Urban River Sediments Research Articles

Electrical current generation from a continuous flow macrophyte biocathode sediment microbial fuel cell (mSMFC) during the degradation of pollutants in urban river sediment.

A new type of sediment microbial fuel cell (SMFC) with floating macrophyte Limnobium laevigatum, Pistia stratiotes, or Lemna minor L. biocathode was constructed and assessed in three phases at different hydraulic retention time (HRT) for electrical current generation during the degradation of urban river sediment. The results showed a highest voltage output of 0.88 ± 0.1V, maximum power density of 80.22mWm-3, highest columbic efficiency of 15.3%, normalized energy recovery of 0.030kWhm-3, and normalized energy production of 0.005kWhm-3 in the Lemna minor L. SMFC during phase 3 at HRT of 48h, respectively. Highest removal efficiencies of total chemical oxygen demand of 80%, nitrite of 99%, ammonia of 93%, and phosphorus of 94% were achieved in Lemna minor L. system, and 99% of nitrate removal and 99% of sulfate removal were achieved in Pistia stratiotes and Limnobium laevigatum system during the SMFC operation, respectively. Pistia stratiotes exhibited the highest growth in terms of biomass and tap root system of 29.35g and 12.2cm to produce the maximum dissolved oxygen of 16.85 ± 0.2mgL-1 compared with other macrophytes. The predominant bacterial phylum Proteobacteria of 62.86% and genus Exiguobacterium of 17.48% were identified in Limnobium laevigatum system, while the class Gammaproteobacteria of 28.77% was observed in the control SMFC. The integration of technologies with the continuous flow operation shows promising prospect in the remediation of polluted urban river sediments along with the generation of electrical current.

The remediation of urban freshwater sediment by humic-reducing activated sludge

Organic pollution of urban rivers caused by stormwater discharge is a global problem. Traditional bioremediation of organic matters (OM) by aerobes could be restrained in anaerobic environments, which usually occurr in polluted river sediments. In this study, an anaerobic remediation technology has been developed to enhance the in-situ removal of organic matters in river sediments, humic-reducing sludge (HRS) was adapted from traditional activated sludge; it exhibited a strong humic-reducing ability. Nitrate and biostimulants were used to stimulate HRS. The change of microbial community between AQDS-adapted and non-AQDS-adapted was analyzed, and the effect of HRS augmentation and Nitrate/biostimulant addition on TOM removal were discussed from the perspective of light and heavy fraction organic matters (LFOM and HFOM). The results have indicated that, after adaptation, HRS had increased the bacterial population of Anaerolineales and Desulfuromonadales, which was related to the carbon metabolism and electron-transfer ability. On the other hand, the adaptation decreased the population of bacteria related to the sulfur/sulfate circulation. This characteristic of the HRS was potentially benificial to reducing the occurrence of black-odor phenomenon. Also, the removal efficiency of TOM in sediment was significantly improved by using HRS because HRS could facilitate the removal of HFOM. Fourier Transform Infrared Spectroscopy (FTIR) analysis indicated that the advantage of decomposing HFOM using HRS resulted from the fact that the HFOM contained redox mediators to facilitate humic-reducing respiration. In addition, nitrate appeared to be crucial for the enhancement of HRS in sediments. These findings have allowed for the development of a technology for in-situ anaerobic remediation of urban river sediments. They could also help to understand humic-reducing mechanism in the sediment during anaerobic bioremediation.

Organohalide-Respiring Bacteria in Polluted Urban Rivers Employ Novel Bifunctional Reductive Dehalogenases to Dechlorinate Polychlorinated Biphenyls and Tetrachloroethene.

Polluted urban river sediments could be a sink of persistent and toxic polychlorinated biphenyls (PCBs) in urban areas and provide desired growth niches for organohalide-respiring bacteria (OHRB). In this study, microcosms were set up with surface sediments of nationwide polluted urban rivers in China, of which 164 cultures could dechlorinate tetrachloroethene (PCE) to dichloroethenes (DCEs) and to vinyl chloride and/or ethene. Further in vivo tests showed extensive PCB dechlorination with different pathways in 135 PCE pregrown cultures. Taking reductive dechlorination of PCB180 (2345-245-CB) as an example, 121 and 14 cultures preferentially removed flanked para- and meta-chlorines, respectively. Strikingly, all in vitro assays with the 135 PCE pregrown cultures showed identical PCB dechlorination pathways with their living cultures, implying the involvement of bifunctional reductive dehalogenases (RDases) to dechlorinate both PCBs and PCE. Further 16S rRNA and RDase gene-based analyses, together with enantioselective dechlorination of chiral PCBs, suggested that Dehalococcoides and Dehalogenimonas in the 135 cultures largely employed distinctively different novel bifunctional RDases to catalyze PCB/PCE dechlorination. Quantitative assessment of the community assembly process with the modified stochasticity ratio (MST) indicated three different stages in enrichment of OHRB. The second stage, as the only one controlled by stochastic processes (MST > 0.5), required extra attention in monitoring community successional patterns to minimize stochastic variance for enriching the PCB/PCE-dechlorinating OHRB.

Environmental forensics of complexly contaminated sites: A complimentary fingerprinting approach

The environmental forensics approach is most often applied in petroleum and fuel spill incidents, for which sophisticated chemical fingerprinting procedures have evolved. In cases in which pollutant discharges occur in settings with prior contamination, more care must be taken in source discrimination, requiring further advances in methodology. Additional obstacles can arise if the spill is an atypical industrial discharge. This would necessitate painstaking characterization of unfamiliar substances lying outside of existing regulatory regimes and thus overlooked by mandated analytical protocols (i.e., contaminants of emerging concern). Towards these ends, this paper presents a systematic, multi-faceted GC-MS approach using the saturated, aromatic, and resin fractions of contaminated soil extracts, alongside soil thermal desorption and analytical pyrolysis of the soil and its asphaltene fraction. This complimentary “extract + thermal” approach is applied to a typical fuel oil spill, sediments of a severely-impacted urban river, and brownfield soils from coke, petrochemical, and Hg-As pyrometallurgical plants. The insights thus attained can serve to better inform brownfield remediation planning in the public interest.

Seasonal Variation and Sources of Heavy Metals in Urban Street Dusts and River Sediments of Dongluo River Watershed in Ji'nan City, China

Due to intense human activities, urban street dusts and river sediments are usually polluted by heavy metals. This study investigated the seasonal variations (summer and winter) of pollution level, spatial distribution and potential sources of heavy metals in street dusts (SD) and river sediments (RS) of Dongluo River watershed, Ji'nan, China. Results showed cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn) contents were 3.5 (8.6), 3.0 (1.4), 4.9 (2.6), 4.1 (1.1) and 3.9 (4.0)-fold of their geochemical soil background values (BGV) of Shandong Province, China in summer (winter). Mercury (Hg) and arsenic (As) contents were lower than their background values in both summer and winter. The differences of Cd, Cr, Cu, Pb, Zn, Mn and As contents in river sediments between winter and summer were not statistically significant. The correlation coefficients between metal contents and the distance between sampling sites and the east-west boundary of study area were higher in summer than those in winter. Based on principal component analysis (PCA) and multivariate linear regression (MLR), coal combustion and traffic-related sources were the main sources in winter, and agricultural activities and traffic-related sources were the main sources in summer.

Spatial Distribution of Heavy Metals and Associated Risks in Sediment of the Urban River Flowing into the Pearl River Estuary, China.

Twenty-eight transects in six urban rivers located in the Qianhai area of Baoan District, Shenzhen, China, were selected to study the contamination of heavy metals in its sediment, reveal the spatial distribution of heavy metals in these rivers, and assess the ecological risk of heavy metals in the urban river sediment. The result showed that the concentration of heavy metals displayed considerable variation in the study area. The results showed that southern airport drainage river had exposure to high concentrations of Cu, Nanchang Chung exposure to high concentrations of Zn, Cr, and Pb, Gongle Chung exposure to high concentrations of Ni, and Xixiang River exposure to high concentrations of Hg. The results of correlation analysis and cluster analysis indicated that Cu had significant correlations with Zn and Cr respectively (P < 0.05). There was significant correlation, and the same cluster existed among Zn, Cr, and Pb (P < 0.01), whereas Hg was not significantly correlated with other metals. The potential risk of the six rivers could be sorted as Gushu Chung < Gongle Chung < Tiegang reservoir flood discharge river < Xixiang River (a), Nanchang Chung < and Southern Airport drainage river.

Coexistence of the blaNDM-1-carrying plasmid pWLK-NDM and the blaKPC-2-carrying plasmid pWLK-KPC in a Raoultella ornithinolytica isolate

To date, blaNDM and blaKPC genes have been found predominantly in clinical settings around the world. In contrast, bacteria harbouring these two genes from natural environments are relatively less well studied compared to those found in clinical settings. In this study, a carbapenem-resistant Raoultella ornithinolytica strain, WLK218, was isolated from urban river sediment in Zhengzhou City, Henan Province, China. This isolate was subjected to PCR and antimicrobial susceptibility testing. PCR results showed that this isolate was positive for both the blaNDM-1 and blaKPC-2 genes. The antimicrobial susceptibility testing results showed that this isolate exhibited resistance or intermediate resistance to all the antibiotics tested except for streptomycin (susceptible) and cefepime (susceptible-dose dependent). The complete genome sequence of the WLK218 isolate was then determined by using a combination of the PacBio and Illumina sequencing technologies. The de novo assembly of the genome generated one chromosome and six plasmids. Among the six plasmids, the blaNDM-1 gene was carried on the IncX3 plasmid pWLK-NDM, while the blaKPC-2 gene was located on the untypeable plasmid pWLK-KPC. This is the first report of an environmental Raoultella ornithinolytica isolate co-harbouring the blaNDM-1 and blaKPC-2 genes.

Effect of different ecological treatment methods on microbial community in black and odorous sediment of urban river

底泥细菌代谢是城市河道底泥代谢物的主要来源，最终决定城市河道的生态状况.本文研究了黑臭河道底泥经添加硝酸钙、生物促生剂和种植沉水植物处理后底泥中细菌群落结构的响应，以期为城市黑臭河道细菌群落的改善和综合治理提供理论依据.实验结果表明：经过不同生态处理后，上覆水中，添加硝酸钙组总氮（TN）含量显著高于对照组，添加生物促生剂组溶解氧浓度显著高于对照组.沉积物中，所有处理组的氧化还原电位值（ORP）均显著高于对照组，种植沉水植物组和添加硝酸钙组TN含量均显著低于对照组，沉积物理化性质得到一定改善.对不同生态处理组底泥细菌群落的研究发现，处理组底泥细菌群落产生了较大变化，且不同处理组细菌群落变化不同，生物促生剂组底泥中细菌的Sobs指数和Chao 1指数显著高于对照组和硝酸钙组，且生物促生剂组Shannon指数和PD指数显著高于硝酸钙组.Proteobacteria（Deltaproteobacteria、Betaproteobacteria、Gammaproteobacteria）、Chloroflexi、Firmicutes、Bacteroidetes和Spirochaetae是各实验组的主要优势菌门；非度量多维尺度分析表明：硝酸钙和生物促生剂的投加可明显改变底泥细菌群落结构组成.在属水平上，uncultured_Anaerolineaceae、Ferribacterium、uncultured_Xanthomonadales_Incertae_Sedis是导致底泥细菌群落发生变化的主要菌属.冗余分析结果表明，底泥ORP的变化是驱动细菌群落结构变化的关键环境因素.;Sediment microorganisms are the main source of sediment metabolism in urban rivers, which ultimately determine the ecological status of the rivers. In this paper, to analyze the effect of different ecological treatments on sediment microbial community, we established artificial mesocosms to mimic sediment status of the black-stinking river with different ecological treatments as calcium nitrate, bio-energizer addition, and submerged macrophytes transplantation. Illumina Miseq sequencing was applied to reveal the bacteria community variations of all treated and untreated sediments. The results showed that in the overlying water, the total nitrogen (TN) content of calcium nitrate addition group was significantly higher than that in the control group, dissolved oxygen concentration in the bio-energizer addition group was significantly higher than that in the control group. In the sediment, the oxidation reduction potential (ORP) values of all the treatment groups were significantly higher than those in the control group; TN content of calcium nitrate addition group and submerged macrophytes transplantation group were both significantly lower than those in the control group, which indicate the improvement of sediment status of treatment group. Bacterial communities were also varied in treatment group, and showed diverse variations with different treatments. The Sobs and Chao 1 microbial diversity indices in the bio-energizer addition group were both significantly higher than those in the control group and calcium nitrate addition group; the Shannon and PD diversity indices for microbes in the bio-energizer addition sediment were both significantly higher than those in calcium nitrate addition group. All sediment microbial communities were dominated by Proteobacteria (Deltaproteobacteria, Betaproteobacteria, Gammaproteobacteria), Chloroflexi, Firmicutes, Bacteroidetes and Spirochaetae phyla. Nonmetric multidimensional scaling analysis showed that the addition of calcium nitrate and bio-energizer can significantly alter the composition of bacterial community structure. Uncultured_Anaerolineaceae, Ferribacterium and uncultured_Xanthomonadales_Incertaeae_Sedis were the main genus causing variations in the bacterial community. Redundancy analysis indicated that the change of sediment ORP is a key environmental factor driving the variation of bacterial community structure.

Heavy metal pollution and potential ecological risk in urban river sediment of Huai’an City, China

Sediment heavy metal pollutant monitoring was carried out at 16 monitoring points of three rivers and one lake in Huai’an city. The contamination degree of heavy metals was evaluated by geoaccumulation index. The potential ecological risk of heavy metals was assessed. The results showed that Hg and Cu geoaccumulation index class exceeded moderately polluted level, especially Hg, and two monitoring points reached highly polluted level. Hg pollution is at a high/extremely high potential ecological risk. Most of the other single-factor heavy metal indexes are at a low ecological risk level. The comprehensive ecological risk index of 6 monitoring points showed a high potential ecological risk. The Hg in urban rivers sediment of Huai’an may come from the deposition of long-term domestic sewage discharge or domestic refuse dump.

Bacterial Community Shifts Driven by Nitrogen Pollution in River Sediments of a Highly Urbanized City.

Effects of nitrogen pollution on bacterial community shifts in river sediments remain barely understood. Here, we investigated the bacterial communities in sediments of urban and suburban rivers in a highly urbanized city, Shanghai. Sediment nitrate (NO3−) and ammonia (NH4+) were highly accumulated in urban river. Operation Taxonomic Units (OTUs), Abundance-based Coverage Estimators (ACEs) and Chao 1 estimator in urban rivers were slightly lower than those in suburban rivers, while Shannon and Simpson indices were higher in urban rivers than those in suburban rivers. Proteobacteria, Firmicutes, and Bacteroidetes were the dominant bacterial phylum communities, accounting for 68.5–84.9% of all communities. In particular, the relative abundances of Firmicutes and Nitrospirae were significantly higher in suburban rivers than in urban rivers, while relative abundances of Bacteroidetes, Verrucomicrobia, and Spirochaetes were significantly lower in suburban rivers than in urban rivers. NH4+ was significantly and negatively correlated with abundances of Firmicutes, Nitrospirae, and Actinobacteria. Importantly, the significant and negative effects of sediment NH4+ on bacterial richness and diversity suggested that nitrogen pollution likely contribute to the decrease in the bacterial richness and diversity. The results highlight that nitrogen enrichment could drive the shifts of bacterial abundance and diversity in the urban river sediments where are strongly influenced by human activities under the rapid urbanization stress.

Pollutant removal and bioelectricity generation from urban river sediment using a macrophyte cathode sediment microbial fuel cell (mSMFC)

Sediment microbial fuel cell (SMFC) efficacy depends highly on organic matter flux and dissolved oxygen (DO) at the anode and cathode, respectively. However, utilizing floating-macrophyte for elevated DO supply at the cathode has not been fully explored. Therefore, a novel floating-macrophyte implanted biocathode single-chamber SMFC (mSMFC) was developed for the simultaneous removal of pollutant and bioelectricity generation from polluted urban river sediment. With Lemna minor L. employed in mSMFC, high pollutant removal was feasible as opposed to the control bioreactor. Total COD, nitrate and sulfate removal reached 57%, 99%, and 99%, respectively. Maximum voltage output, power density, columbic efficiency, normalized energy recovery, and net energy production observed was 0.56 ± 0.26 V, 86.06 mW m−3, 24.7%, 0.033 kWh m−3 and 0.020 kWh m−3, respectively. Alternatively, when floating-macrophyte (predominantly Pistia stratiotes) was employed in the catholyte, DO increased significantly to about 10 mg L−1 in the mSMFC. 16S rRNA gene sequencing revealed Euryarchaeota-(90.91%) and Proteobacteria-(59.68%) as the dominant phyla affiliated to archaea and bacteria, respectively. Pollutant removal mechanisms observed within the mSMFC included bioelectrochemical oxidation at the anode and reduction reaction and macrophyte hyperaccumulation at the cathode. The novel mSMFC system provided an effective approach for the removal of pollutant and bioelectricity generation.

Occurrence and distribution of antibiotics and antibiotic resistant genes in water and sediments of urban rivers with black-odor water in Guangzhou, South China

Urban rivers in some countries have been heavily polluted and the water became black and odor. Nevertheless, only few studies reported the occurrence of antibiotics and their corresponding antibiotic resistant genes (ARGs) in urban rivers with black-odor water with and without remediation. In this study, nine antibiotics (belonging to sulfonamides, tetracyclines, quinolones, and macrolides) and their corresponding ARGs in water and sediments of six urban rivers in Guangzhou, South China were analyzed to investigate their spatial distribution and the influence of water remediation. The concentrations of individual antibiotics varied from ND (not detectable) to 2702 ng/L and ND to 449 μg/kg in surface water and sediments, respectively. Norfloxacin displayed the highest average concentrations, followed by ciprofloxacin. The relative abundance of quinolone-resistance gene qnrA (~103 ARGs/16S rRNA) was the highest, followed by tetracyclines-resistance genes tetC (~10−2 ARGs/16S rRNA). The antibiotics and ARGs in sediments from various rivers exhibited distinct spatial distribution with large variation from upstream to downstream. Generally, levels of antibiotics and tetracyclines-resistance genes (tetA, tetC and tetM) in urban rivers with black-odor water (affected by industrial and domestic sewage) were higher than those in remediated urban rivers. Significant positive correlations were observed only between the relative abundances of tetA (or tetC) with the concentrations of some antibiotics (e.g., ciprofloxacin and norfloxacin). TetA was also significantly positively correlated with the concentrations of Ni, Cr, and As in sediments. This study found that urban rivers remediated with dredging might lower antibiotic levels in sediment, but high relative abundance of certain ARGs (e.g., tetB, qnrA) may still exist.

Biochar as an Effective Material on Sediment Remediation for Polycyclic Aromatic Hydrocarbons Contamination

The high-speed urbanization and associated human activities have led to dramatic alternations on urban river ecosystems [1, 2], which consequently degrades surface water quality [3]. As a pollutant sink in the river ecosystem, sediment can accumulate various polycyclic aromatic hydrocarbons (PAHs), which derive from ship traffic petrol leaking and urban wastewater runoff [4]. PAHs are difficult to degrade under anaerobic conditions in the environments [5] and remain risks to ecosystems as well as human health [6]. Therefore, the removal of PAHs in sediment is a key technique in urban river remediation. Several approaches were developed to remediate the PAHs contaminated sediments, including dredge, bioaugmentation, biostimulation and capping with clean material [7]. Among these methods, capping with viable substances were widely used as low cost approaches for the natural recovery of sediments [8]. For the capping treatments, selection of cap-material is the critical part of this technology. These materials, such as clean sand, zeolite, and activated carbon [9], are all expected to have high adsorption capacities and be able to block the diffusion of organic pollutants from sediments. However, the utilization of these materials would consume natural resources (such as sand and zeolite) and require excessive energy in put (activated carbon). Development of a more environmental friendly materials is of great concern on capping treatment for PAHs degradation. Biochar is unknown as an environmental friendly material, since it involve in carbon sequestration pathway and it always be produced from various agriculture wastes such as straws, branches, and nut shells [10]. The characteristics of biochar depend on its raw matrix and pyrolysis conditions. Biochar that derived from natural plants are usually porous and hydrophobic, which have high adsorption capacity for organic components [11]. Therefore, biochar has the potential capability to be used as a capping material for PAHs treatments. This study aims to investigate the mechanism of biochar as capping materials for PAHs removal in urban river sediments.

Microscopy and elemental analysis characterisation of microplastics in sediment of a freshwater urban river in Scotland, UK

Understanding of the sources, fate, and impact of microplastics (MPs, < 5 mm) remains limited, particularly in freshwater environments, while limited comparability across available surveys hinders adequate monitoring and risk assessment of these contaminants. Here, the distribution of microscopic debris in an urban river close to the marine environment in the West of Scotland was investigated to assess concentration and distribution of primary and secondary MPs. Also, the efficiency of light and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) was evaluated for characterisation and quantification of MPs sized 2.8 mm–11 μm. Bank sediment samples were collected twice from the River Kelvin in Glasgow and were size-fractionated and processed for extraction of MPs by density separation. Sample MPs spiking and use of procedural blanks allowed the influence of processing on field data quality to be considered. Total abundances were 161–432 MPs kg−1 dry sediment, with fibres as the dominant type, comprising > 88% of total counts. Nevertheless, fibres in blanks suggest potential contributions from atmospheric contamination. Moreover, fibres concentrated mainly in fractions < 0.09 mm suggesting that their fate may be influenced by drivers of fine sediment dynamics in rivers. While no primary MPs were observed, metallic and glass pellets were present in high abundances in settled material and could be easily misidentified by visual inspection, demonstrating that compositional analysis is needed to avoid analytical errors from MP misidentification and overestimation. SEM-EDS allowed for a quick screening of plastic vs non-plastic pellets and improved identification of smaller fragments, whereas more advanced techniques are needed for proper identification of fibres. This study is the first to report on MPs in freshwater rivers in Scotland and suggests that diffuse sources of pollution may be delivering secondary MPs to the river. Their sources, fate, and risk in these systems will thus warrant further attention.

Bacterial community composition and function shift with the aggravation of water quality in a heavily polluted river

Blackening and odorization of heavily polluted rivers has become a vital aquatic environmental problem in developing countries and has threatened river ecosystems. Monitoring the contamination and functional degradation conditions is important for bioremediation of river ecosystems. In this study, the diversity, composition, co-occurrence pattern, and function of bacterial communities collected from a heavily polluted urban river sediment were investigated using 16S rRNA amplicon sequencing analysis. The degree of pollution in the river was divided into three levels, and the clustering result based on the relative abundance of bacterial communities was consistent with the pollution levels in the river. The community assembly analysis further demonstrated that bacterial community assembly was mainly driven by environmental selection (95.84%) in Jinchuan River. Composition of bacterial communities were clearly different at different pollution level sites, although no apparent changes in alpha diversity were observed. The complexity of the bacterial co-occurrence network decreased with aggravation of the pollution level, as indicated by topological features, suggesting that the interactions among bacterial communities were weakened. A phylogenetic Investigation of Communities by Reconstruction of Unobserved States analysis predicted that the relative abundance of functional genes was negatively correlated with pollution levels, and those related to energy metabolism as well as xenobiotic biodegradation and metabolism decreased significantly. These results provide an ecological reference for monitoring and bioremediation of aquatic ecosystems.

Na2SO4 addition on electro-dewatering of urban river sediment by horizontal circular electric field: Comparison of three different electrodes

The influence of Na2SO4 addition on electro-dewatering of urban river sediment with iron, copper, or graphite anodes was investigated using the constant cell voltage of 30 V. The dewatering rate and energy consumption were affected by the concentration of Na2SO4. The greatest dry solids content was achieved at Na2SO4 dosage of 10 (DS – dry solids) with dry solids content for the iron, copper, and graphite electrodes of 56.8, 52.4, and 52.2 wt.%, respectively. With respect to an initial solid content of about 40 wt.%, the iron electrode performed the best with the dewatering rate of 3.62 g m−2 s−1 and energy consumption of 0.167 . Due to the formation of a nonconductive coherent oxide film on the copper anodes, these performed the worst with dewatering rate of 2.31 g m−2 s−1 and energy consumption of 0.129 . These outcomes help to provide the basis for the choice of electrodes and electrolyte dosage for electro-osmostic dewatering of river sediment.

Occurrence, sources and ecotoxicological risks of polychlorinated biphenyls (PCBs) in sediment cores from urban, rural and reclamation-affected rivers of the Pearl River Delta, China

Sediment cores were collected to a depth of 40 cm (50 cm for urban river sediments) in the Pearl River Delta of China from rural river sediments and river sediments undergoing the process of urbanization and reclamation. Polychlorinated biphenyls (PCBs) in sediment cores were determined to evaluate their levels, distribution, possible sources and potential risks aimed at providing effective information of management practices for local governments. Our results showed that the total concentrations of PCBs (∑16PCBs) in urban, rural and reclamation-affected river sediments ranged from 16.15 to 477.85 μg kg−1 (dry weight), with mean values of 121.94, 150.49 and 124.20 μg kg−1 (dry weight), respectively. The most abundant PCB congeners among the study area were light PCBs. Generally, PCBs showed a decreasing trend with depth along sediment cores at most sampling sites. Source analysis indicated that PCBs in the three types of river sediments mainly originated from Aroclor 1242, 1248, 1254 and 1016. Risks evaluation based on sediment quality guideline quotient (SQGQ) showed PCBs at most sampling sites would cause no or moderate adverse biological effects on benthic organisms except surface sediments of U4 and R5 (high adverse biological effects). However, threshold effects level (TEL) is ignored when calculating SQGQ, which might underestimate the risks of PCBs. Thus, a new SQGQ (NSQGQ) taken TEL into consideration was established. Results showed that NSQGQ could evaluate ecotoxicological risks of PCBs better. Redundancy analysis (RDA) showed that PCBs in sediments were positively correlated with sand content and microbial biomass carbon (MBC) (p < 0.05).

Bioremediation of contaminated urban river sediment with methanol stimulation: Metabolic processes accompanied with microbial community changes

The intense pollution of urban river sediments with rapid urbanization has attracted considerable attention. Complex contaminated sediments urgently need to be remediated to conserve the ecological functions of impacted rivers. This study investigated the effect of using methanol as a co-substrate on the stimulation of the indigenous microbial consortium to enhance the bioremediation of petroleum hydrocarbons (PHs) and polycyclic aromatic hydrocarbons (PAHs) in an urban river sediment. After 65 days of treatment, the PAHs degradation efficiencies in the sediment adding methanol were 4.87%–40.3% higher than the control. The removal rate constant of C31 was 0.0749 d−1 with 100 mM of supplied methanol, while the corresponding rate was 0.0399 d−1 in the control. Four-ring PAHs were effectively removed at a degradation efficiency of 65%–69.8%, increased by 43.3% compared with the control. Sulfate reduction and methanogenesis activity were detected, and methane-producing archaea (such as Methanomethylovorans, with a relative abundance of 25.87%–58.53%) and the sulfate-reducing bacteria (SRB, such as Desulfobulbus and Desulfobacca) were enriched. In addition, the chemolithoautotrophic sulfur-oxidizing bacteria (SOB, such as Sulfuricurvum, with a relative abundance of 34%–39.2%) were predominant after the depletion of total organic carbon (TOC), and markedly positively correlated with the PHs and PAHs degradation efficiencies (P < 0.01). The SRB and SOB populations participated in the sulfur cycle, which was associated with PHs and PAHs degradation. Other potential functional bacteria (such as Dechloromonas) were also obviously enriched and significantly positively correlated with the TOC concentration after methanol injection (P < 0.001). This study provides a new insight into the succession of the indigenous microbial community with methanol as a co-substrate for the enhanced bioremediation of complexly contaminated urban river sediments.

Spatial and Temporal Distribution of Di-(2-ethylhexyl) Phthalate in Urban River Sediments.

This study investigated the spatial distribution of di-(2-ethylhexyl) phthalate (DEHP), and its potential biological effects, in the surface sediments that were collected from 10 sites at the Love River during dry and wet seasons. The grain size and organic matter were measured to understand the key factors that affect the distribution of DEHP concentrations in the sediments of Love River. The mean DEHP concentrations in the sediments that were collected during the wet and dry seasons were 28.6 ± 19.5 and 17.8 ± 11.6 mg/kg dry weight, respectively. The highest DEHP concentration was observed in the sediments that were sampled in the vicinity of the estuary. The correlation analysis showed that the grain size and organic matter may play a key role in the DEHP distribution in the sediments during the dry season, whereas the DEHP concentrations in the wet season may be mainly affected by other environmental and hydrological conditions. By a comparison with the sediment quality guidelines, the levels of DEHP in the sediments of Love River were found to have the potential to result in an adverse effect on aquatic benthic organisms. Specifically, during the wet season, wastewater from upstream of Love River is flushed downstream, causing a higher DEHP concentration in the sediments. Future pollution prevention and management objectives should move towards reducing the discharge of upstream wastewater and establishing a complete sewer system to reduce DEHP pollution in the environment.

Relationships between chemical and microbial faecal source tracking markers in urban river water and sediments during and post-discharge of human sewage

This study explores the relationships between faecal source tracking (FST) markers (quantitative Polymerase Chain Reaction (qPCR) markers and steroids), microbial indicators, the faecal ageing ratio of atypical colonies/total coliforms (AC/TC) and potential human pathogens (Giardia, Cryptosporidium and Campylobacter). Faecal source PCR markers tested were GenBac3, HumM3, HumBac (HF183-Bac708R); Bifidobacterium adolescentis, wildfowl and canine-associated markers. Sediment and water samples from the Avon River were collected during and post-discharge of untreated human sewage inputs, following a series of earthquakes, which severely damaged the Christchurch sewerage system.Significant, positive Spearman Ranks (rs) correlations were observed between human-associated qPCR markers and steroid FST markers and Escherichia coli and F-specific RNA bacteriophage (rs 0.57 to 0.84, p < 0.001) in water samples. These human source indicative FST markers demonstrated that they were also effective predictors of potentially pathogenic protozoa in water (rs 0.43–0.74, p ≤ 0.002), but correlated less well with Campylobacter. Human-associated qPCR and steroid markers showed significant, substantial agreement between the two FST methods (Cohen's kappa, 0.78, p = 0.023), suggesting that water managers could be confident in the results using either method under these contamination conditions.Low levels of fluorescent whitening agents (FWA) (mean 0.06 μg/L, range 0.01–0.40 μg/L) were observed in water throughout the study, but steroids and FWA appeared to be retained in river sediments, months after continuous sewage discharges had ceased. No relationship was observed between chemical FST markers in sediments and the overlying water, and few correlations in sediment between chemical FST markers and target microorganisms. The low values observed for the faecal ageing ratio, AC/TC in water, were significantly, negatively correlated with increasing pathogen detection. This study provides support for the use of the AC/TC ratio, and qPCR and steroid FST markers as indicators of health risks associated with the discharge of raw human sewage into a freshwater system.