When Philadelphia officials learned last year that the city’s water supply and the region’s waterways showed elevated levels of radioactive iodine-131, their initial instinct was to blame the Fukushima nuclear disaster in Japan, as I-131 is found in nuclear power plant fallout. Around the same time, however, they also learned that RadNet, an obscure EPA radiation testing program, had been showing I-131 in Philadelphia’s drinking water for years, long before Fukushima. Although levels were well below drinking-water limits, officials worried because the source was unknown, and they hoped to eliminate it.

 

That will not be happening. As unlikely as it may seem, officials now believe that the source of the I-131 is the urine of thyroid patients who are being either diagnosed or treated with I-131, which collects in the thyroid gland and is used in thousands of people every year. After patients swallow I-131, some of it passes into their urine, which enters the wastewater-treatment system and winds up in rivers that provide drinking water. The I-131 has a short half-life of eight days: every eight days, the radioactivity declines by half, and would be considered gone after 80 days. Water treatment has no effect on it.

 

Despite the presence of I-131, Philadelphia’s water is safe, according to the EPA, the state Department of Environmental Protection, the Philadelphia Water Department, and the city Department of Health. Noting that levels of iodine-131 have remained well below federal drinking-water limits, these experts point out that i-131 saves literally thousands of lives every year. “This is an issue that is not going to go away any time soon,” explained Dr. Caroline Johnson of the Philadelphia Department of Health. “These are very effective treatments.”

 

The Philadelphia region is a center for medical care, and a lot of sewage-treatment plants discharge into waterways that then flow past Philadelphia and into its drinking-water intakes.

-Matt Bewig