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ARCHIVED - Proposed Re-evaluation Decision PRVD2011-06, MCPB

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Notice to the reader:

The online consultation is now closed. Comments and suggestions received during the public consultation period are being considered in the finalization of this document. The final report will be made available as soon as possible.

February 7, 2011
ISSN: 1925-0959 (print version)
ISSN: 1925-0967 (PDF version)
Catalogue number: H113-27/2011-06E (print version)
Catalogue number: H113-27/2011-06E-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 Re-evaluation Decision PRVD2011-06, MCPB, please contact our publications office.

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

Summary

Table of Contents

Proposed Re-evaluation Decision for MCPB

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

An evaluation of available scientific information found that, under the proposed conditions of use:

The PMRA will accept written comments on this proposal up to 60 days from the date of publication of this document. Please forward all comments to Publications.

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:

Before making a re-evaluation decision on MCPB, the PMRA will consider all comments received from the public in response to this consultation document. The PMRA will then publish a Re-evaluation Decision document on MCPB, 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 overview, please refer to the Science Evaluation section of the Proposed Re-evaluation Decision PRVD2011-06, MCPB.

What is MCPB?

MCPB is a selective systemic herbicide. It is registered for the post-emergence control of annual and perennial broadleaf weeds in terrestrial food crops, terrestrial feed crops and industrial oil seed crops and fibre crops. The rate of application for MCPB ranges from 1.031 to 1.594 kg a.i./ha. It is applied once per year. MCPB can be applied by ground and/or aerial equipment.

Health Considerations

Can Approved Uses of MCPB Affect Human Health?

MCPB is unlikely to affect human health when used according to revised label directions.

Potential exposure to MCPB may occur through diet or when handling and/or applying the product. When assessing health risks, two key factors are considered: the levels where 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, pregnant women, nursing mothers and children). Only the uses for which exposure is well below levels that cause no effects in animal testing are considered acceptable for continued registration.

Toxicology studies in laboratory animals describe potential health effects from varying levels of exposure to a chemical and identify the dose at which 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 MCPB are used according to label directions.

MCPB is of moderate acute oral toxicity, low acute dermal toxicity, and slight acute inhalation toxicity in laboratory animals. MCPB is non-irritating to the skin, moderately irritating to the eyes and is not a dermal sensitizer.

The most sensitive endpoint for non-pregnant animals from the oral route of exposure is kidney toxicity. Test data indicated that MCPB is not likely to be carcinogenic or mutagenic in humans.

When MCPB is administered to pregnant rats and rabbits, reduced skeletal ossification and increased incidences of cranio-facial malformations are observed. Due to the nature of the effects and their potential implications on the health and survival of the fetus, extra protective factors are applied during the risk assessment to further reduce the allowable level of human exposure to MCPB.

With the proposed mitigation measures, the risk assessment protects against these effects by ensuring that the level of human exposure is well below the lowest dose at which these effects occur in animal tests.

Residues in Food and Water

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 (ADI) 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.

Dietary exposure to MCPB was estimated from residues in treated crops and drinking water for different subpopulations representing different ages, genders and reproductive status. Acute and chronic exposure estimates were determined for the general population and all subpopulations including females of child-bearing age (13 to 49 years old), infants and children.

The aggregate acute exposure (i.e. to MCPB from food and drinking water) represents 39% of the acute reference dose for females 13 to 49 years old and is in the range of 1 to 5% of the acute reference dose for all the other population subgroups when using drinking water concentrations generated from water modelling. The aggregate chronic exposure represents 5% of the chronic reference dose for the general population and is in the range of 4 to 10% of the chronic reference dose for all subpopulations. Thus, acute and chronic dietary risks are not of 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. Each MRL value defines the maximum concentration in parts per million (ppm) of a pesticide allowed in or on certain foods. Food containing a pesticide residue that is at or below the established MRL does not pose an unacceptable health risk.

MRLs in/on all commodities treated with MCPB are currently regulated under B.15.002(1) of the Food and Drug Regulations which requires that residues do not exceed 0.1 ppm. Details regarding MRLs for MCPB can be found in the Science Evaluation Section.

Risks in Residential and Other Non-Occupational Environments

Residential and other non-occupational risks are not of concern.

MCPB is not registered for use in residential areas. Therefore, a non-occupational risk assessment was not required.

Occupational Risks from Handling MCPB

Occupational risks for handlers are not of concern with most crops provided that risk mitigation measures are applied. Occupational risks for handlers of MCPB for dry/field peas are of concern even with consideration of feasible risk mitigation measures. All aerial application scenarios are of concern with MCPB.

Based on the precautions and directions for use on the original product labels reviewed for this re-evaluation, the risk assessment of mixing/loading and application activities indicate that target margins of exposure (MOEs) are achieved for most crops provided that risk mitigation measures are applied. The MOEs for mixing/loading and application reach target MOEs for pastures, cereals (wheat, oats, barley and rye), seedling alfalfa, seedling clover, field corn, seedling grasses, and succulent/processing peas with the addition of mitigation measures including the use of additional protective equipment, engineering controls, and limiting the amount of kilograms handled per day.

Occupational post-application risks are not of concern for all crops provided that risk mitigation measures are applied.

Occupational post-application risk assessments consider exposure to workers entering treated agricultural sites. Based on the precautions and directions for use on the original product labels reviewed for this re-evaluation, post-application risks to workers meet current standards and are not of concern for all crops provided that restricted entry intervals (REIs) are modified accordingly on the "use directions" (12 hours to 1 day) for most crops. For field corn, REIs were 15 and 23 days, depending on the activity. These REIs are considered to be agronomically feasible due to the timing of application. Consultation with user groups on the acceptability of these health protective use conditions is sought.

Environmental Considerations

What Happens When MCPB is Introduced Into the Environment?

MCPB poses a risk to terrestrial broadleaf plants, birds, small wild mammals and aquatic organisms including macrophyte plants and amphibians; therefore, additional risk-reduction measures need to be observed.

MCPB can enter non-target terrestrial habitats by drift from aerial or ground application such as pasture use, and it can enter aquatic habitats by run-off and leaching. It is water soluble and can move through the soil profile horizontally and vertically, thereby contaminating ground water and surface water, including drinking water sources. MCPB does not accumulate or bioconcentrate in the environment, and it is not persistent in soil, having a degradation half-life of 8.3 days depending on the type of soil. In aquatic environments, biotransformation eliminates fifty percent of the chemical in less than 18 days, and degradation by sunlight in surface water can be even more rapid.

Because of the specific mode of action affecting broadleaf plants (MCPB is a synthetic auxin plant hormone similar to other phenoxy herbicides such as 2,4-D), it is highly toxic to terrestrial plants such as trees, shrubs, crops and others. Non-target invertebrates including bees and beneficial insects are not likely to be affected by this chemical. Although vertebrate animals including birds and small wild mammals are not usually affected by MCPB's specific mode of action, some species show slight to moderate toxicity for oral/dietary exposure. In aquatic habitats, fish and invertebrates are not likely to be affected by MCPB based on available data, however, aquatic plants such as duck weed are sensitive.

The use of MCPB poses a risk to terrestrial and aquatic organisms, including plants, birds, mammals, aquatic plants and amphibians. To reduce exposure of terrestrial organisms, environmental hazard label statements are recommended. Terrestrial plants including crops and non-target plant habitats such as shelter belts and riparian zones along streams and ponds can be protected from adverse effects by the observance of specified spray restrictions which provide a spray buffer zone between sites of the application and non-target areas. Furthermore, precautionary label statements will be used to help reduce the potential for surface runoff and for ground water contamination.

Value Considerations

What is the Value of MCPB?

MCPB continues to contribute to weed management in a variety of crops when used in accordance with the label directions.

MCPB is one of the few post-emergent herbicides that controls a broad spectrum of annual and perennial broadleaf weeds in peas (dry/field and succulent/processing). MCPB is co-formulated with MCPA to broaden the spectrum of weed control. When formulated with MCPA, it is the only alternative to 2,4-DB registered for use in seedling clovers (wild white, Dutch white, ladino, alsike, and red clovers) alone or with a companion crop (wheat, barley and oats). It is one of the few post-emergent herbicides for use in seedling grasses and in seedling alfalfa grown for seed production. MCPB also plays a role in mitigating resistance development in weeds to other herbicide groups when used in rotation with them.

Measures to Minimize Risk

Registered pesticide product labels include specific instructions for use. Directions include risk-reduction measures to protect human and environmental health. These directions must be followedby law.

Risk-reduction measures are being proposed to address potential risks identified in this assessment. These measures, in addition to those already identified on existing thiophanate-methyl product labels, are designed to further protect human health and the environment. The following additional key risk-reduction measures are being proposed.

Human Health

Environment

What Additional Scientific Information Is Required?

Although the risks and value have been found to be acceptable when all risk-reduction measures are followed, with the exception of some uses, additional information is being requested from registrants and other stakeholders as a result of this re-evaluation:

Recent analytical data from at least five batches of the technical grade active ingredient (TGAI) must be provided for all identifiable dioxins and furans from a GLP-compliant or government-accredited laboratory.

The report should include data for the 17 substances listed in Table 4 of the Priority Substances List 1 document "Polychlorinated dibenzodioxins and polychlorinated dibenzofurans".

The analytical method(s) used must utilize the lowest practical limits of quantitation and be fully specified, either by reference to a standard method or by inclusion of a detailed description together with validation data.

As a result of the proposed restrictions on the amount of MCPB handled per day as well as the proposed REIs, the PMRA is requesting feedback on:

Due to the proposed phase out of dry/field peas and aerial application, the PMRA is requesting feedback on:

Next Steps

Before making a re-evaluation decision on MCPB, the PMRA will consider all comments received from the public in response to this consultation document. 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. At this time, information to confirm or refine the risk assessment will also be required (see Section 8.2 of the Science Evaluation section of the Proposed Re-evaluation Decision PRVD2011-06).

Other Information

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).

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2019-12-19