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CSIR limnologist Dr Paul Oberholster. |
In March 2008 Lake Loskop experienced the first ever massive Microcystis sp. Bloom since the construction of the dam in 1937. |
CSIR researchers are predicting an increase in blooms of toxic blue-green algae and subsequent poisoning incidences in South Africa in the near future if current trends in climate change continue. This is due to warmer surface waters being conducive to the formation of these blooms.
The situation is further aggravated by the fact that higher surface water temperatures, combined with heavily polluted waters, could lead to circumstances ideal for mixed and much more lethal toxic blooms - toxins produced by biological organisms can affect both the liver and nerve system.
According to CSIR limnologist, Dr Paul Oberholster, cyanobacterial blooms have become an increasing problem in South Africa, posing a significant threat to the health of animals and humans.
"The massive proliferation of these organisms in rivers and lakes is
largely due to progressive eutrophication. However, a warming trend in
the southern hemisphere, with minimum temperatures increasing three
times faster than maximum temperatures, is likely the cause of the
increasing occurrence of toxic cyanobacterial bloom forming species.
Previously these were hampered by low water temperatures," he explains.
In an article published in the African Journal of Biotechnology, Oberholster together with plant geneticist Prof Anna-Maria Botha from Stellenbosch University, and ecotoxicologist Dr Jan Myburgh from the Faculty of Veterinary Science at the University of Pretoria, provide evidence of a strong positive correlation between the increase in surface water temperature and the increased occurrence of toxic blooms in South Africa's inland water resources even in the winter months.
"The most alarming characteristic of cyanobacteria is the ability of many species to produce a range of extremely potent low-molecular-weight cyanotoxins. These cyanotoxins are grouped according to the target physiological systems, organs, tissues or cells. Cyanotoxins that affect the nervous system are called neurotoxins, while hepatotoxins break down liver cell integrity. Cytotoxins, also known as cellular toxins, cause cell death or damage genetic material, while lipopoly-saccharide (LPS) endotoxins can cause skin, eye and respiratory irritation," they explain in the article.
Concerns over the health risks to humans by these cyanotoxins have prompted the World Health Organization (WHO) to adopt a provisional guideline value for microsytin-LR in drinking water. In the case of South Africa there are guidelines for cyanotoxins in domestic water (only for microcystins) but values are not specified for drinking water guidelines or national drinking water standards.
In South Africa, most drinking water comes from surface waters, where cyanobacteria have been recorded in many, if not most instances. Due to climatic conditions and excessive nutrient loads from agriculture and discharge of treated sewage, Microcystis and Anabaena cyanobacterial genera often dominate the phytoplankton of reservoirs and rivers in the central and northern regions of South Africa.
Oberholster, Botha and Myburgh plead for early warning systems and risk management strategies to be put in place in South Africa.
Prior to 1994, animal deaths due to toxic blooms were largely confined to the central and northern provinces of South Africa.
Since 1994
- 1994 Malmesbury-Darling region: First south-western Cape poisonings occurred in the Malmesbury-Darling region, leading to the death of 3 cattle and poisoning of 29 sheep due to the presence of Nodularia spumigena - recorded for the first time in this area.
- 1996 Kareedouw: massive live stock loss of 290 milk dairy cows and a further 70 animals had to be slaughtered. First record of poisoning due to presence of Oscillatoria sp. in that region.
- 2000 Orange River System: First incidence of fish kills by a bloom of mixed species (Cylindrospermopsis raciborskii, Anabaena sp. and Oscillatoria sp.) in the Orange River system downstream of the confluence with the Harts River in the Northern Cape. This was also the first report on the occurrence of a bloom of Cylindrospermopsis sp. in South Africa, and is of particular concern from a water quality perspective due to its known ability to produce a potent hepatotoxic alkaloid cylindrospermopsin and the neurotoxic PSP toxin (paralytic shellfish poisoning). This freshwater cyanobacteria of tropical origin is not only increasingly found in sub-tropical water bodies, but also in temperate regions.
- July 2005 Kruger National Park - death of wildlife near Lake Nhlanganzwane in the extreme south eastern are of the KNP. Reason for deaths ascribed to cyanobacterial intoxification from a bloom of Microcystis aeruginosa in the lake. A total of 52 carcasses were detected during the winter month of July 2005 (7 white rhinoceros, 2 lions, 2 cheetahs, 9 zebras, 23 wildebeest, 1 hippopotamus, 1 giraffe, 5 buffalo, 1 warthog and 1 Kudu).
- June 2007 Kruger National Park, Lake Nhlanganzwane: another 22 carcasses of white rhinoceros, zebras and wildebeest discovered by rangers. This was the first report of animal mortalities during winter.
- March 2008 Lake Loskop: First ever massive Microcystis sp. bloom since the construction of the dam in 1937.
- July 2008 Tuli block on the border between Botswana and South Africa: Toxic bloom of Oscillatoria sp. caused mortalities of more than 70 Bushbuck and Impalas over a month. This incidence also represent the first ever report of bloom formation and intoxification of animals from this particular cyanobacterial species in this geographical region.
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