Dioxins in Foods

What are Dioxins

1. Dioxins are a group of polychlorinated aromatic compounds arising either naturally or as by-products of industrial activities e.g. metal smelting, molding or burning of chlorine-containing organic chemicals such as plastics. It is toxic and stable. Once produced, it tends to persist in the environment and concentrates in the food chain.

2. Different dioxin compounds have different degree of toxicity. Of all types of dioxin-related compounds that have been identified, the most toxic one is 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD).

3. The incidences of some dioxin-related food crisis in overseas countries have raised considerable public attention and concern. Recently, there has also been local media enquiry and questions on the surveillance of dioxins in Hong Kong.

Public Health Significance of Dioxins

1. Dioxins are lipophilic in nature and not easily broken down. They tend to accumulate in fatty tissues and are passed up the food chain from plants to animals to humans. The most significant food items for dioxin contamination are fatty foods such as meat, fish and dairy products.

2. Studies have shown that high exposure to dioxins may cause chloracne and other adverse health effects. Animal studies have also shown an increased risk of cancer from long-term exposure to dioxins.

3. Sources of human exposure to dioxins include food intake, drinking water, air inhalation and skin contact. Dietary intake is by far the most important and accounts for over 90% of dioxins exposure.

Assessment of Dioxins

1. The level of dioxins in food is expressed as toxic equivalence TEQ (unit is picogram (pg)/g TEQ/g or parts per trillion (ppt)).

2. There is no international consensus on standard of dioxin level in food. In Hong Kong, the Food and Environmental Hygiene Department adopts 1.0 ppt as alert level for initiating follow up action in the food surveillance program.

3. To accurately determine the risk of the population due to exposure to dioxins, an exposure assessment needs to be performed. In evaluating dietary exposure to dioxins, one needs to examine the dioxin levels in different food groups and the food consumption pattern of the population. The assessment needs to be performed throughout the lifespan and the average dioxin levels in different kinds of food are used instead of individual results.

4. In terms of health risk, the World Health Organization has recommended the tolerable daily intake (TDI) for dioxins at 1-4 TEQ pg per kilogram of body weight in 1998 (prior to that, the TDI was set at 10 TEQ pg/Kg body weight).

5. TDI is the amount of a toxic substance, expressed on a body weight basis, which an individual may ingest daily over a lifetime without appreciable risk to health. It stresses on lifetime exposure. Occasional short-term exposure above the TDI would have no health consequences provided that the averaged intake over long period is not exceeded.

6. Dietary intake of dioxins is estimated by assessing the average level of dioxins in food and food consumption pattern of the population.

7. Individual food item exceeding alert level of dioxin monitoring does not imply presence of immediate health hazard.

Food Surveillance of Dioxins in Hong Kong

1. Starting from 1999, the Food and Environmental Hygiene Department has been monitoring dioxins in foods.

2. Of the 243 food samples tested since 1999, the results were all satisfactory. The surveillance program will be continued and closely monitored.

3. The Department had recently completed a food consumption study on secondary school students in Hong Kong. The findings in this survey will be used to evaluate the dietary exposure of secondary school students to dioxins. Results of the assessment are expected to be available later this year.

How to reduce the risk of dioxin exposure

1. Prevention of excessive exposure to dioxins should start with environmental control.

2. As dioxins are mainly present in the fatty part of food, lowering fat intake in the diet would be helpful to minimize dietary dioxin exposure. The public is advised to have a balanced diet and healthy lifestyle to stay healthy.