"The vulnerability to toxins is most prevalent in childhood," Ma said. "It could cause harm to babies, and we should do everything we can." Phthalates have been banned by the European Union and at least 14 other countries after studies found that the chemical mimics the hormone estrogen and could cause developmental problems. Those could include early puberty in girls, low sperm counts, genital defects and lower testosterone in boys. Scientists in the United States, however, are divided on the health risks. A 1998 study by the U.S. Consumer Product Safety Commission found that few if any children are at risk from the chemical because the amount ingested from sucking on toys is at such low levels.

The commission also noted that substitutes were unproven and could be more toxic. Toy manufactures say the chemical, which has been used for the past 20 years in baby items, poses no harm. In addition, they note substitutes could leave plastic toys more brittle and prone to breaking."If you don't make a safe product, you'll never succeed in the business," said Joan Lawrence, vice president of standards and regulatory affairs at the Toy Industry Association. "If there was any concern (about phthalates), we would not be having this conversation." Environmentalists and public health advocates remain concerned that phthalates, like other hormonal-mimicking chemicals such as the pesticide DDT, are dangerous even in small amounts. "With hormones, its not just the concentration of the exposure but the timing of the exposure, and that's why developing fetuses and children are particularly vulnerable," said Cynthia Li, a staff physician of internal medicine at San Francisco General Hospital. "We should use foresight in really trying to reduce the number of chemicals that pass through our bodies." California lists the chemical as a toxin under Proposition 65, a measure passed by voters in 1986 that requires businesses to post warnings about dangerous chemicals.