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1.  The Chemophytostabilisation Process of Heavy Metal Polluted Soil 
PLoS ONE  2015;10(6):e0129538.
Industrial areas are characterised by soil degradation processes that are related primarily to the deposition of heavy metals. Areas contaminated with metals are a serious source of risk due to secondary pollutant emissions and metal leaching and migration in the soil profile and into the groundwater. Consequently, the optimal solution for these areas is to apply methods of remediation that create conditions for the restoration of plant cover and ensure the protection of groundwater against pollution. Remediation activities that are applied to large-scale areas contaminated with heavy metals should mainly focus on decreasing the degree of metal mobility in the soil profile and metal bioavailability to levels that are not phytotoxic. Chemophytostabilisation is a process in which soil amendments and plants are used to immobilise metals. The main objective of this research was to investigate the effects of different doses of organic amendments (after aerobic sewage sludge digestion in the food industry) and inorganic amendments (lime, superphosphate, and potassium phosphate) on changes in the metals fractions in soils contaminated with Cd, Pb and Zn during phytostabilisation. In this study, the contaminated soil was amended with sewage sludge and inorganic amendments and seeded with grass (tall fescue) to increase the degree of immobilisation of the studied metals. The contaminated soil was collected from the area surrounding a zinc smelter in the Silesia region of Poland (pH 5.5, Cd 12 mg kg-1, Pb 1100 mg kg-1, Zn 700 mg kg-1). A plant growth experiment was conducted in a growth chamber for 5 months. Before and after plant growth, soil subsamples were subjected to chemical and physical analyses. To determine the fractions of the elements, a sequential extraction method was used according to Zeien and Brümmer. Research confirmed that the most important impacts on the Zn, Cd and Pb fractions included the combined application of sewage sludge from the food industry and the addition of lime and potassium phosphate. Certain doses of inorganic additives decreased the easily exchangeable fraction from 50% to 1%. The addition of sewage sludge caused a decrease in fraction I for Cd and Pb. In combination with the use of inorganic additives, a mobile fraction was not detected and an easily mobilisable fraction was reduced by half. For certain combinations of metals, the concentrations were detected up to a few percent. The application of sewage sludge resulted in a slight decrease in a mobile (water soluble and easily exchangeable metals) fraction of Zn, but when inorganic additives were applied, this fraction was not detected. The highest degree of immobilisation of the tested heavy metals relative to the control was achieved when using both sewage sludge and inorganic additives at an experimentally determined dose. The sequential extraction results confirmed this result. In addition, the results proved that the use of the phytostabilisation process on contaminated soils should be supported.
doi:10.1371/journal.pone.0129538
PMCID: PMC4482681  PMID: 26115341
2.  Microbial production of surfactants and their commercial potential. 
Many microorganisms, especially bacteria, produce biosurfactants when grown on water-immiscible substrates. Biosurfactants are more effective, selective, environmentally friendly, and stable than many synthetic surfactants. Most common biosurfactants are glycolipids in which carbohydrates are attached to a long-chain aliphatic acid, while others, like lipopeptides, lipoproteins, and heteropolysaccharides, are more complex. Rapid and reliable methods for screening and selection of biosurfactant-producing microorganisms and evaluation of their activity have been developed. Genes involved in rhamnolipid synthesis (rhlAB) and regulation (rhlI and rhlR) in Pseudomonas aeruginosa are characterized, and expression of rhlAB in heterologous hosts is discussed. Genes for surfactin production (sfp, srfA, and comA) in Bacillus spp. are also characterized. Fermentative production of biosurfactants depends primarily on the microbial strain, source of carbon and nitrogen, pH, temperature, and concentration of oxygen and metal ions. Addition of water-immiscible substrates to media and nitrogen and iron limitations in the media result in an overproduction of some biosurfactants. Other important advances are the use of water-soluble substrates and agroindustrial wastes for production, development of continuous recovery processes, and production through biotransformation. Commercialization of biosurfactants in the cosmetic, food, health care, pulp- and paper-processing, coal, ceramic, and metal industries has been proposed. However, the most promising applications are cleaning of oil-contaminated tankers, oil spill management, transportation of heavy crude oil, enhanced oil recovery, recovery of crude oil from sludge, and bioremediation of sites contaminated with hydrocarbons, heavy metals, and other pollutants. Perspectives for future research and applications are also discussed.
PMCID: PMC232600  PMID: 9106364
3.  Assessing potential dietary toxicity of heavy metals in selected vegetables and food crops*  
Heavy metals, such as cadmium, copper, lead, chromium and mercury, are important environmental pollutants, particularly in areas with high anthropogenic pressure. Their presence in the atmosphere, soil and water, even in traces can cause serious problems to all organisms, and heavy metal bioaccumulation in the food chain especially can be highly dangerous to human health. Heavy metals enter the human body mainly through two routes namely: inhalation and ingestion, ingestion being the main route of exposure to these elements in human population. Heavy metals intake by human populations through food chain has been reported in many countries. Soil threshold for heavy metal toxicity is an important factor affecting soil environmental capacity of heavy metal and determines heavy metal cumulative loading limits. For soil-plant system, heavy metal toxicity threshold is the highest permissible content in the soil (total or bioavailable concentration) that does not pose any phytotoxic effects or heavy metals in the edible parts of the crops does not exceed food hygiene standards. Factors affecting the thresholds of dietary toxicity of heavy metal in soil-crop system include: soil type which includes soil pH, organic matter content, clay mineral and other soil chemical and biochemical properties; and crop species or cultivars regulated by genetic basis for heavy metal transport and accumulation in plants. In addition, the interactions of soil-plant root-microbes play important roles in regulating heavy metal movement from soil to the edible parts of crops. Agronomic practices such as fertilizer and water managements as well as crop rotation system can affect bioavailability and crop accumulation of heavy metals, thus influencing the thresholds for assessing dietary toxicity of heavy metals in the food chain. This paper reviews the phytotoxic effects and bioaccumulation of heavy metals in vegetables and food crops and assesses soil heavy metal thresholds for potential dietary toxicity.
doi:10.1631/jzus.2007.B0001
PMCID: PMC1764924  PMID: 17173356
Heavy metals; Dietary toxicity; Vegetables; Food crops
4.  Bioremediation of multi-metal contaminated soil using biosurfactant — a novel approach 
Indian Journal of Microbiology  2008;48(1):142-146.
An unconventional nutrient medium, distillery spent wash (1:3) diluted) was used to produce di-rhamnolipid biosurfactant by Pseudomonas aeruginosa strain BS2. This research further assessed the potential of the biosurfactant as a washing agent for metal removal from multimetal contaminated soil (Cr-940 ppm; Pb-900 ppm; Cd-430 ppm; Ni-880 ppm; Cu-480 ppm). Out of the treatments of contaminated soil with tap water and rhamnolipid biosurfactant, the latter was found to be potent in mobilization of metal and decontamination of contaminated soil. Within 36 hours of leaching study, di-rhamnolipid as compared to tap water facilitated 13 folds higher removal of Cr from the heavy metal spiked soil whereas removal of Pb and Cu was 9–10 and 14 folds higher respectively. Leaching of Cd and Ni was 25 folds higher from the spiked soil. This shows that leaching behavior of biosurfactant was different for different metals. The use of wastewater for production of biosurfactant and its efficient use in metal removal make it a strong applicant for bioremediation.
doi:10.1007/s12088-008-0014-5
PMCID: PMC3450211  PMID: 23100708
Pseudomonas aeruginosa; Rhamnolipid Biosurfactant; Distillary waste; Metals; Column studies
5.  Reclamation of tannery polluted soil through phytoremediation 
The huge volume of sludge emanating from the tannery effluent treatment plants poses a serious environmental problem. Phytoremediation is an emerging technology in which the plants are employed to reclamate the contaminated soil strewn with heavy metals (metalloids) and toxic compounds. This work focuses the impact of application of tannery sludge on biochemical properties of 6 months old tree saplings of Azadirachta indica A. Juss. (Neem), Melia azedarach Linn. (Wild Neem) and Leucaena leucocephala (Lam) de Wit (Subabool) raised over the tannery sludge in an attempt to use these plants for phytoremediation. The plants raised over the garden soil served as the control. The porosity and water holding capacity of the tannery sludge were higher. The plant growth supporting elements such as Ca, total N2, NO3 and Mg were higher in the sludge. The plants raised over the sludge were found to be dark green with increased morphometric parameters. Electrophoretic profile revealed amplification of a few polypeptides (100, 105, 49 and 55 KDa). The levels of biomolecules and the CO2 absorption increased in 6 months old plants. There was a significant uptake and transport of chromium in all the three tree species suggesting that these plants could be employed in phytoremediation of soils contaminated with heavy metals.
doi:10.1007/s12298-009-0020-z
PMCID: PMC3550371  PMID: 23572927
Azadirachta indica (Neem); CO2 uptake; Leucaena leucocephala (Subabool); Melia azedarach (Wild Neem); metalloids; Phytoremediation; Stress biomolecules; Tannery sludge
6.  Diversity of Arbuscular Mycorrhizal Fungus Populations in Heavy-Metal-Contaminated Soils 
High concentrations of heavy metals have been shown to adversely affect the size, diversity, and activity of microbial populations in soil. The aim of this work was to determine how the diversity of arbuscular mycorrhizal (AM) fungi is affected by the addition of sewage-amended sludge containing heavy metals in a long-term experiment. Due to the reduced number of indigenous AM fungal (AMF) propagules in the experimental soils, several host plants with different life cycles were used to multiply indigenous fungi. Six AMF ecotypes were found in the experimental soils, showing consistent differences with regard to their tolerance to the presence of heavy metals. AMF ecotypes ranged from very sensitive to the presence of metals to relatively tolerant to high rates of heavy metals in soil. Total AMF spore numbers decreased with increasing amounts of heavy metals in the soil. However, species richness and diversity as measured by the Shannon-Wiener index increased in soils receiving intermediate rates of sludge contamination but decreased in soils receiving the highest rate of heavy-metal-contaminated sludge. Relative densities of most AMF species were also significantly influenced by soil treatments. Host plant species exerted a selective influence on AMF population size and diversity. We conclude based on the results of this study that size and diversity of AMF populations were modified in metal-polluted soils, even in those with metal concentrations that were below the upper limits accepted by the European Union for agricultural soils.
PMCID: PMC91085  PMID: 9925606
7.  Long-Term Effects of Metal-Rich Sewage Sludge Application on Soil Populations of Bradyrhizobium japonicum 
The application of sewage sludge to land may increase the concentration of heavy metals in soil. Of considerable concern is the effect of heavy metals on soil microorganisms, especially those involved in the biocycling of elements important to soil productivity. Bradyrhizobium japonicum is a soil bacterium involved in symbiotic nitrogen fixation with Glycine max, the common soybean. To examine the effect of metal-rich sludge application on B. japonicum, the MICs for Pb, Cu, Al, Fe, Ni, Zn, Cd, and Hg were determined in minimal media by using laboratory reference strains representing 11 common serogroups of B. japonicum. Marked differences were found among the B. japonicum strains for sensitivity to Cu, Cd, Zn, and Ni. Strain USDA 123 was most sensitive to these metals, whereas strain USDA 122 was most resistant. In field studies, a silt loam soil amended 11 years ago with 0, 56, or 112 Mg of digested sludge per ha was examined for total numbers of B. japonicum by using the most probable number method. Nodule isolates from soybean nodules grown on this soil were serologically typed, and their metal sensitivity was determined. The number of soybean rhizobia in the sludge-amended soils was found to increase with increasing rates of sludge. Soybean rhizobia strains from 11 serogroups were identified in the soils; however, no differences in serogroup distribution or proportion of resistant strains were found between the soils. Thus, the application of heavy metal-containing sewage sludge did not have a long-term detrimental effect on soil rhizobial numbers, nor did it result in a shift in nodule serogroup distribution.
PMCID: PMC203658  PMID: 16347281
8.  A pilot plant for removing chromium from residual water of tanneries. 
Environmental Health Perspectives  1995;103(Suppl 1):63-65.
The purpose of this study is to develop a technical process for removing trivalent chromium from tannery wastewater via precipitation. This process can be considered an alternative that avoids a remediation procedure against the metal presence in industrial wastes. This process was verified in a treatment pilot plant located in León, México handling 10 m3/day of three types of effluents. The effluent streams were separated to facilitate the elimination of pollutants from each one. The process was based on in situ treatment and recycle to reduce problems associated with transportation and confinement of contaminated sludges. Two types of treatment were carried out in the pilot plant: The physical/chemical and biological treatments. Thirty-five experiments were conducted and the studied variables were the pH, type of flocculant, and its dose. The statistical significance of chromium samples was 94.7% for its precipitation and 99.7% for recovery. The objectives established for this phase of the development were accomplished and the overall efficiencies were measured for each stage in the pilot plant. The results were: a) chromium precipitation 99.5% from wastewater stream, b) chromium recovery 99% for recycling, and c) physical/chemical treatment to eliminate grease and fat at least 85% and 65 to 70% for the biological treatment. The tanning of a hide lot (350 pieces) was accomplished using 60% treated and recycled water without affecting the product quality. The recovered chromium liquor was also used in this hide tanning. This technical procedure is also applicable for removing heavy metals in other industrial sectors as well as in reducing water consumption rates, if pertinent adjustments are implemented.
PMCID: PMC1519324  PMID: 7621802
9.  Heavy metals removal from aqueous environments by electrocoagulation process– a systematic review 
Heavy metals pollution has become a more serious environmental problem in the last several decades as a result releasing toxic materials into the environment. Various techniques such as physical, chemical, biological, advanced oxidation and electrochemical processes were used for the treatment of domestic, industrial and agricultural effluents. The commonly used conventional biological treatments processes are not only time consuming but also need large operational area. Accordingly, it seems that these methods are not cost-effective for effluent containing toxic elements. Advanced oxidation techniques result in high treatment cost and are generally used to obtain high purity grade water. The chemical coagulation technique is slow and generates large amount of sludge. Electrocoagulation is an electrochemical technique with many applications. This process has recently attracted attention as a potential technique for treating industrial wastewater due to its versatility and environmental compatibility. This process has been applied for the treatment of many kinds of wastewater such as landfill leachate, restaurant, carwash, slaughterhouse, textile, laundry, tannery, petroleum refinery wastewater and for removal of bacteria, arsenic, fluoride, pesticides and heavy metals from aqueous environments. The objective of the present manuscript is to review the potential of electrocoagulation process for the treatment of domestic, industrial and agricultural effluents, especially removal of heavy metals from aqueous environments. About 100 published studies (1977–2016) are reviewed in this paper. It is evident from the literature survey articles that electrocoagulation are the most frequently studied for the treatment of heavy metal wastewater.
doi:10.1186/s40201-015-0233-8
PMCID: PMC4624377  PMID: 26512324
Electrocoagulation; Wastewater treatment; Heavy metals removal
10.  Compacted Sewage Sludge as a Barrier for Tailings: The Heavy Metal Speciation and Total Organic Carbon Content in the Compacted Sludge Specimen 
PLoS ONE  2014;9(6):e100932.
Acid mine drainage (AMD) was the main environmental problem facing the mining industry. For AMD had high heavy metals content and low pH, the compacted sewage sludge might be a barrier for tailings whose oxidation and weathering produced AMD, with its own carbon source, microorganism reduction ability and impermeability. To study the heavy metals environmental risk, under the simulate AMD, the deionized water (DW), and the pH 2.1 sulfuric acid water (SA) seepage conditions, respectively, the changes of the chemical speciation of heavy metals Cd, Cu, Fe, Ni, Zn and total organic carbon (TOC) content in the compacted sewage sludge were assessed in the different periods. The results indicated according to the distribution of heavy metals, the potential mobility was for Cd: 6.08 under AMD, 7.48 under SA, ∞ under DW; for Cu: 0.08 under AMD, 0.17 under SA, 0.59 under DW; for Fe: 0.15 under AMD, 0.22 under SA, 0.22 under DW; for Ni: 2.60 under AMD, 1.69 under SA, 1.67 under DW; and for Zn: 0.15 under AMD, 0.23 under SA and 0.21 under DW at the second checking time. TOC content firstly decreased from 67.62±0% to 66.29±0.35%, then increased to 67.74±0.65% under the AMD seepage while TOC decreased to 63.30±0.53%, then to 61.33±0.37% under the DW seepage, decreased to 63.86±0.41%, then to 63.28±0.49% under SA seepage. That indicated under the AMD seepage, the suitable microorganisms communities in the compacted sewage sludge were activated. And the heavy metals environmental risk of compacted sewage sludge was lower with AMD condition than with other two. So the compacted sewage sludge as a barrier for tailings was feasible as the aspect of environmental risk assessment.
doi:10.1371/journal.pone.0100932
PMCID: PMC4076238  PMID: 24979755
11.  Evaluation and Source Apportionment of Heavy Metals (HMs) in Sewage Sludge of Municipal Wastewater Treatment Plants (WWTPs) in Shanxi, China 
Heavy metals (HMs) in sewage sludge have become the crucial limiting factors for land use application. Samples were collected and analyzed from 32 waste water treatment plants (WWTPs) in the Shanxi Province, China. HM levels in sewage sludge were assessed. The multivariate statistical method principal component analysis (PCA) was applied to identify the sources of HMs in sewage sludge. HM pollution classes by geochemical accumulation index Igeo and correlation analyses between HMs were also conducted. HMs were arranged in the following decreasing order of mean concentration: Zn > Cu > Cr > Pb > As > Hg > Cd; the maximum concentrations of all HMs were within the limit of maximum content permitted by Chinese discharge standard. Igeo classes of HMs pollution in order from most polluted to least were: Cu and Hg pollution were the highest; Cd and Cr pollution were moderate; Zn, As and Pb pollution were the least. Sources of HM contamination in sewage sludge were identified as three components. The primary contaminant source accounting for 35.7% of the total variance was identified as smelting industry, coking plant and traffic sources; the second source accounting for 29.0% of the total variance was distinguished as household and water supply pollution; the smallest of the three sources accounting for 16.2% of the total variance was defined as special industries such as leather tanning, textile manufacturing and chemical processing industries. Source apportionment of HMs in sewage sludge can control HM contamination through suggesting improvements in government policies and industrial processes.
doi:10.3390/ijerph121215022
PMCID: PMC4690958  PMID: 26690464
sewage sludge; heavy metals; geoaccumulation index; classes of pollution; principal component analysis; source apportionment; Shanxi
12.  Influence of urban activity in modifying water parameters, concentration and uptake of heavy metals in Typha latifolia L. into a river that crosses an industrial city 
Background
Heavy metals like Cu, Cd, Pb, Ni, Co and Cr can naturally be found almost all over this planet in various amounts. Urban activities such as heavy metal industry, traffic and waste can rapidly increase the metal concentrations in a fresh water ecosystem.
Methods
This study was done in natural conditions to capture as many aspects in heavy metals pollution and bioremediation of Nicolina River, Romania considered a stream model which is under anthropogenic pressure. Water, sediment and leaves samples of Typha latifolia L. were collected during October 2013 and analyzed in order to assess certain heavy metals (Cu, Cd, Pb, Ni, Co and Cr) from each sampling site using GF-HR-CS-AAS with platform. Heavy metals in significant concentrations in cattail samples were correlated with the water parameters to show the possibility to use the cattail leaves as indicators in heavy metals pollution with potential in bioremediation because they can be easily harvested in autumn and this species is spread worldwide.
Results
The levels of metals concentrations in leaves were: Cu > Ni > Cr > Pb > Co knowing that copper is an essential element for plants. The sampling time was important to draw the river diagnosis for heavy metal pollution. The samples were collected, from river, after more than 60 days without rain same as a “human patient” prepared for blood test. Cobalt was considered the metal marker because it was an element with the lowest level of usage in the city. Compared with it only lead, cadmium and copper were used intensively in the industrial activities.
Conclusions
T. latifolia L. can be use as an indicator for the health of the studied stream and it was noticed that the heavy metals were not accumulated, although the metal uptake was influenced by sediments and water parameters. The alkalinity of the studied river acts as an inhibitor in the bioremediation process of cattail for cadmium and copper. Lead was uptake by leaves and the water parameters influenced it but it wasn’t concentrated enough in leaves to propose this species in lead bioremediation process for Nicolina River.
doi:10.1186/s40201-015-0161-7
PMCID: PMC4324655  PMID: 25674352
Bioremediation; Heavy metals; Environmental interactions; Metal uptake; Typha latifolia; Urban activities
13.  Effect of Drying on Heavy Metal Fraction Distribution in Rice Paddy Soil 
PLoS ONE  2014;9(5):e97327.
An understanding of how redox conditions affect soil heavy metal fractions in rice paddies is important due to its implications for heavy metal mobility and plant uptake. Rice paddy soil samples routinely undergo oxidation prior to heavy metal analysis. Fraction distribution of Cu, Pb, Ni, and Cd from paddy soil with a wide pH range was investigated. Samples were both dried according to standard protocols and also preserved under anaerobic conditions through the sampling and analysis process and heavy metals were then sequentially extracted for the exchangeable and carbonate bound fraction (acid soluble fraction), iron and manganese oxide bound fraction (reducible fraction), organic bound fraction (oxidizable fraction), and residual fraction. Fractions were affected by redox conditions across all pH ranges. Drying decreased reducible fraction of all heavy metals. Curesidual fraction, Pboxidizable fraction, Cdresidual fraction, and Niresidual fraction increased by 25%, 33%, 35%, and >60%, respectively. Pbresidual fraction, Niacid soluble fraction, and Cdoxidizable fraction decreased 33%, 25%, and 15%, respectively. Drying paddy soil prior to heavy metal analysis overestimated Pb and underestimated Cu, Ni, and Cd. In future studies, samples should be stored after injecting N2 gas to maintain the redox potential of soil prior to heavy metal analysis, and investigate the correlation between heavy metal fraction distribution under field conditions and air-dried samples.
doi:10.1371/journal.pone.0097327
PMCID: PMC4019631  PMID: 24823670
14.  Heavy metal removal from MSS fly ash by thermal and chlorination treatments 
Scientific Reports  2015;5:17270.
The thermal behavior of heavy metals in the co-incineration of municipal solid waste-sludge incinerator fly ash (MSS fly ash) was studied using a laboratory-scale tube furnace. The results indicate that without the addition of chlorinating agents, temperature was an important parameter and had significantly influenced on heavy metal removal, whereas the residence time had a weak effect. Between 900 and 1000 °C for 60 to 300 min, heavy metals reacted with chloride-inherent in the fly ash, and approximately 80 to 89% of Pb, 48% to 56% of Cd, 27% to 36% of Zn and 6% to 24% of Cu were removed. After the adding chlorinating agents, the evaporation rate of the heavy metals improved dramatically, where the evaporation rates of Cu and Zn were larger than that of Pb and Cd. As the amount of added chlorinating agents increased, the removal rate of heavy metals increased. However, the effect of the type of chlorinating agent on the chlorination of heavy metals differed considerably, where NaCl had the weakest effect on the removal rate of Cu, Cd and Zn. In terms of resource recovery and decontamination, MgCl2 and CaCl2 are the best choices due to their efficient removal of Zn.
doi:10.1038/srep17270
PMCID: PMC4658559  PMID: 26602592
15.  Hazardous solid waste from metallurgical industries. 
Types of land disposed residuals from selected metal smelting and refining industries are described, as are the origin and disposition of land disposed residuals from the primary copper industry as an example. Quantities of land-disposed or stored residuals, including slags, sludges, and dusts, are given per unit of metal production for most primary and secondary metal smelting and refining industries. Assessments of the hazard potential of residuals are given. Present treatment and disposal of residuals are discussed and assessed for health and environmental protection. Possible technologies for protection of ground and surface water contamination are presented. These include lined lagoons, chemical fixation of sludge, and ground sealing. Possibilities of resource recovery from residuals are discussed. Data are presented showing attenuation of heavy metal ions and fluorides in selected soils. The leachability and mobility of smelting and refining residuals constituents, including heavy metals and fluorides, and other potential toxicants in specific soil, geologic, and hydrologic disposal environments must be carefully considered in setting disposal requirements.
PMCID: PMC1637303  PMID: 738242
16.  Distribution of Biosurfactant-Producing Bacteria in Undisturbed and Contaminated Arid Southwestern Soils 
Biosurfactants are a unique class of compounds that have been shown to have a variety of potential applications in the remediation of organic- and metal-contaminated sites, in the enhanced transport of bacteria, in enhanced oil recovery, as cosmetic additives, and in biological control. However, little is known about the distribution of biosurfactant-producing bacteria in the environment. The goal of this study was to determine how common culturable surfactant-producing bacteria are in undisturbed and contaminated sites. A series of 20 contaminated (i.e., with metals and/or hydrocarbons) and undisturbed soils were collected and plated on R2A agar. The 1,305 colonies obtained were screened for biosurfactant production in mineral salts medium containing 2% glucose. Forty-five of the isolates were positive for biosurfactant production, representing most of the soils tested. The 45 isolates were grouped by using repetitive extragenic palindromic (REP)-PCR analysis, which yielded 16 unique isolates. Phylogenetic relationships were determined by comparing the 16S rRNA gene sequence of each unique isolate with known sequences, revealing one new biosurfactant-producing microbe, a Flavobacterium sp. Sequencing results indicated only 10 unique isolates (in comparison to the REP analysis, which indicated 16 unique isolates). Surface tension results demonstrated that isolates that were similar according to sequence analysis but unique according to REP analysis in fact produced different surfactant mixtures under identical growth conditions. These results suggest that the 16S rRNA gene database commonly used for determining phylogenetic relationships may miss diversity in microbial products (e.g., biosurfactants and antibiotics) that are made by closely related isolates. In summary, biosurfactant-producing microorganisms were found in most soils even by using a relatively limited screening assay. Distribution was dependent on soil conditions, with gram-positive biosurfactant-producing isolates tending to be from heavy metal-contaminated or uncontaminated soils and gram-negative isolates tending to be from hydrocarbon-contaminated or cocontaminated soils.
doi:10.1128/AEM.69.6.3280-3287.2003
PMCID: PMC161513  PMID: 12788727
17.  Assessment of Heavy Metals in Municipal Sewage Sludge: A Case Study of Limpopo Province, South Africa 
Heavy metals in high concentrations can cause health and environmental damage. Nanosilver is an emerging heavy metal which has a bright future of use in many applications. Here we report on the levels of silver and other heavy metals in municipal sewage sludge. Five towns in Limpopo province of South Africa were selected and the sludge from their wastewater treatment plants (WWTPs) was collected and analysed. The acid digested sewage sludge samples were analysed using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) methods. The concentrations of silver found were low, but significant, in the range 0.22 to 21.93 mg/kg dry mass. The highest concentration of silver was found in Louis Trichardt town with a concentration of 21.93 ± 0.38 mg/kg dry mass while the lowest was Thohoyandou with a concentration of 6.13 ± 0.12 mg/kg dry mass. A control sludge sample from a pit latrine had trace levels of silver at 0.22 ± 0.01 mg/kg dry mass. The result showed that silver was indeed present in the wastewater sewage sludge and at present there is no DWAF guideline standard. The average Cd concentration was 3.10 mg/kg dry mass for Polokwane municipality. Polokwane and Louis Trichardt municipalities exhibited high levels of Pb, in excess DWAF guidelines, in sludge at 102.83 and 171.87 mg/kg respectfully. In all the WWTPs the zinc and copper concentrations were in excess of DWAF guidelines. The presence of heavy metals in the sewage sludge in excess of DWAF guidelines presents environmental hazards should the sludge be applied as a soil ameliorant.
doi:10.3390/ijerph110302569
PMCID: PMC3986993  PMID: 24595211
heavy metals; sewage sludge; effluent; silver
18.  Interaction of Soil Heavy Metal Pollution with Industrialisation and the Landscape Pattern in Taiyuan City, China 
PLoS ONE  2014;9(9):e105798.
Many studies indicated that industrialization and urbanization caused serious soil heavy metal pollution from industrialized age. However, fewer previous studies have conducted a combined analysis of the landscape pattern, urbanization, industrialization, and heavy metal pollution. This paper was aimed at exploring the relationships of heavy metals in the soil (Pb, Cu, Ni, As, Cd, Cr, Hg, and Zn) with landscape pattern, industrialisation, urbanisation in Taiyuan city using multivariate analysis. The multivariate analysis included correlation analysis, analysis of variance (ANOVA), independent-sample T test, and principal component analysis (PCA). Geographic information system (GIS) was also applied to determine the spatial distribution of the heavy metals. The spatial distribution maps showed that the heavy metal pollution of the soil was more serious in the centre of the study area. The results of the multivariate analysis indicated that the correlations among heavy metals were significant, and industrialisation could significantly affect the concentrations of some heavy metals. Landscape diversity showed a significant negative correlation with the heavy metal concentrations. The PCA showed that a two-factor model for heavy metal pollution, industrialisation, and the landscape pattern could effectively demonstrate the relationships between these variables. The model explained 86.71% of the total variance of the data. Moreover, the first factor was mainly loaded with the comprehensive pollution index (P), and the second factor was primarily loaded with landscape diversity and dominance (H and D). An ordination of 80 samples could show the pollution pattern of all the samples. The results revealed that local industrialisation caused heavy metal pollution of the soil, but such pollution could respond negatively to the landscape pattern. The results of the study could provide a basis for agricultural, suburban, and urban planning.
doi:10.1371/journal.pone.0105798
PMCID: PMC4174504  PMID: 25251460
19.  The Dublin SURGE Project: geochemical baseline for heavy metals in topsoils and spatial correlation with historical industry in Dublin, Ireland 
The Dublin SURGE (Soil Urban Geochemistry) Project is Dublin’s first baseline survey of heavy metals and persistent organic pollutants in topsoils and is part of a Europe-wide initiative to map urban geochemical baselines in ten cities. 1,058 samples were collected as part of a stratified random sampling programme in the greater Dublin area to give an overview of baseline conditions in the city. Samples were analysed for 31 inorganic elements including heavy metals. Analysis of results indicates that the concentrations of lead, copper, zinc and mercury are strongly influenced by human activities, with elevated concentrations in the city docklands, inner city and heavy industry areas. Sources of heavy metals in these areas may include historical industry, coal burning, re-use of contaminated soil, modern traffic and leaded paint and petrol. Concentrations of other inorganic elements in topsoil show patterns which are strongly related to regional bedrock parent material. The spatial distributions of heavy metals, in particular Pb and As, are explored in detail with respect to regional geology and the influence of historical industry on soil quality. Exploratory data, geostatistical and correlation analyses suggest that the concentrations of heavy metals tend to increase as the intensity of historical industrial activity increases. In particular, drinks production, power generation, oil/gas/coal, metals and textile historical industries appear to be the contamination source for several heavy metals. The data provide a geochemical baseline relevant to the protection of human health, compliance with environmental legislation, land use planning and urban regeneration.
doi:10.1007/s10653-013-9561-8
PMCID: PMC3938859  PMID: 23990170
Urban geochemistry; Heavy metals; Soil pollution; Historical industry; Human health
20.  Leachability of Heavy Metals from Lightweight Aggregates Made with Sewage Sludge and Municipal Solid Waste Incineration Fly Ash 
Lightweight aggregate (LWA) production with sewage sludge and municipal solid waste incineration (MSWI) fly ash is an effective approach for waste disposal. This study investigated the stability of heavy metals in LWA made from sewage sludge and MSWI fly ash. Leaching tests were conducted to find out the effects of MSWI fly ash/sewage sludge (MSWI FA/SS) ratio, sintering temperature and sintering time. It was found that with the increase of MSWI FA/SS ratio, leaching rates of all heavy metals firstly decreased and then increased, indicating the optimal ratio of MSWI fly ash/sewage sludge was 2:8. With the increase of sintering temperature and sintering time, the heavy metal solidifying efficiencies were strongly enhanced by crystallization and chemical incorporations within the aluminosilicate or silicate frameworks during the sintering process. However, taking cost-savings and lower energy consumption into account, 1100 °C and 8 min were selected as the optimal parameters for LWA sample- containing sludge production. Furthermore, heavy metal leaching concentrations under these optimal LWA production parameters were found to be in the range of China’s regulatory requirements. It is concluded that heavy metals can be properly stabilized in LWA samples containing sludge and cannot be easily released into the environment again to cause secondary pollution.
doi:10.3390/ijerph120504992
PMCID: PMC4454949  PMID: 25961800
sewage sludge; municipal solid waste incineration fly ash; heavy metals; sludge lightweight aggregate
21.  Bioremediation of Heavy Metals in Liquid Media Through Fungi Isolated from Contaminated Sources 
Indian Journal of Microbiology  2011;51(4):482-487.
Wastewater particularly from electroplating, paint, leather, metal and tanning industries contain enormous amount of heavy metals. Microorganisms including fungi have been reported to exclude heavy metals from wastewater through bioaccumulation and biosorption at low cost and in eco-friendly way. An attempt was, therefore, made to isolate fungi from sites contaminated with heavy metals for higher tolerance and removal of heavy metals from wastewater. Seventy-six fungal isolates tolerant to heavy metals like Pb, Cd, Cr and Ni were isolated from sewage, sludge and industrial effluents containing heavy metals. Four fungi (Phanerochaete chrysosporium, Aspegillus awamori, Aspergillus flavus, Trichoderma viride) also were included in this study. The majority of the fungal isolates were able to tolerate up to 400 ppm concentration of Pb, Cd, Cr and Ni. The most heavy metal tolerant fungi were studied for removal of heavy metals from liquid media at 50 ppm concentration. Results indicated removal of substantial amount of heavy metals by some of the fungi. With respect to Pb, Cd, Cr and Ni, maximum uptake of 59.67, 16.25, 0.55, and 0.55 mg/g was observed by fungi Pb3 (Aspergillus terreus), Trichoderma viride, Cr8 (Trichoderma longibrachiatum), and isolate Ni27 (A. niger) respectively. This indicated the potential of these fungi as biosorbent for removal of heavy metals from wastewater and industrial effluents containing higher concentration of heavy metals.
doi:10.1007/s12088-011-0110-9
PMCID: PMC3209935  PMID: 23024411
Industrial wastewater; Fungi; Biosorbent; Bioaccumulation; Heavy metals
22.  Speciation of Chromium in Soil and Sludge in the Surrounding Tannery Region, Ranipet, Tamil Nadu 
ISRN Toxicology  2011;2011:697980.
The distribution and mobility of chromium in the soils and sludge surrounding a tannery waste dumping area was investigated to evaluate its vertical and lateral movement of operational speciation which was determined in six steps to fractionate the material in the soil and sludge into (i) water soluble, (ii) exchangeable, (iii) carbonate bound, (iv) reducible, (v) oxidizable, and (vi) residual phases. The present study shows that about 63.7% of total chromium is mobilisable, and 36.3% of total chromium is nonbioavailable in soil, whereas about 30.2% of total chromium is mobilisable, and 69.8% of total chromium is non-bioavailable in sludge. In contaminated sites the concentration of chromium was found to be higher in the reducible phase in soils (31.3%) and oxidisable phases in sludge (56.3%) which act as the scavenger of chromium in polluted soils. These results also indicate that iron and manganese rich soil can hold chromium that will be bioavailable to plants and biota. Thus, results of this study can indicate the status of bioavailable of chromium in this area, using sequential extraction technique. So a suitable and proper management of handling tannery sludge in the said area will be urgently needed to the surrounding environment as well as ecosystems.
doi:10.5402/2011/697980
PMCID: PMC3658852  PMID: 23724287
23.  Improving the phytoremediation of heavy metals contaminated soil by use of sewage sludge 
ABSTRACT
Sewage sludge, in particular from the food industry, is characterized by fertilizing properties, due to the high content of organic matter and nutrients. The application of sewage sludge causes an improvement of soil parameters as well as increase in cation exchange capacity, and thus stronger binding of cations in the soil environment, which involves the immobilization of nutrients and greater resistance to contamination. In a field experiment sewage sludge has been used as an additive to the soil supporting the phytoremediation process of land contaminated with heavy metals (Cd, Zn, and Pb) using trees species: Scots pine (Pinus silvestris L.), Norway spruce (Picea abies L.), and oak (Quercus robur L.). The aim of the research was to determine how the application of sewage sludge into the soil surface improves the phytoremediation process. The conducted field experiment demonstrated that selected trees like Scots pine and Norway spruce, because of its excellent adaptability, can be used in the remediation of soil. Oak should not be used in the phytoremediation process of soils contaminated with high concentrations of trace elements in the soil, because a significant amount of heavy metals was accumulated in the leaves of oak causing a risk of recontamination.
doi:10.1080/15226514.2015.1086308
PMCID: PMC4819837  PMID: 26368503
tree species; trace elements; sewage sludge
24.  Highly efficient removal of lead and cadmium during wastewater irrigation using a polyethylenimine-grafted gelatin sponge 
Scientific Reports  2016;6:33573.
Wastewater irrigation is a very important resource for heavy metal pollution in soil and then accumulation in vegetable crops. In this study, a polyethylenimine (PEI)-grafted gelatin sponge was prepared to effectively adsorb heavy metals during wastewater irrigation. Based on the strong water adsorption ability, wastewater remained in the PEI-grafted gelatin sponge for a sufficient time for the heavy metals to interact with the sorbents. The binding capacities of Pb(II) ions and Cd(II) ions on the PEI-grafted gelatin sponge were 66 mg g−1 and 65 mg g−1, which were much more than those on the gelatin sponge (9.75 mg g−1 and 9.35 mg g−1). Subsequently, the PEI-grafted gelatin sponge was spread on the surface of soil planted with garlic and then sprayed with synthetic wastewater. The concentrations of cadmium and lead in the garlic leaves were 1.59 mg kg−1 and 5.69 mg kg−1, respectively, which were much lower than those (15.78 mg kg−1 and 27.98 mg kg−1) without the gelatin sponge, and the removal efficiencies were 89.9% and 79.7%. The PEI-grafting gelatin sponge could effectively remove heavy metals during wastewater irrigation, which improved the soil environment and reduced human exposure to heavy metals.
doi:10.1038/srep33573
PMCID: PMC5025662  PMID: 27633732
25.  Spatial patterns of heavy metals in soil under different geological structures and land uses for assessing metal enrichments 
Environmental Monitoring and Assessment  2013;185(12):9871-9888.
One hundred and thirty composite soil samples were collected from Hamedan county, Iran to characterize the spatial distribution and trace the sources of heavy metals including As, Cd, Co, Cr, Cu, Ni, Pb, V, Zn, and Fe. The multivariate gap statistical analysis was used; for interrelation of spatial patterns of pollution, the disjunctive kriging and geoenrichment factor (EFG) techniques were applied. Heavy metals and soil properties were grouped using agglomerative hierarchical clustering and gap statistic. Principal component analysis was used for identification of the source of metals in a set of data. Geostatistics was used for the geospatial data processing. Based on the comparison between the original data and background values of the ten metals, the disjunctive kriging and EFG techniques were used to quantify their geospatial patterns and assess the contamination levels of the heavy metals. The spatial distribution map combined with the statistical analysis showed that the main source of Cr, Co, Ni, Zn, Pb, and V in group A land use (agriculture, rocky, and urban) was geogenic; the origin of As, Cd, and Cu was industrial and agricultural activities (anthropogenic sources). In group B land use (rangeland and orchards), the origin of metals (Cr, Co, Ni, Zn, and V) was mainly controlled by natural factors and As, Cd, Cu, and Pb had been added by organic factors. In group C land use (water), the origin of most heavy metals is natural without anthropogenic sources. The Cd and As pollution was relatively more serious in different land use. The EFG technique used confirmed the anthropogenic influence of heavy metal pollution. All metals showed concentrations substantially higher than their background values, suggesting anthropogenic pollution.
doi:10.1007/s10661-013-3298-9
PMCID: PMC3825593  PMID: 23797635
Heavy metals; Spatial variability; Land use patterns; Geostatistics; Multivariate statistics; Gap statistical analysis

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