The Food and Drug Administration rejected a petition from environmentalists that would have banned the hotly debated plastic-hardening chemical bisphenol-A from all food and drink packaging, including plastic bottles and canned food. The agency said that petitioners from the Natural Resources Defense Council did not present compelling scientific evidence to justify new restrictions on the much-debated chemical, commonly known as BPA, though federal scientists continue to study the issue. Some scientists believe exposure to BPA can harm the reproductive and nervous systems, particularly in babies and small children, potentially leading to cancer and other diseases. What does the science really say? The Los Angeles Times examines the issue.