Hongkongers have been unknowingly eating potentially carcinogenic inorganic arsenic in their daily meals.
According to a new study, the intake has come mainly from eating rice, but the good news is that it is still below a safe threshold.
The study by the Centre for Food Safety found the dietary exposure to inorganic arsenic for those with an average food intake was 0.22 micrograms per kg of body weight per day, while those with a high intake ingested 0.38 mcg per kg of body weight per day.
This was well below the 3.0 mcg per kg of body weight per day that would cause a slight increase in cancer incidence.
Arsenic is a metalloid that occurs in inorganic and organic forms and is natural to the environment. Inorganic arsenic may cause cancer, skin lesions, cardiovascular disease, neurotoxicity and diabetes.
The study found that absorption of low levels of the toxin may be unavoidable. It tested 600 composite food samples and found 51 per cent to contain the substance.
The highest levels were found in eggs and their products, with a mean measurement of 23 mcg per kg. This was followed by fish, seafood and their products, with a mean of 15 mcg per kg, and vegetables and their products with a mean of 9 mcg per kg.
In the whole-food sample tests, water spinach contained the highest level of inorganic arsenic, with a mean measurement of 74 mcg per kg, followed by salted egg and oysters, both with a mean measurement of 58 mcg per kg.
However, the study said rice was the major contributor of dietary exposure to the chemical in the local population, with cooked white rice alone accounting for 45.2 per cent of total exposure.
The findings were consistent with data reported in other Asian countries, where rice is a staple food.
Cereals and their products in general were also the main dietary source of inorganic arsenic for Hongkongers, contributing 53.5 per cent of the total exposure. Similar findings were seen in other regions, including Britain and the mainland, according to the study.
The study said the findings had fallen within the middle range of levels found in other countries or regions, so had provided no grounds to suggest changes in traditional healthy-eating advice: to keep a balanced and varied diet, and to include cereals as the major dietary source.
Individuals who wanted to cut exposure to the toxin might skip rice and choose other cereals, which generally contain lower levels of the toxin. Washing rice thoroughly was another option.
The report is the second in the first Hong Kong Total Diet Study series, launched in March 2010. It will examine more than 130 contaminants and nutrients in 150 selected food items and will be completed in 2014.
The number of food contaminants and nutrients being examined in the ongoing study of the city's diet, which wraps up in 2014