A number of cyanophyte species produce potent hepatotoxins or neurotoxins that can be transferred through the food web where they may kill other life forms such as zooplankton, shellfish, fish, birds, marine mammals and humans that feed, either directly or indirectly, on them. Scientists use the term, harmful algal bloom, HAB, to refer to these high density populations that contain toxins or that cause negative impacts. Most toxic marine blooms are caused by algae; toxic freshwater algal blooms are rare. Almost all toxic freshwater blooms are caused by cyanophytes; they also cause many toxic marine blooms.
The very potent toxins produced by many solitary, filamentous or colonial aquatic cyanophytes, are responsible for an increasing number of water-related poisonings of both wildlife and people worldwide since the 1970s. The neurotoxic alkaloids produced by Anabaena flos-aquae and Nodularia spumigena are fatal at 20 micrograms/kilogram body weight; the hepatotoxins of Aphanizomenon flos-aquae and Microcystis aeruginosa are fatal at 9 micrograms/kilogram body weight. These are roughly equivalent to 1/20000 and 1/10000 of an ounce of toxin or about the same potency as cobra venom. Some toxins are tumour promoters and oncogenic in lab animals. They block neuromuscular activity, affect the cardiovascular system and cause lesions on the liver.
Researchers understand much of the biochemistry of many of these toxins once they are consumed or absorbed, but not as much about what causes the microorganisms to produce them and how they can be prevented from flourishing. Pollution with high nutrient runoff, particularly high phosphorus levels, encourages and prolongs the blooms, it also causes blooms to occur in nearshore and estuarine areas where there is the highest chance of contact by people and the most effect on the harvesting of marine resources. However, there are significant economic and political obstacles impeding efforts to clean up polluted, high-nutrient, runoff which contributes to such algal blooms or to enforce adequate drinking water treatment and watershed protection guidelines.
While most blooms kill other marine life by depleting oxygen in the water or producing toxic chemicals, some kill other organisms by starvation. Prawn larvae feeding on Trichodesmium blooms may die from starvation because the algae become the major or only food supply but do not provide sufficient nutrition for larval development. Blooms of the cyanobacterium Trichodesmium are common in tropical and subtropical waters. Few banana prawns, Penaeus merguiensis, reared in enclosures in Albatross Bay on the northern Australian coast, survived during Trichodesmium blooms.
Larvae fed with Trichodesmium in the laboratory did not progress beyond the first stage of their development. Most larvae fed on another green flagellates developed successfully. Trichodesmium filaments were found in the prawns' guts but these were of such poor nutritional value that the prawns starved in the midst of plenty. Quality is more important than quantity. The early feeding stages are feeble swimmers and at the mercy of currents so the type of food they eat depends on chance. In a Trichodesmium bloom, the only food they are likely to find is Trichodesmium. Prawn larvae numbers were lowest during previous summer blooms of Trichodesmium.
A number of species produce toxins which are feeding deterrents, metabolic poisons and lethal toxicants. The microcystins and nodularins produced by Microcystis are the best known examples. Anatoxin is produced by Anabaena and Aphanizomenon.
Table of Cyanophyte Species and Toxin Types
|Anabaena circinalis||PSP-Paralytic Shellfish Poisoning|
Blooms that occur in areas where fish and shellfish are commercially farmed or harvested can result in serious economic losses in several ways.
The direct economic importance of the cyanophytes is considerable and is likely to increase rapidly as the human population of the world expands faster than the conventional sources of protein foodstuffs. It is certain that man's contact with these organisms will increase, and it is probable that their role in human disease either as toxin sources or as cutaneous irritants or sensitizers has been underestimated and unsuspected. While most are never toxic and some species are not toxic most of the time, some species have strains or varieties which are sometimes toxic. This usually occurs under heavy bloom conditions when there are high nutrients, lots of sunshine and warm temperatures in quiet waters.
Many species produce novel compounds that exhibit potent biological activities. These are generally considered to be secondary metabolites, that is, compounds which are not essential to the basic metabolism and growth of the organism, which are present in restricted taxonomic groups. The biosynthesis of secondary metabolites is common in bacteria, as well as in eukaryotic microbes and plants. The roles played by secondary metabolites in the life history of the producing organism are much debated. Many are considered to be chemical defenses, which confer competitive advantage over other microbes or discourage predation by higher trophic level organisms. Others may serve roles in chemical signaling, and yet others have been proposed to be evolutionary relics. The elaborate biosynthetic pathways required to synthesize these compounds, and the observation that genes involved in biosynthesis of a given secondary metabolite are often clustered within the genome, are consistent with the notion that these metabolites do serve a specific and valuable function for the organism.
Among the many secondary metabolites that have been identified, a number are potent toxins responsible for a wide array of human illnesses, marine mammal and bird morbidity and mortality and extensive fish kills. Some species and certain isolated strains of all common planktonic cyanophyte genera have been identified as toxin sources.
The cyanophytes are among the oldest organisms still extant. They have a considerable and increasing economic importance and have both beneficial and harmful effects on human life. They are not algae or bacteria. They have no nucleus, the structure that encloses the DNA, and no chloroplast, the structure that encloses the photosynthetic apparatus, all structures that are evident in eukaryotic true algae. Because they are photosynthetic and aquatic, cyanophytes are often called blue-green algae. This name does not reflect any cladistic relationship between the cyanophytes and other organisms called algae. Cyanophytes are related to the bacteria which have similar biochemical and structural characteristics, not to the eukaryotic algae, and it is only the chloroplasts and mitochondria in eukaryotic algae to which the cyanophytes are related.
The process of nitrogen fixation and the occurrence of gas vesicles are especially important to the success of nuisance species of cyanophytes. They are also important providers of nitrogen fertilizer in the cultivation of rice and beans. The cyanophytes are widely distributed over land and water, often in environments where no other organisms can survive. They are referred to in the literature by various names including Cyanophyta, Myxophyta, Cyanochloronta, Cyanobacteria, blue-green algae and blue-green bacteria.
The majority of cyanophytes are aerobic photo-autotrophs, their life processes require only oxygen, light and inorganic substances. A species of Oscillatoria that is found in mud at the bottom of the Thames River, is able to live anaerobically. They can live in extremes of temperatures -60oC to +85oC, and a few species are halophilic or salt tolerant to as high as 27%, for comparison the concentration of salt in seawater is 3%. They can grow in full sunlight and in almost complete darkness and are often the first organisms to colonize bare areas of rock and soil subsequent to cataclysmic volcanic explosions like Krakatoa, Indonesia in 1883. Unlike eukaryotic organisms, cyanophytes are self-sufficient, they need no substances that have been previously made by other organisms.
At the onset of nitrogen limitation during bloom conditions, certain cells in Anabaena and Aphanizomenon evolve into heterocysts, which convert nitrogen gas into ammonium, which is then distributed to the neighboring cells of a filament. In addition, cyanophytes that form symbiotic, mutually beneficial, relationships with a wide range of other life forms, can convert nitrogen gas into ammonium. At the onset of adverse environmental conditions, some cyanophytes can develop modified cells, called aikinetes which contain large reserves of carbohydrates, and owing to their density and lack of gas vesicles, eventually settle to the lake bottom. They can tolerate adverse conditions such as the complete drying of a pond or cold winter temperatures, and germinate into new juvenile filaments when favorable conditions return. Heterocysts and aikinetes are unique to the cyanophytes.
Cyanophytes are quite small and usually unicellular, though they often grow in colonies large enough to see. They are the oldest known fossils, more than 3.5 billion years old and are one of the oldest and most important groups of organisms on earth. Many Proterozoic oil deposits are the result of cyanophytes. Cyanophytes have also been important in shaping the course of evolution and ecological change throughout earth's history. The oxygen atmosphere that we depend on was generated by numerous cyanophytes during the Archaean and Proterozoic Eras. They were probably the chief primary producers of organic matter and the first organisms to release elemental oxygen, O2 into the primitive atmosphere which was, until then an anaerobic reducing atmosphere, free from O2. Thus cyanophytes were most probably responsible for a major evolutionary transformation leading to the development of aerobic metabolism, the Krebs cycle and abundant energy which made possible the subsequent evolution of highly mobile animals. The other great contribution of the cyanophytes is the origin of plants. The chloroplast with which plants make food for themselves is actually an endosymbiotic cyanophyte living within the plant's cells. Sometime in the late Proterozoic, or in the early Cambrian, cyanophytes began to take up residence within certain eukaryote cells, making food for the eukaryote host in return for a home. This kind of endosymbiosis is also the origin of the eukaryotic mitochondrion.
Cyanophytes are found throughout the world in terrestrial, freshwater and marine habitats. However, it is the freshwater habitat that typically experiences a cyanophyte bloom. Two genera of cyanophytes account for the vast majority of toxic blooms world-wide: Microcystis and Anabaena. Anabaena and Nodularia have been implicated in skin and eye irritations in man and dogs, while Microcystis, Anacystis and Lyngbya have been reported to cause hay fever symptoms, particularly as aerosols. It has been suggested that toxic products released from cyanophytes may be the cause of unexplained forms of human gastro-enteritis. Microcystis aeruginosa, Anabaena circinalis and Nodularia spumigen blooms produce a characteristic pungent, musky or earthy smell. Fish deaths during cyanophyte blooms may be caused by the toxin in the cyanophyte, by the depletion of oxygen in the water, by the liberation of hydrogen sulphide and ammonia caused by cell decomposition or by clogging of the gills.
Their reputation as only a nuisance or noxious is not justified. While periodic blooms are considered a nuisance in recreational lakes and water supply reservoirs of North America, the near continuous blooms of cyanophytes in some tropical lakes are a valuable source of food for humans. Some cyanophyte species make major contributions to the world food supply by naturally fertilizing soils and rice paddies with nitrogen. The introduction of cyanophytes to saline and alkaline soils in India increases the soils' content of nitrogen and organic matter and also their capacity for holding water. This treatment has enabled formerly barren soils to grow crops. The introduction of Tolypothrix tenuis resulted in a 20% increase of the rice crop. A coating of cyanophytes on prairie soil binds the particles of the soil to their mucilage coating, maintains a high water content and reduces erosion.
Humans also harvest and eat Spirulina. It contains all of the amino acids essential for humans and its protein content is high, over 60%. It is a staple food in parts of Africa and Mexico. In China, Taiwan and Japan, several cyanophytes are served as a side dish and are considered a delicacy. Several areas in North America culture and commercially process certain cyanophytes for various food and medicinal products such as vitamins, drug compounds and growth factors.
Heterocystous cyanophytes possess the unique ability to simultaneously evolve O2 by photosynthesis in vegetative cells, and H2 by nitrogenase catalyzed electron transfer to H+ ions in heterocysts, in the absence of N2 or other substrates of nitrogenase. This is the basis for the attempts of several workers to exploit the potential through the development of a bio-photolytic system for solar energy conversion, even though to-date the thermodynamic efficiency has been low.
Nevertheless, the utilization of cyanophytes in food production and in solar energy conversion may hold immense potential for the future, and could be exploited for man's economy. Progress in the study of the genetics of cyanophytes may enable us to manipulate the N2-fixation and associated genes, and produce strains which fix N2, evolve H2 or release ammonia with great efficiency.
The freshwater cyanophyte species are found worldwide and there are reports of toxic outbreaks from Canada, United States, Australia, New Zealand, Japan, China, South Africa and Europe.
Virtually all freshwater blooms are caused by cyanophytes rather than species of algae and all the toxic freshwater blooms are cyanophytes. In a healthy and balanced aquatic ecosystem, cyanophytes are a small but important component of the natural plankton population. Unfortunately, human impact can stimulate massive growth of cyanophytes, and in the worst cases the resulting bloom can turn a lake or river bright green or blue-green and potentially poisonous. The severity of the blooms varies from year to year depending on the climate, blooms tend to be worst in particularly dry summers or during droughts and least severe in wetter summers. Although blooms occur naturally, water bodies which have been enriched with plant nutrients from municipal, industrial or agricultural sources are particularly susceptible to these growths. Water inflow from fertile agricultural land and from sewage or certain industrial wastes encourages cyanophyte growth. Poisoning of livestock attributed to cyanophytes usually occurs during summer and the ponds or lakes involved have been found to be enriched in some way by the inflow of water from arable land or by animal excreta.
Blooms formed by cyanophytes are most common in warm, calm, shallow bodies of water, ponds, reservoirs, sloughs, roadside ditches and other man-made impoundments, where the water is hard, alkaline and rich in nitrogen, phosphates, carbonates and organic matter. Blooms do not normally occur in flowing waters, rivers, streams, springs, irrigation canals or wells. The cyanophytes affect drinking water for humans, livestock and wildlife, the food chain for wildlife and fish, irrigation water, recreational water use where there is immersion or where shellfish, crustaceans or fish are harvested for food and the commercial harvesting of algae and other cyanophytes for the drug and health food trade. Toxic cyanophytes occur in ponds and lakes throughout the world. In Canada blooms occur primarily in the prairie provinces and the Cariboo region of British Columbia. Toxicity has caused the death of cows, dogs and other animals. Although humans ordinarily avoid drinking water that has a bloom or scum, they may be affected by toxic strains when they swim or ski in recreational water bodies during a bloom. Typical symptoms include redness of the skin and itching around the eyes, a sore, red throat, headache, diarrhea, vomiting and nausea.
There are two main types of human activity that stimulate cyanophyte blooms.
Marine outbreaks occur worldwide but usually only cause concern in near-coastal waters when they affect shellfish or fin fish. Ocean warming has combined with nutrient enrichment to create larger, more frequent cyanophyte blooms around the world. Satellite images have confirmed increases in the size and scope of blooms during the 1980s and early 1990s. El Niņo-precipitated events that bring heavier rainfall and regional warming have been associated with the emergence or resurgence of harmful blooms, especially at higher latitudes. Other environmental stresses that encourage blooms include over-harvesting of fish that feed on plankton and destruction of wetlands that filter nitrogen and phosphorus.
The toxic cyanophytes have been grouped as fresh or marine, some genera are listed in both categories. The cyanophytes are ecologically very versatile and are found in many extreme habitats and commensal associations. They are found in estuarine and hyper-saline habitats, in soil associations, in marine, terrestrial and freshwater lithic associations, in associations with the roots and stems of many plants, as plastids in eukaryotic cells and as part of the lichen association. Any simple classification such as fresh or marine will be full of exceptions. Generally, they are responsible for freshwater toxicity blooms but they are also responsible for some marine dermatitis problems. Brackish and estuarine species have been included under marine.Freshwater
Stinging seaweed disease is a skin irritation caused by direct exposure to Lyngbya majuscula. The fine, hair-like, dark-brown seaweed, commonly known as lyngbya, is distributed worldwide. Lyngbya can be found in near-shore waters but only at certain times of the year. You can get stinging seaweed disease by direct exposure to the seaweed while swimming or wading in areas where the seaweed grows. Lyngbya can get under the swimsuit and next to the skin where it produces a rash. It usually, but not always, produces a rash in areas covered by the swimsuit, there have also been outbreaks of stinging seaweed where the rash affected areas of the body not covered by the swimsuit.
The presumptive role of many of these complex toxins, which require a significant investment in cellular machinery and energy expenditure, is as feeding deterrents to prevent or reduce predation by other organisms. Copepods and other macro-zooplankton reduce their grazing rates when they encounter toxic blooms, perhaps as a result of impaired motor control and elevated heart rates. There is no way to tell for sure if water is toxic unless some of it is actually injected into an experimental laboratory animal. Harmless strains of potential toxin-producing cyanophytes look the same as deadly strains under a microscope. A toxin will not give a distinguishing odor, test or color to the water in which it is dissolved. There are two basic kinds of toxins, the milder peptide type is rarely fatal but may produce liver damage and general long term debility while the more potent alkaloid type is usually fatal within a short time. The toxins are complex organic compounds. While the chemical structures of some have been known for many years new ones are still being determined. There is no antidote known to be effective at counteracting the effects of the toxins once they have been ingested.
Paralytic shellfish poisoning, PSP, toxins and domoic acid are naturally occurring marine toxins. Marine animals that filter their food from seawater may accumulate these toxins. The toxins do not appear to directly harm the filter feeders, but people or some predatory animals eating contaminated sea foods may become poisoned. PSP toxins and domoic acid have no taste or odor. There is no visible difference between toxic and safe sea foods. Cleaning sea foods in many cases will not remove the toxins. Cooking does not destroy the toxins.
The common classification of public health problems caused by harmful marine algae and cyanophytes consists of the following syndromes.
The cyanophyte, Microcystis, is known to produce a family of toxins called microcystins or hepatotoxins. They are heptapeptides that primarily affect the liver in animals. Microcystin-LR is a phosphatase inhibitor which will stop or interfere with mitochondrial activity. More recent experimental evidence shows that these toxins may also act as liver tumor promoters in extremely small amounts. A tumor promoter does not initiate cancer formation but helps a previously developed cancer to survive. This type of toxin has been shown to persist in water for a week or more after the bloom has disappeared. Symptoms may take 30 minutes to 24 hours to appear, depending upon the size of the animal affected and the amount of toxic bloom consumed. Microcystin toxicosis may include jaundice, shock, abdominal pain and distention, weakness, nausea and vomiting, severe thirst, rapid and weak pulse and death.
Some cyanophytes found in Australia appear to produce toxic compounds which are not known in other parts of the world. A good example of this is Anabaena circinalis, which is a major bloom-forming species in Australia. This produces nerve toxins known as Paralytic Shellfish Poisons (PSPs), which were previously only known from toxic marine red tide algae.
Microcystins and nodularins have been demonstrated to be liver tumor promotors in laboratory animals. Epidemiological studies of certain areas in China show positive correlation between the presence of microcystin in water supplies and the incidence of human primary liver cancer. Thus, both acute and chronic exposure to cyanophyte hepatotoxins may be significant human health risks. Cyanophyte toxins represent a major source of poisonings due to drinking water contamination and seafood consumption. Most classes of toxins are neurotoxins, while others target protein phosphatases, critical regulators of signal transduction pathways. Most toxins of human health significance are characterized by their high toxic potency and consist of suites of related congeners. The metabolic conversion, bioaccumulation, and food web transfer of toxins are incompletely understood in many cases. These characteristics make the analysis of cyanophyte toxins difficult and the determination of human health risk complex.
These are neurotoxins that result in respiratory arrest and death.
This is one of three major causes of dermatitis produced by Lyngbya majuscula, a worldwide, tropical, filamentous, marine cyanophyte. This toxin is a tumor promoter.
This and other DSP's are phosphatase inhibitors and interfere with the essential process of phosphorylation. These are eukaryotic poisons and do not affect prokaryotes or the plastids in eukaryotic cells. They cause non-fatal gastrointestinal effects.
An alkaloid hepatotoxin generally not fatal. Produced by Aphanizomenon ovalisporum and Cylindrospermopsis raciborskii.
This is one of three major causes of dermatitis produced by Lyngbya majuscula, a worldwide, tropical, filamentous, marine cyanophyte. This toxin is a tumor promoter.
This is a neural toxin and ties up the synapses interfering with nerve impulse transmission. It is also a glutamate antagonist and causes gastrointestinal problems. It may be fatal.
This is trans-1,10-dimethyl-trans-9-decalol, C12H12O. Geosmin is a colorless natural oil, a metabolite produced by several cyanophyte species in varying amounts. The species which seem to produce the most geosmin are Anabaena circinalis, and various straight-chain Anabaena species.
This is one of three major causes of dermatitis produced by Lyngbya majuscula, a worldwide, tropical, filamentous, marine cyanophyte. This toxin is a tumor promoter. Lyngbyatoxin has also been linked to a human fatality due to consumption of sea turtle meat.
This is a gastrointestinal and neurotoxic compound and rarely fatal.
These are protein phosphatase inhibitors and tumour promotors. There are at least 50 different microcystins.
This is a neurotoxin that results in respiratory arrest and death.
These are hepatotoxins.
These are neurotoxins that result in respiratory arrest and death.
If livestock or other domestic animals have no other source of drinking water, they may be poisoned by having to drink water from open water bodies, lakes and ponds, contaminated with toxic strains of cyanophytes, particularly in the interior of British Columbia. In some cases, wind may blow the organisms floating on the surface towards the edge of the shoreline, concentrating them along that part of the shore. Older livestock may wade out into the lake beyond the bloom before they drink and be less affected. Young livestock usually drink closer to the shore and are more likely to be poisoned.
Some cyanophytes release neurotoxins which cause scouring, red urine and sudden death in cattle and sheep. The toxins can also cause liver damage. Surviving animals show photosensitivity, a sunburn that is restricted to white areas of cattle and the nose and ears of sheep. Photosensitivity around the mouth can affect feeding and the condition of stock. Dairy cows and sheep have been observed not to drink water containing toxic algal blooms, resulting in sudden decreases in milk production and deaths. Scouring has also been recorded in poultry, where it leads to a reduction in egg production. Deaths have been recorded in bees and dogs. Dogs are particularly susceptible because scums stick to their coats and are swallowed during licking. When the bloom decomposes, the reduced level of oxygen in the water may cause fish to die. Stranded, sun-dried scums can remain toxic for five months or more, animal deaths have been recorded after eating scums.
Symptoms of poisoning vary in livestock. Sheep poisoned with Nodularia spumigena suffer from difficulty breathing, muscular weakness and may exhibit paralysis or nervous twitching. They may lapse into a coma before dying quietly. Most commonly they are simply found dead near affected water. Post-mortem examination will often reveal pronounced bleeding from the small blood vessels under the skin and between the muscles. Severe liver damage also occurs and this may be detected by the presence of pale areas throughout the liver, or more often by microscopic examination. Some reports of sheep deaths due to Microcystis aeruginosa describe similar effects. Fish are usually found dead or gasping at the surface, sometimes with bleeding throughout the body. It may be difficult to make a confident diagnosis of cyanophyte poisoning, since the clinical signs and post-mortem findings resemble a variety of other diseases. If cyanophyte poisoning is suspected, fence off the water and give stock access to alternative water.
Most freshwater fish kills associated with blooms are generally due to depletion of dissolved oxygen rather than toxicity, although some fish kills resulting directly from toxins have been reported. Human illness, ranging from minor rashes and other allergic reactions to gastroenteritis and even more severe illnesses, is known to result from contact with affected water during recreational activities. The exact causes of human illness and levels of concern for exposure are poorly understood.
A frequently occurring marine swimmers itch is attributed to contact with Lyngbya majuscula, Schizothrix calcicola and Oscillatoria nigroviridis, which are commonly found in tropical and subtropical seawaters. The toxins responsible are lipid-soluble phenolic compounds. Symptoms of stinging seaweed disease caused by Lyngbya majuscula include a red rash similar to a burn, and blister formation with peeling or irritation and itching. Other symptoms include swollen eyes, irritation of the nose and throat, skin sores, headaches and fatigue. The rash frequently appears in the genital and anal areas. In men with genital involvement, swelling of the scrotum is common. Symptoms may begin several minutes to several hours after exposure to the algae and typically last 4 to 48 hours. In more serious cases, skin sores may appear, which can last up to 12 days.
There are a few reports of swimmers with symptoms likely caused by cyanophyte toxins which lasted up to a week. Likely such effects are greatly under reported since people, including physicians, are not aware of the symptoms and do not connect them to the presence of cyanophytes. There are also reports of effects due to ingestion of water with cyanophytes or their toxins. One occurred on Palm Island off the coast of Queensland, Australia and one in Salisbury, Rhodesia, now Harare, Zimbabwe. Both took place while a bloom was in effect or just after it was killed with copper sulphate. In Armdale, Australia, people drinking water from an affected reservoir had elevated levels of certain liver enzymes. An adult man fell into a lake with a heavy bloom of cyanophytes ans swallowed about 250 mL of water. Within several hours he had stomach pains, nausea, vomiting, diarrhea, fever, headache and limb and joint pains which persisted for several days.
In late September Washington State, USA staff responded to a citizen's call about bloom on Lake Sammamish. Not all of the lake was surveyed but an extensive bloom that extended along much of the south shore of the lake was observed and a large bloom was reported on the west side extending about two-thirds of the way up the lake. The swimming area of Lake Sammamish State Park had sufficient cyanophytes to tint the water a bright green and extensive surface film was present at the beach. A grab sample of this surface bloom was collected from within the swimming area of the park and identified as primarily Microcystis aeruginosa which tested positive for toxicity.
In China the high incidence of liver disease in one area was linked to liver toxins in the drinking water contaminated by cyanophytes. The large amount of liver disease that had previously been attributed to alcoholism may actually have been due to microcystins in the water. In Brazil, 26 of 75 kidney dialysis patients were killed in one day when cyanophytes bloomed in the reservoir that supplied the water used in the dialysis machines. A large bloom of Cylindrospermopsis recently caused the closure of one of the main water supplies for the city of Brisbane in Queensland, Australia. One group of British Army recruits were given a day of swimming in full packs and doing rolls in canoes as part of their training, in a lake with a toxic bloom of Microcystis. The soldiers developed blisters on their mouths and suffered vomiting, diarrhea, very sore eyes and in two cases, acute pneumonia.
A toxic strain of the cyanophyte Cylindrospermopsis, which accounts for up to 90 percent of the phytoplankton in Lake Griffin, Florida, is the likely cause in the recent large number of alligator deaths. Two or three alligator deaths a year would be normal, not the 200-plus of recent years. The types of toxins normally associated with Cylindrospermopsis have been hepatotoxins, which affect the liver and kidney, but in the alligator deaths, there has been no indication of the action of hepatotoxins. However, a new study indicated that some forms of Cylindrospermopsis produce a neurotoxin which would be consistent with the alligator deaths occurring in the lake.
Initial examinations of the alligators revealed nothing unusual; they didn't exhibit the liver problems usually associated with any of the known Cylindrospermopsis toxins. After a very extensive examination all of their internal organs and systems appeared to be normal and their blood values were similar to those reported for other alligators. However, more testing revealed other problems. The alligators were found to have neural impairments Their nerve conduction velocity was about half of normal alligators. Many of them had microscopic signs of damage to their peripheral nerves and they had lesions in their brains. It is difficult to establish exactly how long the cyanophyte has been in Florida, but it has become a major feature of the plankton community of Lake Griffin for more than five years. In recent years, it has become very abundant in the 9,000-acre lake.
Microcystis occurs widely in Australia and has caused many cases of livestock poisoning in New South Wales and Victoria. The other common cyanophyte in the rivers and lakes of the Murray-Darling Basin is Anabaena circinalis which was the cause of the big Darling River bloom in 1990-1991. Many sheep and cattle died along the river and samples of the Anabaena from the water have since been found to contain the same paralytic poisons that are present in shellfish PSP toxicity. In the 1970's Cylindrospermopsis occurred seasonally in Solomon Dam on Palm Island off Queensland, Australia in large quantities. On one occasion in 1979 the reservoir was treated by the supply authority with copper sulphate to kill the 'algae' which, upon death, released their endotoxins into the water. A week later about 150 people drinking from the water supply became ill, and many ended up in the hospital. They showed evidence of gastrointestinal, liver and kidney damage, with no evidence of any causative virus or other pathogen.
Dermatitis and Allergies
In addition to toxins many cyanophytes are allergenic or cause dermatitis in some people. The genera of cyanophytes which have so far proved to be of interest to the dermatologist are Microcystis, Anabaena and Lyngbya.
Phycocyanin in cyanophytes has been suspected of allergenicity on the basis of patch tests. A toxic compound which may play some part in causing dermatitis has been isolated. A hepatotoxic and photosensitizing substance is present in Microcystis and other water-blooms. Four clinical dermatitis syndromes have been attributed to the effects of cyanophytes. An eruption on areas of skin not protected by a bathing costume was reported in a child who had been swimming in a lake with a bloom of cyanophytes. Patch tests to Anabaena were positive. Another cyanophyte, Lyngbya majuscula, causes sea-bather's dermatitis in Hawaii. The dermatitis may effect only skin covered by a tight fitting bathing suit. Cyanophytes of various genera produced toxic or allergic dermatitis in Czechoslovakia. Cyanophytes are responsible for seasonal rhinitis, related to swimming in lakes. Many cyanophytes and green algae are airborne in significant numbers at certain seasons.
The greatest risk in fresh water is to small children and pets which require a smaller dose of the toxin to be harmful. Local residents and visitors should be cautioned to keep children and pets out of any area containing a bloom until the bloom has disappeared completely. The greatest human risk in marine waters, apart from eating contaminated shellfish, is probably from inhalation of aerosols. There are periodic extensive marine mammal losses as toxins accumulate up the food chain.
The risks to humans from eating fish and other animals from contaminated waters are difficult to quantify but are potentially significant. Freshwater mussels, for example, accumulate sufficient PSP toxins within five days of feeding on Anabaena to exceed national food guidelines for contaminated shellfish. Mussels form a significant part of the diet for indigenous people, especially during some traditional feasts and celebrations. Freshwater fish are also suspected to accumulate algal and cyanophyte toxins and it is the practice to recommend that the organs of fish not be eaten if the fish were caught from areas where blooms occur. In addition, the increasing popularity of native fish and crustaceans for aquaculture production may further enhance the exposure risk of human consumers.
Risk profiles for cyanophyte toxin contamination need to be established for several primary industries. Examples are the dairy industry, the grape and wine industry and the vegetable industry, with leafy vegetables such as lettuce being special problems since contaminated water can collect between the leaves. We do know that many toxins are extremely persistent in the environment, often being resistant to chemical or bacterial degradation. Preliminary investigations have shown that some toxins persist for more than a week on irrigated pasture grass.
The mode of irrigation and the type of crop being irrigated may also affect toxin persistence. For example flood irrigation of grapes may not cause any problems because the fruit does not come into direct contact with the cyanophytes and water. However, spray irrigation may lead to direct contact between water and fruit and it is possible that the toxic cyanophytes will dry on the grape surface. It is unknown which plants actually take up the toxins. However, it is known that some toxins persist in dried form for several months.
With the necessity for high stocking densities and high irrigation frequency, particularly in the dairy and beef industries, there is sufficient opportunity for toxins to be accumulated by stock and dairy animals. Toxins are known to accumulate in some aquatic invertebrates, zooplankton and mussels, and in marine mammals; therefore it is reasonable to assume that toxins may also accumulate in agricultural stock.
Concerns about cyanophyte toxins contaminating eggs and carcasses in intensive poultry farms have led to the extensive use of environmentally undesirable pesticides to control blooms in farm water supplies. Freshwater aquaculture is also at risk from cyanophytes since little or no monitoring for toxins is conducted routinely. Even recreational anglers are now concerned about possible toxin residues in fish.
Any chemical residue scare could highlight the potential vulnerability of Canadian agriculture to the international perception that our products might be contaminated by toxic chemicals. There need be no actual health risk to consumers, the mere perception that toxins are present in food, at any level, is enough to damage major export markets. We must undertake the necessary work to ensure that the quality control of agricultural produce can be maintained. The science base is available to provide the actual extent of health risks, possible pathways of toxin accumulation and options for reducing the risk of contamination. In addition, appropriate research would lead to adequate testing for toxins in the routine produce surveys that are already standard procedure.
In rivers and lakes the natural food chain consists of primary producers, mostly cyanophytes and algae, micro-crustaceans, Daphnia, small fish and large fish. Algae and cyanophytes are consumed by the micro-crustaceans, which in turn are consumed by the small fish, which themselves are eaten by larger fish. In addition there are filter-feeding animals such as freshwater mussels that may consume the cyanophytes directly, and animals such as native water rats that eat the mussels. Bacteria and protozoa also play an important role in the functioning of a healthy aquatic food chain.
Laboratory trials have shown that micro-crustaceans and mussels can accumulate cyanophyte toxins. We do not known how much toxin is accumulated under natural conditions in freshwater habitats, and what effects these toxins have on the organisms along the food chain. The potential effects may be subtle, perhaps only a small reduction in growth rate, brood size or body weight. However, in a complex and dynamic natural ecosystem even small changes can be sufficient to cause a major decline in the survival of sensitive species. Laboratory studies have shown that the feeding rate and vigour of freshwater mussels is reduced when they are fed exclusively on a diet of toxic algae or cyanophytes. The same deleterious effects could occur in the natural environment; for instance, during a bloom, a single species of cyanophyte can represent more than 95% of the total biomass.
Shifts in aquatic community structure caused by cyanophyte toxins may already be occurring. We have simply lacked the means or resources to identify them or their impacts on the health of our waterways. It is even possible that toxic algae and cyanophytes have impacted sufficiently on our rivers and lakes to have stimulated or assisted in the decline of native fish.
Microcystis, a cyanophyte that is harmful to humans and deadly to plants and fish has returned to a small area of western Lake Erie after a 10-year absence. Researchers are examining whether the reappearance of Microcystis might be associated with the recent arrival of zebra mussels in 1986. It was discovered that high phosphorus levels in Lake Erie, caused by fertilizers, laundry detergent and human sewage caused the large outbreak in the 1970s. Phosphorus is one of the most vital nutrients for Microcystis growth and as a result millions of dollars were spent to control the Microcystis by reducing phosphorus levels in Lake Erie. By the late 1980s, the blooms had ceased. So a Microcystis outbreak in 1995 caught many people by surprise.
The re-occurrence of Microcystis could be due to a change in phosphorus levels or it could be due to the possibility that the zebra mussels are recycling phosphorus faster. Zebra mussels are using the phosphorus over and over again so a little bit goes a long way. Small changes in the re-use of phosphorus can make it much more available. The zebra mussels may be impacting Microcystis blooms in two ways, recycling nutrients that normally would have spent more time in sediment, provides more available phosphorus for further growth and the mussels remove Microcystis from water columns in pseudo-feces, which are more readily accessed by bottom dwellers, which are in turn eaten by fish. This possibility would provide the Microcystis with better access to the food chain. If zebra mussels are responsible for the blooms of Microcystis we could expect the blooms to become more frequent.
While conventional water treatment does not remove or inactivate cyanophyte toxins, activated carbon filtration does. Ozone will oxidize microcystin-LR very rapidly. The cyanophytes can be removed from the water by filtration and should be removed before they enter the disinfection stage of water treatment. Killing the cyanophytes with chlorine, heat, mechanical disruption or any other process causes them to lyse and release their endotoxins into the water supply. Using copper sulphate in the source water also causes release of the toxins and the copper itself is toxic to benthic organisms. Lime may sediment the cyanophytes, along with the phosphorus, without releasing the toxins.
Reducing nutrient concentrations, particularly phosphorus, in runoff to rivers may reduce nearshore and estuarine blooms or reduce their severity. Any nutrient reduction programs should be designed for entire watersheds, a process that has worked effectively in the Chesapeake Bay region.
To address transport of exotic species in ballast water, including harmful cyanophytes, a 1995 international agreement called the Jakarta Mandate encourages ships to dump ballast water from the previous port at sea and then replace it with offshore ocean water. Organisms from the open ocean are unlikely to survive when discharged into estuaries. The United States has similar guidelines. In 1990 Congress passed a law requiring ships to dump ballast water before they enter the Great Lakes. In 1996 Congress passed a law that establishes voluntary guidelines on ballast for ships that enter all US waters. After three years, if voluntary compliance is inadequate to address the problems, then the ballast guidelines will be made mandatory.
Mussels are very dangerous because people eat the entire mussel including the viscera.
Dermatitis and Allergies
Dermatitis and Allergies
Neurotoxins produced by cyanophytes include the saxitoxins and anatoxins. Saxitoxins have been identified in Aphanizomenon flos-aquae in New Hampshire, USA. An extensive bloom of Anabaena circinalis in southern Australia in 1991, which resulted in significant numbers of animal deaths, was found to contain saxitoxin. Several PSP toxins were found in Lyngbya wollei from Alabama. including decarbamoyl saxitoxins and six new saxitoxin derivatives. No human intoxications from cyanophyte saxitoxins have been reported.
Anatoxin produced by certain strains of Anabaena flos-aquae, Aphanizomenon flos-aquae and Oscillatoria is a potent agonist for the nicotinic acetylcholine receptor which causes a depolarizing neuromuscular block. Toxic symptoms include staggering, gasping, convulsions and death due to respiratory paralysis. As with many of the other cyanophyte toxins no antidote is available. One anatoxin produced by certain other strains of Anabaena, is an organophosphate inhibitor of acetylcholinesterase shown to be responsible for intoxication of domestic animals. Toxic symptoms include hypersalivation, ataxia, diarrhea, tremors, dyspnea and cyanosis.
The hepatotoxins produced by cyanophytes include the cyclic peptide toxins, microcystins and nodularins. Microcystins are produced by certain species and certain strains within these species belonging to the genera Microcystis, Anabaena, Nodularia, Nostoc and Oscillatoria. At least fifty-two microcystin analogues are known. Nodularin is produced by certain strains of Nodularia spumigena. Cyclic peptide toxins are synthesized through a non-ribosomal thio-template mechanism.
Microcystins and nodularins are inhibitors of serine/threonine protein phosphatases. Both the cyanophyte cyclic peptide toxins and the dinoflagellate-derived protein phosphatase inhibitor, okadaic acid, bind to the catalytic sub-unit of the protein phosphatases. X-ray crystal structures, molecular modeling and mutational analyses indicate that all three toxin classes bind to the same site. However, unlike the other toxin classes, the microcystins form covalent adducts with Cys273 in the enzyme subsequent to binding.
Unlike okadaic acid and the diarrhetic toxins the microcystins and nodularins are highly selective for liver protein phosphatases. Their selective activity is conferred by their membrane impermeability to most cell types, and their specific uptake in liver cells through the bile acid transport pathway. Toxicity is mediated by the depolymerization of the actin and microtubule cytoskeleton resulting in intra-hepatic hemorrhage within hours and death induced by hypovolemic shock. Microcystins were found to be the causative agent in an 1996 outbreak in which 26 out of 75 patients died of liver failure at a hemodialysis clinic in Caruaru, Brazil which drew its water from a contaminated reservoir. Microcystin is also implicated in net pen liver disease in pen reared salmon.
There is an extensive bibliography on this topic at the following website. http://www.chbr.noaa.gov/CoastalResearch/DiversityEssay.htm.