Historic Exposure Assessment
By Abby Roberts
June 4, 2026—If an OEHS professional has to characterize the health effects of chronic exposures, how should they go about it? This was the subject of “Forensic Hygiene: Your Work Matters Longer Than You Think,” an AIHA Connect educational session given on Tuesday by Meghan Friesen and Krista Thompson, MHSc, ROH, CRSP. Both Thompson and Friesen are occupational hygienists with Occupational Health Clinics for Ontario Workers. Their work involves investigating historic exposures that may have caused workers’ present illnesses.
After Friesen summarized the history of occupational exposure limits—noting that they tend to be reduced over time—Thompson discussed the kinds of epidemiological studies OEHS professionals may find useful when assessing past exposures. Case-control studies compare people with a disease to those without it. Cohort studies follow groups with shared exposures for comparison with groups lacking those exposures. Rapid reviews, scoping reviews, systematic reviews, and meta-analyses may also be helpful. “When these are done well, I love to use them,” Thompson said, but she cautioned audience members to make sure they choose sources with useful methods and criteria. “Garbage in, garbage out.”
Historical data on occupational exposures may be found in peer-reviewed literature as well. Thomson also suggested checking employer records, white papers by organizations such as AIHA, scientific evaluations by national and international health agencies, and other OEHS-related publications, such as NIOSH health hazard evaluation reports.
Thompson then walked participants through a case study about a man who had worked in the coke making industry from 1980 to 2020, during which time he’d been exposed to coal tar pitch volatiles and benzene. The worker was diagnosed with B-cell non-Hodgkin lymphoma. When Thompson interviewed the worker about his job and exposure history, she found his memories closely matched employer records, which she noted was not always the case. She also reviewed several relevant epidemiological studies, including a report by the International Agency for Research on Cancer that found a positive association between non-Hodgkin lymphoma and cancer. Ultimately, Thompson concluded it was possible, though not certain, that the worker’s occupational exposures had increased his risk of cancer.
“We do not make drawn conclusions,” she explained. “We are talking about what is most likely.”
Friesen took center stage to present the second case study, this one focused on an industrial worker diagnosed with liver cancer after a career lasting from 1960 to 2000. This worker also described his work practices and tasks to Friesen in an interview. She also consulted union records, employer records, and scientific literature, including a 1973 data sheet that identified significant concentrations of solvents in paints likely used by the worker. In a rejected workers’ compensation claim, he had described direct and prolonged exposure to sludge containing trichloroethylene (TCE) and other solvents. Friesen also noted that the current occupational exposure limit for TCE is much lower than the historic OEL. Solvent exposures had likely increased the worker’s risk of liver cancer, she said.
Thompson and Friesen reminded their audience to assume additive effects from simultaneous occupational exposures, unless the evidence suggests synergistic effects. They wrapped up by echoing their presentation’s subtitle: OEHS professionals’ work matters longer than they think.
Abby Roberts is the assistant editor for The Synergist.