Lysosomal membrane stability and respiration rate in zebra mussel (Dreissena polymorpha) as biomarkers for ex situ heavy metal exposure

Background and purpose: In the current study we aimed to investigate the lysosomal membrane stability in haemocytes of the invasive mollusk zebra mussel (Dreissena polymorpha Pallas, 1771) by applying the neutral red retention assay (NRRA), as well as changes in the respiration rate and survival under acute heavy metal exposure. Materials and methods: The mussels were treated with different decreasing concentrations of nickel (Ni) and lead (Pb) in laboratory conditions for a total acute period of 72 hours. These metals are considered as priority substances in surface waters according to Directive 2013/39/EU of the European parliament and of the Council amending Directives 2000/60/EC and 2008/105/EC as regards priority substances in the field of water policy. The metal concentrations were prepared as 75, 50 and 25 % of the maximum allowable concentrations (100% MAC) set by law. Results and conclusions: In sum, after 24 and 72 h we found that the lysosomes in the mussels exposed to all Ni and Pb concentrations, including the ones below the MAC (75 and 50 % from MAC) retained the dye shorter than the accepted minimum of 90 min. In addition, the respiration rate increased in a dose-dependent manner. Overall, we can conclude that the acute metal exposure lead to destabilization of the lysosomal membrane stability and changes in the respiration rate of zebra mussel, therefore altered physiological functions. We consider that such experiments could be successfully applied in risk assessment and monitoring programs on metal-contaminated aquatic systems, and the obtained results could be used in the field of water policy, respectively.