Effectiveness of Grassed Buffer in Reducing Spinosad Runoff: Real Data and FOCUS Output

In Italy high-quality vines are grown on sloping fields where pesticide runoff to surface water is possible and vegetated buffers are suggested as mitigation measure. Spinosad is an insecticide used to control pests in vineyards. For regulatory purposes, FOCUS modelling is used to calculate pesticides runoff reduction provided by a vegetated buffer, but there is an urgent need for field-based results. A field trial with artificial runoff was performed in September 2017 in Northern Italy to evaluate the efficiency of a grassed buffer to reduce spinosad runoff. Trial conditions were based on FOCUS scenarios but made worse to draw prudent conclusions. For the first time in Italy, the trial was conducted according to Good Laboratory Practices to increase reliability of results and reproducibility of the study for regulatory purposes. Five plots were tested, each simulating a grassed buffer of 12 m length on a slope of 10% 13%. The artificial runoff was 200 mm in 3 hours and rainfall preand during runoff was 45 mm. Results show that the 12 m buffer completely retained runoff and effectively mitigated runoff concentration, and mean reduction of spinosad concentration was 59%. A width effect exists, and every 6.5 m of buffer reduces concentration by 50%. Comparison of field results with FOCUS modelling shows that both VFSMod and LM models provide acceptable estimation of runoff reduction for a 5 m buffer, while LM seems more precise. For a 10 m buffer the VFSMod is very accurate, while LM underestimates reduction observed in the field. How to cite this paper: Otto, S., Gottardi, S., Pasini, M., Menaballi, L., Bradascio, R. and de Cirugeda Helle, O. (2020) Effectiveness of Grassed Buffer in Reducing Spinosad Runoff: Real Data and FOCUS Output. Journal of Environmental Protection, 11, 169-195. https://doi.org/10.4236/jep.2020.113011 Received: December 6, 2019 Accepted: March 6, 2020 Published: March 9, 2020 Copyright © 2020 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Abstract
In Italy high-quality vines are grown on sloping fields where pesticide runoff to surface water is possible and vegetated buffers are suggested as mitigation measure. Spinosad is an insecticide used to control pests in vineyards. For regulatory purposes, FOCUS modelling is used to calculate pesticides runoff reduction provided by a vegetated buffer, but there is an urgent need for field-based results. A field trial with artificial runoff was performed in September 2017 in Northern Italy to evaluate the efficiency of a grassed buffer to reduce spinosad runoff. Trial conditions were based on FOCUS scenarios but made worse to draw prudent conclusions. For the first time in Italy, the trial was conducted according to Good Laboratory Practices to increase reliability of results and reproducibility of the study for regulatory purposes. Five plots were tested, each simulating a grassed buffer of 12 m length on a slope of 10% -13%. The artificial runoff was 200 mm in 3 hours and rainfall pre-and during runoff was 45 mm. Results show that the 12 m buffer completely retained runoff and effectively mitigated runoff concentration, and mean reduction of spinosad concentration was 59%. A width effect exists, and every 6.5 m of buffer reduces concentration by 50%. Comparison of field results with FOCUS modelling shows that both VFSMod and LM models provide acceptable estimation of runoff reduction for a 5 m buffer, while LM seems more precise. For a 10 m buffer the VFSMod is very accurate, while LM underestimates reduction observed in the field.

Introduction
Pesticides runoff to surface water poses a risk to the aquatic environment, and recent studies show that pesticides from agricultural land use are a major threat to small streams and their biodiversity [1] [2].
Compared with several other land uses, vines often create favourable conditions for water runoff and sediment loss, mainly because vines are planted in the direction of slope and cultivation practices increase soil compaction [3]. Inter-row management is also important, the highest runoff rates and soil losses are observed for chemically weeded vineyards, while grassing might be the best option for runoff reduction [4].

Spinosad (Dow Agrosciences, Indianpolis, IN) is a naturally derived insecti-
cide containing a mixture of two structurally similar molecules widely used in all the Southern Europe Registration Zone, to control pests on several crops including vineyards, also in organic farming.
According to EPA Toxicity categories, Spinosad is classified "slightly to moderately toxic" to fish, most aquatic invertebrates and algae [5]. In Europe Spinosad is classified as "Very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment" and requires ecosystem protection.
Additional labelling with risk phrases and safety phrases is affixed, particularly to enforce prevention of any entry into surface waters; furthermore the K OW values ranging from 2.78 to 5.21 (depending to pH) indicate that bioaccumulation or accumulation in sediment can occur [6]. For use in vineyards in Italy the label of the most recent formulation (Tracer 120 SC, released 30 January 2019) indicates the requirement of a no-spray zone of 15 m to protect water courses. Protection from drift can involve both no-spray zone and drift reduction techniques, while protection from runoff can take advantage of soil incorporation, treatment localization and a properly managed vegetated filter strip (hereafter: Various recent studies show that VFS are in general effective for runoff reduction and can be suggested as a mitigation measure [7] [8]. Studies on soil erosion [9] showed that to be effective the grass cover must be dense.
In Italy high-quality vines are grown on hilly fields, where spinosad runoff to surface water is possible. However, no experimental data are available on spinosad displacement in VFS on sloping fields.
Results from field trials are few since they are difficult and very time and labour consuming, so the main evaluation of runoff magnitude and reduction provided by VFS derives from model outcomes [10]. FOCUS Landscape and Mi-tigation v2 (hereafter: FOCUS L & M) allows VFS as a mitigation measure against the risk of pesticides runoff to surface water, and provides values of pesticide removal efficiency [11] [12].
The current mitigation approach of FOCUS L&M is based on static reduction factors related to buffer width. Recent models have been developed to estimate VFS trapping efficiency dynamically after single runoff events, and to identify the importance of factors for the prediction of runoff, pesticide reduction, the VFS hydraulic properties being the most important [13].
Mitigation capacity of a VFS depends on width, slope, grass and litter cover [8]. Models account for complete grass cover, laminar flux and lack of preferential flow.
A recent study performed in Germany [14] showed that efficacy calculated by models is 35% -40% higher than that obtained in real, not perfect, conditions. Field trials are indeed of great importance, 1) to enlarge the database on which the model can rely, 2) because they can improve model parametrisation to take into account grass cover conditions, and 3) provide hard evidence for Authorities for pesticide use regulation based on real VFS efficiency, for example in hilly areas rich in water courses.
Furthermore, a recent Document from the Italian Ministry of Health [15] allows VFS as a mitigation measure for runoff to surface water, but for sloping fields considers reduced mitigation efficiency, i.e. with a >5% slope the efficiency is 30% of that for plain fields. The Document is regularly under revision in the light of new and hard evidence, such as results from field trials. Publication of an updated revision is expected in March 2020.
It is worth noting that for regulatory purpose, National Authorities evaluate mainly, or only, studies performed according to accepted procedures, such as those from Good Laboratory Practices, the results of which are officially validated after a formal audit by the competent Ministry. The important extra-cost of this approach makes runoff field studies "GLP compliance" very rare or completely lacking, as in Italy.
The aim of this field study was to evaluate in a real vineyard-buffer system the capacity of a grassed buffer to reduce runoff concentration of spinosad. Runoff conditions were based on FOCUS R2 and R3 scenarios, but with a steeper slope to draw more prudent conclusions. More specifically, the aim was to evaluate mitigation capacity of a grassed buffer, both on spinosad concentration and runoff displacement, and provide recommendation for regulatory purposes.

Experimental Site
The trial site was near Verona, in a hilly area with many vineyards and famous for high-quality wine production (45.39N, 10.77E). The site was selected as it was highly representative of vineyards on sloping fields in the Mediterranean EPPO zone, and similar to the FOCUS R2 and R3 scenarios. The site was a slop-ing area permanently grassed for 10 years, surrounded by vineyards. It was not subject to extensive grazing by livestock as the grass was typically cut twice a year for hay. The soil type on site was sandy loam or sandy-clay loam according to the Soil Texture Calculator (www.nrcs.usda.gov, based on [16]) (Supplementary data, Table S1).
The site texture was similar to the mean texture of R2 and R3, and the critical hydraulic properties of field capacity very close to those of R2 and R3 (Supplementary data, Table S2).

Plot Layout
In the middle of the grassed area, 5 plots of 50 m 2 (4.17 m wide * 12 m length) were selected. Slope was measured with a laser level, and ranged from 10.6% to 13.2% (Supplementary data, Table S3). This slope is at least double that considered in FOCUS R2 and R3 scenarios, where it is set at 5%.
Grass cover was assessed visually, and ranged from 75% to 90%. Vegetation cover and species spectrum was uniform across plots (Supplementary data, Table S4).
From May to September 2017 the grassed area was managed to allow a runoff flow free of obstacles according to the creation of a worst-case scenario. Grass cutting was regular every 8 days to avoid formation of thatch or a residue layer, to stabilize grass cover density and avoid runoff preferential flow. With this high frequency, cuttings were of about 1 cm and their removal was not needed as they quickly dried out in summer. The last cut was done 7 days before the first runoff application and vegetation height was about 5 cm in all 5 plots.

Source-To-Buffer Ratio
The trial accounts for a source-to-buffer ratio of 10 to 1, as if the runoff generates in an area of 500 m 2 (5 m wide * 120 m length, source) flowing into the plot of 50 m 2 (4.17 m wide * 12 m length, buffer).
For this, 20 mm of rainfall and runoff generated in the source correspond to a runoff flow of 10,000 L in the buffer. This volume of runoff water was applied to the plot using a custom runoff applicator at the upslope edge of each plot over a 2.25 hours period, following completion of the initial irrigation phase.
The contributing area (source) was broadly representative of typical field size in the area, as determined by the following expert judgement. In Veneto and other Regions in Northern Italy, the most frequent cropping unit for vineyards is about 3500 m 2 . On sloping fields, to ease operations, vine rows are usually planted about 3 m apart according to the iso-level lines. A common crop unit includes at least 10 rows, so it has a short side of 30 m and a front side of 110 m.
The front side is usually used as tractor path and is 3 -4 m wide, accounting for an area of 350 m 2 . In this scenario a cropped area of 3500 m 2 (source) has a non-cropped edge of 350 m 2 (buffer). What makes this scenario worst is the hypothesis that runoff generated inside the source doesn't infiltrate between rows but flows entirely to the buffer, accounting for a source-to-buffer ratio of 10 to 1.

Chemicals and Analytical Procedure
Spinosad is an insecticide widely used in Italy for many crops, included orchards and vineyards. It consists of two active ingredients (spinosyn A and spinosyn D) and two primary N-demethylated metabolites (spinosyn B and N-demethyl spinosyn D, also referred to as spinosyn B of D). Hereafter those 4 compounds are

Mechanics of the Experiment and System Set-Up
The 4 spinosyns were dissolved in the laboratory then released into tanks filled with pure water, the run-on reservoir. Input concentration was 2.0 μg/L. After 0.5 hours mixing and recirculation, the solution was conveyed to the custom runoff applicator 5 m away. From here the solution was continuously released into the plot for 2.25 hours, and sampled at 0.75 -1.5 -2.25 hours after runoff start. Mixing and recirculation in the run-on reservoir continued until the end of runoff sampling (Supplementary data, Figure S1).
Irrigation was applied throughout the experiment. Detection of the tracer KBr guarantees proper sampling (water from runoff, not from irrigation only), and expected concentrations of spinosyns in runoff must be lower than input.
Before the first application with the spinosyns, 8 preliminary tests were done using pure water from June to September in order to fine-tune the system mechanics, i.e. timing of irrigation and sampling, engine settings, sprinkler position and height. Results show that runoff displacement was of variable length but did not breach the 12 m length buffer in any preliminary test, the final length of plots and sampling timing were then set accordingly.

Selection of Rainfall Event
Analysis of FOCUS scenarios indicated that the R4 scenario would be the realistic worst-case scenario to be applied in the field trial. Representative rainfall, associated runoff volume and target spinosyns concentrations are similarly derived, and rainfall/runoff duration determined using long-term climate data obtained for the Mediterranean area.
Particularly, the return periods for daily rainfall events are calculated from long-term climate data obtained for the R4 scenario (weather station in Roujan, France) since both the Roujan and Verona areas belong to the same R4 scenario, rainfall erosivity for both areas is the same [17], and outcomes are consistent with results from recent studies conducted in Northern Italy [18]. Given the se-lected parameters, conditions of the experiment can be considered highly precautionary.
The runoff in R4 scenario is generated by a rainfall event of 45 mm in 1 day.
According to FOCUS (daily data), this type of event is quite frequent and has a return period of about 0.34 years (4.1 months). Run-on water contained a precise amount of the 4 spinosyns and a tracer (KBr). The tracer was added to run-on water to ensure that samples of runoff water were not generated by irrigation only.

Timing
(Details on spinosyns application are in Supplementary data, text S4).
Once released into the buffer area, the "run-on" solution in the reservoir becomes "runoff", and runoff water was sampled at 0.75 hours (0 h: 45 min), 1.5 hours (1 h: 30 min) and 2.25 hours (2 h: 15 min) after run-on start.
During run-on, irrigation continued until the end of run-on (other 33 mm), and a total of 45 mm was applied to the buffer area in 3.08 hours (3 h: 05 min) (mean intensity: 14.6 mm/h) (Supplementary data, Figure S2).
One artificial runoff application was made to each plot, and the five applications were performed from 12 to 29 September 2017 when the plot vegetation was well developed and the cover uniform. Each application was concluded on the same day, in 3.08 hours (Supplementary data, Table S5).

The Custom Runoff Applicator
To achieve an even application of run-on water, a custom runoff applicator was built ( Figure 1). This consisted of a wooden frame that spanned the width of the plot (i.e. 5 m), with plexiglass plates connected to the frame and touching the ground at an angle of c. 45˚. The artificial runoff was applied with an array of nozzles (ARAG micro-spray 180˚) directed on to the plexiglass plates to create laminar runoff flow from the custom runoff applicator down to the end of the plot.
Plots were separated by 3 -4 m space, but to prevent lateral movement of runoff to an adjacent plot, the full length of the plot was bordered by overlapping stainless steel metal sheets inserted into the soil.

Summary of the Selected Trial Conditions
Trial conditions were based on FOCUS R4 scenario, but made worse: 1) High source-to-buffer area proportion (10 to 1); 2) High runoff/rainfall rate in the source area (20 mm runoff for 45 mm rain = 45%); 3) Heavy rainfall (245 mm in 3 hours, return period of 2 years); 4) Steep buffer slope (from 10% to 13%); 5) Low grass cover height (5 cm, without residues on soil).
Selected conditions can be considered highly favourable for runoff, allowing precautionary conclusions and recommendations.

Run-On Sampling
For spinosyns and KBr grab samples of run-on water were collected at the application nozzles of the custom runoff applicator, at 0.75 hours and 2.25 hours after run-on start, i.e. at the start and end of the runoff sampling. Results for KBr are in Table 1, for spinosyns in Table 2.

Runoff Sampling
Runoff samples were taken: 1) For KBr at 2.25 hours from runoff start (results in Table 1); 2) For spinosyns at 0.75 -1.5 -2.25 hours from runoff start (results in Table   2). S. Otto et al. The sample at 2.25 hours was that at the furthest point reached by runoff down the grassed buffer. Each sample was taken directly from the ground using an amber glass jar. Plastic marker sticks were used to indicate runoff displacement (Supplementary data, Figure S3). Samples were processed, frozen and shipped (Supplementary data, Table S6).

Data Analysis
It is expected that concentration of spinosyns decreases as water flows from the custom runoff applicator to the end of the plot 12 m downslope because of adsorption to the plant-soil system [19] [20]. The reference concentration is run-on concentration at the custom runoff applicator (average of the 2 values) and the concentration reduction is called "mitigation". For example, for Sp. A in Plot 1, run-on concentrations were 1.579 μg/L and 0.937 μg/L; the mean value (1.258 μg/L) is the reference value for the calculation of mitigation in runoff samples.
This means that in 5.6 m displacement concentration of Sp. A in runoff decreased by 62%.
Reduction was calculated for each of the 3 runoff samples collected in each plot (Table 3).

Meteorological Parameters and Soil Moisture
Standard meteorological parameters were recorded for each plot during runoff events. In brief, runoff events occurred on warm days (17˚C -29˚C), without wind. The soil moisture was measured with the EC5 Soil moisture sensor TM (Decagon devices Inc., Pullman, WA) 3 times: 1) before trial start (pre-storm); 2) at run-on start (i.e. at end of pre-runoff irrigation); 3) at end of trial (Supplementary data, Table S7).

FOCUS Modeling
A comparison was made between experimental results and runoff reductions VFSMod is a computer simulation model created to study hydrology, sediment and pollutant transport through vegetative buffer strips.
Both these approaches depend on the buffer width, but they can provide very different results. During this study, a comparison was made between the two approaches and the experimental results, in order to analyze the reliability of the modelling methods and to define which one is more suitable for PEC SW calculation.
The FOCUS crop "Grass/alfalfa" was selected to reproduce the experimental conditions. R2 and R3 scenarios were selected, because FOCUS models do not associate "Grass/alfalfa" crop with the R4 scenario.

Irrigation Efficiency
Soil moisture increased regularly as irrigation proceeded: before trial start it was 18% -30% (%v/v), after pre-runoff irrigation, i.e. at field capacity, it was 37% -43%, at end of runoff final moisture was at least 40% for the five plots. Irrigation system and application timing was 100% efficient (Supplementary data, Figure   S4). Field capacity was very close to that considered in R2 and R3 scenarios (36% -37%).

KBr and Spinosyns Release and Sampling Precision
Detection of KBr and spinosyns in all samples were always positive. This showed that release with run-on and sampling procedure of runoff were 100% effective (119 positive over 119 possible detections) (Supplementary data, Table S8).

KBr Concentration in Run-On
KBr was detected in all samples, with a concentration of 0.281 ± 0.009 (CV = 3%) g/L, very regular and lower than input concentration (0.5 g/L) ( Table 1).

Spinosyns Concentration in Run-On
The 4 spinosyns were detected in all samples, with a concentration of 1.397 ± 0.379 (CV = 27%) μg/L, regularly lower than input concentration (2.0 μg/L) except in two cases ( Table 2). These results show that dissolution and release of spinosyns by custom runoff applicator were 100% effective (Supplementary data, Figure S5).

KBr Concentration in Runoff
KBr was detected in all samples, with a concentration of 0.208 ± 0.030 (CV = 14%) g/L, very regular and lower than run-on concentration (Table 1).
Taking into account the 57 positive values, mitigation provided by the grassed buffer was 65 ± 21 (CV = 33%) percent, and the maximum mitigation value was 96%.
Taking into account the entire set of 60 mitigations, included the 3 negatives, Upper Confidence Limit for mean (UCL) 95% is 67%, this means that in 95% of possible events concentration of runoff was reduced by 67%.

Runoff Displacement
In the 5 plots, runoff displacement ranged from 3.7 to 11.6 m (7.4 ± 2.5 (CV = 34%)). Inter-plot variability was observed, i.e. in Plot 2 the range was 8.7 -11.6 m, in Plot 5 was 3.7 -5.3 m. This variability of displacement is acceptable since runoff in field trials is usually very variable even in very small plots. For example, in an experiment with plots of 0.25 m 2 , [9] found for soil erosion a runoff coefficient variable from 0.4% to 77%.
According to the aim of the study to explore worst-case conditions, the focus was on maximum displacement in each plot: this ranged from 5.3 to 11.6 m (8.8 ± 2.7 (CV = 31%)).
UCL95% is 12 m, this means that in 95% of possible events, the entire runoff flow remains inside a 12 m grassed buffer. UCL99% is 14 m.

Effect of Buffer Width on Mitigation
For the evaluation of the distance-to-mitigation effect no generally accepted method is available, particularly when displacements are of variable length.
In this study a method based on mean concentrations in two selected displacement ranges was used. Limits were based on quartile range of 15 runoff displacements observed: 25 th = 5.3 m, 75 th = 9.8 m. To separate an equal number of lower and higher displacements, quartile range was rounded to 5.2 m and 10.0 m. According to this procedure, results show that a grassed buffer of 6.7 m provides a concentration mitigation of 44.8% (Figure 2) (Supplementary data, Table S9).

Field Data and FOCUS Output Comparison
Considering a 5 m VFS, with LM model the runoff mass reduction was 50.2% ± 1.3%, with a related PEC SW reduction of 44.8% ± 0.5%. Results from this model were of low variability and not affected by the scenario or application period.
With VFSMod model higher reduction values were obtained, with a runoff mass reduction of 91.4% ± 12.7%, and a related PEC SW reduction of 92.6% ± 11.6%. These values are very different for R2 and R3 scenarios (runoff mass reduction was 100% ± 0.0% for R2 and 82.7% ± 13.1% for R3), showing that the model output was significantly affected by the properties of the scenarios. Application period also had an influence on mean runoff mass reduction, which was 95.7%, 98.6%, 91.7%, 84.5% for T1, T2, T3, T4. Results for this model were of quite high variability, mainly affected by the meteorological and pedological conditions of scenarios, while effect of application periods was minor.
Considering 10 m VFS runoff reduction was higher for both models. With LM the runoff mass reduction was 95.6% ± 8.3%, with a related PEC SW reduction of 60.2% ± 1.0%. With VFSMod the runoff mass reduction was 95.6% ± 8.3%, with a related PEC SW reduction of 96.3% ± 6.9%. Detailed results are reported in Supplementary data (Tables S10-S12). Comparison of field trial results with models outputs for a 10 m grassed buffer show that VFSMod provides a very accurate estimation of what was observed in the field: in the field runoff mass reduction was 100% (12 m VFS), for VFSMos it was 90% -100% (10 m VFS), the second value is for R2 scenario, with soil texture more similar to the field. Instead, LM model underestimates the runoff reduction provided by the buffer strip (runoff mass reduction for LM was 60%).
Comparison of models outputs for a 5 m grassed buffer with field trial results is not possible since runoff volume was not measured after 5 m displacement. Yet, visual assessment of runoff flow suggested that most of the runoff volume was retained in the first 5 -6 m buffer, so it can be concluded that for a 5 m grassed buffer the VFSMod model (runoff reduction was 82% -100%) slightly overestimates field observations, while LM model (runoff reduction of 50%) is in very good agreement.
From a scientific point of view therefore, both VFSMod and LM models seem to describe the behaviour of the vegetated buffer strip with some imprecisions, and are thus not totally reliable.
From a regulatory point of view, the dependence of VFSMod on pedological and meteorological properties of FOCUS scenarios can be considered a disadvantage. Since the reproducibility and reliability of the results of evaluations are the main goals in regulatory processes, LM should be preferred.
When models results are compared with field results, a general conclusion is that both models provide acceptable estimation for runoff reduction for a 5 m grassed buffer, where LM seems more precise. For a 10 m grassed buffer the VFSMod is very accurate, while LM underestimates the reduction.
In any case, the procedure for artificial runoff used in this field trial proved to be adequate to evaluate or improve models parametrisation; furthermore, the low variability of results support the use of this field method for chemicals and scenarios comparison, and to provide evidence for regulatory purposes.

Conclusions
1) A reliable run-on and runoff method is available for runoff experiments with pesticides for scientific and regulatory purposes. The study was acknowledged for its "GLP compliance" by the Italian Ministry of Health [21]. In order to ease replication of the experiment, a complete set of information is provided in the Supplementary data.
2) A grassed buffer of 12 m can completely retain runoff even with a 10% -13% slope and under heavy rainfall conditions, and effectively mitigate concentration of spinosad in runoff, providing a reduction of up to 96%. This is consistent with the quite high lipophilicity of this insecticide.
3) An effect of grassed buffer length on mitigation exists. Using rounded values, a 6.5 m grassed buffer can mitigate spinosad concentration by about 50%. According to the iterative method suggested by the Italian Ministry of Health [15], a total length of 13 m provides a total mitigation of 75%. A further length

4)
Comparison with the FOCUS outcome shows that both VFSMod and LM models provide acceptable estimation of runoff reduction for a 5 m grassed buffer, where LM seems more precise. For a 10 m grassed buffer, the VFSMod is very accurate, while LM underestimates reduction.
It is important to note that conditions of the grassed buffer in this study were very good, so the observed runoff reduction can be considered as the highest possible. The outcome from FOCUS modelling underestimates this runoff reduction, and calculated values can be considered as for a grassed area with standard management and average conditions, but the likely grassed buffer potential can be further exploited.
It is known that VFS are dynamic systems, their performance does not remain constant over the years indicating the need to define suitable buffer management [8], and data from this study demonstrate the high potential of a well-maintained This width value of the grassed buffer is interesting since the latest formulation of spinosad requires ecosystem protection for drift and runoff. According to the latest approach for mitigation in Italy, the no-spray zone width for drift protection can be reduced when anti-drift technologies are used, and results of this study show that this reduction can reach 12 m even in steeply sloping fields since this also provides protection for runoff, making application of spinosad, and other similar pesticides, of low risk to aquatic ecosystems.
Field trials of pesticide runoff provide only case-studies of the very large parameter combinations that occur in the environment, but can be very useful to tune fine mechanistic modelling often used to supplement the limited number of field data.

Chemicals application
In the laboratory, 0.020 g of each of the 4 spinosyns was weighed into a single 500 ml amber glass jar and dissolved in approximately 150 ml of acetonitrile organic solvent solution and shaken until fully mixed. Preparation of items showed some differences in the dissolution, spinosyn B of D being the less soluble. The solution of the 4 spinosyns and acetonitrile was therefore subsequently mixed with a laboratory magnetic stirrer for 4 -5 minutes. This was then topped up with tap water to a final volume of approximately 500 ml and shaken again. This was taken to the trial site on the same day in a secure, lockable transport box.
Prior to adding the test item mixture to the 10,000 L of run-on water reservoir, the jar was shaken again to ensure the spinosyns had completely dissolved, after which it was added to the 10,000 L of water previously metered into the plastic bowser tank to give the required concentration for each of the 4 spinosyns in the run-on water of 2.0 μg/L.

Runoff samples processing
The 120 ml KBr water samples were transferred into a 250 ml amber glass jar.
The 40 ml spinosyns water sample was transferred into a 150 ml amber glass jar, mixed with 40 ml of acetonitrile organic solvent solution, and then shaken until fully mixed. The jars were closed with PTFE lined screw caps.
Once collected, the water samples were immediately stored in a cool box then stored at −18˚C. Shipment to the analytical laboratory (CEMAS) was by freezer truck.
Analytical procedure. Samples were allowed to thaw and reach room temperature. An aliquot of 1.5 mL of field sample was filtered and transferred to an auto-sampler vial for analysis. Residue determination was by ion chromatography with conductivity detection (IC-CD). Conductivity was measured in micro Siemens (μS). The specimens were analysed in batches, each batch containing at least one control specimen, three procedural recovery specimens and a reagent blank. Results were quantified using a 1/x weighted calibration.

Supplementary Data, Table S8
Table S8. Summary of samples and detection in run-on and runoff water.  BofD. Only in two cases concentration was higher than input.