Chlorine-rich dioxins (cancer causing chemicals) were first identified as highly toxic and persistent pollutants associated with 20th century manufacture of organochlorine chemicals and as a by-product of modern waste incinerators (think back to the Seveso disaster in Norther Italy or the more recent problem of contaminated pasteur).Why then have scientists found dioxin-laced soil samples from the 19th century? Andy Meharg and Kenneth Killham of the University of Aberdeen in Scotland discovered that the burning of coastal peat (also rich in salt and therefore chlorine) forms dioxins that are concentrated in peat ash. They found that one kilogram of peat ash contains about 61 billionths of a gram of dioxin. In treeless regions of Scotland and Ireland peat was the standard fuel source for centuries. The scientists concluded that in the 18th and 19th centuries, the remote highlands and islands of Scotland probably produced around one kilogram of dioxin a year. A surprisingly large amount, given that municipal waste incinerators for the entire United Kingdom produce around 10.9 kilograms of dioxin a year. Andrew A. Meharg, "Nature" tel +44 1224 272264, e-mail a.meharg@abdn.ac.uk