Bioremediation of copper using indigenous fungi Aspergillus species isolated from an abandoned copper mine soil.

Bioremediation of mining soils using metal tolerant fungi is widely considered as a promising cost-effective and ecofriendly approach. This study assessed the copper removal efficiency and bioaccumulation ability of the indigenous species Aspergillus hiratsukae LF1 and Aspergillus terreus LF2 isolated from the soils of an abandoned copper mine in Oman. Nutrient medium containing five different Cu (II) levels (0 - control, 100, 200, 300 and 500 mg/L) was employed for assessing both parameters. The removal efficiency from nutrient medium (100-500 mg Cu per L) ranged from 57% to 21% for A. hiratsukae LF1, and from 69% to 24% for A. terreus LF2. A. hiratsukae LF1 and A. terreus LF2 accumulated a maximum of 4.63 and 5.95 mg Cu/g,espectively, at 500 mg/L of Cu (II) concentration. The compositional analysis of extracellular polymeric substances excreted by both species revealed a hormetic response by A. hiratsukae LF1 at 100 mg/L; whereas increasing media Cu levels induced carbohydrates production in A. terreus LF2. These results hint at the involvement of carbohydrates in the Cu-tolerance mechanism of the latter. Copper accumulation in both species was further demonstrated through scanning electron microscopy and energy dispersive spectrometry. In line with the pertaining literature, our results are somewhat inconclusive concerning whether proteins or carbohydrates play a more pivotal role in copper complexation in both species; yet, FTIR analysis showed the participation of different functional groups in Cu sorption. Overall, although additional research is required to advance the knowledge about both Aspergillus species, our findings suggest that A. terreus LF2 presents greater promise for copper bioremediation due to enhanced tolerance and accumulation capacity.

Potential of Salvinia biloba Raddi for removing atrazine and carbendazim from aquatic environments.

In this exploratory study, naturally occurring Salvinia biloba Raddi specimens were assessed for atrazine and carbendazim polluted water remediation. Experiments were carried out over 21 days in glass vessels containing deionized water artificially contaminated with 0, 5, 10, and 20 mg L-1 of atrazine or carbendazim. Atrazine had a pronounced detrimental impact on S. biloba, as no biomass development was observed in all macrophytes exposed to this herbicide in the entire concentration range. However, carbendazim-treated plants were able to grow and survive in the polluted medium even when subjected to the highest concentration of this fungicide (i.e., 20 mg L-1). In addition, increased chlorosis and necrosis were also detected in plants subjected to carbendazim as a result of the high phytotoxicity caused by atrazine. A maximal removal efficiency of ~ 30% was observed for both pesticides at 5 mg L-1 and decreased with increasing concentrations of the pollutants. The spectrum of the FTIR-ATR analysis revealed the existence of various functional groups (e.g., amide, carboxyl, hydroxyl, phosphate, sulfate) on the plants, which could be related to pesticide biosorption. In addition, at the end of the 21-day assay, seven carbendazim-resistant bacteria could be isolated from the roots of fungicide-treated plants. Therefore, the use of autochthonous free-floating S. biloba macrophytes for phytoremediation of aquatic environments contaminated with carbendazim shows great promise. Still, additional research is required to further elucidate the plant-mediated carbendazim elimination process and the role of the herbicide-resistant bacteria, and seek alternative species capable of mitigating atrazine contamination.

Deposition of trace metals associated with atmospheric particulate matter: Environmental fate and health risk assessment.

Anthropogenic and natural sources influence trace metals (TMs) bound to different sized particulate matter (PM) in dry and wet atmospheric deposition, which can create ecosystem and human health issues in the long run. Limited reviews are available summarizing worldwide concentrations in TMs in atmospheric PMs, their sources and pathways. Simultaneously, quantitative assessment of the potential human and ecosystem health risks imposed by the atmospheric particulate matter has not been adequately reviewed. Addressing this gap, here we review, the concentration of TMs in dry deposition mainly varies with the responsible sources, whereas, in wet deposition, it depends on the solubility of TMs. Other than deposition on impervious surfaces, the TMs incorporated PM can be deposited on biological agents. Health risk assessments show that ingestion and dermal contact pathways are more likely to cause health issues, however, the probability of occurring ingestion and dermal contact pathways is limited. Attention must be paid to the contribution from non-exhaust and exhaust vehicular emissions for TMs in atmospheric deposition, understanding their impact on stormwater management and urban agriculture. Behaviors of TMs in the atmosphere depends on many complex factors including origin, wind patterns, and weather conditions. Therefore, future research needs to be carried to model and predict the fate and transfer of TMs once they are generated through natural and anthropogenic sources. We believe that such research would allow establishing pollution control policies and measures in urban environments which will be critical to reduce the levels of TMs associated with atmospheric deposition in the environment.

Plant growth-promoting bacteria in phytoremediation of metal-polluted soils: Current knowledge and future directions.

Soil metal contamination is a major concern due to the ever-rising number of areas afflicted worldwide and the detrimental effects of metals to the environment and human health. Due to their non-biodegradability and toxicity, it is paramount to prevent further metal contamination and remediate the thousands of contaminated sites across the planet. Yet, conventional reclamation based on physical and chemical methods is often expensive, impractical, and triggers secondary pollution issues. Hence, microbe-aided phytoremediation has been gaining significant traction due to its environment-friendly character, cost-effectiveness, and the breakthroughs achieved during the past few decades. Microorganisms are an essential part of natural ecosystems and play a crucial role in their restoration. Indeed, plant-microbe associations in metal-polluted soils are pivotal for plants to tolerate metal toxicity and thrive in these harsh environments. Therefore, improving the understanding of this intricate relationship is invaluable for boosting phytoremediation. In this review, we focus on the potential of plant growth promoting bacteria (PGPB) for enhancing phytoremediation of metal-polluted soils. We discuss the mechanisms employed by microbes to promote plant growth and assist the removal or immobilization of metals in soil, thereby enhancing phytoextraction and phytostabilization, respectively. Microbe-mediated metal removal and detoxification through processes entailing adsorption, chelation, transformation, and precipitation, to list but a few, are also critically examined. Moreover, this work covers the direct and indirect mechanisms used by PGPB to facilitate plant acquisition of nutrients like nitrogen and phosphorus, supply and regulate phytohormones, and exert control over antagonistic microorganisms. Lastly, we provide an outlook on the future directions of microbe-aided phytoremediation and phytomining. Clearly, to fully validate and comprehend the potential of PGPB-aided phytoremediation, a considerable shift from bench-scale to field research is necessary. What's more, it is envisaged that recent advancements in genetic engineering may soon help furthering the efficiency of microbe-assisted phytoremediation.

Evaluation of Cadmium Bioaccumulation-Related Physiological Effects in Salvinia biloba: An Insight towards Its Use as Pollutant Bioindicator in Water Reservoirs.

Free-living macrophytes play an important role in the health of aquatic ecosystems. Therefore, the use of aquatic plants as metal biomonitors may be a suitable tool for the management of freshwater reservoirs. Hence, in this study, we assessed the effects of cadmium (Cd) in Salvinia biloba specimens collected from the Middle Paraná River during a 10-day experiment employing artificially contaminated water (100 µM Cd). S. biloba demonstrated a great ability for Cd bioaccumulation in both the root-like modified fronds (named "roots") and the aerial leaf-like fronds (named "leaves") of the plants. Additionally, Cd toxicity was determined by the quantification of photosynthetic pigments (chlorophylls a and b, and carotenoids), flavonoids, and soluble carbohydrate contents in S. biloba over time (1, 3, 5, 7, and 10 days). In general, deterioration was more pronounced in leaves than in roots, suggesting a greater implication of the former in long-term Cd sequestration in S. biloba. Deleterious effects in the appraised parameters were well correlated with the total amount of Cd accumulated in the leaves, and with the qualitative changes observed in the plants' phenotype during the 10-day metal exposure assay. The flavonoids and carotenoids in leaves were highly affected by low Cd levels followed by root carbohydrates. In contrast, chlorophylls and root flavonoids were the least impacted physiological parameters. Therefore, our results demonstrate that S. biloba displays dissimilar organ-linked physiological responses to counteract Cd phytotoxicity and that these responses are also time-dependent. Though further research is needed, our work suggests that easy-handled physiological data obtained from autochthonous free-floating S. biloba specimens may be used as a valuable tool for metal-polluted water biomonitoring.

Metal accumulation in roadside soils of Rio de Janeiro, Brazil: impact of traffic volume, road age, and urbanization level.

Traffic-related metal emissions have become a global concern due to their deposition in roadside soils and potential hazardous effects. This study evaluates metal levels in soils adjoining four highways of Rio de Janeiro (Linha Vermelha, Via Dutra, BR-465, and Avenida Brasil), chosen for their diverse traffic volumes, age, and urban/rural settings. In addition to soil physicochemical properties, 11 elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V, and Zn) were assessed on samples collected at different distances from the road (1, 3, 5, 10, 15 m) and soil depths (0-15 and 15-30 cm). Moreover, the geoaccumulation index was also computed to infer the soil contamination extent. The results indicate that soil metal levels at each highway are highly dependent on factors like traffic volume, distance to road, other anthropogenic sources of pollution, and their rural or urban location. The highways with greater traffic volume, Linha Vermelha and Avenida Brasil (154,000 and 126,000 vehicles day-1, respectively), clearly presented the highest soil metal concentrations. Still, as stressed by the principal component analysis, traffic volume alone fails to explain the distribution of metals in soils neighboring these highways. Thus, factors like their urban setting and larger exposure to anthropogenic activities may play a pivotal role. On the other hand, soils from Via Dutra and BR-465, both on a rural backdrop, were mostly influenced by traffic as their metal levels decreased with increasing distances from the road. Comparison with reference and preventive values for Brazilian soils and the assessment of the geoaccumulation index have shown that concentrations of Pb and V have reached concerning thresholds at Linha Vermelha and Avenida Brasil.

The effects of rhenium accumulation on Indian mustard.

Rhenium (Re) is one of Earth's scarcest and more largely scattered elements, with an estimate concentration of 0.4-0.6 µg kg-1 in the upper crust. Still, considerable concentrations of bioavailable ReO4- ions are often found, particularly in copper-molybdenum mines, where their uptake by plants of these regions has been reported. Yet, the impact of Re on plants remains a question mark, as the only available knowledge derives from a limited investigation carried out over 60 years ago. The aim of this study was to evaluate the ecophysiological response of Brassica juncea, a species known to endure and accumulate various metals, to a broad range of Re concentrations. B. juncea plants were allowed to grow and on a substrate amended with KReO4 to attain soil Re levels ranging from 0 to 80 mg kg-1. Plants were collected 45 days after sowing for analysis. The results have shown that greater Re levels reduce growth, photosynthetic activity, soluble carbohydrate mobilization, and protein contents, and increase the plant's oxidative stress (anthocyanins, H2O2, lipid peroxidation) and corresponding response (ascorbic acid, superoxide dismutase activity). Nevertheless, B. juncea exhibited a remarkable ability to endure and uptake Re, featuring shoot Re concentrations that ranged from 1615 to 24,987 mg kg-1 among the 5 and 80 mg kg-1 treatments.

Genome Editing Weds CRISPR: What Is in It for Phytoremediation?

The arrival of sequence-specific endonucleases that allow genome editing has shaken the pillars of basic and applied plant biology. Clustered regularly interspaced palindromic repeats (CRISPR) is a revolutionary genome-engineering tool that enables the enhancement of targeted traits in plants. Numerous plants, including energy crops, known for their potential to tolerate, immobilize, and stabilize inorganic and organic pollutants, have already been edited using different CRISPR systems. Moreover, a large array of genes responsible for increased metal tolerance, metal uptake and hyperaccumulation have already been identified. Thus, the CRISPR-mediated genome reprogramming of plants, including its use in gene expression regulation through transcriptional repression or activation (CRISPRi and CRISPRa), could be of paramount importance for phytoremediation. The simplicity, inexpensiveness, and capabilities of this gene editing technique could soon be used to enhance plants and bacteria involved in phytotechnologies, such as phystabilization, phytoextraction, phytomining, phytovolatilization, and bio-energy generation. In this brief viewpoint piece, we posit some of the potential benefits of CRISPR for phytoremediation.

Germination and early growth of Brassica juncea in copper mine tailings amended with technosol and compost.

Mine tailings represent a serious threat to the environment and human health; thus their restoration has become a major concern. In this study, the interactions between Brassica juncea and different mine soil treatments were evaluated in order to understand their effect on germination and early growth. Three soil treatments containing 25% and 50% of technosol and 30% of compost were prepared. Germination and early growth were assessed in soil and pore water extracts from the treatments. Unlike the untreated mine soil, the three treatments allowed germination and growth, achieving levels comparable to those of seedlings from the same species developed in normal conditions. The seedlings grown in 50% of technosol and 30% of compost exhibited greater germination percentages, higher growth, and more efficient mechanisms against oxidative stress, ascribed to the organic matter and nutrients content of these treatments. Considering the unequivocal ability of B. juncea for phytoremediation, the results suggest that technosol and compost may be an auspicious solution to allow the germination and early growth of this species in mine tailings.

Effect of salinity on zinc uptake by Brassica juncea.

Salinity is a major worldwide problem that affects agricultural soils and limits the reclamation of contaminated sites. Despite the large number of research papers published about salt tolerance in Brassica juncea L., there are very few accounts concerning the influence of salinity on the uptake of trace metals. In this study, B. juncea plants divided through soil sets comprising 0, 900 and 1800 mg Zn kg(-1), were treated with solutions containing 0, 60 and 120 mmol L(-1) of NaCl, with the purpose of observing the effect of salt on Zn uptake, and some physiological responses throughout the 90 days experiment. Increasing concentrations of NaCl and Zn produced a decline in the ecophysiological and biochemical properties of the plants, with observable synergistic effects on parameters like shoot dry weight, leaf area, or photochemical efficiency. Nevertheless, plants treated with 60 mmol L(-1) of NaCl accumulated striking harvestable amounts of Zn per plant that largely exceed those reported for Thlaspi caerulescens. It was concluded that salinity could play an important role on the uptake of Zn by B. juncea. The potential mechanisms behind these results are discussed, as well as the implications for phytoremediation of Zn on saline and non-saline soils.