Dioxins in Foods
What are Dioxins
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.
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).
Some dioxin-related food crises occurred in overseas countries have raised considerable public attention and concern. In Hong Kong , the situation of dioxins in foods has been closely monitored by the Food and Environmental Hygiene Department.
Public Health Significance of Dioxins
- Dioxins dissolve in fat in nature and are not easily broken down. They tend to accumulate in fatty tissues and are passed up the food chain from plants to animals to humans.
- 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. Fatty foods such as meat, poultry, seafood, milk, egg and their products are the major dietary sources of dioxins.
- Accidental exposure to large amount of dioxins could lead to the development of chloracne, a skin condition, excessive body hair and other skin lesions such as skin rashes and skin discolouration. The International Agency for Research on Cancer (IARC) has classified the TCDD congener as human carcinogen. Long-term exposure to dioxins is linked to impairment of the immune system, reproductive function, endocrine system and the developing nervous system. Associations with diabetes, thyroid dysfunction and heart diseases in humans have been reported in some studies.
Assessment of Dioxins
- The level of dioxins in food is expressed as toxic equivalent TEQ (unit is picogram (pg) TEQ per gram or parts per trillion (ppt)).
- There is no international consensus on standard of dioxin level in food. In Hong Kong , the Food and Environmental Hygiene Department initiates follow up action for foods found to contain high levels of dioxins in the food surveillance program.
- 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 items and the food consumption amount in the population.
- The World Health Organization (WHO) has set a tolerable daily intake (TDI) for dioxins and dioxin-like compounds at a range of 1 - 4 pg TEQ per kilogram of body weight (bw) per day in 1998. WHO also stressed that the upper range of the TDI of 4 pg TEQ/ kg bw/ day should be considered as a maximal tolerable intake on a provisional basis and that the ultimate goal is to reduce human intake levels below 1 pg TEQ/ kg bw/ day.
- Following a further evaluation carried out in 2001, the Joint Food and Agriculture Organization / World Health Organization Expert Committee on Food Additives (JECFA) concluded that, in view of their long half-lives, tolerable intakes for dioxins and dioxin-like compounds should be expressed as a monthly value and allocated a Provisional Tolerable Monthly Intake (PTMI) of 70 pg WHO-TEQ/ kg bw per month.
- PTMI is the amount of a toxic substance, expressed on a body weight basis, which an individual may ingest monthly over a lifetime without appreciable risk to health. It stresses on lifetime exposure. Occasional short-term exposure above the PTMI would have no health consequences provided that the average intake over long period is not exceeded.
- Dietary intake of dioxins is estimated by assessing the level of dioxins in food and food consumption pattern of the population. The estimated dioxins intake is then compared with the PTMI established by JECFA to assess the associated health risk.
- Individual food item exceeding action level of dioxin monitoring does not imply presence of immediate health hazard.
Food Surveillance of Dioxins in Hong Kong
- Starting from 1999, the Food and Environmental Hygiene Department has been monitoring dioxins in foods.
- Of the 330 food samples tested from the year 2006 to April 2008, the results were all satisfactory. The surveillance program will be continued and closely monitored.
How to reduce the risk of dioxin exposure
- Prevention of excessive exposure to dioxins should start with environmental control.
- As dioxins are mainly present in the fatty part of food, consuming low-fat products, trimming fat from meat and meat products, reducing the amount of animal fat used in food preparation and using cooking methods that reduce fat (e.g. broiling, baking) are useful measures to minimise dietary dioxin exposure.
- The public is advised to maintain a balanced diet so as to avoid excessive exposure to contaminants from a small range of food items
Risk Assessment Section
Centre for Food Safety