Study of the Potential Pollution of Heavy Metals in Sediments of Anzali Wetland Based on Sequential Extraction Technique

In present century, population growth, technology development and agriculture development are causing environmental pollutions. Many pollutants are entering into the environment by humans; one of the major environmental pollutants is heavy metals which enter to the aquatic ecosystems. These elements are very stable and because of their toxic effects and accumulation have a particular importance. Level of heavy metals in aquatic ecosystems like wetland by measuring their concentration in water, sediments and organisms is considered. Sediments are the potential source of contamination in aquatic environments and act as sink for pollutants. As forms of heavy metals are varying to make different mobility, bioavailability and toxicity, the measurement of total elements cannot provide the complete information of the characteristics of heavy metals. Therefore, sequential extraction processes of elements of sediments have been developed.

In this study, concentration of cadmium, copper, lead, zinc and chromium in surface of sediments at the southwest regions of Anzali wetland were studied by sequential extraction process in four stages. Sediments were sampled from six sites by Grab sampler. Concentration of elements in these samples was determined by Atomic Absorption Spectrophotometer (AAS).

Average concentrations of elements in the sequential extraction method showed that metals rates in the different fractions was: Residual > Organic Oxidation > Acid Reduction > Exchangeable. In total, metals concentration in sediment samples of the southwest of Anzali wetland was: Zn>Cu>Pb>Cr>Cd.

Geochemical Accumulation Index (Igeo) was calculated for these elements. According to this factor, cadmium pollution in this area was moderate (Igeo=1.65). Other elements had shown no pollution. Individual Contamination Factor (ICF) for heavy metals calculated, also. These results showed that lead and chromium had the highest bioavailability so they can be dangerous for organisms.