Science: Making Milk Safer

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Homogenized, pasteurized, refrigerated, U.S. milk is an eminently safe beverage. But U.S. laboratories are hard at work trying to make it even safer. In a cold war world, scientists must somehow learn how to extract the radioactive strontium 90 that is showered down on pasture grass from atmospheric nuclear tests. At present, U.S. cows do not take in enough strontium to make their milk dangerous, but testing may well continue; the problem may well get worse.

One promising solution makes use of ion exchange resins, bits of plasticlike material with metallic atoms built into their molecules. This material can be made to release certain elements in exchange for others. So when milk that has been slightly acidified with citric acid passes through the resin, it loses most of its strontium and picks up a little extra sodium or calcium. A process using this principle was developed by scientists of the U.S. Department of Agriculture, captures 98% of the strontium, but it costs nearly 10¢ per quart—more than most dairy farmers get for their milk.

A cheaper process developed by Chemistry Professor Harry P. Gregor of Polytechnic Institute of Brooklyn uses thin plastic membranes containing submicroscopic pores that permit the passage of small atoms with positive electric charges. Milk is made to flow along one side of a membrane; on the other side is a solution of such salts as calcium and sodium chlorides that are naturally present in milk. If the milk contains strontium 90 atoms, they pick up positive electric charges from a current flowing through the solution. Then they slip through the membrane and lose themselves in the harmless salts. Dr. Gregor thinks that his process can extract 90% of the strontium 90 from milk at the cost of about ½¢ per quart. Annual cost of keeping U.S. milk reasonably safe: $230 million.

Strontium 90, however, is not the only kind of radioactive fallout that can get into milk; iodine 131 can become a problem too. But its threat does not justify the scare advertisement (showing a bottle of milk with a death's-head label) that the National Committee for a SANE Nuclear Policy ran last week in the New York Times.

While strontium 90 is long-lasting (half life: 28 years), the half life of iodine 131 is only eight days. If the iodine 131 level in milk ever rises above the danger point, the prescription will be simple: stop drinking fresh milk for a couple of weeks. No one need go hungry. Most other foods will be free of iodine 131; they will have been stored long enough to let its activity fall to the vanishing point.