Since the recent water tests in The Acreage, I have wondered what the source of iridium-192 (Ir-192) discovered in the well water of 10 homes in The Acreage could be.
Ir-192 is used in “gamma-metallurgy” to look for stress cracks and the like. Ir-192 has a “half-life” (time for 50 percent decay) of only 73.8 days. Thus, according to first-order kinetics, after 10 half-lives of 738 days (two years, eight days) it will be below detectable limits. Transport time, the amount needed and other factors potentially rule out a source such as Pratt-Whitney.
However, Ir-192 is also used in seeds that are implanted for “brachytherapy” of prostate and other cancers. According to the American Brachytherapy Society, urine of those under such therapy should be passed through a screen to capture pellets that dislodge. This may form a more likely localized source for the Ir-192 detected in a few samples from The Acreage. That is, urine with Ir-192 pellets or residue going into the toilet, then to the septic tank and subsequently being leached into groundwater. This route is well known for many endocrine disruptors and other chemicals that are flushed into septic and sewer systems. This potential should be vigorously explored by the Department of Health.
Also reported are some elevated “trans-uranics.” That is, uranium-238 (U-238) and its decay products. Test results that I have seen have three natural radioactive series. First, U-238 and its decay products, namely uranium-234 (U-234), lead-214 (Pb-214) and bismuth-214 (Bi-214). Second, uranium-235 (U-235) and third, actinium-228 (Ac-228), which comes from the decay of thorium-232 (Th-232). Natural percentages of U-238 and U-235 are 99.27 and 0.72 percent respectively. These isotopes occur naturally in carbonates (limestones) and other minerals, especially phosphate mineral such as the phosphorites of the Bone Valley and Hawthorne formations in Desoto and Hardee counties.
According to E. Petuch and C. Roberts (2007: Geology of the Everglades and Adjacent Areas, CRC Press), there was a cross Florida seaway formed from the Caloosahatchee and Loxahatchee straits with an embayment (the Kissimmee Embayment) located where the central western communities (Loxahatchee and The Acreage) are today.
It is not all inconceivable that erosional events in the late Pliocene re-deposited materials richer in uranium, such as the Caloosahatchee Marl and Hawthorne formation, into this embayment. That is, typically flow-ways drop their suspended load when current speeds lessen when entering a larger body of water.
The possibility of areas in the central western communities having naturally increased background levels of uranium-238 and its decay products should be investigated by a joint venture of Palm Beach County, the State of Florida and the United States Geologic Survey.
Dr. J. William Louda
Editor’s note: Dr. Louda is a senior scientist and professor at Florida Atlantic University.