Proposed Interim Provincial Water Quality Objectives for Methoprene

This notice was originally posted in the old Environmental Registry under number PA05E0003

Description of policy

Methoprene has been identified as a chemical of environmental concern due to its toxicity and wide spread use in the aquatic environment to control vectors of the West Nile virus. Methoprene is sold for mosquito control in Canada under the trade name Altosid, and is classified as "Restricted", which signifies that it is only to be used by persons who are certified or licensed by provincial agencies. Pellet and granular formulations of Methoprene are registered in Canada for use in storm sewers, catch basins and temporary and permanent surface waters.

Methoprene is classified as an insect growth regulator and instead of controlling immature insects through direct toxicity, it disrupts the life cycle of the developing insect and prevents it from reaching maturity. Methoprene is reported to be toxic to true flies, moths, butterflies and beetles.

Methoprene degrades rapidly in the aquatic environment by photodegradation and decomposition by microorganisms, and has a photolysis (chemical decomposition induced by light) half life of less than one day. While the chemistry suggests that Methoprene may have the potential to bioaccumulate in fatty tissue, biological studies have shown that it does not.

There is no current Provincial Water Quality Objective (PWQO) for Methoprene. The minimum data base required to develop a PWQO was not met for Methoprene because there was a lack of chronic data available. As a result the Interim Provincial Water Quality Objective (iPWQO) was developed by selecting the lowest measurable chronic study and applying a 10-fold safety factor. The approach for the 10 fold safety factor was chosen in order to harmonize with the method used by the Canadian Council of Ministers of the Environment (CCME) for development of Canadian Water Quality Guidelines. It has been recommended that the iPWQO for non-target organisms is 2.0 x 10-4 mg/L (200 ng/L) and that the iPWQO for target organisms is 1.0 x 10-6 mg/L (1 ng/L).

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; and
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 an Interim Provincial Water Quality Objective (iPWQO) for Methoprene to protect Ontario's surface waters. This notice seeks comments on this iPWQO. Comments received will be evaluated and considered in finalizing the iPWQO.