Mobile dynamic passive sampling of trace organic compounds: Evaluation of sampler performance in the Danube River
Graphical abstract
Introduction
Organic compounds are often present in the water column of rivers and lakes at trace concentrations that are difficult to detect when conventional low volume spot sampling of water is applied. Despite the low concentrations, chemicals can present a significant risk to aquatic organisms and humans, and many of them are regulated in surface waters (EU, 2013, EU, 2000). Reliable and representative monitoring is required for assessing compliance of water bodies with environmental quality standards, or for characterizing spatial and temporal contamination trends.
Among available methods, passive sampling presents a promising approach to future regulatory monitoring of trace organic compounds (Booij et al., 2016; Lohmann et al., 2012). Besides practical advantages that include passive in situ concentration and preservation of sampled compounds in sorbent materials, passive sampling provides freely dissolved compound concentrations, Cw (Vrana et al., 2005). The Cw is considered to play a key role in understanding chemical's exposure of aquatic organisms (Reichenberg and Mayer, 2006).
When conventional passive water samplers are applied, they must be deployed for several weeks or months, because their ambient sampling rates (Rs), representing the volume of water extracted per unit of time, are low. However, when the time period available for passive sampling is restricted, compensation by high sampling rate is needed to sample a sufficient volume of water for instrumental quantification or measuring chemical effects using bioanalytical tools.
Since Rs proportionally increase with the surface area of a sampler (Booij et al., 2007) they can be increased by using samplers in the form of large thin sheets. Furthermore, Rs increase when the water flow rate or turbulence on the sampler surface is higher (Estoppey et al., 2014; Li et al., 2010; Vermeirssen et al., 2009; Vrana and Schüürmann, 2002). Faster flow conditions cause a thinner water boundary layer (WBL) and lead to lower resistance to mass transfer (Levich, 1962). This is because the mass transfer of hydrophobic compounds is typically controlled by their diffusion through the WBL (Rusina et al., 2007). Flow turbulence can be increased by positioning samplers in a natural or artificially created current, by shaking, rotating or vibrating them during exposure in water (Qin et al., 2009). Allan et al. (2011) have shown increased Rs by towing samplers fastened to the end of a benthic trawl net. In general, input of some external mechanical energy is needed for increasing the water turbulence in vicinity of the samplers.
In this study, we investigated the applicability of a novel “dynamic” passive sampling device (DPS) that was developed with the aim to maximize the sampling rates of pollutants by forcing water at high flow rate along the passive sampler surface. The high flow was achieved by jetting water through a narrow flow-through sampler exposure chamber using a pump. Hereto we 1) compared the performance of DPS with conventional deployment of passive samplers in cages; 2) tested the performance of the DPS device by deployment from a moving ship in the Danube river to obtain integrated freely dissolved concentrations of pollutants in the water column over time and space; 3) compared the uptake of compounds by silicone rubber, low density polyethylene and SDB-RPS Empore™ disks samplers co-deployed inside the DPS device. The first two materials are commonly used for sampling hydrophobic compounds, whereas the latter is used also for sampling hydrophilic compounds. Finally, 4) we evaluated aqueous concentrations of atrazine derived from DPS in relation to those from spot water sampling.
Section snippets
Passive samplers
Three types of passive samplers were applied: two partitioning samplers, SR and LDPE sheets and one adsorption sampler based on styrene-divinylbenzene solid phase extraction disks, SDB-RPS Empore™ disks (ED). AlteSil™ translucent SR sheets 0.5 mm thick (Altec, UK) were cut into samplers with a size of 14 × 28 cm (392 cm2, 23 g), Soxhlet extracted in ethylacetate for 72 h and spiked according to the procedure described in Smedes and Booij (2012) with 14 performance reference compounds (PRC: D10
Comparison of caged sampler and DPS
The Cw,SR of PAHs, PCBs and HCB were calculated using analyte amounts accumulated in SR and the Rs,SR obtained as described in Section 2.4. The Cw,SR for stationary caged samplers and stationary DPS devices downstream Bratislava agreed very well (Fig. 3, left graph), with a median ratio of 0.93 and 0.83 for individual PAHs and PCBs, respectively. Similarly, a reasonably good median Cw,SR ratio was obtained for individual PAHs and PCBs from caged samplers and mobile passive samplers in the
Conclusions and perspectives
The main DPS usage domain is a representative measurement of compound levels, averaged in time (TWA) and/or space. The DPS device presents a useful alternative approach to the conventional sampler deployment technique in cages in situations where integrative uptake of compounds accumulated under WBL control must be maximized.
We demonstrated the robustness of the DPS technique in stationary and mobile deployments in a large river. When DPS is used for sampling from a cruising ship, the device
List of terms and abbreviations
- Ax
sampler × surface area in contact with water
- Caged passive sampler
a passive sampler deployed in a cage made of perforated stainless steel sheet; It was deployed stationary in the Danube downstream Bratislava (see Table 1).
- DPS
Dynamic Passive Sampling device; a novel water sampling device which forces water along the surface of sorbent sheets in a stainless steel flow-through chamber. Water passes through the chamber at a high flow rate assisted by a pump. This leads to a high turbulence close to
Acknowledgement
We acknowledge the NORMAN association www.norman-network.net, the SOLUTIONS Project supported by the European Union Seventh Framework Programme (FP7-ENV-2013-two-stage Collaborative project) under grant agreement 603437. The research activities were carried out in the RECETOX Research Infrastructure supported by the Czech Ministry of Education, Youth and Sports (LM2015051) and the European Structural and Investment Funds, Operational Programme Research, Development, Education
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