By Mariah Blake, Mother Jones

Each night at dinnertime, a familiar ritual played out in Michael Green’s home: He’d slide a stainless steel sippy cup across the table to his 2-year-old daughter, Juliette, and she’d howl for the pink plastic one. Often, Green gave in. But he had a nagging feeling. As an environmental-health advocate, he had fought to rid sippy cups and baby bottles of the common plastic additive bisphenol A (BPA), which mimics the hormone estrogen and has been linked to a long list of serious health problems. Juliette’s sippy cup was made from a new generation of BPA-free plastics, but Green, who runs the Oakland-based Center for Environmental Health, had come across research suggesting some of these contained synthetic estrogens, too.

He pondered these findings as the center prepared for its anniversary celebration in October 2011. That evening, Green, a slight man with scruffy blond hair and pale-blue eyes, took the stage and set Juliette’s sippy cups on the podium. He recounted their nightly standoffs.

“When she wins … every time I worry about what are the health impacts of the chemicals leaching out of that sippy cup,” he said, before listing some of the problems linked to those chemicals—cancer, diabetes, obesity. To help solve the riddle, he said, his organization planned to test BPA-free sippy cups for estrogenlike chemicals.

The center shipped Juliette’s plastic cup, along with 17 others purchased from Target, Walmart, and Babies R Us, to CertiChem, a lab in Austin, Texas. More than a quarter — including Juliette’s — came back positive for estrogenic activity. These results mirrored the lab’s findings in its broader National Institutes of Health-funded research on BPA-free plastics.

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