Proposed Special Review Decision PSRD2018-02, Special Review of Thiamethoxam Risk to Aquatic Invertebrates: Proposed Decision for Consultation

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Pest Management Regulatory Agency
15 August 2018
ISSN: 2561-636 (PDF version)
Catalogue number: H113-30/2018-2E-PDF (PDF version)

To obtain a full copy of Proposed Special Review Decision PSRD2018-02, Special Review of Thiamethoxam Risk to Aquatic Invertebrates: Proposed Decision for Consultation please contact our publications office.

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Web Summary

Table of Contents


Health Canada is consulting Canadians on its proposed special review decision of the neonicotinoid pesticide thiamethoxam following a risk assessment to aquatic invertebrates.

The Pest Management Regulatory Agency (PMRA) initiated a special review of thiamethoxam under subsection 17(1) of the Pest Control Products Act based a preliminary analysis of available information on the concentrations and frequency of detection of thiamethoxam in aquatic environments.

As required by subsection 18(4) of the Pest Control Products Act, the PMRA has evaluated the aspects of concern that prompted the special review of pest control products containing thiamethoxam.  The aspect of concern for this review is to assess potential risk to aquatic invertebrates exposed to thiamethoxam applied as a seed, foliar or soil treatment.

Uses of Thiamethoxam in Canada

Appendix I of PSRD2018-02 lists all thiamethoxam products with outdoor agricultural and ornamental uses that are registered under the authority of the Pest Control Products Act as of May 2018 that were subject to this special review. Thiamethoxam is currently found in 18 agricultural end-use products to which aquatic invertebrates may be exposed. These products may be used in greenhouses (peppers and ornamentals), as a seed dressing (various cereal, pulse and vegetable crops, sunflower, and potato as a seed piece treatment), foliar spray application (ornamentals, potato, pome fruit, stone fruit, bush berries, caneberries, and various vegetable crops), or in-furrow drench (potato, various vegetable crops). Foliar spray applications can be made by ground boom, airblast or aerial sprayers, depending on crop. Appendix II of PSRD2018-02 lists all registered uses of Commercial Class end-use products containing thiamethoxam that were subject to this special review.  

Aspects of Concern that Prompted the Special Review

This special review was initiated on November 23, 2016, at the same time the PMRA’s proposed cyclical re-evaluation decision was published for imidacloprid (PRVD2016-20). The aquatic risk assessment for imidacloprid identified risks of concern to aquatic invertebrates. Thiamethoxam shares the same mode of action with a similar toxicity profile. Available monitoring data indicated that thiamethoxam was being detected at concentrations and frequencies in aquatic environments that may pose a risk to aquatic invertebrates. A preliminary assessment was conducted to determine if a special review was required. Based on the available fate, toxicity and water monitoring information for thiamethoxam, there were reasonable grounds to believe that the potential risk to aquatic invertebrates from the use of thiamethoxam may exceed the PMRA’s level of concern under the current conditions of use.

The initiation of the special review was announced in REV2016-17, Initiation of Special Reviews: Potential Environmental Risk to Aquatic Invertebrates Related to the Use of Clothianidin and Thiamethoxam. The aspect of concern for this special review is to assess potential risk to aquatic invertebrates exposed to thiamethoxam applied as a seed, foliar or soil treatment.

PMRA Evaluation of the Aspects of Concern

The PMRA required the pesticide manufacturer to submit all available data that are relevant to the environmental fate of thiamethoxam, including Canadian surface water monitoring data, and to its toxicity to aquatic invertebrates. In addition, the PMRA requested the same information from provinces and other relevant federal departments and agencies, in accordance with subsection 18(2) of the Pest Control Products Act. In response to PMRA’s requests, information was received related to the aspect of concern.

Additional data supplied by the pesticide manufacturer included information on the environmental fate of thiamethoxam in soil and water as well as the ecotoxicity of thiamethoxam and its major transformation products to aquatic invertebrates. Data on thiamethoxam toxicity to aquatic invertebrates generated by Environment and Climate Change Canada (ECCC) and by academic researchers was included for this special review. A comprehensive literature review of current data relevant to the special review provided additional ecotoxicity data for thiamethoxam. In total, the PMRA considered acute ecotoxicity data for 44 species of aquatic invertebrates and chronic data for 8 species, as well as higher-tier community-based endpoints from two studies. Environmental incidents for aquatic invertebrates were not identified in North America.

Published and unpublished Canadian freshwater monitoring data were received from federal and provincial governments and academic researchers, pesticide manufacturers and members of Agriculture and Agri-Food Canada’s Multi-stakeholder Environmental Monitoring Working Group. Freshwater monitoring data consisted of several robust datasets often with large numbers of samples taken at high frequencies from agricultural areas from 2010 to 2017.

Key Findings

The environmental assessment showed that, in aquatic environments in Canada, thiamethoxam is being measured at concentrations that are harmful to aquatic insects. These insects are an important part of the ecosystem, including as a food source for fish, birds and other animals. Based on currently available information, most outdoor uses in Canada are not sustainable. For more information on Health Canada’s proposed decision for this special review of thiamethoxam, refer to Section Proposed Special Review Decision for Thiamethoxam.

Risk Assessment Conclusions

In conducting environmental risk assessments, it is the PMRA’s policy to always consider both monitoring data (when available) and estimated environmental concentrations (EECs) generated using water models as part of its overall risk assessment. Although valid monitoring data are considered preferable to modelled EECs, the weight given to these data varies depending on the circumstances.

When determining the most appropriate toxicity endpoints for consideration in the risk assessment, the PMRA considers both pesticide manufacturer submitted studies and publically available studies. The ecotoxicity data is considered in a tiered approach, which consists of the following:

  • the endpoint of the most sensitive species,
  • a species sensitivity distribution when enough data points are available, and
  • mesocosm studies which considers effects at the community level.

For thiamethoxam, Species Sensitivity Distributions (SSDs) for both acute and chronic exposure in freshwater environments were determined. In addition, two acceptable mesocosm studies were available to assess the concentrations at which community level effects would be observed. For the chronic assessment, the endpoints from the most sensitive mesocosm study, the SSD and the most sensitive single species were considered in a weight-of-evidence approach in the risk assessment.

A major transformation product of thiamethoxam in soil is clothianidin, another registered insecticide, which is also toxic to aquatic invertebrates. The risk assessment conclusion for thiamethoxam considers thiamethoxam alone and not the combination of thiamethoxam and clothianidin. Given that both pesticides are registered for use on many of the same crops, it is often not possible to determine whether concentrations of clothianidin measured in water are a result of the transformation of thiamethoxam, a result of the use of clothianidin as an insecticide, or a combination of the two. Concurrent with this special review of the risk of thiamethoxam to aquatic invertebrates, the PMRA has conducted a separate special review of the risk of clothianidin to aquatic invertebrates. The clothianidin special review is published in PSRD2018-01.

The risk assessment based on the modelling results indicates that exposure to thiamethoxam poses a minimal acute risk to freshwater invertebrates; however, on a chronic basis, exposure to thiamethoxam poses a risk to freshwater invertebrates. Typically, modelling inputs and assumptions are conservative and the EECs generated are likely to be higher than actual concentrations present in waterbodies. For thiamethoxam, however, the range of surface water EECs predicted from modelling overlaps with the range of concentrations measured in surface freshwater bodies.

Thiamethoxam concentrations measured in Canadian waterbodies did not exceed the acute level of concern. Chronic risks to freshwater invertebrates were identified based on robust Canadian monitoring data sets. Monitoring data likely provide an underestimate of acute exposure, as sampling typically does not capture peak concentrations.
Thiamethoxam concentrations detected in the following areas frequently exceeded the chronic SSD endpoint for freshwater invertebrates (the registered methods of application of clothianidin are listed in parentheses):

  • Corn and soybean growing regions (seed treatment),
  • Potatoes (seed treatment, soil application or foliar spray), and
  • Vegetables (seed treatment or foliar spray, depending on the type).

Concentrations of thiamethoxam occasionally exceeded the chronic SSD endpoint for freshwater invertebrates in a few waterbodies located in areas where orchards occupy large portions of the cultivated area of the watershed.

The chronic SSD endpoint was exceeded in wetlands primarily associated with seed treatment uses in the Prairies; however, there was uncertainty surrounding the duration of exposure.

Concentrations detected in some waterbodies located in regions growing potatoes, mixed vegetables and corn/soybean exceeded the PMRA level of concern based on the mesocosm endpoint for periods of weeks to months. This chronic exposure may result in effects at the community level, including changes in insect species abundance and emergence. Concentrations of thiamethoxam exceeding the community-level endpoint were also detected in other crop-growing regions, however, they were sporadic and of short duration. The occurrence of thiamethoxam concentrations at or above the community-level endpoint may have significant impacts on community invertebrate structure which is a primary protection goal of the PMRA.

No Canadian monitoring data for thiamethoxam in marine or estuarine water were available to exclude risks to marine/estuarine invertebrates.

Proposed Special Review Decision for Thiamethoxam

The evaluation of available scientific information related to the aspects of concern indicated that most of the registered products containing thiamethoxam that are subject to this special review pose environmental risks that have not been shown to be acceptable. Therefore, under the authority of the Pest Control Products Act and based on the evaluation of currently available scientific information, Health Canada is proposing to cancel all outdoor uses of thiamethoxam on food and feed crops (use site categories 13 and 14), including seed treatments (use site category 10), and outdoor ornamentals (use site category 27), over three to five years, taking into account Regulatory Directive DIR2018-01, Policy on Cancellations and Amendments Following Re-evaluation and Special Review. The PMRA will consider alternate risk management proposals, provided that they can achieve acceptable levels in the environment within the same timeframe.

Additional mitigation measures may be required during the phase-out period  (see Appendix VIII of PSRD2018-02).

The risks to aquatic invertebrates associated with greenhouse uses of thiamethoxam (use site categories 5 and 6) are acceptable and continued registration of these greenhouse uses is proposed, provided wastewater mitigation instructions on product labels are followed.

The proposed special review decision is open for public consultation for 90 days from the date of this publication. The PMRA is inviting the public to submit comments on the proposed special review decision for thiamethoxam including proposals that may refine the risk assessment and risk management. Once the PMRA considers the comments and any information that are received during the public consultation period, the Agency will publish a final decision.

Next Steps

Before making a special review decision on thiamethoxam, the PMRA will consider all comments received from the public in response to this consultation document. A science-based approach will be applied in making a final decision on thiamethoxam. 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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