Environmental emergency planning: BNST risk evaluation  

Benzenamine, N-phenyl-, reaction products with styrene and 2,4,4-trimethylpentene (BNST)(CAS No. 68921-45-9)

Risk Evaluation Conclusion:

  • Threshold Quantity of 0.22 tonnes (concentration 10%) due to aquatic toxicity
  • Is a candidate for the Environmental Emergency Regulations

1.0  Introduction

The Environmental Emergency Regulations, developed under Part 8 of the Canadian Environmental Protection Act (CEPA), 1999 (Government of Canada, 2011), establish a list of substances for which fixed facilities must notify Environment Canada that they store or use the substance on-site, by providing notices to Environment Canada, reporting when the substance is released into the environment, and developing an environmental emergency plan (E2 plan) for each substance stored or used at a fixed facility at or above specified threshold quantities. 

To determine if a substance is a candidate to be added to the Environmental Emergency Regulations, Environment Canada has developed a risk evaluation methodology based on the following hazard categories:

  • Physical: flammable and combustible or oxidizing substances, or those having a potential to cause vapour cloud explosions or pool fires.
  • Human Health: substances that are toxic by inhalation, are carcinogenic, or are corrosive.
  • Environmental Health: substances that are: corrosive, persistent, bioaccumulative, or aquatically toxic.

For more information on the methodology for setting threshold quantities in the Environmental Emergency Regulations, please refer to Environment Canada (2014).

BNST (CAS No. 68921-45-9) was selected for risk evaluation because it is a substance (under the Government of Canada’s Chemicals Management Plan) that, if spilled, could be immediately harmful to humans and/or the environment.

Following the risk evaluation, Environment Canada recommends that this substance be proposed for addition to Schedule 1 of the Environmental Emergency Regulations at a threshold quantity of 0.22 tonnes.

2.0  Summary of the Risk Evaluation

2.1 Physical Hazard: Flammable, Combustible or Oxidizing Substances

Because BNST has a flash point of 176°C (MSDS, 2007), and has a boiling point of 361.98°C (Government of Canada, 2009), this substance does not present the possibility of a vapour cloud explosion.Therefore, no threshold is set for this substance as a result of its potential for flammability or combustibility.

2.2 Physical Hazard: Potential for Pool Fires

BNST has not been modeled for pool fire risks and it is not known whether it is capable of causing a pool fire.

2.3 Human Health Hazard: Inhalation Toxicity

Because BNST does not have a vapour pressure greater than 10 mmHg (1.33 kPa) at 25°C (Government of Canada, 2009), the substance does not have sufficient volatility to constitute an inhalation danger.

Therefore, no threshold is set for the inhalation toxicity to humans.

2.4 Human Health Hazard: Carcinogenicity

Because BNST is not classified in any group of International Agency for Research on Cancer (IARC, 2014) or the U.S. EPA (2005), and because the substance does not have a half-life longer than five years in any medium, no threshold is set for the carcinogenicity of this substance.

2.5 Human and Environmental Health Hazard: Corrosive Substances

The measured pH is greater than 2 and less than 11.5, therefore the substance is not considered corrosive and there is no associated threshold with this category.

2.6 Environmental Health Hazard: Persistent, Bioaccumulative, or Aquatically Toxic

Lethal concentration

The acute (short-term) aquatic toxicity for BNST has been determined to be extremely toxic based on modelingwith a lethal concentration (LC50 96 hours) of 0.06 mg/L (OASIS, 2005).


BNST is classified as beinghighly persistent in water.


BNST is extremely bioaccumulative.


Following the evaluation of the aquatic toxicity, the threshold is set at 0.22 tonnes.

2.7 Assigned Threshold

Following the risk evaluation methodology developed under section 200 of CEPA 1999, the categories (flammability, combustibility, oxidizers, inhalation toxicity, aquatic toxicity, carcinogenicity, corrosiveness, pool fires) having the lowest scientific threshold will be compared against other risk management considerations. For example, the threshold will be compared to other provincial and federal legislation or voluntary programs that may already provide adequate management of the risk from an environmental emergency. Proposed thresholds may also be modified based on policy and other considerations as assessed during the preliminary public consultation period. For more information regarding the determination of thresholds, please refer to the Implementation Guidelines for the Environmental Emergency Regulations 2011 (Environment Canada, 2011).

Other Considerations

The Prohibition of Certain Toxic Substances Regulations (Government of Canada, 2012) lists BNST as having permitted uses as an additive in rubber (except in tires), and an additive in lubricants.  The regulation does not restrict the quantities in commerce, therefore BNST is still being recommended for addition to the Environmental Emergency Regulations.

At this time, there are no other considerations to take into account for this substance that would result in an increase or a decrease in the calculated threshold quantity.


A proposed threshold of 0.22 tonnes is assigned for BNST based on its assessed aquatic toxicity.  The threshold quantity and its respective concentration will not be finalized until after preliminary public consultation.

3.0 Conclusion

Information concerning the quantities of BNST (CAS No. 68921-45-9) in use in Canada indicates that the substance exists in commerce. Following the risk of BNST and taking into consideration the quantities in use in Canada, Environment Canada recommends that this substance be proposed for addition to Schedule 1 of the Environmental Emergency Regulations under CEPA 1999 at a threshold quantity of 0.22 tonnes at a concentration of 10%. 

When doing the emergency planning of a substance, it is important to take into consideration not only the most stringent assigned threshold quantity, but all of the other higher-threshold quantities that are noted in association with this substance. 

Even if the quantity of a substance in use is below the threshold quantity indicated in the Environmental Emergency Regulations, Environment Canada recommends that emergency planning be applied to this substance in order to minimize, or prevent, any impacts on humans or the environment in the event of a release of the substance.

4.0 References

Environment Canada. 2011. Implementation Guidelines for the Environmental Emergency Regulations 2011. 100 p.

Environment Canada. 2014. Summary of Risk Evaluation Framework for Determining Quantity Thresholds and Concentrations for Substances under the Environmental Emergency Regulations Set under the Canadian Environmental Protection Act, 1999 (CEPA 1999). Environment Canada.

Government of Canada, 2009. Environment Canada, Health Canada. Final Screening Assessment for the Challenge. Benzenamine, N-phenyl-, Reaction Products with Styrene and 2,4,4-Trimethylpentene (CAS RN 68921-45-9).

Government of Canada. 2011. Environmental Emergency Regulations, Canadian Environmental Protection Act, 1999. Environment Canada. Registered on December 8, 2011.

Government of Canada. 2012. Prohibition of Certain Toxic Substances Regulations, 2012 (SOR/2012-285). Canadian Environmental Protection Act, 1999. Environment Canada.

IARC (International Agency for Research on Cancer). 2014. IARC Monographs Database on Cancer Risks to Humans. International Agency for Research on Cancer, World Health Organization.

MSDS (Material Safety Data Sheets). 2007. Benzenamine, N-phenyl-, reaction products with styrene and 2,4,4-trimethylpentene. 2007. R.T. Vanderbilt Company, Inc.

OASIS (Optimized Approach based on Structural Indices Set). 2005. Version 1.20. Bourgas, BG, Bourgas, A. Zlatarov University. Laboratory of Mathematical Chemistry.

U.S. EPA (United States Environmental Protection Agency). 2005. Guidelines for Carcinogenic Risk Assessment.

5.0 Further Reading

Ketcheson K, Shrives J. 2010. Comparison of Threshold Quantities for Substances with Final AEGL-2 and IDLH Values under CEPA’s Environmental Emergency Regulations. In: Proceedings of the Thirty-third Arctic and Marine Oilspill Program Technical Seminar on Environmental Contamination and Response. Environment Canada: Ottawa (ON). pp. 843-861.

U.S. EPA (U.S. Environmental Protection Agency). 1994. List of Regulated Toxic and Flammable Substances and Thresholds for Accidental Release Prevention. Federal Register, 59(20). Document Number 94-1556. 31. Washington (DC).

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