The New Zealand Total Diet Study (NZTDS) aims to estimate the dietary exposure of the New Zealand population to pesticide residues, contaminant elements and selected nutrients, and to then assess if they pose a potential health risk.
The dose from chemical hazards is estimated across a typical New Zealand diet, and then compared with international health standards to see if there is any potential health risk.
The latest NZTDS has 123 foods in its food list. These foods have been chosen to represent the majority of foods consumed by the general public. A few food types known to be a richer source of certain contaminants, although eaten in relatively minor amounts (e.g. lamb liver, oysters); or foods that cater for specific sectors of the population (e.g. infant foods) are also included.
"The key issue in risk assessment is the dose,for 'it is the dose that makes the poison'. There are many hazards in the world around us, but no matter how dangerous, if we are not exposed to them, then there is no risk," says survey leader, Dr Richard Vannoort.
New Zealand regularly carries out total diet surveys, which have helped to identify contaminants such as lead and tin in canned foods, mercury in fish, and pesticides in various foods.
The NZTDS is funded by the Ministry for Primary Industries - Food safety and undertaken by ESR's Food Safety group.
Link to current Total Diet Study results
'Lead in flour' search
As part of the 2004 Total Diet Study sampling plan, a range of different baby foods: fruit, desserts and custards was assessed. One brand showed elevated levels of lead. This sparked a search for the source of the lead which led to an investigation into lead in cornflour across three countries.
"The levels in the baby food were unexpected and significantly elevated, and action needed to be taken."
The 1997/98 NZTDS showed that the typical New Zealand diet has among the lowest lead levels in the world. Previous NZTDSs have also shown that the trend of dietary lead exposure is continuing downwards.
Two factors have contributed significantly to this downward trend:
- the removal of lead solder from canned foods in the 1980s, and
- the reduction and then complete removal of leaded petrol in the mid to late 90s.
Other sources of lead exposure are:
- flakes, dust and contaminated soil in and about homes with lead-based paints
- drinking water from lead plumbing systems
- lead-glazed pottery
- food from lead-soldered cans and air and industrial pollution.