By JOSH FUNKOMAHA, Neb. (AP) â¿¿ Asarco wants environmental regulators to examine whether Union Pacific contributed to lead pollution along railroad lines to make sure the $1.8 billion it has paid for cleanups is effective. The Tucson, Ariz.-based Asarco is a lead and copper mining company that ran lead smelters, metal refineries and numerous mines. It recently started writing to state and federal regulators to urge more scrutiny of Union Pacific's rail lines because tests Asarco paid for show high lead levels in places. Asarco lawyer Gregory Evans said the railroad used rock from lead mines in ballast for its rail lines and some ore fell out of trains in transit. These new rail line concerns that extend beyond the lead contamination in Omaha to southeast Missouri and Idaho grew out of the multiyear legal fight over pollution between Union Pacific and Asarco. It's not clear whether Asarco would be able to recover any of what it paid for cleanups from Union Pacific if regulators did find railroad contamination. Evans said regulators could order the railroad to pay for its own cleanup effort on top of what Asarco has done if they agree the rail lines are polluting. "This waste threatens the remedy that Asarco has paid for in Omaha and other locations," Evans said. Some of the rail lines Asarco is concerned about have been abandoned by Union Pacific and converted into trails by covering up the rail bed with asphalt, Evans said. UP spokesman Tom Lange said Asarco is rehashing old allegations that the railroad believes lack merit. Asarco has been trying to get other companies to contribute to environmental cleanups it agreed to pay for ever since it emerged from bankruptcy in 2009. "Union Pacific has responded in court and plans to vigorously defend against Asarco's allegations," Lange said.