Quinones et al., (2009) carried out a quantitative study to determine the lead bioaccumulation from a hydroponic medium using Pistia stratiotes. They used a number of aquatic plants to be grown in greenhouse conditions. The results indicated that the low desorption rate being constant. The irreversible kinetic model is best to describe data of experiment. It can be used to describe the heavy metal removal dynamics from wastewaters in artificial wetlands.
Mufarrege et al., (2009) worked on response of Pistia stratiotes to heavy metals (Cr, Ni and Zn) and phosphorous. For this they used plastic aquaria having 50 g of wet plants and 5 L of pond water added with the contaminant(s) were disposed. Chlorophyll a was an indicator, more sensitive to Zn and Cr toxicity than the relative growth rate. The results showed that the addition of P to the treatment with combined metals attenuated the decrease in plant growth and root length; however P increased the tolerance of P. stratiotes to metals. This fact has important applications for the use of Pistia stratiotes in constructed wetlands for the treatment of industrial wastewater.
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Mishra and Tripathi, (2009) carried out a study on accumulation of zinc and chromium by using water hyacinth (Eichornia crassipies) This species was grown at four concentrations of chromium and zinc, i.e. 1.0, 5.0, 10.0 and 20.0mg/l in single metal solution. The results indicated that this plant was capable of removing up to 84% of chromium and 95% of zinc during 11 days incubation period. At 10.0 and 20.0mg/l, concentrations of chromium, plants have shown some morphological symptoms of toxicity. On the other hand E. crassipes removed Zn efficiently without any symptoms at all the four concentrations. Protein, sugar and chlorophyll contents in experimental plants were decreased due to accumulation of zinc and chromium.
Agunbiade et al., (2009) worked in Nigeria. They conducted a study on Phytoremediation potential of Eichornia crassipes in metal contaminated coastal water. Ten metals such as Cd, As, Cu, Fe, Cr, Mn, Ni, Zn, Pb, and V were estimated in water and the plant shoots and roots from the coastal area of Ondo State, Nigeria were used to assess the translocation factor (TF) and enrichment factor (EF) in the plant. According to the results, the TF and EF indicated that the plant accumulated the high degree of toxic metals such as Cd, Cr, Pb and As both at the root and shoot, which revealed that the plant that produce a large biomass on the water surface and is not fed upon by animals can serve as a plant for both rhizofiltration and phytoextraction in phytoremediation technique.
Megateli et al., (2009) carried out an experiment to study the toxicity and removal of heavy metals (cadmium, copper, and zinc) by using the aquatic plant Lemna gibba. The effects of heavy metals on aquatic plant were examined under controlled conditions. The results indicated that these three heavy metals affected plant growth. After 4 days the concentrations of cadmium reduced growth by 25ââ‚¬"100% and increased proline content by 44ââ‚¬"567%. Under the same conditions, the concentrations of copper reduced growth by 36ââ‚¬"75%, and increased proline content by 67ââ‚¬"288%. Comparatively the effects of zinc on plant growth were very less. Monitoring metal concentrations in the medium revealed that L. gibba was able to remove metals from the medium. Zinc and copper removal was biphasic; it was rapid during the first 2 days and slow during the following 8 days. For cadmium, removal was linear and based on the initial concentrations.
Mishra et al., (2008) investigated about phytoremediation of mercury and arsenic from tropical opencast coalmine effluent using aquatic macrophytes namely Eichornia crassipes, Lemna minor and Spirodela polyrrhiza. The mercury and arsenic were found to be removed within 21 days. The results from plant tissue analysis indicated the fact that the studied metals deteriorated the N, P, K and chlorophyll contents in these plants. The results revealed that the selected species are favorable to be used for metal accumulation.
Mishra and Ttipathi, (2008) conducted a study on simultaneous removal and accumulation of heavy metals by the three aquatic macrophytes. Pistia stratiotes L. (water lettuce), Spirodela polyrrhiza W. Koch (duckweed) and Eichhornia crassipes were used for the removal of five heavy metals (Fe, Cu, Zn, Cd and Cr). At three different concentrations (1.0, 2.0 and 5.0 mg/l) of metals the aquatic plants were grown in laboratory experiment. The results indicated greater than 90% removal of different metals during 15 days experiment. Highest removal was estimated on 12th day of experiment, thereafter it decreased. According to the results of the study E. crassipes was more efficient for the removal of selected heavy metals as compared to the S. polyrrhiza and P. stratiotes. Moreover these plants have the potential for the accumulation of heavy metals in their bodies without reduction in growth and the production of any toxicity. Therefore these aquatic plants could be used for the removal of heavy metals from waste water.
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Galvan et al., (2008) determine the hyperaccumulating lead capacity of Salvinia minima by utilizing the bioadsorption (BAF) and intracellular accumulation factors (IAF). According to the results of the study, on hyperaccumulating capacity, the effect of metal concentration, the presence of organic and inorganic compounds and its physicochemical properties are still unknown. Moreover, the specific accumulation and adsorption mechanisms existing in the plant are not clear yet. Therefore by using compartmentalization analysis, BAF and IAF were calculated in order to quantify and differentiate these two mechanisms. Kinetic model was also used to assess the uptake mechanisms. Healthy plants were treated with five different concentration of lead in batch systems. A synthetic wastewater, altered with magnesium sulfate and propionic acid, and deionized water were used as media. Surprisingly, the potential of S. minima to accumulate the metal into the cells was not inhibited at very high concentrations
Quinones et al., (2008) carried out a study on phytoaccumulation of chromium ions by using three free floating macrophytes from a nutrient medium. In this study Pistia stratiotes, Eicchornia crassipes and Salvinia auriculata, were examined in greenhouse conditions for phytoaccumulation of trivalent and hexavalent chromium. These aquatic plants were grown in hydroponic solutions treated with non-toxic trivalent and hexavalent chromium concentrations. By utilizing the Synchrotron radiation X-ray fluorescence technique the total chromium concentrations into Cr-doped hydroponic media and aerial parts and dry roots were estimated. The chromium removal data was displayed by using a nonstructural kinetic model. The results of the study indicated that E. crassipes and S. auriculata have the ability to remove trivalent chromium up to 90% while P. stratiotes can remove up to 50%. On another hand S. auriculata is more efficient for the removal of hexavalent chromium as compared to the other aquatic plants. It has the potential to remove hexavalent chromium up to 90% while E. crassipes and P. stratiotes can remove up to 50% and 70% respectively.
Quaggiotti et al., (2007) undertook an experimental study on phytoremediation of chromium using Salix species. In this research cDNA-AFLP (Amplified Fragment Length Polymorphism) markers were used to identify candidate genes, which were potentially involved in the regulation of the response to chromium in four different willow species (Salix alba, Salix eleagnos, Salix fragilis and Salix matsudana). These species were selected on the basis of their ability in phytoremediation techniques. According to the results of this research a number of expressed mRNAs were scored in each species and a total of 68 transcripts showed an altered expression in response to Cr were sequenced and isolated. The results showed the existence of common mechanisms of gene regulation in response to Cr.
Skinner et al., (2007) conducted a comparative study on Mercury uptake and accumulation by using four aquatic plants. The aquatic plants including water hyacinth (Eichornia crassipes), water lettuce (Pistia stratiotes), zebra rush (Scirpus tabernaemontani) and taro (Colocasia esculenta) were examined for their potential in removing mercury from wastewater. The plants were treated with different concentrations of mercury for 30 days. By utilizing Microtox (water) and cold vapor Atomic Absorption Spectroscopy (AAS) (roots and water) the assays were conducted. The results indicated that these aquatic plants minimized the mercury concentrations in water by root uptake and accumulation. Moreover Pistia stratiotes and Eichornia crassipes are more efficient in the uptake and accumulation of mercury as compared to the Scirpus tabernaemontani and Colocasia esculenta.
Fritioff and Greger, (2006) carried out a study on distribution and uptake of zinc, copper, cadmium and lead in an aquatic plant Potamogeton natans. This study revealed the uptake of zinc, copper, cadmium, and lead by Potamogeton natans in its stems, leaves and roots, and translocation from organs to other plant parts. The results of the study indicated that the highest accumulation of copper, zinc, cadmium, and lead was found in the roots as compared to the leaves and stems. No translocation of the metals to other parts of the plant was found, except for cadmium which was translocated from stem to leaf and vice versa. Moreover distribution of metals from sediment to water through P. natans is therefore unlikely.
Zimmels et al., (2006) studied the utilization of Pistia stratiotes and Eichornia crassipies for the treatment of urban sewage in Isreal. The experiments confirmed that these aquatic plants have the ability of decreasing all tested indicators of water quality to levels that permit the use of the purified water for irrigation of tree crops. In this study different parameters such as chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solids (TSS), and turbidity were studied. The laboratory-scale tests verify the tendency of the plants to reach and hold reasonably low levels of BOD and COD and very low levels of TSS and turbidity. The results showed that the use of free water surface flow system (FWS) and its low maintenance system for treatment of agricultural and urban sewage is a feasible option.
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Miretzky et al., (2004) worked in Argentina, they studied the potential of aquatic macrophytes for the simultaneous removal of heavy metals. Three aquatic macreophytes, which were very common in pampean shallow lakes (Argentina), were used in laboratory experiences for the removal of heavy metals (Fe, Cu, Zn, Mn, Cr and Pb). These aquatic plants were Pista stratiotes, Lemna minor and Spirodela intermedia. The experiment was performed for different concentrations of metals for 15 days. The results showed the highest metal removal percentages by these three aquatic plants. L. minor did not survive the conditions of the experiment. High correlation between the final water and the macrophytes metal concentration was obtained, some deviations were due to PbCrO4 precipitation. The metal uptake rate was dependent on the metal concentrations for the 3 species studied.
Odjegba and Fasidi, (2004) worked on accumulation of trace elements by using Pistia stratiotes as an implication for phytoremediation. They examined toxicity response, tolerance and metal accumulation capacities of Pistia stratiotes against eight potentially toxic trace elements (Ag, Cd, Cr, Cu, Hg, Ni, Pb, and Zn). Equal sized young plants were grown hydroponically in different concentrations of heavy metals for 21 days. According to the results of the study biomass production was significantly reduced in metal treatment plants in comparison with control plants. High concentration of all trace elements was accumulated in root tissue rather than in shoot. Pistia stratiotes indicated different tolerance level and accumulation capacities for different metals at similar treatment conditions.
Lu et al., (2004) studied the potential of water hyacinth, Eichornia crassipies for the removal of cadmium and zinc. Water hyacinths were grown in tap water, and treated with 0.5, 1, 2 and 4 mg/L of cadmium and 5, 10, 20, and 40 mg/L of zinc, and were separately harvested after 4, 8 and 12 days. The results showed that both cadmium and Zinc had significant effects on plant growth. In the first four days, removal of metals from solution was very fast. Plants treated with 4 mg/L of cadmium accumulated the highest concentration of metal in roots and shoots after 8 days while those treated with 40 mg/L of zinc accumulated the highest concentration of metal in roots and shoots after 4 days. This study suggested that Eichornia crassipies was a moderate accumulator of cadmium and zinc and could be used for the treatment of water contaminated with low concentration of cadmium and zinc.
Kamal et al., (2004) worked on phytoaccumulation of heavy metals by using three aquatic plants. These three aquatic plants were parrot feather (Myriophylhum aquaticum), creeping primrose (Ludwigina palustris), and water mint (Mentha aquatic). These plants were collected from a Solar Aquatic System irrigating with municipal wastewater. These three plants were able to remove iron, zinc, copper, and mercury from the contaminated water. According to results of the study these plants are very efficient to remove 98.8% mercury, 76.7% iron, 41.62% copper and 33.9% zinc. Myriophylhum aquaticum showed greater tolerance as compared to the Mentha aquatic and Ludwigina palustris.
Sarita et al., (2002) conducted a comparative study on accumulation of chromium from metal solution and tannery effluent by utilizing aquatic plants i.e, Najas indica Cham, Vallisneria spiralis L. and Alternanthera sessilis. The first plant was submerged, second one was rooted submerged and last one was rooted emergent. In order to assess the maximum metal accumulation potential, these three aquatic plants were treated with different concentrations of chromium under repeated exposure. The results reveled that V. spiralis is more significant in accumulation capacity than others. According to the results of the study, these plants showed their effective removal capacity in case of chromium from tannery effluent.
Liao and Chang, (2002) worked on phytoremediation of heavy metals by using water hyacinth at constructed wetlands in Taiwan. Water hyacinth plants had a high bioconcentration of copper, lead, cadmium, nickel, and zinc, when grown in aquatic environments with low concentrations of these five elements. The results showed that the concentration of these five elements in the roots was 3 to15 times higher than in the shoots. This study revealed that water hyacinth play a vital role in phytoremediation of wastewater contaminated with copper, lead, zinc, cadmium and nickel.