a b s t r a c tThough flood plains are considered as most fertile areas across the world but they have come under severe stress due to the flow of untreated domestic and industrial effluents and therefore, needed attention for its characterisation and subsequent treatment plans. The sediment samples, collected at 0e15, 15e35 and 30e60 cm depth levels during pre and post monsoon season from east and west sides of the river Yamuna around the national capital region of Delhi, were assessed for bioavailability of lead (Pb), zinc (Zn) and nickel (Ni) using Ethylene Diamine Tetra Acetic Acid (EDTA) and acetic acid. The average concentrations of Zn (25 ± 6 mg kg À1 ) and Pb (33 ± 6 mg kg À1 ) leached in EDTA were higher than that of in acetic acid (Zn: 22 ± 6 mg kg À1 ; Pb: 24 ± 5 mg kg À1 ) whereas Ni (24 ± 6 mg kg À1 ) leached more in acetic acid compared to EDTA (Ni: 21 ± 4 mg kg À1 ). The bioavailable concentrations of metals were comparable among 0e15 and 15e35 cm depth samples but decreased in 35e60 cm depth samples. The post monsoon samples contained lower amounts of total metals in comparison to pre-monsoon samples, an indication of washout/dilution effects of flood/high water flow during monsoon season. The percentages of metals, with reference to their respective total concentrations, in the flood plain sediments as extracted by EDTA were in the range of 14e47% for Pb,17e54% for Zn, and 15e39% for Ni. The Zn, Ni and Pb were soluble in acetic acid in the range of 12e39%, 16.7e36.5% and 14e36%, respectively. The chemical nature of extracting agent affected the metal leaching. Acetic acid, a weak acid, extracted the metals that were present in exchangeable fraction and easily movable whereas EDTA, hexa-dentate complexing agent, extracted metals from carbonate and organically bound fractions of the sediment samples. This could result in metal accumulation in the floodplains, biomagnification, adverse effects on water quality, sediments, aquatic lives and the vegetables grown in the flood plains. Steps should be taken to stop the direct flow of untreated waste into the river to safeguard the floodplains and life forms.
Selected heavy metals Cu, Ni, Zn and Pb were studied in two different types of coal fly ash samples, dyke and field, collected from Badarpur Thermal Power Station, Delhi, India for their total metal concentration as well as geochemical differentiation in different chemical fraction namely exchangeable, easily reducible or Fe -Mn bound, organic or sulfide bound and residual fractions. The total concentration of heavy metals in both types of fly ash samples followed the order Cr4Zn4Pb4Ni4Cu. Among the two types of samples, field fly ash samples were more enriched in these heavy metals compared with the dyke type samples. The fine grain size of field type samples possibly provided the sufficiently large surface area for the adsorption of these metals, resulting in higher concentrations compared with those in the coarse grained dyke samples. But, interestingly, the dyke type fly ash samples contain most of the metals in the exchangeable fraction. Metals in this fraction are easily mobilisable or can be made mobile depending upon the environmental conditions of Eh and pH. This suggests that the dyke type samples with low bulk metal content can even pose serious environmental hazards compared to the high total metal containing samples of field type. This suggests that it is the presence of metal in particular fraction(s) and not the total metal concentrations which are harmful to the environment, in particular to the soil and aquatic life.
Wastewater from textile industries is a potential source of organic dyes in natural water bodies. Environmental concerns of chemical methods for removal of dyes from wastewater are no more a viable solution, and there is growing concern to develop alternative approaches such as green chemistry and phytoremediation. This study reports the removal of organic dyes from wastewater using Eichhornia crassipes (Mart.) Solms (water hyacinth), as an easily available and fast-growing plant species. Growth of water hyacinth among individual cationic (rose bengal (RB), methylene blue (MB), crystal violet (CV), auramine O (AO), rhodamine B (RhB) and anionic (xylenol orange (XO), phenol red (PR), cresol red (CR), methyl orange (MO)) dye solutions and degradation of dyes were monitored. Results indicated that water hyacinth has good absorption and degradation potential for both types of dyes (cationic or anionic) and effectively removes dyes from solution. Water hyacinth can be used as a suitable and effective phytoremediate for removal of organic dyes from the wastewater.
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