Potential of Hydrocotyle vulgaris for phytoremediation of a textile dye: Inducing antioxidant response in roots and leaves

Co-contamination by heavy metal and organic pollutant alters impacts of genotypic richness on soil nutrients

Co-contamination by heavy metal and organic pollutant may negatively influence plant performance, and increasing the number of genotypes for a plant population may reduce this negative effect. To test this hypothesis, we constructed experimental populations of Hydrocotyle vulgaris consisting of single, four or eight genotypes in soils contaminated by cadmium, cypermethrin or both. Biomass, leaf area and stem internode length of H. vulgaris were significantly lower in the soil contaminated by cypermethrin and by both cadmium and cypermethrin than in the soil contaminated by cadmium only. A reverse pattern was found for specific internode length and specific leaf area. In general, genotypic richness or its interaction with soil contamination did not influence plant growth or morphology. However, soil nutrients varied in response to soil contamination and genotypic richness. Moreover, plant population growth was positively correlated to soil total nitrogen, but negatively correlated to total potassium and organic matter. We conclude that co-contamination by cadmium and cypermethrin may suppress the growth of H. vulgaris population compared to contamination by cadmium only, but genotypic richness may play little role in regulating these effects.

Effect of using Celosia argentea grown from seeds treated with a magnetic field to conduct Cd phytoremediation in drought stress conditions

The mechanisms of the stimulatory effect of external magnetic fields on plant growth have been revealed; however, the role of magnetic fields in the efficiency of phytoremediation with Celosia argentea grown under drought stress which results in detrimental influences on food security has not been reported. Therefore, this study evaluated the physiological responses of C. argentea to the interactions between exposure to a magnetic field and drought stress. Compared with a control, a drought treatment negatively affected the dry weight, transpiration rate, and Cd extraction efficiency of the species and caused oxidative damage in plant cells, as manifested by the increase in malondialdehyde levels and antioxidant enzyme activities. The biomass production, pigment levels, Cd content, and phytoremediation efficiency of the plant were positively affected by all magnetic field treatments compared to the control. All magnetic treatments, except those at 30 mT, alleviated the detrimental effects induced by a 10-day irrigation regime by enhancing the dry weight, chlorophyll content, and activities of antioxidant enzymes in the leaves of the plant. In terms of the interaction between pre-sowing magnetic field seed treatment and drought stress, a 100 mT treatment increased most of the measured parameters, particularly under a 3-day irrigation regime; this corresponded to the optimal phytoremediation efficiency. The results suggest that magnetic field treatment is a novel, economical, and practicable strategy by which to increase the efficiency of phytoremediation using C. argentea under drought stress.

Hydrocotyle vulgaris L.: a new cadmium-tolerant landscape species and its physiological responses to cadmium exposure

Landscape plants have both ecological and aesthetic value and may also represent ideal candidates for phytoremediation. In the present study, one round of hydroponic culture for 14 days with different cadmium (Cd) concentrations (0, 0.5, 1, and 2 mg L^-1 Cd) was carried out to test whether Hydrocotyle vulgaris L. is a Cd-tolerant plant. Furthermore, physiological parameters, including pigment concentrations, photosynthesis, antioxidant enzyme activities (AEAs), and nutrient uptake, were also examined to determine the tolerance of H. vulgaris to Cd exposure. The results showed that H. vulgaris could grow normally under all Cd supply levels. The Cd removal efficiency reached 100% at Cd concentrations ≤1.0 mg L^-1. The concentrations of Cd in roots and shoots increased (P < 0.05) with Cd supplementation. The maximum concentrations of Cd reached 26.4 and 118 mg kg^-1 in shoots and roots, respectively. The translocation factor values were similar under all Cd treatments. The highest mean daily increase in biomass (MDIB) was obtained under 1 mg L^-1 Cd exposure, which increased by 69.86% compared to that in the control, which may be due to the increased photosynthetic pigments, photosynthetic rate, and the consistent nutrient concentrations under this Cd level, as there were positive relationships between these parameters and MDIB. Moreover, the activities of AEA also generally explicated highest among all Cd levels. All these results indicate that the above physiological parameters play a positive role in promoting plant growth and alleviating Cd stress. In summary, H. vulgaris was verified as a potential Cd-tolerant plant, providing new information for Cd phytoremediation. Furthermore, given its extensive habitat distribution, this species might be tested for phytoremediation of contaminated soils in future work.

Toxicity, uptake and transport mechanisms of dual-modal polymer dots in penny grass (Hydrocotyle vulgaris L.)

The use of polymers such as plastic has become an important part of daily life, and in aqueous environments, these polymers are considered as pollutants. When macropolymers are reduced to the nanoscale, their small particle size and large specific surface area facilitate their uptake by plants, which has a significant impact on aquatic plants. Therefore, it is essential to study the pollution of nanoscale polymers in the aquatic environment. In this work, we prepared nanoscale polymer dots (Pdots) and explored their toxicity, uptake and transport mechanisms in penny grass. From toxicological studies, in the absence of other nutrients, the cell structure, physiological parameters (total soluble protein and chlorophyll) and biochemical parameters (malondialdehyde) do not show significant changes over at least five days. Through in vivo fluorescence and photoacoustic (PA) imaging, the transport location can be visually detected accurately, and the transport rate can be analyzed without destroying the plants. Moreover, through ex vivo fluorescence imaging, we found that different types of Pdots have various uptake and transport mechanisms in stems and blades. It may be due to the differences in ligands, particle sizes, and oil-water partition coefficients of Pdots. By understanding how Pdots interact with plants, a corresponding method can be developed to prevent them from entering plants, thus avoiding the toxicity from accumulation. Therefore, the results of this study also provide the basis for subsequent prevention work.

Effects of elevated CO2 on the phytoremediation efficiency of Noccaea caerulescens

Concentrations of atmospheric carbon dioxide have been continuously increasing, and more investigations are needed in regard to the responses of various plants to the corresponding climatic conditions. In particular, potential variations in phytoremediation efficiency induced by global warming have rarely been investigated. Objective of this research was to evaluate the changes in phytoremediation efficiency of Noccaea caerulescens exposed to different concentrations of CO₂. The concentrations of CO₂ in the elevated CO₂ treatments were adjusted to 550 ± 50 ppm to match the level of atmospheric CO₂ predicted in 2050-2070. Compared to ambient controls (400 ppm), biomass yields and metal concentrations of N. caerulescens increased under elevated CO₂ conditions, thus indicating that the phytoremediation efficiency of the species could increase in higher CO₂ environment. In addition, water soluble and exchangeable Pb and Cu concentrations in soils decreased under elevated CO₂ conditions, which reduced the leaching risks of the metals. The concentrations of malondialdehyde (MDA) of N. caerulescens decreased to different degrees with the increased CO₂ concentrations. The overall findings suggested that elevations in CO₂ can reduce the oxidative damage caused by metals in this species. The phytoremediation efficiency of N. caerulescens grown in multiple metal-enriched soils could be enhanced with global warming.

Biological treatment of slaughterhouse wastewater: kinetic modeling and prediction of effluent

In this study three modeling approaches consisting Modified Stover-Kincannon, multilayer perceptron neural network (MLPANN) and B-Spline quasi interpolation were applied in order to predict effluent of up-flow anaerobic sludge blanket (UASB) reactor and also to find the reaction kinetics. At first run, the average total chemical oxygen demand (TCOD) removal efficiency was 48.3% with hydraulic retention time (HRT) of 26 h and 63.8% with HRT of 37 h, at OLR of 0.77-1.66 kg TCOD/m³ d. At the second run, UASB reactor operated with OLR of 1.94-3.1 kg TCOD/m³ d and achieved the average TCOD removal efficiency of 64.74 and 72.48% with HRT of 26 and 37 h, respectively. The Modified Stover-Kincannon performed well in terms of kinetic determination with a high value of regression coefficient over 0.98. The B-Spline quasi interpolation and MLPANN indicated a great fit for effluent prediction with average R of 0.9984 and 0.9986, and MSE of 157.6050 and 129.7796, respectively; however, they gave no information about reactions occurred in the system.

Are the green synthesized nanoparticles safe for environment? A case study of aquatic plant Azolla filiculoides as an indicator exposed to magnetite nanoparticles fabricated using microwave hydrothermal treatment and plant extract

It has been claimed that the green synthesized NPs possess no toxicity in comparison to the NPs fabricated via conventional protocols like reduction by sodium borohydride. Therefore, it is necessary to test the toxic effects of NPs on environment. In the current study, we report the binding of Fe₃O₄ NPs to galate ions containing biomaterial namely "galate bio-capping agent". The bio-capping agent is simply mixed with the Fe³⁺ cations at pH 8 to produce negatively charged bio-capped Fe₃O₄ NPs. Finally, the toxic effects of the Fe₃O₄ NPs were investigated on some growth and developmental indices of the aquatic plant species Azolla filiculoides. The relative frond number and relative growth rate were calculated after treatment of plants with different concentrations of bio-capped Fe₃O₄ NPs. In addition, the content of phenolics as well as antioxidant enzymes' activity including superoxide dismutase and peroxidase were assessed. The Fe₃O₄ NPs led to growth reduction and significant changes in total phenol and flavonoid content as well as in antioxidant enzymes' activity. All these findings confirm reactive oxygen species formation due to the nanoparticle toxicity. In consequence, the enzymatic and non-enzymatic antioxidant defense systems of plant were stimulated against oxidative stress.

Removal of prometryn from hydroponic media using marsh pennywort (Hydrocotyle vulgaris L.)

The aquatic plant Hydrocotyle vulgaris was evaluated for its efficacy in removing prometryn from nutrient solution. Under optimized experimental conditions, up to 94.0% of the initial prometryn was removed from the hydroponic culture medium by H. vulgaris in 30 days. The concentration of prometryn decreased from the initial level of 0.55 ± 0.013 mg/L to 0.036 ± 0.001 mg/L at the end of the experimental period. The removal kinetics followed first-order kinetic equation (Ct = 0.4569e^-0.09t). Half-life (t_1/2) of prometryn was greatly shortened from 27.16 days (without plant) to 5.58 days (with H. vulgaris). Approximately 22% of the initial prometryn residue was found in H. vulgaris tissue, while 11.7% was degraded by the plant in 30 days. The metabolites of prometryn detected were 2,4-diamino-1,3,5-triazine (in the hydroponic culture medium) and 2,4,6-trihydroxy-1,3,5-triazine (in plant tissue) after 30 days. The results indicate that H. vulgaris can be used for phytoextraction of prometryn and could potentially be effective in removing other s-trazine pesticides from contaminated aquatic ecosystems.

Concurrent uptake and metabolism of dyestuffs through bio-assisted phytoremediation: a symbiotic approach

Manipulation of bio-technological processes in treatment of dyestuffs has attracted considerable attention, because a large proportion of these synthetic dyes enter into natural environment during synthesis and dyeing operations that contaminates different ecosystems. Moreover, these dyestuffs are toxic and difficult to degrade because of their synthetic origin, durability, and complex aromatic molecular structures. Hence, bio-assisted phytoremediation has recently emerged as an innovative cleanup approach in which microorganisms and plants work together to transform xenobiotic dyestuffs into nontoxic or less harmful products. This manuscript will focus on competence and potential of plant-microbe synergistic systems for treatment of dyestuffs, their mixtures and real textile effluents, and effects of symbiotic relationship on plant performances during remediation process and will highlight their metabolic activities during bio-assisted phytodegradation and detoxification.

Ipomoea hederifolia rooted soil bed and Ipomoea aquatica rhizofiltration coupled phytoreactors for efficient treatment of textile wastewater

Ipomoea aquatica, a macrophyte was found to degrade a highly sulfonated and diazo textile dye Brown 5R up to 94% within 72 h at a concentration of 200 mg L(-1). Induction in the activities of enzymes such as azoreductase, lignin peroxidase, laccase, DCIP reductase, tyrosinase, veratryl alcohol oxidase, catalase and superoxide dismutase was observed in leaf and root tissue in response to Brown 5R exposure. There was significant reduction in contents of chlorophyll a (25%), chlorophyll b (17%) and carotenoids (30%) in the leaves of plants. HPLC, FTIR, UV-vis spectrophotometric and HPTLC analyses confirmed the biotransformation and removal of parent dye from solution. Enzymes activities and GC-MS analysis of degradation products lead to the proposal of a possible pathway of phytotransformation of dye. The proposed pathway of dye metabolism revealed the formation of Napthalene-1,2-diamine and methylbenzene. Toxicity study on HepG2 cell lines showed a 3 fold decrease in toxicity of Brown 5R after phytoremediation by I. aquatica. Hydrophytic nature of I. aquatica leads to its exploration in a combinatorial phytoreactor with Ipomoea hederifolia soil bed system. Rhizofiltration with I. aquatica and soil bed treatment by I. hederifolia treated 510 L of effluent effectively within 72 h. I. aquatica along with I. hederifolia could decolorize textile industry effluent within 72 h of treatment as evident from the significant reductions in the values of COD, BOD, solids and ADMI. Further on field trials of treatment of textile wastewater was successfully carried out in a constructed lagoon.

Phytoremediation of textile dyes and effluents: Current scenario and future prospects

Phytoremediation has emerged as a green, passive, solar energy driven and cost effective approach for environmental cleanup when compared to physico-chemical and even other biological methods. Textile dyes and effluents are condemned as one of the worst polluters of our precious water bodies and soils. They are well known mutagenic, carcinogenic, allergic and cytotoxic agents posing threats to all life forms. Plant based treatment of textile dyes is relatively new and hitherto has remained an unexplored area of research. Use of macrophytes like Phragmites australis and Rheum rhabarbarum have shown efficient removal of Acid Orange 7 and sulfonated anthraquinones, respectively. Common garden and ornamental plants namely Aster amellus, Portulaca grandiflora, Zinnia angustifolia, Petunia grandiflora, Glandularia pulchella, many ferns and aquatic plants have also been advocated for their dye degradation potential. Plant tissue cultures like suspension cells of Blumea malcolmii and Nopalea cochenillifera, hairy roots of Brassica juncea and Tagetes patula and whole plants of several other species have confirmed their role in dye degradation. Plants' oxidoreductases such as lignin peroxidase, laccase, tyrosinase, azo reductase, veratryl alcohol oxidase, riboflavin reductase and dichlorophenolindophenol reductase are known as key biodegrading enzymes which break the complex structures of dyes. Schematic metabolic pathways of degradation of different dyes and their environmental fates have also been proposed. Degradation products of dyes and their fates of metabolism have been reported to be validated by UV-vis spectrophotometry, high performance liquid chromatography, high performance thin layer chromatography, Fourier Transform Infrared Spectroscopy, gas chromatograph-mass spectroscopy and several other analytical tools. Constructed wetlands and various pilots scale reactors were developed independently using the plants of P. australis, Portulaca grandiflora, G. pulchella, Typha domingensis, Pogonatherum crinitum and Alternanthera philoxeroides. The developed phytoreactors gave noteworthy treatments, and significant reductions in biological oxygen demand, chemical oxygen demand, American Dye Manufacturers Institute color removal value, total organic carbon, total dissolved solids, total suspended solids, turbidity and conductivity of the dye effluents after phytoremediation. Metabolites of dyes and effluents have been assayed for phytotoxicity, cytotoxicity, genotoxicity and animal toxicity and were proved to be non/less toxic than untreated compounds. Effective strategies to handle fluctuating dye load and hydraulics for in situ treatment needs scientific attention. Future studies on development of transgenic plants for efficacious phytodegradation of textile dyes should be focused.