Ont. report finds workers’ risk from 2,4,5-T ‘very low’

A fact-finding panel assessing the Ontario government’s use of 2,4,5-T herbicide, and possible health impacts from exposure, expects a “very low” risk of disease even among those most exposed.

Deregistered Canada-wide at the end of 1985, 2,4,5-T was used from the 1950s through the 1970s for weed and brush control on non-crop farmland, as well as in the forestry and transportation sectors and by municipalities, private companies and others.

The herbicide and TCDD — a dioxin impurity formed in the manufacture of 2,4,5-T products — came to wider notoriety following their use in the Vietnam War-era defoliant Agent Orange, a 50-50 mixture of 2,4,5-T and 2,4-D.

The Ontario government notes it took “early action” on the product’s use, as studies in the 1970s began to look at TCDD and see whether it posed human health risks, though it noted “not all studies pointed to a problem.”

The province, which restricted 2,4,5-T’s use in 1979 and banned it in 1980, named retired University of Guelph biochemist Leonard Ritter, the executive director of the Canadian Network of Toxicology Centres, to lead its independent fact-finding panel on 2,4,5-T starting in 2011.

The panel was tasked with seeing “where, when and how” 2,4,5-T was used in the province in the 1950s through the 1970s for weed or brush control by government ministries and agencies — and whether provincial workers’ and bystanders’ exposure may have potential health impacts.

The report from Ritter’s panel was publicly released Thursday. It’s now under review by Ontario’s Workplace Safety and Insurance Board (WSIB), which is adjudicating claims from workers who believe their medical conditions were caused by workplace exposure to herbicides such as 2,4,5-T, the province said.

Over 200 herbicide products were registered for use in Canada between 1948 and 1985 containing some form of 2,4,5-T, the province noted Thursday.

Natural Resources Minister David Orazietti and Environment Minister Jim Bradley said jointly Thursday that the province will also review the report to see “if any additional steps need to be taken to address its findings.”

Health and safety of current and former provincial employees and the Ontario public is “vitally important,” the ministers added.

“Will not necessarily occur”

The panel report noted the work of the U.S. Institute of Medicine (IOM), which has developed a list of diseases for which people exposed to 2,4,5-T and its contaminants may be at “increased risk.”

Ritter’s panel agreed the IOM’s findings “reasonably reflect the current state-of-hazard assessment for these exposures.”

In Ontario, the panel wrote, “individuals with occupational exposures and a few bystander populations with the highest estimates exceeded the margin of safety benchmark” but added the associated risk of developing diseases for an individual in these categories would “likely be very low.”

Furthermore, the panel stressed, “an adverse effect will not necessarily occur, even in those cases where the margins the panel estimated have exceeded the benchmark.”

The province’s application records showed “many” provincial departments used 2,4,5-T to some extent, but “most uses” by Ontario government departments and agencies were carried out by the natural resources and transportation ministries and by Ontario Hydro.

Thus, the panel said, it focused on 2,4,5-T’s use by those three departments, along roadways, in hydro transmission corridors and in forested areas.

That said, “most” use of the herbicide in Ontario was by private and municipal users, but those non-government uses were “beyond the panel’s scope and not included in the evaluations.”

Applying its “best estimate” of exposure, the panel found exposures “exceeded the benchmark” for some transportation ministry and Hydro staff involved in ground mixing, loading and applying 2,4,5-T, as well as for some natural resources ministry staff and junior rangers involved in backpack mixing/loading and application and in aerial mixing/loading and flagging.

Bystander margins of safety, meanwhile, “were not necessarily reflective of adverse health outcomes.”

Considering the “array of possible adverse health outcomes” reported to be associated with exposure to TCDD and/or 2,4,5-T, the panel granted that some people exposed to these chemicals “may have experienced” such outcomes — but it “cannot be concluded that the outcome was due to the exposure.”

Ritter’s panel noted its risk assessment was “directed at the population level and not intended to describe risks to any specific individual,” indicating just that “acceptable margins of safety were exceeded, and people’s health could be affected.”

Orazietti and Bradley, in their statement, encouraged “anyone who has questions about their health” to see their health care provider.

The province noted it has a dedicated phone line for the public (1-888-338-3364) and a dedicated WSIB line (1-800-387-0750) for Ontario workers with concerns about possible workplace exposure. –– AGCanada.com Network

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