Blue-green algae toxicity is caused by ingestion of water contaminated with cyanotoxins, during harmful algal blooms (HABs). Blooms are dense accumulations of cyanobacterial cells, or colonies. They occur most commonly in nutrient-rich, warm, bodies of water with little movement or mixing in layers. Bloom events have both direct and indirect effects on ducks and other waterfowl. Direct intoxication may occur after exposure to harmful cyanobacteria, or cyanotoxin-contaminated food or water. Indirect effects of blooms are an increased risk of botulism, resulting from a decrease in dissolved oxygen and the proliferation of Clostridium botulinum
Blooms can seen floating along the water surface or they can develop below the water surface. Many different environmental factors influence the growth of algae blooms. The current global climate change and increased CO2 concentrations have resulted in an increased frequency of blooms occurring worldwide. Blooms occur most frequently during the summer and early fall months, when water temperatures are at their highest due to abundant sunlight exposure and high temperatures.
Cyanotoxins are essentially endotoxins that are characterized into multiple functional classes including:
- Hepatotoxins: include the cyclic peptides, microcystins and nodularins.
- Neurotoxins: Includes saxitoxin and neosaxitoxin (complex alkaloid sodium channel blockers), anatoxin-a and homoanatoxin-a (cyclic alkaloid nicotinic agonists), and the organophosphorus cholinesterase inhibitor anatoxin-a(s).
- Dermatotoxins: Lyngbyatoxins
- Cytotoxins: Cylindrospermopsin is a potent sulfated tricyclic guanidine cytotoxin with bioactive metabolites.
Ducks need only ingest but 1.2 oz (40 ml) of algae bloom to be fatal. In most cases of poisoning, ducks are usually found dead, due to the potency of the toxin.