Performance of a passive sampler for the determination of time averaged concentrations of nitrate and phosphate in water

Innovative receiving phase for Chemcatcher® passive sampler for phosphorus in the water environment: Calibration of sampling rate by water temperature and pH

Passive sampling is a technique for monitoring orthophosphate (PO4-P) in the water environment. Compared with traditional grab sampling followed by PO4-P quantification, kinetic-type passive samplers such as Chemcatcher® express representative concentrations of PO4-P as time-weighted average concentrations (CTWA). They can also potentially evaluate much lower PO4-P concentrations, but the available receiving phases of Chemcatcher® used for PO4-P were extremely limited. We developed a new receiving phase, the PSfZS sheet, comprising a zirconium sulfate-surfactant micelle mesostructure and polysulfone matrix. We examined its performance in terms of PO4-P sorption characteristics, PO4-P selectivity, and PO4-P sampling rate (Rs). Its capacity was adequate (12.0 μg-P/cm2) and selectivity for PO4-P uptake was good. The Rs for PO4-P increased with increasing water temperature (8.1-29.1 °C) and decreasing pH (4.1-9.7) in a laboratory calibration, and ranged from 5.27 × 10-2 L/d to 1.66 × 10-1 L/d. We placed the samplers in a municipal wastewater treatment plant, a shallow eutrophic lake, and an oligotrophic caldera lake. The Rs in the deployment sites was calibrated by monitored water temperature and pH. The estimated CTWA of PO4-P in the municipal wastewater treatment plant was similar to the averaged concentration of soluble reactive phosphorus determined by multiple grab samplings. In the lake deployments, we found that the new sampler can quantify CTWA values of PO4-P below 10 μg/L, and thus it provides more technical monitoring options and contributes to the conservation and management of the water environment.

River network alteration of C-N-P dynamics in a mesoscale agricultural catchment

The majority of freshwater ecosystems worldwide suffer from eutrophication, particularly because of agriculture-derived nutrient sources. In the European Union, a discrepancy exists between the scale of regulatory assessment and the size of research catchments. The Water Framework Directive sets water quality objectives at the mesoscale (50-500 km²), a scale at which both hillslope and in-stream processes influence carbon (C), nitrogen (N) and phosphorus (P) dynamics. Conversely, research catchments focus on headwaters to investigate hillslope processes while minimising the influence of river processes on C-N-P dynamics. Because hillslope and river processes have common hydro-climatic drivers, the relative influence of each on C-N-P dynamics is difficult to disentangle at the mesoscale. In the present study, we used repeated synoptic sampling throughout the river network of a 300 km² intensively farmed catchment, spatial stochastic modelling and mass balance calculations to analyse this mesoscale conundrum. The main objective was to quantify how river processes altered C-N-P hydrochemical dynamics in different flow, concentration and temperature conditions. Our results show that flow was the main control of alterations of C-N-P dynamics in the river network, while temperature and source concentration had little or no influence. The influence of river processes peaked during low flow, with up to 50% of dissolved organic carbon (DOC) production, up to 100% of nitrate (NO₃) retention and up to 50% of total phosphorus (TP) retention. Despite high percentages of river processes at low flow, their influence on annual loads was low for NO₃ (median of -10%) and DOC (median of +25%) but too variable to draw conclusions for TP. Because of the differing river alteration rates among carbon and nutrients, stoichiometric ratios varied greatly from headwaters to the outlet, especially during the eutrophication-sensitive low-flow season.

Spinel Cobalt Ferrite Nanoparticles for Sensing Phosphate Ions in Aqueous Media and Biological Samples

Phosphate ions perform a variety of functions in metabolic processes and are essential for all living organisms. The determination of the concentration of phosphate ions is useful in clinical diagnosis of various diseases as an inadequate phosphate level could lead to many health problems. In the search for a cost-effective method of fast monitoring, we investigated the use of cobalt ferrite nanoparticles (CoFeNPs) in the selective recognition of phosphate ions dissolved in aqueous media and more complex samples, such as human blood serum. We prepared these NPs by a chemical coprecipitation route and subjected them to annealing at 600 °C for 1 h. The successful formation of the NPs was confirmed by Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and hysteresis loop measurements. The NPs exhibited a ferrimagnetic behavior, a spinel-type crystalline structure, and hexagonal shape in the nanoscale range. We demonstrated that CoFeNPs containing immobilized fluorescent-labeled single-chain DNA (ssDNA*) probes can be applied for the fast selective detection of phosphate ions dissolved in a liquid medium. We have explored the fact that phosphate groups can displace ssDNA* probes attached to the nanoparticles, therefore causing a perceptible change in the fluorescence signal of the supernatant liquid. This detection method has been tested for the sensing of phosphate ions present both in aqueous solutions and in biological samples, with excellent selectivity and a low limit of detection (∼1.75 nM).

Using high-frequency phosphorus monitoring for water quality management: a case study of the upper River Itchen, UK

Increased concentrations of phosphorus (P) in riverine systems lead to eutrophication and can contribute to other environmental effects. Chalk rivers are known to be particularly sensitive to elevated P levels. We used high-frequency (daily) automatic water sampling at five distinct locations in the upper River Itchen (Hampshire, UK) between May 2016 and June 2017 to identify the main P species (including filterable reactive phosphorus, total filterable phosphorus, total phosphorus and total particulate phosphorus) present and how these varied temporally. Our filterable reactive phosphorus (considered the biologically available fraction) data were compared with the available Environment Agency total reactive phosphorus (TRP) values over the same sampling period. Over the trial, the profiles of the P fractions were complex; the major fraction was total particulate phosphorus with the mean percentage value ranging between 69 and 82% of the total P present. Sources were likely to be attributable to wash off from agricultural activities. At all sites, the FRP and Environment Agency TRP mean concentrations over the study were comparable. However, there were a number of extended time periods (1 to 2 weeks) where the mean FRP concentration (e.g. 0.62 mg L^-1) exceeded the existing regulatory values (giving a poor ecological status) for this type of river. Often, these exceedances were missed by the limited regulatory monitoring procedures undertaken by the Environment Agency. There is evidence that these spikes of elevated concentrations of P may have a biological impact on benthic invertebrate (e.g. blue-winged olive mayfly) communities that exist in these ecologically sensitive chalk streams. Further research is required to assess the ecological impact of P and how this might have implications for the development of future environmental regulations.

Methods for Sample Collection, Storage, and Analysis of Freshwater Phosphorus

Although phosphorus (P) is an essential nutrient for biological productivity, it can cause freshwater degradation when present at fairly low concentrations. Monitoring studies using continuous sampling is crucial for documenting P dynamics in freshwater ecosystems and to reduce the risk of eutrophication. Despite literature updates of developments of the analytical methods for measurement of P species in natural waters, there has been no comprehensive review addressing freshwater sample collection, sample preparation, and sample treatment to fractionate and characterize different forms of P. Therefore, this paper aims to elaborate the different techniques for freshwater sampling and to introduce alternative laboratory methods for sample preservation and P fractionation. The advantages and disadvantages of various sampling techniques, including the traditional manual and the recently developed automatic and passive methods, are presented to highlight the importance of collecting representative freshwater samples. Furthermore, we provide suggestions for sample pretreatment, including filtration, transportation, and storage steps to minimize microbial activity and to maximize the accuracy of measurement of various P fractions. Finally, the most common laboratory methods to measure dissolved and particulate as well as the organic and inorganic freshwater P fractions are efficiently provided. Using this guide, a comprehensive monitoring program of P dynamics in freshwater ecosystems can be developed and applied to improve water quality, particularly of P-rich freshwaters.

Highly selective and sensitive phosphate anion sensors based on AlGaN/GaN high electron mobility transistors functionalized by ion imprinted polymer

A novel ion-imprinted electrochemical sensor based on AlGaN/GaN high electron mobility transistors (HEMTs) was developed to detect trace amounts of phosphate anion. This sensor combined the advantages of the ion sensitivity of AlGaN/GaN HEMTs and specific recognition of ion imprinted polymers. The current response showed that the fabricated sensor is highly sensitive and selective to phosphate anions. The current change exhibited approximate linear dependence for phosphate concentration from 0.02 mg L⁻¹ to 2 mg L⁻¹, the sensitivity and detection limit of the sensor is 3.191 μA/mg L⁻¹ and 1.97 μg L⁻¹, respectively. The results indicated that this AlGaN/GaN HEMT-based electrochemical sensor has the potential applications on phosphate anion detection.