Ana P. G. C. Marques

Remediation of heavy metal contaminated soils: phytoremediation as a potentially promising clean-up technology.

Increased soil pollution with heavy metals due to various human and natural activities has led to a growing need to address environmental contamination. Some remediation technologies have been developed to treat contaminated soil, but a biology-based technology, phytoremediation, is emerging. Phytoremediation includes phytovolatilization, phytostabilization, and phytoextraction using hyperaccumulator species or a chelate-enhancement strategy. To enhance phytoremediation as a viable strategy, microbiota from the rhizosphere can play an important role, but the use of genetic engineering can also increase the success of the technique. Here we review the key information on phytoremediation, addressing both potential and limitations, resulting from the research established on this topic.

Inoculating Helianthus annuus (sunflower) grown in zinc and cadmium contaminated soils with plant growth promoting bacteria – Effects on phytoremediation strategies

Plant growth promoting bacteria (PGPR) may help reducing the toxicity of heavy metals to plants in polluted environments. In this work the effects of inoculating metal resistant and plant growth promoting bacterial strains on the growth of Helianthus annuus grown in Zn and Cd spiked soils were assessed. The PGPR strains Ralstonia eutropha (B1) and Chrysiobacterium humi (B2) reduced losses of weight in metal exposed plants and induced changes in metal bioaccumulation and bioconcentration - with strain B2 decreasing up to 67% Zn accumulation and by 20% Zn bioconcentration factor (BCF) in the shoots, up to 64% Zn uptake and 38% Zn BCF in the roots, and up to 27% Cd uptake and 27% Cd BCF in plant roots. The impact of inoculation on the bacterial communities in the rhizosphere of the plant was also assessed. Bacterial community diversity decreased with increasing levels of metal contamination in the soil, but in rhizosphere soil of plants inoculated with the PGPR strains, a higher bacterial diversity was kept throughout the experimental period. Inoculation of sunflower, particularly with C. humi (B2), appears to be an effective way of enhancing the short term stabilization potential of the plant in metal contaminated land, lowering losses in plant biomass and decreasing aboveground tissue contamination.

Arsenic, lead and nickel accumulation in Rubus ulmifolius growing in contaminated soil in Portugal.

This work investigates the potential of Rubus ulmifolius, indigenous to a metal contaminated site--Esteiro de Estarreja--for phytoremediation purposes. The site has a long history of metal contamination. The accumulation of lead (Pb), arsenic (As) and nickel (Ni) in different sections--roots, stems and leaves - of the plant was assessed and compared to the levels of those metals in the soil and in the available fraction. The distribution of metals throughout the area was quite heterogeneous, presenting levels of As, Pb and Ni of up to 3078, 1400 and 135 mg kg(-1), respectively, and the metal content in the sections of R. ulmifolius collected in the banks of the stream varied among sites of collection. Levels of metals were higher in the plant roots: As levels (mgkg(-1)) ranged from 277 to 1721 in the roots, 30 to 110 in the stems, and 60 to 265 in the leaves; Pb concentrations (mgkg(-1)) ranged from 248 to 1178 in the roots, 35 to 133 in the stems, and 25 to 149 in the leaves; and Ni (mgkg(-1)) ranged from 48 to 151 in the roots. Significant correlations were found between the total levels of Pb and As in the soil and the levels in the roots of the plant; further correlations between total and available levels in the soil and metals in other plant tissues were generally found as non-significant. According to the metal accumulation patterns of R. ulmifolius, this species seems to be valuable for application in phytostabilisation strategies.

Degradation of phenols in olive oil mill wastewater by biological, enzymatic, and photo-Fenton oxidation.

Background, aim, and scopeOlive oil mill wastewater (OOMW) environmental impacts minimization have been attempted by developing more effective processes, but no chemical or biological treatments were found to be totally effective to mitigate their impact on receiving systems. This work is the first that reports simultaneously the efficiency of three different approaches: biological treatment by two fungal species (Trametes versicolor or Pleurotus sajor caju), enzymatic treatment by laccase, and chemical treatment by photo-Fenton oxidation on phenols removal.Materials and methodsThose treatments were performed on OOMW with or without phenol supplement (p-coumaric, vanillin, guaiacol, vanillic acid, or tyrosol). OOMW samples resulted from treatments were extracted for phenols using liquid–liquid extraction and analyzed by gas chromatography coupled to mass spectrometry.ResultsTreatment with T. versicolor or P. sajor caju were able to remove between 22% and 74% and between 8% and 76% of phenols, respectively. Treatment by laccase was able to reduce 4% to 70% of phenols whereas treatment by photo-Fenton oxidation was responsible for 100% phenols reduction.DiscussionRange of phenol degradation was equivalent between T. versicolor, P. sajor caju and laccase for p-coumaric, guaiacol, caffeic acid, and tyrosol in supplemented OOMW, which enhances this enzyme role in the biological treatment promoted by these two species.ConclusionsPhenols were removed more efficiently by photo-Fenton treatment than by biological or enzymatic treatments.Recommendations and perspectivesUse of fungi, laccase, or photo-Fenton presents great potential for removing phenols from OOMW. This should be further assessed by increasing the application scale and the reactor configurations effect on the performance, besides a toxicity evaluation of treated wastewater in comparison to raw wastewater.

The effect of ectomycorrhizal fungi forming symbiosis with Pinus pinaster seedlings exposed to cadmium

Cadmium is one of the most toxic heavy metals and its accumulation in the upper layers of forest soils affects plants, microorganisms and their interactions. Adequate strategies for the reforestation of metal contaminated sites are of vital importance. The aim of this work was to evaluate the response of Pinus pinaster seedlings to Cd exposure and to assess the effect of inoculation with two selected ectomycorrhizal fungi, Suillus bovinus and Rhizopogon roseolus on that response. Seedlings were exposed to soil contaminated at 15 and 30 mg Cd kg(-1). Shoot biomass of P. pinaster decreased ca. 36% when exposed to 15 mg Cd kg(-1). Overall, colonization by S. bovinus significantly enhanced shoot development up to 30% in contaminated soil while colonization by R. roseolus produced no significant effect at both Cd concentrations tested and significantly increased the level of Cd in the shoots at both Cd concentrations. Metal accumulation in the shoots and roots of non-inoculated and S. bovinus-inoculated seedlings increased at the higher Cd levels whereas R. roseolus-inoculated seedlings were not sensitive to Cd variation in the soil. The results from our research show that inoculation with ECM fungi has a significant impact on metal uptake and development of P. pinaster seedlings; the differential response induced by the two tested species highlights the importance of selecting the appropriate strains for nursery inoculation, and, as such, this biological tool ought to be considered in reforestation processes of heavy metal contaminated areas by woody species.

Remediation of heavy metal contaminated soils: an overview of site remediation techniques

This article has been retracted.

Removal of heavy metals using different polymer matrixes as support for bacterial immobilisation.

Great attention is focused on the microbial treatment of metal contaminated environments. Three bacterial strains, 1C2, 1ZP4 and EC30, belonging to genera Cupriavidus, Sphingobacterium and Alcaligenes, respectively, showing high tolerance to Zn and Cd, up to concentrations of 1000ppm, were isolated from a contaminated area in Northern Portugal. Their contribution to Zn and Cd removal from aqueous streams using immobilised alginate, pectate and a synthetic cross-linked polymer was assessed. In most cases, matrices with immobilised bacteria showed better metal removal than the non-inoculated material alone. For the immobilisation with all the polymers, 1C2 was the strain that increased the removal of Zn the most, whereas EC30 was the most promising for Cd removal, especially when combined with the synthetic polymer with up to a ca. 11-fold increase in metal removal when compared to the polymer alone. Removal of individual metals from binary mixtures showed that there was differential immobilisation. There was greater removal of Cd than Zn (removals up to 40% higher than those showed for Zn). The results show that metal contaminated environments constitute a reservoir of microorganisms resistant/tolerant to heavy metals that have the capacity to be exploited in bioremediation strategies. Capsule immobilisation of bacteria in the naturally occurring alginate and pectate and in a synthetic cross-linked polymer increased the Zn and Cd removal abilities from single and binary contaminated waters; the applications with the synthetic polymer were the most promising for Cd and Zn removal in single and binary mixtures.