PASADENA – This month, for the first time, the state will begin regulating the amount of the toxin perchlorate in drinking water.

As of Oct. 18, California will require that water contain no more than six parts per billion of the rocket-fuel additive, putting regulatory force behind what had been just a suggested limit for the past five years.

That amount is about the same as a tablespoon of ink in an Olympic-size pool.

The change, lauded by some environmentalists, will make California only the second state, behind Massachusetts, to regulate the chemical in drinking water.

But there are also concerns that even the seemingly minuscule amount set by the new limit is still too high.

Perchlorate has been shown to block the release of thyroid gland hormones critical for normal growth and nervous system development, making it particularly dangerous for pregnant women and young children.

“We believe there is really no safe level of rocket fuel in our drinking water,” said Bernadette Del Chiaro of the advocacy group Environment California. “We are disappointed.”

The Association for California Water Agencies, however, supports the new standard. It notes that the state’s Office of Environmental Health Hazard Assessment has declared that the six-parts-per-billion limit would cause no ill effects even after 70 years of water consumption.

“Six parts per billion has been a good, health-effective, cost-effective number,” said Krista Clark, the association’s director of regulatory affairs. “There’s no justifiable reason to have a standard lower than that. To treat lower than that would be to spend public tax dollars on a standard that provides zero net health benefits.”

However, the chemical’s health impacts remain under debate.

In a 2002 study, the U.S. Environmental Protection Agency recommended a maximum limit of one part per billion for perchlorate in drinking water, a limit which Massachusetts adopted last year.

The EPA estimates perchlorate contamination exists in at least 25 states.

In Los Angeles County alone, according to the California Department of Public Health, 67 water sources have exceeded six parts per billion of perchlorate at some point during the past five years. Several of those sources are in the San Gabriel Valley.

In Pasadena, the major sources of perchlorate contamination are waste pits used at JPL during the 1940s and 1950s.

At a treatment plant on the laboratory grounds, water drawn from beneath the surface has perchlorate levels of about 400 parts per billion, said Steve Slaten, the plant project’s manager for the National Aeronautics and Space Administration.

After treatment, he said, the water is returned to the ground with a concentration of less than two parts per billion.

Drinking water from wells in Altadena tainted by the plume of JPL toxins is cleaned until it has less than six parts per billion of perchlorate.

Although some of Pasadena’s water sources do contain perchlorate, the new regulations will have little impact on Pasadena Water and Power, said Shan Kwan, the agency’s director of water.

Six parts per billion “is what we originally thought that the maximum contaminant level would be, so we were already keeping that in mind,” Kawn said.

“When we blend (water sources), we always put a big safety factor in there,” he added.

But although Pasadena has been “pretty careful,” said Tim Brick, chairman of the Metropolitan Water District, “I, frankly, believe that there are some agencies that are blending water for whom this will be a problem.”

Still, he said, “personally, I have concerns that six parts might not be fully protective for the health of pregnant women and children.”