10/25/2012 05:40 EDT | Updated 12/25/2012 05:12 EST

Post-Fukushima, Are Japan's Fish Safe to Eat?

FILE - In this Nov. 12, 2011 file photo, workers in protective suits and masks wait to enter the emergency operation center at the crippled Fukushima Dai-ichi nuclear power station in Okuma, Japan. Japanese labor officials said Sunday, July 22, 2012 that they are investigating subcontractors on suspicion they forced workers at the tsunami-hit nuclear plant to underreport their dosimeter readings so they could stay on the job longer. (AP Photo/David Guttenfelder, Pool, File)

A year and a half after Fukushima and contamination levels in nearby fish are not declining as should be expected, reports marine chemist Dr. Ken Buesseler in an article appearing tomorrow in Sciencemagazine. We need to know why, the Woods Hole Oceanographic Institute scientist has been saying publicly for months now.

Buesseler has been at the forefront of an international effort to study Fukushima's footprint and recently analyzed the data Japan publishes regularly on contamination levels in fish. His conclusion: Perhaps there's a continuing source of radioactive material in the ocean -- hotspots of contamination on the ocean floor and/or low level leaks that haven't been plugged.

How are the Japanese reacting? While Japan's government has been sampling fish extensively, its work is "more about seeing if levels in fish are below some threshold, and less about oceanographic context and interpretation of various sources and sinks, " Buesseler said in an email interview.

The problem is primarily radioactive cesium, which accumulates in fish and can stick around in the environment for up to 300 years.

According to Buesseler's analysis of Japan's nearly 9000 samples, bottom-feeding fish register the most contamination -- a category that includes cod, conger, flounder, halibut, pollock, rockfish, skate and sole. In August, a pair of greenlings, bottom feeders caught 20 kilometres offshore of Fukushima, contained the highest levels yet -- 258 times those that Japan deems safe for human consumption. Up to then, the highest levels had been seen in Japan's cherry salmon.

Indeed, fish that live near the surface -- called "pelagic" fish and including salmon, mackerel, seabass, tuna and amberjack -- are also continuing to show contamination, as are freshwater fish, which excrete radiation less efficiently than ocean species. But according to the stats, the vast majority of fish caught off the northeast coast of Japan are within the limits deemed safe for consumption -- limits that Japan tightened significantly earlier this year. Reassuring, but is eating their fish worth the risk?

Last week, to my chagrin, my husband ordered sushi in one of Montreal's finest Japanese restaurants. Among the offerings: flounder -- bottom feeders -- from somewhere in Japan. From where? They didn't know.

Fortunately, Japan's federal authorities have restricted fishing off of Fukushima prefecture (other than for sampling), but elsewhere, fishing is allowed. Fish do migrate, of course. And until Japan's Nuclear Emergency Response Headquarters deems otherwise, safety is in the hands of the prefects, not the feds. If radiation exceeds standards in any sample of fish caught within the prefect's jurisdiction, the local government must request that fishing of that species stop. "To date, the reactions of fishers have been in full conformity with the requests made," Japan's website states.

Nice to know, but Japan does need to address Buesseler's concern: Why are the radiation levels not declining, as they should be if the water were cleaner?

Next month, Buesseler is off to the troubled land to lead a scientific symposium in conjunction with his colleague at the University of Tokyo. Let's hope they can get the authorities to start figuring out why the situation is still fishy.

Read the Woods Hole press release.

Fukushima Nuclear Plant