Rock oysters growing along the Taiwan nation’s west coast have been found to contain alarming levels of heavy metals, with the highest concentration of the toxic substances detected in molluscs from the environmental activist Huang Chun-nan., environmental groups and legislators said yesterday.
He first realized there might be a problem when he was collecting data on the nation’s western coastline and noticed a large number of abnormally colored wild rock oysters, prompting him to launch the survey with the help of the groups and a professor.The surveyors collected 20 to 30 wild rock oysters from 42 river mouths along the west coast, but due to budget constraints could only send samples from 14 locations for testing.
Intertek Testing Services analyzed the samples for the presence of 12 types of heavy metals, in line with the Food and Drug Administration’s standard testing method, and the results showed that the rock oysters collected near Taoyuan industrial park had the highest levels of lead, copper, zinc and iron among the molluscs tested, as well as the second or third-highest concentrations of nickel, cadmium, mercury and gallium.
National Taiwan University Institute of Occupational Medicine and Industrial Hygiene professor Dr. Wu said the mollusc samples from industrial park had about 1.4 times as much copper and 2.45 times as much zinc as the infamous “green oysters” found in 1998. Those molluscs’ arresting coloring was the result of the copper wastewater discharged in rivers by the electronics industry. Based on the WHO and the Food and Agriculture Organization’s acceptable daily intake of heavy metals, and used by the US and Canada to calculate the health risks of eating wild rock oysters, only the oysters inhabiting) in Greater Tainan can be eaten. The daily intake guidelines are based on a person weighing about 60kg eating 50g of the oysters a day.
Wu said that nine of the locations that the groups took oysters from were near the Environmental Protection Administration’s river water quality monitoring stations, which he said was puzzling because nearly all the heavy metals tests carried out by the stations over the past decade found the toxicity levels of the water in these areas to be acceptable, but the survey results showed that about 93 percent of the molluscs the groups took from those sites were inedible.
He said one possible explanation is that the agency tests the water only once per season and heavy metals can easily be diluted or swept into the ocean, but those that do not, can accumulate in the bottom layers of mud in a body of water, thereby contaminating the aquatic animals that live there.
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