Summary of Public Comments Received on the Government of Canada’s Draft Screening Assessment Report and Risk Management Scope on Thiourea (CAS 62-56-6)

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Formal comments made during the 60-day public comment period that took place from May 17, 2008 to July 16, 2008 on the draft screening assessment report and risk management scope on thiourea, a substance included in Batch 2 of the substances to be addressed as part of the Chemicals Management Plan Challenge under the Canadian Environmental Protection Act, 1999 (CEPA 1999), were provided by Reach for Unbleached! and Crofton Airshed Citizens Group.

A summary of comments and responses is included below, organized by topic:

  • Effects on Human Health
  • Food & Consumer Products
  • Releases to the Environment
Summary table
Effects on Human HealthThe screening assessment for thiourea does not clearly demonstrate exposures to Canadians greater than the critical threshold value (CTV).  Accordingly, there is no finding to be addressed by risk management actions.

Both cancer (non-threshold) and non-cancer (threshold) effects were considered in the screening assessment of thiourea.

With respect to cancer, one of the critical effects found in the screening assessment, there is considered to be no threshold of exposure. In such cases, it is assumed that there is a probability of harm to human health at any level of exposure, as the mode of action for the induction of tumours has not been elucidated. Therefore, the screening assessment concludes that thiourea “may be entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.”

For non-cancer effects, the margin of exposure derived from the lowest short-term oral effect value and the estimated inhalation and dermal exposures (combined) from consumer products in the screening assessment is considered potentially inadequate for the protection of human health when the uncertainties of both the exposure and hazard databases are taken into consideration, in accordance with the application of a precautionary approach as required by CEPA, 1999.

 Thiourea should not be permitted in food packaging as it is a genotoxic carcinogen. At the pulp and paper mills where thiourea is used in the manufacture of paper and paperboard for food containers, treated surfaces are thoroughly rinsed with potable water to ensure no contamination of food.
Food & Consumer ProductsIn the absence of any data that implies that the chemical is entering the environment in safe quantities, and considering the potential for carcinogenic and reproductive impacts, options for risk management should include assessing opportunities for alternatives and for ensuring that the potential for exposure of the general Canadian population is reduced.  The screening assessment did not identify any significant risks associated with Canadians current exposures to thiourea as they were considered to be negligible under current use conditions. Should notifications to the government identify new uses with elevated risks, all available risk management tools, including opportunities for alternatives, will be considered.
Releases to the EnvironmentThe reporting threshold of the National Pollutant Release Inventory (NPRI) – 10 tonnes manufactured, processed or otherwise used - should be re-evaluated as it may not be appropriate to capture the release to air and disposal. For example, the current threshold level indicates no releases of thiourea.

Environment Canada will make a decision on whether or not to change the NPRI reporting thresholds.  Changes to the Inventory may include the addition, modification or removal of substances as well as changes in the thresholds at which they must be reported. This will be discussed during the risk management phase of the CEPA process.

For further details on NPRI, please see:

 An assessment should have been done on exposures to humans and the environment resulting from the potential presence of thiourea in recycled pulp mill sludge, given the various uses of thiourea in paper products, including imported paper products. This sludge may subsequently be spread onto agricultural land.

Environment Canada does take into consideration recycling activities, such as landspreading, and resulting potential releases to the Canadian environment. Quantities of thiourea that could eventually end up in landspreading would be captured upstream in the screening assessment since, under section 71 of CEPA, 1999, companies were asked to provide information on thiourea, either alone, in a product or a manufactured item, which included paper products, for the 2006 calendar year.

Although available data are insufficient to permit quantification of the potential contribution of sludge to human exposure to thiourea, exposure from this source is expected to be negligible.

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