Effect of plant growth promoting bacterium; Pseudomonas putida UW4 inoculation on phytoremediation efficacy of monoculture and mixed culture of selected plant species for PAH and lead spiked soils.

Plant growth promoting bacteria (PGPB) enhanced phytoremediation (PEP) is an attractive remedial strategy for the remediation of polycyclic aromatic hydrocarbon (PAH) and heavy metal (HM) contaminated sites. The effect of PGPB; Pseudomonas putida UW4 inoculation on the phytoremediation efficiency of Medicago sativa, Festuca arundinacea, Lolium perenne, and mixed plants (L. perenne and F. arundinacea) was assessed. This involved two contaminant treatments; "PAH" (phenanthrene; 300 mg·kg-1, fluoranthene; 200 mg·kg-1, and benzo[a]pyrene; 5 mg·kg-1) and "PAH + HM" ('PAH' treatments +100 mg of Pb/kg). PGPB inoculation significantly enhanced root biomass yield of F. arundinacea in PAH treatment, and the mixed plant shoot biomass and L. perenne root biomass yields of the PAH + HM treatment. PGPB significantly enhanced dissipation of phenanthrene and fluoranthene for M. sativa-PAH + PGPB treatment and fluoranthene for F. arundinacea-PAH + HM + PGPB treatment. In others, PGPB inoculation either had no impact or inhibited PAH dissipation. PAH dissipation for the single and mixed plant treatments with PGPB inoculation were not different. The efficiency of PEP is dependent on different factors such as PGPB inoculum biomass, plant species, plant-microbe specificity and type of contaminants. Exploiting PEP technology would require proper understanding of plant tolerance and growth promoting mechanisms, and rhizosphere activities.

Effect of single and mixed polycyclic aromatic hydrocarbon contamination on plant biomass yield and PAH dissipation during phytoremediation.

Polycyclic aromatic hydrocarbon (PAH)-contaminated sites have a mixture of PAH of varying concentration which may affect PAH dissipation differently to contamination with a single PAH. In this study, pot experiments investigated the impact of PAH contamination on Medicago sativa, Lolium perenne, and Festuca arundinacea biomass and PAH dissipation from soils spiked with phenanthrene (Phe), fluoranthene (Flu), and benzo[a]pyrene (B[a]P) in single and mixed treatments. Stimulatory or inhibitory effects of PAH contamination on plant biomass yields were not different for the single and mixed PAH treatments. Results showed significant effect of PAH treatments on plant growth with an increased root biomass yield for F. arundinacea in the Phe (175%) and Flu (86%) treatments and a root biomass decrease in the mixed treatment (4%). The mean residual PAHs in the planted treatments and unplanted control for the single treatments were not significantly different. B[a]P dissipation was enhanced for single and mixed treatments (71-72%) with F. arundinacea compared to the unplanted control (24-50%). On the other hand, B[a]P dissipation was inhibited with L. perenne (6%) in the single treatment and M. sativa (11%) and L. perenne (29%) in the mixed treatment. Abiotic processes had greater contribution to PAH dissipation compared to rhizodegradation in both treatments. In most cases, a stimulatory effect of PAH contamination on plant biomass yield without an enhancement of PAH dissipation was observed. Plant species among other factors affect the relative contribution of PAH dissipation mechanisms during phytoremediation. These factors determine the effectiveness and suitability of phytoremediation as a remedial strategy for PAH-contaminated sites. Further studies on impact of PAH contamination, plant selection, and rhizosphere activities on soil microbial community structure and remediation outcome are required.

The application of graph theory and percolation analysis for assessing change in the spatial configuration of pond networks.

Pond networks support high levels of biodiversity when compared to other freshwater ecosystems such as rivers, lakes and streams. The persistence of species in these small, sometimes ephemeral, aquatic habitats depends on the dispersal of individuals among ponds in the landscape. However, the number of ponds across the landscape is at a historical low as urbanisation and intensified agricultural practices have led to a substantial loss of ponds (nodes in the pond network) over more than a century. Here, we examine the extent and drivers of pond loss in a heavily urbanised landscape (Birmingham, UK) over 105 years and determine how pond loss influences key structural properties of the pond network using graph theoretic approaches. Specifically, we calculated minimum spanning trees (MST) and performed percolation analyses to determine changes in both the spatial configuration and resilience of the pond network through time. Pond numbers declined by 82% between ca1904 and 2009, such that pond density decreased from 7.1 km-2 to 1.3 km-2. The MST analyses revealed increased distance between ponds in the network (i.e. edge length increased) by up to 49% over the 105-year period, indicating that ponds in the modern landscape (2009) were considerably more isolated, with fewer neighbours. This study demonstrates that graph theory has an excellent potential to inform the management of pond networks in order to support ecological communities that are less vulnerable to environmental change.

Local and landscape scale determinants of macroinvertebrate assemblages and their conservation value in ponds across an urban land-use gradient.

Urbanisation represents a growing threat to natural communities across the globe. Small aquatic habitats such as ponds are especially vulnerable and are often poorly protected by legislation. Many ponds are threatened by development and pollution from the surrounding landscape, yet their biodiversity and conservation value remain poorly described. Here we report the results of a survey of 30 ponds along an urban land-use gradient in the West Midlands, UK. We outline the environmental conditions of these urban ponds to identify which local and landscape scale environmental variables determine the biodiversity and conservation value of the macroinvertebrate assemblages in the ponds. Cluster analysis identified four groups of ponds with contrasting macroinvertebrate assemblages reflecting differences in macrophyte cover, nutrient status, riparian shading, the nature of the pond edge, surrounding land-use and the availability of other wetland habitats. Pond conservation status varied markedly across the sites. The richest macroinvertebrate assemblages with high conservation value were found in ponds with complex macrophyte stands and floating vegetation with low nutrient concentrations and little surrounding urban land. The most impoverished assemblages were found in highly urban ponds with hard-engineered edges, heavy shading and nutrient rich waters. A random forest classification model revealed that local factors usually had primacy over landscape scale factors in determining pond conservation value, and constitute a priority focus for management.

Phytoremediation for co-contaminated soils of chromium and benzo[a]pyrene using Zea mays L.

A greenhouse experiment was carried out to investigate the single effect of benzo[a]pyrene (B[a]P) or chromium (Cr) and the joint effect of Cr-B[a]P on the growth of Zea mays, its uptake and accumulation of Cr, and the dissipation of B[a]P over 60 days. Results showed that single or joint contamination of Cr and B[a]P did not affect the plant growth relative to control treatments. However, the occurrence of B[a]P had an enhancing effect on the accumulation and translocation of Cr. The accumulation of Cr in shoot of plant significantly increased by ≥ 79 % in 50 mg kg(-1) Cr-B[a]P (1, 5, and 10 mg kg(-1)) treatments and by ≥ 86 % in 100 mg kg(-1) Cr-B[a]P (1, 5, and 10 mg kg(-1)) treatments relative to control treatments. The presence of plants did not enhance the dissipation of B[a]P in lower (1and 5 mg kg(-1)) B[a]P contaminated soils; however, over 60 days of planting Z. mays seemed to enhance the dissipation of B[a]P by over 60 % in 10 mg kg(-1) single contaminated soil and by 28 to 41 % in 10 mg kg(-1)B[a]P co-contaminated soil. This suggests that Z. mays might be a useful plant for the remediation of Cr-B[a]P co-contaminated soil.

Phytoremediation potential of Brassica juncea in Cu-pyrene co-contaminated soil: comparing freshly spiked soil with aged soil.

A comparison was made between the dissipation of pyrene as well as the uptake of copper (Cu) in soil freshly spiked with Cu, pyrene or Cu + pyrene and in aged soil. The potential of B juncea for phytoremediation was also investigated. The biomass of Brassica juncea significantly decreased (>50% reduction) in freshly spiked soil when compared to aged soil in all treatments. However, the accumulation of Cu in shoot was significantly reduced (60-88%) in aged soil after 60 days of planting. The total removal of Cu from co-contaminated soil was always higher (>2-3 fold) in aged soil than in freshly spiked soil when lower Cu concentration (50 mg kg(-1)) was co-contaminated with 250 or 500 mg kg(-1) of pyrene while in other co-contaminated treatments, the total removal of Cu from aged soil were significantly lower. The level of pyrene in both planted and un-planted freshly spiked soil decreased significantly (>67%) over the 60 days of plant trial. In aged soils, there were no significant differences in residual pyrene concentration between planted and unplanted soil. This suggests that the presence of B. juncea in aged soil did not enhance the dissipation of pyrene and that the prediction of pyrene dissipation in laboratory prepared soil may not have reflected the true situation in the fields.

Effect of EDTA and citric acid on phytoremediation of Cr- B[a]P-co-contaminated soil.

Polycyclic aromatic hydrocarbons and heavy metals in the environment are a concern, and their removal to acceptable level is required. Phytoremediation, the use of plants to treat contaminated soils, could be an interesting alternative to conventional remediation processes. This work evaluates the role of single and combined applications of chelates to single or mixed Cr + benzo[a]pyrene (B[a]P)-contaminated soil. Medicago sativa was grown in contaminated soil and was amended with 0.3 g citric acid, 0.146 g ethylenediaminetetraacetic acid (EDTA), or their combination for 60 days. The result shows that in Cr-contaminated soil, the application of EDTA + citric acid significantly (p<0.05) decreased the shoot dry matter of M. sativa by 55 % and, as such, decreased the Cr removal potential from the soil. The soluble Cr concentration in single Cr or Cr + B[a]P-contaminated soil was enhanced with the amendment of all chelates; however, only the application of citric acid in Cr-contaminated soil (44 %) or EDTA and EDTA + citric acid in co-contaminated soil increased the removal of Cr from the soil (34 and 54 %, respectively). The dissipation of B[a]P in single B[a]P-contaminated soil was effective even without planting and amendment with chelates, while in co-contaminated soil, it was related to the application of either EDTA or EDTA + citric acid. This suggests that M. sativa with the help of chelates in single or co-contaminated soil can be effective in phytoextraction of Cr and promoting the biodegradation of B[a]P.

Effect of combined pollution of chromium and benzo(a)pyrene on seed growth of Lolium perenne.

The single and joint effects of chromium (Cr) and benzo (a) pyrene (B (a) P) on the seed germination and the elongation of root and shoot of Lolium perenne were investigated. Seed germination represents the first important step to effective phytoremediation. Young seedlings may be susceptible to PAH and heavy metal contaminants. The results showed that in solution, increasing concentration of Cr could inhibit the germination rate as well as root and shoot elongation of L. perenne. Also, the increasing concentration of B (a) P (1-4 mg L(-1)) could accelerate the germination rate. The joint toxicity of Cr and B (a) P showed that increasing concentration of Cr and B (a) P had significant antagonistic effect on the germination rate of L. perenne. In the single factor experiments and joint effect tests of Cr and B (a) P on the seedling growth, the root and shoot elongation were inhibited significantly (p<0.05) for higher concentration of Cr whereas increasing concentration of B (a) P accelerated the shoot elongation. There were significant relationships between the concentration of pollutants and root and shoot elongation (p<0.05). Higher concentration of B (a) P with low concentration of Cr had significant antagonistic effect on shoot and root elongation of L. perenne in solution tests. Also, low concentration of B (a) P with increasing concentration of Cr had a significant synergistic effect on shoot elongation. The toxicity effects of Cr and B (a) P to seed germination, root and shoot elongation are-root elongation>shoot elongation>germination rate.

Interactions of copper and pyrene on phytoremediation potential of Brassica juncea in copper-pyrene co-contaminated soil.

Phytoremediation which is a plant based remediation process is an emerging technology for treating inorganic (heavy metals) as well as organic pollutants. It may also be suitable for remediation of sites co-contaminated with heavy metals and organics which have become more prevalent. A glasshouse experiment was carried out to investigate the effect of 50 and 100 mg kg(-1) of copper or 250 and 500 mg kg(-1) of pyrene and the combined effect of copper and pyrene on the growth of Brassica juncea together with the uptake and accumulation of copper as well as dissipation of pyrene. Results showed a negative effect of copper-pyrene co-contamination on shoot and root dry matter and an inhibition of copper phytoextraction. Pyrene was significantly decreased in planted and non-planted soils accounting for 90-94% of initial extractable concentration in soil planted with B. juncea and 79-84% in non-planted soil which shows that the dissipation of pyrene was enhanced with planting. The occurrence of copper tended to increase the residual pyrene in planted soil, however in the presence of high concentration of Cu (100 mg kg(-1)), the residual pyrene concentration in soil were similar to those in unplanted soil. This may suggest that changes in the root physiology or rhizospheric microbial activity resulting from Cu stress could be an impediment to pyrene dissipation. The inhibition of Cu phytoextraction and degradation of pyrene by B. juncea under co-contamination may reduce the viability of phytoremediation in sites containing multiple pollutants.

Phytotoxicity of silver nanoparticles to Lemna minor L.

The use of silver nanoparticles (AgNPs) in commercial products has increased significantly in recent years. Although there has been some attempt to determine the toxic effects of AgNPs, there is little information on aquatic plants which have a vital role in ecosystems. This study reports the use of Lemna minor L. clone St to investigate the phytotoxicity of AgNPs under modified OECD test conditions. AgNPs were synthesised, characterised and subsequently presented to the L. minor. Results showed that inhibition of plant growth was evident after exposure to small (~ 20 nm) and larger (~100 nm) AgNPs at low concentrations (5 µg L⁻¹) and this effect became more acute with a longer exposure time. There was a linear dose-response relationship after 14 d exposure. Using predicted environmental concentrations for wastewaters it was found that AgNPs may pose a significant potential risk to the environment.

Effect of a polycyclic aromatic hydrocarbon on the phytoremediation of zinc by two plant species (Brassica juncea and Festuca arundinacea).

The redevelopment of contaminated land is becoming increasingly necessary under sustainable- development legislation; however, many of the contaminated sites are "orphan" sites and therefore require a low-cost remediation technology. These sites often contain a cocktail of pollutants including organics and inorganics. Phytoremediation provides a possible solution, but there is little information available on the tolerance of plant species to multiple pollutants and their ability to remediate in mixed-contaminant soils. The effect of a polycyclic aromatic hydrocarbon (pyrene) in soil upon the remediation of zinc by Brassica juncea and Festuca arundinacea was investigated under normal climatic conditions in the United Kingdom. Zinc was effectively removed from mixed-contaminant soils in the presence of both species, in comparison to a control treatment. Both species accumulated zinc in plant tissues in the presence of pyrene, but the growth of B. juncea was significantly reduced when zinc and pyrene were supplied in combination. Zinc was predominantly associated with root tissues for F. arundinacea, whereas B. juncea contained higher concentrations in shoot tissues. F. arundinacea provides a possible species to be used for the phytoremediation of brownfield sites, but further research is required to determine a range of species that may be used and their applicability to different contaminants.

Iron and manganese removal in wetland treatment systems: rates, processes and implications for management.

Mine water drainage is a significant environmental problem throughout the world and constructed wetlands are being increasingly used to treat such contaminating discharges. Iron and manganese removal within a wetland treatment system at Whittle Colliery, UK which receives alkaline waters, was monitored to determine rates and processes within the different components of the system. In addition hourly samples were taken for a period of 24 h to determine the effect of photosynthetic organisms on metal removal. Significant iron removal occurred, with removal rates of 98% at Whittle. Oxidation of iron to form iron hydroxide precipitates was the dominant removal process in the proximal sections of the treatment system (i.e. oxidation ponds and initial reaches of the wetland), whereas biotic removal processes appeared to become more important in distal parts of the systems, where iron concentrations were much lower. Significant manganese removal was also observed, although this did not become substantial until iron concentrations had fallen below 5 mg/L. The process by which manganese was removed is not clear, but bacterially-mediated oxidation may be involved. Further elucidation of the relative importance of abiotic and biotic removal processes within treatment systems is important in the design and long-term management of constructed systems.

The effect of pH on plant litter decomposition and metal cycling in wetland mesocosms supplied with mine drainage.

The long term effectiveness of compost-based wetland systems treating net-acidic mine waters is reliant upon a continuing supply of decomposed organic matter which provides the basic foodstock for sulphate reducing bacteria. The annual turnover of wetland vegetation within these systems has been suggested to be the primary source for this material once the original substrate has been consumed. This study aimed to determine whether plant litter (of Common Reed, Phragmites australis) decomposition rates and release of metals and nutrients were affected by pH using controlled experiments under laboratory conditions. Loss of plant biomass was found to be unaffected by pH (3.0-6.5) suggesting that plant litter could be an important source of organic molecules for bacterial populations even under acidic conditions. The decomposing plant litter also acted as a focus for the precipitation of Fe oxides and sorption of Zn thereby acting as a short-term sink for these contaminants. This has important implications for geochemical cycling within the wetland system and potential transport out of the system. The essential nutrients (K and Mg) released from plant litter were affected by pH which could be important in nutrient availability for re-use by vegetation and other organisms within the system.

Growth of Phragmites australis (Cav.) Trin ex. Steudel in mine water treatment wetlands: effects of metal and nutrient uptake.

The abandoned mine of Shilbottle Colliery, Northumberland, UK is an example of acidic spoil heap discharge that contains elevated levels of many metals. Aerobic wetlands planted with the common reed, Phragmites australis, were constructed at the site to treat surface runoff from the spoil heap. The presence of a perched water table within the spoil heap resulted in the lower wetlands receiving acidic metal contaminated water from within the spoil heap while the upper wetland receives alkaline, uncontaminated surface runoff from the revegetated spoil. This unique situation enabled the comparison of metal uptake and growth of plants used in treatment schemes in two cognate wetlands. Results indicated a significant difference in plant growth between the two wetlands in terms of shoot height and seed production. Analyses of metal and nutrient concentrations within plant tissues provided the basis for three hypotheses to explain these differences: (i) the toxic effects of high levels of metals in shoot tissues, (ii) the inhibition of Ca (an essential nutrient) uptake by the presence of metals and H+ ions, and (iii) low concentrations of bioavailable nitrogen sources resulting in nitrogen deficiency. This has important implications for the engineering of constructed wetlands in terms of the potential success of plant establishment and vegetation development.

Critical role of macrophytes in achieving low iron concentrations in mine water treatment wetlands.

Aerobic wetlands are increasingly being included in mine water treatment systems which need to achieve low residual iron concentrations (<0.5 mg L(-1)) in final discharges. Traditionally the macrophyte components of such systems have been thought to be insignificant sinks for major contaminants such as iron. However, we report high rates of plant uptake of iron where the latter is present at relatively low concentrations, suggesting that macrophytes may well be critical to achieving low residual iron concentrations in final effluents from such systems. The wetland macrophyte Phragmites australis was grown in waters with a range of iron concentrations (0-50 mg L(-1)). At an Fe supply of 1 mg L(-1) almost 100% of the Fe was taken up into plant tissues. The majority of iron was stored in and around the roots of the plants, which helps allay fears of possible release of contaminants during seasonal die-back of emergent shoots and leaves. The 1 mg L(-1) threshold also proved to be important in terms of plant growth, with significant inhibition (evident in root length and in dry weights of shoots and roots) in plants grown in waters with Fe above this concentration. No direct causal relationship between iron content in aerial tissues and growth inhibition was found, which strongly suggests that iron toxicity cannot explain these results. These results have implications for the design of mine water treatment wetlands, particularly with regard to initial establishment of vegetation and achieving sufficient Fe removal in "polishing" applications (i.e. where it is intended to remove the last few mg L(-1) of Fe).

Aluminium and phosphate uptake by Phragmites australis: the role of Fe, Mn and Al root plaques.

Aluminium, a potentially phytotoxic metal, is an important constituent of many mine water discharges but has largely been neglected in the literature. The behaviour of this element in the rhizosphere of the wetland plant Phragmites australis was investigated in the laboratory in the presence and absence of Mn and Fe root plaques. Electron microscopy and chemical extraction techniques were utilized to determine the physico-chemical properties of the plaques and any association of Al. Both Mn and Fe plaques occurred as amorphous coatings on root surfaces with uneven distributions. Al was not adsorbed onto the surface of either plaque type but formed a separate phosphate deposit closely resembling the Fe and Mn plaques. Phosphorus was also found to be adsorbed to the surface of the Fe plaques (but not the Mn plaques). Both mechanisms were found to immobilize P at the root surface but this did not significantly reduce the concentration of P in aerial plant tissues that was sufficient to ensure adequate growth.