Interaction of polycyclic aromatic hydrocarbons and heavy metals on soil enzyme

Ryegrass uptake behavior and forage risk assessment after exposing to soil with combined polycyclic aromatic hydrocarbons and cadmium

Internalization of chemicals and the forage risks of ryegrass under the combined exposure to PAHs and Cd at environmental concentrations were studied here. The effect of soil pH was also concerned due to the widely occurred soil acidification and general alkali remediation for acidification soil. Unexpectedly, as same as the acid-treated group (pH 6.77), the alkali-treatment (pH 8.83) increased Cd uptake compared with original soil pH group (pH 7.92) for the reason of CdOH+ and CdHCO3+ formed in alkali-treated group. Co-exposure to PAHs induced more oxidative stress than Cd exposure alone due to PAHs aggregated in young root regions, such as root tips, and consequently, affecting the expression of Cd-transporters, destroying the basic structure of plant cells, inhibiting the energy supply for the transporters, even triggering programmed cell death, and finally resulting in decreased Cd uptake. Even under environmental concentrations, combined exposure caused potential risks derived from both PAHs and Cd. Especially, ryegrass grown in alkali-treated soil experienced an increased forage risks despite the soil meeting the national standards for Cd at safe levels. These comprehensive results reveal the mechanism of PAHs inhibiting Cd uptake, improve the understanding of bioavailability of Cd based on different forms, provide a theoretical basis to formulate the safety criteria, and guide the application of actual soil management.

How does the biochar-supported sulfidized nanoscale zero-valent iron affect the soil environment and microorganisms while remediating cadmium contaminated paddy soil?

In previous studies, iron-based nanomaterials, especially biochar (BC)-supported sulfidized nanoscale zero-valent iron (S-nZVI/BC), have been widely used for the remediation of soil contaminants. However, its potential risks to the soil ecological environment are still unknown. This study aims to explore the effects of 3% added S-nZVI/BC on soil environment and microorganisms during the remediation of Cd contaminated yellow-brown soil of paddy field. The results showed that after 49 d of incubation, S-nZVI/BC significantly reduced physiologically based extraction test (PBET) extractable Cd concentration (P < 0.05), and increased the immobilization efficiency of Cd by 16.51% and 17.43% compared with S-nZVI and nZVI/BC alone, respectively. Meanwhile, the application of S-nZVI/BC significantly increased soil urease and sucrase activities by 0.153 and 0.446 times, respectively (P < 0.05), improving the soil environmental quality and promoting the soil nitrogen cycle and carbon cycle. The results from the analysis of the 16S rRNA genes indicated that S-nZVI/BC treatment had a minimal effect on the bacterial community and did not appreciably alter the species of the original dominant bacterial phylum. Importantly, compared to other iron-based nanomaterials, incorporating S-nZVI/BC significantly increased the soil organic carbon (OC) content and decreased the excessive release of iron (P < 0.05). This study also found a significant negative correlation between OC content and Fe(II) content (P < 0.05). It might originate from the reducing effect of Fe-reducing bacteria, which consumed OC to promote the reduction of Fe(III). Accompanying this process, the redistribution of Cd and Fe mineral phases in the soil as well as the generation of secondary Fe(II) minerals facilitated Cd immobilization. Overall, S-nZVI/BC could effectively reduce the bioavailability of Cd, increase soil nutrients and enzyme activities, with less toxic impacts on the soil microorganisms.

Microbial community composition and degradation potential of petroleum-contaminated sites under heavy metal stress

Total petroleum hydrocarbons (n-alkanes), semi-volatile organic compounds, and heavy metals pose major ecological risks at petrochemical-contaminated sites. The efficiency of natural remediation in situ is often unsatisfactory, particularly under heavy metal pollution stress. This study aimed to verify the hypothesis that after long-term contamination and restoration, microbial communities in situ exhibit significantly different biodegradation efficiencies under different concentrations of heavy metals. Moreover, they determine the appropriate microbial community to restore the contaminated soil. Therefore, we investigated the heavy metals in petroleum-contaminated soils and observed that heavy metals effects on distinct ecological clusters varied significantly. Finally, alterations in the native microbial community degradation ability were demonstrated through the occurrence of petroleum pollutant degradation function genes in different communities at the tested sites. Furthermore, structural equation modeling (SEM) was used to explain the influence of all factors on the degradation function of petroleum pollution. These results suggest that heavy metal contamination from petroleum-contaminated sites reduces the efficiency of natural remediation. In addition, it infers that MOD1 microorganisms have greater degradation potential under heavy metal stress. Utilizing appropriate microorganisms in situ may effectively help resist the stress of heavy metals and continuously degrade petroleum pollutants.

Antimony and naphthalene can be simultaneously leached from a combined contaminated soil using carboxymethyl-β-cyclodextrin as a biodegradable eluant

In this study, we have investigated the removal efficiency of antimony (Sb) and naphthalene (Nap) from a combined contaminated soil by carboxymethyl-β-cyclodextrin (CMCD) leaching and reveal its remediation mechanisms by FTIR and ¹H NMR analyses. The results show that the highest removal efficiencies of Sb and Nap were 94.82% and 93.59%, respectively, with a CMCD concentration of 15 g L^-1 at a pH of 4 and a leaching rate of 2.00 mL min^-1 over an interval-time of 12 h. The breakthrough curves show that CMCD had a stronger inclusion capacity of Nap than Sb, and Sb could enhance the adsorption capacity of Nap, while Nap weakened the adsorption of Sb during CMCD leaching. Furthermore, the FTIR analysis suggests that the removal of Sb from combined contaminated soil involved complexation with the carboxyl and hydroxyl groups on CMCD, and the NMR analysis suggests that the inclusion of Nap occurred. These results indicate that CMCD is a good eluant for remediating soil contaminated by a combination of heavy metals and polycyclic aromatic hydrocarbons (PAHs), and its remediation mechanisms depend on the complexation reactions between the surface functional groups and inclusion reactions in the internal cavities.

A system-scale environmental risk analysis with considering a conceptual conversion from material/energy flow to information flow under uncertainties

A conceptual conversion from material/energy flow to information flow is presented in this study for evaluating network environment analysis (NEA) within the naphthalene-contaminated groundwater ecosystems under stochastic-fuzzy uncertainties. Four components (i.e., vegetation, herbivore, soil microorganism, and carnivore) are considered into the NEA framework for quantifying their direct and integral ecological risks. Carcinogenic risk related to human health concern is also evaluated under four remediation periods. The developed method is then applied to a power plant site. Results reveal that the average naphthalene concentration after pump-and-treat treatment would significantly decrease from 8.672 to 1.232 μg/L when remediation period extends to 10 years. The probabilities of suffering from carcinogenic risk would reach 0.9862, 0.9566, 0.8746, and 0.6142 under different remediation periods. Soil microorganism would receive more input risk than vegetation owing to its higher vulnerability. Although the upper-layer components (such as herbivore and carnivore) are not exposed to risk sources, they would gradually accumulate to a high-level ecological risk through food chains. Sensitivity analysis shows that variations in standard boundaries would have a significant impact on the risks of all components within groundwater ecosystems. This study can offer a novel perspective and methodology for comprehensively assessing the system-scale environment risks.

Engineering Microbial Consortia towards Bioremediation

Bioremediation is a sustainable remediation technology as it utilizes microorganisms to convert hazardous compounds into their less toxic or non-toxic constituent elements. This technology has achieved some success in the past decades; however, factors involving microbial consortia, such as microbial assembly, functional interactions, and the role of member species, hinder its development. Microbial consortia may be engineered to reconfigure metabolic pathways and reprogram social interactions to get the desired function, thereby providing solutions to its inherent problems. The engineering of microbial consortia is commonly applied for the commercial production of biomolecules. However, in the field of bioremediation, the engineering of microbial consortia needs to be emphasized. In this review, we will discuss the molecular and ecological mechanisms of engineering microbial consortia with a particular focus on metabolic cross-feeding within species and the transfer of metabolites. We also discuss the advantages and limitations of top-down and bottom-up approaches of engineering microbial consortia and their applications in bioremediation.

Field study on the soil bacterial associations to combined contamination with heavy metals and organic contaminants

The understanding of soil microbial associations to combined contamination would substantially benefit the restoration of damaged ecosystems, which is currently limited at the field scale. In this study, we investigated the soil bacterial associations to combined contamination with metals (Cd, Cu, Hg, Pb, and Zn), polyaromatic hydrocarbons (PAHs), and polybrominated diphenyl ethers (PBDEs). Samples were collected from field sites under five land-use patterns with electronic waste recycling. Results showed that the contents of Cd (0.22-12.86 mg/kg), Cu (17-14,136 mg/kg), Pb (4.6-77,014 mg/kg), Hg (0.28-22 mg/kg), Zn (26-42,495 mg/kg), PAHs (4.6-1753 μg/kg), and PBDEs (1.9-1079 μg/kg) varied significantly across sites. We observed positive correlations between catalase activity and heavy metals, indicative of a resistance response to the oxidative stress induced by metals. Furthermore, the bacterial community diversity was found to be determined primarily by PBDEs, whereas acenaphthylene, available phosphorus, and 2,2',3,3',4,5,6-heptabrominated diphenyl ether (BDE-183) were the three major drivers affecting community composition. The co-occurrence network constructed for bacterial communities exposed to combined contamination was non-random with scale-free, small-world and modularity features. We further proposed functional roles of the modules including stress resistance, hydrocarbon degradation, and nutrient cycling. Overall, the findings of redundancy analysis, variation partition analysis and the co-occurrence network indicated that soil bacterial community under combined contamination cooperated to survive. Members including Rhodoplanes and Nitrospira were capable of degrading PAHs and PBDEs in various pathways, while others, including Acinetobacter, Citrobacter, and Pseudomonas, reduced the metal toxicity to the community. Our findings provide new insights into the responses of soil bacteria, particularly in terms of inter-specific relationships, under combined contamination at the field scale.

Ecological improvement of antimony and cadmium contaminated soil by earthworm Eisenia fetida: Soil enzyme and microorganism diversity

Vermiremediation on improvement of antimony (Sb) and cadmium (Cd) contaminated soil was less reported. In this study, earthworm Eisenia fetida was exposed into soil spiked with Sb and Cd and their mixture for 30 days, and then we measured multiple soil enzyme activities and bacteria communities via enzymatic reaction and high-throughput sequencing of 16 S rRNA genes. The results showed that Sb and Cd at high treatment levels inhibited the activities of urease, neutral phosphatase and protease significantly, but earthworm could promote the activities of urease and neutral phosphatase by 17.75%-121.91% and 1.46%-118.97%, respectively. However, earthworms inhibited catalase and had no effect on protease. The Geometric Mean Index suggested that earthworms led to a higher soil biochemistry function. According to a taxonomic analysis, bacterial community structure predominantly consisted of phylum Proteobacteria, Actinobacteria, Firmicutes, etc. and class Gammaproteobacteria, Actinobacteria, Alphaproteobacteria, etc.; furthermore, Pielou index and Shannon index (Alpha diversity in the habitat) indicated that bacteria diversity and evenness increased in the presence of earthworms. The heating map revealed that earthworms made genus Sphingomonas, Flavobacterium, etc. and species Sphingomonas jaspsi, Conexibacter, etc. dominate. Overall, earthworm is a suitable remediation species to improve the ecological function of heavy metal polluted soil. However, the specific mechanism and causal relationship of how earthworm to control enzyme activity and bacteria community remained to be explored.

Oxidative stress, growth inhibition, and DNA damage in earthworms induced by the combined pollution of typical neonicotinoid insecticides and heavy metals

Heavy metals pollution of soil and widespread application of neonicotinoid insecticides have caused environmental problems worldwide. To evaluate ecological toxicity resulting from the combined pollution of neonicotinoids and heavy metals, typical representatives of neonicotinoid insecticides (imidacloprid, thiamethoxam, dinotefuran) and heavy metals (cadmium, copper, zinc) were selected as soil pollutants; earthworms were used as test organisms. Analysis of the main and interaction effects of a combined pollution process were performed using a uniform design method. Results showed that the reactive oxygen species (ROS) content of earthworms in most treatment groups was higher during exposure than that of the control group. The malondialdehyde (MDA) and ROS content of earthworms demonstrated relatively low values on the 21st day and increased by the 28th day. The interaction between dinotefuran and Cd had significant antagonistic effects on ROS and MDA. The combined pollution adversely affected both the growth and genes of earthworms and also caused damage to the epidermis, midgut, and DNA. The interaction between imidacloprid and Cd was synergistic to ROS, weight inhibition rate, and Olive tail moment (OTM), but was antagonistic to MDA. Of all the single and combined exposures, Zn as a single chemical affected ROS and DNA damage the most, and MDA was significantly enhanced by imidacloprid. Composite pollutants may create different primary effects and interactions causing potential harm to soil organisms.

Responsiveness change of biochemistry and micro-ecology in alkaline soil under PAHs contamination with or without heavy metal interaction

Co-presence of organic pollutants and heavy metals in soil is causing increasing concerns, but the lack of knowledge of relation between soil ecology and pollutant fate is limiting the developing of specific control strategy. This study investigated soil change under pyrene stress and its interaction with cadmium (Cd). Soil physicochemical properties were not seriously influenced. However, pollutants' presence easily varied soil microbial activity, quantity, and diversity. Under high-level pyrene, Cd presence contributed to soil indigenous microorganisms' adaption and soil microbial community structure stability. Soils with both pyrene and Cd presented 7.11-12.0% higher pyrene degradation compared with single pyrene treatment. High-throughput sequencing analysis indicated the proportion of Mycobacterium sp., a commonly known PAHs degrader, increased to 25.2-48.5% in treatments from 0.52% in control. This phenomenon was consistent with the increase of PAHs probable degraders (the ratio increased to 2.86-6.57% from 0.24% in control). Higher Cd bioavailability was also observed in soils with both pollutants than that with Cd alone. And Cd existence caused the elevation of Cd resistant bacterium Limnobacter sp. (increased to 12.2% in CdCK from 2.06% in control). Functional gene prediction also indicated that abundance of genes related to nutrient metabolism decreased dramatically with pollutants, while the abundances of energy metabolism, lipid metabolism, secondary metabolites biosynthesis-related genes increased (especially for aromatic compound degradation related genes). These results indicated the mutual effect and internal-interaction existed between pollutants and soils resulted in pollutants' fate and soil microbial changes, providing further information regarding pollutants dissipation and transformation under soil microbial response.

Potential application of Pseudomonas stutzeri W228 for removal of copper and lead from marine environments

High concentrations of metals in the environment alter bacterial diversity, selecting resistant and tolerant species. The study evaluated the selection of a potential bacterial strain from Sepetiba Bay-Rio de Janeiro, Brazil marine sediments to remove Cu and Pb. The bacterial strain isolated from the sediments was used in three different bioassays: (1) Cu at concentrations of 0 (control), 6 and 50 μg.mL^-1; (2) Pb at concentrations of 0 (control), 6 and 50 μg.mL^-1; (3) Cu + Pb in concentrations of 3 μg.mL^-1 Cu + 3 μg.mL^-1 Pb (6 μg.mL^-1) and 25 μg.mL^-1 Cu + 25 μg.mL^-1 Pb (50 μg.mL^-1). The number of cells and the enzymatic activities of dehydrogenases and esterases were quantified. Results of taxonomic identification indicated the selection of the Pseudomonas stutzeri W228 strain, showing a greater degree of similarity (±73%) with the database used. There was no significant variation in the number of cells, 10⁸ cells.mL^-1, which represents a high biomass production in the presence of stressors. However, we observed a reduction in dehydrogenase activity at all tested concentrations of Cu, Pb and Cu + Pb. The activity of esterase increased, indicating a higher energy demand to complete the bacterial life cycle. The study showed significant results for the absorption of Pb by the extracellular polymeric substances (EPS) and the efflux of Cu. The capacity of Pb absorption by EPS can be considered a resistance mechanism, as well as the efflux of Cu, so that the available EPS sites could be occupied by the most toxic ions demonstrating that Pseudomonas stutzeri is resistant to Pb and Cu.

Microbial community shift under exposure of dredged sediments from a eutrophic bay

Microbial communities occur in almost every habitat. To evaluate the homeostasis disruption of in situ microbiomes, dredged sediments from Guanabara Bay-Brazil (GB) were mixed with sediments from outside of the bay (D) in three different proportions (25%, 50%, and 75%) which we called GBD25, GBD50, and GBD75. Grain size, TOC, and metals-as indicators of complex contamination-dehydrogenase (DHA) and esterase enzymes (EST)-as indicators of microbial community availability-were determined. Microbial community composition was addressed by amplifying the 16S rRNA gene for DGGE analysis and sequencing using MiSeq platform (Illumina).We applied the quality ratio index (QR) to the GB, D, and every GBD mixture to integrate geochemical parameters with our microbiome data. QR indicated high environmental risk for GB and every GBD mixture, and low risk for D. The community shifted from aerobic to anaerobic profile, consistent with the characteristics of GB. Sample D was dominated by JTB255 marine benthic group, related to low impacted areas. Milano-WF1B-44 was the most representative of GB, often found in anaerobic and sulfur enriched environments. In GBD, the denitrifying sulfur-oxidizing bacteria, Sulfurovum, was the most representative, typically found in suboxic or anoxic niches. The canonical correspondence analysis was able to explain 60% of the community composition variation and exhibit the decrease of environmental quality as the contamination increases. Physiological and taxonomic shifts of the microbial assemblage in sediments were inferred by QR, which was suitable to determine sediment risk. The study produced sufficient information to improve the dredging plan and management.

Spatial distribution of phthalate esters and the associated response of enzyme activities and microbial community composition in typical plastic-shed vegetable soils in China

The widespread use of phthalate esters (PAEs) in plastic products has made them ubiquitous in environment. In this study, 93 soil samples were collected in 31 plastic-sheds from one of China's largest vegetable production bases, Shouguang City, Shandong Province, to investigate the pollution characteristics and composition of PAEs in soils. Eleven PAEs were detected in the soil samples with the total concentration of 756-1590 μg kg^-1 dry soil. Di (2-ethylhexyl) phthalate (DEHP), bis (2-n-butoxyethyl) phthalate (DBEP), di-isobutyl phthalate (DiBP) and di-n-butyl phthalate (DBP) were the main pollutants with the highest concentrations. Moreover, soil properties, including pH, total organic carbon (TOC), soil enzyme activities, and soil microbial community characteristics, were monitored to explore the associated formation mechanisms. The concentration of PAEs in the plastic-shed vegetable soils was regionalized and the contamination degree in different regions was related to soil microbial characteristics and soil enzyme activities. Phthalate ester is positively correlated with catalase and sucrase, and negatively correlated with dehydrogenase and urease. Furthermore, some tolerant and sensitive bacteria were selected, which possibly could be used as potential indicators of PAE contamination in soil. Dimethyl phthalate (DMP) and DBP also had greater effects on the soil microbial community than other PAEs. The results will provide essential data and support the control of PAEs in plastic-shed vegetable soils in China.

Effects of Sepiolite and Biochar on Enzyme Activity of Soil Contaminated by Cd and Atrazine

The effects of sepiolite and biochar on the enzymatic activities of the soil in Cd- and atrazine-contaminated soils were studied. During the growth of pakchoi, the activities of acid phosphatase, sucrase, acid protease, and cellulase decreased, catalase activity increased, and urease activity decreased first and then increased. At the first harvest, compared with that for the control group, the soil pH after treatment with remediation materials increased from 5.41 to 7.43; the activities of urease, acid protease, and catalase increased by 62.8%, 38.6%, and 86.1%, respectively. And the activities of sucrase and acid phosphatase decreased by 17.3% and 24.7%, respectively. At the second harvest, the activities of acid phosphatase, acid protease, and cellulase continued to increase, but those of sucrase and catalase decreased. The results showed that soil enzyme activity was closely related to the type and addition of remediation materials, as well as the type of the enzyme.

Effect of phenanthrene on the biological characteristics of earthworm casts and their relationships with digestive and anti-oxidative systems

Earthworms as ecosystem engineers partially improve soil properties by egesting casts. Our previous study confirmed that soil pollution affects the physico-chemical properties of earthworm casts. It is still unclear whether the biological properties (e.g. cellulase, urease, and acid and alkaline phosphatase activities, as well as microbial biomass carbon) of casts are affected by foreign substances in soil. The present study aimed to investigate the effect of phenanthrene (PHE) on the biological characteristics of earthworm (Eisenia fetida) casts. Furthermore, correlations between cast properties and the digestive and antioxidant systems were explored by the determination of digestive enzyme (urease, protease, acid and alkaline phosphatase) activities, antioxidant indexes [superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD)], as well as malondialdehyde (MDA) content. Exposure at a range of PHE doses (0, 2, 5, 10, and 20 mg kg^-1) for 15 d resulted in the following observations: (1) Compared with urease, as well as acid and alkaline phosphatase activities, cellulase activities in both soil and casts were sensitive to PHE, and could potentially act as biomarkers to provide early-warning signals for soil pollution. (2) Microbial biomass carbon in casts was modified, but with no clear pattern. (3) Cellulase and POD activities, as well as MDA content in earthworms, increased with elevated exposure to PHE in soil. Protease, SOD, and CAT activities exhibited a biphasic dose response to PHE, while acid and alkaline phosphatase activities were inhibited under treatment conditions. (4) Correlation analysis suggested that microbial biomass carbon in casts significantly and positively correlated with cellulase and acid phosphatase activities of earthworms, but negatively correlated with protease activities. A significant but weak negative correlation between alkaline phosphatase activities in casts and POD activities was also observed. Based on these results, we concluded that PHE content in soil modified some biological properties of casts, by partially affecting the earthworm's digestive and antioxidant systems. This study advances our knowledge of earthworm ecology in polluted soil by providing a better understanding of their ecological functions.

Effect of Rhamnolipids on Microbial Biomass Content and Biochemical Parameters in Soil Contaminated with Coal Tar Creosote

The objective of the present study was to compare the effect of rhamnolipids on the microbial biomass content and the activity of dehydrogenases (DHA), acid phosphatase (ACP), alkaline phosphatase (ALP), and urease (URE) in soil contaminated with two types of coal tar creosote: type C and type GX-Plus. The experiment was carried out on samples of sandy clay loam under laboratory conditions. Coal tar creosote was added to soil samples at a dose of 0 and 10 g·kg⁻¹ DM, along with rhamnolipids at a dose of 0, 10, 100, and 1000 mg·kg⁻¹ DM. The humidity of the samples was brought to 60% maximum water holding capacity, and the samples were incubated at 20°C. Microbial and biochemical parameters were determined on days 1, 7, 21, and 63. The obtained results demonstrated that the addition of rhamnolipids did not result in any significant changes in the activity of the determined parameters in the uncontaminated soil. However, it was observed that the application of these biosurfactants, particularly at the dose of 1000 mg·kg⁻¹ DM, largely decreased the effect of coal tar creosote on the determined parameters. Moreover, the microbial biomass and the activity of ALP and URE were found to be the best indicator of bioremediation of soil contaminated with coal tar creosote.

Ecological risk of combined pollution on soil ecosystem functions: Insight from the functional sensitivity and stability

Assessing the ecological risk of combined pollution, especially from a holistic perspective with the consideration of the overarching functions of soil ecosystem, is crucial and beneficial to the improvement of ecological risk assessment (ERA) framework. In this study, four soils with similar physicochemical properties but contrasting heavy metals contamination levels were selected to explore changes in the integrated functional sensitivity (MSI), resistance (MRS) and resilience (MRL) of soil microbial communities subjected to herbicide siduron, based on which the ecological risk of the accumulation of siduron in the four studied soils were evaluated. The results suggested that the microbial biomass carbon, activity of denitrification enzyme and nitrogenase were indicative of MSI and MRS, and the same three parameters plus soil basal respiration were indicative of MRL. Significant dose-effect relationships between siduron residues in soils and MSI, MRS and MRL under combined pollution were observed. Heavy metal polluted soils showed higher sensitivity and lower resistance to the additional disturbance of herbicide siduron due to the lower microbial biomass, while the resilience of heavy metal polluted soils was much higher due to the pre-adaption to the chemical stresses. The quantifiable indicator microbial functional stability was incorporated in the framework of ERA and the results showed that the accumulation of siduron in the studied soils could exhibit potential harm to the integrated functional stability of soil microbial community. Thus, this work provides insights into the application of integrated function of soil microbial community into the framework of ERA.

New insights into the responses of soil microorganisms to polycyclic aromatic hydrocarbon stress by combining enzyme activity and sequencing analysis with metabolomics

Polycyclic aromatic hydrocarbons (PAHs), some of the most widespread organic contaminants, are highly toxic to soil microorganisms. Whether long-term polluted soils can still respond to the fresh input of pollutants is unknown. In this study, the soil enzyme activity, soil microbial community structure and function and microbial metabolism pathways were examined to systematically investigate the responses of soil microorganisms to fresh PAH stress. Microbial activity as determined by soil dehydrogenase and urease activity was inhibited upon microbe exposure to PAH stress. In addition, the soil microbial community and function were obviously shifted under PAH stress. Both microbial diversity and richness were decreased by PAH stress. Rhizobacter, Sphingobium, Mycobacterium, Massilia, Bacillus and Pseudarthrobacter were significantly affected by PAH stress and can be considered important indicators of PAH contamination in agricultural soils. Moreover, the majority of microbial metabolic function predicted to respond to PAH stress were affected adversely. Finally, soil metabolomics further revealed specific inhibition of soil metabolism pathways associated with fatty acids, carbohydrates and amino acids. Therefore, the soil metabolic composition distinctively changed, reflecting a change in the soil metabolism. In summary, fresh contaminant introduction into long-term polluted soils inhibited microbial activity and metabolism, which might profoundly affect the whole soil quality.

Effects of aeration on the suspended matter from a tropical and eutrophic estuary

A comprehensive understanding of the complex biogeochemical interactions between organic matter and persistent contaminants in the suspended matter is vital for eco-efficient estuary recovery. However, little is known regarding aeration effects in suspended particulate aggregates. Therefore, this study aimed to investigate the effects of aeration on the suspended matter from a Tropical and Eutrophic estuarine environment. Anoxic water with 60 g/L of suspended particulate matter (SPM) was collected from Guanabara Bay, Rio de Janeiro, Brazil, transferred to experimental boxes and aerated for 61 days. SPM aggregates monitoring included abiotic variables measurements and, determination of total organic matter (TOM), biopolymers composition, bacterial activity, trace metals, and polycyclic aromatic hydrocarbons (PAHs) concentrations. The aeration enhanced dissolved oxygen (DO) concentration and the redox potential (Eh). However, from days 0 to 61 the predominant bacterial activities were denitrification and fermentation. Electron transport system activity increased after day 10, and aerobic activity was detected after day 19. In summary, aeration increased aerobic bacterial activity, lipids (LIP) and trace metal concentrations, although diminished protein/carbohydrate ratio and PAH concentration. Trace metals concentration (Ni, Pb, Cu, Cr, Mn, and Fe) were the highest on day 19 when the pH was 5.9. Copper presented toxic values (Cu > 20.0 μg/g). The pH showed a strong negative correlation with Eh (r = -0.94; p < 0.001). Acidic environment (pH ≤ 5.9) in marine ecosystems with high loads of toxic trace metals is unsafe for biota. Therefore, managers must be aware of the environmental and biological risks of introducing the aeration technique into a eutrophic marine environment.

Environmental forensic characterization of former rail yard soils located adjacent to the Statue of Liberty in the New York/New Jersey harbor

Identifying inorganic and organic soil contaminants in urban brownfields can give insights into the adverse effects of industrial activities on soil function, ecological health, and environmental quality. Liberty State Park in Jersey City (N.J., USA) once supported a major rail yard that had dock facilities for both cargo and passenger service; a portion remains closed to the public, and a forest developed and spread in this area. The objectives of this study were to: 1) characterize the organic and inorganic compounds in Liberty State Park soils and compare the findings to an uncontaminated reference site (Hutcheson Memorial Forest); and 2) identify differences between the barren low-functioning areas and the forested high-functioning areas of the brownfield. Soil samples were solvent-extracted, fractionated, and analyzed by gas chromatography-mass spectrometry and subjected to loss-on-ignition, pyrolysis-gas chromatography-mass spectrometry, inductively-coupled-plasma mass spectrometry, and optical microscopy analyses. Compared to soil from the reference site, the forested soils in Liberty State Park contained elevated percentages of organic matter (30-45%) and more contaminants, such as fossil-fuel-derived hydrocarbons and coal particles. Microscopy revealed bituminous and anthracite coal, coke, tar/pitch, and ash particles. Barren and low-functioning site 25R had a similar organic contaminant profile but contained a higher metal load than other Liberty State Park sites and also lacked higher plant indicators. These can obscure the signatures of contaminants, and data from adjacent barren and vegetated sites are valuable references for soils studies. A deeper understanding of the chemistry, biochemistry, and ecology of barren soils can be leveraged to prevent land degradation and to restore dysfunctional and phytotoxic soils.

Acute biotoxicity assessment of heavy metals in sewage sludge based on the glucose consumption of Escherichia coli

As a simple and feasible method for acute biotoxicity assessment, personal glucose meter (PGM) can be successfully applied in the early warning of environmental pollutants in sewage. In this paper, the acute biotoxicity of single and joint heavy metals in sewage and real sludge samples was systematically described based on the glucose metabolism of Escherichia coli (E. coli). Results indicated that the biotoxicity order of five single heavy metals in sewage was Hg2+ > As3+ > Cu2+ > Zn2+ > Cd2+. The joint heavy metals of Cu2+ + Zn2+, Cu2+ + Cd2+, and Cu2+ + Hg2+ produced synergistic effects, while Cu2+ + As3+ and Cd2+ + Zn2+ possessed antagonistic effects for the combined biotoxicity. In spiked sludge, Cd2+ and Zn2+ owned higher biotoxicity than Cu2+ and As3+. Notably, the electroplate factory and housing estate sludge respectively showed the highest and lowest inhibition rates as 57.4% and 17.7% under the real sludge biotoxicity assessment. These results demonstrated that PGM was a sensitive and portable method, which could be widely used for acute biotoxicity assessment of heavy metals in sewage sludge.

Insights into mixed contaminants interactions and its implication for heavy metals and metalloids mobility, bioavailability and risk assessment

Mobility of heavy metals at contaminated sites is mainly influenced by the soil physicochemical properties and environmental conditions, therefore assessing heavy metals (HMs) and metalloids fractionation can provide insights into their potential risk and the mechanisms that regulate bioavailability. A 12-months mesocosms experiment was setup to investigate the effect of physicochemical factors (pH, moisture, and temperature) and weathering (time) on HMs and metalloids fractionation in three different multi-contaminated soil matrices (low, medium, and high contamination) collected from a soil treatment facility located in the United Kingdom, and two rural contaminated soil samples. The study demonstrates that even though Pb and Zn were found associated with the exchangeable fraction in the soil with the highest contamination (total average Pb 3400 mg/kg, and total average Zn 2100 mg/kg in Soil C), neither the condition applied nor the weathering caused an increase in their mobility. Although it was expected that lower pH (4.5) would favours the dissociation of HMs and metalloids, no significant differences were observed, potentially due to the initial alkaline pH of the genuine-contaminated soil samples. The results show that even though total concentration of Pb, Cu, and Zn exceed the soil standards and guideline values, HMs were predominantly associated with the non-exchangeable fraction, while only 5% were dissolved in the pore water fraction (potentially bioavailable). In addition, the mobility and bioavailability of HMs remained constant over the 12 months monitoring, suggesting that these soils pose negligible risk to the environment.

Microcalorimetry and enzyme activity to determine the effect of nickel and sodium butyl xanthate on soil microbial community

In non-ferrous metal tailings, combined pollution in the surrounding soil is caused by heavy metals and flotation chemicals. The combined effects of nickel (Ni) and its primary ore processing collector, sodium butyl xanthate (SBX), on soil microbial activity were investigated following the fluorescein diacetate hydrolase (FDA) and sucrase (SA) activities, and isothermal microcalorimetry during 60 days. FDA and SA activities as well as overall soil microbial activity were significantly affected by Ni, SBX and Ni/SBX mixture. The inhibition rate (I) of the growth rate constant (k) being higher with the Ni/SBX mixture than with SBX alone during the experiment. The growth rate constant (k) was positively correlated (p < 0.05 or p < 0.01) with enzyme activities (FDA and SA) indicating that k represented a valuable proxy to evaluate the toxic effect of metals and flotation reagents on soil microorganisms. Thus, microcalorimetry was a useful method to characterize soil microbial communities.

Response of soil phosphatase activities to contamination with two types of tar oil

Tar oil is a complex mixture of hydrocarbon compounds obtained from high-temperature distillation of coal tar. It has been used for over 100 years from now to protect wood and has been applied to wood products, primary utility poles, and railroad ties by pressure methods. Composition of the tar oil depends on the source and typically consists of 85% polycyclic aromatic hydrocarbons (PAHs), 10% phenolic compounds, and 5% heterocyclic compounds. In this research, we performed the laboratory experiment to compare two types of tar oil: C and GX-Plus, and their effects on P-cycling enzymes (phosphatases) in sandy loam and loamy sand. Tar oil was applied to soil samples at the following doses: 2, 10, and 50 g kg^-1. Soil without tar oil was used as a control sample. The experiment showed that the contamination of soil with tar oil affects the enzyme activities measured and with this most probably the P-cycle in soil. Phosphomonoesterases were the most sensitive to the contamination of soil with both type of tar oil: typeC and type GX-Plus. Greater changes in the enzymatic activity were observed in the loamy sand. Moreover, the type C tar oil demonstrated higher toxicity for phosphatases than type GX-Plus.

Influence of a mixture of metals on PAHs biodegradation processes in soils

In order to assess the effect of mixed pollutants, the influence of different concentration levels of a mixture of metals (Cr, Co, Pb, Mn, Ni, Cu, Zn) on the biodegradation of some PAHs (phenanthrene, fluoranthene, pyrene, benzo[b]fluoranthene and benzo[a]pyrene) in soil samples was evaluated. To do so, groups of microcosms of a natural soil from the region of Sabadell (Barcelona, Spain) were prepared as a reproduction of the native environment at laboratory scale, under controlled conditions. Mixtures of PAHs and metals were carefully selected, according to soil characterization and microbiological growth preliminary assays, and were added to microcosms. These microcosms were analyzed at various times, along two months, to obtain PAHs dissipation time-courses. A first-order kinetic modelling allowed obtaining different rate constants and DT50 values as a function of the metal levels introduced in microcosms. As a general observation, the higher the concentration of metals, the lower the biodegradation of PAHs of 3-4 rings (phenanthrene, fluoranthene and pyrene). On the other hand, no important effect on the biodegradation of higher molecular weight PAHs (benzo[b]fluoranthene and benzo[a]pyrene) was observed at the different concentration levels of metals tested.

Degradation of polycyclic aromatic hydrocarbons in a mixed contaminated soil supported by phytostabilisation, organic and inorganic soil additives

In soil, mixed contamination with potentially toxic trace elements and polycyclic aromatic hydrocarbons (PAHs) may persist for a long time due to strong adsorption to the soil matrix and to its toxicity to microorganism. We conducted an incubation batch experiment to test the effect of soil amendments (biochar, gravel sludge, iron oxides) on the immobilisation of trace elements. To monitor microbial degradation, a ¹³C-PHE (phenanthrene) label was introduced to soil for ¹³C-PLFA (phospholipid fatty acid) analysis. Soil amendments increased soil pH, reduced mobility of NH₄NO₃-extractable trace elements Cd and Zn, and increased mobile Cu. A small consortium of PHE degraders was identified mainly in the microbial groups of gram-negative bacteria and actinomycetes. The degradation process of PHE peaked 9days after incubation start. PAH concentrations remained constant in the soil within the 30-day incubation, except for the easily available ¹³C-PHE in the amended treatment. In order to test the effect of plants and soil amendments under more realistic conditions, we also conducted an outdoor pot experiment with black locust (Robinia pseudoacacia Nyirsegi). Furthermore, soil amendments increased the mobility of soil Cu and As and decreased the mobility of Cd, Pb and Sb. The uptake of trace elements to leaves was low. Σ 16 U.S. EPA PAHs were significantly reduced only in the combined treatment of black locust and soil amendments after 12months of plant growth. Soil amendment-assisted phytoremediation showed a high efficiency in PAH dissipation and may be a useful remediation technique for mixed contaminated soils.

Investigations of microbial degradation of polycyclic aromatic hydrocarbons based on 13C-labeled phenanthrene in a soil co-contaminated with trace elements using a plant assisted approach

Co-contaminations of soils with organic and inorganic pollutants are a frequent environmental problem. Due to their toxicity and recalcitrance, the heterogeneous pollutants may persist in soil. The hypothesis of this study was that degradation of polycyclic aromatic hydrocarbons (PAHs) is enhanced if heavy metals in soil are immobilized and their bioavailability reduced. For metal immobilization and enhanced biodegradation, distinct mineral and organic soil amendments (iron oxides, gravel sludge, biochar) were deployed in an incubation batch experiment. The second part of the experiment consisted of a greenhouse pot experiment applying fast-growing and pollution-tolerant woody plants (willow and black locust). Soil amendments initially immobilized NH₄NO₃-extractable zinc, cadmium, and lead; after 100 days of incubation, soil amendments showed reductions only for cadmium and a tendency to enhance arsenic mobility. In order to monitor the remediation success, a ¹³C-phenanthrene (PHE) label was applied. ¹³C-phospholipid fatty acid analysis (¹³C-PLFA) further enabled the identification of PHE-degrading soil microorganisms. Both experiments exhibited a similar PLFA profile. Gram-negative bacteria (esp. cy17:0, 16:1ω7 + 6, 18:1ω7c) were the most significant microbial group taking up ¹³C-PHE. Plants effectively increased the label uptake by gram-positive bacteria and increased the biomass of the fungal biomarker, although their contribution to the degradation process was minor. Plants tended to prolong PAH dissipation in soil; at the end of the experiment, however, all treatments showed equally low total PAH concentrations in soil. While black locust plants tended not to take up potentially toxic trace elements, willows accumulated them in their leaves. The results of this study show that the chosen treatments did not enhance the remediation of the experimental soil.

Impact of pyrene and cadmium co-contamination on prokaryotic community in coastal sediment microcosms

Acute ecological impacts of co-contamination of polycyclic aromatic hydrocarbons (PAHs) and heavy metals on diversity and composition of coastal benthic prokaryotes were unclear. We took pyrene (Pyr) and cadmium (Cd) as the representatives and mimicked an eight-week exposure of moderate and high levels of Pyr, Cd and their mixtures. 16S rRNA amplicon sequencing was used to investigate interaction of the contaminants in temporal succession of prokaryotes. Generally, concentrations of Pyr and HCl-extractable Cd in the sediments were stable over time. Effects and interaction of Pyr and Cd on prokaryotic α-diversity were temporally- and dose-dependent with a decreasing trend in richness and Shannon index under various contamination regimes, particularly in the single-Cd contaminated groups at the early stage. Temporal variability and Pyr-induced pattern in prokaryotic composition were observed. However, Pyr and Cd showed a persistent interaction in prokaryotic composition after 7 days, altering successional trajectories of communities. The communities under Pyr contamination regardless of Cd could be at a developing stage for an active PAH-degrading community with appearance of a pioneer Cycloclasticus phylotype, persistently showing a strong correlation with Pyr level. The associations of phylotypes and Cd level were short-lived and weak, corresponding to the overall resistance of prokaryotic composition to Cd. In the high-throughput sequencing era, using microcosm experiment, we renewed the knowledge about how prokaryotes vary in terms of α-diversity, composition and specific taxa in response to co-contamination of model contaminants at a temporal scale.

Influence of root components of celery on pyrene bioaccessibility, soil enzymes and microbial communities in pyrene and pyrene-diesel spiked soils

Though phytoremediation is deemed as a promising approach to restore polycyclic aromatic hydrocarbon (PAHs) contaminated sites, studies about how the biodegradation of PAHs is enhanced still remains incomprehensive. Effects of root components on pyrene bioaccessibility, soil enzymes and microbial communities were explored in the paper, and their interactions in simulated pyrene and pyrene-diesel spiked microcosms were tried to give a reasonable explanation. Results indicated that root components enhanced the pyrene removal of bioaccessible and adsorbed fractions by 16.10 and 1.80mgkg^-1, respectively, in pyrene-spiked soils at the end of the experiment. By contrast, root components increased the degradation of bioaccessible fraction by only 3.3mgkg^-1 in pyrene-diesel spiked soils. Although the bound fractions of pyrene increased over time in treatments without root components, they remained relatively stable, ranging from 0.02 to 0.03mgkg^-1, in root components amended treatments. Activities of soil enzymes (polyphenol oxidase, catalase, invertase, urease and alkaline phosphatase) varied differently in response to pollutants and root components. Analysis of phospholipid fatty acids revealed that root components increased the biomass of soil microorganisms and altered the microbial structure. Pearson correlation analysis proved positive correlations between all the microbial subgroups and pyrene removal in pyrene-spiked soils, but the degradation of bioaccessible pyrene was only positively related with microorganisms confirmed by monounsaturated fatty acids in pyrene-diesel spiked soils.

Rhizospheric soil enzyme activities and phytominimg potential of Aeluropus lagopoides and Cyperus conglomeratus growing in contaminated soils at the banks of artificial lake of reclaimed wastewater

This work investigates the phytoremediation potential of Aeluropus lagopoides and Cyperus conglomeratus, growing indigenously in the vicinity of an artificial lake of reclaimed water in Tabuk, Saudi Arabia . The sampling sites were located at different distances from the wastewater treatment plants. Trace metal contents were higher in roots than shoots in both these plants. Soil urease activity in rhizophere increased linearly along the sampling sites, however, soil alkaline phosphatase and β-glucosidase activities were higher at site 2 but at site 3, the activities of both these soil enzymes reduced. Significant correlations were observed between soil urease activity and the bioconcentration factor (BCF) of Cd, Cu, Pb, and As in A. lagopoides and translocation factor (TF) for all metals in both these plants. Soil β-glucosidase activity was negatively correlated with the TF of Cd, Cu, Pb, and As in A. lagopoides and positively in C. conglomeratus, respectively. Higher BCF of Cd, Cu and Pb than C. conglomeratus and suitable for phytostabilization, however at site 3, C. conglomeratus showed better phytostabilization efficiency for As, as the BCF of As was higher than the A. lagopoides. On the basis of metal accumulation efficiency and rhizospheric soil urease and β-glucosidase activities, A. lagopoides species proved to be a better option for application in phytostabilization strategy than C. conglomeratus plants in the area surrounding the artificial lake of reclaimed water in Tabuk, Saudi Arabia.

Agricultural utilization of biosolids: A review on potential effects on soil and plant grown

Environmental and economic implications linked with the proper ecofriendly disposal of modern day wastes, has made it essential to come up with alternative waste management practices that reduce the environmental pressures resulting from unwise disposal of such wastes. Urban wastes like biosolids are loaded with essential plant nutrients. In this view, agricultural use of biosolids would enable recycling of these nutrients and could be a sustainable approach towards management of this hugely generated waste. Therefore biosolids i.e. sewage sludge can serve as an important resource for agricultural utilization. Biosolids are characterized by the occurrence of beneficial plant nutrients (essential elements and micro and macronutrients) which can make help them to work as an effective soil amendment, thereby minimizing the reliance on chemical fertilizers. However, biosolids might contain toxic heavy metals that may limit its usage in the cropland. Heavy metals at higher concentration than the permissible limits may lead to food chain contamination and have fatal consequences. Biosolids amendment in soil can improve physical and nutrient property of soil depending on the quantity and portion of the mixture. Hence, biosolids can be a promising soil ameliorating supplement to increase plant productivity, reduce bioavailability of heavy metals and also lead to effective waste management.

Alteration in successional trajectories of bacterioplankton communities in response to co-exposure of cadmium and phenanthrene in coastal water microcosms

Coexistence of heavy metals and organic contaminants in coastal ecosystems may lead to complicated circumstances in ecotoxicological assessment for biological communities due to potential interactions of contaminants. Consequences of metals and polycyclic aromatic hydrocarbons (PAHs) co-contamination on coastal marine microbes at the community level were paid less attention. We chose cadmium (Cd) and phenanthrene (PHE) as representatives of metals and PAHs, respectively, and mimicked contaminations using coastal water microcosms spiked with Cd (1 mg/L), PHE (1 mg/L), and their mixture over two weeks. 16S rRNA gene amplicon sequencing was used to compare individual and cumulative effects of Cd and PHE on temporal succession of bacterioplankton communities. Although we found dramatic impacts of dimethylsulfoxide (DMSO, used as a carrier solvent for PHE) on bacterial α-diversity and composition, the individual and cumulative effects of Cd and PHE on bacterial α-diversity were temporally variable showing an antagonistic pattern at early stage in the presence of DMSO. Temporal succession of bacterial community composition (BCC) was associated with temporal variability of water physicochemical parameters, each of which explained more variation in BCC than two target contaminants did. However, Cd, PHE, and their mixture distinctly altered the successional trajectories of BCC, while only the effect of Cd was retained at the end of experiment, suggesting certain resilience in BCC after the complete dissipation of PHE along the temporal trajectory. Moreover, bacterial assemblages at the genus level associated with the target contaminants were highly time-dependent and more unpredictable in the co-contamination group, in which some genera possessing hydrocarbon-degrading members might contribute to PHE degradation. These results provide preliminary insights into how co-exposure of Cd and PHE phylogenetically alters successional trajectories of bacterioplankton communities in the manipulated coastal water microcosms.

Bioremediation mechanisms of combined pollution of PAHs and heavy metals by bacteria and fungi: A mini review

In recent years, knowledge in regard to bioremediation of combined pollution of polycyclic aromatic hydrocarbons (PAHs) and heavy metals by bacteria and fungi has been widely developed. This paper reviews the species of bacteria and fungi which can tackle with various types of PAHs and heavy metals entering into environment simultaneously or successively. Microbial activity, pollutants bioavailability and environmental factors (e.g. pH, temperature, low molecular weight organic acids and humic acids) can all affect the bioremediation of PAHs and heavy metals. Moreover, this paper summarizes the remediation mechanisms of PAHs and heavy metals by microbes via elucidating the interaction mechanisms of heavy metals with heavy metals, PAHs/PAHs metabolites with PAHs and PAHs with heavy metals. Based on the above reviews, this paper also discusses the potential research needs for this field.

Assessment of toxicity using dehydrogenases activity and mathematical modeling

Dehydrogenase activity is frequently used to assess the general condition of microorganisms in soil and activated sludge. Many studies have investigated the inhibition of dehydrogenase activity by various compounds, including heavy metal ions. However, the time after which the measurements are carried out is often chosen arbitrarily. Thus, it can be difficult to estimate how the toxic effects of compounds vary during the reaction and when the maximum of the effect would be reached. Hence, the aim of this study was to create simple and useful mathematical model describing changes in dehydrogenase activity during exposure to substances that inactivate enzymes. Our model is based on the Lagergrens pseudo-first-order equation, the rate of chemical reactions, enzyme activity, and inactivation and was created to describe short-term changes in dehydrogenase activity. The main assumption of our model is that toxic substances cause irreversible inactivation of enzyme units. The model is able to predict the maximum direct toxic effect (MDTE) and the time to reach this maximum (TMDTE). In order to validate our model, we present two examples: inactivation of dehydrogenase in microorganisms in soil and activated sludge. The model was applied successfully for cadmium and copper ions. Our results indicate that the predicted MDTE and TMDTE are more appropriate than EC50 and IC50 for toxicity assessments, except for long exposure times.

Organic and inorganic amendment application on mercury-polluted soils: effects on soil chemical and biochemical properties

On the basis of a previous study performed in our laboratory, the use of organic and inorganic amendments can significantly modify the Hg mobility in soil. We have compared the effectiveness of organic and inorganic amendments such as digestate and fly ash, respectively, reducing the Hg mobility in Chernozem and Luvisol soils differing in their physicochemical properties. Hence, the aim of this work was to compare the impact of digestate and fly ash application on the chemical and biochemical parameters in these two mercury-contaminated soils in a model batch experiment. Chernozem and Luvisol soils were artificially contaminated with Hg and then incubated under controlled conditions for 21 days. Digestate and fly ash were applied to both soils in a dose of 10 and 1.5 %, respectively, and soil samples were collected after 1, 7, 14, and 21 days of incubation. The presence of Hg in both soils negatively affected to processes such as nitrification, provoked a decline in the soil microbial biomass C (soil microbial biomass C (MBC)), and the microbial activities (arylsulfatase, and β-glucosaminidase) in both soils. Meanwhile, the digestate addition to Chernozem and Luvisol soils contaminated with Hg improved the soil chemical properties (pH, dissolved organic carbon (DOC), N (Ntot), inorganic-N forms (N-NH4 (+) and N-NO3 (-))), as consequence of high content in C and N contained in digestate. Likewise, the soil MBC and soil microbial activities (dehydrogenase, arylsulfatase, and β-glucosaminidase) were greatly enhanced by the digestate application in both soils. In contrast, fly ash application did not have a remarkable positive effect when compared to digestate in Chernozem and Luvisol soil contaminated with mercury. These results may indicate that the use of organic amendments such as digestate considerably improved the soil health in Chernozem and Luvisol compared with fly ash, alleviating the detrimental impact of Hg. Probably, the chemical properties present in digestate may determine its use as a suitable amendment for the assisted-natural attenuation of mercury-polluted soils.

A proposal of "core enzyme" bioindicator in long-term Pb-Zn ore pollution areas based on topsoil property analysis

To study the effects of long-term mining activities on the agricultural soil quality of Mengnuo town in Yunnan province, China, the heavy metal and soil enzyme activities of soil samples from 47 sites were examined. The results showed that long-term mining processes led to point source heavy metal pollution and Pb, Cd, Zn and As were the primary metal pollutants. Polyphenoloxidase was found the most sensitive soil enzyme activity and significantly correlated with almost all the metals (P < 0.05). Amylase (for C cycling), acid phosphatase (for P cycling) and catalase (for redox reaction) activities showed significantly positive correlations (P < 0.05) with Pb, Cd, Zn and As contents. The correlations between soil enzymes activities and Cd, Pb and Zn contents were verified in microcosm experiments, it was found that catalase activity had significant correlations (P < 0.05) with these three metals in short-term experiments using different soils under different conditions. Based on both field investigation and microcosm simulation analysis, oxidoreductases activities (rather than a specific enzyme activity) were suggested to be used as "core enzyme", which could simply and universally indicate the heavy metal pollution degrees of different environments. And hydrolases (for C, N, P and S recycling) could be used as a supplement to improve correlation accuracy for heavy metal indication in various polluted environments.

Changes of lead speciation and microbial toxicity in soil treated with repeated Pb exposure in the presence of BDE209

Lead (Pb) and decabromodiphenyl ether (BDE209) are main pollutants at electric waste (e-waste) recycling sites (EWRSs), and their joint toxicological effects have received extensive attention. Frequently, soil pollution at EWRSs usually results from the occurrence of repeated single or multiple pollution events, with continuous impacts on soil microorganisms. Therefore, a laboratory incubation study was conducted to determine Pb bioavailability and microbial toxicity in repeated Pb-polluted soil in the presence of BDE209 for the first time. We evaluated the impacts of repetitive exposure trials on chemical fractions of Pb, and the results showed that repeated single Pb pollution event resulted in an increase of carbonates fraction of Pb, which was different from one-off single Pb exposure. Moreover, one-off Pb-treated groups exhibited higher I R (reduced partition index) values on day 30 and all treatments remained the same I R level at the end of incubation period. The parameters of microbial toxicity were well reflected by soil enzymes. During the entire incubation, the dehydrogenase and urease activities were significantly inhibited by Pb (P < 0.01), and BDE209 supply could weaken the adverse influence. Additionally, significant correlations between available or metastable Pb and the two soil enzymes were clearly observed (P < 0.05 or 0.01). Such observations would provide useful information for ecological effects of Pb and BDE209 at EWRSs.

The binary, ternary and quaternary mixture toxicity of benzo[a]pyrene, arsenic, cadmium and lead in HepG2 cells

Polycyclic aromatic hydrocarbons (PAHs) and heavy metal/loid(s) are common environmental pollutants. Toxicological interaction data on benzo[a]pyrene (B[a]P) and heavy metal/loid(s) are lacking. In this study, we have determined the combined toxicity of B[a]P, arsenic (As), cadmium (Cd) and lead (Pb) in HepG2 cells. The binary, ternary and quaternary mixture toxicity of B[a]P and heavy metal/loid(s) was predicted by using the combination index (CI)-isobologram method. This method is useful to predict the quantitative nature of an interaction between chemicals at different effect (inhibitory concentration) levels from 0.1 to 99% using computerised quantitation. A total of 11 mixtures including six binary mixtures, four ternary and one quaternary mixtures of B[a]P and heavy metal/loid(s) were evaluated for their interactions. The cytotoxicity of individual and multi-component mixtures was evaluated by MTS assay. The selected concentrations for the individual dose response study were 0-100 μM - B[a]P; 0-40 μM - Cd; 0-400 μM - As and Pb. The individual dose response results showed that all four chemicals were toxic to liver cells with Cd being the most potent toxicant. Mixtures of B[a]P and heavy metal/loid(s) were prepared based on their individual Dm concentration using a 1 : 1 ratio and exposed to HepG2 cells. By using the CI-isobologram method, the predicted interactions between these chemicals were synergism, additivity or antagonism at different effect levels. All the mixtures except the ternary mixture of B[a]P + As + Pb displayed synergism at a lower effect level (IC10-IC30), and additivity, synergism or antagonism at 50-90% effect levels. Among these mixtures, mixtures of heavy metal/loid(s) (both binary and ternary combinations) and a quaternary mixture of B[a]P + As + Cd + Pb showed a strong synergistic response at lower effect levels compared to other mixtures. The predicted interaction response by the CI method was compared with classical models of concentration addition and independent action. The CI method displayed an improved prediction power compared to classical models. The predicted synergistic interaction between B[a]P and heavy metal/loid(s) may have important implications in the human health risk assessment of these mixed chemical mixtures at contaminated sites.

Bioremediation of multi-polluted soil by spent mushroom (Agaricus bisporus) substrate: Polycyclic aromatic hydrocarbons degradation and Pb availability

This study investigates the effect of three spent Agaricus bisporus substrate (SAS) application methods on bioremediation of soil multi-polluted with Pb and PAH from close to a shooting range with respect natural attenuation (SM). The remediation treatments involve (i) use of sterilized SAS to biostimulate the inherent soil microbiota (SSAS) and two bioaugmentation possibilities (ii) its use without previous treatment to inoculate A. bisporus and inherent microbiota (SAS) or (iii) SAS sterilization and further A. bisporus re-inoculation (Abisp). The efficiency of each bioremediation microcosm was evaluated by: fungal activity, heterotrophic and PAH-degrading bacterial population, PAH removal, Pb mobility and soil eco-toxicity. Biostimulation of the native soil microbiology (SSAS) achieved similar levels of PAH biodegradation as SM and poor soil detoxification. Bioaugmented microcosms produced higher PAH removal and eco-toxicity reduction via different routes. SAS increased the PAH-degrading bacterial population, but lowered fungal activity. Abisp was a good inoculum carrier for A. bisporus exhibiting high levels of ligninolytic activity, the total and PAH-degrading bacteria population increased with incubation time. The three SAS applications produced slight Pb mobilization (<0.3%). SAS sterilization and further A. bisporus re-inoculation (Abisp) proved the best application method to remove PAH, mainly BaP, and detoxify the multi-polluted soil.

Diversity of organotrophic bacteria, activity of dehydrogenases and urease as well as seed germination and root growth Lepidium sativum, Sorghum saccharatum and Sinapis alba under the influence of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons are organic compounds with highly toxic, carcinogenic, and mutagenic properties, which adversely affect the basic biological parameters of the soil, including the count of microorganisms, and the enzymatic activity. In addition to disturbances to the biological activity of the soil, PAHs may also exhibit toxic effects on plants. In view of the above, the study involved testing aimed at the determination of the effects of polycyclic aromatic hydrocarbons in a form of naphthalene, phenanthrene, anthracene and pyrene on the count, colony development (CD) index, ecophysiological (EP) diversity index of organotrophic bacteria, and the activity of soil dehydrogenases and soil urease. Moreover, an attempt was made to determine the soil's resistance based on the activity of the above-listed enzymes, and the effect of polycyclic aromatic hydrocarbons on seed germination and root growth was assessed by Lepidium sativum, Sorghum saccharatum, and Sinapis alba. In addition, the species of bacteria found in a soil subjected to strong pressure of polycyclic aromatic hydrocarbons were isolated. The experiment was performed in a laboratory on samples of loamy sand. Polycyclic aromatic hydrocarbons were introduced into the soil in an amount of 0, 1000, 2000, and 4000 mg kg(-1) of soil dry matter. Germination and growth of cress (L. sativum), white mustard (S. alba), and sweet sorghum (S. saccharatum) were determined using Phytotoxkit tests. It was found that the tested PAHs increased the average colony counts of organotrophic soil bacteria; pyrene did so to the greatest extent (2.2-fold relative to non-contaminated soil), phenanthrene to the smallest extent (1.4-fold relative to non-contaminated soil). None of the PAHs changed the value of the bacterial colony development (CD) index, while anthracene and pyrene increased the value of the eco-physiological (EP) diversity indicator. PAHs lowered the activity of the tested enzymes. The activity of dehydrogenases was dependent on a greater extent by the type of hydrocarbon (54.56%) rather than by the dose (10.64%), while for the activity of urease, it was the opposite. The greater extent was dependent on dose (95.42%) rather than by type (0.21%). Dehydrogenases are characterised by greater resistance to the action of PAHs than urease. Based on seed germination and root growth, it has shown that S. alba is best suited, being the most vulnerable plant, while S. saccharatum is the least suited. Subjecting a soil to strong pressure of PAHs leads to disturbances to the biological parameters of the soil, seed germination, and root growth L. sativum, S. saccharatum, and S. alba.

Dynamics of the biological properties of soil and the nutrient release of Amorpha fruticosa L. litter in soil polluted by crude oil

Litter from Amorpha fruticosa, a potential phytoremediating plant, was collected and used in a decomposition experiment that involved the litterbag in soil polluted by crude oil. The dynamics of the biological properties of soil and the nutrient release of the litter were detected. The results indicated that (1) in lightly polluted soil (LP, petroleum concentration was 15 g kg(-1)), the bacteria (including actinomycetes), and fungi populations were significant higher than those in unpolluted soil (CK) at the 1st month after pollution, and the bacteria (including actinomycetes) populations were higher than those in the CK at the 6th and 12th months. In moderately polluted soil (MP, 30 g kg(-1)), the bacteria (including actinomycetes) populations were higher than those in the CK at the 1st and 6th months, whereas only the actinomycetes population was greater than that in the CK at the 12th month. In seriously polluted soil (SP, 45 g kg(-1)), only the fungi population was higher than that in the CK at the 6th month. (2) The activities of soil protease, carboxymethyl cellulase, and sucrase were generally inhibited in polluted soil. Peroxidase activity was generally inhibited in the LP and MP soil, and polyphenol oxidase activity was inhibited in the SP soil at 6-12 months. (3) At the end of litter decomposition, the LP soil significantly increased the release rate of all nutrients, except for K. The MP soil reduced the release rate of Fe and Mn, whereas it increased that of C and Cu. The SP soil decreased the release rate of all nutrients except for Cu and Zn. In conclusion, SP by crude oil would lead to limitations in the release of nutrients from the litter and to decreases in the community stability of a phytoremediating plant. A. fruticosa could only be used in phytoremediation of polluted soil at concentrations below 45 g kg(-1) (crude).

Ecological impacts of long-term application of biosolids to a radiata pine plantation

Assessment of the ecological impact of applying biosolids is important for determining both the risks and benefits. This study investigated the impact on soil physical, chemical and biological properties, tree nutrition and growth of long-term biosolids applications to a radiata pine (Pinus radiata D. Don) plantation growing on a Sandy Raw Soil in New Zealand. Biosolids were applied to the trial site every 3 years from tree age 6 to 19 years at three application rates: 0 (Control), 300 (Standard) and 600 (High) kg nitrogen (N) ha(-1), equivalent to 0, 3 and 6 Mg ha(-1) of dry biosolids, respectively. Tree nutrition status and growth have been monitored annually. Soil samples were collected 13 years after the first biosolids application to assess the soil properties and functioning. Both the Standard and High biosolids treatments significantly increased soil (0-50 cm depth) total carbon (C), N, and phosphorus (P), Olsen P and cation exchange capacity (CEC), reduced soil pH, but had no significant effects on soil (0-20 cm depth) physical properties including bulk density, total porosity and unsaturated hydraulic conductivity. The High biosolids treatment also increased concentrations of soil total cadmium (Cd), chromium (Cr), copper (Cu) and lead (Pb) at 25-50 cm depth, but these concentrations were still considered very low for a soil. Ecotoxicological assessment showed no significant adverse effects of biosolids application on either the reproduction of springtails (Folsomia candida) or substrate utilisation ability of the soil microbial community, indicating no negative ecological impact of bisolids-derived heavy metals or triclosan. This study demonstrated that repeated application of biosolids to a plantation forest on a poor sandy soil could significantly improve soil fertility, tree nutrition and pine productivity. However, the long-term fate of biosolids-derived N, P and litter-retained heavy metals needs to be further monitored in the receiving environment.

Interaction effects of polycyclic aromatic hydrocarbons and heavy metals on a soil microalga, Chlorococcum sp. MM11

Environmental risk assessment of sites contaminated with chemicals needs to also consider mixtures of chemicals as these toxicants act more differently in a mixture than when they occur alone. In this study, we describe, for the first time, the use of a full factorial design experiment to evaluate the toxicity of a quaternary mixture comprising two polycyclic aromatic hydrocarbons (PAHs; benzo[a]pyrene (BaP) and phenanthrene (Phe)) and two heavy metals (cadmium (Cd) and lead (Pb)) toward a soil microalga, Chlorococcum sp. MM11. Biomass, in terms of cell number, and proline accumulation were used to evaluate toxicity responses. Factorial analysis of the data revealed statistically significant interaction effects between the mixtures of toxicants on 96-h biomass endpoint, while no significant interaction effects were observed on proline accumulation in the microalga. A comparison of the data on the toxicity of individual chemicals and those of the factorial main effect analysis clearly showed that Cd is more toxic to the alga, followed by BaP, Pb, and Phe. There was a substantial heavy metal accumulation and PAH degradation by the strain MM11 at EC10 and EC50 of the chemical mixtures.

Hydrodynamic voltammetry as a rapid and simple method for evaluating soil enzyme activities

Soil enzymes play essential roles in catalyzing reactions necessary for nutrient cycling in the biosphere. They are also sensitive indicators of ecosystem stress, therefore their evaluation is very important in assessing soil health and quality. The standard soil enzyme assay method based on spectroscopic detection is a complicated operation that requires the removal of soil particles. The purpose of this study was to develop a new soil enzyme assay based on hydrodynamic electrochemical detection using a rotating disk electrode in a microliter droplet. The activities of enzymes were determined by measuring the electrochemical oxidation of p-aminophenol (PAP), following the enzymatic conversion of substrate-conjugated PAP. The calibration curves of β-galactosidase (β-gal), β-glucosidase (β-glu) and acid phosphatase (AcP) showed good linear correlation after being spiked in soils using chronoamperometry. We also performed electrochemical detection using real soils. Hydrodynamic chronoamperometry can be used to assess the AcP in soils, with a detection time of only 90 s. Linear sweep voltammetry was used to measure the amount of PAP released from β-gal and β-glu by enzymatic reaction after 60 min. For the assessment of soil enzymes, the results of hydrodynamic voltammetry assay compared favorably to those using a standard assay procedure, but this new procedure is more user-friendly, rapid and simple.

Effect of Pb(ii) on phenanthrene degradation by new isolated Bacillus sp. P1

A new strain of bacteria, Bacillus sp. P1, was isolated from compost to degrade PHE in the presence of Pb(ii).

Photodegradation of α-cypermethrin in soil in the presence of trace metals (Cu2+, Cd2+, Fe2+ and Zn2+)

The influence of trace metals (Cu(2+), Zn(2+), Cd(2+) and Fe(2+)) on the photodegradation of α-cypermethrin (α-CYM) in agricultural soil was studied. The soil samples were spiked with α-cypermethrin with/without the presence of metal ions, irradiated under a UV irradiation chamber for a regular period of time and analyzed by using HPLC. The dark control sterile and unsterile soil samples spiked with α-cypermethrin and selected trace metals were incubated for the same interval of time at 25 °C. The results obtained indicated that α-cypermethrin photodegradation followed biphasic kinetics. α-cypermethrin photodegradation half-lives (t1/2) were increased to 0.71 and. 4.5 hours from 0.64 hours respectively in the presence of elevated Zn(2+) and Cu(2+) concentrations. Fe(2+) and Cd(2+) increased the photodegradation reaction kinetics from -1.078 h(-1) to -1.175 h(-1) and -1.397 h(-1) and varied the t1/2 from 0.64 ± 1.41 to 0.59 ± 2.07 and 0.49 ± 2.01 in the soil. Microbes also affected the degradation of α-cypermethrin in metal contaminated soil. The degradation rate was inhibited in unsterile soil and was found to be in the following order: Cd(2+)< Zn(2+)< Cu(2+)< Fe(2+). The degradation/persistence of α-cypermethrin was affected linearly with the increasing soil metal concentrations.

Combining phytoextraction and biochar addition improves soil biochemical properties in a soil contaminated with Cd

The main goal of phytoremediation is to improve ecosystem functioning. Soil biochemical properties are considered as effective indicators of soil quality and are sensitive to various environmental stresses, including heavy metal contamination. The biochemical response in a soil contaminated with cadmium was tested after several treatments aimed to reduce heavy metal availability including liming, biochar addition and phytoextraction using Amaranthus tricolor L. Two biochars were added to the soil: eucalyptus pyrolysed at 600 °C (EB) and poultry litter at 400 °C (PLB). Two liming treatments were chosen with the aim of bringing soil pH to the same values as in the treatments EB and PLB. The properties studied included soil microbial biomass C, soil respiration and the activities of invertase, β-glucosidase, β-glucosaminidase, urease and phosphomonoesterase. Both phytoremediation and biochar addition improved soil biochemical properties, although results were enzyme specific. For biochar addition these changes were partly, but not exclusively, mediated by alterations in soil pH. A careful choice of biochar must be undertaken to optimize the remediation process from the point of view of metal phytoextraction and soil biological activity.

Selection of wild macrophytes for use in constructed wetlands for phytoremediation of contaminant mixtures

Constructed wetlands (CWs) offer an alternative to traditional industrial wastewater treatment systems that has been proved to be efficient, cost-effective and environmentally friendly. Most of the time, CWs are planted with proliferative species such as Phragmites australis or with plants originating from nurseries, both representing a risk for the natural biodiversity conservation of aquatic ecosystems located downstream of the CWs. For the removal of metals and organic pollutant mixtures present in industrial effluents, it is necessary to select tolerant plant species that are able to produce a high aboveground biomass and to develop a healthy belowground system. Wild plant species growing in aquatic bodies at industrial outfalls could constitute suitable tolerant species to use in CWs for industrial effluent treatment. To test this hypothesis, we assessed, under laboratory conditions (using an experimental design), the tolerance to mixtures of metals (Al, As, Cd, Cu, Cr, Fe, Mn, Ni, Pb, Sn, Zn) or/and organic pollutants (THC, PHE, PYR, LAS) of five European sub-cosmopolitan native macrophytes (Alisma lanceolatum, Carex cuprina, Epilobium hirsutum, Iris pseudacorus and Juncus inflexus) that had been collected in a polluted Mediterranean wetland, after a field study (crossing ecological relevés and analyses of contaminant concentrations in water and sediments). Our results demonstrated that research on phytoremediation of industrial effluents should focus much more on the use of native macrophytes growing at short distances from industrial discharges (such as C. cuprina in this study), and that root/shoot ratio, aerial height and proportion of green leaves are good and cost-effective indicators of plant tolerance to metals and organic pollutant mixtures in laboratory studies.

Enzymes as useful tools for environmental purposes

In the environment enzymes may play important and different roles at least in three cases: as main agents (as isolated, cell-bound or immobilized enzymes) in charge of either the transformation and/or degradation of compounds polluting the environment and the restoration of the polluted environment; as reliable and sensitive tools to detect and measure the amount and concentration of pollutants before, during and after the restoration process; as reliable, easy and sensitive indicators of quality and health status of the environment subjected to the restoration process. To our knowledge papers or reviews integrating findings on these three functions of enzymes are missing in literature. Therefore the main scope of the present paper is to briefly encompass general and specific concepts about roles of enzymes as decontaminating agents, pollutant assaying agents and indicators of environment safety. Examples chosen among those published very recently, supporting and confirming peculiarities, features, and performance of enzymatic agents will be illustrated.

Balance between herbicidal activity and toxicity effect: a case study of the joint effects of triazine and phenylurea herbicides on Selenastrum capricornutum and Photobacterium phosphoreum

The use of herbicide mixtures has become a cost-effective strategy against the evolution of herbicide resistance to protect global food production. Much research has focused on investigating either the herbicidal activities or the toxicity effects of herbicides; however, few of them have investigated both factors. This study investigates the balance between herbicidal activity for Selenastrum capricornutum and toxicity effect toward Photobacterium phosphoreum by determining the joint effects of triazine (simetryn, atrazine, prometon and prometryn) and phenylurea (fenuron, monuron, monolinuron and diuron) herbicides. The results showed that among the four triazines, only simetryn exhibited a unique effect (formation of a pi-sigma bond with the D1 microalga protein and an H-bond with the Luc photobacterial protein); and among 16 triazine-phenylurea binary mixtures, only the mixtures containing simetryn resulted in TU1 values (herbicidal activities of mixtures on S. capricornutum) >TU2 values (toxicity effects of mixtures on P. phosphoreum). However, the other 12 mixtures, which did not contain simetryn, showed the opposite result (TU1<TU2). A comparison of TU1 with TU2 showed that additive effects occurred more frequently for TU1, whereas antagonism effects occurred more frequently for TU2. Based on these results, a preliminary mechanistic hypothesis of herbicide mixtures was proposed. Meanwhile, some suggestions are provided firstly for herbicide combinations based on the balance between herbicidal activity and toxicity effect, which will encourage thoughtful efforts for how to best combine herbicides in a sustainable way.