Reuters: High levels of a toxic substance called strontium-90 have been found in groundwater at the devastated Fukushima nuclear power plant in Japan, the utility that runs the facility said on Wednesday. Strontium-90 is a by-product of the fission of uranium and plutonium in nuclear reactors as well as nuclear weapons, the U.S. Environmental Protection Agency says on its website. The discovery of rising levels of such radioactive material is likely to complicate efforts by the utility, Tokyo Electric Power...