Table 3: Phytoremediation study on water medium (hydroponic).

No.ResearcherResearch scale and durationUptake mechanisms and media (substrate)Contaminant or parameter and concentrationPlantsResult

(1)[67]Field study (October–July 2005)Water of Tasik ChiniCd, Cu, and PbFive aquatic plant species, Lepironia articulata,
Pandanus helicopus, Scirpus grossus, Cabomba furcata, and Nelumbo nucifera—aquatic
The highest concentration of heavy metals among the aquatic plants and plant parts was found in the roots of S. grossus. The concentrations of Cd in the leaves and stems of submerged aquatic plant, C. furcata, were higher than that in the leaves and stems of emergent aquatic plant and floating leaf plant. The concentration of Cu in the stem of C. furcata was greater than that in the leaf, while the concentration of Cd was more in the leaf than that in the stem. The heavy metal contents of the aquatic plants were in descending order of Pb > Cu > Cd. The highest internal translocation was found in P. helicopus, while the lowest internal translocation was found in S. grossus.

(2)[68]Laboratory (pot experiment)/14 daysHydroponicAs and Se as Na2HAsO4·7H2O and Na2SeO3/0, 0.73, 2.5, 4.27, 5.00 mg/LChinese brake fern (Pteris vittata L.)—terrestrialAt low levels of Se, As enhanced both Se uptake and the translocation of Se from roots to fronds. At higher levels of Se, As suppressed the uptake of Se. These results suggest that As serves to both stimulate and suppress Se uptake. The result is also in agreement with the well-known fact that Se is an element with both beneficial and toxic properties. The effect can change from beneficial to toxic based on the concentration of Se in plants.

(3)[47]Laboratory and Field study: wetland-pond system (Laboratory scale: 3 days cultivative and 84 hours exposure)Field study: contaminated soil. Medium of laboratory scale experiment: L 0.1% Hoagland solutionField study: Zn, Cu, Cd, and Pb. Laboratory: ZnCl2, CuCl2, CdCl2, and Pb(NO3)2 (mixture of 20 μmol Zn, 0.5 μmol Cu, 1.5 μmol Cd, and 1.5 μmol Pb/L)Potamogeton natans L.-aquatic
Lemna gibba L.-aquatic
Alisma plantago-aquatica L.- aquatic
Sagittaria sagittifolia L.-aquatic Juncus effusus L-aquatic Lemna minor L.-aquatic Elodea canadensis Michx.-aquatic
Lythrum salicaria L.-aquatic Phalaris arundinacea L.-aquatic
Impatiens parviflora DC.-terrestrial Urtica dioica L.terrestrial
Filipendula ulmaria L.-aquatic
P. natans-aquatic
A. plantago-aquatica-aquatic
F. ulmarina-aquatic
The aquatic plants seem to have a higher metal accumulation capacity in shoots than terrestrial plants. This may be due to the capacity of aquatic plants to take up by shoot directly from the water. When submersed and free-floating plants are actively growing and accumulating metals directly from the water, they will function as an effective filter in stormwater treatment. Emergent plants in general mediate the binding of these metals in the sediment. Also, the terrestrial plants have the capacity to bind Cd and Zn to their roots, and; therefore, they can mediate a good stabilization of these metals in soil.

(4)[32]Laboratory (15 days)HydroponicPb as (Pb(NO3)2)Indian mustard (Brassica juncea var. megarrhiza)—terrestrialBrassica juncea is one plant which accumulates high levels of Pb and other heavy metals. The results indicate that lead nitrate obviously inhibits the root, hypocotyls, and shoot growth of Brassica juncea at the concentration of 10−3 M Pb2+. Brassica juncea has the ability to accumulate Pb primarily in its roots, transport, and concentrate it in its hypocotyls and shoots in much lesser concentrations.

(5)[30]Laboratory (5 days)Phytofiltration (water)Mercury as HgCl2 (0, 0.05, 0.5, 1, 2.5, 5, 10 mg/L)Indian mustard (Brassica juncea)—terrestrialRoots-concentrated Hg 100–270 times (on a dry weight basis) above initial solution concentrations. Mercury was more toxic to plants at 5 and 10 mg/L. The plants translocated little Hg to the shoots, which accounted for just 0.7–2% of the total Hg in the plants. Most Hg volatilisation occurred from the roots. Volatilised Hg was predominantly in the Hg(0) vapour form. Volatilisation was dependant on root uptake and absorption of Hg from the ambient solution. Efficiency process >95%.

(6)[69]LaboratoryHydroponicArsenate (As(V)) and dimethylarsinic acid (DMAA)Duckweed (Spirodela polyrhiza L.)—aquaticThe results show that not only internalized, but also surface-adsorbed arsenic (mostly arsenate) contributes significantly to the total amount of arsenic uptake in aquatic macrophyte S. polyrhiza L. The arsenic uptake in S. polyrhiza L. occurred through the phosphate uptake pathway as well as by physicochemical adsorption on Fe plaques of plant’s surfaces. The arsenate uptake in the plant is related to the Fe ion and phosphate concentrations in culture medium while DMAA was not.

(7)[2]Laboratory (the contact times of 25–200 min were selected for the metal solutions (Co = 1.00 mM) with 2.0 g biomass/l at the obtained optimal pHs for each metal ion from the previous study)Adsorption (water)The Hg2+, Cr3+, Cr6+ and Cu2+ stock solutions were prepared by dissolving their corresponding salts, viz. HgCl2, CrCl3·3H2O, K2Cr2O7, CuCl2 (analytical grade from Merck) in distilled water (pH values were almost 7.0, 5.0, 3.0 and 6.0 for Hg2+, Cr3+, Cr6+ and Cu2+, respectively)Lemna minor—aquaticThe potentiometric titration can be useful to study the pretreatment process of biomass (L. minor) using the acidic and alkali agents, the Qmax and KL values to remove Hg(II), Cr(III), Cr(VI), and Cu(II) from the aqueous solution by the activated L. minor at the alkali solution and by CaCl2/MgCl2/NaCl with 1 : 1 : 1 molar ratio were higher than those for the reference one at the same conditions, the removal percents of metal ions by no. ACS L. minor was higher than ACS one at the pre-treatment pHs before 7.0, but it was higher by ACS biomass than no. ACS one at the pre-treatment pHs after 7.0.

(8)[70]Laboratory (seedling 2 weeks and treatment 2 weeks)HydroponicHg and Au (0, 50, 100, and 200 uMHg (as Hg (CH3COO)2) and 0 and 50 uMAu (as KAuCl4) in hydroponics)Chilopsis linearis (Cav.) sweet—terrestrialThe data showed that Au equimolar to Hg reduced the Hg toxicity. The concentration of Au and Hg in shoots indicated that C. linearis absorbed and translocated both Au and Hg at higher concentrations, compared to reported data. The data showed that the treatments produced structural alterations in both the vascular cylinder and the cortex. At the highest concentration, Hg produced a breakdown of the spongy parenchyma.

(9)[71]Laboratory (30 days)Phytoextraction (water)Mercury as HgSO4 (0, 0.5 and 2 mg/L)Water hyacinth (Eichornia crassipes)—aquatic Water lettuce (Pistia stratiotes)—aquatic Zebra rush (Scirpus tabernaemontani)—semi aquatic
Taro (Colocasia esculenta)—aquatic
The higher the mercury concentration, the greater the amount of mercury removed by the plants. The largest uptake and accumulation capability is for water lettuce, followed by water hyacinth, taro and rush, respectively.

(10)[72]Laboratory—(pot experiment (10 days))HydroponicAs and Se (0, 150, or 300 uM of arsenat (Na2HAsO4·7H2O) in the presence of 0, 5 or 10 uM of selenat (Na2SeO4))Pteris vitatta L.—terrestrialApplication of 5 uM Se enhanced As concentration by P. vittata fronds by 7–45%. At 5 uM, Se acted as an antioxidant, inhibiting lipid peroxidation (reduced by 26–42% in the fronds) via increased levels of thiols and glutathione (increased by 24% in the fronds). The results suggest that Se is either an antioxidant, or it activates plant protective mechanisms, thereby alleviating oxidative stress and improving arsenic uptake in P. vittata.

(11)[45]Laboratory (72 hours (for kinetics of Arsenic uptake), 3 days (effects of plant density, Plant re-use, and plant age), 10 days (groundwater remediation))The groundwater was collected from a location which may have been contaminated from application of arsenical herbicides in the past.As (pH 7.0, total As of 46 μg/L, As3+ of 1.6 μg/L, and total P of 20 μg/L)Chinese Brake fern (Pteris vittata L.) plants—terrestrialChinese brake fern was efficient in taking up arsenic from a contaminated groundwater and was capable of reducing arsenic concentrations in the groundwater. One plant was sufficient to reduce arsenic in 600 mL groundwater to below 10 μg/L in 3 days. Young fern plants were more effective in arsenic removal than old fern plants of similar size. Ferns can be reused to remove arsenic from groundwater, but at a slower rate given the interval between exposures and nutritional status.

(12)[73]LaboratoryHydroponicCu and NiSalix viminalis clones and the basket willow Black Maul (S. triandra).
S. burjatica “Germany”, S.x dasyclados, S. candida and S. spaethii—terrestrial
The more resistant clones produced more biomass in the glasshouse and field and had higher metal concentrations in the wood. The less resistant clones had greater concentrations of Cu and Ni in the bark and produced less biomass in the glasshouse and field. Significant relationships were found between the response of the same clones grown in the short-term glasshouse hydroponics system and in the field.

(13)[74]Laboratory (10 days cultivate and 7 days exposure)Nutrient solutionAs (0, 5, 10, 20, 40 and 80 uM)Azolla: A. caroliniana and A. filiculoides—aquaticThe efflux of arsenate was much higher (by about 9-fold) than that of arsenite. This may be because most of arsenite inside the cells was complexed with thiol compounds. The high As-accumulating Azolla (A.caroliniana) released approximately two times more As than the low-As accumulating Azolla (A. filiculoides). It appears that the amount of As efflux was proportional to the amount of As accumulation in the two strains of Azolla.

No. (12) adapted from no. (20). Phytoremediation Bibliography, Annotated Bibliography on Phytoremediation prepared by Mark Coleman, Biological Scientist, USDA Forest Service Southern Research Station and Ronald S. Zalesny Jr., Research Plant Geneticist, USDA Forest Service North Central Research Station, May 1, 2006.