Development of a novel DGT passive sampler for measuring polycyclic aromatic hydrocarbons in aquatic systems.

Polycyclic aromatic hydrocarbons (PAHs) are priority pollutants and need to be measured reliably in waters and other media, to understand their sources, fate, behaviour and to meet regulatory monitoring requirements. Conventional water sampling requires large water volumes, time-consuming pre-concentration and clean-up and is prone to analyte loss or contamination. Here, for the first time, we developed and validated a novel diffusive gradients in thin-films (DGT) passive sampler for PAHs. Based on the well-known DGT principles, the sampler pre-concentrates PAHs with typical deployment times of days/weeks, with minimal sample handling. For the first time, DGT holding devices made of metal and suitable for sampling hydrophobic organic compounds were designed and tested. They minimize sorption and sampling lag times. Following tests on different binding layer resins, a MIP-DGT was preferred - the first time applying MIP for PAHs. It samples PAHs independent of pH (3.9 -8.1), ionic strength (0.01 -0.5 M) and dissolved organic matter < 20 mg L-1, making it suitable for applications across a wide range of environments. Field trials in river water and wastewater demonstrated that DGT is a convenient and reliable tool for monitoring labile PAHs, readily achieving quantitative detection of environmental levels (sub-ng and ng/L range) when coupled with conventional GC-MS or HPLC. ENVIRONMENTAL IMPLICATIONS: PAHs are carcinogenic and genotoxic compounds. They are environmentally ubiquitous and must be monitored in waters and other media. This study successfully developed a new DGT passive sampler for reliable in situ time-integrated measurements of PAHs in waters at the ng/L level. This is the first time to use passive samplers for accurate measurements of hydrophobic organic contaminants in aquatic systems without calibration, a big step forward in monitoring PAHs. The application of this new sampler will enhance our understanding of the sources, fate, behavior and ecotoxicology of PAHs, enabling improved environmental risk assessment and management of these compounds.

Engineering the pore environment of antiparallel stacked covalent organic frameworks for capture of iodine pollutants.

Radioiodine capture from nuclear fuel waste and contaminated water sources is of enormous environmental importance, but remains technically challenging. Herein, we demonstrate robust covalent organic frameworks (COFs) with antiparallel stacked structures, excellent radiation resistance, and high binding affinities toward I2, CH3I, and I3- under various conditions. A neutral framework (ACOF-1) achieves a high affinity through the cooperative functions of pyridine-N and hydrazine groups from antiparallel stacking layers, resulting in a high capacity of ~2.16 g/g for I2 and ~0.74 g/g for CH3I at 25 °C under dynamic adsorption conditions. Subsequently, post-synthetic methylation of ACOF-1 converted pyridine-N sites to cationic pyridinium moieties, yielding a cationic framework (namely ACOF-1R) with enhanced capacity for triiodide ion capture from contaminated water. ACOF-1R can rapidly decontaminate iodine polluted groundwater to drinking levels with a high uptake capacity of ~4.46 g/g established through column breakthrough tests. The cooperative functions of specific binding moieties make ACOF-1 and ACOF-1R promising adsorbents for radioiodine pollutants treatment under practical conditions.

Development and validation of an in situ high-resolution technique for measuring antibiotics in sediments.

Important biogeochemical processes occur in sediments at fine scales. Sampling techniques capable of yielding information with high resolution are therefore needed to investigate chemical distributions and fluxes and to elucidate key processes affecting chemical fates. In this study, a high-resolution diffusive gradients in thin-films (DGT) technique was systematically developed and tested in a controlled sediment system to measure organic contaminants, antibiotics, for the first time. The DGT probe was used to resolve compound distributions at the mm scale. It also reflected the fluxes from the sediment pore-water and remobilization from the solid phase, providing more dynamic information. Through the fine scale detection, a reduction of re-supply was observed over time, which was concentration and location dependent. Compared to the Rhizon sampling method, antibiotic concentrations obtained by DGT probes were less than the pore-water concentrations, as DGT measures the labile fraction of the compounds. The DGT probe was also tested on an intact sediment core sampled from a lake in China and used to measure the distribution of labile antibiotics with depth in the core at the mm scale. ENVIRONMENTAL IMPLICATION: The abuse of antibiotics and widespread of their residues influences the ecosystem, induces the generation of super-bacteria, and finally poses threat to human health. Sediments adsorbs pollutants from the aquatic environment, while may also release them back to the environment. We systematically developed DGT probe approach for measuring antibiotics in sediment in situ in high resolving power, it provides information at fine scale to help us investigate biogeochemical processes take place in sediment and sediment-water interface.

Evaluation and Application of a Novel Diffusive Gradients in Thin-Films Technique for In Situ Monitoring of Glucocorticoids in Natural Waters.

The potential environmental risks of glucocorticoids (GCs) have attracted attention in the past few decades. In this study, a novel diffusive gradients in thin-films (DGT) device and analytical technique based on the second generation of polar enhanced phase (PEP-2), PEP-2-DGT, were developed for sampling and quantifying natural and synthetic GCs in aquatic systems. The capacity of PEP-2 gels for accumulating all target compounds was >600 µg per disc, sufficient for long-term passive sampling of selected GCs, even in wastewaters. Systematic tests were carried out to verify the application of DGT in natural waters and wastewaters. The performance of PEP-2-DGT devices was independent (CDGT/Csoln was in the acceptable range of 0.9-1.1) of a wide range of environmental conditions: ionic strength (0.001-0.5 mol L-1), dissolved organic matter (0-20 mg L-1), and pH (3.06-9.02). It was tested for various diffusive layer thicknesses (0.565-2.065 mm) and different deployment times (10-168 h). Diffusion coefficients (D) of selected GCs through an agarose-based diffusive gel were determined for the first time (3.80-4.85 × 10-6 cm-2 s -1 at 25 °C). Linear correlations between D and log Kow were established for three groups of target GCs (R2 = 0.96-0.99). This could enable prediction of D values for other GCs with similar structures in the future, which will help for rapid screening and emergency monitoring. Concentrations and distribution patterns of analytes obtained by PEP-2-DGT devices in five rivers after 7- and 14-day deployments were in accordance with those measured from grab samples, with total GC concentrations ranging from 7 to 27 ng L-1 at all sampling sites, confirming the reliability and robustness of the DGT devices for monitoring GCs in natural waters. The development of the new DGT technique will help improve understanding of the behavior and fate of these compounds in the aquatic environments.

Assessing the Impact of Atrazine on the Availability of Arsenic in Soils Using DGT Technique.

Arsenic (As) has been observed to co-exist with atrazine (ATR) in soils worldwide. ATR, as an organic chemical, may affect the availability of As and further influence its uptake by organisms. Here we used a novel passive sampling technique, DGT (diffusive gradients in thin-films), to compare with other two conventional sampling approaches (soil solution extraction and 'Olsen As' measurement) to investigate the influence of ATR addition (normal recommended level and contaminated level) on the availability of As in soils, to further interpret the potential risk of As in soil environment. The effect of adding ATR on the behaviour of As in soils was limited. When the concentration of ATR was much higher, the availability of As in soils was supressed, the labile pool size was also affected, but the R value did not change much. The properties of the soils also played an important role by affecting the states of the compounds.