CFS 2012 — First Hong Kong Total Diet Study: Inorganic Arsenic
The Centre for Food Safety (CFS) of Hong Kong’s Food and Environmental Hygiene Department conducted the First Hong Kong Total Diet Study (1st HKTDS) to estimate dietary exposure of the Hong Kong population to inorganic arsenic, specifically using direct iAs speciation rather than total-arsenic conversion factors. A total of 600 composite samples (from 150 food items, 3 purchases per item across 4 sampling occasions) were tested using hydride generation ICP-MS, with an LOD of 3 µg/kg in food. Dietary exposure estimates were 0.22 µg/kg bw/day for average consumers and 0.38 µg/kg bw/day for high consumers, both below the JECFA BMDL0.5 of 3.0 µg/kg bw/day (range 2-7), with MOEs of 9-32 and 5-18 respectively. Rice dominates the iAs exposure picture: cooked white rice alone contributed 45.2% of total dietary exposure, with cereals and their products accounting for 53.5% overall.
Note on series: this report is No. 2 in the 1st HKTDS series (published February 2012). The companion report covering the full metallic contaminants panel (Al, Sb, Cd, Pb, MeHg, Ni, Sn) is Report No. 5 (January 2013), ingested as cfs2013-hktds-metallic-contaminants. The year 2013 in the cite key follows the series convention adopted for that related page; this report’s actual publication date is February 2012.
Key numbers
Food group mean iAs concentrations (µg/kg, composite samples, wet weight as consumed):
| Food group | n composites | % < LOD | Mean (µg/kg) | Range (µg/kg) |
|---|---|---|---|---|
| Cereals and their products | 76 | 29 | 8 | ND–46 |
| Vegetables and their products | 140 | 49 | 9 | ND–120 |
| Legumes, nuts and seeds | 24 | 63 | 4 | ND–14 |
| Fruits | 68 | 78 | 4 | ND–88 |
| Meat, poultry and game | 48 | 54 | 4 | ND–27 |
| Eggs and their products | 12 | 33 | 23 | ND–93 |
| Fish and seafood | 76 | 17 | 15 | ND–74 |
| Dairy products | 20 | 100 | 1.5 (½ LOD) | ND |
| Fats and oils | 8 | 100 | 1.5 (½ LOD) | ND |
| Beverages, alcoholic | 8 | 50 | 3 | ND–7 |
| Beverages, non-alcoholic | 40 | 95 | 2 | ND–12 |
| Mixed dishes | 48 | 21 | 6 | ND–19 |
| Snack foods | 4 | 0 | 8 | 6–10 |
| Sugars and confectionery | 8 | 63 | 4 | ND–8 |
| Condiments, sauces and herbs | 20 | 40 | 8 | ND–65 |
Selected food-item highlights (from Appendix 1):
| Food item | Mean iAs (µg/kg) | Range (µg/kg) |
|---|---|---|
| Water spinach | 74 | 35–120 |
| Salted egg | 58 | 31–93 |
| Oyster | 58 | 49–74 |
| Rice, cooked unpolished | 43 | 37–46 |
| Preserved vegetables | 38 | 11–48 |
| Dried shiitake mushroom | 45 | 36–53 |
| Oyster sauce | 21 | 3–65 |
| Rice, cooked white | 22 | 16–26 |
| Watercress | 19 | 8–34 |
| Spring onion | 14 | 9–18 |
| Tomato paste/ketchup | 12 | 6–17 |
| Soya sauce | 1.5 (½ LOD) | ND |
| Table salt | 1.5 (½ LOD) | ND |
| Cornstarch | 2 | ND–4 |
Condiments and sauces group (20 composite samples, 40% below LOD, mean 8 µg/kg, range ND–65 µg/kg): The outlier driving this range is oyster sauce (mean 21 µg/kg, range 3–65 µg/kg), which is derived from shellfish and thus carries elevated iAs consistent with seafood origin. Other condiments were at or near LOD.
Dietary exposure estimates:
| Population | Average (µg/kg bw/day) | High consumer 95th percentile (µg/kg bw/day) | MOE range |
|---|---|---|---|
| All adults 20-84 | 0.22 | 0.38 | 9-32 (avg) / 5-18 (high) |
| Male 20-29 | 0.21 | 0.39 | — |
| Female 20-29 | 0.19 | 0.33 | — |
| Male 60-69 | 0.26 | 0.46 | — |
| Female 60-69 | 0.22 | 0.40 | — |
Dietary exposure by food group (average adult population):
| Food group | Dietary exposure (µg/kg bw/day) | % of total |
|---|---|---|
| Cereals and their products | 0.12 | 53.5% |
| Beverages, non-alcoholic | 0.03 | 13.0% |
| Vegetables and their products | 0.02 | 10.4% |
| Fish and seafood | 0.02 | 7.9% |
| Mixed dishes | 0.01 | 5.4% |
| Fruits | 0.01 | 3.3% |
| Meat, poultry and game | 0.01 | 3.2% |
| Condiments, sauces and herbs | 0.00 | 1.0% |
| Dairy products | 0.00 | 0.6% |
Cooked white rice alone contributed 45.2% of total dietary exposure (84.5% of the cereals group contribution). Brown/unpolished rice had nearly double the iAs concentration (mean 43 µg/kg vs 22 µg/kg for white rice) but contributed only 1.3% of total population exposure due to its minor role in Hong Kong diet (consumed by approximately 5% of the population).
Reference benchmark: JECFA 2010 withdrew the former PTWI of 15 µg/kg bw/week (2.1 µg/kg bw/day) for iAs as it falls within the BMDL0.5 range of 2-7 µg/kg bw/day. Hong Kong population average exposure (0.22 µg/kg bw/day) represented approximately 10% of the former PTWI and generated MOEs of 9-32 against the BMDL0.5.
Methods (brief)
The 1st HKTDS purchased 150 commonly consumed food items (based on the Hong Kong Population-Based Food Consumption Survey 2005-2007), prepared them as consumed, combined into composites (3 purchases per item per occasion), and collected on four occasions March 2010 to February 2011 for a total of 1,800 individual samples reduced to 600 composites. Laboratory analysis for inorganic arsenic was conducted by CFS’s Food Research Laboratory using solubilisation in concentrated HCl, arsenite extraction into chloroform, back-extraction to diluted HCl, dry-ashing destruction of organic matter, and quantification by hydride generation ICP-MS. The method specifically measures arsenite (As(III)) plus arsenate (As(V)); note the extraction procedure is also known to capture a small amount of monomethylarsenic (MMA). LOD = 3 µg/kg food, 1.5 µg/kg water; LOQ = 10 µg/kg food, 5 µg/kg water. Non-detects assigned ½ LOD for exposure calculations per WHO GEMS/Food-EURO guidance. About 51% of composite samples detected above LOD. Dietary exposures combined analytical results with food consumption data via the EASY (Exposure Assessment System) web-based tool; mean and 95th percentile used to represent average and high consumer respectively.
Analytical note: Direct iAs speciation, not total arsenic with conversion factor. This is the critical methodological distinction from the previous 2002 FEHD secondary-school study, which used a 10% conversion factor applied to total arsenic from surveillance data with LOD of 76 µg/kg; that approach systematically overestimated iAs in seafood and underestimated the rice contribution.
Implications
Certification: Rice is confirmed as the dominant contributor to dietary iAs exposure in rice-consuming populations; the 22 µg/kg (white rice) and 43 µg/kg (unpolished rice) concentration values from a government TDS support the wiki’s rice iAs profile. Oyster sauce is notable as the outlier condiment with iAs up to 65 µg/kg due to shellfish derivation; relevant for any product category using oyster sauce as an ingredient. The unpolished vs white rice differential (43 vs 22 µg/kg, approximately 2x) supports the processing-effect evidence for the rice ingredient page.
Courses: Illustrates the methodological superiority of direct iAs speciation over total-arsenic conversion factors, and how using a universal 10% conversion factor can shift the apparent major contributor from seafood to cereals. Also provides the concrete washing-and-cooking mitigation data: rinsing removes approximately 10% of iAs; cooking with high water volume (1:6 ratio) removes an additional 35-45%; total removal approximately 45-55% under optimal cooking conditions.
App: TDS-level iAs data for 150 food items as consumed (cooked) rather than raw commodity. Condiments group mean (8 µg/kg) and oyster sauce specifically (21 µg/kg, up to 65 µg/kg) are relevant for any ingredient-list based exposure model. Soya sauce at ND, table salt at ND, cornstarch at 2 µg/kg.