Proposed Re-evaluation Decision PRVD2017-22, Metam Sodium and Metam Potassium and Its Associated End-use Products

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Pest Management Regulatory Agency
7 December 2017
ISSN: 1925-0967 (PDF version)
Catalogue number: H113-27/2017-22E-PDF (PDF version)

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Table of Contents

Proposed Re-evaluation Decision

Under the Pest Control Products Act, all registered pesticides must be regularly re-evaluated by Health Canada's Pest Management Regulatory Agency (PMRA) to ensure that they continue to meet current health and environmental safety standards and continue to have value. The re-evaluation considers data and information from pesticide manufacturers, published scientific reports, and other regulatory agencies. The PMRA applies internationally accepted risk assessment methods as well as current risk management approaches and policies.

Metam sodium and metam potassium are non-selective pre-plant soil fumigants used to control pathogens including insects, nematodes, bacteria, fungi and weeds in soil. These active ingredients are also used as remedial wood preservatives to treat structural timber (such as poles). In addition, metam sodium is registered for use in sewer lines to control tree roots, and metam potassium is registered for use in water cooling systems and petroleum secondary recovery waters to control microbial activity.

Metam sodium and metam potassium have been re-evaluated based on the health and environmental risk assessments published in the United States Environmental Protection Agency (USEPA) Reregistration Eligibility Decision (RED)Footnote 1(2008) and the amended REDFootnote 2 (2009) documents. Additional risk assessments were conducted by the PMRA where deemed necessary and presented in Proposed Re-evaluation Decision PRVD2017-22, Metam Sodium and Metam Potassium and Its Associated End-use Products.

PRVD2017-22 presents the proposed regulatory decision for the re-evaluation of metam sodium and metam potassium including the proposed risk mitigation measures to further protect human health and the environment, as well as the science evaluation on which the proposed decision was based. All products containing metam sodium and metam potassium registered in Canada are subject to this proposed re-evaluation decision. PRVD2017-22 is subject to a 90-day public consultation period, during which the public including the pesticide manufacturers and stakeholders may submit written comments and additional information to the PMRA. The final re-evaluation decision will be published taking into consideration the comments and information received.

Outcome of Science Evaluation

Upon application, metam sodium and metam potassium are broken down into several degradates; the primary being methyl isothiocyanate (MITC) which accounts for most of the pesticidal properties. Metam sodium and metam potassium have value as pre-plant soil fumigants and as remedial wood preservatives. Pre-plant soil fumigants are an important tool for the control of soil pests and pathogens in Canada, which can disrupt plant growth and production. When metam sodium or metam potassium is used as a remedial wood preservative, MITC moves rapidly as a gas into treated structural timber and poles to control decay in wood. Metam sodium also has value as a root control agent for sewer lines. The intrusion of roots into sewer lines can block or reduce flow, cause overflows, or reduce hydraulic capacity. Finally, metam potassium has value as an antimicrobial agent for control of microbial activity in recirculating water cooling systems and petroleum secondary recovery waters.

Metam sodium and metam potassium are not registered for residential use in Canada. Risk from residential postapplication or bystander exposure to metam sodium, metam potassium or MITC is not of concern under the current conditions of use.

Extensive risk reduction measures were implemented in Canada in 2012 as part of the re-evaluation to minimize exposure to workers and bystanders. However, additional risk-reduction measures and label updates are proposed for all end-use products containing metam sodium or metam potassium to further mitigate risk to workers. Occupational risks are not of concern when products containing metam sodium or metam potassium are used according to the proposed label directions.

Risk from dietary exposure to metam sodium, metam potassium or MITC is not of concern for all registered uses under the current conditions of use.

Overall, metam sodium and metam potassium are unlikely to affect human health when used according to label directions.

With respect to the environment, metam sodium and metam potassium enter the environment when they are applied for soil fumigation. In addition, metam sodium enters the environment when it is applied to sewer lines for root control. Environmental exposure from wood treatment and industrial process fluid uses is expected to be minimal. Metam sodium and metam potassium break down quickly to MITC and are not expected to build-up in soil and water. MITC dissipates quickly in the environment by volatilization followed by photolytic degradation in the atmosphere. MITC is mobile in soil but is not expected to reach ground water due to its volatilization and rapid degradation in soil. Metam sodium, metam potassium and MITC are not expected to accumulate in the tissues of organisms.

Currently registered labels include the risk reduction measures required to minimize potential exposure to non-target organisms. No additional risk reduction measures are proposed. Minor label amendments are proposed to meet current labelling standards.

Overall, when used according to the label directions, metam sodium and metam potassium are not expected to pose risks of concern to the environment.

Proposed Regulatory Decision for Metam Sodium and Metam Potassium

Under the authority of the Pest Control Products Act and based on the evaluation of currently available scientific information, Health Canada is proposing that products containing metam sodium and metam potassium are acceptable for continued registration for use and sale in Canada, provided that the required risk mitigation measures and label amendments are in place.

Registered pesticide product labels include specific directions for use. Directions include risk mitigation measures to protect human health and the environment that must be followed by law.

As a result of the re-evaluation of metam sodium and metam potassium, further risk mitigation measures and label updates are being proposed for all end-use products containing metam sodium and metam potassium.

The labels of Canadian end-use product must be amended to include the label statements listed in Appendix III of PRVD2017-22. A submission to implement label revisions will be required within 90 days of finalization of the re-evaluation decision.

International Context

Metam sodium and metam potassium are currently acceptable for use in other Organisation for Economic Co-operation Development (OECD) member countries, including Australia, the European Union and the United States. As of 24 October 2017, no decisions by any OECD member country to prohibit all uses of metam sodium or metam potassium for health or environmental reasons have been identified.

Next Steps

Before making a final re-evaluation decision on metam sodium and metam potassium, the PMRA will consider all comments received from the public in response to PRVD2017-22. A science-based approach will be applied in making a final decision on metam sodium and metam potassium. The PMRA will then publish a Re-evaluation DecisionFootnote 3 that will include the decision, the reasons for it, a summary of comments received on the proposed decision and the PMRA's response to these comments.

Additional Scientific Information

No additional data is required.

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