The use of Anodonta cygnea as an indicator of heavy metal contamination in Anzali wetland

Background: Wetlands are among the most important ecosystems and areas of life that are ecologically and economically important in the world and susceptible for heavy metal contamination. The elements in water and sediment may be easily and in large quantities available to animals in aquatic ecosystems. This study aimed to investigate the level of heavy metal contamination in Anodonta cygnea. Methods: Anodonta cygnea sampling was carried out in the summer 2023. A total of 35 specimens were collected randomly by fishing net. Following the laboratory analyses, the concentration of aluminum (Al), arsenic (As), copper (Cu), cobalt (Co), cadmium (Cd), iron (Fe), manganese (Mn), magnesium (mg), lead (Pb), nickel (Ni), tin, vanadium (V) and zinc (Zn) were determined by ICP-OES. Results: Target hazard quotient (THQ) values of Mn were above 1. The pi index showed that A. cygnea is slightly contaminated by Pb. Analyses of the metal accumulation showed that A. cygnea bivalve was moderately contaminated by Zn and severely contaminated by As. The results showed no significant relationship between the total weight of the organism and concentration of Al, Fe, and Ni. Conclusion: Aquatic organisms, including bivalves, do not possess an advanced excretory system, therefore the excretion of metabolites and pollutants is a is a slow process. once the concentration of heavy metals in the aquatic environment increases, they become easily available to aquatic organisms and enter the biological system. In this study, the absorption rate of metals was higher than its excretion or removal by the excretory system which results in their accumulation in various tissues and organs of the organism.