September 4, 2019

007 – Freshwater algal toxins – Nodularins

As is the case for Microcystins, Nodularins are also cyclic peptides, which primarily target the liver (hepatotoxins).  Nodularins are very similar to Microcystins in terms of their structure, mechanism of action and clinical effects and, as such, they are commonly grouped together.

Nodularins are potent toxins produced by the cyanobacterium Nodularia spumigena which is often responsible for algal blooms in brackish waters world-wide. Blooms of Nodularia spumigena can be amoung the largest cyanobacterial mass occurrences in the world.

The first-ever documented case of cyanotoxin poisoning involved the death of livestock after drinking water thick with a Nodularia spumigena scum from Lake Alexandrina in South Australia in 1878.

Locally, before the mid-1990s, the Peel-Harvey Estuarine system south of Perth (Western Australia), experienced choking blooms of Nodularia spumigena for several decades.  These toxic blooms caused frequent fish kills, disrupted local fisheries and had an adverse impact on human health.  In 1994, construction of an artificial channel (the Dawesville Channel) linking the Peel Harvey Estuary with the Indian Ocean was completed.  This channel, the largest marine environmental project undertaken in Western Australia at the time, dramatically increased the flushing of the estuary removing the excess nutrients (especially phosphorus) which were the major cause of the Nodularia blooms.

There are ten known Nodularin variants with Nodularin-R being the predominant one.  Similarly to Microcystins, Nodularins are a very stable group of compounds and will not degrade as a result of light, temperature, and microwaves.

Symptoms of acute exposure to Nodularins include blistering around the mouth, sore throat, headache, abdominal pain, nausea and vomiting, diarrhea, dry cough, and pneumonia.  Symptoms of chronic, long term exposure to non-lethal doses, associated with damage to the liver include jaundice, bleeding, swelling of the abdomen, mental disorientation or confusion, sleepiness, or coma.

Symptoms of acute exposure can present in as little as a few hours or days, but generally, the symptoms take around a week to show up.  There is no treatment for Nodularin poisoning other than to cease contact with the source of the toxin.

Typical exposure sources for these toxins in humans and mammals are by ingestion (swallowing), direct skin contact with or inhaling contaminated water or aerosols.  Aeroslised cyanotoxins, Microcystin and Nodularin in particular, can travel many kilometres from the source water without undergoing any degradation.

There is considerable evidence to suggest that Nodularins may be carcinogenic, particularly concerning liver and colorectal cancers.  The tumour-promoting activity level of Nodularins is much stronger than that of Microcystins.

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