Proposed Adoption of the Interim Canadian Water Quality Guideline for the Nitrate Ion as a Provincial Water Quality Objective

This notice was originally posted in the old Environmental Registry under number PA06E0004.

Description of policy

The Interim Canadian Water Quality Guideline (CWQG) for the Protection of Aquatic Life for the Nitrate Ion was published by the Canadian Council of Ministers of the Environment (CCME) in 2003. Available information on the physical-chemical properties, aquatic toxicity, and environmental persistence were considered in developing the guidelines.

Nitrate occurs naturally in the environment and is constantly being produced and consumed through the processes of the nitrogen cycle. Nitrate is also produced through various commercial activities such as the production of industrial materials and chemicals (e.g. plastics and explosives), as well as in the formulation of fertilizers. Significant anthropogenic sources of nitrate input to surface waters include agricultural runoff, municipal and industrial wastewaters, and precipitation of nitrogen compounds from vehicular exhaust.

Nitrate has wide-ranging effects in invertebrates, fish and amphibians, with larval stages generally showing greater sensitivity than adults. Adverse effects observed in aquatic organisms include: mortality, growth reduction, reduced feeding rates, reduced fecundity, reduced hatching success, lethargy, behavioural signs of stress, bent spines and other physical deformities.

The CWQG for nitrate was derived from toxicity data according to the CCME water quality guideline development protocol which is consistent with Ontario's Water Quality Objective Development Process. There is no current Provincial Water Quality Objective for nitrate. The proposed Provincial Water Quality Objective for the Nitrate Ion is 13 milligrams nitrate per litre (2.9 milligrams nitrate-nitrogen per litre).

Provincial Water Quality Objectives (PWQOs) are maximum desirable concentrations of chemicals which ensure that surface waters are satisfactory for aquatic life and recreation. They are developed with a margin of safety to protect the most sensitive aquatic life-stage of an organism for an indefinite exposure. Technical feasibility and economics are not considered during the standard development, but are considered on a case-by-case basis in the Ministry's approval process for individual discharges. Most objectives are adopted or developed in partnership through the national Canadian Water Quality Guideline Task Group which reports to the Canadian Council of Ministers of the Environment (CCME).

Contaminants that impair the aquatic environment are an important environmental concern. Provincial Water Quality Objectives are used to assist in managing these contaminants. The policies and procedures which govern their uses are contained in the booklet - Water Management (1994) - which deals with all aspects of Ontario's water management policy. PWQOs are used to: i) classify receiving waters for water management purposes; ii) assess contaminant discharges to the aquatic environment; and iii) derive water quality-based effluent limits which may be included in Certificates of Approval which are issued to regulate effluent discharges. PWQOs are not the only consideration in controlling discharges.

Purpose of policy

The ministry is proposing to add a surface water quality standard for nitrate through adoption of the approved CCME Interim Canadian Water Quality Guideline. This notice seeks comments on the proposed adoption. Comments received will be evaluated and considered in finalizing the PWQOs.