In the present study, heavy metal (HM)-tolerant phosphate solubilizing bacteria (PSB) were isolated and their performance during the remediation of Pb and Cd in contaminated soil was studied. A total of 16 bacterial strains and one consortium were isolated, and the consortium had the highest phosphate solubilizing ability and HM tolerance. Great variations between the Fourier transform infrared (FTIR) spectra of consortium cells before and after adsorption of Pb2+ and Cd2+ revealed that amide I/amide II bonds and carboxyl on the cell surface were involved in binding of metal ions. High-throughput sequencing technique revealed that the consortium was composed of Enterobacter spp., Bacillus spp., and Lactococcus spp. The consortium was added into contaminated soil, and its potential ability in dissolution of phosphate from Ca3(PO4)2 and subsequent immobilization of HMs was tested. Results showed that when Ca3(PO4)2 was applied at 10.60 mg/g soil, PSB addition significantly increased soil available phosphate content from 12.28 to 17.30 mg/kg, thereby enhancing the immobilization rate of Pb and Cd from 69.95 to 80.76% and from 28.38 to 30.81%, respectively. Microcalorimetric analysis revealed that PSB addition significantly improved soil microbial activity, which was possibly related with the decreased HMs availability and the nutrient effect of the solubilized phosphate. The present study can provide a cost-effective and environmental-friendly strategy to remediate multiple HM-contaminated soils.

In this study, a gram-positive fluoranthene-degrading bacterial strain was isolated from crude oil in Dagang Oilfield and identified as Microbacterium paraoxydans JPM1 by the analysis of 16S rDNA sequence. After 25 days of incubation, the strain JPM1 could degrade 91.78 % of the initial amount of fluoranthene. Moreover, four metabolites 9-fluorenone-1-carboxylic acid, 9-fluorenone, phthalic acid, and benzoic acid were detected in the culture solution. The gene sequence encoding the aromatic-ring-hydroxylating dioxygenase was amplified in the strain JPM1 by PCR. Based on the translated protein sequence, a homology modeling method was applied to build the crystal structure of dioxygenase. Subsequently, the interaction mechanism between fluoranthene and the active site of dioxygenase was simulated and analyzed by molecular docking. Consequently, a feasible degrading pathway of fluoranthene in the strain JPM1 was proposed based on the metabolites and the interaction analyses. Additionally, the thermodynamic analysis showed that the strain JPM1 had high tolerance for fluoranthene, and the influence of fluoranthene for the bacterial growth activity was negligible under 100 to 400 mg L−1 concentrations. Taken together, this study indicates that the strain JPM1 has high potential for further study in bioremediation of polycyclic aromatic hydrocarbon (PAH)-contaminated sites.

Artisanal zinc smelting activities, which had been widely applied in Bijie City, Guizhou Province, southwestern of China, can pollute surrounding farmlands. In the present study, 177 farmland topsoil samples of Bijie City were collected and 11 potentially toxic trace elements (PTEs), namely Pb, Zn, Cu, Ni, Co, Mn, Cr, V, Hg, As, and Cd were tested to characterize the concentrations, sources, and ecological risks. Mean concentrations of these PTEs in soils were (mg/kg) as follows: Pb (127), Zn (379), Cu (93.1), Ni (54.6), Co (26.2), Mn (1095), Cr (133), V (206), Hg (0.15), As (16.2), and Cd (3.08). Pb, Zn, and Cd had coefficients of variation greater than 100% and showed a high uneven distribution and spatial variability in the study area. Correlation coefficient analysis and principal component analysis (PCA) were used to quantify potential pollution sources. Results showed that Cu, Ni, Co, Mn, and V came from natural sources, whereas Pb, Zn, Hg, As, and Cd came from anthropogenic pollution sources. Geoaccumulation index and potential ecological risk indices were employed to study the pollution degree of PTEs, which revealed that Pb and Cd shared the greatest contamination and would pose serious ecological risks to the surrounding environment. The results of this study could help the local government managers to establish pollution control strategies and to secure food safety.

Flotation reagents are hugely and increasingly used in mining and other industrial and economic activities from which an important part is discharged into the environment. China could be the most affected country by the resulting pollution. However, their ecotoxicological dimension is still less addressed and understood. This study aimed to analyze the toxic effect of sodium isobutyl xanthate (SIBX) and sodium isopropyl xanthate (SIPX) to soil microbial richness and activity and to make a comparison between the two compounds in regard to their effects on soil microbial and enzymes activities. Different methods, including microcalorimetry, viable cell counts, cell density, and catalase and fluorescein diacetate (FDA) hydrololase activities measurement, were applied. The two chemicals exhibited a significant inhibitory effect (P < 0.05 or P < 0.01) to all parameters, SIPX being more adverse than SIBX. As the doses of SIBX and SIPX increased from 5 to 300 μg g−1 soil, their inhibitory ratio ranged from 4.84 to 45.16 % and from 16.13 to 69.68 %, respectively. All parameters fluctuated with the incubation time (10-day period). FDA hydrolysis was more directly affected but was relatively more resilient than catalase activity. Potential changes of those chemicals in the experimental media and complementarity between experimental techniques were justified.

The adsorption of U(VI) onto Elodea canadensis was studied via a batch equilibrium method. Kinetic investigation indicated that the U(VI) adsorption by E. canadensis reached an equilibrium in 120 min and followed pseudo-second-order kinetics. The solution pH was the most important parameter controlling adsorption of U(VI) and the optimum pH for U(VI) removal is 6.0. The U(VI) biosorption can be well described by Langmuir model. IR spectrum analysis revealed that –NH2, –OH, C=O and C–O could bind strongly with U(VI). XPS spectrum analysis implied that ion exchange and coordination mechanism could be involved in the U(VI) biosorption process.

The strain Pseudomonas sp. JPN2 had a high potential to degrade phenanthrene degrading 98.52 % of the initial amount of 100 mg L−1 after 10 days incubation. The analysis of metabolites demonstrated that the cleavage of phenanthrene started at the C9 and C10 positions on the aromatic ring by the dioxygenation reaction, and then further degraded via a phthalate pathway. To understand the interaction between phenanthrene and the amino acid residues in the active site of the target enzyme, a molecular docking simulation was performed. The results showed that the distances of C9–O1 and C10–O2 atoms were 3.47 and 3.67 Å, respectively. The C9 and C10 positions of the phenanthrene ring are much closer to the dioxygen molecule in the active site relative to the other atoms. Therefore, the C9 and C10 positions are vulnerable to attack in the initial oxygenation process.

A significant knowledge gap in nanotechnology is the absence of standardized protocols for examining the effect of engineered nanoparticles on soil microorganisms. In this study, agricultural soil was exposed to ZnO, SiO2, TiO2 and CeO2 nanoparticles at 1 mg g−1. The toxicity effect was evaluated by thermal metabolism, the abundance of functional bacteria and enzymatic activity. ZnO and CeO2 nanoparticles were observed to hinder thermogenic metabolism, reduce numbers of soil Azotobacter, P-solubilizing and K-solubilizing bacteria and inhibit enzymatic activities. TiO2 nanoparticles reduced the abundance of functional bacteria and enzymatic activity. SiO2 nanoparticles slightly boosted the soil microbial activity. Pearson’s correlation analysis showed that thermodynamic parameters had a strong correlation with abundance of functional bacteria and enzymatic activity. These findings demonstrated that the combined approach of monitoring thermal metabolism, functional bacteria and enzymatic activity is feasible for testing the ecotoxicity of nanoparticles on agricultural soil.

Carbon dots (Cdots), as a class of novel photoluminescence nanoprobes, has attracted tremendous interest for its broad application in recent years. Thus, the toxicity and behavior of Cdots in biological systems become important fundamental problems that require significant attention. In this study, Cdots with diameters of 5 nm are produced using mixed-acid treatment. The Cdots exhibit strong yellow fluorescence under UV irradiation and shifted emission peaks as the excitation wavelength is changed. Gram-negative bacteria Escherichia coli (E. coli) are applied as testing model to study the biological effect of Cdots on the cell growth by microcalorimetric, spectroscopic, and microscopic investigation. The introducing of Cdots caused a gradual increase of the maximum heat power (Ppeak) and the total heat produced (Qtotal) at low concentrations (0.0–5.00 mg/L). The metabolism rate constant (k) and half inhibitory concentration (IC50) were calculated from the microcalorimetric data. The results indicated that Cdots had a concentration-dependent effect on the growth of E. coli. For confirmation, the growth curves and colony-forming units at different concentration of Cdots were studied. The morphology of E. coli in the absence and presence of Cdots was determined by scanning electron microscopy (SEM). The results of these studies were in agreement well with the analysis explored from microcalorimetry.

Various reaction sequences of mutual sorptions of dimethyl phthalate (DMP) or diethyl phthalate (DEP) and humic acid (HA) on single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) were studied. The results indicate that the sorption of DMP and DEP on CNT decreases owing to its competition effect in the presence of HA. The competition is stronger at lower HA concentration. At higher HA concentration, weaker competition has occurred because there are steric hindrance and pore blockage of HA on CNT. The reaction sequences of DMP (or DEP) and HA sorption could affect their sorption mechanisms. The initial sorbed HA can modify the surface properties of CNT with a concomitant effect on the partial complexation of DMP (or DEP) with the sorbed HA. The Fourier transform infrared (FTIR) spectra indicate that SWCNT and MWCNT contain mainly −COO– and −COOH moieties, respectively. In addition, the IR spectroscopic and thermogravimetric analyses illustrate that CNTs provide similar sorption capacity regardless of the interaction sequence of DMP (or DEP) and HA. Finally, the fluorescence quenching results indicate that DEP exhibits stronger binding to HA than that of DMP.Keywords: Carbon nanotubes; Dialkyl phthalate esters; Humic acid; Mutual sorption; Reaction sequence

Microcalorimetric technique was applied to assess the toxic effect of EDTA-chelated trivalent iron on Pseudomonas putida (P. putida) (bacterium), Candida humicola (C. humicola) (fungus) and their mixture in sterilized soil. Microbial growth rate constant k, total heat evolution QT, metabolic enthalpy ∆Hmet, mass specific heat rate JQ/S, microbial biomass C and inhibitory ratio I were calculated. Results showed that microcalorimetric indexes decreased with the increasing Fe(III)-EDTA complex concentration. Comparing the single and mixed strains, the effect of Fe(III) on bacterium-fungus interaction was dominant at lower dose, whereas, the metal toxicity at high dose of Fe was the main factor affecting P. putida and C. humicola activity. Thus, the mixture had moderate tolerance to the iron overload, and exhibit synergistic interaction in exponential growth phase (0–0.3 mg g−1). The results of glucose degradation showed that glucose was consumed totally at the end of exponential phase of microbial growth.

•Characterized an indigenous biosurfactant producing and crude oil-degrading strain.•Optimum conditions for growth of Bacillus sp. USTBa strain were standardized.•Stability studies of biosurfactant were carried out under the extreme conditions.•Biosurfactant showed high emulsification index with crude oil and no toxicity.•It shows high potential to use in remediation of crude oil contaminated sites.An effective biosurfactant-producer and hydrocarbon degrading bacterial strain, Bacillus methylotrophicus USTBa was isolated from hydrocarbon contaminated aqueous medium using crude oil as sole source of carbon. The growth parameters such as pH, temperature, and salinity were optimized for degradation of hydrocarbons and 92% degradation of crude oil removal was observed in 2 weeks. The biosurfactant produced during the course of hydrocarbon degradation was monitored by surface tension and cell hydrophobicity measurements. The produced biosurfactant had the ability to decrease the surface tension of water from 72 to 28 mN/m, with the critical micelle concentration (CMC) of 35 mg/L. The biosurfactant exhibited 90% emulsification activity (EI) on crude oil. Nuclear magnetic resonance spectroscopy (NMR), X-ray diffraction (XRD), and thermal gravimetric (TG) analysis revealed the functional groups, surface nature and thermostability of the biosurfactant, respectively. Gas chromatography analysis demonstrated that the strain USTB efficiently degraded different alkanes from crude oil. The biosurfactant did not exhibit inhibitory effect to various vegetables, however strong antibiotic activity against gram positive and gram negative bacteria was observed. The study suggest application of the USTBa biosurfactant as an appropriate candidate for bioremediation of crude oil contaminants.

The influence of two neonicotinoids, i.e., imidacloprid (IMI) and acetamiprid (ACE), on soil microbial activities was investigated in a short period of time using a combination of the microcalorimetric approach and enzyme tests. Thermodynamic parameters such as QT (J g−1 soil), ∆Hmet (kJ mol−1), JQ/S (J g−1 h−1), k (h−1), and soil enzymatic activities, dehydrogenase, phosphomonoesterase, arginine deaminase, and urease, were used to evaluate whole metabolic activity changes and acute toxicity following IMI and ACE treatment. Various profiles of thermogenic curves reflect different soil microbial activities. The microbial growth rate constant k, total heat evolution QT (expect for IMI), and inhibitory ratio I show linear relationship with the doses of IMI and ACE. QT for IMI increases at 0.0–20 μg g−1 and then decreases at 20–80 μg g−1, possibly attributing to the presence of tolerant microorganisms. The 50 % inhibitory ratios (IC50) of IMI and ACE are 95.7 and 77.2 μg g−1, respectively. ACE displays slightly higher toxicity than IMI. Plots of k and QT against microbial biomass-C indicate that the k and QT are growth yield-dependent. IMI and ACE show 29.6; 40.4 and 23.0; and 23.3, 21.7, and 30.5 % inhibition of dehydrogenase, phosphomonoesterase, and urease activity, respectively. By contrast, the arginine deaminase activity is enhanced by 15.2 and 13.2 % with IMI and ACE, respectively. The parametric indices selected give a quantitative dose-response relationship of both insecticides and indicate that ACE is more toxic than IMI due to their difference in molecular structures.

TAM III multi-channel calorimetry was applied to study the effect of different concentrations petroleum on soil microbial activity and community. The microbial activities of the soil samples were recorded as power-time curves. The thermokinetic parameters such as microbial growth rate constant k, total heat evolution QT, metabolic enthalpy ∆Hmet and mass specific heat rate JQ/S were calculated. Results showed that petroleum had a certain extent effects to soil microorganisms. The results indicate that the soil microbial activity was promoted with a petroleum concentration lower than 0.52 % ± 0.24 %, but inhibited with further increase in petroleum.

The adsorption and desorption of dimethyl phthalate (DMP) on five types of carbon nanotubes (CNTs) were studied in the absence and presence of 50 mg/L copper(II) (Cu2+) ion. The adsorption and desorption data are well described by the Freundlich model and the first-order two-compartment model, respectively. The adsorption capacity of CNTs for DMP is inversely related to the average outer diameter of the CNTs. The surface acidic functional groups of CNTs increases in the order of lactones < hydroxyl < carboxyl functionalities and decreases with the increase in the outer diameter. The adsorption of DMP on CNTs increases in the presence of Cu2+ ions. The adsorption coefficient increases in pH 3–6 and is nearly the same at pH > 6 for all CNTs. The presence of Cu2+ ions decreases the amounts of desorbed DMP from CNTs, inferring that Cu2+ ions could suppress the DMP desorption from CNTs and reduce DMP toxicity to our environment.Graphical abstractHighlights► Copper(II) ions could enhance the adsorption of DMP on CNTs. ► Acidic functional groups produced strong competitive between DMP and copper ions. ► Copper(II) ions could suppress the DMP desorption from CNTs. ► Cu2+ caused the most effect for DMP adsorption contrast to other species. ► Effect of adsorption and desorption by Cu2+ increased in larger outer diameters.

The objective of the present study was to evaluate effects of petroleum hydrocarbon contaminated soil on the leguminous plant, Vigna radiata L. Seed germination, metabolism and early growth performance of V. radiata L. were studied as parameters by applying a combined approach. The employed combined method which included microcalorimetry and analysis of the root cross section revealed dose dependent effects of petroleum hydrocarbon contaminated soil on V. radiata L. for most parameters. Although significant reductions in measured parameters were observed even at low total petroleum hydrocarbon (TPH) levels such as 1 % and 1.5 %, calculated inhibitions, IC50 values and metabolic heat emission-time curves inferred that substantial negative effects can be expected on V. radiata L. in soils with comparatively high contamination levels, such as 2.5 % TPH and higher.

In this study, an isothermal microcalorimetric technique was used to demonstrate the impact of dimethyl phthalate (DMP), di-n-octyl phthalate (DOP) and diethyl phthalate (DEP) on soil microbial activity. The effect of these phthalate esters (≤100 μg g−1 soil) follows the order: DEP > DMP > DOP but changed to DMP > DEP > DOP when the concentrations of the phthalate esters are above 100 μg g−1 soil. DMP, DEP and DOP significantly decreased (p < 0.05) the soil urease activity. The effect of phthalate esters on soil microbial activity is not the same with those on enzymatic activity. In addition, DEP, which has a lower bioavailability, is less toxic to soil microbes than that of DMP when its concentration is above 100 μg g−1 soil.

In this study, the toxicity effects of benzene (B), toluene (T), ethylbenzene (E), xylene (X) alone and substrate interactions in binary mixtures of BT, BE and BX mixed with equal mass concentrations on facultative anaerobic Rhodococcus sp. ustb-1 in LB medium were examined by a microcalorimetric method. The results showed that T, E and X alone aren't severely toxic to strain ustb-1 when the concentrations reach 800 μg mg−1, but B alone and these binary mixtures exhibit obvious inhibitory effects on the growth of ustb-1 at the dose of 100 μg mg−1. The toxicity of B in the presence of T and X is not significantly different from B alone, but E increased the toxicity of B. In mineral salt medium, all T and X were removed within 72 h, while complete degradation of B and E did not occur during biodegradation of these binary mixtures. The degradation of B was stimulated in the presence of T and X, but it was inhibited by E. The decreased degradation of B in BE, compared with the degradation of B alone, was attributed to an increase in the toxicity of B in the presence of E.Highlights► We isolated and identified a facultative anaerobic Rhodococcus sp. ustb-1. ► It can degrade benzene (B), toluene (T), ethylbenzene (E), and xylene (X). ► It preferentially degrades T and X in BT and BX mixtures. ► E increases the toxicity of B to strain ustb-1 in BE mixture.

•PFCs can quench the fluorescence of BSA through a static quenching procedure.•The binding of PFOS to BSA is much stronger than that of PFOA.•The dominant binding forces were van der Waals forces and hydrogen bonds.•The binding of PFOA to BSA took place at Sudlow site I whereas PFOS at site I and II.•The secondary structure of BSA has been changed in the presence of PFCs.Perfluorinated compounds (PFCs), an emerging class of globally environmental contaminations, pose a great threat to humans with wide exposure from food and other potential sources. The effects of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) on bovine serum albumin (BSA) under normal physiological conditions were characterized by fluorescence, UV–Vis absorption, Fourier transform infrared (FT-IR) spectroscopy and molecular docking methods. The fluorescence study suggested that the fluorescence quenching of BSA by PFCs was a static procedure forming a PFCs–BSA complex. The negative values of enthalpy change (ΔH) and entropy change (ΔS) indicated that van der Waals forces and hydrogen bonds were the dominant intermolecular forces in the binding of PFCs to BSA. The displacement experiments of site markers and molecular docking revealed that the binding of PFOA to BSA took place in sub-domain IIA (Sudlow site I) whereas PFOS was mainly located in the sub-domain IIIA (Sudlow site II) and partially bound into site I. Furthermore, the results of UV–Vis and FT-IR spectra demonstrated that the microenvironment and the secondary structure of BSA were changed in the presence of PFCs. These results indicated that PFCs indeed impact the conformation of BSA and PFOS was more toxic than PFOA, which were supported by theoretical molecular modeling methods.Graphical abstractDownload full-size image

Cropping activities may affect soil microbial activities and biomass, which would affect C and N cycling in soil and thus the crop yields and quality. In the present study, a combination of microcalorimetric, enzyme activity (sucrase, urease, catalase, and fluorescein diacetate hydrolysis), and real–time polymerase chain reaction (RT–PCR) analyses was used to investigate microbial status of farmland soils, collected from 5 different sites in Huazhong Agriculture University, China. Our results showed that among the 5 sites, both positive and negative impacts of cropping activities on soil microbial activity were observed. Enzyme activity analysis showed that cropping activities reduced soil sucrase and urease activities, which would influence the C and N cycles in soil. Much more attentions should be given to microbial status affected by cropping activities in future. According to the correlation analysis, fluorescein diacetate hydrolysis showed a significantly (P < 0.05) negative correlation with the time to reach the maximum power output (R = −0.898), but a significantly (P < 0.05) positive correlation with bacterial gene copy number (R = 0.817). Soil catalase activity also showed a significantly (P < 0.05) positive correlation with bacterial gene copy number (R = 0.965). Using combined methods would provide virtual information of soil microbial status.

We studied the interaction mechanisms between carbonaceous nanomaterials (CNMs) and sulfamethoxazole (SMX) to elucidate their adsorption behaviors. Three graphene-based materials, reduced graphene oxide (rGO), graphene oxide (GO), and graphene nanoplatelet pastes (GNP), and five multiwalled carbon nanotubes (MWCNTs), MWCNT10, MWCNT15, MWCNT15-OH, MWCNT15-COOH, and N-doped MWCNTs, were used as sorbents. Oxygen-containing functional groups and graphene wrinkling suppressed SMX adsorption on GO and GNPs due to fewer Csp2 ring sites for π-π stacking and fewer accessible flat surface adsorption sites, respectively. Ring current-induced 1H NMR upfield chemical shifts increased as the π-donor concentration increased, as well as π-donor strength of polycyclic aromatic hydrocarbons (PAHs) (pyrene > phenanthrene > naphthalene) as model graphene compounds, suggesting that π-π interaction strength of SMX with PAHs associated with π-donor strength. Moreover, 1H NMR results further verified that carboxylic and hydroxyl groups in PAHs (9-phenanthrol and 3-phenanthrenecarboxylic acid) weakened the complexation between SMX and the graphitic surface. Additionally, the morphologies of rGO and MWCNT10 were observed using AFM, and transformed from being linear to scattered as the loading dose of the humic acid increased. Our results are useful to understand the distinct interaction mechanisms and subsequent adsorption behaviors resulting from various carbon nanomaterials with SMX in water.

•Biosorption of uranium onto Eichhornia crassipes is strongly pH dependent.•Langmuir isotherm and pseudo-second-order kinetics best describe U(VI) biosorption.•The U(VI) biosorption onto E. crassipes is spontaneous and endothermic.•Coordination and ion exchange mechanisms could be involved U(VI) biosorption.Batch experiments were conducted to investigate the biosorption of U(VI) from aqueous solutions onto the nonliving biomass of an aquatic macrophyte Eichhornia crassipes. The results showed that the adsorption of U(VI) onto E. crassipes was highly pH-dependent and the best pH for U(VI) removal was 5.5. U(VI) adsorption proceeded rapidly with an equilibrium time of 30 min and conformed to pseudo-second-order kinetics. The Langmuir isotherm model was determined to best describe U(VI) biosorption with a maximum monolayer adsorption capacity of 142.85 mg/g. Thermodynamic calculation results indicated that the U(VI) biosorption process was spontaneous and endothermic. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis implied that the functional groups (amino, hydroxyl, and carboxyl) may be responsible for the U(VI) adsorption process, in which the coordination and ion exchange mechanisms could be involved. We conclude that E. crassipes biomass is a promising biosorbent for the removal of uranium pollutants.