Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation

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Pest Management Regulatory Agency
30 November 2016
ISSN: 1925-0649 (PDF version)
Catalogue number: H113-5/2016-18E-PDF (PDF version)

Table of Contents

1.0 Introduction

The Pest Management Regulatory Agency (PMRA) has initiated a special review of diazinon under subsection 17(1) of the Pest Control Products Act based on the toxicology information submitted under section 12 of the Pest Control Products Act, following the re-evaluation of diazinon (Canada, 2009; Canada, 2016).

As required by subsection 18(4) of the Pest Control Products Act, the PMRA has evaluated the aspects of concern that prompted the special review of pest control products containing diazinon.

2.0 Uses of Diazinon in Canada

Diazinon is an organophosphate insecticide with acetylcholinesterase inhibition activity. Diazinon is registered for cattle ear tags and as a soil drench application on blackberry, loganberry, raspberry, onion, rutabaga and turnip. All currently registered pest control products containing diazinon (Appendix I of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation) are considered in this special review.

All seed treatment, foliar and granular uses of diazinon were cancelled as part of the re-evaluation decision (Canada, 2009). The last date of use for these uses is 31 December 2016. These uses have not been considered in the special review.

3.0 Aspects of Concern that Prompted the Special Review

The PMRA reviewed information submitted under Section 12 of the Pest Control Products Act (Appendix II of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation) following the re-evaluation, and re-assessed the existing toxicological database for diazinon. The findings of the comparative cholinesterase and developmental neurotoxicity studies confirmed that inhibition of brain and erythrocyte cholinesterase activities were the most sensitive toxicological effects. Furthermore, the studies indicated sensitivity of the young to cholinesterase inhibition.

Based on the reassessed database, new diazinon toxicological endpoints for dermal exposure have been established (Appendix III of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation). The revised toxicological endpoints for dermal risk assessment affect the existing occupational assessment (Canada, 2009). Consequently, the following aspects of concerns are identified for the special review under subsection 17(1) of the Pest Control Products Act:

  • Potential risk to workers mixing/loading/applying;
  • Potential risk to postapplication workers.

Endpoints for characterization of potential dietary risks are higher than the existing risk assessment, whereas endpoints for inhalation risk assessment remained the same. No update to the dietary assessment is required.

Regarding the Pest Control Products Act factor, the toxicity data are considered complete. Based on the nature and level of concern for the cholinesterase endpoint and the fact that, for certain risk assessments, the endpoint was established from data on the sensitive subpopulation, the Pest Control Products Act factor is reduced to 1-fold.

4.0 PMRA Evaluation of the Aspects of Concern that Prompted the Special Review

Following the initiation of the special review of diazinon, the PMRA requested information from provinces and other relevant federal departments and agencies, in accordance with subsection 18(2) of the Pest Control Products Act. No information was received related to the aspects of concern.

In order to evaluate the aspects of concern for diazinon, the PMRA has considered currently available relevant scientific information, which includes information considered for the re-evaluation, and information submitted under section 12 of the Pest Control Products Act following the re-evaluation (Appendix II of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation). No information related to the aspects of concern was identified in the Canadian incident report database.

4.1 Potential Risk to Workers Mixing/Loading/Applying (M/L/A)

Occupational risk is estimated by comparing potential exposures with the most relevant endpoint from toxicology studies (Appendix III of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation) to calculate a margin of exposure (MOE). This is compared to a target MOE incorporating uncertainty factors protective of the most sensitive subpopulation. If the calculated MOE is less than the target MOE, it does not necessarily mean that exposure will result in adverse effects, but mitigation measures to reduce risk would be required.

4.1.1 Potential Risk to Workers (M/L/A) from Field Applications (Soil Drench)

Diazinon, as a soil drench, can be applied once for onion, blackberry, loganberry and raspberry (at the early stage of the plant growth cycle) or multiple times for rutabaga and turnip (at different plant growth stages) (Appendix IV of of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation). The national production data indicates that the planted areas of these crops are small (AAFC, 2007, 2012(a) and 2012(b)). Based on the above, exposure of workers mixing, loading and applying diazinon, as a soil drench, is expected to be of a short-term duration and to occur via both dermal and inhalation routes. In turn, the following potential exposure scenarios are identified for the current conditions of use:

  • Mixing/loading of wettable powder in water soluble packaging with workers wearing a long-sleeved shirt, long pants, socks, shoes, and chemical-resistant gloves;
  • Mixing/loading of emulsifiable concentrates using a closed mechanical transfer loading system with workers wearing a long-sleeved shirt, long pants, socks, shoes, and chemical-resistant gloves;
  • Mixing/loading of emulsifiable concentrates using an open mechanical transfer loading system with workers wearing chemical resistant coveralls over a long-sleeved shirt and long pants, chemical-resistant gloves and footwear, and a NIOSH-approved respirator; and
  • Applying to onion, rutabaga, turnip, blackberry, loganberry and raspberry by soil drench groundboom equipment with a closed cab with workers wearing a long-sleeved shirt, long pants, socks and shoes.

Dermal and inhalation exposures were combined because these exposures occur simultaneously and they have a common toxicological endpoint (cholinesterase inhibition). Combined (dermal and inhalation) handler exposure doses were estimated using data from the Pesticide Handlers Exposure Database (PHED), Version 1.1. Details of the assumptions and calculations are presented in Appendix V.

The target MOE of 100 was not met for most of the assessed scenarios (MOEs = 17-90), when the personal protective equipment (PPE) as stated on the current label was considered. However, the identified risks can be mitigated with additional PPE and by limiting the amount of active ingredient handled per day (MOEs = 100-549; Appendix V of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation), except for emulsifiable concentrates, with an open mechanical transfer loading system. The proposed risk reduction measures to minimize exposure to workers are presented in Appendix VII of of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation.

4.1.2    Potential Risk to Workers from Applying Ear Tags to Cattle

Ear tags are applied once a year and are handled by using an ear tag application tool. Tags are removed at the end of the season and before slaughter. Ear tags are impregnated plastic designed as slow release generators. Considering the low frequency of application, the design of the product (as a slow release of diazinon), and the current label requirement to wear chemical-resistant gloves when handling the tag, potential worker exposure is expected to be minimal. On this basis, the potential risk to workers handling ear tags is not of concern and no mitigation measures are proposed for this scenario.

4.2 Potential Risk to Postapplication Workers

There is a potential for postapplication exposure of agricultural workers re-entering sites, treated with diazinon, to conduct agricultural activities. To protect workers involved in postapplication activities, restricted-entry intervals (REIs) are calculated to determine the minimum length of time required before people can enter the field to conduct hand labour following pesticide application. An REI is the duration of time that must elapse before residues decline to a level where performance of a specific activity results in exposures below the level of concern.

For these workers, dermal exposure is considered to be the primary route of exposure. Considering the low volatility of this active ingredient (1.4 × 10-4 mm Hg) relative to the NAFTA criterion for a waiver of inhalation exposure data for outdoor uses (NAFTA, 1999), and the current label directions which include REIs, inhalation exposure to diazinon is not expected to be of concern for postapplication workers re-entering treated sites.

For onion, following a single soil drench application at planting and soil incorporation, residues on onion plants are expected to be negligible and thus, soil contact is the most likely exposure scenario for postapplication workers. For berries, following a single application in the early spring at the time when new canes reach 10 cm height, residues on berry canes are expected to also be negligible. Considering that larvae of raspberry crown borers usually locate at crown areas and/or under the soil surface, scouters usually dig up and cut through crowns using tools to look for larvae. It should also be noted that most varieties of blackberries, loganberries and raspberries have prickles and thus, it is reasonably expected that gloves are commonly used in these fields. Therefore, soil contact is considered as the major route of exposure and the likelihood of plant (cane) contact with bare hands is considered to be unlikely. Given the timing of application of diazinon, harvesting activities are not considered for onion and berries. For rutabaga and turnip, diazinon can be applied at early growth season for control of larvae of root maggots, followed by weekly applications 5-6 weeks after the second application for control of adult root maggot. Considering possible multiple application of diazinon to rutabaga and turnip, thinning, hand weeding, handset irrigation and hand harvesting are considered as likely exposure scenarios. Consequently, the following potential postapplication exposure scenarios are considered as part of the special review:

  • Onion: scouting with potential contact with soil.
  • Blackberry, loganberry and raspberry: scouting with potential contact with soil.
  • Rutabaga and turnip: scouting, thinning, hand weeding, handset irrigation and hand harvesting with potential contact with soil, seedlings, leaves and stems.

The postapplication risk assessment is summarized in Appendix VI of of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation.

Onion: Potential dermal exposure of workers to diazinon from soil contact during scouting was not of concern. No additional mitigation measures are proposed.

Blackberry, Loganberry and Raspberry: Potential dermal exposure of workers to diazinon from soil contact during scouting was not of concern. The use of gloves (as described above) is expected to further limit the potential exposure to diazinon for these crops. No additional mitigation measures are proposed.

Rutabaga and Turnip: The PMRA calculated daily dermal exposure estimates for postapplication agricultural workers using default dislodgeable foliar residue (DFR) assumptions. Additional inputs included transfer coefficient (TC) values from studies conducted by the Agricultural Re-Entry Task Force (ARTF), an 8-hour work day, 50% dermal absorption, and an average worker body weight of 80 kg.

In rutabaga and turnip, diazinon is used for the control of root maggot larvae and adults.

For control of root maggot larvae using 1-2 applications at seedling stage, the calculated REIs needed to mitigate potential risks to postapplication workers are 15, 25 and 45 days for thinning/hand weeding, foliar-contact scouting, and handset irrigation, respectively. This is an increase from the existing REI of 4 days on the current label. As the monitoring for disease pressure can also be done by using yellow pan traps and visual scouting, which results in no contact with foliage of rutabagas and turnips, potential exposure during non-foliar contact scouting is expected to be negligible for such activity. On this basis, a default REI of 12 hours would apply for non-foliar contact scouting (Appendix VII of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation).

For control of root maggot adult at the stage when foliage is developed, the calculated REIs needed to mitigate potential risks to postapplication workers are 10, 20, 40 and 36 days for hand weeding, plant-contact scouting, handset irrigation and hand harvesting, respectively. These REIs may not be agronomically feasible due to the timing of application relative to the activities. Therefore, use of diazinon for the control of root maggot adults is proposed for cancellation (Appendix VII of Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation)

5.0 Proposed Special Review Decision for Diazinon

Evaluation of available scientific information related to the aspects of concern, indicated that the registered products containing diazinon do not pose unacceptable risk to human health and the environment with the proposed mitigation measures. On this basis, the PMRA is proposing to confirm the current registration of products containing diazinon for sale and use in Canada with the proposed risk mitigation measures pursuant to subsection 21(1) of the Pest Control Product Act.

Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation is a consultation document. The PMRA will accept written comments on REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation up to 45 days from the date of publication of REV2016-18. Please forward all comments to Publications.

6.0 Next Steps

Before making a special review decision on diazinon, the PMRA will consider any comments received from the public in response to Re-evaluation Note REV2016-18, Special Review of Diazinon - Subsection 17(1) of Pest Control Products Act: Proposed Decision for Consultation. A science-based approach will be applied in making a final decision on diazinon. The PMRA will then publish a special review decision document, which will include the decision, the reasons for it, a summary of the comments received on the proposed decision and the PMRA’s response to these comments.

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