Use of lead-free petrol or diesel is recommended to reduce the pollutants emitted by automobiles. What role does lead play? 

Explanation

Catalytic converters having expensive metals namely, platinum, palladium and  rhodium as the catalysts are fitted into automobiles for reducing emission of poisonous gases.
They also convert unburnt hydrocarbons into `CO_(2) and H_(2)O`.
Motor vehicles equipped with catalytic to converter need to use unleaded petrol because lead in petrol inactivates the catalyst.
It increases the hydrocarbon emission.
Because of this environment is badly affected.
Lead accumulates in bones, blood and soft organs.
It adversely affects kidney, liver, nervous system  and other organs.