuit for any information it has.