Humans have been putting highly toxic chemicals into the environment by burning peat for centuries, scientists say.
Peat bogs have been a vital fuel source for centuries
Today, large amounts of these dioxins are released from waste incinerators, but research shows we have been exposed to these toxins since even before the industrial revolution.
The new study reveals that past emissions, from peat burning in the Highlands and Islands of Scotland, were about a tenth of those produced by modern incinerators.
Dioxins are compounds that can stay in the environment for many years and are found virtually everywhere in the world. They are produced when carbon is burnt with chlorine.
Although environmentalists suspected that dioxins were not only produced by industry, they were not sure what these other sources could be.
Researchers from the University of Aberdeen analysed the dioxins in soil samples from 19th century Scotland.
They found they could reproduce the same concentrations by burning peat.
During the 18th and 19th centuries, peat burning was how people in much of the British Isles kept themselves warm.
Trees were scarce in coastal regions, but peat was an easily accessible fuel resource. However, it was also very salty, which meant it had high levels of chlorine.
The researchers worked out that Scotland, with well under half a million people, probably produced as much as a kilogram of dioxins each year.
That is a tenth of the amount produced by municipal waste incinerators in the whole of the United Kingdom today.
Professor Andrew Meharg, who led the team behind the work, told BBC News Online the research showed that modern society was the primary cause of the world's dioxin pollution.
But even prehistoric man was producing dioxins by burning peat, he said.
Professor Meharg added that the organochlorine-based industries were not solely to blame for the massive increase in dioxins in the latter half of the 20th Century.
However, he said: "Once we regulated pollution by putting limits on the organochlorine industries, [dioxin] levels dropped significantly."
The Aberdeen research is published in the journal Nature.