Registration Decision RD2017-19, Bifenthrin and Capture 240 EC

Pest Management Regulatory Agency
21 December 2017
ISSN: 1925-0940 (PDF version)
Catalogue number: H113-25/2017-19E-PDF (PDF version)

This page is a summary of the final decision document.

To obtain a full copy of Registration Decision RD2017-19, Bifenthrin and Capture 240 EC please contact our publications office.

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

Summary

Table of Contents

Registration Decision Statement for Bifenthrin

Health Canada's Pest Management Regulatory Agency (PMRA), under the authority of the Pest Control Products Act and Regulations, is cancelling the registration of Bifenthrin Technical Insecticide and Capture 240 EC, containing the technical grade active ingredient bifenthrin, as it meets the criteria for Track 1 substances under the Toxic Substances Management Policy (TSMP). In order to allow for the phase-out of Bifenthrin Technical Insecticide and Capture 240 EC for use on raspberries in British Columbia to control several insect pests, particularly those that are present at the time of harvest, and on potatoes to control wireworm, the PMRA requires that the following implementation timelines are followed.

Date of Last Sale by Registrant: December 31, 2018
Last Date of Sale by Retailers: December 31, 2019
Last Date of Permitted Use by Users: December 31, 2020

The Proposed Registration Decision PRD2017-11, Bifenthrin and Capture 240 EC contains a detailed evaluation of the information submitted and a proposal for cancelling the uses of bifenthrin on potato and raspberry, along with providing a three year phase-out for the critical need use on raspberry. Based on the information received during the public consultation, the PMRA agrees that the use of bifenthrin on potato to control wireworm also represents a critical need at this time. Therefore, the phase-out of bifenthrin on both raspberries in British Columbia and potato is subject to the three year phase-out period timeline, as provided above. The interim risk mitigation measures listed in PRD2017-11 will be integrated with additional protective instructions for use on potato to mitigate risks posed by use that may continue until 2020. See Appendix I for a summary of comments received during the consultation process as well as the PMRA's response to these comments.

Other Information

The relevant test data on which the decision is based (as referenced in PRD2017-11) are available for public inspection, upon application, in the PMRA's Reading Room (located in Ottawa). For more information, please contact the PMRA's Pest Management Information Service by phone (1-800-267-6315) or by e-mail.

Any person may file a notice of objection regarding this registration decision within 60 days from the date of publication of this Registration Decision. For more information regarding the basis for objecting (which must be based on scientific grounds), please refer to the Pesticides and Pest Management portion of Canada.ca website (Request a Reconsideration of Decision) or contact the PMRA's Pest Management Information Service.

Appendix I Comments and Responses

Comment 1:

Twenty-seven comments were received from individuals or organisations that outlined their support for the registration of Capture 240 EC, containing bifenthrin, to manage wireworm populations in potato. Several comments included rationales summarising why bifenthrin should be considered a critical need and outlined the following points:

  • In locations with high populations, bifenthrin offers full season protection of long-season varieties (e.g., russet burbank), preventing damage of tubers up to harvest which is not achieved with registered alternatives.
  • The importance of resistance management of wireworm using a rotation of bifenthrin, a group 3 insecticide, with phorate, a group 1B insecticide.
  • Increasing wireworm pressure, especially in Prince Edward Island where the predominant species (Agriotes sputator) is difficult to manage.
  • Significant economic loss in Prince Edward Island potatoes attributed to wireworms that include insecticide costs, crop insurance losses, processing losses, and the cost of cover crops used to suppress wireworm.

PMRA Response:

The PMRA acknowledges the submitted comments and agrees that use of bifenthrin on potato to control wireworms is a critical need.

Comment 2:

One comment was received that agreed with PMRA's decision to cancel the registration of bifenthrin on potatoes. It also expressed concern with the health and environmental risk indices of alternative products containing phorate and chlorpyrifos, and that cancellation of bifenthrin would result in greater use of these alternatives.

PMRA Response:

The PMRA assesses each pest control product individually for risks to human health and the environment. Before a product is approved for use in Canada, and during regular re-evaluation, it must undergo a thorough science-based risk assessment and have acceptable value.

Comments on the Environmental Review Presented in PRD2017-11

FMC submitted several documents during the public consultation on PRD2017-11. The FMC comments included the following documents:

  • A review of PRD2017-11 from an environmental perspective completed by Intrinsic,
  • Twenty journal publications relating to environmental issues that were cited in the Intrinsic review,
  • Reference to reports previously submitted to the PMRA that address specific comments.

The following comments relate to environmental issues noted in the Intrinsic review document. The PMRA reviews of the 20 journal publications are included in the Appendix II of Registration Decision RD2017-19, Bifenthrin and Capture 240 EC.

Comment 3:

The PMRA does not present any method for evaluating studies. The PMRA should use the Klimisch et al. (1997) criteria for evaluating study validity.

PMRA Response:

All studies reviewed by the PMRA are evaluated for data quality against generally recognized methods of the Organisation for Economic Co-operation and Development (OECD) or of other similar organisations. If no such methods exist, studies are reviewed in accordance with generally recognized methods within the scientific community and taking into account the intrinsic properties of the substance, the ecosystem under consideration and the conditions in the environment.

Although the PMRA does not strictly adhere to the Klimisch scoring method for reviewing studies, the elements of the Klimisch criteria are considered when assessing the acceptability of studies. All of the studies were fully reviewed in terms of their quality and acceptance for consideration in the risk assessment. While some studies were not conducted to guideline requirements, valuable information was still obtained. Any deficiencies, limitations, uncertainties identified were considered and taken into account when deriving the conclusion.

Additionally, the following guidance specific to assessing persistence and bioaccumulation under the Government of Canada's Toxic Substances Management Policy - Persistence and Bioaccumulation Criteria (Environment Canada, 1995) was used:

Protocols and test methods

At this stage, specific protocols and test methods are not prescribed by the ad hoc Science Group.  As much as possible, internationally accepted methods (e.g., OECD protocols) should be used to generate the appropriate data. In the absence of such protocols, methods generally recognized and acceptable within the scientific community should be used.

Data Quality

Because of the inherent complexity of measurements and the numerous factors influencing persistence and bioaccumulation processes, there will often be a wide range of values for any one criterion for a given substance. For this reason, the ad hoc Science Group recommends the use of expert judgment to assess the quality of the data. In assessing quality, consideration should be given, among other things, to 1) the age of the data, objectives of the study, and discussion or acknowledgement of conflicting and supporting evidence; 2) the documentation of specific environmental and/or experimental conditions; 3) the method(s) used, its limitations, precision and accuracy.

Comment 4:

The level of detail provided in the PRD2017-11 was insufficient to allow for the reproducibility of the Estimated Environmental Concentrations (EECs), effects endpoints and/or risk quotients (RQs).

PMRA Response:

The Overview of the PRD2017-11 'describes the key points of the evaluation'. Clarification on how specific EECs were calculated are provided in the relevant responses to comments that follow.

Comment 5:

The risk assessment should be reflective of the expected lawful application of the end-use product, including the inclusion of the vegetative strips, buffer zones, no contamination of adjacent water bodies, etc. The commenter suggested that the aquatic EECs and risk assessment should include the required buffer zones in the calculation. The commenter considered the PMRA refined assessment for drift is exceedingly conservative.

PMRA Response:

The risk assessment conducted by the PMRA is reflective of the use pattern that was proposed by the registrant at the time of the submission. For consistency, a standard regulatory approach is used for risk assessment and determining mitigation measures (for example, a whole system half-life is used in calculations as this represents degradation of a substance and not movement between environmental compartments). The requirement for specific mitigation measures, such as vegetative filter strips and buffer zones, is dependent on the hazards and risks identified during the risk assessment.

The risk assessment incorporates available mitigation measures to determine if the risk can be made acceptable under the proposed use pattern.

Comment 6:

Further refinements to exposure and effects assessments were not considered, including probabilistic methods. This prevents understanding the potential ranges of bifenthrin exposure and risk to aquatic and terrestrial biota.

PMRA Response:

The PMRA conducted a refined risk assessment for bifenthrin. The available data demonstrated that bifenthrin is persistent, bioaccumulative and toxic and, thus, met the Government of Canada's TSMP criteria for a Track 1 substance. A probabilistic risk assessment for bifenthrin would not have altered the classification of bifenthrin as a Track 1 substance. Therefore, a probabilistic risk assessment was not conducted nor required given that the registration decision is based on bifenthrin meeting the criteria for a Track 1 substance. Consequently, virtual elimination is the appropriate risk mitigation measure according to the Government of Canada policy.

Specific comments related to fate and behaviour in the environment

Comment 7:

Why did the PMRA report the solubility of bifenthrin as being < 1 µg/L instead of 14 ng a.i./L?

PMRA Response:

The PMRA evaluated all physiochemical studies submitted and re-confirmed that the appropriate solubility of bifenthrin is < 1 µg/L as reported in Section 1.2 (pg. 10) of PRD2017-11. The study submitted is a GLP laboratory study conducted following an internationally accepted guideline. The laboratory study in which the solubility of 14 ng/L is reported did not follow any international guideline to determine solubility, and, therefore, was not accepted by the PMRA to determine solubility. Moreover, surface water monitoring data show that under natural environmental conditions, bifenthrin concentrations in water can exceed the limit of solubility values established under laboratory conditions. For this reason, the PMRA chose to report the solubility value as < 1 µg/L.

Comment 8:

The reported Kd values on pg. 24, 3rd paragraph should be corrected to "453-2685".

PMRA Response:

The PMRA agrees that the Kd values should be "453-2685". The Koc values were incorrectly reported as the Kd values in PRD2017-11.

Comment 9:

Clarification is required as to whether the foreign terrestrial field studies in PRD2017-11, Appendix I, Table 12 are representative of Canadian conditions, and were used to support the laboratory findings for DT50s.

PMRA Response:

Terrestrial field dissipation studies are accepted if they are scientifically valid and are conducted in an ecoregion relevant to Canada. The submitted terrestrial field studies were assessed by the PMRA using the Europe-North America Soil Geographic Information for Pesticide Studies (ENASGIPS) to determine if these were conducted in Canadian relevant regions. According to the results of ENASGIPS, the PMRA concluded that these studies were conducted in ecoregions similar to those found in Canada and were used to assess persistence under field conditions and to support the laboratory findings.

Comment 10:

The Alabama pond study should not be used for risk assessment purposes. Additional environmental fate and ecotoxicity studies available in the public literature should be considered. In particular, the mean aerobic aquatic metabolism half-life of 189 days calculated based on half-lives ranging from 87.3 to 455 days in Meyer (2012) and reported in Melendez (2013).

PMRA Response:

The Alabama pond study (Primary Report, PMRA 1755966) was used to estimate bioaccumulation under field conditions and as supporting information to characterize the persistence and ecotoxicity of bifenthrin under field conditions. There are currently no standard international guidelines for conducting and assessing aquatic field studies. Consequently, the PMRA assessed the aquatic field studies based on existing guidelines for similar types of bioaccumulation (for example, OECD Guideline 305), field and mesocosm studies. Studies were evaluated in accordance with generally recognized methods within the scientific community with endpoints and conclusions reflecting the identified limitations of the study. All comments, documents and reports provided to the PMRA regarding the deficiencies and uncertainties of this study were considered in the review. For details, see Appendix II of RD2017-19. Despite the deficiencies and uncertainties that were identified, the PMRA considers the study design and results to be of sufficient quality to establish bioaccumulation under field conditions. The results from the Alabama pond study were not considered in isolation, but along with other lines of evidence (laboratory data) following a weight-of-evidence approach. Collectively, the information indicates that bifenthrin exceeds the TSMP criterion for biaoccumulation.

The ecotoxicity and persistence information obtained from the Alabama pond study was used in a qualitative manner and integrated with information from the laboratory and other field studies. The toxic effects observed in aquatic invertebrates in the pond study occurred at similar water concentrations to those observed under laboratory conditions as well as in other outdoor mesocosm studies. The toxicity results were not used directly in the risk assessment to quantify acute or chronic risk to aquatic organisms; however, the results were considered in a qualitative manner as a weight of evidence. The environmental concentration obtained from the pond study demonstrated that bifenthrin was much more persistent in a terrestrial-aquatic field study conducted in Alabama than was predicted by the laboratory biotransformation studies.

In the quantitative risk assessment, the PMRA used the whole system half-life value of 276 days determined from a registrant-generated GLP laboratory aerobic water-sediment study (reported in PRD2017-11, Appendix I, Table 12) to calculate estimated environmental concentrations (EECs) used in the risk assessment. The half-lives reported in Meyer (2012) of 87.3 to 455 days bracket the half-life of 276 days considered by the PMRA in the risk assessment. In addition, the mean aerobic aquatic metabolism half-life of 189 days from the Meyer (2012) study meets the TSMP persistence criterion of ≥182 days.

Comment 11:

The commenter requested clarification on how the half-life from the Alabama pond study was determined.

PMRA Response:

The results of the Alabama aquatic field and pond study were used in a qualitative manner as presented in Table 24 on page 99 of the PRD2017-11 to capture the long-term behaviour of bifenthrin in aquatic systems under realistic agricultural conditions. In the terrestrial environment, the DT50 estimate in the top 0-15 cm of soil was 195 days. In the aquatic environment, bifenthrin remained very persistent at low concentrations with estimated DT50 values of 609 days in the pond water. Although half-lives could not be estimated in the sediment, the mean concentration in sediment samples collected 737 days after the final application were approximately 21% of the highest mean observed. Bifenthrin residues in the runoff water and sediment were significantly higher than bifenthrin residues in pond water and sediment by at least one order of magnitude and very likely contributed to bifenthrin residues in Hagan's pond for months during the bifenthrin application periods and weeks after the last application.

Given the various potential routes of transformation/losses, a dissipation rate (DT50) was estimated using the PestDF Tool developed by PMRA using R (R Core Team 2013) and the reported concentrations for the first sample after the final application of bifenthrin to the last sample date (471 days after the final application). Of the models considered, the single-first order SFO DT50 of 609 days was the best fit. The DT50s give a realistic picture of the potential aquatic exposure under field conditions resulting from all routes of exposure (for example, direct overspray, drift, run-off) and how a substance that is persistent in soil can contribute to the long term exposure in aquatic systems through run-off

Comments related to bioaccumulation

Comment 12:

The commenter disagrees with the PMRA's evaluation of study validity and reliability of the bioaccumulation studies.

PMRA Response:

The PMRA has considered all previous comments on this issue provided by the registrant and disagrees with the classification of these studies by the registrant. While respecting the limitations of the individual studies, the PMRA integrates information from all the acceptable studies in making a final determination of bioaccumulation. The results and the study limitations that were considered, along with other data (laboratory and field) that were used in assessing potential bioaccumulation are provided in Appendix II of RD2017-19.

Comments related to the bioaccumulation assessment under field conditions

Comment 13:

The commenter suggested that the Alabama field and pond study should not be considered in evaluating BAFs due to deficiencies in its study design and methodology. According to the commenter, the validity criteria of the OECD 305 (2012) guidance for determining bioaccumulation in fish were not met.

PMRA Response:

Under the TSMP, bioaccumulation is assessed through a sequential, tiered process by examining log Kow, BCF and BAF. Field bioaccumulation factors (BAFs) usually provide a larger weight of evidence than laboratory studies as they take into account exposure from all sources (water, food), bioavailability and interactions under environmentally relevant conditions. The PMRA considered the Alabama pond to be an acceptable study for characterising the bioaccumulation potential of bifenthrin under field conditions. All comments, documents and reports provided to the PMRA regarding the deficiencies and uncertainties of this study were considered in the review. For details, see Appendix II of RD2017-19.

Comment 14:

The study by Alonso et al. (2012) should not be considered for TSMP evaluation of bifenthrin. According to the commenter, the study limitations preclude the data from determining the exposure pathway (diet vs. water) and the exposure is not reflective of the Canadian use pattern.

PMRA Response:

While the results reported by Alonso et al. (2012) were not used as part of a quantitative assessment against the TSMP criteria, the results did provide evidence of the potential for maternal transfer of bifenthrin as well as bioavailability of bifenthrin in the upper trophic levels of the food chain in a marine habitat at a significant distance from the source of release.

Comment 15:

The PMRA did not consider European field biomonitoring studies when evaluating the bioaccumulation criterion.

PMRA Response:

As stated in PRD2017-11, page 26 the PMRA evaluated the European field biomonitoring studies. The results of these European studies are considered to be of limited value in terms of assessing bioaccumulation in aquatic biota because in most cases, residues in water and sediment were undetectable, very close to or below the limit of quantitation (LOQ) and could not confirm exposure which precluded calculating a bioaccumulation ratio under field conditions.

The applied European application rate was only 9% of the Canadian label rate. The lack of detections in aquatic environment under the European conditions may be attributable to the low application rate that was used in comparison to the application rates for Canada and, therefore, cannot be interpreted as a lack of exposure under Canadian use conditions.

Specific comments related to risks to terrestrial organisms

Comment 16:

The commenter noted an error in risk quotients for the screening level assessment for bees. They also noted that PRD2017-11 does not mention a repellent effect on bees that was documented in the EFSA (2011) and the draft assessment report prepared by France (2006). The commenter suggested the bee risk assessment should be refined based on application timing for potatoes, label instructions for raspberry and off-field exposure.

PMRA Response:

The PMRA confirms that an error was made in the reporting of risk quotients for the screening level assessment for bees in PRD2017-11. The corrected EEC values for acute oral and contact exposure for bee are 3.25 µg a.i./bee and 0.269 µg a.i./bee, respectively. The corrected RQ values for acute oral and contact exposure for bee are 3.8 and 25, respectively. The level of concern for bees of 0.4, as per the risk assessment guidance for bees (EPA, PMRA and CDPR, 2014), is exceeded.

The EFSA (2011) and the draft assessment report prepared by France (2006) accepted and reported the results of several field and tunnel studies. Two studies reported no repelling effect of bifenthrin on bees; however, one study reported repellent effects of bifenthrin on bees within the first 30 minutes of application, while another study reported repellent effects observed within the first 5 hours post-treatment with bifenthrin (in one of two trials). The PMRA does not consider that these results provide strong enough evidence of a repelling effect of bifenthrin to bees due to lack of consistency among the studies.

Capture 240 EC is applied to potatoes in-furrow. Given that bifenthrin is not systemic, exposure to bees is not expected to occur. As risks to bees from application of bifenthrin on raspberries were identified, the PMRA implemented label statements which prohibit application during the crop blooming period which will reduce exposure to bees.

Further refinement of the bee risk assessment will not be revisited, given that the registration decision is based on bifenthrin meeting the criteria for a Track 1 substance. For the remaining period of use during the phase-out period, the implemented label statements are expected to limit the exposure of bees to bifenthrin.

Comment 17:

The commenter asked for clarification on the uses considered in the EEC calculation, how the EEC was calculated and how uncertainty factors were used for non-target arthropod risk assessment.

PMRA Response:

Given that bifenthrin use on potatoes is limited to in-furrow application, negligible exposure to non-target arthropod is anticipated. Hence, the non-target arthropod risk assessment was conducted on exposure from uses on raspberries.

The maximum cumulative application rate for bifenthrin was calculated using the application rate and the re-application intervals for use on raspberries. In the absence of foliar dissipation data, a default foliar dissipation half-life of 10 days was used to account for dissipation between applications. The resulting maximum cumulative application rate for bifenthrin for the use on raspberries is 126 g a.i./ha. The maximum spray drift deposition at one meter downwind from the point of application is assumed to be 59% of the application rate for late season airblast. The maximum percent deposition on non-target plants located one metre downwind from the point of application would therefore be 74.3 g a.i./ha for late season airblast application on raspberries. As such, non-target arthropods located on the field could be exposed to a level of 126 g a.i./ha and those located off field could be exposed to a level of 74.3 g a.i./ha.

The PMRA does not apply an uncertainty factor for endpoints of laboratory studies which are conducted on natural substrates for non-target arthropods.

Comment 18:

The commenter requested clarification and explanation on the applications of foliar interception factors and a vegetation distribution factor for non-target arthropod risk assessment.

PMRA Response:

For the in-field exposure assessment, crop-specific interception factors (F) proposed by Linders et al. (2000) are applied to estimate the ratio of pesticide residues reaching the foliage (Fint) and the soil (Fsoil). The Fint value of 0.8 for plants implies that 80% of the applied active ingredient is present on plant surfaces and 20% is present on the soil. The foliar deposition fractions are applicable to the standard test species (T. pyri and A. rhopalosiphi) and to foliar-dwelling arthropod species from the extended laboratory tests. Soil deposition fractions are applicable to ground-dwelling arthropods. These are based on the assumption that the foliar deposition fraction plus the soil deposition fraction is unity (Fint + Fsoil = 1), and that these processes are instantaneous.

Refined in-field EEC for foliar-dwellers = cumulative application rate × Fint
Refined in-field EEC for ground-dwellers = cumulative application rate × Fsoil

For the off-field exposure estimate, a vegetation distribution factor of 0.10 is applied since the drift values overestimate drift to the lower or interior portions of a three-dimensional habitat structure. Most of the drift would be intercepted by the top or side portions of the habitat structure. This default value was estimated to be appropriate based on data presented at the ESCORT workshop (Candolfi et al. 2001).

Refined off-field EEC = off-field EEC × vegetation distribution factor of 0.10

Comment 19:

The commenter noted that with the information provided within the PRD2017-11, it was not possible to reproduce the values presented for estimated daily exposures (EDEs) and RQs. The commenter noted that EDEs calculated by EPA T-REX are different from those reported in the PMRA public document for small mammals risk assessments.

PMRA Response:

The PMRA does not calculate EDEs using the USEPA tool T-REX. The PMRA estimated the concentration of pesticide residues on potential food items (vegetation, seeds, insects) using a nomogram developed by the USEPA from the data of Hoerger and Kenaga (1972) and Kenaga (1973), and modified according to Fletcher et al. (1994).

Specific comments related to risks to aquatic organisms

Comment 20:

Why does the PMRA consider direct overspray in their screening assessment if bifenthrin is not allowed to be applied directly to water? This is overly conservative, unrealistic and not representative of what is on the label.

PMRA Response:

The overspray scenario used by the PMRA is a screening assessment which considers the most conservative exposure situation. While this is highly conservative and may not represent realistic conditions, it is intended to be a quick screening tool designed to quickly identify those pesticide and uses where there are no risks of concern. Further refinements to the risk assessment (as were completed with bifenthrin) are considered only if the level of concern is exceeded at the screening level.

Comment 21:

The commenter requested that the PMRA include citations of ecotoxicity data considered in the effect assessment. In addition, there is no information on the data collection criteria, nor on the criteria for determining data quality of this data.

PMRA Response:

All registrant-provided studies were compared against the appropriate internationally-accepted guideline or protocol. The endpoints of accepted ecotoxicity studies are reported with reference in Appendix I, Table 15 and Table 20 of PRD2017-11.

The published ecotoxicity literature studies that were considered in the risk assessment [i.e., species sensitivity distribution (SSD) studies] were omitted from PRD2017-11 in error. A list of these studies is provided in the References section of RD2017-19.

Comment 22:

The commenter requested more detailed information related to aquatic SSD methodology and calculations. Specifically, although the software and HC5 are reported, there is no discussion of the minimum data requirements (for example, number of unique species required), the datasets used for SSD generation including any averaging of within-species values, and goodness-of-fit statistics indicating whether the model fit was acceptable.

PMRA Response:

Details related to the calculation of the SSDs were omitted from PRD2017-11 and are provided in Appendix III of RD2017-19.

Comment 23:

The commenter noted a typographical error of acute HC5 for freshwater fish on page 32 (0.008 µg a.i./L).

PMRA Response:

The PMRA agrees the correct value should be 0.078 µg a.i./L, and not the reported value of 0.008 µg a.i./L, which was a typographical error. The correct value of 0.078 µg a.i./L was used in the risk assessment.

Comment 24:

Why did the PMRA only calculate risk quotients based on water exposures of bifenthrin and did not derive EECs for bifenthrin in sediment or pore water given that bifenthrin is strongly bound by sediment? The commenter mentioned that previous PMRA assessments have compared both sediment and overlying water EECs to endpoints of Chironomus riparius sediment toxicity studies. In addition, the USEPA has recently released guidance for the ecological risk assessment of benthic invertebrates which recommends calculating RQs based on exposure and toxicity data for pore water, sediment and water column concentrations.

PMRA Response:

The PMRA agrees that additional analysis with respect to organisms that may be exposed to pore water would add further context to the risk posed to aquatic organisms; however, given that the registration decision is based on bifenthrin meeting the criteria for a Track 1 substance, the risk assessment for freshwater aquatic invertebrates will not be further refined at this time.

Comment 25:

The commenter noted the reference table was missing PMRA document numbers 1755962, 1755966, 1759123 and 1755945.

PMRA Response:

The references that were missing in PRD2017-11 are as follows:

Table - references
PMRA Reference
1755962 2005, Bifenthrin 80 g as/L SC: Assessment of the Ecological Effects on Aquatic Communities Using Outdoor Aquatic Mesocosms after Duplicate Treatment at 14 Days Interval, DACO: 9.9
1755966 1989, Bifenthrin Pond Study: Ecological Effects during Treatment and Post-Treatment Follow-Up Studies of Hagans Pond, Orrville, Alabama, DACO: 9.9
1759123 1992, The Acute Toxicity of Talstar 80 g/l Flowable Formulation to Rainbow Trout, DACO: 9.5.4
1755945 2002, Testing of Toxic Effects of Talstar 8 SC on the Single Cell Green Alga Desmodesmus Subspicatus (formerly Scenedesmus Subspicatus), DACO: 9.3.5,9.8.6

Comment 26:

The commenter considers the results of the Alabama study by Sherman (1989) not relevant to the assessment of bifenthrin risks to aquatic invertebrate communities for current labeled uses in Canada.

PMRA Response:

As identified in responses to Comment 10, the Alabama pond study (PMRA 1755966) was determined to be scientifically sound and used in the risk assesment; however, the PMRA recognizes the limitations of this study. As noted in PRD2017-11 page 33, the results of this study were not used in the quantitative risk assessment. The PMRA noted the results of this study support the findings of other studies because the concentrations in the pond resulted in effects to the aquatic invertebrate population consistent with the ecotoxicity information derived from laboratory and mesocosm studies. As reported in PRD2017-11, neither the EECs nor the ecotoxicity endpoints used in the aquatic risk assessment were derived from the results of the Alabama pond study.

Comment 27:

The commenter provided a list of published literature for higher tier studies with bifenthrin on aquatic taxa. The commenter suggested the PMRA incorporate the results of these studies into the PMRA's assessment.

PMRA Response:

The PMRA has reviewed the list of published literature provided by the commenter; however, given that the registration decision is based on bifenthrin meeting the criteria for a Track 1 substance, the risk assessment for aquatic organisms will not be further refined at this time.

Comment 28:

The commenter questioned the use of PRZM/EXAMS to calculate EECs used in the runoff risk assessment scenario. The commenter suggested that the PMRA use Surface Water Concentration Calculator (SWCC) and Soil and Water Assessment Tool (SWAT) developed by the USEPA to calculate sediment, pore water and surface water EECs.

PMRA Response:

When the EECs for surface and pore water were originally calculated for bifenthrin, PMRA was conducting water modelling using PRZM/EXAMS as a standard model for all pesticide risk assessments. Since then, PMRA has adopted the Pesticides in Water Calculator (PWC) model to estimated EECs in water. The PWC model is harmonized with that used by the USEPA.  Currently, the PMRA does not use the SWAT model. Given that the registration decision is based on bifenthrin meeting the criteria for a Track 1 substance, the EECs will not be refined at this time.

Comment 29:

The method employed by the PMRA to derive the new restrictions and buffer zones for field spray is not explained, and should be made explicit in the registration decision.

PMRA Response:

The proposed restrictions on field spray applications are warranted as the initial spray buffer zone determination exceeded the limit of the field sprayer model (>120 m) for protection of marine habitats. Without these restrictions on ground application, there is the potential that the risk posed by spray drift to marine habitats would not be mitigated with a maximum buffer zone of 120 m. Also, the buffer zones for freshwater habitats are large and therefore, potentially less practical from a user perspective. Overall, spray application restrictions are required to facilitate more practical spray buffer zones.

Additional drift mitigation measures required for field sprayer application of bifenthrin include: a minimum ASAE medium spray quality, an 8 km/h wind speed restriction and the requirement to use drift-reducing air induction nozzles. Calculated buffer zone distances were adjusted according to windspeed (0.2×) and low drift nozzle (0.75×) modifiers.

The adjusted windspeed factor of 0.2× (for 8 km/h) is based on field data obtained from Wolf and Caldwell (the same researchers that generated the data for the field sprayer model). The low-drift nozzle factor of 0.75× is the minimum spray drift reduction of 25% as obtained through information from nozzle manufactures.

Buffer zones that exceed the 120 m limit are adjusted manually based on restricted spray parameters (such as wind speed and nozzle type) that would effectively reduce spray drift. In this case, wind speed is restricted to no greater than 8 km/h and the nozzle type to low drift. Thus, the buffer zone of 368 m was modified manually as follows:

368 m × 0.20 (windspeed) × 0.75 (low drift) = 55.2 m rounded off to 55 m.

Buffer zones for all water depths for field sprayer applications were modified according to this calculation.

Note: the initial buffer zone determination did not utilize the correct aerobic whole system half-life of 276 days. Hence, the corrected spray buffer zones are as follows:

Table - buffer zones
Method of application Crop Buffer Zones (metres) Required for the Protection of:
Freshwater Habitat of Depths: Estuarine/Marine Habitats of Depths:
Less than 1 m Greater than 1 m Less than 1 m Greater than 1 m
Field sprayer Raspberries 15 5 55 25
Airblast Raspberries Late growth stage 60 55 75 65

Comment 30:

Why did the PMRA not take the limit of solubility of bifenthrin into consideration when conducting the risk assessment for green algae, eastern oyster embryos and acute sheepshead minnow for which the endpoints are above the limit of solubility for bifenthrin?

PMRA Response:

The PMRA did consider the solubility limit of bifenthrin for the aquatic risk assessment; however, since water monitoring data included measured concentrations of bifenthrin that exceeding the reported solubility values under environmentally-relevant conditions, the EECs were not capped at the solubility limit.

Comment 31:

The PMRA's assessments and EEC calculations gave no consideration to the solubility, degradation or expected rapid partitioning of bifenthrin to sediment and particulate over time and are unrealistic.

PMRA Response:

The EECs were modelled using PRZM/EXAM which requires a variety of fate input parameters including half-lives, Koc and solubility that consider degradation/transformation and partitioning to sediment. However, since water monitoring data included measured concentrations of bifenthrin that exceeded the reported solubility values under environmentally-relevant conditions, the EECs were not capped at the solubility limit.

Comment 32:

The commenter thought that using a pond scenario to derive marine EECs was not realistic and overly conservative.

PMRA Response:

It is acknowledged that the marine scenario used by the PMRA is conservative and the PMRA is in the process of revising its approach to conducting marine/estuarine risk assessments; however, given that the registration decision is based on bifenthrin meeting the criteria for a Track 1 substance, no revisions to the marine assessment are warranted at this time.

Comment 33:

The commenter also reported calculation errors for the acute RQ for mysid and chronic mesocosm RQ for freshwater invertebrates.

PMRA Response:

The PMRA agrees that the acute RQ for mysid and chronic mesocosm RQ for freshwater invertebrates should be 13 568 and 3200, respectively.

Comment 34:

Considering the water solubility limit, the commenter questioned why the PMRA used a surface water EEC of 5.2 µg/L to assess risk to freshwater invertebrates when PRZM/EXAMS EECs for runoff were used to calculate RQs for all other aquatic taxa. The commenter speculates this value was a maximum concentration for bifenthrin in whole water samples from urban flowing water sites based on the information presented in the USEPA's recent preliminary risk assessment for pyrethroids and pyrethrins. The commenter considers this value inappropriate given that urban uses of bifenthrin are not registered in Canada. Moreover, the PMRA should take into account bifenthrin bioavailability in surface water in calculating EECs.

PMRA Response:

The EEC of 5.2 µg/L is reported in the California Department of Pesticide Regulation water monitoring data (2013). As the use pattern in the US is different than the use pattern in Canada, the EEC should be 4.1 µg a.i./L. Given that the registration decision is based on bifenthrin meeting the criteria for a Track 1 substance, the EECs will not be refined at this time.

Vegetative Filter Strips for Reducing Runoff to Aquatic Habitats

Comment 35:

The PMRA did not present any data, analyses or scientific justifications to demonstrate that a 10-m vegetative filter strip (VFS) is necessary to be protective of aquatic habitats with label uses of Capture 240 EC in Canada.

PMRA Response:

As reported in Section 4.2.4 (pg. 37) of PRD2017-11, the PMRA is proposing a mandatory 10-metre vegetative filter strip for all pyrethroid insecticides based on their common chemical and toxicological properties. This is consistent with the use of vegetative filter strips for pyrethroid pesticides by other jurisdictions (in particular, USEPA and Province of Prince Edward Island).

As of October 2017, the PMRA is proposing vegetative buffer strips for chemicals that demonstrate characteristics of being practically insoluble in water, having a high soil adsorption coefficient, being expected to partition to sediment, and showing a potential risk to aquatic organisms from exposure to runoff from treated fields.

Toxic Substances Management Policy Considerations

Comment 36:

The commenter disagrees with the PMRA's conclusion that bifenthrin is bioaccumulative.  The commenter considers the key studies on which the PMRA relied to be not reliable and should therefore be excluded from the TSMP assessment while other studies were reliable and showed BCF values of bifenthrin below the criterion of 5000 for a variety of taxa. In addition, an aquatic food web model predicts BAFs less than 5000 and BMFs below 1.

PMRA Response:

The PMRA disagrees with the commenter's conclusion that three bioaccumulation studies should be classified as not reliable and excluded from the TSMP assessment. As per the PMRA Response to Comment 12, the PMRA reviewed the studies and found them acceptable for inclusion in the bioaccumulation assessment. Any deficiencies and limitations were identified and considered when interpreting study results and conclusions. A summary of the PMRA's assessment of the submitted bioconcentration and bioaccumulation studies is provided in Appendix II in this document.

The PMRA identified a number of deficiencies in all of the submitted laboratory BCF studies (Appendix II of RD2017-19); however, deficiencies identified in one study were often addressed through information provided in another study. As an example, OECD Guideline 305 (2012) requires testing of a substance at two or more concentrations; however, the Suprenant (1986) study only tested one concentration of bifenthrin. The OECD Guideline 305 indicates that one test concentration is sufficient if it can be shown that BCF is independent of concentration. This was confirmed in the Gries and Schanné (2006) study which showed that the BCF of bifenthrin is independent of exposure concentrations. Therefore, having only one exposure concentration in the Suprenant (1986) study does not affect the validity and acceptability of this study.

In addition, if limitations to a study were identified, these were considered when reporting the PMRA conclusion of a study. As an example, in McAllister (1988), the authors reported BCF values for embryo, larval and F0 adult generation. After a review of the information, the PMRA concluded that the estimated BCF values for embryo and larval were unreliable due to low sample numbers and high variability in tissue concentrations; however, the PMRA also concluded that the BCF values for the F0 adult generation were considered reliable and relevant to exposure in the environment. Therefore, the PMRA only reported one of the three endpoints.

One study showed that bifenthrin does not biomagnify in fish when only considering the dietary route of exposure under laboratory conditions (BMFs <1.0).

The BAF results of the aquatic food web model depend on the laboratory BCF studies chosen as input parameters. As discussed previously, the PMRA disagrees with the exclusion of key studies from the bioaccumulation assessment.

Under the TSMP, field BAFs are prefered over laboratory BCFs as they take into account exposure from all sources (water, food), bioavailability and interactions under environmentally-relevant conditions. Sufficient information was provided to show that bifenthrin BAFs > 5000 were sustained in the Alabama pond study.

Although the European field studies demonstrated that mitigation measures may reduce exposure in aquatic systems, the bioaccumulation potential of bifenthrin could not be assessed as exposure concentrations were too low in the water to calculate a BAF.

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