Microcystin uptake and biochemical responses in the freshwater clam Corbicula leana P. exposed to toxic and non-toxic Microcystis aeruginosa: Evidence of tolerance to cyanotoxins

Abstract

We investigated the accumulation and adverse effects of toxic and non-toxic <i>Microcystis</i> in the edible clam <i>Corbicula leana</i>. Treated clams were exposed to toxic <i>Microcystis</i> at 100 μg of MC (microcystin)-LR_eq L^-1 for 10 days. The experimental organism was then placed in toxin-free water and fed on non-toxic <i>Microcystis</i> for the following 10 days for depuration. Filtering rates (FRs) by <i>C. leana</i> of toxic and non-toxic <i>Microcystis</i> and of the green alga <i>Chlorella vulgaris</i> as a control were estimated. Adverse effects were evaluated though the activity of catalase (CAT), superoxide dismutase (SOD) and glutathione S-transferase (GST). Clam accumulated MCs (up to 12.7 ± 2.5 μg g^-1 dry weight (DW) of free MC and 4.2 ± 0.6 μg g^-1 DW of covalently bound MC). Our results suggest that although both toxic and non-toxic cyanobacteria caused adverse effects by inducing the detoxification and antioxidant defense system, the clam was quite resistant to cyanotoxins. The estimated MC concentration in <i>C. leana</i> was far beyond the World Health Organization's (WHO) provisional tolerable daily intake (0.04 μg kg^-1 day^-1), suggesting that consuming clams harvested during cyanobacterial blooms carries a high health risk.