Toxicity of mercury and post-exposure recovery in Corbicula fluminea: Neurotoxicity, oxidative stress and oxygen consumption

The toxicity of mercury to the invasive species Corbicula fluminea and the post-exposure recovery were investigated in relation to previous developmental exposure to distinct environmental conditions. Bivalves were collected in the estuaries of Minho River (M-est) and Lima River (L-est) that have several abiotic differences, including in environmental contamination, with the former being generally less contaminated. After 14 days of acclimation to laboratory conditions, two 14-day bioassays were performed simultaneously: one with bivalves from the M-est and the other with bivalves from the L-est. In each bioassay, the treatments were: dechlorinated tap water (clean medium) for 8 days, clean medium for 14 days, 31 µg/L of mercury for 8 days, 31 µg/L of mercury for 14 days and 31 µg/L of mercury for 8 days followed by 6 days in clean medium (post-exposure recovery). The effect criteria were the oxygen consumption rate (OCR), the activity of the enzymes cholinesterases (ChE), NADP-dependent isocitrate dehydrogenase (IDH), octopine dehydrogenase (ODH), catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx) and glutathione S-transferases (GST) and lipid peroxidation (LPO) levels. Exposure to mercury for 8 days caused significant (p ≤ 0.05) inhibition of GR activity in M-est bivalves, whereas no significant adverse effects were observed in L-est animals. Moreover, evidences of delayed toxicity caused by 8-day exposure to mercury in OCR, IDH activity and LPO levels were found in M-est individuals but not in those of the L-est. Exposure to mercury for 14 days caused significant (p ≤ 0.05) depression of the OCR and of IDH activity in animals from both estuaries, indicating reduced individual fitness and hypoxia conditions. Moreover, oxidative stress and lipid peroxidation damage were observed in bivalves from the M-est exposed to mercury for 14 days but not in L-est animals. Differences in M-est and L-est environmental conditions to which animals were exposed in the wild likely contributed to the differences of sensitivity to mercury between M-est and L-est bivalves. The results of this study highlight the importance of investigating delayed toxicity, post-exposure recovery, and of taking into consideration the background contamination and other abiotic conditions of the original habitats when assessing the effects of environmental contaminants on animals from wild populations.