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DWE Home > Home > Water Management > Water quality > Algal information > Problems caused by toxic algae

Problems caused by toxic algae

Freshwater, estuarine and marine algae can impact on water quality, in some cases leading to health risks for people, stock, wildlife and domestic animals.

Freshwater Algae

Water Quality Problems

The presence of blue–green algae may lead to water quality problems.

In potable water supplies (ie. drinking water), high numbers of blue–green algae may cause taste and odour problems. When the algae die, they can cause blockages in the filters used for water treatment. Blue–green algae also pose a challenge for water supply authorities, as some species are capable of producing toxins. These toxins need to be removed from the water supply before it is supplied for domestic use and consumption, or an alternative supply sought.

The over growth of blue–green algae reduces the sunlight available to the plants and may lead to their death. When aquatic plants and algae die, large amounts of oxygen are required as decomposition occurs. This decrease in available oxygen can lead to the death of aquatic animals such as fish and can increase the release of nutrients and toxic chemicals from the sediments.

Risks to Humans and Animals

Blue–green algae can pose a risk to human health because of the toxins they produce. These toxins can damage the liver and neurological system of both humans and animals and in severe cases can cause death. The cell walls of all blue–green algae contain contact irritants which can cause gastrointestinal, skin, eye and respiratory irritations to humans and animals.

Toxins Produced by Blue–Green Algae

Toxins are compounds that have a harmful effect on other cells, tissues and organisms. In the natural environment, these toxins are generally contained within the blue–green algal cell but they are released into the water when the cell is damaged or dies.

Blue–green algal toxins can be divided into the following groups:

1. Hepatotoxins

• Hepatotoxins cause blood to collect in the liver causing circulatory shock and can lead to death by internal hemorrhaging.
• Hepatotoxins can cause weakness, vomiting and diarrhoea.
• Nodularin and microcystin are two types of hepatotoxins.
• Nodularin is produced by the algal species Nodularia spumigena.
• In NSW, microcystin is produced by Microcystis.
• Microcystins can bioaccumulate in aquatic invertebrates such as mussels so aquatic animals caught from water where there is an algal bloom should not be eaten.

2. Neurotoxins

• Neurotoxins interfere with the functioning of the nervous system and can cause death of humans and animals within minutes by causing paralysis of the respiratory muscles.
• In NSW, a neurotoxin known as saxitoxin is produced by the blue-green alga Anabaena.
• Marine dinoflagellates (red tides) produce saxitoxins (also known as paralytic shellfish poisons) which concentrate in shellfish and have been known to cause death in humans.

3. Non–specific Toxins

• Cylindrospermopsin is a non-specific toxin that in NSW is produced by the blue-green algae Cylindrospermopsis raciborskii and Aphanizomenon ovalisporum.
• This toxin is a relatively slow acting toxin that damages most organs in the body including the liver.

4. Dermatoxic Lipopolysachharides

• When non–toxic species of blue-green algae are present at concentrations above 10 cubic mm per litre, the water may still pose a risk to recreational and domestic users as all blue–green algae have lipopolysachharides in their cell walls.
• Lipopolysachharides are less toxic than hepatotoxins or neurotoxins but are significant in terms of water supply for drinking, showering and recreation.
• Lipopolysachharides have been associated with outbreaks of gastroenteritis, skin and eye irritations and hayfever, in humans that have come into contact with algal blooms. Humans that contact Lipopolysachharides in the aerosol form (fine spray eg sprinkler) may suffer asthma, eczema, and blisters in the lining of the nose and mouth.

Incidences of Blue–green Algal Poisoning

(i) Lake Alexandrina, Australia

The first recorded incidence of animal poisoning from a blue–green algal bloom was in Lake Alexandrina , Australia in the late 1800s. Cattle, horses, pigs, sheep and dogs died after drinking water covered by a scum of the blue–green algae Nodularia spumigena .

Animal deaths from blue–green algae have also been reported in North and South America , Europe, and Africa. The major cause of deaths in animals is from liver poisoning and neurotoxicity that leads to respiratory failure.

(ii) Soloman Dam, Palm Island, Australia

In 1979, an outbreak of hepato–enteritis occurred in the community of Palm Island, off the north–east coast of Queensland, Australia. The outbreak resulted in the hospitalisation of 140 children and 10 adults with symptoms including vomiting, headache, painful liver enlargement, initial constipation followed by bloody diarrhoea, and varying levels of dehydration. The outbreak was considered to be due to an algal bloom in Soloman Dam which supplies water to over 2,000 people on Palm Island. The presence of algae in the dam was causing taste and odour problems so authorities treated the dam with copper sulphate. The copper sulphate killed the algae (later identified as Cylindrospermopsis raciborskii) but caused it to release the toxin cylindrospermopsin into the water.

(iii) Barwon–Darling River, Australia

Australia experienced the world's largest recorded blue–green algal bloom along the Barwon–Darling River during 1991/1992. This bloom focused the attention of both the government and community on the issue of blue–green algae.
The bloom, dominated by the species Anabaena circinalis, was spread along the river for over 1000 km. Anabaena circinalis is a potentially toxic blue–green alga that produces neurotoxins.

A State of Emergency was declared and drinking water supplies had to be bought into those areas dependent on the Barwon–Darling as a water supply. A number of stock died from drinking contaminated water

(iv) Brazil

The most human deaths reported from an algal bloom occurred in Brazil in 1988 when a new dam developed a large bloom of blue–green algae. 2,000 people suffered from gastro–enteritis, which resulted in 88 deaths. The gastro–enteritis was attributed to toxins from the blue–green algae Microcystis and Anabaena which were present in the untreated water, although no clinical confirmation was ever established.

In 1996, a bloom of Microcystis in Brazil led to the deaths of 50 patients at a dialysis clinic after water contaminated with the toxin microcystin was used to treat patients.

Estuarine and Marine Algal Toxins

Similar to freshwater blue–green algae, some estuarine and marine algal species have been found to produce irritants that can cause severe respiratory irritation and severe contact dermatitis. Most of these impacts are derived from dinoflagellates. The toxin found in Lyngbya (blue-green alga) is also known to promote tumours. People who came into contact with Lyngbya (mermaids hair or fire weed) in Queensland reported stinging, burning or itching within minutes of exposure with red swellings and blisters common. Those people prone to asthma or eczema are most sensitive to these contact irritants.

Another species (Pfiesteria piscidia) (a dinoflagellate) caused massive fish kills and devastated local tourism and fishing industries in Chesapeake Bay in USA. It may also cause problems such as skin irritation or cognitive impairment (Estuarine Associated Syndrome) through water or aerosol contact.

To a lesser extent, the non–toxigenic red tide, Trichodesmium erythraeum (blue–green algae) has similar effects as its freshwater counterpart and can cause nausea and respiratory irritation. Another species, Noctiluca scintillans (dinoflagellate), is responsible for the majority of red tides along the east coast of NSW and produces bioluminescence at night but does not produce any toxins. It does however produces high levels of ammonia that could be irritating if concentrated.

Estuarine and marine algae that affect humans through seafood consumption

Apart from algae that may cause problems through direct contact and exposure, the major route for human illness caused by toxic algae is through consumption of seafood and shellfish, as some species of algae produce potent toxins that can accumulate in fish and shellfish. Even low densities of toxic algae may be sufficient to cause illnesses such as paralytic shellfish poisoning (PSP), diarrhetic shellfish poisoning (DSP), amnesic shellfish poisoning (ASP), neurotoxic shellfish poisoning (NSP), azaspiracid poisoning (AZP), and ciguatera fish poisoning (CFP).

PSP can result from eating bivalve shellfish or planktivorous fish, while DSP and ASP are caused by eating shellfish, and ciguatera by eating tropical fish. The toxins cause a variety of gastro–intestinal and neurological symptoms in humans, but not in fish. However another group of toxins (ichthyotxins) selectively kill fish by inhibiting their respiration.
The symptoms of toxin poisoning in humans varies according to the type of toxin produced:

• Amnesic Shellfish Poisoning (ASP): The causative toxin for this affliction is domoic acid and its isomers. Typical symptoms are amnesia (which may last days, if not longer), nausea, vomiting, abdominal cramps, diarrhoea, seizures and disorientation. In severe cases coma may occur followed by death. Species producing this toxin include Pseudo–nitzschia diatoms.
  
  
• Paralytic Shellfish Poisoning (PSP): The causative toxin for this affliction is saxitoxin and its congeners. Symptoms include tingling and numbness of the mouth, tongue and extremities, nausea and vomiting. In severe cases the patient will exhibit more severe neurological symptoms such as ataxia, weakness, dizziness, a sense of dissociation followed by complete paralysis. Death may result from respiratory paralysis. Species producing this toxin include some dinoflagellate species of Alexandrium, Gymnodinium and Pyrodinium. The freshwater blue–green algae Anabaena circinalis also produces this toxin.
  
  
• Diarrhetic Shellfish Poisoing (DSP): The causative toxin for this affliction is okadaic acid and its derivatives. Typical symptoms include vomiting and diarrhoea. This toxin is produced by some species of the dinoflagellates Prorocentrum and Dinophysis .
  
  
• Neurotoxic Shellfish Poisoning (NSP): This affliction is caused by the dinoflagellate toxin brevetoxin. Typical symptoms include tingling, dizziness, fever, chills, muscle pains, nausea, diarrhoea, vomiting, headache, reduced heart rate and pupil dilation, but is never fatal. Species producing this toxin include the dinoflagellate, Gymnodinium breve (ARNAT,2003).
  
  
• Ciguatera Fish Poisoning (CFP): Ciguatera follows consumption of fish that have accumulated, through the food chain, a number of cigatoxin analogues derived from gambiertoxins produced by the benthic dinoflagellate, Gambierdiscus toxicus. This is found in association with coral reefs and as such some coral fish should not be eaten, eg grouper, coral trout, narrow–barred spanish mackeral and maori wrasse. Symptoms included diarrhoea, vomiting, nausea and abdominal pain. Neurological symptoms include numbness and tingling of hands and feet, cold objects feel hot, balance difficulties, low heart rate and blood pressure, rashes. Extreme cases can cause death from respiratory failure.