Screening Plant Species for Growth on Weathered,Petroleum Hydrocarbon-Contaminated Sediments

Rapid and cost-effective techniques are needed to select plant species and genotypes for use in phytoremediation, vegetative capping, or revegetation at hazardous waste sites. A greenhouse screening procedure to aid the selection of plant materials would help increase success and decrease the cost. Twenty-nine vascular plant species were compared for growth in weathered sediments contaminated with petroleum hydrocarbons. An uncontaminated reference soil was used to estimate relative seedling growth in stressed and unstressed conditions. Plants were grown in a greenhouse and harvested at 60 and 180 days after planting to estimate variation in seedling growth and full-season growth. Plant growth characteristics measured included height, aboveground biomass, root biomass, root diameter, root-length density, and root surface area density. Concentration of total petroleum hydrocarbons (TPH) was estimated at the final harvest. Considerable variation existed among species for all characteristics except TPH concentration. Under the conditions and length of this trial, no variations in rates of TPH degradation were detected. In general, plant growth was stunted in the contaminated soil compared with the uncontaminated soil; however, differences among plant species for relative seedling growth indicated that they varied in their tolerance to the petroleum hydrocarbon-contaminated soil. For example, tall fescue, Festuca arundinacea, seemed tolerant to the contaminated soil, whereas barley, Hordeum vulgare, seemed sensitive. Comparison of results from the 60- and 180-day harvests suggested that a short-season greenhouse screening could aid selection of species for planting in contaminated soil, if plant growth results are interpreted along with information on the life history characteristics of the species under consideration.     

Association of microbial community composition and activity with lead,chromium, and hydrocarbon contamination

Microbial community composition and activity were characterized in soil contaminated with lead (Pb), chromium (Cr), and hydrocarbons. Contaminant levels were very heterogeneous and ranged from 50 to 16,700 mg of total petroleum hydrocarbons (TPH) kg of soil(-1), 3 to 3,300 mg of total Cr kg of soil(-1), and 1 to 17,100 mg of Pb kg of soil(-1). Microbial community compositions were estimated from the patterns of phospholipid fatty acids (PLFA); these were considerably different among the 14 soil samples. Statistical analyses suggested that the variation in PLFA was more correlated with soil hydrocarbons than with the levels of Cr and Pb. The metal sensitivity of the microbial community was determined by extracting bacteria from soil and measuring [(3)H]leucine incorporation as a function of metal concentration. Six soil samples collected in the spring of 1999 had IC(50) values (the heavy metal concentrations giving 50% reduction of microbial activity) of approximately 2.5 mM for CrO(4)2- and 0.01 mM for Pb2+. Much higher levels of Pb were required to inhibit [14C]glucose mineralization directly in soils. In microcosm experiments with these samples, microbial biomass and the ratio of microbial biomass to soil organic C were not correlated with the concentrations of hydrocarbons and heavy metals. However, microbial C respiration in samples with a higher level of hydrocarbons differed from the other soils no matter whether complex organic C (alfalfa) was added or not. The ratios of microbial C respiration to microbial biomass differed significantly among the soil samples (P < 0.05) and were relatively high in soils contaminated with hydrocarbons or heavy metals. Our results suggest that the soil microbial community was predominantly affected by hydrocarbons.     

Phytoremediation efficiency OF CD by Eucalyptus globulus transplanted from polluted and unpolluted sites

The capacity of plants to uptake heavy metals from contaminated soils has shown great phytoremediation potential. The development, resistibility and Cd extraction of Eucalyptus globulus individuals from metalliferous and clean sites in different years were analyzed under a specific environment. Eucalyptus globulus planted in Guiyu for phytoremediation or cultivated in an uncontaminated, natural environment for economic purposes were transplanted to Yuecheng town, which, in recent years, has been involved in the e-waste dismantling and recycling business, to compare the phytoremediation efficiency of Eucalyptus globulus trees grown in different environments. Trees cultivated in polluted areas can remove far more Cd and Hg from the contaminated soil than the individuals from clean soils because metalliferous Eucalyptus globulus can produce more biomass and uptake more heavy metals than nonmetalliferous plants per year. As polluted environments negatively affect the growth of plants, we speculated that the phytoremediation efficiency of metalliferous Eucalyptus globulus should decrease over time and that nonmetalliferous trees should adapt to the local environment.     

Screening of herbaceous plants for peat-enhanced rehabilitation of contaminated soil with oily sludge

A batch pot experiment using nine herbaceous species were conducted for peat enhanced rehabilitation of contaminated soil with oily sludge in the initial contents of 0%, 1.3%, 7.4%, and 12.2%, respectively. The results showed that petroleum hydrocarbons removal, plant growth indices and enzyme activities varied depending on plant species and oil contents. Cotton, ryegrass and tall fescue were effective in the rehabilitation of oily sludge contaminated soils. The total petroleum hydrocarbon (TPH) removal ranged from 30.0% to 40.0% after 170 days of treatment. Plant biomass was shown to be the preferred indicator for screening phytoremediation plant because it was closely correlated with TPH removal and enzyme activities. Peat-enhanced plant rehabilitation could be a good strategy for the treatment of oily sludge contaminated saline soils.     

Greenhouse and field assessment of phytoremediation for petroleum contaminants in a riparian zone

Greenhouse and field studies were conducted to evaluate the feasibility of phytoremediation for clean-up of highly contaminated sediments from Indiana Harbor. In the greenhouse study, plant species evaluated were willow (Salix exigua), poplar (Populus spp.), eastern gamagrass (Tripsacum dactyloides), arrowhead (Sagitaria latifolia), switchgrass (Panicum virgatum), and sedge (Carex stricta). Sediments with sedge, switchgrass, and gamagrass had significantly less residual total petroleum hydrocarbons (TPH) after one year of growth (approximately 70% reduction) than sediments containing willow, poplar, or no plants (approximately 20% reduction). Although not all polycyclic aromatic hydrocarbons (PAH) had concentration differences due to the presence of plants, residual pyrene concentrations in the unvegetated pots were significantly higher than in pots containing sedge, switchgrass, arrowhead, and gamagrass. As evaluated by TPH dissipation in the upper section of the pots, the sedge, switchgrass, and gamagrass treatments had higher TPH degradation than the unvegetated, willow and poplar treatments. These trends were similar for soil at the bottom of the pots, with the exception that in the switchgrass treatment, degradation was not significantly different than in the unvegetated soil. Two target contaminants, pyrene and benzo[b]fluoranthene, showed differences in degradation between planted and unvegetated treatments. In the field study, phytoremediation plant species were eastern gamagrass (T. dactyloides), switchgrass (P. virgatum), and sedge (C. stricta). In addition, rhizosphere characteristics of arrowhead (S. latifolia) and sedge were assessed. Arrowhead- and sedge-impacted soils were found to contain significantly more PAH-degrading bacteria than unvegetated soils. However, over the 12-month field study, no significant differences in contamination were found between the planted and unplanted soils for TPH and PAH concentrations. TPH concentrations near the canal were greater than concentrations further from the canal, indicating that the canal may have served as a continuous source of contamination during the study.     

Characterization of hydrocarbon-degrading microbial populations in contaminated and pristine Alpine soils

Biodegradation of petroleum hydrocarbons in cold environments, including Alpine soils, is a result of indigenous cold-adapted microorganisms able to degrade these contaminants. In the present study, the prevalence of seven genotypes involved in the degradation of n-alkanes (Pseudomonas putida GPo1 alkB; Acinetobacter spp. alkM; Rhodococcus spp. alkB1, and Rhodococcus spp. alkB2), aromatic hydrocarbons (P. putida xylE), and polycyclic aromatic hydrocarbons (P. putida ndoB and Mycobacterium sp. strain PYR-1 nidA) was determined in 12 oil-contaminated (428 to 30,644 mg of total petroleum hydrocarbons [TPH]/kg of soil) and 8 pristine Alpine soils from Tyrol (Austria) by PCR hybridization analyses of total soil community DNA, using oligonucleotide primers and DNA probes specific for each genotype. The soils investigated were also analyzed for various physical, chemical, and microbiological parameters, and statistical correlations between all parameters were determined. Genotypes containing genes from gram-negative bacteria (P. putida alkB, xylE, and ndoB and Acinetobacter alkM) were detected to a significantly higher percentage in the contaminated (50 to 75%) than in the pristine (0 to 12.5%) soils, indicating that these organisms had been enriched in soils following contamination. There was a highly significant positive correlation (P < 0.001) between the level of contamination and the number of genotypes containing genes from P. putida and Acinetobacter sp. but no significant correlation between the TPH content and the number of genotypes containing genes from gram-positive bacteria (Rhodococcus alkB1 and alkB2 and Mycobacterium nidA). These genotypes were detected at a high frequency in both contaminated (41.7 to 75%) and pristine (37.5 to 50%) soils, indicating that they are already present in substantial numbers before a contamination event. No correlation was found between the prevalence of hydrocarbon-degradative genotypes and biological activities (respiration, fluorescein diacetate hydrolysis, lipase activity) or numbers of culturable hydrocarbon-degrading soil microorganisms; there also was no correlation between the numbers of hydrocarbon degraders and the contamination level. The measured biological activities showed significant positive correlation with each other, with the organic matter content, and partially with the TPH content and a significant negative correlation with the soil dry-mass content (P < 0.05 to 0.001).     

Root development of the Zinc-hyperaccumulator plant Thlaspi caerulescens as affected by metal origin,content and localization in soil

Penetration into and exploitation of contaminated soils by roots of hyperaccumulator plants is a prerequisite for efficient removal of heavy metals, i.e. efficacy of phytoextraction. This work was undertaken to study the development of roots of the Zn-hyperaccumulator Thlaspi caerulescens under various conditions of soil contamination. Rhizoboxes were constructed with a removable plastic front cover, and filled with soils containing different amounts and forms of metals (Zn, Cd and Pb). Treatments were: homogeneous soil profile, superposition of three layers, inclusion of contaminated soil into uncontaminated soil, or inclusion of uncontaminated soil into uniformly contaminated soil. Four seedlings were transplanted into each rhizobox, and development of the root system was periodically recorded for 133 days. At harvest, the biomass and size of the rosette of aerial parts were determined. The aerial biomass/root length fraction as well as the kinetics of root development varied according to the presence and localization of Zn. The distribution and morphology of roots at harvest were strongly dependent upon the metal content and form in soil. Roots exhibited a high affinity for the Zn-contaminated patches and showed two distinct morphologies according to the concentration of Zn in soil. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of Piriformospora indica on the root development of maize (Zea mays L.) and remediation of petroleum contaminated soil

As the depth of soil petroleum contamination can vary substantially under field conditions, a rhizotron experiment was performed to investigate the influence of endophyte, P. indica, on maize growth and degradation of petroleum components in a shallow and a deep-reaching subsurface layer of a soil. For control, a treatment without soil contamination was also included. The degree in contamination and the depth to which it extended had a strong effect on the growth of the plant roots. Contaminated soil layers severely inhibited root growth thus many roots preferred to bypass the shallow contaminated layer and grow in the uncontaminated soil. While the length and branching pattern of these roots were similar to those of uncontaminated treatment. Inoculation of maize with P. indica could improve root distribution and root and shoot growth in all three contamination treatments. This inoculation also enhanced petroleum degradation in soil, especially in the treatment with deep-reaching contamination, consequently the accumulation of petroleum hydrocarbons (PAHs) in the plant tissues were increased.     

Biostimulation and Phytoremediation Treatment Strategies of Gasoline-Nickel Co-Contaminated Soil

This study investigated the potential effect of poultry dung (biostimulation) and stubborn grass (Sporobolus pyramidalis) (phytoremediation) on microbial biodegradation of gasoline and nickel uptake in gasoline-nickel-impacted soil. In addition, the potential stimulatory effects of nickel on hydrocarbon utilization were investigated over a small range of nickel concentrations (2.5–12.5 mg/kg). The results showed that an increase in nickel concentration increased hydrocarbon degraders in soil by a range of 8.4–17.2% and resulted in a relative increase in gasoline biodegradation (57.5–62.4%). Also, under aerobic conditions, total petroleum hydrocarbons’ (TPH) removal was 62.4% in the natural gasoline-nickel microcosm (natural attenuation), and a maximum of 78.5%, 85.7%, and 95.8% TPH removal was obtained in phytoremediation, biostimulation, and a combination of biostimulation- and phytoremediation-treated microcosms, respectively. First-order kinetics described the biodegradation of gasoline and nickel uptake very well. Half-life times obtained were 28.88, 18.24, 14.44, and 8.56 days for gasoline degradation under natural attenuation, phytoremediation, biostimulation, and combined biostimulation and phytoremediation treatment methods, respectively. The results indicate that these remediation methods have promising potential for effective remediation of soils co-contaminated with petroleum hydrocarbons and heavy metals.     

Phytoremediation in the Tropics—The Effect of Crude Oil on the Growth of Tropical Plants

Phytoremediation is a nondestructive, cost-effective in-situ technology to clean up contaminated soils. In the case of contamination with petroleum hydrocarbons, plants enhance microbial degradation of the contaminant in the rhizosphere. The potential of this technology for the tropics should be high due to prevailing climatic conditions favoring plant growth and stimulating microbial activity. Investigations of the potential of tropical plants for phytoremediation, however, are scarce. The present work studied two grasses and six legumes from the eastern savannah of Venezuela on their reaction to crude oil contamination in soil. Results shall help to identify plants with a potential for phytoremediation and subsequent studies. Seedling emergence and biomass production were determined for plants growing in soil contaminated with 0%, 3%, and 5% heavy crude oil. Contamination had, in general, a tendential but not significant negative influence on seedling emergence. Dry matter production was reduced by only a few percent to up to 85%. Furthermore, in some legumes inhibition of nodulation was observed. The grass Brachiaria brizantha and the legumes Centrosema brasilianum and Calopogonium mucunoides are promising for phytoremediation because in contaminated soil they combined high seedling emergence with least affected biomass production. Since they are cultivated forage/soil cover species also in other regions of the tropics, their potential for phytoremediation of petroleum contaminated soils extends beyond Venezuela.     

Compositional changes during landfarming of weathered michigan crude oil‐contaminated soii

Laboratory landfarming experiments were conducted to study the bioremediation potential of weathered Michigan crude oil‐contaminated soils. It was found that landfarming was successful in removing up to 90% of the total petroleum hydrocarbons (TPH) in the soil within 22 weeks of treatment. Boiling point analyses of untreated and treated soils indicate a significant removal of TPH compounds independent of molecular weight or carbon number. Up to 85% of heavy petroleum hydrocarbons with carbon numbers above 44 were biode‐graded. In addition, approximately 93% of saturated and 79% of aromatic compounds of the TPH were biodegraded during the 22 week treatment period. The use of polyethylene sheeting as a landfarm cover does not appear to adversely affect biodegradation kinetics under laboratory conditions. Finally, equilibrium leachate concentrations for BTEX and regulated (in Michigan) polynuclear aromatics (PNAs) were below the respective detection limits for each compound. It can be concluded that landfarming of these weathered soils will be highly successful in removing petroleum hydrocarbons while not adversely impacting either ground‐water or surface water quality.     

Association of Microbial Community Composition and Activity with Lead, Chromium, and Hydrocarbon Contamination

Microbial community composition and activity were characterized in soil contaminated with lead (Pb), chromium (Cr), and hydrocarbons. Contaminant levels were very heterogeneous and ranged from 50 to 16,700 mg of total petroleum hydrocarbons (TPH) kg of soil⁻¹, 3 to 3,300 mg of total Cr kg of soil⁻¹, and 1 to 17,100 mg of Pb kg of soil⁻¹. Microbial community compositions were estimated from the patterns of phospholipid fatty acids (PLFA); these were considerably different among the 14 soil samples. Statistical analyses suggested that the variation in PLFA was more correlated with soil hydrocarbons than with the levels of Cr and Pb. The metal sensitivity of the microbial community was determined by extracting bacteria from soil and measuring [³H]leucine incorporation as a function of metal concentration. Six soil samples collected in the spring of 1999 had IC₅₀ values (the heavy metal concentrations giving 50% reduction of microbial activity) of approximately 2.5 mM for CrO₄²⁻ and 0.01 mM for Pb²⁺. Much higher levels of Pb were required to inhibit [¹⁴C]glucose mineralization directly in soils. In microcosm experiments with these samples, microbial biomass and the ratio of microbial biomass to soil organic C were not correlated with the concentrations of hydrocarbons and heavy metals. However, microbial C respiration in samples with a higher level of hydrocarbons differed from the other soils no matter whether complex organic C (alfalfa) was added or not. The ratios of microbial C respiration to microbial biomass differed significantly among the soil samples (P < 0.05) and were relatively high in soils contaminated with hydrocarbons or heavy metals. Our results suggest that the soil microbial community was predominantly affected by hydrocarbons.     

Phytoremediation Effect and Growth Responses of Cynodon spp. and Agropyron desertorum in a Petroleum-Contaminated Soil

In order to compare the petroleum tolerance and phytoremediation ability of a native grass, Agropyron desertorum (desert Wheatgrass) with Cynodon spp. (Bermuda grass) in a petroleum hydrocarbon-contaminated soil, a 7-month greenhouse experiment was performed. There were 4 soil treatments with 0% (uncontaminated soil), 2%, 4%, and 12% (w_oil/w_soil) petroleum concentration. Parameters including shoot and root fresh weight and dry weight, root penetration depth and root density depth, soil respiration, and total petroleum hydrocarbons (TPH) degradation were measured during and after experiments. The results showed an increase in shoot fresh weight of A. desertorum in soil polluted with 2% petroleum sludge compared to the uncontaminated soil, whereas the growth of Bermuda grass significantly decreased in corresponding treatment. Root growth of A. desertorum was decreased in 2% and 4% petroleum sludge, whereas it was increased in Bermuda grass species. Overall, root fresh weight of Bermuda grass was higher than that of A. desertorum in all treatments. Significant increase in microorganisms' activity was observed in the presence of petroleum sludge and plants in soil compared with uncontaminated soil without plants, and the highest soil respiration (37.6 mg C-CO₂/kg soil day) has been observed in the rhizosphere of Bermuda grass in treatment with 12% petroleum sludge. Plants had a significant role in the degradation of soil contaminants as TPH degradation in planted soils was significantly higher than that in unplanted soil (TPH degradation (%) was 30.4 and 38.9 in A. desertorum and Bermuda grass, respectively, whereas it was just 13.3 in unplanted soil). The rhizosphere of Bermuda grass had significantly less residual TPHs compared to A. desertorum. The results indicated that both Cynodon spp. and A. desertorum had a peculiar tolerance to petroleum pollution. Therefore, as Bermuda grass has already been suggested to be a typical and efficient species for phytoremediating petroleum-contaminated sites, A. desertorum may also prove to be a suitable native alternative.     

Phytoremediation in the Tropics—The Effect of Crude Oil on the Growth of Tropical Plants

Phytoremediation is a nondestructive, cost-effective in-situ technology to clean up contaminated soils. In the case of contamination with petroleum hydrocarbons, plants enhance microbial degradation of the contaminant in the rhizosphere. The potential of this technology for the tropics should be high due to prevailing climatic conditions favoring plant growth and stimulating microbial activity. Investigations of the potential of tropical plants for phytoremediation, however, are scarce. The present work studied two grasses and six legumes from the eastern savannah of Venezuela on their reaction to crude oil contamination in soil. Results shall help to identify plants with a potential for phytoremediation and subsequent studies. Seedling emergence and biomass production were determined for plants growing in soil contaminated with 0%, 3%, and 5% heavy crude oil. Contamination had, in general, a tendential but not significant negative influence on seedling emergence. Dry matter production was reduced by only a few percent to up to 85%. Furthermore, in some legumes inhibition of nodulation was observed. The grass Brachiaria brizantha and the legumes Centrosema brasilianum and Calopogonium mucunoides are promising for phytoremediation because in contaminated soil they combined high seedling emergence with least affected biomass production. Since they are cultivated forage/soil cover species also in other regions of the tropics, their potential for phytoremediation of petroleum contaminated soils extends beyond Venezuela.     

Efficiency of Opuntia ficus in the phytoremediation of a soil contaminated with used motor oil and lead,compared to that of Lolium perenne and Aloe barbadensis

Industrial pollutants such as heavy metals and hydrocarbons in soils represent a serious concern due to their persistence and negative effects on the environment, affecting cellular processes in living organisms and even causing mutations and cancer. The main objectives of this work were to evaluate the efficiency of Opuntia ficus in the phytoremediation of a soil polluted with used motor oil. Two other species, one with different and one with similar characteristics, relatively, were used for comparison purposes: Lolium perenne and Aloe barbadensis. The effect of the plants on lead solubility and bioaccumulation, the biomass production of each specie and the microbial counts and bacterial identification for each experiment was studied. Total petroleum hydrocarbons (TPH) were measured every 5 weeks throughout the 20-week phytoremediation experiment. At the end of the experiment soluble Pb, Pb extracted by the plant species, microbiological counts, total biomass and bacterial species in soil were analyzed. Even though Lolium perenne showed the highest TPH removal (47%), Opuntia ficus produced the highest biomass and similar removal (46%). Since Opuntia ficus requires low amounts of water and grows fast, it would be a suitable option in the remediation of soils polluted with hydrocarbons and/or heavy metals.     

Identification of nitrogen-incorporating bacteria in petroleum-contaminated arctic soils by using [15N]DNA-based stable isotope probing and pyrosequencing

Arctic soils are increasingly susceptible to petroleum hydrocarbon contamination, as exploration and exploitation of the Arctic increase. Bioremediation in these soils is challenging due to logistical constraints and because soil temperatures only rise above 0°C for ∼2 months each year. Nitrogen is often added to contaminated soil in situ to stimulate the existing microbial community, but little is known about how the added nutrients are used by these microorganisms. Microbes vary widely in their ability to metabolize petroleum hydrocarbons, so the question becomes: which hydrocarbon-degrading microorganisms most effectively use this added nitrogen for growth? Using [¹⁵N]DNA-based stable isotope probing, we determined which taxonomic groups most readily incorporated nitrogen from the monoammonium phosphate added to contaminated and uncontaminated soil in Canadian Forces Station-Alert, Nunavut, Canada. Fractions from each sample were amplified with bacterial 16S rRNA and alkane monooxygenase B (alkB) gene-specific primers and then sequenced using lage-scale parallel-pyrosequencing. Sequence data was combined with 16S rRNA and alkB gene C quantitative PCR data to measure the presence of various phylogenetic groups in fractions at different buoyant densities. Several families of Proteobacteria and Actinobacteria that are directly involved in petroleum degradation incorporated the added nitrogen in contaminated soils, but it was the DNA of Sphingomonadaceae that was most enriched in ¹⁵N. Bacterial growth in uncontaminated soils was not stimulated by nutrient amendment. Our results suggest that nitrogen uptake efficiency differs between bacterial groups in contaminated soils. A better understanding of how groups of hydrocarbon-degraders contribute to the catabolism of petroleum will facilitate the design of more targeted bioremediation treatments.     

Breakdown of low-level total petroleum hydrocarbons (TPH) in contaminated soil using grasses and willows

A phytoremediation study targeting low-level total petroleum hydrocarbons (TPH) was conducted using cool- and warm-season grasses and willows (Salix species) grown in pots filled with contaminated sandy soil from the New Haven Rail Yard, CT. Efficiencies of the TPH degradation were assessed in a 90-day experiment using 20–8.7–16.6 N-P-K water-soluble fertilizer and fertilizer with molasses amendments to enhance phytoremediation. Plant biomass, TPH concentrations, and indigenous microbes quantified with colony-forming units (CFU), were assessed at the end of the study. Switchgrass grown with soil amendments produced the highest aboveground biomass. Bacterial CFU's were in orders of magnitude significantly higher in willows with soil amendments compared to vegetated treatments with no amendments. The greatest reduction in TPH occurred in all vegetated treatments with fertilizer (66–75%) and fertilizer/molasses (65–74%), followed sequentially by vegetated treatments without amendments, unvegetated treatments with amendments, and unvegetated treatments with no amendment. Phytoremediation of low-level TPH contamination was most efficient where fertilization was in combination with plant species. The same level of remediation was achievable through the addition of grasses and/or willow combinations without amendment, or by fertilization of sandy soil.     

Bioremediation and phytoremediation of total petroleum hydrocarbons (TPH) under various conditions

Remediation of contaminated soils is often studied using fine-textured soils rather than low-fertility sandy soils, and few studies focus on recontamination events. This study compared aerobic and anaerobic treatments for remediation of freshly introduced used motor oil on a sandy soil previously phytoremediated and bioacclimated (microorganisms already adapted in the soil environment) with some residual total petroleum hydrocarbon (TPH) contamination. Vegetated and unvegetated conditions to remediate anthropogenic fill containing residual TPH that was spiked with nonaqueous phase liquids (NAPLs) were evaluated in a 90-day greenhouse pot study. Vegetated treatments used switchgrass (Panicum virgatum). The concentration of aerobic bacteria were orders of magnitude higher in vegetated treatments compared to unvegetated. Nevertheless, final TPH concentrations were low in all saturated soil treatments, and high in the presence of switchgrass. Concentrations were also low in unvegetated pots with fertilizer. Acclimated indigenous microbial communities were shown to be more effective in breaking down hydrocarbons than introducing microbes from the addition of plant treatments in sandy soils. Remediation of fresh introduced NAPLs on pre-phytoremediated and bioacclimated soil was most efficient in saturated, anaerobic environments, probably due to the already pre-established microbial associations, easily bioavailable contaminants, and optimized soil conditions for microbial establishment and survival.     

Effects of modified carbon black nanoparticles on plant-microbe remediation of petroleum and heavy metal co-contaminated soils

Abstract

Little is known about the effect of modified carbon black nanoparticles (MNCB) on the availability of heavy metals and petroleum degradation in petroleum and heavy metals co-contaminated soils. The overall objective of this study was to investigate the simultaneous effect of MNCB on heavy metal immobilization and petroleum biodegradation in co-contaminated soil in plant and plant-microbe combined remediation. The results showed that the petroleum degradation increased by 50% in petroleum-Cd co-contaminated soil and 65% in petroleum-Ni co-contaminated soil in plant-microbe combined remediation, comparing with the plant remediation and the application of MNCB did not show significant improvement on petroleum degradation in both plant and plant-microbe combined remediation. MNCB could significantly reduce the availability of heavy metals in soil and the uptakes of Cd and Ni by Suaeda salsa by roughly 18 and 10% and improve the growth of plant by alleviating the growth inhibition caused by heavy metals. The application of Bacillus subtilis and Sphingobacterium multivorum (heavy metal tolerant bacteria) inhibited the biomass of Suaeda salsa by enhancing the petroleum degradation. It could be concluded that MNCB played a major role in immobilizing the heavy metals and bacteria dominated the petroleum degradation in petroleum-metal co-contaminated soil.     

Characterization of Hydrocarbon-Degrading Microbial Populations in Contaminated and Pristine Alpine Soils

Biodegradation of petroleum hydrocarbons in cold environments, including Alpine soils, is a result of indigenous cold-adapted microorganisms able to degrade these contaminants. In the present study, the prevalence of seven genotypes involved in the degradation of n-alkanes (Pseudomonas putida GPo1 alkB; Acinetobacter spp. alkM; Rhodococcus spp. alkB1, and Rhodococcus spp. alkB2), aromatic hydrocarbons (P. putida xylE), and polycyclic aromatic hydrocarbons (P. putida ndoB and Mycobacterium sp. strain PYR-1 nidA) was determined in 12 oil-contaminated (428 to 30,644 mg of total petroleum hydrocarbons [TPH]/kg of soil) and 8 pristine Alpine soils from Tyrol (Austria) by PCR hybridization analyses of total soil community DNA, using oligonucleotide primers and DNA probes specific for each genotype. The soils investigated were also analyzed for various physical, chemical, and microbiological parameters, and statistical correlations between all parameters were determined. Genotypes containing genes from gram-negative bacteria (P. putida alkB, xylE, and ndoB and Acinetobacter alkM) were detected to a significantly higher percentage in the contaminated (50 to 75%) than in the pristine (0 to 12.5%) soils, indicating that these organisms had been enriched in soils following contamination. There was a highly significant positive correlation (P < 0.001) between the level of contamination and the number of genotypes containing genes from P. putida and Acinetobacter sp. but no significant correlation between the TPH content and the number of genotypes containing genes from gram-positive bacteria (Rhodococcus alkB1 and alkB2 and Mycobacterium nidA). These genotypes were detected at a high frequency in both contaminated (41.7 to 75%) and pristine (37.5 to 50%) soils, indicating that they are already present in substantial numbers before a contamination event. No correlation was found between the prevalence of hydrocarbon-degradative genotypes and biological activities (respiration, fluorescein diacetate hydrolysis, lipase activity) or numbers of culturable hydrocarbon-degrading soil microorganisms; there also was no correlation between the numbers of hydrocarbon degraders and the contamination level. The measured biological activities showed significant positive correlation with each other, with the organic matter content, and partially with the TPH content and a significant negative correlation with the soil dry-mass content (P < 0.05 to 0.001).