Asarco wants environmental regulators to examine whether Union Pacific contributed to lead pollution along railroad lines, so Asarco might recover some of the roughly $1.8 billion it paid for the cleanups.

This pollution fight between the company that operated lead smelters for decades and the railroad that delivered ore has already gone on for several years, but now it has expanded beyond Omaha to include southeast Missouri and Idaho.

Asarco 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 says the railroad used rock from lead mines in its rail lines.

UP spokesman Tom Lange says Asarco is rehashing old allegations that the railroad believes lack merit.