Heavy metals in mangrove sediments of the United Arab Emirates shoreline (Arabian Gulf)

The levels and distributions of eight heavy metals in the sediments of four mangrove areas, namely Abu Dhabi, Umm al-Quwain, Ras al-Khaimah, and Khor Khuwair along the shoreline of the United Arab Emirates (U.A.E.) were investigated. The metal levels, expressed as mu g g(-1) as well as organic carbon (%) in different mangrove areas were scattered in the ranges: 3.12-6.94 for cadmium (mean 4.82), 5.70-14.0 for cobalt (mean 10.2), 8.28-18.9 for chromium (mean 11.9), 5.31-29.4 for copper (mean 7.21), 28.8-169 for manganese (mean 84.1), 14.8-109 for nickel (mean 36.4), 13.2-49.8 for lead (mean 28.1), 4.59-22.4 for zinc (mean 11.3), and ND-2.13 for organic carbon (mean 0.63%). Significant variations in the levels of these metals were considered due to: 1) organic carbon content; 2) presence of well developed mangrove forests; and 3) anthropogenic inputs such as discarded automobiles, transformers, batteries, tires and spilled crude oil, atmospheric fallout as well as waste-waters disposal. In addition recreational activities cause negative effects. Concentrations of manganese, nickel and lead were significantly higher than the other metals. The high concentrations of Mn and Ni were due to non-anthropogenic sources (the geological nature formations and the presence of high mountains of basic igneous rocks), whereas the high levels of lead were due to inputs from oil spills, discarded solid wastes such as automobiles, batteries and the prior high rate of petrol combustion lead. Significant relationships were observed between several couples of metals in different mangrove regions, as well as between a number of heavy metals and organic carbon, indicating that complexation with organic materials may play an important role in the distribution patterns of these metals. Metals and organic carbon analyses for different grain-size fractions showed higher levels in the finest fraction (<63 mu m) specially for manganese and copper. Except for lead, comparison of metal levels in mangrove sediments with those of the Arabian Gulf indicated that the mangrove sediments along U.A.E. shorelines contained similar concentrations as other Arabian Gulf regions.