ICCE 2017 Monitoring water quality using passive sampling in kinetic mode:

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1 ICCE 217 Monitoring water quality using passive sampling in kinetic mode: A new calibration approach using the concentration ratio of passive samplers with different thicknesses Hanna Fuchte Hanna.Fuchte@bio5.rwth-aachen.de Institute of Environmental Research, RWTH Aachen University Andreas Schäffer, Kees Booij, Kilian Smith 1

2 Introduction Monitoring pollutants in natural and waste water is essential to protect ecosystems and human health. Passive sampling: Promising tool to measure freely dissolved concentrations of a broad range of pollutants. How it works: pollutants distribute between water and sampler phases driven by the difference in the pollutants chemical potential in the two phases C w C s 2

3 Introduction Monitoring pollutants in natural and waste water is essential to protect ecosystems and human health. Passive sampling: Promising tool to measure freely dissolved concentrations of a broad range of pollutants. Advantages: clean samples with upconcentrated analytes; time weighted average (in kinetic mode); bioavailable concentration C w C s 3

4 Introduction Monitoring pollutants in natural and waste water is essential to protect ecosystems and human health. Passive sampling: Promising tool to measure freely dissolved concentrations of a broad range of pollutants. This approach was tested using silicone passive samplers for non - polar substances C w C s 4

5 Introduction Kinetic region C S = C W K SW 1 exp k e t Uptake kinetics have to be known Performance Reference Compounds: Sometimes expensive and not always available Equilibrium C S = C W K SW For very hydrophobic substances equilibrium attainment can take month C w C s C S = passive sampler conc. (ng/ml), C W = dissolved concentration (ng/ml), K SW = equilibrium sampler to water partitioning coefficient, k e = uptake rate constant (1/h), t = time (h) 5

6 Passive Sampling with two samplers of different thicknesses same architecture same hydrodynamic regime same surface area different volumes (V thick and V thin ) Temporal evolution of concentrations (C thick and C thin ): Temporal evolution of accumulated amounts (N thick and N thin ): C thin C thick in equilibrium: N thick /N thin = V thick /V thin N thick N thin Similar amounts 6

7 Concentration Ratio Approach for Determining Dissolved Environmental Concentrations C thin C thick Equilibrium sampling: C S = C W K SW differences in amounts measurement error Hypothesis: When two samplers made of the same silicone material and with the same surface area but different volumes are deployed in parallel in the same hydrodynamic regime, measuring the ratio of their concentrations at a single point during the kinetic uptake phase allows the dissolved concentration in the surrounding medium to be determined. C S = passive sampler conc. (ng/ml), C W = dissolved concentration (ng/ml), K SW = equilibrium sampler to water partitioning coefficient 7

8 C s [ng/ml] Considerations and Calculations k e,thin and k e,thick can be derived from measurements but also from theory: From kinetic measurements: thin sampler thick sampler C S = passive sampler conc. (ng/ml), C W = dissolved concentration (ng/ml), K SW = equilibrium sampler to water partitioning coefficient, k e = uptake rate constant (1/h), t = time (h) 8

9 Considerations and Calculations From theory: When samplers are deployed in parallel: Same k O, same A and same K SW : Concentration Ratio Approach - equation C S = passive sampler conc. (ng/ml), C W = dissolved concentration (ng/ml), K SW = partitioning coefficient, k e = uptake rate constant (1/h), t = time (h), k O = mass-transfer coefficient (cm/h), A = sampler surface area (cm 2 ), V S = volume of the sampler (cm 3 ) 9

10 Experimental setup Stirred and unstirred system Constant dissolved concentrations via passive dosing sheets loaded with polycyclic aromatic hydrocarbons (PAHs) at ca..1 ng/ml Water samples taken at start and end for extraction and analysis Passive samples thick and thin PDMS discs (n=5 each) A=1.57 cm 2 ; V=.16 and.64 cm 3 ; Ø=1cm taken out at t = 8, 24, 56, 12 and 223 hours extracted and analysed via GC-MS 1

11 C s [ng/ml] Calculation example Phenanthrene stirred 24 h 8 6 Artificially vary C w 4 2 thin sampler thick sampler Look where equation approaches zero (= where graph crosses the x axis) C S = passive sampler conc. (ng/ml), C W = dissolved concentration (ng/ml), K SW = equilibrium sampler to water partitioning coefficient 11

12 C s [ng/ml] Results - all timepoints Example: Phenanthrene stirred thin sampler thick sampler KINETIC UPTAKE REGIME C W calculated by different thicknesses approach EQUILIBRIUM C W calculated by K sw 24 h 56 h 12 h 223 h C S = passive sampler conc. (ng/ml), C W = dissolved concentration (ng/ml), K SW = equilibrium sampler to water partitioning coefficient 12

13 C s [ng/ml] C s [ng/ml] C s [ng/ml] C s [ng/ml] C w [ng/ml] C s [ng/ml] C s [ng/ml] C s [ng/ml] C s [ng/ml] Results early and late timepoint different substances stirred and unstirred thin sam thick sam, ,5,4,3,2,1, Cw measured C w sampler 56 h Cw sampler 223 h FLU stirred FLU unstirred PHE stirred PHE unstirred PYR stirred PYR unstirred BKF stirred thin sampler thick sampler Phenanthrene static C S = passive sampler conc. (ng/ml), C W = dissolved concentration (ng/ml) thin sampler thick sampler 13 1

14 Outlook Practical application: When an appreciable degree of equilibrium in at least the thin sampler is attained efficient possibility of determining environmental dissolved concentrations during kinetic sampling thin thick Limitations of approach: In those cases where sampling in the early stage of kinetic uptake is needed (e.g. highly hydrophobic substances) Method needs further optimization 14

15 Thank you for your attention! Acknowledgements: This research was funded by the Ministry of Innovation, Higher Education and Research of North Rhine-Westphalia