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The chemical residue and contaminant status of New Zealand foods

Total Diet Survey

The primary focus of the New Zealand Total Diet Survey (NZTDS) is to assess exposure to chemical residues, contaminant elements and selected nutrients, from approximately 120 representative foods, across the average diet of different age-sex groups within the New Zealand population. By its very nature, the NZTDS is relatively large and complex, and is thus carried out only on a periodic basis. NZTDSs have been undertaken since the mid-1970s. The seventh and most recent survey is being undertaken by NZFSA in 2009/10, the first five surveys were undertaken by the New Zealand Ministry of Health. NZFSA has committed to undertake future NZTDSs on a five-yearly basis.

A distinguishing characteristic of total diet surveys, including the NZTDS, is that foods are analysed on an ‘as consumed’ basis (ie: banana – peeled; meat – cooked), thus providing a more accurate assessment of the consumer’s exposure. As such, the NZTDS contrasts with commodity-based surveillance or monitoring programmes, which analyse foods as they are available for sale or ‘as produced’, ie: bananas – whole with skin; meat – raw.

The initial samples are sent to a food preparation laboratory and prepared into food as it is normally consumed. A portion of this prepared food is frozen and sent to the analytical laboratory for testing. The laboratories that undertake this testing are the same laboratories that test dairy, meat and honey products and are subject to the same level of quality control.

The NZTDS is made up of two types of investigations: the ‘core components’ – those food types and contaminants/nutrients that are always investigated; and ‘add-ons or additional components’ – those that are included every second or third survey. This approach is intended to give a structure that allows for continuity with what has occurred in past surveys and can be expected to continue into future surveys. This allows trends over time to be identified and monitored, and also allows for the NZTDS to consider emerging or specific issues. The core components of the NZTDS are:

• an agricultural compound multi-residue screen

• a residue screen for seven dithiocarbamate (DTC) fungicides

• the contaminant elements arsenic, cadmium, lead, and mercury

• the nutrient elements iodine and selenium.

The 2003/04 NZTDS included the above core components as well as an acid herbicide multi-residue screen for 18 compounds; and the nutrient elements iron and sodium.

In 2003/04 it covered over 200 agricultural compounds or their metabolites. The screen included currently or previously New Zealand registered compounds, compounds registered for use in countries for which New Zealand imports food, and compounds on the WHO/GEMS priority list for total diet surveys, including persistent organochlorines, organophosphorus compounds, fungicides, insecticides, and post-harvest treatments.

The NZTDS also takes an individual food and simulated diet approach, ie, the foods sampled are analysed on their own without being mixed with other foods. The results of this analysis are then combined with simulated diet information, ie, diets made up for each of the population groups using only the 121 foods sampled and in amounts appropriate for each population group. The foods to be sampled are chosen to represent the average and typical diets of New Zealanders across the population groups, and along with the amount of food in each simulated diet are based on consumption data from the New Zealand national adult and national children’s nutrition surveys undertaken by the Ministry of Health. The 2003/04 NZTDS had eight populations groups: 6–12 month infants; 1–3 year toddler; 5–6 year child; 11–14 year girl; 11–14 year boy; 19–24 year young male; 25+ year male; and 25+ year female.

Foods sampled for the NZTDS are categorised as either a ‘national’ food – indicating the same product can be purchased anywhere in New Zealand without any variation – or a ‘regional’ food – indicating the food will vary around the country (there were four regional locations). Each food is sampled twice over a 12-month period to allow for seasonal variation, each quarterly sample round is undertaken over 5–6 weeks to ensure sample preparation and analysis are manageable.

The results from each quarter are publicly released following each quarter. However, NZFSA is advised of any unusual or unexpected results as each analysis round progresses to allow NZFSA to respond speedily to any concerns.

The NZTDS also provides valuable information that can contribute to the review of Maximum Permissible Concentrations (MPCs) in food with FSANZ, and the setting of food standards by NZFSA.