MS maps actinides in exposed workers - Analytical Chemistry (ACS

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MS maps actinides in exposed workers To understand and quantify human exposure to radioactive elements, scientists have traditionally faced a conundrum: methods that would allow them to visualize radioactive distribution within tissue have not allowed them to simultaneously pinpoint the identities and concentrations of the elements involved. An autoradiograph shows a visual distribution of alpha particle decay but does not reveal the identity of the element causing it. Radiochemical methods identify and quantify elements by dissolving the sample, but this eliminates information about the distribution of the elements. In AC (DOI 10.1021/ac902650w), Philip Doble, Sergei Tolmachev, and colleagues report that they have used MS as a bio-imaging technique to simultaneously identify, visualize, and quantify long-lived actinides within tissue samples. The method applies laser ablation-inductively coupled plasma-MS (LA-ICP-MS) to the analysis of radionuclides within slivers of tissue from lungs and lymph nodes of exposed workers. This technique “should be a nice complement to the more traditional autoradiographic techniques,” says Raymond Guilmette of the Lovelace Respiratory Research Institute. Tolmachev’s group from the U.S. Transuranium and Uranium Registries (USTUR) at Washington State University teamed up with Doble’s group at the University of Technology (Australia) to analyze the samples. Doble’s laboratory collaborates with and is supported by Agilent Technologies. USTUR houses the National Human Radiobiological Tissue Repository, a unique collection of tissues that has existed since 1944, donated by workers who were occupationally exposed to nuclear materials, says Tolmachev. Tolmachev’s group sent samples from USTUR to Doble’s group for analysis. Although LA-ICP-MS has been widely used to study geological samples, Doble and his team have been developing the technique and corresponding software as an imaging tool for elemental analysis in biological samples such as slices of brain

first case, the worker had contact with insoluble Pu in a fire in 1965, and localized regions of a lymph node and lung tissue indicated mass peaks of 239 and 240 in relative concentrations that were consistent with weapons grade Pu. In another case, a worker had a skin wound that was contaminated with soluble Pu, but no Pu was detected in the lymph node. This was expected because soluble plutonium shouldn’t accumulate within that tissue. In a third case, in which a worker was injured in a lab accident involving Am, LA-ICP-MS maps the distribution of radioactivity within a slice of a the levels in the tissue lymph node. (top) Photomicrograph of a lymph node. (middle and botwere below the detectom) LA-ICP-MS images that compare the effects of natural exposure tion limit for this to thorium (middle left, m/z 232) and uranium (middle right, m/z 238) method (1 ng/g). A with occupational exposure to plutonium (bottom left, m/z 239 and botfourth worker had tom right, m/z 240). chronic and acute exposure to high levels and tumors. The laser ablation system, of uranium, as well as an exposure to pluwhich includes a 213 nm Nd:Yag laser, tonium on two occasions. Though no Pu traverses the tissue samples, sweeping parwas detected in the lymph node from this ticles into the ICP-MS. A sample with an worker, the tissue showed detectable levels area of 1 cm2 takes 3 to 12 hours to abof 235U (70 ng/g) consistent with his conlate, Doble says. He and his colleagues tact with high levels of uranium. devised a quantification procedure that Because the technique can localize and compares the results of the analyses to a identify multiple elements, the researchers set of tissue standards. (They couldn’t simultaneously examined the effects of determine absolute quantities of Pu beexposure to natural background radioaccause standards for this element are not tivity, particularly 232Th, to which none of available in Australia, Doble says.) The these workers had a known occupational researchers also developed software that exposure, and 238U. Natural exposure to 232 processes the data into two- and threeTh by inhalation resulted in concentradimensional images. tions in the range of 40⫺200 ng/g in the The investigators describe the results lung and lymph node samples. “A major from tissues donated by four individuals advance of this method is its ability to diswho were occupationally exposed to uratinguish occupational exposures from nium, plutonium, or americium. In the those due to naturally occurring airborne

10.1021/AC100626P  2010 AMERICAN CHEMICAL SOCIETY

Published on Web 03/22/2010

MAY 1, 2010 / ANALYTICAL CHEMISTRY

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radioactivity,” says Richard Toohey of the Oak Ridge Associated Universities. Whether from natural or occupational exposure, the inhaled radioactive particles accumulated in patches within the tissues. That information about spatial distribution is critical for understanding the mechanisms of uptake and retention of radionuclides in biological tissues, Guilmette says. With this added information, researchers

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may be able to make more accurate recommendations about what constitutes a harmful exposure. “As we gain more data on the deposition sites of inhaled radionuclides, we can refine dose estimates to particular regions of the lung, rather than averaging the dose over rather large tissue regions,” Toohey adds. In further studies, the investigators are extending the method to look at the

effects of occupational exposure to other materials. They’re starting with beryllium, Doble says, attempting to detect unique signatures in workers with berylliosis. The researchers also will study asbestos to look for unique signatures of those silicate minerals within the lung. —Sarah Webb