The risk posed by a substance is determined by considering both its hazardous properties (its potential to cause adverse human health or ecological effects) and the amount of exposure there is to people and the environment.
As a result of the draft screening assessment, the Government is proposing that 2-mercaptobenzothiazole (MBT) and its precursors, including the six substances in the benzothiazoles subgroup, may be harmful to the environment due to their releases from the sectors of concern identified in the draft screening assessment. In addition, the Government is proposing that the 15 substances in the Benzotriazoles and Benzothiazoles Group are not harmful to human health at current levels of exposure. Although the six substances in the Benzothiazoles subgroup are associated with health effects of concern, the risk to human health is low at levels of exposure considered in the assessment.
Also, the Government has released the Risk Management Scope for MBT and its Precursors to initiate discussions with stakeholders on the development of risk management options.
About these substances
The screening assessment focuses on 15 of 17 substances referred to collectively as the Benzotriazoles and Benzothiazoles Group under the Chemicals Management Plan (CMP). The 15 substances addressed in this screening 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).
Substances in the benzotriazoles subgroup are used in cosmetics, food packaging, and lubricants and greases. Some of these substances are also used as UV light stabilizers and corrosion inhibitors.
Substances in the benzothiazoles subgroup have major uses in automotive products, rubber products, lubricants and greases, and mining.
The MBT moiety was identified as the key part of the molecule in the benzothiazoles subgroup, which may be released to the Canadian environment based either on direct use and release of MBT, or through indirect release due 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.
Human and ecological exposures
Canadians may be exposed to these substances from drinking water, indoor air, eating certain fish and seafood, breast 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).
Canadians are not expected to be exposed to UV-320.
According to the information considered under the ERC Approach, the 9 substances in the benzotriazoles subgroup were identified as having low ecological exposure potential.
Canadians 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 rubber product manufacturing from the automotive industry (tires and other rubber products).
Indirect releases to soil from wastewater treatment systems are a possibility.
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 draft screening 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 body and 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 potential ecotoxicity and potential to accumulate in aquatic organisms.
Risk assessment outcomes
Based upon a comparison of levels to which Canadians 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 substances in the benzotriazoles subgroup are considered unlikely to be causing ecological harm.
Considering all information presented in the draft screening assessment, it was determined that there may be risk of harm to the environment from MBT and its precursors, including the substances in the benzothiazoles subgroup.
As a result of the draft screening assessment, the Government is proposing 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 is also proposing that MBT and its precursors, including the six substances in the benzothiazoles subgroup, are entering the environment at concentrations that may be harmful to the environment. It is also proposed that the nine substances in the benzotriazoles subgroup are not harmful to the environment at levels considered in the assessment.
Also, it is proposed that MBT meets the persistence criteria, but not the bioaccumulation criteria as set out in the Persistence and Bioaccumulation Regulations of CEPA 1999. The remainder of the substances in the benzothiazoles subgroup do not meet the persistence and bioaccumulation criteria as set out in the Persistence and Bioaccumulation Regulations of CEPA 1999.
If the proposed conclusions are confirmed in the final screening assessment, the Government will consider adding MBT and its precursors to Schedule 1 of CEPA 1999, also called the List of Toxic Substances. Adding a substance to the list does not restrict its use, manufacture or import. Rather, it enables the Government to take risk management actions under CEPA 1999.
The Government will also consider the following actions to address ecological concerns:
Implementation of certain risk management instruments, such as, but not limited to: regulations, environmental release guidelines, codes of practice, environmental performance agreements, pollution prevention planning notices, and environmental labelling, to minimize the release of the MBT moiety to water bodies from the industrial use of MBT and its precursors.
The main industrial sectors with exposures of concern for the environment are the tire and other rubber products manufacturing sector, the metalworking fluids sector, and some subsectors of the mining industry.
Information is being sought by the Government to inform risk management decision-making. Details can be found in the risk management scope, including where to send information during the public comment period, ending May 5, 2021.
Risk management actions may evolve based on the conclusions of the final screening assessment, or as a result of risk management actions published for other substances. This is to ensure effective, coordinated, and consistent risk management decision-making.
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 if exposures to these substances were to increase. For this reason, follow-up activities to track changes in exposure to these substances are being considered.
The information collected to inform the risk management options of these substances may help inform the choice of follow-up activity to track changes in human exposure.
MBT and its precursors may be found in products available to consumers. Canadians should follow any safety warnings and directions related to the product and dispose of products responsibly.