The massive Tohoku earthquake and tsunami of March 11, 2011, caused extensive damage in northeastern Japan, including damage to the Fukushima Dai-ichi nuclear power installation, which resulted in the release of radiation. Some have called this incident the biggest manmade release ever of radioactive material into the oceans. Concerns arose about the potential effects of this released radiation on the U.S. marine environment and resources. The North Pacific Current is formed by the collision of the Kuroshio Current, running northward off the east coast of Japan in the eastern North Pacific, and the Oyashio Current, running southward from Russia ( Figure 1 ). As it approaches the west coast of North America, the North Pacific Current splits into the southward California Current and the northward Alaska Current. Although these currents have the potential for bringing radiation from Japan's Fukushima Dai-ichi nuclear accident to U.S. waters, their flow is slow, and no radiation above background levels has yet been detected in marine waters under U.S. jurisdiction. Regardless of the slow flow, radioactive contaminants with long half-lives (e.g., cesium-137, with a half-life of about 30 years) could still pose concerns if transported over long distances by ocean currents. Seawater was monitored by the Tokyo Electric Power Company (TEPCO) near the discharge points of the Fukushima Dai-ichi plant following the March 2011 events. Water with a dose rate of greater than 1,000 millisievert per hour was confirmed by TEPCO on April 2, 2011, in a pit located next to Fukushima Dai-ichi's Unit 2 seawater inlet point. A cracked sidewall of this pit was leaking water from the pit directly into the ocean. Analyses of seawater taken from near the discharge from Fukushima Dai-ichi Units 1-4 yielded readings of 130,000 Becquerels/liter (Bq/l) of iodine-131 (half-life of about 8 days), 32,000 Bq/l of cesium-137 (half-life of about 30 years), and 31,000 Bq/l of cesium-134 (half-life of about 2 years). Although the leak in the cracked sidewall was stopped after several days, the total amount of radioactive contaminants that entered the ocean was unknown, and discharges, both accidental and deliberate, continued for several weeks. Radioisotope concentrations at offshore sampling points decreased with time; by early April 2011, at sampling points about 30 km east of Fukushima Dai-ichi, concentrations were between 5 and 18 Bq/l for iodine-131 and between 1 and 11 Bq/l for cesium-137. The highest concentrations, found closest to the coast, were about 38 Bq/l for iodine-131 and 4.5 Bq/l for cesium-137. The occurrence of cesium-137 is of greater concern because of its much longer half-life. The natural radioactivity of seawater is 13 or 14 Bq/l, of which 95% comes from potassium-40. Experts cite this incident as the largest recorded accidental release of radiation to the ocean. Atmospheric transport (i.e., wind) also is capable of transporting radiation eastward, where it may settle or precipitate into U.S. marine waters ( Figure 2 ). The U.S. Department of Energy and the U.S. Environmental Protection Agency (EPA) monitor atmospheric radiation. In early April 2011, EPA monitors in California, Idaho, and Minnesota detected trace amounts of radioactive iodine, cesium, and tellurium in rainwater, consistent with the Japanese nuclear incident; to date, concentrations have been far below any level of concern. One study estimated a total atmospheric release of 35.8 petabecquerels of cesium-137, with the highest release from March 12 to 19 and about 79% of subsequent deposition over the North Pacific Ocean. It is unknown whether marine organisms that migrated through or near Japanese waters to locations where they might subsequently be harvested by U.S. fishermen (possibly some tuna or salmon in the North Pacific) might have been exposed to radiation in or near Japanese waters, or might have consumed prey that had accumulated radioactive contaminants. Two minke whales harvested by Japanese whalers off the coast of Hokkaido in May 2011 were found to have slightly elevated radioactive cesium-137 levels. In August 2011, bluefin tuna off the coast of California were found to have slightly elevated levels of cesium-137 and cesium-134. A British scientist reportedly stated that, "given the scale of the Pacific—the world's vastest body of water—radioactivity in the sea at Fukushima will be flushed out beyond the local area by tides and currents and dilute to very low levels. It [radioactive contamination] will get into the (ocean) food chain but only in that vicinity. Should people in Hawaii and California be concerned? The answer is no." Although not at harmful levels, significant radiation from cesium-137 was reported to be detected 400 miles offshore of Japan three months after the tsunami. There is also the possibility that there could be bioaccumulation of longer-half-life radioactive elements by fish whose migratory habits subsequently may take them far from Japanese waters. Scientists at the Woods Hole Oceanographic Institution advised that radiation levels in seafood should continue to be monitored, but stated that radiation in the ocean very quickly becomes diluted and should not be a problem beyond the coast of Japan. The same is true of radiation carried by winds around the globe. Radioactive contaminants from Fukushima appear to have become sufficiently dispersed over time that they will not prove to be a serious health threat elsewhere, unless they bioaccumulate in migratory fish or find their way directly to another part of the world through food or other commercial products. However, there remains the slight potential for a relatively narrow corridor of highly contaminated water leading away from Japan and a very patchy distribution of contaminated fish—extensive monitoring will determine the exact dispersion of these radioactive contaminants. It does not appear that nuclear contamination of seafood will be a food safety problem for consumers in the United States. Among the main reasons are that damage from the disaster limited seafood production in the affected areas, radioactive material would be diluted before reaching U.S. fishing grounds, and seafood imports from Japan are being examined before entry into the United States. According to the U.S. Food and Drug Administration (FDA), because of damage from the earthquake and tsunami to infrastructure, few if any food products were being exported from the affected region. For example, according to the National Federation of Fisheries Cooperative Associations, the region's fishing industry stopped landing and selling fish. Furthermore, a fishing ban has been enforced within a 2-kilometer radius around the damaged nuclear facility. U.S. fisheries are unlikely to have been affected because radioactive material that entered the marine environment would be greatly diluted before reaching U.S. fishing grounds. However, some have advocated vigilance, especially for seafood from areas near the damaged nuclear facility. It has been suggested that cesium-137 could move up the food chain and become concentrated in fish muscle or that radiation hot spots could occur. Another potential concern is related to accumulation of strontium-90 in fish bone, because its chemical properties are similar to those of calcium. Radioactive contaminants have been collecting in sediments in coastal areas near the damaged nuclear facility and exposing bottom-dwelling fish, shellfish, and other organisms to relatively high contaminant levels. The Japanese Ministry of Health, Labor, and Welfare has reported fish samples from Fukushima prefecture that are above the provisional regulation values for cesium-134 and cesium-137. Contaminated fish samples have included greenling, several types of flounder, common skate, rock fish, Japanese seabass, and brown hakeling. The most common foods imported from Japan include seafood, snack foods, and processed fruits and vegetables. In 2011, the United States imported 40.1 million pounds of seafood from Japan with a value of $268.3 million. The FDA has primary responsibility for the safety of all domestic and imported seafood, under the Federal Food, Drug, and Cosmetic Act (FFDCA), as amended (21 U.S.C. §301 et seq.). The FFDCA requires that all foods be safe, wholesome, and accurately labeled. FDA's general approach to ensuring the safety of seafood imports is based on identifying risks from the production process, from specific types of seafood, and from certain countries or firms. On March 22, 2011, FDA issued an import alert for food products from four Japanese prefectures. The alert has been updated periodically since then to reflect changing conditions with regard to food items and areas (prefectures) covered. FDA's import tracking system is being used to identify all shipments of FDA-regulated products from Japan, with special attention to shipments from companies within the affected area. As of March 2012, FDA field examinations and tests of food products had not found any radionuclide contamination above the established derived intervention level. FDA has divided all food products from Japan into the following four categories. Category 1—Products that are not allowed entry to the United States. Consists of products that the government of Japan has restricted for sale or export. Category 2—Products that may be detained under Import Alert 99-33 and may be released if the importer can show the products are safe. Consists of products from Fukushima, Ibaraki, and Tochigi Prefectures that the Government of Japan has not banned from sale or export. Category 3—Products from Fukushima, Ibaraki, and Tochigi Prefectures that are not covered by the FDA's import alert. These products are examined and may be sampled and tested as needed.