Evaluation of heavy metal phytoremediation potential of six tree species of Faisalabad city of Pakistan during summer and winter seasons

Season-based phytoremediation potential of brown mustard for lead decontamination: effect of EDTA chelation and antioxidant enzyme activity

Phytoremediation technology is an environmentally benign, potent, and cost-effective approach for treating contaminated ecological sites. To yield a worthwhile remediation performance, phytoremediation technology involves amalgamating multifarious techniques and strategies. The primary objective of this research was to look into the effects of seasonal changes, contamination level, and EDTA chelation on Brown mustard's potential to extract Lead (Pb) from synthetically contaminated soil and its response to antioxidant enzyme activity. Soil samples containing 5 mg kg-1 of EDTA were spiked with 200, 500, and 1000 mg kg-1 of Pb, while the control group (unspiked) without EDTA addition was used. The results indicated that adding EDTA in winter (winter + EDTA) significantly increased (p < 0.05) plant growth by 18.83%. Observing the seasonal variation, the removal efficiency of Pb was achieved in this order: summer + EDTA > winter + EDTA > summer + No EDTA > winter + No EDTA. The results also showed that the removal rate had improved up to 52.53% as the concentration of Pb rose from 67 to 500 mg kg-1 but showed a decline after reaching 1000 mg kg-1, indicating a maximum Pb stress level. Additionally, the EDTA chelation during winter demonstrated a significant effect on the ability of Brown mustard to accumulate higher levels of Pb in both roots and leaves, with 500 mg kg-1 as the optimal level taken by the plant throughout the experiment. Except for CAT, the increased enzyme activities were observed under EDTA chelation while Pb-stress (1000 mg kg-1) reduced the enzyme activities by over 4%. The findings suggest that having 143 U/g CAT, 285 U/g SOD, and 14.9 U/g MDA in the summer season with EDTA amendments were the most suitable recourse for decontamination of Pb-polluted soil compared to a single-factor treatment.

Review on the impact of heavy metals from industrial wastewater effluent and removal technologies

The incidence of water pollution in developing countries is high due to the lack of regulatory policies and laws that protect water bodies from anthropogenic activities and industrial wastewater. Industrial wastewater contains significant amounts of heavy metals that are detrimental to human health, aquatic organisms, and the ecosystem. The focus of this review was to evaluate the sources and treatment methods of wastewater, with an emphasis on technologies, advantages, disadvantages, and innovation. It was observed that conventional methods of wastewater treatment (such as flotation, coagulation/flocculation, and adsorption) had shown promising results but posed certain limitations, such as the generation of high volumes of sludge, relatively low removal rates, inefficiency in treating low metal concentrations, and sensitivity to varying pH. Recent technologies like nanotechnology, photocatalysis, and electrochemical coagulation have significant advantages over conventional methods for removing heavy metals, including higher removal rates, improved energy efficiency, and greater selectivity for specific contaminants. However, the high costs associated with these advanced methods remain a major drawback. Therefore, we recommend that future developments in wastewater treatment technology focus on reducing both costs and waste generation.

Air pollution tolerance and metal accumulation potential of some plant species growing in educational institutions of Amritsar, India

Poor air quality in urban areas increases the exposure of individuals to air pollutants. Hence, it becomes mandatory to grow such plant species that have more potential to tolerate air pollution and can aid in its mitigation. Air pollution tolerance index (APTI) and anticipated performance index (API) are two indices that help in scientific evaluation of plant species before recommending them for plantation. In this study, six plant species from three educational institutions of Amritsar city were screened for their tolerance and performance against air pollution as well as for their capability to act as accumulators of nine metals viz., aluminium (Al), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn). On the basis of APTI, Cassia fistula (C. fistula) was categorized as a tolerant species while Alstonia scholaris (A. scholaris), Cascabela thevetia (C. thevetia), Monoon longifolium (M. longifolium), Pongamia pinnata (P. pinnata) and Syzygium cumini (S. cumini) were categorized as intermediately tolerant plant species. API results suggested that A. scholaris, C. fistula, M. longifolium, P. pinnata and S. cumini should be planted for air pollution mitigation. Geo-accumulation Index (Igeo) results showed that soil samples were moderately contaminated with three (Pb, Cu and Zn) metals. Bioaccumulation factor (BAF), for all metals among six plant species, was found to be less than one implying that these plants were absorbers of metals. Metal Accumulation Index (MAI) indicated that C. thevetia, C. fistula and P. pinnata exhibited relatively higher potential for metal accumulation.

Assessment of selected tree species as phytoremediation agents in polluted soils

The study investigates the ability of selected tree species to absorb heavy metals (Pb, Ni, Zn) from polluted soils. Seedlings of Adansonia digitata (P1), Jatropha curcas (P2), and Hildegardia barteri (P3) were transplanted into polythene pots with soils from a dumpsite (T1), highway (T2), industrial area (T3), and farmland (T4), forming a 3x4 factorial experiment replicated five times in a Completely Randomized Block Design. Pre-sowing analysis showed T1 and T2 had the highest Pb and Zn concentrations, T3 had the highest Ni, and T4 had the lowest heavy metal concentrations. After 12 weeks, heavy metal concentrations decreased in all soils. P1 concentrated metals in the root, P2 in the shoot, and P3 in various plant parts, with significant differences between species. P2 was identified as an effective phytoextractor for Pb and Zn (TF > 1), and P3 for Ni. All species showed potential for phytostabilization. The study concludes that these species are viable options for phytoremediation of heavy metals in contaminated soils.

Organic fertilizer improved the lead and cadmium metal tolerance of Eucalyptus camaldulensis by enhancing the uptake of potassium, phosphorus, and calcium

Phytoremediation is a strategy for the amelioration of soil heavy metal contamination that aligns with ecological sustainability principles. Among the spectrum of phytoremediation candidates, woody plants are considered particularly adept for their substantial biomass, profound root systems, and non-participation in the food chain. This study used Eucalyptus camaldulensis-a tree species characterized for its high biomass and rapid growth rate-to assess its growth and metal uptake in mining tailings. The results were as follows: exposure to heavy metals reduced the E. camaldulensis uptake of potassium (K), phosphorus (P), and calcium (Ca). Heavy metal stress negatively affected the biomass of E. camaldulensis. Lead (Pb) primarily accumulated in the roots, while cadmium (Cd) predominantly accumulated in the stems. The application of organic fertilizers bolstered the stress tolerance of E. camaldulensis, mitigating the adverse impacts of heavy metal stress. A synergistic effect occurred when organic fertilizers were combined with bacterial fertilizers. The plant's enrichment capacity for Cd and its tolerance to Pb was augmented through the concurrent application of bacterial and organic fertilizers. Collectively, the application of organic fertilizers improved the heavy metal tolerance of E. camaldulensis by enhancing the uptake of K, P, and Ca and elevating the content of glutathione peroxidase (GPX) and gibberellin acid (GA) in roots. These findings provided nascent groundwork for breeding E. camaldulensis with enhanced heavy metal tolerance. Moreover, this proved the potentiality of E. camaldulensis for the management of heavy metal-contaminated tailings and offers a promising avenue for future environmental restoration.

Phytoremediation efficiency of poplar hybrid varieties with diverse genetic backgrounds in soil contaminated by multiple toxic metals (Cd, Hg, Pb, and As)

Fifteen poplar varieties were used in a field trial to investigate the phytoremediation efficiency, stress resistance, and wood property of poplar hybrid varieties with diverse genetic backgrounds under the composite pollution of heavy metals. The coefficient of variation and clone repeatability for growth traits and Cd concentration were large. The Cd accumulation of poplar varieties 107 and QHQ reached 1.9 and 1.7 mg, respectively, followed by QHB, Ti, 69, and Pa, in which Cd accumulation reached 1.3 mg. Most of the intra-specific hybrid varieties (69, QH1, SL4, T3, and ZL46) had low Cd concentrations and small biomass, resulting in weak Cd accumulation and low phytoremediation efficiency for Cd-polluted soil. By contrast, the inter-sectional and inter-specific hybrid varieties exhibited better growth performance and accumulated higher concentrations of heavy metals than the intra-specific hybrids. The bioconcentration factor and translocation factor of Hg, As, and Pb were less than 1, indicating that poplars have low phytoremediation efficiency for these heavy metals. The hybrids between section Aigeiros and Tacamahaca (QHQ and QHB) and the inter-specific hybrid 107 within section Aigeiros were more resistant to composite heavy metal stress than the other poplar varieties were partially because of their high levels of free proline that exceeded 93 μg·g-1 FW. According to the correlation analysis of the concentrations of the different heavy metals, the poplar roots absorbed different heavy metals in a cooperative manner, indicating that elite poplar varieties with superior capacity for accumulating diverse heavy metals can be bred feasibly. Compared with the intra-specific hybrid varieties, the inter-sectional (QHQ and QHB) and inter-specific (107) hybrid varieties had higher pollution remediation efficiency, larger biomass, higher cellulose content, and lower lignin content, which is beneficial for pulpwood. Therefore, breeding and extending inter-sectional (QHQ and QHB) and inter-specific hybrid varieties can improve the phytoremediation of composite pollution.

Elucidating the phytoremediation potentials and ecophysiological mechanisms of indicator plants in the industrial polluted region

The integrity of natural ecosystems, particularly in the Global South, is increasingly compromised by industrial contaminants. Our study examines the growth of plant species adapted to ecosystems impacted by heavy metal pollution, specifically focusing on their phytoremediation capabilities and tolerance to contaminants. The potential of pollution-tolerant species was evaluated in the industrial subtropical wetland of Sialkot, Pakistan. Employing quantitative ecological methods, data on vegetation, phytosociological attributes, and soil properties were gathered from 450 plots across different pollution gradients. The study pinpointed 17 key indicator species tolerating high heavy metal pollution out of 182 surveyed, using a combination of Indicator Species Analysis (ISA) and the Importance Value Index (IVI). These species demonstrated diverse capacities to extract, stabilize, and accumulate heavy metals (Cr, Zn, Cu, As, Cd, Ni, Hg, and Pb) across varying pollution zones. Notably, Cannabis sativa demonstrated substantial phytoextraction of Zn and Cd, with concentrations reaching 1977.25 μg/g and 1362.78 μg/g, respectively. Arundo donax showed marked hyperaccumulation of Cd, peaking at 410.531 μg/g. Achyranthes aspera was remarkable for its extraction and accumulation of Ni and Cu, with concentrations of 242.412 μg/g and 77.2997 μg/g, respectively. Physiological changes, such as increased proline levels in Cannabis sativa and Achyranthes aspera reaching 39.041 μg/g and 27.523 μg/g under high metal concentrations, indicated adaptation to metal stress. Declines in chlorophyll and carotenoid levels were also observed as metal contamination increased, with up to 35% reductions in some species. These findings underscore the potential efficacy of selected plant species in phytoremediation and highlight the importance of physiological responses in their tolerance to metals, providing valuable information for targeted remediation strategies in polluted ecosystems and improving environmental management and sustainable practices.

Pinus eldarica (L.) bark as urban atmospheric trace element pollution bioindicator: pollution status, spatial variations, and quantitative source apportionment based on positive matrix factorization receptor model

In this study, a total of 180 Pinus eldarica bark samples were collected from different regions of Hamedan megacity, Iran, in 2023, and contents of Cd, Cr, Cu, Mn, Ni, Pb, and Zn in the samples were determined using ICP-OES. The results illustrated that the average contents of all the analyzed elements were greater than those in the background contents, which presumably demonstrated anthropogenic sources of these potentially toxic elements (PTEs). The greatest concentrations of the analyzed PTEs for different functional areas were observed in specimens collected from commercial or industrial areas, indicating the impact of human entries. The I-geo values were in the range of "unpolluted to moderately polluted" to "moderately to heavily polluted", PI showed "moderate to very high pollution", and PLI reflected high to very high pollution levels for the whole study area. Additionally, the cumulative mean value of ecological risk (RI) was found to be 152, demonstrating moderate ecological risk across the study area. The results of positive matrix factorization (PMF) showed that the PTE contamination in the air of Hamedan could mainly have an anthropogenic origin (82.7%) and that the traffic emissions as the primary pollution source (33.6%) make the highest contribution to the PTE pollution and ecological risks in the study area. In residential areas, demolition and construction activities could be considered the main sources of PTEs, while in commercial and industrial areas traffic emissions and industrial emissions, could be regarded as the main sources of such pollution, respectively. In conclusion, this study provides a useful approach to identifying the sources and contributions of the toxic elements in different functional areas and can inform future endeavors that aim at managing and controlling metal element pollution.

Nature-based solution enhances resilience to flooding and catalyzes multi-benefits in coastal cities in the Global South

Coastal cities are facing a rise in groundwater levels induced by sea level rise, further triggering saturation excess flooding where groundwater levels reach the topographic surface or reduce the storage capacity of the soil, thus stressing the existing infrastructure. Lowering groundwater levels is a priority for sustaining the long-term livelihood of coastal cities. In the absence of studies assessing the possibility of using tree-planting as a measure of alleviating saturation excess flooding in the context of rising groundwater levels, the multi-benefit nature of tree-planting programs as sustainable Nature-based solutions (NBSs) in coastal cities in the Global South is discussed. In environments where groundwater is shallow, trees uptake groundwater or reduce groundwater recharge, thereby contributing to lower groundwater levels and increasing the unsaturated zone thickness, further reducing the risk of saturation excess flooding. Tree-planting programs represent long-term solutions sustained by environmental factors that are complementary to conventional engineering solutions. The multi-benefit nature of such NBSs and the expected positive environmental, economic, and social outcomes make them particularly promising. Wide social acceptance was identified as crucial for the long-term success of any tree-planting program, as the social factor plays a major role in addressing most weaknesses and threats of the solution. In the case of Nouakchott City (Mauritania), where a rise in groundwater levels has led to permanent saturation excess flooding, a tree-planting program has the potential to lower the groundwater levels, thereby reducing flooding during the rainy season.

Assessment of metals and metalloids agglutinated to airborne suspended particulate matter in selected plant species during the pre-and post-monsoon in the urban area

The elemental accumulation has emerged as a major environmental concern due to various anthropogenic sources such as vehicles, road dust, and industrial activities, contributing to the agglutination of elements to airborne Suspended Particulate Matter (SPM). SPM-bound elements accumulate on plant surfaces impact air quality and human health due to their noxiousness. Therefore, plants' ability to capture and mitigate air pollutants plays a crucial role in urban areas. This study aimed to investigate the levels and distribution of twenty-six elements, comprised of heavy metals (Cd, Pb, Cr, Cu Zn, Co, Ni, Fe, Mn, Ag, Mo, V, Ga, and Bi), light metals (B, As, Te, and Se), and metalloids (Al, Li, Sr, K, Mg, Na, Ca, and Ba) accumulated on the surface and inside the leaves of dominant plant species during the pre-and post-monsoon at six categorized (commercial, traffic-prone, residential, educational, greenbelt and industrial areas) locations in Delhi, India. In addition, the Metal Accumulation Index (MAI) was determined, and the statistical analysis was conducted using two-way ANOVA, Principal Component Analysis (PCA), and Hierarchical Cluster Analysis (HCA). In the pre-and post-monsoon, two-way ANOVA revealed significant differences (P < 0.05) in metal concentrations. During the pre-monsoon plants exhibited the highest metal accumulation (∼21%) at the Anand Vihar (commercial) in Delhi, with the maximum average concentrations of Cr (118.25 mg/kg), Cu (204.38 mg/kg), Zn (293.27 mg/kg), and Fe (2721.17 mg/kg). Ficus benghalensis L exhibited the maximum 213.73 MAI at the Anand Vihar in the pre-monsoon. Ni and Cr indicated the highest correlation (P < 0.05, r = 0.82) in the PCA test. HCA test revealed similarity (∼87.7%) at ITO (traffic-prone) and Okhla Phase-2 (industrial) in F. religiosa regarding metal concentration patterns. Findings highlighted seasonal elemental pollutants uptake dynamics of plant species and explored species-specific metal accumulation, revealing potential implications of metal-tolerant plants for urban greenbelt.

Phytohormones-mediated strategies for mitigation of heavy metals toxicity in plants focused on sustainable production

KEY MESSAGE

In this manuscript, authors reviewed and explore the information on beneficial role of phytohormones to mitigate adverse effects of heavy metals toxicity in plants. Global farming systems are seriously threatened by heavy metals (HMs) toxicity, which can result in decreased crop yields, impaired food safety, and negative environmental effects. A rise in curiosity has been shown recently in creating sustainable methods to reduce HMs toxicity in plants and improve agricultural productivity. To accomplish this, phytohormones, which play a crucial role in controlling plant development and adaptations to stress, have emerged as intriguing possibilities. With a particular focus on environmentally friendly farming methods, the current review provides an overview of phytohormone-mediated strategies for reducing HMs toxicity in plants. Several physiological and biochemical activities, including metal uptake, translocation, detoxification, and stress tolerance, are mediated by phytohormones, such as melatonin, auxin, gibberellin, cytokinin, ethylene, abscisic acid, salicylic acid, and jasmonates. The current review offers thorough explanations of the ways in which phytohormones respond to HMs to help plants detoxify and strengthen their resilience to metal stress. It is crucial to explore the potential uses of phytohormones as long-term solutions for reducing the harmful effects of HMs in plants. These include accelerating phytoextraction, decreasing metal redistribution to edible plant portions, increasing plant tolerance to HMs by hormonal manipulation, and boosting metal sequestration in roots. These methods seek to increase plant resistance to HMs stress while supporting environmentally friendly agricultural output. In conclusion, phytohormones present potential ways to reduce the toxicity of HMs in plants, thus promoting sustainable agriculture.

Biochar impacts on carbon dioxide, methane emission, and cadmium accumulation in rice from Cd-contaminated soils; A meta-analysis

Climate change and cadmium (Cd) contamination pose severe threats to rice production and food security. Biochar (BC) has emerged as a promising soil amendment for mitigating these challenges. To investigate the BC effects on paddy soil upon GHG emissions, Cd bioavailability, and its accumulation, a meta-analysis of published data from 2000 to 2023 was performed. Data Manager 5.3 and GetData plot Digitizer software were used to obtain and process the data for selected parameters. Our results showed a significant increase of 18% in soil pH with sewage sludge BC application, while 9% increase in soil organic carbon (SOC) using bamboo chips BC. There was a significant reduction in soil bulk density (8%), but no significant effects were observed for soil porosity, except for wheat straw BC which reduced the soil porosity by 6%. Sewage sludge and bamboo chips BC significantly reduced carbon dioxide (CO2) by 7-8% while municipal biowaste reduced methane (CH4) emissions by 2%. In the case of heavy metals, sunflower seedshells-derived materials and rice husk BC significantly reduced the bioavailable Cd in paddy soils by 24% and 12%, respectively. Cd uptake by rice roots was lowered considerably by the addition of kitchen waste (22%), peanut hulls (21%), and corn cob (15%) based BC. Similarly, cotton sticks, kitchen waste, peanut hulls, and rice husk BC restricted Cd translocation from rice roots to shoots by 22%, 27%, 20%, and 19%, respectively, while sawdust and rice husk-based BC were effective for reducing Cd accumulation in rice grains by 25% and 13%. Regarding rice yield, cotton sticks-based BC significantly increased the yield by 37% in Cd-contaminated paddy soil. The meta-analysis demonstrated that BC is an effective and multi-pronged strategy for sustainable and resilient rice cultivation by lowering greenhouse gas emissions and Cd accumulation while improving yields under the increasing threat of climate change.

Toxic effects of cadmium on the physiological and biochemical attributes of plants, and phytoremediation strategies: A review

Anthropogenic activities pose a more significant threat to the environment than natural phenomena by contaminating the environment with heavy metals. Cadmium (Cd), a highly poisonous heavy metal, has a protracted biological half-life and threatens food safety. Plant roots absorb Cd due to its high bioavailability through apoplastic and symplastic pathways and translocate it to shoots through the xylem with the help of transporters and then to the edible parts via the phloem. The uptake and accumulation of Cd in plants pose deleterious effects on plant physiological and biochemical processes, which alter the morphology of vegetative and reproductive parts. In vegetative parts, Cd stunts root and shoot growth, photosynthetic activities, stomatal conductance, and overall plant biomass. Plants' male reproductive parts are more prone to Cd toxicity than female reproductive parts, ultimately affecting their grain/fruit production and survival. To alleviate/avoid/tolerate Cd toxicity, plants activate several defense mechanisms, including enzymatic and non-enzymatic antioxidants, Cd-tolerant gene up-regulations, and phytohormonal secretion. Additionally, plants tolerate Cd through chelating and sequestering as part of the intracellular defensive mechanism with the help of phytochelatins and metallothionein proteins, which help mitigate the harmful effects of Cd. The knowledge on the impact of Cd on plant vegetative and reproductive parts and the plants' physiological and biochemical responses can help selection of the most effective Cd-mitigating/avoiding/tolerating strategy to manage Cd toxicity in plants.

Macroalgae for biomonitoring of trace elements in relation to environmental parameters and seasonality in a sub-tropical mangrove estuary

Being a resourceful ecosystem, mangrove estuaries have always been subjected to trace elements (TEs) contamination, and therefore, the biomonitoring approach holds immense potential for surveilling the aquatic environment. To investigate the potentiality of mangrove macroalgae as biomonitors, estuarine water, intertidal-sediment, and macroalgal samples were collected from the Pasur River estuary of Sundarbans mangrove ecosystem, Bangladesh, and afterward studied through Atomic Absorption Spectrometer to quantify the levels of six concerned TEs (Fe, Mn, Zn, Cu, Pb, and Cd). This study utilized the geo-environmental and ecological indices and sediment characterization approaches (sediment quality guidelines-SQGs) for assessing the contamination scenario of the adjacent environment to macroalgae whereas the performance of studied algal groups was evaluated using Bio-contamination factor, Comprehensive bio-concentration index, and Metal accumulation index. Metal occurrence scheme in the water followed the order of Fe > Zn > Mn > Pb > Cd while Fe > Mn > Zn > Cu > Pb > Cd for both sediment and macroalgae. Both Pb and Cd exceeded the guideline limit in estuarine water and the indices approach manifested low to moderate contamination with enrichment from anthropogenic origin of Mn, Zn, and Cu in sediment. Moreover, the SQGs revealed rare biological effects of Cu on an aquatic community. Within algal samples, Chlorophyta contributed the highest biomass production, followed by Phaeophyta and Rhodophyta. Statistical relationship disclosed the influence of environmental variables on TE's accumulation in Chlorophyta. By contrast, hydrochemical's association showed prevalence over the TEs accumulation process for Phaeophyta and Rhodophyta. Bioaccumulation performance analysis revealed that the ability to accumulate TEs in macroalgal groups varied with seasons. Therefore, biomonitoring with macroalgae for the region of interest might require further temporal considerations.

Assessment and Removal of Heavy Metals and Other Ions from the Industrial Wastewater of Faisalabad, Pakistan

The contamination of surface and groundwater is of major concern around the globe due to the fast industrialization and urbanization. The groundwater and water quality of rivers, Ravi and Chenab in Faisalabad, Pakistan are contaminated due to the industrial wastewater. The aim of this study was the assessment of the physiochemical contaminants of Faisalabad’s industrial wastewater area and the adsorptive removal of ions present in high concentrations following the National Environmental Quality Standards (NEQS) for the municipal and industrial liquid effluents of Pakistan. One of the two samples was collected from a drain carrying wastewater from different industries and other from the outlet of a drain discharging wastewater into river Chenab. The analysis results obtained indicate that most of the contaminants were below the acceptable limit of industrial wastewater NEQS, Pakistan. However, contaminants like sulfate ions (714 mg/L), total dissolved solids (33,951–34,620 mg/L) and barium ions (11–15 mg/L) were found to be higher than the allowable level of NEQS for the municipal and industrial liquid effluents for Pakistan. A novel biosorbent synthesized indigenously from Monotheca buxifolia seeds was used for the removal of sulfate, barium and TDS from the wastewater effluent samples. This biosorbent successfully reduced the sulfate ion concentration in the wastewater sample from 714 to 420 mg/L at pH 6 in 1 h. Similarly, the concentration of TDS reduced to 33,951 from 6295 mg/L at pH 4, whereas barium ions were removed from 15 to 1 mg/L at pH 10 in 1 h. Treatment of wastewater through the synthesized biosorbent efficiently removed the high concentration ions and could potentially be applied to reduce the toxic effects of these contaminants on local public health.