Proposed Registration Decision PRD2022-01, Tiafenacil, Tiafenacil 70WG Herbicide, Tiafenacil 339SC Herbicide

• Pest Management Regulatory Agency
• 6 January 2022
  ISSN: 1925-0886 (PDF version)
  Catalogue number: H113-9/2022-1E-PDF (PDF version)

Summary

Table of Contents

• Proposed registration decision for tiafenacil
• What does Health Canada consider when making a registration decision?
• What is tiafenacil?
• Health considerations
• Environmental considerations
• Value considerations
• Measures to minimize risk
• Next steps
• Other information

Proposed registration decision for tiafenacil

Health Canada's Pest Management Regulatory Agency (PMRA), under the authority of the Pest Control Products Act, is proposing registration for the sale and use of Tergeo Technical Herbicide, Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide, containing the technical grade active ingredient tiafenacil, to control weeds in field corn, soybean, spring wheat, grapes, summerfallow and non-crop areas.

An evaluation of available scientific information found that, under the approved conditions of use, the health and environmental risks and the value of the pest control products are acceptable.

This summary describes the key points of the evaluation, while the Science Evaluation of Proposed Registration Decision PRD2022-01, Tiafenacil, Tiafenacil 70WG Herbicide, Tiafenacil 339SC Herbicide provides detailed technical information on the human health, environmental and value assessments of tiafenacil, Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide.

What does Health Canada consider when making a registration decision?

The key objective of the Pest Control Products Act is to prevent unacceptable risks to people and the environment from the use of pest control products. Health or environmental risk is considered acceptable if there is reasonable certainty that no harm to human health, future generations or the environment will result from use or exposure to the product under its proposed conditions of registration. The Act also requires that products have value when used according to the label directions. Conditions of registration may include special precautionary measures on the product label to further reduce risk.

To reach its decisions, the PMRA applies modern, rigorous risk-assessment methods and policies. These methods consider the unique characteristics of sensitive subpopulations in humans (for example, children) as well as organisms in the environment. These methods and policies also consider the nature of the effects observed and the uncertainties when predicting the impact of pesticides. For more information please refer to the following:

• Protecting Your Health and the Environment
• Pesticide Registration Process
• Pesticide Risk Reduction Program.

Before making a final registration decision on tiafenacil, Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide, Health Canada's PMRA will consider any comments received from the public in response to PRD2022-01. Health Canada will then publish a Registration Decision on tiafenacil, Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide, which will include the decision, the reasons for it, a summary of comments received on the proposed registration decision and Health Canada's response to these comments.

For more details on the information presented in this summary, please refer to the Science Evaluation of PRD2022-01.

What is tiafenacil?

Tiafenacil is a non-selective, contact herbicide for weed management early in the season in certain crops, and throughout the season in grapes and non-crop areas.

Health considerations

Can approved uses of tiafenacil affect human health?

Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide, containing tiafenacil, are unlikely to affect your health when used according to label directions.
Potential exposure to tiafenacil may occur through the diet (food and drinking water), when handling and applying the end-use products, or when coming into contact with treated surfaces. When assessing health risks, two key factors are considered:

• 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). As such, sex and gender are taken into account in the risk assessment. Only uses for which the exposure is well below levels that cause no effects in animal testing are considered acceptable for registration.

Toxicology studies in laboratory animals describe potential health effects from varying levels of exposure to a chemical and identify the dose levels at which no effects are observed. The health effects noted in animals occur at doses more than 100-fold higher (and often much higher) than levels to which humans are normally exposed when pesticide products are used according to label directions.

In laboratory animals, the technical grade active ingredient tiafenacil was of low acute toxicity by the oral, dermal and inhalation routes of exposure. Tiafenacil was minimally irritating to the eyes and non-irritating to the skin, and did not cause an allergic skin reaction.

The acute toxicity of the end-use product Tiafenacil 70WG Herbicide was low by the oral, dermal and inhalation routes of exposure. Tiafenacil 70WG Herbicide was minimally irritating to the eyes and non-irritating to the skin, and did not cause an allergic skin reaction.

The acute toxicity of the end-use product Tiafenacil 339SC Herbicide was low by the oral, dermal and inhalation routes of exposure. Tiafenacil 339SC Herbicide was non-irritating to the eyes and skin, and did not cause an allergic skin reaction.

Registrant-supplied short- and long-term (lifetime) animal toxicity tests were assessed for the potential of tiafenacil to cause neurotoxicity, immunotoxicity, chronic toxicity, cancer, reproductive and developmental toxicity, and various other effects. The most sensitive endpoints for risk assessment were effects on red blood cell parameters and the liver. The overall evidence suggests low concern for young animals and their sensitivity to tiafenacil when compared to adult animals. The risk assessment protects against the effects noted above and other potential effects by ensuring that the level of exposure to humans is well below the lowest dose level at which these effects occurred in animal tests.

Occupational risks From handling Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide

Occupational risks are not of health concern when Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicideare used according to the proposed label directions, which include protective measures.

Workers mixing, loading or applying Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide, and workers entering recently treated areas can come in direct contact with tiafenacil residues on the skin. Therefore, the labels specify that anyone mixing, loading and applying Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide must wear a long-sleeved shirt, long pants, chemical-resistant gloves, socks and shoes. The labels also require that workers do not enter or be allowed entry into treated crops during the restricted-entry interval (REI) of 12 hours for agricultural areas and until sprays have dried in non-crop areas. Taking into consideration the label statements, the number of applications and the duration of exposure for handlers and postapplication workers, the risks to these individuals are not of health concern.

Health risks to bystanders

Bystander risks are not of health concern when Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicideare used according to the proposed label directions and spray drift restrictions are observed.

A standard label statement to protect against drift during application is on the label. Therefore, health risks to bystanders are not of concern.

Residues in food and drinking water

Dietary risks from food and drinking water are not of health concern.

Animal studies revealed no acute health effects. Consequently, a single dose of tiafenacil is not likely to cause acute health effects in the general population (including infants and children).

Aggregate dietary intake estimates (food plus drinking water) revealed that the general population and infants less than one-year-old, the subpopulation that would ingest the most tiafenacil relative to body weight, are expected to be exposed to less than 92%of the acceptable daily intake (ADI). When the common metabolite trifluoroacetic acid (TFA) is included for rotational crops, the highest exposure estimate is 102% of the ADI (infants less than one-year old). Based on these estimates, the chronic dietary risk from tiafenacil is not of health concern for all population subgroups due to the level of conservatism inherent in the assessment.

The Food and Drugs Act prohibits the sale of adulterated food, that is, food containing a pesticide residue that exceeds the established maximum residue limit (MRL). Pesticide MRLs are established for Food and Drugs Act purposes through the evaluation of scientific data under the Pest Control Products Act. Given that dietary risks from the consumption of foods are shown to be acceptable when tiafenacil is used according to the supported label directions, MRLs are being proposed as a result of this assessment (refer to PMRL2022-01, Tiafenacil).

MRLs for tiafenacil determined from the acceptable residue trials conducted throughout Canada and the United States on grapes, corn, soybeans and wheat can be found in the Science Evaluation of PRD2022-01.

Environmental considerations

What happens when tiafenacil is introduced into the environment?

When tiafenacil is used according to the label directions, the risks to the environment are acceptable.

When tiafenacil is used in accordance with label directions and the required precautions, the risks associated with tiafenacil are acceptable from the viewpoint of environmental protection.

When tiafenacil is applied as a foliar spray to control grassy and broadleaf weeds, it breaks down very quickly to a number of transformation products in the presence of sunlight in shallow water. Tiafenacil can also break down quickly through the action of microbes in soil and aquatic systems. Many of the transformation products of tiafenacil are formed in significant amounts in the environment. Most of these transformation products can move downward through the soil and reach groundwater. The transformation products can also move off the treatment area to reach surface waters such as ponds, streams, and rivers. However, adverse effects of the transformation products to terrestrial and aquatic life are not expected when the label directions are followed. Tiafenacil and its transformation products are not likely to accumulate in tissues of organisms.

Tiafenacil can affect non-target plants adjacent to treated fields following application. If it enters bodies of water after it is sprayed, tiafenacil can affect freshwater fish, amphibians and aquatic plants and algae. To minimize exposure to sensitive non-target species, spray buffer zones are required. In addition, precautionary statements and best management practices are required on the label. When tiafenacil is used in accordance with the label and the required precautions, the resulting environmental risk is considered to be acceptable.

Value considerations

What is the value of Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide?

Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide are conventional, non-selective, contact herbicides for the control or suppression of certain annual broadleaf weed species when applied in the early season in field corn, soybean and spring wheat, and throughout the season in grapes, summerfallow and non-crop areas.

Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide will serve as additional options for early season weed management and can be included as a component of integrated weed management programs that include tillage and other preplant, pre-emergent and/or postemergent herbicides for season-long weed management.

Measures to minimize risk

Labels of registered pesticide products include specific instructions for use. Directions include risk-reduction measures to protect human and environmental health. These directions must be followed by law.

The key risk-reduction measures being proposed on the label of Tergeo Technical Herbicide, Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide to address the potential risks identified in this assessment are as follows.

Key risk-reduction measures

Human health

To reduce the potential of workers coming into direct contact with tiafenacilon the skin or through inhalation of sprays, workers mixing, loading and applying Tiafenacil 70WG Herbicide or Tiafenacil 339SC Herbicideand performing cleaning and repair activities must wear a long-sleeved shirt, long pants, chemical-resistant gloves, socks and shoes. Additionally, standard label statements to protect against drift during application are on the labels. The labels also require that workers do not enter or be allowed entry into treated agricultural fields during the REI of 12 hours and until sprays have dried in non-crop areas.

Environment

With the following risk reduction measures on the label, the risks are considered acceptable:

• Environmental hazard statements for terrestrial plants and aquatic organisms;
• Precautionary label statements for run-off and leaching; and
• Label statements and spray buffer zones to protect non-target aquatic and terrestrial habitats.

Next steps

Before making a final registration decision on tiafenacil, Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide, Health Canada's PMRA will consider any comments received from the public in response to PRD2022-01. Health Canada will accept written comments on this proposal up to 45 days from the date of publication of PRD2022-01. Please note that, to comply with Canada's international trade obligations, consultation on the proposed MRLs will also be conducted internationally via a notification to the World Trade Organization. Please forward all comments to Publications. Health Canada will then publish a Registration Decision, which will include its decision, the reasons for it, a summary of comments received on the proposed decision and Health Canada's response to these comments.

Other information

When Health Canada makes its registration decision, it will publish a Registration Decision on tiafenacil, Tiafenacil 70WG Herbicide and Tiafenacil 339SC Herbicide (based on the Science Evaluation of PRD2022-01). In addition, the test data referenced in this consultation document will be available for public inspection, upon application, in the PMRA's Reading Room.