Thiocarbamates Group - information sheet

Thioperoxydicarbonic diamide ([(H2N)C(S)]2S2), tetramethyl- (TMTD, also referred to as Thiram or Thiuram)
CAS Registry Number 137-26-8

Piperidine, 1, 1'-(tetrathiodicarbonothioyl)bis- (DPTT)
CAS Registry Number 120-54-7

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Overview

  • The Government of Canada conducted a science-based screening assessment under the Canadian Environmental Protection Act, 1999 (CEPA 1999) to address the potential for harm to Canadians and the environment from 2 substances (TMTD and DPTT), referred to as the Thiocarbamates Group. The screening assessment focused on non-pesticidal uses.
  • Under CEPA 1999 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 or the environment.
  • As a result of the screening assessment, the Government concluded that TMTD is harmful to the environment but not to human health, based on exposures from non-pesticidal uses considered in the assessment. Although TMTD is associated with human health effects of concern, the risk is considered low at levels of exposure considered in the assessment. It was also concluded that DPTT is not harmful to human health or to the environment, as the risk posed by this substance is low at levels of exposure considered in the assessment.

About these substances

  • The screening assessment focused on 2 substances: thioperoxydicarbonic diamide ([(H2N)C(S)]2S2), tetramethyl- and piperidine, 1,1'-(tetrathiodicarbonothioyl)bis-, also referred to as TMTD (or thiram) and DPTT, respectively. They were assessed under the third phase of the Chemicals Management Plan (CMP).
  • According to information gathered by the Government, TMTD and DPTT are industrial chemicals that do not occur naturally in the environment.
  • In Canada, TMTD is primarily used as a process regulator (accelerator and curing agent) in the manufacture of solid rubber products. It is used as a component in automotive parts, in sealants and adhesives, and in the manufacture of a limited number of food packaging materials.
  • TMTD is also registered as an active ingredient in pest control products in Canada, under the name thiram. Health Canada’s Pest Management Regulatory Agency (PMRA) final re-evaluation decision for thiram included a risk assessment and risk mitigation measures to protect human health and the environment from pesticidal uses of TMTD, under the authority of the Pest Control Products Act. Therefore, exposures to TMTD resulting from pesticidal sources and uses of thiram are not characterized further in the screening assessment summarized here.
  • In Canada, DPTT is only used in the manufacture of rubber products.

Human and ecological exposures

  • Exposure of Canadians to TMTD from products available to consumers (for example, rubber products, adhesive tape products, automotive parts), or from food packaging materials, is minimal or not expected.
  • The human health risk of DPTT was characterized using the Threshold of Toxicological Concern (TTC)-based Approach for Certain Substances. The estimate of exposure generated for DPTT was lower than the TTC value, indicating low concern to human health on the basis of current levels of exposure.
  • TMTD and DPTT have the potential to be released to the environment through discharges from wastewater treatment systems associated with manufacturing facilities for solid rubber products. Such releases are likely to result in exposure to aquatic organisms near points of release.

Key health and ecological effects (hazard)

  • To identify human health and ecological effects information, national and international reports on TMTD were reviewed and used to inform the screening assessment. This includes the PMRA’s review of thiram as well as reviews of TMTD internationally through the Organisation for Economic Cooperation and Development Cooperative Chemicals Assessment Programme and the European Chemicals Agency, among others.
  • The health effects of concern identified for TMTD include developmental neurotoxicity and carcinogenicity (potential to cause cancer).
  • Empirical data suggest that TMTD is highly toxic to aquatic organisms.
  • There were limited ecological effects (hazard) data for DPTT; therefore, a comparative approach using a similar chemical, called read-across, was used to inform the ecological assessment. Based on the read-across data, DPTT is not expected to demonstrate any effect on aquatic organisms at water solubility limits.

Risk assessment outcomes

  • Using the Threshold of Toxicological Concern (TTC)-based Approach for Certain Substances, DPTT is considered to be a low concern for human health at levels of exposure current at the time of the assessment.
  • Considering all information presented in the screening assessment, there is low risk of harm to the environment from DPTT.
  • Based on the information presented in the screening assessment, the risk to human health from non-pesticidal uses of TMTD is low.
  • Although TMTD is not expected to remain in the environment for a long time or to accumulate in organisms, it is highly toxic to aquatic organisms. Exposure associated with uses of this substance considered in the assessment poses a risk of harm to the environment.
  • The Government of Canada published the Final Screening Assessment for the Thiocarbamates Group on January 9, 2021.

Screening assessment conclusions

  • The Government concluded that TMTD is not harmful to human health at levels of exposure considered in the assessment.
  • However, the Government concluded that TMTD is entering or may enter the environment at levels that are harmful to the environment, from its uses in the manufacture of rubber products.
  • The Government also concluded that DPTT is not harmful to human health at levels of exposure considered in the assessment, and is not entering the environment at levels that are harmful to the environment.
  • It was also determined that TMTD does not meet the persistence or bioaccumulation criteria as set out in the Persistence and Bioaccumulation Regulations of CEPA 1999.

Preventive actions and reducing risk

  • The Government of Canada published the proposed Risk Management Approach for TMTD on January 9, 2021. The public is invited to comment on this document during the 60-day public comment period ending on March 10, 2021.
  • The Government intends to add TMTD to Schedule 1, also called the List of Toxic Substances, of CEPA 1999. Adding a substance to the List of Toxic Substances does not restrict its use, manufacture or import. Rather, it enables the Government to take risk management actions under CEPA 1999.
  • The Government is considering the following actions to address ecological concerns:
    • Implementing a code of practice under section 54 of CEPA 1999 in order to reduce releases of TMTD from its use in the rubber products manufacturing sector, and
    • Applying the Significant New Activity (SNAc) provisions of CEPA 1999 to require that the Government be notified of new manufacturing activities related to TMTD. The new activity would then be assessed for potential risks to human health and the environment before being undertaken.
    • Additionally, regulatory and non-regulatory instruments (for example, Environmental Performance Agreements (EPAs), pollution prevention planning notices, as examples), which could include use thresholds and release limits, are being investigated as part of a sector-wide approach.
  • Information is being sought by the Government to 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 January 27, 2021.
  • Benzothiazoles, such as 2-mercaptobenzothiazole (MBT), may be used as alternatives to TMTD in certain applications. This group of chemicals is currently under assessment under the CMP. Depending on the outcome of the screening assessment, benzothiazoles may not be considered suitable alternatives. For more information regarding alternatives, please consult section 6.1 of the proposed Risk Management Approach for TMTD.
  • Information on the risk management of substances addressed under the CMP is available.

Additional considerations

  • Although TMTD is not considered to be harmful to human health at levels of exposure from non-pesticidal uses at the time of the assessment, this substance is recognized as having potential effects of concern (developmental neurotoxicity and potential to cause cancer). Therefore, there may be a concern if exposures were to increase.
  • For these reasons, additional tracking of TMTD for changes in exposure are being proposed. For example, information gathering using the Domestic Substances List inventory update mechanism may be used to track changes in exposure and/or commercial use patterns for TMTD.

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