Cows that consume feed, grass or water contaminated with radioactive iodine-131 can concentrate the element in their milk. Peter Elvidge/iStockphoto.com hide caption

itoggle caption Peter Elvidge/iStockphoto.com

Mike Barlow has been installing geothermal systems for 20 years. But he says a 30 percent federal tax credit is increasing the popularity of the systems for families with modest houses. Elizabeth Shogren/NPR hide caption

itoggle caption Elizabeth Shogren/NPR

Tokyo Electric Power Co. Chairman Tsunehisa Katsumata (second from right) and other executives bow prior to a press conference at the company's headquarters in Tokyo on Wednesday. Kazuhiro Nogi/AFP/Getty Images hide caption

itoggle caption Kazuhiro Nogi/AFP/Getty Images

In 1992, 28,800 rubber ducks were lost at sea. What happened to them is the subject of Donovan Hohn's book Moby-Duck. Jose Gil/iStockphoto.com hide caption

itoggle caption Jose Gil/iStockphoto.com

Cooling towers from the Limerick Generating Station, a nuclear power plant in Pottstown, Pa., sit near a neighborhood. Environmentalists agree that in light of Japan's nuclear crisis, the U.S. should examine existing nuclear plants for safety risks. Stan Honda/AFP/Getty Images hide caption

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Japan Self-Defence Force officers in radiation protection suits hold a blue sheet over workers who were exposed this week to high levels of radiation at the Fukushima Dai-ichi plant. Jiji Press/AFP/Getty Images hide caption

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This computer model shows how a plume of radioactive iodine-131 could spread in the atmosphere. ZAMG hide caption

itoggle caption ZAMG

Japanese Buddhist monk Tanaka Tokuun, who was evacuated from Fukushima prefecture, looks over an instrument measuring radiation levels at a hotel on March 17. Buddhika Weerasinghe/Getty Images hide caption

itoggle caption Buddhika Weerasinghe/Getty Images

Keiji Nagashima has been farming spinach in Ibaraki prefecture for 25 years but will be destroying this year's crop because of fears of radiation exposure. "I can't have a life without the spinach," he says. Richard Harris/NPR hide caption

itoggle caption Richard Harris/NPR