Margaret McCaul

Screen-printed electrodes for environmental monitoring of heavy metal ions: a review

AbstractHeavy metals such as lead, mercury, cadmium, zinc and copper are among the most important pollutants because of their non-biodegradability and toxicity above certain thresholds. Here, we review methods for sensing heavy metal ions (HMI) in water samples using screen-printed electrodes (SPEs) as transducers. The review (with 107 refs.) starts with an introduction into the topic, and this is followed by sections on (a) mercury-coated SPEs, (b) bismuth-coated SPEs, (c) gold-coated SPEs (d) chemically modified and non-modified carbon SPEs, (e) enzyme inhibition-based SPEs, and (f) an overview of commercially available electrochemical portable heavy metal analyzers. The review reveals the significance of SPEs in terms of decentralized and of in situ analysis of heavy metal ions in environmental monitoring. Graphical AbstractThis review summarises recent advances in the use of screen-printed electrodes (SPEs) for the electrochemical detection of heavy metal ions in water samples. Research proofs of concept and commercially available portable equipments for ‘in situ analysis’ are discussed.

Online High-Performance Size Exclusion Chromatography−Nuclear Magnetic Resonance for the Characterization of Dissolved Organic Matter

The substantial heterogeneity of dissolved organic matter (DOM) inhibits detailed chromatographic analysis with conventional detectors as little structural information can be obtained in the presence of extensive coelution. Here we examine the direct hyphenation of high-performance size exclusion chromatography (HPSEC) with nuclear magnetic resonance (NMR) spectroscopy to determine how size-distinguished fractions differ in composition. The results support the applicability of using HPSEC to generate more homogeneous fractions of DOM prior to NMR analysis and demonstrate that structure is significantly altered with size. The largest fractions are enriched in carbohydrate- and aromatic-type structures. The midsized material is substantial and is representative of carboxyl-rich alicyclic molecules (CRAMs). The smallest material has strong signatures of material derived from linear terpenoids (MDLT). Both CRAMs and MDLT have been recently hypothesized as major components of DOM, and detection by HPSEC-NMR confirms their existence as unique and separable entities. This preliminary work focuses on NMR hyphenation to HPSEC due to widespread use of HPSEC to characterize DOM. Online hyphenation is useful not only for time-efficient analysis of DOM but also for that of other highly complex samples such as those found in many environmental analyses.

Composition of dissolved organic matter within a lacustrine environment

Environmental context Freshwater dissolved organic matter is a complex chemical mixture central to many environmental processes, including carbon and nitrogen cycling. Questions remain, however, as to its chemical characteristics, sources and transformation mechanisms. We studied the nature of dissolved organic matter in a lake system and found that it is influenced by anthropogenic activities. Human activities can therefore influence the huge amounts of carbon sequestered in lakes as dissolved organic matter. Abstract Freshwater dissolved organic matter (DOM) is a complex mixture of chemical components that are central to many environmental processes, including carbon and nitrogen cycling. However, questions remain as to its chemical characteristics, sources and transformation mechanisms. Here, we employ 1- and 2-D nuclear magnetic resonance (NMR) spectroscopy to investigate the structural components of lacustrine DOM from Ireland, and how it varies within a lake system, as well as to assess potential sources. Major components found, such as carboxyl-rich alicyclic molecules (CRAM) are consistent with those recently identified in marine and freshwater DOM. Lignin-type markers and protein/peptides were identified and vary spatially. Phenylalanine was detected in lake areas influenced by agriculture, whereas it is not detectable where zebra mussels are prominent. The presence of peptidoglycan, lipoproteins, large polymeric carbohydrates and proteinaceous material supports the substantial contribution of material derived from microorganisms. Evidence is provided that peptidoglycan and silicate species may in part originate from soil microbes.

Combining Remote Temperature Sensing with in-Situ Sensing to Track Marine/Freshwater Mixing Dynamics

The ability to track the dynamics of processes in natural water bodies on a global scale, and at a resolution that enables highly localised behaviour to be visualized, is an ideal scenario for understanding how local events can influence the global environment. While advances in in-situ chem/bio-sensing continue to be reported, costs and reliability issues still inhibit the implementation of large-scale deployments. In contrast, physical parameters like surface temperature can be tracked on a global scale using satellite remote sensing, and locally at high resolution via flyovers and drones using multi-spectral imaging. In this study, we show how a much more complete picture of submarine and intertidal groundwater discharge patterns in Kinvara Bay, Galway can be achieved using a fusion of data collected from the Earth Observation satellite (Landsat 8), small aircraft and in-situ sensors. Over the course of the four-day field campaign, over 65,000 in-situ temperatures, salinity and nutrient measurements were collected in parallel with high-resolution thermal imaging from aircraft flyovers. The processed in-situ data show highly correlated patterns between temperature and salinity at the southern end of the bay where freshwater springs can be identified at low tide. Salinity values range from 1 to 2 ppt at the southern end of the bay to 30 ppt at the mouth of the bay, indicating the presence of a freshwater wedge. The data clearly show that temperature differences can be used to track the dynamics of freshwater and seawater mixing in the inner bay region. This outcome suggests that combining the tremendous spatial density and wide geographical reach of remote temperature sensing (using drones, flyovers and satellites) with ground-truthing via appropriately located in-situ sensors (temperature, salinity, chemical, and biological) can produce a much more complete and accurate picture of the water dynamics than each modality used in isolation.

Investigation into dissolved neutral sugars and their microbial conversion in natural and artificially produced dissolved organic matter using ion chromatography with pulsed amperometric detection and reversed-phase liquid chromatography-high resolution mass spectrometry

Ion-exchange chromatography with pulsed amperometric detection (IEC-PAD) was employed to investigate dissolved neutral sugars and their microbial conversion in both artificially prepared dissolved organic matter (ADOM), and naturally occurring dissolved organic matter (DOM) obtained from seawater and freshwater sources. The analysis of ADOM and naturally occurring DOM samples using IEC-PAD resulted in chromatograms suggesting very similar composition, each characterised by three early eluting peaks, the latter of which being a broad co-elution of multiple compounds. For naturally occurring DOM, several sugars, including arabinose, glucose, galactose, xylose and ribose, could also be identified. The three distinctive peaks obtained from IEC-PAD of ADOM were collected and further analysed by means of reversed-phase high performance liquid chromatography-high resolution mass spectrometry (RPLC-HRMS), the latter showing that glucose was totally consumed during microbial production of ADOM and potentially transformed into higher molecular weight materials and CO2.

A colorimetric method for use within portable test kits for nitrate determination in various water matrices

A method using zinc powder in conjunction with the common Griess assay was developed for the detection of nitrate in water. This method is applicable to portable water test kits and allows for the accurate determination of nitrate in freshwater. The linear range for the method was shown to be 0.5–45 mg L−1 NO3− and the limit of detection (LOD) was 0.5 mg L−1 NO3−. The proposed method was validated over a five-day period and acceptable recovery and uncertainties were achieved when analysing freshwater matrices. The performance of the developed method was compared to an ISO-accredited ion chromatographic (IC) method by carrying out blind sample analysis. A good agreement between the two methods was achieved as comparable concentrations were determined using each method. In addition, the Zn method was compared to the performance of a novel solid-phase reagent method, previously developed within the group. The most accurate performance was demonstrated by the Zn powder method when analysing freshwater samples. The novel solid-phase reagent method demonstrated the greater accuracy when analysing seawater samples.

The occurrence of PAHs and faecal sterols in Dublin Bay and their influence on sedimentary microbial communities

The source, concentration, and potential impact of sewage discharge and incomplete organic matter (OM) combustion on sedimentary microbial populations were assessed in Dublin Bay, Ireland. Polycyclic aromatic hydrocarbons (PAHs) and faecal steroids were investigated in 30 surface sediment stations in the bay. Phospholipid fatty acid (PLFA) content at each station was used to identify and quantify the broad microbial groups present and the impact of particle size, total organic carbon (%TOC), total hydrogen (%H) and total nitrogen (%N) was also considered. Faecal sterols were found to be highest in areas with historical point sources of sewage discharge. PAH distribution was more strongly associated with areas of deposition containing high %silt and %clay content, suggesting that PAHs are from diffuse sources such as rainwater run-off and atmospheric deposition. The PAHs ranged from 12 to 3072ng/g, with 10 stations exceeding the suggested effect range low (ERL) for PAHs in marine sediments. PAH isomer pair ratios and sterol ratios were used to determine the source and extent of pollution. PLFAs were not impacted by sediment type or water depth but were strongly correlated to, and influenced by PAH and sewage levels. Certain biomarkers such as 10Me16:0, i17:0 and a17:0 were closely associated with PAH polluted sediments, while 16:1ω9, 16:1ω7c, Cy17:0, 18:1ω6, i16:0 and 15:0 all have strong positive correlations with faecal sterols. Overall, the results show that sedimentary microbial communities are impacted by anthropogenic pollution.

Normal‐phase high‐performance counter‐current chromatography for the fractionation of dissolved organic matter from a freshwater source

Normal-phase high-performance counter-current chromatography (HPCCC) is used to obtain a preliminary fractionation of components in dissolved organic matter (DOM) from a freshwater source. The HPCCC solvent system involved a normal-phase approach with water/methanol (1:1) as the lower stationary phase and hexane/ethyl acetate (1:1) as the upper mobile phase. The critical experiment parameters were optimised: revolution speed 1800 rpm and flow rate 0.15 mL/min. Under these conditions 50 μL of a 0.50 mg/mL DOM solution was loaded. The detection wavelength was monitored at 330 nm in order to isolate the main portion of DOM, which includes substances such as carboxyl-rich alicyclic molecules. By optimising this system it was possible to isolate materials that, according to GC-MS, can be related to molecules with an analogous structural background. Where fraction analysis was not suitable for GC-MS, RP-HPLC with UV absorbance detection was used, showing unique chromatograms for each fraction at both 210 and 330 nm.

COMMON SENSE: Cost-effective sensors, interoperable with international existing ocean observing systems, to meet EU policies requirements

The COMMON SENSE (CS) project aims to develop cost-effective, multi-functional innovative sensors to perform reliable in-situ measurements in the marine environment. The COMMON SENSE sensors will focus on key parameters including eutrophication, heavy metals, marine litter (microplastics) and underwater noise. The project will focus on increasing the availability of sensor data and observations through the development and implementation of the Common Sensor Web Platform (CSWP), a software platform that will integrate the COMMON SENSE sensor data and observations and deliver them to the Web, in standard formats and through standard interfaces.

Wearable Platform for Real-time Monitoring of Sodium in Sweat

A fully integrated and wearable platform for harvesting and analysing sweat sodium concentration in real time during exercise has been developed and tested. The platform was largely produced using 3D printing, which greatly simplifies fabrication and operation compared to previous versions generated with traditional production techniques. The 3D printed platform doubles the capacity of the sample storage reservoir to about 1.3 ml, reduces the assembly time and provides simple and precise component alignment and contact of the integrated solid-state ion-selective and reference electrodes with the sorbent material. The sampling flowrate in the device can be controlled by introducing threads to enhance wicking of sweat from the skin, across the electrodes to the storage area. The platform was characterised in the lab and in exercise trials over a period of about 60 minutes continuous monitoring. Sweat sodium concentration was found to rise initially to approximately 17 mM and decline gradually over the period of the trial to about 11-12 mM.