Abstract
This study aimed at assessing heavy metals (Fe, Mn, Zn, Cu, Cr and Pb) in four perennial halophytes (viz. Heliotropium bacciferum, Halopyrum mucronatum, Ipomoea pes-caprae and Salsola imbricata) growing at two sites on the Karachi coast. Site - II, closer to the Industrial area had higher bioavailability as well as translocation factor (TF) for most of the heavy metals and Na+ where soil sediments had lower pH (approximately 7.5), higher salinity (EC) and organic matter (OM). Site - I which was far from Industrial area had comparatively higher bio-concentration factor (BCF) and lower TF for metal ions and soil pH of 8.1-9. Metal accumulation in plants was both site and species specific. Extractable concentration of shoot Pb in all tested halophytes was above normal of the threshold values (i.e., >0.3mgkg-1) while Mn (<50mgkg-1) and Cu (<40mgkg-1) were within permissible limits. Salsola imbricata had highest Na+ at both sites (site - I=73; site - II=98mgkg-1) with and 10mgkg-1 extractable shoot Pb at site - I. Ipomea pes-caprae also accumulated shoot Pb higher than normal (site - I=3.3; site - II=0.8mgkg-1) with lowest Na+ content. Heliotropium bacciferum had higher extractable Pb (site - I=10.5; II=2.75) with >20mgkg-1 Na+ in shoot while maintaining>1TF for Pb, Cu, Mn and Zn at site - I and all tested metals at site - II. Halopyrum mucronatum had highest shoot Fe (644mgkg-1), Zn (63mgkg-1) and Cr (9.2mgkg-1) at site - II and above threshold values of Pb at both sites (site - I=8.2; site - II=2.5mgkg-1) which makes this species an ideal bio-indicator candidate while other species could be potentially used for Pb phytoremediation.
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