Proposed Registration Decision PRD2019-12, Pethoxamid and Pethoxamid 480EC
Notice to the reader:
This consultation is now closed.
Pest Management Regulatory Agency
21 November 2019
ISSN: 1925-0886 (PDF version)
Catalogue number: H113-9/2019-12E-PDF (PDF version)
This page is a summary of the consultation document. If you would like to comment, please request the full consultation document.
To obtain a full copy of Proposed Registration Decision PRD2019-12, Pethoxamid and Pethoxamid 480EC please contact our publications office.
Should you require further information please contact the Pest Management Information Service.
Table of Contents
- Proposed Registration Decision for Pethoxamid
- What Does Health Canada Consider When Making a Registration Decision?
- What Is Pethoxamid?
- Health Considerations
- Environmental Considerations
- Value Considerations
- Measures to Minimize Risk
- Next Steps
- Other Information
Proposed Registration Decision for Pethoxamid
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 Pethoxamid Technical and Pethoxamid 480EC, containing the technical grade active ingredient pethoxamid, for pre-emergent control or suppression of grass and broadleaf weeds in field corn and soybeans, using ground application equipment only.
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 PRD2019-12, Pethoxamid and Pethoxamid 480EC provides detailed technical information on the human health, environmental and value assessments of pethoxamid and Pethoxamid 480EC.
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 pethoxamid and Pethoxamid 480EC, Health Canada’s PMRA will consider any comments received from the public in response to this PRD2019-12. Health Canada will then publish a Registration Decision on pethoxamid and Pethoxamid 480EC, 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 PRD2019-12.
What Is Pethoxamid?
Pethoxamid is a herbicide that inhibits shoot and root growth by affecting formation of cell membranes and the cuticle materials in developing plants.
Pethoxamid enters plants through the growing tips of roots and shoots, where it inhibits growth of susceptible plants soon after germination. It is primarily effective against annual grasses, but also provides control of certain broadleaf weeds. Pethoxamid only controls weeds that have not yet emerged.
Pethoxamid is classified as a Group 15 herbicide by the Weed Science Society of America and as a Group K3 by the Herbicide Resistance Action Committee.
Can Approved Uses of Pethoxamid Affect Human Health?
Pethoxamid 480EC containing pethoxamid is unlikely to affect your health when used according to label directions.
Potential exposure to pethoxamid may occur through the diet (food and water) or when handling and applying the product. When assessing health risks, two key factors are considered:
- the levels where 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 where no effects are observed. The health effects noted in animals occur at doses 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 pethoxamid was of moderate acute toxicity by the oral route; consequently, the hazard signal words “WARNING POISON” are required on the label. It was of low acute toxicity dermally and through inhalation exposure. Pethoxamid was minimally irritating to the eyes and skin. It caused an allergic skin reaction and therefore, the hazard signal words “POTENTIAL SKIN SENSITIZER” are required on the label.
The end-use product Pethoxamid 480EC was of low acute toxicity dermally and through inhalation exposure. It was of slight acute toxicity by the oral route, moderately irritating to the eyes and skin and caused an allergic skin reaction; consequently, the hazard signal words “POISON”, “WARNING EYE AND SKIN IRRITANT” and “POTENTIAL SKIN SENSITIZER” are required on the label.
Registrant-supplied short- and long-term (lifetime) animal toxicity tests were assessed for the potential of pethoxamid to cause neurotoxicity, chronic toxicity, cancer, reproductive and developmental toxicity, and various other effects. The most sensitive endpoints used for risk assessment included clinical signs, abortions and effects on body weight. There is low concern for increased sensitivity of the young exposed to pethoxamid. Overall, pethoxamid did not cause damage to genetic material; however, it did cause liver tumours in mice and thyroid tumours in rats. The risk assessment protects against the effects of pethoxamid by ensuring that the level of human exposure is well below the lowest dose at which these effects occurred in animal tests.
Risk in Residential and Other Non-Occupational Environments
Risk to bystanders is not of concern when Pethoxamid 480EC is used according to the proposed label directions.
Application is limited to agricultural crops, only when the potential for drift to areas of human habitation or areas of human activity, such as houses, cottages, schools and recreational areas, is minimal, taking into consideration wind speed, wind direction, temperature inversion, application equipment and sprayer settings. Therefore, bystander exposure is expected to be minimal and not of health concern.
Occupational Risks From Handling Pethoxamid 480EC
Occupational risks are not of concern when Pethoxamid 480EC is used according to the proposed label directions, which include protective measures.
Farmers and custom applicators who mix, load or apply Pethoxamid 480EC can come in direct contact with pethoxamid residues on the skin. Therefore, the label specifies that anyone mixing/loading and applying Pethoxamid 480EC must wear chemical-resistant coveralls over a long-sleeved shirt, long pants, chemical-resistant gloves, socks and chemical-resistant footwear during mixing, loading, application, clean-up and repair, as well as protective eyewear (goggles or face shield) during mixing and loading. Gloves are not required during application within a closed cab. Also, when handling more than 700 L of Pethoxamid 480EC per day, workers must use a closed mix/load system.
The label, Pethoxamid 480EC, also requires that workers do not enter treated fields for 12 hours after application. Taking into consideration these label statements, the number of applications, and the expectation of the exposure period for handlers and workers, the risk to these individuals from exposure to pethoxamid are not a concern.
Residues in Water and Food
Dietary risks from food and drinking water are not of health concern.
Aggregate dietary intake estimates (food plus drinking water) revealed that the general population and all population subgroups are expected to be exposed to less than 93% of the acceptable daily intake. Infants are the subpopulation expected to be subject to the highest exposures relative to body weight. Based on these estimates, the chronic dietary risk from pethoxamid is not of health concern for all population subgroups.
On the strength of the overall information, it was determined that a threshold approach was appropriate for the cancer risk assessment based on the observed tumours (liver and thyroid tumours). Overall, the endpoints selected for the non-cancer dietary risk assessment are considered protective of the findings.
Acute dietary (food plus drinking water) intake estimates for the general population and all population subgroups were less than 28% of the acute reference dose, and are not of health concern.
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. Food containing a pesticide residue at or below the established MRL does not pose an unacceptable health risk.
MRLs for pethoxamid determined from the acceptable residue trials conducted throughout Canada and the United States on field corn and soybeans can be found in the Science Evaluation of PRD2019-12.
What Happens When Pethoxamid Is Introduced Into the Environment?
When used according to label directions, pethoxamid is not expected to pose risks of concern to the environment.
Pethoxamid enters the environment when applied onto bare soil to control emerging weeds before field corn and soybeans are planted. On land, pethoxamid breaks down quickly and is not expected to move downward through the soil and reach groundwater. After pethoxamid is sprayed, it can enter bodies of water (for example, ponds, streams and rivers), where it will remain dissolved in water and will break down rapidly.
Pethoxamid is not expected to be found in air, or travel long distances in the atmosphere from where it is applied. Pethoxamid is not expected to build-up in the tissues of plants or animals.
Pethoxamid presents a negligible risk to earthworms, bees, beneficial arthropods, wild birds and mammals, amphibians, fish and aquatic invertebrates. Pethoxamid may present a risk to vegetation adjacent to treated fields, which can affect native plants and habitat for wildlife. In bodies of water, pethoxamid may pose a risk to algae and vascular aquatic plants. Therefore, precautionary measures such as spray buffer zones, are required to minimize the exposure to plants in terrestrial and aquatic habitats. When pethoxamid is used in accordance with the label directions and when the required risk reduction measures are applied, the reduced environmental exposure is deemed acceptable and the risks are considered to be acceptable.
What Is the Value of Pethoxamid 480EC?
Pethoxamid 480EC provides pre-emergent control or suppression of several grasses and broadleaf weed species in corn and soybean, with some residual activity.
Pethoxamid 480EC, which is formulated with the active ingredient pethoxamid at 480 g/L, provides pre-emergent control or suppression of several common weed species, including foxtail, crabgrass, ragweed, pigweed, nightshade, and lamb’s-quarters.
Pethoxamid 480EC reduces early season weed competition to the emerging crop allowing the crop to benefit from additional moisture, nutrients, and light that would otherwise be captured by weeds. Management of weeds at this time is critical as corn and soybean do not compete well with weeds until crop canopy closure. As Pethoxamid 480EC has residual activity on certain weed species, reduction in competition with the crop is extended.
Registration of Pethoxamid 480EC provides Canadian growers with access to a product that is currently available in other countries and another option for control or suppression of common grassy and broadleaf weeds with a single herbicide application early in the field season.
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 Pethoxamid Technical and Pethoxamid 480EC to address the potential risks identified in this assessment are as follows.
Key Risk-Reduction Measures
Because there is a concern with users coming into direct contact with pethoxamid residues on the skin, anyone mixing/loading and applying Pethoxamid 480EC must wear chemical-resistant coveralls over a long-sleeved shirt, long pants, chemical-resistant gloves, socks and chemical-resistant footwear during mixing, loading, application, clean-up and repair, as well as protective eyewear (goggles or face shield) during mixing and loading. Gloves are not required during application within a closed cab. Also, when handling more than 700 L of Pethoxamid 480EC per day, workers must use a closed mix/load system. In addition, standard label statements to protect against drift during application are on the label.
- The preharvest interval (PHI) for soybeans is proposed to be changed to 90 days based on the submitted crop field trial data.
- A pre-grazing interval of 7 days for soybean forage is required.
- A PHI of 7 days for soybean hay is required.
- A pre-grazing interval of 40 days for field corn forage is required.
- A PHI of 70 days for field corn stover is required.
- Label statements and spray buffer zones to reduce the risk of spray drift to terrestrial and aquatic ecosystems are required.
- Label statements indicating the potential for surface runoff from the soil and methods of reducing this potential are required.
Before making a final registration decision on pethoxamid and Pethoxamid 480EC, Health Canada’s PMRA will consider any comments received from the public in response to PRD2019‑12. Health Canada will accept written comments on PRD2019-12 up to 45 days from the date of publication of its publication. 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.
When the Health Canada makes its registration decision, it will publish a Registration Decision on pethoxamid and Pethoxamid 480EC (based on the Science Evaluation of PRD2019‑12). In addition, the test data referenced in PRD2019-12 will be available for public inspection, upon application, in the PMRA’s Reading Room (located in Ottawa).
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