Proposed Special Review Decision PSRD2020-02, Special Review for Metaldehyde and Its Associated End-use Products

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Pest Management Regulatory Agency
20 July 2020
ISSN: 2561-636 (PDF version)
Catalogue number: H113-30/2020-2E-PDF (PDF version)

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Table of Contents

1.0 Introduction

Pursuant to subsection 17(2) of the Pest Control Products Act, Health Canada's Pest Management Regulatory Agency (PMRA) has initiated a special review of metaldehyde (Canada, 2018) based on the decision taken by Norway to prohibit the use of metaldehyde due to environmental concerns (Rotterdam Convention, 2018; PIC Circular XLVII).

Pursuant to subsection 18(4) of the Pest Control Products Act, the PMRA has evaluated the aspect of concern that prompted the special review of pest control products containing metaldehyde. The aspect of concern for this special review is relevant to the environment.

2.0 Uses of metaldehyde in Canada

Metaldehyde is a molluscicide used to control snails and slugs in a wide variety of use areas, including agricultural crops and home gardens, such as fruit and vegetable crops, and greenhouse and outdoor ornamentals. Metaldehyde is formulated as granular or liquid bait form and is applied by band treatment for commercial class products or by hand spray or dispersal for domestic class products to soil surfaces. All currently registered products containing metaldehyde (Appendix I of Proposed Special Review Decision PSRD2020-02, Special Review for Metaldehyde and Its Associated End-use Products) are considered in this special review.

3.0 Aspects of the pest control product that prompted the special review

Based on the review of the Norwegian decision (Rotterdam Convention, 2018; PIC Circular XLVII), the PMRA identified the aspect of concern that prompted the special review of metaldehyde as:

4.0 Evaluation of the aspect of concern that prompted the special review

In order to evaluate the aspect of concern, the PMRA has considered all currently available relevant scientific information, which includes existing reviews (Canada, 2008a; Canada, 2008b), and other relevant information (for example, incident reports, Norwegian decision, and relevant information published by the European Union (European Commission, 2011) and the United States Environmental Protection Agency (USEPA) (USEPA, 2006).

Following the initiation of the special review, the PMRA requested information related to the aspect of concern from provinces and other relevant federal government departments and agencies in accordance with subsection 18(2) of the Pest Control Products Act. No information was received.

4.1 Potential risk to birds and mammals

The PMRA assessed potential acute risks to birds and mammals resulting from application of metaldehyde (Canada, 2008a, Canada, 2008b).

Metaldehyde is moderately toxic to mammals (LD50 of 398 mg/kg) and slightly to moderately toxic to birds (LD50 of 181 mg/kg) on an acute exposure basis (US EPA, 2006). Birds and mammals could be exposed to metaldehyde through direct ingestion of metaldehyde granules applied to the soil. Exposure estimates for terrestrial wildlife were based on the assumption that 100% of the applied granules were present on the surface of the soil following application. The screening level risk assessment showed that small- and medium-size avian and mammalian species are at risk from acute exposure to metaldehyde granules (RQs ≤13) (Canada, 2008a, USEPA, 2006).

To reduce the potential exposure of metaldehyde to non-target organisms (birds and mammals), several mitigation measures are currently included on product labels (Canada, 2008b, 2016a, 2016b).

For example, broadcast and foliar applications of all metaldehyde products are prohibited. Only soil application as a barrier around gardens or individual plants is permitted. In addition, application is prohibited unless domestic animals can be excluded from the treated areas from the time of application until the applied product is no longer visible. All granular products are formulated so pellet size is small (>35 pellets/gram) to avoid products being mistaken for pet foods/wildlife forage items.

For domestic uses, exposure to non-target organisms is minimized when pellets are covered once applied to soil or mulch (Canada, 2016a, 2016b). Currently, this requirement is included on several domestic product labels. For consistency, this requirement is proposed for all domestic uses. To avoid attracting domestic animals, a bittering agent, such as denatonium benzoateFootnote 1, has been added to all domestic class products to deter ingestion. Most granular product labels indicate that piling of pellets should be avoided and all labels require spilled pellets to be removed.

Warnings of the dangers to domestic animals as well as instructions on treatment if the product were ingested are on all commercial and domestic class end-use product labels. Label statements informing users of the toxicity of metaldehyde to birds and mammals are also currently included on all labels (Canada, 2008b).

Several labels have cultural controls that provide supplemental controls of slugs and snails which may reduce the damage and possibly decrease the need for metaldehyde use. Cultural controls include hand-picking, removing of plant debris that can shelter slugs and snails, and watering in the morning rather than in the evening (snails and slugs favour damp conditions and feed at night) (USEPA, 2006).

As part of the special review, the PMRA incident reporting database was searched for incident reports related to the identified aspect of concern for metaldehyde. No incident reports involving birds and granivorous mammals exposed to metaldehyde were submitted to the PMRA. However, there are 92 incident reports, including 86 domestic animal reports, in the PMRA database. Most cases (80 reports) involving domestic animals occurred in the United States

The six (6) Canadian incidents had minor or moderate effects. The subset of serious American. incidents indicates a potential for life-threatening effects including death in animals (involving mainly dogs) via ingestion when applied granular metaldehyde products are accessible to animals.

An USEPA review of domestic animal incidents conducted in 2015 indicated a decrease in the number of metaldehyde animal poisoning cases over time. A similar pattern is also observed in the number of serious American incidents submitted to the PMRA database. The observed decrease in serious American incidents may be due to the mitigation strategies that were implemented in the United States following the 2006 RED for metaldehyde. As the use pattern in the United States encompasses Canadian uses, the PMRA (as part of the re-evaluation of metaldehyde in 2008), adopted similar risk reduction measures, such as, prohibiting broadcast applications and adding a bittering agent to all domestic products (Canada, 2008a). Hence, no additional mitigation measures relevant to the current aspect of concern are being proposed following the incident report review.

Based on the above considerations, the PMRA concluded that the potential risk to birds and mammals are considered to be acceptable under the current conditions of use. However, for consistency, the following proposed risk reduction measures are proposed:

5.0 Proposed special review decision for metaldehyde

Evaluation of available information related to the aspect of concern indicates that the potential risk to birds and wild mammals are considered to be acceptable under current conditions of use. However, for consistency between product labels, label amendments are proposed to be included on product labels.

On this basis, Health Canada's Pest Management Regulatory Agency, pursuant to subsection 21(1) of the Pest Control Products Act, is proposing continued registration of metaldehyde products for sale and use in Canada with additional mitigation measures (for consistency). The proposed label amendments are summarized in Appendix II of PSRD2020-02.

This proposed special review decision (PSRD2020-02) is a consultation document. The PMRA will accept written comments on this proposal up to 45 days from the date of publication of this document. All comments are to be directed to PMRA Publications.

6.0 Next steps

Before making a final decision on the special review of metaldehyde, the PMRA will consider all comments received from the public in response to PSRD2020-02. The PMRA will then publish a special review decision document, which will include the decision, the reasons for it, a summary of the comments received on the proposed decision, and the PMRA's response to these comments.

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