Proposed Special Review Decision PSRD2019-04, Special Review of Tetrachlorvinphos and Its Associated End-use Products

 

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Pest Management Regulatory Agency
26 April 2019
ISSN: 2561-636 (PDF version)
Catalogue number: H113-30/2019-4E-PDF (PDF version)

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Web Summary

Table of Contents

1.0 Introduction

Pursuant to subsection 17(1) of the Pest Control Products Act, Health Canada’s Pest Management Regulatory Agency (PMRA) initiated a special review of tetrachlorvinphos (Canada, 2016) based on the toxicology information submitted under section 12 of the Pest Control Products Act, following the re-evaluation of tetrachlorvinphos (Canada, 2003; and Canada, 2004).

Pursuant to 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 tetrachlorvinphos. The aspects of concern for this special review are relevant to human health (potential occupational and residential risks).

2.0 Uses of Tetrachlorvinphos in Canada

Tetrachlorvinphos is a broad spectrum organophosphate insecticide registered for use on animals for food production (beef cattle, dairy cattle, poultry), companion animals (cats, dogs) and their bedding and living quarters, and in structures (for example, dairy barns, poultry houses, swine barns). All currently registered pest control products containing tetrachlorvinphos are considered in this special review (Appendix I of Proposed Special Review Decision PSRD2019-04, Special Review of Tetrachlorvinphos and Its Associated End-use Products).

3.0 Aspects of Concern that Prompted the Special Review

The PMRA reviewed toxicology information that was submitted under section 12 of the Pest Control Products Act (Appendix II of PSRD2019-04) as well as re-examined the existing toxicological database for tetrachlorvinphos (Canada, 2004) in accordance with the current PMRA policies, including the application of the Pest Control Products Act factor (PCPA factor) (for more details refer to Appendix III of PSRD2019-04). This resulted in revisions to the non-cancer reference values used in the human health risk assessment. The revised reference values may affect the existing occupational and residential assessments. Consequently, the following aspects of concern were identified for the special review under subsection 17(1) of the Pest Control Products Act:

  • Potential occupational risk
  • Potential residential risk

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

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

In order to evaluate the aspects of concern for tetrachlorvinphos, the PMRA considered currently available relevant scientific information, which includes information submitted as part of the special review and under section 12 of the Pest Control Products Act, following re-evaluation of tetrachlorvinphos (Appendix II of PSRD2019-04), and information considered for its re-evaluation (Canada, 2003; and Canada, 2004). Information pertaining to the use pattern of commercial-class product received during the special review was considered in the assessment. The new exposure data for the pet collar use and other information received in the later phase of the special review will be considered along with other comments received during consultation of the proposed special review decision before making the final decision.

In addition, published information related to postapplication residential exposure was considered along with conducting the residential assessment as per current practices, which relies upon the 2012 United States Environmental Protection Agency (USEPA) Standard Operation Procedures (SOPs) for Residential Pesticide Exposure Assessments (USEPA, 2012).

4.1 Occupational Risks

Based on the current use pattern of tetrachlorvinphos, there is a potential for exposure for workers handling commercial and/or domestic-class pest control products containing tetrachlorvinphos and for workers entering treated sites or coming in contact with treated animals.

The PMRA estimates non-cancer risk by comparing an exposure estimate with the most relevant reference value from toxicology studies to calculate a margin of exposure (MOE). Route-specific and combined MOEs (for example, dermal and inhalation) were determined as applicable. 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, if possible. If mitigation measures are not possible, the use can be proposed for cancellation.

For the cancer assessment, the lifetime average daily dose (LADD) was estimated and multiplied by the q1* (1.83 × 10-3 (mg/kg/day)-1) (Appendix III of PSRD2019-04) to obtain lifetime cancer risk estimates. For occupational workers, a lifetime cancer risk of less than 1 × 10-5 is considered acceptable by the PMRA.

Toxicological reference values for use in the human health risk assessment for tetrachlorvinphos are presented in Appendix III of PSRD2019-04.

4.1.1 Dermal Absorption

The dermal absorption value for tetrachlorvinphos was re-assessed as part of the special review in accordance with current PMRA policies. The dermal absorption value of 22% was used for tetrachlorvinphos based on an in vivo rat dermal absorption study (for more details refer to Appendix IV of PSRD2019-04).

4.1.2 Occupational Mixer/Loader and Applicator Exposure and Risk

Commercial applicators or workers can be exposed to tetrachlorvinphos while mixing, loading, and applying the commercial-class product formulated as a wettable powder to livestock housing (for example, dairy barns, poultry houses, and swine barns) and poultry, and while applying the commercial-class product formulated as an ear tag to cattle.

Typically, it is assumed that commercial applicators or workers would not be using domestic-class products. However, for tetrachlorvinphos, since there are no commercial-class products registered for application to pets or pet bedding, it was assumed that workers would be using domestic-class products (for example, in veterinary clinics).

Based on the current use pattern for tetrachlorvinphos, potential exposure scenarios include:

  • Mixing/loading of wettable powders.
  • Mixing/loading of wettable powder and applying with handheld sprayer equipment.
  • Applying wettable powder with dusting equipment.
  • Applying paint with paintbrush or airless sprayer.
  • Applying ear tags to cattle.
  • Applying domestic-class powder/dust product to pets and pet bedding.
  • Applying domestic-class trigger spray product to pets.
  • Applying domestic-class pet collars.

Commercial applicators or workers may use tetrachlorvinphos for short to extended periods of time from spring to fall to manage insect pressures. Therefore, mixer/loaders and applicators have the potential for short- to intermediate-term exposure (via dermal and inhalation routes) to tetrachlorvinphos.

For the following scenarios, exposure was assessed using chemical-specific mixer/loader and/or applicator exposure studies (for more details refer to Appendix IV of PSRD2019-04):

  • Mixing, loading, and applying wettable powder product with a mechanically pressurized handgun.
  • Application of domestic-class powder/dust product to pets and pet bedding.
  • Application of domestic-class pet collars.

For the remaining scenarios, dermal and inhalation exposures were estimated using data from the Pesticide Handlers Exposure Database (PHED). In addition, the USEPA 2012 Residential SOPs (sections 7 and 8) were used to assess scenarios including trigger spray applications to pets and dust/powder application on poultry and in livestock housing.

The PMRA derived exposure estimates for workers assuming the following personal protective equipment (PPE):

  • Direct wettable powder application: Single layer and chemical-resistant gloves for mixers/loaders. Short-sleeved shirt and short pants for applicators.
  • Spray applications with backpack and mechanically-pressurized handgun (MPHG): Coveralls over a single layer clothing, chemical-resistant gloves, and respirator for mixers/loaders and applicators.
  • Paint applications with brush or sprayer: Single layer clothing and chemical-resistant gloves for mixers/loaders and applicators.
  • Application of domestic-class products: Short-sleeved shirt and short pants for applicators.

A 90% protection factor was applied to inhalation exposure estimates when a respirator is specified on the label. A 75% protection factor was applied to PHED dermal exposure estimates for the body when coveralls over a single layer are specified on the label.

Dermal and inhalation exposures were combined because these exposures occur simultaneously and they have the same toxicology reference value.

Commercial-Class Products

Potential exposure of workers from ear tag application is expected to be relatively low in consideration of the low frequency of application, design of the product (as a slow release of tetrachlorvinphos), and the current label requirements to wear chemical-resistant gloves during application. Thus, mixer/loader and applicator risks are considered to be acceptable for ear tag use.

For workers mixing, loading, and applying the commercial wettable powder product, the risk assessment is presented in Appendix V, Table 1 of PSRD2019-04.

For the following uses on the commercial wettable powder label, potential non-cancer and cancer risks (MOEs greater than the target MOE of 300 and cancer risks less than 1×10-5) are considered to be acceptable:

  • Handheld spray application to poultry.
  • Roost paint application to treat lice, mites, and lesser meal-worms.
  • Handheld spray application for poultry house floor management to treat lice, mites, and lesser meal-worms.
  • Handheld spray application to poultry droppings, manure piles, garbage piles, and under feed troughs to treat maggots.
  • Handheld spray application to livestock housing (1% and 2% dilution). The combined MOE for the 2% dilution was just below the target MOE of 300 at 267. This MOE is considered acceptable when considering conservatisms (that is, assumptions which may result in upper bound risk estimates) in the assessment, such as the use of maximum application rates.

In addition, revised PPE statements and additional precautionary statements are proposed for the current wettable powder end-use product label in order to ensure consistency, improve clarity, and to meet current labelling standards. For more details refer to Appendix VIII of PSRD2019-04.

For the following uses, potential occupational risks are not considered to be acceptable:

  • Direct wettable powder applications to poultry and poultry facilities - both non-cancer (MOEs 1-17, target MOE of 300) and cancer risks (exceeding 1 × 10-5) are not considered to be acceptable. The registrant submitted additional information for commercial dust uses at the later phase of this special review. The information along with other comments received during consultation of this proposed special review decision will be considered before making the final decision.
  • Handheld spray application to poultry housing walls, ceilings, floor cracks and crevices for fowl ticks - the cancer risk is considered to be acceptable but the non-cancer risk (MOE=107, target MOE of 300) is not considered to be acceptable.

Based on the above, the PMRA proposes cancellation of the following commercial uses of tetrachlorvinphos:

  • Direct wettable powder (duster) applications to poultry and poultry facilities.
  • Handheld spray application to treat fowl ticks in poultry housing.
Domestic-Class Products

The risk assessment for commercial applicators handling domestic-class products is presented in Appendix V, Table 2 of PSRD2019-04.

  • Applying ready-to-use powder/dust product to pets and pet bedding. For commercial applicators handling ready-to-use powder/dust domestic-class products, the cancer risks are considered acceptable; however, the non-cancer risks (MOE=52–74, target MOE of 300) are not considered to be acceptable under current conditions of use.
  • Applying ready-to-use liquid (trigger spray) to pets. For commercial applicators handling liquid (trigger spray) products, the cancer risk is considered to be acceptable; however, the non-cancer risk (MOE=88, target MOE of 300) is not considered acceptable under current conditions of use.
  • Applying ready-to-use pet collar products. For commercial applicators handling pet collars, the cancer risk is considered to be acceptable; however, the non-cancer risk (MOE=58, target MOE of 300) is not considered to be acceptable under current conditions of use.

For trigger spray products, non-cancer risks could be mitigated with the use of lower application rates and implementation of additional spray instructions for different size dogs and cats. These rates and label directions would be similar to what is on the current American labels. For more details on the proposed mitigation measures for domestic-class products refer to Section 4.2.3.

Mitigation measures for powder/dust and pet collar products are limited, thus all domestic-class powder/dust products and pet collars are proposed for cancellation.

4.1.3 Occupational Postapplication Exposure and Risk

There is potential for exposure of workers entering livestock housing or coming in contact with animals treated with tetrachlorvinphos. Possible occupational postapplication exposure scenarios include:

  • Commercial applicator or pest control operator returning to treated commercial or residential sites for scouting or to conduct other activities,
  • Workers entering animal buildings to conduct typical activities (for example, milking, feeding),
  • Workers handling treated pets or cleaning pet bedding areas.
Postapplication Risks Following Application of Commercial-class Products

For workers exposed to tetrachlorvinphos residues following application of commercial-class products (wettable powder and ear tag), the postapplication dermal and inhalation exposure from contact with treated surfaces or animals is expected to be low given the nature of activities that are performed in livestock facilities and the chemical properties of tetrachlorvinphos (for example, vapour pressure). Based on this, potential postapplication risks for these workers are considered to be acceptable under current conditions of use.

To further reduce the potential for exposure of postapplication workers, a precautionary label statement to not enter or allow entry into treated areas until sprays have dried, is also proposed to be included on the commercial-class wettable powder product label.

Postapplication Risks Following Application of Domestic-class Products

For workers exposed to tetrachlorvinphos residues following application of domestic-class products, potential postapplication exposure and risk are addressed in the assessment for the residential individuals (Section 4.2.2).

Based on results of the residential postapplication exposure and risk assessment (Section 4.2.2), postapplication dermal risks (non-cancer and cancer) to adults following application of domestic-class powder/dust, liquid, and pet collar products are not considered to be acceptable under current conditions of use.

For liquid (trigger spray) products, postapplication dermal risks (non-cancer and cancer) can be mitigated with the use of lower applications rates and additional spray instructions for different size dogs and cats. A precautionary statement, to avoid contact with the treated animal prior to residues drying, is also proposed on the liquid product label to further reduce the potential for exposure. The remaining domestic-class products (powder/dust and pet collar products) are proposed for cancellation.

For details on the proposed mitigation measures for domestic-class liquid products refer to Section 4.2.3.

4.1.4 Overall Occupational Risk Conclusions and Proposed Mitigation Measures

  1. Potential occupational risk is considered to be acceptable for the following uses:

    Commercial-class ear tag product:

    • Cattle

    Commercial-class wettable powder product:

    • Roost paint application to treat lice, mites, and lesser mealworms.
    • Handheld spray application to poultry.
    • Handheld spray application to poultry house floor management to treat lice, mites, and lesser meal-worms.
    • Handheld spray application to poultry droppings, manure piles, garbage piles, and under feed troughs to treat maggots.
    • Handheld spray application to livestock housing (1% and 2% dilution).

    In addition, revised PPE statements and additional precautionary statements are proposed for the current wettable powder end-use product label in order to ensure consistency, improve clarity, and to meet current labelling standards. For more details refer to Appendix VIII of PSRD2019-04.

  2. Potential occupational risk is considered acceptable with additional risk reduction measures (for example, additional application instructions) for the following tetrachlorvinphos uses:

    Domestic-class liquid (trigger spray) products:

    • Flea and tick spray for dogs and cats.

    For details on the proposed mitigation measures for domestic-class liquid products refer to Section 4.2.3.

  3. Potential occupational risk is not considered acceptable for the following tetrachlorvinphos uses and, therefore, these uses are proposed for cancellation:

    Commercial-class wettable powder product

    • Direct wettable powder/dust application to poultry and poultry facilities.
    • Handheld spray application to poultry housing walls, ceilings, floor cracks and crevices to treat fowl ticks.

    Domestic-class powder/dust product:

    • Applications to pet bedding and to pets.

    Domestic-class pet collar products

    • Applications to pets.

    The proposed label amendments are summarized in Appendix VIII of PSRD2019-04.

Additional information was submitted by registrants at the later phase of the special review, and will be considered along with other comments received during consultation of this proposed special review decision before making the final decision.

4.2 Residential Risk

The general population can be exposed to tetrachlorvinphos while applying domestic-class products (residential applicators) and/or when coming in contact with residues on treated surfaces or pets (postapplication exposure of adults and children).

Commercial-class products containing tetrachlorvinphos are not expected to be used in residential areas. A standard precautionary label statement prohibiting the use of the commercial-class wettable powder in residential areas is proposed to be added to the product label.

The USEPA has generated standard default assumptions for developing residential exposure assessments for both applicator and postapplication exposures when chemical- and/or site-specific field data are limited. The assumptions and algorithms may be used in the absence of, or as a supplement to, chemical- and/or site-specific data and generally result in high-end estimates of exposure. The assumptions and algorithms relevant to the tetrachlorvinphos re-evaluation are outlined in the USEPA Residential SOPs (USEPA, 2012) in the following sections:

  • Section 7: Indoor Environments
  • Section 8: Treated Pets

4.2.1 Residential Applicator Exposure and Risk

A residential applicator is an individual (≥16 years old) who applies a domestic-class tetrachlorvinphos product in and around the home or directly to pets. Residential applicators are assumed to be wearing shorts, short-sleeved shirts, shoes, and socks during application. The residential applicator has the potential for short to intermediate term exposure (1–180 days) when applying products containing tetrachlorvinphos.

Based on typical use patterns, the representative exposure scenarios identified were:

  • Applying ready-to-use powder/dust products to pet bedding.
  • Applying ready-to-use powder/dust, trigger spray, and pet collar products to pets.

Potential exposure was estimated using a combination of chemical-specific studies (for more details refer to Appendix IV of PSRD2019-04) and the USEPA 2012 Residential SOPs. The potential risks were estimated using toxicology reference values summarized in Appendix III of PSRD2019-04. For the non-cancer assessment, the route-specific and combined dermal and inhalation MOEs greater than 300 are considered acceptable. For the general population, a lifetime cancer risk below 1 × 10-6 is considered by the PMRA as an acceptable risk.

The risk assessment for residential applicators is summarized in Appendix VI, Table 1 of PSRD2019-04.

  • Applying ready-to-use powder/dust products to pets and pet bedding: For residential applicators handling dust/powder products, the cancer risks are considered to be acceptable for both pet and pet bedding uses. The non-cancer risk is considered to be acceptable under current conditions of use for the pet use but not for the pet bedding use (MOE = 209, target MOE of 300).
  • Applying ready-to-use liquid (trigger spray) to pets. For the residential applicators applying liquid (trigger spray) products to pets, both cancer and non-cancer risks are considered to be acceptable under current conditions of use.
  • Applying ready-to-use pet collar products. For residential applicator handling pet collars, the cancer risk is considered acceptable; however, the non-cancer risk (MOE = 232, target MOE of 300) is not considered to be acceptable under current conditions of use.

Based on the currently considered information, no additional risk reduction measures were identified to mitigate potential non-cancer risks for residential applicators of domestic-class powder/dust (pet bedding treatment) and pet collar products. Consequently, the PMRA proposes to cancel these two uses.

4.2.2 Residential Postapplication Exposure and Risk Assessment

Postapplication exposure can occur when an individual is exposed through dermal and/or incidental oral (non-dietary ingestion) routes as a result of being in a residential environment or contacting a pet that has been treated with a pesticide. The area or animal could have been treated by a residential or commercial applicator using a domestic-class tetrachlorvinphos product.

The following residential postapplication scenarios were assessed for domestic-class products containing tetrachlorvinphos:

  • Adults, youth, and children (1<2 years old) dermal exposure from contact with treated pet bedding.
  • Children (1<2 years old) incidental oral exposure from contact with treated pet bedding
  • Adult, youth, and children (1<2 years old) dermal exposure from contact with treated pets.
  • Children (1<2 years old) incidental oral exposure from contact with treated pets.

Short- to intermediate-term postapplication exposure is expected from powder/dust and trigger spray use scenarios. Intermediate- to long-term exposure may occur for pet collar use, as collars may be active and worn for several months at a time. For the non-cancer assessment, a single assessment was conducted to reflect all durations of exposure, as the toxicological reference value is the same for all exposure durations and routes.

The residential postapplication dermal exposure and risk assessment also addresses potential postapplication exposure of workers following application of domestic-class products.

Postapplication dermal exposure was calculated using activity-specific transfer coefficients, estimates for fur or surface residue, dislodgeable residue (residue transfer to skin) and exposure time. A transfer coefficient (TC) is a factor that relates exposure to dislodgeable residue and the amount of treated surface that a person contacts while performing activities in a given period (usually expressed in units of cm² per hour). It is specific to a particular population and activity (for example, children contacting treated pets).

Based on the information in the USEPA Assessment for tetrachlorvinphos (USEPA, 2016), both the solid and liquid TCs were used to assess postapplication exposure and risk for individuals handling pet collar products. It is unclear whether residues resulting from the flea collar use would be a fine powder or a liquid. The PMRA has requested additional information on the formulation type for pet collars. This information was submitted at the later phase of this special review and will be considered along with other comments received during the consultation of this proposed special review decision before making the final decision.

Incidental oral exposure occurs when pesticide residues are transferred to the hands of children playing on treated indoor surfaces or with treated pets, and are subsequently ingested as a result of hand-to-mouth (HtM) transfer. Residues can also be transferred to objects in treated areas (for example, a child’s toy) and subsequently ingested as a result of object-to-mouth transfer.

In terms of inhalation risk, the USEPA Residential SOPs specify that inhalation risks be considered on a case-by-case basis, taking into consideration the vapour pressure and the use pattern. The combination of the low vapour pressure for tetrachlorvinphos, the type of domestic-class products registered (trigger spray, dust can, or pet collar), and the relatively small amount of pesticide applied is expected to result in negligible inhalation exposure.

Potential postapplication dermal and incidental oral exposure was assessed using chemical-specific exposure studies (for more details refer to Appendix IV of PSRD2019-04) in combination with the USEPA Residential SOPs. The residential postapplication non-cancer and cancer exposure and risk estimates are presented in Appendix VI (Tables 2–9) of PSRD2019-04.

  • Powder/dust products: The non-cancer and cancer dermal risks from contact with treated pets and pet bedding are not considered to be acceptable (Appendix VI, Tables 2–5 of PSRD2019-04). The non-cancer and cancer incidental oral risks are considered to be acceptable (Appendix VI, Tables 6–9 of PSRD2019-04) for all scenarios except for pet bedding use where the MOE was below the target of 300.
  • Pet collar products: The non-cancer and cancer dermal risks from contact with treated pets are not considered to be acceptable (Appendix VI, Tables 4 and 5 of PSRD2019-04). In addition, the non-cancer and cancer incidental oral risks are not considered to be acceptable (Appendix VI, Tables 8 and 9 of PSRD2019-04).
  • Liquid (trigger spray) products: With additional mitigation measures (additional application instructions for spray strokes to different size cats and dogs), non-cancer and cancer dermal risks from contact with treated pets are considered to be acceptable (Appendix VI, Tables 4 and 5 of PSRD2019-04). Under the revised conditions of use, the dermal MOEs for trigger spray products are greater than the target MOE of 300 for all scenarios, except for children contacting small cats (MOE=260). However, the MOE of 260 is considered to be acceptable given the conservatism in the assessment (for example, the use of the 22% dermal absorption factor). A precautionary statement, to avoid contact with the treated animal prior to residues drying, is also proposed on the liquid product label to further reduce exposure. The non-cancer and cancer incidental oral risks are also considered to be acceptable for liquid (trigger spray) under the revised conditions of use (Appendix VI, Tables 8 and 9 of PSRD2019-04).

Based on the results of the postapplication residential risk assessment, the PMRA proposes:

  • Cancellation of all domestic-class powder/dust products.
  • Cancellation of all domestic-class pet collar products.
  • Additional mitigation measures for liquid (trigger spray) products. Refer to Section 4.2.3 for the proposed mitigation measures.

4.2.3 Overall Residential Risk Conclusions and Proposed Mitigation Measures

  1. With additional risk reduction measures, potential residential risk is considered to be acceptable for the following tetrachlorvinphos uses:
    • Domestic-class flea and tick liquid (trigger spray) products.

    The proposed mitigation measures for domestic-class liquid (trigger spray) products include additional instructions for spray strokes to different size cats and dogs. Additional details on the size of cats and dogs may be added to the label instructions following consultation:

    • Cat Products: Spray 15–25 strokes for a small cat, spray 25–35 strokes for a medium or large cat.
    • Dog Products: Spray 25–35 strokes for small dogs. Spray 30–40 strokes for a medium dog. Spray 40–70 strokes for a large dog.

    A precautionary label statement to avoid contact with the treated animal prior to residues drying is also proposed to further reduce the potential for exposure.

  2. Under the current conditions of use, potential residential risk is not considered acceptable for the following tetrachlorvinphos products and, therefore, these products are proposed for cancellation:
    • Domestic-class flea and tick powder/dust products.
    • Domestic-class flea and tick pet collar products.

    The proposed label amendments are summarized in Appendix VIII of PSRD2019-04.

Additional information submitted at the later phase of this special review for the pet collar use will be considered along with other comments received during consultation of this proposed special review decision before making the final decision.

4.3 Aggregate Risk

Aggregate exposure is the total exposure to a single pesticide that may occur from food, drinking water, residential, and other non-occupational sources, and from all known or plausible exposure routes (oral, dermal, and inhalation).

For tetrachlorvinphos, the aggregate exposure and risk assessment was conducted for domestic-class liquid (trigger-spray) products. This scenario is the only residential use where application and postapplication exposure risks to the general public were considered to be acceptable with the proposed risk mitigation measures.

The following activities for the trigger spray use have the potential for co-occurrence:

Adults:

  • Residential applicator dermal and inhalation + postapplication pets dermal + chronic dietary.

Youth 6 to <11 years:

  • Postapplication pets dermal + chronic dietary.

Children 1 to <2 years:

  • Postapplication pets dermal + postapplication pets incidental oral + chronic dietary.

The results of the aggregate assessment are presented in Appendix VII (Tables 1 and 2) of PSRD2019-04.

For liquid (trigger-spray) products, aggregate cancer risks to adults and children are considered to be acceptable with the proposed mitigation measures specified above (Section 4.2.3). Aggregate non-cancer risks for spray trigger products were greater than the target MOE of 300 for most scenarios and therefore, risks are considered to be acceptable. There was one scenario where MOEs were less than 300 for children contacting small cats at the MOE of 260. The MOE of 260 is considered acceptable due to conservatisms in the assessment such as the use of the 22% dermal absorption factor.

4.4 Cumulative Assessment

Tetrachlorvinphos belongs to a group of chemicals classified as organophosphates. Organophosphates have a common mechanism of toxicity wherein they all possess the ability to interact with the cholinesterase enzyme ultimately leading to neurotoxicity. A cumulative assessment will be undertaken upon completion of the re-evaluation of the individual chemicals in the organophosphate group with all relevant chemicals and scenarios of the common mechanism group.

5.0 Incident Reports

The PMRA incident reporting database was searched for human incident reports related to the identified aspects of concern for tetrachlorvinphos.

As of 2 October 2018, the PMRA has received 14 incidents (12 in Canada and 2 in the United States) where individuals were exposed to the active ingredient tetrachlorvinphos in a residential setting, and the signs reported were considered to be at least possibly related to exposure. Individuals (9 adults and 5 children) were exposed either during application, through contact with the treated pet, or from product misuse. Most individuals reported minor signs, including headache, nausea, vomiting, skin irritation, and eye irritation. Overall, given the low severity and frequency of tetrachlorvinphos incidents, no additional mitigation measures specific to health are proposed as a result of the incident reports.

6.0 Proposed Special Review Decision for Tetrachlorvinphos

Evaluation of available scientific information related to the aspects of concern, indicated that the potential risk to human health is considered to be acceptable for the following registered products containing tetrachlorvinphos with the proposed additional mitigation measures (Appendix VIII of PSRD2019-04). On this basis, the PMRA is proposing to confirm the current registration for the following products containing tetrachlorvinphos for sale and use in Canada with the proposed risk mitigation measures pursuant to subsection 21(1) of the Pest Control Product Act:

Commercial-Class

  • Ear tag product.
  • Wettable power product.
  • Roost paint application to treat lice, mites, and lesser mealworms.
  • Handheld spray application to poultry.
  • Handheld spray application to poultry house floor management to treat lice, mites, and lesser meal-worms.
  • Handheld spray application to poultry droppings, manure piles, garbage piles, and under feed troughs to treat maggots.
  • Handheld spray application to livestock premises (1% and 2% dilution).

Domestic-Class

  • Flea and tick liquid (trigger spray) products.

Assessment indicated that the potential risk to human health for the following uses of tetrachlorvinphos is not considered to be acceptable, and they are proposed for cancellation:

Commercial-Class

  • Wettable powder product.
  • Direct application as a wettable powder or dust to poultry and poultry facilities.
  • Handheld spray application to poultry housing walls, ceilings, floor cracks and crevices to treat fowl ticks.

Domestic-Class

  • All flea and tick powder/dust products.
  • All flea and tick pet collar products.

This proposed special review decision (PSRD2019-04) is a consultation document.Footnote 1 The PMRA will accept written comments on this proposal up to 45 days from the date of publication of this document. Please forward all comments to Publications.

7.0 Next Steps

Before making a special review decision on tetrachlorvinphos, the PMRA will consider all comments received from the public in response to PSRD2019-04. A science-based approach will be applied in making a final decision on tetrachlorvinphos. 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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