A government panel is warning Americans are being “bombarded” with cancer-causing sources including chemicals, radiation and other hazards threatening “grievous harm.” The President’s Cancer Panel says cancers caused by environmental exposures have been “grossly underestimated” and require stronger government regulation. In a cover letter to a 240-page report, the panel urges President Obama to “most strongly use the power of your office to remove the carcinogens and other toxins from our food, water and air that needlessly increase health care costs, cripple our nation’s productivity, and devastate American lives.”