By MATTHEW PERRONEWASHINGTON (AP) ¿ Sunoco has begun restricting sales of a controversial chemical used in baby bottles and food containers that some researchers believe can harm infants. The move by the gas and chemical giant makes Sunoco the first manufacturer to acknowledge safety concerns about bisphenol-A, or BPA, which recently led retailers like Wal-Mart to pull thousands of baby and water bottles off store shelves. Environmental groups want to ban BPA in products for infants because of concerns that it can interfere with biological functions needed for growth. But government scientists have issued conflicting opinions about the chemical's risks. In light of that uncertainty, Sunoco said in a letter Thursday it has begun requiring customers to guarantee that its BPA will not be used in food and water containers for children under 3. "We will no longer sell BPA to customers who cannot make this promise," Thomas Golembeski, head of public relations, wrote in a letter to two investors. The company's policy, which took effect last November, was prompted by concerns from local investors, including an order of Franciscan nuns.