Investigations into a baffling number of thyroid cancers in southern Iredell County are picking up momentum, even as answers so far elude researchers.
Some of the state’s top health and environment officials, legislators and scientists from Duke University and UNC Chapel Hill met Thursday night with local physicians to brief them on ongoing research. The officials announced formation of an advisory panel of state and national experts.
Duke researchers said they will dig deeper into two potential sources of ionizing radiation, the only environmental source clearly linked to thyroid cancer: radon, a naturally-occurring radioactive gas, and coal ash, which can contain radioactive elements and is stored nearby.
Occurrences of papillary thyroid cancer, the most common form, are rising globally and in North Carolina since the mid-1990s, said a N.C. Department of Health and Human Services report released in January. But between 2005 and 2009, the rate in Iredell County rose significantly higher than in the state as a whole. Two southern Iredell zip codes — 28115 and 28117 — had still higher cancer rates.
While 11.6 cancer cases were diagnosed for every 100,000 people statewide between 2012 and 2016, Iredell’s rate was 21.8 cases. Southeastern and southwestern Iredell, in turn, had higher rates than the overall county rate.
Eleven other counties also reported thyroid cancers above the state rate, including Rowan and Cabarrus near Iredell County. Another apparent hot spot is in the Cape Fear region near Wilmington.
Scientists are rarely able to pinpoint environmental sources of cancer. The disease may appear only years after an exposure, and people have often moved from place to place in that time. Specific forms may afflict relatively few people, complicating the work.
“To be in a situation where people are getting sick and there are no ready answers, it’s hard,” Dr. Elizabeth Tilson, the state health director, told the gathered physicians. State health officials got involved in 2017 at the request of the Iredell County Health Department.
Radiation is the only known environmental source clearly linked to thyroid cancer, DHHS said, but some research suggests that chemicals in flame retardants, benzene, nitrates and some pesticides might also be associated with the disease.
Duke researchers reported in 2017 that exposure to chemicals that reduce the flammability of furniture, carpet and other household items appear to be associated with thyroid cancer.
DHHS says its review of the southern Iredell County environment found “no radiation releases and very few community-level exposures to concentrations in excess of the relevant regulatory limit” or at levels that would trigger investigation of chemicals that might be associated with thyroid cancer.
The department said it found no evidence of increased radiation from Duke Energy’s McGuire nuclear station, which stands on the shore of Lake Norman 13 miles southwest of Mooresville. No studies have linked thyroid cancer to coal ash, which Duke stores at its Marshall power plant 8 miles west of Mooresville and has been used elsewhere to fill gullies, the report said.
But Duke University scientists, who are using research money raised by a local mother whose daughter had thyroid cancer, Susan Wind, say coal ash and radon deserve more scrutiny.
Radioactive elements called radionuclides can occur in ash at levels five times higher than in untainted soil, they say. Elements in ash might also be dispersed by wind into the air. Neither mode of potential exposure has been thoroughly investigated, said Duke environmental chemist Heather Stapleton.
A construction crew exposed a coal ash deposit near Lake Norman High School last September, the Mooresville Tribune reported. Ash didn’t spread off the site, state officials said, but alarmed some in the community.
Duke Energy, in response, says the previous research that found no links between thyroid cancer and coal ash included airborne exposure. Monitoring at the McGuire nuclear plant covers any potential radiation sources, including ash, the company says.
Duke Energy quotes the U.S. Geological Survey as saying coal ash in soil “should not be sources of alarm.” Research by the National Toxicology Program found that trace elements in ash don’t cause thyroid cancer, Duke says. The company’s consulting toxicologist estimates that the level of radioactive radium in ash is one million times lower than the concentration shown to cause cancer.
Radon can cause lung cancer and is estimated to kill thousands of people a year, the Environmental Protection Agency says. It comes from the natural breakdown of uranium in soil and gets into the air inside homes and other buildings. Radon is most prevalent in western North Carolina and was detected in the homes of three Iredell County thyroid cancer patients, the Duke researchers said.
As researchers continue their work, DHHS said it is still reviewing new cancer and environmental data and working with local hospitals and physicians to make sure all thyroid cases are reported. It’s assessing other counties where thyroid cases above the state rate have been reported.
The state Division of Public Health is working with UNC’s Lineberger Comprehensive Cancer Center and the N.C. Policy Collaboratory, which was created by the legislature to make practical use of research by UNC scientists, to convene the advisory panel to review past research on thyroid cancer and identify new approaches.
As the community waits for answers, what should local residents do?
DHHS advises well owners to routinely test their water. Virginia Tech and UNC Chapel Hill researchers are testing private wells in the community under federal grants, but the sampling is aimed at helping well owners understand their water quality and not at the thyroid cancer issue.
Iredell health officials recommend that people with a lump or swelling in the neck, trouble breathing or swallowing, pain when swallowing, hoarseness that doesn’t go away or constant coughs not because of a cold see their doctor.