35 years after Chernobyl’s meltdown, the fallout of radiation continues

The fallout from Chernobyl is both vast and ongoing. In 1986, the Chernobyl Nuclear Power Plant accident killed two workers at the plant immediately, and in the following days and weeks, the fatalities rose. Today, two studies show how the accident’s effects continue to manifest in ripples of illness and death.

In one study, researchers based in the United States and Ukraine looked at genetic mutations in the children of people who had been exposed to radiation; in the other, scientists evaluated the genomic profile of cancerous tumors removed from people exposed to the blast’s radiation.

The reason why the scientists are looking again at the fallout from the explosion today is not out of morbid curiosity. Rather, these studies are a bid to better understand how genetic material may be changed by radiation — and how exposure manifests in the genetics of future generations, too. With ongoing threats to staff and residents around the Fukushima Daiichi nuclear power plant, and 440 active nuclear reactors around the globe, it’s crucial to understand the long-term, and generational effects, of ionizing radiation.

What happened at the Chernobyl Nuclear Power Plant?

Shortly after midnight on April 26, 1986, a nuclear power plant 2 miles from the city of Pripyat, in what was then the Soviet Union (now Ukraine), started to malfunction. Reactor 4 of the Chernobyl Nuclear Power Plant was in trouble. The reactor and its emergency cooling core had been shut down the day before for routine maintenance and tests. But the test had to be postponed. Despite the delay, communication and safety protocols lapsed, and, the cooling core was kept offline. Steam started to build in the cooling pipes, causing a power surge the plant’s engineers couldn’t shut down.

The explosions began at 1:23 am, spreading a toxic cloud full of radioactive debris into the air above the plant. The explosion also caused a fire, which tore through another building and further spread the radioactive cloud across the surrounding communities. Over the next several hours, two plant workers died of acute radiation poisoning. The people of Pripyat, meanwhile, started vomiting and reporting a metallic taste in their mouths. They weren’t evacuated until more than 24 hours after the planet blew up.

What does Chernobyl radiation do to your body?

Exposure to even low doses of ionizing radiation can damage the body in any number of ways, but one of the biggest concerns is cancer. This happens because ionizing radiation damages DNA. It is why Marie Curie, the famous scientist who discovered both polonium and radium, two radioactive elements, died of cancer. It is also why you need to wear a lead apron when you get an X-Ray to protect your body.

The severity and kind of illness people develop from ionizing radiation depends on several factors, including:

• How much radiation they were exposed to
• What tissue in the body was exposed to the radiation
• Length of exposure (and/or the number of times exposed)
• Vehicle for exposure — in other words, eating contaminated food, breathing it in, touching a radioactive element, etc)

What diseases did Chernobyl cause?

The World Health Organization estimates that the health of 5 million people in the former USSR was affected by the disaster in some way By other estimates, as many as 800,000 people in Belarus, a neighboring state, were affected by the radiation alone.

Some of the workers drafted to do the initial cleanup later developed leukemia. Lindsay Morton is a Senior Investigator with the National Institute of Health and an author on one of the new studies examining Chernobyl. She tells Inverse that people in the surrounding areas were likely exposed to radiation from Chernobylthrough “leafy greens and milk.” The radiation-contaminated plants, including the plants farm animals ate, and therefore any animal products those animals produced were contaminated, too.

In the years after the explosion, incidences of thyroid cancer skyrocketed in the surrounding areas. “Iodine is one of the building blocks in thyroid hormones,” Morton explains, “and the body can’t distinguish between iodine and radioactive iodine. So when a person ingests radioactive iodine, it concentrates in the thyroid.”

The rates of thyroid cancer increased the most in children, a morbid finding that suggests, according to one study, that children under the age of five are “particularly vulnerable to the effects of radiation.”

Do mutations from radiation exposure pass down?

There is some good news from the new studies. The first study, published Thursday in Science, found that parents who had been exposed to radiation from the accident were no more likely to have children with so-called de novo genetic mutations than parents who experienced no radiation exposure.

De novo mutations are genetic alterations that happen after conception and are not inherited directly from one’s parents; rather, they may be the result of other factors, like age, environment, health, and other things that affect the biology of cells.

Stephen Chanock, one of the researchers on the new papers, tells Inverse that typically, you expect to see between 50 and 100 de novo mutations occur in any conception. Chanock is the Director of the Division of Cancer Epidemiology & Genetics at the National Institute of Health. In this study, Chanock and his colleagues couldn’t find any significant difference in the germline of parents who had been exposed to radiation and those who hadn’t.

“In science, it’s very difficult to prove a negative,” he says. “We modeled it many, many different ways, and we didn’t find any significant differences.”

Chanock and his colleagues note in the study that the children were conceived “months or years” after their parents had been exposed. As a result, the findings may not apply to children conceived closer to the moment when their parents are exposed to ionizing radiation.

How does radiation cause tumors?

The second study analyzed thyroid tumors, thyroid tissue, and blood collected from people who were exposed to radiation from Chernobyl, and then compared these samples to equivalent issues and blood taken from people who were not exposed to radiation. The comparison reveals a significant dose-dependent increase in double-strand DNA breaks among the exposed group.

Why it matters — Sometimes, when there’s a clean, double-strand DNA break, the cell can repair it quickly, Morton says. Other times, the repair job is less clean and efficient. When something like ionizing radiation is responsible for a double-strand DNA break, she says, there can be multiple double-strand DNA breaks.

“The DNA is broken in one place, and you have two of part A. Then the DNA is broken in another place, and you have two of part B.” Instead of the As being rejoined and the Bs being rejoined, Morton says, “A and B are joined. And that makes what's called a gene fusion. The cell has fused the wrong parts back together.”

Picture two shoelaces. One gets split in half and the other gets split in half. But instead of reconnecting each shoelace with its former part, you swap them. Half of shoelace 1 is now fused with shoelace 2, and vice versa. Not such a big deal when we’re talking about shoelaces. But with DNA, which has important instructions for your cells? That kind of mismatch, or gene fusion, is likely to cause some problems.

The higher dose of radiation the person had been exposed to, the more double-strand DNA breaks the researchers found. The association was clear, Morton says.

“We measured DNA double-strand breaks in multiple ways. And all of them showed consistent, clear, strong associations with radiation.”

Previous studies have shown double-strand DNA breaks in the blood of people recently exposed to ionizing radiation. But “double-strand DNA breaks have never actually been linked to a human tumor before,” Morton says.

Taken together, these findings have important consequences for how we understand ionizing radiation and how to protect ourselves from it.

“There’s a bit of a debate in radiation science about whether very low doses of ionizing would cause damage,” Morton says. The linear relationship between dose-dependent exposure and double-strand DNA breaks puts that question to rest.

Abstract 1: Effects of radiation exposure from the Chernobyl nuclear accident remain a topic of interest. We investigated whether children born to parents employed as cleanup workers or exposed to occupational and environmental ionizing radiation post-accident were born with more germline de novo mutations (DNMs). Whole-genome sequencing of 130 children (born 1987-2002) and their parents did not reveal an increase in the rates, distributions, or types of DNMs versus previous studies. We find no elevation in total DNMs regardless of cumulative preconception gonadal paternal (mean = 365 mGy, range = 0-4,080 mGy) or maternal (mean = 19 mGy, range = 0-550 mGy) exposure to ionizing radiation and conclude over this exposure range, evidence is lacking for a substantial effect on germline DNMs in humans, suggesting minimal impact on health of subsequent generations.

Abstract 2: The 1986 Chernobyl nuclear power plant accident increased papillary thyroid cancer (PTC) incidence in surrounding regions, particularly for 131I-exposed children. We analyzed genomic, transcriptomic, and epigenomic characteristics of 440 PTCs from Ukraine (359 with estimated childhood 131I exposure and 81 unexposed children born after 1986). PTCs displayed radiation dose-dependent enrichment of fusion drivers, nearly all in the mitogen-activated protein kinase pathway, and increases in small deletions and simple/balanced structural variants that were clonal and bore hallmarks of non-homologous end-joining repair. Radiation-related genomic alterations were more pronounced for those younger at exposure. Transcriptomic and epigenomic features were strongly associated with driver events but not radiation dose. Our results point to DNA double-strand breaks as early carcinogenic events that subsequently enable PTC growth following environmental radiation exposure.