A meta-analysis of metal biosorption by suspended bacteria from three phyla

Biosorption of heavy metals by bacterial biomass has been the subject of significant research interest in last decades due to its efficiency, relatively low cost and minimal negative effects for the surrounding environment. In this meta-analysis, the biosorption efficiencies of different bacterial strains for Cu(II), Cd(II), Zn(II), Cr(III), Mn(II), Pb(II) and Ni(II) were evaluated. Optimum conditions for the biosorption process such as initial metal concentration, temperature, pH, contact time, metal type, biomass dosage and bacterial phyla, were evaluated for each heavy metal. According to the results, the efficiencies of bacterial biomass for removal of heavy metal were as follows: Cd(II) > Cr(III) > Pb(II) > Zn(II) > Cu(II) > Ni(II) > Mn(II). Firmicute phyla showed the highest overall (living and dead) biosorption efficiency for heavy metals. Living biomass of Proteobacteria had the best biosorption performance. Living bacterial biomass was significantly more efficient in biosorption of Cu(II), Zn(II) and Pb(II) than dead biomass. The maximum biosorption efficiency of bacterial strains for Cd(II), Pb(II) and Zn(II) was achieved at pH values between 6 and 7.5. High temperatures (>35 °C) reduced the removal efficiencies for Cu(II) and Zn(II) and increased the efficiencies for Cd(II) and Cr(III) ions. The maximum biosorption efficiency of non-essential heavy metals occurred with short contact times (24 h). The mean biosorption capacity of bacterial biomass was between 71.26 and 125.88 mg g−1. No publication bias existed according to Egger’s and Begg’s test results

Cu(II) biosorption by living biofilms:Isothermal, chemical, physical and biological evaluation

Dissolved copper in stormwater runoff is a significant environmental problem. Biosorption of dissolved metals using microorganisms is known as a green, low-cost and efficient method. However, the role of live biological agents in the remediation of dissolved copper in Sustainable Drainage (SuDS) has not been reported. In this study, the effect of pH, initial concentration and temperature, on bacteria in different stages of biofilm development on a geotextile, along with Cu(II) removal efficiencies, were evaluated. Maximum Cu(II) removal efficiency (92%) was observed at pH 6. By decreasing the pH from 6 to 2, a log 5 reduction in bacteria was observed and Carboxyl groups transformed from -COO- to –COOH. The maximum biosorption capacity (119 mg g−1) was detected on day 1 of biofilm development, however, maximum removal efficiency (97%) was measured on day 21 of biofilm incubation. Extracellular Polymeric Substance (EPS) showed a better protection of CFUs in more mature biofilms (day 21) with less than 0.1 log decrease when exposed to 200 mL−1 Cu(II), whereas, biofilm on day 1 of incubation showed a 2 log reduction in CFUs number. Thermodynamic studies showed that the maximum Cu(II) biosorption capacity of biofilms, incubated for 7 days (117 mg g−1) occurred at 35 °C. Thermodynamic and kinetic modelling of data revealed that a physical, feasible, spontaneous and exothermic process controlled the biosorption, with a diffusion process observed in external layers of the biofilm, fitting a pseudo-second order model. Equilibrium data modelling and high R2 values of Langmuir model indicated that the biosorption took place by a monolayer on the living biofilm surface in all stages of biofilm development

Effects of sodium chloride and methylthioninium chloride on Persian sturgeon, Acipenser persicus (Borodin, 1897): A histopathological and bacteriological study

360 pieces of Persian sturgeon fingerlings (1.94 ± 0.75 g) were exposed to various sublethal doses of disinfecting chemicals commonly used in aquaculture such as sodium chloride and methylthioninium chloride in order to investigate their impacts on bacterial loads of skin, gill and surrounding water and to define the histopathological status of gill and liver tissues. The sublethal concentrations were determined after a pre-test, then the experiment was performed  in four treatments with three replicates inside the glass aquariums with stocking density of 10 fish (1-3 g) per aquarium. The treatments included 5, 6.3, 8.06 and 10.23 mg L-1 sodium chloride and  also 1, 1.56, 2.45 and 3.83 mg L-1 methylthioninium chloride. A control group (with no chemical added) was set up for each experiment. After exposure to treatments during 96 h, the microbial and histopathological examinations were carried out. Hemorrhage, elongation of secondary lamellae, adhesion of secondary lamellae, hypertrophy of supporter cartilage, mucus coagulation and secretion, hyperplasia, lamellar necrosis and clubbing of gill lamellae were observed on the fish gills. Biliary depression, hemorrhage, cell necrosis and degeneration of lipid were also found in liver. The severity of these effects was  dose-dependent. Only the sublethal concentration of methylthioninium chloride significantly influenced bacterial load (CFU g-1) on skin, while other treatments of sodium chloride and methylthioninium chloride did not exhibit any significant effects. In conclusion, the sublethal doses of methylthioninium chloride and sodium chloride showed no obvious disinfecting effect on gill, skin and surrounding water of Persian sturgeon fingerling. Nevertheless, histopathological alterations were observed on fish gill, skin and also  liver of all treatments

Thermally Treated Waste Silt as Filler in Geopolymer Cement

This study aims to investigate the feasibility of including silt, a by-product of limestone aggregate production, as a filler in geopolymer cement. Two separate phases were planned: The first phase aimed to determine the optimum calcination conditions of the waste silt obtained from Società Azionaria Prodotti Asfaltico Bituminosi Affini (S.A.P.A.B.A. s.r.l.). A Design of Experiment (DOE) was produced, and raw silt was calcined accordingly. Geopolymer cement mixtures were made with sodium or potassium alkali solutions and were tested for compressive strength and leaching. Higher calcination temperatures showed better compressive strength, regardless of liquid type. By considering the compressive strength, leaching, and X-ray diffraction (XRD) analysis, the optimum calcination temperature and time was selected as 750 °C for 2 h. The second phase focused on determining the optimum amount of silt (%) that could be used in a geopolymer cement mixture. The results suggested that the addition of about 55% of silt (total solid weight) as filler can improve the compressive strength of geopolymers made with Na or K liquid activators. Based on the leaching test, the cumulative concentrations of the released trace elements from the geopolymer specimens into the leachant were lower than the thresholds for European standards

Mechanical and leaching characterisation of impact-absorbing rubberised asphalts for urban pavements

A new impact-absorbing material is being developed to protect vulnerable road users in urban areas and has been produced and tested, mechanically and environmentally in the laboratory. The main constituent of this innovative material is the rubber recycled from end-of-life tyres to foster a circular use of resources and exploit rubber’s elastic properties. The study aims to provide a complete Uniaxial Compression Test (UCT) and leaching analysis of the material to propose and optimise a mix that is mechanically sound, durable, and respectful of the environment, in view of in-situ applications. Therefore, the UCT and Dynamic Surface Leaching Test (DSLT) were carried out on rubberised asphalt specimens with different mix designs. The 64 days cumulative concentrations of leached heavy metals and trace elements from unit surface of specimens were calculated and quantified, according to the CEN/TS 16637 standard. In parallel, thanks to a specific mechanical characterisation, compressive stress–strain curves were obtained, and the relaxation and elastic modulus were evaluated. The results from the compression tests showed that the A-mixes have the best elastic and absorbing behaviour, especially those made with an SBS-modified bituminous emulsion (A4). The results from DSLT showed that the cumulative concentration of released elements, per unit surface of specimens were lower than the Dutch Soil Quality Decree (SQD) thresholds, taken as a reference. The low and early release of leachant observed for the mixtures, especially A4 as the most promising one, leave the possibility to handle the leaching with several solutions, including rubber coating treatment or water washing before their incorporation into the mix to limit and prevent their leaching while permitting very high injury reduction performances

Leaching of PAHs from rubber modified asphalt pavements

The present study aimed to, for the first time, quantify the total content of 16 priority EPA PAHs in end-of-life tyre derived crumb rubber granulates and various manufactured rubberised asphalt mix designs. After identifying the availability of 16 EPA PAHs, the leaching behaviour of rubberised asphalt specimens, were evaluated using the Dynamic Surface Leaching Test (DSLT) based on CEN/TS 16637-2:2014 standard. This was prior to modelling the release mechanisms of PAHs by utilizing a mathematical diffusion-controlled leaching model. According to the results, the total content of 16 EPA PAHs in crumb rubber granulates ranged between 0.061 and 8.322 μg/g, which were associated with acenaphthene and pyrene, respectively. The total content of PAHs in rubberised asphalt specimens varied between 0.019 and 4.992 μg/g depending on the volume of crumb rubber granulates in the asphalt concrete mix design, and type of binder. Results of the leaching experiments revealed that the highest leached PAHs were benzo[b]fluoranthene, benzo[k]fluoranthene and naphthalene with a 64-days cumulative release per specimen surface area > 1 μg/m2. Acenaphthylene, fluoranthene, fluorene and indeno[1,2,3-c,d]pyrene were released in cumulative concentrations between 0.1 and 1 μg/m2. The PAHs with a cumulative release potential below 0.1 μg/m2 during DSLT were benzo[a]anthracene, benzo[a]pyrene, benzo[g,h,i]perylene and chrysene. The diffusion coefficients, which were calculated by mathematical modelling of DSLT data, revealed that the leaching process of 16 EPA PAHs from surface of rubberised asphalt concrete mix designs fitted all the criteria set by the NEN 7345 standard for diffusion-controlled leaching during all stages of leaching experiments

The biosorption of mercury by permeable pavement biofilms in stormwater attenuation

This study reports on the evaluation of the equilibrium, thermodynamics and kinetics of mercury (II) biosorption using a living biofilm, developed on a nonwoven polypropylene and polyethylene geotextile, typically used within the structure of Sustainable Drainage System (SuDS) devices. Batch biosorption assays were carried out with variables such as pH, initial concentrations, contact time, temperature and biofilm incubation time. Langmuir, Freundlich and Dubinin Radushkevich (D-R) models were applied to the equilibrium data which revealed the maximum biosorption capacities and efficiencies at pH 5.5 with a contact time of 120 min at 25 °C. With 20 mg L-1 added Hg (II), living biofilm samples with incubation times of 1, 7, 14, 21 and 28 days, biosorption values were 101.31 (55.72%), 24.41 (67.12%), 16.81 (61.37%), 9.70 (62.57%) and 13.34 (65.38%) mg g-1, respectively. Free mean biosorption energy from the D-R model was between 2.24 and 2.36 kJ mol-1 for all biofilm development incubation times, that revealed the physical biosorption mechanism for Hg(II). The thermodynamic studies showed that the Hg(II) biosorption of living biofilm was thermodynamically feasible and had a spontaneous and exothermic nature. Kinetic parameters revealed that Hg(II) biosorption onto living biofilm had a good correlation with a pseudo second-order kinetic model. FTIR spectra after biosorption suggested that amine, hydroxyl and carboxyl groups were the main functional groups available and responsible for Hg(II) biosorption onto living biofilm. Experimental data suggested that a living biofilm developed on a nonwoven polypropylene and polyethylene geotextile can be efficient in the removal of mercury ions from contaminated urban and industrial runoff

Expression of Some Genes Involved in Epigenetic in Breast Cancer Cell Lines: The Effect of Quercetin

Background & Objectives: Breast cancer is one of the most common cancers among women. Incorrect pattern of gene expression involved in epigenetic including APOBEC3B, DNMT-1, and TET-1 can develop breast cancer. Quercetin is a natural flavonoid with antioxidant and anti-cancer properties that have been reported in other studies. To investigate the effect mechanism of quercetin, this study examined the effect of quercetin on the expression of genes which were referred to in two classes of breast cancer cell lines. Materials & Methods: Cell lines including MCF-7 and MDA-MB-453 in separate boxes in the control group and the treated groups with two dosages of 50 and 100 mm of quercetin were cultured for 24 and 48 hours, respectively. RNA was extracted from the cells and then was converted to cDNA. Real-time PCR was used for APOBEC3B, DNMT_1, and TET-1 expression. Results: The results showed that quercetin had conflicting results after 24 hours in two cell lines as there was a decrease in the gene expression of APQBEC3B and an increase in that of DNMT-1 in MCF-7 cell line. In contrast, the cell line of MDA-MB-453, APOBEC3B, and DNMT-1 gene expression increased. While the 48-hour results showed that quercetin reduced the gene expression of APOBEC3B and DNMT-1 and increased that of the TET-1 in both cell lines. Conclusion: Due to the satisfactory effects of quercetin on breast cancer cells after 48 hours, these effects can be probably applied through epigenetic mechanisms. However, the final decision needs further investigation