The diving beetle, Cybister lateralimarginalis (De Geer, 1774), as a bioindicator for subcellular changes affected by...

The present study assessed Cybister lateralimarginalis as a model species for ecotoxicological studies of metal(loid) bioaccumulation in freshwater ecosystems, by optimising protocols and analysing biomarker activities and metal(loid) concentrations from different sites and investigating their association. To accomplish this, levels of arsenic (As), selenium (Se), cadmium (Cd), mercury (Hg), and lead (Pb) were analysed, as well as a set of biomarkers were evaluated, esterase activity and oxidative stress biomarkers: fluorescence- and glutathione-based. C. lateralimarginalis were sampled in the spring/summer of 2023 along the Sava, Drava and Danube floodplains in Croatia. C. lateralimarginalis samples from Sava floodplain (Mužilovčica) showed altered carboxylesterase (CES) activity, lower glutathione (GSH) levels, and elevated Hg and As concentrations. The Weighted Pollution Index (WPI) indicated moderate pollution at the Sava floodplain, possibly due to agricultural or petrochemical impacts. At the Drava floodplain (Podravlje), higher glutathione S-transferase (GST) activity and elevated Cd, Hg, and As concentrations were observed, likely from soil accumulation, while Stara Drava beetles had lower GSH levels, suggesting agricultural impacts. Despite this, the Drava floodplain showed the lowest WPI. Higher GST activity was noted at the Danube floodplain (Kopački rit and Topoljski Dunavac), with reactive oxygen species (ROS) concentrations (Kopački rit and Podunavlje) possibly reflecting agricultural practices or illegal hunting. The present research successfully applied C. lateralimarginalis as a bioindicator species for assessing metal(loid)s in different environments, highlighting its reliability as an abundant apex predator, emphasizing the significance of integrating biomarker response evaluation into pollutant monitoring for efficient environmental risk assessment in freshwater ecosystems.