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Among the pollutants inaquatic ecosystems, heavy metalsare considereddangerouspollutants due to theirtoxic effectsand bioaccumulation in organisms. They can cause chronicand acutepoisoning when consumed by human. Mercury is one of the most toxic metals, which can accumulate in a food chain and in the most top of it, the human body. Inthisstudyconcentrations ofmercury were measured infour speciesofaquaticorganisms, black pomfret, white Indian prawn, white leg shrimp and crayfish andthe consumptionrisk assessment for each of theseseafood species were assessed. Samples were obtained from Tehran market and the muscles of species were dissected and wetdigested. The concentrations of mercury insolutions were determined usingcold vaportechnique andatomic absorption spectroscopy. The average concentrations of mercury in muscle of the species were0.331, 0.323, 0.346 and 0.113 μg g-1 wet weight, respectively. These concentrations were within standard levels determined by the international organizations such asWHO,FAO, EPA, FDA, EC and MAFF. HQ index was below 1 for all species. Therefore, the consumption of these seafood species is not a serious threat to the consumer’s health in terms ofmercury concentration.