Hugh William Davies

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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Veterinary practices use antineoplastic (chemotherapeutic) drugs to treat various cancers in companion animals. The primary health concern with this is that veterinary staff largely use drugs designed for human treatments that can involuntarily harm those who handle them. Antineoplastic drugs are known to cause cancer and adverse reproductive health effects that have been largely studied in human health care settings. However, it is unknown the degree to which these drugs affect veterinary workers with respect to their unique protocols. This thesis furthers the understanding of antineoplastic drug use and exposure in veterinary practices. The thesis was comprised of two parts to address the research objectives. First, an online survey was administered in veterinary clinics to examine the drug preparation and administration practices, COVID-19 implications, training and guidelines, and personal protective equipment used with antineoplastic drugs. Second, surface wipe sampling was conducted to quantify the contamination on various surfaces, examine which drugs were found and where they were located within veterinary settings. The survey was completed by 80 participants in British Columbia and Minnesota. Twenty-four percent (19/80) reported that their clinic ever administered antineoplastic drugs. Eighty-two percent of participants who did not handle antineoplastic drugs referred animals to other practices. Sixty-eight percent (13/19) of respondents who administered antineoplastic drugs never received any formal safe handling training while 74% (14/19) of practices reported not following any specific guidelines on antineoplastic drug handling. Most clinics did not report significant change in their preparation and administration processes during the COVID-19 pandemic. In the surface wipe sampling, cyclophosphamide was the drug found most frequently for contamination. The surfaces most commonly contaminated included the floor where antineoplastic drugs were prepared and administered, door handles of antineoplastic storage and waste bins near antineoplastic drug administration and preparation, suggesting potential for exposure among workers. This thesis builds upon the limited existing literature to address how veterinary protocols affect exposure to antineoplastic drugs. Further research is recommended both on best practices specific to veterinary settings and on determining occupational exposure limits for antineoplastic drugs.

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Workers in the construction industry are known to be at risk of high exposures to respirable crystalline silica (RCS). Local exhaust ventilation (LEV) has been proposed by regulators as a primary method to control RCS exposure to construction workers. However, real-world data on the effectiveness of LEV in controlling RCS exposure is limited with available studies providing varying results.This study looks at the use and performance of vacuums, a common type of LEV available, used in conjunction with different hand tools on real-world constructions sites. A combination of study methods including field sampling, worker survey and simulated tests were used. During the field sampling, information regarding the vacuums, work environment conditions and dust exposure measurements were collected. These data were later used in regressions models to determine the determinants that strongly influenced the performance of the vacuums. The worker surveys provided information on the knowledge and attitude of workers. The simulated tests were used to corroborate information from the field sampling or to test specific scenarios where there is potential secondary dust exposure due to the use of vacuums.The study results show that the age and maintenance of the vacuums had the strongest effect on the airflow of the vacuum. However, while maintaining a sufficient airflow is important to ensure dust capture, the correlation of airflow with respirable dust exposure was weak. Both age and maintenance of the vacuums as well as environmental factors play a large part in determining the respirable dust exposure to the worker. It is recommended that all vacuum users are trained in both basic principles of ventilation as well as the standard operating procedure of the specific vacuum model being used. This is as each vacuum operates differently and may require different maintenance processes.

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Occupational noise exposure is associated with an increased risk of cardiovascular disease. A biological model explains this association through a general stress reaction and the dysregulation of otherwise normal psychoneuralhormonal pathways. Given this evidence and the hypothesized link between stress and metabolic disorders or immunologic response (i.e. inflammation) we hypothesized that risk of diabetes and arthritis are elevated in those exposed to noise at work.Cases and controls were drawn from the National Population Health Survey (NPHS), a longitudinal survey conducted by Statistics Canada. Eligible subjects were aged 18 to 55 in the first cycle (1994/1995) and who did not have the health outcome of interest up to and including the fourth cycle (2000/2001). Cases were determined from self reports in the fifth (2002/2003) through eighth cycle (2008/2009); each case was matched to five controls who were disease free at the time when the case was diagnosed. Subjects’ noise exposure at work was assessed using cumulative exposure. Noise levels by various occupations/industries were derived from a job exposure matrix built from WorkSafeBC’s noise exposure dataset and exposure duration was estimated according to the self-reported work status in the NPHS. Conditional logistic regression was used to estimate the odds ratios of developing the health outcomes of interest; models were adjusted for life style factors (physical activity, smoking, drinking), socio-economic factors (education, family income), and health status factors (hypertension, obesity).In the current study the adjusted diabetes ORs (95% CI) for medium and high exposure groups (using low exposure group as reference) were 0.93 (0.61 – 1.41) and 1.04 (0.67 – 1.59), respectively. The corresponding ORs (95% CI) for rheumatoid arthritis were 1.01 (0.56 – 1.82) and 1.07 (0.57 – 2.01). For cardiovascular disease, the ORs (95% CI) were 0.87 (0.59 – 1.28) and 0.85 (0.57 – 1.27). We did not find evidence of an increased risk of diabetes, rheumatoid arthritis, or cardiovascular disease in those exposed to occupational noise. Possible biases in this study may explain the lack of an observed association including misclassification bias – particularly of exposure - and the healthy worker effect. Future studies are warranted and should focus on improving exposure assessment.

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Background: Sawfilers are a sub-group of sawmill workers who repair and maintain saw blades, and are exposed to multiple inhalable occupational hazards some of which were carcinogens or have non-malignant respiratory effects. Sawmill workers in general may be exposed to endotoxins from gram-negative bacteria of the wood. Previous studies across different industries have shown that endotoxin would increase the risk of COPD, but may decrease the risk of lung cancer. The main goal of this thesis was to examine the associations between the two exposures (sawfiling employment and endotoxin) and two diseases (lung cancer and COPD) by using an existing cohort of 25,685 BC sawmill workers. Method: Sawfiling exposure was categorized into ever-exposed and never-exposed groups. For endotoxin, we used a previous endotoxin monitoring study of 216 samples in BC sawmills to build a predictive model through forward-stepwise linear regression, based on which we assigned quantitative endotoxin exposure values and calculated cumulative endotoxin exposure levels. Relative risk of lung cancer (ICD9=162) and COPD (ICD9=490,491,492,496) for each exposure group were assessed using Poisson regression, controlling for age, race, calendar period, and time since first exposure, with workers in lowest exposed category as the reference. Results: A total of 523 cases of lung cancer (follow-up period 01/01/1959 to 12/31/1995) and 120 cases of COPD (follow-up period 01/01/1985 to 12/31/1998) were included in the analysis. With respect to sawfiling, risk of lung cancer (lagged 20 years) and COPD (lagged 5 years) were slightly elevated (RR=1.4, 95% CI=0.9-2.2 and RR=1.3, 95% CI=0.6-2.5, respectively) but neither significantly. Decreased risk of lung cancer was observed among subjects with highest endotoxin exposure (RR=0.8, 95% CI=0.5-1.1), and the dose-response trend was borderline significant (p=0.059). Increased risk of COPD was observed among subjects with highest endotoxin exposure (RR=1.9, 95% CI=1.0-3.7), and the dose-response relationship was again borderline significant (p=0.065). Conclusion: This study provided evidence of a link between cumulative endotoxin exposure and a decreased trend of lung cancer and an increased trend of COPD. However, the association between lung cancer, COPD and sawfiling employment remained unclear.

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Methylmercury is a common contaminant found in fish. Chronic exposure can have detrimental effects on the nervous, cardiovascular and immune systems. Since mercury exposure can come from consuming fish that is caught as well as fish that is purchased, recreational anglers are a group that may have higher exposure than non-anglers. It was the primary goal of this study to determine whether exposure to methylmercury in Vancouver Island recreational anglers was greater from the consumption of sport-fish or from commercial fish.Study participants were recruited from the BC Ministry of Environment freshwater fishing license list. A comprehensive questionnaire was administered over the telephone to enumerate potential sources of exposure to methylmercury. While the questionnaire primarily focused on the frequency, mass and species of fish consumed, other exposure sources were also examined. Following the questionnaire, a blood sample was collected and analyzed for mercury.A total of 195 anglers between the ages of 21 and 85 participated in the study. 80% of the subjects were male and approximately 90% were born in Canada. The geometric mean blood-mercury concentration was 2.33 ± 2.16 μg/L. In multiple regression analysis, the consumption of caught rockfish, shellfish and cutthroat trout as well as bought fresh/frozen albacore tuna, fresh/frozen ‘other’ tuna, i.e. ahi, skipjack or yellowfin, and snapper were found to be the greatest predictors of exposure.The results of this study demonstrated that exposure to methylmercury in Vancouver Island anglers was equally distributed between recreational and commercial fish species. The observed blood-mercury concentrations were consistent with similar studies, as was the discovery that it was primarily the frequent consumption of fish species containing low to moderate amounts of mercury that drove exposure. While this study determined that three recreational and three commercial fish species were predictors of exposure, five of these six were saltwater species while the sixth, cutthroat trout, was anadromous. Future studies should therefore focus on evaluating the differences in exposure between fresh and saltwater fish consumption. In addition, conducting a comprehensive survey of tissue-mercury levels in Vancouver Island fish would provide valuable region-specific data, leading to better exposure estimates in anglers.

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In Bangladesh, shipbreaking is often carried out by internal migrant workers from the impoverished northern regions. Ships can contain hazardous substances such as polychlorinated biphenyls, heavy metals and asbestos, which are all recognized carcinogens. Work is done by hand, without heavy equipment, adequate training or protection, and with high potential for exposures. This pilot study examined asbestosis and non asbestos-related respiratory symptoms among these migrant workers.Shipbreakers were recruited from their home communities in northern Bangladesh. They were interviewed in Bangla, and received anteroposterior chest x-rays and physical exams. Information was collected on: a) respiratory symptoms using validated questions from the American Thoracic Society, b) work history and past occupational exposures, c) clinical history, d) attitudes around occupational health and safety, e) and knowledge of the potential heath risks and fate of asbestos. Chest x-rays were read by a B-reader for asbestosis diagnosis. One hundred and four male shipbreakers were recruited with average age 40 years and 2.5 years education. On average they had nine years shipbreaking experience and 17 years since first year of employment on the yards. Radiographic results indicated a six percent prevalence of asbestosis, and results from the interviews indicated a thirteen percent and eight percent prevalence of work-related cough and phlegm, and work-related shortness of breath, respectively.The prevalence of asbestosis appears lower than seen in previous studies of shipbuilders and ship-repairers. However, beach-based shipbreakers (steel plate loaders and cable-pullers) were overrepresented in comparison to ship-based (cutters and fitters) workers. This, and the small sample size, inclusion criteria, and a possibly exaggerated healthy worker effect, could have resulted in an underestimate of prevalence. Ships typical of those being dismantled contain several tons of asbestos; there is a need for improvements in exposure control, including educating the shipbreakers about asbestos and where it is found. Future research should focus on subjects who have worked closer to the source of exposure, as well as better characterizing the exposure and learning about the fate of the asbestos after it leaves the yards.

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