DETROIT (AP) — Environmentalists have filed a lawsuit against DTE Energy Co. and two subsidiaries over emissions from their coal-fired power plants.

The Sierra Club contends that four of the company's plants in southeastern Michigan have committed a combined 1,400 violations of the federal Clean Air Act.

The lawsuit was filed Tuesday in U.S. District Court in Detroit and targets the Belle River, River Rouge, St. Clair and Trenton Channel plants. It says they threaten human health by emitting mercury, soot, sulfur dioxide and nitrogen oxide.

DTE spokesman John Austerberry said the plants comply with applicable state and federal emission regulations and have required pollution control systems.

He said DTE has invested more than $2 billion over the past decade on emission controls and expects to spend a similar amount to meet new requirements.