Atrazine is an herbicide commonly used in several countries. Due to its long half-life, associated with its use in large scales, atrazine residues remain as environmental pollutants in water bodies. Phytoremediation is often pointed out as an interesting approach to remove atrazine from the aquatic environment, but its practical application is limited by the high toxicity of this herbicide. Here, we characterize the damages triggered by atrazine in Pistia stratiotes, evaluating the role of nitric oxide (NO), a cell-signaling molecule, in increasing the tolerance to the pollutant and the phytoremediation potential of this species. Pistia stratiotes plants were exposed to four treatments: Control; Sodium nitroprusside (SNP) (0.05 mg L⁻¹); Atrazine (ATZ) (150 μg L⁻¹) and ATZ + SNP. The plants remained under those conditions for 24 h for biochemical and physiological analysis and 3 days for the evaluation of relative growth rate. The presence of atrazine in plant cells triggered a series of biochemical and physiological damages, such as the increase in the generation of reactive oxygen species, damages to cell membranes, photosynthesis impairment, and negative carbon balance. Despite this, the plants maintained greater growth rates than other aquatic macrophytes exposed to atrazine and showed high bioconcentration and translocation factors. The addition of SNP, a NO donor, decreased the herbicide toxicity, with an increase of over 60% in the IC₅₀ value (Inhibitor Concentration). Indeed, the NO signaling action was able to increase the tolerance of plants to atrazine, which resulted in increments in pollutant uptake and translocation, with the maintenance of overall cell (e.g. membranes) and organs (root system) structure, and the functioning of central physiological processes (e.g. photosynthesis). These factors allowed for more quickly and efficient removal of the pollutant from the environment, reducing costs, and increasing the viability of the phytoremediation process.

Pistia stratiotes is a common aquatic plant of the northern region of the state of Rio de Janeiro, and its use as adsorbent material was studied in the present work. The preparation process included washing, drying, grinding, and acid activation. The sorption potential for removal of the indigo carmine dye from aqueous solutions was tested under various conditions, such as initial concentration, contact time, and temperature. The tests showed that the obtained biosorbent showed good performance for dye removal with a maximum capacity of 41.2 mg/g. The kinetic studies revealed that the pseudo-second-order equation provided the best fit of the experimental data. The Freundlich isotherm provided the best fit of the experimental sorption data for the system under study. The results obtained show that Pistia stratiotes has great potential to be used as biosorbent for the removal of dyes from aqueous solutions.

The removal and sorption of oil from saline solutions by leaves (L) and roots (R) of Pistia stratiotes are described for the first time. The effects of biomass dose (0.5 and 1.0 g), contact time (30, 60, 90, and 120 min), and initial oil concentration (IOC = 979 ± 9.82, 1,968 ± 8.01, 3,935 ± 40.09, 7,778 ± 196.42, and 15,694 ± 196.41 mg L⁻¹) on removal and sorption (q) were evaluated. Studies included a physicochemical characterization of the biomass. High oil removal (L = 93.71 ± 0.18 % and R = 80.93 ± 0.11 %) and sorption values (L = 2,904.47 ± 4.49 mg g⁻¹ and R = 2,324.38 ± 29.29 mg g⁻¹) were found. Such a high sorption might be related to factors such as a high surface area (128.38 ± 0.61 and 112.62 ± 5.17 m² g⁻¹, for leaves and roots, respectively), a high degree of relative hydrophobicity in the case of the leaves (71.05 ± 0.71 %), and capillary action. A high correlation was found between IOC and sorption, suggesting that the biomass could adsorb oil at IOCs higher than 15,694 ± 196.41 mg L⁻¹. The Freundlich isotherm model was found to best describe crude oil sorption by leaves and roots of P. stratiotes. These sorbent materials could be good candidates to be used during an oil spill.

The goal of this work was to study quantitatively lead bioaccumulation from a lead-doped nutrient medium by using a living aquatic macrophytes Pistia stratiotes. Several sets of aquatic plants with approximately 30 g weight were grown in greenhouse conditions and in hydroponic solutions supplied with a non-toxic Pb²⁺ concentration. The synchrotron radiation total X-ray fluorescence spectrometry was used to determine the metal concentrations in dry plants and hydroponic media as a function of time. Four different non-structural bioaccumulation models were applied to describe the process dynamics and to estimate the accumulated lead maximum capacity and rate constants. According to the experimental data, both biosorption and bioaccumulation mechanisms can be considered. Due to the low desorption rate constant, the experimental data were well described by the irreversible kinetic model. The results concerning modeling of living macrophytes' metal bioaccumulation kinetics can be used to predict the heavy metal removal dynamics from wastewaters in artificial wetlands.

The effectiveness of four aquatic floating plants: Eichhornia crassipes, Pistia stratiotes, Lemna minor, Salvinia sp., and a submerged plant Hydrilla sp. on decolorization and detoxification of five structurally different textile dyes: CI Direct Blue 201 (DB 201), Cibacron Blue FR, Cibanone Gold Yellow RK, Vat Green FFB, and Moxilon Blue GRL were studied. The E. crassipes and P. stratiotes showed complete decolorization of all the dyes tested, while Salvinia sp. (79–86%), L. minor (16–24%), and Hydrilla sp. (6–13%) were recorded as the least tolerance for all the dyes even after 14 days of incubation. Therefore, E. crassipes and P. stratiotes were selected for further studies using DB 201 as the model dye. E. crassipes and P. stratiotes showed complete decolorization of DB 201 at 48 and 84 h of incubation, respectively, and decolorization was well effective in the pH range 6–9. The crude extract of intracellular enzymes obtained from the roots of E. crassipes (46%) and P. stratiotes (20%) showed significant involvement on decolorization of DB 201, compared with the activity of crude extracellular extract and isolated endophytic bacteria and fungi (p ≤ 0.05). Further, 18 and 22% of biosorption of DB 201 dye were recorded by E. crassipes and P. stratiotes, respectively, suggesting that decolorization mechanisms of DB 201 dye by E. crassipes and P. stratiotes were based on biosorption and intracellular enzyme activities. The FTIR spectra and seed germination assay confirmed biodegradation and detoxification of DB 201 dye by E. crassipes and P. stratiotes plants along with complete color removal. Thus, present study confers the potential applicability of E. crassipes and P. stratiotes plants for textile dye removal and release to the environment without further treatment.

Copper contamination of industrial waste streams is increasingly common with copper used in an array of industrial processes. Phytoremediation of copper-contaminated water with Pistia stratiotes presents a cost-effective, efficient and uncomplicated alternative for copper removal from industrial wastewater. This study examines the ability of Pistia stratiotes to remove copper from distilled water representing a highly nutrient-deficient medium and natural surface water containing plant nutrients inherently. Control and experimental sets were set up with growth solutions of distilled water and natural surface water spiked with 5 g/mL, 10 g/mL, 15 g/mL, 20 g/mL and 25 g/mL copper. The control sets were devoid of Pistia stratiotes while the experimental sets contained Pistia stratiotes. Copper concentration and pH of the solutions were tracked over 10 days. This study revealed the ability of Pistia stratiotes to remove copper in both types of growth solution with contamination level ranging from 5 to 25 mg/L and pointed to its ability to phytoremediate higher level of copper contamination. Pistia stratiotes also raised the pH of the growth solutions. Copper removal from both types of growth solution demonstrated a predominantly first-order elimination kinetics except for copper concentrations above 15 mg/L in distilled water where the zero-order elimination kinetics predominated. Copper removal efficiency decreased with increasing copper concentrations in both types of growth solution with removal efficiency in natural surface water growth solutions consistently higher. It highlights the ability of Pistia stratiotes to phytoremediate highly nutrient-deficient and natural surface water media.

Algal blooms are one of the greatest aquatic environmental concerns, and the control of algal blooms has become a great challenge in recent years. In this study, we evaluated the effects of Bidens pilosa plant extracts in comparison to those of several widespread plants, including rice (Oryza sativa), Pistia stratiotes, Eichhornia crassipes, and Pteris vittata, on the growth of the bloom-forming blue-green alga Microcystis aeruginosa. Both ethanolic and methanolic extracts of B. pilosa, in contrast to the other plant extracts, exhibited high inhibitory effects on M. aeruginosa growth at a concentration of 500 mg/L (dry weight equivalent, DWE). The inhibition efficiency in terms of the cell density and chlorophyll a concentration significantly reached 84–88% (p < 0.05). In these treatments, a change in algal culture color (from green to brown) and cell death were obviously observed. When we determined the effective concentrations, the B. pilosa extract at concentrations of 250 and 500 mg/L DWE showed significant inhibitory effects on M. aeruginosa growth (p < 0.05), whereas lower concentrations (50–125 mg/L DWE) showed slight or no effects. These data indicate that B. pilosa plant extracts could be used to control M. aeruginosa algal blooms.

The aim of the study was to determine the changes in suspension particle size identified in biologically treated wastewater, which was then treated in hydroponic system with use of engineering lighting by the light-emitting diodes (LED). The study was subjected to wastewater purified under laboratory conditions, in a hydroponic system using the effect of macrophytes Pistia stratiotes and growing algae. Measurement of particle size was made using a laser granulometer. Analysis of the results showed that the additional lighting of the hydroponic system with LED can significantly influence the ability of the suspension particles to agglomerate and, consequently, determine their sedimentation properties. In hydroponic system supported by additional lighting, more particles were observed with equivalent diameter D(3.2) smaller than 10 μm than those in the tank without additional lighting, indicating a higher reactivity of the particles. Determining the size of equivalent diameters D(4.3) allowed us to observe that in hydroponic system, particles of relatively small size predominate, which negatively affects the sedimentation process of the suspensions. Determination of particle size of suspensions consisting mainly of algae and the dynamics of their changes are the basis for specification of an effective method of removing particles from the system to protect the receiver from excessive suspension concentrations.

Arsenic (As) toxicity and the effects of nitric oxide (NO), supplied as sodium nitroprusside (SNP), were analyzed in Pistia stratiotes. The plants, which were grown in nutrient solution at pH 6.5, were exposed to four treatments for 24 h: control; SNP (0.1 mg L-1); As (1.5 mg L-1); and As + SNP (1.5 and 0.1 mg L-1). As accumulated primarily in the roots, indicating the low translocation factor of P. stratiotes. The As accumulation triggered a series of changes with increasing production of reactive oxygen intermediates and damage to cell membranes. The application of SNP was able to mitigate the harmful effects of As. This attenuation was probably due to the action of the SNP as an antioxidant, reducing the superoxide anion concentration, and as a signaling agent. Acting as a signal transducer, SNP increased the activity of enzymatic antioxidants (POX, CAT, and APX) in the leaves and stimulated the entire phytochelatins biosynthetic pathway in the roots (increased sulfate uptake and synthesis of amino acids, non-proteinthiols, and phytochelatins). The As also stimulated the phytochelatins biosynthesis, but this effect was limited, probably because plants exposed only to pollutant showed small increments in the sulfate uptake. Thus, NO also may be involved in gene regulation of sulfate carriers. © 2013 Springer Science+Business Media Dordrecht.

Pollution of water bodies with heavy metal ions is a major worldwide environmental problem. The objective of this study was to elucidate the mechanism in which metallic ions are adsorbed and reduced to metallic nanoparticles onto plant materials using microwave radiation. In this research, we have fabricated metallic silver and lead nanoparticles from their corresponding ions using the aquatic plants Azolla filiculoides and Pistia stratiotes (since identical results are obtained for both plants, the emphasis will be on the Azolla) under microwave radiation. Our data show that metallic silver and metallic lead nanoparticles were completely removed from the polluted solution and were embedded in the A. filiculoides surface after 5 min of microwave reaction. It was also found that, for both metals, reduction of the metallic ions was accomplished by the plant matrix without the need of an external reducing agent. Most of the particles had a spherical shape within the 10–50 nm size range. Mass balance data clearly indicate that most of the silver particles were found on the surface of the plant and not in the clean water. Pectin and α-glucuronic acid did not reduce the silver or lead ions under microwave radiation. We therefore hypothesize that perhaps the proteins or sugar alcohols in the plant matrix were serving as the reducing agents. We believe that this technique in which adsorption and reduction are combined using microwave radiation can be applied for removing and recycling metallic ions from contaminated water and industrial wastewater.