The effects of some disasters live on for years.  Radiation has been found in many different food items since the 2011 Great Japanese Trifecta (earthquake, tsunami and nuclear incident).  More than 18 months after the nuclear disaster, Japan still has bans on the sale of 36 species of fish caught off Fukushima, rendering the bulk of its fishing boats idle and denying the region one of its mainstay industries. The journal Science has just highlighted the challenges facing Japan as it seeks to protect its food supply and rebuild the local fisheries industry.

Some local fishermen are trying to return to work. Since July, a small number of them have resumed commercial fishing for species, like octopus, that have cleared government radiation tests. Radiation readings in waters off Fukushima and beyond have returned to near-normal levels.

About 40 percent of fish caught off Fukushima and tested by the government still have too much cesium to be safe to eat under regulatory limits set by the Japanese government last year. An unnerving comment in the article is that cesium tends not to stay in the tissues of saltwater fish very long, and because high radiation levels have been detected — particularly in bottom-feeding fish — it is likely that fish are being newly contaminated by cesium on the seabed.

The article went on to say that the fact that many fish are just as contaminated today with cesium 134 and cesium 137 as they were more than one year ago implies that cesium is still being released into the food chain. This kind of cesium has a half-life of 30 years, meaning that it falls off by half in radioactive intensity every 30 years. The finding? Sediments are likely to remain contaminated for decades to come.

As much as four-fifths of the radioactive substances released from the Fukushima Daiichi nuclear power plant are thought to have entered the sea, either blown offshore or released directly into the ocean from water used to cool the site’s reactors in the wake of the accident.

Sea currents quickly dispersed that radioactivity, and seawater readings off the Fukushima shore returned to near-normal levels. But fish caught in the area continue to show elevated readings for radioactive cesium, which is associated with an increased risk of cancer in humans.

Just two months ago, two greenling caught close to the Fukushima shore were found to contain more than 25,000 becquerels a kilogram of cesium, the highest cesium levels found in fish since the disaster and almost 250 times the government’s safety limit.

The operator of the Fukushima plant, the Tokyo Electric Power Company, said that the site no longer released contaminated water into the ocean, and that radiation levels in waters around the plant had stabilized. But Yoshikazu Nagai, a spokesman for the company, said he could not rule out continued leaks into the ocean from its reactors, the basements of which remain flooded with cooling water.

To stop water from seeping out of the plant, Tokyo Electric is building a 2,400-foot-long wall between the site’s reactors and the ocean. But Mr. Nagai said the steel-and-concrete wall, which will reach 100 feet underground, would take until mid-2014 to build.