Heavy Metal Pollution and Biomonitoring Plants in Lake Manzala, Egypt

Abstract

In this study, the pollution levels and the toxicity status were estimated regarding four heavy metals (Zn, Pb, Cd and Hg) thought to be among the major contaminants in the environment of Lake Manzala. Our target was to define and utilize certain plant species, from the lakeþs vegetation, as bio-monitors, in comparison with the sediments as abiotic monitor for heavy metal pollution. The native wild plants (passive bio- monitors) were represented by eight species (Atriplex portulacoides, Zygophyllum album, Typha domingensis Juncus rigidus, Cyperus laevigatus, Arthrocnemum macrostachyum, Salsola sp. and Phragmites australis). The introduced plants (active bio-monitors) were represented by two crop- species (Trifolium alexandrinum and Raphanus sativa) grown and irrigated by polluted water at some islands in the southern sector of LM. Based on the concentration and toxicity status, induced in the lake's vegetation and sediments, the four metals are arranged in the following decreasing order: Hg greater than Zn greater than Pb greater than Cd. Compared with the standard normal and critical toxicity ranges in plants and soils, the detected values of Zn, Pb and Cd were within the critical ranges. However, Hg showed the highest values and alarming toxicity levels and it is considered as one of the most hazardous pollutants in Lake Manzala. The overall evaluation of the tested metals showed that their ratios were as much as 2.5 - 5 times higher in active monitors than in passive ones and 2 times than in sediments. They were also 2 times higher in sediments than in passive monitors. The monitoring materials are arranged in a decreasing order, based on their efficiency for accumulating heavy metals as follows: Introduced (active) monitors greater than Sediments greater than Native (passive) monitors. Certain species are also proposed as bio-monitors (and/or bio-filters) for the studied heavy metal pollutants. The results showed that there is a significant difference between the accumulation rate of some metals in different plant organs (e.g. Zn, Hg) since they showed more tendency for accumulation in root more than shoot systems. Also, there is a high positive correlation between combinations of different metal pairs in either plantþs root or shoot system. It is evident that while the degree of metal pollution in the lake increased southwards, the values of water-quality parameters (e.g. dissolved oxygen %, salinity and pH-value) increased northwards.