Chapter 2: Atoms, Molecules, and LifeIssues in Biology |
How Might the Radioactive Decay of Isotopes Help Make Our Food Safer?
Each year about 50 million Americans will lose a day or two of their normal life activities due to consumption of contaminated food. Most commonly the organisms that cause these illnesses are bacteria, including Staphylococcus, Salmonella, Listeria, and E. coli. Sometimes, particularly in young children, the infection that follows consumption of a contaminated food product causes serious symptoms that can lead to permanent organ damage or even death.
A relatively common source of foodborne illness is a strain of bacteria known as E. coli O157:H7. Our intestines—as well as the intestines of many vertebrates, including cattle and pigs—are inhabited by billions of E. coli cells that normally cause no trouble. In fact, they actually are beneficial in a number of ways, not least of which is that they produce vitamin K for us. Unfortunately, certain strains of E. coli, including the infamous 0157:H7 strain, are lurking in the environment, and this bacterial strain can cause serious illness. In the past few years, outbreaks of E. coli O157:H7 infections have occurred throughout the world. Often the culprit is contaminated meat, but vegetable and fruit products can also spread the bacteria. For example, contaminated apple juice, alfalfa sprouts, and radish sprouts have caused disease in hundreds and resulted in the deaths of at least several children, usually from hemolytic uremic syndrome.
There are several commonsense approaches to protecting yourself from E. coli infection, including cooking foods thoroughly and washing your hands properly. However, one treatment that might help to reduce contamination before it reaches consumers is sterilization of food by irradiation. In this process, the food is exposed to radioactive energy produced by the decay of radioactive cobalt (atomic symbol: Co). The major nonradioactive isotope of cobalt is Co-59, an atom with 27 protons and 32 neutrons. The radioactive isotope of cobalt used for food irradiation (and for cancer radiation therapy) is known as Co-60 and contains 27 protons and 33 neutrons. That 1 extra neutron makes the Co-60 nucleus unstable and, as in all radioactive isotopes, the Co-60 nucleus will break apart or change at a certain frequency. In the process of “radioactive decay” of this particular isotope, 1 neutron within the Co-60 nucleus is converted to a proton. This change in atomic structure converts the cobalt atom into a nonradioactive atom of nickel with 28 protons and 32 neutrons. The conversion also releases high-energy radiation known as gamma rays.
Gamma rays contain a considerable amount of energy. When they crash into another atom, they damage it, usually causing it to lose an electron (i.e., form an ion). The ionizing effects of gamma rays on molecules give gamma radiation the capacity to kill cells, including bacteria. For example, gamma rays can break DNA molecules, preventing the cell from reproducing. Although it can damage and even kill cells, irradiation of food does not make the food itself radioactive, any more than having an X ray makes you radioactive. However, it does cause subtle changes to the food that make some opponents of the technology leery of its safety. Most studies indicate that these changes are similar to the changes produced by conventional cooking of the food. After considerable study, the Federal Drug Administration has found that the method is safe and effective. In addition, the American Dietetic Society, among other groups, has also endorsed the use of irradiation to help minimize foodborne illness. In fact, although you may not be aware of it, irradiation of certain foods such as grains and spices has been going on since the 1960s.
So, the next time you are having a nice salad at a salad bar or chomping a juicy cheeseburger, perhaps you will think about how the structure of atoms can be harnessed to make your food safer.