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).
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
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.
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.
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
The
level of dioxins in food is expressed as toxic
equivalence TEQ (unit is picogram (pg)/g TEQ/g
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 adopts 1.0
ppt as alert level for initiating follow up action
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 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.
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).
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.
Dietary intake of dioxins is estimated by assessing
the average level of dioxins in food and food
consumption pattern of the population.
Individual
food item exceeding alert 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 243 food samples tested since 1999, the
results were all satisfactory. The surveillance
program will be continued and closely monitored.
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
Prevention of excessive exposure to dioxins should
start with environmental control.
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.
Last
review date: 19-01-2005