If it's not one thing, it's another as the Japanese nuclear power plant crisis nears the end of its second week. The most recent news is that radioactive elements appear to be leaking out of a couple of the partially melted-down reactors. Tests show that seawater off the plant site has elevated amounts of radioactive iodine, while others have found traces of plutonium isotopes in the soil around the plant sites. Meanwhile, some workers have been exposed to dangerously high levels of radiation as they work to repair the failed cooling systems.
Japanese regulators have also found high levels of radiation being emitted by radionuclides in milk from cows grazing near the broken reactors, as well has higher radiation levels in produce grown nearby. Elevated amounts of radioactive iodine have been found Tokyo's drinking water.
A Rasmussen poll found in mid-March that 43 percent of Americans are at least somewhat concerned that Japanese radiation will reach the United States. Worried Americans are calling their physicians for advice about the dangers of radiation and pharmacists report that that they are running short of potassium iodide pills that can protect the thyroid gland from absorbing radioactive iodine.
Meanwhile, the U.S. Environmental Protection Agency RadNet system of air monitors has detected slightly elevated radiation levels that are consistent with radiation having wafted across the Pacific. In addition, a test of rainwater in Massachusetts found slightly higher radiation levels, but not in Bay State drinking water. Should these findings cause Americans be concerned about their health? No.
As the EPA reported last week, radioactive particles detected in the West Coast monitors are hundreds of thousands to millions of times below levels of concern. The EPA statement also noted, "In a typical day, Americans receive doses of radiation from natural sources like rocks, bricks and the sun that are about 100,000 times higher than what we have detected coming from Japan." The agency added, "For example, the levels we're seeing coming from Japan are 100,000 times lower than what you get from taking a round trip international flight." An agency update this week "continues to confirm that no radiation levels of concern have reached the United States." Go here to check the RadNet monitor nearest you.
But what about the radiation found in rainwater in Massachusetts and Pennsylvania? At a press conference on Sunday, John Auerbach, the Massachusetts commissioner of public health, reported that one sample of rainwater found a slightly elevated level of the radioactive isotope iodine-131 which was likely emitted from the stricken Japanese power plants. The amount of iodine-131 detected exceeded the EPA's maximum contamination level of 3 picocuries (0.1 becquerel) per liter for drinking water. However, the agency notes that this limit on ingesting "iodine-131 was calculated based on long-term chronic exposures over the course of a lifetime—70 years." And keep in mind that this is in rainwater, not drinking water.
The EPA states that "short-term elevations such as these do not raise public health concerns" and that "the levels seen in rainwater are expected to be relatively short in duration." The agency also promises to step up its rainwater monitoring. The good news is that radiation emitted by iodine-131 rapidly decays, because it has a half-life of just eight days. That is, its emissions drop to less than 1 percent of its original level within 60 days.
In Japan itself, iodine-131 and cesium-137 leaked from the Fukushima plants have contaminated some produce and milk in nearby regions. For example, tests of Japanese horseradish have found samples with iodine-131 emitting 2,500 becquerels per kilogram and cesium-137 at 340 becquerels per kilogram.
The U.S. Food and Drug Administration has set "derived intervention levels" (DILs) in foods contaminated by radionuclides. In this case, the DIL for iodine-131 is 160 bequerels per kilogram and for two cesium isotopes the DIL is 1,200 becquerels per kilogram. DILs are based on calculations showing how much contaminated food a person would have to eat over a specified period before that person's accumulated dose of radiation reaches five millisieverts over his or her lifetime. One millisievert is roughly equal to exposure to 10 chest x-rays. Americans experience about three millisieverts of natural background radiation annually. The Nuclear Regulatory Commission limits the radiation exposure of nuclear power plant workers to 50 millisieverts per year.
The Japanese horseradish radioactive iodine contamination is 15 times the level set by the FDA. Extrapolating from calculations cited by Reuters, it would take someone eating a kilogram of horseradish daily (a quite heroic assumption) with that level of contamination for somewhere around 400 days for that person to accumulate 50 millisieverts of exposure, the annual limit set for nuclear power workers. One concern is that iodine concentrates strongly in the thyroid, which boosts the chance that an exposed person would get cancer in that gland. Again, keep in mind that the level of contamination by radioactive iodine decays to below the FDA's limit in just over a month.
In the meantime, the FDA has banned the importation of produce and milk from the affected regions of Japan. The agency does note that the massive amount of damage caused by the earthquake and the tsunami is cutting down on the quantity of food that might be exported from Japan in any case.
Bottom line: Relax. Americans will likely experience no detectable health effects from the radionuclides released by the broken Fukushima reactors.
Science Correspondent Ronald Bailey is author of Liberation Biology: The Scientific and Moral Case for the Biotech Revolution (Prometheus Books).