Summary of Risk Assessment Conducted Pursuant to subsection 83(1) of the Canadian Environmental Protection Act, 1999

Significant New Activity Notification: 1,4-Benzenediol, (Hydroquinone) Chemical Abstracts Service Registry Number 123-31-9

Health Canada & Environment and Climate Change Canada

September 2016


1,4-Benzenediol, Chemical Abstracts Service Registry Number (CAS RN) 123-31-9 (hydroquinone), was identified during the categorization of the Domestic Substances List as a high priority for assessment. It underwent a screening assessment in Batch 1 of the Challenge (Canada 2008a), which was followed by a proposed Risk Management Approach document on July 5, 2008 (Canada 2008b). In the screening assessment, it was concluded that hydroquinone met the criteria of section 64(c) of the Canadian Environmental Protection Act, 1999 (CEPA), meaning that it is a substance which is entering or may enter the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health (Canada 1999). It was added to Schedule 1 of CEPA on May 12, 2010 (Canada 2010).

The risk management objective identified in the proposed Risk Management Approach document was to reduce exposure to the substance. The risk management actions proposed for hydroquinone included:

  • a provision to notify the federal government, for the purpose of assessment, of certain proposed manufacture, import, or use of hydroquinone above a quantity threshold, through the Significant New Activity provisions under CEPA (Canada 2011);
  • the requirement of appropriate short-term exposure labelling for photographic chemicals purchased at retail, in accordance with the Consumer Chemicals and Containers Regulations, 2001;
  • further restrictions on the use of hydroquinone in hair dyes and artificial nail systems through amendments to the Cosmetic Ingredient Hotlist; and
  • the addition of natural health products containing hydroquinone at any concentration, except when in natural substances (e.g. plant materials), to the Prescription Drug List (PDL), so that they can be regulated as prescription drugs.

Substance Identity

The substance is a chemical that can be classified as a phenol.

Significant New Activity Notification

In October 2015, the Government of Canada received a Significant New Activity Notification (SNAN) for a new activity involving hydroquinone. The notifier proposed to purchase, through a Canadian importer, up to 200 kg of hydroquinone in its pure form in order to formulate a polycarboxylate ether (PCE), which is used downstream in the formulation of ready-to-use mixes and prefabricated concrete products. According to the notification, the concentration of hydroquinone in PCE would be 50 mg/kg. The PCE is then sold to cement manufacturers where it is added to cement formulations at a concentration ranging from 0.0025–0.22% (1–100 µg/kg).

Environmental Fate and Behaviour

The environmental fate and behaviour of the substance was described in the original screening assessment report (Canada 2008). The substance is not volatile (vapour pressure of 2.3×10-3 Pa) and is very water soluble (73 g/L). The log Kow was reported to be 0.59. It is not expected to be adsorptive and is considered to be moderately mobile in the environment based on the log Koc of 2.64. The substance was reported to be readily biodegradable in water and is not considered persistent in environmental media, as defined by the Persistence and Bioaccumulation Regulations (Canada 2000).

Ecological Assessment

Based on experimental ecological data, the substance poses a high hazard to fish and daphnia at low concentrations (LC50 and EC50 values < 1 mg/L) and a moderate hazard to algae (EC50 values < 20 mg/L). However, given the low use volumes and negligible exposure pathways resulting from the notified activity, low exposure is expected.

Given the ecotoxicological and release profiles, the use of the substance as proposed in the notification does not pose a risk to the environment, and therefore is not likely to cause ecological harm in Canada.

Human Health Assessment

Based on the information provided in the SNAN and existing labelling present on all cement packaging pertaining to use of personal protective equipment, no significant anticipated exposure to the general population that would occur as a result of this notified use. Consequently, it has been concluded that the notified use of the substance is not likely to pose a significant risk to the general population, and is therefore not likely to be harmful to human health.

Assessment Conclusion

No information received in this notification puts into question the prior determination that the substance meets the criteria set out under section 64(c) of CEPA. However, when used as notified, use of the substance to formulate a polycarboxylate ether (PCE) is not likely to present a significant risk to human health or the environment.

Risk Management

Based on the information provided in the notification, and the risk assessment analysis, this activity does not result in an increase in exposure to the general public and does not pose an additional risk to human health. Additionally, the substance does not pose an ecological risk. Therefore, no additional risk management is recommended for hydroquinone.

As no specific concerns have been identified for this activity, the government is considering amending the existing SNAc requirements in relation to hydroquinone to target only the use(s) of the substance that may result in potential exposure(s) of concern. However, the current Order remains in force until an amended order is registered and published in the Canada Gazette, Part II.


Canada. 1999. Canadian Environmental Protection Act, 1999. S.C. 1999, c.33, Canada Gazette Part III, vol. 22, no. 3.

Canada. 2000. Canadian Environmental Protection Act, 1999: Persistence and Bioaccumulation Regulations. P.C. 2000-348, 29 March, 2000, SOR/2000-107.

Canada. 2008a. Screening assessment for the Challenge: 1,4‑Benzenediol (hydroquinone): Chemical Abstracts Service Registry Number 123‑31‑9.

Canada. 2008b. Proposed Risk Management Approach for 1,4-Benzenediol (Hydroquinone), Chemical Abstracts Service Registry Number (CAS RN) 123‑31‑9.

Canada. 2010. Order adding a toxic substance to schedule 1 to the Canadian Environmental Protection Act, 1999. SOR/2010-98. Canada Gazette, Part II, vol. 144, no. 10, May 12, 2010 (portable document format, 3.9 megabytes).

Canada. 2011. Order 2011-87-12-01 Amending the Domestic Substances List, Canadian Environmental Protection Act, 1999. SOR/2011-293. Canada Gazette, Part II, vol. 145, no. 26, December 21, 2011.

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