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.

The ability of untreated and acid-treated biomass from Pistia stratiotes (PL and APL, respectively) and Eichhornia crassipes (ELS and AELS, respectively) to remove color from anaerobically digested sugar cane stillage (ADS) was investigated. The effects of pH (3–8), particle size (< 0.75, 0.75–1, 1–4 mm), and biomass concentration (5–15 g/L) on decolorization of ADS were assessed using untreated biomass. After acid modification of biomass (acid-treated), the effects of pH (3–8), biomass concentration (6–10 g/L), time (20–480 min), and ADS dilution (non-diluted, 1:2, 1:10, 1:20) on color removal from ADS were evaluated. Scanning electron microscopy and Fourier transform infrared spectroscopy (FTIR) analyses were also performed. A clear effect of particle size on ADS decolorization was found (21.04 ± 0.75 and 27.87 ± 0.30 % for 0.75–1 and <0.75 mm, respectively, for ELS; 31.65 ± 0.23 and 37.82 ± 0.53 for 1–4 and 0.75–1 mm, respectively, for PL). Decolorization also increased when the untreated biomass concentration was higher (15.41 ± 0.3 and 27.89 ± 0.2 % for 5 and 10 g/L, respectively, for ELS; 15.61 ± 0.11 and 33.06 ± 1.09 % for 5 and 10 g/L, respectively, for PL). The use of acid-treated biomass enhanced the effect of pH on color removal (48.30 ± 1.27 and 12.96 ± 0.27 % for pH of 3 and 7, respectively, for AELS; 47.11 ± 1.72 and 6.62 ± 0.21 % for pH of 3 and 7, respectively, for APL). The highest rate of color removal obtained using acid-treated biomass was 55.58 ± 1.82 and 56 ± 0.77 % for AELS and APL, respectively. The FTIR spectra analysis suggested the electrostatic attraction between protonated carboxylic groups on biomass and anionic colored compounds as being one of the adsorption mechanisms for ADS decolorization. The use of dry biomass from invasive macrophytes is an effective alternative for color removal from ADS.

In the greenhouse and container nursery production industry there is potential for runoff of nitrogen (N) and phosphorus (P), which may contaminate surface and groundwater. Since the 1950s constructed wetlands (CWs), as a simple, low-technology method, have been shown to effectively treat agricultural, industrial, and municipal wastewater. We investigated the N and P attenuating potential of three floating hydrophytes planted in a laboratory-scale subsurface flow (SSF) CW system. Over an 8-week period plants were supplied with N and P (0.39 to 36.81 mg·L⁻¹ N and 0.07 to 6.77 mg·L⁻¹ P) that spanned the rates detected in nursery runoff between the discharge and inflow locations of a commercial nursery currently employing CWs. Whole plant dry weight was positively correlated with N and P supplied. Highest N recovery rates were exhibited by water hyacinth (Eichhornia crassipes [Mart.] Solms.) and water lettuce (Pistia stratiotes L.). P recovery rates were similar for water hyacinth, water lettuce, and dwarf redstemmed parrotfeather (Myriophyllum aquaticum [Vell.] Verdc.). These floating hydrophytes can be cultivated in a SSF CW to remediate runoff losses of N and P. The possibility exists for integrating them into a polycultural remediation system that includes emergent aquatic macrophytes for processing and polishing nursery/greenhouse wastewater.

Aquatic macrophytes are well known accumulators for heavy metals, the reason why they are used as bioindicators for water quality and in phytoremediaton strategies. This study reports on the elemental concentrations in four free-floating aquatic macrophytes (S. auriculata; P. stratiotes; E. crassipes and E. azurea) growing in two water reservoirs (Santana e Vigário, Rio de Janeiro State, Brazil) of an electric power plant that receive input from the polluted Paraíba do Sul River. Filtered water samples and water suspended solids from these environments were also analysed. Inductively coupled plasma mass spectrometry was used as the principal method, allowing the determination of up to 41 elements, including the rare-earth elements (REEs) and other trace metals not assayed before in these macrophytes. The results show that all elements studied are accumulated by the macrophytes with concentration ratios (CR = [plant]: [water]) varying from about 1,000 to 200,000, based on the dry weight of the plant species. With a few exceptions, highest accumulations were observed in E. crassipes in which CRs increase in the sequence: Cu < Mo < Cr < Pb < Tl < Fe < La < Zn < Ce< Mn. Surprisingly high CRs (e.g. Ce: 74,000) and corresponding mass concentrations were observed for the rare-earth elements (e.g. [summation operator]REE: 112 mg kg-¹), also measured in the water suspended particle fraction. The results show that this fraction acts as an effective sink for trace metals in the aquatic system studied and seems to play also an important role in the transfer of metals from water to the plant species.

Due to the public and environmental health impact of cyanotoxins, investigations have been focused on finding environmental friendly algaecides from aquatic plants. The present study had the objective to evaluate the population control and physiological response of Microcystis aeruginosa (Kützing) Kützing (strain BCCUSP232) exposed to Pistia stratiotes L. extracts. Aqueous and ethanolic extracts of P. stratiotes at different concentrations (10, 25, and 50 mg L⁻¹) were submitted to M. aeruginosa and reduced significantly (p<0.05) the cyanobacterium cell density. The ethanolic extract presented the greatest growth inhibition of the strain at the highest concentration. During exposure to P. stratiotes extracts, intracellular hydrogen peroxide levels, malondialdehyde content, and antioxidant enzymes (peroxidase, catalase, and glutathione S-transferase) activities increased in M. aeruginosa, while total protein concentration decreased when compared to the control group. Superoxide dismutase (SOD) activities presented a sharp decline, suggesting superoxide radical and peroxide accumulation. This implied that SOD was a target for bioactive substance(s) from aqueous and ethanolic extracts of P. stratiotes. Phytochemical screening of the extracts revealed that the ethanolic extract presented 93.36 mg gallic acid equivalent (GAE) per gram dry weight (g⁻¹ DW) total polyphenols and 217.33 mg rutin equivalent (RE) per gram dry weight total flavonoids, and for the aqueous extract, 5.19 mg GAE g⁻¹ DW total polyphenols and 11.02 mg RE g⁻¹ DW total flavonoids were detected. Gas chromatography (GC)/mass spectrometry (MS) analyses of the ethanolic and aqueous extracts presented palmitic acid ethyl ester as major allelochemical. In view of these results, it can be concluded that P. stratiotes showed potential in controlling M. aeruginosa populations.

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.

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.

Aquatic plant biomass has been shown to have a great potential for biogas production. The use of ruminal fluid has been shown to improve the degradation of the lignocellulosic material with its conversion into volatile fatty acids (VFA) during a first phase of hydrolysis–acidogenesis. VFAs are important as the feedstock for methane and hydrogen production in a second phase process within a biorefinery. The objective of this work was to produce a high yield of VFA during a first phase of anaerobic hydrolysis–acidogenesis of Pistia stratiotes biomass assessing the effect of the use of rumen fluid as inoculum and of daily adjustment of pH in batch-operated reactors. One liter anaerobic reactors containing 15 gSV L⁻¹ of P. stratiotes biomass were incubated at 30 ± 2 °C and agitated once a day. The inoculum concentration had no significant effect on the increase in VFA concentration and 20 % (V/V) was used in all treatments. The final average VFA concentration and conversion coefficients from VS to VFA in the inoculated treatment with no pH adjustment (T1) and with pH adjustment (T2) (1817 mgCOD L⁻¹ and 0.1319 mgVFA mgVS⁻¹, respectively) were significantly higher than those found in the treatment with no inoculum (T0). There were no significant differences between T0 and T1 in the VS degradation rate. In contrast, the degradation rate in T2 was significantly higher. Thus, the addition of ruminal fluid promoted the production of VFA, and the pH adjustment had no significant effect on this parameter but did influence the biomass degradation.

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.

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.