Chemcatcher® and DGT passive sampling devices for regulatory monitoring of trace metals in surface water

Abstract

This work aimed to evaluate whether the performance of passive sampling devices in measuring time-weighted average (TWA) concentrations supports their application in regulatory monitoring of trace metals in surface waters, such as for the European Union's Water Framework Directive (WFD). The ability of the Chemcatcher and the diffusive gradient in thin film (DGT) device sampler to provide comparable TWA concentrations of Cd, Cu, Ni, Pb and Zn was tested through consecutive and overlapping deployments (7-28 days) in the River Meuse (The Netherlands). In order to evaluate the consistency of these TWA labile metal concentrations, these were assessed against total and filtered concentrations measured at relatively high frequencies by two teams using standard monitoring procedures, and metal species predicted by equilibrium speciation modeling using Visual MINTEQ. For Cd and Zn, the concentrations obtained with filtered water samples and the passive sampling devices were generally similar. The samplers consistently underestimated filtered concentrations of Cu and Ni, in agreement with their respective predicted speciation. For Pb, a small labile fraction was mainly responsible for low sampler accumulation and hence high measurement uncertainty. While only the high frequency of spot sampling procedures enabled the observation of higher Cd concentrations during the first 14 days, consecutive DGT deployments were able to detect it and provide a reasonable estimate of ambient concentrations. The range of concentrations measured by spot and passive sampling, for exposures up to 28 days, demonstrated that both modes of monitoring were equally reliable. Passive sampling provides information that cannot be obtained by a realistic spot sampling frequency and this may impact on the ability to detect trends and assess monitoring data against environmental quality standards when concentrations fluctuate.

Evaluation of Discrete and Passive Sampling (Diffusive Gradients in Thin-films – DGT) Approach for the Assessment of Trace Metal Dynamics in Marine Waters – a Case Study in a Small Harbor

“…For short term studies, which include collection of composite samples over the deployment period or for sites with relatively stable and expressed concentration gradient of trace metals, high degrees of correlation were found between dissolved and DGT-labile concentrations. [22,24,33,40,44] In our study this was not the case. The only common characteristic for all metals was the lower average concentration of both dissolved and DGT-labile concentrations of trace metals at site SP2 compared to SP1 and SP3, over the duration of the study.…”

“…Such specific variability patterns clearly show the overall dynamics of trace metal concentrations at the study area, but also demonstrates that the discrete sampling methodology, most widely used in environmental monitoring programs and research studies, [2,3,37,38] is not ideal for (highly) dynamic aquatic systems. [39][40][41] Examining the entire 5-month period, specific trends of trace metal concentrations varied by metals and sites. There was no clear correlation (Pearson's coefficient; all samples/sites) found between the metals.…”

Passive Sampling Technologies for the Monitoring of Organic and Inorganic Contaminants in Seawater

“…The diffusion process is influenced by water temperature and by hydrodynamic conditions (water turbulence) at the surface of the sampler. Comparisons between the Chemcatcher and DGT were undertaken by Allan et al (2008) in a 28-day trial during which fluctuating concentrations of metals (Cd, Cu, Ni, Pb, Zn) were observed in frequent spot samples. This study assessed the potential of these two devices for the regulatory monitoring of trace metals in surface water.…”

Passive Sampling Technologies

“…Comparisons between the Chemcatcher and DGT were undertaken in a 28 day trial during which fluctuating concentrations of metals (Cd, Cu, Ni, Pb, Zn) were observed in frequent spot samples. This study assessed the potential of these two devices for the regulatory monitoring of trace metals in surface water (Allan et al ., 2008). It demonstrated that the two sampling devices provided similar information, and were able to integrate concentrations reliably even where there were fluctuations in concentration during the deployment period.…”