Characterizing exposure to environmental chemicals in a cohort of women firefighters and office workers in San Francisco

Cancer in the fire service is well documented and studies have identified elevated rates of several different cancers compared to the general population. Meta-analyses have shown that firefighters have a higher incidence of cancer than the general population and the elevated rates of cancer are suspected to be related to occupational exposures. Firefighters are exposed to multiple different toxic chemicals through their work and their exposure levels to certain compounds are higher than among non-firefighters. Many of the chemical exposures previously measured in firefighters are suspected or known carcinogens, some of which have been associated with mammary tumor development in animal and human studies. To date, the overwhelming majority of health and exposure studies of firefighters have been done on men. Women remain understudied in many occupational settings including firefighting and exposure and health data for women firefighters remains limited./nThe Women Workers Biomonitoring Collaborative (WWBC) was created to address the gender-based data gap in occupational health and exposure research. This collaborative was developed to explore exposures to toxic occupational and environmental chemicals in nurses, firefighters and office workers in San Francisco. The collaborative was started in 2014-2015 with an initial cohort of 86 firefighters and 84 office workers (initially called the Women Firefighters Biomonitoring Collaborative (WFBC)) and expanded in 2017 to resample 18 women firefighters after a fire event. The WWBC has also integrated a cohort of nurses and a new cohort of office workers. This dissertation analyzes the firefighter and first wave of office worker data collected with the Women Workers Biomonitoring Collaborative and characterizes environmental chemical exposures, their potential sources, and upstream effect biomarkers among women firefighters and office workers in San Francisco./nChemical exposure levels were measured in women firefighters and office workers using both targeted and non-targeted analytical approaches. Using chemicals measured via targeted analytical methods, I analyzed exposure to environmental chemicals that have been previously measured in firefighters but that have not been characterized in women firefighters. I conducted statistical analysis to characterize exposure levels of perfluoroalkyl substances (PFAS) in serum and flame-retardants and their metabolites in urine for women firefighters and office workers; each chemical was evaluated separately (Chapters 2 and 3). I then limited the analysis to firefighters to assess how firefighter-specific activities could influence their exposure levels. For flame-retardants, I also assessed the relationship between exposure to flame-retardant chemicals and thyroid hormones via thyroxine and thyroid stimulating hormone levels in firefighters and office workers (Chapter 3). In Chapter 4, I applied a non-targeted or generalized suspect screening approach on a small dataset of firefighter samples collected after a fire event to identify novel chemical exposures. Serum samples were scanned using high-resolution mass spectrometry (HRMS). I matched the chromatogram peaks (aka features) to an in-house curated database of environmental chemicals that were selected based on their relevance for mammary tumor development and occupational exposures. I then selected a subset of features for validation and confirmation./nCharacterizing exposures using targeted approaches I found that all participants, both firefighters and office workers, were exposed to multiple PFAS chemicals (Chapter 2). Women firefighters had higher levels of perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), and perfluoroundecanoic acid (PFUnDA) compared to office workers. In analyses limited to firefighters, I found that firefighter assignment in the fire department (firefighter and officer versus driver) and use of firefighting foam in the prior year were associated with higher PFAS levels. Similarly, when I characterized exposure to flame-retardant chemicals (Chapter 3), I found that firefighters had higher average flame-retardant levels compared to office workers. Firefighters’ assigned position in the fire department and whether the participant was on duty at the time of the sample collection were slightly associated with flame-retardant levels, however, the association was not statistically significant. In this chapter I also assessed the relationship between exposure to flame-retardants and thyroid hormone levels and found that higher levels of bis(1,3-dichloro-2-propyl) phosphate (BDCPP) and, to a lesser extent, dibutyl phosphate (DBuP) were associated with decreased thyroxine levels in firefighters, but not in office workers. I did not observe an association between flame-retardant levels and thyroid stimulating hormones in either group. In the final chapter, applying the generalized suspect screening approach (Chapter 4), I matched the over 20,000 peaks detected from the HRMS to our in-house database, tentatively identifying 341 features that will be validated in future studies. In addition, I selected a subset of chemicals that did not match our in-house database but that may be relevant to firefighting, either because the features had different detection frequencies or had median concentrations in at least one of the three temporal post-fire visits. Together, these chapters demonstrate how the GSS approach, coupled with the targeted characterization of chemicals, can help identify novel chemicals associated with a fire event, and, systematically characterize environmental exposures present in firefighting./nThis study corroborates evidence of exposures to PFAS and flame-retardant compounds in the general public and in occupational settings. This is the first study to characterize exposures among women firefighters and contributes to the limited research on environmental exposures and adverse biomarker effects (thyroid perturbations) in women firefighters. As more women enter the fire service and other first responder professions, it is important to understand the extent of exposures among women workers and evaluate potential health effects from exposure. A better understanding of occupational exposures among women workers can facilitate development of adequate prevention efforts and ensure equitable workers’ compensation benefits are granted to women workers.

Advisor: Morello-Frosch, Rachel