From the article,

Thus, radiation from a meltdown in the reactor core of reactor No. 2 is leaking out into the water and soil, with other reactors continuing to experience problems.

Yet scientists and activists question these government and nuclear industry "safe" limits of radiation exposure.

"The U.S. Department of Energy has testified that there is no level of radiation that is so low that it is without health risks," Jacqueline Cabasso, the Executive Director of the Western States Legal Foundation, told Al Jazeera.

Her foundation monitors and analyzes U.S. nuclear weapons programs and policies and related high technology energy, with a focus on the national nuclear weapons laboratories.

Cabasso explained that natural background radiation exists, "But more than 2,000 nuclear tests have enhanced this background radiation level, so we are already living in an artificially radiated environment due to all the nuclear tests."

"Karl Morgan, who worked on the Manhattan project, later came out against the nuclear industry when he understood the danger of low levels of ionizing radiation-and he said there is no safe dose of radiation exposure," Cabasso continued, "That means all this talk about what a worker or the public can withstand on a yearly basis is bogus. There is no safe level of radiation exposure. These so-called safe levels are coming from within the nuclear establishment."

Here is a link to a fun website that has been providing time-lapse coverage of the dispersal clouds of the various radioactive isotopes.