Of all the concerns a parent faces in raising a child, Margaret Thomas didn't think her daughter's sippy cup would be a problem.

But after hearing about potential developmental and reproductive problems associated with Bisphenol A (BPA), a chemical that can leach out of hard, clear plastic containers such as a sippy cup, the 35-year-old mother of two thought differently.

Her 4-year-old's cup has been replaced with a BPA-free substitute. But unease lingers for Thomas and many other parents who are throwing out the old, buying the new and wondering if they're too late.

"Am I concerned? Yes. Am I panicked? No. What damage may have been done is done. I can make good choices going forward. Now I can make more informed choices for my [6-month-old] son," said Thomas, of Stillwater. She co-founded the Twin Cities East branch of Mothers & More, which provides moms with support, education and advocacy.

While BPA in baby bottles and sippy cups has parents worried, there may be reason for concern among the broader population. Everyday items such as Nalgene bottles and certain food packaging also contain the chemical. Microwaving plastic containers is believed to cause BPA seepage.

No study has yet revealed direct BPA impact on humans. But lab tests on rodents have shown adverse reproductive and developmental effects, such as onset of Type 2 diabetes or obesity, said William Toscano, head of environmental health science at the University of Minnesota School of Public Health. He has done studies on the chemical and believes the rodent research reflects how BPA affects humans.

But proving a direct link between BPA and those conditions is difficult. Almost everyone is exposed to BPA to some degree. Plus, the conditions researchers suspect such exposure may provoke, such as obesity and Type 2 diabetes, are already common.

BPA was initially made as a synthetic estrogen, which explains its effect on hormones, he said. Because it's also durable, manufacturers turned to BPA in plastics production.

Which plastic is safe?

Infants and young children face the greatest risk because they eat and drink more, pound for pound, than adults, Toscano said. Women of childbearing age are also vulnerable, he added.

The best thing for parents to do is clear their cupboards of hard, clear plastic containers marked with a recycle symbol and a "7" or "PC," said Kim Schumacher, program organizer for Clean Water Action, a Minnesota environmental advocacy group. If the plastic item is soft or does not have those marks, it is considered safe.

She has been making the rounds at parent groups to talk about BPA since January and has spoken before Thomas' group. Some people are generally aware of concerns about BPA, but few understand details of the risk.

Mary Ann Cogelow, a parent educator for Early Childhood Family Education, said a recent presentation for 125 St. Paul parents was eye opening.

"If you've been feeding your baby something from a bottle which is hazardous and you learn it when your child is a year old, that's pretty scary business," she said.

Thomas said moms in Mothers & More were concerned after a presentation. Those moms aren't panicking, but they're definitely irritated, Thomas said.

"Why didn't we know about this sooner?" she asked.

Has damage been done?

Even if parents pitch the problematic plastics as soon as they hear of potential risks, some worry damage might already be done.

"Children are the most vulnerable," Schumacher said. "With chemicals like BPA that disrupt hormones, and do so even at low levels, it's concerning that these children at young ages were exposed."

Parents of older children also should ditch BPA products, Schumacher said.

She is among the experts and parents who are taking a better-safe-than-sorry approach. So is Kimberly Schroeder of Owatonna. When she first heard murmurs that the plastic in her everyday food and water containers might be unsafe, she switched to glass products.

Although she doesn't have kids yet, 26-year-old Schroeder said when she does she'll opt for glass bottles.

"I'm sure most of the children that have used plastic bottles more than likely are going to be fine, but I think anything we can do to eliminate toxins going into our bodies, it's all the better," she said.

Karlee Weinmann is a University of Minnesota student reporter on assignment for the Star Tribune.