Bisphenol-A (BPA), the endocrine-disrupting chemical in plastics — and the go-to environmental health villain — has vexed public-health experts for at least a decade. Reams of inconclusive and conflicting studies on the health effects of the compound, which is found in plastic food containers, water bottles and the epoxy lining of cans, have hampered a verdict on the lingering question: Is BPA safe?