The Dirty Dozen – 12 foods with the most pesticide residues

Organic NZ Magazine: May/June 2010
Section: Health and Food
Author: Alison White

Alison White of the Safe Food Campaign answers these questions

– Which foods in New Zealand have the most pesticide residues?
– What’s wrong with pesticide residues in food?
– How can pesticide residues in food be reduced?


Which foods have the most pesticide residues?

Celery, a range of fruit, dairy products and bread are all ranked in the top dozen of foods available in New Zealand that are likely to contain more pesticide residues.1 Close contenders behind the ‘dirty dozen’ (see table for the list) were cucumber, nectarines, lettuce, tomatoes, wine and pears.


Why worry about pesticides in food?

Should we be concerned about pesticide residues in food? Every mouthful of nonorganic food we eat is also a cocktail of pesticides. Many of these pesticides have not been adequately tested to see what effects they may produce, particularly long-term ones. The little testing that is carried out does not reflect actual human exposure to a multitude of chemicals, nor does it usually test the most vulnerable: the foetus and young child.

We do not know enough about the effects of these chemicals in our food. However,there are various serious long-term effects associated with particular pesticides that are found in our food, including endocrine or hormonal disruption, cancer, immune system suppression, nervous system damage, genetic damage and birth defects. We also know that various pesticides used to grow food have damaging effects on wildlife and the ecosystem.


Reduce pesticide load: eat organic

If you buy organic at least the foods listed in this table, then you will be signifi cantly reducing the pesticide load on your body. This is particularly so for infants and children, as they take in more food in proportion to their body weight than adults do, and they also tend to eat more of the types of food that are more heavily sprayed, such as fruit. Indeed, an American study has found that if children eat mostly organic food, then the average amount of organophosphate residues as measured in their urine is nine times lower than those children eating conventional food.2


Protect your children

In 2007 more than 200 scientists from five continents called for a precautionary approach to toxic chemicals, to protect foetuses and children from chemical exposures that may cause serious disease later in life, and which may also affl ict their children and grandchildren.3

Exposure may result in an array of health problems, including diabetes, attention deficit disorders, prostate cancer, fertility problems, thyroid disorders and even obesity. If the foetus is exposed to even a minute amount of an endocrine disruptor at a particular time, then growth of critical organs and functions can be skewed. Reducing the exposure of the foetus to organophosphate pesticides, in particular, could reduce the risk of attention defi cit hyperactivity disorder.

In a 2006 study, children who were exposed prenatally to the organophosphate insecticide chlorpyrifos, as measured in the umbilical cord, were significantly more likely to have poorer mental and motor development by three years of age and increased risk for behaviour problems.4

Chlorpyrifos is used on a range of fruit and vegetables and grain in New Zealand. It has been found recently in celery, peaches, apricots, apples, pears, mandarins, oranges, raisins, sultanas, grapes, tomatoes and bread, among others.


Cancer, hormone disruption and more

Celery is also likely to contain a fungicide chlorothalonil, which is a probable human carcinogen, and in laboratory studies has caused DNA damage and embryo loss. Chlorothalonil has been included in a list of pesticides that the EPA in the US intends to study as potential endocrine disruptors. This pesticide has also been found in groundwater, seawater and air, and is toxic to many species, including earthworms.

Another fungicide used on celery, mancozeb, has a breakdown product, ethylene thiourea, which has been found to cause cancer, endocrine disruption, goitre and birth defects. Exposure to heat increases the amount of metabolite, so think of that before you add non-organic celery to your soup!


Organic food: worth it for health, growers and environment

Usually, washing, peeling and cooking reduces the amount of pesticide residues, however some persist. If you think organic food is too expensive, remember that nonorganic food does not include the cost of biodiversity loss and other environmental degradation. With organic food you pay the real cost for real food, and you give the grower a fairer return. By having organic food you support a system that better protects our children and the environment.

The dirty dozen
Food in New Zealand with the most pesticide residues ranked according to number of pesticides detected in total samples and percentage with pesticides.


Food  % with residues no. of pesticides sample size
Celery  98.2 21 56
Peaches, fresh/canned 96.4 15 56
Apricots, fresh/canned 96.4 14 56
Butter/cream/cheese 100 3 24
Wheat: bread, all products 79.3 23 232
Apples 80.5 20 288
Plums 91.6 8 48
Mandarins 83.3 10 36
Raspberries 85.4 7 48
Oranges 82.1 9 56
Strawberries 71.1 16 92
Grapes/raisins/sultanas 57.1 25 28



  1. Data obtained from New Zealand Food Safety Authority surveys: ‘2003–04 New Zealand Total Diet Survey’, ‘NZ Food Residue Surveillance Programmes 2004–2008’, available at Results from several years were combined to produce sample sizes that were more robust for analysis. A summary of residues from 280 apple samples taken from 120 orchards after harvest but before washing was supplied courtesy of Apple Futures.
  2. Curl, Cynthia L, Fenske, Richard A, Elgethun, Kai, ‘Organophosphorus pesticide exposure of urban and suburban pre-school children with organic and conventional diets’, Environmental Health Perspectives, 13 October 2002, National Institute of Environmental Sciences,
  3. Grandjean, P et al, ‘The Faroes Statement: Human Health Effects of Developmental Exposure to Chemicals in Our Environment’, Basic & Clinical Pharmacology & Toxicology, 2007, 102, 73–75.
  4. Rauh, V, ‘Impact of prenatal chlorpyrifos exposure on neurodevelopment in the first three years of life among inner-city children’, Pediatrics Vol. 118 No. 6, December 2006, pp 1845–1859. Available at:–0338