Sacramento -- California took an aggressive step on Wednesday to ensure that mercury-laden thermostats in homes and businesses do not wind up in landfills and pollute the environment with the hazardous toxin.

The Department of Toxic Substances Control released new regulations requiring manufacturers of thermostats to significantly increase the safe disposal of those products that contain mercury. The regulations take effect July 1.

As a contributor to pollution, "if you look at controllable releases of mercury, it's fairly large," said Andre Algazi, supervisor in the safer consumer products unit at the department, of old thermostats.

Selling thermostats that contain mercury has been banned in California since 2006, but there are somewhere between 5 million and 10 million that are still in homes and business across the state, according to estimates in an industry-funded report.

That report was used by the state to create the regulation, which requires 30 percent of such thermostats to be properly disposed of this year, increasing to 75 percent by 2017.

In 2013, there will be 217,000 thermostats containing mercury either replaced by newer models in changes to heating and cooling systems or taken out of use because of demolition, according to the report, which estimates they will virtually be eliminated in California in about 25 years.

Rates of proper disposal are low, with between 18,000 and 19,000 collected as part of an industry-sponsored program in 2012.

Each thermostat contains up to 4 grams of mercury, which translates into nearly a ton of mercury going into landfills in the state every year, Algazi said. From there, the hazardous material can seep into the water supply.

Exposure to mercury can have harmful neurological and cognitive effects on humans, and high amounts can cause kidney problems, respiratory failure and even death, according to the U.S. Environmental Protection Agency.

Under the regulation, manufacturers would have to dispose of a certain percentage of mercury thermostats at designated collection centers for recycling or risk facing an enforcement order from regulators, which could require costly fixes.

"The reason why this is so important is there has been a low-level program in place for a significant number of years, basically operating with little accountability and no way to judge the performance," said David Lennett, senior attorney at the Natural Resources Defense Council.

"This is a watershed moment when it comes to this particular product and collection."

California isn't the first state to require proper disposal of thermostats that contain mercury, as about a dozen other states have some type of restriction. California's regulation will also require manufacturers to give statistics on disposal from other states that regulators here can use to determine whether other states have different and more effective programs.

Some of the most common thermostats with mercury are the older, round-dial models. The mercury is used in a switch that activates a furnace or air conditioner.