Wood heating is reintroducing lead into the air of local communities and homes, a systematic investigation by academics has found.
Overwhelming evidence of lead’s neurotoxicity meant the metal was banned as an additive in petrol more than 25 years ago. The research by academics from the University of Massachusetts Amherst began by analysing samples of particle pollution from five suburban and rural towns in the north-east US. They looked for tiny particles of potassium that are given off when wood is burned and also particles containing lead.
Samples from seven winters revealed associations between potassium and lead. When there were more wood burning particles in a daily sample, there was more lead in the air, with clear straight-line relationships in four of the five towns.
Prof Richard Peltier, the senior author of the research, said: “For the most part, wood burning produces significant amounts of particle air pollution, and a small but measurable fraction of this is a powerful neurotoxicant.”
Tricia Henegan, a PhD student at Umass Amherst and the first author on the research, said: “Wood fuels have been a popular choice in much of the world. We were concerned that there were harmful elements that place the public at risk. It turns out that we were right.”
The project was extended to 22 other towns across the US. The relationships between lead and potassium varied from place to place, being strongest in the Rocky Mountains. By factoring in the effects of temperature, moderate to strong associations in their analysis strengthened the conclusion that the extra lead came from wood burning.
The lead concentrations were less than the US legal limits, but any exposure to the metal is harmful.
Lead was used globally as a petrol additive from the 1920s. It found its way into oceans, soils and people but evidence on harms from exposure to lead were systematically suppressed by industry. Today it is acknowledged that lead exposure causes harm at all stages of life and that exposure comes from many sources.
Although less than legal limits, lead particles are routinely measured in UK cities in winter when people are also burning wood. This is normally attributed to waste wood covered with old lead paint, but the Umass Amherst study suggests the metal is coming from the wood itself. This means that any wood burning could increase exposure in neighbourhoods and at home.
Henegan said: “The most logical answer is that it comes from uptake in the soil, probably riding along with the nutrients and water that trees need. Once in the tree, it deposits in the tree’s tissues and remains until that tree is burned.”
Other research on old and modern stoves shows combustion temperatures are high enough for lead to become part of the smoke. A 2003 study in rural Sweden found higher levels of lead in homes with wood heating compared with those that did not use wood.
Henegan said: “The use of wood as an energy source is a relic of the past, one that should not be relived if given a choice. Although wood fuel use can feel nostalgic, it does have negative consequences on air quality, and therefore public health.”
