Δευτέρα, 18 Φεβρουαρίου 2019

Environmental Sciences

News: Dr. Xing-Fang Li is awarded Canada Research Chair in Analytical Chemistry and Environmental Toxicology

Publication date: April 2019

Source: Journal of Environmental Sciences, Volume 78

Author(s):



Mercury bioaccumulation in fish in an artificial lake used to carry out cage culture

Publication date: April 2019

Source: Journal of Environmental Sciences, Volume 78

Author(s): Yongmin Wang, Qing Xie, Qinqin Xu, Jinping Xue, Cheng Zhang, Dingyong Wang

Abstract

As a global toxic pollutant, mercury (Hg) bioaccumulation within food chain could be influenced by human disturbance. Ten typical fish species were collected from Changshou Lake, an artificial lake used to carry out cage fish culture, to investigate the C/N isotopic compositions and Hg bioaccumulation in fish. The results showed that the total Hg (THg) and methylmercury (MeHg) levels in fish muscles ((56.03 ± 43.96) and (32.35 ± 29.57) ng/g, wet weight), comparable with those in most studies in China, were significantly lower than the international marketing limit (0.5 mg/kg). Past human input for cage culture in this lake led to abnormal 15N enrichment in food chain, as the quantitative trophic levels based on δ15N were different with that classified by feeding behaviors. This phenomenon subsequently demonstrated that it should be considered thoughtfully with respect to the application of the traditional method for understanding Hg bioaccumulation power by the slope of log10[Hg] with δ15N regression in specific water body (i.e., Changshou Lake). In addition, no significant linear correlation between Hg and body weight or length of some fish species was observed, suggesting that the fish growth in the eutrophic environment was disproportionate with Hg bioaccumulation, and fish length or weight was not the main factor affecting Hg transfer with food web. The occurrence of human disturbance in aquatic system presents a challenge to a better understanding of the Hg bioaccumulation and biomagnification within the food chain.

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The effect of interaction between Bacillus subtilis DBM and soil minerals on Cu(II) and Pb(II) adsorption

Publication date: April 2019

Source: Journal of Environmental Sciences, Volume 78

Author(s): Jun Bai, Yuanqing Chao, Yanmei Chen, Shizhong Wang, Rongliang Qiu

Abstract

The effects of interaction between Bacillus subtilis DBM and soil minerals on Cu(II) and Pb(II) adsorption were investigated. After combination with DBM, the Cu(II) and Pb(II) adsorption capacities of kaolinite and goethite improved compared with the application of the minerals independently. The modeling results of potentiometric titration data proved that the site concentrations of kaolinite and goethite increased by 80% and 30%, respectively after combination with DBM. However, the involvement of functional groups in the DBM/mineral combinations resulted in lower concentrations of observed sites than the theoretical values and led to the enhancement of desorption rates by NH4NO3 and EDTA-Na2. The DBM-mineral complexes might also help to prevent heavy metals from entering DBM cells to improve the survivability of DBM in heavy metal-contaminated environments. During the combination process, the extracellular proteins of DBM provided more binding sites for the minerals to absorb Cu(II) and Pb(II). In particular, an especially stable complexation site was formed between goethite and phosphodiester bonds from EPS to enhance the Pb(II) adsorption capacity. So, we can conclude that the DBM–mineral complexes could improve the Cu(II) and Pb(II) adsorption capacities of minerals and protect DBM in heavy metal-contaminated environments.

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Enhanced removal of organic matter and typical disinfection byproduct precursors in combined iron–carbon micro electrolysis-UBAF process for drinking water pre-treatment

Publication date: April 2019

Source: Journal of Environmental Sciences, Volume 78

Author(s): Yinghan Chen, Tao Lin, Wei Chen

Abstract

The organic matter and two types of disinfection byproduct (DBP) precursors in micro-polluted source water were removed using an iron–carbon micro-electrolysis (ICME) combined with up-flow biological aerated filter (UBAF) process. Two pilot-scale experiments (ICME-UBAF and UBAF alone) were used to investigate the effect of the ICME system on the removal of organic matter and DBP precursors. The results showed that ICME pretreatment removed 15.6% of dissolved organic matter (DOM) and significantly improved the removal rate in the subsequent UBAF process. The ICME system removed 31% of trichloromethane (TCM) precursors and 20% of dichloroacetonitrile (DCAN) precursors. The results of measurements of the molecular weight distribution and hydrophilic fractions of DOM and DBP precursors showed that ICME pretreatment played a key role in breaking large-molecular-weight organic matter into low-molecular-weight components, and the hydrophobic fraction into hydrophilic compounds, which was favorable for subsequent biodegradation by UBAF. Three-dimensional fluorescence spectroscopy (3D-EEM) further indicated that the ICME system improved the removal of TCM and DCAN precursors. The biomass analysis indicated the presence of a larger and more diverse microbial community in the ICME-UBAF system than for the UBAF alone. The high-throughput sequencing results revealed that domination of the genera SphingomonasBrevundimonas and Sphingorhabdus contributed to the better removal of organic matter and two types of DBP precursors. Also, Nitrosomonas and Pseudomonas were beneficial for ammonia removal.

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Investigation of adsorption/desorption behavior of Cr(VI) at the presence of inorganic and organic substance in membrane capacitive deionization (MCDI)

Publication date: April 2019

Source: Journal of Environmental Sciences, Volume 78

Author(s): Lin Chen, Chengyi Wang, Shanshan Liu, Liang Zhu

Abstract

The adsorption and desorption behavior of Cr(VI) in membrane capacitive deionization (MCDI) was investigated systematically in the presence of bovine serum albumin (BSA) and KCl with different concentrations, respectively. Results revealed that Cr(VI) absorption was enhanced and the adsorption amount for Cr(VI) increased from 155.7 to 190.8 mg/g when KCl concentration increased from 100 to 200 mg/L in the adsorption process, which was attributed to the stronger driving force. However, the adsorption amount sharply decreased to 90.2 mg/g when KCl concentration reached up to 1000 mg/L suggesting the negative effect for Cr(VI) removal that high KCl concentration had. As for the effect of BSA on ion adsorption, the amount for Cr (VI) significantly declined to 78.3 mg/g and pH was found to be an important factor contributing to this significant reduction. Then, the desorption performance was also conducted and it was obtained that the presence of KCl had negligible effect on Cr(VI) desorption, while promoted by the addition of BSA. The incomplete desorption was obtained and the residual chromium ions onto the electrode after desorption was detected via energy-dispersive X-ray spectroscopy (EDS). Based on above analysis, the enhanced removal mechanism for Cr(VI) in MCDI was found to be consisted of ion adsorption onto electrode surface, the redox reaction of Cr(VI) into Cr(III) and precipitation, which was demonstrated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM).

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A monitoring-modeling approach to SO42 − and NO3 secondary conversion ratio estimation during haze periods in Beijing, China

Publication date: April 2019

Source: Journal of Environmental Sciences, Volume 78

Author(s): Xiaoqi Wang, Wei Wei, Shuiyuan Cheng, Chong Zhang, Wenjiao Duan

Abstract

SO42 − and NO3 are important chemical components of fine particulate matter (PM2.5), especially during haze periods. This study selected two haze episodes in Beijing, China with similar meteorological conditions. A monitoring-modeling approach was developed to estimate the secondary conversion ratios of sulfur and nitrogen based on monitored and simulated concentrations. Measurements showed that in Episode 1 (24th–25th October, 2014), the concentrations (proportions) of SO42 − and NO3 reached 35.1 μg/m3 (14.9%) and 55.0 μg/m3 (22.9%), while they reached 14.4 μg/m3 (9.3%) and 59.1 μg/m3 (38.1%) in Episode 2 (26th–27th October, 2017). A modeling system was applied to apportion Beijing's SO42 − and NO3 in primary and secondary SO42 −/NO3 emitted from local and regional sources. Thus, secondary conversion contributions considering the local and regional level were defined. The former primarily focused on Beijing atmospheric oxidation ability and the latter mainly considered the existence form of Beijing SO42 −/NO3 under the regional transport impacts. Finally, secondary oxidation ratios were estimated through combining secondary conversion contribution coefficients for simulated and monitored concentrations. At regional level, sulfur oxidation ratios in polluted (clean) days during two sampling periods were 0.57–0.72 (0.07–0.52) and 0.74–0.80 (0.08–0.61), nitrogen oxidation ratios were 0.20–0.29 (0.05–0.15) and 0.34–0.38 (0.02–0.29), indicating that atmospheric oxidation was enhanced when considering regional transport through 2014–2017. At the local level, sulfur oxidation ratios were 0.66–0.71 (0.04–0.48) in haze (clean) days, while nitrogen oxidation ratios were 0.16–0.29 (0.02–0.16). The atmospheric oxidation ability markedly increased in PM2.5 pollution days, but changed only slightly between the two periods.

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Removal of cyanide adsorbed on pyrite by H2O2 oxidation under alkaline conditions

Publication date: April 2019

Source: Journal of Environmental Sciences, Volume 78

Author(s): Yubo Tu, Peiwei Han, Lianqi Wei, Xiaomeng Zhang, Bo Yu, Peng Qian, Shufeng Ye

Abstract

Large amounts of cyanide tailings are produced during the cyanidation process in gold extraction, which are hazardous solid wastes due to the toxic cyanide. Pyrite is one of the main minerals in cyanide tailings. The removal of cyanide adsorbed on pyrite by H2O2 oxidation under alkaline conditions was investigated in this study. It was found that the removal efficiency was positively correlated with pH from 5 to 12, but remained almost constant when pH was higher than 12. The highest cyanide removal efficiency of 91.10% was achieved by adding no less than 0.6 wt.% of H2O2. Cyanide removal was positively correlated with the CN adsorption amount between 1.06 and 8.5 mg/g, and temperature between 25 and 85°C. The removal of cyanide adsorbed on pyrite by H2O2 oxidation under alkaline conditions was due to the oxidation of pyrite. Hexacyanoferrate, thiocyanate and sulfate were generated with mole ratios of about 2.03:1.12:3.17 during the cyanide removal.

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Changes in distribution and microstructure of bauxite residue aggregates following amendments addition

Publication date: April 2019

Source: Journal of Environmental Sciences, Volume 78

Author(s): Shengguo Xue, Yuzhen Ye, Feng Zhu, Qiongli Wang, Jun Jiang, William Hartley

Abstract

Bauxite residue is a highly alkaline byproduct which is routinely discarded at residue disposal areas. Improving soil formation process to revegetate the special degraded lands is a promising strategy for sustainable management of the refining industry. A laboratory incubation experiment was used to evaluate the effects of gypsum and vermicompost on stable aggregate formation of bauxite residue. Aggregate size distribution was quantified by fractal theory, whilst residue microstructure was determined by scanning electron microscopy and synchrotron-based X-ray micro-computed tomography. Amendments addition increased the content of macro-aggregates (> 250 μm) and enhanced aggregate stability of bauxite residue. Following gypsum and vermicompost addition, fractal dimension decreased from 2.84 to 2.77, which indicated a more homogeneous distribution of aggregate particles. Images from scanning electron microscopy and three-dimensional microstructure demonstrated that amendments stimulate the formation of improved structure in residue aggregates. Pore parameters including porosity, pore throat surface area, path length, and path tortuosity increased under amendment additions. Changes in aggregate size distribution and microstructure of bauxite residue indicated that additions of gypsum and vermicompost were beneficial to physical condition of bauxite residue which may enhance the ease of vegetation.

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Removal characteristics of microplastics by Fe-based coagulants during drinking water treatment

Publication date: April 2019

Source: Journal of Environmental Sciences, Volume 78

Author(s): Baiwen Ma, Wenjing Xue, Yanyan Ding, Chengzhi Hu, Huijuan Liu, Jiuhui Qu

Abstract

Microplastics have caused great concern worldwide recently due to their ubiquitous presence within the marine environment. Up to now, most attention has been paid to their sources, distributions, measurement methods, and especially their eco-toxicological effects. With microplastics being increasingly detected in freshwater, it is urgently necessary to evaluate their behaviors during coagulation and ultrafiltration (UF) processes. Herein, the removal behavior of polyethylene (PE), which is easily suspended in water and is the main component of microplastics, was investigated with commonly used Fe-based salts. Results showed that although higher removal efficiency was induced for smaller PE particles, low PE removal efficiency (below 15%) was observed using the traditional coagulation process, and was little influenced by water characteristics. In comparison to solution pH, PAM addition played a more important role in increasing the removal efficiency, especially anionic PAM at high dosage (with efficiency up to 90.9%). The main reason was ascribed to the dense floc formation and high adsorption ability because of the positively charged Fe-based flocs under neutral conditions. For ultrafiltration, although PE particles could be completely rejected, slight membrane fouling was caused owing to their large particle size. The membrane flux decreased after coagulation; however, the membrane fouling was less severe than that induced by flocs alone due to the heterogeneous nature of the cake layer caused by PE, even at high dosages of Fe-based salts. Based on the behavior exhibited during coagulation and ultrafiltration, we believe these findings will have potential application in drinking water treatment.

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Iron toxicity resistance strategies in tropical grasses: The role of apoplastic radicular barriers

Publication date: April 2019

Source: Journal of Environmental Sciences, Volume 78

Author(s): Advanio Inácio Siqueira-Silva, Camilla Oliveira Rios, Eduardo Gusmão Pereira

Abstract

The revegetation of mined areas poses a great challenge to the iron ore mining industry. The initial recovery process in degraded areas might rely on the use of Fe-resistant grasses. Tropical grasses, such as Paspalum densum and Echinochloa crus-galli, show different resistance strategies to iron toxicity; however, these mechanisms are poorly understood. The Fe-resistance mechanisms and direct iron toxicity as a function of root apex removal were investigated. To achieve this purpose, both grass species were grown for up to 480 hr in a nutrient solution containing 0.019 or 7 mmol/L Fe-EDTA after the root apices had been removed or maintained. Cultivation in the presence of excess iron-induced leaf bronzing and the formation of iron plaque on the root surfaces of both grass species, but was more significant on those plants whose root apex had been removed. Iron accumulation was higher in the roots, but reached phytotoxic levels in the aerial parts as well. It did not hinder the biosynthesis of chloroplastidic pigments. No significant changes in gas exchange and chlorophyll afluorescence occurred in either grass when their roots were kept intact; the contrary was true for plants with excised root apices. In both studied grasses, the root apoplastic barriers had an important function in the restriction of iron translocation from the root to the aerial plant parts, especially in E. crus-galli. Root apex removal negatively influenced the iron toxicity resistance mechanisms (tolerance in P. densum and avoidance in E. crus-galli).

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