An Assessment of Chemical Exposure in Aviation

Aircraft pneumatic systems are pressurized by air bled from the engines. This air and engine interaction can result in contamination of the air with intact, degraded, and pyrolyzed oil. Additionally, other pneumatically pressurized aircraft components, such as the hydraulic reservoirs, can contribute to chemical fouling of the air. The pneumatic system then facilitates the transport of this contaminated air to locations that allow for interactions with human receptors; most commercial aircraft use this bleed air to pressurize the cabin, and all use it to pressurize the onboard potable water systems. Human interactions with these contaminants, coupled with an increased prevalence of neurological illness and injury, anecdotally reported and described in cohorts of those who have careers in aviation, has led to our description of an associated occupational risk (Chapter 1). In this chapter, we systematically examine the available literature and describe several gaps in knowledge that, if addressed, could better qualify the chemical exposures and verify the pathways of contaminants from source to receptor. Of those knowledge gaps, three were the most pressing. Historical exposure to known contaminants of concern, in particular organophosphates like tricresyl phosphate, had been theorized to potentially contribute to pilot illness. The mechanisms of this historical exposure had yet to be explored. We completed an elemental assessment on new and used oil of small single-engine aircraft; this aircraft type is often used for training pilots prior to commercial flying careers (Chapter 2). In this oil, we found an enrichment of organophosphates in the used product, indicative of the addition of contaminants of concern as a fuel or oil additive. We also found elevated concentrations of lead in the used oil product (average concentration 5.77g kg-1), which described a significant enrichment from its source of leaded aviation fuel and is at concentrations capable of exposure-induced neurological injury. Additionally, in this chapter we examine a number of turboprop and jet aircraft oils and noted that phosphorus is lost from the new oil product with use at rates that exceed oil attrition. This validates the contaminant source determination of aircraft engine oil for organophosphates; the loss of the phosphorus from the oil implies its availability to the bleed air systems of the aircraft as either intact or degraded compounds. The second pressing knowledge gap identified described a previously unexamined contaminant pathway that originated in the engines and hydraulic reservoirs of aircraft and resulted in contamination of the potable water system due to the pneumatic connection with all aforementioned systems (Chapter 3). We qualitatively assessed the potable water onboard aircraft, utilizing liquid chromatography coupled with high-resolution mass spectrometry. We detected hydraulic oil (tributyl phosphate) in more than half of the unconcentrated water samples taken from flights and tentatively identified several additional organophosphates also in relatively high percentages (tris(chloropropyl) phosphate: 20%; triphenyl phosphate: 10%; tributoxyethyl phosphate: 10%). This confirmed the contamination pathway from the pneumatic system to the potable water and described a new exposure route for contaminants of concern to receptors that was undescribed by prior research. The contaminants known to be present on aircraft make up only a small fraction of the actual exposures that one experiences in the cabin environment. This is because previous assessments of the cabin had largely been targeted, sampling or monitoring the cabin for specific chemical compounds or classes, and completed with instrumentation (typically conventional Gas Chromatography Mass Spectrometry) that lacked the chromatographic resolution to detect and identify unknown compounds. We conducted the first non-targeted assessment of the aircraft cabin that was not restricted to a particular chemical class, and used this analytical technique to compare bleed air-pressurized and non-bleed air-pressurized aircraft (Chapter 4). Our analysis demonstrated increased contamination of bleed air pressurized aircraft in terms of compound number and abundance and tentatively identified contaminants associated with the degradation of aircraft engine oil (short-chain organic acids), exclusively on bleed air pressurized flights. This non-targeted assessment, contrary to previous comparison of aircraft in the literature, seems to demonstrate a marked difference in pressurization system-associated contamination, and helps verify cabin pressurization via the bleed air pneumatic system as a contaminant exposure pathway. When examining the results of the thesis as a whole, we have, through literature review, demonstrated a probable occupational risk and, through experimentation, shown that the risk may extend to training prior to employment in the commercial occupation. We have shown that the primary contaminant source, as described in the literature (aircraft engine oil), loses the element associated with the principal contaminant class of concern (phosphorus) with use, allowing the contaminant to enter bleed air systems as theorized. We have identified and validated a new source-to-receptor pathway involving the pneumatic and potable water systems on aircraft. And we have demonstrated, with a non-targeted qualitative chemical comparison with bleed-free aircraft, that pressurization of the cabin via bleed air from the engines is an important source of contamination, strengthening that pathway’s validity. While we have closed some of the knowledge gaps associated with chemical exposure and occupational risk in aviation, some remain to be answered. We hope that the contents of this thesis can influence decisions to mitigate some of this risk and inform future experimentation and research.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.