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Proposal for the 2003/04 New Zealand Total Diet Survey (NZTDS) - December 2002

• Introduction
• Background and general
• Food List for 2003/04 NZTDS
• Age -sex groups suggested for 2003/04 NZTDS simulated diets
• 2003/04 NZTDS Core analytes
• NZTDS suggested ’add-ons'

Introduction

This paper contains general information on what a total diet survey is and what it is generally intended to deliver. The paper proposes, and explains why, certain analytical tests should be undertaken as a ’core' part of the NZTDS and then suggests a number of other possible options that could be added to the NZTDS. These additions or ’add-ons' could expand the NZTDS in terms of the way its carried out (individual verses composite samples), the types of specific tests (analytes) undertaken, or the chemicals or elements tested for.

The idea of looking at the NZTDS as having these two components, a core and add-ons, 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 and components that would be included in the NZTDS on a less regular basis, e.g. once every second or third survey. Similarly there is the potential for smaller projects or focused mini-surveys to be undertaken between each NZTDS. Such focused work could be drawn from the data gathered in a specific NZTDS to rework the data for a specific age, sex or cultural group, or could involve a wider sampling of a particular type of food(s) to look at a particular chemical or element that may have been identified as of concern.

The New Zealand Food Safety Authority (NZFSA) would like feedback on the proposals contained in the paper, particularly what particular ’add-ons' should be considered for the 2003/04 NZTDS and why these are should take precedence over the other options. We would also be interested to hear if you have any suggestions that are not mentioned here, please support your suggestions with any information you may have on why your suggestion should be considered.

Your written response is requested by 5.00pm Thursday 30 January 2003. Please forward your response to:

Mariana Van Niekerk

Executive Assistant

New Zealand Food Safety Authority

P O Box 2835

Welllington

Ph: 04 463 2673

Fx: 04 463 2501

Email: mariana.vanniekerk@nzfsa.govt.nz

Background and general

The primary focus of the 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.

A distinguishing characteristic of TDSs, including the NZTDS, is that foods are analysed on an ’as consumed' basis (ie banana, peeled; meat, cooked). Thus providing an assessment of any potential risk to the consumer at the point of consumption of the food. 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 TDS is also different from the National Nutrition Surveys (NNS). In the TDS simulated diets, using the foods in the food list, are developed to represent an average New Zealand dietary pattern. This differs from the NNS where individual actual food intakes are surveyed and the nutrient intake is calculated from food composition data. Food contributions to the nutrient intake data within the NNS are in the thousands rather than the representative 120 odd foods used in the TDS.

By its very nature, the NZTDS is relatively large and complex, and is thus carried out only on a periodic basis. There have been five NZTDSs the first in 1974/75. All were undertaken by the New Zealand Ministry of Health (MoH). The responsibility for the next NZTDS, to be undertaken in 2003/04, has transferred to the recently established New Zealand Food Safety Authority (NZFSA).

A feature of TDSs is that they should be undertaken on an on-going and regular basis, which enables monitoring of trends of exposures and levels of contaminants (and selected nutrients) in the food supply, some of which can vary significantly over time. By monitoring trends, appropriate management strategies can be implemented and their effectiveness assessed.

The individual representative foods approach used in the NZTDS (rather than food groups approach) does provide much greater flexibility with regard to assessing the dietary exposures of different age-sex groups within the population and tracing back issues to key foods, but this increased flexibility does have associated costs.

The NZTDS contributes to international commitments and obligations, such as the World Health Organization Global Environmental Monitoring Systems Food programme (WHO GEMS/Food), Codex Alimentarius and the WHO/FAO Joint Expert Committeee on Food Additives (JECFA), and WHO/FAO Joint Meeting on Pesticide Residues (JMPR).

The NZTDS also provides valuable information that can contribute to the review of Maximum Permissible Concentration (MPCs) in food with Food Standards Australia New Zealand and the setting of food standards by the NZFSA.

The NZTDS is of international standing, and is recommended by WHO as a template for developing countries initiating their first TDSs.

Food List for 2003/04 NZTDS

A report on the recommended food list for the 2003/04 NZTDS has been prepared for the NZFSA, and contains 121 foods aimed at representing those foods most commonly consumed by average New Zealanders (ie 85-95% of the diet) across a range of age-sex groups.

Some key changes from the 1997/98 NZTDS food list are the inclusion of:-

• a range of infant foods,
• some foods children specifically like, that were previously absent such as
•  
  • strawberries
  • grapes
  • flavoured milk
  • snack bars;
• and other foods to better reflect changing consumption such as
•  
  • muffins
  • sliced ham replaces luncheon
  • corned beef
  • avocado.

Age -sex groups suggested for 2003/04 NZTDS simulated diets

• Infant 6-12 months
• Young Child 1-3 years
• Child 4-6 years
• Adolescent 13-15 years
• Young male 19-24 years
• Adult male 25 years and over
• Adult female 25 years and over

Two of these groups are new (shown in italics), and they have been introduced to better reflect the population demographics. Consideration is also being given to combining the young child and child age groups into one, for example ’Child 2 - 8 years' and perhaps adding a ’Senior Adult - 65 years and over'.

The lacto-ovo vegetarian female diet of the 1997/98 NZTDS has been removed as it was not felt sufficiently representative of the population as a whole, or that it could be justified in its own right, given limited resources.

2003/04 NZTDS Core analytes

The following are the specific tests that are intended to form the core of this and future NZTDSs. While there is always potential for aspects of the survey to move in or out of the core, it is expected that these core components would remain reasonably stable over the longer term.

Gas chromatographic (GC) Multi-residue (MR) agricultural compounds - This will assess up to 150 agricultural compound residues possible in the New Zealand diet. The list includes those agricultural compounds on the WHO GEMS/Food priority list for TDSs; it maintains continuity of most agricultural compounds screened in previous NZTDSs, thus enabling trends to be investigated; but is also significantly expanded from 90 agricultural compounds assessed in the 97/98 NZTDS. Agricultural compounds suggested in the NZTDS Core are not currently assessed in independent routine surveillance or monitoring programmes in domestic or imported foods in New Zealand, or in foods ’ready for consumption' by New Zealanders.

Dithiocarbamates (DTCs) - These are the most used fungicides in New Zealand; they are on the WHO GEMS/Food priority list for TDSs; they maintain continuity with DTCs assessed in previous NZTDSs, thus enabling trends to be investigated. DTCs suggested in the NZTDS Core are not currently assessed in independent routine surveillance or monitoring programmes in domestic or imported foods in New Zealand, or foods ’ready for consumption'.

Four contaminant elements - Arsenic (As), lead (Pb), cadmium (Cd) and mercury (Hg). All are toxic, cumulative poisons on the WHO GEMS/Food priority list for TDSs. It remains desirous to have exposure to these contaminants as low as is practically possible. Their inclusion maintains continuity with previous NZTDSs, thus enabling trends to be investigated. The NZTDS is the key tool whereby As, Cd, Pb and Hg are assessed in foods ’ready for consumption' by New Zealanders, and any associated risks to public health assessed.

Two nutrient elements - Both iodine and selenium are essential micronutrients that are deficient in New Zealand soils, and this is reflected in our dietary intake. Iodine is involved in thyroid function, and affects both mental and physical development. Previous NZTDS have demonstrated the continuing decline of iodine intakes, which have been supported by thyroid hormone and urinary excretion studies. Recent research has indicated an increasing prevalence of Iodine Deficient Disorder in a sample of New Zealand children, and it is important that the most up to date dietary intakes of iodine are to hand to provide a baseline to demonstrate effectiveness of public health measures to redress this issue. Selenium is an antioxidant that plays a part in the bodies defence mechanisms, including cancer prevention. Inclusion of iodine and selenium in the 2003/04 NZTDS reflects their characteristic importance in New Zealand, and will also enable trends to continue to be compared with previous NZTDS.

NZTDS suggested ’add-ons'

In addition to a Core programme of work suggested for the NZTDS, which would be carried out on an on-going regular basis (every 3-4 years), a number of desirable NZTDS "add-ons" are identified. These should be prioritised for periodic inclusion in the 2003/04 and future NZTDSs. The number and extent to which they will be included will be dependent on a number of factors, including ability to adequately detect and quantify the analytes with appropriate quality assurance, relative toxicity/nutritional importance of analytes, risk intelligence information from other surveillance or monitoring programmes in New Zealand or internationally, cost of respective analyses, available resources, NZFSA and international priorities at the time etc.

We would welcome feedback on the following ’add-ons', and others you may wish us to consider. It would also be useful to hear which you believe should have higher priority, and why.

Wider sampling base than in 1997/98 NZTDS, in which 2440 food purchases were made for the 114 foods. By investing some extra resources into purchasing a more robust sampling base, one can have more confidence that the diet better represents those that New Zealanders are consuming, and the key chemical analytes to which they are being exposed. This also has flow on costs in regards to increased sample preparation costs.

More extensive individual sample analyses than in 1997/98 NZTDS. By their very nature, trade-offs have to be made in TDSs because of limited resources, either between budget, size of the food list, number of different analyses, and number of analyses per food. Thus internationally TDSs inevitably involve compositing of samples within the same food type, or even within the same food group, to accommodate this trade-off. While the 1997/98 NZTDS was targeted for certain analytes to certain foods, in many cases a significant proportion of compositing was essential. It would, therefore, be highly desirable and advantageous to have more samples analysed separately. More individual analyses would also make it easier to estimate residues in other individual or ethnic diets than the those identified above as the intended ’simulated diets'.

Iodine - Given the intake of this essential micronutrient in the 1997/98 NZTDS, and the indicative trend, and more recent information to hand, it seems critical that extra resource be allocated to the 2003/04 NZTDS, over and above that of the 1997/98 NZTDS, to enable more extensive sampling and individual analysis for this trace nutrient.

Moisture - This will be necessary to make the extra Iodine food composition data useful and worthwhile for the NZ food Composition database.

Polychlorinated dibenzo-p-dioxins (PCDDs)/ polychlorinated diibenzofurans (PCDFs)/ Polychlorinated biphenyls (PCBs). These environmental contaminants are fat soluble and extremely stable, thus can accumulate up the food chain. Over 90% of exposure to dioxin-like compounds is through the diet. All are included in the WHO GEMS/Food priority list of analytes. They were the subject of a major food contamination scare in Belgium in 1999, and continue to be the subject of debate in New Zealand. The Ministry for the Environment (MfE), as part of their Organochlorines programme, did measure PCDDs, PCDFs and PCBs in composites of retail foods prepared ’table ready' in early 1997, and an associated dietary exposure risk assessment carried out. The Ministry of Health have recently completed another breast milk survey of such compounds, and given the other aforementioned issues nationally and internationally, it would seem that these compounds are worthy of consideration for inclusion. They are, however, much more expensive to analyse than MR pesticides, so cannot be included every TDS, and have thus far not been able to be included in any NZTDSs.

Polycyclic aromatic hydrocarbons (PAHs) - These compounds are ubiquitous in the environment and are formed during normal combustion processes. They are the main carcinogenic (cancer forming) compounds found in cigarette smoke, automobile emissions, and domestic and industrial fire emissions. They are also formed during cooking of foods. They are expensive to analyse, but New Zealand currently has no dietary exposure estimates for these compounds or their associated risk to public health.

Liquid chromatography (LC) agricultural compound screen - Not all agricultural compounds are able to be screened by a GC MR method. Agricultural compounds such as some carbamates, benzimidazoles and others require liquid chromatography (LC). The LC methodology screens only approximately 15 agricultural compounds, and is a separate but comparable cost to the GC MR agricultural compound screen in the Core NZTDS, which can screen up to 150 pesticides.

Other nutrient elements of possible concern - Sodium (Na), Sodium has been identified as a nutrient element where high intakes are associated with increased risk of hypertension. Trends with data in 1987/88 and 90/91 NZTDS could be ascertained, as could estimated dietary intakes complementary to those traditionally derived from food composition databases. Other possible nutrient elements include Calcium (Ca), Zinc (Zn) and Iron (Fe).

Other nutrient elements -Copper (Cu), magnesium (Mg), Manganese (Mn), Phosphorus (P), and Potassium (K). With new technology such as Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and ICP Atomic Emission Spectroscopy (AES), these elements can be included for investigation at relatively reasonable cost. Nutrient elements such as these are increasingly being included into some TDSs internationally, to update or corroborate food composition databases and nutrient intake estimates. They are not, however, part of the Core TDS, which traditionally focuses resources on toxic contaminants, and their associated dietary exposures.

Nitrate/nitrite - Primarily found in vegetables and cured meats, nitrate/nitrite levels may reflect fertiliser application and its use as a food additive. Nitrite is produced within the body from nitrate, and is toxic. Nitrate/nitrite are included on the WHO GEMS Food priority analyte list, but have not been included in previous NZTDSs.

Herbicides - These require another separate dedicated screen. As these compounds are designed to be toxic to weeds and plants, they are highly unlikely to be used inappropriately near fruit or vegetable crops. In the context of most agricultural compounds screened for, herbicides are generally classified among the least toxic category, and for all these reasons would rank as a low priority for inclusion as an add-on, given competing options for limited resources.

Glyphosate - A herbicide, it is the active ingredient in Round-up. With some crops being genetically modified to resist Round up, it has been suggested that more of this pesticide may be used resulting in increased residues in foods. New Zealand currently has a moratorium on genetically modified new organisms and there are therefore no ’Round-up Ready' plants in New Zealand, imported products may however contain material derived from such crops. Analysis for glyphosate is a separate, complex and expensive undertaking. It is thus not very cost effective when compared to other analytes.

Tin - This is a contaminant that mainly occurs in canned products. It has been included in the 5 previous NZTDSs, but as it has much lower toxicity (mainly producing tin taste and gastroenteritis) than the other four core contaminant elements, it is suggested that this now be considered as an add-on only periodically.

Bisphenol A or alkyl phenols - These two groups of compounds provide more than half the theoretical xenoestrogenicity for New Zealand males or females, yet we have no reliable measurement of the actual exposure to these compounds. Xenoestrogens, which are endocrine disruptors (interfere with the human hormonal system), are of international concern. Phytoestrogens are the other major source of theoretical dietary estrogenicity for New Zealanders.