Proposed Adoption of the Canadian Water Quality Guideline for Mercury as a Provincial Water Quality Objective and the Interim Canadian Water Quality Guideline for Methylmercury as an Interim Provincial Water Quality Objective

This notice was originally posted in the old Environmental Registry under number PA05E0002.

Description of policy

The Canadian Water Quality Guideline (CWQG) for the Protection of Aquatic Life for mercury and the interim CWQG for methylmercury 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.

Mercury (Hg) occurs naturally, but significant amounts enter ecosystems through anthropogenic emissions, re-emissions and discharges. Natural sources of mercury include geological mercury deposits, rock weathering, forest fires and other wood burning, faults/volcanoes (land-based and oceanic), hotsprings and a portion of the volatilization from the oceans. The primary anthropogenic sources of Hg in Canada include: metal smelting; coal-burning power plants; municipal waste incineration; sewage and hospital waste incineration; coal and other fossil fuel combustion; cement manufacturing; and, mercury waste in landfills or storage.

Typically, methylmercury (MeHg) represents less than 10% of the total Hg in surface waters, but can exceed 30% in perturbed systems such as newly formed reservoirs. In natural surface waters, concentrations of total mercury range from 1 to 20 nanograms per litre (ng/L), while concentrations of MeHg are usually less than 1 ng/L. Methylmercury is of special concern not only because of its toxicity, but also because of its tendency to biomagnify in upper trophic levels of aquatic food webs. 1,000 ng = 1 microgram and 1,000,000 micrograms = 1 gram.

Acute toxicity concentrations for inorganic mercury range from 5 to 566 ug Hg/L in invertebrates and from 150 to 900 ug Hg/L in fish. An LC50 is a calculated concentration of a substance that would be lethal to 50% of the tested organisms (e.g. trout) based on a laboratory experiment. Algae appear more sensitive with 24h-LC50s ranging from 9 to 27 micrograms Hg/L. Chronic toxicity concentrations in invertebrates range from 1.28 to 12.0 ug Hg/L, and for fish range from 0.26 to >64 ug Hg/L. Adverse effects reported include reduced growth, impaired reproduction and development, and death. Acute toxicity concentrations from methylmercury ranged from 25 to 125 ug Hg/L in fish and from 3.5 to 6.3 ug Hg/L in algae (no invertebrate data was available). In chronic tests, effects occurred at concentrations ranging from 0.04 to 1.1.4 ug Hg/L in fish.

The current Provincial Water Quality Objective for mercury is 200 n/L (in a filtered water sample), there is no current Provincial Water Quality Objective for methylmercury. The CWQG for mercury and the interim CWQG for methylmercury were derived from toxicity data according to the CCME water quality guideline development protocol which is consistent with Ontario's Water Quality Objective Development Process. The proposed Provincial Water Quality Objective (PWQO) for mercury is 26 ng/L, and the proposed Interim Provincial Water Quality Objective (iPWQO) for methylmercury is 4 ng/L. These values were developed by selecting the lowest measurable chronic study and applying a 10-fold safety factor.

Provincial Water Quality Objectives (PWQOs) and Interim Provincial Water Quality Objectives (iPWQO) 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), however, PWQOs may be developed by the Ontario Ministry of the Environment if there is a provincial need.

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:

1. classify receiving waters for water management purposes
2. assess contaminant discharges to the aquatic environment
3. 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 the surface water quality standards for mercury and methylmercury through adoption of the approved Canadian Council of Ministers of the Environment (CCME) Canadian Water Quality Guidelines. This notice seeks comments on the proposed adoption. Comments received will be evaluated and considered in finalizing the Provincial Water Quality Objective (PWQO) and Interim Provincial Water Quality Objective (iPWQO).