Report No FR0492/DoE 372

Nov 1994

Blue-green algae can, under certain conditions, massively increase in numbers in some water bodies and may form visible surface blooms. Toxic effects on animals ingesting significant quantities of blue-green algal cells, usually from such blooms, have been recognised for over a century and some of the toxins were classified according to their mode of action e.g. hepatotoxins, neurotoxins. The most common neurotoxin is an alkaloid called anatoxin-a which occurs in the UK and has probably been responsible for the deaths of dogs at Loch Insh in Scotland.

As blue-green algal blooms have occurred in raw water supply reservoirs, toxicity data were needed in order to enable a risk assessment of potential exposure by ingestion via drinking water. However, studies in vitro could not provide suitable information and it was necessary to carry out some studies in laboratory mice.

These studies and studies in vitro showed that:

Anatoxin-a is a potent neurotoxin which blocks neuromuscular activity by its pharmacological action as a nicotinic agonist. In various pharmacology studies it was between 7 and 136 times more potent than nicotine.

In vivo studies showed that recovery from a single sub-lethal dose producing symptoms was rapid and apparently complete.

Anatoxin-a did not cause any apparent adverse effects in the foetus in pregnant females given 2.46 mg/kg bodyweight by oral gavage from days 6-15 of pregnancy.

The clear no effect level in mice given anatoxin-a by oral gavage for four weeks was about 0.1 mg kg^-1 bodyweight per day.

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