This study demonstrated that nitrogen-doped carbon materials (NCMs) could effectively catalyze the chlorine elimination process in hexachloroethane (HCA) declorination in sulfide-containing environments for the first time. The kₒbₛ values of HCA dechlorination by sulfide in the presence of 10 mg/L NCMs were higher than that of no mediator at pH 7.3 by one or two orders of magnitude. The catalytic capabilities of NCMs on HCA dechlorination were evident in common ranges of natural pH (5.3–8.9) and it could be accelerated by the increase of pH but be suppressed by the presence of dissolved humic acid. Moreover, NCMs exhibited much better catalytic capability on HCA dechlorination compared to the carbon materials, mainly owing to the combined contributions of pyridine N, including enhanced nucleophilic attack to HCA molecule by generating newborn C–S–S and activation of HCA molecule by elongating C–Cl bonds. The functions of pyridine N in micron-sized NCMs with mesopores were better than in nano-sized NCMs on HCA dechlorination. These findings displayed the potential of NCMs, when released into sulfide-containing environments, may significantly increase the dechlorination of chlorinated aliphatic hydrocarbons.

Microbial denitrification is a main source of nitrous oxide (N₂O) emissions which have strong greenhouse effect and destroy stratospheric ozone. Though the importance of sulfide driven chemoautotrophic denitrification has been recognized, its contribution to N₂O emissions in nature remains elusive. We built up long-term sulfide-added microcosms with sediments from two freshwater lakes. Chemistry analysis confirmed sulfide could drive nitrate respiration in long term. N₂O accumulated to over 1.5% of nitrate load in both microcosms after long-term sulfide addition, which was up to 12.9 times higher than N₂O accumulation without sulfide addition. Metagenomes were extracted and sequenced during microcosm incubations. 16 S rRNA genes of Thiobacillus and Defluviimonas were gradually enriched. The nitric oxide reductase with c-type cytochromes as electron donors (cNorB) increased in abundance, while the nitric oxide reductase receiving electrons from quinols (qNorB) decreased in abundance. cnorB genes similar to Thiobacillus were enriched in both microcosms. In parallel, enrichment was observed for enzymes involved in sulfur oxidation, which supplied electrons to nitrate respiration, and enzymes involved in Calvin Cycle, which sustained autotrophic cell growth, implying the coupling relationship between carbon, nitrogen and sulfur cycling processes. Our results suggested sulfur pollution considerably increased N₂O emissions in natural environments.

With the burst of silver nanoparticles (AgNPs) applications, their potential entry into the environment has attracted increasing concern. To date, researches about the impacts of AgNPs on microbial communities have been scarcely conducted in the brackish waters. Here, the effects of interactions of AgNPs and Ag⁺ (as a positive control) with dissolved oxygen on natural brackish water microbial communities were investigated for 30 d. The introduction of AgNPs and Ag⁺ in natural brackish waters resulted in distinct bacterial community composition and structure as well as reduction of the richness and diversity, effects that were not eliminated completely during the tested periods. Anoxic conditions could attenuate the effects of AgNPs and Ag⁺ on the community, and dissolved oxygen made more contributions to community compositions for short-term exposure. High doses of AgNPs had more pronounced long-term impacts than Ag⁺ amendment. Compared with the controls, two general AgNP and Ag⁺ responses, namely, sensitivity and resistance, were observed. Sensitive species mainly included those of the genera Synechococcus and unclassified_f_Rhodobacteraceae, while resistant species mostly belonged to the phylum Bacteroidetes and participated in carbon metabolic processes. Our results indicated that the microbial communities that were involved in nutrient cycles (such as carbon, nitrogen, and sulfide) and photoautotrophic bacteria that contained bacteriochlorophyll were adversely affected by AgNPs and Ag⁺. In addition, dissolved oxygen could further change the microbial communities. These results implied that under different oxygen conditions AgNPs possibly resulted in varying microbial survival strategies and affected the biogeochemical cycling of nutrients in natural brackish waters.

The release of fine particles from biochar materials applied in the environment may have important environmental implications, such as mobilization of environmental contaminants. In natural environments biochar fine particles can undergo various transformation processes, which may change their surface chemistry and consequently, the mobility of the particles. Here, we show that sulfide reduction can significantly alter the transport of wheat-straw- and pine-wood-derived biochar fine particles in saturated porous media. Counterintuitively, the sulfide-reduced biochar particles exhibited greater mobility in artificial groundwater than their non-reduced counterparts, even though reduction led to decrease of surface charge negativity and increase of hydrophobicity (from the removal of surface O-functional groups), both should favor particle deposition, as predicted based on extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. Using transport experiments conducted in single-cation background solutions containing K⁺, Mg²⁺ or Ca²⁺ under different pH conditions, we show that the surprisingly greater mobility of sulfide-reduced biochar particles was attributable to the removal of surface carboxyl groups during reduction, as this markedly alleviated particle deposition through cation bridging, wherein Ca²⁺ acted as the bridging agent in linking the surface O-functional groups of biochar particles and quartz sand. These findings show the critical roles of surface properties in dictating the mobility of biochar fine particles and call for further understanding of their transport properties, which apparently cannot be simply extrapolated based on the findings of other (engineered) carbonaceous nanomaterials.

After the exploitation of coal mines in the 19th and 20th centuries in northern France, many mining slag heaps (SH) were left without any particular management or monitoring. Currently, the influence of these SHs on the quality of surrounding wetlands is hardly known.The purpose of this work is to determine the water quality in the neighbourhood of two SHs located near the city of Douai and its influence on the distribution of aquatic invertebrates in local wetlands. Our approach involves (1) the spatial and temporal characterization of the water composition (anions, major elements, sulphide, DOC and alkalinity) and of the biological diversity (aquatic invertebrates) and (2), based on this chemical and biological screening, the establishment of relationships between water quality and biodiversity distribution through multivariate data analysis. The results clearly indicate that substantial leaching from the slag heaps occurs, given the very high concentrations of dissolved sulphates (in the range of 2 g L⁻¹). While the pH remains weakly basic, indicating that the leaching water has been neutralized by the highly carbonated regional substratum, high levels of biodegradable organic matter and sulphate contents have been noticed. They sporadically cause significant drops in dissolved oxygen and the occurrence of dissolved sulphides that massively reduce biodiversity, qualitatively and quantitatively. In Summer, oxygen saturation is generally lower due to the higher rate of organic matter degradation, and the risk of anoxic episodes therefore increases. Finally, as wetlands are vulnerable environments, these preliminary results suggest that monitoring and management of these sites must be attempted quickly to avoid the degradation of those valuable habitats.

To understand the effect of reaction temperature on sulfur during hydrothermal carbonization (HTC) of sewage sludge (SS), seven group of temperature (180–300 °C) were chosen to investigate the distributions and evolution of sulfur-containing compounds in hydrochar and the liquid products. Elemental analysis, X-ray photoelectron spectroscopy (XPS), and X-Ray powder diffraction (XRD) were used to characterize the distribution of sulfur in hydrochar. The concentrations of sulfate ions and sulfide were determined in the liquid sample. The experimental results showed that as the temperature increased, the O/C ratio decreased because of the improved carbonization degree of SS. After hydrothermal carbonization, 90% of the sulfur in SS remained in hydrochar. As the temperature increased, the amount of sulfur in the liquid, mainly in the form of sulfate ions, tended to decrease. However, the experimental results for the gas phase were the opposite of the liquid phase.

Nitrogen pollution of groundwater has created problems worldwide. Riparian zones form a connection hub for terrestrial and aquatic ecosystems. As a potential source of ammonium in groundwater, aquitards have an important effect on the environment of riparian zones. The spatial distribution and factors influencing the ammonium content in the riparian zone aquitard of a small watershed were analyzed through three geological boreholes with increasing distances from the river: boreholes A > B > C. The results show that the distribution of ammonium was closely related to the lithology of sediments. Under the influence of the river and floods, the average content of ion exchange form of ammonium of sediments in borehole A (stable sedimentary environment) was 94.31 mg kg⁻¹, accounting for 21.2% of the transferable ammonium. The average proportions of ion exchange form of ammonium in the transferable ammonium of boreholes B and C (unstable sedimentary environment) were 19.1% and 17.4%, respectively. The carbonate and iron-manganese oxide forms of ammonium content of sediments in three boreholes were 0.96–15.28 mg kg⁻¹ and 2.3–54.4 mg kg⁻¹, respectively; this was mainly affected by the pH and Eh of the sedimentary environment. Organic sulfide, the form of transferable ammonium of sediments mainly exists in organic matter. The ammonium content in pore water generally increased with depth and was mainly derived from the mineralization of humic-like organic matter in borehole A. The ammonium in pore water in boreholes B and C mixed with ammonium from the mineralization of organic matter and the desorption of ion exchange form ammonium within sediments. The ammonium content in the pore water (up to 5.34 mg L⁻¹) was much higher than the limit for drinking water of 0.5 mg L⁻¹ in China. Therefore, the aquitard has a high risk of releasing ammonium and poses a certain threat to the quality of groundwater.

Eutrophic freshwater lake ecosystems are receiving increasing public attention due to a global increase in large-scale harmful cyanobacterial blooms in surface waters. However, the contribution of phytodetritus accumulation in benthic sediments post-bloom remains unclear. In this study, field investigations were performed using microsensors to evaluate benthic phytodetritus mats by measuring TOC/TN ratios, pigments, biodegradable compounds and odorants as descriptive parameters. Results show that the massive amount of phytodetritus trapped by aquatic plants gradually evolved into benthic cyanobacterial detritus mats, which were characterized as anoxic, reductive and low pH. It was confirmed that the occurrence of odorants is more serious in the detritus mats due to decay and decomposition of the accumulated phytodetritus. The mean odorant content in the vegetated zones was 3–52 times higher than that in the unvegetated zones. The dominant odorants were dimethyl trisulfide (DMTS), β-ionone and β-cyclocitral, with mean contents of 52.38 ng·(g·dw)-1, 162.20 ng·(g·dw)-1 and 307.51 ng·(g·dw)-1, respectively, in the sediment. In addition, odorant production appears to be associated with the distribution of biodegradable compounds in the sediment. This is supported by the marked correlation observed between biodegradable compounds and odorants. Multiple regression analysis showed that biodegradable compounds can be used as indicators to predict odorant content in the sediment. It is noteworthy that the odorant trend in the water column and sediment is symmetrical, indicating a risk of diffusion from the sediment to the water column. This study helps to clarifying the contributions of benthic cyanobacterial detritus mats to odorant production in shallow eutrophic lakes. The information provided herein may also be useful for future management of aquatic ecosystems.

The Keban Reservoir, which is the second man-made waterbody in Turkey, has the biggest rainbow trout production in the country. In this study, the impacts of rainbow trout farms on water and sediment chemistry were investigated. Water and sediment samples were taken at distances of 0, 10, 25, 50 and 100 m from the edge of the cages at the three fish farms, and at the respective reference stations. Samples were also taken at 0 m stations and reference stations in the late August when there were no fish in the cages. Physico-chemical variables and trace metals were analysed in all samples. Due to likely high dilution rates and recycling processes in the water column of the reservoir, little changes in the water quality parameters associated with wastes of the fish farms were noticed. When compared with those in the sediment samples at the stations near the edge of cages, the lower concentrations of total phosphorus (TP), total nitrogen (TN), organic matter (OM), total carbon (TC), sulfide (S2−), arsenic (As), cobalt (Co), copper (Cu), manganese (Mn) and zinc (Zn), and higher values of redox potential (Eh) were found at the reference stations. According to organic enrichment classification based on S2− and Eh values, sediments of the three fish farms in the period when there were fish in the cages fell into the oxic category, whereas sediments in the August (no fish farming activity) fell into the normal category. Also, it was found in the August that most of sediment quality parameters at the 0 m stations had close values to those at the reference stations. These results revealed that a three-month period when there were no fish in the cages allows for sediments to return to reference station conditions.

Sediments nearby harbors are dredged regularly, and the sediments require the stringent treatment to meet the regulations on reuse and mitigate the environmental burdens from toxic pollutants. In this study, FeCl₃ was chosen as an extraction agent to treat marine sediment co-contaminated with Cu, Zn, and total petroleum hydrocarbons (TPH). In chemical extraction process, the extraction efficiency of Cu and Zn by FeCl₃ was compared with the conventional one using inorganic acids (H₂SO₄ and HCl). Despite the satisfactory level for extraction of Cu (78.8%) and Zn (73.3%) by HCl (0.5 M) through proton-enhanced dissolution, one critical demerit, particularly acidified sediment, led to the unwanted loss of Al, Fe, and Mg by dissolution. Moreover, the vast amount of HCl required the huge amounts of neutralizing agents for the post-treatment of the sediment sample via the washing process. Despite a low concentration, extraction of Cu (70.1%) and Zn (69.4%) was done by using FeCl₃ (0.05 M) through proton-enhanced dissolution, ferric-organic matter complexation, and oxidative dissolution of sulfide minerals. Ferric iron (Fe³⁺) was reduced to ferrous iron (Fe²⁺) with sulfide (S²⁻) oxidation during FeCl₃ extraction. In consecutive chemical oxidations using hydrogen peroxide (H₂O₂) and persulfate (S₂O₈²⁻), the resultant ferrous iron was used to activate the oxidants to effectively degrade TPH. S₂O₈²⁻ using FeCl₃ solution (molar ratio of ferrous to S₂O₈²⁻ is 19.8–198.3) removed 42.6% of TPH, which was higher than that by H₂O₂ (molar ratio of ferrous to H₂O₂ is 1.2–6.1). All experimental findings suggest that ferric is effectively accommodated to an acid washing step for co-contaminated marine sediments, which leads to enhanced extraction, cost-effectiveness, and less environmental burden.