A new report from the Environmental Protection Agency indicates dangerous dioxin levels in Ireland have dropped by a fifth over the past five years, and now rank among the lowest in Europe.
Dioxins are organic compounds which, in a minority of cases, can be highly toxic and cause cancer, affect the skin or damage the immune system.
They are generated by a number of industrial practices such as the incineration of medical waste, burning coal to generate electricity or making copper.
This sector is now tightly regulated but others are not, such as the burning of waste in people's backyards or bonfires or forest fires.
To identify dioxin levels here, the EPA tested the fat content of cows' milk, on the basis that the animals tend to graze over relatively large areas and would therefore be exposed to the organic compounds.
The study found dioxin levels are down by a fifth when compared with five years ago and down by a third when compared with a decade ago.
The EPA said the fall could be mainly accounted for through the banning of lead in petrol and tightening dioxin regulations.
But cancer-causing dioxins in the air around Cork Harbour have almost doubled in four years. In its report, the EPA says it cannot explain this particular increase.