Proposed Re-evaluation Decision PRVD2012-01, Amitrole

Pest Management Regulatory Agency
13 March 2012
ISSN: 1925-0967 (PDF version)
Catalogue number: H113-27/2012-1E-PDF (PDF version)

Summary

Table of Contents

• Proposed Re-evaluation Decision for Amitrole
• What Does Health Canada Consider When Making a Re-evaluation Decision?
• What Is Amitrole?
• Health Considerations
• Environmental Considerations
• Value Considerations
• Measures to Minimize Risk
• What Additional Scientific Information is Being Requested?
• Next Steps
• Other Information

Proposed Re-evaluation Decision for Amitrole

After a thorough re-evaluation of the herbicide amitrole, Health Canada's Pest Management Regulatory Agency (PMRA), under the authority of the  Pest Control Products Act, is proposing continued registration for the sale and use of certain amitrole uses in Canada.

An evaluation of available scientific information found that under the proposed conditions of use, the use of amitrole on spruce bare root nursery stock (seedbeds) has value and does not present an unacceptable risk to human health or the environment. Higher levels of personal protective equipment are required for groundboom and handwand application. A closed cab is also required for groundboom application.

Most uses of amitrole are being phased out because the human health risks do not meet current standards. 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.

Proposed Re-evaluation Decision PRVD2012-01, Amitrole affects all end-use products containing amitrole registered in Canada. Once the final re-evaluation decision is made, the registrant will be instructed on how to address any new requirements.

Proposed Re-evaluation Decision PRVD2012-01, Amitrole is a consultation document that summarizes the science evaluation for amitrole and presents the reasons for the proposed re-evaluation decision. It also proposes additional risk-reduction measures to further protect human health and the environment.

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 or exposure to the product under its conditions or 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 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, please refer to the following:

• Protecting Your Health and the Environment
• Pesticide Risk Reduction Program
• Pesticide Risk Reduction Program

Before making a final re-evaluation decision on amitrole, the PMRA will consider all comments received from the public in response to Proposed Re-evaluation Decision PRVD2012-01, Amitrole. The PMRA will then publish a Re-evaluation Decision document on amitrole, which will include the decision, the reasons for it, a summary of comments received on the proposed registration decision and the PMRA's response to these comments.

For more details on the information presented in this summary, please refer to the Science Evaluation of Proposed Re-evaluation Decision PRVD2012-01, Amitrole.

What Is Amitrole?

Amitrole is a non-selective systemic 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, 1-11 kg a.i./ha on pasture, poplar and non-crop land.

Based on the PMRA's records, two products are registered 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.

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 and domestic 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 (i.e. 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 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 highly exposed subpopulation (infants less than 1 year of age). This aggregate (i.e. 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 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 (one 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 the PMRA's Science Policy Note SPN2000-01, A Decision Framework for Risk Assessment and Risk Management in the Pest Management Regulatory Agency.

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 Drugs 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)]. Additional details regarding MRLs can be found in the Science Evaluation of Proposed Re-evaluation Decision PRVD2012-01, Amitrole.

Dietary exposure to triazolyl alanine (TA) may occur from the use of amitrole on food commodities. Residues of TA 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 myclobutanil and 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 cumulative risk assessment. Further information on TA can be found in Decision Document E93‑01, 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 MOE are spruce bare-root (seedlings and seedbeds) and, using the lowest application rates for low-pressure handwand application, pastures, roadsides, fencerows, and ditchbanks.

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, personal protective equipment 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 4 to 70 days and may not be agronomically feasible for most crops. The only use with an agronomically feasible REI is spruce bare root (seedbeds) with an REI of 4 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.

Environmental Considerations

What Happens When Amitrole is Introduced Into the Environment?

Amitrole is toxic to certain terrestrial 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. However in soil, amitrole is non-persistent to moderately persistent as it is broken down by soil microbes. Amitrole is not expected to volatilize significantly. Laboratory studies indicate that amitrole is mobile in soil. However, there is no field evidence that the use of this herbicide will result in groundwater contamination, most probably due to the microbiological breakdown of amitrole in soil. In water, amitrole is moderately persistent as it is also susceptible to biotransformation by microbial action.

Amitrole poses a risk to terrestrial plants as a result of spray drift and a potential chronic risk to birds and small mammals. In order to minimize the potential exposure of sensitive plants or animals, an unsprayed area is needed between the sprayer and a downwind sensitive habitat. The width of these spray buffer zones are proposed in this document. Amitrole presents negligible risk to bees, other arthropods and aquatic organisms.

Value Considerations

What is the Value of Amitrole?

Amitrole contributes to weed management in a variety of crop and non-crop sites. Due to risk concerns, all uses listed on the amitrole label except for the use on spruce bare root nursery stock (seedbeds) are proposed to be phased out.

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 as 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, only one alternative herbicide is registered.

The viability of alternatives to amitrole needs to be confirmed through consultation.

Measures to Minimize Risk

Based on health concerns, the PMRA proposes to phase out uses of amitrole and all associated end-use products except spruce bare root nursery stock (seedbeds).

What Additional Scientific Information is Being Requested?

The PMRA is seeking quantitative and/or qualitative information on the economic and social importance of amitrole to specific industries and information on the availability and viability of alternative chemical and non-chemical pest management practices for the site and pest combinations registered for amitrole. This information will allow the PMRA to refine sustainable pest management options for amitrole as well as for alternatives to amitrole.

Next Steps

Before making a re-evaluation decision on amitrole, the PMRA will consider all comments received from the public in response to Proposed Re-evaluation Decision PRVD2012-01, Amitrole. The PMRA will accept written comments on this proposal up to 60 days from the date of publication of Proposed Re-evaluation Decision PRVD2012-01, Amitrole. Please forward all comments to Publications. The PMRA will also consider quantitative and/or qualitative information on the economic and social importance of amitrole to specific industries and information on the availability and viability of alternative chemical and non-chemical pest management practices for the site and pest combinations registered for amitrole.

The PMRA will then publish a Re-evaluation Decision, which will include the decision, the reasons for it, a summary of comments received on the proposed decision and the PMRA's response to these comments.

Once all triazole pesticides have been re-evaluated, a cumulative risk assessment will be conducted, which will consider potential exposure to all chemicals with the same mechanism of toxicity. The results of the cumulative risk assessment may affect any previous re-evaluation decisions.

Other Information

At the time that the re-evaluation decision is made, the PMRA will make available an Evaluation Report on amitrole in the context of this re-evaluation decision (based on the Science Evaluation section of Proposed Re-evaluation Decision PRVD2012-01, Amitrole). In addition, the test data on which the decision is based will also be available for public inspection, upon application, in the PMRA's Reading Room (located in Ottawa, Ontario, Canada).