OMAHA, Neb. (AP) — 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.