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Established in 1985, the Workplace Safety and Insurance Appeals Tribunal (WSIAT) is the final level of appeal to which workers and employers may bring disputes concerning workplace safety and insurance matters in Ontario. WSIAT has always been separate from and independent of the Workplace Safety and Insurance Board.

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  Decision 983 17
3/22/2019
R. McCutcheon - M. Christie - M. Ferrari

  • Evidence (epidemiological)
  • Exposure (herbicide)
  • Exposure (pesticides)
  • Alzheimer's disease

The worker was a landscaper from 1969 to 2009. The worker appealed a decision of the Appeals Resolution Officer denying entitlement for cognitive impairment. The worker related his condition to herbicide and pesticide exposure.
A high standard of scientific certainty is not required when determining causation in cases of occupational exposure; rather, the Tribunal must be satisfied, on the balance of probabilities, that the work exposure is a significant contributing factor to the development of the condition. Generally, an odds ratio of 2 or more supports an inference of causation. When the odds ratio is less than 2, consideration is given to the presence of any special factors in the individual case.
The worker clearly had a cognitive impairment but there were various diagnoses of his condition. Considering the totality of the evidence and the report of a Tribunal medical assessor, the Panel found that Alzheimer's disease was most likely the correct diagnosis.
Medical literature suggested that pesticide exposure could potentially contribute to the development of Alzheimer's disease but study results remain uncertain and the main positive study indicated that the strength of the association was weak, with an odds ratio of 1.42.
Considering the worker's personal factors of age, education and hypertension, the worker had a baseline risk for developing Alzheimer's disease of 4.2, in addition to a three-fold risk due to the worker's family history. The Panel found that these factors overwhelmed any possible contribution made by occupational exposure. There was medical opinion that, regardless of occupational exposure to pesticides and herbicides, the worker would likely had developed Alzheimer's disease in any event. The Panel noted the Decision No. 600/97 held that employment is not considered to be a significant contributing factor if the disease would have occurred when it did regardless of any employment exposure.
The appeal was dismissed.