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Uptake and depuration of cyanotoxins in the common blue mussel Mytilus edulis.

Waack, Julia

Authors

Julia Waack



Contributors

Abstract

Cyanobacteria produce a variety of secondary metabolites that possess - amongst other things - antifungal, antibacterial and antiviral properties. Being primary producers, they are also a vital component within the food web. However, certain strains also produce toxic metabolites such as the hepatotoxins microcystin (MC) and nodularin (NOD). Their toxicity - in combination with the increasing global occurrence - has resulted in a drinking water guideline limit of 1 μg L-1 being issued by the World Health Organisation (WHO). However, these toxins are not only present in water, but can be accumulated by fish and shellfish. Currently, no regulations regarding cyanotoxin-contaminated seafood have been established, despite similar toxicity to routinely-monitored marine toxins such as domoic acid (DA). To facilitate regular monitoring, a high-performance liquid chromatography photo diode array (HPLC-PDA) analysis method for the detection of DA was optimised to enable the simultaneous detection of DA and nine cyanotoxins. This method was then utilised to determine cyanotoxin concentration in laboratory cyanobacteria strains. To assess the accumulation and depuration of cyanotoxins in the common blue mussel Mytilus edulis, three feeding trials were performed. During these, mussels were exposed to two cyanobacteria strains - Nodularia spumigena KAC66 and Microcystis aeruginosa PCC 7813 - both individually and simultaneously. A rapid dose-dependent accumulation of cyanotoxins was observed with maximum concentration of 3.4 -17 μg g-1 ww accumulated by M. edulis, which was followed by a much slower depuration. During the final feeding trial with the two cyanobacteria strains, cyanotoxins were still detectable following twenty-seven days of depuration. Mortality in all studies was 7% or less, indicating that most mussels were unaffected by the maximum dose of 480 μg L-1 NOD (feeding study 1), 390 μg L-1 MC (feeding study 2), or 130 μg L-1 total cyanotoxins (feeding trial 3). Mortality in negative control tanks was lower throughout all three feeding trials ( < 1 - 2.6%). Consumption of a typical portion size (twentty mussels) would result in ingestion of cyanotoxins at levels significantly higher than the WHO recommended tolerable daily intake (TDI) of 2.4 μg NOD and/or MCs for a 60 kg adult. This value was exceeded not only during the exposure period (maximum levels 270 - 1370 μg cyanotoxins per twenty mussels), but also at the end of the depuration period 39-600 μg cyanotoxins per twenty mussels. These results illustrated that cyanotoxin monitoring of seafood should be considered not only during, but also following bloom events. In an attempt to investigate the cyanotoxin budget of the experimental system, not only mussels but also cyanobacteria cultures, the tank water and the mussel faeces were also analysed for their cyanotoxin content. Results showed that large quantities of MCs and NOD were unaccounted for during all exposure trials. The combined effect of cyanotoxin metabolism in M. edulis, biotic and/or abiotic degradation, protein binding, and losses during the extraction and analysis were thought to have contributed to the unaccounted cyanotoxin fraction. Mussel flesh was analysed for the presence of glutathione or cysteine conjugates; however, there was no evidence of their occurrence in the samples tested. Due to these discrepancies in the toxin budget of the system, the introduction of correction factors for the analysis of cyanotoxins in M. edulis was suggested in order to protect the general public.

Citation

WAACK, J. 2017. Uptake and depuration of cyanotoxins in the common blue mussel Mytilus edulis. Robert Gordon University, PhD thesis.

Thesis Type Thesis
Publication Date Jun 1, 2017
Deposit Date Aug 17, 2017
Publicly Available Date Aug 17, 2017
Keywords Cyanobacteria; Cyanotoxins; Microcystin; Nodularin; Mytilus edulis; Microcystis aeruginosa; Nodularia spumigena
Public URL http://hdl.handle.net/10059/2447

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