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Why was tetraethyl lead removed from gasoline?

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Labeled cross-sectional diagram of a V-type gasoline engine for an automobile, showing internal components such as pistons, crankshaft, camshaft, intake and exhaust valves, connecting rods, spark plugs, and intake manifold. — gasoline engine Cross section of a V-type engine.

Tetraethyl lead (TEL) was removed from gasoline primarily due to its significant negative impact on public health and its incompatibility with modern vehicle technology.

While TEL was effective at preventing "engine knock"—the spontaneous and undesirable ignition of fuel in a gasoline engine—it is a toxic organometallic compound that contributes to lead poisoning through the emission of lead particulates in exhaust.123

The phase-out, which began in the 1970s, was driven by two main factors:

Public Health Concerns: Research, including studies by Clair Patterson and Herbert Needleman, highlighted the accumulation of lead in the environment and its detrimental effects on human health, particularly regarding intellectual development in children.123
Pollution-Control Technology: In the United States, the Environmental Protection Agency mandated the removal of leaded gasoline because lead interfered with the catalytic converters required in new vehicles to reduce smog.1

Following these regulations, the use of leaded gasoline was progressively banned worldwide to protect both the environment and human health.13