Total Diet Study – the findings analysed

Ministry of Agriculture and Forestry (MAF) officials say the five-yearly Total Diet Study — analysis based on research done in 2009 — showed estimated dietary exposures to all the 241 agricultural compound residues for which it tested were below the relevant acceptable daily intake (ADI) levels.

“The New Zealand diet poses no food safety concerns from chemical residues or contaminants,” MAF’s Acting Policy Manager Cherie Flynn. She said 93 percent of the dietary exposures to residues were calculated to be less than 0.1% of the ADI for the 123 commonly-eaten foods tested for some chemical residues, and contaminant and nutrient elements. About half the foods were sampled as regional foods, and all samples were tested after being prepared for eating: nearly 250,000 analyses were done.

“Although we are getting more residue detections than in the past because more sophisticated testing equipment can pick up residues at levels well below what we’ve been picked up in our previous total diet studies, it is very pleasing to see that the actual levels found are trending down,” said Mrs Flynn.

She said that tests for contaminants such as lead, mercury, methylmercury, cadmium and arsenic also did not show any cause for concern, and that levels of lead in the nation’s diet were now likely to be “as low as reasonably achievable”.

Estimated dietary exposures to cadmium, were below the provisional tolerable monthly intake set by the World Health Organisation (WHO). Total mercury and methylmercury were below WHO’s provisional tolerable weekly intakes, “however, those who eat a lot of certain types of fish that have the highest concentrations of mercury … have the potential to have significantly higher exposures to methylmercury,” said Mrs Flynn.

But checks on key nutrients (iodine, selenium and sodium) showed the mean sodium (salt) intake was too high — 116 percent -148 percent over levels that carry health risks — in six of the test groups.  Only the diet of women over 25 years was below this level, but it was still two to four times the recommended intake. Trend data suggested that the sodium intake in some of the consumer groups was slowly dropping.

Read the full 2009 New Zealand Total Diet Study

The 2009 study — commissioned by the NZ Food Safety Authority, which has since been merged back into MAF — was the seventh since the initial study was conducted in 1974/75.

The initial surveys were conducted by the Health Ministry, but MAF took a role after the 1990-91 MOH survey showed chemical residues in 97 percent of celery and the samples contained 17 different pesticide residues. In 2009, celery had detectable residues of nine different pesticides.

Overall, 45 percent of the food samples screened  contained detectable residues, down on the 40 percent found in 2003-2004, and the 59 percent found in 2997-98. Residues of 75 different agricultural compounds were detected in 2009 study, compared to 82 in 2003/04, and 910 (0.4 percent) of the 236,662 individual analyses detected residues, compared with 0.5 percent in 2003/04 and 1.4 percent in 1997/98.

But MAF said the  frequency of residue detections had “little bearing” on food safety risks based on  dietary exposures: the amount of food eaten and the residue concentrations in those foods. In the latest study, dietary exposures to agricultural compounds for all age and gender groups were well below the relevant acceptable daily intake (ADI) levels, ” and are therefore unlikely to represent a risk to public health”.

Highest exposures

The highest estimated dietary exposures were for dithiocarbamate (DTC) fungicides such as Thiram, Ziram, Mancozeb and Metiram– mainly on apples, potatoes (even when peeled) and brassicas such as broccoli — and for infants and other young children these exposures ranged up to 52 percent of the ADI. Some vegetables such as brassicas have natural compounds which show up in analysis for DTC residues.

Two insecticides banned in New Zealand in 1989 — DDT and dieldrin — are still showing up in New Zealand food, though MAF officials think it make be because of either long-live breakdown products of the chemicals persisting in the soil, or arriving on imported foods.

Battered fish with chlorpyrifos-methyl

Officials who have given New Zealand foods a clean bill of health on pesticide residues and other contaminants after a massive study of diners’ exposure at average consumption levels say they they suspect some of the residues are arriving on imported foods, such as Australian wheat.

Analysis of the five-yearly Total Diet Survey done in 2009 was recently completed and showed 910 detections of residues, with 245 (27  percent) involving 30 different organophosphate compounds. Nearly 153 of these were fumigants used on stored grain — pirimiphos-methyl, fenitrothion, and chlorpyrifos-methyl —  and they not only showed up on ceareal products but hamburgers, pies, pizza and battered fish.

“Those are used generally on stored grain — so the levels being found would reflect the grain content of those foods — but the levels weren’t high,” said one of the study authors, Dr Richard Vannoort, of Environmental Science and Research (ESR). He said the key issue for the study was not the concentration but exposures consumers faced.

The study’s project manager, Cherie Flynn, told journalists that food production systems used agricultural compounds that had been assessed for safety and none of the residues found had been near the limits for good agricultural practice. Compounds used in Australia would all have been checked for safety. “In the North Island the majority of wheat is imported, in the South Island there is still a significant amount of locally-grown (wheat),” she said.

Dr Vannoort said the study had not looked at whether more insecticides were used on Australian wheat, such as when it was stored, than on wheat produced in this country, and whether that was why organophosphates had shown up in breads, biscuits, and muffins other products with a cereal content.

MAF toxicologist John Reeve said the type of chemical used and the amount used would depend on the pests involved. “You would get differences both possibly in the chemical used and the amount used,” he said.

Eight other organophasphates found for the first time had not yet been registered for use in New Zealand, so imported foods were the most likely sources, the study said.

Leading question

Dietary exposure sources of lead are spread fairly evenly and “reflect the ubiquitous environmental presence of residual lead in NZ,” said the Total Diet Study.

There was a  “slightly elevated” level of lead found in some of the  breads from Napier in a regional survey, said project manager Mrs Flynn.”It wasn’t a health issue”. Assessments at the time showed that even a large daily  bread-eater would only be exposed to around 10 percent of the safe weekly intake of lead.

The New Zealand lead exposure for males over 25 was low, at 0.9 micrograms per kilogram of body weight per week, when compared to Australia’s 1.6 micrograms. In  2003-2004, high levels of lead found in infant foods were traced back to cornflour from corn imported in a bulk carrier which had previously taken lead ore to China. That boosted lead levels to 0.472 mg/kg lead in infant custard weaning food, when normal levels were 0.002 mg/kg.

But checks on wheat samples — through the the annual Food Residues Surveillance Programme (FRSP) —  did not find a similar scenario of contaminated shipments. The high-lead bread in Napier appeared to have been a one-off incident, and now MAF considered that lead exposure levels had been reduced “as low as reasonably achievable,” Mrs Flynn said.

Mr Reeve said the finding that the level of lead in food had gone as low as  it was possible to get it was “very pleasing” because last year a global committee of experts on food additives had found that the previous “provisional tolerable weekly intake” of 25 micrograms of lead per kilogram of bodyweight — the exact amount that that young New Zealand men were consuming in 1982 — reduced the intelligence quotient (IQ) in children by three points. It also  boosted the sytolic blood pressure of adults.

Infants have markedly higher intakes of lead than adults — 2.1 micrograms  — because they are growing rapidly and eat a higher proportion of their bodyweight each week.

Mercury not rising

Fish and shellfish provide up to 73 percent of the total mercury in the diet of young New Zealand men, and 55 percent of the mercury in the diet of infants, but Total Diet Survey researchers said this should not turn people off all fish.

“Fish is a very important source of protein, vitamins, minerals and omega fatty acids, but they also contribute mercury” said Dr Vannoort.

“Keep eating fish — it’s only certain types of those larger fish where you should limit the consumption”. Advice was available on a MAF website, which show that for over 50 percent of fish such as terakihi, people could eat as much as they liked, but large predatory species such as shark, tuna, and lemonfish had higher levels of mercurymethyl.

In the Total Diet Study, the highest concentrations of total mercury were in battered fish, up to 0.48mg/kg, just below the trans-Tasman limit of 0.50mg/kg. But asked whether this meant poorer housholds who bought the cheapest fish and chips would be exposed to higher mercury levels, Dr Vannoort said risk was not related to concentration of the contaminant, but how much of the fish they ate.

“It’s the whole issue of food security,” he told journalists at a briefing on the study.

“Because they’re at lower socio-economic (end of the market) their choices tend to gravitate to things that are easier to get: they don’t have to grow their own foods. I’m generalising .. but they would tend to have foods that are more processed, so higher in sodium, they would tend to be higher in fats as well  if you’ve got pizzas and takeaways. You can grow your own vegetables and cook your food, and it’s certainly more nutritious and cheaper and more cost effective as well”.

Sodium only so-so

Sodium levels in the NZ diet — about 90-percent of it accounted-for by the salt often used for flavour or as a preservative — were above “adequate intake” levels for all population groups, and exceeded the advised upper levels of intake by up to 48 percent for the average consumer — before any salt was added to food during cooking or at the table.

High intakes are associated with increased risk of hypertension, a risk factor for cardiovascular disease, and kidney damage, but some young males had up to 6800mg/day — close to three times the upper levels that were advised.

The highest levels were in yeast-based spreads (35,000 mg/kg), while bacon contained 16,910 mg/kg. There was a much lower level in bread — where salt content had dropped 22 percent since 1988 — but the quantity of bread eaten meant it provided between 14 percent and 28 percent of the population’s sodium intake. Sodium levels in milk dropped by 54 percent over the same time.

“We love the taste of salty foods,” said Dr Vannoort.  He said the lower salt levels in bread were an example of industry cooperation, but if people wanted to reduce their salt intake, they should cut back their consumption of processed foods, which provided 70 percent of the sodium in the surveyed diet. A tomato had a sodium level of only 9mg/kg, but tomato sauce 8300mg/kg. “You could have tomato puree rather than tomato sauce”.

Iodine – averting mental retardation

The levels of iodine in the average New Zealander’s diet have stopped dropping, but they have plateaued below estimated requirements.

The latest Total Diet Survey — based on samples taken in 2009 and analysed over the next two years — only captured the start of the September 2009 standard  which made fortification of bread with iodised salt mandatory for many commercial bread-bakers.

Study author, Dr Vannoort said iodine was important because it was not only needed for physical development and the thyroid gland, but for mental development, particularly in young children.

“The mental development is more crucial — if you don’t get enough iodine in those formative years, the retardation, the lack of development is irreversable”. Serious deficiencies could lead to cretinism.

Pregnant and lactating women were being offered iodine supplements, and further research was being commissioned to look at more specific measures of iodine in adults, said MAF nutrition manager David Roberts.

“We’re just starting now to look at the preliminary results of the first post-fortification period,” he said.

“If the standard is not working we will look why it’s not working  and maybe some other risk-management options”. One of these could be to extend the requirement for iodised salt to be extended from bread to other iodised foods.


The Study
* The NZ Total Diet Study takes place every five years, though the latest was delayed by the Christchurch earthquake.
* Individual foods were prepared and sampled, with exposure calculated on simulated diets for eight different age and gender groups
* In the 2009 survey, Weetbix were treated as a regional food because they are made in at two different factories with gains from different sources; tap water and bottle water were treated as separate foods, and an Indian dish was added to the takeaways.

Testing By The Numbers:
* 123 foods — each purchased over two seasons – in 12 groups, representing 70 percent of commonly-consumed foods.
* 62 “national” foods and 61 which varied according to region.
* 4330 food samples were purchased
* 982 samples sent for analysis, 545 (55 percent) had detectable residues.
* 69 percent of dietary exposures calculated to have zero exposure to individual compounds
* Nearly 250,000 individual analyses:
– 241 pesticide residues, including nine dithiocarbamate (DTC) fungicide checked as one chemical, (carbon disulphide)
– 5 other contaminants (arsenic, lead, mercury, cadmium, and methylmercury)
– 3 nutrients (iodine, selenium and sodium)

The Results
* Similar to the 2003-2004 study, but fewer pesticide residues found, and at lower levels this time.
* Lead contamination now “as low as reasonably achievable”
* No health risk from arsenic
* Cadmium below WHO provisional tolerable intakes
* Total mercury and the most dangerous organic methylmercury below WHO provisional tolerable intake levels.
* Iodine below adeqate levels but has stopped dropping.
* Selenium is steady at around adequate levels.
* Sodium (salt) still high “but trending down”