Bystanders and Residents

Spray drift is a key exposure pathway for bystanders and residents. For orchard and vineyard crops, the 2014 EFSA guidance clearly identified the limitations of the Lloyd et al., 1987 study data in that bystanders were positioned at only one distance (8 m) downwind and also no monitoring was carried out for children. To address these shortcomings of the guidance, CLE established the Bystander Resident Orchard Vineyard (BROV) research programme to generate more pertinent drift data under representative European conditions. Sixteen studies were carried out across four EU countries at early and late growth stages with exposure monitored on adult and child mannequins at 3 downwind distances. The result was a much more comprehensive database allowing tiered and more specific assessments.

Since the advent of the 2014 EFSA guidance, risk assessments for bystanders and residents have become very challenging and often represent the most critical consideration in the registration of PPPs in Europe; this is an artefact of the risk assessment paradigm rather than a genuine scenario where the user is less exposed than members of the public who are only ever likely to be briefly and sporadically directly in the vicinity of PPP applications.

One of the pathways which generates high exposures is direct dermal and inhalation exposure to spray drift during foliar applications. For broadacre crops, exposure from boom sprayers is predicted by the Bystander and Resident Exposure Assessment Model (BREAM) (Kennedy et al., 2012). This model surpasses older guidance, but a re-evaluation of the model was carried out to investigate whether the component of BREAM which relates airborne spray concentrations to dermal exposure could be improved to better capture the inherent variability in the model (Butler-Ellis et al. 2018). The new approach was determined to be the better predictor of real exposures measured in the field. This “BREAM2” model was submitted to EFSA for their consideration and potential inclusion in the update of the non-dietary exposure guidance. Although this has yet to happen, it is hoped that future modular updates would advocate this less conservative but more scientifically valid approach.

BREAM assumes the use of standard spray nozzles, but there is improving availability and uptake of drift reducing technologies (DRT). The 2014 EFSA guidance suggested that DRT could be expected to give 50% reduction in exposure on vertical targets (humans), A CLE member company carried out 2 wind tunnel studies at an accredited facility in the UK (Butler-Ellis et al., 2021). which indicated that the nominal ratings assigned to drift reduction nozzles for their ability to reduce horizontal deposition reflects the reduction in human exposure which they give. A new version of the BREAM2 calculator (v2 including drift mitigation) which gives the option to select 50%, 75% or 90% DRT was published on the Silsoe Spray Applications Unit (SSAU) website and advocated to EFSA by CLE.

The Bystander and Resident Exposure Assessment Model (BREAM) model predicts potential dermal exposures which effectively reflects individuals who are wearing no clothes. The EFSA guidance addresses this unlikely scenario by making the default assumption that light clothing for bystanders and residents provides an 18% reduction in exposure. CLE (Felkers et al., 2023) collated data from 32 field studies where it was possible to calculate the actual degree of protection provided by light clothing (t-shirt and shorts). The 32 field studies which involved the use of mannequins to measure drift exposure were carried out either by individual CLE member companies to address specific regulatory challenges for active substances or PPPs or by CLE as a consortium (i.e., the BROV project). This exercise revealed that the mean protection factor was about 43% when considering all data from adult and child mannequins, for standard nozzles and DRT, low and high crops, with one exception in early growth stage vineyards where the factor was 27%.

Bystander and resident assessment according to EFSA considers 4 distinct pathways, one of which is exposure to volatilised pesticides. The guidance relies on very limited data and assigns a default air concentration to an active substance based purely on its vapour pressure, not even taking into account how much active substance is applied. Believing this approach to be fundamentally flawed and incredibly conservative, CLE embarked on a series of activities to confirm this and suggest ways in which a more realistic risk assessment could be carried out.

Felkers et al. 2022a discussed the database which informs the choice of default air concentration values by EFSA in more detail and suggested that normalising air concentrations with respect to application rate would account for the strength of the emission source. This showed that categorising active substances by vapour pressure alone creates random defaults as the normalised values for the studies which underpin the 2 air concentration defaults were similar and not a factor of 15 apart.

In a subsequent paper (Felkers et al, 2022b), concentrations of pesticides in air measured by CLE member companies to support product registration were reported and compared with the EFSA defaults. Of 961 individual measurements, 45 were quantifiable and only 10 exceeded 0.1 µg/m 3 with the highest being 0.427 µg/m 3 for a sample taken soon after application. This makes even the lowest EFSA default of 1 µg/m 3 look very conservative, especially as decline with time is not considered. A single normalised default air concentration value of 0.144 μg/m³/kg active substance applied/ha would allow more realistic inhalation exposure estimates across a wide range of vapour pressures.

The BROWSE (Bystanders, Residents, Operators and WorkerS Exposure) model (Butler-Ellis et al., 2017) includes a component which can predict post application vapour inhalation exposures. CLE undertook an exercise to validate this model using the measured values previously mentioned and this revealed that BROWSE is sufficiently conservative to provide a refined alternative to the current EFSA approach where no specific data are available (Butler-Ellis et al., 2023).

A literature search was carried out to identify papers and regulatory documents which reported concentrations of active substances at regional and/or national scale, including monitoring campaigns carried out by the French regulatory authority ANSES (2020) and the Belgian PROPULPPP Project (Ruthy et al., 2019). Almost all quantifiable air concentrations were well below the EFSA defaults.

However, the PROPULPPP study demonstrated the importance of only measuring volatilised material and not sprays or aerosols for a risk assessment which considers only the vapour phase. Risk assessments for a number of active substances approved in the EU were presented alongside those from the open literature, all showing acceptable risk against current health protective reference values.