METAL UPTAKE AND ALLOCATION IN TREES GROWN ON CONTAMINATED LAND: IMPLICATIONS FOR BIOMASS PRODUCTION

Phytostabilization aims to reduce environmental and health risks arising from contaminated soil. To be economically attractive, plants used for phytostabilization should produce valuable biomass. This study investigated the biomass production and metal allocation to foliage and wood of willow (Salix viminalis L.), poplar (Populus monviso), birch (Betula pendula), and oak (Quercus robur) on five different soils contaminated with trace elements (TE), with varying high concentrations of Cu, Zn, Cd, and Pb as well as an uncontaminated control soil. In the treatment soils, the biomass was reduced in all species except oak. There was a significant negative correlation between biomass and foliar Cd and Zn concentrations, reaching up to 15 mg Cd kg^?1 and 2000 mg Zn kg ^?1 in willow leaves. Lead was the only TE with higher wood than foliage concentrations. The highest Pb accumulation occurred in birch with up to 135 mg kg ^?1 in wood and 78 mg kg ^?1 in foliage. Birch could be suitable for phytostabilization of soils with high Cd and Zn but low Pb concentrations, while poplars and willows could be used to stabilise soils with high Cu and Pb and low Zn and Cd concentrations.     

Effects of mine effluent on uptake of Co,Ni, Cu,As, Zn,Cd, Cr and Pb by aquatic macrophytes

Concentrations of Ni, Co, Cu, Pb, Zn, Cd, Cr and As were determined in aquatic sediments, water and macrophytes collected from a fluvial system, contaminated by mine effluents. Myriophyllum verticillatum collected in May below the trace element point source accumulated 169 µg/g of Ni, 860 µg/g of Co, 37 µg/g of Cu, 31 µg/g of Pb, 92 µg/g of Zn, 6.9 µg/g of Cr and 1,200 µg/g of As (concentrations in dry weight). The aquatic macrophytes Nymphaea odoratae and Pontederia cordata accumulated the investigated trace elements to a much lesser extent. The concentrations of trace elements in Myriophyllum verticillatum decreased from May to August. Correlations were found between the concentrations of total Ni, Co and Cu in the bottom sediment and in the submerged macrophytes. However, there was no correlation between the amounts of these trace elements extractable by 0.5 N HCl from the sediments and the concentrations in the macrophytes.     

Phytostabilization of Acidic Soils with Heavy Metal Contamination Using Three Forage Grasses in Combination with Organic and Inorganic Amendments

Two experiments were conducted to investigate the effects of organic and inorganic amendments on metal stabilization and the potential of three forage grasses, i.e., Pennisetum americanum × Pennisetum, Euchlaena mexicana, and Sorghum dochna, for phytostabilization of acidic heavy metal-contaminated soils. The three grasses died 5 days after transplanting into the contaminated soils. Organic fertilizer (pig slurry and plant ash) only or combined with lime, NPK fertilizer, and sewage sludge resulted in adequate grass growth in the contaminated soils through a significant increase in the soil pH, N, P, K, and organic matter contents, and a decrease in the metal concentrations. The shoot biomass of P. americanum×P. purpureum and S. dochna was 1.92 and 2.00 times higher than that of E. Mexicana. The solubility of Cd, Pb, and Zn strongly depends on organic matter, while the solubility of Cu strongly depends on both soil organic matter and pH. The concentrations of Cd, Pb, and Zn in plant shoots growing in soil with a mixed amendment were significantly lower than plants growing in soil amended with an organic fertilizer only, whereas the Cu concentrations in plant shoots exhibited the opposite trend. The results indicated that 5% organic fertilizer only or combined with 5% sewage sludge were appropriate amendments and S. dochna and P. americanum × Pennisetum are suitable plants for phytostabilization of acidic heavy metal-polluted soils.     

Soil trace element changes during a phytoremediation trial with willows in southern Québec,Canada

This study determined the changes in trace elements (TE) (As, Cd, Cu, Ni, Pb, Zn) chemistry in the soils of a willow (“Fish Creek” – Salix purpurea, SV1 – Salix x dasyclados and SX67 – Salix miyabeana) plantation growing under a cold climate during a three-year trial. The soil HNO₃-extractable and H₂O-soluble TE concentrations and pools significantly decreased under most cultivars (Fish, SX67). Yet, TE changes showed inconsistent patterns and localized soil TE increases (Ni, Pb) were measured. Temporal changes in soil TE were also detected in control plots and sometimes exceeded changes in planted plots. Discrepancies existed between the amount of soil TE change and the amount of TE uptake by willows, except for Cd and Zn. Phytoremediation with willows could reduce soil Cd and Zn within a decadal timeframe indicating that they can be remediated by willows in moderately contaminated soils. However, the time needed to reduce soil As, Cu, Ni and Pb was too long to be efficient. We submit that soil leaching contributed to the TE decrease in controls and the TE discrepancies, and that the plantation could have secondary effects such as the accelerated leaching of soil TE.     

Hydroponic screening of poplar for trace element tolerance and accumulation

Using the nutrient film technique, we screened 21 clones of poplar for growth in the presence of a mix of trace elements (TE) and for TE accumulation capacities. Poplar cuttings were exposed for four weeks to a multipollution solution consisting in 10 microM Cd, Cu, Ni, and Pb, and 200 microM Zn. Plant biomass and TE accumulation patterns in leaves varied greatly between clones. The highest Cd and Zn concentrations in leaves were detected in P. trichocarpa and P. trichocarpa hybrids, with the clone Skado (P. trichocarpa x P. maximowiczii) accumulating up to 108 mg Cd kg(-1) DW and 1510 mg Zn kg(-1) DW when exposed to a multipollution context. Our data also confirm the importance of pH and multipollution, as these factors greatly affect TE accumulation in above ground biomass. The NFT technique applied here to a large range of poplar clones also revealed the potential of the Rochester, AFO662 and AFO678 poplar clones for use in phytostabilization programs and bioenergy production, where production of less contaminated above ground biomass is suitable.     

Variation in the uptake of Arsenic, Cadmium, Lead, and Zinc by different species of willows Salix spp. grown in contaminated soils

The experiment assessed the variability of in seven clones of willow plants of high biomass production (Salix smithiana S-218, Salix smithiana S-150, Salix viminalis S-519, Salix alba S-464, Salix ’Pyramidalis’ S-141, Salix dasyclados S-406, Salix rubens S-391). They were planted in a pots for three vegetation periods in three soils differing in the total content of risk elements. Comparing the calculated relative decrease of total metal contents in soils, the phytoextraction potential of willows was obtained for cadmium (Cd) and zinc (Zn), moderately contaminated Cambisol and uncontaminated Chernozem, where aboveground biomass removed about 30% Cd and 5% Zn of the total element content, respectively. The clones showed variability in removing Cd and Zn, depending on soil type and contamination level: S. smithiana (S-150) and S. rubens (S-391) demonstrated the highest phytoextraction effect for Cd and Zn. For lead (Pb) and arsenic (As), the ability to accumulate the aboveground biomass of willows was found to be negligible in both soils. The results confirmed that willow plants show promising results for several elements, mainly for mobile ones like cadmium and zinc in moderate levels of contamination. The differences in accumulation among the clones seemed to be affected more by the properties of clones, not by the soil element concentrations or soil properties. However, confirmation and verification of the results in field conditions as well as more detailed investigation of the mechanisms of cadmium uptake in rhizosphere of willow plants will be determined by further research.     

Effect of Compost and Biochar on Heavy Metals Phytostabilization by the Halophytic Plant Old Man Saltbush [Atriplex Nummularia Lindl]

Remediation of soils is vital to mitigate the negative effects of heavy metals in ecosystems. There is little information available about the metals’ phytostabilization potential of old man saltbush plants [Atriplex nummularia]. A pot experiment in a randomized complete block design was conducted to study the accumulation of heavy metals by old man saltbush plants, as affected by the application of compost and biochar. The cultivation of A. nummularia is an effective tool in immobilizing metals in the contaminated soils. The cultivation of metal-contaminated soil with A. nummularia reduced the availability of Zn, Cu, Cd, and Pb by 20%, 4%, 21%, and 28%, respectively, in comparison to the non-cultivated soil. Zn, Cu, Cd, and Pb concentrations in the aboveground parts of old man saltbush plants were 70–100, 50–80, 4–5, and 50–90 mg/kg of dry biomass. The higher Zn, Cu, Cd, and Pb concentrations were accumulated in the roots, and the lower concentrations were transferred to the shoots of old man saltbush plants. Compost reduced the concentration of Zn, Cu, Cd, and Pb in the shoots by 10%, 19%, 20%, and 6%, respectively, compared to the control soil. Biochar reduced the concentrations of Zn, Cu, and Pb in the shoots by 30%, 38%, and 44%, respectively, compared to the control. Compost had a lower effect in reducing the metals uptake as biochar. Biochar reduced the uptake of Zn, Cu, and Pb in the shoots of the tested plant by 22%, 23%, and 41%, respectively, in comparison to compost. Based on the obtained results, old man saltbush has good characteristics to be a promising candidate for phytostabilization strategies of metal-contaminated soils. Moreover, biochar is a good tool to enhance metals’ phytostablization.     

Exposure assessment of potentially toxic trace elements via consumption of fruits and vegetables grown under the impact of Alaverdi's mining complex

This study is aimed to investigate the transfer of potentially toxic trace elements from soils to plants grown under the impact of Alaverdi's mining complex and assess the related dietary exposure to local residents. Contamination levels of potentially toxic trace elements (Cu, Ni, Pb, Zn, Hg, As, Cd) in soils and plants were determined and afterwards, transfer factors, estimated daily intakes, target hazard quotients, and hazard indexes were calculated.

Some trace elements (Pb, Zn, Cd) exceeded the maximum allowable levels. EDIs of Cu, Ni, Hg for the majority of studied fruits and vegetables exceeded the health-based guideline values. Meanwhile, in case of combined consumption of the studied food items, the estimated cumulative daily intakes exceeded health-based guideline values not only for the aforementioned trace elements but also for Zn in the following sequence: Zn > Hg > Ni > Cu. HI > 1 values highlighted the potential adverse health effects for local population through more than one trace element.

Detailed investigations need to be done for the overall assessment of health risks, taking into consideration not only adverse health effects posed by more than one toxic trace element but also through other exposure pathways.     

Sorption behavior of Cd, Cu, Pb, and Zn and their interactions in phytoremediated soil

The aim of our study was to compare the sorption properties of a contaminated soil before and after two types of phytoremediation (natural phytoextraction vs. phytostabilization with dolomite limestone (DL) application). Soil from a pot experiment in controlled greenhouse conditions performed for two vegetation periods was used for the study. Lead, as the main contaminant in the studied soil, was easily desorbed by Cu, especially due to the increased affinity of Cu for soil organic matter; hence input of Cu to the studied soil can present another environmental risk in soils contaminated with other metals (such as Pb). In addition, the sorption behavior of chosen metals from single-element solutions differed from multielement solutions. The obtained results proved the different sorption behavior of metals in the single-element solution compared to the multi-element ones. Soil sorption behavior of Cd, Cu, and Zn decreased with the presence of the competitive metals; nevertheless, Pb sorption potential was not influenced by other competitive metals. Natural phytoextraction showed no significant effect on the sorption of Cd, Cu, Pb, and Zn onto the soil On the other hand, phytostabilization associated with DL application improved the soil sorption efficiency of all chosen metals, especially of Cu.     

PHYTOREMEDIATION OF INORGANICS: REALISM AND SYNERGIES

There are very few practical demonstrations of the phytoextraction of metals and metalloids from soils and sediments beyond small-scale and short-term trials. The two approaches used have been based on using 1) hyperaccumulator species, such as Thlaspi caerulescens (Pb, Zn, Cd, Ni), Alyssum spp. (Ni, Co), and Pteris vittata (As) or 2) fast-growing plants, such as Salix and Populus spp. that accumulate above-average concentrations of only a smaller number of the more mobile trace elements (Cd, Zn, B). Until we have advanced much more along the pathway of genetic isolation and transfer of hyperaccumulator traits into productive plants, there is a high risk in marketing either approach as a technology or stand-alone solution to clean up contaminated land. There are particular uncertainties over the longer-term effectiveness of phytoextraction and associated environmental issues. Marginally contaminated agricultural soils provide the most likely land use where phytoextraction can be used as a polishing technology. An alternative and more useful practical approach in many situations currently would be to give more attention to crops selected for phytoexclusion: selecting crops that do not translocate high concentrations of metals to edible parts. Soils of brownfield, urban, and industrial areas provide a large-scale opportunity to use phytoremediation, but the focus here should be on the more realistic possibilities of risk-managed phytostabilization and monitored natural attenuation. We argue that the wider practical applications of phytoremediation are too often overlooked. There is huge scope for cross-cutting other environmental agenda, with synergies that involve the recovery and provision of services from degraded landscapes and contaminated soils. An additional focus on biomass energy, improved biodiversity, watershed management, soil protection, carbon sequestration, and improved soil health is required for the justification and advancement of phytotechnologies.     

The phytoremediation of an organic and inorganic polluted soil: A real scale experience

A phytoremediation process with horse manure, plants (Populus alba, Cytisus scoparius, Paulownia tomentosa) and naturally growing vegetation was carried out at a real-scale in order to phytoremediate and functionally recover a soil contaminated by metals (Zn, Pb, Cd, Ni, Cu, Cr), hydrocarbons (TPH) and polychlorobiphenyls (PCB).

All the plants were effective in two years in the reclamation of the polluted soil, showing an average reduction of about 35%, 40%, and 70% in metals, TPH and PCB content, respectively. As regards the plants, the poplar contributed the most to organic removal. In fact, its ability to take up and detoxify organic pollutants is well known. Paulownia tomentosa, instead, showed high metal removal. The Cytisus scoparius was the least effective plant in soil decontamination. The recovery of soil functionality was followed by enzyme activities, expressing the biochemical processes underway, and nutrient content useful for plant growth and development. Throughout the area, an enhancement of metabolic processes and soil chemical quality was observed. All the enzymatic activities showed a general increase over time (until 3-4 fold than the initial value for urease and β-glucosidase). Moreover, Cytisus scoparius, even though it showed a lower decontamination capability, was the most effective in soil metabolic stimulation.     

Hair Trace Elements Concentration to Describe Polymetallic Mining Waste Exposure in Bolivian Altiplano

Severe polymetallic contamination is frequently observed in the mining communities of Bolivian Altiplano. We evaluated hair trace elements concentrations at the population level to characterise exposure profile in different contexts of contact with mining and metallurgical pollution. We sampled 242 children aged 7 to 12 years in schools from five Oruro districts located in different contexts of potential contamination. Hair trace elements concentrations were measured using ICP-MS (Pb, As, Hg, Cd, Sb, Sn, Bi, Ag, Ni, Se, Cu, Cr, Mn, Co and Zn). We compared concentration according to school areas and gender. Concentrations were markedly different depending on school areas. Children from schools near industrial areas were far more exposed to non essential elements than children from downtown and suburban schools, as well as the rural school. The most concentrated non-essential element was Pb (geometric means (SD): 1.6 (1.3) μg/g in rural school; 2.0 (2.3) μg/g in suburban school; 2.3 (3.0) μg/g in downtown school; 14.1 (2.7) μg/g in the mine school and 21.2 (3.3) μg/g in the smelter school). Boys showed higher levels for all non-essential elements while girls had higher levels of Zn. Hair trace elements concentrations highlighted the heterogeneity of exposure profiles, identifying the most contaminated districts.     

贵州水银洞金矿紫茎泽兰重金属元素测定与分析

利用原子吸收法对贵州水银洞金矿紫茎泽兰及其基质中Cr、Pb、Zn、Cd、Hg和As含量进行了测定和分析。结果表明,贵州水银洞金矿废水处理区土壤Hg(12.575 mg·kg^-1)和As(501.374 mg·kg^-1)已严重超标,Hg和As的平均含量分别是国家土壤环境质量三级标准(GB15618-1995)的8.383倍和12.534倍,污染极为严重;紫茎泽兰对该矿区不同的重金属富集能力不同,尤其对该矿区Cr有较强的富集作用,具有一定的Cr污染修复潜力。紫茎泽兰对所测定的6种重金属元素的吸收转移能力有较大的差异,整个植株对Pb、Zn 和Cr具有很强的吸收转移能力。其茎、叶对不同的重金属元素的吸收转移能力也呈现出很大的差异,紫茎泽兰茎对Cr、Pb和Cd具有很强的吸收转移能力,而叶对Zn、Pb和Hg具有很强的吸收转移能力。除As外,紫茎泽兰对Cr、Pb、Zn、Cd和Hg都具有不同程度的耐受能力,对该矿区的生态恢复具有重要的作用。     

An Investigation of the Soil Property Changes and Heavy Metal Accumulation in Relation to Long-term Wastewater Irrigation in the Semi-arid Region of Iran

Concentrations and spatial distribution of Zn, Cu, Cd, and Pb along two landscapes including a wastewater-irrigated area and a control area were determined to assess the impact of long-term wastewater irrigation and landscape properties on heavy metal contamination. Some disturbed and undisturbed soil samples were taken from soil trenches and soil cores, located on three main landscape positions (upper slope, midslope, and lower slope) in northwestern Iran. The investigation showed that the mean concentration of the heavy metals followed the order Zn > Cu > Pb > Cd in the wastewater-irrigated soil and Pb > Zn > Cu > Cd in the control soils. On average, compared to similar positions in the control region, the wastewater-irrigated regions contained 3.0 (midslope) to 4.9 (lower slope), 2.7 (midslope) to 4.6 (lower slope), 3.3 (upper slope) to 4.1 (lower slope), and 1.7 (upper slope) to 2.6 (lower slope) times higher amounts of Zn, Cu, Cd, and Pb, respectively. Significant positive relationships (P < 0.05) were recorded between the heavy metals concentration with <0.002 mm particle-size fraction and organic matter content, the fractions linked to runoff and soil erosion. It is believed that the two soil fractions play a crucial role in the distribution of the metals along the wastewater-irrigated landscape. Despite the significant increase of heavy metals (P < 0.05) in the wastewater-irrigated soils compared with control soils, the concentration of all evaluated metals was below the maximum accepted limits (Zn < 300 mg/kg, Cu < 100 mg/kg, Cd < 5 mg/kg, and Pb < 100 mg/kg), and grouped as “not-enriched” to “moderately-enriched” categories regarding the topsoil enrichment index. Overall, the lower slope was shown to be more contaminated with the heavy metals compared to the other positions.     

EFFECTS OF INOCULATION WITH ARBUSCULAR MYCORRHIZAL FUNGI ON MAIZE GROWN IN MULTI-METAL CONTAMINATED SOILS

Pot culture experiments were established to determine the effects of colonization by arbuscular mycorrhizal fungi (AMF) (Glomus mosseae and G. sp) on maize (Zea mays L.) grown in Pb, Zn, and Cd complex contaminated soils. AMF and non-AMF inoculated maize were grown in sterilized substrates and subjected to different soil heavy metal (Pb, Zn, Cd) concentrations. The root and shoot biomasses of inoculated maize were significantly higher than those of non-inoculated maize. Pb, Zn, and Cd concentrations in roots were significantly higher than those in shoots in both the inoculated and non-inoculated maize, indicating the heavy metals mostly accumulated in the roots of maize. The translocation rates of Pb, Zn, and Cd from roots to shoots were not significantly difference between inoculated and non-inoculated maize. However, at high soil heavy metal concentrations, Pb, Zn, and Cd in the shoots and Pb in the roots of inoculated maize were significantly reduced by about 50% compared to the non-inoculated maize. These results indicated that AMF could promote maize growth and decrease the uptake of these heavy metals at higher soil concentrations, thus protecting their hosts from the toxicity of heavy metals in Pb, Zn, and Cd complex contaminated soils.     

Distribution of Cd and Zn in annual xylem rings of young spruce trees [Picea abies (L.) Karst.] grown in contaminated soil

Concentrations and total amounts of Cd and Zn in individual annual xylem increments of 5-year-old spruce trees (Picea abies) were investigated after one growing season in contaminated soils. The plants had been potted in soils amended with different concentrations of Cd and Zn and kept in open air conditions. In the outer xylem rings formed during the treatment period lowest concentrations of Cd and Zn were found. In inner rings concentrations of both elements increased and were highest at the pith. Total amounts of both elements showed reversed distribution patterns with highest values in the outermost rings. The observed increase of total dry matter of the rings from pith towards the outer rings was stronger than the parallel increase in total element amounts in the rings. Thus, concentrations dropped in younger rings. The time of the soil contamination event cannot be inferred from element concentrations in annual rings. The results challenge the concept of monitoring historical trends in trace element pollution using analytical data of tree rings of conifers.     

Use of Cordia Africana in the Phytostabilization of Substrates from Excavations of the Ore Courtyard at the Port of Itaguai,Brazil

The objective of this study was to evaluate the phytostabilization of two substrates contaminated with heavy metals from excavations of the ore courtyard at the port of Itaguai, Brazil. Initially, an inventory of tree species located near the study area was performed to select species for phytostabilization. The species Cordia africana exhibited deeper roots, a larger diameter at chest height (DCH) and crown diameter, as well as higher concentrations of Zn, Cd, and Pb in the trunk, bark, and roots compared to the other investigated species. The tolerance of the selected species to the metals Zn, Cd, and Pb was subsequently assessed through a greenhouse test. The substrates used in the experiment also obtained from excavations at the ore courtyard and showed different levels of heavy metals, indicating either low contamination (Substrate 1) or high contamination (Substrate 2). Alkaline industrial waste steel slag (SS) was used as an amendment to reduce the solubility of heavy metals. Application of the amendment agent to the substrates reduced the bioavailability of heavy metals, favoring the growth of C. africana. This species presents potential for use in phytostabilization programs due to its tolerance for heavy metals and the observed higher accumulation of these metals in the roots and especially the trunk of this species compared to other vegetal parts.     

Effects of trace elements on the growth of Phellinus pachypholeus pat.

Fifteen trace elements have been tested to determine the requirements for the growth of Phellinus pachypholeus Pat. The fungus requires in ppm, Fe: 10, Zn: 10–100, Mn: 1.0, Cu: 1.0, Mo: 1.0, B: 10.0–100. It does not require Ca, Pb, Br, I, Cr, Hg, W, Li or Cd. Concentrations higher than the optimum were progressively inhibitory for its growth.     

The Effect of Compost Treatments and A Plant Cover with Agrostis tenuis on the Immobilization/Mobilization of Trace Elements in a Mine-Contaminated Soil

A semi-field experiment was conducted to evaluate the use of mixed municipal solid waste compost (MMSWC) and green waste-derived compost (GWC) as immobilizing agents in aided-phytostabilization of a highly acidic soil contaminated with trace elements, with and without a plant cover of Agrostis tenuis. The compost application ratio was 50 Mg ha^–1, and GWC amended soil was additionally limed and supplemented with mineral fertilizers.Both treatments had an equivalent capacity to raise soil organic matter and pH, without a significant increase in soil salinity and in pseudo-total As, Cu, Pb, and Zn concentrations, allowing the establishment of a plant cover. Effective bioavailable Cu and Zn decreased as a consequence of both compost treatments, while effective bioavailable As increased by more than twice but remained as a small fraction of its pseudo-total content. Amended soil had higher soil enzymatic activities, especially in the presence of plants.Accumulation factors for As, Cu, Pb, and Zn by A. tenuis were low, and their concentrations in the plant were lower than the maximum tolerable levels for cattle. As a consequence, the use of A. tenuis can be recommended for assisted phytostabilization of this type of mine soil, in combination with one of the compost treatments evaluated.     

Chemical speciation distribution characteristics and ecological risk assessment of heavy metals in soil from Sunan mining area,Anhui Province,China

In this study, the content characteristics, comprehensive pollution assessment, and morphological distribution characteristics of heavy metals (Mn, Cd, Cr, Pb, Ni, Zn, and Cu) were researched based on the processes of field investigation, sample collection, and experimental analysis. Results showed that the mean concentrations of Mn, Pb, Cr, Cu, Cd, Zn, and Ni in surface soils were 522.77, 22.56, 55.10, 25.41, 0.25, 57.02, and 48.47 mg kg^?1, respectively. The surface soil from Sunan mining area was contaminated by Cu, Cd, and Ni in different degrees, and high CV values of Cd, Zn, Pb, and Ni were influenced by local human activities possibly. The evaluation results suggested that the mean I_geo values were in the sequence of Cd (0.657) > Ni (0.052) > Cu (?0.293) > Mn (?0.626) > Zn (?0.761) > Cr (?0.884) > Pb (?0.899). Besides, Cd was the most significant potential risk factor among all elements. Nevertheless, the Cd of bioavailable speciations with higher proportion had stronger migration and toxicity, and was more easier to be absorbed and enriched than other elements by some crops (e.g., vegetables, rice), and being at a relatively higher potential ecological risk in soil.