Habitat function of agricultural soils as affected by heavy metals and polycyclic aromatic hydrocarbons contamination

Microbiological status of natural and anthropogenic soils of the Taganrog Bay coast at different levels of combined pollution with heavy metals and PAHs

The effect of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) pollution on the microbiological status of soils on the coast of the Taganrog Bay and adjacent areas was studied. The content of total and exchangeable forms of HMs, the content of 16 priority PAHs and the abundance of several groups of culturable microorganisms was determined, namely copiotrophic, prototrophic, aerobic spore-forming bacteria, actinomycetes, molds and yeasts. The content of total and exchangeable forms of HMs in urban coastal soils in industrial zone significantly exceeded that in non-urban soils. The maximum concentrations of total forms of Mn, Cr, Ni, Cu, Zn, Pb and Cd are 1821, 871, 143, 89, 1390, 317 and 10 mg/kg, respectively. The median value of the total content of 16 PAHs in urban soils is 3 times higher than in the soils of natural areas and reached 4309 ng/g. The lowest numbers of copiotrophic bacteria, prototrophic bacteria and aerobic spore-forming bacteria were found in the soils of industrial zone: 6.8, 13.8 and 0.63 million CFU g-1 dry soil, respectively. The largest numbers of copiotrophic bacteria, prototrophic bacteria and aerobic spore-forming bacteria were recorded in the soils of natural areas-72.5, 136 and 5.73 million CFU g-1 dry soil, respectively. It was found that the abundance of copiotrophs, prototrophs, and aerobic spore-forming bacteria is more affected by the urbanization of coastal soils including the pollution of HMs and PAHs. Other groups of microorganisms (actinomycetes, molds and yeasts) turned out to be more resistant to anthropogenic factors.

Occurrence of organic micropollutants and heavy metals in the soil after the application of stabilized sewage sludge

Stabilized sewage sludge could be used as a fertilizer in the soil because of nitrogen, phosphorus, and other micronutrition material to improve the properties of the soil. In this study, clover and fodder corn plants were planted in the soil to which stabilized sewage sludge was applied. The soil was analyzed and evaluated by collecting samples to determine changes in the application fields before plantation and one year after the harvest. To monitor changes in the soil and after the application of stabilized sludge to the soil, the stabilized sewage sludge was evaluated for the suitability of parameters such as heavy metals, halogenated organic compounds including adsorbable organic halogens (AOX), nonylphenol ethoxylates (NPE), polycyclic aromatic hydrocarbon compounds (PAH), polychlorinated biphenyls (PCB), di(2-ethylhexyl) phthalate (DEHP), linear alkylbenzene sulphonates (LAS), polychlorinated dibenzo-p-dioxins and dibenzo-p-furans (PCDD/F), and pathogens and other parameters containing organic matter (OM), pH, conductivity (EC), total nitrogen (TN), and total phosphorus (TP). After the sludge application, the heavy metal content increased, except for Zn. The application of stabilized sludge as a soil conditioner and humus caused a significant increase in the TN and TP content since the product increased the harvest that increased soil nutrition. After the sludge application to the soil, the concentration of organic micropollutants in the soil did not change. The concentration of AOX and PCDD/F in the soil increased by 141% and 125%, respectively.

Combined Phenanthrene and Copper Pollution Imposed a Selective Pressure on the Rice Root-Associated Microbiome

Combined organic and inorganic pollutants can greatly impact crops and microbes, but the interaction between coexisted pollutants and their effects on root-associated microbes under flooding conditions remains poorly understood. In this study, greenhouse experiments were conducted to investigate the individual and combined effects of phenanthrene (PHE) and copper (Cu) on rice uptake and root-associated microbial coping strategies. The results showed that more than 90% of phenanthrene was degraded, while the existence of Cu significantly reduced the dissipation of PHE in the rhizosphere, and the coexistence of phenanthrene and copper promoted their respective accumulation in plant roots. Copper played a dominant role in the interaction between these two chemicals. Microbes that can tolerate heavy metals and degrade PAHs, e.g., Herbaspirillum, Sphingobacteriales, and Saccharimonadales, were enriched in the contaminated soils. Additionally, microbes associated with redox processes reacted differently under polluted treatments. Fe reducers increased in Cu-treated soils, while sulfate reducers and methanogens were considerably inhibited under polluted treatments. In total, our results uncover the combined effect of heavy metals and polycyclic aromatic hydrocarbons on the assemblage of root-associated microbial communities in anaerobic environments and provide useful information for the selection of effective root-associated microbiomes to improve the resistance of common crops in contaminated sites.

Polycyclic aromatic hydrocarbons (PAHs) in soils of an industrial area in semi-arid Uzbekistan: spatial distribution, relationship with trace metals and risk assessment

The concentrations, composition patterns, transport and fate of PAHs in semi-arid and arid soils such as in Central Asia are not well known. Such knowledge is required to manage the risk posed by these toxic chemicals to humans and ecosystems in these regions. To fill this knowledge gap, we determined the concentrations of 21 parent PAHs, 4,5-methylenephenanthrene, 6 alkylated PAHs, and biphenyl in soils from 11 sampling locations (0-10, 10-20 cm soil depths) along a 20-km transect downwind from the Almalyk metal mining and metallurgical industrial complex (Almalyk MMC), Uzbekistan. The concentrations of Σ29 PAHs and Σ16 US-EPA PAHs were 41-2670 ng g^-1 and 29-1940 ng g^-1, respectively. The highest concentration of Σ29 PAHs occurred in the immediate vicinity of the copper smelting factory of the Almalyk MMC. The concentrations in topsoil decreased substantially to a value of ≤ 200 ng g^-1 (considered as background concentration) at ≥ 2 km away from the factory. Low molecular weight PAHs dominated the PAH mixtures at less contaminated sites and high molecular weight PAHs at the most contaminated site. The concentration of Σ16 US-EPA PAHs did not exceed the precautionary values set by the soil quality guidelines of, e.g., Switzerland and Germany. Similarly, the benzo[a]pyrene equivalent concentration in soils near the Almalyk MMC did not exceed the value set by the Canadian guidelines for the protection of humans from carcinogenic PAHs in soils. Consequently, the cancer risk due to exposure to PAHs in these soils can be considered as low.

Effects of agrochemicals on the beneficial plant rhizobacteria in agricultural systems

Conventional agriculture relies heavily on chemical pesticides and fertilizers to control plant pests and diseases and improve production. Nevertheless, the intensive and prolonged use of agrochemicals may have undesirable consequences on the structure, diversity, and activities of soil microbiomes, including the beneficial plant rhizobacteria in agricultural systems. Although literature continues to mount regarding the effects of these chemicals on the beneficial plant rhizobacteria in agricultural systems, our understanding of them is still limited, and a proper account is required. With the renewed efforts and focus on agricultural and environmental sustainability, understanding the effects of different agrochemicals on the beneficial plant rhizobacteria in agricultural systems is both urgent and important to deduce practical solutions towards agricultural sustainability. This review critically evaluates the effects of various agrochemicals on the structure, diversity, and functions of the beneficial plant rhizobacteria in agricultural systems and propounds on the prospects and general solutions that can be considered to realize sustainable agricultural systems. This can be useful in understanding the anthropogenic effects of common and constantly applied agrochemicals on symbiotic systems in agricultural soils and shed light on the need for more environmentally friendly and sustainable agricultural practices.

Evaluating the metabolic functional profiles of the microbial community and alfalfa (Medicago sativa) traits affected by the presence of carbon nanotubes and antimony in drained and waterlogged sediments

Antimony (Sb) is the ubiquitous re-emerging contaminant greatly accumulated in sediments which has been revealed risky to ecological environment. However, the impacts of Sb (III/V) on microbes and plants in sediments, under different water management with presence of engineering materials are poorly understood. This study conducted sequential incubation of sediments (flooding, draining and planting) with presence of multiwall carbon nanotubes (MWCNTs) and Sb to explore the influence on microbial functional diversity, Sb accumulation and alfalfa traits. Results showed that water management and planting led to greater impacts of sediment enzyme activities and microbial community metabolic function and bioavailable Sb fractions (defined as sum of acid-soluble fraction and reducible fraction, F1 + F2). Available fractions of Sb (V) showed higher correlation to microbial metabolism (r = 0.933) than that of Sb (III) (r = -0.480) in planting stage. MWCNTs with increasing concentrations (0.011%, w/w) positively correlated to microbial community metabolic function in planting stage whereas resulted in decreasing of Sb (III/V) concentrations in alfalfa, although 0.01% MWCNT led to increase of Sb (V) and decrease of Sb (V) by 50.97% and 32.68% respectively. This study provided information for investigating combined ecological impacts of heavy metal and engineering materials under different water managing sediments.

Soil texture as a key driver of polycyclic aromatic hydrocarbons (PAHs) distribution in forest topsoils

Due to the dynamic development of civilization and the increasing demand for energy, pollution by harmful chemicals, including polycyclic aromatic hydrocarbons (PAHs) compounds, is a serious threat to forest soils. The aim of the study was to determine the role of texture in the distribution of polycyclic aromatic hydrocarbons (PAHs) and trace elements in forest soils. The areas with different texture ranging from sand through sandy loam to silt loam were selected for the study. The study was carried out in the Chrzanów Forest District in southern Poland (50° 7' 18 N; 19° 31' 29 E), which in one of the most intensive industrial emission zones in Europe. The soil samples for properties determination were collected from locations distributed on a regular grid 100 × 100 m (20 points). The samples were collected from the humus horizon (0-10 cm) after removing organic horizon. Basic chemical properties, heavy metal content, polycyclic aromatic hydrocarbons (PAHs) content and magnetic susceptibility values were determined in soil samples. Additionally, enzymatic activity and microbiological biomass was determined in the samples. Our study confirmed the importance of texture in PAHs distribution. A strong correlation between PAHs content and silt content in the soils studied was noted. The regression tree analysis confirmed the importance of the silt content, followed by soil organic carbon in PAHs distribution. Organic carbon content and nitrogen content played a predominant role in controlling the microbial activity. In our study, we did not note a relationship between enzymatic activity, microbiological soil biomass and the amount of PAHs. This may be due to the effective sorption and immobilization of PAHs by particles of fine fractions, especially silt. Obtained results confirmed the usefulness of magnetic susceptibility in the assessment of heavy metals contamination of forest soils. We noted high correlation between magnetic susceptibility value and heavy metals content. Moreover, the relationship between magnetic susceptibility and soil texture of the topsoil was also observed.

Assembly strategies of the wheat root-associated microbiome in soils contaminated with phenanthrene and copper

Plants can cope with stressful conditions by indirectly regulating root-associated microbial structures. However, the recruitment strategies of the root-associated microbiome in combined organic and inorganic contaminated soils are not well known, especially for common agricultural crops. In this study, we performed greenhouse experiments to investigate the interactive effects of joint copper (Cu) and phenanthrene (PHE) pollution on wheat growth and microbial detoxication processes. Results show that heavy metals did not affect PHE dissipation in the rhizosphere but significantly enhanced the accumulation of PHE in the endosphere. In contrast, the addition of PHE did not influence the absorption of Cu by wheat roots. Cu was the primary factor affecting the variation of microbial communities in cocontaminated treatments among each rhizocompartment while the interactive effects of combined pollutants were only detected in unplanted bulk soil. Microbes are known to degrade polycyclic aromatic hydrocarbons and tolerant heavy metal stress e.g. Novosphingobium, Sphingomonas, Sphingobium and Pseudomonas enriched in the contaminated treatments. Our results provide an integrated understanding of the synthetic effects of combined pollutants on the root-microbial assemblage process in plant-soil systems and offer useful information on the selection of effective bioremediating root-associated microbes for the application of self-remediation by common crops.

Expatiating the impact of anthropogenic aspects and climatic factors on long-term soil monitoring and management

This article is an extensive collection of scientific literature related to the impact of fertilizers on soil microbial and enzymatic activity. Due to the significance of technology in quantitative and qualitative evaluation of agricultural production, this is a basic problem for the present and future of mankind, where the scientific data being of utmost importance related to the topic. The comparison, including pedo-enzymological evaluation of minerals along with organic fertilization, highlights significant differences between mineral and organic fertilizers, confirming the superiority of complex mineral-organic fertilization. Enzymatic indicators that describe and define the soil quality resulted from enzymatic activities value and provide valuable information regarding the soil fertility status. Moreover, soil enzyme responds to soil management as well as to environmental pollutants. Changes of environmental conditions and pollutants like heavy metals and other toxic substances result in a shift in the biological activity of the soil. These changes can destabilize the soil system and cause a decrease in the nutrient pools. To ensure the improvement of fertilization techniques, the properties of nanoparticles are exploited that can efficiently release nutrients to plant cells. Numerous researches were performed in order to follow the long-term effects of incorporating nanofertilizers into the soil, obtaining an exhaustive overview of this new technology over the development of sustainable agriculture.

Global distribution of oxygenated polycyclic aromatic hydrocarbons in mineral topsoils

Hazardous oxygenated polycyclic aromatic hydrocarbons (OPAHs) originate from combustion (primary sources) or postemission conversion of polycyclic aromatic hydrocarbons (PAHs) (secondary sources). We evaluated the global distribution of up to 15 OPAHs in 195 mineral topsoils from 33 study sites (covering 52° N-47° S, 71° W-118 °E) to identify indications of primary or secondary sources of OPAHs. The sums of the (frequently measured 7 and 15) OPAH concentrations correlated with those of the Σ16EPA-PAHs. The relationship of the Σ16EPA-PAH concentrations with the Σ7OPAH/Σ16EPA-PAH concentration ratios (a measure of the variable OPAH sources) could be described by a power function with a negative exponent <1, leveling off at a Σ16EPA-PAH concentration of approximately 400 ng g^-1 . We suggest that below this value, secondary sources contributed more to the OPAH burden in soil than above this value, where primary sources dominated the OPAH mixture. This was supported by a negative correlation of the Σ16EPA-PAH concentrations with the contribution of the more readily biologically produced highly polar OPAHs (log octanol-water partition coefficient <3) to the Σ7OPAH concentrations. We identified mean annual precipitation (Spearman ρ = .33, p < .001, n = 143) and clay concentrations (ρ = .55, p < .001, n = 33) as important drivers of the Σ7OPAH/Σ16EPA-PAH concentration ratios. Our results indicate that at low PAH contamination levels, secondary sources contribute considerably and to a variable extent to total OPAH concentrations, whereas at Σ16EPA-PAH contamination levels >400 ng g^-1 , there was a nearly constant Σ7OPAH/Σ16EPA-PAH ratio (0.08 ± 0.005 [SE], n = 80) determined by their combustion sources.

A critical review on energy recovery and non-hazardous disposal of oily sludge from petroleum industry by pyrolysis

This review systematically reports the pyrolysis of oily sludge (OS) from petroleum industry in regards to its dual features of the energy recovery potential and the environmental risks. The petroleum hydrocarbons are the nonbiodegradable fractions in OS that possess hazardous properties, i.e. ignitability and toxicity. Besides, complicated hazardous elements (i.e. N, S and Cl) and heavy metals inherently existing in OS further aggravate the environmental risks. However, the high oil content and heating value of OS contribute to its huge energy resource potential. Considering the energy demand and the environmental pressure, the ultimate purposes of the OS management are to enhance the oil recovery efficiency to minimize the oil content as well as to stabilize the hazardous elements and heavy metals into the solid residue. Among various OS management technologies, pyrolysis is the most suitable approach to reach both targets. In this review paper, the pyrolysis principle, the kinetics and the product distribution in three-phases are discussed firstly. Then the effects of operating parameters of the pyrolysis process on the quality and the application potential of the three-phase products, as well as the hazardous element distribution are discussed. To further solve the dominant concerns, such as the oil content in the solid residue, the pyrolytic oil quality and the migration of hazardous elements and heavy metals, the potentials of the catalytic pyrolysis and the co-pyrolysis with additives are also summarized. Also, the typical pyrolysis reactors are then presented. From the perspective of the energy efficiency and the non-hazardous disposal, the integrated technology combining the pyrolysis and the combustion for the OS management is recommended. Finally, the remaining challenges of OS pyrolysis encountered in the research and the industrial application are discussed and the related outlooks are itemized.

Effect of enhancers on the phytoremediation of soils polluted by pyrene and Ni using Sudan grass (Sorghum sudanense (Piper) Stapf.)

Remediation of heavy metal and polycyclic aromatic hydrocarbon (PAH)-co-contaminated soils has drawn much more attention; phytoremediation is an often-used technique. Sudan grass (Sorghum sudanense (Piper) Stapf.) with developed root system and strong PAHs and heavy metal tolerance is a potential choice for phytoremediation. In this study, the application of tea saponin (TS) (1 g kg^-1 soil) and nitrilotriacetic acid (NTA) (1 g kg^-1 soil) was to improve the removal efficiency of Ni and pyrene. TS and NTA had no obvious effects on the growth and soluble proteins of Sudan grass. Ni concentration in root was higher than that in the shoot. The addition of TS and NTA increased the Ni concentration in the root by 25.98% in Ni-contaminated treatment. Pyrene was mainly accumulated in the shoot of Sudan grass. Pyrene concentration in shoot increased by 20.14% with TS-NTA in pyrene-contaminated treatment and increased by 31.97% in Ni-contaminated treatment. TS and NTA had significantly improved dissolved organic matter and soil microbial activity. Microbial activity increased by 16.75%, 18.07%, and 23.364% in pyrene-contaminated, Ni-contaminated, and pyrene and Ni-co-contaminated treatment, respectively. This study showed that phytoremediation of pyrene and Ni-co-contaminated soil by Sudan grass could be enhanced by the application of TS-NTA and the interaction between pyrene and Ni impacted the accumulation of Ni and pyrene in Sudan grass.

River water irrigation with heavy metal load influences soil biological activities and risk factors

The Yamuna is one of the most polluted rivers in India and the land adjacent to river flowing through Delhi city is widely irrigated with its water for growing various food crops. Present study was undertaken to assess the heavy metal load in Yamuna water and surrounding soils of the river bank and its impact on soil enzyme activities. Long term impact of irrigation by Yamuna water on the activities of various soil enzymes namely dehydrogenase (DHA), urease (UA), fluroscein diacetate (FDA), aryl sulphatase (ASA), nitrate reductase (NRA), microbial biomass carbon (MBC) and potentially mineralizable nitrogen (PMN) were assessed. The sensitivity of soil enzymes to heavy metals were observed as DHA>UA>ASA>NRS. Total organic carbon, easily oxidisable soil organic carbon, available phosphorus and available potassium in different sites varied significantly. Total heavy metal contents in soils showed a decreasing order: Fe>Mn>Zn>Cr>Ni>Cu>Pb>Co>As>Cd and the DTPA extractable heavy metal contents followed the order: Mn>Cu>Pb>Zn >Fe>Ni>Cd>Cr>Co>As. Potential ecological risk factors (Er) were under low risk and comprehensive potential ecological risk indices (Ri) were found to be under low, moderate and high risk categories. Copper (Cu) is the main pollutant contributing considerable load to Ri. From (Ri) principal component analysis and cluster analysis, it is evident that the Okhla site (S8) is most contaminated. The water from Yamuna river needs to be cautiously used for growing various food crops on land adjacent to the river as its long-term usage might cross the permissible limits of heavy metals in the soil.

Peculiar attenuation of soil toluene at contaminated coking sites

In the soil of contaminated coking sites, polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene and xylene (BTEX) are typical indicator compounds. Generally, PAHs are enriched in the topsoil layer. BTEX, with higher water solubilities and lower organic carbon-water partitioning coefficients (K_oc), are distributed deeper than PAHs. However, current models have employed predictions using single compounds to mimic the migration of BTEX at contaminated coking sites. Such models have not considered the influence of the upper soil layer, where PAHs are enriched. An attempt to fill this gap was made by setting up a control soil column experiment in this study. One column was filled with undisturbed soil (column #1) and the other with PAH-contaminated soil (column #2) to simulate the theoretical and actual surface soil layers, respectively. The results showed that in column #2, the toluene gas concentration of the headspace and time required to reach steady state were notably greater than those in column #1. High-throughput sequencing revealed that there were large microbial community structure differences between the two soil columns throughout the experiment, while some genera that degrade toluene with high efficiency emerged noteworthily in column #2. This implied that the upper soil layer enriched with PAHs was conducive to the degradation of toluene vapor. Applying this finding to human health exposure assessment of toluene suggests that the potential exposure level should be reduced from the current predicted level given the unanticipated attenuation at contaminated coking sites.

Phytoremediation effect of Medicago sativa colonized by Piriformospora indica in the phenanthrene and cadmium co-contaminated soil

BACKGROUND

The coexistence of polycyclic aromatic hydrocarbons (PAHs) and heavy metals has deleterious effects on environmental quality. Few reports have studied the mechanisms of plant inoculation with Piriformospora indica to remediate PAH-metal co-contaminated soil by analyzing the chemical speciation of the contaminants. This study investigated the influence of the inoculation of Medicago sativa with P. indica to remediate soil co-contaminated with phenanthrene (a kind of PAH) and cadmium (a heavy metal) by analyzing plant growth, physiological parameters and chemical speciation in rhizosphere and nonrhizosphere soils.

RESULTS

The presence of P. indica significantly increased plant tolerance, chlorophyll a, chlorophyll b, maximum quantum efficiency of PSII photochemistry and electron transport rate values in phenanthrene- and/or cadmium-contaminated soil. P. indica inoculation in M. sativa roots increased fluorescein diacetate activities in soils contaminated with phenanthrene, cadmium or both, especially in the nonrhizosphere. The presence of phenanthrene prevented the inoculated plant from accumulating cadmium to some extent, whereas the presence of cadmium did not prevent the degradation of phenanthrene in either the rhizosphere or the nonrhizosphere after P. indica colonization. Although the low bioavailability of cadmium in the rhizosphere restricted its transportation into the stem, P. indica colonization in plants effectively increased cadmium accumulation in roots in soil co-contaminated with cadmium and phenanthrene.

CONCLUSIONS

In conclusion, this work provides a theoretical basis for the use of P. indica combined with M. sativa for the remediation of PAH-metal co-contaminated soil.

Effect of plant-growth-promoting rhizobacteria on phytoremediation efficiency of Scirpus triqueter in pyrene-Ni co-contaminated soils

The aim of this study was to investigate whether the plant-growth-promoting rhizobacteria (PGPR) could enhance phytoremediation efficiency of Scirpus triqueter (S.triqueter) in the pyrene-Ni co-contaminated soil. We also expected to reveal the possible mechanism for the affected phytoremediation efficiency induced by PGPR. We used three kinds of contaminated soils (Ni-contaminated soil, pyrene-contaminated soil and pyrene-Ni co-contaminated soil) to conduct this pot study. After harvest, plants growth indicators, polyphenol oxidase (PPO) activity and soil microbial community structure of each treatment were investigated to explain the different dissipation rates of pyrene and removal rates of Ni between treatments with and without PGPR. The results showed that PGPR-inoculated S. triqueter increased dissipation rates of pyrene and removal rates of Ni in all three contaminated soils, among which Ni removal rates in Ni single contaminated soil was elevated most significantly, from 0.895‰ to 8.8‰, increasing nearly 9 folds. However, Ni removal rate efficiency in co-contaminated soil was weakened because more toxic and complicated co-contaminated soil restrained plant growth and Ni absorption. We also observed that co-contamination harmed the soil microbial community more severely than that in single pyrene or Ni contaminated soil through phospholipid fatty acids analysis. Furthermore, dissipation rates of pyrene and removal rates of Ni were found positively correlated to the PPO activity and the abundance of branched and saturated fatty acids reflected by Pearson correlation analysis.

Rhizospheric Organic Acids as Biostimulants: Monitoring Feedbacks on Soil Microorganisms and Biochemical Properties

The biostimulant potential of three different organic acids (OAs) present in the rhizosphere, specifically lactic, oxalic, and citric acids, have been studied. The results showed a rapid and complete metabolism of these three acids with soil microorganisms using them as a source of carbon and energy. Biostimulation was confirmed by soil biochemical studies which showed an increase in enzymatic activities, such as dehydrogenase and phosphatase, lactic and citric acids being those that produced the greatest biostimulation. With regard to microbiota composition, amplicon sequencing of the 16S rRNA gene showed changes in the structure of soil microbial communities. Applying OAs produced a decrease in richness and diversity indices, inducing specific changes in the structure of the microbiological communities. Applying lactic acid induced rapid changes in microbiota composition at both phylum and family taxonomic levels, favoring the proliferation of microorganisms involved in its degradation and soil fertility, such as the genus Bacillus and the family Micrococcaceae. Once the lactic acid was degraded, the biodiversity tended to return to similar phyla, but specific distinctive families and genera remained, leaving a pattern of induction of taxa described as plant growth-promoting bacteria (PGPB), such as the Sinorhizobium and Lysobacter genera, and the Pseudomonaceae family. Similar behavior was found with citric acid, which favored the proliferation and dominance of microorganisms of the Clostridiaceae family, involved in its degradation, as well as microorganisms of both the Micrococcaceae and Pseudomonadaceae families which were found on day 7, leaving a similar pattern of induction as that found after the mineralization of lactic acid. On the other hand, oxalic acid induced long-lasting changes in the bacterial community composition. This was characterized by an increase in the proportion of the Burkholderiales order, which includes microorganisms involved in the degradation of this acid and microorganisms described as PGPB. This study presents evidence supporting the use of OAs as potential soil fertility inducers, due both to their effects in enhancing the dominance of taxa described as PGPB and to their stimulating soil microbial activity.

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.

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.

Study on removal of pyrene by Agropyron cristatum L. in pyrene-Ni co-contaminated soil

Heavy metals and polycyclic aromatic hydrocarbons (PAHs) co-contamination in the soil is widespread. Phytoremediation is often used to remediate co-contaminated soil, but few studies focused on the effects of nickel on the dissipation and uptake of pyrene in phytoremediation. The dissipation of pyrene, the uptake, and distribution of pyrene in Agropyron cristatum L. (A. cristatum) were investigated in this study in the presence of nickel. The pyrene removal rate in single pyrene-contaminated soil with A. cristatum cultivation (48.97%) was the highest, which was higher than that of the co-contamination (47.88%). This was due to the high soil microbial activity and high dissolved organic matter (DOM) contents. In single pyrene-contaminated soil, pyrene was mainly accumulated in the soluble fraction in shoots and on the cell wall in roots of A. cristatuma. Besides, nickel could promote the adsorption of pyrene on the cell wall. Pyrene in A. cristatum could be transported through the apoplast and symplast, and the pyrene contents in the symplast were 2-3 times that of the apoplast. The uptake of pyrene by A. cristatum included both active absorption and passive transportation. Active absorption involved H⁺ transport and energy conversion processes, and passive transport was associated with water protein channels.

Effects of multi-walled carbon nanotubes on metal transformation and natural organic matters in riverine sediment

In this study, pragmatic prospection of multi-walled carbon nanotubes (MWCNTs) is conducted considering their impacts on Cd transformation, microbial activity and natural organic matter (NOM) in sediments. Indeed, dose-dependent of MWCNTs acceleration in Cd sedimentation and immobilization in water-sediment interface has been found. Unexpectedly, even with the reduced Cd bioavailability, high ratios of MWCNTs incorporation led to exacerbated microbial inactivation. Besides, we noted that MWCNTs significantly lowered NOM contents in sediments. Chemical characterization results also demonstrated that high ratios of MWCNTs incorporation reduced the aromaticity, hydrophobicity and humification of fulvic acid (FA) and humic acid (HA) in sediments. The Cd binding results confirmed that quantity and chemical variation of NOM affected their central ability to Cd binding, referring to significant decrease in combined Cd contents. The findings indicated that reduction in humic substances and chemical structure variation might be the important reason attributed to the MWCNTs toxicity. This study provides novel mechanisms understanding the fate of carbon nanotubes considering the balance in environmental benefit and potential risks.

Co-pyrolysis of metal contaminated oily waste for oil recovery and heavy metal immobilization

The treatment of metal-contaminated oily waste was investigated by using an approach of co-pyrolysis with hog fuel in a fixed bed reactor. Both oil recovery and heavy metal immobilization were evaluated. Three experimental factors, including pyrolysis temperature, reaction time, and hog fuel addition in the feedstock, were examined to find their effects on the treatment performance. Metal immobilization in the solid char obtained from co-pyrolysis was examined from its speciation characteristics. A higher pyrolysis temperature led to a decreased oil recovery but more non-bioavailable metal species in the char residue. This is also evident from the calculated risk index (RI) for eco-toxicity assessment, with RI of 34.6 and 117.1 at 600 °C and 400 °C, respectively. The addition of hog fuel into oily waste for co-pyrolysis also led to increased metal immobilization but a decreased overall oil recovery. A low temperature co-pyrolysis (400 °C) by adding 20% of hog fuel was found as the most effective oily waste disposal strategy with satisfactory oil recovery and an acceptable risk index of 54.1.

The Use of Bioassays for the Risk Assessment of Toxic Leachates: An Experimental Study

Solid wastes from the oil-shale industry produce leachates containing toxic compounds such as heavy metals and persistent polycyclic aromatic hydrocarbons (PAH). The hazard to the environment represented by waste leachates depends not only on their chemical composition, but also on the mobility and bioavailability of toxic contaminants in soils. We evaluated the applicability of bioassays for toxicity assessment of the bioavailable fraction of heavy metals and PAH in soils, in experiments with samples of four different soil types (Rendzina, Brown pseudopodzolic, Typical brown, Sodpodzolic), the pH of which ranged from 6.2 to 7.2. The toxicity of the bioavailable fraction of the soil contaminants was assessed with the dehydrogenase enzyme activity assay, and with a Toxkit microbiotest with the crustacean, Thamnocephalus platyurus, after treatment of the soil samples with an artificial solution containing chromium (III), lead (II), copper (II), cadmium (II) and pyrene. The test results confirm those of earlier experiments, which characterised the sorption potential of investigated soils for the same compounds. Both tests turned out to be sufficiently sensitive, and hence can be recommended as effective and useful tools for the assessment of the bioavailable fraction of soil contaminants.

Ambient geochemical baselines for trace elements in Chernozems-approximation of geochemical soil transformation in an agricultural area

The legal regulatory/action levels of trace elements in soils are established at high concentrations, at which the crucial functions of soil are at risk or are eliminated. However, concentrations below these action levels, but above presumed natural levels, may also limit particular ecosystem services, including organic food production. Thus, defining the (ambient) background concentrations is an essential part of environmental or health risk assessment, e.g., on Chernozems, which are considered to be the most productive soils and ones that should be protected against all forms of contamination. Based on 28 profiles of chernozemic soils developed from loess in an agricultural region of SW Poland presumed to be free of industrial contamination, ambient geochemical baselines have been derived for Fe and six trace metals for four standardized soil layers, including the topsoil (plow layer) and parent material layers. The median values for the plow layer (1.89% for Fe, and 537, 49, 17, 14, and 26 mg kg^-1 for Mn, Zn, Pb, Cu, and Ni, respectively) are lower than the values reported for other Chernozems in SE Poland/Europe/the world, and thus may serve as a general geochemical baseline for chernozemic soils developed from loess. The concentration of Cd, although lower than in other Chernozems around the world, is higher than in Ukrainian Chernozems and thus may serve as a local (or Central European) baseline only. The median concentrations of Fe, Cu, Mn, and Zn are very close to their concentrations in the Chernozem buried under the Neolithic kurgan. However, Pb and Cd concentrations are two times higher than in the buried soil, indicating the scale of general contamination of the topsoil horizons of arable soils. Concentrations of the elements under study, excluding Fe, in both the buried and surface soils are significantly higher in the topsoil layer compared to parent material (loess), and this justifies the separate baseline values for topsoil horizons, instead of background values derived universally for parent rock types. This is essential, in particular in soils texturally differentiated within profiles, where the subsoil material has a different origin and cannot be considered the parent material for topsoil horizons. Underlying or locally outcropped bedrock (e.g., serpentinite rocks) may naturally enhance the total concentration of trace elements in the entire soil profile by the addition of metal-rich regolith particles during the formation of surface covers, e.g., by eolian processes under periglacial conditions (Late Pleistocene). Such soils are naturally enriched with metals (with nickel in the case of serpentinite bedrock), cannot be considered contaminated, and thus require a separate legal treatment, including separate (or individually suited) background baselines for health risk assessments.

Effects of pharmaceuticals on microbial communities and activity of soil enzymes in mesocosm-scale constructed wetlands

Cyperus alternifolius based mesocosm-scale constructed wetland was employed to remove pharmaceuticals. We investigated the microbial community composition using phosphor lipid fatty acids (PFLAs) analysis and substrate enzyme activity during long-term exposure to pharmaceuticals in mesocosm-scale constructed wetlands. The results showed that there was no visible inhibition effect of pharmaceuticals on CW substrate enzymes activities in the experimental range (0-500 μg/L). Microbial communities, as revealed by PFLAs, were enhanced by the presence of plants, while the PFLAs content was highest when the pharmaceutical concentration was 10 μg/L or 30 μg/L at CWs. Except for anaerobic bacteria and Saturated fatty acids, the maximum PLFAs levels were reached when the pharmaceuticals were 10 μg/L or 30 μg/L, while Bacteria, G (-), fungal bacteria, Aerobic bacteria and Monounsaturated fatty acids were remarkably affected by high pharmaceuticals (100-500 μg/L). However, the main microbial florae were not changed among the treatments. In this study, the removal efficiencies of the studied pharmaceuticals in Planted (30) was greatest, which could be attributed to the higher microbial biomass. These results indicate that C. alternifolius can phytoremediate pharmaceutical-contaminated waters in CWs. Individual fatty acid cannot be used to represent specific species; therefore, more approaches to species identification such as rRNA-based methods must be included in future studies to better understand the metabolic mechanisms of microorganisms involved in the removal of studied pharmaceuticals and improve the performance of CWs.

Isolation and characterization of organic matter-degrading bacteria from coking wastewater treatment plant

As a step toward bioaugmentation of coking wastewater treatment 45 bacteria strains were isolated from the activated sludge of a coking wastewater treatment plant (WWTP). Three strains identified as Bacillus cereus, Pseudomonas synxantha, and Pseudomonas pseudoaligenes exhibited high dehydrogenase activity which indicates a strong ability to degrade organic matter. Subsequently all three strains showed high naphthalene degradation abilities. Naphthalene is a refractory compound often found in coking wastewater. For B. cereus and P. synxantha the maximum naphthalene removal rates were 60.4% and 79.8%, respectively, at an initial naphthalene concentration of 80 mg/L, temperature of 30 °C, pH of 7, a bacteria concentration of 15% (V/V), and shaking speed of 160 r/min. For P. pseudoaligenes, the maximum naphthalene removal rate was 77.4% under similar conditions but at 35 °C.

Effect of Bacillus subtilis and NTA-APG on pyrene dissipation in phytoremediation of nickel co-contaminated wetlands by Scirpus triqueter

A complex mix of organic pollutants and heavy metal made the remediation of contaminated wetlands more difficult. Few research focus on the remediation for pyrene enhanced by chemical reagents and pyrene degrading bacteria in the nickel co-contaminated soil. In this paper, the effect of chemical reagents (nitrilotriacetic acid and alkyl polyglucoside) and Bacillus subtilis on pyrene dissipation in phytoremediation of nickel co-contaminated soil by Scirpus triqueter was investigated. Similar seedlings of Scirpus triqueter were moved to uncontaminated soil and pyrene-nickel co-contaminated soil. The pots (14.8 cm diameter and 8.8 cm height) were set up in greenhouse and treated in different ways. After 60 days, plant biomass, radial oxygen loss (ROL), soil dehydrogenase activity (DHA) and pyrene concentration in soil were determined. Results showed that ROL rate and DHA in different groups was positively correlated with pyrene dissipation from soil. In the process of remediation, chemical reagents might have an indirect slight effect on pyrene dissipation (pyrene dissipation increased 21%) by affecting DHA firstly and redistributing pyrene fractions in the presence of pyrene degrading bacteria. Pyrene degrading bacteria were likely to affect pyrene dissipation by impacting ROL rate and DHA and played a more vital role in contributing to pyrene dissipation (pyrene dissipation increased 45%) from wetland. This study demonstrated that phytoremediation for pyrene in nickel co-contaminated soil by Scirpus triqueter can be enhanced by the application of NTA-APG and pyrene degrading bacteria and they could be reasonably restore the ecological environment of PAH-contaminated wetlands.

Surfactant flushing remediation of o-dichlorobenzene and p-dichlorobenzene contaminated soil

Surfactant-enhanced remediation is used to treat dichlorobenzene (DCB) contaminated soil. In this study, soil column experiments were conducted to investigate the removal efficiencies of o-dichlorobenzene (o-DCB) and p-dichlorobenzene (p-DCB) from contaminated soil using micellar solutions of biosurfactants (saponin, alkyl polyglycoside) compare to a chemically synthetic surfactant (Tween 80). Leachate was collected and analyzed for o-DCB and p-DCB content. In addition, soil was analyzed to explore the effect of surfactants on soil enzyme activities. Results showed that the removal efficiency of o-DCB and p-DCB was highest for saponin followed by alkyl polyglycoside and Tween 80. The maximum o-DCB and p-DCB removal efficiencies of 76.34% and 80.43%, respectively, were achieved with 4 g L^-1 saponin solution. However, an opposite result was observed in the cumulative mass of o-DCB and p-DCB in leachate. The cumulative extent of o-DCB and p-DCB removal by the biosurfactants saponin and alkyl polyglycoside was lower than that of the chemically synthetic surfactant Tween 80 in leachate. Soil was also analyzed to explore the effect of surfactants on soil enzyme activities. The results indicated that surfactants were potentially effective in facilitating soil enzyme activities. Thus, it was confirmed that the biosurfactants saponin and alkyl polyglycoside could be used for remediation of o-DCB and p-DCB contaminated soil.

Influence of polycyclic aromatic hydrocarbons on nitrate reduction capability in mangrove sediments

In the present study, we investigated the influence of phenanthrene (PHE), a three-ring polycyclic aromatic hydrocarbon (PAH) compound, on nitrate (NO₃^-) reduction processes in mangrove sediments using microcosms. After 10days, nitrate/nitrite reductase activity and abundance of narG and nirS significantly decreased in the bulk sediment at both 10/50mgPHEkg^-1 contamination groups. In the rhizosphere, abundance of narG, nirS and nirK markedly declined at PHE treated sediments, while the drop in reductase activity at 10mgkg^-1 PHE treatment was insignificant. After 50days, apart from 10mgPhekg^-1 treated bulk sediment, abundance of denitrifiers and reductase activity in all PHE spiked sediment samples significantly dropped. Therefore, the influence of PAHs on NO₃^- reduction capability in mangrove sediments is dependent on spiked concentration, temporal scale of exposure and interaction with roots. Generally, PAHs play an inhibitor role, slowing NO₃^- turnover rates, which warrant attention from coastal managers.

The naphthalene catabolic protein NahG plays a key role in hexavalent chromium reduction in Pseudomonas brassicacearum LZ-4

Soil contamination by PAH and heavy metals is a growing problem. Here, we showed that a new isolate, Pseudomonas brassicacearum strain LZ-4, can simultaneously degrade 98% of 6 mM naphthalene and reduce 92.4% of 500 μM hexavalent chromium [Cr (VI)] within 68 h. A draft genome sequence of strain LZ-4 (6,219,082 bp) revealed all the genes in the naphthalene catabolic pathway and some known Cr (VI) reductases. Interestingly, genes encoding naphthalene pathway components were upregulated in the presence of Cr (VI), and Cr (VI) reduction was elevated in the presence of naphthalene. We cloned and expressed these naphthalene catabolic genes and tested for Cr (VI) reduction, and found that NahG reduced 79% of 100 μM Cr (VI) in 5 minutes. Additionally, an nahG deletion mutant lost 52% of its Cr (VI) reduction ability compared to that of the wild-type strain. As nahG encodes a salicylate hydroxylase with flavin adenine dinucleotide (FAD) as a cofactor for electron transfer, Cr (VI) could obtain electrons from NADH through NahG-associated FAD. To the best of our knowledge, this is the first report of a protein involved in a PAH-degradation pathway that can reduce heavy metals, which provides new insights into heavy metal-PAH contamination remediation.

The effect of multiple contamination of soil on LMW and MMW PAHs accumulation in the roots of Rubus fruticosus L. naturally growing near The Copper Mining and Smelting Complex Bor (East Serbia)

Samples of roots and spatial soils of native Rubus fruticosus L. were collected from the spots positioned at different distances from the copper smelter and city heating plants in the industrial zone of the town of Bor (Serbia) and subjected to chemical analyses in order to determine the content of several heavy metals, and 15 priority polycyclic aromatic hydrocarbons (PAHs). In this study, the results for 9 low and medium molecular weight PAHs (LMW and MMW PAHs) are represented and processed using the calculation of bio-concentration factors and statistical methods such as hierarchical cluster analysis and Pearson's correlation study with the aim of investigating the plant capabilities for their uptake from the soil and later accumulation into the root tissue, under the hostile circumstances of multiple contamination. The obtained data revealed different accumulation rates for the investigated PAHs and showed that in several cases, the contents of root PAHs were under the strong influence of present contaminants such as soil copper and some soil PAHs, indicating at the same time that R. fruticosus can regulate the processes of LMW and MMW PAHs extraction/accumulation using different mechanisms, depending on the existing environmental circumstances. The used mechanisms could be exploited in phytoremediation methods based not only on the extraction and concentration of PAHs in plant roots but also on PAH degradation or stabilization in the soil. Also, the results of this study confirmed that, except in the case of naphthalene and fluoranthene, there was no PAH pollution, which originated solely from the industrial zone.

Phytoremediation effect of Scirpus triqueter inoculated plant-growth-promoting bacteria (PGPB) on different fractions of pyrene and Ni in co-contaminated soils

At present, few reveal the mechanism of inoculation plants with PGPB to remediate PAH-metal co-contaminated soil by analyzing the chemical speciations of contaminants. This study investigated the influence of inoculation plants with PGPB on different fractions of pyrene and Ni in rhizospheric and non-rhizospheric soil. The results demonstrated that the addition of PGPB brought the extensive increase of FDA activities in pyrene-Ni co-contaminated soil. PGPB increased the resistance of plants in nickel and pyrene-Ni contaminated soil, but decreased the plant biomass in single pyrene contaminated soil. The addition of PGPB efficiently decreased bioaccessible fractions of pyrene and increased the bioavailability of Ni in both rhizospheric and non-rhizospheric soil. Although inoculation plants with PGPB significantly increased the accumulation of Ni in single Ni and pyrene-Ni co-contaminated soil, the poor bioavailability of Ni in rhizospheric soil still restricted the phytoremediation of the heavy metal. The presence of pyrene hindered the inoculated plant from accumulating Ni to some extent. On the contrary, the presence of Ni significantly promoted the degradation of pyrene in both rhizospheric and non-rhizospheric soil after inoculation plants with PGPB.

Mass balance-based regression modeling of Cd and Zn accumulation in urban soils of Beijing

Accumulation of heavy metals in urban soil can pose adverse impacts on public health and terrestrial ecosystems. We developed a mass balance-based regression model to simulate the heavy metal accumulation in urban soils as a function of time and to explore connections between metal concentration and urbanization processes. Concentrations of Cd and Zn in 68 residential soil samples in the urban area of Beijing were used. The background concentrations, the loss rates and the input fluxes of Cd and Zn in urban soils of Beijing during the last three decades were estimated using a regression of the time series of accumulations of the metals. Based on the regression estimates, we simulated the general trends of Cd and Zn accumulation in the soils from 1978 to 2078. The concentrations of Cd and Zn in urban soil generally increased with the population growth, vehicle use and coal consumption. The mean concentrations of Cd and Zn in urban soil of Beijing would increase by 3 fold over the next 70years for the current development scenario. The mass balance-based regression approach, which is able to reconstruct the history data of urban soil pollution, provides fundamental information for urban planning and environmental management.

Interaction effects on uptake and toxicity of perfluoroalkyl substances and cadmium in wheat (Triticum aestivum L.) and rapeseed (Brassica campestris L.) from co-contaminated soil

A vegetation study was conducted to investigate the interactive effects of perfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), and Cadmium (Cd) on soil enzyme activities, phytotoxicity and bioaccumulation of wheat (Triticum aestivum L.) and rapeseed (Brassica campestris L.) from co-contaminated soil. Soil urease activities were inhibited significantly but catalase activities were promoted significantly by interaction of PFASs and Cd which had few effects on sucrase activities. Joint stress with PFASs and Cd decreased the biomass of plants and chlorophyll (Chl) content in both wheat and rapeseed, and malondialdehyde (MDA) content, superoxide dismutase (SOD) and peroxidase (POD) activities were increased in wheat but inhibited in rapeseed compared with single treatments. The bioconcentration abilities of PFASs in wheat and rapeseed were decreased, and the translocation factor of PFASs was decreased in wheat but increased in rapeseed with Cd addition. The bioaccumulation and translocation abilities of Cd were increased significantly in both wheat and rapeseed with PFASs addition. These findings suggested important evidence that the co-existence of PFASs and Cd reduced the bioavailability of PFASs while enhanced the bioavailability of Cd in soil, which increased the associated environmental risk for Cd but decreased for PFASs.

Bioaccumulation of HMW PAHs in the roots of wild blackberry from the Bor region (Serbia): Phytoremediation and biomonitoring aspects

In this work, the samples of roots and soils from the rooting zone of wild blackberry were collected from the urban-industrial and rural locations near "The Copper Mining and Smelting Complex Bor" (Serbia); they were analyzed by gas chromatographic-mass spectrometric method to determine the content of high-molecular weight polycyclic aromatic hydrocarbons (HMW PAHs). The obtained results were further processed using bio-concentration factor, Pearson's correlation study and hierarchical cluster analysis with the aim of investigating if they may be in favor of wild blackberry as a suitable plant for biomonitoring or phytoremediation purposes. In spite of the fact that numerous complex factors can affect the assimilation and accumulation of PAHs in plants, the obtained data expressed clearly many interesting specifics related to HMW PAH accumulation in roots of wild blackberry that naturally grows in an area, which is heavily polluted by heavy metals. The accumulation of individual PAH compounds in plant roots was at different level. The most abundant compound in all plant samples was benzo[a]pyrene and based on the results obtained for this environmental indicator of carcinogenic PAHs, it was possible to make several central conclusions: wild blackberry showed an excellent potential for its extraction from the soil and further accumulation in root tissues which indicate that this plant species may be applied in phytoremediation procedures based on mechanisms such as phytoextraction/phytoaccumulation in roots; phytostabilization and rhizodegradation are also possible as remediation mechanisms; utilization of plant roots in soil monitoring is possible but in this case, only the combination with soil data can provide correct information.

Toxicity of combined chromium(VI) and phenanthrene pollution on the seed germination, stem lengths, and fresh weights of higher plants

Studies of the interaction and toxicity of pollutant combinations such as heavy metals and PAHs are of practical importance in the remediation and monitoring of the industrial soil environment. This study investigated the single and combined toxicity of chromium(VI) and phenanthrene on three important higher plants: mung beans (Phaseolus aureus), pakchoi cabbage (Brassica chinensis), and rice (Oryza sativa). In experiments using artificial soil matrix, the EC10 and EC20 of the two pollutants, alone and in combination, were analyzed with respect to seed germination, stem length, and above-ground fresh weight of these higher plants. The additive index method was used to evaluate the combined biological toxicity of chromium(VI) and phenanthrene. The results showed that the EC20 of chromium(VI) on the stem lengths of mung beans, pakchoi cabbage, and rice was 289, 248, and 550 mg kg(-1), respectively. The corresponding EC20 values for the fresh weights of the three plants were 334, 307, and 551 mg kg(-1). The EC20 of phenanthrene on the stem lengths of mung beans, pakchoi cabbage, and rice was 528, 426, and 628 mg kg(-1), respectively. The corresponding EC20 values for the fresh weights of the three plants were 696, 585, and 768 mg kg(-1). The EC20 of a combination of chromium(VI) and phenanthrene on the stem lengths of mung beans, pakchoi cabbage, and rice was 192, 173, and 279 mg kg(-1), respectively, and 200, 205, and 271 mg kg(-1) for the fresh weights of the three plants. The single and combined exposure of soil to chromium(VI) and phenanthrene had deleterious effects on plants in the early stage of growth. Overall, pakchoi cabbage was more sensitive than mung beans and rice. The two pollutants exerted synergistic effects on the stem lengths and above-ground fresh weights of both mung beans and rice but antagonistic effects on pakchoi cabbage. The results of this study also suggested pakchoi cabbage as a sensitive indicator of soil pollution.

The Effects of Heavy Metals and Total Petroleum Hydrocarbons on Soil Bacterial Activity and Functional Diversity in the Upper Silesia Industrial Region (Poland)

Various inorganic and organic pollutants in industrial soils may adversely affect soil microorganisms and terrestrial ecosystem functioning. The aim of the study was to explore the relationship between the microbial activity, microbial biomass, and functional diversity of soil bacteria and the metals and total petroleum hydrocarbons (TPHs) in the Upper Silesian Industrial Region (Poland). We collected soil samples in pine-dominated forest stands and analyzed them according to a range of soil physicochemical properties, including metal content (cadmium, lead, and zinc) and TPH content. Metal concentrations were normalized to their toxicity to soil microorganisms and integrated in a toxicity index (TI). Soil microbial activity measured as soil respiration rate, microbial biomass measured as substrate-induced respiration rate, and the bacterial catabolic activity (area under the curve, AUC) assessed using Biolog® ECO plates were negatively related to TPH pollution as shown in multiple regressions. The canonical correspondence analysis (CCA) showed that both TPH and TI affected the community-level physiological profiles (CLPPs) of soil bacteria and the pollutants' effects were much stronger than the effects of other soil properties, including nutrient content.

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).

The influence of nickel on the bioremediation of multi-component contaminated tropical soil: microcosm and batch bioreactor studies

Large petrochemical discharges are responsible for organic and inorganic pollutants in the environment. The purpose of this study was to evaluate the influence of nickel, one of the most abundant inorganic element in crude oil and the main component of hydrogen catalysts for oil refining, on the microbial community structure in artificially petroleum-contaminated microcosms and in solid phase bioreactor studies. In the presence of metals, the oil biodegradation in microcosms was significantly delayed during the first 7 days of operation. Also, increasing amounts of moisture generated a positive influence on the biodegradation processes. The oil concentration, exhibiting the most negative influence at the end of the treatment period. Molecular fingerprinting analyses (denaturing gradient gel electrophoresis--DGGE) indicated that the inclusion of nickel into the contaminated soil promoted direct changes to the microbial community structure. By the end of the experiments, the results of the total petroleum hydrocarbons removal in the bioreactor and the microcosm were similar, but reductions in the treatment times were observed with the bioreactor experiments. An analysis of the microbial community structure by DGGE using various markers showed distinct behaviors between two treatments containing high nickel concentrations. The main conclusion of this study was that Nickel promotes a significant delay in oil biodegradation, despite having only a minor effect over the microbial community.

Uptake and Bioaccumulation of Pentachlorophenol by Emergent Wetland Plant Phragmites australis (Common Reed) in Cadmium Co-contaminated Soil

Despite many studies on phytoremediation of soils contaminated with either heavy metals or organics, little information is available on the effectiveness of phytoremediation of co-occurring metal and organic pollutants especially by using wetland species. Phragmites australis is a common wetland plant and its potential for phytoremediation of cadmium pentachlorophenol (Cd-PCP) co-contaminated soil was investigated. A greenhouse study was executed to elucidate the effects of Cd (0, 10, and 20 mg kg(-1)) without or with PCP (0, 50, and 250 mg kg(-1)) on the growth of the wetland plant P. australis and its uptake, accumulation and removal of pollutant from soils. After 75 days, plant biomass was significantly influenced by interaction of Cd and PCP and the effect of Cd on plant growth being stronger than that of PCP. Coexistence of PCP at low level lessened Cd toxicity to plants, resulting in improved plant growth and increased Cd accumulation in plant tissues. The dissipation of PCP in soils was significantly influenced by interactions of Cd, PCP and plant presence or absence. As an evaluation of soil biological activities after remediation soil enzyme was measured.

Effects of low molecular-weight organic acids and dehydrogenase activity in rhizosphere sediments of mangrove plants on phytoremediation of polycyclic aromatic hydrocarbons

This work evaluated the roles of the low-molecular-weight organic acids (LMWOAs) from root exudates and the dehydrogenase activity in the rhizosphere sediments of three mangrove plant species on the removal of mixed PAHs. The results showed that the concentrations of LMWOAs and dehydrogenase activity changed species-specifically with the levels of PAH contamination. In all plant species, the concentration of citric acid was the highest, followed by succinic acid. For these acids, succinic acid was positively related to the removal of all the PAHs except Chr. Positive correlations were also found between the removal percentages of 4-and 5-ring PAHs and all LMWOAs, except citric acid. LMWOAs enhanced dehydrogenase activity, which positively related to PAH removal percentages. These findings suggested that LMWOAs and dehydrogenase activity promoted the removal of PAHs. Among three mangrove plants, Bruguiera gymnorrhiza, the plant with the highest root biomass, dehydrogenase activity and concentrations of LMWOAs, was most efficient in removing PAHs.

Does a concomitant exposure to lead influence unfavorably the naphthalene subchronic toxicity and toxicokinetics?

Rats were given 20 times during 40 d either naphthalene per gavage or the same and lead acetate intraperitoneally in single doses corresponding to 5% of the respective 50% lethal doses. The concomitant exposure to lead not only added some typical indicators of lead toxicity to the moderate naphthalene intoxication picture but also exaggerated some less specific indices for intoxication. However, a number of such indices testified to attenuation of naphthalene's adverse effects under the impact of lead. Lead also lowered urinary excretion of both total and conjugated naphthalene, while the free- to total naphthalene ratio in urine sharply increased. These results corroborate implicitly the initial hypothesis that lead, being an inhibitor of cytochrome P450, hinders phase I of the naphthalene biotransformation and, thus, the formation of derivates which can be more toxic but are capable of entering into reactions of conjugation with resulting detoxication and elimination of naphthalene from the body.

Evaluating the phytoremediation potential of Phragmites australis grown in pentachlorophenol and cadmium co-contaminated soils

Pot-culture experiments were conducted to evaluate the phytoremediation potential of a wetland plant species, Phragmites australis in cadmium (Cd) and pentachlorophenol (PCP) co-contaminated soil under glasshouse conditions for 70 days. The treatments included Cd (0, 5 and 50 mg kg(-1)) without or with PCP (50 and 250 mg kg(-1)). The results showed that growth of P. australis was significantly influenced by interaction of Cd and PCP, decreasing with either Cd or PCP additions. Plant biomass was inhibited and reduced by the rate of 89 and 92% in the low and high Cd treatments and by 20 and 40% in the low and high PCP treatments compared to the control. The mixture of low Cd and low PCP lessened Cd toxicity to plants, resulting in improved plant growth (by 144%). Under the joint stress of the two contaminants, the ability of Cd uptake and translocation by P. australis was weak, and the BF and TF values were inferior to 1.0. A low proportion of the metal is found aboveground in comparison to roots, indicating a restriction on transport upwards and an excluding effect on Cd uptake. Thus, P. australis cannot be useful for phytoextraction. The removal rate of PCP increased significantly (70%) in planted soil. Significant positive correlations were found between the DHA and the removal of PCP in planted soils which implied that plant root exudates promote the rhizosphere microorganisms and enzyme activity, thereby improving biodegradation of PCP. Based on results, P. australis cannot be effective for phytoremediation of soil co-contaminated with Cd and PCP. Further, high levels of pollutant hamper and eventually inhibit plant growth. Therefore, developing supplementary methods (e.g. exploring the partnership of plant-microbe) for either enhancing (phytoextraction) or reducing the bioavailability of contaminants in the rhizosphere (phytostabilization) as well as plant growth promoting could significantly improve the process of phytoremediation in co-contaminated soil.

Impact of Zn and Cu on the development of phenanthrene catabolism in soil

Mixtures of polycyclic aromatic hydrocarbons (PAHs) and heavy metals are of major concern in contaminated soil. Biodegradation of PAHs in metal-contaminated soils is complicated because metals are toxic and cannot be degraded by biological processes. This investigation considered the effects of Zn and Cu (50, 100, 500 and 1,000 mg/kg) on (14)C-phenanthrene biodegradation in soil over 60-day contact time. The presence of Zn at all concentrations and low concentrations of Cu (50 and 100 mg/kg) had no significant effect (p > 0.05) on the development of phenanthrene catabolism; however, at higher Cu concentrations, the development of phenanthrene catabolism and bacterial cell numbers were significantly reduced (p < 0.05). This suggests that Cu is more toxic than Zn to soil microbial PAH catabolic activity. Metal/PAH-contaminated soils represent one of the most difficult remedial challenges and insights into PAH biodegradation in the presence of metals is necessary in order to assess the potential for bioremediation.

Recent development in the treatment of oily sludge from petroleum industry: a review

Oily sludge is one of the most significant solid wastes generated in the petroleum industry. It is a complex emulsion of various petroleum hydrocarbons (PHCs), water, heavy metals, and solid particles. Due to its hazardous nature and increased generation quantities around the world, the effective treatment of oily sludge has attracted widespread attention. In this review, the origin, characteristics, and environmental impacts of oily sludge were introduced. Many methods have been investigated for dealing with PHCs in oily sludge either through oil recovery or sludge disposal, but little attention has been paid to handle its various heavy metals. These methods were discussed by dividing them into oil recovery and sludge disposal approaches. It was recognized that no single specific process can be considered as a panacea since each method is associated with different advantages and limitations. Future efforts should focus on the improvement of current technologies and the combination of oil recovery with sludge disposal in order to comply with both resource reuse recommendations and environmental regulations. The comprehensive examination of oily sludge treatment methods will help researchers and practitioners to have a good understanding of both recent developments and future research directions.

Impact of Zn, Cu, Al and Fe on the partitioning and bioaccessibility of (14)C-phenanthrene in soil

This investigation considered the effects of Zn, Cu, Al and Fe (50 and 500 mg kg(-1)) on the loss, sequential extractability, using calcium chloride (CaCl2), hydroxypropyl-β-cyclodextrin (HPCD) and dichloromethane (DCM) and biodegradation of (14)C-phenanthrene in soil over 63 d contact time. The key findings were that the presence of Cu and Al (500 mg kg(-1)) resulted in larger amounts of (14)C-phenanthrene being extracted by CaCl2 and HPCD. Further, the CaCl2 + HPCD extractions directly predicted the biodegradation of the PAH in the presence of the metals, with the exception of 500 mg kg(-1) Cu and Zn. The presence of high concentrations of some metals can impact on the mobility and accessibility of phenanthrene in soil, which may impact on the risk assessment of PAH contaminated soil.

Effect of pyrene and cadmium on microbial activity and community structure in soil

In this study, a greenhouse experiment was conducted to investigate interactive effects of cadmium (Cd) × pyrene × plant treatments on soil microbial activity and community structure. The results demonstrated that the basal respiration, microbial biomass carbon and metabolic quotient in both unplanted and rhizosphere soil were significantly influenced by interaction of Cd and pyrene. The combined application of Cd and pyrene caused a significantly greater biocidal influence on the soil microorganisms than the single spiking of Cd or pyrene. The soil basal respiration increased with the spiking of 2.5 mg kg(-1) Cd in both unplanted and rhizosphere soil. The eco-physiological index of Cd-tolerant populations was significantly different among the unplanted soil, rhizoplane and rhizosphere soil of tall fescue, indicating a slightly uneven distribution of fast- and slow-growing tolerant bacteria. Obvious differences in microbial activity were observed among treatments due to different physicochemical characteristics of the rhizosphere soils depending on the plant species.