Lead used in petrol decades ago still pollutes London’s air: Study

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An incorrect combination of fuel and air can lead to uneven combustion of fuel inside an automobile engine cylinder, causing the engine to produce a thudding sound, commonly known as ‘engine knocking’. In the early twentieth-century, tetraethyl lead was adopted as an antiknock additive in the fuel to avoid this.

However, the harmful effects of lead consumption were not known in the 1920s, when the practice gained widespread acceptance. In the 1970 and 80s, there was increasing awareness about the harmful effects of lead on the environment and health and it led to the use of lead as an antiknock additive in fuel being illegalised and phased out in most developed countries.

Years after it was phased out in most countries (currently it is legal only in six countries: Algeria, Iraq, Yemen, Myanmar, North Korea and Afghanistan), lead from automobile fuel still poses a serious health risk. This is because lead from fuel exhaust gets deposited on soils or finds its way into water bodies. Lead deposited in soils becomes airborne and finds its way to the pulmonary tract. Lead in water can be used in irrigation or even be directly ingested.

In a recent study, researchers from the UK and EU find that lead from fuel banned almost two decades ago (around the same time when it was banned in India) pervades London’s air to this day. The study was conducted by comparing the lead isotopic signature over both space and time.

In order to account for spatial variation, samples from road dust and topsoil were juxtaposed with those collected from rooftops. This was done for the years 2014-2018 and was then supplemented with lead isotope data from different years from the 1960s through the 2000s.

Airborne particle sampling Airborne particle sampling at Marylebone Road (Eleonore Resongles)

The key takeaway from the study is that there was little difference in lead levels in both the spatial and temporal assessments i.e. the airborne samples were similar to those of soil and road dust; and that the content has remained largely unchanged over the last decade.

Lead levels in London air plummeted rapidly from 500-600 ng/m³ to 300 ng/m³ in the 1980s, a decade when nearly “7000 tonnes were emitted in road traffic exhaust in the UK”, before dropping further to 20 ng/m³ in 2000 – but the concentrations measured in 2018 stood at 8-10 ng/m³.

Remobilisation or resuspension of contaminated dust contributed nearly as much as 800 kg lead into London’s air, according to the study. Further, researchers found little intra-annual variation, which led them to conclude that coal burning in the vicinity cannot be deemed responsible for lead contamination.

A similar study conducted for Sao Paulo, Brazil, had also reached a similar conclusion: that the lead isotopic signatures from aerosol samples were “mainly derived from vehicular exhaust and traffic dust resuspension.”

This has serious consequences, particularly for children, in whom it can lead to permanent brain damage. Exposure to lead in pregnancy can even lead to stillbirth and miscarriage, the World Health Organisation states while highlighting that there are no safe limits for lead consumption.

“Atmospheric lead has reached a baseline in London which is difficult to push down further with present policy measures. We need more research to identify the effect of present air concentrations – even if they meet data air quality targets – on human health, and to find the best way to rid London of lead’s legacy for good,” said Dr Elenore Resongles, the lead author of the study, in a press release.

– The author is a freelance science communicator. (mail[at]ritvikc[dot]com)

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