Sorption of polycyclic aromatic hydrocarbons to soils enhanced by heavy metals: perspective of molecular interactions

Purpose

Combined pollution by polycyclic aromatic hydrocarbons (PAHs) and heavy metals are commonly found in industrial soils. This study aims to investigate the effect of the coexistence of heavy metals on the sorption of PAHs to soils. We focused specifically on the relationship of the sorption capacity with the estimation of the binding energy between PAHs and heavy metals.

Materials and methods

The sorption of typical PAHs (naphthalene, phenanthrene, and pyrene) to soils coexisting with heavy metals (Cu(II), Pb(II), and Cr(III)) was characterized in batch sorption experiments. The binding energy between PAHs and heavy metals in aqueous solution was estimated by quantum mechanical (QM) method using density functional theory (DFT) at the M06-2x/def2svp level of theory.

Results and discussion

Sorption capacity and nonlinearity of the PAHs to the soils were enhanced by the coexisting heavy metals. The extent of increment was positively associated with the hydrophobicity of the PAHs and the electronegativity and radius of the metal cations: Cr(III)?>?Pb(II)?>?Cu(II). The cation-π interaction was revealed as an important noncovalent binding force. There was a high correlation between the binding energies of the PAHs and K _f ′ (K _f adjusted after normalizing the equilibrium concentration (C _e) by the aqueous solubility (C _s)) (R ²?>?0.906), indicating the significant role of the cation-π interactions to the improved PAH sorption to soils.

Conclusions

In the presence of heavy metals, the sorption capacities of naphthalene, phenanthrene, and pyrene to soils were enhanced by 21.1–107 %. The improved sorption capacity was largely contributed from the potent interactions between PAHs and heavy metals.

     

Pollution assessment and spatial variation of soil heavy metals in Lixia River Region of Eastern China

Purpose

The effect of soil heavy metals on crops and human health is an important research topic in some fields (Agriculture, Ecology et al.). In this paper, the objective is to understand the pollution status and spatial variability of soil heavy metals in this study area. These results can help decision-makers apportion possible soil heavy metal sources and formulate pollution control policies, effective soil remediation, and management strategies.

Materials and methods

A total of 212 topsoil samples (0–20 cm) were collected and analyzed for eight heavy metals (Cd, Hg, As, Cu, Pb, Cr, Zn, and Ni) from agricultural areas of Yingbao County in Lixia River Region of Eastern China, by using four indices (pollution index (PI), Nemerow pollution index (PI_N), index of geo-accumulation (I _geo), E _i /risk index (RI)) and cluster analysis to assess pollution level and ecological risk level of soil heavy metals and combining with geostatistics to analyze the concentration change of heavy metals in soils. GS+ software was used to analyze the spatial variation of soil heavy metals, and the semi-variogram model is the main tool to calculate the spatial variability and provide the input parameters for the spatial interpolation of kriging. Arcgis software was used to draw the spatial distribution of soil heavy metals.

Results and discussion

The result indicated that the eight heavy metals in soils of this area had moderate variations, with CVs ranging from 23.51 to 64.37 %. Single pollution index and Nemerow pollution index showed that about 2.7 and 1.36 % of soil sampling sites were moderately polluted by Cd and Zn, respectively. The pollution level of soil heavy metals decreased in the order of Cd?>?Zn?>?Pb?>?As?>?Cu?>?Cr?>?Ni?>?Hg. The I _geo values of heavy metals in this area decreased in the order of Zn?>?Cd?>?As?>?Pb?>?Cu?>?Cr?>?Hg?>?Ni. According to the E _i index, except Cd that was in the moderate ecological risk status, other heavy metals in soils were in the light ecological risk status, and the level of potential ecological risk (RI) of soil sampling sites of the whole area was light.

Conclusions

The results of four indices and the analysis of spatial variation indicated that the contents of Cd and Zn were contributed mainly by anthropogenic activities and located in the south-east of this study area. However, the contents of Hg, As, Cu, Pb, Cr, and Ni in soils were primarily influenced by soil parent materials.

     

Grasses and legumes facilitate phytoremediation of metalliferous soils in the vicinity of an abandoned chromite–asbestos mine

Purpose

The present study was carried out in Roro region, Chaibasa, Jharkhand, India, to assess the impact of chromite–asbestos mine waste (CMW) on a nearby agroecosystem. The role of metal-accumulating grass–legume association in facilitating phytoremediation was investigated.

Materials and methods

Soil and plant samples were collected from (i) chromite–asbestos mine waste (CMW) with Cynodon dactylon, Sorghastrum nutans, and Acacia concinna; (ii) contaminated agricultural soil-1 (CAS1) from a foothill with Cajanus cajan; (iii) contaminated agricultural soil-2 (CAS2) distantly located from the hill, cultivated with Oryza sativa and Zea mays; and (iv) unpolluted control soil (CS). Total metal concentrations were quantified in both soils and plants by digesting the samples using HNO₃, HF, HClO₄ (5:1:1; v/v/v), and HNO₃ and HClO₄ (5:1; v/v), respectively, and analyzed under flame atomic absorption spectrophotometry. Metal grouping and site grouping cluster analysis was executed to group the metals and sampling sites. Translocation factor (TF) and bioconcentration factor (BCF) were calculated to determine the phytoremediation efficiency of grasses and legumes.

Results and discussion

Results indicate that total metal concentrations in the CMW were in the order of Cr?>?Ni?>?Mn?>?Cu?>?Pb?>?Co?>?Zn?>?Cd. High concentrations of Cr (1983 mg kg^?1) and Ni (1293 mg kg^?1) with a very strong contamination factor were found in the CAS, which exceeds the soil threshold limits. Further, metal and site grouping cluster analysis also revealed that Cr and Ni were closely linked with each other and the CMW was the main source of contamination. Among all the metals, Cr and Ni were mainly accumulated in grasses (C. dactylon and S. nutans) and legumes (A. concinna and C. cajan) as compared to cereals (Z. mays and O. sativa). The TF of Cr was >1 for grasses. Except for Zn, the BCF for all the metals were <1 in roots and shoots of all the plants and cereals.

Conclusions

The present study revealed that abandoned CMW is the source of contamination for agriculture lands. Phytoremediation relies on suitable plants with metal-scavenging properties. Grass–legume cover (C. dactylon, S. nutans, A. concinna, and C. cajan) has the ability to accumulate metals and act as a potential barrier for metal transport, which facilitate the phytoremediation of the CMW. Possibilities for enhancing the barrier function of the grass–legume cover need to be explored with other low-cost agronomic amendments and the role of rhizospheric organisms.

     

Response of CaCl<Subscript>2</Subscript>-extractable heavy metals,polychlorinated biphenyls,and microbial communities to biochar amendment in naturally contaminated soils

Purpose

Biochar can be used to reduce the bioavailability and leachability of heavy metals, as well as organic pollutants in soils through adsorption and other physicochemical reactions. The objective of the study was to determine the response of microbial communities to biochar amendment and its influence on heavy metal mobility and PCBs (PCB52, 44, 101, 149, 118, 153, 138, 180, 170, and 194) concentration in application of biochar as soil amendment.

Materials and methods

A pot (macrocosm) incubation experiment was carried out with different biochar amendment (0, 3, and 6 % w/w) for 112 days. The CaCl₂-extractable concentration of metals, microbial activities, and bacterial community were evaluated during the incubation period.

Results and discussion

The concentrations of 0.01 M CaCl₂-extractable metals decreased (p?>?0.05) by 12.7 and 20.5 % for Cu, 5.0 and 15.6 % for Zn, 0.2 and 0.5 % for Pb, and 1.1 and 8.9 % for Cd, in the presence of 3 and 6 % of biochar, respectively, following 1 day of incubation. Meanwhile, the total PCB concentrations decreased from 1.23 mg kg^?1 at 1 day to 0.24 mg kg^?1 at 112 days after 6 % biochar addition, representing a more than 60 % decrease relative to untreated soil. It was also found out that biochar addition increased the biological activities of catalase, phosphatase, and urease activity as compared with the controls at the same time point. Importantly, the Shannon diversity index of bacteria in control soils was 3.41, whereas it was 3.69 and 3.88 in soils treated with 3 and 6 % biochar soil. In particular, an increase in the number of populations with the putative ability to absorb PCB was noted in the biochar-amended soils.

Conclusions

The application of biochar to contaminated soils decreased the concentrations of heavy metals and PCBs. Application of biochar stimulated Proteobacteria and Bacteroides, which may function to absorb soil PCB and alleviate their toxicity.

     

Comparison of the <Emphasis Type="Italic">Rhodotorula mucilaginosa</Emphasis> Biofilm and Planktonic Culture on Heavy Metal Susceptibility and Removal Potential

This study compares the effect of heavy metals (Hg²⁺, Cu²⁺, and Pb²⁺) on the Rhodotorula mucilaginosa and Saccharomyces boulardii biofilm and planktonic cells. A MBEC^TM-HTP assay was used to test the levels of tolerance to heavy metals. The minimum inhibitory concentration (MICp) and minimum lethal concentration (MLCp) of the R. mucilaginosa and S. boulardii planktonic cells were determined, as well as minimum biofilm eradication concentration (MBEC). Metal removal efficiency was determined by batch biosorption assay. Previous studies had focused on heavy metal tolerance and removal efficiency of planktonic cells from Rhodotorula species only. Hence, our study presents and compares results for metal tolerance and removal efficiency of the R. mucilaginosa planktonic cells and biofilm. Biofilm tolerance was higher than the planktonic cells. The R. mucilaginosa planktonic cells showed the tolerance in the presence of Hg²⁺ (MICp 0.08 mM), Cu²⁺ (MICp 6.40 mM), and Pb²⁺ (MICp 3.51 mM), while the S. boulardii planktonic cells only tolerated Pb²⁺ (MICp 0.43 mM). The R. mucilaginosa biofilm showed the highest tolerance in the presence of Hg²⁺ (MBEC >0.31 mM), Cu²⁺(MBEC >12.81 mM), Pb²⁺ (MBEC >7.12 mM), and obtained results were confirmed by fluorescence microscopy. S. boulardii did not show potential in biofilm formation. The R. mucilaginosa biofilm exhibited better efficiency in removal of all tested metals than the planktonic cells. Metal removal efficiency was in the range from 4.79–10.25% for planktonic cells and 91.71–95.39% for biofilm.     

Heavy metal content and toxicity of mine and quarry soils

Purpose

Soils formed in metallic mines and serpentinite quarries, among other unfavourable features, have high levels of heavy metals. They can release into the environment causing surface and subsurface water contamination, uptake by plants, their accumulation in the food chain and adverse effects on living organisms. In this work, we studied the magnitude of the soils’ toxic effects not only on spontaneous plants but also on two species with phytoremediation potential.

Materials and methods

Several soils from two different exploitations were selected: a lead and zinc mine and a serpentinite quarry. Soils were characterized, and the pseudo-total and extractable contents of Co, Cr and Ni in soils from a serpentinite quarry were determined. The Cd, Pb and Zn pseudo-total and extractable contents were determined in soils developed in the Pb/Zn abandoned mine. Using a biotest, the chronic toxicity of the soil samples on higher plants was determined. Festuca ovina L., Cytisus scoparius (L.) Link., Sinapis alba L. and Brassica juncea L. were selected, the first two because they are spontaneous plants in the study areas and the last two because they have heavy metal phytoremediation potential.

Results and discussion

Pseudo-total contents of Co, Cr and Ni in the serpentinite quarry soils and of Zn, Pb and Cd in the Zn/Pb mine soils exceed generic reference levels. CaCl₂ is the reactant that extracts the highest proportion of Co, Cr and Ni in the quarry soils and EDTA the largest proportion of Pb Zn and Cd content in the mine soils. The germination index values based on seed germination and root elongation bioassays revealed increasing plant sensitivity to the mine soils in the following order: B. juncea?<?S. alba?<?F. ovina?<?C. scoparius. The wide range of GI values indicates that the response of test plants to soil heavy metals depended on their concentrations and soil characteristics, especially pH and organic matter content.

Conclusions

The pollution index indicates severe Cd, Pb and Zn contamination in the mine soils, as well as high Cr and Ni and moderate Co contamination in the serpentinite quarry soils. The performed biotests were suitable for identifying toxic soils and showed that the studied soils are toxic to the spontaneous plants, more to C. scoparius than to F. ovina. They also indicate that the mine soils are more toxic than the quarry soils for both species.

     

Potentialities of Six Plant Species on Phytoremediation Attempts of Fuel Oil-Contaminated Soils

A field experiment investigating the phytoremediation potential of six plant species—Goosegrass (Eleusine indica), Bermuda grass (Cynodon dactylon), Sessile joyweed (Alternanthera sessilis), Benghal dayflower (Commelina benghalensis), Lovanga (Cleome ciliata), and Chinese violet (Asystasia gangetica)—on soil contaminated with fuel oil (82.5 ml/kg of soil) have been conducted from March to August 2016. The experiments consider three modalities—Tn: unpolluted planted soils, To: unplanted polluted soils, and Tp: polluted planted soil—randomized arranged. Only three (E. indica, C. dactylon, and A. sessilis) of the six species survived while the others died 1 month after the beginning of experimentations. The relative growth indexes showed a strong similarity between the growth parameters of E. indica and C. dactylon, each on polluted and control soils, unlike A. sessilis. Total petroleum hydrocarbons (TPHs) removal efficiency were 82.56, 80.69, and 77% on soil planted with E. indica, C. dactylon, and A. sessilis, respectively; and 57.25% on non-planted soil. According to the bioconcentration and translocation factors, E. indica and A. sessilis are involved on rhizodegradation and phytoextraction of hydrocarbons whereas C. dactylon is only involved into rhizodegradation. Overall, E. indica and C. dactylon out-yielded A. sessilis in the phytoremediation capacity of fuel oil-contaminated soils.     

Study of Heavy Metal Accumulation and Residual Toxicity in Soil Saturated with Phosphate Processing Wastewater

The effects of phosphate processing wastewater (PPWW) on heavy metal accumulation in a Mediterranean soil (Tunisia, North Africa) were investigated. Moreover, the residual toxicities of PPWW-irrigated soils extracts were assessed. Results showed that heavy metal accumulation was significantly higher in PPWW-irrigated soil extracts than in control soil. The heavy metal accumulation increased over time in treated soil samples and their average values followed the following order: Iron (Fe 252.72 mg l^?1) > Zinc (Zn 152.95 mg l^?1) > Lead (Pb 128.35 mg l^?1) > Copper (Cu 116.82 mg l^?1) > Cadmium (Cd 58.03 mg l^?1). The residual microtoxicity and phytotoxicity of the various treated soil samples extracts were evaluated by monitoring the bioluminescence inhibition (BI %) of Vibrio ficheri and the measurement of the germination indexes (GI %) of Lepidium sativum and Medicago sativa seeds. The results showed an important increase of residual toxicities of PPWW-treated soil extracts over time.     

Geographic distance and amorphous iron affect the abundance and distribution of <Emphasis Type="Italic">Geobacteraceae</Emphasis> in paddy soils in China

Purpose

Geobacteraceae are important dissimilatory Fe (III)-reducing microorganisms, influencing the cycling of metals, nutrients as well as the degradation of organic contaminants. However, little is known about their distribution, diversity, and abundance of Geobacteraceae and the effects of environment factors and geographic distance on the distribution and diversity of Geobacteraceae in paddy soils remain unclear. Therefore, the objectives of this study were to investigate the distribution, diversity, and abundance of Geobacteraceae in paddy soils and to determine key factors in shaping the Geobacteraceae distribution, environmental factors, geographic distance, or both and to quantify their contribution to Geobacteraceae variation.

Materials and methods

Illumina sequencing and quantitative real-time PCR using a primer set targeting 16S rRNA genes of bacteria affiliated with the family Geobacteraceae were employed to measure the community composition, diversity, and abundance patterns of 16S rRNA genes of Geobacteraceae in 16 samples collected from north to south of China. MRT, Mantel test, and VPA were used to analyze the relationship between communities of Geobacteraceae and environmental factors and geographic distance.

Results and discussion

Quantitative PCR showed that the abundance of 16S rRNA genes of Geobacteraceae ranged from (1.20?±?0.18)?×?10⁸ to 1.13?×?10⁹?±?2.25?×?10⁸ copies per gram of soil (dry weight) across different types of soils. Illumina sequencing results showed Geobacter was the dominant genus within the family of Geobacteraceae. Multivariate regression tree (MRT) analysis showed that soil amorphous iron contributed more (22.46 %) to the variation of dominant species of Geobacteraceae than other examined soil chemical factors such as pH (14.52 %), ammonium (5.12 %), and dissolved organic carbon (4.74 %). Additionally, more geographically distant sites harbored less similar communities. Variance partitioning analysis (VPA) showed that geographic distance contributed more to the variation of Geobacteraceae than any other factor, although the environmental factors explained more variation when combined. So, we detected the uneven distribution of Geobacteraceae in paddy soils of China and demonstrated that Geobacteraceae community composition was strongly associated with geographic distance and soil chemical factors including aFe, pH, Fe, DOC, C:N, and NO₃ ^?-N. These results greatly expand the knowledge of the distribution of Geobacteraceae in environments, particularly in terrestrial ecosystems.

Conclusions

Our results showed that geographic distance and amorphous iron played important roles in shaping Geobacteraceae community composition and revealed that both geographic distance and soil properties governed Geobacteraceae biogeography in paddy soils. Our findings will be critical in facilitating the prediction of element cycling by incorporating information on functional microbial communities into current biogeochemical models.

     

Characteristics of Organic Carbon Changes in Brown Earth under 37-year Long-Term Fertilization

To investigate the impacts of different fertilization on characteristics of organic carbon (OC) changes in brown earth (Hapli-Udic Cambisol), an experiment was conducted with long-term located fertilization experiment from 1979–2015. The experiment field divided into chemical fertilization group, low levels of organic manure group and high levels of organic manure group. The results showed that: the OC was mainly stored in >1.0 mm size aggregates. As the organic fertilizers application grew, the mass percentage of the water-stable aggregates (WSA) for >1.0 mm aggregates significantly increased by 2.3–30.1 times and when the organic and inorganic fertilizers were combined to be applied, the mass percentage of >2.0 mm aggregates and carbon preservation capacity (CPC) increased significantly. Over 37 years of fertilization, the organic carbon concentration, stock and rate of change in brown soil presented the following rank: high-levels of organic manures group > low-levels of organic manures group> chemical fertilization group. Based on the experimental data over the last 37 years, we examined the relationship between total carbon input and the change of organic carbon stock, and constructed a curve: y = 0.153x–0.129.     

Microbial and Physico-chemical Characteristics Associated with the Incidence of <Emphasis Type="Italic">Legionella</Emphasis> spp. and <Emphasis Type="Italic">Acanthamoeba</Emphasis> spp. in Rainwater Harvested from Different Roofing Materials

The incidence of Legionella and Acanthamoeba spp. was correlated to microbial indicator analysis and physico-chemical characteristics of rainwater harvested from catchment areas constructed from galvanized zinc, Chromadek®, and asbestos, respectively. Quantitative PCR (qPCR) analysis indicated that no significant difference (p?>?0.05) in copy numbers of Legionella spp. and Acanthamoeba spp. was recorded in tank water samples collected from the respective roofing materials. However, significant positive Spearman (ρ) correlations were recorded between the occurrences of Legionella spp. gene copies vs. nitrites and nitrates (p?=?0.05) in all tank water samples. Significant positive correlations were also established between Acanthamoeba spp. vs. barium (p?=?0.03), magnesium (p?=?0.02), sodium (p?=?0.02), silicon (p?=?0.05), arsenic (p?=?0.03), and phosphate (p?=?0.01), respectively. Additionally, while no significant correlations were observed between Legionella spp. vs. the indicator bacteria (p?>?0.05), positive correlations were observed between Acanthamoeba spp. vs. total coliforms (p?=?0.01) and Acanthamoeba spp. vs. Escherichia coli (p?=?0.02), respectively. Results obtained in the current study thus indicate that the incidence of Acanthamoeba and Legionella spp. in harvested rainwater was not influenced by the roofing material utilized. Moreover, it is essential that the microbial quality of rainwater be assessed before this water source is implemented for potable and domestic uses as untreated harvested rainwater may lead to legionellosis and amoebae infections.     

<Emphasis Type="Italic">Trichoderma</Emphasis> improves the growth of <Emphasis Type="Italic">Leymus chinensis</Emphasis>

Bio-fertilizer application has been proposed as a strategy for enhancing soil fertility, regulating soil microflora composition, and improving crop yields, and it has been widely applied in the agricultural yields. However, the application of bio-fertilizer in grassland has been poorly studied. We conducted in situ and pot experiments to investigate the practical effects of different fertilization regimes on Leymus chinensis growth, with a focus on the potential microecological mechanisms underlying the responses of soil microbial composition. L. chinensis biomass was significantly (P?<?0.05) increased by treatment with 6000 kg ha^?1 of Trichoderma bio-fertilizer compared with other treatments. We found a positive (R² =?0.6274, P <?0.001) correlation between bacterial alpha diversity and L. chinensis biomass. Hierarchical cluster analysis and nonmetric multidimensional scaling (NMDS) revealed that soil bacterial and fungal community compositions were all separated according to the fertilization regime used. The relative abundance of the most beneficial genera in bio-fertilizer (BOF) (6000 kg ha^?1Trichoderma bio-fertilizer) was significantly higher than in organic fertilizer (OF) (6000 kg ha^?1 organic fertilizer) or in CK (non-amend fertilizer), there the potential pathogenic genera were reduced. There were significant negative (P?<?0.05) correlations between L. chinensis biomass and the relative abundance of several potential pathogenic genera. However, the relative abundance of most beneficial genera were significantly (P?<?0.05) positively correlated with L. chinensis biomass. Soil properties had different effects on these beneficial and on these pathogenic genera, further influencing L. chinensis biomass.     

Land contamination by toxic elements in abandoned mine areas in Italy

Purpose

The present paper concerns the distribution and mobility of heavy metals (Cu, Pb, Zn and Fe) in the soils of some abandoned mine sites in Italy and their transfer to wild flora.

Materials and methods

Soils and plants were sampled from mixed sulphide mine dumps in different parts of Italy, and the concentrations of heavy metals were determined.

Results and discussion

The phytoremediation ability of Salix species (Salix eleagnos, Salix purpurea and Salix caprea), Taraxacum officinale and P?lantago major for heavy metals and, in particular, zinc was estimated. The results showed that soils affected by mining activities presented total Zn, Cu, Pb and Fe concentrations above the internationally recommended permissible limits. A highly significant correlation occurred between metal concentrations in soils.

Conclusions

The obtained results confirmed the environmental effects of mine waste; exploring wild flora ability to absorb metals, besides metal exploitation, proved a useful tool for planning possible remediation projects.

     

Effect of Cadmium Stress on Growth and Electrical Impedance Spectroscopy Parameters of <Emphasis Type="Italic">Cotinus coggygria</Emphasis> Roots

The use of plants for ecological remediation is an important method of controlling heavy metals in polluted land. Cotinus coggygria is a landscape plant that is used extensively in landscaping and afforestation. In this study, the cadmium tolerance level of C. coggygria was evaluated using electrical impedance spectroscopy (EIS) to lay a theoretical foundation for broad applications of this species in Cd-polluted areas and provide theoretical support to broaden the application range of the EIS technique. Two-year-old potted seedlings of C. coggygria were placed in a greenhouse to analyse the changes in the growth, water content and EIS parameters of the roots following treatment with different Cd concentrations (50, 100, 200, 500, 1000 and 1500 mg kg^?1), and soil without added Cd was used as the control. The roots grew well following Cd treatments of 50 and 100 mg kg^?1. The Cd contents increased with the increase in Cd concentration in the soil. However, the lowest root Cd content was found at 4 months of treatment. The extracellular resistance r_e and the intracellular resistance r_i increased first overall and then decreased with the increasing Cd concentration, and both parameters increased with a longer treatment duration. The water content had a significant negative correlation with the Cd content (P?<?0.01) and the r_e (P?<?0.05). C. coggygria could tolerate a soil Cd concentration of 100 mg kg^?1. There was a turning point in the growth, water content and EIS parameters of the C. coggygria roots when the soil Cd concentration reached 200 mg kg^?1. The root water content and r_e could reflect the level of Cd tolerance in C. coggygria.     

Study Potential of Indigenous <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> and <Emphasis Type="Italic">Bacillus subtilis</Emphasis> in Bioremediation of Diesel-Contaminated Water

Petroleum products which are used in a wide variety of industries as energy sources and raw materials have become a major concern in pollution of terrestrial and marine environments. The purpose of this study was to assess the potential of indigenous microbial isolates for degradation of diesel fuel. Two most proficient bacterial strains among five isolated strains from polluted soil of an industrial refinery were studied. The isolates then were identified as Pseudomonas aeruginosa and Bacillus subtilis using biochemical tests and 16S rRNA gene sequence analyses. P. aeruginosa showed higher biodegradation efficiency than B. subtilis in shaking flask containing diesel-contaminated water. P. aeruginosa and B. subtilis degraded about 87 and 75% of total hydrocarbons, respectively, in flasks containing 2% diesel and 98% water. The biodegradation efficiency of the isolates decreased as diesel contamination increased from 2 to 5%. The isolates showed significantly higher efficiency on degradation of short-chain hydrocarbons in 20 days, i.e., by using P. aeruginosa, removal efficiency of C₁₀ hydrocarbons was near 90%, while about 69% of C₂₀₊ hydrocarbons and 47% of aromatic hydrocarbons were removed. Therefore, the isolates showed high capability in biodegradation of diesel contamination of the refinery.     

Effect of the Simultaneous Action of Zinc and Chromium on <Emphasis Type="Italic">Arthrobacter</Emphasis> spp.

Bacteria are regarded as the most effective in the detoxification of heavy metals, being environmental compatible. Metalloresistant bacteria are usually found in nature in highly contaminated environment where they interact with a combination of several toxic metals. For the present research, Arthrobacter oxydans and Arthrobacter globiformis have been isolated from the soil samples of the most polluted regions of Georgia, rich with manganese and iron, and contain co-produced toxic metals such as Cr, V, Zn, Ni, Pb, and Mo. We have studied the effects of the metals with different valence/charge on the metalloresistant Arthrobacter spp., the divalent cation—Zn(II) and the hexavalent anion—Cr(VI). The permanent presence of a nontoxic concentration of zinc alone or zinc together with the subtoxic concentration of chromium at the growth of A. oxydans and A. globiformis as batch culture causes the activation of the zinc primary uptake system transporters from the ZIP family (Zrt1). Chromium does not affect the process. The studied Arthrobacter spp. differ by the character of the activation of the antioxidant defense system. Chromium and zinc concomitant action causes the strongest oxidative stress in the case of A. globiformis that is demonstrated by the increased activity of superoxide dismutase (SOD) and catalase. In the case of A. oxydans, the zinc separate action, and the joint action of zinc and chromium decreases the activity of SOD and catalase. The antioxidant system is active in A. globiformis at the prolonged action of metals (96 h), whereas the cells of A. oxyidans activate the other defense mechanisms to survive.     

Restoration of Vegetation in Relation to Soil Properties of Spoil Heap Heavily Contaminated with Heavy Metals

The main objectives of our study were to evaluate soil contamination on a zinc-lead spoil heap in the Upper Silesian Industrial Region in southern Poland using pollution indices, and to investigate the relation between soil properties and the natural succession of vegetation. Organic carbon and nitrogen, pH, soil texture, base cations, and heavy metal content were analyzed in soil samples at depths of 0–15 cm below the organic horizon over a regular grid of 14 sampling plots. The contents of Zn, Pb, and Cd exceeded by several times the acceptable thresholds. Measurements of soil enzyme activity were used to evaluate the progress of vegetation development in relation to soil chemical properties. The results indicate that heavy metals had a significant impact on soil enzyme activity and the development of vegetation cover. High contents of Pb and Cd reduced enzyme activity, while this activity increased with increasing amounts of soil organic matter. Further, the accumulative capacities of heavy metals in needles of Scots pine (Pinus sylvestris L.) and aboveground biomass of bladder campion (Silene vulgaris (Moench) Garcke) were examined. A high accumulation of Zn, Pb, and Cd in the aboveground tissues of S. vulgaris indicated an unusual tolerance of this species to heavy metals and the possibility of using this species in phytoremediation of post-industrial sites.     

Assessment of heavy metal tolerance in two plant species growing in experimental disturbed polluted urban soil

Purpose

Urban soil, which is strongly influenced by anthropogenic activities, receives a major proportion of trace metal wastes. The aim of this work was to determine heavy metal concentration in (a) soil, to know the degree of the soil pollution; (b) roots and leaves of two plant species, Brassica juncea as an accumulator plant and Solanum lycopersicum as a crop plant; and (c) drainage water, to evaluate the heavy metal mobility.

Materials and methods

The study area is located in Sants, a neighborhood in Barcelona (Catalonia, Spain). Thirty kilograms of two representative soil depths (0–15 and 15–40 cm) was sampled and subsequently mixed. The two studied species were cultivated for 3 weeks in greenhouse conditions, and all pots were irrigated with water weekly to field capacity with a nutrient solution (pH = 6.5). If not otherwise stated, given results are means ± standard deviation of four replicated pots each with a composite sample of 12 individual plants per treatment. X-ray fluorescence (FRX) and diethylenetriaminepentaacetic acid soil extraction (DTPA) were used for total and available metal soil contents, respectively. Weekly cumulative drainage water of each pot was collected in polyethylene bottles and stored at 4 °C until analysis.

Results and discussion

The main pollutants are Cu, Pb, and Zn with topsoil total concentrations of approximately 1355, 2230, and 6239 mg kg^?1, respectively. The same soil elements for available fractions were slightly elevated (9.6, 5.8, and 6.7% of total concentration). The concentrations of Cu, Pb, and Zn in the plants’ leaves are greater in B. juncea than in S. lycopersicum. Furthermore, they are greater in the roots than in leaves. The Pb concentrations in a crop plant exceeded the 0.10 mg kg^?1 limit established for vegetables devoted for food in the European legislation. Unusually elevated concentrations of Pb (over 10 μg L^?1) were detected in the drainage water. These values exceeded the acceptable toxic concentrations in waters, according to the Spanish legislation.

Conclusions

The urban soil studied was highly contaminated by Cu, Pb, and Zn, and this pollution is more evident in the topsoil. A great part of these heavy metals was bioavailable for plants. Thus, the two plants (S. lycopersicum and B. juncea) had an ability to transport heavy metals from the roots to the shoots, especially for Zn. Great contents of heavy metals in the drainage water after the irrigation of plants were observed.

     

Geochemical monitoring of organic and inorganic pollutants in the sediment of the Eastern Posavina (Serbia)

Purpose

The aim of this study was to obtain a complete picture of the geochemical character of the sediment in the eastern Posavina region, Serbia, an area which has thus far not been systematically investigated. Geological mapping and impact assessment were thus carried out for this area.

Materials and methods

Sediments were sampled (from 0 to 0.5 m depth) in four locations in eastern Posavina between 2002 and 2014. Eight heavy metals (Ni, Zn, Cd, Cr, Cu, Pb, As and Hg) and a wide variety of organic parameters (16 EPA polycyclic aromatic hydrocarbons (PAHs), mineral oils, selected pesticides and polychlorinated biphenyls (PCBs)) were monitored. Metals were analysed by flame and graphite atomic absorption spectrometry, and gas chromatography with mass detection was used for the PAH analyses. The origins of the monitored substances were classified using geoaccumulation index (I _geo), ecological risk index (RI) and principal component analysis (PCA/FA).

Results and discussion

The sediments all contained higher heavy metals concentrations than the upper continental crust (UCC), suggesting dynamic natural and anthropogenic processes in this unique region. Significant variations (RSD values from 13 to 190) were observed for Cd (0.001–80.00 mg kg^?1), Hg (0.01–5.40 mg kg^?1), mineral oil (2.00–1851 mg kg^?1) and the sum of 16 EPA PAHs (0.003–5.57 mg kg^?1). The I _geo index classified the pollution risk due to Cr as strong, Cd, Zn and Hg as moderate to strong and Ni as moderate. Based on PCA/FA analysis, the parameters were grouped somewhat differently, with anthropogenic activity found to be responsible for much of the Hg, Cd and Cr pollution present in the sediments.

Conclusions

The analysis revealed eight heavy metals (Ni, Zn, Cd, Cr, Cu, Pb, As and Hg), the sum of 16 EPA PAHs and mineral oil as parameters of great interest for this unique region. These parameters must be the focus of future monitoring programs, in support of appropriate remediation techniques and/or dredging activities, which are required in order to comply with the new Serbian regulations and the relevant EU recommendations.

     

Predicting soil loss in central and south Italy with a single USLE-MM model

Purpose

The USLE-MM estimates event normalized plot soil loss, A_e,N, by an erosivity term given by the runoff coefficient, Q_R, times the single-storm erosion index, EI₃₀, raised to an exponent b₁?>?1. This modeling scheme is based on an expected power relationship, with an exponent greater than one, between event sediment concentration, C_e, and the EI₃₀/P_e (P_e = rainfall depth) term. In this investigation, carried out at the three experimental sites of Bagnara, Masse, and Sparacia, in Italy; the soundness of the USLE-MM scheme was tested.

Materials and methods

A total of 1192 (A_e,N, Q_REI₃₀) data pairs were used to parameterize the model both locally and considering all sites simultaneously. The performances of the fitted models were established by considering all erosive events and also by distinguishing between events of different severity.

Results and discussion

The b₁ exponent varied widely among the three sites (1.05–1.44) but using a common exponent (1.18) for these sites was possible. The A_e,N prediction accuracy increased in the passage from the smallest erosion events (A_e,N?≤?1 Mg ha^?1, median error =?3.35) to the largest ones (A_e,N?>?10 Mg ha^?1, median error =?1.72). The Q_REI₃₀ term was found to be usable to predict both A_e,N and the expected maximum uncertainty of this prediction. Soil erodibility was found to be mainly controlled by the largest erosion events.

Conclusions

Development of a single USLE-MM model appears possible. Sampling other sites is advisable to develop a single USLE-MM model for a general use.