Phytoremediation of Heavy Metals Iaden Waste Water Using Duckweed Species

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Title : Phytoremediation of Heavy Metals laden Waste Water using Duckweed species
INTRODUCTION
Presservation of the environment quality is one of the major concern of this century. Our biosphere is getting degraded by the release of natural and synthetic substances that can cause deleterious effects on living organisms. Among all the pollutants , heavy metals are easily transported and accumuted in the environment. Many industries like textile and steel, electroplating, metal producing release heavy metal such as cadmium, copper, chromium, nickel and lead in the wastewater (Demirenzen et al., 2007). Most of the heavy metals are toxic or carcinogenic in nature and pose a threat to human health and the environment (Shakibaie et al., 2008;
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Dushenkov et al.,1995, Prasad et al.,2003).Duckweeds belong to four genea; Lemna, Spirodela, Wolfia and Wolffiella. About 40 species are known world wide. All of the species have flattened minute, leaflike oval to round "fronds" from about 1mm to less than 1cm across. Some species develop root-like structures in open water which either stabilise the plant or assist it to obtain nutrients where these are in dilute concentrations.
Duckweeds are aquatic plants which often form dense floating mats in eutrophic ditshes and ponds (Driever et al., 2005). The macrophytes are fast growing, adapt easily to various conditions and can tolerate a wide pH range (4.5-8.3) (Environnement Canada, 1999). The small size, simple structure and rapid growth make duckweed very suitable for toxicity tests (OECD, 2002), able to remove and accumulate large amounts of heavy metals, principally through the fronds (Zayed et al. 1998). The Lemna gibba L. and the Lemna minor L. are the most studied species of Lemnaceae family in phytoremediation and ecotoxicology (Mkandawire et al., 2004; Mkandawire and Dudel,2005). Most members of the Lemna genus are used as model plants for ecotoxicological assessment, phytoremediation, nutrient and metal uptake studies, and bioassays (Sandra Redic et al.,2009, H.E. Ensley et

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