Nutritionists have extolled the virtues of seafood for decades, recommending everyone eat fish at least twice a week. Thursday, however, a group of scientists added a cautionary note.

Eating too much fish over a long period of time may lead to mercury poisoning, which can cause brain damage and other physiological dysfunctions, said the experts.

"This is a result of environmental pollution. The mercury comes mostly from the combustion of coal, in the process of which particles of mercury are re-emitted to the air and later brought down to the sea by rain. After being organized in the sea, the fish are condemned to carry the substance," explained Samuel C. L. Lo, professor and associate head of the Department of Applied Biology and Chemical Technology of the Hong Kong Polytechnic University.

Professor Lo has worked with a team to conduct an experiment on mice, chronically exposed to low dosages of methyl-mercury, an organized morpha of mercury and an environmental contaminant commonly found in seafood.

The team discovered that the cerebellum had accumulated the highest amount of mercury, leading to failure to maintain equilibrium.

The experiment also found the presence of proteins that are related to neurotransmitters and energy metabolism had been reduced by half. That leads to possible motor difficulties, numbness on the skin, and lack of energy.

There has no been solid evidence for the same reaction in the human body. But the concern is bound to exist, as methyl-mercury cannot be decomposed or excreted.

According to the World Health Organization, there are about one billion people around the world who eat fish in their daily diet.

A study by the organization also found higher amounts of mercury inside the hair of those who eat lots of fish, while another study showed that babies who are just born were also found mercury in their bodies if the mothers carry them.

Yet nor did the scientists suggest people stop consuming fish, which offers rich nutrition that is good for cardiovascular health and growth of the brain.

Dr Leung Ka-sing, former under secretary for Food and Health, cited the international standard of the highest amount of methyl-mercury that can be tolerated in human body, and said only those who consume fish every meal for around 30 years will reach that critical level.

"I don't think eating fish is a problem. I eat it almost every day," said 76-year-old Lau Pui-ying, adding that she has diabetes and high blood pressure and was advised not to eat too much meat such as pork and beef.

A 55-year-old man surnamed Cheung who enjoys fresh-water fish said he might reduce the consumption of fish responding to the findings.

However, a balanced diet is highly recommended. People who love fish are advised to concentrate on fish that are lower on the food chain, such as grey mullets, salmon, mandarin fish, mud carps and so on. Tuna fish and sharks might contain higher percentages of methyl-mercury, as specified on the website of the Centre for Food Safety. (http://www.cfs.gov.hk/eindex.html)

China Daily

(HK Edition 03/04/2011 page1)