Transport for London (TfL) must take “urgent” action to ensure the public is not at risk from toxic Tube dust, the London Assembly says.

The Assembly’s environment committee said the dust could be dangerous and “little progress” has been made under Sadiq Khan’s mayoralty.

There is up to thirty times more pollution on the Underground than by London roads, according to Parliament’s Committee on the Medical Effects of Air Pollutants.

But most of the dust particles below ground are micro-shavings from train wheels and rails.

This dust can be an irritant, causing inflammation in the lungs – but unlike toxic car fumes, the full health effects of are not yet known.

The tiny particles, known as PM2.5s, can pass from the lungs into the bloodstream – making them especially dangerous if they are toxic.Air pollution on London streets has been linked to heart and lung disease, strokes, and infertility.

TfL currently spends £60 million a year cleaning trains, tunnels and stations, and is trialling ways to reduce dust further.

The transport network is also carrying out a long-term workforce study, and a short-term report on sick leave to find out what the dangers could be.

Workers on the Tube are particularly at risk from dust, because of long hours spent below ground.

Though pollution is below legal health limits for staff, the RMT union has said the official standards are not sufficient, and people could be at risk.

Environment Committee chairman Caroline Russel said: “There are very high concentrations of small particles in the underground and worryingly we just don’t know if they are harmful or not.

“While we know TfL has commissioned studies on the matter, the findings must be publicly available as soon as possible.

“We are particularly concerned about contract cleaners working on the Tube. The Committee has been told that no one is monitoring the health of these cleaners simply because they are not directly employed by TfL. This is unacceptable.”

TfL safety chief Lilli Matson said: “We are doing all we can to ensure that the air on the Tube is as clean as possible.

“The particulates found there are very different to those found above ground and are not known to have the same adverse health effects.

“We know that further research is needed, which is why we are funding academics to conduct studies and gain a better understanding of the health risks associated with air on the Tube.”

A spokesperson for the Mayor said: “Londoners deserve to breathe clean air and Sadiq is committed to improving air quality both above and under ground.

“Following the recommendation of experts, the Mayor has tasked TfL – which is responsible for managing dust levels on the Tube – with undertaking additional research to understand potential health impacts, trialling innovative approaches to address the problem and ensuring the Underground is as clean as possible.”