DENVER (AP) — Some Colorado legislators want a new state health department study on the potential health risks of the oil and gas industry, saying an earlier assessment that found low risk was inadequate.

Eighteen Democratic lawmakers wrote a letter to health department Director Dr. Larry Wolk criticizing the earlier assessment as narrow and incomplete. They also said it had a "dismissive tone."

The letter was dated April 4 and made public Tuesday.

The March assessment concluded the risk of harmful human effects appears to be low but stressed more study was needed. It reviewed a dozen earlier...