Bystander exposure to pesticide spray drift: New data for model development and validation

doi:10.1016/j.biosystemseng.2010.05.017

Biosystems Engineering

Volume 107, Issue 3, November 2010, Pages 162-168

https://doi.org/10.1016/j.biosystemseng.2010.05.017 Get rights and content

Experimental measurements were made of airborne spray, ground deposits and potential bystander dermal exposure under field conditions, using application techniques representative of those typically used in UK arable crops. Measured values of bystander dermal exposure were greater than those currently used in the UK regulatory risk assessment (Lloyd & Bell, 1983). This was as expected since compared with the earlier study a greater boom height and reduced distances between bystander and sprayer were used. Measurements of airborne spray were correlated with measurements of bystander exposure in order to define the relationship between the two so that model predictions of airborne spray can be mapped to bystander dermal exposure in the Bystander and Residential Exposure Assessment Model (BREAM).

Introduction

There is a clear need to obtain new information about the potential exposure of the public to pesticides used in agricultural applications following the publication of a report by the Royal Commission on Environmental Pollution (RCEP, 2005) and continued public concern related to potential health risks. One of the main recommendations in the RCEP report was to replace the current exposure assessment for residents and bystanders to pesticides, which is based on a single set of empirical data (Lloyd & Bell, 1983) with a computational model, which should be rigorously validated by field studies.

The Bystander and Residential Exposure Assessment Model (BREAM) project was therefore undertaken, commencing in June 2006, to develop a model suitable for regulatory use in the assessment of bystander exposure to pesticides resulting from spray drift from typical arable boom sprayers. In order to develop and ultimately validate the model, new data were required that covered the range of nozzle types commonly used in the UK: a reasonable range of distances between the bystander and sprayer and typical application practices, such as forward speeds up to 16 km h⁻¹ and boom heights greater than the previously used value of 0.5 m above the crop.

The Silsoe spray drift model (Butler Ellis and Miller, 2010) predicts concentrations of airborne spray downwind of a boom sprayer. The total amount of this spray that is likely to be deposited on the surface of a bystander will depend upon many variables and full characterisation of the ‘collection efficiency’ of a human was beyond the scope of the BREAM project. Therefore, the approach taken was to translate the amount of airborne spray into bystander exposure using an empirical relationship. In this context the collection efficiency may be defined by the proportion of airborne spray collected by the bystander.

There is no published data that can be used to estimate collection efficiencies of a bystander. The quantity of spray from a boom sprayer deposited on a bystander has previously been correlated with ground deposits (Gilbert, 2002), but the relationship with the component of airborne spray up to the height of the bystander could not be determined because measurements were only available of the total quantity up to 11 m above the ground (Lloyd & Bell, 1983). Although one European Union member state uses ground deposits of spray drift to determine bystander exposure to ground deposits of spray drift (Hamey et al., 2008) this is scientifically flawed since the bystander is not exposed to the droplets sedimenting onto the ground, but to those remaining airborne.

A further set of data was obtained in order to inform the UK regulatory authorities where both airborne spray and bystander contamination were determined (Glass, Mathers, Harrington, Gilbert, & Smith, 2002). This small data set is included in the analysis presented in this paper. Other published data relates to significantly different crops and application equipment (e.g. Lloyd et al., 1987, Moreira et al., 1999, Vercruysse and Steurbaut, 2001) where the levels of bystander exposure would be expected to be significantly different from those produced by arable boom sprayers.

Three new experiments were conducted, the first in November–December 2007 (Glass et al., 2010), the second in March 09 and the final experiment in June 2009. The first two experiments were conducted over short grass (approximately 50 mm tall) at Wrest Park, Silsoe, Bedfordshire, UK. The third experiment was conducted over a mature winter wheat canopy on a commercial farm in Bedfordshire. These experiments measured the potential dermal exposure of bystanders, using mannequins and human volunteers, airborne spray using passive line collectors and ground deposits using strips of filter paper. Previous research had attempted to measure inhalable droplets (Defra, 2005, Lloyd and Bell, 1983) but in both experiments, measurements were found to be below the limit of quantification and therefore were not included in this work.

This paper reports the data obtained in the second and third experiments undertaken as part of the BREAM project and combines this with previously published bystander exposure data to provide a relationship between predicted airborne spray from the spray drift model and potential bystander exposure. The data set itself does not provide a balanced set of scenarios on which to base an ideal exposure assessment: however, some analysis is carried out in order to establish how the regulatory assessment of exposure could be improved by its use. Ground deposits are not reported in this paper because they are not directly relevant to bystander exposure. The measurements were made to ensure that the data obtained was consistent with other published data, where ground deposits are more frequently reported than airborne spray.

Section snippets

Experimental methods

Similar protocols were employed for all three experiments. Applications were made with a 24 m width boom sprayer travelling along a track at right angles to the predominant wind direction. Plots were laid out downwind of the sprayed area in which drift collectors, including bystanders dressed in coveralls, were placed at distances from the edge of the sprayed area (defined as 0.25 m from the centre of the end nozzle). Airborne drift collectors were horizontal 0.5 m length, 0.2 mm diameter polythene

Results of bystander exposure

All values given in the Table 4, Table 5, Table 6, Table 7, Table 8, Table 9, Table 10 are ml spray liquid per bystander per pass of the sprayer. They are grouped according to nozzle type and distance from the sprayed area. Further details of boom height and forward speed can be identified from Table 1, Table 2, Table 3.

Measurements of ground deposits and airborne spray are not presented explicitly here, but were used to compare with model predictions (Butler Ellis and Miller, 2010) and were

Discussion

While the above data were not gathered in order to provide an appropriate data set to replace the Lloyd and Bell data currently used in the regulatory exposure assessment for bystanders, some analysis can be helpful in assessing the likely implications for updating the UK bystander exposure assessment. The new data covers three different nozzles, used at two different forward speeds, a number of different nominal booms heights and two crop heights. There was also a wide range of wind speeds

Conclusions

Data relating to airborne spray drift, ground deposits and potential dermal exposure of bystanders have been obtained in three field experiments. The relationship between measured airborne spray and bystander contamination has been investigated and it is proposed that this empirical relationship can be used to map model predictions of airborne spray to potential exposure of bystanders. Further work to refine this relationship and to identify any variables that could influence it would be

Acknowledgements

The work reported in this paper was funded by Defra through the Health and Safety Executive’s Chemicals Regulation Directorate.

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Citation Excerpt :
The basic principles of the protocol are outlined below. The same collectors as those that have been used in field studies to capture airborne spray drift (Butler Ellis et al., 2010) were used in the wind tunnel. The wind tunnel was set up with a single moving nozzle mounted at 0.5 m above the lowest collecting lines (which were 0.1 m above the floor) on a track sprayer.
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Research PaperBystander exposure to pesticide spray drift: New data for model development and validation

Introduction

Section snippets

Experimental methods

Results of bystander exposure

Discussion

Conclusions

Acknowledgements

Biosystems Engineering

The assessment of the risk of bystander contamination during the application of pesticides to field arable crops in typical UK conditions

EUROPOEM bystander working group report

Generation of field data for bystander exposure and spray drift with arable sprayers

Aspects of Applied Biology

Research Paper
Bystander exposure to pesticide spray drift: New data for model development and validation