State regulators have begun reviewing a drinking-water standard for a common inland contaminant.

The California Office of Environmental Health Hazard Assessment will review the public health goal for perchlorate - an ingredient in explosives and some fertilizers - in 2009, said the office's deputy director for external and legislative affairs, said Sam Delson via e-mail.

The public health goal is the first step in setting a drinking-water standard.

Environmentalists, who complained the last public health goal of 6 parts per billion set in 2004 was too high, welcomed the news. One part per billion translates into a drop of water in an Olympic-size swimming pool.

"We're happy but really how happy we will remain depends on what number they end up with and how long it takes them to get there," said Renee Sharp, director of the nonprofit Environmental Working Group's California office.

When setting a public health goal, regulators only take into consideration a substance's effect on health. The state's Department of Public Health sets the final standard after also considering cost and technical feasibility.

Perchlorate is found throughout the country and in Southern California at old industrial sites. Some agricultural areas also have relatively low levels of perchlorate because it was found in some fertilizers.

The chemical affects the thyroid gland, which is involved in metabolism, mental and physical development.

Environmentalists say they are particularly concerned about the impacts on unborn babies and small children.

While the state is required to review public health goals every five years, Sharp said in reality officials aren't always able to follow through.

A number of new studies about perchlorate have been published in recent years that are relevant to the public health goal, including a 2006 study by the Centers for Disease Control and Prevention that found low levels of perchlorate can affect thyroid hormone levels in women, Delson wrote in the e-mail.

But requiring all the water purveyors in the state to remove even more perchlorate from water could be pricey. Many purveyors can mix contaminated water with clean water to get the concentration down, but that work would be more difficult if the standard were around 1 ppb or 2 ppb. Systems that remove perchlorate from water are not cheap.

Anthony "Butch" Araiza, who runs the West Valley Water District, said he doesn't mind if the standard is reduced because he already treats water contaminated at low levels.

West Valley, which is located in Rialto, home to one of the nation's most perchlorate-contaminated sites, will soon have five wells with treatment systems, Araiza said.

Araiza said he expects the state standard to stay around 6 ppb.

"I think if they go below that they'll probably have a hue and cry from some of those agencies," he said.

At the national level, the U.S. Environmental Protection Agency is in the final stages of making a formal determination not to set a standard for perchlorate in drinking water. In 2002, EPA scientists developed a draft protective level of 1 ppb, assuming all perchlorate intake comes through water. That level would have to be lower for drinking water to take into account other sources of perchlorate, like milk and lettuce. Environmentalists have criticized White House involvement in the process to set a standard since that time.