Dozens of insurance companies say they're not obligated to help pay for Duke Energy Corp.'s multi-billion dollar coal ash cleanup. They say the nation's largest electric company long knew about but did nothing to reduce the threat of potentially toxic pollutants.

The claim is in a filing by lawyers for nearly 30 international and domestic insurance companies Duke Energy sued in March. The Charlotte-based company wants to force insurance payments to cover part of the utility's coal ash cleanup in the Carolinas.

The insurers say they're not paying because Duke Energy stored its coal ash in unlined pits as part of its normal business practices. Insurance company lawyers say no distinct pollution events triggered coverage.

Coal ash contains arsenic, mercury and other elements that may be hazardous in sufficient concentrations.