engleski

Dissolved and total metal concentrations in water of the karst Krka River: bioavailability and influence of industrial wastewaters

Industrial wastewaters are important source of metal contamination in aquatic ecosystems. Typical example is the Krka River in Croatia, which lower part is protected as the Krka National Park (KNP), but its upstream watercourse is under the impact of improperly purified industrial effluents from the nearby screw factory. Our aim was to assess metal exposure in four seasons of 2021 by comparing dissolved and total metal concentrations (Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Tl and Zn) in water from four sites: industrial wastewaters (IWW), the Orašnica tributary (TOR) directly affected by IWW, Krka River source (KRS) as the reference site and Brljan Lake (KBL) located in KNP. Dissolved metal concentrations represent fraction available for the organisms, while the ratios of dissolved and total concentrations indicate metal tendency to bind with particles. The highest dissolved concentrations of all elements were evident in IWW and their spatial distribution mostly followed the order IWW>TOR>KRS≥KBL. The most prominent increase in IWW compared to other locations was observed for Fe, Cu, and Zn, elements commonly used in industry. Macroelements were almost completely present (≥95%) in the dissolved fraction in all locations. Average ratios of dissolved and total Tl, Cr, Mn, Cu, and Zn concentrations were around 70-85%, pointing to their still relatively low affinity of binding to particles in this ecosystem and high bioavailability for organisms. Only Fe was present in dissolved form in low percentage, showing predominant association with particles and suspended matter and lower toxicity risk for aquatic organisms. The majority of trace elements (Fe, Cu, Cr and Zn) showed lower dissolved/total metal ratios in IWW than in other locations, indicating higher association to particulate matter of the industrial source. Still, much higher metal concentrations at this site, despite lower bioavailability, point to significant risk of metal exposure on the Krka River and possible toxic effects for biota. Seasonal differences were more obvious for trace than macroelements, probably as a result of their irregular discharges from industrial and agricultural activities. Therefore, proper treatment of the wastewaters and regular monitoring are necessary to protect this sensitive karst ecosystem and KNP.

ICP-MS ; water quality ; pollution impact ; national park ; water conservation

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