engleski

Metal accumulation in the digestive gland of mussel Unio crassus as an indicator of metal contamination in freshwater ecosystem: total vs. cytosolic metals

High metal contamination of aquatic ecosystems can have a huge impact on water quality and lead to series of health issues in aquatic organisms. The Mrežnica River, a Croatian karst river, has long been exposed to various types of industrial loads in its lower course. Freshwater mussels from family Unionidae, are benthic, filter-feeding organisms which are very susceptible to any changes of water chemistry. Since they reflect a quality of water and sediment, these species are considered as the best indicators of ecological conditions. In addition, these bivalves live relatively long and are therefore suitable for monitoring long-term metal exposure. For this investigation we select U. crassus because this species has very abundant populations in the river Mrežnica. Aim of this study was to compare concentrations of twenty eight metals in the digestive gland of U. crassus from two different locations of Mrežnica River, the industrial zone of Karlovac (KAR) and upstream from the Town of Duga Resa as the reference site (REF), and establish if river contamination with metals in industrial zone of Karlovac city has influenced metal bioaccumulation in bivalves. An additional aim was to determine whether total or cytosolic metal concentrations in digestive gland of U. crassus are better indicators of metal exposure in freshwater ecosystems. Measurements of metal concentrations in homogenates (total metal) and water-soluble fraction of digestive gland tissue (cytosolic metal) were performed using a high-resolution inductively coupled plasma mass spectrometer (HR ICP-MS) after sample digestion with mixture of nitric acid and hydrogen peroxide. Higher total concentrations of several elements (Bi, Cs, Cu, Mo, Pb, Sb and U) were found in specimens at the KAR site, whereas Cd and Se were, unexpectedly, increased at the REF site. Among the elements significantly increased at the KAR site, the largest differences compared with the REF site were recorded for Cs and Cu, which were approximately twice as high. Only total concentrations of Cs correlated with concentration in water, while seven elements (Ca, Cu, Cs, Mo, Sb and U) followed the trend of concentrations in sediments. Metal concentrations in cytosolic fractions were increased for almost half of analyzed elements in digestive gland of U. crassus from the KAR site. Significantly higher cytosolic concentrations at KAR site were additionally proven for Al, Co, Fe and Ni, which correlated with their higher concentrations in water and sediment. Results suggest that U. crassus is a good indicator of water quality, which provides information of different bioavailable metal species and forms in aquatic environments, especially by analysing cytosolic (potentially toxic) metal concentrations in their digestive glands.

Metals ; Bioaccumulation ; Unionidae ; Freswater ; Contamination ; Cytosol ; Homogenate ; HR ICP-MS

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