The levels are low, but if some microparticles are inhaled or ingested by nuclear-site workers or their families, the radioactive dust is a “potential source of internal radiation exposure,” the study’s author writes.

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Dust samples from the homes of six Hanford nuclear-site workers in the Tri-City area contained traces of radioactive contamination, according to a study published this month in the Journal of Environmental Engineering Science.

The levels are low, but if some microparticles are inhaled or ingested by the workers or their families, the radioactive dust is a “potential source of internal radiation exposure,” writes Marco Kaltofen, a civil engineer whose peer-reviewed study also found radioactive particles in dust samples in nuclear workers’ homes near the Los Alamos National Laboratory in New Mexico and the former Rocky Flats Plant in Colorado.

The particles were found in samples collected over a period of years from the homes of the nuclear workers and those of their neighbors. Inhalation of the particles, which included uranium, thorium, plutonium and americium, can increase the risk of cancer.

Kaltofen told The Seattle Times that, in several of the Hanford homes, the dust represented a public-health risk level above what is considered acceptable under the standards developed by the International Commission on Radiological Protection.

“These radioactive particles are tiny and difficult to detect once you get a few inches away,” said Kaltofen, who is affiliated with Worcester Polytechnic Institute in Massachusetts. “But once inside the body, the distance from our tissue is essentially zero.”

Kaltofen said his research indicates that some other homes likely have low levels of radioactive contamination, and he recommended more testing.

The Times on Tuesday forwarded the study to John Martell, the state Department of Health’s manager of Radioactive Air Emissions Section, for comment.

After an initial read, Martell said the levels found in the study appear to be low, and “is not jumping out to us as a public health risk.” But he said that his staff was still reviewing the numbers reported in the study, numbers that are in a different format than he typically sees.

“The bottom line is we want to make sure everything is OK. We take public health seriously.”

Kaltofen used an unusual technique that involves both electron microscopy and a specialized X-ray analysis that can detect extremely low levels of radioactive particles.

The six houses where dust was extensively tested were part of a broader group of 36 homes in the Tri-Cities and areas near Hanford that provided samples. The smaller group was selected after an initial screening indicated the likelihood of radioactive particles.

“A special population”

Kaltofen obtained many of these samples through a yearslong collaborative effort with Hanford Challenge, a Seattle-based organization that focuses on accountability in the federal cleanup of decades of plutonium production for atomic bombs at the 562-square-mile federal site near Richland.

“We took samples from anyone who let us in their homes,” said Tom Carpenter, of Hanford Challenge, who said the dust was collected with help of cloth wipes and vacuum cleaners.

Dust samples also were taken at the Hanford site to generate a kind of fingerprint of radioactive particles, which could then be compared to what was found in the homes.

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The particles could have spread off the site via workers’ vehicles, or their clothes, as well as through windstorms or wildfires that have burned at Hanford, according to Carpenter.

An Energy Department spokesman at Richland referred a request for comment on Kaltofen’s study to the national headquarters in Washington, D.C. In an email response, the department wrote that it does not comment “on studies conducted by third parties.”

At Hanford, the Energy Department does undertake environmental monitoring to measure radionuclide concentrations in the air, water, soils, fish and wildlife. That effort is “to assure the public that the dose and risk from Hanford contaminants are well understood,” according to an Energy Department document.

Kaltofen, through the course of his study, found three of the highest levels of thorium radioactivity in the dust of three Hanford workers’ homes. Two of these dust samples were collected from older homes built in Richland for Hanford workers during the 1940s.

The third home was a newer suburban house outside the Tri-City areas owned by a Hanford employee who worked at a tank farm that stores radioactive and chemical wastes.

Kaltofen said he did inform the owners of these three homes of the findings.

“We are dealing with a very special population — people that worked at Hanford,” Kaltofen said. “I think they understand that they have some risks from their job but I think they were uncomfortable with the idea that the materials could follow them home.”

Demolition on hold

All of the samples in Kaltofen’s study were taken before 2017, a year in which the spread of radioactive contamination during the demolition of Hanford’s Plutonium Finishing Plant increased concerns about contamination spreading off-site and prompted the work to be put on hold.

During the past year, the Energy Department offered bioassays — which measure the concentration of the potency of a substance — to several hundreds workers and reported that 42 workers had ingested or inhaled very low amounts of radioactive contamination. In a statement released this year, an Energy Department official said that the amounts were less than 1 percent of regulatory limits, which are set below levels considered to have negative health effects.

In December 2017, some contamination was found on worker vehicles. Surveys were done on more than a half-dozen homes, but no signs of contamination were found, according to the federal Energy Department.

The state Department of Health also was involved in the monitoring.

Air sampling detected “elevated results” but no threat to public health, according to a Jan. 30 letter that Clark Halvorson, the state Department of Health’s assistant secretary, sent to a U.S. Energy Department official.

For state officials, a particular source of concern was alpha contamination, which was also found in some of the dust collected in previous years for Kaltofen’s study.

Halvorson wrote that this contamination is difficult to detect and has the potential for “lifelong internal contamination” if particles make their way into a person’s body.