Previous risk assessment studies conducted by the Food and Environmental Hygiene Department focused on individual food chemical hazards for a specific population group, namely secondary school students in Hong Kong.
With the availability of local food consumption data from the Hong Kong Population-based Food Consumption Survey (FCS), dietary exposure studies can be expanded by incorporating a Total Diet Study (TDS) approach. More comprehensive and accurate dietary exposure of the Hong Kong population can be obtained, and it provides the scientific basis for assessing food safety risks and regulating food supply. The 1st HKTDS was conducted between March 2010 and December 2014.
Objectives of the Study
The 1st HKTDS aimed to estimate dietary exposures of the Hong Kong population and various population sub-groups to a range of substances, including contaminants and nutrients, and thus assess any associated health risks.
TDS food list
The study covered majority of food consumed by the Hong Kong population, in which a TDS food list containing 150 different food items was developed, based on the food consumption data of the FCS. The FCS was a survey on 5,008 Hong Kong people aged 20-84 using two non-consecutive 24-hour dietary intake (24-hr recall) questionnaires supplemented by a food frequency questionnaire, and revealed that over 1,400 food items were consumed by the Hong Kong people. Foods were selected according to the following criteria: (a) food commonly consumed by the population; and (b) food that is likely to contain high concentration of concerned substances even its consumption is low.
Sampling and Food Preparation
The Centre for Food Safety (CFS) commissioned the Chinese University of Hong Kong (CUHK) to carry out sampling and food preparation work of the 1st HKTDS which was conducted on four sampling occasions of a year from March 2010 to February 2011. On each sampling occasion, three samples of each TDS food item were purchased from various retail outlets and from different regions of territory, and were then be prepared and combined to form a single sample for laboratory analysis.
Substances to be tested
Substances tested were selected based on the following criteria: (a) recommendation from international authorities, (b) public health significance, and (c) public concern. On the other hand, certain substances which can be tested simultaneously with other selected substances were also included. Finally, a list of over a hundred of substances such as persistent organic pollutants, pesticide residues, heavy metals, processing contaminants, mycotoxins and nutrients, was included in the study.
Laboratory analysis was mainly performed by the Food Research Laboratory (FRL) of the CFS while analysis of dioxins and polybrominated diphenyl ethers (PBDEs) was conducted by the Government Laboratory. Laboratory analysis was completed in mid 2013.
Dietary Exposure Estimation
Since over 1,400 food items were captured by the FCS, the 150 TDS food items were required to be mapped with the food items in the FCS as far as possible, so as to cover the whole diet of the Hong Kong people. After mapping, majority (over 99% of food consumption amount) of FCS food consumed by the population were included in the dietary exposure estimation. Food items that could not be mapped with TDS food were mainly herbs and spice, traditional Chinese herbs, food additives and seaweed items. Analytical results of concerned substances in the TDS food items were then assigned to the mapped food items in the FCS. For adjusting the possible difference such as the differences in water contents between the TDS food and mapped food in FCS, "conversion factors" were also assigned such as the differences in water contents.
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 foods consumed by an individual. Dietary exposures of average and high consumers of the Hong Kong population, as well as various population sub-groups will then be estimated and compared to (a) the relevant safety reference for the food chemical of concern, and (b) the nutritional reference values for the nutrient of concern to assess the associated health risk.
Reports of the 1st HKTDS had been released in phases. The released reports can be downloaded from the CFS webpage.