By Dan May
On Our Land
Dan May
The surges of COVID that occur as people move indoors for the winter and gather with family and friends for holiday celebrations are a reminder that indoor air quality can be a health hazard. This is true not only for infectious diseases, but also for indoor air contaminants. The concentration of many pollutants indoors exceeds the concentration outdoors. Most people also spend more than 90 percent of their time indoors, and for vulnerable groups like infants, the elderly and those with chronic diseases, that proportion is likely higher.
Most indoor contaminants arise from human behavior (secondhand smoke, aerosols), HVAC systems that allow mold buildup, and/or the presence of hazardous materials that can become airborne (such as dust from old lead paint) or are released as gases from furnishings or building materials. Many health effects are linked to poor indoor air quality, including a rising incidence of asthma.
However, one pollutant of concern is solely of natural origin – radon. This is an invisible, odorless and radioactive gas. It is present at low levels in the atmosphere but can increase in concentration to dangerous levels in buildings – particularly single-family homes. Long-term exposure to elevated levels of radon can cause lung cancer, with up to 20 percent of US lung cancer cases likely due to radon.
Radon is a radioactive element formed as the element uranium slowly undergoes radioactive decay via a multi-step series to ultimately form the stable element lead. This decay process was investigated by Marie Curie about a century ago, and the concentration of radon present in the air is now measured in terms of picoCuries per liter of air.
Radon is an inert gas that does not chemically combine with any other elements. When it appears during this decay series, it can leak from rocks which originally contained uranium into the atmosphere or enter homes through foundation floors and walls, sump pump basins, groundwater well systems and other connections between the house and subsurface.
Radon is very unstable, with a half-life of about four days before it decays by releasing alpha and gamma radiation into another radioactive element called polonium. Polonium is also a toxic poison, and one used by Russia in several notorious assassinations. Both radiation damage and polonium toxicity impact cells when radon atoms happen to decay in an individual’s lungs.
In 2020, the US Department of Health and Human Services articulated environmental health goals in a document entitled Healthy People 2020. Two goals addressed radon exposure: increase the proportion of existing homes at risk for radon exposure with radon mitigation systems; and increase the proportion of new single-family homes being constructed in high-radon-potential areas with radon-reducing features.
Both goals focus on homes in high-radon-potential areas. The emphasis on single family homes is due to the fact that most residential HVAC systems do not bring in new fresh air at the rate of commercial or other large building air handling systems. The focus on high-radon-potential areas is due to the fact that radon is connected to geology. Since underlying rock types vary by location and generally possess different uranium concentrations, the amount of radon released from the ground varies from place to place.
Connecticut’s public health agencies produced maps of indoor radon potential based on the underlying bedrock, the overlying glacial or river sediments and/or measurements of uranium in groundwater in the 1990s. Areas with low radon potential in this region included river valleys like those adjacent to the West River or the Quinnipiac River, as well as the glacial lake deposits that underlie downtown New Haven.
West Haven’s radon potential is also considered low, largely because it sits above ancient volcanic rocks with only trace uranium. In contrast, the coastal areas of East Haven and Branford are built on granitic rocks and derived sediments. The higher uranium concentrations inherent to these materials suggest high radon potential, with 40 percent or more of homes likely to need mitigation.
Milford, Orange, Woodbridge and Hamden are considered to have moderate indoor radon potential, with action needed for perhaps one in four homes. However, public health agencies continue to update the older potential maps with in-home testing. Results can be very specific to a given home site and type of construction.
If you have never had your home tested or are considering a move to another home in the region, a radon test is a good safeguard. Mid-winter is the ideal time to test. Contact your local or state public health office for what is often a free test.
Dan May is a geologist and professor of environmental science at the University of New Haven. He can be contacted at dmay@newhaven.edu.