Fish still radioactive near Fukushima, but mostly safe elsewhere

Recent catches of fish with record levels of radiation show there is still contamination in the waters around Fukushima following the nuclear disaster in March 2011, but fears of dangerous levels reaching the West Coast of the United States seem to be mostly exaggerated.

In January 2013, a bottom-dwelling Murasoi fish was caught with 2,540 times the legal limit for radioactivity of 100 becquerels per kilogram (about the same level as a banana). And then in February 2013, a greenling with 7,400 times the limit was caught in a cage next to the Fukushima Dai-ichi plant.

Fat greenling, Hexagrammos otakii, seen on some oyster shells
Fat greenling, Hexagrammos otakii, the fish (not the actual fish) found near Fukushima with radioactive caesium at a record level of 740,000 becquerels per kilogram (photo from OpenCage, via Wikimedia Commons)

Although most fish caught in the area are actually below the safe level, a paper published by Ken Buessler of the Woods Hole Oceanographic Institute in the United States found that the number above the limit is not decreasing with time as you’d expect. This indicates that radioactive caesium is still entering the food chain, either from sediments—these were bottom-feeding fish, remember—or from ongoing leaks (Buessler Ken O 2012, “Fishing for answers off Fukushima”, Science, vol. 338, pp. 480–482, DOI: 10.1126/science.1228250 [PDF 3.7 MB]).

This has since been admitted by the Japanese government, with radioactive water leaking from containment tanks into groundwater, which then flows into the Pacific Ocean at a rate of about 300 tons per day. This could mean that fish from Fukushima will be inedible for at least a decade, which could paradoxically mean that they benefit from the lack of fishing—although the long-term effects of radiation on the fish themselves is rarely discussed.

This may be because many of the fish don’t live long enough for it to have an impact, and conversely could be why radioactive isotopes have been detected in long-lived, migratory species like Pacific bluefin tuna (Thunnus orientalis), although even then at levels comparable to natural sources (Fisher NS, Beaugelin-Seiller K, Hinton TG, Baumann Z, Madigan DJ and Garnier-Laplace J 2013, “Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood”, Proceedings of the National Academy of Sciences, vol. 110, no. 26, pp. 10670–10675, doi: 10.1073/pnas.1221834110).

(Of course, there are other reasons to avoid tuna, such as overfishing or build-up of mercury and other toxic chemicals.)

As for fears of radiation directly reaching the United States, it was expected to take about 3 years to travel across the Pacific, so should be arriving right about now. The Woods Hole Oceanographic Institute is keeping an eye on that too, with a citizen science project asking people to send in samples of seawater for testing. As of yet though, their results are showing no detectible caesium from Fukushima.

But what about Australia, you may ask? Well, because we’re in the southern hemisphere, it will take even longer to reach here—about 5 years, according to a report from the Australian Radiation Protection and Nuclear Safety Agency [PDF 1.7 MB] (although a small amount of atmospheric fallout was detected here in April 2011).  By then though, it will be diluted even more than it is in the United States, so is unlikely to be of concern.

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