In current study, the enhanced efficiency of copper (Cu) phytoremediation potential of Calendula officinalis L. was investigated in a Cu-spiked calcareous soil, using foliar and soil application of humic acid. For this purpose, in a greenhouse experiment, seedlings of C. officinalis were transferred to Cu-spiked soils (0, 250 and 500 mg/kg) and treated separately with soil (soil drench) and foliar (spraying plant leaves) humic acid applications at different levels (0, 10, 20 μM). The humic acid treatments were applied 2 weeks after transferring plant, and eventually the various biochemical-physiological traits and phytoremediation indices of Cu in C. officinalis were measured at (specific) time points. According to the results, C. officinalis grew normally without any toxicity signs in Cu-spiked soils, however with increasing the Cu levels, the dry weight biomass decreased and antioxidant enzymes activities increased. Both foliar and soil humic acid application in Cu-spiked soils increased dry weight biomass, photosynthetic pigment contents, Cu concentration, and bioconcentration factor (BCF). Furthermore, the application of this organic substance, obviously moderated the Cu stress since the antioxidant enzymes activities reduced compared to the control. Based on the results, the obtained translocation factor (TF) and BCF values of Cu, which were >1, indicated that this plant is a Cu-hyperaccumulator, which could extract Cu via phytoextraction mechanism. Generally, the results of this study showed that, among the humic acid treatments, application of 20 μM (especially soil drench application) had the best effect on increasing Cu phytoremediation efficiency in the studied soil and it recommended to enhance the efficiency of Cu phytoremediation in calcareous soils.

International audience | Gentle remediation options (GRO) are based on the combined use of plants, associated microorganisms and soil amendments, which can potentially restore soil functions and quality. We studied the effects of three GRO (aided-phytostabilisation, in situ stabilisation and phytoexclusion, and aided-phytoextraction) on the soil microbial biomass and respiration, the activities of hydrolase enzymes involved in the biogeochemical cycles of C, N, P, and S, and bacterial community structure of trace element contaminated soils (TECS) from six field trials across Europe. Community structure was studied using denaturing gradient gel electrophoresis (DGGE) fingerprinting of Bacteria, α- and β-Proteobacteria, Actinobacteria and Streptomycetaceae, and sequencing of DGGE bands characteristic of specific treatments. The number of copies of genes involved in ammonia oxidation and denitrification were determined by qPCR. Phytomanagement increased soil microbial biomass at three sites and respiration at the Biogeco site (France). Enzyme activities were consistently higher in treated soils compared to untreated soils at the Biogeco site. At this site, microbial biomass increased from 696 to 2352 mg ATP kg-1 soil, respiration increased from 7.4 to 40.1 mg C-CO2 kg-1 soil d-1, and enzyme activities were 2-11-fold higher in treated soils compared to untreated soil. Phytomanagement induced shifts in the bacterial community structure at both, the total community and functional group levels, and generally increased the number of copies of genes involved in the N cycle (nirK, nirS, nosZ, and amoA). The influence of the main soil physico-chemical properties and trace element availability were assessed and eventual site-specific effects elucidated. Overall, our results demonstrate that phytomanagement of TECS influences soil biological activity in the long term.

Soil Cd and Zn contamination has become a serious environmental problem. This work explored the performance of wood vinegar (WV) in enhancing the phytoextraction of Cd/Zn by hyperaccumulator Sedum alfredii Hance. Rhizosphere chemical properties, enzyme activities and bacterial community were analyzed to determine the mechanisms of metal accumulation in this process. Results demonstrated that, after 120 days growth, different times dilution of WV increased the shoot biomass of S. alfredii by 85.2%–148%. In addition, WV application significantly increased soil available Cd and Zn by lowing soil pH, which facilitated plant uptake. The optimal Cd and Zn phytoextraction occurred from the 100 times diluted WV (D100), which increased the Cd and Zn extraction by 188% and 164%, compared to CK. The 100 and 50 times diluted WV significantly increased soil total and available carbon, nitrogen and phosphorus, and enhancing enzyme activities of urease, acid phosphatase, invertase and protease by 10.1–21.4%, 29.1–42.7%,12.2–38.3% and 26.8–85.7%, respectively, compared to CK. High-throughput sequencing revealed that the D 100 significantly increased the bacterial diversity compared to CK. Soil bacterial compositions at phylum, family and genera level were changed by WV addition. Compared to CK, WV application increased the relative abundances of genus with plant growth promotion and metal mobilization function such as, Bacillus, Gemmatimonas, Streptomyces, Sphingomonas and Polycyclovorans, which was positively correlated to biomass, Cd/Zn concentrations and extractions by S. alfredii. Structural equation modeling analysis showed that, soil chemical properties, enzyme activities and bacterial abundance directly or indirectly contributed to the biomass promotion, Cd, and Zn extraction by S. alfredii. To sum up, WV improved phytoextraction efficiency by enhancing plant growth, Cd and Zn extraction and increasing soil nutrients, enzyme activities, and modifying bacterial community.

Phytoextraction using hyperaccumulator, Pteris vittata, to extract arsenic (As) from soil has been applied to large areas to achieve an As removal rate of 18% per year. However, remarkable difference among different studies and field practices has led to difficulties in the standardization of phytoextraction technology. In this study, data on As concentration in P. vittata and related environmental conditions were collected through literature search. A conceptual framework was proposed to guide the improvement of phytoextraction efficiency in the field. The following influencing factors of As concentration in this hyperaccumulator were identified: total As concentration in soil, soil available As, organic matter in soil, total potassium (K) concentration in soil, and annual rainfall. The geodetection results show that the main factors that affect As concentration in P. vittata include soil organic matter (q = 0.75), soil available As (q = 0.67), total K (q = 0.54), and rainfall (q = 0.42). The predictive models of As concentration in P. vittata were established separately for greenhouse and field conditions through multivariate linear stepwise regression method. Under greenhouse condition, soil available As was the most important influencing factor and could explain 41.4% of As concentration in P. vittata. Two dominant factors were detected in the field: soil available As concentration and average annual rainfall. The combination of these two factors gave better prediction results with R² = 0.762. The establishment of the model might help predict phytoextraction efficiency and contribute to technological standardization. The strategies that were used to promote As removal from soil by P. vittata were summarized and analyzed. Intercropping with suitable plants or a combination of different measures (e.g., phosphate fertilizer and water retention) was recommended in practice to increase As concentration in P. vittata.

To explore the performance of Streptomyces pactum (Act12) alone (A) and jointly with sulfur (SA) in the phytoextraction practice of potentially toxic elements (PTEs) (Cd and Zn), as well as their effects on soil chemical properties and microbial community composition, this paper selected potherb mustard (Brassica juncea, Coss.) as the test plant to assess the feedback of soil-plant ecosystems. Metal uptake values in lone Act12 treatments were higher than that of Act12 + sulfur treatments, and showed dose dependent with Act12 due to the higher biomass production. According to the biochemical analyses of rhizosphere soils, Act12 inoculation significantly increased urease (20.4%) and dehydrogenase (58.5%) while reducing alkaline phosphatase (68.0%) activity. The production of soil organic acids was, in descending order, formic acid > oxalic acid > malic acid > propionic acid and indicated a stimulated variation under treatments (SA > A > control). High-throughput sequencing revealed that bacterial community compositions were consistent in both phylum and genus taxonomies, while the final overall proportions were modified. The populations of the predominant phyla Proteobacteria and Bacteroidetes increased after sulfur application. The contribution of Act12 to the relative abundance of microbiota was minor compared to sulfur. Based on a redundancy analysis, soil chemical properties are the drivers of microbial activities and the main contributor to plant growth. Our results suggested Act12 inoculation may be part of an effective strategy enhancing phytoremediation of PTE-contaminated soils through chemical and biotic processes, and provided important implications for sustainable land utilization and crop production.

The traditional assessment of agricultural soil remediation technologies pay limited attention to sustainability and only considers the decrease in contaminant concentrations and cost, even though the sustainability of these technologies has been prioritized. This 3-year field study comprehensively assessed the sustainability of four commonly used agricultural soil remediation technologies in terms of metal(loid) removal efficiency, environmental merit, and cost. The farmland was contaminated by previous sewage irrigation with excessive amounts of As, Cd, and Pb. The four selected remediation technologies used were phytoextraction, intercropping of hyperaccumulators and cash crops, chemical immobilization, and turnover and attenuation (T&A). A risk reduction–environmental merit–cost model was utilized to compare these four technologies. Results showed that T&A reduced the health risks posed by excess metal(loid)s by ∼47% and yielded the highest risk reduction and lowest cost. Phytoextraction achieved the highest environmental merit because it produced the least interruption to the environment. A simplified assessment frame for soil remediation technology was established from a retrospective aspect using data from a real soil remediation project. Environmental merit is a less considered factor and more difficult to quantify than risk reduction or cost, thus requiring increased attention.

The present work was done to explore the joint effect of Streptomyces pactum (Act12) and plant nutrients on phytoremediation of smelter-contaminated soils. The physiological indicators and phytoextraction indices of potherb mustard (Brassica juncea, Coss) grown in Act12 inoculated soil with or without Hoagland’s solution (H), humic acid (HA) and peat (PS) were evaluated. The results indicated that H, HA and PS acted synergistically with Act12, notably increasing chlorophyll and soluble protein contents and thereby promoting plant growth. Soil nutrient treatments reduced the antioxidant activities (PPO, CAT and POD) by 28.2–41.4%, 22.3–90.1% and 15.2–59.4% compared to control, respectively. Act12 and H treatments markedly facilitated plant to accumulate more cadmium (Cd) and zinc (Zn), but it was observed decreases when applied with HA and PS. Metal uptake (MU) values further indicated the differences in phytoextraction efficiency, i.e., H > PS > Control > HA. Taken together, Act12 combined with plant nutrients contributed to alleviating metal toxicity symptoms of plant. Hoagland’s solution and peat were highlighted in the present phytoextraction trial, and recommended as soil additives.

The work was conducted to establish contamination from improper disposal of hazardous wastes containing lead (Pb) and antimony (Sb) into nearby soils. Besides other elements in the affected area, the biological role of Sb, its behaviour in the pedosphere and uptake by plants and the food chain was considered. Wastes contained 139532 ± 9601 mg kg−1 (≈14%) Pb and 3645 ± 194 mg kg−1 (≈0.4%) Sb respectively and variability was extremely high at a decimetre scale. Dramatically high concentrations were also found for As, Cd, Cu, Mn, Ni, Sn and Zn. In adjacent natural soils metal(oid)s amounts decreased considerably (Pb 5034 ± 678 mg kg−1, Sb 112 mg kg−1) though largely exceeded the directives for a given soil use. Metal(oid)s potential mobility was assessed by using H2O→KNO3→EDTA sequential extractions, and EDTA extracts showed the highest concentration suggesting stable humus-metal complexes formation. Nevertheless, selected plants showed high absorption potential of the investigated elements. Pb and Sb values for Dittrichia viscosa grown in wastes was 899 ± 627 mg kg−1 and 37 ± 33 mg kg−1 respectively. The same plant showed 154 ± 99 mg kg−1 Pb and 8 ± 4 mg kg−1 Sb in natural soils. Helichrysum stoechas had 323 ± 305 mg kg−1 Pb, and 8 ± 3 mg kg−1 Sb. Vitis vinifera from alongside vineyards contained 129 ± 88 mg kg−1 Pb and 18 ± 9 mg kg−1 Sb, indicating ability for metal uptake and warning on metal diffusion through the food chain. The biological absorption coefficient (BAC) and the translocation factor (TF) assigned phytoextraction potential to Dittrichia viscosa and Foeniculum vulgare and phytostabilization potential to Helichrysum stoechas. Dissolved metal (oid)s in the analysed water strongly exceeded the current directive being a direct threat for livings. Data warned against the high contamination of the affected area in all its compartments. Even though native plants growing in metal-contaminated sites may have phytoremediation potential, high risk of metal diffusion may threat the whole ecosystem.

The in situ use of carbon amendments such as activated carbon (AC) and biochar to minimize the bioavailability of organic contaminants is gaining in popularity. In the first in situ experiment conducted at a Canadian PCB-contaminated Brownfield site, GAC and two types of biochar were statistically equal at reducing PCB uptake into plants. PCB concentrations in Cucurbita pepo root tissue were reduced by 74%, 72% and 64%, with the addition of 2.8% GAC, Burt's biochar and BlueLeaf biochar, respectively. A complementary greenhouse study which included a bioaccumulation study of Eisenia fetida (earthworm), found mechanically mixing carbon amendments with PCB-contaminated soil (i.e. 24 h at 30 rpm) resulted in shoot, root and worm PCB concentrations 66%, 59% and 39% lower than in the manually mixed treatments (i.e. with a spade and bucket). Therefore, studies which mechanically mix carbon amendments with contaminated soil may over-estimate the short-term potential to reduce PCB bioavailability.

In this work, arsenic (As) accumulation and distribution over time in Pteris vittata young fronds from adult plants and in whole plantlets, grown on a highly contaminated As-soil, was determined by μ-XRF. A linear increase in As content up to 60 days was found in young fronds at different times, and a progressive distribution from the apex to the base of the fronds was observed. In whole plantlets, As signal was detectable from 9 to 20 days in the apex of a few fronds and fiddleheads. Later, up to 60 days, As was localized in all fronds, in the rhizome and in basal part of the roots. The dynamics of expression of As-related genes revealed a good correlation between As content and the level of the As (III)-antiporter PvACR3 transcript in plantlets roots and fronds and in young fronds. Moreover, the transcription of As (V)-related gametophytic genes PvGAPC1, PvOCT4 increases over time during As accumulation while PvGSTF1 is expressed only in roots. Here, we demonstrate the suitability of the μ-XRF technique to monitor As accumulation, which allowed us to propose that As is initially directly transported to fiddleheads and apex of fronds, is later distributed to the whole fronds and simultaneously accumulated in the rhizome and roots. We also provide indications on the expression of candidate genes possibly involved in As (hyper)accumulation.