Lead particles from decades-old petrol emissions persist in London’s air
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According to a study from Imperial College London, airborne particles in London’s atmosphere remain highly lead-enriched compared to natural background levels, despite a 1990s ban on leaded petrol.
The use of lead in petrol is banned in most countries due to evidence that exposure causes neurodevelopmental problems in children and cardiovascular, kidney and reproductive problems in adults.
Lead levels in London’s atmosphere have dropped significantly since a 1999 ban on leaded petrol and now meet UK air quality targets. The ban on leaded additives in petrol in the UK was phased in gradually; since 1992, all newly sold cars were required to contain catalytic convertors to take unleaded fuel.
However, this study found that up to 40 per cent of lead in airborne particles today can be traced to the long legacy of leaded petrol, highlighting the very stubborn persistence of anthropogenic contaminants in the environment.
“Petrol-derived lead deposited decades ago remains an important pollutant in London. Despite the leaded petrol ban, historically combusted lead is still present in London’s air more than 20 years later,” said Dr Eléonore Resongles, who led the study.
The researchers compared the chemical and isotopic composition of airborne particles with samples of road dust and urban soil taken from street level in Marylebone and Imperial College’s South Kensington campus. Their samples confirmed the role of the re-suspension of dust, which had been contaminated from leaded petrol pre-1999, consequent to lead’s persistence in London air today.
In the 1980s, annual average airborne lead concentrations in central London dropped from 500-600ng/m3 of air to around 300ng/m3, before dropping to around 20ng/m3 in 2000. The researchers in this study measured lead concentrations of 8ng/m3 of air on average in 2018 at Marylebone Road. The findings from the London-based study are in line with similar results from studies conducted in Sao Paolo, Brazil.
The researchers explained that - once it has settled in the environment - lead from historic leaded petrol is stirred up (most likely by wind and vehicle movement), resulting in a significant and persistent source of lead in the atmosphere. They warn this could be a potential hazard warranting further investigation into its health impacts; while these levels meet air quality targets, there is no ‘safe’ threshold for lead in humans.
Professor Dominik Weiss, senior author of the study, explained: “We used to have a lot of lead circulating in the air, but it dropped dramatically when leaded petrol was phased out at the turn of the millennium. However, the evolution of isotope composition since then suggests that lead in the air, soil and dust persists at background levels and this could turn out to be a concern for health.
“Our findings highlight the need for an in-depth study of blood lead levels in the population, as was done recently in the US. Legacy lead deposited pre-1999 is significantly contributing to the overall lead burden, so we must try to reduce further the amount of lead we are releasing today if we want to offset legacy metals.
“Long-term low-level exposure to lead can adversely affect health,” Resongles continued. “While we don't yet know the health implications of our findings, they suggest that leaded petrol might still be providing low level exposure which can have detrimental effects on health.”
According to the researchers, if these levels of lead prove harmful, measures should be taken to target the sources of the lead in soil and on roads. Among other possible measures, this could include covering contained urban soil with fresh soil; this has been effective in reducing levels of lead in children’s blood in the US.
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