Analytical Techniques for the in situ Measurement and Speciation of Trace Compounds in Natural Waters

A major research component of the analytical activities of the Analytical and Biophysical Environmental Chemistry group of the University of Geneva (CABE) is focused on the development of chemical sensors and mini or microanalytical systems for in situ measurements of trace compounds in aquatic environmental systems, including surface waters, sediments or water treatment plants. In this field, new concepts are required in order to determine not only the total concentration of environmental analytes but also the concentrations and physicochemical properties of their environmentally relevant chemical forms (chemical speciation). New selective analytical systems integrating reliable and rugged sensors with simple separation principles must be imagined to perform in situ (at depth), real-time, automatic measurements. Microtechnology is a key factor in such developments. New analytical methods must also be developed to characterize the nature and properties of the major natural, often colloidal or polymeric, complexing agents. In this context, the scientific approach of CABE is explained

Trace metal speciation at the sediment-water interface of Vidy Bay: influence of contrasting sediment characteristics

Trace metal analysis and speciation were performed at the sediment-water interface of Vidy Bay (Lake Geneva, Switzerland). This bay is impacted by hazardous compounds released via the sewage effluent of a major wastewater treatment plant (WWTP). Sediment cores and overlying water were sampled simultaneously at 12 sites characterized by contrasting sediment surface characteristics (color, methanogenic activity, bacterial mat) using corers deployed from a MIR submarine or research boat. The concentrations of trace metals in particulate form in the sediment and dissolved in the interstitial water, as well as the particulate, colloidal and dynamic fractions of trace metals in the overlying water were determined by combining an in situ and laboratory multi-method analytical approach. The results indicate differences in trace metal speciation in the sediment and overlying water at the 12 investigated sites. The observed differences were found to be more correlated to bacterial community, abundance, type and activity than to distance from the WWTP sewage outlet

Bacterial communities in trace metal contaminated lake sediments are dominated by endospore-forming bacteria

Lake sediments in areas close to the outlet of wastewater treatment plants are sinks for pollutants. Bacterial communities in sediments are likely affected by the released effluents, but in turn they might modify the distribution and bioavailability of pollutants. On the shore of Lake Geneva, Switzerland, wastewater from the City of Lausanne is treated and discharged into the lake via an outlet pipe in the Vidy Bay. The objectives of this study were to assess (1) the impact of the treated wastewater release on the bacterial communities in the Vidy Bay sediments and (2) the potential link between bacterial communities and trace metal sediment content. Bacterial community composition and abundance were assessed in sediments collected in three areas with different levels of contamination. The main factors affecting bacterial communities were inferred by linking biological data with chemical analyses on these sediments. Near to the outlet pipe, large quantities of bacterial cells were detected in the three upper most cm (3.2 × 109 cells assessed by microscopy and 1.7 × 1010 copies of the 16S rRNA gene assessed by quantitative PCR, per gram of wet sediment), and the dominant bacterial groups were those typically found in activated sludge (e.g. Acidovorax defluivii and Hydrogenophaga caeni). Three samples in an area further away from the outlet and one sample close to it were characterized by 50 % of endospore-forming Firmicutes (Clostridium spp.) and a clear enrichment in trace metal content. These results highlight the potential role of endospore-forming Firmicutes on transport and deposition of trace metals in sediments

Bacterial communities in trace metal contaminated lake sediments are dominated by endospore-forming bacteria

Lake sediments in areas close to the outlet of wastewater treatment plants are sinks for pollutants. Bacterial communities in sediments are likely affected by the released effluents, but in turn they might modify the distribution and bioavailability of pollutants. On the shore of Lake Geneva, Switzerland, wastewater from the City of Lausanne is treated and discharged into the lake via an outlet pipe in the Vidy Bay. The objectives of this study were to assess (1) the impact of the treated wastewater release on the bacterial communities in the Vidy Bay sediments and (2) the potential link between bacterial communities and trace metal sediment content. Bacterial community composition and abundance were assessed in sediments collected in three areas with different levels of contamination. The main factors affecting bacterial communities were inferred by linking biological data with chemical analyses on these sediments. Near to the outlet pipe, large quantities of bacterial cells were detected in the three upper most cm (3.2×109 cells assessed by microscopy and 1.7×1010 copies of the 16S rRNA gene assessed by quantitative PCR, per gram of wet sediment), and the dominant bacterial groups were those typically found in activated sludge (e.g. Acidovorax defluivii and Hydrogenophaga caeni). Three samples in an area further away from the outlet and one sample close to it were characterized by 50% of endospore-forming Firmicutes (Clostridium spp.) and a clear enrichment in trace metal content. These results highlight the potential role of endospore-forming Firmicutes on transport and deposition of trace metals in sediments

In situ monitoring and speciation of trace metals in natural waters

This paper gives an overview of the problems related to metal speciation measurements and interpretation, as well as the criteria which should be used for the development of in situ techniques. Three promising methods are examined in greater detail: diffusion gradients in thin films (DGT), integrated diffusion in gel and voltammetry and the supported liquid membrane (SLM) preconcentration technique. The present state of the art in this field is discussed with suggestions for future research directions

Integrated Microanalytical System for Simultaneous Voltammetric Measurements of Free Metal Ion Concentrations in Natural Waters

A complexing gel integrated microelectrode (CGIME) for direct measurements of free metal ion concentrations in natural waters has been developed. It is prepared by the successive deposition of microlayers of a chelating resin, an antifouling agarose gel and Hg on a 100-interconnected Ir-based microelectrode array. The trace metals of interest are in a first step accumulated on the chelating resin in proportion to their free ion concentration in solution, then released in acidic solution and detected simultaneously by using square wave anodic stripping voltammetry (SWASV). The reliability of this sensor for the simultaneous measurement of copper, lead and cadmium has been studied by a series of replicate laboratory tests. The proportionality between the voltammetric peak current intensity and the free metal ion concentrations in solution has been demonstrated by using malonate as a model ligand. Finally, the CGIME sensor was applied to the Cu and Pb free concentration measurement in sea water samples and the results compared to the free metal ion concentrations measured using hollow fiber based permeation liquid membrane (HF-PLM) coupled to inductively coupled plasma mass spectrophotometer (ICP-MS). Comparable concentration values were found for both metals with both techniques allowing to validate the CGIME measurements in complex media

Voltammetric Detection of Hg2+ Using Peptide-Functionalized Polymer Brushes

Polymer brushes grafted by surface-initiated atom transfer radical polymerization (SI-ATRP) from the surface of Ir-based microelectrode arrays are explored as a platform for the fabrication of sensory coatings for the voltammetric detection of Hg2+. The polymer brush coatings are post-modified with a metallothionein derived peptide to enable the selective detection of Hg2+. The performance of the polymer brush modified microelectrode arrays was evaluated using both cyclic voltammetry (CV) as well as square-wave anodic stripping voltammetry (SWASV) experiments. These studies revealed that the polymer brush based coatings allowed the selective detection of Hg2+ with detection limits in the subnanomolar range

On-Chip Antifouling Gel-Integrated Microelectrode Arrays for In Situ High-Resolution Quantification of the Nickel Fraction Available for Bio-Uptake in Natural Waters

We aimed to monitor in situ nickel (Ni(II)) concentrations in aquatic systems in the nanomolar range. To achieve this, we investigated whether an analytical protocol for the direct quantification of cobalt (Co(II)) using adsorptive cathodic sweep voltammetry (Ad-CSV) on antifouling gel-integrated microelectrode arrays (GIME) we recently developed is also suitable for direct Ni(II) quantification. The proposed protocol consists of the reduction of the complex formed between Ni(II) (or Ni(II) and Co(II)) and nioxime adsorbed on the surface of the GIME-sensing element. The GIME enables to (i) avoid fouling, (ii) control the metal complex mass transport and, when interrogated by Ad-CSV, (iii) selectively determine the dynamic (kinetically labile Ni-nioxime) fraction that is potentially bioavailable. The nioxime concentration and pH were optimized. A temperature correction factor was determined. The limit of detection established for 90 s of accumulation time was 0.43 ± 0.06 in freshwater and 0.34 ± 0.02 nM in seawater. The sensor was integrated in a submersible probe in which the nioxime-containing buffer and the sample were mixed automatically. In situ field measurements at high resolution were successfully achieved in Lake Geneva during a diurnal cycle. The determination of the kinetically labile Ni-nioxime fraction allows one to estimate the potential ecotoxicological impact of Ni(II) in Lake Geneva. Additional Ni fractions were measured by ICP-MS and coupled to the in situ Ad-CSV data to determine the temporal Ni(II) speciation