Science Scene: Texas capitol's granite emits trace radiation

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Photo Credit: Victoria Smith | Daily Texan Staff

There may be more addling the minds of legislators in the Texas State Capitol than the quagmires of politics — radiation.   

The Texas State Capitol gets its distinctive color from the overlay of sunset red granite, which emits radon, a colorless, odorless gas. Radon is one of the products created when uranium decays in soil and rock — especially granite. Radon is responsible for the majority of background radiation, a mixture of radiation from the earth and outer space that most people are exposed to all the time.

Ruben Cortez, radiation safety officer for the Department of State Health Services, said the radiation levels inside the capitol might occasionally rise above 10 microrem per hour. The state regulatory standard for public dose for buildings is 2 millirem per hour. Rem is a unit scientists use to measure the extent to which radiation damages the human body. Radiation exposure over time can cause increased cancer risks, according to the National Institute of Health. 

“There is a noticeable amount of radon at the capitol,” Cortez said. “Over the weekend, it will build up in the basement and you’ll actually be able to detect it.”

The problem is not just Austin’s capitol building. Travis County has particularly high background radon levels compared to other Texas counties. The average indoor radiation level because of radon in Texas is about 1.3 picocuries per liter, or about 1.3 rem measured over a year in a sealed room, but Travis County has radiation levels at about 3.2 rem under the same conditions, according to the Department of State Health Services. 

This may be because of the presence of red granite throughout the county. The owners of Granite Mountain donated sunset red granite for the construction of the capitol building after the limestone quickly began to rust in the 1850s. This granite was used to create many other historic Texas buildings, such as the Wyndham Hotel in Dallas. Enchanted Rock, a popular camping spot for students, is also made up of mostly red granite. 

Employers must follow strict federal regulations with any risk of radiation. The maximum radiation level an average citizen can be exposed to is 0.1 rem per year, according to the Texas Administrative Code. One rem carries the equivalent of about a 0.055 percent increase in cancer risk, according to the International Commission on Radiological Protection. Employers can expose their workers to up to 5 rem of radiation per year, with the worker’s informed consent. 

Skin usually blocks radon radiation from entering the body, but it may be dangerous to the lungs when inhaled. Radon is the second greatest cause of lung cancer after smoking and is responsible for about 21,000 out of the 160,000 lung cancer deaths every year, according to the United States Environmental Protection Agency. When smoking and radon interact, they cause lung cancer risks greater than the individual weight of either of these risk factors, according to three studies in the Radiation Research journal. 

Each person needs to weigh the radon risks with the other radiation exposures they encounter on a regular basis. Radiation from radon is relatively minor compared to a routine computed tomography (CT) scan, which exposes patients to 0.5 to 6 rem of radiation at once, according to the U.S. Food and
Drug Administration.

“On the whole, as an industry, we stand on the side of safety,” Cortez said. “We have found that there are no demonstrable effects for individuals from radiation exposure under about 5 rem.”