Total Diet Survey Results Encouraging
30 March 2000
New Zealand Total Diet Survey Results Encouraging
NEW Zealand's food supply has been studied in a survey which aimed to assess the level of selected contaminants, pesticide residues and nutrients in our food.
The 1997/98 New Zealand Total Diet Survey, released today by the Ministry of Health, analysed 114 commonly eaten foods for five contaminant elements, 90 different pesticide residues, and three key nutrient elements.
The survey was conducted by the Institute of Environmental Science and Research Limited (ESR) and the New Zealand Institute for Crop & Food Research Limited with assistance from Health Protection Officers. It was funded and co-ordinated by the Ministry of Health's Public Health Group.
Dr Bob Boyd, Chief Advisor Safety and Regulation, said that overall the results are very encouraging and has shown that any risk to public health is negligible.
"Intakes of pesticide residues remain low in comparison to international standards and contaminant element intakes are comparable with levels in overseas countries. The only exception is that New Zealand intakes of lead have fallen and appear to be lower than most other developed countries."
"Lead intakes have dropped by more than half since the previous survey (1990/1991 NZTDS). It is likely that this reduction has been due, at least in part, to the removal of lead from retail petrol sold in New Zealand."
Of the 460 samples of foods tested for the 90 different pesticide residues, 272 of the samples (59 percent) were found to contain detectable pesticide residues. Only 20 of the 90 pesticide residues tested for, were found.
"With the exception of the dithiocarbamates, a group of fungicides which are used on fruits and vegetables, all estimated intakes were lower than 3 percent of the acceptable daily intake (ADI)" The estimated exposure to dithiocarbamates was 23 percent or less than the ADI.
"The higher level of dithiocarbamates is possibly due to the fact that brassica vegetables, which include cabbage, broccoli and cauliflower contain natural compounds which cannot be differentiated from the pesticide compound, during analysis."
Despite the higher level of dithiocarbamates found, Dr Boyd said the estimated intake of pesticide residues and contaminant elements were not expected to have any adverse effects on human health.
The New Zealand Total Diet Survey also examined the nutrient elements iodine and selenium, which are essential to human health and naturally low in the New Zealand environment.
"New Zealanders’ intakes of iodine are lower than recommended and this is possibly due to the lower levels of iodine in dairy products. This has occurred due to a change in cleaning procedures whereby cleaning compounds containing iodine have largely been replaced by iodine-free products."
The study also shows that the levels of selenium in the diet have increased significantly over the past ten years.
"This is probably due to higher concentrations in animal products and the use of more Australian wheat and wheat-based products, particularly in the North Island which contain high levels of selenium. However, in the South Island the wheat used is predominantly locally grown and low in selenium, which means selenium intakes will be lower."
For more information contact Selina Gentry Media Advisor 04 4962483/025 277 5411 A full copy of the New Zealand Total Diet Survey can be found on our website Internet address: http://www.moh.govt.nz/media.html
Questions and Answers
How was the 1997/98 New Zealand Total Diet Survey (NZTDS) compiled? The survey involved sampling 114 different foods of which 105 were considered to be those most commonly consumed by the majority of New Zealanders. Approximately 2,440 different food samples were taken. The survey's key purpose was to analyse the foods to determine the concentrations of pesticide residues, contaminant elements and selected nutrients and to assess exposure by using modelled "typical" New Zealand diets, for six age/gender categories. Fortnightly diets were developed for young children (1-3 years), children (4-6 years), female vegetarian, adult male, adult female and a young male.
The samples were collected over a 12-month period (during 1997 and 1998) and food was collected from four regional sites (Auckland, Napier, Christchurch and Dunedin) and at one site for foods distributed nationally, during two seasons.
There have been some minor changes to the food list since the 1990/91 NZTDS. The list now includes a wider range of snack and take-away foods, more vegetables and some vegetarian foods, such as hummus and tofu.
What is an acceptable daily intake (ADI)? Acceptable Daily Intake (ADI) is an intake level of a food contaminant (pesticide) usually determined by the World Health Organization (WHO) expert groups or New Zealand experts using standard techniques. ADI levels are usually based on long-term animal toxicology studies from which a level known not to cause adverse effects in the animal is determined. The ADI for human intake is obtained by dividing this intake level without toxic effect in the animal by uncertainty factors, usually a factor of 100, to provide a safety margin. The ADI is considered to be an intake to which a person can be exposed during his/her entire lifetime without adverse effect.
What does a tolerable intake or provisional tolerable weekly intake mean? Tolerable daily intakes or a provisional tolerable weekly intakes are those derived by WHO for the contaminant elements. The use of a weekly figure reflects the understanding that it is the average intake over a week rather than a daily exposure, which may be high on a particular day, which is important.
What is a recommended dietary intake (RDI) or recommended daily allowance (RDA) for a nutrient element? The recommended dietary intake is the intake recommended for an essential nutrient (e.g. vitamin or mineral) which is adequate for practically all healthy people and includes a margin of safety. The RDA is an alternative term which has been used in the United States of America. The levels are based on current scientific knowledge and the recommendations are usually developed by authoritative bodies, such as the US National Academy of Sciences.
Why were only five contaminant elements selected? The five contaminant elements, arsenic, cadmium, lead, mercury and tin were selected as they are of key importance and interest in New Zealand, and this maintains continuity with previous New Zealand Total Diet Surveys. They are also priority contaminants for TDSs, as determined by the WHO's Global Environmental Monitoring System/Food Programme.
Why were only three nutrients selected? Nutrient elements iodine, selenium and zinc were included in the 1997/98 survey. This was because iodine and selenium are essential to human health and both are in short supply in the New Zealand environment, especially the soil. Whereas, zinc was included because it is believed to protect against the toxic effects of cadmium, which is one of the main contaminant element risks in the New Zealand diet.
How do New Zealanders' dietary intakes of lead compare with those of other countries? New Zealanders' intakes of lead continue to decrease and are 12 percent or less than the provisional tolerable weekly intake for all age groups. The decline in the lead levels in most foods is considered to be due, at least in part, to the removal of lead additives from retail petrol. Intakes of lead from food in New Zealand are now considerably lower than a number of other countries including Australia, Japan and the UK.
How can people limit their mercury intake? The highest concentration of total mercury is found in fish, especially large old fish, particularly predatory species like shark or tuna and fish taken from waters downstream from geothermal or volcanic activity. Trout and other freshwater species (like eels) from geothermal lakes and rivers, which are relatively common in the central North Island, may also contain high levels of mercury. Mercury leaches into the water from volcanic soils or is released from active geothermal areas.
Pregnant or breast-feeding women and young children, who are most susceptible to high concentrations of mercury, should select fish which are lower in mercury such as gurnard, tarakihi, cod (red and blue), warehou, monkfish (stargazer), and hoki.
Where does cadmium come from in New Zealand? Cadmium is a metal which occurs naturally at low levels in the environment in close association with zinc. Agricultural activity, such as the addition of fertilisers may increase the levels of cadmium in agricultural areas. Volcanic activity is also a major source of cadmium released into the environment. High intakes of cadmium can have serious effects on health, as it is a cumulative and toxic element. The report recommends that consumption of dredge oysters should be limited as they have the potential to significantly increase dietary intake of cadmium.
What is the significance of the decrease in iodine identified in the Total Diet Survey? Intakes of iodine were low, but were also underestimated because salt added to food during cooking and at the table was not included. This and other work undertaken by the University of Otago show that iodine intakes in New Zealand have decreased again.
A decrease in the use of iodine-based cleaning compounds (iodophors) in the dairy industry resulting in a lower concentration of iodine in dairy products, probably accounts for some of the decrease in iodine intakes. However, milk and dairy products remain important sources of iodine for many New Zealanders. The Ministry of Health is undertaking further work on the low iodine intakes, including investigating the practicality of including iodine assessment as part of the Children's Nutrition Survey (CNS) and seeking external advice on what action maybe appropriate. The preliminary work, which includes developing the methods, for the CNS is expected to be completed by the end of the year.
Why have selenium intakes increased and why is there a difference between intakes in the North and South Island? Overall, selenium intakes have increased significantly over the past ten years and are now at, or reasonably close to, the recommended intakes for selenium in Australia and the US. The increase is likely to be as the result of increases in the selenium content of eggs, meat, chicken, wheat and wheat-based products. However, there is a difference between the wheat and wheat-based products produced in the North and South Islands of New Zealand. New Zealand soils, especially in the South Island are low in selenium. The majority of the wheat used for milling in the North Island is from higher selenium wheat from Australia and North America, whereas in the South Island most of the wheat used is low in selenium as it is grown locally.
What are the health implications of pesticide residues found in food? Only 20 of the 90 pesticide residues screened for in the 1997/98 survey were detected in any of the food samples and, with the exception of the dithiocarbamates, the estimated intakes were all less than 3 percent of the ADI. According to the survey the levels of pesticide residues are well within international standards and therefore considered safe and very unlikely to cause any adverse health effects.
What is so difficult about the analysis of the dithiocarbamates (DTC)? Why is the proportion of the ADI for the intake of DTC so much higher than other pesticide residues? Dithiocarbamate insecticides cannot be analysed by the method used for other pesticide residues. Instead they are degraded to carbon disulphide and the concentration of this compound related to the level of residue that might produce it. This causes two problems: · it is impossible to distinguish between the different DTC fungicides. This method can only give an estimate for the total amount of this family of fungicides present. · a larger problem is that carbon disulphide occurs naturally or can be produced from naturally occurring sulphur compounds in some plants (particularly the brassica vegetables). Therefore the estimate of the amount of DTC fungicides present on these crops (based on the carbon disulphide level) is likely to substantially over-estimate the level of fungicide present.
A similar number of findings of pesticide residues occurred overall compared to the previous survey, which suggests pesticide use in New Zealand has not declined. Although the number of residues found is similar to the previous survey, in this (1997/98) survey the laboratory has been able to achieve a marked improvement in the detection of low levels of substances compared to previous years due to improved analytical testing. Therefore, many of the reported ?findings? of pesticides in the current work would not have been detected in the previous surveys, and overall the degree of contamination of the diet with pesticide residues is lower than previously.
Why was there a specific recommendation to follow up the possible recent exposure to DDT in eggs? DDT residues are reported as the ?total? DDT, which includes DDT, and it's common, persistent metabolites DDE and DDD. Since, DDT has not been registered for use in horticulture or agriculture for about 20 years, most residues now found are of the metabolites (DDE and DDD). NZTDSs commonly find DDE in a range of animal products but the concentrations have been decreasing over time. In a boiled egg sample in this survey, it was found that the proportion of DDT to the metabolite DDE was relatively high. The levels found were very low and do not constitute a non-compliance with the Food Regulations 1984, or pose a risk to human health. However, as there may have been recent use on, or contamination of, an egg production operation with DDT the finding requires further investigation.
What is the Ministry of Health doing to follow up this finding? The Ministry of Health has already discussed this finding with the industry, health protection officers and the Ministry of Agriculture and Forestry. To date no explanation for the result has been found.
As the result relates to a mixed sample of hen house eggs from four areas, the Ministry of Health has undertaken further analyses of the regional samples to see if the area and supplier/s that contained the DDT can be identified. Based on this information health protection officers may be able to identify how the contamination occurred. At this stage there are a number of possible sources, including the poultry feed, the hens immediate environment e.g. wood or soil, or use of DDT for lice or vermin control.
Similar overseas surveys undertaken recently in the United Kingdom and Australia have both found DDT in eggs at higher levels than found in the egg sample in the 1997/98 NZTDS. The concentrations of total DDT in five samples of backyard eggs in South Australia in 1996 exceeded the maximum residue limit.
What about free range eggs? Are any tests being taken on these as well to check if they have signs of DDT? No free range eggs were tested in this survey and they represent a relatively small proportion of the eggs consumed in New Zealand. Depending on the outcome of the investigation the Ministry will consider whether or not further work on eggs is necessary.
Who should people turn to for further advice on the NZTDS results and nutrition? You should contact your local public health unit and speak to a health protection officer if you want to discuss the findings of the pesticide residue or contaminant elements in the 1997/98 NZTDS. Alternatively, if you need advice about the nutrient elements or nutrition you should contact a dietitian at your local public health unit.