Evaluation Report ERC2010-04, Pyroxsulam

14 May 2010
HC Pub: 100115
ISBN: 978-1-100-14144-2 (print version)
ISBN: 978-1-100-14145-9 (PDF version)
Catalogue number: H113-26/2010-4E (print version)
Catalogue number: H113-26/2010-4E-PDF (PDF version)

Summary

Table of Contents

• Registration Decision for Pyroxsulam
• What Does Health Canada Consider When Making a Registration Decision?
• What Is Pyroxsulam?
• Health Considerations
• Residues in Water and Food
• Environmental Considerations
• Value Considerations
• Measures to Minimize Risk
• What Additional Scientific Information Is Being Requested?
• Other Information

Registration Decision for Pyroxsulam

Health Canada's Pest Management Regulatory Agency (PMRA), under the authority of the  Pest Control Products Act and  Regulations, has granted conditional registration for the sale and use of Pyroxsulam Technical Herbicide and Simplicity Herbicide, containing the technical grade active ingredient pyroxsulam, to control broadleaf and grassy weeds in spring wheat and durum wheat using ground or aerial application equipment.

An evaluation of available scientific information found that, under the approved conditions of use, the product has value and does not present an unacceptable risk to human health or the environment.

Although the risks and value have been found acceptable when all risk reduction measures are followed, the applicant must submit additional scientific information as a condition of registration.

This summary describes the key points of the evaluation, while the Science Evaluation section of Evaluation Report ERC2010-04, Pyroxsulam, provides detailed technical information on the human health, environmental and value assessments of Pyroxsulam Technical Herbicide and Simplicity 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 (such as children) as well as organisms in the environment (for example, those most sensitive to environmental contaminants). 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

What Is Pyroxsulam?

Pyroxsulam is the active ingredient in the end-use product Simplicity Herbicide. Simplicity Herbicide is a postemergence herbicide, in other words, a herbicide applied after the crop has emerged from the ground, which is applied to spring wheat and durum wheat using ground or aerial application equipment to control broadleaf and grassy weeds. Pyroxsulam inhibits the plant enzyme acetolactate synthase (ALS) in target weeds. Complete desiccation of the plant may occur in seven to ten days under ideal growing conditions.

Health Considerations

Can Approved Uses of Pyroxsulam Affect Human Health?

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

Exposure to pyroxsulam may occur through diet (food and water), or when handling or 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.

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 products containing pyroxsulam are used according to the label directions.

Both the technical grade active ingredient, Pyroxsulam Technical Herbicide, and the end-use product, Simplicity Herbicide, are considered to be potential skin sensitizers; consequently, the label statement "Potential Skin Sensitizer" is required. The end-use product, Simplicity Herbicide, was considered to be of slight acute toxicity by the inhalation route and moderately irritating to eyes and skin, resulting in the requirement for the label statements "Warning Poison" and "Eye and Skin Irritant".

Pyroxsulam was not genotoxic and did not cause cancer in animals. There were no indications that pyroxsulam caused damage to the developing fetus, the reproductive system, or the nervous system. Health effects in animals given daily doses of pyroxsulam over long periods of time included effects on the liver.

A risk assessment is conducted to ensure that the level of human exposure is well below the lowest dose at which these effects occurred in animal tests. The dose levels used to assess risks are established to protect the most sensitive human population (for example, children and nursing mothers). Only those uses for which exposure is well below levels that cause no effects in animal testing are considered acceptable for registration.

Residues in Water and Food

Residues in Water and Food

Dietary risks from food and water are not of concern

Reference doses define levels to which an individual can be exposed over a single day
(acute) or lifetime (chronic) and expect no adverse health effects. Generally, dietary exposure from food and water is acceptable if it is less than 100% of the acute reference dose or chronic reference dose (acceptable daily intake). An acceptable daily intake is an estimate of the level of daily exposure to a pesticide residue that, over a lifetime, is believed to have no significant harmful effects.

Aggregate dietary intake estimates (food plus water) revealed that the general population and infants, the subpopulation that would ingest the most pyroxsulam relative to body weight, are expected to be exposed to less than 1% of the acceptable daily intake. Based on these estimates, the chronic dietary risk from pyroxsulam is not of concern for all population subgroups. The lifetime cancer risk from the use of pyroxsulam on wheat is considered acceptable.

Animal studies revealed no acute health effects. No endpoint of concern attributable to a single dose was identified. Consequently, a single dose of pyroxsulam is not likely to cause acute health effects in the general population (including infants and children).

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. Pesticide maximum residue limits 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 that does not exceed the established maximum residue limit does not pose an unacceptable health risk.

Residue trials conducted throughout Canada using pyroxsulam on wheat were acceptable. The maximum residue limits for this active ingredient can be found in the Science Evaluation section of Evaluation Report ERC2010-04, Pyroxsulam.

Risks in Residential and Other Non-Occupational Environments

Estimated risk for non-occupational exposure is not of concern as this is a commercial agricultural product.

Occupational Risks From Handling

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

A quantitative risk assessment was conducted for individuals handling Simplicity Herbicide. The risk to workers is not of concern when the product is used according to the label directions.

Pesticide applicators mixing, loading and applying Simplicity Herbicide can come in direct contact with the product on the skin or through inhalation. Therefore, the label will specify the following.

At all times: Wear clean clothing with full length sleeves and pants. Wear coveralls over long sleeved shirt and long pants, chemical-resistant gloves, socks and chemical-resistant footwear during mixing, loading, application, clean up and repair. Wear goggles or face shield during mixing/loading. For closed cab or aerial application, coveralls and gloves are not necessary.

The potential exposure of workers entering treated areas for postapplication activities, such as scouting or irrigation, is acceptable.

Environmental Considerations

What Happens When Pyroxsulam Is Introduced Into the Environment?

Pyroxsulam can pose a risk to terrestrial and aquatic vascular plants, and the formulation Simplicity Herbicide can pose a risk to amphibians; therefore, buffer zones are required during application.

Pyroxsulam enters the environment when used as a herbicide on wheat. It is stable to hydrolysis but can phototransform in shallow, clear, water bodies. Pyroxsulam is non-persistent to slightly persistent in aerobic soil and in water. It is however considered persistent under anaerobic conditions. Pyroxsulam and its transformation products are expected to leach through the soil profile beyond 30 centimetres in some soils and therefore may be expected to enter groundwater. Based on Canadian field studies, residues of pyroxsulam and its transformation products are not expected to significantly carry over into the next growing season. Based on its low volatility, pyroxsulam residues are not expected in the air.

Pyroxsulam and its major transformation products present a negligible risk to wild mammals, birds, earthworms, bees and other arthropods, aquatic invertebrates, fish, and green algae. However, given that pyroxsulam is a herbicide, it is expected to adversely affect terrestrial plants in adjacent areas. Buffer zones of 2 metres for ground application and 55 to 65 metres for aerial application (depending on application equipment) are required to protect nearby terrestrial plants from the effects of spray drift. Pyroxsulam can potentially affect aquatic vascular plants in adjacent areas, while an aromatic petroleum distillate in the formulation Simplicity Herbicide can potentially affect amphibians in adjacent areas. Therefore, a buffer zone of 1 metre is required to protect aquatic vascular plants and amphibians from the effects of spray drift.

Value Considerations

What Is the Value of Simplicity Herbicide

Simplicity Herbicide, a postemergence herbicide, controls wild oats and broadleaf weeds in spring wheat and durum wheat.

A single application of Simplicity Herbicide provides effective control of a range of broadleaf weeds and wild oats in spring wheat and durum wheat. It is also compatible with integrated weed management practices and with conservation tillage and conventional crop production systems. Because Simplicity Herbicide is applied after weeds have emerged, producers can better assess whether the herbicide is necessary or suitable for particular weed species. Simplicity Herbicide provides an alternative to Group 1 herbicides, which are of concern given the spread of acetyl-CoA carboxylase resistant (ACCase-resistant) wild oats.

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 Simplicity Herbicide to address the potential risks identified in this assessment are as follows.

Key Risk-Reduction Measures

Human Health

Because there is a concern with users coming into direct contact with Simplicity Herbicide on the skin or through inhalation of spray mists, anyone mixing, loading and applying Simplicity Herbicide must wear the PPE that is recommended on the label. As this product could be applied by aerial application, a statement was added to the label to not use human flaggers. In addition, standard statements to protect against drift during application were added to the label.

Environment

Spray drift of Simplicity Herbicide can pose a risk to terrestrial plants, aquatic vascular plants and amphibians. To mitigate the risk from the effects of spray drift, a buffer zone of 1 metre is required for the protection of sensitive freshwater habitats, and buffer zones of 2 to 65 metres, depending on the type of application equipment, are required to protect sensitive terrestrial habitats. These buffer zones are specified on the product label.

Other environmental concerns associated with pyroxsulam and Simplicity Herbicide were as follows:

• the leaching potential of pyroxsulam and its transformation products;
• runoff; and
• the aromatic petroleum distillate present as a component in the formulation.

These concerns were mitigated with label statements on the product label.

What Additional Scientific Information Is Being Requested?

Although the risks and value have been found acceptable when all risk-reduction measures are followed, the applicant must submit additional scientific information as a condition of registration. More details are presented in the Science Evaluation of this Evaluation Report or in the Section 12 Notice associated with these conditional registrations.

Environment

1. Provide the n-octanol-water partition coefficient (log Kow) for the transformation product pyroxsulam sulfonamide to determine its potential bioaccumulation under the  Toxic Substances Management Policy. The study should be conducted under good laboratory practices.
2. Provide a new toxicity study for pyroxsulam on the freshwater diatom, Navicula pelliculosa. The study must conform to standard international guidelines (for example, the United States Environmental Protection Agency, the Organisation for Economic Co-operation and Development) and be conducted under good laboratory practices.

Chemistry

1. Analytical data from at least five batches of Pyroxsulam Technical Herbicide representing full-scale production.

Other Information

As these conditional registrations relate to a decision on which the public must be consulted, the PMRA will publish a consultation document when there is a proposed decision on applications to convert the conditional registrations to full registrations or on applications to renew the conditional registrations, whichever occurs first.

The test data cited in this Evaluation Report (in other words, the test data relevant in supporting the registration decision) will be made available for public inspection when the decision is made to convert the conditional registrations to full registrations or to renew the conditional registrations (following public consultation). If more information is required, please contact the PMRA's Pest Management Information Service.