Introduction

The emergence of synthetic pyrethroids in place of their natural forerunners, pyrethrins, took place over 70 years ago due to the poor environmental stability of the latter (Bradberry et al. 2005). Since then, the use of pyrethroids has increased in many areas of industry, agriculture, veterinary medicine, and forestry, mainly in pest control (Kaneko 2011). The mechanism of action relies on modulating the action of sodium channels by preventing their closure, which results in prolonged depolarization of nerve cells (Chrustek et al. 2018). The described mechanism is more than 2000 times more effective in insect nervous systems than in mammals due to the higher affinity and thus sensitivity of insect sodium channels to pyrethroids (Bradberry et al. 2005). Although pyrethroids are thus assumed to pose minimal threats to human health, several studies have indicated that these compounds may become of greater concern in future because of their potential detrimental effects on mammals and humans (Elbetieha et al. 2001; Moniz et al. 2005). Given the widespread use of pyrethroids, it is of utmost importance that wide-scale exposure assessment studies are carried out consistently and with the use of reliable, validated sampling methods. Chemicals characterized by a short half-life, such as pyrethroids, are usually measured (their metabolites) in urine, so the spot sample concentration represents a very brief period of time, within hours of exposure (Wielgomas 2013; Koch et al. 2014). Although single measurements of biomarkers in biologic matrices (especially urine) represent a “snapshot” of exposure, the determination of pyrethroid metabolites in urine is still the most commonly used method in human exposure assessment studies. A means of personal passive sampling that allows for capturing a large cohort of diverse chemicals (including those metabolized rapidly) (Doherty et al. 2020; Wise et al. 2020) over a prolonged sampling period, therefore achieving a time-weighted average of exposure values to said chemicals (Manzano et al. 2019), are silicone wristbands (WBs). This non-invasive sample collection method (Bergmann et al. 2017; Dixon et al. 2019; Travis et al. 2020) has been an object of interest for many research groups since its introduction by O’Connell in 2014 (O’Connell et al. 2014). Silicone wristbands can provide information regarding both inhalatory and dermal routes of exposure (Bergmann et al. 2017; Reddam et al. 2020), and because they are easily accessible, inexpensive (Bergmann et al. 2017), unobtrusive, and simple to use, they might serve as tools of great utility in large-scale exposure assessment studies (Manzano et al. 2019; Baum et al. 2020), especially among sensitive populations (elderly individuals, children, pregnant women) (Doherty et al. 2020; Travis et al. 2020).

The aim of this paper is to summarize the results of a pilot study concerning exposure assessment to synthetic pyrethroids with the use of WBs as personal passive samplers compared to the levels of urinary pyrethroid metabolites quantified in simultaneously collected urine samples.

The native substances quantified in WBs included cyhalothrin, cyfluthrin, permethrin, cypermethrin, deltamethrin and flumethrin, which the authors considered to be of greatest importance given their versatile applications and, consequently, widespread use. Selected substances are among the most frequently found products with insecticidal properties and are commercially available every day, which leads to an ever-pressing need to carry out a widespread exposure assessment to those compounds among the general population. Analytes of particular interest have been chosen in consideration of upcoming research projects to be conducted in our laboratory. Determining the parent pyrethroid compounds in WBs could provide valuable additional information for exposure assessment and could serve as a significant supplement to biomonitoring. Furthermore, investigations of patterns of substances quantified in urine and WBs sampled simultaneously from the same person may yield new conclusions regarding routes and sources of exposure to synthetic pyrethroids. To our knowledge, this is the first study in Europe to assess exposure to synthetic pyrethroids simultaneously using WBs and urine sample analysis.

The study described in detail in this paper was preceded by the optimization and validation of a method for the measurement of six pyrethroids: cyhalothrin, cyfluthrin, permethrin, cypermethrin, deltamethrin, and flumethrin in WBs; detailed experimental descriptions and corresponding results can be found in the Supplementary Information (SI).

Materials and Methods

All WBs employed in this study were purchased in bulk from an online vendor (www.allegro.pl) and sold as an accessory used for marketing purposes or event tags (items not predefined for research purposes). For method development, white WBs were used (average weight before pre-exposure cleanup: 5.05 g; average weight after pre-exposure cleanup: 4.86 g). Width: 12 mm, length: 20.13 cm (SD = 0.095; CV = 0.47%). The average thickness was 1.48 mm (SD = 0.19; CV = 13.05%).

The following solvents were used in this study: ethyl acetate (EtAc) (for gas chromatography MS, Supelco, Saint Louis, USA), n-hexane (Hex) (n-hexane 95% for GC, for pesticide residue analysis, POCH, Gliwice, Poland), diethyl ether (ACS grade, Sigma-Aldrich, Saint Louis, USA), methanol (MeOH) (technical grade, POCH, Gliwice, Poland), n-hexane (fraction from petroleum pure, POCH, Gliwice, Poland), 2-propanol (IPA) (for HPLC, 99.9%, Sigma-Aldrich, Saint Louis, USA), and ethyl acetate (technical grade, POCH, Gliwice, Poland). Deionized water (DI H2O) was obtained from a laboratory water demineralizer (Hydrolab, Wiślina, Poland).

The following sorbents were used in the described experiments: Z-Sep Supel™QuE, Z-Sep + Supel™QuE (Sigma-Aldrich, Saint Louis, USA), graphitized carbon black (GCB)—SampliQ Carbon SPE Bulk Sorbent (Agilent Technologies, Santa Clara, USA), primary secondary amine (PSA) (Scharlab, Barcelona, Spain), Florisil (Fluka, Buchs, Switzerland), and silica gel (pore size 60 Å, 220–240 mesh particle size (Sigma-Aldrich, Saint Louis, USA)).

Other reagents used in this study included 1,1,1,3,3,3-hexafluoro-2-propanol (Sigma-Aldrich, USA), DIC (N,N′-diisopropylcarbodiimide) (99%, Sigma-Aldrich, Saint Louis, USA), potassium carbonate-anhydrous pure p.a. (POCH, Gliwice, Poland), sodium hydroxide pure p.a. (POCH, Gliwice, Poland), and hydrochloric acid (J.T. Baker, Radnor, USA).

Pilot Study

Study Design and Study Population

The study design assumed the duration of sampling to be 7 consecutive days, during which study participants were asked to wear a precleaned WBs on the wrist of their dominant hand (except for bath/shower time—the wristband was to be temporarily removed and placed on a clean surface). During this period, study participants were also asked to collect a total of 3 spot urine samples, with each sample collected on a separate day within the 7-day sampling period. The primary objective of the experiment was to assess exposure to synthetic pyrethroids by quantifying the levels of native pyrethroids in WBs collected from study participants. These measurements were subsequently compared with the concentrations of the metabolites quantified in the urine samples. Furthermore, a survey mentioned earlier was conducted to preliminarily identify potential sources of exposure to the tested substances, as the questions it contained involved both sociodemographic issues and potential exposure to synthetic pyrethroids.

Participants were informed of the experiment by word of mouth by the researchers and volunteered to participate. The study obtained the approval of the Independent Bioethics Committee for Scientific Research of the Medical University of Gdańsk (NKBBN/536/2020, December 04, 2020). Written informed consent was obtained from all individual participants included in the study. Sample collection took place in December 2020.

The tested population of volunteers included a total of 24 people of both genders (12 males, 12 females) and various ages (AM: 33.3 years, range 14–65 years). The study questionnaires completed by the participants included questions regarding basic sociodemographic information, as well as information regarding possible sources of exposure to synthetic pyrethroids. The information collected via these questionnaires is shown in Table 1.

Table 1 Descriptive statistics of demographic and exposure related information regarding the studied population
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Sample Collection, Transportation, and Storage

Silicone wristbands were precleaned in the laboratory using a developed protocol before they were provided to the study participants and further packaged in airtight plastic zip-lock bags. Study participants were asked to place them in the same packaging after having worn them during the sampling period. Study participants were also equipped with screw-top cups for collecting urine samples. All urine samples collected by the study participants, as well as WBs, were placed in a freezer immediately after collection at a temperature of approximately – 18 °C. Fully collected sets of samples were acquired from the participants by the researchers and transported to the laboratory to be further stored at − 20 °C until analysis.

Quantification of Pyrethroids

Determination of Pyrethroid Metabolites in Urine

The methods used to determine the pyrethroid metabolites 3-phenoxybenzoic acid (3-PBA), 4-fluoro-3-phenoxybenzoic acid (4F-3PBA), cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid (DBCA), and cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (cis- and trans-DCCA, respectively) in urine applied in this study are described in detail elsewhere (Rodzaj et al. 2021) with slight modifications. Briefly, sample preparation involved thawing the urine samples and transferring 3 mL of each sample into screw-top glass test tube (16 × 100 mm). The urine samples were spiked with 20 µL of a mixture of internal standards (cis-DCCA (1, carboxyl-13C2), 2-PBA (2-phenoxybenzoic acid), 1 µg/mL in acetonitrile) and then concentrated hydrochloric acid (600 µL/sample) was added to the mixture, followed by hydrolysis for 90 min in a laboratory oven at 95 °C. After reaching room temperature, 4 mL of hexane were added to each of the samples, which were then shaken on a multitube vortex (10 min, 2500 rpm) and centrifuged (2 min, 5500 rpm).Resulting organic layer was transferred to a separate test tube. The extraction was repeated, and the resulting extract (approximately 8 mL per sample) was again shaken with 0.5 mL of 0.1-M NaOH aqueous solution. After centrifugation, the top organic layer was discarded, and 0.1 mL of hydrochloric acid and 2 mL of hexane were added to each test tube and subsequently shaken and centrifuged. Further separation of the organic layer led to its collection and transfer to another screw-top glass test tube for subsequent evaporation to dryness at 40 °C, aided by a stream of nitrogen. The dry residue that remained in the test tube was derivatized with 10 µL of 1,1,1,3,3,3-hexafluoroispropanol (HFIP), 15 μL of diisopropylcarbodiimide (DIC), and 250 µL of hexane (10 min, 2200 rpm, multitube vortex). Finally, to neutralize the excess derivatizing agents used (HFIP, DIC), 1 mL of 5% potassium carbonate solution was added, followed by further shaking and centrifugation. The last step of the procedure was separation of the final extract from the bottom layer. A total of 170 μL of the extract was carefully collected and transferred to a glass chromatographic vial for subsequent instrumental analysis.

Instrumental analyses of the prepared sample extracts were carried out with a gas chromatograph (Varian GC-450) coupled with an ion trap mass spectrometer (Varian 225-MS). A detailed description of the method and more information regarding the hardware used can be found in the Supplementary Information (SI).

Concentrations of metabolites of synthetic pyrethroids in urine were subjected to urine specific gravity (SG) adjustment to prevent urine dilution from influencing the obtained results. The calculations were performed following the same procedure as that described by Rodzaj et al. 2021 (Rodzaj et al. 2021). The urinary SG of every sample was measured with the use of a hand-held pocket-size PAL-10S refractometer (Atago Co., Tokyo, Japan). The arithmetic mean SG of the studied population was considered the reference SG in the calculations.

Determination of Native Pyrethroids in Silicone Wristbands

The collected WBs were cut into small pieces (approx. 10 mm × 2 mm × 2 mm) with the use of a surgical scalpel (No. 4) with disposable blades. A separate clean blade was used for each wristband. In this study, WBs were stored in plastic Eppendorf test tubes prior to analysis. For each analysis, 0.5 g of previously mixed WB pieces (which were considered a single sample throughout this study) was weighed into glass screw-top test tubes and subjected to postexposure cleanup, consisting of a single 30-s vortex-aided wash with deionized water and a subsequent 30-s vortex wash with IPA, after which the samples were left for 12 h to dry. Next, 5 mL of ethyl acetate were added, and the samples were extracted twice by sonication (15 min). After each extraction cycle, the solvent was collected into the next glass test tube. Next, 10 mL of the obtained (primary) extract were evaporated to dryness at 40 °C under a stream of nitrogen. The dry residue was mixed with 1 mL of hexane and subjected to silica gel cleanup (0.5 g of 3% water-deactivated silica gel and 3–4 mm of sodium sulfate on top). Substances of interest were eluted with 4 mL of 30% diethyl ether solution in hexane. The solvents were subsequently evaporated to dryness, and the dry residue was reconstituted in 1 mL of hexane. The final hexane extract was collected into a glass autosampler vial and subjected to instrumental analysis via gas chromatography (SCION Instruments, 456-GC) with an electron capture detector (GC-ECD). The selection of GC-ECD as the technique of choice for this study was validated by its sensitivity, which, in the case of the use of WBs, has been argued to be essential for analyte detection, as preliminary studies are in most cases burdened by a lack of initial knowledge regarding expected concentrations to be determined in field samples. Another advantage of using GC-ECD in this study is its high selectivity for analytes of interest. A detailed description of the method and more information regarding the hardware used can be found in the SI.

Internal and External Quality Control

Quality control samples at two concentrations (low concentration (LQC) = 0.25 ng/mL; high concentration (HQC) = 1.5 ng/mL) were prepared with the use of pooled physiological urine in 20 repetitions over a period of 3 weeks. The results obtained via GC‒MS analysis served to construct control plots for each of the tested metabolites. Furthermore, each batch of analyzed study samples was spiked with two control samples prepared at both aforementioned concentrations (LQC and HQC). For 3-PBA, DBCA, cis-DCCA, and trans-DCCA, the established (using signal/noise ratio of 3) limit of detection (LOD) was 0.05 ng/mL, with a value of 0.1 ng/mL for 4F-3PBA. The coefficient of variation of the results obtained for the control samples ranged between 3.43 and 17.85% for the LQC samples and between 1.17 and 10.79% for the HQC samples, corresponding to the interday variability of the assay. The Department of Toxicology of the Medical University of Gdańsk also successfully participated in the annual German External Quality Assessment Scheme for Analyses in Biological Materials (G-EQUAS). Calibration curves were also prepared with the use of pooled urine in accordance with the Bioanalytical Method Validation Guidelines (U.S. Department of Health and Human Services, Food and Drug Administration, Center for Drug Evaluation and Research (CDER), Center for Biologics Evaluation and Research (CBER) 2005).

Statistical Analysis

The normality of the distribution of the analytical results was assessed with the use of the Shapiro‒Wilk test. Urinary metabolite concentrations, as well as WBs concentrations of pyrethroids, were log-normally distributed; thus, a nonparametric Mann‒Whitney U test was applied to compare values between groups. Descriptive statistics, as well as the results of the aforementioned nonparametric analyses, are summarized in Tables 1, 2, and 3.

Table 2 Descriptive statistics and predictors of urinary SG-adjusted concentrations (ng/mL) of pyrethroid metabolites with detection rate > 50%
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Table 3 Descriptive statistics and predictors of concentrations of parent pyrethroids quantified in silicone wristbands (ng/g)
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Method Development and Validation

A series of experiments were carried out to develop and optimize the method for the determination of the parent synthetic pyrethroids in WBs using gas chromatography with an electron capture detector (GC-ECD). The following aspects of sample preparation were evaluated: pre-deployment cleanup of WBs, post-deployment rinsing, extraction time, extraction method, and extraction cleanup procedure. The results of these experiments are described in detail in the Supplementary Information (SI).

Method validation was carried out in accordance with method validation guidelines (U.S. Department of Health and Human Services, Food and Drug Administration, Center for Drug Evaluation and Research (CDER) 2005). Method selectivity was assessed by comparing signal levels between a blank and a pyrethroid-fortified (32 ng/g) WBs sample. The presence of interfering components has been rare, and in cases of their positive detection, their signals did not surpass 20% of the lower limit of quantification of analytes of interest. No carry-over effect was observed. A six-point matrix-matched calibration curve was prepared, covering a concentration range of 10–400 ng/g, with each concentration level analyzed in triplicate. The accuracy and precision were investigated by analyzing a series of samples at 3 concentration levels (32, 160, and 340 ng/g). More detailed information regarding the process of method validation, as well as the results obtained during this process, can be found in the Supplementary Information (SI).

Results

An analytical method was developed for the determination of 6 native pyrethroids in WBs using ultrasound-assisted extraction, silica gel cleanup of the extract and instrumental analysis by gas chromatography with an electron capture detector. The key conditions of the preparation of the WBs before their use and the preparation for instrumental analysis were established. The use of GC-ECD significantly facilitates the availability of the method in other laboratories, but we realize that GC‒MS or GC‒MS/MS may have better specificity. In our case, the initial GC‒MS analysis of the WBs extracts showed that sufficient sensitivity was not achievable, while the purity of the WBs extracts was high enough for us to finally decide to use GC-ECD instead.

In the course of the study, 24 participants whose samples were collected from 24 WBs and 72 urine samples were further analyzed for native pyrethroids and their metabolites, respectively.

The population involved in the described pilot study consisted of a total of 24 participants who were equally distributed between sexes (50% female, 50% male). The average age of the participants was 36, with 3 participants (12.5%) being under the age of 20 at the time of study sample collection, 13 (54.3%) persons declaring the age between 20 and 30 and 8 (33.3%) people being over the age of 30. Most of the study volunteers were nonsmokers (n = 19, 79.2%). Those with the highest education level were divided into primary school (n = 2, 8.3%), vocational school (n = 2, 8.3%), technical school (n = 4, 16.67%), high school (n = 10, 41.7%), and higher education (n = 6, 25%) groups. Most (n = 19, 79.2%) of the study participants lived in an urban setting, with only 5 (20.8%) participants declaring their housing location to be rural. Accordingly, 16 (66.6%) people reported living in multifamily housing, with 8 participants (33.3%) assessing their housing conditions as living in a detached house. When asked about their knowledge of past pest control within the last 5 years, most (n = 12, 50%) participants declared that there had been none, while 5 people (20.8%) reported that controls had taken place in their building, with 7 people (29.2%) having no knowledge of said occurrences. Furthermore, almost half of the study participants (n = 11, 45.8%) reported the indoor use of commercially available pesticides, 12 people (50%) reported that no pesticides were used by them in-house and only 1 person (4.2%) reported having no knowledge of pesticides. Among the tested population, more than half of the study participants declared themselves to be pet owners (n = 13, 54.2%), with 11 persons (45.8%) having no indoor-dwelling animals. Eleven people (45.8%) reported using anti-ectoparasitic drugs on pets.

Table 4 summarizes the statistics of the SG-adjusted concentrations of pyrethroid urinary biomarkers, as well as the concentrations of native permethrin quantified in WBs. The urinary biomarker detection range varied from 12.5% to 68.06% for 4F-3PBA and 3-PBA, respectively.

Table 4 Distribution of concentrations of urinary biomarkers of synthetic pyrethroids and parent pyrethroids determined in silicone wristbands
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Pyrethroid metabolites were detected with various frequencies from 12.5% (4F-3PBA) to 68% (3-PBA). The detection rate of the analyzed native pyrethroids in the tested WBs varied from 0 (flumethrin, cyfluthrin) to 58.3% for permethrin. Therefore, further statistical analyses have been conducted only on permethrin concentrations quantified in WBs, as it is the only analyte of interest to have exceeded the detection rate of 50%.

According to the data analysis, a 5-year history of pest control in an occupied building led to higher urinary 3-PBA (p = 0.0001), DBCA (p = 0.0267), cis-DCCA (p < 0.0001), trans-DCCA (p < 0.0001), and WBs permethrin (p < 0.0001) concentrations. Similarly, the urinary concentrations of 3-PBA (p = 0.0002), cis-DCCA (p < 0.0001), trans-DCCA (p < 0.0001), and native wristband-quantified permethrin (p < 0.0001) were greater when commercial insecticides were used in house. The geometric means of urinary 3-PBA, cis-DCCA, trans-DCCA, and wristband-quantified permethrin were greater in the study participants who were confirmed to use indoor insecticide-containing products. Over half of the volunteers declared themselves pet owners, with only a slightly lower percentage of the tested population reporting using anti-ectoparasitic veterinary products on their pets. Among pet owners, the concentrations of 3-PBA (p = 0.0009), cis-DCCA (p = 0.0002), trans-DCCA (p = 0.0004), and permethrin (p = 0.0016) (Fig. 1a) were noticeably greater. Furthermore, the presence of detectable levels (> LOD) of permethrin in the WBs was a significant (p < 0.01) predictor of higher trans-DCCA concentrations (Fig. 1b).

Fig. 1
figure 1

Concentrations of wristband permethrin [ng/g] between pet owners and participants not owning pets (A). A statistically significant difference in permethrin concentrations has been noted (p < 0.01 (**)). Urinary concentrations of specific permethrin metabolite trans-DCCA [ng/mL] between samples with negative and positive detection of wristband permethrin (B)

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Similarly, greater concentrations of 3-PBA (p = 0.0004), cis-DCCA (p < 0.0001), trans-DCCA (p < 0.0001), and permethrin (p < 0.0001) were detected in the abovementioned veterinary antectoparasitic products on pets. Both in the case of pet owners and among participants using veterinary drugs on pets, the geometric means of the concentrations of the quantified substances were noticeably greater than those of the other subpopulations. Furthermore, a statistically significant association was observed between smoking and urinary concentrations of cis-DCCA (p = 0.0059) and trans-DCCA (p = 0.0073); however, due to considerable differences in sample size between smokers and nonsmokers participating in this study, this association should not be used to draw any far-reaching conclusions.

Factors such as having performed pest control in currently occupied buildings within the last 5 years, declining in-house usage of commercially available insecticides, pet ownership, and the use of anti-ectoparasitic drugs have been identified as possible predictors of exposure to pyrethroids in this particular population.

Furthermore, a Spearman correlation test was carried out between urinary concentrations of pyrethroid metabolites with detection rates exceeding 50% (3-PBA, trans-DCCA) and concentrations of native permethrin in WBs. The correlation coefficient reached 0.7041 for the pair WBs permethrin and urinary trans-DCCA. Figure 2 depicts the scattering of permethrin concentrations quantified in WBs in relation to the SG-adjusted concentrations of urinary trans-DCCA concentrations.

Fig. 2
figure 2

Relationship between wristband permethrin concentration [ng/g] and SG-adjusted concentrations of urinary trans-DCCA [ng/mL]. All available individual spot urine samples with quantifiable concentrations are shown

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Discussion and Conclusions

This project has resulted in the successful development and optimization of an analytical method for the determination of 6 synthetic pyrethroids in WBs via gas chromatography and electron capture detection (GC-ECD). The wrought procedure involved postexposure cleanup of worn WBs with sequential washes with IPA and H2O, sonication-assisted extraction of analytes of interest with ethyl acetate, purification of the primary extract with solid-phase extraction with silica gel, and finally instrumental analyses of the WBs extracts with GC-ECD. The limits of detection achieved for the respective analyzed substances are satisfactory and make the procedure useful in exposure assessment studies.

The optimized analytical method is suitable for routine use, does not require any advanced laboratory equipment in the process of sample preparation, and is relatively easy to employ in any laboratory setting.

The urinary concentrations and detection rates of pyrethroid metabolites are in accordance with other studies conducted within the last 10 years in Poland (Table 5). The detection rates of 3-PBA were consistently the highest among all pyrethroid metabolites (with the exception of Klimowska 2020 (Klimowska et al. 2020), where trans- and cis-DCCA had achieved higher detection rates since the method LODs were two times lower than those in the remaining studies) all reviewed studies (Wielgomas et al. 2013; Wielgomas 2013; Jurewicz et al. 2015, 2020; Klimowska et al. 2020; Rodzaj et al. 2021; Radwan et al. 2022) and ranged from 66.5% (Jurewicz et al. 2020) to 82.4% (Wielgomas and Piskunowicz 2013). The population geometric means of the urinary concentrations of these metabolites have over the years been determined to range from 0.17 ng/mL (Jurewicz et al. 2015) to 0.32 ng/mL (Jurewicz et al. 2020). The detection rates of trans-DCCA have been calculated to range from 34.9% (Jurewicz et al. 2020) to 93.9% (Klimowska et al. 2020), with our results reaching 52.78%. The geometric means of the concentrations of these substances varied from 0.16 ng/mL (Jurewicz et al. 2015) to 0.44 ng/mL (Jurewicz et al. 2020).

Table 5 Comparison of several population studies involving assessment of urinary metabolites of synthetic pyrethroids carried out in Poland within the last 10 years
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Urinary pyrethroid metabolites have also recently attracted the interest of several exposure assessment studies carried out in other locations on varying populations: the Czech Republic, a study conducted on parent–child pairs (Šulc et al. 2022); Spain, where occupationally and environmentally exposed adults were tested (Bravo et al. 2022); and New Zealand, a study regarding pyrethroid exposure in children between 5 and 14 years of age (Li et al. 2022; Ueyama et al. 2022). The 3-PBA detection rates and concentrations were in some cases comparable to ours (51.8%, median 0.16 ng/mL—(Šulc et al. 2022), with several research papers reporting much higher detection rates of 91% (Bravo et al. 2022), 99.3% (Li et al. 2022), and 98% (Ueyama et al. 2022). The high detection rates of metabolites in urine indicate widespread exposure in all studied populations.

Other studies focused on the determination of native synthetic pyrethroids in WBs have similarly reported that the frequency of detection was the highest for permethrin (Arcury et al. 2021)—49.7%, (Wise et al. 2020)—100%, and (Doherty et al. 2020)—67%. The permethrin detection rates reported in the abovementioned studies partially confirmed the effectiveness of our method, as we were able to achieve a detection rate of 58.3% in the general population. In a study conducted by Harley et al. (Harley et al. 2019), cypermethrin was detected more often than any other pyrethroid compound, and the study described by Donald et al. (Donald et al. 2016) reported the highest detection rate of deltamethrin. The concentrations of permethrin shown in other studies (Doherty et al. 2020; Wise et al. 2020) are noticeably greater than the concentrations calculated in our study; however, this difference can be explained not only by the distinctive diversity of the studied populations and specific communities (rural areas, farmworkers, dog owners) but also by the study locations. To our knowledge, our study is the first in Europe to involve the use of WBs in the determination of synthetic pyrethroids among the general population (the present pilot study).

The data analysis carried out as part of this pilot study highlighted that pet ownership appears to be a significant predictor of exposure to synthetic pyrethroids. In fact, the use of these substances indoors in various settings (on pets or as part of pest control) and at various times prior to sample collection heavily contributed to noticeably higher concentrations of both urinary pyrethroid metabolites and native permethrin quantified with the use of WBs, thus further confirming their lengthy half-lives within closed indoor spaces, such as inside a home. The pilot study demonstrated the utility of WBs as personal passive samplers for exposure assessment to synthetic pyrethroids. It is worth noting that analyses of metabolite concentrations in urine and native pyrethroids in WBs, independently identified the same exposure predictors (pest control history in building (within the past 5 years); in-house employment of commercially available insecticides; pet ownership; and anti-ectoparasitic drug employment on pet). This fact allows us to speculate that the analysis of synthetic pyrethroids in WBs may add value to health risk assessment, complementing biomonitoring with personalized, and non-invasive environmental monitoring. The correlation coefficients calculated to characterize the relationship between urinary concentrations of pyrethroid metabolites and the WBs permethrin showed a weak (3-PBA) to moderate (cis-DCCA, trans-DCCA) association. The results obtained for the WBs and urine extracts show that the use of WBs in the assessment of exposure to synthetic pyrethroids can very well serve as a complementary tool, providing a new array of interesting information regarding exposure to native compounds.

The observed correlations between the concentration of permethrin in WBs and the concentration of metabolites in urine may suggest that nondietary sources of exposure could be significant, contrary to numerous reports in the literature that point to dietary sources as the primary sources in the general population (Heudorf et al. 2006; Riederer et al. 2008, 2010; Morgan et al. 2016, 2018). Our study indicates that especially in the case of high concentrations of metabolites in urine, a significant contribution to total exposure may come from nondietary routes. Several studies have also revealed that permethrin is one of the most commonly identified pesticides present in household dust (Glorennec et al. 2017; Hung et al. 2018; Navarro et al. 2023), which is an additional argument for the significance of nondietary sources in total exposure. While dietary exposure is still a concern, it tends to be lower in comparison to nondietary sources for most individuals. It is worth noting that the relative importance of dietary versus nondietary exposure can vary by region and individual circumstances. Pesticide residues in food and water sources, although of significant concern, are governed by stringent regulatory frameworks and are continuously subjected to vigilant surveillance to mitigate potential human exposure risks. In contrast, the application of pesticides within indoor environments remains largely unregulated and lacks systematic monitoring procedures.

This study has some limitations. The work is preliminary, so these observations require confirmation in a larger population or in conditions where elevated exposure from nondietary sources can be expected, such as the use of biocidal products in residential areas or antiparasitic medications for pets. Some methodological aspects require further investigation, namely the stability of pyrethroids in the silicone matrix during deployment and storage and impact of factors such as contact with water (during bathing) or exposure to sunlight.

While biomonitoring provides reliable information about the internal dose, regardless of the source or route of exposure, it does not allow for the identification of the source and the route of exposure. We hypothesize, based on these preliminary observations, that WBs may provide qualitative and possibly semi-quantitative data mainly regarding nondietary sources of exposure. Involvement of WBs in this pilot study has shown their utility for employment as personal passive samplers for determination of exposure to synthetic pyrethroids, as their analysis can provide unique information regarding the exposure that took place to native compounds, which cannot be determined in urinalysis, while simultaneously showing correlation to results obtained via employment of the ‘golden standard’—quantification of urinary metabolites of synthetic pyrethroids. This opens up the possibility of future use of WBs in exposure assessment studies as a supplement to biomonitoring without relying solely on urinalysis.