Effect of Miscanthus cultivation on metal fractionation and human bioaccessibility in metal-contaminated soils: comparison between greenhouse and field experiments

Arsenic uptake by Agrostis capillaris, as related to its genotypic diversity in the area of historical ore mining and processing

Common bentgrass Agrostis capillaris L. is known as tolerant to toxic elements. A hypothesis was examined that its ecotypes growing in historically polluted sites show a limited arsenic uptake and have genetic features that distinguish them from commercially available cultivars. The study was conducted in Złoty Stok, a historical area of arsenic mining. Additionally, two commercial cultivars were grown in pots with arsenic-rich soils. Based on arsenic concentrations in plant roots and shoots, bioconcentration and translocation factors BCF and TF were calculated. Commercial cultivars indicated many times higher BCF shoots and TF values compared to field plants. DNA analysis of leaf blades showed a clear distinction between the plants growing in some sites and patches in the field, and also a gene overlap between the plants in the field and commercial forms. The research did not allow for identification of ecotypes with exceptionally limited arsenic uptake. Moreover, there were no significant differences between the genotypic characteristics of plants growing in polluted sites and those poorly tolerant grown from commercially available seeds. Apparently, other factors, and not genetically determined features, are responsible for A. capillaris tolerance to arsenic in Złoty Stok.

Response of Three Miscanthus × giganteus Cultivars to Toxic Elements Stress: Part 2, Comparison between Two Growing Seasons

The positive impact on restoring soil functionality, decreasing toxic elements (TE) bioaccessibility, and enhancing soil physicochemical and biological parameters established a consensus on considering a Miscanthus × giganteus convenient species for phytomanaging wide TE contaminated areas. Nevertheless, information about the plant's mode of reaction to elevated soil multi-TE concentrations is still scarce. For the sake of investigating the miscanthus response to stressful TE concentrations, an ex-situ pot experiment was initiated for 18 months, with three miscanthus cultivars referred to as B, U, and A planted in soils with gradient Cd, Pb, and Zn concentrations. A non-contaminated control soil was introduced as well, and plants were cultivated within. Results revealed that the long exposure to increasing soil TE concentrations caused the number of tillers per plant to decline and the TE concentrations in the leaves to boost progressively with the soil contamination. The photosynthetic pigments (chlorophyll a, b, and carotenoids) were negatively affected as well. However, the phenolic compounds, flavonoids, tannins, and anthocyanins, along with the antioxidant enzymatic activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase elevated progressively with the TE concentration and exposure duration. Conclusively, miscanthus plants demonstrated an intensified and synchronized antioxidative activity against the TE concentration.

The phytoextraction power of Cichorium intybus L. on metal-contaminated soil: Focus on time- and cultivar-depending accumulation and distribution of cadmium, lead and zinc

This study is focused on the evaluation of the accumulation of Cd, Pb and Zn in five cultivars of Cichorium intybus L. (chicory) which were produced on contaminated agricultural soil. Over a growth period of 211 days, the roots and leaves were collected in four stages and then analyzed by flame atomic absorption spectrometry to measure the concentration and distribution of the target metals in these two chicory organs considering the weather and the nature of the cultivar. For all cultivars, sharp decreases of Pb (from 165 mg kg-1 to 3 mg kg-1), Cd (from 11 mg kg-1 to 5 mg kg-1) and Zn concentrations (from 157 mg kg-1 to 40 mg kg-1) in the roots were highlighted over time. The data collected enabled the calculation of the variation of the bioconcentration factor, the biological absorption coefficient and the translocation factor for Cd, Pb and Zn. These parameters were then correlated with the distribution of the fresh biomass of leaves and roots and several indicators such as chlorophyll content, flavonols, anthocyanin and nitrogen balance index were measured. The study concludes with the discussion on the ability of chicory to clean up contaminated agricultural soil. The current investigation has shown: i) a translocation of Cd (and Zn to a lesser extent) from the roots to the leaves; ii) an increase in the level of anthocyanins with the increase of the metal trace elements concentration in the leaf, while the content of chlorophyll and the nitrogen balance index decrease, which could be linked to the phenomenon of senescence; iii) an ability of the chicory to reduce the bioavailable pool of the three metal trace elements studied, in particular for Cd.

A risk management framework for Gentle Remediation Options (GRO)

Gentle Remediation Options (GRO) are remediation measures involving plants, fungi, bacteria, and soil amendments that can be applied to manage risks at contaminated sites. Several studies and decision-support tools promote the wider range of benefits provided by GRO, but there is still skepticism regarding GRO implementation. Key issues that need to be better communicated are the various risk mitigation mechanisms, the required risk reduction for an envisioned land use, and the time perspective associated with the risk mitigation mechanisms. To increase the viability and acceptance of GRO, the phytomanagement approach implies the combination of GRO with beneficial green land use, gradually reducing risks and restoring ecosystem services. To strengthen the decision basis for GRO implementation in practice, this paper proposes a framework for risk management and communication of GRO applications to support phytomanagement strategies at contaminated sites. The mapping of the risk mitigation mechanisms is done by an extensive literature review and the Swedish national soil guideline value model is used to derive the most relevant human health exposure pathways and ecological risks for generic green land use scenarios. Results indicate that most of the expected risk mitigation mechanisms are supported by literature, but that knowledge gaps still exist. The framework is demonstrated to support the identification of GRO options for the case study site given two envisioned land uses: biofuel park and allotment garden. A more easily understandable risk management framework, as proposed here, is expected to act as a communication tool to educate decision-makers, regulatory bodies and other stakeholders for better understanding of risk mitigation mechanisms and preliminary timeframes of various GRO, particularly in the early stages of a brownfield redevelopment project.

Response of Three Miscanthus × giganteus Cultivars to Toxic Elements Stress: Part 1, Plant Defence Mechanisms

Miscanthus × giganteus demonstrated good phytostabilization potentials in toxic element (TE) contaminated soils. However, information about its tolerance to elevated concentrations is still scarce. Therefore, an ex-situ pot experiment was launched using three cultivars (termed B, U, and A) grown in soils with a gradient Cd, Pb and Zn concentrations. Control plants were also cultivated in non-contaminated soil. Results show that the number of tillers per plant, stem diameter as well as leaf photosynthetic pigments (chlorophyll a, b and carotenoids) were negatively impacted by soil contamination. On the other hand, phenolic compounds, flavonoids, tannins, and anthocyanins levels along with the antioxidant enzymatic activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase increased in the plants grown on contaminated soils. Altogether, these data demonstrate that miscanthus is impacted by concentrations of toxic elements yet is able to tolerate high levels of soil contamination. These results may contribute to clarifying the miscanthus tolerance strategy against high contamination levels and its efficiency in phytoremediation.

Potentials of Miscanthus x giganteus for phytostabilization of trace element-contaminated soils: Ex situ experiment

Phytomanagement is proposed as a cost-effective and environmentally-friendly suggestion for sustainable use of large metal-contaminated areas. In the current work, the energy crop miscanthus (Miscanthus × giganteus) was grown in ex situ conditions on agricultural soils presenting a Cd, Pb and Zn contamination gradient. After 93 days of culture, shoot and root growth parameters were measured. Soils and plants were sampled as well to study the TE accumulation in miscanthus and the effects of this plant on TE mobility in soils. Results demonstrated that miscanthus growth depended more on the soils silt content rather than TE-contamination level. Moreover, soil organic carbon at T93 increased in the soils after miscanthus cultivation by 25.5-45.3%, whereas CaCl₂-extractible TEs decreased due to complex rhizosphere processes driving plant mineral uptake, and organic carbon inputs into the rhizosphere. In the contaminated soils, miscanthus accumulated Cd, Pb and Zn mainly in roots (BCF in roots: Cd " Zn > Pb), while strongly reducing the transfer of these elements from soil to all organs and from roots to rhizomes, stems and leaves (average TFs: 0.01-0.06, 0.11-1.15 and 0.09-0.79 corresponding to Cd, Pb and Zn respectively). Therefore, miscanthus could be considered a TE-excluder, hence a potential candidate crop for coupling phytostabilization and biomass production on the studied Metaleurop TE-contaminated soils.

Stress Response of Miscanthus Plants and Soil Microbial Communities: A Case Study in Metals and Hydrocarbons Contaminated Soils

Second-generation biofuel crop miscanthus is one of the most promising plants tested for phytomanagement of contaminated sites. In this preliminary pot case study, the most used hybrid Miscanthus x giganteus was cultivated in three different real contaminated soils: agricultural soil contaminated with Cd; post-military soil slightly contaminated with Zn, Pb and Cd; and soil contaminated by petroleum industry with metals and hydrocarbons. The stress response of plants and soil microbial communities was monitored to receive data that are important for successful phytomanagement application. With metals only, the plant grew well, and chlorophyll fluorescence measurement proved their good vitality. Changes in leaf anatomy (leaf thickness and sclerenchyma cells area) were additionally determined in post-military soil compared to agricultural. On the contrary, in petroleum-contaminated soil, the biomass yield was too reduced and also physiological parameters were significantly decreased. The response of microbial communities also differed. In agricultural soil, no microbial stress was determined. In post-military soil, it became reduced during the experiment, and in petroleum contamination, it increased year-on-year. It could be concluded that miscanthus is suitable for cultivation in metals contaminated soils with potential for microbial communities support, but in soil contaminated by the petroleum industry, its application did not seem meaningful.

Miscanthus x giganteus culture on soils highly contaminated by metals: Modelling leaf decomposition impact on metal mobility and bioavailability in the soil-plant system

Miscanthus x giganteus is suggested as a good candidate for phytostabilization of metal-polluted soils. Its late harvest in winter generates large amounts of leaf litter on the soil surface. However, little is known about the mobility and the bioavailability of metals following leaf decomposition and the consequences on the succeeding culture. Ex situ artificial aging for 1, 3, and 6 months was conducted with miscanthus leaf fragments incorporated into three agricultural soils displaying a gradient concentration in Cd (0.6, 3.1 and 7.9 mg kg^-1), Pb (32.0, 194.6 and 468.6 mg kg^-1), and Zn (48.4, 276.3 and 490.2 mg kg^-1) to simulate the leaf litter input over 20 years of miscanthus culture. We investigated the impacts on physicochemical and biological soil parameters, CaCl₂-extractable metal, and their subsequent ryegrass shoot concentrations, and hence on ryegrass health. The results showed that the amended soils possessed higher pH along with greater available phosphorous and soil organic carbon values. The respiratory activity and microbial biomass carbon in the amended soils increased mainly after 1 month of aging, and decreased afterwards. Despite the higher Pb- and Zn-CaCl₂ extractability in the amended soils, the phytoavailability slightly increased only in the most contaminated soils. Moreover, leaf incorporation did not affect the ryegrass biomass, photosynthetic pigment contents, nor the antioxidative enzyme activities. Conclusively, leaf incorporation induced slight variations in soil physicochemical and biological parameters, as well as metal extractability, but not to an extent that might cause a considerable threat to the subsequent culture. Nevertheless, these results are preliminary data that require confirmation by long-term in-situ experimentations as they reflect the modelization of long-term impact of leaf decomposition on soil-plant system.

Bioaccessibility and human health risk assessment of metal(loid)s in soil from an e-waste open burning site in Agbogbloshie, Accra, Ghana

Environmental pollution and human health issues due to unrestricted electronic waste (e-waste) recycling activities have been reported at a number of locations. Among different e-waste recycling techniques, open burning of e-waste releases diverse metal(loid)s into the environment, which has aroused concern worldwide. In human health risk assessments (HHRAs), oral ingestion of soil can be a major route of exposure to many immobile soil contaminants. In vitro assays are currently being developed and validated to avoid overestimation of pollutants absorbed by the human body when calculating total pollutant concentrations in HHRAs. In this study, Cu, As, Cd, Sb, and Pb bioaccessibility in polluted soils (n = 10) from e-waste open burning sites at Agbogbloshie in Accra, Ghana, was assessed using an in vitro assay, the physiologically based extraction test. A bioaccessibility-corrected HHRA was then conducted to estimate the potential health risks to local inhabitants. The in vitro results (%) varied greatly among the different metal(loid)s (Cu: 1.3-60, As: 1.3-40, Cd: 4.2-67, Sb: 0.7-85, Pb: 4.1-57), and also showed marked variance between the gastric phase and small intestinal phase. The particle sizes of soil samples and chemical forms of metal(loid)s also influenced bioaccessibility values. Using these bioaccessibility values, both the hazard index and carcinogenic risk were calculated. The hazard index was above the threshold value (>1) for 5/10 samples, indicating a potential health risk to local inhabitants.

Environmental availability and oral bioaccessibility of Cd and Pb in anthroposols from dredged river sediments

Dredging and disposal of sediments onto land sites is a common practice in urban and industrial areas that can present environmental and health risks when the sediments contain metallic elements. The aim of this study was to characterise and study the environmental and toxicological availability of Cd and Pb in anthroposols from dredged river sediments. To do this, 67 surface samples spread over 12 sediment disposal sites in northern France were studied. The results showed substantial heterogeneity for this matrix in terms of physicochemical parameters and contamination degree; however, ascending hierarchical clustering made it possible to classify the samples into eight groups. For each group, the mobile fraction of Cd and Pb was studied using single EDTA extraction, solid-phase distribution was analysed with sequential extractions and toxicological availability was assessed with the oral bioaccessibility test. The results showed that (i) Cd had a higher environmental and toxicological availability than Pb; (ii) this availability depends on the physicochemical characteristics of the matrix; and (iii) it is necessary to take into account the environmental and toxicological availability of contaminants when requalifying these sites in order to propose appropriate management measures. In the first years after sediment disposal, it would appear that the environmental and toxicological availability of Cd and Pb increased (from 52.5 to 71.8% and from 28.9 to 48.9%, respectively, by using EDTA and from 50.2 to 68.5% for Cd with the bioaccessibility test). Further studies would therefore be required to confirm this trend and understand the mechanisms involved.

Ex situ evaluation of the effects of biochars on environmental and toxicological availabilities of metals and polycyclic aromatic hydrocarbons

The present study experimented five biochars, one made from wood (400 °C, 12 h) and four made from miscanthus cultivated on contaminated soils (temperature 400/600 °C, duration 45/90 min). They were used as amendments at a 2% application rate on soil, cultivated or not cultivated with ryegrass, contaminated with (i) metals (Cd, Pb, and Zn), (ii) eight polycyclic aromatic hydrocarbons (PAHs), and (iii) a mix of metals and PAHs. The objectives were (i) to compare the effectiveness of the five biochars on soil parameters and pollutant availability and (ii) to determine the influence of soil multicontamination and ryegrass cultivation on biochar effectiveness. The results showed that biochar application did not necessarily lead to lower pollutant extractability and metal bioaccessibility. However, differences were highlighted between the biochars. The miscanthus biochars produced at 600 °C (BM600) showed higher effectiveness at decreasing metal extractability than the miscanthus biochars produced at 400 °C (BM400) due to its better sorption characteristics. In addition, ryegrass cultivation did not impact pollutant availability but modified metal bioaccessibility, especially for the soil amended with the BM600 and the woody biochar. Moreover, the presence of PAHs also negatively impacted the metal bioaccessibility in the soil amended with the BM600, and, on the contrary, positively impacted it in the soil amended with the BM400. Complementary studies are therefore necessary to understand the mechanisms involved, particularly in a context where soils requiring remediation operations are often multicontaminated and vegetated.

Influence of amendments on metal environmental and toxicological availability in highly contaminated brownfield and agricultural soils

The immobilizing effects of wood biochar (BW2%) and iron grit (Z1%) applied alone or in combination (BW2% + Z1%) to agricultural (M750) and brownfield (MAZ) soils highly contaminated by metals were assessed in a greenhouse experiment. The results showed that Z1% and BW2% + Z1% were the most efficient amendments to reduce Cd, Cu, Pb, and Zn mobility, environmental availability, and phytoavailability in the M750 soil. The oxidation of Z1% allowed part of the Cu and Zn pools present in exchangeable or carbonate-bound forms (labile fraction) to complex in less mobile forms. In this soil, the metal chemical extractions (0.01 M CaCl₂ and 0.05 M EDTA) and the DGT (diffusive gradient in thin films) devices to assess metal in soil solution and soil pore water (SPW) also highlighted the immobilizing characteristic of Z1%. In most cases, the addition of BW2% to Z1% (BW2% + Z1%) did not improve this effect, except for the dissolved Pb and Zn concentrations in the M750 soil solution. It was also observed that Cd, Pb, and Zn passed throughout DGT mimicking the biological cell membrane were reduced by all amendments of the M750 soil corroborating metal concentrations measured in rye grass shoots. In the MAZ soil, metals were less available as shown by their low extractability rate, low capacity of metal resupply from the solid phase to pore water, and low phytoavailability. The poor metal availability could be explained by the high levels of carbonate and organic matter contents in this soil. Nevertheless, a decrease of the Cu environmental availability and the Cu concentrations in rye grass shoots grown on the MAZ soil was also observed in the soil amended with Z1% alone or in combination with BW2%. From a health point of view, the most effective amendment to reduce human exposure through ingestion of soil particles for the M750 and MAZ soils was BW2% for Cd and BW2% + Z1% for Pb. However, the presence of rye grass minimized the amendments' beneficial effects.

Bioavailability of mercury in contaminated soils assessed by the diffusive gradient in thin film technique in relation to uptake by Miscanthus × giganteus

We assessed the relationship between the diffusive gradient in thin film (DGT) technique using the new ion-exchange resin Ambersep GT74 and the uptake of mercury (Hg) by a model plant cultivated on metal-contaminated agricultural soils under greenhouse conditions. Based on the total Hg content, 0.37 to 1.17% of the Hg passed to the soil porewater from the solid phase, and 2.18 to 9.18% of the Hg is DGT-available. These results were confirmed by calculating the R value (the ratio of the concentrations of bioavailable Hg measured by DGT and soil solution), which illustrated the strong bonding of Hg to the solid phase of soil and its extremely low mobility. Only inorganic Hg²⁺ species were found in the metal-contaminated agricultural soils, as determined by a high-performance liquid chromatography-cold vapor atomic fluorescence spectrometry speciation analysis. The Hg was distributed in Miscanthus × giganteus organs in the following order for all sampling sites: roots (55-82%) >> leaves (8-27%) > stems (7-16%) > rhizomes (4-7%). Environ Toxicol Chem 2019;38:321-328. © 2018 SETAC.

Opinion: Taking phytoremediation from proven technology to accepted practice

Phytoremediation is the use of plants to extract, immobilize, contain and/or degrade contaminants from soil, water or air. It can be an effective strategy for on site and/or in situ removal of various contaminants from soils, including petroleum hydrocarbons (PHC), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), solvents (e.g., trichloroethylene [TCE]), munitions waste (e.g., 2,4,6-trinitrotoluene [TNT]), metal(loid)s, salt (NaCl) and radioisotopes. Commercial phytoremediation technologies appear to be underutilized globally. The primary objective of this opinion piece is to discuss how to take phytoremediation from a proven technology to an accepted practice. An overview of phytoremediation of soil is provided, with the focus on field applications, to provide a frame of reference for the subsequent discussion on better utilization of phytoremediation. We consider reasons why phytoremediation is underutilized, despite clear evidence that, under many conditions, it can be applied quite successfully in the field. We offer suggestions on how to gain greater acceptance for phytoremediation by industry and government. A new paradigm of phytomanagement, with a specific focus on using phytoremediation as a "gentle remediation option" (GRO) within a broader, long-term management strategy, is also discussed.