A study by scientists has found that several fish caught off the South African coastline are contaminated with poisonous levels of mercury that could damage the health of people who regularly eat fish.
Several fish caught off Durban, Cape Town and the West Coast have been found to contain mercury levels well above World Health Organisation (WHO) guidelines, prompting fears for the health of subsistence fishing communities and people who eat fish regularly - particularly pregnant women and children.
Mercury is a highly toxic heavy metal that can cause brain and nerve system damage, birth defects and other health problems, including fever, tremors, mood swings and insomnia.
The study, carried out by researchers from the Council for Scientific and Industrial Research (CSIR) with analytical support from the University of Connecticut in the US, is one of the first attempts to measure mercury pollution in local sea fish and is part of a broader study to measure mercury pollution levels in South African soil, water, animals and the environment.
Several fish were collected and some of the highest mercury levels were found in popular table fish like red romans, silver fish and red panga.
The lead author, Durban-based CSIR researcher Mamopeli Matooane, said the results were preliminary and based on a small sample of fish.
Nevertheless, they suggested that fishing communities along the South African coast were "potentially at risk" if they consumed fish every day, she said.
People who ate fish often should be told about these risks, and further tests should be carried out to check their health status, she said.
The highest levels of mercury were found in samples from False Bay, Cape Town, followed by those from the West Coast and Durban.
The study provides no data for other parts of the KwaZulu-Natal or Eastern Cape coastline.
The highest recorded level was 0.486 micrograms of mercury to a million parts of fish tissue, in a red roman caught in False Bay.
This is more than double the WHO guideline of 0.2 micrograms for vulnerable people.
In Durban, two of the three red roman samples were above the guideline.
In some cases, adults who ate fish daily could be exposed to risks 11 times above guidelines developed by the US Environmental Protection Agency, while the risks were up to 32 times higher among children.
Based on some of these risk calculations, Matooane and her fellow CSIR researchers suggested red roman and red panga fish should not be eaten more than twice a month.
Eating cob, yellowtail and silver fish should be restricted to four meals a month, while white stumpnose and hottentot sea bream should not be eaten more than eight to 12 times a month.
Although mercury levels in mullet, snoek and blueskin seabream were much lower, these fish should not be eaten more than 16 times a month.
Ideally, children should not eat some of these fish more than once a week.
The latest edition of the CSIR journal Sciencescope says mercury contamination in fish is not a problem unique to South Africa and that government agencies in the US have warned that nearly all types of fish and shellfish contain varying levels of methylmercury, a more toxic form of mercury.
"Therefore, one should control one's intake and vulnerable groups like young children and pregnant women should be very careful.
"The best advice would be for consumers to be aware of these risks and to obtain information from advisory groups if they have questions."
The source of the mercury pollution in South African fish is unclear, as there have been very few published studies on mercury contamination levels in the general environment.
This article was originally published on page 1 of The Mercury on January 21, 2010
Several fish caught off Durban, Cape Town and the West Coast have been found to contain mercury levels well above World Health Organisation (WHO) guidelines, prompting fears for the health of subsistence fishing communities and people who eat fish regularly - particularly pregnant women and children.
Mercury is a highly toxic heavy metal that can cause brain and nerve system damage, birth defects and other health problems, including fever, tremors, mood swings and insomnia.
The study, carried out by researchers from the Council for Scientific and Industrial Research (CSIR) with analytical support from the University of Connecticut in the US, is one of the first attempts to measure mercury pollution in local sea fish and is part of a broader study to measure mercury pollution levels in South African soil, water, animals and the environment.
Several fish were collected and some of the highest mercury levels were found in popular table fish like red romans, silver fish and red panga.
The lead author, Durban-based CSIR researcher Mamopeli Matooane, said the results were preliminary and based on a small sample of fish.
Nevertheless, they suggested that fishing communities along the South African coast were "potentially at risk" if they consumed fish every day, she said.
People who ate fish often should be told about these risks, and further tests should be carried out to check their health status, she said.
The highest levels of mercury were found in samples from False Bay, Cape Town, followed by those from the West Coast and Durban.
The study provides no data for other parts of the KwaZulu-Natal or Eastern Cape coastline.
The highest recorded level was 0.486 micrograms of mercury to a million parts of fish tissue, in a red roman caught in False Bay.
This is more than double the WHO guideline of 0.2 micrograms for vulnerable people.
In Durban, two of the three red roman samples were above the guideline.
In some cases, adults who ate fish daily could be exposed to risks 11 times above guidelines developed by the US Environmental Protection Agency, while the risks were up to 32 times higher among children.
Based on some of these risk calculations, Matooane and her fellow CSIR researchers suggested red roman and red panga fish should not be eaten more than twice a month.
Eating cob, yellowtail and silver fish should be restricted to four meals a month, while white stumpnose and hottentot sea bream should not be eaten more than eight to 12 times a month.
Although mercury levels in mullet, snoek and blueskin seabream were much lower, these fish should not be eaten more than 16 times a month.
Ideally, children should not eat some of these fish more than once a week.
The latest edition of the CSIR journal Sciencescope says mercury contamination in fish is not a problem unique to South Africa and that government agencies in the US have warned that nearly all types of fish and shellfish contain varying levels of methylmercury, a more toxic form of mercury.
"Therefore, one should control one's intake and vulnerable groups like young children and pregnant women should be very careful.
"The best advice would be for consumers to be aware of these risks and to obtain information from advisory groups if they have questions."
The source of the mercury pollution in South African fish is unclear, as there have been very few published studies on mercury contamination levels in the general environment.
This article was originally published on page 1 of The Mercury on January 21, 2010
