The risks posed by a substance are determined by both its hazardous properties (potential to cause adverse human health or ecological effects) and the amount or extent to which people or the environment are exposed.
When needed, the Government applies risk management instruments under CEPA and other federal acts to help prevent or reduce potential harm.
The Government concluded that MBT and its precursors, including the 6 substances in the benzothiazoles subgroup, are entering the environment at concentrations that may be harmful, due to potential risk to aquatic organisms. The Government intends to apply risk management actions related to tire and other rubber products manufacturing, metalworking, and some subsectors of the mining industry.
The 6 benzothiazole substances in this group are associated with health effects, but were concluded as not harmful to human health at levels of exposure considered in the assessment. The 9 benzotriazole substances are considered to be of low concern and therefore were concluded as not harmful to human health or the environment.
The assessment focused on 15 substances referred to collectively as the Benzotriazoles and Benzothiazoles Group under the third phase of the Chemicals Management Plan (CMP). The 15 substances addressed in the assessment are subdivided into 2 groups:
Benzotriazoles subgroup (includes benzotriazole, UV-329, UV-320, UV-326, tolyltriazole, UV-350, UV-234, CAS RN 80595-74-0, and CAS RN 94270-86-7); and
Benzothiazoles subgroup (includes TBBS, CBS, MBTS, MBT, SMBT, and DCBS).
The other 2 substances from the group were determined to be of low concern through other approaches:
The 2-mercaptobenzothiazole (MBT) moiety was identified as the key part of the molecule in the benzothiazoles subgroup. It may be released to the environment either through the direct use and release of MBT, or through indirect release owing to break down of the parent compounds. Therefore, MBT and its parent compounds (that is, precursors) were included in the ecological assessment, as MBT precursors will contribute to the presence of MBT in the environment.
Substances in the benzotriazoles subgroup are not expected to occur naturally in the environment. The natural occurrence of substances in the benzothiazoles subgroup is expected to be rare.
Substances in the benzotriazoles subgroup are used in cosmetics, food packaging, and lubricants and greases. Some of these substances are also used as ultraviolet (UV) light stabilizers and corrosion inhibitors.
Substances in the benzothiazoles subgroup have major uses in automotive products, rubber products, lubricants and greases, and mining.
Human and ecological exposures
Benzotriazoles subgroup
The assessment indicated that people in Canada may be exposed to these substances from drinking water, indoor air, eating certain fish and seafood, human milk, and from the use of products available to consumers, such as cosmetics (for example, nail products and make-up), ink pens, and automotive products (for example, lubricants).
People in Canada are not expected to be exposed to UV-320.
The human health risk of UV-350 was characterized using the Threshold of Toxicological Concern (TTC)-based Approach for Certain Substances. The estimate of exposure generated for UV-350 was lower than the TTC value, indicating low concern to human health on the basis of levels of exposure considered in the approach.
According to the information considered under the ERC Approach, the 9 substances in the benzotriazoles subgroup were identified as having low ecological exposure potential.
Benzothiazoles subgroup
The assessment indicated that people in Canada may be exposed to these substances from drinking water, eating certain fish and seafood, and from the use of products available to consumers, such as rubber granulates used on synthetic turf and automotive lubricants.
Substances from the benzothiazoles subgroup, which are considered as precursors to MBT, may be released to the aquatic environment primarily from tire and other rubber products manufacturing, use in metalworking fluids, and use in some subsectors of the mining industry. Releases of MBT were reported to the National Pollutant Release Inventory (NPRI), the primary source being tire and other rubber products manufacturing.
Indirect releases to soil from wastewater treatment systems are possible, as a result of the application of biosolids to land.
Details on which critical effects were considered for each substance in the benzotriazoles subgroup, as well as the use of read-across for these substances, are available in the assessment.
For the benzothiazoles subgroup:
The IARC classified MBT as "probably carcinogenic to humans", and the health effect of concern for MBT is cancer of the bladder.
There were limited health effects data for TBBS, CBS, MBTS, SMBT and DCBS; therefore, a comparative approach using the structurally-related substance MBT, called read-across, was used for assessing potential cancer-related health effects for these substances. For non-cancer effects, kidney effects for CBS, reproductive effects for CBS, and changes in liver weights for MBTS, MBT and SMBT were also considered in the human health assessment.
According to information considered under the ERC Approach, 3 substances in the benzotriazoles subgroup were identified as having a low ecological hazard potential. Six substances in this subgroup, however, were identified as having a high hazard potential due to their ecotoxicity and potential to accumulate in aquatic organisms.
For the benzothiazoles subgroup, toxicity experiments indicate that MBT has the potential to cause harm to aquatic organisms at low concentrations.
Consideration of subpopulations who may have greater susceptibility or greater exposure
There are groups of individuals within the Canadian population who, due to greater susceptibility or greater exposure, may be more vulnerable to experiencing adverse health effects from exposure to substances.
Certain subpopulations are routinely considered throughout the assessment process, such as infants, children, and people of reproductive age. For instance, age-specific exposures are routinely estimated and developmental and reproductive toxicity studies are evaluated for potential adverse health effects. These subpopulations were taken into account in the risk assessment outcomes for the substances in the Benzotriazoles and Benzothiazoles Group.
Risk assessment outcomes
Assessments focus on information critical to determining whether substances are harmful to human health or the environment under CEPA. This is done by considering scientific information, including information, if available, on subpopulations who may have greater susceptibility or greater exposure, vulnerable environments and cumulative effects and by incorporating a weight-of-evidence approach and precaution. The potential for cumulative effects was considered in the assessment by examining cumulative exposures from the broader class of benzothiazoles that are precursors to MBT. Additionally, the potential for cumulative effects was considered in this assessment by examining cumulative exposures from oral and dermal (skin) routes from a subset of benzothiazoles (that is, MBT, MBTS, and CBS) that may occur together in rubber granulates.
Based upon a comparison of levels to which people in Canada may be exposed to substances in both subgroups, except for UV-350, and levels associated with health effects, it was found that the risk to human health from these substances is low.
Using the TTC-based Approach for Certain Substances, UV-350 is considered to be a low concern for human health at levels of exposure considered in the assessment.
Based upon the outcome of the ERC Approach, the 9 substances in the benzotriazoles subgroup are considered unlikely to be causing ecological harm.
Exposure scenarios for tire and other rubber products manufacturing, use in lubricants, and use in some mining subsectors indicate that MBT and its precursors pose a risk to aquatic organisms.
Assessment conclusions
The Government concluded that the substances in the Benzotriazoles and Benzothiazoles Group are not harmful to human health at levels of exposure considered in the assessment.
The Government also concluded that MBT and its precursors, including the 6 substances in the benzothiazoles subgroup, are entering the environment at concentrations that may be harmful to the environment.
Also, certain substances included among MBT and its precursors meet the persistence criteria, but MBT and its precursors do not meet the bioaccumulation criteria as set out in the Persistence and Bioaccumulation Regulations of CEPA.
Preventive actions and risk reduction
The Government intends to propose the addition of MBT and its precursors to Part 2 of Schedule 1 to CEPA. Adding a substance to Schedule 1 does not restrict its use, manufacture or import. Rather, it enables the Government to take enforceable risk management actions under CEPA, using a 2-track approach to manage risks.
Toxic substances that pose the highest risk (that is, meet certain criteria) are added to Part 1 of Schedule 1. These are prioritized for total, partial or conditional prohibition.
Other toxic substances are added to Part 2 of Schedule 1 and are prioritized for pollution prevention, which may include prohibition.
Regulations specifying criteria for the classification of substances that pose the highest risk or that are carcinogenic, mutagenic or toxic to reproduction may be developed. When criteria are available, some substances considered for addition to Part 2 of Schedule 1 may instead be considered for addition to Part 1 of Schedule 1.
Publication of the risk management approach aims to inform stakeholders of proposed risk management actions and continue discussion about their development. The risk management approach indicated that the Government is considering the following actions to address ecological concerns:
Tire and other rubber products manufacturing sector: Developing release guidelines under CEPA targeting the tire and rubber products manufacturing sector in order to reduce releases of multiple substances, including MBT and its precursors. The application of best management practices outlined in the Code of Practice for the Environmentally Sound Management of Chemical Substances in the Chemicals, Plastics and Rubber Sectors would also contribute to the risk management of MBT and its precursors. Other regulatory and non-regulatory instruments may also be considered to achieve the risk management objective.
Metalworking fluids sector: Continuing to monitor the potential usage of MBT and its precursors in the metalworking fluids sector in Canada to determine the need for any risk management action in the future.
Some mining industry subsectors: Performing monitoring and surveillance activities in some subsectors of the mining industry to measure concentrations of MBT in industrial effluents and in surface water in the receiving environments once an analytical method has been developed. This will allow Environment and Climate Change Canada to determine what risk management measures should be developed, if any, for these facilities.
The Government plans to collect and analyze data on the presence of MBT in surface water and sediments in order to establish a baseline environmental presence and again following implementation of risk management actions to measure progress towards meeting the environmental objective.
Additional information is being sought by the Government to address data gaps and inform risk management decision-making. Details can be found in the risk management approach, including where to send information during the public comment period, ending May 7, 2025.
Risk management actions may evolve through consideration of assessments and risk management actions published for other substances. This is to ensure effective, coordinated, and consistent risk management decision-making.
Additional considerations
Although TBBS, CBS, MBTS, MBT, SMBT and DCBS are not considered to be harmful to human health at levels of exposure considered in the assessment, there may be a concern to human health if exposures to these substances were to increase. As a result, these substances may be considered in future initiatives to track their commercial status or identify new uses or exposures. Monitoring of MBT in surface water and sediment which is planned as part of the ecological component of the performance measurement evaluation will also help track human exposures. Prior to monitoring, analytical methods will need to be developed.
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Related resources
MBT and its precursors may be found in products available to consumers. People in Canada should follow any safety warnings and directions related to the product and dispose of products responsibly.
Assessments conducted under CEPA focus on risks of exposure of the general population. Hazards related to chemicals used in the workplace are defined within the Workplace Hazardous Materials Information System (WHMIS). If a substance is harmful to the general population, it could also be of concern for individuals in situations where a higher volume of the substance is used or where the substance is used for a longer duration (for example, the workplace). The Government of Canada recognizes that it is the responsibility of the federal, provincial and territorial occupational health and safety organizations to coordinate legislation for the safe use of chemicals in the workplace. We are working to support this role by integrating the information, tools, and technical expertise of the CMP and Health Canada's Workplace Hazardous Products Program.
