Print | Need Larger Text? | Share

Health-Based Guidance Values for Substances on the Second Priority Substances List

1. Introduction

The Canadian Environmental Protection Act, 1999 (CEPA 1999) authorizes the Ministers of the Environment and Health to investigate a wide variety of substances that may contaminate the environment and cause adverse effects on the environment and/or on human health. Under the Act, assessments were completed in 2000 for the 25 environmental contaminants (or groups thereof) on the second Priority Substances List (PSL2).

Based on the assessments conducted for PSL2 substances, health-based Tolerable Intakes/Concentrations (TIs/TCs) and Tumorigenic Dose₀₅s/Concentration05s (TD₀₅s/TC₀₅s) have been developed and are presented herein.

Information on the classification of the weight of evidence of carcinogenicity, the nature of the critical effects, the critical study and the size of the uncertainty factor incorporated for non-neoplastic effects for each substance is included in the respective Assessment Report, available on request from:

• Existing Substances Division
  Environmental Contaminants Bureau
  Safe Environments Programme
  Health Canada
  Environmental Health Centre
  room 145
  Tunney's Pasture
  Postal Locator: 0801C2
  Ottawa, ON K1A 0L2
  
  Email: ExSD@hc-sc.gc.ca
  
  

Synopses of the Assessment Reports are currently available on-line at http://www.hc-sc.gc.ca/hecs-sesc/exsd/psl2.htm, whereas the full  Assessment Reports will soon be available on the Internet at http://www.ec.gc.ca/substances/ese/eng/psap/final/main.cfm. A detailed description of the approach to human health risk assessment for Priority Substances is included in Health Canada (1994), available on-line at http://www.hc-sc.gc.ca/hecs-sesc/exsd/pdf/approach.pdf.

Guidance values developed herein are based on lifetime exposure, and short-term excursions above these values do not necessarily imply that exposure constitutes an undue risk to health. The amount by which and period for which TCs/TIs can be exceeded without posing a health risk must be considered on a case-by-case basis, taking into account the nature of the effects of the specific substance.

For carcinogenic effects for which the weight of evidence indicates that the mode of action involves direct interaction with genetic material, it is assumed that there is some probability of harm to human health at any level of exposure and that continuing efforts should be made, therefore, to reduce exposure to such compounds by the greatest extent possible. However, incremental risks associated with exposure to low levels of such substances (i.e., TD₀₅s/TC₀₅s divided by a suitable margin) may be sufficiently small so as to be essentially negligible compared with other risks encountered in society.

Presentation of the guidance values herein should not be regarded as implying that the quality of various media may be degraded to specified levels. Indeed, continuous efforts should be made to ensure that the media through which humans are exposed are of the highest possible quality.

Information on uncertainties in the data that served as the basis for the development of TIs/TCs and TD₀₅s/TC₀₅s is presented in the relevant tables. This information is relevant to the characterization of the degree of confidence in and flexibility in application of derived guidance values.