ارزيابي آلودگي فلزات سنگين و آلاينده هاي نفتي در رسوبات سطحي جنوب شرقي درياي خزر با استفاده از شاخص هاي موجود

Assessment of Heavy Metal and oil pollution in surface sediments of South Eastern Caspian Sea using Indices

As the largest lake, the Caspian Sea is one of the most important lakes in the world from ecological, political and natural resources points of view. The Caspian Sea is increasingly being under environmental threats and pressures because of residential, industrial and agricultural areas, oil exploitation and production activities within and in the vicinity of long coastlines of this lake. Studying the bottom sediments as the final sink of the fated pollutants has been of interest to evaluate the overall quality of the aquatic environments. Much attention has been paid to the study of the water and sediment quality and ecology of the Caspian Sea. In the present study, heavy metals and petroleum hydrocarbon contents in surface sediment samples of a large area from east to central coasts of southern Caspian sea (from Miankaleh bay in Golestan province to Ramsar coasts in Mazandaran province, Iran) are studied. Twenty sediment samples from different depths in 7 zones along coastline are taken and analyzed for metals (Fe, Al, Ba, Ni, Cu, Zn, V, Cr, Sn and Pb), Total Petroleum Hydrocarbons (TPH) and Polycyclic Aromatic Hydrocarbons (PAHs). Sampling points coordinates; water depths and percentile of fine materials (< 63 |j,m) in sediment samples are presented in Table 1. Samples are taken by a Van Veen grab sampler and preserved, prepared and analyzed for hydrocarbons according to U.S.EPA SW-846 using gas chromatography. Samples for metal analysis aere prepared according to MOOPAM and measured by atomic absorption spectrometry. Hydrocarbons in marine environments may either be originated from biogenic or petrogenic sources. Results of the present study showed that the contents of TPH fall in the range of 10-64 j^g/g of sediments with more enriched (40-64 |j,g/g) sediments of central part of Mazandaran province coasts. It should be pointed out that TPH contents of some other parts of the world that are recognized as polluted areas are as follows: 60-464 j^g/g in Hong Kong, 35-2900 (a,g/g in New York Bay, 11-690 |tig/g in Persian Gulf and 0.059- 34.09 jug/g in northern Caspian sea. Based on some published works, TPH content in sediments more than 500 |Ag/g is indicative of pollution while sediments containing less than 10 jug/g of TPH may be considered as unpolluted. According to this rule of thumb, sediments of the study area may be unpolluted in most of the region except for coasts of Mahmudabad to Tonkabon which may have low pollution of hydrocarbons (30