February 8, 2018
Web Feature

New Dose Reconstruction Method Supports Radiation Exposure Limits for Human Health

Long-term, low-level plutonium exposure linked to increased cancers

Workers walk through the Mayak nuclear fuel reprocessing facility in Russia in the 1960s.

Researchers from Pacific Northwest National Laboratory have developed a better way to estimate past radiation doses to nuclear workers—and the results are getting international attention.

A special journal issue marks the culmination of more than 20 years of research to estimate the radiation doses workers received from Russia’s first plutonium production facility, which began operating in the 1940s. The ultimate goal: determine the levels of plutonium exposure that may have caused cancer in workers over time. The results are giving international organizations better information as they set radiation dose exposure limits to protect human health.

Plutonium Exposure and Health

As the health effects of long-term radiation exposure became more widely known over the past decades, countries began looking more carefully at how people may have been affected. In 1994, Russia and the United States launched the Joint Coordinating Committee on Radiation Effects Research to explore radiation-related health risks in the former Soviet Union. A key part of the committee’s research focused on workers at a Russian nuclear production site called Mayak. The committee wanted to know if chronic, low-to-medium-level radiological exposure increased cancer risks.

The Mayak Production Facility played an important role in the Soviet nuclear weapons program. Starting in 1948, about 26,000 employees worked at the facility in Chelyabinsk, Russia, operating five plutonium production reactors, several nuclear fuel reprocessing plants, and a plutonium metallurgy plant over the course of 60 years. Workers were exposed to radiation on the job as they processed and stored spent nuclear fuel and radioactive waste. The time frame included several accidents.

PNNL scientist Bruce Napier led the team that reconstructed the radiation doses that workers likely received over time through breathing and ingesting small particles of plutonium, one of the radionuclides being studied. The team had access to exposure measurements from dosimeter badges that some workers wore, as well as medical bioassay and autopsy results from thousands of the workers.

When epidemiologists matched the reconstructed dose estimates with health effects in the population, they found something surprising: more cancers than what would normally be expected. They attributed 240 cancer deaths to 8,000 workers who had inhaled plutonium. This is in addition to the 1,600 cancers you’d expect to see from other causes in a group that size. In the larger group of 26,000 workers who had been exposed to external radiation, epidemiologists attributed about 70 additional cancer deaths.

“This is the only study that definitely shows that inhaling and ingesting low-to-medium amounts of plutonium over long periods of time increases the chance of developing liver, bone, and lung cancers,” Napier said. “That goes against the common assumption that chronic, low exposures don’t cause the same kinds of effects as those from one-time, higher doses. We showed that they can.”

The results are available to Mayak officials and to the national and international organizations that set radiation standards worldwide. Such standards are designed to protect people who work at nuclear facilities, transport and dispose of radiative materials, test and dismantle nuclear weapons, and even work in space as astronauts.

More Certainty, Closer to Reality

A unique and important part of reconstructing the radiation doses was reducing the uncertainties associated with them. Uncertainties arise from not knowing exactly how much radiation individuals received from specific exposure pathways, or when. Quantifying and narrowing these uncertainties is important because more accurate dose estimates enable more realistic health effect estimates.

The team developed a statistical method for reconstructing the doses with uncertainties—the first time this has been done for this many people, Napier said. Researchers started with worker bioassay measurements, then worked backward to estimate the plutonium intake over time including uncertainties, then worked forward again to derive annual estimated dose. Uncertainties were calculated separately for different exposure pathways.

Getting the Word Out

The sheer scope of the research is astounding. The team of scientists from PNNL, Russia, U.S. universities, and the United Kingdom has produced more than 100 peer-reviewed journal articles about the Mayak workers, and an additional 225 articles on related dose reconstruction, epidemiology, and supporting science in the program. The Radiation Protection Dosimetry journal published a special issue in 2017 dedicated to the Mayak worker results, produced by the American, British, and Russian team and edited by Napier.

The work was funded by the U. S. Department of Energy’s Office of Domestic and International Health Studies and the Federal Medical Biological Agency of the Russian Federation. More information.

Reference: “ The Department of Energy’s Russian Health Studies Program.” 2017. Radiation Protection Dosimetry, 176: (1-2), Oxford University Press.

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Published: February 8, 2018