Geochemical studies of sediments, water bodies like rivers, estuaries and the sea bed, can be an effective step to find the source and distribution model assessment of environmental pollutants in a region. Sediments are the final destination of heavy metals in aqueous environments contamination, including arsenic entering the water resources in different ways, causing hazards such as poisoning, and carcinogenesis in living bodies. Study arsenic levels in the eastern part of the Caspian Sea, 30 stations were selected in the Calculation of aggregated fine-grained organic matter in two seasons of the arsenic concentration in both summer and winter by using Inductively Coupled Plasma - Mass spectrometry (ICP-MS) was determined. Geochemical index, Enrichment factor and pollution index were determined low pollution to non-pollution area and cause of arsenic to the environment, erosion of the Geological formation of the bay, leading GORGAN River carry deposits upstream of surroundings were. Primary cause of arsenic to the environment, geology and upstream sediment erosion and transport by rivers is leading to Gorgan Bay and surrounding areas. Compare these results with other parts of the Caspian Sea show that arsenic levels observed in this study in the Gorgan Bay and surrounding areas has been less than other part of the Caspian Sea.

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