More than 20 years after lead was banned from petrol in the UK, its polluting effects are still being felt in London.
Airborne particles remain highly lead-enriched compared to natural background levels, Imperial College London said in the scientific journal PNAS.
Up to 40 per cent of lead in airborne particles derives from previous use of leaded petrol, the study, published on Tuesday, found.
Researchers said the work highlighted the long-term existence of air contaminants introduced by human activity.
The city, which has long had a pollution problem, was one of the first to introduce a congestion charge to reduce the volume of traffic in the centre. Last year it set up an ultra-low emissions zone for Greater London.
"Petrol-derived lead deposited decades ago remains an important pollutant in London," said the study's lead author Dr Eleonore Resongles..
“Despite the leaded petrol ban, historically combusted lead is still present in London’s air more than 20 years later.”
The study found that although lead levels had dropped dramatically, what remains is “persistent”.
Dr Resongles said further investigation was needed into it effects on the health of people in London because, despite air quality targets, there is no safe threshold for lead in humans.
“Long-term, low-level exposure to lead can adversely affect health and, 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,” Dr Resongles said.
Scientists compared the composition of particulate matter in the air with samples of road samples and urban soil, which confirmed the presence of dust contaminated by leaded petrol in London.
They said that once settled in the environment the lead particles were steadily recirculated by wind and vehicle movement.
The researchers took 18 samples of airborne particles at street level in Marylebone in summer 2018 and 20 samples from a 24-metre-high rooftop at Imperial College London's South Kensington campus between 2014 and 2018.
They found lead sources remained unchanged over the past decade.
Lead has been used in a variety of ways, from petrol, batteries, alloys and solders to piping and paint in homes and buildings.
Until 1999, leaded petrol remained the primary source of the metal’s emissions in the UK.
But the use of lead in petrol has ceased in most countries worldwide owing to evidence that exposure can cause neurodevelopmental problems in children and cardiovascular, kidney and reproductive problems in adults.
The study was in collaboration with the French National Research Institute for Sustainable Development, Princeton University in the US, the UK's University of Birmingham, the German Meteorological Service and King Abdulaziz University in Jeddah.