Tuna brings radiation from Japan to the United States

Scientists found that many bluefin tuna carry radioactive material from Japan's Fukushima I nuclear power plant to the US coasts, which are 9,600km away from the plant.

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Nicholas Fisher, a researcher at Stony Brook University in the US, and colleagues measured the concentration of cesium (Cs) radioactivity in the body of Pacific tuna along US coasts. They found that the concentration of Cs in tuna bodies was 10 times higher than in previous years, the AP reported.

"We were surprised to see that result ," Fisher said.

This is the first time scientists have found evidence that a migratory fish can swim across the ocean with radioactive material in the body. Even so, the concentration of Cs in tuna bodies is still much lower than the safe levels prescribed by the US and Japanese governments for tuna meat.

Catch tuna

After the nuclear crisis in Japan occurred in March 2011, it was discovered that small fish and plankton near Japanese waters were exposed to radioactive substances with relatively high concentrations.

However, scientists do not think that radioactive substances can survive long in the body of large migratory fish, because their bodies can expel radioactive substances through metabolism.

Pacific bluefin tuna is one of the largest and fastest growing fish species on the planet. Their body length can reach up to 3m, while the average weight is up to more than 450kg. They lay eggs in Japanese waters. After birth, the young tuna migrated to the east at great speed to reach the waters near the state of California in the US and the waters near the tip of Mexico's Baja California Peninsula.

Previously, five months after the incident at the Fukushima I nuclear power plant, Stony Brook University scientists examined the levels of radioactive substances in the body of 15 Pacific blue tuna that they caught close to. San Diego coast. The results showed that the concentrations of two radioactive isotopes Cs-134 and Cs-137 in the tuna tissue samples were higher than before.

To eliminate the possibility of tuna radioactivity increasing due to ocean currents or accumulation in seawater from the air, the team examined the yellowfin tuna in the eastern Pacific and the Bluefin tuna migrated to southern California before the double disaster in Japan occurred on March 11. They did not detect radioactive Cs-134, but only found Cs-137 that contaminated fish from nuclear weapons tests in the 60s.

'Results show that bluefin tuna is contaminated with radioactive material from the Fukushima I power plant , ' commented Ken Buesseler, an expert at Woods Hole Marine Institute in the US. Buesseler did not participate in Stony Brook University research.

Bluefin tuna is contaminated with Cesium when they swim in waters containing radioactive substances and eat radioactive prey, scientists said. Because tuna moves to the east, they push a part of radioactive material out of the body through metabolism. However, their bodies cannot expel all radioactive material.

'Pacific Ocean is a huge ocean. "Trans-Pacific swimmers that still keep radioactive substances in the body are not rewarding bluefin tuna ," Fisher said.