Citizen scientist scans ocean off SLO County coast for radioactivity

Local volunteer helps to track the expected arrival of a radioactive plume from Japan by collecting water samples in Pismo Beach

dsneed@thetribunenews.comMay 6, 2014 

In the next few months, traces of a radioactive plume from the 2011 nuclear disaster at Japan’s Fukushima Dai-ichi power plant are expected to arrive on the beaches of California.

Scientists do not expect radiation levels to be high enough in the ocean or in seafood to pose a threat to human health. But San Luis Obispo retiree Milt Carrigan was frustrated by the fact that no government organization was planning to monitor the spread of the plume and its actual radiation levels.

So Carrigan decided to become a citizen scientist. He volunteered with a public campaign being conducted by the Woods Hole Oceanographic Institution in Massachusetts to track the spread of the plume.

“Woods Hole has a stellar reputation,” he said. “So when I heard about their monitoring program I thought, ‘This is it!’ ”

Over the next two years, Carrigan will collect seawater samples three times a year at Ocean Avenue in Pismo Beach. The samples will be mailed to Woods Hole’s Center for Marine and Environmental Radioactivity, where they will be analyzed for cesium-134, a radioactive isotope released from Fukushima.

The samples will help the Woods Hole lab track the radioactive plume as it spreads 5,000 miles across the Pacific Ocean. Carried by the powerful Kuroshio Current, the plume is expected to arrive in Alaska first, spread down the coast of North America and eventually head toward the Hawaiian Islands.

“What we really need is support to sample the same sites multiple times over the next couple of years in order to fully monitor the plume’s arrival and movement over time,” said Ken Buesseler, a senior scientist at Woods Hole and director of its radioactivity center.

Carrigan’s sampling location is one of 31 along the entire route of the plume’s expected spread from Alaska to Costa Rica and Hawaii. The monitoring began early this year.

Carrigan collected his first sample in February and already has the results back from the lab. Other samples will be taken in June and October and will be repeated again next year.

The results from the sample taken at Pismo Beach are consistent with the other samples throughout the monitoring area. No cesium-134 was detected, but small amounts of another isotope, cesium-137, were detected. These cesium-137 traces are left over from nuclear weapons testing conducted in the 1950s and 1960s.

“That means the radionuclide plume from Fukushima has not arrived in San Luis Obispo yet,” Colleen Durkin, a Woods Hole postdoctoral scholar, wrote to Carrigan in an email. “It also means that we have a baseline measurement and will be able to monitor the timing of its arrival.”

The scientists can differentiate Fukushima radiation from other sources, such as the nuclear weapons testing, based on the half life of the different radioactive isotopes. Half life is the rate at which an isotope loses half of its radioactivity.

Cesium-137 has a half life of 30 years, while cesium-134 has a much shorter two-year half life. Based on this, the Woods Hole scientists can “fingerprint” the contamination from Fukushima and estimate how much was released into the Pacific Ocean.

Carrigan proposed several locations along the San Luis Obispo coast where samples could be taken. Buesseler chose Pismo Beach because it has the most exposure to currents carrying the radiation and will provide the most data.

The process of collecting the sample is simple, Carrigan said.

The ocean lab sends him a sampling kit that consists of a 5-gallon water jug to hold the sample, and packaging and postage to mail it back to the lab. Filling the jug consists of wading knee-deep into the surf and filling it with ocean water.

“I have to make sure the sample collecting procedure is consistent each time, including doing the collecting at the same time of day,” Carrigan said.

In addition to conducting the sampling, Carrigan is responsible for raising the funds to pay for his participation in the study. It costs $550 to collect, ship and process each sample.

That means the total cost for Carrigan’s two-year involvement in the project is $3,300. He has already raised $2,285 from 18 individuals and groups but is asking for donations from the public to fill the gap.

Donations can be made at the monitoring program’s website at

Results of the monitoring can also be found there.

Much of that support has come from members of the antinuclear group San Luis Obispo Mothers for Peace. The group investigated Carrigan and the monitoring program and became enthusiastic supporters, spokeswoman Jane Swanson said.

“Milt understands statistics and the political process,” she said. “He’s absolutely wonderful.”

Carrigan said he decided to get involved in the monitoring program because he was living in Rome and working for the United Nations during the 1986 nuclear disaster in Chernobyl, Ukraine. He saw firsthand the importance of the public being knowledgeable about the danger of nuclear accidents.

“There was a lack of understanding that added to the general anxiety,” he said.

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