The phasing out of this substance as an antiknock agent allowed for the wider adoption of catalytic converters.  
Herbert Needleman vigorously campaigned against the use of this substance, as did Derek Bryce-Smith.  The Harding administration vetoed a 1922 ban on this substance originating from a League of Nations proposal.  A controversial Johns Hopkins study involving this substance in the 1990s divided low-income Baltimore families into structures that had received three different levels of (*) abatement.  A DuPont factory that heavily used this substance earned the nickname of the House of the Butterflies.  The phasing out of this substance as an antiknock agent allowed for the wider adoption of catalytic converters.  J. Julian Chisolm pioneered using chelation therapy to treat people exposed to this substance.  For 10 points, what substance once found in paint, pipes and gasoline may have poisoned citizens of the Roman Empire?
Herbert Needleman vigorously campaigned against the use of this substance, as did Derek Bryce-Smith.  
lead [or tetraethyl lead]