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A thriving population of free-ranging wild boars living in the area surrounding eastern Japan’s Fukushima Daiichi nuclear plant may hold the key to speeding up the process for determining radiation dose in humans after an exposure incident.

Joshua Hayes, a doctoral student in health physics at Colorado State University, spent five weeks at ORAU in 2019, conducting confirmatory evaluations of blood smears from 138 wild boars. He conducted his work in the laboratory at REAC/TS, the Radiation Emergency Assistance Center/Training Site, which is located at the Oak Ridge Institute for Science and Education and managed for the Department of Energy by ORAU.

“The theory is that with an increased radiation dose, you get an increased prevalence of the pseudo Pelger Huet Anomaly,” Hayes said. The pseudo Pelger Huet Anomaly is a defect found in a type of white blood cells called neutrophils where on blood smears the cell nucleus appears to look like dumb bells. While predominantly related to some types of leukemia, this abnormality can also develop as a result of radiation exposure.

Hayes’ hypothesis states that as the radiation dose increases so should the number of abnormal neutrophils.

The wild boar population in Fukushima Prefecture has spiked significantly in the absence of humans since the devastating earthquake and tsunamis of 2011. The natural disasters damaged reactors at the nuclear plant, which sent a plume of radionuclides, including Iodine-131, Cesium-134 and Cesium-137 into the surrounding environment.

“The contaminated environment continues to provide unique research opportunities related to chronic low-dose radiation exposure, in that it would be similar to doses that human inhabitants of the Fukushima Prefecture and clean-up workers would likely experience,” Hayes said.

Over the course of two visits to the region, in the summer of 2017 and the fall of 2018, Hayes was part of the team that trapped and examined the boars. During the first visit, the team anesthetized the boars and conducted ophthalmic evaluations to determine if cataracts had developed, which is a sign of radiation damage. Then, the boars were euthanized for further examination and collection of numerous tissue samples, including blood, for a number of projects that were happening in tandem. Hayes hopes to publish research on the ophthalmic data soon.

The second visit didn’t include the ophthalmic exams, so prefecture hunters would euthanize the animals caught in any of the 300 traps laid up and down the coast, at varying distances from the exclusion zone.

To remove bias from the study, Hayes explained that the blood samples are all marked as having come from the same location, Okuma, where the hunters were located.

“The animals that were captured south of the plume will be considered control animals following computational lifetime dose estimations,” he said.

If successful, Hayes’ research could lead to a faster method of measuring dose response during a mass exposure incident.

“Once we complete this analysis and we build the response curve from it, the validation itself comes from a comparison with cytogenetic biodosimetry,” Hayes said.

Dicentric chromosome analysis is the gold standard for determining the amount of radiation exposure in humans, and is determined by counting the number of dicentric chromosomes, a genetic abnormality which is created by exposure to radiation. The higher the number of dicentric chromosome, the higher the radiation dose.  

While it is the gold standard, cytogenetic biodosimetry results can take two or three days and cost thousands of dollars. On the other hand, if Hayes’ research works, results could be determined with a simple blood smear in as little as two hours.

In addition to the time factor, a faster process would be a psychological benefit to people concerned they had been exposed to radiation.

Hayes uses the example of Goiania, Brazil, where in 1987 an orphaned radiation source, cesium chloride, was taken from an abandoned hospital and handled by a number of people, and resulted in four deaths.

“There were only 20-25 clinically significant cases of exposure, but hundreds even thousands of people feared they were contaminated,” Hayes said, adding that you can’t just tell them they’re okay and expect them to walk away.

“Their fear is legitimate,” he said.

“This test could be a kind of peace of mind for people,” he said. “If you can take a drop of blood from people, ask them to come back in a couple of hours, and then show them proof that they’re not exposed, they could have reason to stop worrying.”

He adds that the samples of clinically significant exposures would still be sent off for cytogenetic biodosimetry analysis.

Hayes hopes to publish his research in 2020.

His project was funded through ORAU’s Visiting Faculty Research Program. The VFRP creates teams to tackle research projects of interest to the organization. Hayes was teamed with Jason Davis, Ph.D., REAC/TS health physicist.