WASHINGTON (AP) - Environmental groups are petitioning the FDA to recall sunscreens that contain particles so small they're measured in the (b) billionths of meters. Eight groups, including Friends of the Earth and Greenpeace, say submicroscopic particles of titanium dioxide and zinc oxide pose a health hazard. One group member says the companies that use these materials are treating their customers like guinea pigs. But an industry official says the sunscreen makers have more than adequate knowledge about the safety of their products. Nano-sized materials are generally less than 100 nanometers in diameter. By comparison, human hair is roughly 80,000 nanometers in diameter. The FDA is planning a meeting this fall on nanotechnology materials being developed for use in drugs, foods, cosmetics and medical devices. George Kimbrell, says the FDA needs to recall all products that used nanotechnology until they know more about the process and its risks. George Kimbrell, says nanotechnology presents a new array of risks to humans and the environment.