Introduction

The Canadian Environmental Protection Act, 1999 (CEPA 1999) requires the Minister of the Environment and the Minister of Health to conduct screening assessments of substances that meet the categorization criteria set out in the Act and Regulations to determine, in an expeditious manner, whether substances present or may present a risk to the environment or to human health. Based on the results of a screening assessment, the Ministers can propose taking no further action with respect to the substance, adding the substance to the Priority Substances List (PSL) for further assessment or recommending that the substance be added to the List of Toxic Substances in Schedule 1 and, where applicable, the implementation of virtual elimination.

A screening assessment involves an evaluation of a substance to determine whether the substance is “toxic” or capable of becoming “toxic” as defined in CEPA 1999. This ecological screening assessment examines various supporting information and develops conclusions based on a weight of evidence approach as specified under Section 76.1 of CEPA 1999. The screening assessment report does not present an exhaustive review of all available data; rather, it presents the most critical studies and lines of evidence supporting the conclusions. One line of evidence includes consideration of risk quotients to identify potential for ecological effects. However, other concerns that affect current or potential risk, such as persistence, bioaccumulation, chemical transformation and trends in ambient concentrations, are also considered.

4,6-Dinitro-o-cresol (DNOC) was included in a pilot project of 123 substances for screening assessment under CEPA 1999, on the basis of its anticipated high potential for human exposure. DNOC is also considered to be persistent and inherently toxic to aquatic organisms.

Data relevant to the ecological screening assessment of DNOC were identified in original literature, review documents and commercial and government databases. Searches were conducted of the open literature, conference proceedings and the Internet for relevant information. Data obtained as of August 2004 were considered in this document. Original studies that form the basis for determining whether the substance is “toxic” under CEPA 1999 have been critically evaluated by Environment Canada. The data from key toxicity studies were evaluated using Robust Study Summary forms similar to those recommended by the Organisation for Economic Co-operation and Development for the evaluation of studies for the Screening Information Data Sets of high production volume substances (OECD, 2003).

This ecological screening assessment report and associated unpublished supporting working documentation were written by Environment Canada evaluators under the lead of Barbara Elliott. The substance matter in this report has been subjected to a science review by individuals having relevant technical expertise, including Pierrette Blanchard (Meteorological Service of Canada, Environment Canada), Mark McMaster (National Water Research Institute, Environment Canada) and Suzanne Lesage (National Water Research Institute, Environment Canada).

The conclusions of the ecological and human health screening assessment reports were approved by the joint Environment Canada/Health Canada CEPA Management Committee. The supporting working documentation for the ecological assessment is available upon request by e-mail from existing.substances.existantes@ec.gc.ca. The supporting working documentation for the human health assessment is available upon request by e-mail from ExSD@hc-sc.gc.ca. Information on ecological and human health screening assessments under CEPA 1999 may be linked from the CEPA Registry.

The critical information and considerations upon which the assessment is based are summarized below.