Distribution and accumulation of heavy metals in sediments of the northern part of mangrove in Hara Biosphere Reserve, Qeshm Island (Persian Gulf)

The mangrove of Hara Biosphere Reserve, stretching over 100 thousand hectares in the southern coast of Iran and in the northwest of Qeshm Island, belongs to the most important and largest mangroves in the Middle East. Twenty sedimentary samples were collected and concentrations of seven heavy metals were investigated in order to assess the extent of pollution distribution in this area and to discuss the origin of these contaminants in sediments. The mean heavy metal concentrations followed the scheme: Fe > Cr > Ni > Zn > Cu > Pb > Cd. Based on the geo-accumulation index, the Fe, Pb, Zn, and Cu levels were graded as non-contamination, the levels of Cr and Ni as non-contamination to moderate contamination, while those of Cd as moderate contamination to moderate to heavy contamination. According to the enrichment factor and quantification of contamination calculations, Cu, Pb, and Zn were derived mainly from natural processes and exposure of material from the Earth’s crust, while the increased values of Cd, Ni, and Cr were ascribed to anthropogenic activities. The ecological risk of heavy metals was moderate, largely due to Cd contamination. The elevated values identified for Cd, Ni, and Cr are supposingly associated with activities including human refuse, shipping, transportation, fuel smuggling, and industrial wastewater discharges from factories located around Hara Biosphere Reserve (e.g. Al-Mahdi aluminum factory, lead and zinc Qeshm factory, and Hormozgan cement factory).