Field scale drift studies to refine standard drift curve values and assumptions. Tim Pepper Cambridge Environmental Assessments

Transcription

1 Field scale drift studies to refine standard drift curve values and assumptions Tim Pepper Cambridge Environmental Assessments

2 Spray drift extent Under certain conditions offtarget movement will occur Proportion depends mainly on Wind velocity & humidity Droplet size and distribution (determined by nozzle) Boom height Type of application equipment (conventional, air-assisted etc.) 2

3 Assessing spray drift May be a significant exposure pathway for aquatic organisms (along with drainage and runoff) Practical difficulties in routinely assessing potential for spray drift generally leads to first tier approach 3

4 First tier approach: Simplistic methods for estimating loadings onto horizontal surfaces (SANCO/3268/2001) Use of standard drift tables (Ganzelmeier et al., 1995; Rautmann et al., 2001) Look-up tables provide drift values (90 th percentile) for various crops at various distances Assume non-vegetated area therefore inaccurate exposure estimates where complex off-crop structures - correct by vegetation distribution factor to give realistic but worst case deposit estimation 4

5 First-tier approach: limitations However, Sometimes very conservative assumptions related to application method (e.g. direct overspray with aerial applications) Regulatory framework currently assumes standard application equipment (horizontal boom sprayer & 110 flat fan nozzles, 50 cm above ground level or air-blast sprayer) May not be appropriate if using non-standard application equipment or low drift nozzles...leads to need for a higher-tier approach 5

6 Higher-tier approaches Options when more accurate assessment of drift required Modelling (e.g. AGDRIFT) Understanding spray physics in development of mitigation strategies Measuring drift and demonstrating effectiveness of mitigation challenge and produce data 6

7 Measuring spray drift Guidelines: ISO 22866:2005 Equipment for crop protection Methods for field measurement of spray drift UK LERAP reference protocol for field measurement of spray drift deposition from agricultural and horticultural spraying systems Approaches and tools for higher tier assessment of environmental fate in the UK (PSD 2005) - discusses both Htier modelling approaches (FOCUS SW) and field studies aimed at demonstrating drift mitigation 7

8 Measurement outdoors in typical field conditions Standard measurement distances Measurement relates to deposition onto horizontal surfaces or to airborne spray profiles, using horizontal or vertical collectors Deposition relevant to surface water Airborne spray profile relevant to bystander exposure or long distance transportation and re-deposition Assessment of relative drift risk from different application systems Involves use of active substance or tracer dye, or other traceable material for representing a plant-protection product formulation 8

9 Using active substance advantages if need to determine concentrations in receiving water bodies, assess dilution or other factors Direct analytical methods for analysing residues therefore less risk when extrapolating data disadvantages cost of analysis can be expensive restricting number of samples analysed tied to label restrictions may necessitate multiple field sites may need experimental permit 9

10 Using tracer dye, or other traceable material advantages No label restrictions therefore allows multiple/repeat applications to be made to the same area Analysis relatively cheap (compared to active substances) Generally low toxicity Allows testing under range of conditions Depending on active, comparable sensitivity (1 ng/ml) Generic robust dataset which can be used for several actives disadvantages Dye costs can be high Photodegradation take steps to minimise May be affected by site specific phys-chem conditions, e.g. temp and water quality 10

11 Scenarios for field measurement of drift 1. Assessment of downwind deposition: different cropping systems different field margins mitigation afforded by different off-crop structures 11

12 2. Measurement of deposition and partitioning within edge of field water body: - use of surrogate static tanks if suitable site cannot be located 12

13 3. Non standard application equipment: Low volume spraying Edge of field deposition for applications made at the same time as drilling Low volume nozzles Nozzles mounted low to ground 13

14 4. Aerial Applications: Investigate mitigation options - Establish standard application conditions to achieve comparison of application equipment 14

15 Case study 1. Field study to measure spray drift deposition for orchard applications with drift-reducing nozzles Background Use of Spray Drift Reduction Technology (SDRT), including Low Drift Nozzles (LDN) part of regulatory framework in several EU member states risk assessments allow reduced no-spray-zone distances Study objective: Generate robust datasets that quantified spray drift deposition from applications made to commercial orchard crops using equipment fitted with LDN and conventional nozzles Under typical UK conditions, demonstrate significant spray drift reduction with LDN (>90%) 15

16 Selected single study site in typical fruit growing region in UK Cropped plot 0.2 ha within a larger orchard 50 m non-cropped buffer surrounding drift measurement positions established in two concentric circles applications made regardless of wind direction Multiple applications (>70) using fluorescent dye tracer Horizontal deposition targets 16

17 Hedge A Adjacent Orchard Legend Weather Station A-D Measuring reference points Uncropped experimental area Hedge D 4 B C Treated, cropped plot (9 rows of 26 trees) Deposition Target ID (20m nominal distance) Deposition Target ID (50m nominal distance) Deposition Target ID (30m nominal distance) Deposition Target ID (35m nominal distance) 50m 32m 20m Magnetic North m m 50m Hedge Adjacent Orchard 31 Not to scale

18 Water soluble surfactant used to ensure physical properties representative of liquids typically used in the application of plant protection products Samples analysed by fluorimetry in mobile laboratory established on-site Almost real time results available within 1hr of application! Excellent field fortification recoveries (70-120%) 18

19 Substantial drift reduction (up to 97%) when compared with standard equipment (air-blast sprayer/convential hollow cone nozzle) Air-assisted tower sprayer Conventional axial fan airblast sprayer 19

20 Case study 2. Field study to monitor spray drift deposition from orchard and vineyard herbicide spraying systems Background Herbicides are typically applied to orchards and vineyards with specialized equipment as a banded application, either to bare ground or to young weeds. Current spray drift risk assessment relies on standard drift curves derived from studies using conventional boom sprayers, which may not be suitable to predict downwind drift from these types of specialised application systems. Study objective: Obtain robust data sets that quantified down-wind spray drift deposition from applications to a commercial orchard and a commercial vineyard, using typical herbicide spraying apparatus. 20

21 Two experimental sites selected in major fruit growing region in UK: Vineyard and apple orchard dormant state timing as per label Sites selected on basis of favourable tree row orientation in relation to the prevailing wind gave best potential for spray applications being made at right angles to the wind direction unobstructed, uncropped 15 m wide border from downwind edge of the directly sprayed area Typical apparatus for banded herbicide application boomless swivel nozzles fitted with off-centre flat spray tips 21

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23 Nozzle height critical 40 cm & 30 cm Timed passes to calculate application volume and hence dose Fluorescent dye tracer as test item Horizontal deposition target 3 sampling arrays at six different downwind distances (1 to 15m) On-site analysis rapid turnaround of results Combined total 23 applications under range of wind speeds amount of spray drift measured on all targets at all distances, at both sites, as a percentage of the applied dose, was extremely low (<1 %). 23

24 Orchard Vineyard Study showed that apparatus typically used for banded herbicide applications made to orchards and vineyards provided significant mitigation against spray drift, even at relatively short downwind distances 24

25 Fluorescent dye tracers -problems encountered: Identifying suitable deposition target material poor field recoveries for much of research carried out to date piloted several inert materials before selecting one which didn t irreversibly absorb tracer Photo-degradation in field Temperature large fluctuations affected fluorimeter precision 25

26 Problems encountered: Site specific water quality issues High levels dissolved nutrients affected fluorimeter precision Overcome by using deionised water for preparing dilute spray and in all analytical procedures (extraction fluid) including cleaning glassware! 26

27 CEA Experience Success in conducting diverse and bespoke higher-tier drift studies edge of field and greater distances row and broad-acre crops Development of robust methodology for conducting single application studies with the compound of interest Novel approaches for repeat application studies, involving the use of fluorescent dye tracers as surrogate compound Regular communication with regulatory authorities to ensure high level regulatory acceptance on study design All studies conducted in accordance with GLP 27