The radioactive substance, radon, also known as the silent killer has been found at high levels in all 100 North Carolina counties. The Environmental Protection Agency says it causes 21,000 deaths annually in the United States.

It’s known as the silent killer for a reason: Every year, radon, a naturally occurring, invisible, odorless, radioactive gas, causes an estimated 21,000 lung cancer deaths in the United States.

In North Carolina, officials with the state Department of Health and Human Services estimate that 435 residents will die from radon-related lung cancer in 2020.

In an effort to make people more aware of the dangers, the state is again giving away 3,000 radon test kits as part of National Radon Action Month.

The kits can be requested by visiting the Department of Health and Human Services’ Radiation Protection Section at www.ncradiation.net.

So what is radon, how does it get into homes, and what areas of North Carolina are most likely to be affected?

Radon comes from natural deposits of uranium in soil, rock and water. Radon gas is usually harmlessly dispersed in outdoor air. The problems arise when homes or other structures are built on top of radon-producing geological formations.

As radon gas moves up through the soil, it can be drawn into a home through differences in air pressure. The gas is sucked inside through any openings in the foundation, basement floor or crawl space.

The U.S. Environmental Protection Agency estimates that one in 15 homes in this country has excessive levels of radon.

High levels of radon have been detected in homes in all 100 North Carolina counties. It is most prevalent in the Blue Ridge Mountain region and in a band of four counties in the Piedmont — Warren, Franklin, Vance and Wake, where the gas is generated in large, subterranean granite formations.

Eight counties are considered most at risk — Alleghany, Buncombe, Rockingham, Cherokee, Henderson, Mitchell, Transylvania and Watauga. Those areas sit atop gneiss, schist and granite, rock types with higher than average concentrations of uranium.

Radon, along with radium and uranium, can also be found in well water. The major concern with a contaminated well is the formation of gasses caused by showering or other household uses, such as washing dishes or doing laundry, according to the Centers for Disease Control and Prevention.

In eastern Wake County, officials estimate that private wells for one in five homes contain excessive levels of radon, uranium or radium. Radium is a solid produced when uranium decays. During the decay process, alpha particles start to be emitted, turning the radium into radon gas.

Last year, Wake County officials mailed notices to 19,000 households that may be affected and urged them to get their wells tested. Shortly afterward, Johnston County also started warning residents with private wells of the possibility of radon contamination.

Levels found to exceed EPA health advisories should be resolved through filtration methods, said Evan Kane, Wake County’s groundwater protection and wells manager. The North Carolina Radon Program provides information on how to rid wells of the contamination.

Kane said the Wake County awareness campaign led to 1,200 well inspections in three months after the notices were mailed. Other means of notifying and working with residents are also being planned, he said.

Although the primary risk of a contaminated well is lung cancer from inhalation of gasses, Kane said radon also presents a risk of developing cancers in other internal organs, as well as kidney toxicity. Either health risk is substantially less than radon gas collecting in homes through the soil.

Based on a National Academy of Science report, the EPA estimates that radon in drinking water causes about 168 cancer deaths per year, 89 percent from lung cancer caused by breathing radon released to the indoor air from water and 11 percent from stomach cancer caused by consuming water containing radon.

In eastern Wake County, Kane said, soil and well water contamination from radon, uranium, and, to a lesser extent, radium, pose significant health threats. He urged people to get their wells tested. Testing is free for households with incomes up to 2.5 times the federal poverty level, about $64,375 for a family of four.

Eliminating radon from a home or well water isn’t cheap. According to the N.C. DHHS, the average cost in 2017 was $1,500 to fix the problem in an existing home and $800 for a home under construction. The cost for a private well treatment system was between $1,500 and $5,000.

Radon gas in homes is measured in picocuries per liter of air, or pCi/l. The EPA has set a health advisory for radon at 4 pCi/l. At that level or above, the agency recommends corrective measures be taken to reduce exposure.

The N.C. DHHS says a radon level in a home between 2 and 4 pCi/L is considered a moderate risk for developing cancer and over 4 pCi/L is considered high risk.

“Not everyone exposed to elevated levels of radon will develop lung cancer, and the amount of time between exposure and the onset of the disease may be many years,” a DHHS spokeswoman said in an email to NC Health News. “The higher the level of radon in the home and the greater the exposure time, the more likely one is to develop lung cancer.”

The cancer risk from radon is far greater for smokers.

At a radon level of 4 pCi/L, seven in 1,000 non-smokers are predicted to develop lung cancer after 60 years, compared with 62 smokers over the same timeframe, according to the EPA.

“When inhaled, radon particles tend to lodge in the lungs and emit radiation, which damages surrounding lung tissue,” according to a report from the N.C. Cooperative Extension.

However, little evidence exists on the health effects of radon in pregnant women and infants.

“There are currently no conclusive data on whether children are at greater risk than adults from radon,” the DHHS spokeswoman said in her email.

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