Re-evaluation Decision RVD2014-02, Amitrole

Pest Management Regulatory Agency
8 July 2014
ISSN: 1925-1025 (PDF version)
Catalogue number: H113-28/2014-2E-PDF (PDF version)

This page is a summary of the decision document. If you would like more detail, please request the full decision document.

To obtain a full copy of Re-evaluation Decision RVD2014-02, Amitrole please contact our publications office.

Should you require further information please contact the Pest Management Information Service.


Table of Contents

Re-evaluation Decision

After a re-evaluation of the herbicide amitrole, Health Canada's Pest Management Regulatory Agency (PMRA), under the authority of the  Pest Control Products Act, is granting continued registration for the sale and use of amitrole on spruce bareroot nursery stock (seedbeds) in Canada. An evaluation of available scientific information found that the use of amitrole on spruce bareroot nursery stock (seedbeds) has value and does not present an unacceptable risk to human health or the environment when used according to the revised label statements.

All uses of amitrole, except use in spruce bareroot seedbeds, will be phased out because human health risks of concern have been identified. These uses include control of annual and perennial broadleaf and grassy weeds in crop and non-crop sites.

The PMRA's pesticide re-evaluation program considers potential risks as well as the value of pesticide products to ensure they meet modern standards established to protect human health and the environment. Regulatory Directive DIR2001-03, PMRA Re-evaluation Program, presents the details of the re-evaluation activities and program structure. Re-evaluation draws on data from registrants, published scientific reports, information from other regulatory agencies and any other relevant information available.

The regulatory approach regarding the re-evaluation of amitrole was first proposed in the consultation documentFootnote 1 Proposed Re-evaluation Decision PRVD2012-01, Amitrole. Re-evaluation Decision RVD2014-02, AmitroleFootnote 2 describes the decision-making stage of the PMRA's regulatory process concerning the re-evaluation of amitrole and summarizes the Agency's decision, the reasons for it and, in Appendix I, a summary of comments received during the consultation process and the PMRA's response to these comments. This decision is consistent with the proposed re-evaluation decision stated in PRVD2012-01. To comply with this decision, registrants of amitrole products will be informed of the specific requirements affecting their product registration(s) and of the regulatory options available to them.

For more details on the information presented in Re-evaluation Decision RVD2014-02, Amitrole, please refer to the related PRVD2012-01.

What Does Health Canada Consider When Making a Re-evaluation 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 of, or exposure to, the product under its conditions or proposed conditions of registration.Footnote 3 The Act also requires that products have valueFootnote 4 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 hazard and risk-assessment methods as well as policies that are rigorous and modern. These methods consider the unique characteristics of sensitive subpopulations in both humans (for example, children) and 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 present when predicting the impact of pesticides. For more information on how the PMRA regulates pesticides, the assessment process and risk-reduction programs, please visit the Pesticides and Pest Management portion of Health Canada's website at

What is Amitrole?

Amitrole is a non-selective systemic Group 11 herbicide. It is registered for the control of a broad spectrum of annual and perennial broadleaf and grassy weeds on both crop and non-crop sites. Amitrole is generally applied as a broadcast spray or spot treatment (once or twice per season) using ground equipment prior to crop planting and when weeds have emerged and are actively growing. Application rates vary by use site: 0.4-0.7 kg a.i./ha on spruce seedlings, 1-4 kg a.i./ha on food/feed crops, and 1-11 kg a.i./ha on pasture, poplar and non-crop land.

Two products are currently registered in Canada under the authority of the Pest Control Products Act including one technical grade active ingredient and one commercial class end-use product. The registrants of the domestic class end-use products containing amitrole voluntarily discontinued their products at the time of initiation of re-evaluation; therefore, these products were not included in the re-evaluation.

Uses of amitrole belong to the following use-site categories: terrestrial food crops, terrestrial feed crops, industrial oilseed and fibre crops, forest and woodlands, and industrial vegetation control for non-food sites.

Health Considerations

Can Approved Uses of Amitrole Affect Human Health?

Risks of concern were identified for both dietary (food and drinking water) and occupational exposure to amitrole.

Potential exposure to amitrole may occur through diet (food and drinking water), when applying the product or by entering treated sites. When assessing health risks, two key factors are considered: the levels at which no health effects occur in animal testing 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 those uses where exposure is well below levels that cause no effects in animal testing are considered acceptable for registration.

Amitrole was of low acute oral and dermal toxicity in laboratory animals. It was considered to be of moderate inhalation toxicity. Amitrole was minimally irritating to the eyes and non-irritating to the skin. Exposure to amitrole can cause skin sensitization.

The target organ was the thyroid gland when animals were exposed via the oral and inhalation routes. A cancer concern exists for amitrole based on increased incidences of liver tumours in mice, and thyroid and pituitary tumours in rats. Amitrole does not present a mutagenic concern.

When amitrole was administered to pregnant rabbits, an increase in the incidence of cranial malformations was observed. Due to the nature of these endpoints and their potential implications on the health of the fetus, additional protective factors were applied during the risk assessment to further reduce the allowable level of human exposure to amitrole.

Residues in Water and Food

Dietary risks from food and water are 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 drinking 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 expected to have no significant harmful effects.

Human exposure to amitrole was estimated from residues in treated crops and drinking water, and considered exposure to the general population as well as various subpopulations including the most sensitive subpopulation (infants less than 1 year of age). This aggregate (food and drinking water) exposure to amitrole represents approximately 640% of the acute reference dose for females 13-49 years of age and 2900% of the chronic reference dose for the most affected population of infants (less than 1 year of age); therefore it is of concern. The cancer risk for amitrole was 3 × 10-3 for the general population and is also of concern. A lifetime cancer risk that is at or below 1 × 10-6 (1 in a million) usually does not indicate a risk concern for the general population when exposure occurs through pesticide residues in/on food and drinking water, and to otherwise unintentionally exposed persons. Further information on how the potential cancer risks from pesticides are assessed can be found in PMRA's Science Policy Note SPN2000-01, A Decision Framework for Risk Assessment and Risk Management in the Pest Management Regulatory Agency. Based on the human health concerns identified, food uses of amitrole are to be phased out.

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. Each MRL value defines the maximum concentration in parts per million (ppm) of a pesticide allowed in/on certain foods. Food containing a pesticide residue that does not exceed the established MRL does not pose a health risk concern.

Canadian MRLs for amitrole are currently established for wheat, barley, canola (rapeseed) and peas at 0.01 ppm. Residues in all other agricultural commodities, including those approved for treatment in Canada but without a specific MRL, are regulated under subsection B.15.002(1) of the Food and Drug Regulations, which requires that residues not exceed 0.1 ppm. However, changes to this general MRL may be implemented in the future, as indicated in Discussion Document DIS2006-01, Revocation of 0.1 ppm as a General Maximum Residue Limit for Food Pesticide Residues [Regulation B.15.002(1)].

Since MRLs represent the maximum concentration of pesticide allowed in/on relevant foods, accompanying the removal of food uses in Canada, the PMRA routinely revokes existing Canadian MRLs specified under the Pest Control Products Act. As a result, residue in such commodities is then regulated under subsection B.15.002(1) of the Food and Drugs Regulations, which requires that residues not exceed the general MRL (general MRL) of 0.1 ppm.

In the case of amitrole, as the revocation of the established MRL of 0.01 ppm for wheat, barley, canola and peas would result in residues being regulated by the higher general MRL of 0.1 ppm, the specified Canadian existing MRL of 0.01 ppm will be maintained. Details regarding the dietary risk assessment can be found in the Science Evaluation section of PRVD2012-01.

Dietary exposure to the amitrole metabolite triazolyl alanine may occur from the use of amitrole on food commodities. Residues of triazolyl alanine are regulated in Canada under the Pest Control Products Act not to exceed 2.0 ppm in plant commodities. This metabolite is common to triazole pesticides such as amitrole. The residue chemistry and human health risks associated with this metabolite that result from the use of all registered triazole-based pesticides will be assessed in a separate cumulative risk assessment. Additional information on triazolyl alanine can be found in PRVD2010-14, Myclobutanil.

Risks in Residential and Other Non-Occupational Environments

Non-occupational risks are not of concern.

No residential uses are being supported by the registrant; as such a risk assessment for this scenario was not required.

Potential exposure and risk from activities at pick-your-own facilities was considered negligible, as amitrole is not directly applied on the fruit or on the crop foliage.

Occupational Risks from Handling Amitrole

Occupational non-cancer risks to handlers are of concern for most uses of amitrole.

Most non-cancer risk estimates associated with mixing, loading, and application activities for amitrole did not reach the target Margin of Exposure (MOE) even with consideration of mitigation measures such as maximum Personal Protective Equipment (PPE) and engineering controls, and are therefore of concern. Even with maximum mitigation, the only uses that reach the target margin of exposure are spruce bareroot (seedlings and seedbeds). Using the lowest application rates for low-pressure handwand application, uses on pastures, roadsides, fencerows, and ditchbanks also reached the target MOE; however, postapplication exposure concerns for these uses were identified.

Occupational cancer risk to handlers is not of concern for most uses of amitrole.

Most occupational cancer risks are not of concern for agricultural scenarios, provided mitigation measures such as additional engineering controls, PPE and restrictions on amount handled per day are employed. Cancer risk is of concern for handlers applying to shelterbelts and poplar crops.

Occupational non-cancer risks for postapplication workers are of concern for most uses of amitrole.

Occupational postapplication risk assessments consider exposures to workers entering treated agricultural sites. Based on the current use pattern for amitrole, non-cancer risks to workers performing scouting activities in most crops did not meet current standards and are of concern. Even with mitigation measures, the Restricted-Entry Intervals (REIs) required to mitigate postapplication risk range from four to 70 days and may not be agronomically feasible for most crops. The only use with an agronomically feasible REI is spruce bareroot (seedbeds) with an REI of four days.

Occupational cancer risks for postapplication workers are not of concern for all uses of amitrole when REIs are considered.

Postapplication cancer risks for workers entering treated sites were not of concern, provided that the long REIs required for entry into a treated site (based on the non-cancer assessment) were considered.

Environment Considerations

What Happens When Amitrole is Introduced Into the Environment?

Amitrole poses a potential risk to terrestrial and aquatic organisms; therefore additional risk reduction measures need to be observed.

When amitrole is released into the environment, some of it can be found in soil and surface water. In soil, amitrole is broken down by microbes; thus, it is not expected to persist in the environment. Laboratory studies indicate that amitrole could leach in soil. However, field studies (relevant to Canadian conditions) conducted in the United States of America, detected amitrole and its transformation products in only the top 30 cm deep soil layer. Leaching is probably offset by microbial transformation.

Amitrole poses a risk to terrestrial and aquatic organisms. Birds and small wild mammals are at risk in and around the site of application due to the consumption of contaminated food items. These risks were determined to be of concern and cannot be mitigated.

Value Considerations

What is the Value of Amitrole?

Amitrole contributes to weed management in a variety of crop and non-crop sites.

Amitrole controls many annual and perennial broadleaf and grassy weeds. It is generally considered to be a specialty herbicide for managing particular perennial broadleaf weeds (for example, Canada thistle in minimum tillage field crop production), toxic plants (for example, poison ivy and poison oak in non-cropped areas), and specific noxious weeds (for example, cattails and horsetails in pastures, shelterbelts or non-crop lands).

As a niche product, the amount of amitrole used in Canada is limited when compared with many other herbicides. Active ingredients other than amitrole are registered for use on all sites listed on the amitrole label. However, for a few difficult to control weeds (for example, cattails, poison oak, milkweed, and hoary cress), only one alternative herbicide is registered.

Measures to Minimize Risk

Based on health concerns, the PMRA is cancelling the registration of amitrole and all associated end-use products for all uses with the exception of use on spruce bareroot nursery stock (seedbeds).

Appendix II of Re-evaluation Decision RVD2014-02, Amitrole lists all required label amendments.

What Additional Scientific Information is Being Requested?

The following data is required under section 12 of the Pest Control Products Act for continued registration:

Chemistry Data

  • Analytical data from fiver recent batches of the technical grade active ingredient to adequately identify any impurities of concern.

Other Information

Any person may file a notice of objectionFootnote 5 regarding this decision on amitrole within 60 days from the date of publication of the Re-evaluation Decision RVD2014-02, Amitrole. For more information regarding the basis for objecting (which must be based on scientific grounds), please refer to the Pesticides and Pest Management portion of Health Canada's website (Request a Reconsideration of Decision) or contact the PMRA's Pest Management Information Service.

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