A Microencapsulation Method for Delivering Tetrodotoxin to Bivalves to Investigate Uptake and Accumulation.

Laura Biessy,Ian Hawes,Joel R D Bowater,Kirsty F Smith,Susanna A Wood,Annabel Tidy,Roel Van Ginkel

doi:10.3390/md19010033

Abstract

Most marine biotoxins are produced by microalgae. The neurotoxin tetrodotoxin (TTX) has been reported in many seafood species worldwide but its source is unknown, making accumulation and depuration studies in shellfish difficult. Tetrodotoxin is a water-soluble toxin and cannot be directly ingested by shellfish. In the present study, a method was developed which involved binding TTX to solid particles of humic acid and encapsulating them in agar-gelatin capsules. A controlled quantity of TTX-containing microcapsules (size range 20–280 μm) was fed to Paphies australis, a bivalve known to accumulate TTX in the wild. The TTX-containing microcapsules were fed to P. australis every second day for 13 days. Ten P. australis (including five controls fed non-toxic microalgae) were harvested after 7 days and ten after 13 days. Paphies australis accumulated TTX, reaching concentrations of up to 103 µg kg−1 by day 13, exceeding the European Food Safety Authority recommended concentration of 44 μg kg−1 in shellfish. This novel method will allow future studies to explore the effects, accumulation and depuration rates of TTX in different animals and document how it is transferred through food webs.

Highlights

Shellfish are a rich source of protein, essential minerals, vitamins and are an important food source worldwide [1]
The results showed that ca. 70% of the TTX was bound to the humic acid and that most of the bound TTX was released after addition of the formic acid to break the ionic bond between TTX and the humic acid, the same way as it would in the acidic digestive glands of P. australis (Table 1)
A method which involved binding TTX to solid particles of humic acid and encapsulating them in agar-gelatin capsules was successfully developed. This is the first study binding TTX to a solid particle that was fed to aquatic organisms. This experiment involved a known quantity of TTX-containing microcapsules being fed to P. australis

Summary

Introduction

Shellfish are a rich source of protein, essential minerals, vitamins and are an important food source worldwide [1]. Bivalves filter large volumes of water and can concentrate contaminants including bacterial pathogens and phycotoxins [2]. With over 66 million tonnes of shellfish consumed by humans annually, the risk of poisoning through contaminated seafood is an increasing public health concern [3,4]. With regards to phycotoxins (biotoxins produced by microalgae), the risk of poisoning increases exponentially during harmful algal blooms (HABs), when microalgal populations form dense concentrations of cells and sometimes visible water discolouration [5]. HABs have negative environmental impacts and can cause mass mortalities of fish, birds and marine mammals, and human illness [1], when they produce biotoxins that contaminate seafood through biomagnification up the food web [6]. About 300 marine microalgal species are known to produce biotoxins and more than 100 of these can cause intoxication or even death in humans and animals [6]

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