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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 PO 4 -P, Fe, ammonium (NH 4 -N), and nitrate (NO 3 -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 (C DGT ) 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 NH 4 -N; (2) denitrification and dissimilatory nitrate reduction to ammonium (DNRA) led to exchangeable ammonium (NH 4 ex) enrichment and NH 4 -N release; anammox depleted NH 4 -N transfer; organic matter (OM) mineralization favored NH 4 -N release; and (3) aerobic nitrification led to NO 3 -N remobilization; denitrification and DNRA reduced NO 3 -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 (PO 4 -P), - 1403 ~ 5010 (NH 4 -N), and - 1395 ~ 149 (NO 3 -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., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The trace element of As and Sb have resulted in serious threats to ecological sustainability and human health in the Xijiang River basin, China. The geoaccumulation index (I geo ) results showed the sediment of Xijiang River was heavily contaminated by Sb as well as moderately contaminated by As. The effect of inorganic anions on the released As and Sb from the sediment increases in the following sequence: Cl - < SO 4 2- < CO 3 2- < PO 4 3- . The presence of PO 4 3- and CO 3 2- had the greater effect over As mobility from the sediment compared to Sb. The effect of Ca(II), Al(III), and Mg(II) on the released amount of Sb from the sediment is negligible. Meanwhile, in the case of As, Ca(II) and Mg(II) had small impacts, but the released amount of As increased slightly with an increase of Al(III) concentration. The stability of As and Sb in the sediment was found to be the best at pH 5. The effect of organic compounds (≤ 0.05 mol/L) on the dissolved As percentages from the sediment increased in the following sequence: ethylenediaminetetraacetate (EDTA) < oxalate < citrate, and the effect on Sb release was oxalate < EDTA < citrate at concentrations (≤ 0.025 mol/L). This study provides the basic theoretical basis to manage the mobilization of co-contamination of sediments with As and Sb under the influence of external perturbations., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Management of tailings at metal mine smelter sites can reduce the potential hazards associated with exposure to toxic metal(loid)s and residual organic flotation reagents. In addition, microbes in the tailings harboring multi-resistance genes (e.g., tolerance to multiple antimicrobial agents) can cause high rates of morbidity and global economic problems. The potential co-selection mechanisms of antibiotic resistance genes (ARGs) and metal(loid) resistance genes (MRGs) during tailings sulfate-reducing bacteria (SRB) treatment have been poorly investigated. Samples were collected from a nonferrous metal mine tailing site treated with an established SRB protocol and were analyzed for selected geochemical properties and high throughput sequencing of 16S rRNA gene barcoding. Based on the shotgun metagenomic analysis, the bacterial domain was dominant in nonferrous metal(loid)-rich tailings treated with SRB for 12 months. KEGGs related to ARGs and MRGs were detected. Thiobacillus and Sphingomonas were the main genera carrying the bacA and mexEF resistance operons, along with Sulfuricella which were also found as the main genera carrying MRGs. The SRB treatment may mediate the distribution of numerous resistance genes. KOs based on the metagenomic database indicated that ARGs (mexNW, merD, sul, and bla) and MRGs (czcABCR and copRS genes) were found on the same contig. The SRB strains (Desulfosporosinus and Desulfotomaculum), and the acidophilic strain Acidiphilium significantly contributed to the distribution of sul genes. The functional metabolic pathways related to siderophores metabolism were largely from anaerobic genera of Streptomyces and Microbacterium. The presence of arsenate reductase, metal efflux pump, and Fe transport genes indicated that SRB treatment plays a key role in the metal(loid)s transformation. Overall, our findings show that bio-treatment is an effective tool for managing ARGs/MRGs and metals in tailings that contain numerous metal(loid) contaminants. [ABSTRACT FROM AUTHOR]

Purpose: The objectives of this study were to (1) analyze heavy metals (Cr, As, Cu, Zn, Cd, and Pb) in the rhizosphere soil and roots, leaves, stems, and grains of maize and wheat crops using different methods; (2) evaluate the advantages of diffusive gradients in thin films technology (DGT) for predicting the bioavailability of heavy metals; and (3) compare the characteristics of DGT with other methods. Materials and Methods: In this study, we collected maize and wheat samples and their rhizosphere soil over a pollution gradient in Kaifeng City, China. Six heavy metal (Cr, As, Cu, Zn, Cd, and Pb) levels in rhizosphere soil were determined using DGT, EDTA, soil solution, and total amount methods, respectively. The heavy metal content in the roots, leaves, stems, and grains of maize and wheat was also analyzed. The relationships between six heavy metal soils concentrations detected by different methods, and their contents in the different parts of wheat and maize, were analyzed using statistical methods. The characteristics and application scope of the different methods were evaluated. Results and Discussion: The accumulation of heavy metals in maize and wheat was generally higher in the roots than in the above-ground parts (i.e., stems, leaves, and grains). For the soil solution method, only soil As levels showed a significantly positive correlation with its content in different parts of wheat and corn. For the EDTA method and the soil total amount method, only As, Zn, and Pb levels were significantly correlated with their contents in different parts of wheat and corn. Six heavy metal concentrations detected by DGT were all significantly positively correlated with their contents in the different parts of wheat and maize. Furthermore, DGT was less affected by the soil pH than EDTA. Conclusions: DGT was more accurate in simultaneously predicting plant-available Cr, As, Cu, Zn, Cd, and Pb. However, other methods, like EDTA, soil solution, and total amount methods, can also be considered when predicting the bioavailability of a single heavy metal (e.g., As or Zn) in rhizosphere soil. [ABSTRACT FROM AUTHOR]

Purpose: Development of new binding gels for rapid and simultaneous quantification of bioavailability concentrations of various heavy metals in soils by diffusive gradients in thin film technique. Methods: Four binding gels including zinc-aluminum hydrogel (ZnAl-LDH), ethylenediaminetetraacetic acid intercalated zinc-aluminum hydrogel (ZnAl-EDTA-LDHs), polyglutamic acid (PGA), and polyglutamic acid–sodium alginate resin (SA-PGA) were prepared and used for the simultaneous measurement of Cr, Ni, Cu, Cd, and Pb. Results: The adsorption process reached equilibrium in 2 h, which could be considered a pseudo-second-order reaction. Three mol L−1 nitric acid was the best eluent with elution efficiency over 91% for the five heavy metals. Then, SA-PGA gel was assembled into DGT device (SA-PGA-DGT). Its performance was virtually unaffected by pH (5–9), ionic strength (1–50 mM), and soil properties with adsorption capacities 5.02 μg cm−2, 11.38 μg cm−2, 8.16 μg cm−2, 17.11 μg cm−2, and 89.43 μg cm−2 for Cr, Ni, Cu, Cd, and Pb, respectively. A good linear correlation was observed between the concentrations of Cr, Ni, Cu, Cd, and Pb determined by SA-PGA-DGT in soil samples from Tanggu District in China and the exchangeable contents of the five metals determined by the Tessier method, with R values of 0.64, 0.63, 0.59, 0.72, and 0.64 (p < 0.01). Conclusion: SA-PGA gel exhibited the best adsorption properties among the four gels. SA-PGA-DGT can be used as a reliable tool for rapid and simultaneous quantification of bioavailability concentrations of multiple heavy metals. [ABSTRACT FROM AUTHOR]

Chemical pollutants present a substantial threat to the survival of the green turtle (Chelonia mydas). In this study, the concentrations of 12 trace elements (TEs) in seawater, sediments, and green turtle forage and eggshells from the Xisha Islands in the South China Sea, along with their patterns of transfer and accumulation, were identified. The results revealed that the median TE concentrations in seawater and sediments were lower than the first-grade limit values of the national standard in China, indicating a low ecological risk. The concentrations (μg·g−1) of TEs in forage ranged from 0.05–0.69, 3.43–14.4, 157–2391, 27.9–124, 2.05–9.39, 0.30–9.78, 2.01–80.50, 0.18–5.76, 0.06–0.98, 2.00–18.4, 0.02–0.24, and 0.01–0.09 for Cr, Mn, Sr, Fe, Ni, Cu, Zn, Se, Cd, As, Pb, and Hg, respectively. Seawater, sediments, turtle forage, and eggshells exhibited different TE profiles, which were driven by Hg, Sr, Cr, and Pb in seawater and sediments; Fe and Ni in sediments; Cd and As in forage; and Zn, Se, and Cu in eggshells. The contents of Cu, Zn, and Se increased slightly with trophic level, indicating that they were transferred through dietary pathways. Although Cd and As appeared to bioaccumulate in green turtle forage, it was not transferred to their eggshells, which may be related to the excretion and metabolism process in the mother's body. Thus, eggshells may be a poor bioindicator for the exposure of female green turtles to these toxic elements. [ABSTRACT FROM AUTHOR]

In recent years, as the abuse of antibiotics, hormones, and herbicides has worsened in aquaculture industry, it is important to monitor the concentrations of those trace contaminants in aquaculture water more effortlessly. The aim of this study was to develop a reliable sampling method for chemical monitoring in aquaculture ponds based on the technique of diffusive gradients in thin films (DGT). A binding material (XDA-1 resin) with high adsorption capacity for antibiotics, hormones, and herbicides was selected. In laboratory, the diffusion coefficients of 11 antibiotics, 3 hormones, and 3 herbicides of the XDA-1-DGT devices were tested and ranged from 1.0×10−6 to 8.7×10−5 cm2/s. During the in situ application of XDA-1-DGT devices in different aquaculture ponds, concentrations of 11 antibiotics, 3 hormones, and 3 herbicides in aquaculture water (CSOLN) via grab sampling were also analyzed and found ranging from 0.03 to 6.3 ng/L, lower than the results based on DGT (CDGT) (1.2–1.3×102 ng/L). The values of CDGT/CSOLN were larger than one unit, suggesting that the rates of resupply of target chemicals (antibiotics, hormones, and herbicides) by the desorption and diffusion of pond water were higher than the rates of uptake by XDA-1-DGT, and pond water was proved a sufficient reservoir of antibiotics for DGT application. The value of Log (CDGT/CSOLN) of 1.1 derived from the application in the aquaculture ponds of 14 regions in Eastern China can be a reference value for future chemical monitoring based on DGT technique. And the accuracy of this value was found hardly affected by the physical and chemical properties of chemicals with pKa ranging from −1 to 12, Log Kow ranging from 0 to 4.5, and Log solubility ranging from 0.0 to 4.0. [ABSTRACT FROM AUTHOR]

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Equilibrium sampling based on silicone polydimethylsiloxane (PDMS) has been used to determine the concentrations of freely dissolved hydrophobic organic compounds (HOCs) and assess the thermodynamic potentials for bioaccumulation of these compounds in the aquatic environment. This allows the use of PDMS‐based sampling techniques in assisting conventional sampling and extraction methods for the determination of the concentrations of HOCs in aquaculture products. The present study is an ex situ demonstration of how well PDMS can inform the tissue residues and dietary risks of legacy or current‐use organic chemicals in aquaculture species from farm ponds in eastern China. For legacy contaminants such as polybrominated diphenyl ethers (PBDEs, n = 10), good agreement between the predicted concentrations based on PDMS and the measured lipid‐normalized concentrations was observed for 60% of the studied biota, including both pelagic and benthic species. For pesticides currently used, such as pyrethroid (PE) (n = 4) and organophosphate pesticides (OPPs, n = 7), the measured tissue residues were consistently higher than those predicted by PDMS, possibly caused by the continuous input from the surroundings. For the organochlorine pesticides (OCPs, n = 5), the only detected chemical was also underestimated. Adjusted by ingestion rates of aquaculture products and toxicology data, the target hazard quotients of these chemicals predicted from PDMS were generally comparable to those derived from measured concentrations in tissue because of the predominance of PBDEs. Overall, PDMS‐based equilibrium sampling offered an alternative approach for the prediction of tissue residues and dietary risks of PBDEs. Moreover, it should be applied with caution for PEs, OPPs, and OCPs. Improving the application of PDMS for these chemicals in farm ponds warrants future study. Environ Toxicol Chem 2021;40:79–87. © 2020 SETAC [ABSTRACT FROM AUTHOR]

Purpose: High water-level fluctuations (WLFs) usually lead to the periodic drying and rewetting of littoral sediment, proven to influence the transformation of various sediment contaminants. However, details regarding metal bioavailability variations remain unclear. In this study, oxidation–reduction status transition, metal fraction transformation, and the development of the acid volatile sulfide (AVS) and the simultaneously extracted metals (SEM) were investigated to assess the variations of metal bioavailability in the littoral anoxic sediment during the drying–rewetting process. Methods: A series of sediment cores were collected from the littoral area near the mouth of Nanfei River in Lake Chaohu, China, with half of them exposed to dark conditions with an overlying water cover (the control treatment). The other half was dried through the removal of overlying water and then exposed to air and sunlight (the drying treatment). Every 5 days, three of the dried sediment cores were rewetted for 3 days with lake water collected in situ. Various characteristics were analyzed for both the control and drying sediment cores. The drying and rewetting experiment was carried out for 30 days, and the bioavailability of metals was then evaluated thoroughly through data analyses. Results and discussion: The periodic drying and rewetting process led to the oxidation of the anoxic sediment with a pronounced increase in oxygen penetration depth and redox potential, and a decrease in AVS concentrations in the drying treatment after 15 days of experimentation. Significant increases in the values of the ratio of SEM and AVS, the difference between SEM and AVS, and the organic carbon normalized difference between ΣSEM and AVS were retrieved for the drying treatment after process completion. The increase of metal bioavailability to aquatic organisms was consequently predicted, with the most significant concerns noted regarding Cd and Pb due to their transformation to less firmly bound fractions. Conclusions: The periodic drying and rewetting process could increase the bioavailability of metals in littoral anoxic sediment. Therefore, this process should be given more attention during future management of water level and remediation of littoral sediment in similar areas. [ABSTRACT FROM AUTHOR]

The deposition and release of heavy metals in sediments often lead to their diffusion in lakes, especially for dispersed elements such as cadmium (Cd), which indirectly introduces pollutants into the food chain. The high rate of deposition or release of heavy metals in sediments is a problem to be solved. Southwest China is most famous in the world for the continuous distribution of karst area, for holding the largest area of bare carbonate rocks and for experiencing the strongest karst development in the world. The trace metals in 15 sites of Yelang Lake were determined by diffusive gradients in thin-films (DGT) method. The distribution and release mechanism of Cr, Ni, Cu, Cd, Zn and Pb under high geochemical backgrounds in the karst area of Guizhou Province in Southwest China were discussed. Based on the DGT concentration and pore water analysis, the distribution order of these heavy metal contents is usually upstream (SC), middle (DCB) and downstream (SW) areas of the lake, which increases during the dry season and decreases during the wet season. There was no significant difference in concentration between 0–4 and 4–8 cm depth (p < 0.05). The R values of heavy metals in the dry and wet seasons were highest with cadmium (Cd) and lowest with chromium (Cr) and lead (Pb). The results of the metal geo-accumulation index (Igeo) and the potential ecological risk index are highest on Cd and lowest on Cr. The mean concentrations of Cr, Cd, Zn, Ni (DCB, SW), Pb (SC, DCB) and Cu (SC) are between the corresponding threshold effect level and the probable effect level, and the average potential ecological risk is ranked in descending order of Cd > Pb > Zn > Cu > Ni > Cr. These three areas are at medium risk levels and the potential ecological risks increases from upstream to downstream. The deposition rate of heavy metals in Yelang Lake sediment was higher than the release rate and the ecological risk from heavy metals was relatively low. Since Cd is the main ecological risk factor in the lake, more attention needs to be given to Cd contamination in the Yelang Lake basin of the karst area. [ABSTRACT FROM AUTHOR]

Water samples and sediments from Liangzi Lake were taken and used to study the vertical distribution characteristics of nitrogen (N) and phosphorus (P) in both the overlying and pore water. Fluxes of ammonia (NH4+-N) and phosphate (PO43−-P) were calculated using a one-dimensional transport-reaction model based on Fick's First Law. The results showed that the mean NH4+-N and NO3−-N concentrations in the overlying water of Liangzi Lake were 2.59 and 0.46 mg L−1, respectively. The mean PO43−-P concentrations were lower than the detection limit. Both N and P displayed peaks at the sediment-water interface. For example, the mean concentration of ammonia in pore water in the surficial layer (0–5 cm) was 4.29 ± 2.74 mg·L−1, which was twice than that of the overlying water. Two PO43−-P vertical profile regimes were identified; one had a gradually increasing trend, while the other first increased and then decreased. The mean orthophosphate concentration in the pore water of the surface layer (0–5 cm) was 0.01 ± 0.01 mg·L−1. The spatial distribution of ammonia flux values was highly heterogeneous. Using these data, the annual load contribution of autochthonous ammonia was calculated to be 481 t a−1. Studying N and P pollution and fluxes in the lakes of urban drinking water sources facilitates the provision of protection measures. [ABSTRACT FROM AUTHOR]

Soil phosphorus fractions in wetland ecosystems have received increasing attention due to its high eutrophication risks. Soil samples were collected to 40 cm depth in three sampling seasons to investigate the seasonal dynamics of organic and inorganic phosphorus fractions, bioavailability, and relationship between those and soil properties in a seasonal-flooding wetland in the Yellow River Estuary. The results showed that inorganic phosphorus (IP) and organic phosphorus (OP) contents exhibited much higher levels in the top 10 cm soils, and declined along soil profiles in spring. IP kept constant along soil profiles in fall, while OP decreased in summer and fall. They were greatly affected by water content (WC), pH, Cl - /SO 4 2- , soil organic matter (SOM), and electrical conductivity (EC). Middle labile organic phosphorus (MLOP) and non-labile organic phosphorus (NLOP) accounted for higher percentages of total OP in summer and fall respectively than labile organic phosphorus (LOP) in spring. MLOP and NLOP levels showed a decrease along soil profiles in spring and in spring/fall, respectively, while NLOP significantly increased with depth in summer. Ca-P was the dominant IP fraction in all soils in three sampling seasons, declined with depth in spring/fall and increased in summer. Comparatively, soluble/loosely-P(S/L-P) generally decreased with depth along soil profiles in three sampling seasons. And residual P (Res-P) kept little change with depth in spring. Fe/Al-P levels decreased firstly and then increased with depth in spring and summer. Available phosphorus and potential bioavailable phosphorus contents decreased with depth in spring and summer not in fall, and had a strong significant positive correlation with WC and SOM. Alkaline phosphatase not acid phosphatase was the key factor influencing soil MLOP levels. Generally, the fractions and bioavailability of phosphorus as well as phosphatase in this region were affected by soil depth, sampling seasons, and soil properties (e.g., WC, pH, Cl - /SO 4 2- , SOM, and EC).