The organics industry body says many products typically eaten through the warmer months are the most heavily contaminated with pesticides and celery has topped a new list of foods with pesticide.

A food safety group, the Safe Food campaign, has released a list of 12 products including celery, canned peaches, apples, plums, butter and bread, that have been shown to have the highest content of pesticide residues in which 23 pesticides were found.

The 'dirty dozen' list which was compiled by food and soil researchers is based on data from the Food Safety Authority.

Organics Aotearoa New Zealand chief executive Jon Tanner said children with lower body weight were the most affected.

Safe Food Campaign researcher Alison White said the combined effect of all the chemicals in food was not known.

"There are various long term effects associated with particular pesticides, including endocrine or hormonal disruption, cancer, immune system suppression, nervous system damage, genetic damage and birth defects," White added.

Washing and peeling could reduce some residues, but researchers advised anyone with a compromised immune system, pregnant women and young children to eat organic foods.

Analysis from the Food Safety Authority released earlier in this year in its Total Diet Survey showed there was a continuing decline in chemical residues and contaminants in food products.