More toxic chemicals than officials previously admitted were unearthed in a New Plymouth playground last month.
Earthworks uncovered the remnants of nine drums in Marfell Park.
The Taranaki Regional Council said it found dioxin in two of the six samples tested.
But the full results, which have still not been issued by the council, show all six samples contain dioxin and four are contaminated with organophosphate insecticide.
The council says it focused on the worst dioxin contamination and none of the chemicals pose a current risk.
But dioxin campaigner Andrew Gibbs says officials keep trying to hide the extent of the problem.