Inhalation and dermal exposure to biocidal products during foam and spray applications

Abstract Objectives Foaming and spraying are common application techniques for biocidal products. In the past, inhalation and dermal exposure during spraying have been investigated extensively. Currently, however, no exposure data are available for foaming, hindering a reliable risk assessment for foam applications of biocidal products. The focus of this project was the quantification of inhalation and potential dermal exposure to non-volatile active substances during the foam application of biocidal products in occupational settings. In some settings, exposure during spray application was measured for comparative purposes. Methods The inhalation and dermal exposure of operators were investigated during the application of benzalkonium chlorides and pyrethroids by foaming and spraying, considering both small- and large-scale application devices. Inhalation exposure was measured by personal air sampling; potential dermal exposure was measured using coveralls and gloves. Results Potential dermal exposure was substantially higher than inhalation exposure. Changing from spraying to foaming reduced inhalation exposure to airborne non-volatile active substances, but had no relevant effect on potential dermal exposure. However, for potential dermal exposure, considerable differences were observed between the application device categories. Conclusions To our knowledge, this study presents the first comparative exposure data for the foam and spray application of biocidal products in occupational settings with detailed contextual information. The results indicate a reduction of inhalation exposure with foam application compared to spray application. However, special attention is necessary for dermal exposure, which is not reduced by this intervention.

The applied foam was rather liquid and the applied amount was perceived as unusually high by the hygiene specialist; the treated surface was at about the height of the stomach; the operator worked with the right hand (surface disinfection by foam application and wiping); during application, the distance between foam nozzle and hand was about 10 cm and the distance to the treated surface was about 30 cm; contact with biocidal product/treated surfaces: right hand, right forearm, right hip.
Application duration: 60 s; change of gloves, then wiping with cellulose cloth: 180 s, Total duration of sampling: 360 s #2 -A Foam Hand-pump foamer (handheld foaming device with a foam nozzle); nozzle: screen, 28.3 mm² orifice The applied foam was rather liquid; the treated surface was at about the height of the stomach; the operator worked with the right hand (surface disinfection by foam application and wiping); during application, the distance between foam nozzle and hand was about 5 cm and the distance to the treated surface was about 30 cm; contact with biocidal product/treated surfaces: right hand, right forearm, possibly stomach area.
Application duration: 33 s; change of gloves, then wiping with a cellulose cloth Total duration of sampling: 220 s #3 -A Spray Hand-compression sprayer (standard) (handheld spraying device, < 3 bar); nozzle: cone, 0.589 mm² orifice Application in a forward-leaning stance; the treated surface was at about the height of the stomach; the operator worked with the right hand (surface disinfection by spray application and wiping); during application, the distance between sprayer head and hand was about 10 cm and the distance to the treated surface was about 20 cm; contact with biocidal product/treated surfaces: right hand, right forearm/elbow, possibly stomach area.
Application duration: 60 s; change of gloves, then wiping with a cellulose cloth Total duration of sampling: 270 s #4 -A Spray Hand-pump sprayer (handheld spraying device); nozzle: cone, 0.02 mm² orifice Application in a forward-leaning stance; the treated surface was at about the height of the stomach; the operator worked with the right hand (surface disinfection by spray application and wiping); during application, the distance between sprayer head and hand was about 5 cm and the distance to the treated surface was about 15-20 cm; contact with biocidal product/treated surfaces: right hand, right forearm/elbow, possibly stomach area. The operator performed both spray application and wiping from right to left. Left-handed employee. During application, the distance between nozzle and hand was about 5 cm and the distance to the treated surface was about 30 cm. The employee applied foam to each table and wiped with cellulose cloths, whereby the employee pumped 20x to 80x depending on the size of the table (rather high usage). The applied foam was quite liquid; at one point, the employee rested the right hand on the surface of the table.
The handheld foaming device was mostly held and operated with the left hand; surface disinfection by wiping was performed with both the right and left hands (each hand was used to wipe about half of each table); the employee pumped 20x to 80x times per table (rather high usage); the applied foam was quite liquid.
Contact with the biocidal product may have occurred via aerosol, with the treated surface, with wet tissues with the right or left hand during wiping, or when resting the right hand on a table surface (1x) as well as when holding the foaming device with the free hand during application. During application, the forearm of the spraying arm was occasionally supported with the hand of the other arm.

Application duration: 19 min #10 -B Spray
Hand-pump sprayer (handheld spraying device); nozzle: cone, 0.02 mm² orifice Left-handed employee. During application, the distance between nozzle and hand was about 5 cm and the distance to the treated surface was about 30 cm. Application and wiping was performed with cellulose cloths for each table. Both the left and right hands were used for spraying; in each case, the other hand was used to support the spray bottle; surface disinfection by wiping was performed with both the left and right hands (seven tables with the left hand, five tables with the right), whereby a substantial amount of product was applied; the spray mist was clearly visible.
Contact with the biocidal product may have occurred via spray mist, with the treated surface, or with wet tissues with the right or left hand during wiping as well as when holding the spray bottle with the free hand during application. During application, the forearm of the spraying arm was occasionally supported with the hand of the other arm.

Work procedure for #11 and #12
In each case, the biocide was applied by one person. For the simulated treatment of wasp nests using a wasp-control foam, in each case two simulated wasp nests (inflated paper bags) were fixed at a height of 2.20 m in the corner of a model room. A foam can with a standard foam nozzle (fan-shaped product stream with a wide cone of distribution) and a nozzle for precise application were used. For each scenario, two cans of wasp-control foam were used. Foam was first applied to the outside of the nests, which were then filled with wasp-control foam using an application tube.

Work procedure for #13
The biocide was applied by one person. For the simulated treatment of wasp nests using a wasp-control spray, a simulated wasp nest (inflated paper bag) was fixed at a height of 2.20 m in the corner of a model room. A can with a standard spray nozzle (fan) was used. One can of wasp-control spray was applied. The outside of the nest was sprayed.

# Application type
Device Scenario description

#11 -C Foam
Pressure can During external foaming, the employee stood a distance of about 1-2 m from the nest; when filling the nest, the employee stood at a distance of about 0.5 m. The distance between nozzle and hand was about 10-15 cm. The casting distance indicated on the foam can (2-3 m) was not achieved, such that foam landed both on the wall and on the floor. Foam flakes settled on both the right and left gloves.
Application duration: 218 s #12 -C Foam Pressure can During external foaming, the employee stood at a distance of about 1-2 m from the nest; when filling the nest, the employee stood at a distance of about 0.5 m. The distance between nozzle and hand was about 15 cm. The first can was held in the left hand and the second can was held in the right. The employee worked in a closed room; direct observation of application was not possible due to a corrugated window pane. The following information was inquired after application: the employee worked at a distance of about 1 m from a given nest, whereby it was necessary during application to close the distance with the hand holding the foam can by about 5-10 cm. The distance between foam nozzle and hand was about 10-15 cm. The applied foam was very stable; small foam flakes formed when foaming the simulated wasp nests. A large foam flake landed on the left upper arm and a smaller one landed on the left forearm. Application was directed upwards, sometimes overhead.
Application duration: 20 min #28 -D Foam Pressure can, foam number (ratio of foam volume to liquid volume): 41 The employee shook the spray can prior to application and placed the tube in direct contact with the wall in order to generate a clean foam line. The distance between foam nozzle and hand was about 10-15 cm. In order to apply a foam barrier to the skirting board, the employee worked in a squatted position/on the knees and held the active arm close to the body. When treating the ceiling strips, the active arm was outstretched and the device held overhead. In addition to skirting boards and ceiling strips, foam barriers were applied around the window and door as well as around connector and light-switch covers, the ceiling-light plinth, and in the crevices around the coat rack.
The employee mostly held the foam can in the right hand and operated the foam nozzle with the left hand. In order to reach the ceiling strips, the employee used a stool which was moved as the work progressed. At times, the employee used the left hand to push the hood back a bit.
Application duration: 20 min Workplace sampling -Large-scale applications with low-and high-pressure devices (#5-#8; #14-#21; #24-#28) Several different scenarios were considered for large-scale spray and foam application. In the following section, application scenarios are grouped to enable, where applicable, a direct comparison between foaming and corresponding spraying scenario(s). Note: The belt, which was equipped with the pumps and sample collectors needed for aerosol measurements, covered small parts of the upper body.

Work procedure for #5 and #6
In each case, the biocide was applied by one person (foaming). A wall with an area of 22.5 m 2 was disinfected. The QAC-containing foam was applied with a foam nozzle, whereby the operator applied the foam at a distance of about 1.20 m. Wide, horizontal foam layers were applied starting from the bottom-right corner. During application, the foam slid downwards along the vertical wall.

Work procedure for #7 and #8
In each case, the biocide was applied by one person. Spray application was conducted in both upwards and downwards motions, starting at the bottom-right corner of the wall and finishing at the left end of the wall.

Work procedure for #14 and #17
In each case, the biocide was applied by one person. For the disinfection of a small pigsty (floor area of 124 m²) by foam (#14) or spray (#17) application, the floor and walls (including windows) were treated using a QAC-containing disinfectant. The ceiling and grids between partitions were partially treated.
The pigsty was disinfected starting from the back outer corner of Partition 3, with the operator working his way from back to front, towards the door. The treated surfaces were mainly at the height of the legs (floor and lower wall area), but some surfaces were also at the height of the stomach (fixtures and walls) as well as over the head (upper wall area and parts of the ceiling).
Application was not a continuous process; it was briefly interrupted multiple times when the operator moved between partitions. Ratio of foam-to-liquid volume: 3.5 Two applications were conducted consecutively (1x 7 min; 1x 5 min), whereby the application solution needed to be replenished by study staff between applications. Application was mostly performed in up-and-down motions. The applied foam was rather fluid. The foam lance was primarily held with the right hand, whereby the hand was located at the height of the stomach and breast area. The water hose was pulled/held with the left hand. Occasionally, the left hand was used for spraying or the foam lance was held with both hands. The distance between hand and nozzle was approx. 60 cm. The distance to treated surface was approx. 1-2 m. Study staff helped the operator move equipment. The reservoir was refilled outdoors.
Treated area: approx. 215 m² Contact with biocidal product/treated surface: hands when moving (opening/closing) box grids; the operator briefly stood in the foam spread on the floor; before starting measurement, the operator was already wearing the whole-body dosimeters when he carried a power cable outside to his car; the operator's hands touched the car and water hose in the context of refilling the reservoir with application solution.
Application duration: 12 min #17 -E Spray Self-built construction. Application solution was supplied from a reservoir via external pump.

Pressure (reservoir pump): 200 bar
Flat-fan nozzle (15/10) Application was mostly performed in up-and-down motions (with occasional horizontal movements) at a rate of approx. 20 L/min. The spray lance was held with both hands (with the left hand on the operating lever); the lance was at the height of the stomach and breast area. The distance between hand and nozzle was approx. 100 cm. The distance to the treated surface was approx. 2 m. Application was not a continuous process; it was briefly interrupted multiple times when the operator moved between partitions. There was not enough prepared application solution to treat the entire pigsty.
Treated area: approx. 215 m² Contact with biocidal product/treated surface: hands when moving (opening/closing) box grids. During application, the operator stood in the sprayed mist; at the start of measurement, the operator was already wearing the whole-body dosimeters when he activated the pump/mixing unit and put on his full-face respiratory protection.
Application duration: 7 min Note: The belt, which was equipped with the pumps and sample collectors needed for aerosol measurements, covered small parts of the upper body.

Work procedure for #15 and #16
In each case, the biocide was applied by one person. A henhouse (type: Louisiana) was disinfected using QAC-containing disinfectant. The floor, walls (up to the height of windows at approx. 3 m), doors, and overhead fixtures (automatic water dispenser and feeding lanes, six lanes in total) were treated. The treated surfaces were located at the height of the legs (floor and lower wall areas), at the height of the breast, and overhead (upper wall area, installations (#15 and #16), and stall ceilings (#16)).
The disinfectant was applied either with a pressure foam gun (#15) or a spray nozzle (#16). During application, one of the two doors remained open, resulting in a slight draft.
The operator's movements are given in the sketch below. During foam application (#15), the operator walked backwards; for movement in Directions 3 and 7, the disinfectant was applied against the draft. During spray application (#16; mainly overhead), the operator walked backwards; for movement in Direction 2, the disinfectant was applied against the draft. Ratio foam-to-liquid volume: 7 Application was performed in both vertical and horizontal motions (occasionally overhead) at a rate of approx. 25 L/min. The applied foam was rather liquid. The casting distance was approx. 4 m, which was not sufficient to treat the ceiling. The foam lance was mainly operated with the right hand and the water hose was pulled/held with the left hand. The distance between hand and nozzle was approx. 0.5 m. The distance to the treated surface was approx. 2-3 m. The walls were disinfected primarily in up-anddown motions; in contrast, the floor and installations were disinfected in horizontal motions from right to left.
Floor area of henhouse: approx. 1100m² Contact with biocidal product/treated surface: The hands came in contact with the foaming lance and water hose. In an initial approach, a pump pressure of 120 bar was applied, causing the hose to burst. The operator was therefore exposed to an aerosol cloud for a short time. After this incident, the cotton gloves (sampling media) were swapped for a clean pair.
Application duration: 12 min #16 -E Spray Self-built construction. Application solution was supplied via pump.

Pressure (reservoir pump): 120 bar
Flat-fan nozzle, type 30 (nozzle capacity: 120 L/min) Application was performed in both vertical and horizontal motions at a rate of approx. 50 L/min. The casting distance was approx. 8-10 m The spraying lance was mainly operated with the right hand and kept at head level. The sprayed mist was distributed throughout the entire henhouse. The distance between hand and nozzle was approx. 1.4 m. The distance to the treated surface was approx. 3-4 m.
Floor area of henhouse: approx. 1100m² Contact with biocidal product/treated surface: The hands came in contact with the spraying lance and water hose. Work procedure for #18-#20 All three scenarios took place in different locations of a public indoor swimming pool (#18 and #20 in the sauna; #19 in the tiled area next to the pool). In each case, the biocide was applied by one person.
#18: The walls, floors and interior of the sauna area were disinfected. The sauna cabins, sanitary facilities (toilets, showers, foot baths), and partition walls were foamed. Prior to disinfection, the surfaces were treated with an alkaline cleaning agent.
#19: Disinfection of a tiled area (415 m²) next to the pool.
#20: In the sauna area, floor areas and corridors were disinfected as well as foot baths and the floors of the sauna itself. Prior to disinfection, the surfaces were treated with an alkaline cleaning agent. Foam was rather liquid and applied in straightforward movements. Application was mostly performed in left-and-right vertical motions (floor and lower wall areas) and in up-and-down, leftand-right motions (upper wall areas and steam sauna), including overhead application (up to 2.7 m). Horizontal areas up to a height of 1.2 m were also treated. Given the complexity of the sauna area, the treated area is estimated to be approx. 140 m². The distance between hand and nozzle was approx. 25 cm. The distance to the treated surface was approx. 0.5-1.2 m. Application was performed at a rate of approx. 2.4 L/min. The diluted biocidal product (application solution) was in the reservoir of the battery-powered pressure sprayer and was applied by a spraying lance. The spraying lance was held with the right hand and the battery-powered pressure sprayer was pulled behind with the left, whereby the leading arm was mostly outstretched. The disinfectant was applied in straightforward movements, whereby the distance from the nozzle to the treated surface was about 20-50 cm; the distance between spraying nozzle and hand was about 60 cm. The pool borders were disinfected with horizontal motions from right to left; the five benches at the side and both shower areas were disinfected using the same pendulum movement. The treated surfaces were located at the height of the legs (floor and lower wall area), and some stood at pelvic height (seatbacks of benches).

Treated area: 415 m²
Contact with biocidal product/treated surface: The hands were in direct contact with the spray lance and battery-powered sprayer; water from the floor splashed back onto the lower legs. The foam lance was mainly held with the right hand and the water hose was pulled/held with the left, whereby the leading arm was outstretched. Foam was applied in straightforward movements and the floor was disinfected in horizontal movements. All treated areas were at leg level (floor and foot baths). The applied foam was rather liquid. The distance between hand and nozzle was approx. 25 cm. The distance to the treated surface was approx. 0.6-1.2m.
Treated area: approx. 167 m² Contact with biocidal product/treated surface: The hands were in direct contact with the foam lance and water hose. The operator also came into contact with lounge chairs in the relaxation area when moving them to disinfect the floor underneath. The operator removed the disinfectant solution from the floor using a telescopic squeegee (touching its handle). The operator attached the foam gun to the water hose and screwed the dispenser head onto the foam gun.

Work procedure for #21
The biocide was applied by one person. A pigsty as part of an animal farm was disinfected using QAC-containing disinfectant. The disinfectant was applied with a pressure foam gun. The pressure foam gun was used to dose the biocidal product and foaming agent to the water jet during foam application. The floor, walls, and interiors of partitions/boxes were treated.

Flat-fan nozzle
Ratio foam-to-liquid volume: 3 (probably too low as foam was directly injected into measuring cylinder) The foam lance was mainly operated with the right hand. The left hand was placed on top of the lance to stabilise it. The right arm was held fairly close to the body at the level of the stomach and chest during foaming. The foam was thick and stable. Foam application was conducted in straightforward movements. At the end of application, the operator applied the foam in a backwards motion down the centre aisle. The treated surfaces were mainly at the height of the legs (floor and lower wall area) and stomach (partition walls of the fattening boxes) as well as at the height of the chest and overhead (upper wall area). The foam was applied in up-and-down motions along the high walls but in horizontal, back-and-forth motions on the floor and low partition walls of the boxes. The distance between hand and nozzle was approx. 25 cm. The distance of the nozzle to the treated surface (floor and partitioning walls of boxes) was approx. 0.5-1 m or 2 m for the upper end of the stable walls.

Work procedure for #24-#26
In each case, the biocide was applied by one person. The application solution was applied in a room of about 22 m². All walls (height: 2.49 m) were treated partially twice or twice, omitting windows and doors. The treated surfaces were at the height of the legs and stomach (lower wall areas) as well as overhead (upper wall areas). During application, the operator faced the respective wall. Application was performed mostly in horizontal back-and-forth movements for #24 and #26 and in both horizontal back-and-forth movements and vertical up-and-down movements for #25. Before the first application, the operator loaded the foamer wearing the Tyvek ® coverall but no cotton gloves. The pressure foamer required multiple manual adjustments of device pressure both before and during application. The walls were partially treated twice. The applied foam was rather liquid and dripped down the walls. The foam lance was operated with the right hand, and the pressure foamer was carried with the left.
During surface treatment at the bottom end of the walls, the right arm was bent and held closer to the body; when applying overhead, the arm holding the foam lance was extended. The distance between nozzle and treated surface was approx. 5 cm. The distance between nozzle and hand was approx. 40-45cm. The distance between operator and treated surface was approx. 50 cm. Treated area: approx. 57 m² Contact with biocidal product/treated surface: Foamer pressure was mostly adjusted with the left hand. The nozzle was readjusted once, also using the left hand. During the work procedure, the reservoir had to be refilled; this step was performed by an assistant, not the operator himself. For this purpose, the door had to be opened for a brief moment. The operator, however, took the canister of application solution in both hands. While refilling the reservoir, the operator knelt on the floor and held the foam lance in his left hand. After the second refill, the operator screwed the foamer shut using his left hand, using his right hand to prop himself up on his right thigh. During foam application, the operator carried the foamer with his left hand, whereby the foamer came into repeated contact with his left leg.
Application duration: 20 min #25 -D Foam Pressure foamer P (1-3 bar), flat-fan nozzle (2.75 mm² orifice) in conjunction with a foam cartridge (highly foaming) Pressure (device): 2.4 bar, the required pressure for the foamer was kept at a constant level using an external compressor.
Ratio foam-to-liquid volume: 10.4 The foam was firmer than that of #24. The foam lance was operated with the right hand, and the pressure foamer was carried with the left. During surface treatment at the bottom end of the walls, the right arm was bent and held closer to the body; when applying overhead, the arm holding the foam lance was extended. Each wall was treated twice. The distance between nozzle and treated surface was approx. 30 cm. The distance between nozzle and hand was approx. 45 cm. The distance between operator and treated surface was approx. 100 cm. Treated area: approx. 67 m² Contact with biocidal product/treated surface: The operator took the pressure foamer in both hands and unscrewed the lid to refill the reservoir with application solution. During the second refill, the operator knelt on the floor with both knees. He also knelt down briefly to treat the floor strips. Foam application performed overhead produced tiny foam flakes which settled on the operator. During application, the operator adjusted his safety goggles twice and touched his head/hood several times with his left hand. The pressure sprayer required multiple manual adjustments of device pressure both before and during application. The spray lance was operated with the right hand, and the pressure sprayer was carried with the left. During application, the arm holding the spray lance was extended. Three of the four walls were treated twice. The distance between nozzle and treated surface was approx. 20-25 cm. The distance between nozzle and hand was approx. 40-45cm. The distance between operator and treated surface was approx. 80-100 cm.
Treated area: approx. 59 m² Contact with biocidal product/treated surface: Sprayer pressure was mostly adjusted with the left hand. The nozzle was readjusted once, also using the left hand. During application, the operator moved flowerpots on the windowsill.
Towards the end of application, the operator placed the sprayer on his left thigh, tilting it to apply the remaining amount of application solution.

Air monitoring
To determine inhalable aerosol exposure during spray or foam application, personal sampling was conducted using GSP sampling heads (samplers for inhalable aerosols, ANALYT-MTC Meßtechnik GmbH, Müllheim, Germany) at flow rates of either 3.5 mL/min or 10 mL/min. Two GSP samplers were positioned within the breathing zone of the operator. Depending on the analyte, active substance, or tracer selected for the determination of inhalable aerosol exposure, a suitable 37 mm filter was chosen for sample collection: MCE (mixed cellulose ester) filters for CsCl; PTFE (polytetrafluoroethylene)-coated filters for BAC, and glass-fibre filters for pyrethroids.

Monitoring of dermal exposure
Sampling procedures and analytical methods were developed in consideration of OECD guidance document No. 9 (OECD/D(97)148) (OECD 2017). Potential dermal exposure was quantified using whole-body dosimeters comprised of whole-body coveralls with hoods made of high-density polyethylene (DuPont ® Tyvek ® Classic Expert CHF5 protective coverall cat. III; type 5B and 6B) and cotton gloves. Study personnel assisted the workers in putting on the dermal samplers to avoid cross-contamination. Coveralls and gloves were worn throughout spray and foam applications and were removed at the end of each application. Following sampling, the dosimeters were either cut into 11 segments (coveralls) or left whole (gloves) (Supplemental Figure 2). Each sample was wrapped in aluminium foil and transported back to the lab at 4 °C, where they were stored at −20 °C until analysis. Dosimeter workup and extract analysis were performed within six weeks of the field study. Individual extracts had to be diluted or concentrated, then newly analysed within ten weeks. method should therefore also be suitable for the quantification of permethrin, as was confirmed by a plausibility check using measurement data; the ratio between permethrin and PBO in the filter extracts was equal to that of the application solution. During method validation, including permethrin was not yet known to be necessary.

Determination of non-volatile active substances and tracer in air and on dermal samplers
During a method-validation procedure conducted in the same laboratory (Elflein et al. 2003), theoretical quantitation limits of 1 ng permethrin/m³ and 0.3 ng PBO/m³ were calculated, and a practical limit of quantification (lowest calibration standard) of 10 ng/m³ was applied. In both instances, a sample volume of 10 m³ was assumed. In this study, the limit of quantification for PBO could be lowered by a factor of about 3, most likely due to technological advancement.
Analyte stability (namely: PBO, tetramethrin, and phenothrin) on filter material at 7-12 °C and at room temperature was investigated during method validation. Stability could be demonstrated for a time period of at least 8 days and 24 h, respectively. For permethrin, VDI Guideline 4301 confirms stability for approximately two weeks when filters are stored at room temperature and in the dark. Samples were analysed within this timeframe.

Theoretical limit of quantification:
(noise + 10x standard deviation of noise) PBO: 0.005 µg/m³ (for an air sample volume of 0.21 m³ and a liquid sample volume of 1 mL) Tetramethrin: 0.005 and 0.02 µg/m³ (Peak 2 and 1); (for an air sample volume of 0.21 m³ and a liquid sample volume of 1 mL) Phenothrin: 0.02 µg/m³ (for an air sample volume of 0.21 m³ and a liquid sample volume of 1 mL) Practical limit of quantification: (lowest calibration standard) 0.024 µg/m³ (for an air sample volume of 0.21 m³ and a liquid sample volume of 1 mL) *Duration of sampling: 60 min at 3.5 L/min (sampling with GSP) ** Calculation according to IFA; URL: http://www.dguv.de/ifa/praxishilfen/praxishilfen-gefahrstoffe/softwareberechnung-der-erweiterten-messunsicherheit-nach-ifa/index.jsp Benzalkonium chlorides (BAC) Sample analysis was based on the work of Van Boxtel et al (2016). Briefly, after sampling and spiking the filter with the internal standard (BAC-d7), the filters were transferred into headspace vials and the residual solvent was removed under a nitrogen stream. After thermal degradation of BAC, the resulting benzyl chloride was sampled from the headspace and quantified by GC-MS analysis. During validation, the storage stability for benzalkonium chloride on PTFE filters was investigated at 7-12 °C and at room temperature and was confirmed over a period of at least two weeks. Samples were analysed within the validated timeframe.

Dermal exposure
Pyrethroids Sampler material was extracted by shaking the coverall segments and gloves with acetone for five minutes each. The solvent volume was adjusted according to sample size. A 1-mL aliquot of the extract was used for further processing. After the addition of bifenthrin as an internal standard, the sample was evaporated to dryness under a stream of nitrogen and the residue was resuspended in 1 mL of toluene. The sample was subsequently filtered using a 1-µm syringe filter, and the pyrethroid levels were quantified by GC-MS. For the measurement range of 5-50 µg/L (Tyvek ® material) and 2.5-25 µg/L (cotton) (accuracy, n=3); 10-500 µg/L (precision, n=8) Quality-control material spiked at three levels, as well as reagent and dosimeter blanks, were included in all analytical runs. No analyte blanks were found in the reagents or dosimeter materials. The quality-control charts did not show any discrepancies over time.
Storage stability of the analytes was tested by spiking 900 cm² Tyvek ® material or one cotton glove with 0.25 µg or 2.5 µg of the pyrethroids, respectively (n=3). The sampler material was wrapped in aluminium foil, sealed in polyethylene bags, and stored for 60 days at −20 °C and 6 °C. No storage-related analyte losses were detectable. The mean recovery rates lied between 85.7% and 106%. Samples were analysed within the validated timeframes. Field recovery was not conducted in parallel to the field study.
Benzalkonium chlorides (BAC) Sampler material was extracted by shaking the coverall segments and gloves with acetone for five minutes each. The solvent volume was adjusted according to sample size. A 1-mL aliquot of the extract was pipetted into a headspace vial and used for further processing. After the addition of the deuterated internal standard, the solvent was removed under a stream of nitrogen, the vial was capped (high-temperature septa), and the residue was heated to 170 °C for thermal decomposition of the analytes. Benzyl chloride, the thermal decomposition product of BAC, was quantified using headspace-GC-MS. For the measurement range of 5-50 µg/L (Tyvek ® material) and 2.5-25 µg/L (cotton) (accuracy, n=3);10-500 µg/L (precision, n=8) Quality-control material spiked at three levels, as well as reagent and dosimeter blanks, were included in all analytical runs. No analyte blanks were found in the reagents or dosimeter materials. The quality-control charts did not show any discrepancies over time.
Storage stability of the analytes was tested by spiking 900 cm² Tyvek ® material or one cotton glove with 6 µg or 30 µg BAC, respectively (n=3). The sampler material was wrapped in aluminium foil, sealed in polyethylene bags, and stored for 60 days at −20°C and 6°C. No storage-related analyte losses were detectable. The mean recovery rates lied between 94.7% and 107%. Samples were analysed within the validated timeframes. Field recovery was not conducted in parallel to the field study.

Application solution
The concentration of active substance in the application solution and, where applicable, tracer concentration, were determined after an appropriate dilution step employing the same analytical methods as for the determination of inhalation and dermal exposure.

Supplementary material -Tables
Tab. S1 Active substance quantified on the coverall segments; absolute amounts of active substance [µg] (n = 26).  Table S5 Potential dermal exposure due to spraying and foaming of biocidal productscategorisation of results. The sample sizes n reflect different application scenarios but not necessarily individual operators.

Supplementary material -Figures
Figure S1 Schematic overview of exposure measurements. Figure S2 Schematic of sample segments for one sampling event generated from each sampling coverall and pair of gloves. Cutting guidance is indicated in red.

Figure S3
Spray applicationinhalation exposure concentration normalised to applied amount of active substance / tracer. *High-pressure applications. Reservoir pressure of >10 bar. Figure S4 Foam nozzles for scenario #25 (a -c) and #24 (d and e). In scenario #25, foam was applied using a flat-fan nozzle (a) with the biocidal product-air mixture passing through a foam cartridge equipped with a felt washer (b and c) before reaching the nozzle. In scenario #24, a screen-based nozzle (d: outlet; e: sideways) was used. Figure S5 Schematic of propellant gas-based foam applicationa) breaking-up of the foam jet observed for the standard nozzle; b) precise and exposure-reduced application with a designated foam nozzle; c) scenarios investigated in this study (as proposed by manufacturer); d) two-step treatment of a wasp nest as recommended by a pest-control professional. Figure S6: Dermal exposure on the coveralls and gloves (application only) for foam and spray applications, respectively. The box-plot visualisation reflects the exposure normalised to the applied amount of active substance [mg/kg], the sample size n different application scenarios but not necessarily individual operators.
The Annals of Work Exposure and Health Figure S7 Dermal exposure on the coveralls and gloves (application only) categorised in three application-device groups. The box-plot visualisation reflects absolute exposure [µg], the sample size n different application scenarios in the respective category, but not necessarily individual operators. Figure S8 Dermal exposure on the coveralls and gloves (application only) categorised in three application-device groups. The box-plot visualisation reflects the absolute exposure normalised to the amount of active substance applied [mg/kg], the sample size n different application scenarios in the respective category, but not necessarily individual operators. Figure S9 Log-log graph of the operators' dermal and inhalation exposure for foaming and spraying. For dermal exposure, "whole-body exposure by aerosol deposition" based on the five least-exposed coverall segments was used. The Pearson correlation was calculated using a two-tailed test (IBM SPSS Statistics; Pearson correlation coefficient r=0.830; p<0.01).
Figure S10 Inhalation exposure-reduction factor between purpose-driven spraying and foaming activities. Note: the exposure data for #14 and #15 were below the limit of quantification (LOQ). In those cases, the LOQ was used to calculate RF. *High-pressure applications. Reservoir pressure of >10 bar.