SAN FRANCISCO — Scientists reported Wednesday that low levels of radiation from Japan's Fukushima disaster first detected off the California coast two years ago have been declining ever since and remain well below any levels considered unsafe for humans.
The scientists, from UC Santa Cruz and Stony Brook University in New York, were responding to public concerns raised this week by an Internet video claiming that dangerously high radiation levels had been detected in the sands of Pacifica State Beach.
The video has gone viral and shows an unidentified man carrying a commercial Geiger counter that displays radiation counts purportedly rising to "alert" levels as he walks along the beach often frequented by surfers.
An Internet "news" site is claiming that news of the radioactivity is being suppressed by unnamed government sources.
Geiger counters are unsophisticated and do measure radiation levels, but they are unable detect the source of radioactivity. More sophisticated tests of beach sand in the Pacifica area by public health officials show that the radiation has come from natural sources — most probably from ancient rocks eroded in the bluffs above.
"There is no public health risk at California beaches due to radioactivity related to events at Fukushima," the California Department of Public Health said Tuesday.
"Recent tests by the San Mateo County Public Health Department show that elevated levels of radiation at Half Moon Bay are due to naturally occurring materials and not radioactivity associated with the Fukushima incident," it said.
The first detection of low-level radiation crossing the Pacific from the damaged Fukushima nuclear reactors following the devastating 2011 earthquake and tsunami was reported in The Chronicle on May 29, 2012. The report was based on an article in the Proceedings of the National Academy of Sciences and interviews with its authors, Daniel J. Madigan, then a marine ecologist at Stanford's Hopkins Marine Station in Pacific Grove, and Nicholas Fisher, a marine scientist at Stony Brook University.
In a telephone interview this week, Fisher, an internationally known specialist in radiation hazards, said that continued sampling of low radiation levels from Fukushima on the California coast shows "they have gone down ever since." The most recent report from Fisher's group is published in the journal Environmental Science and Technology.
At UC Santa Cruz, Daniel Hirsch, a lecturer on nuclear policy, called the low levels of radiation being reported now in California as "trivial."
"No one here in the Bay Area should be concerned about eating fish," he said in a phone interview.