A protocol about the characterization and application of five different passive sampling devices is presented.
Five different water passive samplers were calibrated under laboratory conditions for measurement of 124 legacy and current used pesticides. This study provides a protocol for the passive sampler preparation, calibration, extraction method and instrumental analysis. Sampling rates (RS) and passive sampler-water partition coefficients (KPW) were calculated for silicone rubber, polar organic chemical integrative sampler POCIS-A, POCIS-B, SDB-RPS and C18 disk. The uptake of the selected compounds depended on their physicochemical properties, i.e., silicone rubber showed a better uptake for more hydrophobic compounds (log octanol-water partition coefficient (KOW) > 5.3), whereas POCIS-A, POCIS-B and SDB-RPS disk were more suitable for hydrophilic compounds (log KOW < 0.70).
Pesticides are continuously introduced to the aquatic environment and may pose a risk to aquatic organisms1. Monitoring of pesticides in the aqueous environment is typically performed using grab sampling, however, this sampling technique does not fully account for temporal variations in concentrations due to fluctuations in flow or episodic inputs (e.g., precipitation, combined sewer overflows, sewage lagoon release)2,3. Thus, monitoring methods need to be improved for a better estimation of environmental risks associated with pesticides. Passive sampling allows continuous monitoring over an extended period of time with minimal infrastructure and low contaminant concentrations4,5.
Passive samplers have been shown to be a valuable tool for the monitoring in groundwater6, fresh water7-10, wastewater11 and marine waters12. Besides monitoring purposes13,14, passive samplers have also been used for non-target analysis15, toxicology testing16,17, and as an alternative to sediment- and biomonitoring18. Passive samplers accumulate chemicals continuously from water and provide time weighted average (TWA) concentrations14. The uptake of the contaminant depends on the sampling rate (RS) and passive sampler-water partition coefficient (KPW), which depends on the passive sampler design, sampler material, physicochemical properties of the contaminant, and environmental conditions (e.g., water turbulence, temperature)13,14,19,20.
The detailed video aims to show how to calibrate and apply passive samplers for pesticides in water. The specific objectives included i) to perform preparation, extraction and instrumental analysis for 124 individual pesticides using five different types of passive samplers, including silicone rubber, polar organic chemical integrative sampler (POCIS)-A, POCIS-B, SDB-RPS and C18 disk, ii) to assess RS and KPW for the pesticides in a laboratory uptake study, and iii) to demonstrate how to select the appropriate passive sampler of the target compound of interest and how to calculate TWA concentrations for the respective passive sampler.
Reference standards and passive sampler devices
Target compounds included 124 legacy and currently used pesticides including herbicides, insecticides and fungicides (Table 1). Internal standard mixture (IS mixture) included fenoprop (2,4,5-TP), clothianidin-D3, ethion and terbuthylazine-D5. Other used chemicals included methanol (MeOH), acetonitrile (ACN), acetone (ACE), dichloromethane (DCM), cyclohexane (CH), ethyl acetate (EA), petroleum ether (PE), 2-propanol, 25% ammonia solution, acetic acid (HAc) and formic acid (FA). Five different passive sampling devices were characterized, including silicone rubber, POCIS-A and POCIS-B, SDB-RPS, and C18 disk1,21.
Table 1. Passive sampler sampling rate (R'S, L day-1), sampler-water partition coefficients (K'PW, L kg-1) and equations (Eq.) used for the calculation of concentrations in field samples for individual pesticidesa. (Reprinted from Journal of Chromatography A, 1405, Lutz Ahrens, Atlasi Daneshvar, Anna E. Lau, Jenny Kreuger, Characterization of five passive sampling devices for monitoring of pesticides in water, 1-11, Copyright (2015), with permission from Elsevier.)22 Please click here to download this file.
1. Passive Sampler Design and Preparation
Figure 1. Schematic of silicone rubber. Passive sampler schematic for silicone rubber showing the attachment of the silicone rubber stripe to a stainless steel spider sample holder A) from the top and B) the side view. Please click here to view a larger version of this figure.
Figure 2. Schematic of passive sampler disks. Passive sampler schematic for POCIS A, POCIS B, SDB-RPS disk and C18 disk showing A) the assembling of the passive sampler using stainless steel rings, polyethersulfone (PES) membranes, and the receiving phase, and B) the assembling on a stainless steel sample holder. Please click here to view a larger version of this figure.
2. Laboratory Uptake Experiments
NOTE: The Laboratory uptake experiments were performed to quantitatively characterize the uptake kinetics for 124 individual pesticides for five different passive sampler devices under controlled conditions.
3. Sample Extraction
4. Water Samples
5. Instrumental Analysis
6. Theory on Passive Sampling
NOTE: The uptake profile of the chemical to the passive sampler medium (PSM) is divided into three sections: Linear, curvilinear and equilibrium (Figure 3).
Figure 3. Passive sampler uptake curve. A) and C) uptake curve for the accumulated amount of acetamiprid and dimethoate, respectively, in the passive samplers (Nt) in ng absolute, and B) and D) water tank concentration of acetamiprid and dimethoate, respectively, in ng L-1. Please click here to view a larger version of this figure.
7. Statistical Data Analysis
Five different passive sampler techniques were compared for the uptake of 124 legacy and current used pesticides including silicone rubber (Figure 1), and POCIS A, POCIS B, SDB-RPS and C18 disk (Figure 2). The performance of the extraction method and instrumental analysis was optimized. The outcome of the laboratory uptake experiments can be used to calculate the R'S and log K'PW values (Table 1) based on the uptake profile for individual pesticides (Figure 3). The results showed that silicone rubber is more suitable for hydrophobic compounds (log octanol-water partition coefficient (K'OW) > 5.3), whereas more polar compounds (log K'OW < 0.70) were better taken up by POCIS A, POCIS B and SDB-RPS disk (Figure 4). R'S (L day-1), K'PW (L kg-1) and equations (Eq.) can be used for the calculation of concentrations in field samples for individual pesticides (Table 1)22.
Figure 4. KOW vs passive sampler type. Box-Whisker-Plots for individual pesticides taken up by silicone rubber (n = 86), polar organic chemical integrative sampler (POCIS)-A (n = 106), POCIS-B (n = 110), SDB-RPS disk (n = 65), and C18 disk (n = 54) in relation to their octanol-water partition coefficient (KOW). Note: Pesticides were only included if the mean pesticide concentration in the passive sampler was greater than 0.1% compared to the mean pesticide concentration in the water. (Modified from Journal of Chromatography A, 1405, Lutz Ahrens, Atlasi Daneshvar, Anna E. Lau, Jenny Kreuger, Characterization of five passive sampling devices for monitoring of pesticides in water, 1-11, Copyright (2015), with permission from Elsevier.)22 Please click here to view a larger version of this figure.
For quality control, as standard procedure, laboratory blanks, limits of detection (LOD), recoveries, and repeatability were examined23. A few pesticides were detected in the blank samples at low concentration levels. LODs were set as the value of the lowest point on the calibration curve which meets the criteria of a signal to noise ratio of 3. The average LODs were 8.0 pg absolute injected on column for silicone rubber, 1.7 pg absolute for POCIS-A, 1.6 pg absolute for POCIS-B, 3.0 pg absolute for SDB-RPS disk, and 1.6 pg absolute for C18 disk. All concentrations were corrected by the spiked IS mixture. Average method recoveries based on spiked passive samples of the native pesticides (n = 3) were 68%, 110%, 92%, 89% and 70% for silicone rubber, POCIS-A, POCIS-B, SDB-RPS disk and C18 disk, respectively. The average repeatability for individual pesticides (n = 10) were 19%, 20%, 16%, 33% and 36% for silicone rubber, POCIS-A, POCIS-B, SDB-RPS disk and C18 disk, respectively.
Most pesticides had a short linear uptake curve (5 to 10 days) and equilibrated after 26 days, i.e., 89 of the 124 for silicone rubber, 97 of 124 for POCIS-A, 99 of 124 for POCIS-B, 32 of 124 for SDB-RPS disk and 36 of 124 for C18 disk. Therefore, for most pesticides a log K'PW could be calculated (Table 1). If a pesticide did not equilibrate, a log K'PW was assumed to be higher than the calculated log K'PW for the equilibration phase. The median R'S (L day-1) were 0.86 for silicone rubber, 0.22 for POCIS-B, 0.18 for POCIS-A, 0.05 for SDB-RPS disk and 0.02 for C18 disk. The high R'S for silicone rubber can be explained by the higher sorbent mass (mp) of silicone rubber (mp = 15.6 g) compared to the other passive samplers (mp = 0.22-0.58 g). The median log KPW (L kg-1) were 4.78 for POCIS-B, 4.56 for POCIS-A, 3.17 for SDB-RPS disk, 3.14 for silicone rubber and 2.71 for C18 disk. Differences can be explained by different surface areas (ap) which were higher for POCIS-A and POCIS-B (ap = 1.78 × 106 cm2 and 2.82 × 106 cm2, respectively) compared to silicone rubber (ap = 457 cm2), SDB-RPS disk and C18 disk (ap = 35 cm2 for both). It is important to note that the R'S can vary between different calibration methods and the type of passive sampler, thus there is a need to define standardized protocols for calibration procedures25.
This study was performed using static depletion which has the advantage to have a simple set-up with many replicates but concentration depletion over time needs to be considered. Future uptake studies should be performed using flow-through exposure tanks with constant exposure concentrations or in-situ under realistic field deployment conditions19. Natural water was used in the laboratory calibration experiments, however, the DOC can have an influence on the determination of sampling rates.19 Furthermore, the usage of performance and reference compounds (PRCs), which are spiked to the passive samplers before deployment, can be used to calculate in-situ uptake rates and allow for more accurate estimates of TWA concentrations.26
The log KPW of silicone rubber and C18 disk showed a significant positive correlation with log KOW (Spearman's rho = 0.53 and 0.48, respectively; p < 0.0001). For the log RS values, a significant positive correlation was only found between log RS and log KOW of silicone rubber (Spearman's rho = 0.56, p < 0.0001). In general, the KOW has been shown to be a good parameter to predict the suitability of the passive sampler for specific target compounds14,27. A variety of different pesticides were investigated in this study with a log KOW ranging from -2.6 to 7.0. In general, the five tested passive samplers were capable to accumulate pesticides with a wide range of different KOW for silicone rubber (KOW = 0.70 – 7.0), POCIS A (-1.9 – 5.3), POCIS B (-1.9 – 5.2), SDB-RPS disk (-1.2 – 4.7) and C18 disk (1.3 – 5.3) (Figure 4). Our results showed that silicone rubber is more suitable for hydrophobic compounds (log KOW > 5.3), whereas more polar compounds (log KOW < 0.70) were better taken up by POCIS A, POCIS B and SDB-RPS disk (Figure 4).
The authors have nothing to disclose.
The Swedish EPA (Naturvårdsverket) (agreement 2208-13-001) and Centre for Chemical Pesticides (CKB) are gratefully acknowledged for funding this project. We thank Märit Peterson, Henrik Jernstedt, Emma Gurnell and Elin Paulsson at the OMK-lab, SLU, for skillful assistance with analytical support and supply of pesticide standards.
Methanol | Merck Millipore | 1.06035.2500 | |
Acetonitrile | Merck Millipore | 1.00029.2500 | |
Acetone | Merck Millipore | 1.00012.2500 | |
2-propanol | Merck Millipore | 1.00272.2500 | |
Dichloromethane | Merck Millipore | 1.06054.2500 | |
Ammoniak | Merck Millipore | 1.05428.1000 | Purity 25% |
Formic acid | Sigma-Aldrich | 94318-50ML-F | Purity ~98% |
Ethyl acetate | Sigma-Aldrich | 31063-2.5L | for pesticide residue analysis |
Petroleum ether | Sigma-Aldrich | 34491-4X2.5L | for pesticide residue analysis |
Acetic acid | Sigma-Aldrich | 320099-500ML | Purity ≥99.7% |
Cyclohexane | Fisher Chemicals | C/8933/17 | for residue analysis |
Empty polypropylene SPE Tube with PE frits, 20 μm porosity, volume 6 mL | Supelco | 57026 | |
Empore SPE Disks, C18, diam. 47 mm | Supelco | 66883-U | Passive sampler |
Empore SPE Disks, SDB-RPS (Reversed-Phase Sulfonate), diam. 47 mm | Supelco | 66886-U | Passive sampler |
POCIS-A | EST | POCIS-HLB | Passive sampler |
POCIS-B | EST | POCIS-Pesticide | Passive sampler |
Polyethersulfone (PES) membranes | EST | PES | |
Silicone rubber sheet | Altec | 03-65-4516 | Passive sampler |
Agilent 5975C | Agilent Technologies | 5975C | GC-MS |
HP-5MS UI | J&W Scientific | HP-5MS | Analytical column for GC-MS |
Agilent 6460 | Agilent Technologies | 6460 | HPLC-MS/MS |
Strata C18–E, 20 x 2 mm id and 20–25 μm particle size | Phenomenex | Strata C18–E | Online SPE column for LC-MS/MS |
Strata X, 20 x 2 mm id and 20–25 μm particle size | Phenomenex | Strata X | Online SPE column for LC-MS/MS |
Zorbax Eclipse Plus C18 | Agilent Technologies | Zorbax Eclipse Plus C18 | Analytical column for LC-MS/MS |
Isolute phase separator, 25 mL | Biotage | 120-1907-E | |
Stainless steel blind rivet, 3.2×10 mm | Ejot & Avdel | 951222 |