Investigation into toxic exposure at Dryden paper mill
Investigation into exposure during maintenance project
OHCOW (Occupational Health Clinics for Ontario Workers) is holding an information session on October 8, 2026, in Thunder Bay, Ontario, Canada, about the exposure of hundreds of construction workers to toxic fumes at a paper mill in Dryden, Ontario, Canada. The exposure is reported to have occurred between 2002 and 2004, during the replacement of a recovery boiler at the mill. According to Andrew Zarnke, who leads special projects and occupational disease research at OHCOW, workers at the time stood on scaffolding next to a dismantled flume and came into contact with untreated mill wastewater. “There were a lot of concerns about exposure to toxic fumes,” says Zarnke. According to him, several workers developed serious health complaints at the time, some fainted, and some had to be taken to hospital. The Ministry of Labour was called in at the time.
Hundreds of possible claims, files missing
OHCOW says more than 400 workers filled out an exposure questionnaire at the time, and that an occupational physician saw a pattern in many of the reported complaints consistent with chronic toxic encephalopathy, brain damage caused by exposure to toxic substances. In 2004, OHCOW is said to have helped 134 workers file a formal occupational disease claim (Form 8) with the Workplace Safety and Insurance Board (WSIB), Ontario’s workplace injury insurer. When OHCOW requested these files from the WSIB in 2021 – after mediation by a local advocacy group for injured workers – the organization says no record of them could be found. “That was a huge problem for this group of workers,” Zarnke says. Without the original claim files, which typically contain medical records, work history and exposure information, he says it becomes harder to substantiate a possible link between the Dryden project and current health complaints. An earlier OHCOW study from 2022 already mapped the same exposure and reported that dozens of workers from the original group had already died; whether those deaths are linked to the exposure has not been established.
Follow-up investigation still underway
According to OHCOW, it has now compiled a follow-up list of about one hundred workers and has so far completed around thirty health and exposure interviews; the investigation has yet to determine how many claims can still be reinstated or recognized. The organization has also filed a freedom of information request with Ontario’s Ministry of the Environment to obtain sampling and correspondence data on the composition of the fumes released at the time. Zarnke stresses that OHCOW does not make any determination of fault or liability, but documents workers’ experiences and health status and helps them seek recognition of these as an occupational injury or occupational disease. Attending the Thunder Bay session is not mandatory; according to Zarnke, workers who cannot attend, as well as family members of current or former workers, can contact the clinic at any time.
Context
According to its own guidance, the WSIB, Ontario’s workplace injury insurer, applies no time limit for filing a claim for an occupational disease. The WSIB assigns a decision-maker who specializes in occupational diseases and who reviews information from the worker, the employer and healthcare providers. A medical specialist often has to diagnose the condition. As a result, a claim can still be filed long after an exposure occurred; whether a causal link is recognized depends on the assessment of each individual file.
Source: Dryden paper mill toxic exposure claims get fresh investigation, 5 October 2026
Additional research: WSIB — Occupational disease
