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.

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.

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.

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