MADISON, Wis. (AP) -- State environmental officials say they won't write new air regulations for sand mines.

A group of citizens asked the Department of Natural Resources in November to draft new rules governing dust particles that rise from the mines.

DNR Deputy Secretary Matt Moroney wrote in a letter Monday that existing regulations cover such emissions. He noted the agency has started requiring mine companies to submit dust control strategies earlier in the permitting process to ensure plans are ready before facilities open.

He included a state study that acknowledged long-term exposure can affect human health. However, the study found no evidence that intermittent or occasional exposure causes problems.

Clean Wisconsin attorney Elizabeth Wheeler says the DNR is missing the point. She says the mines can still emit significant dust under existing regulations.