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

Abstract

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) 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 concentrations of Ni and 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 2008/105/EO of the European parliament and the Council. The metal concentrations were prepared as 75, 50 and 25 % of the maximum permissible levels (100%) set by national and EU law.
Results and conclusions: We found that after the first 24 h the lysosomes retained the dye between 60 and 90 min. in the mussels exposed to the higher Ni and Pb concentrations (100, 75 and 50 %). We also registered a negative, statistically significant correlation between the metal concentrations and the average time the lysosomes retained the dye after the 24th and 72nd h. Moreover, we found that the lysosomes could not retain the dye more than 60 min. after the 72nd h of exposure compared to the control (100 min.). The respiration rate increased in a dose-dependent manner after the 24th and 72nd h. We can conclude that the acute metal exposure, including all metal concentrations below the allowable concentrations, lead to destabilization of the lysosomal membrane stability and changes in the respiratory rate of zebra mussel, thus altered physiological functions. Overall, we consider that such experiments can be successfully applied in risk assessment and monitoring programs on metal-contaminated aquatic systems, and the obtained results in the field of water policy, respectively.