How Much Radioactivity Are We Exposed to While Sampling Seawater for Fukushima Radioisotopes?

By Jay T. Cullen

The purpose of this post is to introduce a brief, informal movie made while using a Geiger Counter in the laboratory today. This diary is part of an ongoing effort to communicate what the scientific community is learning about the impact of the Fukushima disaster on environmental and public health. A Geiger Counter was used to examine ionizing radiation counts per minute in the laboratory owing to background radioactivity, the concentrated natural and man made isotopes in 20 liters of seawater collected by InFORM citizen scientist volunteers, the uranium oxide glaze on a Fiestaware dinner platter and Uraninite ore mined from New Hampshire. This simple demonstration supports more sensitive measurements indicating our citizen scientists are exposed to no more ionizing radiation than is typical of background when collecting seawater samples.

The short answer to this question is that the vast majority of ionizing radiation exposure while sampling seawater for Fukushima derived radioisotopes in the North Pacific comes from naturally occurring isotopes. Our exposure processing the samples, and the exposure our volunteers experience collecting them depends on the natural background levels where we live.

To put the counts per minute reported in the video into perspective consider the following. Our potassium nickle ferrocyanide resin (resin-KNiFC) concentrates the positively charged gamma emitting isotopes, largely naturally occurring 40-Potassium (40K half life ~1.3 x 109 years), and traces of the man made isotopes 137-Cesium (137Cs half life ~30 years) and 134-Cesium (134Cs half life ~2 years). These isotopes concentrated from 20 L of seawater onto the resin column are not different from the background counts detected with our simple, and somewhat ancient, Ludlum Model 3 Survey meter. This is not surprising given that the levels of Fukushima derived radiocesium along the coast here in British Columbia Canada are on the order of ~0.006 Bq L-1 (or about 0.4 counts per minute).

The Fiestaware platter on the other hand registers approximately 10,000 counts per minute with the Geiger counter. Studies by Oak Ridge Associated Universities (ORAU) provide estimates of dose experienced by users of Fiestaware. They found that the primary exposure was due to leaching of and subsequent ingestion of uranium from the glaze such that about 0.2 grams of U would be swallowed per year. This results in an effective dose to an adult of 0.4 milliSv (milliSv = 10-3 Sv) per year. This compares to a natural background does to someone living here in Victoria of 1.8 milliSv per year or about a 20% increase (not an increase expected to have measurable negative health impacts). However, keeping Fiestaware in unventilated storage could lead to the buildup of Radon that could represent a significant health risk. The range of natural background in Canada is 1.3 – 4.1 milliSv yr-1.

As is always the case results from the InFORM project will be posted as they are generated and I’ll continue to report results from the peer reviewed literature on Fukushima.


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