Accumulation and translocation of heavy metal by spontaneous plants growing on multi-metal-contaminated site in the Southeast of Rio Grande do Sul state, Brazil

Taking spontaneous plants as a natural strategy for vegetation restoration in construction and demolition waste landfills: a case study in Suzhou, China

Construction and demolition waste (CDW) landfills around the city have caused serious damage to the ecological environment and menaced the public health. Restoration of closed CDW landfills is critical to compensate for the degraded ecosystem and ensure safety in further development and utilization. Vegetation restoration is an essential part of the restoration of CDW landfills, in which the use of spontaneous plants is the foundation of the nature-based strategy. In this study, Fenghuangshan CDW landfill in Suzhou, China, was selected as the research site, and the species composition and diversity of the spontaneous plants were analyzed. Moreover, the types of habitats and growth indexes of 8 species with high frequency and 18 species with medium frequency in the CDW landfill were investigated, and a comprehensive evaluation of growth rate and expansion capacity of the 26 species was conducted. The results showed that, herbs were the main type of the spontaneous plants in the CDW landfill. The species and quantities of the spontaneous plants in the CDW landfill were obviously fewer than those in the surrounding areas of the CDW landfill, and the Shannon-Wiener index and Pielou index of the spontaneous plants were lower compared with the surrounding areas of the CDW landfill. Meanwhile, the differences of dominant families and the distribution of origins, life forms and growth types between these two fields were insignificant. The heliophilous and drought tolerance species were widely distributed in the CDW landfill while the shade-tolerant or hygrophilous species were few. The relatively large comprehensive evaluation indexes of Elymus dahuricus, Daucus carota, Sonchus asper, Geranium carolinianum, Rumex acetosa, Metaplexis japonica, Carex breviculmis, Erigeron canadensis, Trigonotis peduncularis, Lamium amplexicaule reflected their high growth rates and strong expansion capacity, demonstrating their great potentiality in the vegetation restoration of CDW landfills as indispensable components of the nature-based solution.

Lawn or spontaneous groundcover? Residents' perceptions of and preferences for alternative lawns in Xianyang, China

Within urban green spaces, spontaneous groundcovers, as potential alternatives for traditional lawns, have garnered attention due to their ecological adaptability. However, little attention has been paid to whether spontaneous groundcovers can serve as suitable replacements for lawns in terms of the aesthetic values and human preferences for each. Based on questionnaires accompanied by photo elicitation, this study explored the perceptions of and preferences for seven kinds of lawns and six kinds of spontaneous groundcovers in China. The effects of social backgrounds on people's perceptions of and preferences for ground covers were also analyzed. The results indicated a general equivalence in preferences for the lawn and spontaneous groundcover. The Taraxacum mongolicum - Cynodon dactylon - Conyza canadensis community was significantly preferred most among all of the selected ground covers. Spontaneous groundcovers were regarded as more natural, wild, variable, and species-richer compared to lawns, while lawns were perceived as better kept than spontaneous groundcovers. Ground covers were preferred which were perceived to have high ecological aesthetic value and low wildness. Industry and attention to herbaceous plants mostly affected human perceptions and preferences among the social background factors, and gender, age, education level, and occupation also had significant effects. The results thus provide the support for the application of spontaneous groundcovers in moderately developed cities, but such application should consider the comprehensive development of ecological aesthetic value and the applicability of different groups of residents.

Watershed-scale assessment of environmental background values of soil potential toxic elements from the Caatinga and Atlantic forest ecotone in Brazil

The evaluation of the concentration of a potentially toxic element (PTE) in soils under native vegetation is the base study to obtain the quality reference values (QRVs), and the watershed is the strategic planning unit for decision making. The objective of this study was to determine the natural concentrations of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn and to establish QRVs for the Verruga river basin. Soils with no or minimal anthropic intervention from the surface layer (0.0-0.2 m) were collected and processed, and PTEs were extracted according to the USEPA 3051A method and determined by ICP‒OES. The quality of the analyses was checked by blank tests and soil samples certified SRM 2709 - San Joaquin Soil. The data set was subjected to exploratory analysis and multivariate statistics. The mean background concentrations of PTEs in soils showed high variability compared to other locations in Brazil and in the world and were (mg kg-1) Fe (24,300) > Mn (211.10) > Cr (40.98) > Zn (28.28) > Cu (10.68) > Ni (9.44) > Pb (4.95) > Co (4.08) > As (3.48) > Cd (0.09). The QRVs for the PTEs were established based on the 75th percentile, where (mg kg-1) Mn (124.59) > Cr (54.51) > Zn (31.66) > Cu (7.89) > Ni (7.20) > Pb (5.98) > As (4.05) > Co (3.40) > Cd (0.10). The chemical attributes and topography variation along the watershed are very heterogeneous and influence the dynamics of the PTEs. This survey will support future research on the impact of human activities on soil contamination in the watershed. This survey will support future research on environmental monitoring and the impacts caused by increased human activities on soil contamination in the Verruga river watershed, in the state of Bahia, Brazil.

Heavy metal contamination in soils of a decommissioned landfill southern Brazil: Ecological and health risk assessment

The incorrect disposal of waste negatively influences the population's quality of life and harms the environment. In Brazil, waste disposal in the open air is still a reality, which generates concerns about the contamination of the areas surrounding these dumpsites. The present work evaluated the possible environmental risks of a deactivated dumpsite in southern Brazil. The soil was characterized by physical and chemical tests, emphasizing the analysis of heavy metals Al, Fe, Cu, Mn, and Zn. Using geostatistical tools, it was possible to determine the distribution of these heavy metals in the influence of the landfill, since the metals Mn, Fe, and Zn showed a significant difference about the reference soil, indicating that they came from leaching from the landfill. The dispersion of the metals along the slope showed a tendency towards mobility since the highest concentrations were at elevations below the landfill. The area was considered contaminated due to the high scores of the evaluated indexes pollution, as the Improved Nemerow Pollution Index, which considers pollutant concentration, toxicity, and environmental impact to provide a measure of contamination, and was equivalent to 6.44, indicating that the area is contaminated. However, it presented low ecological risks, with a potential ecological risk of 18.55. As well as low risks to human health, with hazard index below the limit considered critical to health (HI < 1). Thus, the results of this study showed that the metals are released around the deactivated deposit, which compromises the environmental safety of the site, mainly due to its proximity to bodies of water that supply the region. Thus, the permanent control and monitoring of the areas of deactivated dumpsites are essential to avoid further pollution and should be included in the management plans for deactivating these deposits throughout the country.

Heavy metals and metalloids accumulation in common beans (Phaseolus vulgaris L.): A review

This review focuses on evaluating the accumulation and translocation of As, Cd, Hg, and Pb in Phaseolus vulgaris L. plants and on the possible effects of these elements on the growth of Phaseolus vulgaris L. in soil contaminated with these elements. Heavy metals (HMs) and metalloids (Ms) such as arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) represent serious environmental threats due to their wide abundance and high toxicity. HMs and Ms contamination in water and soils from natural or anthropogenic sources, is of great concern in agricultural production due to their toxic effects on plants, adversely affecting food safety and plant growth. The uptake of HMs and Ms by Phaseolus vulgaris L. plants depends on several factors including soil properties such as pH, phosphate, and organic matter. High concentrations of HMs and Ms could be toxic to plants due to the increased generation of ROS such as (O₂^•-), (^•OH), (H₂O₂), and (¹O₂) and oxidative stress due to an imbalance between ROS generation and antioxidant enzyme activity. To minimize the effects of ROS, plants have developed a complex defense mechanism based on the activity of antioxidant enzymes such as SOD, CAT, GPX, etc., and phytohormones, especially salicylic acid (SA) that can reduce the toxicity of HMs and Ms in the factors that affect the uptake of these elements by bean plants, and in addition, defense mechanisms under oxidative stress caused by the presence of As, Cd, Hg, and Pb.

Spontaneous Plant Diversity in Urban Contexts: A Review of Its Impact and Importance

To promote sustainability in urban green spaces, it is necessary to know the diversity of spontaneous species in these spaces. Based on the investigation and analysis of the relevant scientific literature, the diversity of spontaneous species and their importance was contextually discussed, along with the assessment of local biodiversity impact in green spaces. Studies on green spaces, spontaneous flora, biodiversity or ecosystem services, and studies on exotic species and adaptability were summarized. Finally, the existing issues regarding biodiversity and urbanization, and the role of spontaneous plants in restoring industrial areas were discussed. Based on the research carried out, it is considered that green spaces contain unique and useful biodiversity resulting from their management. Spontaneous flora can be a generator of plants with aesthetic character, which can be grown in an ecologically sound way in private gardens and natural spaces in town and village zones, with certain remarkable farming-biological characteristics (ecological plasticity, high hardiness, etc.). Biodiversity is a relevant feature of urban landscapes, offering multiple gains, and the conservation of this biodiversity in urban green spaces is fundamental and requires an integrated approach. However, urbanisation usually has a detrimental influence on local species’ diversity.

Driving effects and transfer prediction of heavy metal(loid)s in contaminated courtyard gardens using redundancy analysis and multilayer perceptron

The distribution and migration of heavy metal(loid)s in the soil-vegetable systems of courtyard gardens near mining areas have rarely been investigated, leading to potential food safety risks for residents. Moreover, the existing research is mainly focused on the total content of heavy metal(loid)s (tMetals) rather than the bioavailable contents (aMetals). In this study, 26 and 28 pairs of soil and vegetable samples were collected from the courtyard gardens near the Realgar mine in Baiyun Town and the lead-zinc (Pb-Zn) mine in Shuikoushan Town, respectively. The tMetal and aMetal of cadmium (Cd), mercury (Hg), arsenic (As), Pb, chromium (Cr), nickel (Ni), copper (Cu), Zn, manganese (Mn), iron (Fe), and calcium (Ca) in the samples were analyzed in this study. The results showed that courtyard gardens were polluted by various heavy metal(loid)s at varying degrees. The bioavailabilities of different metals varied significantly, among which Cd has the highest bioavailability (> 30%). In the transfer process of heavy metal(loid)s, the transfer rate (Tf) was ranked as soil-roots (1.50) > stems-leaves (1.07) > roots-stems (0.46) > stems-fruits (0.33). Redundancy analysis was used to evaluate the driving effects, and the results revealed that aCa, aZn, and aFe in soil could inhibit the absorption of aCd by plant roots. Soil organic matter was the inhibiting factor regarding the transfer of aAs and aCu, whereas it was also the promoting factor for transferring aPb, aNi, and aCr. Furthermore, the multilayer perceptron (MLP) could effectively predict the Tf of heavy metal(loid)s based on the aMetal. The R² values of the MLP were ranked as follows: 0.91 for As, 0.88 for Zn, 0.85 for Hg, 0.83 for Cu, 0.79 for Cr, 0.66 for Cd, 0.65 for Pb, and 0.52 for Ni. This study emphasizes the aMetal-based ecological characteristics and prediction ability. The study results are significant for guiding residents to strategize appropriate crop planting and ensure the safe production and consumption of vegetables.

Environmental health and risk assessment metrics with special mention to biotransfer, bioaccumulation and biomagnification of environmental pollutants

The environment pollutants, which are landed up in environment because of human activities like urbanization, mining and industrializations, affects human health, plants and animals. The living organisms present in environment are constantly affected by the toxic pollutants through direct contact or bioaccumulation of chemicals from the environment. The toxic and hazardous pollutants are easily transferred to different environmental matrices like land, air and water bodies such as surface and ground waters. This comprehensive review deeply discusses the routes and causes of different environmental pollutants along with their toxicity, impact, occurrences and fate in the environment. Environment health and risk assessment tools that are used to evaluate the harmfulness, exposure of living organisms to pollutants and the amount of pollutant accumulated are explained with help of bio-kinetic models. Biotransfer, toxicity factor, biomagnification and bioaccumulation of different pollutants in the air, water and marine ecosystems are critically addressed. Thus, the presented survey would be collection of correlations those addresses the factors involved in assessing the environmental health and risk impacts of distinct environmental pollutants.

Suitability of Selected Plant Species for Phytoremediation: A Case Study of a Coal Combustion Ash Landfill

Coal bottom and fly ash waste continue to be generated as a result of energy production from coal in the amount of about 750 million tonnes a year globally. Coal is the main source of energy in Poland, and about 338 million tonnes of combustion waste has already been landfilled. The aim of the research was to identify factors determining the Cd, Pb, Zn and Cu phytostabilisation by vegetation growing on a coal combustion waste landfill. Soil and shoots of the following plants were analysed: wood small-reed, European goldenrod, common reed; silver birch, black locust, European aspen and common oak. The influence of the location where the plants grew and the influence of the interaction between the two factors (species and location) were significant. The tree species were more effective at accumulating heavy metals than the herbaceous plants. European aspen had the highest Bioaccumulation Factor (BCF) for cadmium and zinc. A high capacity to accumulate these elements was also demonstrated by silver birch, and in the case of cadmium, by common oak. Accumulation of both lead and copper was low in all plants. The Translocation Factors (TF) indicated that the heavy metals were accumulated mainly in the roots. European aspen, silver birch and European goldenrod were shown to be most suitable for stabilization of the metals analysed in the research.

Analysis of Baccharis dracunculifolia and Baccharis trimera for Phytoremediation of Heavy Metals in Copper Mining Tailings Area in Southern Brazil

This study aimed to investigate the phytoremediation potential promoted by Baccharis dracunculifolia DC. and Baccharis trimera (Less.) DC. in copper mining tailing area, in the Southern part of Brazil. The plants were selected considering their spontaneous growth in tailing area. The phytoremediation indexes including translocation factor (TF), bioconcentration factor (BCF), metal extraction ratio (MER), and plant effective number (PEN) were assessed. Both species showed higher concentrations of heavy metals in the roots than to the shoots. B. trimera has potential for phytoextraction of Zn, Cd, Cr, and Pb and phytostabilization of Ba and Ni, whereas B. dracunculifolia demonstrated potential for phytoextraction of Pb and phytostabilization of Cu, Zn, and Ba. B. trimera showed higher potential in phytoremediation of the metals such as Cu > Zn > Cr > Ni and Cd than the B. dracunculifolia plants. A smaller number B. trimera plants was required to remove 1 g of Cu, Zn, Cr, Pb, Ni, and Cd than B. dracunculifolia plants, and implies that B. trimera is more efficient for decontamination of the metals. Both species showed potential for phytoremediation of metals in the mining tailing area under study.

Phytoremediation of Heavy Metals in Tropical Soils an Overview

The geomorphological characteristics of the materials inherent in tropical soils, in addition to the excessive use of fertilizers and pesticides, industrial waste and residues, and novel pollutants derived from emerging new technologies such as nanomaterials, affect the functionality and resilience of the soil-microorganism-plant ecosystem; impacting phytoremediation processes and increasing the risk of heavy metal transfer into the food chain. The aim of this review is to provide a general overview of phytoremediation in tropical soils, placing special emphasis on the factors that affect this process, such as nanoagrochemicals, and highlighting the value of biodiversity among plant species that have the potential to grow and develop in soils impacted by heavy metals, as a useful resource upon which to base further research.

Ecological restoration of coal fly ash-dumped area through bamboo plantation

The present study entails the phytoremediation potential of different bamboo species on 5-year-old FA-dumped site near Koradi thermal power plant of Nagpur, Maharashtra, India. The selected FA-dumped site was treated with farmyard manure, press mud, and bio fertilizer followed by plantation of six promising species of bamboo namely Bambusa balcooa Roxb., Dendrocalamus stocksii (Munro.) M. Kumar, Remesh and Unnikrishnan, Bambusa bambos (L.) Voss, Bambusa wamin E.G. Camus, Bambusa vulgaris var. striata (Lodd. ex Lindl.) Gamble, and Bambusa vulgaris var. vittata Riviere and Riviere. The experimental results indicated that the organic input in the FA-dumped site nourished the soil by improving its physico-chemical, and biological characteristics. The results revealed the contamination of the site with different trace elements in varied quantity including Cr (89.29 mg kg-1), Zn (84.77 mg kg-1), Ni (28.84 mg kg-1), Cu (22.91 mg kg-1), Li (19.65 mg kg-1), Pb (13.47 mg kg-1), and Cd (2.35 mg kg-1). A drastic reduction in concentration of heavy metals in FA was observed after 1 year of bamboo plantation as compared to the initial condition. The results showed that bamboo species are good excluders of Ba, Co, Cr, Li, Ni, Mn, and Zn, whereas they are good accumulators of Cd, Pb, and Cu. The values of biochemical parameters, such as pH, total chlorophyll, ascorbic acid (AA), and relative water content of all the bamboo leaves ranged from 5.11-5.70, 1.56-6.33 mg g-1, 0.16-0.19 mg g-1, and 60.23-76.68%, respectively. It is thereby concluded that the bamboo plantation with biofertilizers and organic amendments may indicate adaptive response to environmental pollution on FA-dumped site.

Accumulation of heavy metals and bacteriological indicators in spinach irrigated with further treated secondary wastewater

Shortage of water for agriculture has resulted in the need to explore the use of wastewater for irrigation, however this can pose a health problem to the people emanating from the produced food as a result of the accumulation of pollutants. The purpose of this research was to investigate the accumulation of some heavy metals and bacteriological indicators in the different parts of spinach vegetable irrigated with secondary wastewater effluent treated through a pilot filtration system. There was a variation of heavy metals accumulation in the roots, stem and leafy parts of the vegetable. Bioaccumulation factors of some metals were greater than 1 in the roots and stems but not in the leaves. Three heavy metals being copper, iron and zinc revealed high translocation factors in the stems than leaves; whereas arsenic, chromium, nickel, manganese and lead had high translocation factors in the leaves than stems. Health index coefficients in the stem during the first, second and third months were 2.33, 0.18 and 3.57 respectively, and corresponding values in the leaves were 0.68, 0.09 and 6.75 if consumed by adults. The health index values greater than 1 in children were 2.68 in the stem during the first month and then 4.1 and 7.76 in the stem and leaves during the third month for spinach consumed by children. There was no bacteriological indicators detected in the aboveground parts of the vegetable. To conclude, irrigation of vegetables should be practiced using secondary treated wastewater and monitoring over time intervals in order to safe guard human health.

Bioprospection of indigenous flora grown in copper mining tailing area for phytoremediation of metals

The study evaluated plants with phytoremediation potential that occur spontaneously in an area of copper mining tailings in Southern of Brazil. Eleven plant species were investigated for heavy metal concentrations in its biomass. All species showed copper concentrations greater than 100 mg kg^-1, and seven species highlighted for copper concentrations between 321 and 586 mg kg^-1 and these species showed Cr concentrations between 25 and 440 mg kg^-1. The species S. viarum Dunal and B. trimera Less were highlighted showing the highest concentrations of Cr (586 mg kg^-1) and Cu (440 mg kg^-1), respectively. Seven species showed Pb phytoextraction potential and four species showed Cu phytostabilization potential. It was concluded that the investigated species are adapted to low nutritional conditions and showed tolerance to heavy metals, mainly Cu, Pb and Cr in its biomass.

A Back Propagation Neural Network Model Optimized by Mind Evolutionary Algorithm for Estimating Cd, Cr, and Pb Concentrations in Soils Using Vis-NIR Diffuse Reflectance Spectroscopy

Visible and near infrared spectroscopy is an effective method for monitoring the content of heavy metals in soil. However, due to the difference between polluted soil with phytoremediation and without phytoremediation, the common estimation model cannot meet accuracy requirements. To solve this problem, combined with an ecological restoration experiment for soil contamination using the plant Neyraudia reynaudiana, this study explored the feasibility of using a hyperspectral technology to estimate the heavy metal content (Cd, Cr, and Pb) of soil under phytoremediation. A total of 108 surface soil samples (from depths of 0–20 cm) were collected. Inversion models were established using partial least squares regression (PLSR) and the back propagation neural network optimized by a mind evolutionary algorithm (MEA-BPNN). The results revealed that: (1) modeling with derivative-transformed spectra can effectively enhance the correlation between soil spectral reflectance and heavy metal content. (2) Compared with the BP neural network model, the estimation accuracy (R2) was improved from 0.728, 0.737, and 0.675 to 0.873, 0.884, and 0.857 using the MEA-BP neural network model. The residual prediction deviation (RPD) values for the three heavy metals Cd, Cr, and Pb using the MEA-BPNN model were 2.114, 3.000, and 2.560, respectively. Among them, the estimated model of Cd was an excellent prediction. (3) Compared with PLSR, the model prediction results established by the MEA-BP neural network had higher estimation accuracy. In summary, the use of diffuse reflectance spectroscopy to predict heavy metal content provides a theoretical basis for further study of the large-scale monitoring of soil heavy-metal pollution and its remediation evaluation in the polluted area, which is of great significance.

Trace metal uptake by native plants growing on a brownfield in France: zinc accumulation by Tussilago farfara L

Several human activities such as mining, smelting, or transportations lead to trace metal pollution in soil. The presence of these pollutants can represent environmental and organism health risks. Phytoextraction can be used to remediate trace metal-contaminated soils. It uses the plants' ability to remove trace metals from soil and to accumulate them in their shoots, which can then be harvested. We studied the spontaneous vegetation growing on a brownfield located in France. The use of native plants is interesting since spontaneous vegetation is already well adapted to the site's environmental conditions leading to a better survival and growth than non-native plants. Ten native plant species were sampled, and the Cr, Cu, Cd, Ni, Pb, and Zn concentrations present in their shoots were measured. In order to determine the plant's capacity to extract trace metals from the soil, the bioconcentration factor (BCF) was calculated for each plant and trace metal. Plants with a BCF greater than 1 are able to accumulate trace metals in their shoots and could be a good candidate to be used in phytoextraction. Results underscored one new accumulator plant for Zn, Tussilago farfara L., with a BCF value of 3.069. No hyperaccumulator was found among the other sampled plants. Our preliminary study showed that T. farfara is able to accumulate zinc in its shoots. Moreover, this native plant is a pioneer species able to quickly colonize various habitats by vegetative multiplication. That is why T. farfara  L. could be interesting for zinc phytoextraction and could be worth further studies.

Cutting frequency effect on barium phytoextraction by macrophytes in flooded environment: A field trial

In anoxic environmental conditions and with a drastic reduction of the redox potential, the barium sulphate used in petroleum drilling fluids becomes a hazard to the ecosystem. A field study was conducted in Brazil in an area with a history of accidental Barium (Ba) contamination to evaluate the role of frequent plant cutting on phytoremediation. The plant species Typha domingensis and Eleocharis acutangula, cultivated in a combined plantation, were subjected to four different cut frequencies: every 90 days (four cuts), 120 days (three cuts), 180 days (two cuts), or 360 days (one cut). The total amount of Ba extracted from the soil by the plants was evaluated for each treatment and at different soil depths Overall, total Ba in the soil decreased the most dramatically for cut frequencies of 120 (37.83%) and 180 (47.73%) days at 0-0.2 m below the surface, and with cut frequencies of 120 (51.98%) and 360 (31.79%) at 0.2-0.4 m depth. Further, total Ba in the plant biomass was greatest in the 120 and 360-days frequency groups. Thus, cuts at intervals of 120 days or more are associated with high levels of Ba in the plant tissue and a decrease of soil Ba.

Pb2+ adsorption by a compost obtained from the treatment of tobacco from smuggled cigarettes and industrial sewage sludge

The adsorption of Pb2+ by a compost obtained from the treatment of tobacco from smuggled cigarettes (SCT) and industrial sewage sludge (ISS) was investigated. The Pb2+ adsorption process was evaluated as function of different concentrations of adsorbent and adsorbate, pH variations, and contact time. Fourier transformed infrared spectroscopy (FTIR) and energy dispersive X-ray spectrometry (EDX) were adopted to obtain information regarding structural changes and a better understanding of the adsorption mechanism. The adsorbent maximum adsorption capacity for Pb2+, calculated using the Sips equation, was 21.454 mg/g with 3 g/L adsorbent at pH 5. The adsorption kinetics best adjustment was obtained using the pseudo-second-order model with a time of 240 min to reach the adsorption equilibrium. FTIR and EDX results suggest that Pb2+ might have bonded to phenolic, carboxylic, hydroxyl, and amine groups; they also show formation of organometallic complexes and cationic exchange between the compost and the solution. The study confirmed that the compost evaluated can be used as a potential adsorbent in environments contaminated with Pb2+.

Selection of plants for phytoremediation of barium-polluted flooded soils

The use of barite (BaSO4) in drilling fluids for oil and gas activities makes barium a potential contaminant in case of spills onto flooded soils, where low redox conditions may increase barium sulfate solubility. In order to select plants able to remove barium in such scenarios, the following species were evaluated on barium phytoextraction capacity: Brachiaria arrecta, Cyperus papyrus, Eleocharis acutangula, E. interstincta, Nephrolepsis cf. rivularis, Oryza sativa IRGA 424, O. sativa BRS Tropical, Paspalum conspersum, and Typha domingensis. Plants were grown in pots and exposed to six barium concentrations: 0, 2.5, 5.0, 10.0, 30.0, and 65.0 mg kg^-1. To simulate flooding conditions, each pot was kept with a thin water film over the soil surface (∼1.0 cm). Plants were evaluated for biomass yield and barium removal. The highest amount of barium was observed in T. domingensis biomass, followed by C. papyrus. However, the latter exported most of the barium to the aerial part of the plant, especially at higher BaCl₂ doses, while the former accumulated barium preferentially in the roots. Thus, barium removal with C. papyrus could be achieved by simply harvesting aerial biomass. The high amounts of barium in T. domingensis and C. papyrus resulted from the combination of high barium concentration in plant tissues with high biomass production. These results make T. domingensis and C. papyrus potential candidates for phytoremediation schemes to remove barium from flooded soils.

Pilot scale aided-phytoremediation of a co-contaminated soil

A pilot scale experiment was conducted to investigate the aided-phytoextraction of metals and the aided-phytodegradation of petroleum hydrocarbons (PHC) in a co-contaminated soil. First, this soil was amended with compost (10% w/w) and assembled into piles (Unp-10%C). Then, a phyto-cap of Medicago sativa L. either in monoculture (MS-10%C) or co-cropped with Helianthus annuus L. as companion planting (MSHA-10%C) was sown on the topsoil. Physico-chemical parameters and contaminants in the soil and its leachates were measured at the beginning and the end of the first growth season (after five months). In parallel, residual soil ecotoxicity was assessed using the plant species Lepidium sativum L. and the earthworm Eisenia fetida Savigny, 1826, while the leachate ecotoxicity was assessed using Lemna minor L. After 5months, PH C10-C40, PAH-L, PAH-M PAH-H, Pb and Cu concentrations in the MS-10%C soil were significantly reduced as compared to the Unp-10%C soil. Metal uptake by alfalfa was low but their translocation to shoots was high for Mn, Cr, Co and Zn (transfer factor (TF) >1), except for Cu and Pb. Alfalfa in monoculture reduced electrical conductivity, total organic C and Cu concentration in the leachate while pH and dissolved oxygen increased. Alfalfa co-planting with sunflower did not affect the extraction of inorganic contaminants from the soil, the PAH (M and H) degradation and was less efficient for PH C10-C40 and PAH-L as compared to alfalfa monoculture. The co-planting reduced shoot and root Pb concentrations. The residual soil ecotoxicity after 5months showed a positive effect of co-planting on L. sativum shoot dry weight (DW) yield. However, high contaminant concentrations in soil and leachate still inhibited the L. sativum root DW yield, earthworm development, and L. minor growth rate.

Bioavailability and risk assessment of potentially toxic elements in garden edible vegetables and soils around a highly contaminated former mining area in Germany

Although soil contamination by potentially toxic elements (PTEs) in Europe has a history of many centuries, related problems are often considered as having been dealt with due to the enforcement of tight legislations. However, there are many unsolved issues. We aimed to assess PTE levels in highly contaminated soils and in garden edible vegetables using human health risk indices in order to evaluate the availability and mobilization of arsenic (As), copper (Cu), manganese (Mn), mercury (Hg), lead (Pb), and zinc (Zn). In four gardens in Germany, situated on, or in the vicinity of, a mine dump area, we planted beans (Phaseolus vulgaris ssp. nanus), carrots (Daucus sativus) and lettuce (Lactuca sativa ssp. capitata). We examined soil-to-plant mobilization of elements using transfer coefficient (TC), as well as soil contamination using contamination factor (CF), enrichment factor (EF), and bioaccumulation index (I_geo). In addition, we tested two human health risk assessment indices: Soil-induced hazard quotient (HQ_S) (representing the "direct soil ingestion" pathway), and vegetable-induced hazard quotient (HQ_V) (representing the "vegetable intake" pathway). The studied elements were highly elevated in the soils. The values in garden 2 were especially high (e.g., Pb: 13789.0 and Hg: 36.8 mg kg^-1) and largely exceeded the reported regulation limits of 50 (for As), 40 (Cu), 400 (Pb), 150 (Zn), and 5 (Hg) mg kg^-1. Similarly, element concentrations were very high in the grown vegetables. The indices of CF, EF and I_geo were enhanced even to levels that are rarely reported in the literature. Specifically, garden 2 indicated severe contamination due to multi-element deposition. The contribution of each PTE to the total of measured HQ_S revealed that Pb was the single most important element causing health risk (contributing up to 77% to total HQ_S). Lead also posed the highest risk concerning vegetable consumption, contributing up to 77% to total HQ_V. The presence of lead in both cases was followed by that of As, Mn and Hg. We conclude that in multi-element contamination cases, along with high-toxicity elements (here, Pb, As and Hg) other elements may also be responsible for increasing human health risks (i.e., Mn), due to the possibility of adverse synergism of the PTEs.

Metal-resistant rhizobacteria isolates improve Mucuna deeringiana phytoextraction capacity in multi-metal contaminated soils from a gold mining area

Phytoremediation consists of biological techniques for heavy metal remediation, which include exploring the genetic package of vegetable species to remove heavy metals from the environment. The goals of this study were to investigate heavy metal and bioaugmentation effects on growth and nutrient uptake by Mucuna deeringiana; to determine the metal translocation factor and bioconcentration factor and provide insight for using native bacteria to enhance heavy metal accumulation. The experiment was conducted under greenhouse conditions using a 2 × 4 factorial scheme with highly and slightly contaminated soil samples and inoculating M. deeringiana with three highly lead (Pb⁺²)-resistant bacteria Kluyvera intermedia (Ki), Klebsiella oxytoca (Ko), and Citrobacter murliniae (Cm) isolated from the rhizosphere of native plants identified as Senecio brasiliensis (Spreng.) Less., Senecio leptolobus DC., and Baccharis trimera (Less) DC., respectively. The increased heavy metal concentrations in soil samples do not decrease the root dry mass of M. deeringiana, concerning the number and dry weight of nodules. The shoot dry mass is reduced by the increasing concentration of heavy metals in soil associated with Kluyvera intermedia and Klebsiella oxytoca bacteria. The number of nodules is affected by heavy metals associated with Citrobacter murliniae bacteria. The bacteria K. intermedia, C. murliniae, and K. oxytoca increase the lead and cadmium available in the soil and enhanced metal uptake by Mucuna deeringiana. The M. deeringiana specie has characteristics that make it hyperaccumulate copper and zinc. The translocation and bioconcentration factors for M. deeringiana characterize it as a promising candidate to phytostabilize multi-metal contaminated soils.