CFS announces First Hong Kong Total Diet Study findings on metallic contaminants

The dietary exposure of the local population to seven commonly encountered metallic contaminants (namely aluminium, antimony, cadmium, lead, methylmercury (a type of mercury), nickel and tin) was found to be low, thus unlikely to threaten the health of the general public, according to the fifth report of the First Hong Kong Total Diet Study released by the Centre for Food Safety (CFS) today (January 11).

Nevertheless, the CFS advised pregnant women and other susceptible groups being affected by methylmercury to avoid eating large predatory fish and other fish which may contain high levels of methylmercury.

"Metallic contaminants found in the environment may exist naturally or as the product of human activities (e.g. industrial activities). They are often found in foods in trace amounts. For ordinary adults, the diet is the main source of exposure to metallic contaminants. As these contaminants may accumulate in the human body and cause organ damage, their chronic toxicity is of particular concern," a spokesman for the CFS said.

The current study revealed that the estimated dietary exposures of the local population, including high consumers, to the seven metallic contaminants analysed were unlikely to pose unacceptable health risks, given that all were below their respective health-based guidance values, he noted.

According to the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA), exposure up to 3.3 µg/kg body weight/week of methylmercury would not pose health risks to the average adult. However, pregnant women have to observe a more stringent provisional tolerable weekly intake (PTWI), i.e. 1.6 µg/kg body weight/week, in order to protect the embryo and foetus.

"About 11 per cent of women within the childbearing age (i.e. between 20 and 49) had dietary exposure to methylmercury exceeding the more stringent PTWI," the spokesman said.

Methylmercury is more toxic than mercury and may cause toxicity to nerves. For the aforesaid 11 per cent of women within the childbearing age, their exposure to methylmercury through dietary intake would not pose health risks to themselves. Nevertheless, methylmercury present in their body may adversely affect a baby's growing brain by crossing the placenta into the foetus and accumulate in the foetal brain and other tissues, if they are pregnant.

"Fish and other seafood are the major dietary source of methylmercury exposure in humans. Cooking cannot reduce the level of methylmercury in food," the spokesman said.

In streams, lakes and oceans, mercury may be transformed by bacteria into methylmercury, which is readily taken up by living organisms and passed along the microscopic plants and animals to larger organisms via the food chain. It may accumulate in fish and binds tightly to the protein in fish tissues. Large predatory fish usually contain higher levels of methylmercury.

To minimise the health risks posed by metallic contaminants, the spokesman reminded the public to maintain a balanced and varied diet. Pregnant women, women planning pregnancy and young children (which are groups particularly susceptible to the adverse effects of methylmercury) should avoid eating large predatory fish and the types of fish which may contain high levels of methylmercury, for example, tuna, alfonsino, shark, swordfish, marlin, orange roughy and king mackerel. He said that the level of methylmercury in most fish is low, especially fish that are smaller in size. Besides, fish contain many essential nutrients, such as omega-3 fatty acids and high-quality proteins. Therefore, moderate consumption of a variety of fish is recommended.

He reminded the trade to observe good agricultural and manufacturing practices to minimise metallic contamination of foods. The trade should also obtain food supplies from reliable sources and maintain a good recording system in accordance with the Food Safety Ordinance (Cap. 612) to allow source tracing if needed.

The First Hong Kong Total Diet Study was launched in March 2010 and will be completed in 2014. This is the fifth report in the series. The first four reports that have hitherto been released cover the following substances: dioxins and dioxin-like polychlorinated biphenyls (PCBs), inorganic arsenic, polybrominated diphenyl ethers and pesticide residues.

The Study aims to estimate the dietary exposure of the general population and various population subgroups to a range of substances, including contaminants and nutrients, and to assess any associated health risks. It focuses on the total diet of the population rather than individual foods.

A total of 150 food items were chosen for the study according to the food consumption patterns of the Hong Kong population. They are being used for testing the levels of over 130 substances, including pesticide residues, persistent organic pollutants, metallic contaminants, mycotoxins, macro nutrients and elements. By combining the test results with food consumption data, the dietary exposure of the population to those selected substances may then be estimated.

The full report on the metallic contaminants study is available on the CFS' webpage at Results concerning other substances will be released in phases.

Ends/Friday, January 11, 2013
Issued at HKT 15:37