The Environmental Protection Agency reversed Bush administration drinking water policies Wednesday, announcing that it will regulate perchlorate, a component of rocket fuel, and 16 other chemicals - called volatile organic compounds - that can cause cancer at high enough doses.

The perchlorate decision "is about protecting the health of between 5 [million] and 17 million Americans that are exposed to perchlorate in the water they drink," EPA Administrator Lisa P. Jackson said in remarks to the Senate Committee on Environment and Public Works.

In a statement, Sen. Barbara Boxer (D-Calif.), who has sought to regulate perchlorate since 2002, said, "I will do everything I can to make sure this new protection moves forward."

The EPA said it would take an additional two years to propose a perchlorate regulation, a pace that angered some environmental groups. "The science is already out there," said Jennifer Sass, a scientist with the Natural Resources Defense Council, an environmental advocacy group. "Anything that anybody needed to say about this process is already done." The EPA has collected 39,000 public comments regarding perchlorate regulations.

In October 2008, the Bush administration bucked the advice of its own EPA scientists and announced that it would not regulate perchlorate.

A Washington Post investigation at the time found that officials from the Bush administration heavily edited a key EPA report to play down the risks of the chemical. A Government Accountability Office report also found that the Defense Department - which, along with NASA, is a heavy user of perchlorate - sought to derail any perchlorate standards.

Perchlorate occurs naturally in very small amounts and is also used in rocket fuel, explosives and fireworks.

A 2010 Government Accountability Office study reported perchlorate contamination at 70 percent of Defense Department facilities. A 2006 Food and Drug Administration study found perchlorate in 74 percent of a wide range of food items it tested.

"A very long period of bad public policy was reversed today," said Mae Wu, a lawyer with the Natural Resources Defense Council.

"We're both thrilled and relieved," said Renee Sharp, a scientist with the Environmental Working Group, whose investigations have found perchlorate in California groundwater and vegetables.

The Perchlorate Information Bureau, a group funded by rocket manufacturers, objected to the decision, saying in a statement that "a national perchlorate standard is not needed and would not provide a meaningful public health benefit."

Studies of perchlorate show that it can disrupt the thyroid, a master gland essential for growth and development. That means that fetuses are at the highest risk for perchlorate damage, said Lynn Goldman, dean of the School of Public Health at George Washington University.

The battle over perchlorate now turns on the acceptable drinking water concentration the EPA will set under the Safe Drinking Water Act. Environmental groups on Wednesday called on the EPA to set a standard of one part per billion, which California adopted last month as a "public health goal," a strong step toward reducing the state's current standard of six parts per billion. The only other state to adopt a perchlorate drinking water standard, Massachusetts, sets a limit of two parts per billion.

A 2010 study of 500,000 California newborns reported disrupted thyroid function in infants whose mothers had been exposed to drinking water with at least five parts per billion perchlorate. The study did not assess effects at lower concentrations.

In a separate EPA decision, Jackson said the agency was moving forward with its master drinking water safety strategy announced last year by regulating as a group 16 cancer-causing chemicals called volatile organic compounds.

In the past, the EPA has regulated individual chemicals in drinking water separately. Goldman, a former assistant administrator at the EPA, said treating the compounds as a group is "scientifically justified" because they often appear together as industrial contaminants and can cause cumulative damage to the body.