A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Why does everybody get so worried about radiation levels in milk?

September 16, 2011

Dear Cecil:

We keep hearing in the news about radiation levels in milk and whether they're high enough to be a concern. Your recent column about the safety of nuclear power also mentioned contaminated milk. But nobody explains why contamination is a big issue with milk but not with potatoes, chicken, or water. I always thought radiation was an equal-opportunity contaminant that lands on whatever's in its way. So what's the deal with milk?

Cecil replies:

Milk is nature’s perfect radioactivity delivery system, Danielle, ideally suited to slipping nuclear contaminants into places where they can mess you up good. Let’s review its many insidious advantages:

1. It’s a food. Your mention of potatoes, chicken, and so on makes it evident you’ve already tumbled to this. But for the record: while an external dusting of radionuclides isn’t healthy, for efficient long-term irradiation of vulnerable organs there’s no substitute for actually ingesting the stuff.

2. It’s fast. Not to knock potatoes and chicken, but growing these items can take weeks or months. With milk, the fallout simply drifts over the pasture and lands on the grass, which the cows then eat. The radioactive particles are deposited in the cows’ milk, the farmers milk the cows, and in a day or two the contaminated product shows up in the dairy case.

3. Because it’s processed quickly, milk makes the most effective use of contaminants that would otherwise rapidly decay. Here we get into the technical end of things. A common byproduct of uranium fission is the radioactive isotope iodine-131. Iodine is an essential nutrient readily absorbed by the body, which draws no distinction between the normal and radioactive kinds. Iodine is critical to proper functioning of the thyroid gland, and any iodine-131 consumed will be concentrated there, where it can wreak maximum havoc. However, iodine-131 has a half-life of just eight days. When it falls on most food crops, it decays to relatively harmless levels long before it’s eaten by humans. The speed of dairying eliminates this impediment, and iodine-131 is still likely to be pumping out beta particles by the time you serve contaminated milk to the kids.

4. Milk also does a good job of delivering other radioactive contaminants, such as cesium-134 and cesium-137. Although not important for human health, radioactive cesium mimics potassium, which we do need, and is readily absorbed by the body. Another uranium breakdown product is strontium-90, which behaves like calcium. Strontium-90 in milk is especially hazardous to children, since it can be incorporated into growing bones. In contrast to radioactive iodine, strontium-90 has a half-life of about 29 years, so once it gets embedded in you, you are, as the Irish say, fooked.

5. That brings us to the last, most fiendish property of radioactive milk — it targets a vulnerable population, namely the young. Compared to adults, children (a) drink a lot more milk and (b) are smaller, which when you add it up means they get a much stiffer dose. Some cancers triggered by radioactivity have a long latency period; older people may die of something else first, but kids bear the full brunt.

For all these reasons, testing milk and dumping any found to be contaminated is at the top of the list of standard disaster-response measures following a nuclear accident, and it’s unusual, though not unknown, for bad milk to find its way into the food supply. For example:

  • Iodine contamination of milk during the 1979 Three Mile Island accident was negligible, 20 picocuries per liter. The FDA’s “action level” at the time was 12,000 picocuries per liter; the current limit of 4,600 picocuries is still far in excess of what was observed.
  • After the problems with the Fukushima reactors in Japan, one batch of hot milk did test at about nine times the current radiation limit, and milk and vegetable consumption was prohibited in high-risk areas. But most of the bans were rescinded after a couple months.
  • In 1957, after a fire in the graphite core at the Windscale plutonium processing plant in the UK, radiation levels of 800,000 picocuries per liter and higher were found in local milk. Though nuclear contamination of milk wasn’t well understood at the time, authorities figured 800,000 of anything involving curies can't be good and banned the stuff.
  • Then there’s Chernobyl. Milk sales were banned in nearby cities after the 1986 reactor explosion, but feckless Soviet officials let the sizable rural population fend for itself. Not surprisingly, 6,000 cases of thyroid cancer subsequently developed, proving there’s no catastrophic situation that stupidity can’t make worse.

One last thing. We’ve been talking about cow's milk up till now, but be aware that if the isotopes really hit the fan, iodine-131, strontium-90, and other radioactive contaminants can also be transferred through human milk. Your best bet in that case is to stick to formula prepared before the accident, juice, or Scotch, and you might as well give some to the baby, too.

Related Posts with Thumbnails


Clines, Francis X. “Chernobyl Cloud Keeps Welsh Lamb off Table” New York Times 3 July, 1986: A1.

Commission on Life Sciences Health Risks of Radon and Other Internally Deposited Alpha-Emitters: BEIR IV National Academies Press, 1988.

Corey, G.R. “A Brief Review of the Accident at Three Mile Island” IAEA Bulletin 21.5 (1979): 54-59.

Hicks, Rodney J. “Pattern of Uptake and Excretion of 18F-FDG in the Lactating Breast” The Journal of Nuclear Medicine 42.8 (2001): 1238-1242.

Knox, Richard “Radioactive Milk Only A Danger After 58,000 Glasses” National Public Radio Online, 21 March, 2011.

“The Windscale reactor accident – 50 years on” Journal of Radiological Protection 27 (2007): 211-215.

Thiessen, J.W. “”Public Health Risks of Nuclear Emergencies” International Conference on Non-Military Radiation Emergencies Washington, D.C., 1986.

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