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This critical review explores the quantification, analysis, and detection of radionuclides in the environment using the diffusive gradients in thin films (DGT) technique. Radionuclides, unstable isotopes emitting ionising radiation, are present in the environment due to natural and anthropogenic sources for which concerns are raised about their impact on human health and ecosystems. DGT offers a unique passive sampling approach for understanding the behaviour of radionuclides and other trace elements. This review provides insights into method development, real case scenarios, advantages, limitations, and future perspectives of DGT in radionuclide analysis. In terms of method development, various isotopes have been analysed with varying significance based on origin, concentration, risks, and persistence. Notably, U, Th, Pu, Am, Cm, 99Tc, 226Ra, 137Cs, 134Cs, 232U, 237Np, and 152Eu have been measured, revealing their diverse roles in environmental radioactivity. Real case scenarios illustrate applications in uranium mining, water quality monitoring, and metal speciation studies, shedding light on mobility, bioavailability, and ecological impacts. DGT's advantages include in-situ monitoring, time-averaged mean concentrations, and comprehensive speciation insights. Challenges include potential influences from biofouling, temperature changes and specifically the possible degradation of the binding and diffuse layer due to ionising radiation in long term exposures. In addition, the distinction between fully labile free metal ions and partially labile metal-ligand complexes introduces a potential limitation in the DGT technique, hence being an opportunity for future studies. Looking forward, DGT is expected to contribute to radiation dose modelling, environmental risk assessment, and water quality monitoring, with ongoing developments enhancing its utility and accuracy. [ABSTRACT FROM AUTHOR]

The purpose of this review was to survey the recent applications of the diffusive gradients in thin films (DGT) technique in the assessment of mobility and bioavailability of nutrients and potentially toxic elements (PTEs) in agricultural soil. Many studies compared the capabilities of the DGT technique with those of classical soil chemical extractants used in single or sequential procedures to predict nutrients and PTE bioavailability to crops. In most of the published works, the DGT technique was reported to be superior to the conventional chemical extraction and fractionation methods in obtaining significant correlations with the metals and metalloids accumulated in crops. In the domain of nutrient bioavailability assessment, DGT-based studies focused mainly on phosphorous and selenium labile fraction measurement, but potassium, manganese, and nitrogen were also studied using the DGT tool. Different DGT configurations are reported, using binding and diffusive layers specific for certain analytes (Hg, P, and Se) or gels with wider applicability, such as Chelex-based binding gels for metal cations and ferrihydrite-based hydrogels for oxyanions. Overall, the literature demonstrates that the DGT technique is relevant for the evaluation of metal and nutrient bioavailability to crops, due to its capacity to mimic the plant root uptake process, which justifies future improvement efforts. [ABSTRACT FROM AUTHOR]

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In recent years, the eutrophication of lakes has accelerated in cold arid regions; the release of nutrients from sediments is an important contributor. The sequential extraction method, high-resolution peeper (HR-Peeper), and diffusive gradients in thin films (DGT) techniques were used to study the occurrence characteristics, release risk, and release mechanism of phosphorus (P) at the sediment–water interface (SWI) of Ulanor Wetland in the Hulun Lake Basin, Inner Mongolia, China. The mean total P concentration in overlying water was lower in August than that in May. Dissolved organic P (DOP) or particulate P (PP) was the main form of P in the overlying water. PP dominates in May and DOP in August. Refractory P was the main form of P in sediments. The concentrations of soluble reactive P and DGT-active P in the pore water of the sediment column were higher than those in the overlying water, and the concentrations were higher in August than those in May. Release of P in the wetland sediments occurred during the non-frozen seasons, with a higher risk in August than in May. The good linear correlation between dissolved P, Fe, and Mn in the DGT profiles verified their co-release due to the anaerobic reduction of Fe/Mn oxides. Moreover, alkaline sediments are also conducive to the release of sediment P. This study can provide data and theoretical support for eutrophication control in Ulanor Wetland and other similar water bodies in cold and arid regions. [ABSTRACT FROM AUTHOR]

The pollution of heavy metals (HMs) in agricultural soils profoundly threatens national food safety, and the mobility and environmental behaviors of HMs are closely implicated in crop safety. Here, we assessed the pollution level and mobility of ten HMs and explored their environmental behaviors in the soils of three different land uses from a main crop production zone in eastern China. The concentrations of HMs in the soils were higher in the farmland than the woodland and wasteland, and Cd showed a relatively higher pollution and ecological risk levels compared to other metals. Cadmium was dominated by the reducible (41%) and exchangeable (23%) fractions, and the rest of HMs were mainly in the residual fraction (> 60%). The significant correlation between the exchangeable and DGT-labile Cd indicates relatively higher mobility of Cd in the soils. Soil pH, organic matters and mineral elements had significant correlation with the exchangeable and reducible fractions of most of the HMs (e.g., Cd, Co, Mn, Ni, Pb and V; p < 0.05), indicating their good predictors of the HMs mobility. However, this was not the case for the DGT-labile fraction, which suggests a marked difference in the controlling mechanisms of the mobility versus potential bioavailability of HMs in the soils. The results of this study indicate that both the chemically extracted fractions and the bioavailable fractions of HMs need be considered when effectively assessing the safety of agricultural soils. [ABSTRACT FROM AUTHOR]

Heavy metal dynamics at the sediment-water interface (SWI) has attracted plenty of attention due to their meticulous depiction for metal sorption-release processes. However, little is known about their concentration, migration and release characteristics underneath the ice, especially at the millimeter scale. Here we investigated dynamics of labile As, Cd, Cu, Mn, Pb and Zn by the diffusive gradients in thin-films (DGT) technique during ice-covered and ice-free periods in the Lake Xingkai basin. The concentrations of metals were relatively high at the SWI and ranged for As: 0.001~13.42 jmg L-1, Cd: 0.01~0.45 mg L-1, Cu: 0.001~2.75 mg L-1, Mn: 5.31~2958.29 mg L-1, Pb: 0.06~1.43 mg L-1, and Zn: 2.92~112.96 mg L-1. Particularly, concentration of Mn was extremely higher than other studies, possibly due to diagenetic process. Labile concentrations of heavy metals in January were significantly lower than those in May, suggesting that elevated temperatures lead to the release of heavy metals from the sediment to the overlying water. Based on the Fick's first law, the diffusive fluxes as a source of Mn (413.82-1163.25 mg-m-2d-1) and As (3.53 -8.12 mg-m-2d-1) indicated that heavy metals were released from sediments to the overlying water. While the diffusive fluxes as a sink of Zn (-1.80-(-2.36) mg-m-2-d-1) and Pb (-0.02-(-0.46) mg-m-2-d-1) to sediments. Redundancy Analysis (RDA) revealed that the main factors influencing the heavy metal migration were dissolved oxygen (45.6% of total explanation, P=0.01) in January, and water temperature (52.9%, P=0.006) in May. This study extends theoretical scope for understanding metal migration and release process, and provides valuable suggestions for lake management during the freezing period. [ABSTRACT FROM AUTHOR]

Heavy metal dynamics at the sediment-water interface (SWI) has attracted plenty of attention due to their meticulous depiction for metal sorption-release processes. However, little is known about their concentration, migration and release characteristics underneath the ice, especially at the millimeter scale. Here we investigated dynamics of labile As, Cd, Cu, Mn, Pb and Zn by the diffusive gradients in thin-films (DGT) technique during ice-covered and ice-free periods in the Lake Xingkai basin. The concentrations of metals were relatively high at the SWI and ranged for As: 0.001~13.42 μg L−1, Cd: 0.01~0.45 μg L−1, Cu: 0.001~2.75 μg L−1, Mn: 5.31~2958.29 μg L−1, Pb: 0.06~1.43 μg L−1, and Zn: 2.92~112.96 μg L−1. Particularly, concentration of Mn was extremely higher than other studies, possibly due to diagenetic process. Labile concentrations of heavy metals in January were significantly lower than those in May, suggesting that elevated temperatures lead to the release of heavy metals from the sediment to the overlying water. Based on the Fick’s first law, the diffusive fluxes as a source of Mn (413.82-1163.25 mg·m-2·d-1) and As (3.53 -8.12 mg·m-2·d-1) indicated that heavy metals were released from sediments to the overlying water. While the diffusive fluxes as a sink of Zn (-1.80-(-2.36) mg·m-2·d-1) and Pb (-0.02-(-0.46) mg·m-2·d-1) to sediments. Redundancy Analysis (RDA) revealed that the main factors influencing the heavy metal migration were dissolved oxygen (45.6% of total explanation, P=0.01) in January, and water temperature (52.9%, P=0.006) in May. This study extends theoretical scope for understanding metal migration and release process, and provides valuable suggestions for lake management during the freezing period.

Mercury (Hg) is a toxic, non-essential element for living organisms, frequently present in high concentrations in soils from industrial areas. The total, dissolved, and labile Hg concentrations in garden soils and their accumulation in edible vegetables (onion, garlic, lettuce, and parsley) grown on contaminated soils in localities situated a former mining area were evaluated. The labile Hg fraction was estimated by diffusive gradient in thin films (DGT). The soil-to-vegetable transfer factors, as well as the health risk by exposure to Hg, were calculated based on the labile Hg concentration in soil. The total Hg concentration in soil varied widely (0.11–3.77 mg kg−1), Hg in soil solution ranged between 2.14 and 20.2 μg L−1 and labile Hg between 1.13 and 18.6 μg L−1. About 36–96% (84% on average) of the Hg concentration in soil solution was found in labile form. Multivariate analysis revealed significant correlations between the labile Hg concentration in soil and Hg accumulated in vegetables. The hazard indices showed that, although the study area is affected by legacy pollution, exposure to soil and consumption of locally grown vegetables do not pose health risks. [ABSTRACT FROM AUTHOR]

Trace elements can have a wide variety of effects on microbial populations and their function in the aquatic environment. However, specific impacts on chemical and biological processes are often difficult to unravel, due to the wide variety of chemical species involved and interactions between different elemental cycles. A replicated mesocosm experiment was used to test the effect of increasing copper concentrations, i.e., from 6 mg kg−1 to 30 and 120 mg kg−1, on nitrogen cycling in a freshwater sediment under laboratory conditions. Nitrous oxide emissions from the treated sediments were measured over three consecutive 24 h periods. This was followed by measurements of iron, manganese, copper and mineral nitrogen species (nitrate and ammonium) mobilisation in the sediments using the diffusive gradients in thin films (DGT) and diffusive equilibria in thin films (DET) techniques and sequential extractions. Increasing copper concentrations are shown to have resulted in significantly reduced nitrate formation near the sediment–water interface and increased nitrous oxide emissions from the sediment overall. The concomitant mobilisation and sequestration of iron with ammonium in the sediment with the highest Cu treatment strongly imply links between the biogeochemical cycles of the two elements. Modest Cu contamination was shown to affect the nitrogen cycle in the tested freshwater sediment, which suggests that even relatively small loads of the metal in fresh watercourses can exert an influence on nutrient loads and greenhouse gas emissions from these environments. [ABSTRACT FROM AUTHOR]

Triazines are frequently detected in nature water and agricultural soils worldwide. They are considered harmful to plants, animals, and the human health. In this study, diffusive gradients in thin films (DGT) method was developed for the assessment of several triazines. DGT device was used for the in situ measurement of atrazine in a pesticide factory and obtained reliable data. The atrazine concentrations measured by DGT, and solvent extraction method was in a constant ratio. The DIFS model was coupled with DGT technique to study the desorption kinetics of atrazine in four kinds of different soils. The yellow–brown soil was more inclined to adsorb atrazine than other three soils. 2_D DIFS model was used to obtain the partition coefficient for labile atrazine (Kdl), the values of the response time (Tc), and desorption/adsorption rates (k1 and k−1). The yellow–brown soil has a larger labile pool size, and a faster resupply speed of atrazine. The 1_D DIFS model was used to simulate the profiles of atrazine concentrations in soil solution and solid phase. The results show that the desorption of atrazine in soil was limited by kinetic limitation at short time, and was limited by the solid phase reservoir at long time. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of the mobility of both nitrogen (N) and phosphorus (P) and the inter-relationships between P, N, and iron (Fe) in sediments is important for controlling the "internal loadings" of nutrients in lakes. In this research, diffusive gradients in thin film (DGT) assemblies with binding layers (ZrO-AT, chelex, and ZrO) were designed for PO4-P, Fe, ammonium (NH4-N), and nitrate (NO3-N) at sediment/water interface (SWI) in Western Lake Taihu (China). The biogeochemical processes of N and P related to the physicochemical properties, the dynamic P transfer, the distribution characteristics of P microniches, and the estimation of the release risks in sediments in Western Lake Taihu were simultaneously revealed by the passive sampling technique-DGT with the high spatial resolutions (millimeter and sub-millimeter). Based on DGT concentration (CDGT) related to physicochemical properties in sediments, (1) P biogeochemical reactions included P release from Fe-bound P during Fe reduction, algae biomass decomposition, and phosphatase enzyme activity increased by NH4-N; (2) denitrification and dissimilatory nitrate reduction to ammonium (DNRA) led to exchangeable ammonium (NH4ex) enrichment and NH4-N release; anammox depleted NH4-N transfer; organic matter (OM) mineralization favored NH4-N release; and (3) aerobic nitrification led to NO3-N remobilization; denitrification and DNRA reduced NO3-N release. Redox status, OM, Fe, aluminum, or calcium influenced mobilization of nutrients. The numerical model of DGT-induced fluxes in sediments was used for dynamic P transfers with resupply types ("slow" ~ "fast") controlled by labile P pool, resupply constant, response time, and Dspt rate. The formation of P microniches in two dimensions was revealed. Sediment P release risk index (0.49 ~ 36.85 [lg (nmol cm−3 d−1)]) with "light" ~ "high" risks and diffusive fluxes across SWI (µg m−2 d−1) of 15.0 ~ 639 (PO4-P), − 1403 ~ 5010 (NH4-N), and − 1395 ~ 149 (NO3-N) were derived and lake management strategies were provided. The DGT technique provides the characterization of the mobilization of nutrients and evidence for biogeochemical processes at the fine spatial scales for control of internal loadings in sediments. [ABSTRACT FROM AUTHOR]

Crucian carp (Carassius auratus) is an omni-benthivorous fish common in many shallow lakes in China. The presence of crucian carp can contribute to the nutrient cycles in lakes and thus affect water quality. In this work, a two-by-two factorial mesocosm experiment was performed with crucian carp of different sizes and densities, to investigate their effects on the cycle of phosphorus (P). Results showed that nutrients in particulate form increased in overlying water due to crucian carp disturbance, especially for treatments with higher fish densities and larger individuals. Smaller individuals at high density have a greater ability to promote P release from sediment, due to a stronger combined effects of physical disturbance and excretion. Accumulation of feces led to sediment anaerobiosis and the reductive dissolution of iron oxide-hydroxide, which were the main factors affecting the desorption of P. Our results quantify the endogenous P diffusion fluxes across the sediment-water interface attributed to different densities and sizes of crucian carp disturbance, and suggest controlling crucian carp at low density and small size to minimize their impact on sediment P flux., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Chenxi Wu reports was provided by China Academy of Engineering. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Metal biogeochemistry in the sediment, water, and the sediment–water interface (SWI) was studied in a free water surface constructed wetland. Concentrations of labile copper (Cu), zinc (Zn), sulfate, chloride, and dissolved organic carbon (DOC) were measured with the diffusive gradients in thin film (DGT) and peeper. A good agreement between peeper- and DGT-measured metals was observed for Cu (regression r2 = 0.3, 95% CI of the slopes > 0), but not for Zn (95% CI of the slopes overlapped with 0), which was attributed to the different complexed compounds between Cu and Zn in porewater. The depth profile of labile metals in sediment porewater varied with time and was consistent with the solid-phase metal deposition, showing higher concentrations in the surface layer (3 to − 3 cm) than in the bottom layer (− 4 to − 13 cm). The depth-averaged labile Cu and Zn concentrations measured by DGT were 1.0 and 3.1 µg/L, and labile sulfate, chloride, and DOC concentrations measured by peeper were 1.8, 3.6, and 2.1 mg/L, respectively. A sharp decrease in sulfate occurred in September when sulfate concentrations became the lowest among sampling months. This was caused by the seasonal sulfur cycles in the wetland, where the dominant sulfur reaction is sulfate reduction in warm seasons and sulfide oxidation in cold seasons. Different metal-removal mechanisms were observed in the two wetland cells; sulfur dynamics controlled the removal processes in the cell without frequent disturbance but failed to influence metal removal in the cell with frequent disturbance due to the interruption of anoxic layers. The flux ratios that compare labile element concentrations between the water column and the SWI (R-Cu, R-Zn, R-DOC, R-sulfate, and R-chloride) were generated to determine metal diffusive fluxes at the interface. Labile Zn was mostly transported from the water to the SWI during all seasons (R-Zn < 1 for all months except January). Labile Cu moved from the SWI to the water during the warm months (R-Cu < 1), which was explained by the bioturbation-induced transport of organic matter based on the positive correlations between R-Cu and R-DOC. In general, sediment can serve either as a sink or a source depending on the environmental conditions, metal speciation, and presence of living organisms. Metal flux at the SWI is a key component in the biogeochemical cycling of a constructed wetland. [ABSTRACT FROM AUTHOR]

Novel Diffusive Gradients in Thin Films (DGT) binding agents, Musa cavendishi banana peel (BP) and Moringa Oleifera seeds (MOS) immobilised in agarose gel, have been developed and validated for the determination of Cd, Cu, Pb and Zn in waters. The agarose-BP and agarose-MOS gel disks were characterised by Scanning Electron Microscopy, Energy Dispersive X-ray Spectrometry and Porosimetry by nitrogen adsorption. Elution of analytes from the binding agents was successfully performed with 2 mol L−1 HCl. The accumulation of Cd, Cu, Pb and Zn in DGT devices based on agarose-BP and agarose-MOS (DGT-BP and DGT-MOS) agreed well with the theoretical curves predicted by the DGT equation in synthetic solutions (500 µg L−1 for each analyte). The uptake of DGT-BP and DGT-MOS for Cd, Cu, Pb and Zn was found to be independent of ionic strength of solutions up to 0.005 mol L−1 and for the entire studied pH range (from 3.5 to 8.0). Validation of DGT-BP and DGT-MOS methods was carried out by deploying the devices in spiked river water (the Corumbataí and the Piracicaba river). The recoveries obtained for the natural water matrices ranged between 40% and 150%. DGT-labile concentrations in situ for DGT-BP and DGT-MOS (performed in acid mine drainage) were also consistent with the values measured by conventional DGT-Chelex, albeit DGT-BP had a better binding capacity in acid drainage water. The predictions performed by chemical speciation modelling vMINTEQ were in general agreement for Pb using DGT-MOS (CDGT-MOS/Cdissolved 50% and Pb+2MINTEQ species 41.9%) and for Cu using DGT-BP (CDGT-BP/Cdissolved 55% and Cu+2MINTEQ species 62%). The proposed DGT-BP and DGT-MOS reaffirm the use of residual biomass as binding phase in the DGT technique, featuring low costs in production and 'green' technology approaches. [ABSTRACT FROM AUTHOR]

Metal pollution has become an major issue governing the wetland ecosystem health. The southern coastal wetland of the Qiangtang Estuary are facing unusual perturbation due to rapid development along the embayment in recent decades. This study evaluated the bioavailability of metals (Cu, Pb, Cd, Cr and Zn) in the sediment of the southern coastal wetland of the Qiangtang Estuary using diffusive gradients in thin films (DGT) techniques and compared with several methods based on total metal content. The results showed that the contents of Cr, Pb, Cd and Cu in sediment, as detected using DGT, were considerably correlated with the exchangeable fraction and the content in Phragmites australis roots, while a weak correlation was observed for Zn. Therefore, DGT analysis could be used to evaluate the bioavailability and potential risk of Cr, Cd, Pb and Cu for P. australis. Quantitative indices, such as DGT concentration, bioaccumulation in P. australis, geoaccumulation index (Igeo) and potential ecological risk index (RI), revealed that Cd was a major potential ecological risk factor along the southern coast wetland of the Qiantang Estuary, especially in the upstream region, which is potentially more vulnerable to the anthropogenic pollution. [ABSTRACT FROM AUTHOR]

We used diffusive gradients in thin films (DGT) to measure potentially bioavailable metals in coastal plain streams in the southeastern USA that exhibited strong to moderate blackwater characteristics. Metals were partitioned into particulate metals, DGT-inert metals (i.e., colloidal and refractory organic complexes not accumulated by DGT), and DGT-labile metals (i.e., free metal ions, small inorganic complexes, and labile organic complexes). We also examined the influence of different DGT deployment times using data collected from the field and a follow-up laboratory study. The DGT-measured fraction of dissolved metals in the streams was 15% for Cd, 21% for Zn, 33% for Cu, 37% for Pb, and 98% for Mn. Metals bound to particulates predominated only for Pb. Most of the Cd, Pb, Zn, and Cu were associated with colloids, refractory organic complexes, or particles. Relatively small amounts were in free ion or labile complexes likely to be bioavailable through respiratory surfaces. Modeled concentrations of free and inorganically bound Cu and Pb were lower than the DGT fraction indicating that DGT accumulated some organically bound Cu and Pb that might not have been bioavailable. DGT-exposure times in excess of 5 days may have contributed to the accumulation of partly labile organic–metal complexes and were associated with substantial biofouling that caused metal uptake by DGT to depart from linearity. [ABSTRACT FROM AUTHOR]

Increased focus on the development and application of bioavailability‐based metal water quality guideline values requires increased understanding of the influence of water chemistry on metal bioavailability and toxicity. Development of empirical models, such as multiple linear regression models, requires the assessment of the influence of individual water quality parameters as toxicity‐modifying factors. The present study investigated the effect of pH on the lability and toxicity of zinc (Zn) to a tropical green microalga (Chlorella sp.). Zinc speciation and lability were explored using the Windermere Humic Aqueous Model (WHAM7), ultrafiltration, and diffusive gradients in thin films (DGT). Zinc toxicity increased significantly with increasing pH from 6.7 to 8.3, with 50% growth inhibition effect concentrations decreasing from 185 to 53 µg l–1 across the pH range. Linear relationships between DGT‐labile Zn and dissolved Zn did not vary across the tested pH range, nor did the linear relationship between dissolved (<0.45 µm) and ultrafiltered (<3 kDa) Zn. Our findings show that Zn toxicity to this freshwater alga is altered as a function of pH across environmentally realistic pH ranges and that these toxicity changes could not be explained by Zn speciation and lability as measured by DGT and WHAM7. Environ Toxicol Chem 2021;40:2836–2845. © 2021 SETAC [ABSTRACT FROM AUTHOR]

This study assessed the critical soil characteristics affecting mercury (Hg) bioavailability to the earthworm Eisenia fetida using the diffusive gradient in thin films (DGT) method. The soil samples were collected from a tributary of the Hyeongsan River contaminated with industrial waste and landfill leachates called Gumu Creek. The Hg concentration in the soil had a range of 0.33–170 μg g-1 (average 33 ± 56 μg g-1), and the Hg concentration of earthworms incubated in the soils was 0.83–11 μg g-1 (average 2.9 ± 3.2 μg g-1). When correlation analysis was used to detect the key variables among the soil properties related to Hg accumulation in the soils, earthworms, and resins, the water-holding capacity, which is covaried with the organic matter content, was determined to be a primary factor in increasing Hg accumulation in the soils, earthworms, and resins. However, the experimentally determined earthworm bioaccumulation factor and the DGT accumulation factor were negatively affected by the water-holding capacity. Therefore, the water-holding capacity played a dual role in the Gumu Creek deposits: increasing the soil Hg concentration and decreasing Hg bioavailability and leachability. Further, the DGT–Hg flux was positively correlated with the Hg concentration in earthworms (r = 0.93). Although the earthworm accumulation of Hg is not processed by passive diffusion, this study proves that the DGT method is promising for predicting soil Hg bioavailability to the earthworm E. fetida, and the water-holding capacity simultaneously regulates Hg availability to the DGT and the earthworms. [ABSTRACT FROM AUTHOR]

There have been limited studies on the effects of toxicity‐modifying factors, such as dissolved organic matter (DOM), on the toxicity of metal mixtures to aquatic biota. The present study investigated the effects of DOM concentration (low, 2.8 ± 0.1 mg C/L; high, 11 ± 1.0 mg C/L) and DOM source (predominantly terrestrial or microbial) on the chronic toxicity of copper (Cu) and nickel (Ni) binary mixtures to the green freshwater microalga Chlorella sp. This was assessed by using a full factorial design of 72‐h growth inhibition bioassays. Measured algal growth rate was compared with growth predicted by the concentration addition and independent action reference models. Model predictions were based on concentrations of dissolved metals, labile metals (measured by diffusive gradients in thin films [DGT]), and calculated free metal ions (determined by the Windermere Humic Aqueous Model). Copper/Ni mixture toxicity was synergistic to Chlorella sp. in the absence of added DOM, with evidence of metal concentration‐dependent toxicity at low effect concentrations. As DOM concentration increased, the mixture interaction changed from synergism to noninteraction or antagonism depending on the metal speciation method used. The DOM source had no significant effect on mixture interaction when based on dissolved and free metal ion concentrations but was significantly different when based on DGT‐labile metal concentrations. Ratio‐dependent mixture interaction was observed in all treatments, with increased deviation from the reference model predictions as the mixture changed from Ni‐ to Cu‐dominated. The present study demonstrated that both DOM concentration and source can significantly change metal mixture toxicity interactions and that these interactions can be interpreted differently depending on the metal speciation method used. Environ Toxicol Chem 2021;40:1908–1918. © 2021 SETAC [ABSTRACT FROM AUTHOR]

In this study, the effects of short-term aerobic conditions on phosphorus (P) mobility in sediment were investigated in the eutrophic lakes. To accomplish this, an indoor cultivation system was established and short-term cultivation (3, 8 and 15 days) was conducted under control and aerobic treatments. High-resolution diffusive gradients in thin films (DGT) and dialysis (HR-Peeper) techniques were used to determine the mobility patterns of P in sediments. The results showed that: (1) Aerobic treatment significantly increased oxygen concentrations (maximum 17.1%) in overlying water within 15 days, with no significant effects on sediment oxygen penetration depth or redox potential. Additionally, aerobic treatment inhibited soluble reactive phosphorus (SRP) and DGT-labile P release from sediment to overlying water. (2) Aerobic treatment decreased the pore water SRP and soluble Fe(II) on day 3 with no impact on sediment SRP/DGT-labile P and soluble/DGT-labile Fe on day 8 and 15. (3) Model simulation using DGT Induced Fluxes in Sediments (DIFS) showed that the pore water SRP replenishment ability of sediment particle P was lower in the aerobic group than the control group, and the sediment system equilibration time was elongated after pore water SRP decreased in the aerobic group on day 3. (4) On day 3, SRP and soluble Fe(II), DGT-labile P and DGT-labile Fe showed significant positive correlations (r > 0.888, p

In recent years, calcium nitrate addition has become a promising and usually used method for in situ sediment remediation. In this study, excess calcium nitrate was applied to column sediments to explore the coupling reactions of elements such as N, Fe, S, and P. Diffusive gradients in thin film (DGT) devices were used to collect labile substances at the sediment-water interface. Rhizon samplers were used to collect soluble substances in interstitial water. Results showed that nitrate addition turned the surface sediment into a more oxidized state, and mobile Fe, S, P, and As were removed in surface ~ 10-cm sediment. Due to different nitrate distributions in corresponding sediment depths, the consumption rates of NH3-N and soluble reactive P were faster in the surface sediment than that in deeper layers. Different from previous researches, the transient increase of soluble Fe was observed in this study, which was probably attributed to the solvation of FeS in the autotrophic denitrification process. According to our results, we suggest that a dosage of far less than 141 g N/m2 and slightly more than 45.3 g N/m2 can be used for the remediation of black and odorous sediment and control of internal P by calcium nitrate. [ABSTRACT FROM AUTHOR]

The reliable sampling of root exudates in soil-grown plants is experimentally challenging. This study aimed at developing a citrate sampling and mapping technique with millimetre-resolution using DGT (diffusive gradients in thin films) ZrOH-binding gels. Citrate adsorption kinetics, DGT capacity, and stability of ZrOH gels were evaluated. ZrOH gels were applied to generate 2D maps of citrate exuded by white lupin roots grown in a rhizotron in a phosphorus-deficient soil. Citrate was adsorbed quantitatively and rapidly by the ZrOH gels; these gels can be stored after sampling for several weeks prior to analysis. The DGT capacity of the ZrOH gel for citrate depends on the ionic strength and the pH of the soil solution, but was suitable for citrate sampling. We generated for the first time 2D citrate maps of rhizotron-grown plants at a millimetre resolution to measure an illustrated plant response to phosphorus fertilization, demonstrating that DGT-based citrate sampling is suitable for studying root exudation in soil environments, at high spatial resolution. The change of binding material would also allow sampling of other exudate classes and exudation profiles of entire root systems. These aspects are crucial in cultivar breeding and selection. [ABSTRACT FROM AUTHOR]

The present study accessed the use of diffusive gradients in thin film (DGT) as a surrogate for estimating the bioavailability and bioaccumulation of copper (Cu) and zinc (Zn) in a freshwater mussel. We coupled DGTs with mussels and deployed them in a constructed wetland. Water quality parameters were measured for a 4‐d period on 3 continuous occasions during 12‐d trials in the summer and winter; metal speciation was modeled for each occasion. Higher cumulative rainfall and water turbidity during the summer trial resulted in higher particulate metal concentrations compared to the winter trial. Mussel accumulated metals did not correlate with DGT‐measured metals but positively correlated with particulate metals in the summer because filtering particulate food mainly contributed to the bioaccumulation. In contrast, the winter trial suggested a positive correlation between metal bioaccumulation and DGT‐measured metals because uptake of dissolved organic matter (DOM) from water mainly contributed to the bioaccumulation, and the labile metal species complexed with DOM generally overlapped with DGT‐targeted metals. Though Cu has a higher affinity for organic ligands than Zn, the interactions between Cu and Zn in the mixture did not impede their uptake and bioaccumulation. The deployment duration when DGTs and mussels are coupled to compare metal bioavailability should be no less than 12 d so that mussels have enough time to accumulate contaminants from the environmental media. In summary, DGT is a convenient surrogate for biomonitoring, but it may not fit the real environment such as the aquatic system with unstable water chemistries. Geochemical modeling is good at calculating metal speciation but inferior to DGT in predicting bioavailability and mimicking bioaccumulation. Environ Toxicol Chem 2020;39:2485–2495. © 2020 SETAC [ABSTRACT FROM AUTHOR]

Urban wastewater is one of main sources for the introduction of antibiotics into the environment. Monitoring the concentrations of antibiotics in wastewater is necessary for estimating the amount of antibiotics discharged into the environment through urban wastewater treatment systems. In this study, we report a novel diffusive gradient in thin films (DGT) method based on molecularly imprinted polymers (MIPs) for in situ measurement of two typical antibiotics, fluoroquinolones (FQs) and sulfonamides (SAs) in urban wastewater. MIPs show specific adsorption toward their templates and their structural analogs, resulting in the selective uptake of the two target antibiotics during MIP-DGT deployment. The uptake performance of the MIP-DGTs was evaluated in the laboratory and was relatively independent of solution pH (4.0–9.0), ionic strength (1–750 mmol/L), and dissolved organic matter (DOM, 0–20 mg/L). MIP-DGT samplers were tested in the effluent of an urban wastewater treatment plant for field trials, where three SA (sulfamethoxazole, sulfapyridine, and trimethoprim) and one FQ (ofloxacin) antibiotics were detected, with concentrations ranging from 25.50 to 117.58 ng/L, which are consistent with the results measured by grab sampling. The total removal efficiency of the antibiotics was 80.1% by the treatment plant. This study demonstrates that MIP-DGT is an effective tool for in situ monitoring of trace antibiotics in complex urban wastewaters. [ABSTRACT FROM AUTHOR]

The Tritium Processing Facility at the Savannah River Site releases effluent containing copper (Cu), zinc (Zn), and lead (Pb) to the H-02 constructed wetland for remediation before the final release. Sediment cores were collected in the wetland cells in both summer and winter. Concentrations of total metals in all sediment layers and acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) in surface sediments were determined. Total metal concentrations suggested most metals removed from surface water were retained by the organic-rich flocculent in the top sediment layers instead of being transported to the deeper sulfide mineral layers. The seasonal difference of AVS and SEM indicated a season-related sulfur cycle and metal removal process in the wetland cells. SEM-Zn was the major contributor to total SEM. Metals accumulating in surface sediments were mainly sequestered in AVS and SEM extractable phases including metal-sulfides and organic matter complexes. The general SEM/AVS ratio was > 1, demonstrating the metals associated with sediments were potentially mobile and/or bioavailable, which becomes a concern for the long-term sustainability of the constructed wetland. The disturbance event in the sediment triggered the release of total metals, which were mostly in particulate form and were not bioavailable. Due to the high levels of reduced ion (Fe) in the sediment, the released particulate metals were likely to form metal-scavenging particulate Fe3+ oxyhydroxides under oxic conditions. [ABSTRACT FROM AUTHOR]

Determination of the median effective concentration (EC50) of Cu on Mytilus galloprovincialis larvae by diffusive gradient in thin films (DGT) has been shown to effectively reduce the need to consider dissolved organic carbon (DOC) concentration and quality. A standard toxicity test protocol was used to validate previously modeled protective effects, afforded to highly sensitive marine larvae by ligand competition, in 5 diverse site waters. The results demonstrate significant narrowing of M. galloprovincialis toxicological endpoints, where EC50s ranged from 3.74 to 6.67 μg/L as CDGT Cu versus 8.76 to 26.8 μg/L as dissolved Cu (CuDISS) over a DOC range of 0.74 to 3.11 mg/L; Strongylocentrotus purpuratus EC50s were 10.5 to 19.3 μg/L as CDGT Cu versus 22.7 to 67.1 μg/L as CuDISS over the same DOC range. The quality of DOC was characterized by fluorescence excitation and emission matrices. The results indicate that the heterogeneity of competing Cu binding ligands, in common marine waters, minimizes the need for class determinations toward explaining the degree of protection. Using conservative assumptions, an M. galloprovincialis CDGT Cu EC50 of 3.7 µg/L and corresponding criterion maximum concentration CDGT Cu of 1.8 µg/L, for universal application by regulatory compliance‐monitoring programs, are proposed as a superior approach toward both integration of dynamic water quality over effective exposure periods and quantification of biologically relevant trace Cu speciation. Environ Toxicol Chem 2020;39:873–881. © 2020 SETAC [ABSTRACT FROM AUTHOR]

A passive sampling method based on diffusive gradients in thin films (DGT) using ceria oxide (CeO2) binding gel was developed for in situ measurement of dissolved reactive phosphorus (DRP). CeO2-based DGT showed excellent uptake performance for DRP, and the uptake mass was consistent with the predication by DGT equation. pH (4.2~9.4) and ionic strength (0.01~500 mM) had no effects on the uptake of DRP. Filed deployment of CeO2-DGT in reservoir water and seawater showed that the measureable concentrations of DRP were comparable to those obtained by grab sampling. CeO2-DGT was deployed in sewage sludge, and results showed the ratios (RS) between the concentration (CDGT) by CeO2-DGT and the concentration (CS) obtained by a traditional centrifugation method ranged from 0.23 to 0.58. This result indicated that sludge solid phase was a potential pool of DRP in sludge solution, and the DRP released from sludge solid phase could compensate partly the consumption of DRP at the interface of DGT device during the deployment. The ratios RS had positive correlation with the content of Fe (r = 0.847, p < 0.01) but were reversed with the level of Ca (r = − 0.879, p < 0.01) in sewage sludge. The proposed method provided a powerful tool for in situ measurement of DRP in natural waters and for release behavior of DRP in sludge. [ABSTRACT FROM AUTHOR]

Tidal river networks are affected by the tide and influenced by complex factors related to sediment oxygen demand (SOD). In this study, we used chemical inhibition to measure the oxygen consumption of different types of SOD to explore the specific oxygen consumption mechanism of sediments. Then, we evaluated the diffusion fluxes of the sediment–water interface and factors affecting SOD using diffusive gradients in thin films. Total SOD in the tidal river network area of the Pearl River basin was ∼0.5928 g/m2/day, which was 8.47% higher than that in the non-tidal river network area but lower than that in black and odorous water reported previously. In the tidal river network area, biological SOD was 15.6% higher in summer than in winter, and the difference in total SOD was greatly influenced by human activity. We observed a significant effect of sediment on SOD in winter, whereas there were no significant correlations between sediment and SOD in summer. Different particle-size distributions lead to different organic matter contents, resulting in different biological SOD ratios between seasons. Our study found that seasonal tidal changes can affect ion exchange at the sediment water interface, leading to changes in SOD.These findings will be of great significance for the study of phenomena associated with low dissolved oxygen in tidal river networks and provide directions for future sediment pollution control. [Display omitted] • We evaluated the specific mechanisms of SOD within a tidal river network. • DGT with SOD measurements was used to calculate diffusion flux. • Assessed the effect of the diffusion flux on SOD at the sediment-water interface. • Sediments in TRN area are more easily contaminated than those in the non-TRN areaTides affect the suspended state of sediment. [ABSTRACT FROM AUTHOR]

Cyanobacterial bloom is a pressing issue affecting water supply security and ecosystem health. Phosphorus (P) released from cyanobacterial bloom during recession is one of the most important components involved in the lake P cycle. However, little is known about the consequences and mechanisms of the P cycle in overlying water and sediment due to the anthropogenic treatments of cyanobacterial blooms. In this study, treatment methods using hydrogen peroxide (H 2 O 2), polyaluminum chloride (PAC), and the feces of silver carp were investigated for their influence on the P cycle using microcosm experiments. Results showed that H 2 O 2 treatment significantly increased the internal cycle of sediment-related P, while PAC treatment showed minor effects. H 2 O 2 and PAC treatment suppressed the release of P from sediment before day 10 but promoted the release of P on day 20, while silver carp treatment suppressed the release of P during the whole experiment. The reductive dissolution of iron oxide-hydroxide was the major factor affects the desorption of P. Path analyses further suggested that overlying water properties such as dissolved oxygen (DO) and oxidation-reduction potential (ORP) play critical roles in the treatment-induced sediment P release. Our results quantify the endogenous P diffusion fluxes across the sediment-water interface attributed to cyanobacterial treatments and provide useful guidance for the selection of controlling methods, with silver carp being the most recommended of the three methods studied. [Display omitted] • H 2 O 2 , PAC, and silver carp treatments on P cycle in lake systems were studied. • H 2 O 2 and PAC inhibited P release initially but enhance P release at the end. • Filter-feeding and excretion of algae by silver carp reduced P release. • P release was related to reduction of NaOH–P and changes in DO and ORP. [ABSTRACT FROM AUTHOR]

The diffusive gradients in thin films (DGT) technique serves as a passive sampling method, inducing analyte transport and concentration. Its application is widespread in assessing labile components of metals, organic matter, and nutrients across various environmental media such as water, sediments, and saturated soils. The DGT devices effectively reduce the porewater concentration through irreversible binding of solutes, consequently promoting the release of labile species from the soil/sediment solid phase. However, the precise quantification of simultaneous adsorption and desorption of labile species using DGT devices alone remains a challenge. To address this challenge, the DGT-Induced Fluxes in Soils and Sediments (DIFS) model was developed. This model simulates analyte kinetics in solid phases, solutions, and binding resins by incorporating factors such as soil properties, resupply parameters, and kinetic principles. While the DIFS model has been iteratively improved to increase its accuracy in portraying kinetic behavior in soil/sediment, researchers' incomplete comprehension of it still results in unrealistic fitting outcomes and an oversight of the profound implications posed by kinetic parameters during implementation. This review provides a comprehensive overview of the optimization and utilization of DIFS models, encompassing fundamental concepts behind DGT devices and DIFS models, the kinetic interpretation of DIFS parameters, and instances where the model has been applied to study soils and sediments. It also highlights preexisting limitations of the DIFS model and offers suggestions for more precise modeling in real-world environments. [Display omitted] • DGT technology reveals the kinetic processes of pollutants in soil or sediment. • DIFS model reflects the reservoir and resupply rate of labile analytes. • The limitations and correction approaches of the DIFS model should be considered. [ABSTRACT FROM AUTHOR]

In this work, several binding gels were successfully prepared in Diffusive Gradient in Thin-film (DGT) that targeted the inclusion of novel biomass-derived materials for the determination of the labile fraction of mercury (Hg) in water. First, five biomass-derived materials were tested and the descending order as a function of the average percentage of Hg removal in solution was feathers > biochar > cork > canola meal > rice husk. The best two materials were treated and pulverized into powder to be embedded in a hydrogel; and so, feathers were pyrolyzed preserving the sulfur contained in their keratin structure (FBC), and biochar (BC) was modified and pyrolyzed with sublimated sulfur (SBC) to increase the Hg sorption sites in its structure. Analysis by Energy Dispersive X-ray fluorescence (EDXRF) spectrometry confirmed that the different pyrolysis procedures increased sulfur absorption successfully. The efficiency of the new gels (BC, SBC and FBC) in agarose was evaluated by comparative Hg uptake tests, showing a larger efficacy in the following order: SBC > BC > FBC. To assess the suitability of their application in freshwater environments, novel DGT devices were also evaluated to determine their diffusion coefficients (D). This test was conducted under controlled laboratory conditions, with particular focus on the potential competence of trace elements (Mn, Cu, Zn, Ni, Pb, Cd and As), which are commonly present in natural waters affected by mining. A stronger linear relationship between the Hg uptake by binding layers and the deployment time were obtained for the DGT devices with SBC (R2 = 0.948) vs. BC (R2 = 0.885). Therefore, the D obtained for Hg were 8.94 × 10−6 cm2 s−1 for DGT-SBC and 5.12 × 10−6 cm2 s−1 for DGT-BC devices at 25 °C, both within the same order of magnitude reported by previous studies. The good performance obtained by DGT-SBC devices is a promising result and indicates the potential for valorization of waste materials in the DGT technique. [Display omitted] • Valorization of five waste materials was carried out as binding gels in DGT technique. • Pyrolyzed feathers, biochar and biochar pyrolyzed with S were embedded in a hydrogel. • EDXRF technique confirmed that pyrolysis procedures increased S absorption. • Binding gels with waste materials suitably extract Hg in the presence of trace elements. • Diffusion coefficients (10−6 cm2 s−1) are in the same order of magnitude than reported. [ABSTRACT FROM AUTHOR]

DGT (diffusive gradients in thin films) technique and LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) for heterogeneous distribution of the soluble labile iron (Fe) at submillimeter resolution in lake sediment porewater are reported. The soluble labile Fe species include ion and labile organic complexes. The chemical images in two dimensions (2D) for DGT concentration of Fe (CDGT(Fe)) are investigated for Fe remobilization character. There are 902 CDGT(Fe) values between 1000 and 2000 μg L−1, 463 values between 2000 and 3000 μg L−1, and 112 values over 3000 μg L−1 in all chemical maps. Based on the linear correlation relationships between CDGT (Fe) and total Fe (TFe), total organic carbon (TOC), acid-volatile sulfide (AVS), Eh, concentrations of the soluble reactive phosphorus (P) (SRP), and soluble labile trace metals (Zn, Cu, Pb, and Zn) in a vertical 1D profile of sediment or porewater, Fe release mechanisms are mainly due to the reductive Fe release from iron oxyhydroxides and the decomposition of organic matter in algae biomass and deep sediment layer. It can be used to explain the formation mechanisms of Fe microniches in chemical maps with heterogeneous character to a great extent. CDGT(Fe) peak flux in the center of Fe microniche and the low CDGT (Fe) at the edge of a microniche are due to the formation of the insoluble iron sulfide and the abundant acid-volatile sulfide (AVS) in sediment. The verified co-remobilization of the soluble labile Fe and trace metals or SRP in sediment porewater can be used to predict their simultaneous release from Fe microniches with the large CDGT (Fe) peaks. The different kinds of Fe microniche zones and hot spots from sediment/water interface (SWI) to deep sediment correspond to the formation mechanisms of microniches mentioned above. Moreover, some narrow Fe microniche zones with the large CDGT (Fe) across chemical maps are due to the desorption of Fe(II) from the freshly formed oxide on Myriophyllum verticiilatur roots, which are located at sites of microniche zones. [ABSTRACT FROM AUTHOR]

In this study, the effects of short-term aerobic conditions on phosphorus (P) mobility in sediment were investigated in the eutrophic lakes. To accomplish this, an indoor cultivation system was established and short-term cultivation (3, 8 and 15 days) was conducted under control and aerobic treatments. High-resolution diffusive gradients in thin films (DGT) and dialysis (HR-Peeper) techniques were used to determine the mobility patterns of P in sediments. The results showed that: (1) Aerobic treatment significantly increased oxygen concentrations (maximum 17.1%) in overlying water within 15 days, with no significant effects on sediment oxygen penetration depth or redox potential. Additionally, aerobic treatment inhibited soluble reactive phosphorus (SRP) and DGT-labile P release from sediment to overlying water. (2) Aerobic treatment decreased the pore water SRP and soluble Fe(II) on day 3 with no impact on sediment SRP/DGT-labile P and soluble/DGT-labile Fe on day 8 and 15. (3) Model simulation using DGT Induced Fluxes in Sediments (DIFS) showed that the pore water SRP replenishment ability of sediment particle P was lower in the aerobic group than the control group, and the sediment system equilibration time was elongated after pore water SRP decreased in the aerobic group on day 3. (4) On day 3, SRP and soluble Fe(II), DGT-labile P and DGT-labile Fe showed significant positive correlations (r > 0.888, p < 0.001), indicating that reduced pore water SRP concentration was related to decreased pore water soluble Fe(II). [ABSTRACT FROM AUTHOR]

In many cases, stormwater compliance monitoring is labor intensive, expensive, and largely unsuccessful in providing the data needed to support stormwater management goals. To help address these issues, diffusive gradients in thin film (DGTs), time-integrative passive samplers for metals, were evaluated to monitor copper in stormwater runoff. DGTs were co-located with traditional autosamplers within the stormwater conveyance systems at Naval Base San Diego (NBSD) to provide a direct comparison with composite sampling. DGTs were exposed in the laboratory to flow-averaged composite samples from NBSD stormwater conveyance systems. These experiments showed increasing uptake over time (range = 1.5–24 h) for copper, with positive, linear correlations (r2 > 0.980) between exposure duration and copper mass accumulated. However, it appears that the corresponding calculations of the DGT-labile fraction (C DGT) relative to the dissolved fraction fluctuated across the different exposure durations. In general, trends observed for C DGT measurements from the field were consistent with trends in the lab DGT exposures and traditional dissolved metal measurements from composite samples. Finally, time-weighted average copper concentrations from DGTs deployed for the first and second phases of storm events were within 30% of measurements from DGTs that were deployed for the entire storm event in the same stormwater vault. Cumulatively, these results show promise for continuous monitoring with DGTs as an approach that produces data more representative of exposure to the receiving environment during episodic events than data from traditional grab or composite chemistry sampling, and can represent significant cost savings. • DGT data compared well with more resource intensive autosampler derived data. • DGTs consistently measured labile copper in stormwater with exposure durations ≥ 6 h • DGTs measurements of labile copper were consistent when deployed in stormwater vaults. • Simplicity of DGT makes it a logical alternative to traditional stormwater sampling. [ABSTRACT FROM AUTHOR]

In-situ sampling of 2-chlorophenol (CP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP) in industrial wastewater was carried out by the diffusive gradients in thin films (DGT) device based on mesoporous carbon (MC). The diffusion coefficients of CP ((1.33 ± 0.05) × 10−6 cm2 s−1), DCP((1.35 ± 0.04) × 10−6 cm2 s−1) and TCP((1.09 ± 0.07) × 10−6 cm2 s−1)) in nylon membrane at 25 °C were independent of pH 3–9 and ionic strength as pNaCl from 0.155 to 3, and were less than their values in water, demonstrating that the nylon membrane with good tolerance and constant diffusion coefficients was suitable as the DGT diffusion layer for controlling the diffusion of CPs. MC-DGT accurately measured the concentrations of CP, DCP and TCP in synthetic solution (C DGT / C SOLN = 0.956–1.04) over the deployment of 120 h. The experimental data also agreed well with the theoretical data calculated on the DGT equation. The performance of MC-DGT for sampling CPs was independent of pH (3–8) and ionic strength as pNaCl (1.3–3) due to the change of the interaction between MC and CPs under relatively high pH and ionic strength. Deployments in laboratory and field trials demonstrated that the MC-DGT was a reliable simple, robust and accurate tool for the in-situ sampling of CP, DCP and TCP in the industrial wastewater. Image 1 • In-situ simultaneous sampling of chlorophenols by DGT based on mesoporous carbon. • Mesoporous carbon from SBA-15 mesoporous silica as template and sucrose as carbon source. • No influence on DGT uptakes for analytes in pH (3–8) and ionic strength (0.001–0.05 mol L−1) ranges. • Positive results proved validity of proposed DGT for in-situ sampling in lab and field trials. [ABSTRACT FROM AUTHOR]

Understanding bioavailable metal behaviour in situ is critical for pollution evaluation and contaminant management in mangrove wetland. Here, the diffusive gradients in thin films technique (DGT) was used for characterizing the (bio)available portions of Cr, Zn, Pb, Cu, Fe and Mn in two mangrove wetlands affected by industrial waste discharges (Jiulong Estuary) and domestic discharges (Zhangjiang Estuary), in Fujian Province, China. In addition, fluorescence excitation emission matrices-parallel factor analysis (EEM-PARAFAC) was applied for characterizing the occurrence and behaviour of dissolved organic matter (DOM) in soil solution, as well as their feasibility for assessing behaviours of metals. The results demonstrated that the combination of DGT and EEM, which are well suitable for studying DOM impacted metal behaviors in mangrove sediments. Discharge of difference wastewater into the mangrove wetlands of Jiulong and Zhangjiang Estuaries, gave rise to the DGT-labile metal concentration of Zn > Cu > Cr > Pb and Zn > Cr > Pb > Cu, respectively. A variety of humic-like fluorescent components was characterized here, providing valuable insights into the chemical composition of DOM in rhizosphere and bulk sediment. Terrestrial humic-like compounds indicated a different binding affinity for heavy metals in mangrove sediments. These findings are useful for the future understanding of the metal speciation and molecular binding mechanisms in such mangrove wetlands. Image 1 • DGT was combined with EEM-PARAFAC method to study metal behaviour. • Humic-like substances were found higher in rhizosphere for metal binding. • Humic substances played a key role in controlling the binding of metals. • Mobility and speciation of metals were related to DOM composition. [ABSTRACT FROM AUTHOR]

In general, the diffusive gradients in thin films (DGT) technique is an effective tool for evaluating metal bioavailability; however, its applicability is subject to the type of metal and organism involved. In this study, the accumulated masses of Hg in DGT probes and in the earthworm species Eisenia fetida were monitored for 10 days, to test if the DGT technique can be used as a predicting method for the bioavailability of soil Hg to earthworms. In the Hg exposure tests using soils prepared with different peat moss concentrations of 5, 10, 15, and 20% and varying pH values of 4.6, 5.6, and 6.2, the experimentally determined DGT-soil accumulation factor (DSAF) and biota-soil accumulation factor (BSAF) both increased as the peat moss content decreased and the pH increased. According to a one compartment model, this was a result of the increased Hg uptake rate constant (k1) and the relatively stable Hg elimination constant (k2) under lower peat moss and higher pH conditions. It is interesting to note that the Hg uptake rates by DGT and earthworms were considerably higher for fresh soils than for aged soils, while porewater (and acid-extractable) Hg concentrations were rather similar between the two types of soils. Across diverse soil properties, steady-state Hg in earthworm tissue showed a strong positive correlation with DGT-measured Hg flux ([earthworm Hg] = 354(DGT−Hg flux)−34, r2 = 0.88), while meager correlations were found between Hg concentration in earthworms and that in porewater (and acid-extractable). The overall results indicate that DGT-measured Hg flux is a better tool than conventional methods for predicting Hg bioavailability for earthworms inhabiting diverse types of soil. [ABSTRACT FROM AUTHOR]

Abstract Water, sediment, and biota from two streams on the Savannah River Site were sampled to study mercury (Hg) biogeochemistry. Total and methyl- Hg (MHg) concentrations were measured for all samples, speciation models were used to explore Hg speciation in the water, and Diffusive gradients in thin films (DGT) were applied to indicate the vertical profiles of labile Hg (DGT-Hg). Trophic position (δ15N) was estimated for biota and used to establish MHg biomagnification model. The speciation model indicated Hg methylation in the water occurred on settling particles and the most bioavailable Hg species to bacteria were complexes of inorganic Hg and labile organic ligands. Correspondingly, dissolved organic carbon concentrations were positively related to MHg concentrations in the water. In the sediment, the sharp increase of DGT-Hg around the sediment water interface underscores the importance of this interface, which determines the differences in the accumulation and generation of labile Hg among different waterbodies. The positive correlation between sediment MHg and sulfate concentrations suggested possible methylation reaction by dissimilatory sulfate reducing bacteria in the sediment. The food web magnification factors of MHg were 9.6 (95% CI: 4.0–23.4) and 4.4 (95% CI: 2.5–7.7) for the two streams established with trophic data of biofilm, invertebrates, and fish. Meanwhile, DGT-Hg concentrations in the water were positively correlated to biofilm Hg concentrations, which can be combined with the MHg biomagnification model to generate a modified biomagnification model that estimate MHg bioaccumulation with only labile Hg concentrations in the water. With this approach, Hg accumulation in abiotic and biotic environmental compartments was connected and the different bioaccumulation patterns of Hg in different waterbodies were explained with both geochemical and biological factors. Graphical abstract Unlabelled Image Highlights • Mercury (Hg) methylation in the water occurred on settling particles. • Complexes of Hg(II) and labile organic ligands were most bioavailable to SRB. • Labile and bioavailable Hg was mostly generated in the sediment water interface (SWI). • The SWI determines the differences in Hg accumulation among different waterbodies. • Concentrations of biofilm-Hg and DGT-Hg in the water were positively correlated. [ABSTRACT FROM AUTHOR]

Abstract Due to the limited aeration capacity of current aeration techniques at the sediment-water interface (SWI), we developed a specialized aeration material aimed at the SWI, known as oxygen nano-bubble-modified minerals (ONBMMs). Furthermore, we simulated its aeration efficiency at the SWI and the control effects of internal phosphorous (P) release under anaerobic conditions during 20 days. High resolution diffusive gradients in thin films (DGT) and Planar luminescent optode (PO) technologies were used to measure the temporal variation of reactive P, reactive Fe (II) and dissolved oxygen (DO) of the SWI. These results show that ONBMMs can effectively increase the content of DO at the SWI and decrease the release flux of internal P from sediments. The use of ONBMMs reduced 97.9% of the soluble reactive P concentration of the overlaying water and reduced the release flux of DGT-P from sediments by 78.9%. Inhibition of reductive dissolution of Fe P from sediments was the primary principle that effectively inhibited the input of internal P by ONBMMs. Therefore, ONBMMs are potentially promising technology for the treatment of internal P pollution in eutrophic lakes. Graphical abstract Unlabelled Image Highlights • A specialized aeration material aimed at the sediment-water interface, known as oxygen nano-bubble-modified minerals(ONBMMs) was developed. • ONBMMs effectively increased the DO at the sediment-water interface. • ONBMMs remarkably reduced the release flux of sediment P. • Fe-P precipitation constituted the main mechanism of the inhibition of sediment P release by ONBMMs. [ABSTRACT FROM AUTHOR]

Abstract There is a requirement for simultaneous measurements of diverse analytes to reveal their biogeochemical couplings in the environment. In this study, we first realized simultaneous measurements of three types of analytes, including sulfide [S(-II)], metallic cations, and oxyanions by diffusive gradients in thin films (DGT) using a new mixed ZrO-CA binding gel. The ZrO-CA gel exhibited faster absorption rates for oxyanions than previously reported ZrO-Chelex gel, and faster absorption rates for cations when the gel was saturated with S(-II). It implies that there were synergistic effects among the three binding agents which should facilitate the DGT uptake. The technique's performance was validated under laboratory conditions in mixtures of dissolved compounds. It was shown to be independent of the solution's pH (5–9) and ionic strength (from 1 to 3 mM to 750 mM). The capacities of the ZrO-CA DGTs without or with [S(-II)] saturation to measure As(III), As(V), Cd(II), Fe(II), and P(V) individually were significantly greater than those of other DGTs except for Zr-oxide based DGTs. The measurements in sediment revealed similar distributions of three types of analytes in the vertical profile and confirmed the feasibility and advantage of the ZrO-CA DGT. This study provides a new perspective to enhance the DGT capability in measurement of multiple analytes through utilizing the synergistic effects among different binding agents. Graphical abstract Unlabelled Image Highlights • Simultaneous measurements of three types of analytes were realized using ZrO-CA DGT. • The hybrid binding gel had strong kinetics for determinands whether saturated with S(-II) or not. • The ZrO-CA DGT was independent of solution pH (5–9) and ionic strength (1–3 mM–750 mM). • The incorporation of three binding agents enhanced the DGT performance due to synergistic effects. [ABSTRACT FROM AUTHOR]

Abstract Iron (Fe) and manganese (Mn) reactions have been regarded as the primary factors responsible for the mobilization of phosphorus (P) in lake sediments, although their individual roles are hard to distinguish. In this study, in situ mobilization of P, Fe and Mn in sediments was assessed by high resolution spatio-temporal sampling of their labile forms using diffusive gradient in thin films (DGT) and suction device (Rhizon) techniques. It was found that the monthly concentration distributions showed greater agreement and better correlation coefficients between labile P and labile Fe, than those between labile P and labile Mn, implying that Fe plays a key role in controlling P release in sediments. Furthermore, better correlations were observed between hourly changes in concentrations of soluble reactive phosphorus (SRP) and soluble Fe(II), than those between SRP and soluble Mn. Changes were observed under simulated anaerobic incubation conditions, suggesting that P release was caused by the reductive dissolution of Fe oxides. This was supported by the lack of influences on P release from reductive dissolution of Mn oxides in the sediment-water interface and top sediment layers under the anaerobic incubations. In simulated algal bloom experiments, positive correlations and consistent changes were observed between SRP and soluble Fe(II) concentrations, but not between SRP and soluble Mn concentrations. This further demonstrated the Fe-dependent and Mn-independent release of P in sediments. Therefore, Fe redox reactions have a high impact on P mobilization in sediments, while Mn redox reactions appear to have negligible influences. Graphical abstract Image 1 Highlights • Monthly distribution of labile P concentration correlated with labile Fe concentration in sediments. • Hourly change of SRP correlated with soluble Fe(II) concentrations under anoxic conditions. • Phosphorus was not released during the reductive dissolution of Mn oxides. • Consistent changes in P and Fe but not in Mn occurred in algal bloom sediments. • Fe but not Mn redox reactions should control mobilization of P in sediments. Evidence that Fe redox reactions play a key role in controlling P mobilization in sediments, while Mn redox reactions do not have a significant influence. [ABSTRACT FROM AUTHOR]

Abstract The pollution of antibiotics, including tetracyclines (TCs), in aquatic environments has become an issue of concern in recent years. Herein, an in situ sampling of TCs in pig breeding wastewater that utilizes the technique of diffusive gradients in thin films (DGT), based on commercial nanosized ZnO (nanoZnO) particles as the potential effective binding agent and a polyethersulfone (PES) membrane as the diffusion layer, was developed. The diffusion coefficients of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) in a PES membrane at 25 °C were (1.37 ± 0.06) × 10−6 cm2 s−1, (1.29 ± 0.05) × 10−6 cm2 s−1 and (1.94 ± 0.07) × 10−6 cm2 s−1, respectively. The results showed that the adsorption capacities of a gel disc containing 2.5 g L−1 of nanoZnO particles were as high as 3.93 ± 0.20 mg disc−1 for TC, 3.21 ± 0.20 mg disc−1 for OTC and 4.62 ± 0.22 mg disc−1 for CTC. Both a solution pH in the range of 5–9 and an ionic strength (as pNaCl) in the range of 1–3 had an insignificant influence on the TCs uptake by nanoZnO−DGT samplers. There was no significant influence of fulvic acid or tannic acid on the TC uptake by nanoZnO−DGT samplers at the tested mass ratios. For all spiked freshwater samples, there was no notable interference of matrices on the performance of the nanoZnO−DGT samplers, suggesting that the nanoZnO−DGT samplers yielded satisfactory results for the uptake of TCs at concentrations existing in the spiked freshwater samples. Field deployment of the nanoZnO−DGT samplers in pig breeding wastewater also exhibited excellent precision and accuracy, indicating that the nanoZnO−DGT samplers could be used as a promising method for the in situ sampling of TC antibiotics in aquatic environments. Graphical abstract Unlabelled Image Highlights • A DGT sampler based on ZnO nanoparticles for in-situ sampling of tetracyclines in waters. • An inert polyethersulfone membrane as the diffusion layer of DGT technique • No notable influence on the uptake of nanoZnO−DGT for TCs in the range of pH 5–9 and pNaCl 1–3 • No interference of water matrices on the uptake of tetracyclines by DGT sampler • Reliable and accurate results in field deployment with relative good precision [ABSTRACT FROM AUTHOR]

Three different types of zirconium-modified bentonites (ZrMBs) including zirconium-modified original bentonite (ZrMOB), zirconium-modified magnesium-pretreated bentonite (ZrMMgB), and zirconium-modified calcium-pretreated bentonite (ZrMCaB) were synthesized and used as active covering materials to suppress the release of phosphorus (P) from sediments. To assess the covering efficiency of ZrMBs to inhibit P release from sediments, we examined the impact of ZrMB covering layer on P mobilization in sediments at different depths as well as the release of P through the interface between sediment and overlying water (SWI) by use of simulating P release control experiments and diffusive gradients in thin films (DGT) technology. The results showed that the amount of soluble reactive P (SRP) in the overlying water greatly decreased after covering with ZrMBs. Moreover, both pore water SRP and DGT-liable P (DGT-P) in the top sediments decreased after capping with ZrMBs. An obvious stratification of DGT-P was observed along the vertical direction after covering with ZrMBs, and static and active layers were found in the top sediment and in the lower sediment directly below the static layer, respectively. Furthermore, ZrMB covering led to the change of P species from easily released P to relatively or very stable P, making P in the top sediment more stable compared to that without ZrMB covering. Besides, an overwhelming majority of P immobilized by ZrMBs is hard to be re-released into the water column in a common environment. Overall, the above results demonstrate that sediment covering with ZrMBs could effectively prevent the transport of SRP from sediments into the overlying water through the SWI, and the control of P transport into the overlying water by ZrMB covering could be mostly due to the immobilization of pore water SRP, DGT-P, and mobile P in the top sediment by ZrMBs. [ABSTRACT FROM AUTHOR]