Proposed Registration Decision PRD2023-10, Paclobutrazol and Trimmit

Pest Management Regulatory Agency
16 November 2023
ISSN: 1925-0886 (PDF version)
Catalogue number: H113-9/2023-10E-PDF (PDF version)

Summary

Table of contents

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

Proposed registration decision for paclobutrazol

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 Paclobutrazol Technical and Trimmit, containing the technical grade active ingredient paclobutrazol, for use on turfgrass on golf courses to slow the growth of turfgrass and suppress Poa annua.

Paclobutrazol is currently registered as a plant growth regulator for use on container grown ornamental bedding plants and plugs in greenhouses. For details, see Proposed Re-evaluation Decision PRVD2013-04, Paclobutrazol, and Re-evaluation Decision RVD2014-06, Paclobutrazol.

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 PRD2023-10, Paclobutrazol and Trimmit provides detailed technical information on the human health, environmental and value assessments of paclobutrazol and Trimmit.

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 individuals and the environment from the use of pest control products. Health or environmental risk is considered acceptable^{Footnote 1} 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^{Footnote 2} when used according to the label directions. Conditions of registration may include precautionary measures on the product label to further reduce risk.

To reach its decisions, Health Canada's PMRA applies modern, rigorous risk-assessment methods and policies. These methods consider the unique characteristics of sensitive subpopulations in humans (for example, children). They also consider the unique characteristics of 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 on how the Health Canada regulates pesticides, the assessment process and risk-reduction programs, please visit the Pesticides section of the Canada.ca website.

Before making a final registration decision on paclobutrazol and Trimmit, Health Canada's PMRA will consider any comments received from the public in response to PRD2023-10.^{Footnote 3} Health Canada will then publish a Registration Decision^{Footnote 4} on paclobutrazol and Trimmit, 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 PRD2023-10.

What is paclobutrazol?

Paclobutrazol is a plant growth regulator which reduces internode growth, resulting in shorter and stouter stems. It is absorbed by plant roots and translocated to the growing tissues.

Health considerations

Can approved uses of paclobutrazol affect human health?

Trimmit plant growth regulator, containing paclobutrazol, is unlikely to affect your health when used accordingly to proposed label directions.

Potential exposure to paclobutrazol may occur through the diet (drinking water only), when handling and applying the end-use product, or when entering an area that has been treated with the product. 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 selected 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 level at which no effects are observed. The health effects noted in animals occur at dose levels more than 100-times 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 paclobutrazol was of moderate acute toxicity by the oral route and was mildly irritating to the eyes; consequently, the signal word "Warning" and hazard statements "Poison" and "Eye irritant" are required on the label. It was of low acute toxicity by the dermal and inhalation routes. It was minimally irritating to the skin and did not cause an allergic skin reaction.

The acute toxicity of the end-use product Trimmit, containing paclobutrazol, was low via the oral, dermal and inhalation routes of exposure. It was non-irritating to the eyes and skin and did not cause an allergic skin reaction.

Guideline and supplemental short- and long-term (lifetime) animal toxicity tests were assessed for the potential of paclobutrazol to cause neurotoxicity, immunotoxicity, chronic toxicity, cancer, reproductive and developmental toxicity, and various other effects. There was no evidence of tumourigenicity. The most sensitive endpoints for risk assessment were effects on activity level, body weight, fetal bone development, and the liver. There was an indication that the young were more sensitive than the adult animal.

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.

Residues in water and food

Dietary risks from drinking water are not of health concern.

No food residue data are required to support the registration of paclobutrazol for use on golf course turf in Canada. There are no food or feed uses associated with paclobutrazol, with either the registered uses on nursery and greenhouse ornamentals, or with the proposed use on golf course turf. However, there is the potential for residues to enter drinking water sources as a result of the proposed use on golf course turf.

The proposed use of Trimmit on golf course turf in Canada does not constitute a health risk of concern for acute or chronic dietary exposure to residues of paclobutrazol in drinking water to any segment of the population, including infants, children, adults and seniors.

Acute dietary (drinking water alone) intake estimates indicated that all population subgroups, including females 13–49 years old, are exposed to less than or equal to 16% of the acute reference dose (ARfD), and therefore are not of health concern.

Chronic dietary (drinking water alone) intake estimates indicated that the general population and all population subgroups are exposed to less than 30% of the acceptable daily intake (ADI), and therefore are not a health concern.

As no food residue data are required to support the registration of paclobutrazol for use on golf course turf in Canada, maximum residue limits (MRLs) are not required for this proposed use.

Occupational risks from handling Trimmit

Occupational risks are not of health concern when Trimmit is used according to the proposed label directions, which include protective measures.

Workers mixing, loading or applying Trimmit, and workers entering recently treated golf courses can be exposed to paclobutrazol residues through direct skin contact or through inhalation. Therefore, the label specifies that anyone mixing, loading and applying Trimmit must wear a long-sleeved shirt, long pants, chemical-resistant gloves, socks and shoes. Gloves are not required during application within a closed cab.

The label also requires that workers do not enter or be allowed on treated golf courses until sprays have dried. 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 from exposure to Trimmit are not of health concern when the end-use product is used according to the proposed label directions.

Health risks in residential and other non-occupational environments

Risks in residential and other non-occupational environments are not of health concern when Trimmit is used according to the proposed label directions and restricted-entry interval (REI) is observed.

Adults, youth and children golfing can come into direct contact with paclobutrazol residues from treated turf. Therefore, the label requires that individuals do not enter treated golf courses until sprays have dried. Taking into consideration the label statements, the number of applications and the duration of exposure, the risks to individuals golfing from exposure to Trimmit are not of health concern when the end-use product is used according to the proposed label directions.

Health risks to bystanders

Bystander risks are not of health concern when Trimmit is 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 when the end-use product is used according to the proposed label directions.

Environmental considerations

What happens when paclobutrazol is introduced into the Environment?

When used according to the proposed label directions, environmental risks associated with paclobutrazol and its end-use product, Trimmit, are acceptable.

Paclobutrazol enters the environment when Trimmit is used on golf courses to slow turfgrass growth and to suppress the growth of grassy weeds. Paclobutrazol is not expected to break down by reacting with water or light, or to be found in air. On land, paclobutrazol can be broken down by microorganisms in the soil to form two main breakdown products. Paclobutrazol and its breakdown products may move through soil to reach groundwater. Paclobutrazol and its breakdown products are unlikely to carry over between growing seasons.

Paclobutrazol may move from the treatment area in runoff to reach surface water. In aquatic habitats, paclobutrazol is expected to be persistent and move quickly from water to sediment. It is not likely to build up in aquatic organisms.

Use restrictions and hazard statements on the Trimmit label are required to reduce risks to non-target terrestrial plants and some aquatic organisms. When Trimmit is used according to the proposed label directions, paclobutrazol and its breakdown products pose acceptable risk to terrestrial and aquatic organisms.

Value considerations

What is the value of Trimmit?

Trimmit, formulated with the active ingredient paclobutrazol, reduces the frequency of mowing by slowing down turfgrass growth and suppressing Poa annua on golf courses.

Trimmit can be applied at 0.45–1.12 L/ha once, or multiple times with an interval of 7–21 days, and at a maximum annual rate of 4.05 L/ha in water volumes of 400–800 L/ha. Trimmit slows turfgrass growth, reduces the frequency of mowing by up to 50%, and suppresses Poa annua.

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 Paclobutrazol Technical and Trimmit to address the potential risks identified in this assessment are as follows.

Key risk-reduction measures - Human health

To reduce the potential exposure of workers to paclobutrazol through direct skin contact or inhalation of sprays, workers mixing, loading and applying Trimmit and performing cleaning and repair activities must wear a long-sleeved shirt, long pants, chemical-resistant gloves, socks and shoes. Gloves are not required during application within a closed cab. The label also requires that workers do not enter or allow others to enter treated areas until sprays have dried. Furthermore, a standard label statement to protect against drift during application is present on the label.

Key risk-reduction measures - Environment

• Standard precautionary label statements to inform users of:
  • Toxicity to aquatic organisms and non-target terrestrial plants,
  • The potential for leaching of paclobutrazol residues to groundwater.
• Spray buffer zones of up to 5 metres to protect sensitive aquatic and non-target terrestrial habitats
• Standard runoff label statements to reduce the risks to aquatic organisms

Next steps

Before making a final registration decision on paclobutrazol and Trimmit, Health Canada's PMRA will consider any written comments received from the public in response to PRD2023-10 up to 45 days from the date of publication (by 31 December 2023) of PRD2023-10. 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 paclobutrazol and Trimmit (based on the Science evaluation of PRD2023-10). In addition, the test data referenced in this consultation document will be available for public inspection, upon application, in the PMRA's Reading Room. For more information, please contact the PMRA's Pest Management Information Service.