ABSTRACT Field determination of labile heavy metal(loid)s (HM) is essential for environmental risk assessment. The diffusive gradients in thin film (DGT) technique, though promising for quantifying labile HMs, remains largely limited to laboratory settings for unsaturated soils. This study optimized DGT parameters based on the CDGT-W index (HM accumulation normalized to soil weight in the device cavity) to develop a field method for measuring copper (Cu) and lead (Pb) in soils. Results showed that CDGT-W was minimally affected by pre-equilibration time, variably influenced by soil particle size depending on the HM-soil system, and increased with environmental temperature. Consequently, a 15-min pre-equilibration time without soil sieving was recommended, with ambient temperature recorded in situ. The method was validated using contaminated soils from mining areas, comparing field-measured CDGT-W with laboratory DGT measurements and CaCl2 extraction. Field-measured values positively correlated with both laboratory CDGT-W and CaCl2-extractable concentrations. These findings demonstrate that the refined DGT approach enables effective field assessment of labile Cu and Pb in unsaturated polluted soils, potentially broadening DGT applications in soil environmental monitoring.

Selective sampling and in-situ detection of As(III) and As(V) in groundwater by diffusive gradients in thin-films technique.

Long-term organic fertilization reduces cadmium bioavailability via enhanced binding to organic fractions and Fe-bearing minerals.

This study developed a novel approach to visualize in situ ammonium (NH4+) concentrations in soils at millimeter resolution using the Diffusive Gradients in Thin Films Technique (DGT). Available (diffusible) NH4+ is captured with a zeolite 13X binding gel and visualized through two staining gels utilizing Berthelot color reagents. The NH4+ accumulation is linear up to 3 μmol of NH4+ cm-2; however, the color intensity remains linear only up to 0.06 μmol cm-2, beyond which the color decreases. An adapted method achieves linearity up to 10-fold higher concentration at the expense of sensitivity. A linear relationship was found between NH4+ porewater concentrations and color intensity, with 1.6-fold variation in slope among contrasting soils, reflecting cation competition and local buffering effects. The spatial resolution is about 3 mm, which is highly dependent on the deployment or staining times. This technique was field-tested, identifying NH4+ depth profiles and local heterogeneities in wheat rhizosphere after fertilization.

Diffusive gradients in thin films technique based on porous nitrogen self-doped biochar-binding phase for passive sampling of chloroquine: Featuring a high-capacity binding phase and investigating the effect of microplastics

Copper labile species are involved in oxidation reactions in wine, thus affecting its quality and long-term stability. Consequently, the development of analytical methods capable of assessing the Cu labile fraction in wine is highly important. In this work, we developed an analytical methodology based on the use of the Diffusive Gradient in Thin-films (DGT) technique as passive sampling tool for DGT-labile species, followed by Cu determination using graphite furnace atomic absorption spectrometry (GF-AAS). DGT devices with Chelex resin gel and two types of diffusive gels, open pore (OP) and restricted pore (RP), were used in the experiments. The effective diffusion coefficients of Cu, determined in 12 % ethanol in water solution at 22 °C and pH 3.0, were (5.15 ± 0.28) × 10 −6 cm 2 s −1 for the OP gel and (4.47 ± 0.26) × 10 −6 cm 2 s −1 for the RP gel. Linearity assays for DGT in wine were evaluated over a 48-h deployment period, yielding determination coefficients of 0.9932 and 0.9867 for OP and RP, respectively. No significant differences were found for the Cu DGT-labile concentrations sampled using tools with OP or RP gels. The DGT-labile fraction of Cu in the seven analysed wine samples ranged from 7.0 to 33.1 μg L −1 , representing approximately 6.6 to 11.2 % of the total Cu concentration in the wine. By measuring Cu-labile species, producers in the winery sector can better control the Cu content in wine. • DGT passive sampling was applied to determine the labile fraction of Cu in wine. • Low pH typical to wine does not affect DGT analytical performance for Cu accumulation. • No difference was observed in the Cu DGT-labile concentration measured using OP and RP gels. • The effective diffusion coefficients of Cu in 12 % ethanol solution were determined. • The DGT-labile fraction of Cu ranged from 6.6 % to 11.2 % of the total Cu concentration.

Enhancing the prediction of arsenic bioavailability in soils with the diffusive gradient in thin film technique.

Active aluminum promoted copper uptake by Chinese cabbage grown in an acidic Cu-contaminated soil: A new insight with the diffusive gradients in thin-films technique (DGT)

Utilizing diffusive gradients in thin films technique for enhanced surveillance of drug abuse in two Chinese urban communities

Assessing the risk of metal-contaminated sediments under disturbed conditions is challenging due to the lack of methods that capture instant changes in metal bioavailability. Existing approaches provide inadequate understandings of the processes regulating metal bioavailability under nonequilibrium conditions. Experiments were conducted to improve our understanding of the metal bioavailability dynamics induced by sediment resuspension and subsequent redeposition (reequilibration). An isotopically modified bioassay, a novel stable isotope tracing technique, was used to measure metal bioavailability (assimilation rates) to clams within short time windows. Changes in metal partitioning were characterized by porewater analysis using in situ extraction and the diffusive gradients in thin-films technique. Results showed that sediment resuspension released metals into porewater, while reequilibration scavenged metals from the porewater. The assimilation rates of Ni, Cu, and Pb increased with the resuspension time, aligning with increasing porewater concentrations. Unexpectedly, during reequilibration, the metal assimilation rates did not decrease. The discrepancies between bioavailability to the clam and porewater extrapolations may be due to differing sustained conditions of metals in sediments. Overall, this study unveils the metal bioavailability dynamics in nonequilibrium sediments, which could not be accurately predicted relying solely on porewater analysis. Incorporating rapid bioassays to determine bioavailability offers a valuable tool for robust ecological risk assessment.

Trace elements (TEs) in anaerobic digestion (AD) are known to be essential for optimal biogas production, but inhibitive in excessive concentrations. However, the mechanisms of inhibition are not fully understood. The effects of the addition essential TEs (Co, Cu and Ni) and a non-essential TE (Cd) on the microbial community structure of AD were studied in lab-scale reactors, using total TE concentrations that ranged from 0 to 100 μM. Reactor performance was assessed by monitoring biogas production. The labile fraction of TEs (the most bioaccessible species) was determined by diffusive gradients in thin-films technique. Prokaryotic community composition was characterized through high throughput sequencing (HTS) targeting archaea and bacteria and qPCR to evaluate changes in methanogens and metal resistance genes. Only a minor fraction of added TEs was labile and it decreased over time, with Ni being the most labile. Although only a minor fraction of spiked concentration was labile, all TEs inhibited biogas production at the highest spiking concentration (100 μM), with higher inhibition observed for Cd and Ni. HTS and qPCR revealed changes, particularly in archaea, with reduced relative abundance at higher TE concentrations. Shifts in prokaryotic communities suggest alterations in AD metabolic pathways. High inhibition of biogas was linked to reduced diversity, dominance of the bacterial genus Klebsiella and changes in the ratio acetoclastic / hydrogenotrophic methanogens. This study addresses a research gap in understanding how TEs inhibit AD, and provides a strategy to improve TE dosing by monitoring the labile fraction of TEs to avoid overdosing.

Effect of biodegradable microplastics and Cd co-pollution on Cd bioavailability and plastisphere in soil-plant system

A novel binding gel for the DGT technique, containing biochar produced through the pyrolysis of wheat bran, was developed. The results of this study indicate that wheat bran biochar (WBBC) is a porous material with a surface area of 25 m2/g. The primary functional group on the surface of WBBC was identified as a carbonyl group, although some hydroxyl and imino groups were also detected. Furthermore, the findings demonstrate that the accumulation of Hg on WBBC was significantly influenced by an increase in ionic strength, particularly in NaCl solution, owing to Hg’s high affinity for chloride ions. The performance of the DGT with WBBC binding gel was also affected by solution pH, with the optimal pH for WBBC application falling within the range of 3–7. The diffusion coefficient of Hg, depending on the matrix environment, varied between 5.44 and 6.99 × 10−6 cm2/s. When applying the newly designed DGT technique to spiked samples of river water, an R value of 0.68 was achieved. The results of this work proved that modified DGT technique allows for a cost-effective analysis of Hg in natural waters with lower salinity, while retaining the fundamental properties of the binding gel incorporating a particulate adsorbent with anchored functional groups.Graphical

The occurrence of β-blocker drugs in aquatic environments worldwide has caused increasing attention to their threat to human health in recent years. It is essential to monitor these widely prescribed pharmaceuticals in natural waters and sediments, helping us investigate their potential risk to humans and ecosystems. In this study, a passive sampling technique, diffusive gradients in thin-films (DGT), was systematically developed for eight frequently detected β-blockers. The effective capacities of target compounds were large enough for the devices to deploy for several weeks. The uptake of all compounds was linearly correlated with deployment times during the 7-day laboratory experiment and agreed well with the theoretical line, except for several compounds (e.g., ATL) due to their relatively slow uptake rate. The performance of most compounds was independent of varying pH values and organic matter contents; only a few compounds were affected, while the application in high-salinity environments needs to be conducted with caution. Field deployments of DGT to detect β-blockers in situ in rivers and sediments proved that DGT is an effective tool to monitor β-blocker drugs and their fate in the natural aquatic environment, while DGT probes can provide information for us to investigate the biogeochemical processes occurred in sediment, especially at the sediment–water interface. This novel approach will help us understand the behaviour of β-blocker drugs in the aquatic environment, assess their risks, finally protect human health and maintain the sustainable development of the ecosystem.

A new simple index for characterizing the labile heavy metal concentration in soil by diffusive gradients in thin films technique

Development of diffusive gradients in thin-films technique for monitoring polycyclic aromatic hydrocarbons in coastal waters

A recyclable SERS-DGT device for in-situ sensing of sulfamethazine by Au@g-C3N4NS in water

Insight into the availability and desorption kinetics of Se and Cd in naturally-rich soils using diffusive gradients in thin-films technique

The transformation between Cr(III) and Cr(VI) occurs in Cr-contaminated soil, which can be regulated by root-soil interactions, under natural conditions. In situ investigation of the effectiveness of different reductants in reducing Cr(VI) to Cr(III), and thereby the reoccurrence risk in reduced Cr-contaminated soil, can improve the understanding of Cr biogeochemistry and toxicity. Traditional and high-resolution diffusive gradients in thin films (DGT) were used to measure Cr(VI) availability and rhizosphere effect controlling the chemical behaviors of Cr(VI) in the rice rhizosphere microdomain. The Cr(VI) concentration in the soil solution (Csoln) of the rhizosphere region varied according to the reductant type and followed the order: Molasses > CaS4 >Fe(II). Rice root activity increased the Csoln in the rhizosphere region by 2.16 μg/L, 1.90 μg/L, and 1.08 μg/L for Fe(II), CaS4, and Molasses treatments, respectively. The Cr(VI) concentration measured by DGT (CDGT) in the reduced Cr-contaminated soils increased from 0.96–1.17 μg/L in the bulk region to 1.23–1.76 μg/L in rhizosphere region. The variation in the effective concentration of Cr(VI) (CE) was similar to that of Csoln in the rice rhizosphere microdomain. Csoln accounted for 14.71–19.36% of the CE, further suggesting that bioavailable Cr(VI) mainly originated from the replenishment from the solid phase. The sequence of the average Cr(VI) flux in the reduced Cr-contaminated soil was Molasses, CaS4, and Fe(II). Except for Molasses, there was no obvious Cr(III) in Fe(II) and CaS4. For Fe(II), a higher phosphate flux in the rhizosphere microdomain hindered Cr(VI) uptake. High-resolution imaging provides a theoretical basis for the bioavailability evaluation and remediation of Cr-contaminated soil. Compared with CaS4 and Molasses, Fe(II) was the most effective reductant for remediating Cr-contaminated soils.

Bio-accessibility and mobilization dynamics of soil vanadium during a 48-year vegetation restoration in a vanadium titano-magnetite tailings reservoir