Trace Contaminants Research Articles

Safety of Lemna minor and Lemna gibba whole plant material as a novel food pursuant to Regulation (EU) 2015/2283.

Following a request from the European Commission, the EFSA Panelon Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on Lemna minor and Lemna gibba whole plant material as a novel food (NF) pursuant to Regulation (EU) 2015/2283. Lemna minor and Lemna gibba are aquatic plants commonly named water lentils. The NF is produced by cultivation of Lemna minor and Lemna gibba plants, washing with water and heat treatment. The main constituents of the NF are water, protein and fibre. The Panelnotes that the concentration of trace elements and contaminants in the NF is highly dependent on the conditions of cultivation of the plant and the fertiliser composition. The NF is intended to be used as a vegetable, similar to other leafy vegetables. The target population is the general population. The Panelconsiders that, with the exception of concerns related to the manganese intake, taking into account the composition of the NF and the proposed conditions of use, the consumption of the NF is not nutritionally disadvantageous. The Panelconsiders that the risk that the consumption of the NF may trigger allergic reactions in humans is low. The Panelconcludes that the NF, in consideration of its proposed uses and the concentration of manganese as compared to the normally present concentration of manganese in other leafy vegetables, may be of safety concern, therefore, the safety of the NF cannot currently be established.

EC-SERS detection of thiabendazole in apple juice using activated screen-printed electrodes

Thiabendazole (TBZ), a benzimidazole fungicide used for post-harvest treatment, may be a trace contaminant of food matrices. In this work, we report the first EC-SERS (electrochemical-surface enhanced Raman spectroscopy) detection of TBZ in spiked apple juice using electrochemically (EC) roughened, gold-based screen-printed electrodes (AuSPEs) and portable instrumentation. Polarizing the substrate (−0.8 V vs Ag/AgCl) improves the recorded SERS signal of TBZ, allowing to reach a limit of detection (LOD) in juice of 0.061 ppm with a relatively wide linear range (0.5–10 μM) and good intermediate precision (%RSD < 10). The recovery of TBZ from unprocessed juice was found to be more than 82 %. Furthermore, a proof-of-concept integration of AuSPEs with a miniaturized flow cell for the preconcentration of TBZ and the controlled delivery of sample and reagents has been demonstrated. This approach paves the way for integrated, portable analytical systems applicable for on-site sample collection, processing, and analysis.

Removal of contamination in helium for precise SF6‐based Δ36S measurements

Quantifications of quadruple sulfur isotopic compositions (δ34 S, Δ33 S, and Δ36 S) of sulfur-bearing compounds in nature are valuable for providing new insights into the Earth's evolution such as the crust-mantle cycle, oxygenation of atmosphere and oceans, and the origin and evolution of early life. SF6 -based isotope ratio mass spectrometry is the most widely used method of quantification, but Δ36 S measurements at high precision and accuracy have always been technically difficult due to the low abundance of 36 S (~0.01%). In this paper, we identify a major source of isobaric interferences (i.e., contamination in helium carrier gas in the gas chromatography purification step) and propose a simple strategy to solve this problem. An SF6 fluorination and purification system was built. Laboratory SF6 reference gas and international Ag2 S standard (IAEA-S1) were used as reference materials to test our method. Contamination from helium carrier gas (99.999%) was purified by a simple two-step cryogenic method to allow for accurate and precise measurements of Δ36 S using the SF6 -based isotope ratio mass spectrometry method. Without proper purification of helium carrier gas, large errors in Δ36 S measurements were found. Measured Δ36 S values of SF6 with trace contamination from helium were >10‰ higher than expected values. Using a newly developed purification strategy, the difference in Δ36 S values of SF6 before and after passing through the gas chromatography is less than instrumental errors (<0.2‰). Our improved method yielded an overall Δ36 S precision for IAEA-S1 of 0.12‰ (n = 6). This precision is comparable to that found by other laboratories around the world. Our simple two-step cryogenic method significantly improved the accuracy and precision of Δ36 S measurements and is therefore recommended for future determination of quadruple sulfur isotopic compositions in natural samples.

Electroactive constructed wetland using Fe3C as an anodic exogenous electron donor: Performance and mechanisms

Constructed wetland microbial fuel cells (CW-MFCs) are promising for removing trace contaminants. We investigated using Fe3C as an anodic exogenous electron donor in a CW-MFC to remove bisphenol A (BPA). BPA removal and electricity production were used to evaluate the CW-MFC performance, and bacterial high-throughput sequencing was used to investigate the microbial response. The experimental system removed BPA (91.62 ± 0.85 %), chemical oxygen demand (76.44 ± 2.25 %), total phosphorus (98.40 ± 0.17 %), and ammonium nitrogen (91.62 ± 0.85 %). It also had a high voltage (352.13 ± 31.48 mV) and power density (3.88 mW/m2), and relatively high coulombic efficiency (3.31 %). Fe3C addition enhanced bacterial cooperation and community stability, and increased the abundance of electroactive and ferric ammonium oxidation bacteria (Desulfovibrio and Geobacter). These changes explained the improved water purification effect and electricity production. Fe3C as an anodic electron donor in CW-MFCs is promising for practical applications.

Predicting the Solubility of Mercury in Hydrocarbons

SummaryElemental mercury (Hg0) is a common trace contaminant associated with corrosion of infrastructure impacting exploration, production, and processing of commercial hydrocarbons. Presently lacking is a model for the quantitative prediction of Hg concentration in reservoir fluids, sufficiently reliable for process engineering applications and design of mitigation strategies to ameliorate the potential risk of Hg presence.In this paper, we present a thermodynamic equilibrium mineral-based model for predicting the solubility of mercury in hydrocarbons, Hg0(org), at in-situ reservoir conditions. The model is based on literature experimental data on the solubility of Hg0 in a mixture of alkanes, in equilibrium with Hg0, H2S, O2, cinnabar (HgS), and water. As the model inputs are based on the chlorite-pyrite-H2S model, its application should primarily be limited to clastic hydrocarbon-bearing reservoirs. A global data set of Hg in hydrocarbons reveals a remarkably strong association with the presence of humic coal in subsurface formations.Assuming that pure stoichiometric cinnabar (HgS) is stable at the reducing conditions typical of hydrocarbon reservoirs (i.e., aHgS = 1) results in an overestimation of Hg0(org) solubility by up to three orders of magnitude relative to globally reported concentrations of mercury in natural hydrocarbons. A statistically robust match between model and observed concentrations of Hg0(org) was achieved using an aHgS of 0.003, consistent with reported concentrations of Hg0 from pyrite (FeS2) in coals and hydrocarbon reservoirs. The model has been validated in a case study of reservoir Hg reported in the Gorgon North-1 well, North West Shelf (NWS), Australia.The dominant process of cinnabar precipitation is by oxidation, particularly in the near-surface environment where reduced Hg0-bearing hydrocarbons mix with shallow oxygenated or acidic surface waters. Such processes are typical of the environments where most downhole fluid samples are collected during drilling, sampling, and cleanup of exploration and development wells. This leads to the invariable conclusion that much of the particulate mercury species, specifically HgS, collected with hydrocarbon fluid samples, are metastable with respect to the dissolved Hg0(org) in hydrocarbons at reservoir conditions and should not be included in the estimation of total Hg (i.e., THg) in hydrocarbons.This hypothesis has been confirmed by an extended well test in the Minami-Nagaoka gas condensate field, where it was observed that Hg dissolved in produced water decreased to negligible levels over time, while the Hg0(org) in the condensate liquid reached a stable value like what the new Hg0(org) solubility model would predict for in-situ reservoir conditions.

Unravelling the occurrence of trace contaminants in surface waters using semi-quantitative suspected non-target screening analyses

Several classes of anthropogenic chemicals such as pesticides and pharmaceuticals are frequently used in human-related life activities and are discharged into the aquatic environment. These compounds can exert an unknown effect on aquatic life and humans if the water is used for human consumption. Thus, unravelling their occurrence in the aquatic system is crucial for the well-being of life and monitoring purposes. To this end, we used nanoflow-liquid and ion-exchange chromatography hyphenated with orbitrap high-resolution tandem mass spectrometry to detect several thousands of features (chemical entities) in surface water. Later, the features were narrowed down to a few focused lists using a stepwise filtering strategy, for which the structural elucidation was made. Accordingly, the chemical structure was confirmed for 83 compounds from different application areas, mainly being pharmaceuticals, pesticides, and other multiple application industrial compounds and xenobiotic degradation products. The compounds with the highest concentration were lamotrigine (27.6 μg/L), valsartan (14.4 μg/L), and ibuprofen (12.7 μg/L). Some compounds such as prosulfocarb, fluopyram, and tris(3-chloropropyl) phosphate were found to be the most abundant and widespread contaminants. Of the 32 sampling sites, nearly half of the sites (47%) contained more than 30 different compounds. Two sampling sites were far more contaminated than other sites based on the estimated concentration and the number of identified contaminants they contained. Our triplicate analysis revealed a low relative standard deviation between replicates, advocating for the added value in analysing more sampling sites instead of sample repetition. Overall, our study elucidated the occurrence of organic contaminants from a variety of sources in the aquatic environment. Furthermore, our findings highlighted the role of suspected non-target screening in exposing a snapshot of the chemical composition of surface water and the localized possible contamination sources.

The distribution of trace contaminants in the manned space station atmosphere

The research is based on the results of air quality monitoring for the period from 2000 to 2020. The air samples have been taken onboard the International Space Station (ISS) using AK-1M samplers and delivered to Earth. The representativeness of the research results is confirmed by the long-term duration (20 years of observation) and the amount of experimental data (analysis of more than 30,000 measured concentrations of chemicals identified by gas chromatography and mass spectrometry). Statistical analysis of measured concentrations showed that the vast majority (70%) of trace contaminants detected in the ISS air have a log-normal distribution, which is confirmed by the use of the Kolmogorov-Smirnov goodness-of-fit test (p > 0.2). For the remaining 30%, the significance level of the Kolmogorov-Smirnov goodness-of-fit criterion was less than 0.2, however, the statistical distributions of these trace contaminants are characterized by unimodality, peakedness (kurtosis coefficient significantly >2) and asymmetry (skewness coefficient >1) with a shift towards lower values, which regarded as a “close to normal distribution”. It has been established that the log-normal model can be accepted as a theoretical model describing the distribution of trace contaminants in the air of manned space stations. The established log-normal distribution and the ratio between the average concentrations of different averaging periods (10 : 3: 1.5 : 1) confirms the uneven nature of air pollutants in the modules and the possibility of the formation of “stagnant” zones. This is of great practical importance, which must be taken into account when establishing the air quality standards for trace contaminants and designing life support systems (ventilation and air purification) for manned space stations.

Development of a Nafion-MWCNTs and in-situ generated Au nanopopcorns dual-amplification electrochemical aptasensor for ultrasensitive detection of OTA

Trace detection of ochratoxin A (OTA) in foods is essential to mitigate risks to human health. Herein, a label-free electrochemical (EC) aptasensor based on dual-signal amplification of Nafion dispersed multi-walled carbon nanotubes (Nafion-MWCNTs) and Au nanopopcorns was developed for ultrasensitive detection of OTA. Nafion solution prevented the leaching of MWCNTs, and the Nafion-MWCNTs modified screen-printed carbon electrode (SPCE) acted as the sensing substrate which facilitated the uniform distribution of the electrodeposited Au nanopopcorns. The in-situ generated Au nanopopcorns could not only load a large amount of aptamers for specific identification of OTA, but also promote the electron transfer of the sensing platform. The incorporation of Nafion-MWCNTs and Au nanopopcorns realized dual-amplification of the aptasensor due to the enhanced conductivity and the increased electroactive surface area of the electrode. The modified electrodes were characterized through scanning electron microscopy, X-ray photoelectron spectroscopy and EC evaluation. Under optimal conditions, the electrochemical impedance spectroscopy (EIS) was measured for the determination of OTA. The as-fabricated Au nanopopcorns/Nafion-MWCNTs impedimetric aptasensor displayed excellent sensitivity with a detection limit as low as 1 pg/mL and a wide linear range of 1 pg/mL-10 ng/mL for OTA. Practical application of the aptasensor in the spiked malt samples achieved satisfactory recoveries of 89.82–95.65 %, which was also successfully verified to detect OTA in eleven batches of actual malt samples collected from the local market. The creative aptasensor is simple, cost-effective, sensitive, and accurate, showing great promise for on-site monitoring of other trace contaminants in foods by simply replacing the aptamers.

Assessment of heavy metals and radionuclides in groundwater and associated human health risk appraisal in the vicinity of Rooppur nuclear power plant, Bangladesh

This study was carried out to assess the groundwater quality through estimating trace and heavy metal concentration and radionuclide levels in the vicinity of the Rooppur Nuclear Power Plant (RNPP) sites. Twenty-six (26) parameters, including major cations (K, Na, Mg, Ca) and anions (SO4−2, NO3−), trace and heavy metals (Mn, Fe, Zn, Ni, Co, Pb, Cd, As, Hg, Cu, Li, Be, B, V, Ga, Sr, Ag, Ba) and radionuclides (137Cs, 226Ra, 228Ra, and 40K) were estimated in water samples in the study area. This study revealed that the concentration values (μg/L) of Mn (667.091 ± 7.481), Fe (191.477 ± 3.756), Sr (105.218 ± 13.424), and Zn (23.493 ± 1.134) were the dominant metals in the study area. Different pollution evaluation indices (i.e., HPI, HEI, NI, Cd) data revealed that the study area was under a low to medium level of pollution due to the presence of metals in water. Subsequently, non-carcinogenic and carcinogenic health risks assessments for both adults and children were conducted, which indicated that health risk for the carcinogenic metals were below the threshold level except As through oral exposure for both adult and children. The activity concentrations of 226Ra, 228Ra, and 40K were measured to demonstrate probable radioactivity pollution using Gamma-ray spectrometry (High-resolution HPGe detector). The highest activity concentration of 226Ra, 228Ra, and 40K in groundwater samples were 4.9 ± 1.24 Bq/L (RNPP-15), 1.71 ± 0.43 Bq/L (RNPP-15), and 15.43 ± 3.08 Bq/L (RNPP-15). Among the three studied radionuclides, 40K has the highest average activity concentration. The radiological indicators referred to the annual effective dose (AED) is 0.4273 mSv yr-1, which implies no significant cause of radiological risks and hazards (UNSCEAR guideline value). This study provides a baseline of trace and toxic metal contamination, radioactivity, and radiation levels in the groundwater of the nuclear power plant (being built) area.

Colloidal associations of major and trace elements in the snow pack across a 2800-km south-north gradient of western Siberia

Colloidal (size 1 nm to 1 μm) transport of major and trace elements, notably micronutrients and low-solubility geochemical tracers, is a ubiquitous and well-established feature for all surface and soil waters in boreal and subarctic regions. However, little is known on the colloidal associations of organic carbon (OC) and major and trace elements in atmospheric precipitation such as snow. This is despite significant efforts devoted to distinguishing the soluble and particulate transport of trace metals and contaminants by atmospheric aerosols. To acquire a snap-shot of major and trace element size fractionation in the snow cover of western Siberia, we sampled snow cores integrated over the entire depth (0–50 cm until bottom) across a sizable (2800 km) south - north transect in the Ob River watershed (western Siberia). A number of trace metal pollutants (Cr, Ni, Zn, Cd) exhibited significant linkage, pronounced over the first 20 km, to sources of local pollution. Some elements (P, Mn, Zn, Ba) also demonstrated an increase in their colloidal fraction in the proximity of pollution centers, possibly reflecting input from industrial centers and gas flares.Following centrifuginal ultrafiltration, we analyzed total dissolved (< 0.22 μm), two colloidal (high molecular weight, HMW50 kDa ̶ 0.22 μm; medium molecular weight MMW3 kDa ̶ 50 kDa) and low molecular weight (LMW < 3 kDa) fractions in the melted snow for all major and trace elements. We discovered sizable (20 to 70%) proportion of some major (Ca, SO4) and many trace (Fe, Y, Zn, Sb, La, Ce, Yb, Pb) elements in the colloidal (3 kDa - 0.22 μm) form, without significant link to latitude, type of biome, or the concentration of possible colloidal carrier (DOC, Fe, Al, Ca, SO4). The origin of snow water colloids in snow can be hypothesized to stem from solute freezing on lake surfaces (Fe, OC), frost flowers of the Arсtic ice (Ca, SO4), clays dispersion (Al, Si) and sulphur dioxide oxidation particles (SO4, oxyanions). Via hydrochemical mass balance calculations, we demonstrate an overwhelming impact of snow melt on spring-time riverine export of Cd, Pb, Zn, As, Sb and Cs. These preliminary results call for further studies of atmospheric colloids including those originating from rainwater.

Measurement of polycyclic aromatic hydrocarbons in edible oils and potential health risk to consumers using Monte Carlo simulation, southwest Iran.

Persistent organic pollutants, such as polycyclic aromatic hydrocarbons, are hazardous trace contaminants frequently observed in food ingredients, such as edible oils. This study aimed to measure PAHs in forty brands of edible oils marketed in southwest Iran. Additionally, we characterized the daily intake of MOE and ILCR using Monte Carlo simulation. To analyze the content of PAHs, the liquid-liquid extraction method followed by GC-MS was utilized. The average concentration of PAHs was mostly lower than the maximum value for individual PAH (2 μg/Kg); however, the average concentration of fluorene (3.86 μg/Kg) and benzo(a)anthracene (3.13 μg/Kg) was more than the permitted level. The highest residual concentrations of PAHs were mostly observed in canola and corn oils. The daily intake of BaP and 4-PAH for 95% of consumers was 0.01 ng/kg BW/day and 0.04 ng/kg BW/day, respectively. Also, MOE was more than 10,000 for the percentiles of 5%, 50%, and 95%. The modeled ILCR showed that consumption of oil does not currently pose a cancer risk for Iranian consumers due to PAHs exposure. Concerning potential health risks, consumption of edible oils is safe; however, regular monitoring and assessment are required.

Insights into singlet oxygen generation and electron-transfer process induced by a single-atom Cu catalyst with saturated Cu-N4 sites

SummaryPersulfate-based nonradical oxidation processes are appealing in water treatment for the efficient and selective degradation of trace contaminants in complex water matrices. However, there is still lacking of systematic understanding of the relationship between multiple nonradical pathways and the active sites of catalyst. Herein, a single-atom Cu catalyst with saturated Cu-N4 sites on a carbon substrate (SA-Cu-NC) was constructed to activate peroxymonosulfate (PMS), which exhibited high catalytic performance and selectivity for pollutant degradation in different water conditions. Combined with the results of density functional theory (DFT) calculations, the electron-rich area around Cu site and the electron-poor area around C site in the saturated Cu-N4 configuration could efficiently adsorb and activate PMS, which promoted pollutant degradation through the oxidation of singlet oxygen (1O2) and electron transfer process, respectively. This study advances the understanding of the saturated coordination structure of metals and the superiority of multiple nonradical pathways in wastewater treatment.

A decade of monitoring micropollutants in urban wet-weather flows: What did we learn?

Urban wet-weather discharges from combined sewer overflows (CSO) and stormwater outlets (SWO) are a potential pathway for micropollutants (trace contaminants) to surface waters, posing a threat to the environment and possible water reuse applications. Despite large efforts to monitor micropollutants in the last decade, the gained information is still limited and scattered. In a metastudy we performed a data-driven analysis of measurements collected at 77 sites (683 events, 297 detected micropollutants) over the last decade to investigate which micropollutants are most relevant in terms of 1) occurrence and 2) potential risk for the aquatic environment, 3) estimate the minimum number of data to be collected in monitoring studies to reliably obtain concentration estimates, and 4) provide recommendations for future monitoring campaigns. We highlight micropollutants to be prioritized due to their high occurrence and critical concentration levels compared to environmental quality standards. These top-listed micropollutants include contaminants from all chemical classes (pesticides, heavy metals, polycyclic aromatic hydrocarbons, personal care products, pharmaceuticals, and industrial and household chemicals). Analysis of over 30,000 event mean concentrations shows a large fraction of measurements (> 50%) were below the limit of quantification, stressing the need for reliable, standard monitoring procedures. High variability was observed among events and sites, with differences between micropollutant classes. The number of events required for a reliable estimate of site mean concentrations (error bandwidth of 1 around the “true" value) depends on the individual micropollutant. The median minimum number of events is 7 for CSO (2 to 31, 80%-interquantile) and 6 for SWO (1 to 25 events, 80%-interquantile). Our analysis indicates the minimum number of sites needed to assess global pollution levels and our data collection and analysis can be used to estimate the required number of sites for an urban catchment. Our data-driven analysis demonstrates how future wet-weather monitoring programs will be more effective if the consequences of high variability inherent in urban wet-weather discharges are considered.

Hydrophobic expanded graphite-covered support to construct flexible and stable SERS substrate for sensitive determination by paste-sampling from irregular surfaces

Surface enhanced Raman spectroscopy (SERS) is a promising technique for trace determination. More and more attention is focused on hybrid SERS substrates, which coupled with noble metal nanoparticles and carbon-based materials. Herein, expanded graphite (EG) is used to prepare EG-covered support by ultrasonic washing and filtration. Such support is flexible and can be cut into any shape. And the contact angle (θe) for Au nanorods (Au NRs) sol on the EG-covered support was 108.2° and the hydrophobic surface is helpful for Au NRs to construct ‘hot spots’ during evaporation. The limits of detection (LOD) for crystal violet (CV), thiram, malachite green (MG) and methylene blue (MB) were as low as 1 ppb, 50 ppb, 1 ppb and 1 ppb, respectively. Moreover, a fast and convenient ‘paste-sampling’ method could be employed for trace contaminants on real samples, because EG-based Au NRs substrate is of flexibility and porosity. Thus, CV residue on shrimp could be determined lower than 1 ppb and thiram residue on grapes could be identified lower than 50 ppb. In addition to high sensitivity, the stability of EG-based Au NRs substrate is also very good. Even after acid/alkali pretreatment (pH = 4∼10) or 30 min of thermal treatment (T = 20∼100 °C), the enhancement of the substrate remained stable. What’s more, the substrate could be stored as long as 30 days. The highly stable, sensitive, cost-effective and easy-to-produce EG-based Au NRs substrates exhibit a great potential to promote application of SERS for routine analysis.

Theoretical investigation on degradation of DEET by •OH in aqueous solution: Mechanism, kinetics, process optimization and toxicity evaluation

N , N -diethyl-3-methylbenzamide (DEET), as a widely used insect repellent , is frequently detected in the environment. UV/H 2 O 2 is a valid technology to remove trace contaminants by generating hydroxyl groups. The density functional theory (DFT) calculation method was used to investigate the degradation mechanism and kinetics of DEET in water environment. •OH can attack DEET in two main modes, H-abstraction and •OH-addition, showing different reactivity. H-abstraction reaction is easier to occur compared with •OH-addition reaction. Especially the hydrogen on branch chain of DEET is more readily to be attacked by •OH. In the aqueous phase , the total rate constant is 2.04 × 10 9 M −1 s −1 at 298 K. Calculated results showed that R5, R6, R8, R9 and R12 paths preferentially occur. Under alkaline conditions, it can significantly inhibit the DEET degradation. The influence of natural organic matter (NOM) in water and oxidant dosage, DEET concentration was also considered. The response surface methodology (RSM) was used to optimize the process parameters. The maximum degradation efficiency of 95.64% can be achieved under optimal conditions. Since most of the products are homologues of the parent compound, their acute and chronic toxicity are not significantly reduced. The products are non-mutagenic and non-bioconcentrated, but they are developmentally toxic.

Online detection of trace volatile organic sulfur compounds in a complex biogas mixture with proton-transfer-reaction mass spectrometry

Online monitoring of trace contaminants, especially sulfur-containing compounds, is critical in biogas plants to protect downstream process steps, e.g., fuel cells or catalysts. The high biogas purity requirement for fuel cell applications and the presence of a myriad of unknown contaminants at different concentration levels require untargeted measurement techniques with high sensitivity and high dynamic range. Here, we present an online, real-time measurement of trace contaminants in the cleaning stream of a biogas plant with a Vocus proton-transfer-reaction mass spectrometer (Vocus-PTR-MS). We identified more than 300 Volatile Organic Compounds (VOCs) in the raw biogas in the 30–400 m/z range, with total concentrations varying in 54.6–548.3 ppmv on different days. Among these, more than 30 were Volatile Organic Sulfur Compounds (VOSCs), with total concentration in the range of 0.3–9.3 ppmv during measurement days and dimethyl sulfide (C2H6S, DMS) was the most dominant VOSC. Typical biogas tracers were also identified in the ambient air around the biogas plant at low ppbv levels. These results confirm that VOCUS-PTR-MS can be a rapid, scientific online tool of choice to monitor a biogas facility and, hence, shows excellent ability to characterize biogas production.

(Invited) Chemiresistive Water Quality Sensors: Challenges and Progress

Chemiresistors are solid state devices that change their electronic properties (more specifically, the resistance of a conductive thin film or percolation network) as a result of chemical interactions with their environment. They are a well-established and widely commercialized technology for gas or vapor sensor applications. The active layer may consist of metal oxides, polymers, nanomaterials or composites. In most cases, chemisorption or catalytic activity involving the analyte results in surface doping of the active layer, although other mechanisms (such as conductivity changes due to swelling) have also been reported. A significant part of the sensing literature is taken up by reports of ChemFETs, in which case the conductivity of the active layer can also be modulated by an applied gate voltage. Gate voltage modulation is helpful for establishing the sensing mechanism and - on occasion - for distinguishing multiple simultaneous target analytes. In most cases, however, the actual sensor operation occurs at zero gate voltage, thus reducing the ChemFET to a chemiresistor. [1] Gas sensors can be operated at high voltages and without shielding the contacts to the film from gas exposure, two simplifications that are not afforded to sensors operating in aqueous environments.Water quality sensors are a surprisingly underserved area of sensor applications.[2] Important chemical water quality parameters include pH, dissolved gases, common ions and a range of toxic trace contaminants which may be ionic or uncharged, inorganic or organic. All these water quality parameters are usually monitored using colorimetric sensors, electrochemical sensors and large lab-based instruments. None of these lend themselves to low maintenance, reagent free, low power continuous operation for online monitoring. In particular, colorimetric sensors need a resupply of reagents and electrochemical sensors require reference electrodes. Chemiresistors have the potential to eliminate all these disadvantages, but there has been slow progress in adapting them to aqueous analytes. They are simple and economical to manufacture, and can operate reagent-free and with low or no maintenance. Unlike electrochemical sensors they do not require reference electrodes. Challenges include the need to prevent electrical shorts through the aqueous medium and the need to keep the sensing voltage low enough to avoid electrochemical reactions at the sensor.We have built a chemiresistive sensing platform for aqueous media. The active sensor element consists of a percolation network of low-dimensional materials particles that form a conducting film, e.g. from carbon nanotubes, pencil trace, exfoliated graphene or MoS2. The first members of that platform were free chlorine sensors,[3-5] but we have also demonstrated pH sensitive films [6,7] and cation sensors.[8] While there are some challenges associated with expanding the range of accessible analytes,[9] we have recently expanded the applicability of our platform, in particular anions and cations that are commonly present as pollutants in surface and drinking water. Our sensors can be incorporated into a variety of systems and will also be suitable for online monitoring in remote and resource-poor locations.

Simultaneous removal of atrazine and heavy metal ions using sulfonated polymeric microspheres through an adsorptive filtration process: Insights into the synergistic and competitive adsorption

The combined pollution of surface water caused by organic and inorganic contaminants has become an environmental issue worthy of attention. Adsorption has been acknowledged as a practical and efficient water treatment process. However, the combined interactions between organic and inorganic pollutants on the adsorbents remain ambiguous. In this work, a novel multi-function sulfonated polyacrylate-divinylbenzene (PADVB) microspheres were rapidly and successfully prepared for removing organic pollutants and heavy metals ions from water. The theoretical maximum adsorption capacity of ATZ and Pb(II) by sulfonated PADVB was calculated as 280 mg g −1 and 163 mg g −1 , respectively. Additionally, dynamic adsorption based on an adsorptive-filtration reactor combined with in-situ regeneration was equipped, which proved to be effective and practical for the removal of combined pollution of trace contaminants from natural water. The simultaneous adsorption of ATZ and heavy metal ions could be attributed to the combined effects of multiple adsorption mechanisms, such as electrostatic attraction , complexation, Bronsted acid-base interaction, hydrogen bonds, and π-π interactions. Besides, the complexation between ATZ and heavy metal ions was confirmed by batch adsorption experiments and multiple characterization techniques, which play an important role in the synergistic interactions. In the binary adsorption systems, the heavy metal ions acted as a connector between ATZ and the surface of the microspheres through complexation, which could partly offset the competition of adsorptive binding sites. This work provided a promising adsorptive-filtration reactor to recycle and reuse powder adsorbent for solving the trace-level combined pollution in the environmental water and expanded the insights of adsorptive behaviours between organic pollutants and heavy metal ions.

Assessment of physicochemical parameters and heavy metals contamination in Korle and Kpeshie Lagoons, Ghana

Abstract. Clottey CA, Nukpezah D, Koranteng SS, Darko DA. 2021. Assessment of physicochemical parameters and heavy metals contamination in Korle and Kpeshie Lagoons, Ghana. Indo Pac J Ocean Life 6: 36-50. Lagoons are highly productive coastal systems that could provide natural services to the surrounding ecosystem; however, their pollutions cause adverse changes in their natural environment. Korle and Kpeshie Lagoons in Ghana receive waste from industries and municipal sewage. Controlling and monitoring contaminants in these systems is very important to environmental protection. This study examined the presence of heavy metals (arsenic, chromium, copper, cadmium, lead, and zinc) in sediments, crabs (Callinectes amnicola), and fish (Sarotherodon melanotheron) at Kpeshie and Korle Lagoons. Although lagoons are highly productive coastal systems that offer ecosystem services, their pollution has a negative impact on the surrounding environment. Municipal sewage and industrial waste are dumped into Ghana's Korle and Kpeshie Lagoons. Contaminant monitoring and control in these systems are crucial for environmental protection. The study compared the concentrations of the heavy metals (arsenic, cadmium, copper, chromium, lead, and zinc) in sediments, crabs (C. amnicola), and fish (S. melanotheron) at Kpeshie and Korle Lagoons to the environmental standards set by international organizations like the WHO and US EPA. The sediments from the Korle and Kpeshie Lagoons had traces of contamination in the following metal concentrations in S. melanotheron: cadmium, copper, zinc, lead, chromium, and arsenic, in that order: As, 0.397 ± 0.07; Cd, 1.10 ± 1.31; Pb, 1.227 ± 5.77; Cu, 3.494 ± 4.56; Cr, 5.895 ± 9.76; Zn, 23.225 ± 10.93, and in C. amnicola: As, 0.288 ± 0.07 mgkg-1; Cd, 4.60 ± 2.69 mgkg-1; Cr, 39.521 ± 55.89 mgkg-1; Cu, 31.085 ± 16.26 mgkg-1; Pb, 10.902 ± 12.95 mgkg-1; Zn, 36.042 ± 17.8 mgkg-1. The sediments are severely polluted with Cd and Pb, according to pollution indices like pollution load index (PLI), contamination factor (Cf), and potential ecological risk index (RI). The FAO/WHO-allowable limit for cadmium, chromium, and lead was exceeded in C. amnicola and S. melanotheron. Consumption of C. amnicola and S. melanotheron does not appear to pose a potential non-carcinogenic health risk on an individual's daily basis. The estimated target hazard quotient (THQ) in Kpeshie Lagoon of Cd, Cr, and Pb of the fishery investigated was less than 1.

Optically Transparent Polydimethylsiloxane-Ethylene Oxide-Propylene Oxide Multiblock Copolymers Crosslinked with Isocyanurates as Organic Compound Sorbents.

New crosslinked (polydimethylsiloxane-ethylene-propylene oxide)-polyisocyanurate multiblock copolymers (MBCs) were synthesized, and their supramolecular structure and sorption characteristics were studied. It was found that the interaction of PPEG and D4 leads to polyaddition of D4 initiated by potassium-alcoholate groups. The use of the amphiphilic silica derivatives associated in an oligomeric medium (ASiPs) leads to structuring of the MBC due to the transetherification reaction of the terminal silanol groups of the MBC with ASiPs. It was established that the supramolecular structure of an MBC is built according to the “core-shell” structure. The obtained polymers were tested as sorbents for the development of new methods for the concentration and determination of inorganic compounds. The efficiency of sorption of reagents increased with an increase in the “thickness” of the polydimethylsiloxane component of the “shell” and with a decrease in the size of the polyisocyanurate “core”. The use of the obtained polymers as adsorbents of organic reagents is promising for increasing the efficiency of field methods of chemical testing and inorganic analysis, including the determination of the elemental composition and the detection of traces of contamination.