Question

Why should lead free petrol or diesel be used in automobiles?

Answer 1

Hint: Hazardous chemicals and gases which are harmful to living beings cause pollution. Petrol and diesel come from rock oil, which comes from deep underground. crude is refined to form petrol (in America this can be called gasoline) or diesel

Complete answer:
Though Lead when mixed with Petrol and diesel increases vehicle performance and fuel economy but these fuels that contain lead are emitted within the gaseous form and released by the vehicles.

This lead damages the auto parts just like the converter.
Lead also releases hazardous gases which causes severe problems in humans and other animals. It's also the cause behind slowness in children.
Lead petrol and diesel costs high as compared to the unleaded petrol and diesel. The latter is sort of cheaper and is way safer than lead petrol and diesel which emits hazardous gas in air.
Lead (tetraethyllead) when mixed with petrol and diesel increases vehicle performance and fuel economy. Apart from leading to air pollution lead is highly toxic and is known to induce severe lead poisoning.

Pollutants that are released from auto-mobile, locomotives, aircraft in cities constitute the major part of the total air pollution. Air pollution can occur by both natural and anthropogenics. Anthropogenic pollution is derived from both mobile and fixed sources.
The exposure pathways to lead includes:
Inhaling lead particles causes airborne emissions from automobiles
Lead also lead and make contribution to contaminated soil
Ingesting dust through normal hand to mouth activity also causes lead exposure
Eating contaminated food and drinking contaminated water.
Lead easily crosses and transfers across the blood-brain barrier and accumulates inside the brain. Chronic exposure to lead can also cause long term negative effects like memory loss, insomnia and loss of attention etc. So lead free petrol can prevent all these.

Note: If vehicles are maintained properly by Unleaded petrol and diesel then they're safer for the environment. As for survival, a clean and green environment is required.