Phytoextraction efficiency of Pteris vittata grown on a naturally As-rich soil and characterization of As-resistant rhizosphere bacteria.

This study evaluated the phytoextraction capacity of the fern Pteris vittata grown on a natural arsenic-rich soil of volcanic-origin from the Viterbo area in central Italy. This calcareous soil is characterized by an average arsenic concentration of 750 mg kg-1, of which 28% is bioavailable. By means of micro-energy dispersive X-ray fluorescence spectrometry (µ-XRF) we detected As in P. vittata fronds after just 10 days of growth, while a high As concentrations in fronds (5,000 mg kg-1), determined by Inductively coupled plasma-optical emission spectrometry (ICP-OES), was reached after 5.5 months. Sixteen arsenate-tolerant bacterial strains were isolated from the P. vittata rhizosphere, a majority of which belong to the Bacillus genus, and of this majority only two have been previously associated with As. Six bacterial isolates were highly As-resistant (> 100 mM) two of which, homologous to Paenarthrobacter ureafaciens and Beijerinckia fluminensis, produced a high amount of IAA and siderophores and have never been isolated from P. vittata roots. Furthermore, five isolates contained the arsenate reductase gene (arsC). We conclude that P. vittata can efficiently phytoextract As when grown on this natural As-rich soil and a consortium of bacteria, largely different from that usually found in As-polluted soils, has been found in P. vittata rhizosphere.

Rapid assessment of As and other elements in naturally-contaminated calcareous soil through hyperspectral VIS-NIR analysis.

Although arsenic (As) toxicity in soil vary depending on its chemical forms and oxidation states, regulatory limits for this compartment rely on total As content. Conventional methods of total As determination are expensive and time-consuming. The development of predictive techniques might enable a speditive assessment of As contamination in those scenarios, such as thermal spring sites, where exposure to the metalloid poses a threat to human health. The objective of this study was to assess the suitability of Visible Near Infrared spectrophotometry for predicting the total As content in highly calcareous thermal spring soils and the same aim was pursued for those elements (i.e. Al, Fe and Mn) the chemistry of which is tightly connected with that of As. A Partial Least Square approach, including cross-validation and external independent test, was used to relate the concentrations of the target elements to spectral data. The most accurate prediction was found for As with Pearson's coefficient, RMSE, RPD and SEP being equal to 0.94, 69.65, 2.9 and 66.99, respectively. Less accurate predictions were found for Al (r = 0.88; RMSE = 11014; RPD = 1.96; SEP = 11014), Fe (r = 0.93; RMSE = 6921.1; RPD = 2.45; SEP = 6462.4), and Mn (r = 0.92; RMSE = 542.01; RPD = 2.43; SEP = 529.79).

Mobility and distribution of arsenic in contaminated mine soils and its effects on the microbial pool.

Three soils, coming from a former mining site and characterized by a different degree of pollution, were analysed in terms of Arsenic (As) content, using three different analytical approaches, and its distribution in various soil fractions. The effect of As on soil microbial biomass (size, respiration and microbial quotients) was also analysed. Total arsenic concentration between soil fractions was significantly different and ranged from 189 to 4357mgkg(-1), indicating a high level of pollution. Soil sequential fractioning showed that more than 60 percent of total As was bound to Fe-Al oxides, suggesting a minor availability and environmental risk regardless the total concentration of As in the sample. On the contrary, water soluble As fraction showed a significant difference among the three samples. The largest water soluble As concentration was found in the sample with intermediate total As amount. As far as microbial biomass is concerned, it was found that bioavailable As negatively impacted microbial metabolism in terms of basal and cumulative respiration, and microbial quotients, suggesting a strong selection within microbial pool.

Copper distribution and hydrolase activities in a contaminated soil amended with dolomitic limestone and compost.

Chemical fractionation of copper in bulk soil and its distribution in the particle-size fractions were analyzed in a Cu-contaminated soil (674 ± 122 µg Cu g(-1), up to 1900 µg Cu g(-1) in the clay fraction) sampled from a wood preservation site left untreated and subsequently treated with dolomitic limestone (DL, 0.2% w/w) and compost (CM, 5% w/w), singly and in combination (DL+CM). Soil enzymatic activities of leucine aminopeptidase, cellulase, N-acetyl-ß-glucosaminidase, arylsulfatase, ß-glucosidase, acetate esterase, butyric esterase, and acid phosphatase were determined. Chemical speciation showed that Cu was mostly present in the acid-soluble and reducible fractions in both untreated and treated soils, whereas treatments with DL and CM reduced the soluble and exchangeable Cu fractions, due to Cu precipitation and complexation, and increased Cu bound to soil organic matter. Analysis of the particle-size fractions showed that more than 80% of Cu was in the silt and clay fractions and that treatment with CM increased the concentration of Cu in the sand size fractions. Soil treatment with DL and CM, singly or in combination, increased hydrolase activities, mainly in the clay fraction, with the largest positive effects on N-acetyl-ß-glucosaminidase, leucine aminopeptidase, and ß-glucosidase activities. Overall, results confirm that (1) Cu in contaminated soils is mainly bound to the silt-clay fraction, (2) CM additions change its allocation in the particle-size fractions, and (3) treatments with DL and CM singly and in combination reduce Cu solubility and its inhibitory effects on soil enzyme activities.

Bioconversion of olive-mill dry residue by Fusarium lateritium and subsequent impact on its phytotoxicity.

The present study investigated the ability of the non-pathogenic fungus Fusarium lateritium to either degrade or modify aromatic substances in olive-mill dry residue (DOR) and to reduce its phytotoxicity. The 80% reduction of ethylacetate extractable phenols in DOR colonized by the fungus for 20 weeks appeared to be due to polymerization reactions of phenol molecules as suggested by mass-balance ultrafiltration and size-exclusion chromatography experiments. Several lignin-modifying oxidases, including laccase, Mn-peroxidase and Mn-inhibited peroxidase were detected in F. lateritium solid-state cultures. Tests performed with tomato seedlings in soils containing 6% (w/w) sterilized non-inoculated DOR showed that the waste was highly phytotoxic. By contract, F. lateritium growth on DOR for 20 weeks led to a complete removal of the waste toxicity and to a higher shoot dry weight of tomato plants than that obtained in the absence of DOR.

Reduction of the phenolic components in olive-mill wastewater by an enzymatic treatment and its impact on durum wheat (Triticum durum Desf.) germinability.

Olive-mill wastewater (OMW), an effluent of olive oil extraction process, is annually produced in huge amounts in olive growing areas. An interesting option for its disposal is the spreading on agricultural land, provided that phytotoxic effects are neutralized. The objective of the present investigation was to evaluate the potential of an enzyme-based treatment in removing OMW phytotoxicity. To this aim, germinability experiments on durum wheat (Triticum durum Desf. cv. Duilio) were conducted in the presence of different dilutions of raw or enzyme-treated OMW. OMW treatment with laccase resulted in a 65% and 86% reduction in total phenols and ortho-diphenols respectively, due their polymerization as revealed by size-exclusion chromatography. Raw OMW exerted a significant concentration-dependent inhibition on the germinability of durum wheat seeds which was evident up to a dilution rate of 1:8. When the effluent was treated with a fungal laccase, germinability was increased by 57% at a 1:8 dilution and by 94% at a 1:2 dilution, as compared to the same dilutions using untreated OMW. The treatment with laccase also decreased the mean germination time by about 1 day as compared to untreated controls. These results show that germinability inhibition due to OMW can be reduced effectively using fungal laccase, suggesting that phenols are the main determinants of its phytotoxicity.

Oxirane-immobilized Lentinula edodes laccase: stability and phenolics removal efficiency in olive mill wastewater.

Immobilization of Lentinula edodes laccase on Eupergit C increased pH, thermal and proteolytic stability with slight modifications in laccase oxidation efficiency. Immobilized laccase proved to be efficiently stable in removing olive mill wastewater phenolics.