Application of common duckweed (Lemna minor) in phytoremediation of chemicals in the environment: State and future perspective

LmGSTF3 Overexpression Enhances Cadmium Tolerance in Lemna minor

Glutathione S-transferase (GST) has been established to play an important role in regulating the responses of plants to stress, although its function and mechanisms of action in the cadmium (Cd)-tolerant Lemna minor remain unclear. In this study, we sought to identify a Cd-responsive GST gene from Lemna minor for functional analysis and mechanistic characterization. We accordingly identified a member of the GST gene family, LmGSTF3, which plays a positive role in adaptation of Lemna minor to Cd. Having successfully obtained overexpressing (OE) strains via genetic transformation, we established that these strains were characterized by elevated Cd tolerance compared with the wild-type strain, as evidenced by significant increases in growth rate, chlorophyll content, antioxidant enzyme activities, and Cd removal rate. At the transcriptome level, the OE strains were found to have a stronger regulatory ability in response to Cd, particularly with respect to photoprotection, antioxidant defense, and glycolytic metabolism, which may be key factors contributing to the Cd tolerance of Lemna minor. Our findings provide a basis for further elucidating the biochemical and molecular mechanisms underlying the Cd tolerance conferred by GST genes in Lemna minor and will potentially contribute to the utilization of Lemna minor in remediating aquatic pollution.

Transgenerational Plasticity Enhances the Tolerance of Duckweed (Lemna minor) to Stress from Exudates of Microcystis aeruginosa

Transgenerational plasticity (TGP) refers to the influence of ancestral environmental signals on offspring's traits across generations. While evidence of TGP in plants is growing, its role in plant adaptation over successive generations remains unclear, particularly in floating plants facing fluctuating environments. Duckweed (Lemna minor), a common ecological remediation material, often coexists with the harmful bloom-forming cyanobacterium Microcystis aeruginosa, which releases a highly toxic exudate mixture (MaE) during its growth. In this study, we investigate the TGP of duckweed and its adaptive role under stress from MaE during the bloom-forming process. We found that exposure to MaE induces significant phenotypic plasticity in duckweed, manifested by alterations in morphological, physiological, and transcriptomic profiles. Specifically, MaE exposure significantly affected duckweed, promoting growth at low concentrations but inhibiting it at high concentrations, affecting traits like biomass, frond number, total frond area, and photosynthetic efficiency. Additionally, the activities of antioxidant enzymes, together with the levels of proline, soluble sugars, and proteins, are elevated with increasing MaE concentrations. These plastic changes are largely retained through asexual reproductive cycles, persisting for several generations even under MaE-free conditions. We identified 619 genes that maintain a 'transcriptional memory', some of which correlate with the TGP-linked alterations in morphological and physiological traits in response to MaE stress. Notably, progeny from MaE-exposed lineages demonstrate enhanced fitness when re-exposed to MaE. These results enhance our comprehension of the adaptive significance of TGP in plants and suggest feasible approaches for utilizing duckweed's TGP in the bioremediation of detrimental algal blooms.

Evolution in Response to Management Increases Invasiveness Among Experimental Populations of Duckweed (Lemna minor)

Numerous management methods are deployed to try to mitigate the destructive impact of weedy and invasive populations. Yet, such management practices may cause these populations to inadvertently evolve in ways that have consequence on their invasiveness. To test this idea, we conducted a two-step field mesocosm experiment; we evolved genetically diverse populations of the duckweed Lemna minor to targeted removal management and then tested the impact of that evolution in replicated invasions into experimental resident communities. We found that evolution in response to management increased invasiveness compared to populations evolved without management. This evolution in response to management had little effect on the impact of the invader on the resident species. These results illustrate the potential eco-evolutionary consequences of management practices. Mitigating evolution to physical removal, in addition to pesticides, may be important to the long-term success of integrated pest management.

Efficiency evaluation of wastewater treatment by three macrophytes using a pilot-constructed wetland system in Ota, Nigeria

Three aquatic macrophytes were used to treat wastewater using a pilot-constructed wetland (CW) system to determine the most efficient plants for removing contaminants from wastewater. The three macrophytes are water hyacinth (Eichhornia crassipes), water lettuce (Pistia stratiotes), and duckweed (Lemna minor). Three 150 L capacity tanks with sand and gravel as substrates were used as the pilot CW for each plant. Upon initial examination, the raw wastewater was not compliant with standard discharge limits. The wastewater samples were collected every 7 days for 3 weeks for treatment. From the findings, at 14 days hydraulic retention time (HRT), E. crassipes and P. stratiotes achieved the highest total phosphorus (TP) and chemical oxygen deman (COD) reductions of 99.3 and 99.4%, respectively. E. crassipes indicated better biological oxygen demand removal efficiency of 91.3%, COD (85.0%), electrical conductivity (90.4%), total dissolved solids (89.7%), and total coliforms (66.0%). Albeit, P. stratiotes indicated better results for total suspended solids (96.2%), TP (7.55%), and E. coli (94.4%), while L. minor was better with 90.8% total nitrogen removal. The overall analysis showed E. crassipes to be more efficient than the three macrophytes. However, the other two plants are replaceable options and large-scale implementation of this project in the community would be a major contributor to actualizing SDG number 6.

Recent and sustainable advances in phytoremediation of heavy metals from wastewater using aquatic plant species: Green approach

A key component in a nation's economic progress is industrialization, however, hazardous heavy metals that are detrimental to living things are typically present in the wastewater produced from various industries. Therefore, before wastewater is released into the environment, it must be treated to reduce the concentrations of the various heavy metals to maximum acceptable levels. Even though several biological, physical, and chemical remediation techniques are found to be efficient for the removal of heavy metals from wastewater, these techniques are costly and create more toxic secondary pollutants. However, phytoremediation is inexpensive, environmentally friendly, and simple to be applied as a green technology for heavy metal detoxification in wastewater. The present study provides a thorough comprehensive review of the mechanisms of phytoremediation, with an emphasis on the possible utilization of plant species for the treatment of wastewater containing heavy metals. We have discussed the concept, its applications, advantages, challenges, and independent variables that determine how successful and efficient phytoremediation could be in the decontamination of heavy metals from wastewater. Additionally, we argue that the standards for choosing aquatic plant species for target heavy metal removal ought to be taken into account, as they influence various aspects of phytoremediation efficiency. Following the comprehensive and critical analysis of relevant literature, aquatic plant species are promising for sustainable remediation of heavy metals. However, several knowledge gaps identified from the review need to be taken into consideration and possibly addressed. Therefore, the review provides perspectives that indicate research needs and future directions on the application of plant species in heavy metal remediation.

Selenite (IV) and selenate (VI) uptake and accumulation capacity of Lemna minor L. from an aquatic medium

The uptake of sodium selenite (Se(IV)) and sodium selenate (Se(VI)) from aqueous medium by Lemna minor L. and the influence of different Se concentrations on its growth, morphological and ultrastructural characteristics were studied. L. minor was grown at different concentrations (1, 3, 5 and 10 mg L-1) of Se(IV) and Se(IV). The Se(IV) concentration in the plant tissue ranged between 77.7 (± 4.3) to 453 (± 0) mg kg-1 DW. The Se(VI) concentration in plant tissues ranged between 117 (± 11) to 417 (± 2) mg kg-1 DW. The highest bioconcentration factor for Se(VI) was 127 (± 7) at 3 mg/L, with a Se removal efficiency of 44%. For Se(IV), the highest bioconcentration factor was 77.7 (± 4.3) at 1 mg L-1, which had a Se removal efficiency of 23%. Growth of L. minor was suppressed at 10 mg L-1 Se in both forms. The addition of Se promoted the formation of starch granules in L. minor which occupied a chloroplast area of 74% for Se(IV) and 77% for Se(VI). The efficient uptake of both Se forms by L. minor indicates the potential application of this species for phytoremediation of Se laden wastewaters and its use as an alternative feedstock in biofuel production.

Tolerance and phytoremediation capacity of atrazine and S-metolachlor by two duckweeds

The phytotoxicity and removal of atrazine and S-metolachlor in sterile duckweed systems were estimated in this study. Herbicides were added at environmentally relevant ranges: 0-400 µg/L for atrazine or 0-200 µg/L for S-metolachlor in systems with Spirodela polyrhiza or Lemna minor. Toxicity biomarkers, i.e., changes in plant biomass, surface area, chlorophyll fluorescence parameters, pigments, lipid peroxidation, protein concentration, and antioxidative enzyme activities in plants were estimated after 7 days. S. polyrhiza (RGRbiomass-EC50 = 164.8 µg/L) was more tolerant to atrazine than L. minor (RGRbiomass-EC50 = 101.0 µg/L). Atrazine caused damage to photosystem II (ΦM), a reduction in electron transport between PSII and PSI (Φ'M), as well as disruption in energy distribution pathways (decrease in qPrel and increase in UQFrel), most prominently in L. minor. However, L. minor (RGRbiomass-EC50 = 128.9 µg/L) was more tolerant to S-metolachlor than S. polyrhiza (RGRbiomass-EC50 = 15.5 μg/L). The highest sensitivity of S. polyrhiza to S-metolachlor was attributed to a decrease in absorbed energy used in photochemistry (qPrel) and an increase in lipid peroxidation, indicating that S. polyrhiza plants were experiencing oxidative stress. Residual pesticide analysis in the water after seven days allowed us to conclude that plants were responsible for reducing up to 16.5% of atrazine and 28.7% of S-metolachlor in the duckweed system. S. polyrhiza showed higher atrazine phytoremediation capacity than L. minor. S. polyrhiza was more efficient at an environmentally relevant concentration of S-metolachlor (25 μg/L) and L. minor at higher concentrations (200 μg/L).

Exploring the defense strategies of benzalkonium chloride exposures on the antioxidant system, photosynthesis and ROS accumulation in Lemna minor

With the advent of technological advancements post the industrial revolution, thousands of chemicals are introduced into the market annually to enhance different facets of human life. Among these, pharmaceutical and personal care products (PPCPs), including antibiotics and disinfectants, such as benzalkonium chlorides (BACs), are prominent. BACs, often used for surface and hand disinfection in high concentrations or as preservatives in health products such as nasal sprays and eye drops, may present environmental risks if they seep into irrigation water through prolonged exposure or improper application. The primary objective of this study is to elucidate the tolerance mechanisms that may arise in Lemna minor plants, known for their remarkable capability to accumulate substances efficiently, in response to exogenously applied BACs at varying concentrations. The study applied six different concentrations of BACs, ranging from 0.25 to 10 mg L-1. The experimental period spanned seven days, during which the treatments were conducted in triplicate to ensure reliability and reproducibility of the results. It was observed that low concentrations of BACs (0.25, 0.5 and 1 mg L-1) did not elicit any statistically significant changes in growth parameters. However, higher concentrations of BACs (2.5, 5, and 10 mg L-1) resulted in a reduction in RGR by 20%, 28%, and 36%, respectively. Chlorophyll fluorescence declined significantly at BAC doses of 5 and 10 mg L-1, with Fv/Fm ratios decreasing by 9% and 15%, and Fv/Fo ratios by 40% and 39%, respectively. Proline content decreased in all treatment groups, with a 46% reduction at 10 mg L-1 BAC. TBARS and H2O2 contents increased proportionally with BAC dosage, showing the highest increases of 30% and 40% at 10 mg L-1, respectively. The noticeable increase in SOD enzyme activity at BAC concentrations of 0.5, 1, and 2.5 mg L-1, with increases of 2.7-fold, 2.2-fold, and 1.7-fold respectively, along with minimal accumulation of H2O2, suggests that L. minor plants have a strong tolerance to BAC. This is supported by the efficient functioning of the CAT and GST enzymes, especially evident at the same concentrations, where increased activities effectively reduce the buildup of H2O2. In the AsA-GSH cycle, although variations were observed between groups, the contribution of the GR enzyme to the preservation of GSH content by recycling GSSG likely maintained redox homeostasis in the plant, especially at low concentrations of BACs. The study revealed that L. minor effectively accumulates BAC alongside its tolerance mechanisms and high antioxidant activity. These results underscore the potential for environmental cleanup efforts through phytoremediation.

Phyto-treatment of tannery industry effluents under combined application of citric acid and chromium-reducing bacterial strain through Lemna minor L.: A lab scale study

Contamination of agricultural soils with heavy metals (HMs) poses a significant environmental threat, especially because industrial discharges often irrigate agricultural lands. A prominent source of HM(s) pollution occurs from tannery effluents containing high concentrations of chromium (Cr) in both Cr3+ and Cr6+ forms along with other toxic materials. Cr is known for its carcinogenic and mutagenic properties in biological systems. Microbe-assisted phytoremediation has emerged as a promising and environmentally friendly approach for detoxifying Cr-contaminated environments. This study aimed to evaluate the performance of citric acid (CA) and a Cr-reducing bacterial strain (Staphylococcus aureus) on the phytoextraction potential of Lemna minor within a Constructed Wetland System treated with tannery wastewater. Various combinations of tannery wastewater (0, 50, and 100 %), CA (0, 5 and 10 mM), and microbial inoculants were applied to the test plants. The mitigative effects of Staphylococcus aureus strain K1 were examined in combination with different concentrations of CA (0, 5, 10 mM). Data on growth and yield attributes highlighted the beneficial effects of bacterial inoculation and CA in ameliorating Cr toxicity in L. minor, as evidenced by increased foliar chlorophyll and carotenoid contents, enhanced antioxidant enzyme activities (SOD, POD, APX, CAT), and improved nutrient uptake. Specifically, CA application resulted in an enhancement of Cr ranging from 12% to 15% and 23%-31% in concentration, and 134%-141% and 322%-337% in Cr accumulation, respectively. When combined with the S. aureus inoculation treatment, CA application (5 and 10 mM) further increased the concentration and accumulation of Cr in L. minor. The enhancement in Cr ranged from 12% to 23% and 27%-41% in concentration, 68%-75%, and 179%-185% in accumulation, respectively. These results demonstrated that L. minor is an effective choice for environmentally friendly Cr remediation due to its continued ability to grow in polluted wastewater. This study suggested that microbial-assisted phytoextraction combined with chelating agents such as CA could be a practical and effective approach for remediating tannery effluents.

Lower concentration polyethylene microplastics can influence free-floating macrophyte interactions by combined effects of many weak interactions: A nonnegligible ecological impact

Microplastics (MPs) are ubiquitous in freshwater ecosystems and their accumulation has been considered an emerging threat. Early research on the effects of MPs on macrophytes primarily focused on the toxicological impacts on individual macrophytes, with several studies suggesting that lower concentrations of MPs have little impact on macrophytes. However, the ecological implications of lower MP concentrations on macrophyte communities remain largely unexplored. Here, we experimented to assess the effects of lower concentrations including 25 mg/L, 50 mg/L, 75 mg/L, and 100 mg/L of polyethylene (PE) microplastics on Spirodela polyrhiza and Lemna minor, and their community. Our results also indicated that PE concentrations below 100 mg/L had no significant effect on relative growth rate, specific leaf area, Chlorophyll a, Chlorophyll b, Chlorophyll a + b, carotenoid, malondialdehyde (MDA), catalase, and soluble sugar of monocultural S. polyrhiza. However, a lower concentration of PE significantly decreased the MDA of monocultural L. minor and significantly affected the comprehensive index of S. polyrhiza. These findings suggested that lower concentrations of PE can influence interactions between macrophytes maybe due to the cumulative effects of many weak interactions. Additionally, our study showed that 75 mg/L and 100 mg/L PE additions decreased the competitive balance index value of two macrophytes under mixed-culture condition. This result implied that the ecological influence of lower concentration MPs on macrophytes may manifest at the community level rather than at the population level, due to species-specific responses and varying degrees of sensitivity of macrophytes to PE concentrations. Thus, our study emphasizes the need to closely monitor the ecological consequences of emerging contaminants such as MPs accumulation on macrophyte communities, rather than focusing solely on the morphology and physiology of individual macrophytes.

Removal of contaminants of emerging concern by Wolffia arrhiza and Lemna minor depending on the process conditions, pollutants concentration, and matrix type

Research was carried out on the removal of a group of six contaminants of emerging concern: bisphenol A, N,N-diethyl-m-toluamide, diethylstilbestrol, triclosan, estrone and estradiol from the water matrix during contact with small floating macrophytes Wolffia arrhiza and Lemna minor. The optimal conditions for the process, such as pH, light exposure per day, and plant mass, were determined using the design of experiments chemometric approach based on central composite design. Experiments conducted under the designated optimal conditions showed that after 7 days, the removal efficiency equals 88-98% in the case of W. arrhiza and 87-97% in the case of L. minor, while after 14 days of the experiment, these values are 93-99.6% and 89-98%, respectively. The primary mechanism responsible for removing CECs is the plant uptake, with the mean uptake rate constant equal to 0.299 day-1 and 0.277 day-1 for W. arrhiza and L. minor, respectively. Experiments conducted using municipal wastewater as a sample matrix showed that the treatment efficiency remains high (the average values 84% and 75%; in the case of raw wastewater, 93% and 89%, and in the case of treated wastewater, for W. arrhiza and L. minor, respectively). Landfill leachate significantly reduces plants' ability to remove pollutants (the average removal efficiency equals 59% and 56%, for W. arrhiza and L. minor, respectively).

Uptake, subcellular distribution, and fate of tetracycline in two wetland plants supplemented with microbial agents: Effect and mechanism

The use of wetland plants in the context of phytoremediation is effective in the removal of antibiotics from contaminated water. However, the effectiveness and efficiency of many of these plants in the removal of antibiotics remain undetermined. In this study, the effectiveness of two plants-Phragmites australis and Iris pseudacorus-in the removal of tetracycline (TC) in hydroponic systems was investigated. The uptake of TC at the roots of I. pseudacorus and P. australis occurred at concentrations of 588.78 and 106.70 μg/g, respectively, after 7-day exposure. The higher uptake of TC in the root of I. pseudacorus may be attributed to its higher secretion of root exudates, which facilitate conditions conducive to the reproduction of microorganisms. These rhizosphere-linked microorganisms then drove the TC uptake, which was higher than that in the roots of P. australis. By elucidating the mechanisms underlying these uptake-linked outcomes, we found that the uptake of TC for both plants was significantly suppressed by metabolic and aquaporin inhibition, suggesting uptake and transport of TC were active (energy-dependent) and passive (aquaporin-dominated) processes, respectively. The subcellular distribution patterns of I. pseudacorus and P. australis in the roots were different, as expressed by differences in organelles, cell wall concentration levels, and transport-related dynamics. Additionally, the microbe-driven enhancement of the remediation capacities of the plants was studied comprehensively via a combined microbial-phytoremediation hydroponic system. We confirmed that the microbial agents increased the secretion of root exudates, promoting the variation of TC chemical speciation and thus enhancing the active transport of TC. These results contribute toward the improved application of wetland plants in the context of antibiotic phytoremediation.

Exploring the ecotoxicological impact of meropenem on Lemna minor: Growth, photosynthetic activity, and oxidative stress

Meropenem is a potent carbapenem antibiotic frequently used in medical settings. Several studies have confirmed the pervasive presence of these antibiotics in wastewater treatment plants and aquatic environments. However, the effects of these substances on non-target organisms, such as plants, have not been adequately monitored. Thus, this study aimed to assess the short-term impact of meropenem on the growth, photosynthesis, chlorophyll content, and enzyme activity of the macrophyte plant Lemna minor. The methods involved exposing the plant to meropenem under controlled conditions and assessing physiological and biochemical parameters to determine the impact on photosynthetic activity and oxidative stress. These analyses included growth rate, antioxidant enzyme activity, and photosynthetic capacity. The findings suggest that the growth rate of Lemna minor remained unaffected by meropenem at concentrations <200000 μgL-1. However, plants exposed to concentrations >20 μgL-1showed physiological alterations, such as decreased net photosynthesis rate (17%) and chlorophyll concentration (57%), compared to the control group. For acute toxicity assays, the calculated EC50 7-day and EC20 7-day were 1135 μgL-1and 33 μgL-1, respectively. In addition, in most treatments tested, meropenem caused an increase in the superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activity as a defense mechanism against oxidative stress. Our results suggest that meropenem affects photosynthetic processes and induces oxidative stress in the macrophyte plant Lemna minor. Further studies are needed to assess the physiological and metabolic interactions between antibiotics and primary producers at different long-term trophic levels.

Enhancing water quality and ecosystems of reclaimed water-replenished river: A case study of Dongsha River, Beijing, China

The use of reclaimed water for urban river replenishment has raised concerns regarding its impact on water quality and aquatic ecosystems. This study aims to reveal the improvements seen in an urban river undergoing a practical water eco-remediation after being replenished with reclaimed water. A one-year monitoring of water quality, phytoplankton, and zooplankton was carried out in Dongsha River undergoing eco-remediation in Beijing, China. The results showed that compared to the unrestored river, the concentrations of COD, NH4+-N, TP, and TN decreased by 28.22 ± 7.88 %, 40.24 ± 11.77 %, 44.17 ± 17.29 %, and 28.66 ± 10.39 % in the restoration project area, respectively. The concentration of Chlorophyll-a in the restoration area was maintained below 40 μg/L. During summer, when algal growth is vigorous, the density of Cyanophyta in the unrestored river decreased from 46.84 × 104cells/L to 16.32 × 104cells/L in the restored area, while that of Chlorophyta decreased from 41.61 × 104cells/L to 11.87 × 104cells/L, a reduction of 65.16 % and 71.47 %, respectively. The dominant phytoplankton species were replaced with Bacillariophyta, such as Synedra sp. and Nitzschia sp., indicating that the restoration of aquatic plants reduces the risk of Cyanophyta blooms. Zooplankton species also changed in the restoration area, especially during summer. The density of pollution-tolerant Rotifer and Protozoa decreased by 31.06 % and 27.22 %, while the density of clean water indicating Cladocera increased by 101.19 %. We further calculated the diversity and evenness index of phytoplankton and zooplankton within and outside the restoration area. The results showed that the Shannon-Weaver index for phytoplankton and zooplankton in the restoration area was 2.1 and 1.91, which was higher than those in the river (1.84 and 1.82). This further confirmed that aquatic plant restoration has positive effects. This study can provide a practical reference and theoretical basis for the implementation of water ecological restoration projects in other reclaimed water rivers in China.

Phthalate acid esters: A review of aquatic environmental occurrence and their interactions with plants

The increasing use of phthalate acid esters (PAEs) in various applications has inevitably led to their widespread presence in the aquatic environment. This presents a considerable threat to plants. However, the interactions between PAEs and plants in the aquatic environment have not yet been comprehensively reviewed. In this review, the properties, occurrence, uptake, transformation, and toxic effects of PAEs on plants in the aquatic environment are summarized. PAEs have been prevalently detected in the aquatic environment, including surface water, groundwater, seawater, and sediment, with concentrations ranging from the ng/L or ng/kg to the mg/L or mg/kg range. PAEs in the aquatic environment can be uptake, translocated, and metabolized by plants. Exposure to PAEs induces multiple adverse effects in aquatic plants, including growth perturbation, structural damage, disruption of photosynthesis, oxidative damage, and potential genotoxicity. High-throughput omics techniques further reveal the underlying toxicity molecular mechanisms of how PAEs disrupt plants on the transcription, protein, and metabolism levels. Finally, this review proposes that future studies should evaluate the interactions between plants and PAEs with a focus on long-term exposure to environmental PAE concentrations, the effects of PAE alternatives, and human health risks via the intake of plant-based foods.

The evolution of the duckweed ionome mirrors losses in structural complexity

BACKGROUND AND AIMS

The duckweeds (Lemnaceae) consist of 36 species exhibiting impressive phenotypic variation, including the progressive evolutionary loss of a fundamental plant organ, the root. Loss of roots and reduction of vascular tissues in recently derived taxa occur in concert with genome expansions of ≤14-fold. Given the paired loss of roots and reduction in structural complexity in derived taxa, we focus on the evolution of the ionome (whole-plant elemental contents) in the context of these fundamental changes in body plan. We expect that progressive vestigiality and eventual loss of roots might have both adaptive and maladaptive consequences that are hitherto unknown.

METHODS

We quantified the ionomes of 34 accessions in 21 species across all duckweed genera, spanning 70 Myr in this rapidly cycling plant (doubling times are as rapid as ~24 h). We related both micro- and macroevolutionary ionome contrasts to body plan remodelling and showed nimble microevolutionary shifts in elemental accumulation and exclusion in novel accessions.

KEY RESULTS

We observed a robust directional trend in calcium and magnesium levels, decreasing from the ancestral representative Spirodela genus towards the derived rootless Wolffia, with the latter also accumulating cadmium. We also identified abundant within-species variation and hyperaccumulators of specific elements, with this extensive variation at the fine (as opposed to broad) scale.

CONCLUSIONS

These data underscore the impact of root loss and reveal the very fine scale of microevolutionary variation in hyperaccumulation and exclusion of a wide range of elements. Broadly, they might point to trade-offs not well recognized in ionomes.

Biphasic pretreatment excels over conventional sulfuric acid in pinewood biorefinery: An environmental analysis

This study assesses the environmental impact of pine chip-based biorefinery processes, focusing on bioethanol, xylonic acid, and lignin production. A cradle-to-gate Life Cycle Assessment (LCA) is employed, comparing a novel biphasic pretreatment method (p-toluenesulfonic acid (TsOH)/pentanol, Sc-1) with conventional sulfuric acid pretreatment (H2SO4, Sc-2). The analysis spans biomass handling, pretreatment, enzymatic hydrolysis, yeast fermentation, and distillation. Sc-1 yielded an environmental impact of 1.45E+01 kPt, predominantly affecting human health (96.55%), followed by ecosystems (3.07%) and resources (0.38%). Bioethanol, xylonic acid, and lignin contributed 32.61%, 29.28%, and 38.11% to the total environmental burdens, respectively. Sc-2 resulted in an environmental burden of 1.64E+01 kPt, with a primary impact on human health (96.56%) and smaller roles for ecosystems (3.07%) and resources (0.38%). Bioethanol, xylonic acid, and lignin contributed differently at 22.59%, 12.5%, and 64.91%, respectively. Electricity generation was predominant in both scenarios, accounting for 99.05% of the environmental impact, primarily driven by its extensive usage in biomass handling and pretreatment processes. Sc-1 demonstrated a 13.05% lower environmental impact than Sc-2 due to decreased electricity consumption and increased bioethanol and xylonic acid outputs. This study highlights the pivotal role of pretreatment methods in wood-based biorefineries and underscores the urgency of sustainable alternatives like TsOH/pentanol. Additionally, adopting greener electricity generation, advanced technologies, and process optimization are crucial for reducing the environmental footprint of waste-based biorefineries while preserving valuable bioproduct production.

Comparison of mercury (Hg) bioaccumulation with mono- and mixed Lemna minor and Spirodela polyrhiza cultures

Mercury (Hg) is a prevalent and harmful contaminant that persists in the environment. For phytoremediation, it is important to discover which plants can bioaccumulate meaningful amounts of Hg while also tolerating its toxicity. Additionally, increasing biodiversity could create a more resilient and self-sustaining system for remediation. This study explores whether mixed populations of Lemna minor and Spirodela polyrhiza can better bioaccumulate and tolerate Hg than monocultures. Mono- and mixed cultures of L. minor and S. polyrhiza were grown in mesocosms of 0.5 µg/L or 100 µg/L Hg (HgCl2) spiked water for 96 h. Change in weight of duckweed was used to assess Hg tolerance. Diffusive gradients in thin-films (DGTs) were used as surrogate monitoring devices for bioavailable levels of Hg. For biomass growth, the mixed culture of the L. minor was greater than the monoculture at the high dose. The L. minor accumulated more Hg in the mixed culture at the low dose while the S. polyrhiza was higher in the mixed at the high dose. Hg speciation in water was modeled using Windermere Humic Aqueous Model 7 (WHAM7) to compare the bioavailable species indicated by the DGTs.  Potentially due to the controlled conditions, the WHAM7 output of bioavailable Hg was almost 1:1 to that estimated by the DGTs, indicating good predictive capability of geochemical modeling and passive sampler DGT on metal bioavailability. Overall, the mixed cultures statistically performed as well as or better than the monocultures when tolerating and bioaccumulating Hg. However, there needs to be further work to see if the significant differences translate into practical differences worth the extra resources to maintain multiple species.

Contrasting patterns of 5S rDNA repeats in European and Asian ecotypes of greater duckweed, Spirodela polyrhiza (Lemnaceae)

Ribosomal DNA (rDNA) contains highly conserved, specifically organized sequences encoding ribosomal RNAs (rRNAs) separated by variable non-transcribed intergenic spacers (NTSs) and is abundant in eukaryotic genomes. These characteristics make the rDNA an informative molecular target to study genome organization, molecular evolution, and phylogenetics. In this study, we characterized the 5S rDNA repeats in the greater duckweed Spiroldela polyrhiza, a species known for its small size, rapid growth, highly conserved genome organization, and low mutation rate. Sequence analysis of at least 12 individually cloned PCR fragments containing the 5S rDNA units for each of six ecotypes that originated from Europe (Ukraine) and Asia (China) revealed two distinct types of 5S rDNA repeats containing NTSs of different lengths and nucleotide compositions. The shorter 5S rDNA repeat units had a highly homogeneous 400-bp NTS, with few ecotype- or region-specific single-nucleotide polymorphisms (SNPs). The longer 5S rDNA units had NTSs of 1056-1084 bp with characteristic intra- and inter-genomic variants due to specific SNPs and insertions/deletions of 4-15-bp DNA elements. We also detected significant variability in the ratio of short/long 5S rDNA variants between ecotypes of S. polyrhiza. The contrasting dynamics of the two types of 5S rDNA units, combined with the unusually low repeat copy number (for plants) in S. polyrhiza (46-220 copies per genome), shows that this species could serve as an excellent model for examining the mechanisms of concerted evolution and functional significance of rDNA variability.

Domestic wastewater treatment by Pistia stratiotes in constructed wetland

The objective of the study was to evaluate the performance of Pistia stratiotes for treatment of domestic wastewater in a free surface water flow constructed wetland. The objective of the study was to evaluate contaminants removal efficiency of the constructed wetland vegetated with P. stratiotes in treatment of domestic wastewater against Hydraulic retention time (HRT) of 10, 20 and 30 days was investigated. This asks for newer and efficient low-cost nature-based water treatment system which along with cost takes into consideration the sustainability of the ecosystem. Five constructed wetland setups improved the wastewater quality and purify it significantly by reducing the TDS by 83%, TSS by 82%, BOD by 82%, COD by 81%, Chloride by 80%, Sulfate by 77%, NH3 by 84% and Total Oil and Grease by 74%. There was an increase in pH of about 11.9%. Color and odor of wastewater was also improved significantly and effectively. It was observed that 30 days' HRT was optimum for the treatment of domestic wastewater. The final effluent was found to be suitable as per national environmental quality standards and recycled for watering plants and crop irrigation but not for drinking purposes. The treatment in constructed wetland system was found to be economical, as the cost of construction only was involved and operational and maintenance cost very minimal. Even this research was conducted on the sole purpose of commuting the efficiency of pollutant removal in short span time.

Biomonitoring of heavy metals and their phytoremediation by duckweeds: Advances and prospects

Heavy metals (HMs) contamination of water bodies severely threatens human and ecosystem health. There is growing interest in the use of duckweeds for HMs biomonitoring and phytoremediation due to their fast growth, low cultivation costs, and excellent HM uptake efficiency. In this review, we summarize the current state of knowledge on duckweeds and their suitability for HM biomonitoring and phytoremediation. Duckweeds have been used for phytotoxicity assays since the 1930s. Some toxicity tests based on duckweeds have been listed in international guidelines. Duckweeds have also been recognized for their ability to facilitate HM phytoremediation in aquatic environments. Large-scale screening of duckweed germplasm optimized for HM biomonitoring and phytoremediation is still essential. We further discuss the morphological, physiological, and molecular effects of HMs on duckweeds. However, the existing data are clearly insufficient, especially in regard to dissection of the transcriptome, metabolome, proteome responses and molecular mechanisms of duckweeds under HM stresses. We also evaluate the influence of environmental factors, exogenous substances, duckweed community composition, and HM interactions on their HM sensitivity and HM accumulation, which need to be considered in practical application scenarios. Finally, we identify challenges and propose approaches for improving the effectiveness of duckweeds for bioremediation from the aspects of selection of duckweed strain, cultivation optimization, engineered duckweeds. We foresee great promise for duckweeds as phytoremediation agents, providing environmentally safe and economically efficient means for HM removal. However, the primary limiting issue is that so few researchers have recognized the outstanding advantages of duckweeds. We hope that this review can pique the interest and attention of more researchers.

Heavy metals/-metalloids (As) phytoremediation with Landoltia punctata and Lemna sp. (duckweeds): coupling with biorefinery prospects for sustainable phytotechnologies

Heavy metals/-metalloids can result in serious human health hazards. Phytoremediation is green bioresource technology for the remediation of heavy metals and arsenic (As). However, there exists a knowledge gap and systematic information on duckweed-based metal phytoremediation in an eco-sustainable way. Therefore, the present review offers a critical discussion on the effective use of duckweeds (genera Landoltia and Lemna)-based phytoremediation to decontaminate metallic contaminants from wastewater. Phytoextraction and rhizofiltration were the major mechanism in 'duckweed bioreactors' that can be dependent on physico-chemical factors and plant-microbe interactions. The biotechnological advances such as gene manipulations can accelerate the duckweed-based phytoremediation process. High starch and protein contents of the metal-loaded duckweed biomass facilitate their use as feedstock in biorefinery. Biorefinery prospects such as bioenergy production, value-added products, and biofertilizers can augment the circular economy approach. Coupling duckweed-based phytoremediation with biorefinery can help achieve Sustainable Development Goals (SDGs) and human well-being.

WaterHyacinth: A comprehensive image dataset of various Water hyacinth species from different regions of Bangladesh

The "WaterHyacinth" dataset, a recently gathered collection of images featuring four distinct species of Water hyacinth from different regions of Bangladesh, is presented in this article. There are four different classifications: Lemna minor, Eichhornia crassipes, Monochoria korsakowii, and Pistia stratiotes. The collection consists of 1790 original images and in addition 4050 augmented photos of Water hyacinth species. Every original picture was captured with the appropriate background and in sufficient natural light. Every image was correctly placed in its corresponding subfolder, providing optimal use of the pictures by various machine learning and deep learning models. Researchers could make major progress in agriculture, environmental monitoring, aquatic science, and remote sensing domains by utilizing this enormous dataset and various machine learning and deep learning approaches. In addition to opening opportunities for significant developments in these domains, it offers an essential asset for further study.

Effect of luminescent materials on the biochemistry, ultrastructure, and rhizobial microbiota of Spirodela polyrhiza

Fluorescent materials and technologies have become widely used in scientific research, and due to the ability to convert light wavelengths, their application to photosynthetic organisms can affect their development by altering light quality. However, the impacts of fluorescent materials on aquatic plants and their environmental risks remain unclear. To assess the effects of luminescent materials on floating aquatic macrophytes and their rhizosphere microorganisms, 4-(di-p-tolylamino)benzaldehyde-A (DTB-A) and 4-(di-p-tolylamino)benzaldehyde-M (DTB-M) (emitting blue-green and orange-red light, respectively) were added individually and jointly to Spirodela polyrhiza cultures and set at different concentrations (1, 10, and 100 μM). Both DTB-A and DTB-M exhibited phytotoxicity, which increased with concentration under separate treatment. Moreover, the combined group exhibited obvious stress relief at 10 μM compared to the individually treated group. Fluorescence imaging showed that DTB-A and DTB-M were able to enter the cell matrix and organelles of plant leaves and roots. Peroxidation induced cellular damage, contributing to a decrease in superoxide dismutase (SOD) and peroxidase (POD) activities and malondialdehyde (MDA) accumulation. Decomposition of organelle structures, starch accumulation in chloroplasts, and plasmolysis were observed under the ultrastructure, disrupting photosynthetic pigment content and photosynthesis. DTB-A and DTB-M exposure resulted in growth inhibition, dry weight loss, and leaf yellowing in S. polyrhiza. A total of 3519 Operational Taxonomic Units (OTUs) were identified in the rhizosphere microbiome. The microbial communities were dominated by Alphaproteobacteria, Oxyphotobacteria, and Gammaproteobacteria, with the abundance and diversity varied significantly among treatment groups according to Shannon, Simpson, and Chao1 indices. This study revealed the stress defense response of S. polyrhiza to DTB-A and DTB-M exposures, which provides a broader perspective for the bioremediation of pollutants using aquatic plants and supports the further development of fluorescent materials for applications.

Differentiation between chemo- and radiotoxicity of 137Cs and 60Co on Lemna minor

The uptake and effects of stable Cs and Co on L.minor were extensively studied, together with the effects of gamma radiation using a 137Cs or 60Co source. Innovative is that we combined external irradiation (from 137Cs or 60Co sources) with the direct uptake of certain amounts of stable Cs or Co to simulate the impact of the same mass of a radioisotope compared with that of the stable element. Such approach allows to differentiate between chemo- and radiotoxicity of 137Cs or 60Co, permitting to study the 137Cs and 60Co uptake by L. minor without using high concentrations of these elements in solution. Our results indicate that radiotoxicity of both 137Cs and 60Co has a greater importance compared to their chemotoxicity. This was also supported by the independent action and concentration addition concepts. Both concepts resulted in a good prediction of the dose-response curve of the combination exposure. The maximal removal of 137Cs or 60Co per gram dry matter of L. minor was lower compared with the removal of the corresponding stable isotope. The toxicity of 60Co was higher compared to 137Cs based on EC50 values and uptake data. With respect to the effects on photosynthetic pigments, starch and soluble sugars contents, only starch increased in a concentration- and dose-dependent manner.

Two duckweed species exhibit variable tolerance to microcystin-LR exposure across genotypic lineages

Cyanotoxins produced by harmful cyanobacteria blooms can damage freshwater ecosystems and threaten human health. Floating macrophytes may be used as a means of biocontrol by limiting light and resources available to cyanobacteria. However, genetic variation in macrophyte sensitivity to cyanotoxins could influence their suitability as biocontrol agents. We investigated the influence of such intraspecific variation on the response of two rapidly growing duckweed species, Lemna minor and Spirodela polyrhiza, often used in nutrient and metal bioremediation. We assessed two biomarkers related to productivity (biomass and chlorophyll A production) and two related to fitness measures (population size and growth rate). Fifteen genetic lineages of each species were grown in media containing common cyanotoxin microcystin-LR at ecologically relevant concentrations or control media for a period of twelve days. Genotype identity had a strong impact on all biomarker responses. Microcystin concentration slightly increased the final population sizes of both macrophyte species with a marginal effect on growth rate of L. minor and the chlorophyll A production of S. polyrhiza, but overall these species were very tolerant of microcystin. The strong tolerance supports the potential use of these plants as bioremediators of cyanobacterial blooms. However, differential impact of microcystin exposure discovered in single lineage models among genotypes indicates a potential for cyanotoxins to act as selective forces, necessitating attention to genotype selection for bioremediation.

Physiological response, microbial diversity characterization, and endophytic bacteria isolation of duckweed under cadmium stress

Duckweed is a cadmium (Cd) hyperaccumulator. However, its enrichment characteristics and physiological responses to Cd have not been systematically studied. The physiological responses, enrichment characteristics, diversity of endophytic bacterial communities, and isolation of Cd-resistant endophytes in duckweed (Lemna minor 0014) were studied for different durations and Cd concentrations. The results indicated that peroxidase (POD) and catalase (CAT) activities decreased while superoxide dismutase activity first increased and then decreased with increasing Cd stress duration. POD activities, CAT activities, and O2- increased as Cd concentrations increased. Malondialdehyde content and Cd accumulation in duckweed increased with increasing concentrations and time. This endophytic diversity study identified 488 operational taxonomic units, with the dominant groups being Proteobacteria, Firmicutes, and Actinobacteria. Paenibacillus sp. Y11, a strain tolerant to high concentrations of Cd and capable of significantly promoting duckweed growth, was isolated from the plant. Our study revealed the effects of heavy metals on aquatic plants, providing a theoretical basis for the application of duckweed in water pollution.

Phytosphere purification of urban domestic wastewater

Industrialization and overpopulation have polluted aquatic environments with significant impacts on human health and wildlife. The main pollutants in urban sewage are nitrogen, phosphorus, heavy metals and organic pollutants, which need to be treated with sewage, and the use of aquatic plants to purify wastewater has high efficiency and low cost. However, the effectiveness and efficiency of phytoremediation are also affected by temperature, pH, microorganisms and other factors. The use of biochar can reduce the cost of wastewater purification, and the combination of biochar and nanotechnology can improve the efficiency of wastewater purification. Some aquatic plants can enrich pollutants in wastewater, so it can be considered to plant these aquatic plants in constructed wetlands to achieve the effect of purifying wastewater. Biochar treatment technology can purify wastewater with high efficiency and low cost, and can be further applied to constructed wetlands. In this paper, the latest research progress of various pollutants in wastewater purification by aquatic plants is reviewed, and the efficient treatment technology of wastewater by biochar is discussed. It provides theoretical basis for phytoremediation of urban sewage pollution in the future.

Exposure of Lemna minor (Common Duckweed) to Mixtures of Uranium and Perfluorooctanoic Acid (PFOA)

A variety of processes, both natural and anthropogenic, can have a negative impact on surface waters, which in turn can be detrimental to human and environmental health. Few studies have considered the ecotoxicological impacts of concurrently occurring contaminants, and that is particularly true for mixtures that include contaminants of emerging concern (CEC). Motivated by this knowledge gap, the present study considers the potential ecotoxicity of environmentally relevant contaminants in the representative aquatic plant Lemna minor (common duckweed), a model organism. More specifically, biological effects associated with exposure of L. minor to a ubiquitous radionuclide (uranium [U]) and a fluorinated organic compound (perfluorooctanoic acid [PFOA], considered a CEC), alone and in combination, were monitored under controlled laboratory conditions. Lemna minor was grown for 5 days in small, aerated containers. Each treatment consisted of four replicates with seven plants each. Treatments were 0, 0.3, and 3 ppb PFOA; 0, 0.5, and 5 ppb U; and combinations of these. Plants were observed daily for frond number and signs of chlorosis and necrosis. Other biological endpoints examined at the conclusion of the experiment were chlorophyll content and antioxidant capacity. In single-exposure experiments, a slight stimulatory effect was observed on frond number at 0.3 ppb PFOA, whereas both concentrations of U had a detrimental effect on frond number. In the dual-exposure experiment, the combinations with 5 ppb U also had a detrimental effect on frond number. Results for chlorophyll content and antioxidant capacity were less meaningful, suggesting that environmentally relevant concentrations of PFOA and U have only subtle effects on L. minor growth and health status. Environ Toxicol Chem 2023;42:2412-2421. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Sorption of cadmium, chromium, lead, and vanadium from artificial wetlands using Lemna aequinoctialis

The efficacy of the lesser duckweed, Lemna aequinoctialis (Welw.), to remediate varying concentrations of cadmium, chromium, lead, and vanadium from an organo-metallic contaminated media was tested in artificial surface wetland mesocosm experiment. A 100 g of fresh-weight duckweed was introduced into each of the mesocosm, except for the control setup and monitored for 120 days while the metals removal rate was quantified using an atomic absorption spectrometer. A time-dependent and partial sorption of metals was observed with the highest removal rate recorded for cadmium (71.96%), followed by lead (69.23%), vanadium (55.22%), and chromium (41.64%). The uptake and bioaccumulation of metals were reflected in the increased plant biomass (p < 0.05, F = 97.12) and relative growth rate (p < 0.05, F = 1214.35) in duckweed. A coefficient (r2) of 0.951, 0.919, 0.970, and 0.967 was recorded for cadmium, chromium, lead, and vanadium respectively, indicating that the remediation of metals followed the first-order kinetic rate model. This study highlights the efficacy of the lesser duckweed to preferentially remediate metals in an organo-metallic complex medium for potential wastewater treatment in the petrochemical industry.

Integrated bioprocess for Se(VI) remediation using duckweed: Coupling selenate removal to biogas production

The use of phytoremediation as a method for wastewater treatment or removal of pollutants is garnering significant interest and duckweed (DW), a free floating macrophyte, depicts significant potential for the removal of nutrients and toxic compounds from contaminated waters. The present work aimed to develop an integrated process for remediating selenate (Se(VI)) using DW biomass and subsequent use of Se(VI) enriched DW for biogas production. The main objective is to extend the application of selenium (Se) enriched DW biomass for biogas production. Se(VI) enriched DW biomass (Se-DW) gave higher methane production (48.38 ± 3.6 mL gCOD-1) than control DW biomass (C-DW) (24.46 ± 3.6 mL gCOD-1). To further enhance methane production, three pre-treatment approaches (acid, alkali and hydrothermal) were assessed and the solid and liquid fractions obtained after pre-treatment were used as a substrate. Pre-treatments increased biogas production in both Se-DW and C-DW than untreated conditions. Liquid fractions gave higher biogas production than solid fractions. In Se-DW, highest biogas production was observed in hydrothermal pre-treated Se-DW, while in C-DW, acid pre-treatment gave higher biogas production. Methane production was shown to be enhanced up to a Se(VI) concentration of 1.7 mg L-1, whereas a concentration beyond this lowered biogas production.

Combined toxic effects of polypropylene and perfluorooctanoic acid on duckweed and periphytic microorganisms

Microplastics and perfluorooctanoic acid coexist in the aquatic environment. Duckweed was exposed to a range of concentrations (0.1-1000 μg L-1) of solutions containing polypropylene (PP) and perfluorooctanoic acid (PFOA) for 14 days to measure their toxicity. The result showed the single and combined PP and PFOA treatments did not significantly influence the growth of duckweed. The greatest PP and PFOA concentrations of combined pollution affect plant chlorophyll. Moreover, the combined treatment of duckweed consistently resulted in increased malondialdehyde (MDA) levels, indicating oxidative damage. As an antioxidant stress response, the combination-treated plants were encouraged to produce superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Meanwhile, 3519 Operational Taxonomic Units (OTUs) were identified in the duckweed rhizosphere. Proteobacteria was the most predominant microbial community. Shannon, Simpson, and Chao1 discovered that microbial communities changed in response to single and combination PP and PFOA treatments, with decreased diversity and increased abundance. In addition, SEM analysis also revealed that the combined treatment significantly phyllosphere microorganisms. The findings of this investigation add to our knowledge of how PP and PFOA affect duckweed and the rhizospheric microorganisms, expanding the theoretical basis for employing duckweed in complex contamination.

Open-source workflow design and management software to interrogate duckweed growth conditions and stress responses

Duckweeds, a family of floating aquatic plants, are ideal model plants for laboratory experiments because they are small, easy to cultivate, and reproduce quickly. Duckweed cultivation, for the purposes of scientific research, requires that lineages are maintained as continuous populations of asexually propagating fronds, so research teams need to develop optimized cultivation conditions and coordinate maintenance tasks for duckweed stocks. Additionally, computational image analysis is proving to be a powerful duckweed research tool, but researchers lack software tools to assist with data collection and storage in a way that can feed into scripted data analysis. We set out to support these processes using a laboratory management software called Aquarium, an open-source application developed to manage laboratory inventory and plan experiments. We developed a suite of duckweed cultivation and experimentation operation types in Aquarium, which we then integrated with novel data analysis scripts. We then demonstrated the efficacy of our system with a series of image-based growth assays, and explored how our framework could be used to develop optimized cultivation protocols. We discuss the unexpected advantages and the limitations of this approach, suggesting areas for future software tool development. In its current state, our approach helps to bridge the gap between laboratory implementation and data analytical software for duckweed biologists and builds a foundation for future development of end-to-end computational tools in plant science.

Effects of microplastics and cadmium on growth rate, photosynthetic pigment content and antioxidant enzymes of duckweed (Lemma minor)

Cadmium (Cd) and polyethylene (PE) seriously contaminate the aquatic environment and threaten human health. Many studies have reported the toxic effects of Cd and PE on plants, whereas few have reported the combined contamination of these two pollutants. In this study, duckweed (Lemma minor) was used as an indicator to explore the effect of PE microplastics (PE-MPs) at concentrations of 10, 50, 100, 200, and 500 mg/L on tolerance to 1 mg/L Cd. The results showed that different concentrations of PE-MPs inhibited the growth rate and chlorophyll content of duckweed to different degrees, both of which were minimal at 50 mg/L PE-MPs, 0.11 g/d, and 0.32 mg/g, respectively. The highest Cd enrichment (7.77 mg/kg) and bioaccumulation factors (94.22) of duckweed were detected when Cd was co-exposed with 50 mg/L of PE-MPs. Catalase and peroxidase activity first decreased and then increased with increasing PE-MPs concentrations, showing "hormesis effects", with minimum values of 11.47 U/g and 196.00 U/g, respectively. With increasing concentrations of PE-MPs, the effect on superoxide dismutase activity increased and then declined, peaking at 162.05 U/g, and displaying an "inverted V" trend. The amount of malondialdehyde rose with different PE-MPs concentrations. This research lay a foundation for using duckweed to purify water contaminated with MPs and heavy metals.

Unraveling the toxicity of tire wear contamination in three freshwater species: From chemical mixture to nanoparticles

Tire wear particle (TWP) contamination is of growing concern as recent studies show the ubiquity and toxicity of this contaminant in various environmental compartments. The multidimensional aspect of TWPs makes it difficult to assess toxicity and predict impacts on ecosystems, as it combines a complex mixture of chemicals and can release micro- and nanoparticles when suspended in water. Our work aimed to shed light on the toxicity of the different components of TWP leachate, namely, the dissolved chemicals and the nanoparticle fractions, on three freshwater model species of different trophic levels: Chlorella vulgaris, Lemna minor, and Daphnia magna. Acute toxicity was observed for all three fractions in D. magna, and an additive effect was observed between the nanoparticles and dissolved chemicals. L. minor experienced phytotoxicity from the dissolved chemicals only with a decrease up to 50% in photosynthesis efficiency parameters. C. vulgaris showed minor signs of toxicity on apical endpoints in response to each of the fractions. Our study highlights that nanoparticles from TWP leachate that were mostly overlooked in several previous studies are as toxic as dissolved chemicals for the filter-feeder species D. magna, and we also show the toxicity to photosynthesis in aquatic plants.

Systemic chemical characterization of Lemna minor by UHPLC-Q-Exactive Orbitrap MS coupled with parallel reaction monitoring

Lemna minor L. (LM) has been used for measles opacity, rubella itching, edema, and oliguria, and the main active ingredients were flavonoids, namely, apigenin, apigenin-7-O-glucoside, and luteolin-7-O-glucoside. However, few systematic analyses of their constituents have been performed; thus, it was necessary to establish a fast and efficient method to identify the chemical composition of LM. In this study, the UHPLC-Q-Exactive Orbitrap mass spectrometry coupled with parallel reaction monitoring was established. Finally, a total of 112 constituents, including 30 dipeptides, 28 nucleosides, 11 amino acids, 10 organic acids, 10 flavonoids, and 23 other compounds, were identified by MS, diagnostic fragment ions, and retention time. One hundred one of those chemicals were first found in LM, which was very beneficial for the further development and utilization of nutriments and the medicinal use of LM.

Heavy metals and arsenic stress in food crops: Elucidating antioxidative defense mechanisms in hyperaccumulators for food security, agricultural sustainability, and human health

The spread of heavy metal(loid)s at soil-food crop interfaces has become a threat to sustainable agricultural productivity, food security, and human health. The eco-toxic effects of heavy metals on food crops can be manifested through reactive oxygen species that have the potential to disturb seed germination, normal growth, photosynthesis, cellular metabolism, and homeostasis. This review provides a critical overview of stress tolerance mechanisms in food crops/hyperaccumulator plants against heavy metals and arsenic (HM-As). The HM-As antioxidative stress tolerance in food crops is associated with changes in metabolomics (physico-biochemical/lipidomics) and genomics (molecular level). Furthermore, HM-As stress tolerance can occur through plant-microbe, phytohormone, antioxidant, and signal molecule interactions. Information regarding the avoidance, tolerance, and stress resilience of HM-As should help pave the way to minimize food chain contamination, eco-toxicity, and health risks. Advanced biotechnological approaches (e.g., genome modification with CRISPR-Cas9 gene editing) in concert with traditional sustainable biological methods are useful options to develop 'pollution safe designer cultivars' with increased climate change resilience and public health risks mitigation. Further, the usage of HM-As tolerant hyperaccumulator biomass in biorefineries (e.g., environmental remediation, value added chemicals, and bioenergy) is advocated to realize the synergy between biotechnological research and socio-economic policy frameworks, which are inextricably linked with environmental sustainability. The biotechnological innovations, if directed toward 'cleaner climate smart phytotechnologies' and 'HM-As stress resilient food crops', should help open the new path to achieve sustainable development goals (SDGs) and a circular bioeconomy.

New Insight into the Function of Dopamine (DA) during Cd Stress in Duckweed (Lemna turionifera 5511)

Dopamine (DA), a kind of neurotransmitter in animals, has been proven to cause a positive influence on plants during abiotic stress. In the present study, the function of DA on plants under cadmium (Cd) stress was revealed. The yellowing of duckweed leaves under Cd stress could be alleviated by an exogenous DA (10/20/50/100/200 μM) supplement, and 50 μM was the optimal concentration to resist Cd stress by reducing root breakage, restoring photosynthesis and chlorophyll content. In addition, 24 h DA treatment increased Cd content by 1.3 times in duckweed under Cd stress through promoting the influx of Cd2+. Furthermore, the gene expression changes study showed that photosynthesis-related genes were up-regulated by DA addition under Cd stress. Additionally, the mechanisms of DA-induced Cd detoxification and accumulation were also investigated; some critical genes, such as vacuolar iron transporter 1 (VIT1), multidrug resistance-associated protein (MRP) and Rubisco, were significantly up-regulated with DA addition under Cd stress. An increase in intracellular Ca2+ content and a decrease in Ca2+ efflux induced by DA under Cd stress were observed, as well as synchrony with changes in the expression of cyclic nucleotide-gated ion channel 2 (CNGC2), predicting that, in plants, CNGC2 may be an upstream target for DA action and trigger the change of intracellular Ca2+ signal. Our results demonstrate that DA supplementation can improve Cd resistance by enhancing duckweed photosynthesis, changing intracellular Ca2+ signaling, and enhancing Cd detoxification and accumulation. Interestingly, we found that exposure to Cd reduced endogenous DA content, which is the result of a blocked shikimate acid pathway and decreased expression of the tyrosine aminotransferase (TAT) gene. The function of DA in Cd stress offers a new insight into the application and study of DA to Cd phytoremediation in aquatic systems.

Arsenic contamination in groundwater and food chain with mitigation options in Bengal delta with special reference to Bangladesh

Bangladesh, situated in Bengal delta, is one of the worst affected countries by arsenic contamination in groundwater. Most of the people in the country are dependent on groundwater for domestic and irrigation purposes. Currently, 61 districts out of 64 districts of Bangladesh are affected by arsenic contamination. Drinking arsenic contaminated groundwater is the main pathway of arsenic exposure in the population. Additionally, the use of arsenic-contaminated groundwater for irrigation purpose in crop fields in Bangladesh has elevated arsenic concentration in surface soil and in the plants. In many arsenic-affected countries, including Bangladesh, rice is reported to be one of the significant sources of arsenic contamination. This review discussed scenario of groundwater arsenic contamination and transmission of arsenic through food chain in Bangladesh. The study further highlighted the human health perspectives of arsenic exposure in Bangladesh with possible mitigation and remediation options employed in the country.

The phytoremediation capacity of Lemna minor prevents deleterious effects of anti-HIV drugs to nontarget organisms

We investigated physiological responses of Lemna minor plants and their capacity to remove tenofovir (TNF; 412 ng l^-1), lamivudine (LMV; 5428 ng l^-1) and/or efavirenz (EFV; 4000 ng l^-1) from water through phytoremediation. In addition, the toxicological safety of water contaminated with these drugs after treatment with L. minor plants to photosynthetic microorganisms (Synechococcus elongatus and Chlorococcum infusionum) was evaluated. The tested environmental representative concentrations of drugs did not have a toxic effect on L. minor, and their tolerance mechanisms involved an increase in the activity of P450 and antioxidant enzymes (catalase and ascorbate peroxidase). L. minor accumulated significant quantities of TNF, LMV and EFV from the media (>70%), and the interactive effect of LMV and EFV increased EFV uptake by plants submitted to binary or tertiary mixture of drugs. Photosynthetic microorganisms exposed to TNF + LMV + EFV showed toxicological symptoms which were not observed when exposed to contaminated water previously treated with L. minor. An increased H₂O₂ concentrations but no oxidative damage in S. elongatus cells exposed to non-contaminated water treated with L. minor was observed. Due to its capacity to tolerate and reclaim anti-HIV drugs, L. minor plants must be considered in phytoremediation programs. They constitute a natural-based solution to decrease environmental contamination by anti-HIV drugs and toxicological effects of these pharmaceuticals to nontarget organisms.

Phytoremediation of toxic chemicals in aquatic environment with special emphasis on duckweed mediated approaches

The discharge of toxic chemicals into water bodies and their linked detrimental effects on health is a global concern. Phytoremediation, an environment-friendly plant-based technology, has gained intensive interest over the last decades. For the aquatic phytoremediation process, the commonly available duckweeds have recently attracted significant attention due to their capacity to grow in diverse ecological niches, fast growth characteristics, suitable morphology for easy handling of biomass, and capacity to remove and detoxify various potential toxic elements and compounds. This review presents the progress of duckweed-assisted aquatic phytoremediation of toxic chemicals. A brief background of general phytoremediation processes, including the different phytoremediation methods and advances in understanding their underlying mechanisms, has been described. A summary of different approaches commonly practiced to assess the growth of the plants and their metal removal capacity in the phytoremediation process has also been included. A vast majority of studies have established that duckweed is an efficient plant catalyst to accumulate toxic heavy metals and organic contaminants, such as pesticides, fluorides, toxins, and aromatic compounds, reducing their toxicity from water bodies. The potential of this plant-based phytoremediation process for its downstream applications in generating value-added products for the rural economy and industrial interest has been identified.

Silver Inhibits Lemna minor Growth at High Initial Frond Densities

Silver nanoparticles (AgNPs) are the most popular engineered nanomaterials in consumer products due to their antimicrobial properties. They enter aquatic ecosystems via insufficient purified wastewaters from manufacturers or consumers. AgNPs inhibit growth of aquatic plants, including duckweeds. Growth media nutrient concentration and initial duckweed frond density can affect growth. However, it is not well understood how frond density affects nanoparticle toxicity. We investigated the toxicity of 500 µg/L AgNPs and AgNO₃ on Lemna minor at different initial frond densities (20, 40, and 80 fronds per 28.5 cm²) over 14 days. Plants were more sensitive to silver at high initial frond densities. Growth rates based on frond number and area were lower for plants at 40 and 80 initial frond density in both silver treatments. AgNPs had no effect on frond number, biomass, and frond area at 20 initial frond density. However, AgNO₃ plants had lower biomass than control and AgNP plants at 20 initial frond density. Competition and crowding at high frond densities resulted in reduced growth when silver was present, therefore plant density and crowding effects should be considered in toxicity studies.

Subcellular distribution, chemical forms of cadmium and rhizosphere microbial community in the process of cadmium hyperaccumulation in duckweed

Duckweed is a newly reported Cd hyperaccumulator that grow rapidly; however, little is known about its tolerance and detoxification mechanisms. In this study, we investigated the tissue, subcellular, and chemical form distribution of the Cd in duckweed and studied the influences of Cd on duckweed growth, ultrastructure, and rhizosphere microbial community. The results showed that Cd could negatively affect the growth of duckweed and shorten the root length. More Cd accumulated in the roots than in the leaves, and Cd was transferred from the roots to the leaves with time. During 12-24 h, Cd mainly existed in the cell wall fraction (2.05 %-95.52 %) and the organelle fraction (5.03 %-97.80 %), followed the soluble fraction (0.14 %-16.98 %). Over time, the proportion of Cd in the organelles increased (46.64 %-92.83 %), exceeding that in the cell wall (6.79 %-66.23 %), which indicated that duckweed detoxification mechanism may be related to the retention of cell wall and vacuole. The main chemical form of Cd was the NaCl-extracted state (30.15 %-88.66 %), which was integrated with pectate and protein. With increasing stress concentration and time, the proportion of the HCl-extracted state and HAc-extracted state increased, and they were low-toxic Cd oxalate and Cd phosphate, respectively. Cd damaged the ultrastructure of cells such as chloroplasts and mitochondria and inhibited the diversity of microbial communities in the duckweed rhizosphere; however, the dominant populations that could tolerate heavy metals increased. It was speculated that duckweed distributed Cd in a less toxic chemical form in a less active location, mainly through retention in the root cell wall and sequestration in the leaf vacuoles, and is dynamically adjusted. The rhizosphere microbial communities tolerate heavy metals may also be one of the mechanisms by which duckweed can tolerate Cd. This study revealed the mechanism of duckweed tolerance and detoxification of Cd at the molecular level and provides a theoretical basis for further development of duckweed.

Removing Mn, Cu and Fe from Real Wastewaters with Macrophytes: Reviewing the Relationship between Environmental Factors and Plants' Uptake Capacity

Heavy metal pollution creates environmental health concerns. Among these, iron (Fe), copper (Cu) and manganese (Mn) are commonly found in aquatic environments due to the release of wastewaters. Phytoremediation in hydroponics uses macrophytes to treat contaminated environments, and this is influenced by environmental factors. However, the relationship between these factors and the removal of Fe, Cu and Mn by macrophytes is not known. Therefore, a meta-analysis serves to determine the correlations between environmental factors and the removal of these metals in real wastewater by macrophytes, as well as to identify the role of different aquatic forms of macrophytes in phytoremediation. Emergent macrophytes had higher concentrations of manganese in their tissues, and higher bioconcentrations factor of iron and manganese than floating plants. Regardless of the biotope, higher concentrations of Fe and Cu decreased the ability of plants to bioconcentrate them. The correlations among exposure time, pH, dissolved oxygen, nitrogen, phosphorus, photoperiod and metal phytoremediation by plants were also found. It can be concluded that the emergent macrophytes showed better performance in terms of the removal of Fe, Cu and Mn, and that the significant correlations between environmental factors and removal vary with the type of metal and the environmental factor analyzed.

Duckweeds for Phytoremediation of Polluted Water

Tiny aquatic plants from the Lemnaceae family, commonly known as duckweeds, are often regarded as detrimental to the environment because of their ability to quickly populate and cover the surfaces of bodies of water. Due to their rapid vegetative propagation, duckweeds have one of the fastest growth rates among flowering plants and can accumulate large amounts of biomass in relatively short time periods. Due to the high yield of valuable biomass and ease of harvest, duckweeds can be used as feedstock for biofuels, animal feed, and other applications. Thanks to their efficient absorption of nitrogen- and phosphate-containing pollutants, duckweeds play an important role in the restorative ecology of water reservoirs. Moreover, compared to other species, duckweed species and ecotypes demonstrate exceptionally high adaptivity to a variety of environmental factors; indeed, duckweeds remove and convert many contaminants, such as nitrogen, into plant biomass. The global distribution of duckweeds and their tolerance of ammonia, heavy metals, other pollutants, and stresses are the major factors highlighting their potential for use in purifying agricultural, municipal, and some industrial wastewater. In summary, duckweeds are a powerful tool for bioremediation that can reduce anthropogenic pollution in aquatic ecosystems and prevent water eutrophication in a simple, inexpensive ecologically friendly way. Here we review the potential for using duckweeds in phytoremediation of several major water pollutants: mineral nitrogen and phosphorus, various organic chemicals, and heavy metals.

Short and long-term phytoremediation capacity of aquatic plants in Cu-polluted environments

Freshwater ecosystems face numerous threats from human populations, including heavy metal contamination. Phytoremediation, the use of plants to remediate contaminated soils and sediments, is an effective and low-cost means of removing chemical contaminants, including heavy metals, from polluted environments. However, key questions remain unanswered in the application of this technology in aquatic environments, such as the long-term fate of pollutants following plant uptake. In this study, using two common wetland plant species (duckweed and tape grass), we first examined the capacity of plants to remove copper (Cu) from polluted water. Next, we evaluated the leaching potential of plant tissues following decomposition and how it is affected by a simulated freeze-thaw cycle. Using phytoremediated water and leachates from senesced plants we assessed phytoremediation success and Cu leaching potential by conducting standard toxicity assays using pond snails (Physa acuta), a species with known Cu sensitivity. We found that duckweed outperformed tape grass as a phytoremediator at low Cu concentrations. In addition, for plants grown in low concentrations of Cu, leaching from decaying plant material did not negatively impact snail survival, while at high concentrations of Cu, leaching did result in toxicity. Lastly, we found that a simulated freeze-thaw cycle increased the release of Cu from plant tissue in the presence of high Cu concentrations only, resulting in reduced snail survival. Our results indicate that in moderately Cu-polluted environments, some aquatic plants can remove contaminants without a long-term risk of leaching. In contrast, phytoremediation in highly polluted environments will likely require removal of plant tissue to prevent leaching of previously accumulated metals. Land managers must not only consider plant species and degree of contamination, but also geographic location, as freeze-thaw cycles may enhance plant decomposition and increase the likelihood of contaminant leaching following phytoremediation efforts in aquatic ecosystems.

Effects of Microplastic Contamination on the Aquatic Plant Lemna minuta (Least Duckweed)

Microplastics are widely spread in aquatic environments. Although they are considered among the most alarming contaminants, toxic effects on organisms are unclear, particularly on freshwater plants. In this study, the duckweed Lemna minuta was grown on different concentrations (50, 100 mg/L) of poly(styrene-co-methyl methacrylate) microplastics (MP) and exposure times (T0, T7, T14, T28 days). The phytotoxic effects of MP were investigated by analyzing several plant morphological and biochemical parameters (frond and root size, plant growth, chlorophyll, and malondialdehyde content). Observations by scanning electron microscope revealed MP adsorption on plant surfaces. Exposition to MP adversely affected plant growth and chlorophyll content with respect to both MP concentrations and exposure times. Conversely, malondialdehyde measurements did not indicate an alteration of oxidative lipid damage in plant tissue. The presence of MP induced root elongation when compared to the control plants. The effects of MP on L. minuta plants were more evident at T28. These results contribute to a better understanding of MP's impact on aquatic plants and highlight that MP contamination manifests with chronic-type effects, which are thus detectable at longer exposure times of 7 days than those traditionally used in phytotoxicology tests on duckweeds.

Examination of the Metallothionein Gene Family in Greater Duckweed Spirodela polyrhiza

Duckweeds are aquatic plants that proliferate rapidly in a wide range of freshwaters, and they are regarded as a potential source of sustainable biomass for various applications and the cost-effective bioremediation of heavy metal pollutants. To understand the cellular and molecular basis that underlies the high metal tolerance and accumulation capacity of duckweeds, we examined the forms and transcript profiles of the metallothionein (MT) gene family in the model duckweed Spirodela polyrhiza, whose genome has been completely sequenced. Four S. polyrhiza MT-like genes were identified and annotated as SpMT2a, SpMT2b, SpMT3, and SpMT4. All except SpMT2b showed high sequence homology including the conserved cysteine residues with the previously described MTs from flowering plants. The S. polyrhiza genome appears to lack the root-specific Type 1 MT. The transcripts of SpMT2a, SpMT2b, and SpMT3 could be detected in the vegetative whole-plant tissues. The transcript abundance of SpMT2a was upregulated several-fold in response to cadmium stress, and the heterologous expression of SpMT2a conferred copper and cadmium tolerance to the metal-sensitive ∆cup1 strain of Saccharomyces cerevisiae. Based on these results, we proposed that SpMT2a may play an important role in the metal detoxification mechanism of duckweed.

Experiments on Pilot-Scale Constructed Floating Wetlands Efficiency in Removing Agrochemicals

The efficiency of constructed floating wetlands (CFWs) in their ability to remove agrochemicals (nutrients and pesticides) is here investigated in a series of pilot-scale systems. Four experimental CFWs were designed and constructed; three of them were planted with the aquatic plant species Lemna minor, Azolla pinnata and Eichhornia crassipes. The fourth did not contain any plants and was used as the control. The aim of the study was to evaluate the efficiency of CFW containing aquatic macrophytes in the reduction of pesticides and nutrients, under field conditions. The CFWs operated continuously from May 2021 to September 2021, and their removal efficiencies of nitrogen and phosphorus ions, and five commonly used pesticides were examined. The CFW systems were fed daily with agricultural wastewater which was prepared by mixing a fertilizer and predetermined doses of pesticides. The hydraulic residence time was kept at 14 days. Samples were collected on a weekly basis from both the influent and the effluent of each experimental tank, and were subsequently analyzed in the laboratory. HPLC-DAD and Ion Chromatography were implemented for sample analysis following a very simple sample preparation. Reductions for nutrient ranged from no reduction to 100% removal, whereas for pesticides these varied from no reduction to 98.8% removal, indicating that these systems can be used as efficient and low-cost pollution control technologies for agrochemical wastewater treatment. Significant reduction for certain pesticides was also observed in the algae control tank, thus, proving the efficiency of algae in organic pollution reduction, and recognizing the limitations of aquatic plant use in decontamination.

Duckweed Is a Promising Feedstock of Biofuels: Advantages and Approaches

With the growing scarcity of traditional sources of energy and the accompanying acute environmental challenges, biofuels based on biomass are favored as the most promising alternative. As one of the core raw materials for biomass energy, research on its production methods and synthesis mechanisms is emerging. In recent years, duckweed has been used as a high-quality new biomass feedstock for its advantages, including fast biomass accumulation, high starch content, high biomass conversion efficiency, and sewage remediation. This study provides a systematic review of the growth characteristics, starch metabolism pathways, and methods to improve starch accumulation in the new energy plant, duckweed. The study also presents a prospect that might be used as a reference for the development of duckweed as a new energy-providing plant.