Q. 1 Why did we need to conduct TDS?
A. 1 TDS has been recognised internationally as the most cost effective way to estimate dietary exposures to food chemicals or nutrients for a range of population groups and to assess the health risks of specific chemicals or nutrients. Previous local risk assessment studies conducted by the Food and Environmental Hygiene Department were focused on individual food hazards and applicable only to secondary school students. With the availability of the Hong Kong Population-based Food Consumption Survey (FCS), dietary exposure studies can be expanded by incorporating a TDS approach, which can be used to obtain more comprehensive and accurate estimation of dietary exposures of the Hong Kong population to a range of substances including contaminants and nutrients in one study.
Q. 2 Which countries have conducted TDS?
A. 2 International authorities such as the World Health Organization (WHO), encourage countries to undertake TDS. Since 1960s,various countries, such as the UK , the USA , Canada , Australia , New Zealand and Mainland China , have been conducting their own TDS. The approaches and methodologies for conducting TDS vary from country to country.
Q. 3 How was the plan for the first Hong Kong TDS (1st HKTDS) developed?
A. 3 A Task Force on TDS consisting of colleagues from the Department of Health, the Government Laboratory and the CFS had been formed to formulate the plan and monitor the progress of the 1st HKTDS.
Q. 4 When was the 1st HKTDS started? How were the TDS reports published?
A. 4 The fieldwork on sampling and food preparation of the 1st HKTDS was commenced in March 2010 and ended in February 2011. The whole exercise including laboratory analysis and report writing was completed in December 2014. The reports were published in phases .
Q. 5 What is a TDS food list?
A. 5 For the TDS food list, food items are selected based on the consumption pattern of the Hong Kong population. Individual food items can represent groups of similar items while the whole TDS food list can represent the major components of the diet of the Hong Kong population. Taking into account time constraint and resources, a total of 150 food items were included in the TDS food list of the 1st HKTDS. Sampling and laboratory analysis were only conducted on these 150 food items.
Q. 6 Which types of substances were tested in the 1st HKTDS?
A. 6 Over one hundred of substances were tested in the 1st HKTDS. The substances tested include persistent organic pollutants (POPs), pesticide residues, heavy metals, processing contaminants, mycotoxins and nutrients. Laboratory analysis was mainly performed by the Food Research Laboratory (FRL) of the CFS.
Q. 7 Why did the 1st HKTDS not cover veterinary drug residues, in which some of them such as nitrofurans and malachite green have aroused public concern?
A. 7 Due to limited resources, substances included in the 1st HKTDS had to be prioritised. Although several veterinary drug residues had been considered during the process of selection, these substances had not been ranked with high priority. Furthermore, some veterinary drug residues such as nitrofurans and malachite green are not permitted to be present in food in Hong Kong, and thus they are not expected to be widely spread over the whole diet. Nevertheless, they have been monitored under the routine food surveillance programme, and so far, their levels detected in food are of low human health concern upon normal consumption.
Q. 8 Why did the 1st HKTDS not cover food additives?
A. 8 Various food additives had been considered during selection of substances tested and only sulphites had been ranked with high priority. However, when developing TDS food list, factors for consideration were different for food additives and contaminants, and different sets of mapping table may also be required for dietary exposure. Due to time constraint and resource implication, the 1st HKTDS only covered contaminants and nutrients. Food additives including sulphites were not covered.
Q. 9 Which population groups were covered by the 1st HKTDS?
A. 9

The food consumption data of Hong Kong people aged 20 - 84 captured by the FCS was used for the 1st HKTDS.

As such, the 1st HKTDS can only estimate dietary exposures for average and high consumers of the Hong Kong people aged 20 – 84, as well as various population sub-groups as listed below:

  • Adult males aged 20 – 29 years, 30 – 39 years, 40 – 49 years, 50 – 59 years, 60 – 69 years and 70 – 84 years, respectively;
  • Adult females aged 20 – 29 years, 30 – 39 years, 40 – 49 years, 50 – 59 years, 60 – 69 years and 70 – 84 years, respectively.
Q. 10 How are dietary exposures conducted?
A. 10

The TDS food items were mapped with the related food items available in the FCS as far as possible. Analytical results of concerned substances in the TDS food items were then assigned to the mapped food items in the FCS accordingly.

Dietary exposure to a substance of an individual was estimated by summing over the products of substance levels in various mapped food items and the amounts of food consumed by an individual. Dietary exposures of average and high consumers of the Hong Kong population, as well as various population sub-groups were then estimated.

Finally dietary exposures estimated were compared to the relevant safety reference for the substances of concern or the nutritional reference values for the nutrient of concern to assess the associated health risks.

Q.11 What was the coverage of the diet of the population after food mapping?
A. 11

The TDS food list included 150 food items which represented 88% of the average diet of the population. After food mapping, over 99% of the average diet of the population would be included in the dietary exposure estimation .
For some substances such as dioxins and mycotoxins, not all 150 food items were tested, having taken into consideration their occurrence in the foods, hence it would affect the coverage of the diet of the population. 

For examples, only 71 food items (mainly food of animal origin and their products, fat and oil) were tested for dioxins and about 24% of average diet of population was mapped. The remaining 76% of food consumed, that were not mapped with 71 TDS food, include water (about 1 L/day), non-alcoholic beverages (about 440 ml/day) and food of plant origin such as cereal (about 360 g/day), fruit (about 150 g/day) and vegetables (about 190 g/day) etc, even so, they were not considered as significant sources of dioxins.