Proposed Re-evaluation Decision PRVD2014-04, Isoxaben

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Pest Management Regulatory Agency
20 June 2014
ISSN: 1925-0967 (PDF version)
Catalogue number: H113-27/2014-4E-PDF (PDF version)

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Table of Contents

What Is the Proposed Re-evaluation Decision?

After a re-evaluation of the herbicide isoxaben, Health Canada's Pest Management Regulatory Agency (PMRA), under the authority of the  Pest Control Products Act and  Regulations, is proposing continued registration of products containing isoxaben for sale and use in Canada.

An evaluation of available scientific information found that products containing isoxaben do not present unacceptable risks to human health or the environment when used according to the proposed label directions. As a condition of the continued registration of isoxaben uses, new risk reduction measures are proposed for the end-use product registered in Canada. No additional data are being requested at this time.

This proposal (PRVD2014-04) affects the end-use product containing isoxaben registered in Canada. Once the final re-evaluation decision is made, the registrant will be instructed on how to address any new requirements.

Proposed Re-evaluation Decision PRVD2014-04, Isoxaben is a consultation document that summarizes the science evaluation for isoxaben and presents the reasons for the proposed re-evaluation decision. It also proposes new risk reduction measures to further protect human health and the environment.

The information in Proposed Re-evaluation Decision PRVD2014-04, Isoxaben is presented in two parts. The Overview describes the regulatory process and key points of the evaluation, while the Science Evaluation provides detailed technical information on the assessment of isoxaben.

The PMRA will accept written comments on Proposed Re-evaluation Decision PRVD2014-04, Isoxaben up to 45 days from the date of publication of PRVD2014-04. Please forward all comments to Publications.

What Does Health Canada Consider When Making a Re-evaluation Decision?

The PMRA's pesticide re-evaluation program considers potential risks, as well as value, of pesticide products to ensure they meet modern standards established to protect human healthand the environment. Regulatory Directive DIR2012-02, Re-evaluation Program Cyclical Re-evaluation, presents the details of the cyclical re-evaluation approach, which is in line with the requirements of the Pest Control Products Act.

For more details on the information presented in this summary, please refer to the Science Evaluation of Proposed Re-evaluation Decision PRVD2014-04, Isoxaben.

What Is Isoxaben

Isoxaben is a selective pre-emergent herbicide that belongs to the benzamide group of pesticides. Isoxaben acts by disrupting root and stem development in germinating seeds. In Canada, it is registered for control of certain broadleaf weeds in conifer bareroot and container nursery stock for listed trees, shrubs and groundcovers grown for silviculture purposes, and containerized ornamentals grown in nurseries. It is registered for outdoor use only and is not for use on cut flowers. Isoxaben is applied by growers or commercial applicators using a low pressure field sprayer.

Health Considerations

Can Approved Uses of Isoxaben Affect Human Health?

Isoxaben is unlikely to affect your health when used according to the proposed label directions.

Potential exposure to isoxaben may occur when applying the product, by entering treated sites or handling treated plants, or through drinking water. Isoxaben is not registered for food use in Canada. The PMRA considers two key factors when assessing health risks: the levels at which no health effects occur and the levels to which people may be exposed. The dose levels used to assess risks are established to protect the most sensitive human population (for example, children and nursing mothers). Only uses for which exposure is well below levels that cause no effects in animal testing are considered acceptable for continued registration.

Occupational mixer/loader/applicator exposure and postapplication exposure are not of concern under the current conditions of use.

Residential postapplication dermal exposure could occur through contact with treated ornamentals. Residential exposure and risk was qualitatively assessed and is not expected to be of concern. No mitigation measures are proposed with regards to residential exposure to isoxaben.

Exposure to isoxaben through drinking water is not expected to be of concern in Canada. No mitigation is proposed with regards to dietary exposure to isoxaben.

Environmental Considerations

What Happens When Isoxaben Is Introduced Into the Environment?

Isoxaben is unlikely to affect non-target organisms when used according to the proposed label directions.

Non-target terrestrial and aquatic organisms could be exposed to isoxaben in the environment. The use of isoxaben as per current conditions of use is not expected to present a hazard to earthworms or pollinators, or to present an acute hazard to wild birds or mammals through oral ingestion of their food sources. Furthermore, no toxicity to adult birds or effects on reproduction or hatchling survival is expected.

Environmental risk to aquatic organisms and terrestrial plants from spray drift was assessed by the risk quotient method - the ratio of the estimated environmental concentration to the relevant effects endpoint of concern. In this screening level assessment, the resulting risk quotients were compared to corresponding levels of concern. A risk quotient less than the level of concern is considered a negligible risk to non-target organisms, whereas a risk quotient greater than the level of concern indicates some potential risks of concern. Based on this screening-level assessment, the PMRA is proposing the requirement of aquatic and terrestrial buffer zones for isoxaben to protect aquatic organisms and terrestrial plants from spray drift. Additional environmental label statements are also required to further protect the environment.

Measures to Minimize Risk

Labels of registered pesticide products include specific instructions for use. Directions include risk-reduction measures to protect human health and the environment. These directions must be followed by law. As a result of the re-evaluation of isoxaben, the PMRA is proposing further risk-reduction measures for product labels:

Human Health

  • Additional standard statements to reduce potential for contamination of food and feed.
  • Clarification of Personal Protective Equipment requirements.


  • Additional advisory label statements to reduce potential surface water contamination.
  • Buffer zones to protect non-target, sensitive aquatic and terrestrial habitats.

A submission to implement label revisions will be required within 90 days of finalization of the re-evaluation decision.

Next Steps

Before making a final re-evaluation decision on isoxaben, the PMRA will consider all comments received from the public in response to Proposed Re-evaluation Decision PRVD2014-04, Isoxaben. The PMRA will then publish a Re-evaluation Decision 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.

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