Re-evaluation Decision RVD2015-04, Dimethoate

Pest Management Regulatory Agency
30 December 2015
ISSN: 1925-1025 (PDF version)
Catalogue number: H113-28/2015-4E-PDF (PDF version)

Table of Contents

Re-evaluation Decision

After a thorough re-evaluation of the insecticide dimethoate, 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 dimethoate products in Canada.

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

  • Certain uses of dimethoate products have value in the food and crop industry, and do not pose unacceptable risks to human health or the environment. As a requirement of continued registration for these particular dimethoate uses, new risk-reduction measures must be included on the labels of certain dimethoate products.
  • Some uses of dimethoate are, however, being phased out because the human health risks and/or risks to the environment do not meet current standards. These uses include the following: application to structural sites, paint-on treatments to birch, roses and lilac, as well as, soil drench application to carnations.

The regulatory approach regarding the re-evaluation of dimethoate was first proposed in the consultation document Proposed Re-evaluation Decision PRVD2011-12, Dimethoate. Re-evaluation Decision RVD2015-04, Dimethoate describes the PMRA’s regulatory process concerning the re-evaluation of dimethoate, as well, summarizes the Agency’s decision, the reasons for it. Appendix I of RVD2015-04, Dimethoate, a summary of comments received during the consultation process, and subsequently, the PMRA’s response to these comments.

To comply with this decision, new and revised risk mitigation measures should be implemented as soon as possible but no later than 30 December 2017. Registrants of dimethoate products will be informed of the specific requirements affecting their product registration(s), as well as of the regulatory options available to them.

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 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, as well as the uncertainties present when predicting the impact of pesticides. For more information, please refer to the following:

What is Dimethoate?

Dimethoate is a broad spectrum organophosphate insecticide and acaricide. It is used to control a broad range of insects and mites on a variety of agricultural sites and contributes to insecticide resistance management.

Health Considerations

Can Approved Uses of Dimethoate Affect Human Health?

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

Potential exposure to dimethoate may occur through the diet, when handling and applying the product, or when entering or contacting treated sites. 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 populations (for example, children and pregnant women). 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 as well as identify the dose where no adverse 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. Please see PRVD2011-12 for a detailed description of the dimethoate toxicology assessment.

Residues in Water and Food

Dietary risks from food and drinking water are not of concern.

Reference doses define levels to which an individual can be exposed over a single day (acute) or a 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.

Human exposure to dimethoate was estimated from residues in food and drinking water, including the most highly exposed subpopulation (for example, infants, and children 1-2 years old). Residue estimates in food were primarily based on monitoring data from the Canadian Food Inspection Agency, and the United States Department of Agriculture (USDA) Pesticide Data Program. Residues in drinking water were estimated using modeling data. The drinking water modeling estimates and residue estimates for some foods have been revised since PRVD2011-12 in consideration of new data submitted during the consultation period. Details on these changes can be found in Appendix I of Re-evaluation Decision RVD2015-04, Dimethoate.

The revised aggregate acute and chronic exposure (for example, to dimethoate exposure from food and drinking water) accounted for no more than 71% of the acute reference dose and 16% of the chronic reference dose for all population groups. As a result, dietary exposure from food and drinking water were not of concern to the PMRA.

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 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 an unacceptable health risk.

MRLs for dimethoate are currently specified for a wide range of commodities. Where no specific MRL has been established, a default MRL of 0.1 ppm applies, which means that pesticide residues in a food commodity must not exceed 0.1 ppm.

Canadian MRLs for dimethoate on apples, cabbage, and spinach will be revoked as the use on these commodities has been discontinued by the registrant in both Canada and the United States. In addition, the MRL for lettuce will be changed to leaf lettuce as the use on head lettuce has also been discontinued.

Risks in Residential and Other Non-Occupational Environments

Aggregate risk from exposure incurred as a patron of a “Pick Your Own” orchard or berry facility is not of concern.

“Pick Your Own (PYO)” facilities are commercial farming operations that allow public access for harvesting in large-scale fields or orchards treated with commercially labelled dimethoate products. Estimates of exposure that aggregate the dermal exposure incurred during harvest and the dietary exposure from consuming fresh fruit reach the target Margin of Exposure (MOE) for orchard and berry crops, and are therefore, not of concern.

Occupational Risks from Handling Dimethoate

The majority of occupational risks are not of concern provided additional mitigation measures are followed.

Occupational risk assessments from handling dimethoate consider exposure to workers who mix, load and apply the pesticide. Most occupational risks are not of concern for commercial, and agricultural scenarios provided additional protective measures are followed.

Based on additional use pattern information submitted in response to PRVD2011-12 for dimethoate, the occupational risk assessments for forestry uses (Douglas fir (seed tree), Sitka spruce (seed tree) and spruce (seed tree and woodland)) and right-of-way sprayer application were reassessed. Following consideration of additional mitigation measures, including additional personal protective equipment and engineering controls, calculated margins of exposure (MOE) reach the target margin and are not of concern. Additional mitigation measures are required to minimize potential exposure and protect worker’s health.

Use scenarios that remain of concern include paint-on-applications (ornamentals), soil drench applications (carnations), and applications to structural sites. Due to occupational risk concerns these uses will be cancelled.

Occupational postapplication risks are not of concern based on revised label directions.

Postapplication occupational risk assessments consider exposures to workers entering treated sites. When the proposed mitigation measures such as lengthened restricted-entry intervals (REIs) are considered, occupational postapplication risk estimates meet the target MOE, and are not of concern.

Based on additional use pattern information submitted in response to PRVD2011-12 for dimethoate, the REIs for forestry uses (Douglas fir (seed tree), Sitka spruce (seed tree) and spruce (seed tree and woodland)) were recalculated. Users have indicated that the calculated REIs for seed cone harvesting of 48 and 49 days are agronomically feasible.

Environmental Considerations

What Happens When Dimethoate Is Introduced into the Environment?

When used according to label directions, dimethoate is not expected to pose an unacceptable risk to the environment.

When dimethoate is released into the environment, it can enter soil and surface water, where it breaks down rapidly. Although laboratory studies indicate that dimethoate is mobile in soil, it is not detected in groundwater, most likely due to its rapid break down. Dimethoate is not expected to volatilize significantly.

In laboratory studies, dimethoate was found to be toxic to some terrestrial and aquatic organisms. Therefore, risk mitigation measures in the form of use restrictions and precautionary label statements are required in order to minimize exposure and mitigate risks. For pollinators, risks are mitigated by restricting applications to periods when bees are not actively foraging. The risk to aquatic organisms is mitigated with spray buffer zones and recommendations on the label to reduce runoff from fields. When dimethoate is used in accordance with the label and the mitigation measures have been applied, the reduced environmental exposure is deemed adequate and the risk is considered to be acceptable.

Value Considerations

In Canada, dimethoate is registered to control a wide range of insect pests such as: aphids, beetles, weevils, grasshoppers, flies, leafhoppers, scale insects, thrips, moths and spider mites.

Dimethoate is used on both agricultural and non-agricultural sites which include feed, food, industrial oil seed and fibre, forestry and ornamental crops. It is also effective as residual spray for fly control around farm buildings, animal quarters (empty), food processing plants (outdoor use), garbage cans (outdoor use), loading docks (outdoor use), warehouses (outdoor), outdoor refuse areas, pastures and wasteland.

Dimethoate contributes to insecticide resistance management. Dimethoate plays an important role in delaying resistance when used in rotation with insecticidal active ingredients from different Mode of Action (MoA) groups. Based on Canadian pesticide labels, dimethoate is the only insecticide currently registered in Canada to control insect pests of Douglas fir (seed tree), Sitka spruce (seed tree) and spruce (seed tree and woodland use).

Incident Reports

An incident involving adverse effects to cherry trees following application of a dimethoate product occurred in June 2011. It was reported that leaf necrosis and leaf drop were observed in a block of Lapin cherry trees in British Columbia. This variety of cherry trees has been documented to be sensitive to dimethoate. The label for this dimethoate product will be amended to better warn users of the sensitivity some plants may have to dimethoate (see Appendix IV of Re-evaluation Decision RVD2015-04, Dimethoate). Details regarding this incident can be found under Incident Reports 2011-4810 and 2011-4464.

As of January 2015, eleven individual Canadian incident reports linked to dimethoate and bee mortality have been submitted to the PMRA. The classification of the reports ranged from probable to highly probable that application of dimethoate contributed to the mortality of the bees. The incidents occurred throughout Canada (Ontario, Manitoba, Saskatchewan and Nova Scotia) from June to August 2012 with the majority occurring in Saskatchewan. The reports indicated that dimethoate was being sprayed on strawberries (one report), soybeans (one report), alfalfa (one report) and canola (eight reports from two beekeepers). The reported magnitude of effects ranged from 2000 to 3000 dead bees in front of 95 colonies in Nova Scotia to a reported 50% loss of honey bees at sites in Saskatchewan. Many of the bees from the Nova Scotia and Saskatchewan sites contained dimethoate residues, as determined by laboratory analysis.

There were also twelve American incident reports involving dimethoate and bee mortality. Of the twelve incident reports, 10 were possible, one was probable and one was highly probable. Some (four) of the reports indicated that beans were the target crop. Other crops included corn, soybean and orchard. Of the known areas of the effects, three were a result of on-site application to agricultural areas, orchards or fields, and five were a result of application in the vicinity, indicating spray drift. The majority of the incidents indicated the route of exposure was ingestion or spray drift. The magnitude of effects ranged from 20 hives to 150 colonies, and up to 1256 dead bees.

The label for the dimethoate products will be amended to reduce exposure to pollinators (see Appendix IV of Re-evaluation Decision RVD2015-04, Dimethoate).

Organisation for Economic Co-operation and Development Status

Canada is part of the Organisation for Economic Co-operation and Development (OECD), which assembles member countries as well as provides a forum for which governments can work together to share experiences and seek solutions to common problems.

As part of the re-evaluation of an active ingredient, the PMRA takes into consideration recent developments and new information on the status of an active ingredient in other jurisdictions, including OECD member countries. In particular, decisions by an OECD member country to prohibit all uses of an active ingredient for health or environmental reasons are considered for relevance to the Canadian situation.

Dimethoate is currently acceptable for use in other OECD countries, including the United States, New Zealand and the European Union. As of 18 March 2015, no decision by an OECD member country to prohibit all uses of dimethoate for health or environmental reasons has been identified.

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 followed by law.

Risk-reduction measures are being implemented to address potential risks identified in this assessment. These measures, in addition to those already identified on existing dimethoate product labels, are designed to further protect human health and the environment. Registrants will be required to amend their labels to reflect these additional measures. The following additional key risk-reduction measures are to be implemented:

Additional Key Risk-Reduction Measures

Human Health

After consideration of all other possible mitigation measures, the following use registrations are to be cancelled due to occupational risk concerns:

  • application to structural sites,
  • paint-on treatments to birch, roses and lilac, and
  • soil drench application to carnations.

These uses must be removed from all dimethoate labels.

For all remaining uses, to protect mixer/loader/applicators using commercial products, additional personal protective equipment, engineering controls and restrictions on amount of product handled per day are required.

For all remaining uses, to protect workers entering treated sites: restrictions on the number of applications, increased application intervals and restricted-entry intervals are to be added to product labels.

Precautionary statements to avoid drift to areas of human habitation or areas of human activity are to be added to product labels.

Aggregate dietary and drinking water exposure including risk will be mitigated by increasing preharvest intervals (PHI) and reducing maximum application rates.


Changes to label statements, including precautionary statements; use restrictions, and spray buffer zones for non-target aquatic habitats are required as a result of the environmental risk assessment.

To reduce the potential for dimethoate to runoff to adjacent aquatic habitats, changes to label statements will include precautionary statements for sites with characteristics that may be conducive to runoff and when heavy rain is forecasted.

To protect pollinators, dimethoate cannot be applied to blooming crops when bees are foraging. This includes restricting applications during the blooming period of bee attractive crops.

What Additional Scientific Information is Being Requested?

Human Health

There are no outstanding data requirements with regard to human health.


There are no outstanding data requirements with regard to environment.

Other Information

Any person may file a notice of objection based on scientific grounds regarding this decision on dimethoate within 60 days from the date of publication of Re-evaluation Decision RVD2015-04, Dimethoate. For more information regarding the basis for objecting, 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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