Lead was the bigger problem. Introduced in the 1920s. (Tetraethyl lead was identified as an additive in 1921, its commercial production lagged by a few years,

Lead was the bigger problem. Introduced in the 1920s. (Tetraethyl lead was identified as an additive in 1921, its commercial production lagged by a few years, see: <https://en.wikipedia.org/wiki/Tetraethyllead https://en.wikipedia.org/wiki/Tetraethyllead>.)