Research by scientists at the University of Otago has found traces of long-abandoned pesticides in waterways on New Zealand farms - and organic farms are not exempt.
Pourya Shahpoury looked at five sites across the east coast of the South Island and at each site took sediment samples from a stream and also from a conventional, an integrated and an organic farm.
He says the research looked at whether farming practices can make a difference to pesticide levels in streams.
Dr Shahpoury said overall the quality of the streams that they investigated was good, although there were some individual samples that exceeded toxicity thresholds.
He said the reason pesticides are found on organic farms is because of vapour, or spray drift.
But the nature of some of the pesticides found in those samples has alarmed some environmental groups.
Traces of the organophosphate, chlorpyrifos, were frequently detected.
The Pesticide Action Network said chlorpyrifos is especially dangerous for pregnant women and small children - because it affects brain development in babies in the womb and in newborns.
Also detected was endosulfan sulfate which was banned in New Zealand in 2008.
The Pesticide Action Network is calling for an immediate reassessment of chlorpryifos.
Dr Meriel Watts said the Environmental Protection Authority recently approved chlorpyrifos for aerial spraying.
She said it is a persistant organic pollutant that is very easily spread by the air and the EPA should reassess its use.
Dr Watts said it's extremely dangerous to foetuses and new-born children.
But AgCarm chief executive Graeme Peters said only tiny residues were found and that the lesson is: If you look hard enough you can find anything.
Dow AgroSciences has withdrawn chlorpyifos from industrial and home garden use. But the company says it is safe when used correctly in outdoor agriculture and horticultural settings.