Benzothiazoles that can form 2-mercaptobenzothiazole - guidance for reporting to the National Pollutant Release Inventory

Background

According to Assessment - Benzotriazoles and benzothiazoles group, the substances in the benzothiazoles group have applications across sectors, including: 

• automotive products
• tire and rubber manufacturing industries
• metalworking fluids
• certain subsectors of the mining industry

Each substance in this group contains the 2-mercaptobenzothiazole (MBT) moiety, as a key molecular component. MBT may be released into the Canadian environment:  

• directly through its use
• indirectly due to the degradation of precursor compounds through pathways, such as:
  • hydrolysis
  • oxidation-reduction reactions
  • digestive processes
  • metabolic transformations under: 
    • environmentally relevant conditions
    • industrially relevant conditions
    • physiologically relevant conditions 

To align with the substance definition used in:

• Assessment - Benzotriazoles and benzothiazoles group  
• Risk management approach for 2-mercaptobenzothiazole (MBT) and its precursors (from the Benzotriazoles and Benzothiazoles Group)

the National Pollutant Release Inventory (NPRI) considers a group of 20 benzothiazole substances for reporting purposes. Facilities are to report these substances based on their MBT moiety content. Reporting requirements under the NPRI are structured to reflect the MBT moiety equivalent, focusing on the cumulative total of releases associated with all 20 substances in this group.

Reporting of benzothiazoles to the NPRI

Overview of NPRI listings for benzothiazoles

Starting in the 2025 reporting year, there were changes to the NPRI reporting requirements for benzothiazoles:

1. the individual listing for 2-mercaptobenzothiazole (MBT; Chemical Abstracts Services Registry Number [CAS RN] 149-30-4) was removed from Part 1A of the NPRI substance list
2. a group of 20 benzothiazoles (including MBT), listed in Table 1 below was added to Part 1B of the NPRI substance list with: 
   • a 100-kilogram manufacture, process, otherwise use (MPO) threshold
   •  a 0.1% concentration by weight threshold

The threshold for the group applies to the cumulative total of the 20 substances, rather than to each individual substance.

Threshold calculations

NA - 50 (Benzothiazoles that can form 2-mercaptobenzothiazole) is limited to 20 specific MBT containing substances identified by their CAS Registry Numbers (see Table 2).The NPRI lists NA - 50 under Part 1B of the substance list with an MPO threshold of 100 kg and a 0.1% concentration by weight threshold. The MPO threshold applies to the cumulative total of the group of substances, rather than to each individual substance. The MPO threshold includes all quantities:

• incidentally manufactured, processed or otherwise used:
  • at a concentration of at least 0.1%
  • as a by-product at any concentration
• present in tailings or in waste rock that is not considered clean or inert, regardless of concentration

When calculating if your facility meets the reporting threshold is met for NA - 50, you will need to calculate the equivalent weight (in terms of MBT) of each of the 20 benzothiazoles listed under the NPRI that is MPO’ed. This can be done using the molecular weight of MBT (167.24 g/mol) and the molecular weight of each of the 20 benzothiazoles. As a reference, Table 2 lists the molecular weights. This approach aligns with the assessment of the benzothiazoles group and ECCC risk management to manage the releases of benzothiazole substances based on the MBT moiety.

MBT Content refers to the mass fraction of MBT moiety units per molecule, calculated using the MBT molecular weight of 167.24 g/mol. Typical molecular structures contain either one or two MBT moiety units (based on ChemIDplus - PubChem Data Source).

The MBT mass fraction is defined as:

   

As UVCBs are variable mixtures, we cannot provide the MBT moiety mass fraction as a single precise number. To calculate this fraction, you should review the Safety Data Sheet and/or Technical Data Sheet.

To calculate the MPO quantities of NA - 50 expressed as MBT moiety, add the quantities of the substances multiplied by the MBT moiety applicable mass fraction from Table 2. The threshold applies to the cumulative total of the 20 substances, rather than to each individual substance.

The total quantity of MBT moiety manufactured, processed or otherwise used (MPO’ed) is estimated using the following equation and the mass fractions found in Table 2:

Where:

• "i" = one of the 20 substances comprising NA - 50 (A to T)
• MPO_{NA -50 (as MBT)} = the total quantity (kg/year) of MBT moiety MPO'ed
• MBT Mass Fraction_i = the MBT Mass Fraction of substance "i" (see Table 2)
• MPO_i = the annual quantity (kg/year) of substance "i" MPO'ed

Reporting of releases, disposals and transfers

Facilities are to report the releases, disposals and transfers of NA – 50 based on the cumulative total of the 20 substances rather than each individual substance:  

Where:

• "i" = one of the 20 substances comprising NA - 50 (A to T)
• Q_{NA -50 (as MBT)} = the total quantity (kg/year) of NA – 50, expressed as MBT, that was released, disposed of or transferred
• MBT Mass Fraction_i = the MBT Mass Fraction of substance "i" (see Table 2)
• Q_i = the quantity released, disposed of or transferred (kg/year) of substance "i"

Please note that for release/disposal/transfer quantities reported as MBT, the mass ratios used in the equation above may differ from the actual ratios for some of the 20 substances. This is because certain substances, such as CBS (CAS RN 95-33-0), can degrade into MBT and other compounds. This reduces the applicable theoretical mass ratio.

For further details, refer to:

• Assessment - Benzotriazoles and benzothiazoles group

If information is available on degradation and actual mass ratios for these substances when released to water, you should use it to replace the theoretical ratios in the equation above. 

If facilities in the rubber sector have none of the following:

• site‑specific measurements
• site‑specific emission factors
• other release data

they may apply an uncontrolled emission factor of 0.03%, where applicable. This factor represents a conservative estimate for releases to water and transfers to wastewater treatment facilities from rubber sector operations. This factor was used in the tire and general rubber goods generic exposure scenario in Assessment - Benzotriazoles and benzothiazoles group:

Where:

• R_Q_{NA - 50 (as MBT)} = the total quantity (kg/year) of NA – 50, expressed as MBT, that was released to water, or transferred to wastewater treatment facilities
• MPO_{NA - 50 (as MBT)} = the total quantity (kg/year) of MBT moiety MPO’ed

Bases of estimate you can use to report to NPRI

When a facility estimates the quantity of a substance:

• manufactured, processed or otherwise used
• released, disposed of or transferred for recycling

they can use one of the following methods:

• continuous emission monitoring systems (reporting system code M1)
• predictive emission monitoring (M2)
• source testing (M3)
• remote quantification (RQ)
• mass balance (C)
• site-specific emission factor (E1)
• published emission factor (E2)
• speciation profile (SP)
• engineering estimates (O)

For NPRI reporting purposes, if emissions are already monitored or measured under provincial or federal legislation or a municipal bylaw, those measurements must be used to report to the NPRI. However, all releases, disposals or transfers off site for recycling must be included in threshold calculations and reported, unless otherwise specified, not just those that are measured or monitored. An NPRI report is mandatory for any substances that meet the reporting thresholds, regardless of whether the substance is being measured or monitored for other jurisdictions. If emissions are not monitored or measured under provincial or federal legislation or a municipal bylaw, reasonable efforts must still be undertaken to gather information on releases, disposals and transfers of a substance.

What is “reasonable” depends on individual circumstances but may include additional monitoring for NPRI substances. In deciding whether additional efforts should be undertaken to generate new information for the purposes of NPRI reporting, the following factors, among others, should be considered:

• the health and environmental risks posed by a substance, including whether the substance has been declared toxic under CEPA
• the relative contribution of the industrial sector to releases, disposals and transfers for recycling of a substance in Canada
• the relative contribution of the facility to releases, disposals and transfers for recycling of a substance in Canada
• the cost of additional monitoring