engleski

Metallothionein responses to metal(loid) exposure in tissues of fish from the karst ecosystems

Introduction: Metal-associated stress in the organism can be reflected as the induction of metallothioneins (MTs), cytosolic proteins responsible for essential metal homeostasis (Cu, Zn) and detoxification of toxic metals (Ag, Cd, Hg). The aim of this study was to evaluate changes in MT levels in liver, as a site of metal detoxification and in intestine, as a site of metal uptake, in the brown trout from the karst Krka River, Croatia. The lower part of the river was proclaimed national park due to its exceptional natural beauty, but 2 km upstream from the park border industrial and municipal wastewaters are released in the river without proper purification. Therefore, MT levels, physiological state of fish (condition and hepatosomatic indices), metal(loid)s in sediment and total and dissolved metal(loid)s in the river water were compared among Krka River source (reference location), downstream of the industrial and municipal outlets (wastewater impact) and near Brljan Lake (location in the national park). Materials and methods: Fish indices were calculated as the ratio of total body mass (g) and total length (cm3) for Fulton condition index (g cm-3 x100), and liver mass (g) and total body mass (g) for hepatosomatic index (%). Levels of metal(loid)s (Ag, Al, As, Cd, Co, Cr, Cs, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Rb, Sr, Tl, Zn) in water (total and dissolved) and sediment were measured by high resolution inductively coupled plasma mass spectrometry (HR ICP-MS), while of MTs by differential pulse voltammetry (DPV). Results: Fish condition and hepatosomatic indices were slightly increased at the site impacted by wastewaters, reflecting the presence of nutrients which were available to fish at this site. Levels of most metal(loid)s in both water and sediment were increased in the industrial wastewater pools, specifically for As, Co, Cu, Fe, Mo, Ni, and Zn. Also, some of these metals were higher in the Krka River near locations directly exposed to wastewater outlets, like Al, Co, Mn, Ni, Sr, and Zn in water and Cd, Cs, Mn, Rb, and Tl in sediments, most of them known as metals used in industry. Comparison between total and dissolved metal levels indicated that only the presence of Ag, Al, Cr, Cs, and Fe in dissolved water fraction was less than 80%. Generally, levels of MTs in liver and intestine were comparable between locations (average 0.84 mg g-1), indicating that cellular disturbances in fish were not evident. Exception was significantly higher MT in intestine (0.96 mg g-1) of fish from the Krka River source than other locations, possibly following the trend of higher Cd and Tl levels in water at the same site, and Cd is known as important MT inducer. In addition, fish diet should be considered as important metal source. Conclusion: Fish intestine was shown as important indicator tissue, which reflects dietary metal exposure. Metal(loid) levels confirmed the impact of inappropriately treated wastewaters on the sensitive karst ecosystem. Therefore, continuous biomonitoring and strict regulations must be established if serious consequences want to be avoided on the Krka River National Park.

Krka River ; fish intestine ; bioindicator ; wastewater

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