Approval for the commercial use of a fungicide has been revoked by the Environmental Risk Management Authority (ERMA).
The authority found that Quintozene, which is used on seedlings, bulbs and recreational turf, contains dioxin impurities.
It decided to review the substance after dioxin was found in Quintozene products in Australia.
Dioxins, which can cause cancer, are on a list of substances covered by the Stockholm Convention on Persistent Organic Pollutants.
ERMA says only one quintozene-containing product, Terraclor 75 WP, is registered in New Zealand.