1923 June - the US public health service made aware of the leaded gasoline and started asking for safety tests. (Kovarik 2011)

1923 Sept - workers started dying in the DuPont TEL works… “sickening deaths and illnesses of hundreds of TEL workers… Gripped by violent bursts of insanity, the afflicted would imagine they were being persecuted by butterflies and other winged insects before expiring, their bodies having turned black and blue.” (Kitman 2000a)

1925 Apr - Yale university public health scientist claims Ethyl gasoline represents "the greatest single question [whether leaded gasoline is safe] in the field of public health which has ever faced the American public." (Kovarik 2011)

1925 May 20 - US Public Health Service holds conference (PHS US 1925) to discuss viewpoints on Ethyl controversy and appoints blue-ribbon committee to conduct independent inquiry. Consideration of alternatives to lead as anti-knock is suspended as conference is cut back from two to three days to only one day. (Kovarik 2011)

1926 Jan 26 - PHS committee finds "no good grounds" for prohibiting Ethyl gasoline but insists on continued tests. No independent tests conducted until 1960s. List of alternatives to tetraethyl lead proposed by C.E.A. Winslow of Yale kept from final report. (Kovarik 2011)

1928 - New York City ends its ban on leaded gasoline. (Kovarik 2011)

1953 - First post-war concerns about lead as air pollutant surface in Los Angeles. General Motors follow issues closely (Kovarik 2011) [preparing to argue case for continuing to produce TEL]

1954 - A young academic at King’s College London, (later Professor) Derek Bryce-Smith first concerned (about the health effects of leaded petrol) when he asked the manufacturers for a sample of the kind of lead added to fuel for use in an experiment. “I got a phone call to say they did not want to make it available because it was extremely toxic,” he later recalled. “They finally gave me some, but told me that if I spilt any on the floor, I would have to take the whole floor up. And if I got any on my finger, it would be absorbed through my skin and drive me mad or kill me.” (Lean 2011) 

1960 - Tetramethyllead introduced as an additive to automotive fuel.

1960-1975 – A 2010 study stated that “the PbB [mean blood-lead level] during the peak years of maximum leaded gasoline usage (1960–1975) could be estimated at about 48 μg/dL [micrograms per decilitre]” and possibly as high as 63 and: “The extrapolated peak level of 48 μg/dL (range 40 to 63) is associated with clinical and behavioral impairments, which may have implications for adults who were children during the peak gasoline lead exposure …. leaded gasoline emission was the predominant source of lead exposure of African-American Cleveland children during the latter two-thirds of the 20th century.” (Robbins et al 2010)

1965 Sept – Clair Patterson publishes "Contaminated and Natural Lead Environments of Man," the first research to show that high lead levels in industrial nations are man-made and endemic. (Arch Environ Health. 1965 Sep; 11:344-60) (Kovarik 2011), thus beginning his campaign to phase-out leaded gasoline and lead solder in food cans.

1966 – US Congressional hearings on air pollution lead to long debate about new agencies and new regulations. (Kovarik 2011)

1969 - WHO Expert Committee reports on ambient air lead concentrations; non-urban sites show less than 0.5 µg/m3 [micrograms per cubic metre], while urban sites have values ranging from 1 to 5-10 µg/m3. Highest levels recorded on highways during rush hours, 14-25 µg/m3. (IPCS 1977)

1970’s - a legal basis for the precautionary principle is established by a court decision called the Ethyl decision involving banning leaded gasoline. (Charnley 2000)

In the 1970s, research showed that low environmental levels of lead exposure could cause permanent learning and behavior problems in children exposed before birth and in infancy and toddlerhood. Lead paints and leaded gasoline were the major sources of exposure.  Efforts to reduce lead exposure began in 1975-76 when lead paints were banned and leaded gasoline was phased out. 

Exposure models predicted that lead levels in the population would change very little, but biomonitoring at the CDC found the opposite:  as lead levels in gasoline declined, so did blood lead in the US population.  Today, the average US citizen has a blood lead level under 2µg/dL.  The level that triggers public health action to prevent further exposure is 5µg/dL, and the average 1976 blood lead level is now considered lead poisoning.

1970 – US Environmental Protection Agency created. Car manufacturers ordered to begin building engines to run on unleaded gasoline by 1975. Ethyl Corp. unsuccessfully opposes phase-out of leaded gasoline in courts.

1970 – US auto makers develop catalytic converter as a stop-gap technology while they develop cleaner engines. TEL poisoned the catalytic converters so the pressure was on to get lead-free gasoline (petrol) on the market to permit catalytic converters. In response to this the US Environmental Protection Agency (EPA) orders introduction of unleaded gasoline and issues an order for lead-gasoline-free cars by 1975, thus beginning the world’s first national phase-out of leaded petrol. A health model predicted that the effect of the introduction of unleaded gasoline on lead concentrations in the blood of US residents would be minor. Ref and graph (adapted from USCDC) (Sexton et al 2004 )

1971 July – Japan introduces a maximum permissible level of 0.31 grams of lead per litre (IPCS 1977) which may have been the first such restriction and thus the first national lead-in-petrol phase-down policy.

1972 Apr – Unleaded petrol begins to be marketed in Japan. (IPCS 1977)

1975 - New US car models made with catalytic converters which require unleaded gasoline. Ethyl Corp. unsuccessfully proposes "lead tolerant" catalytic converters. (Kovarik 2011)

1976 Mar – US Court of Appeals ratifies maximum permissible level of 0.13 g of lead per litre of gasoline by 1 January 1979. (IPCS 1977)

1977-82 - Extensive tests by public health scientists show marked correlations between high levels of lead in children's blood and brain damage, hypertension and learning disorders. 

1981 – The US EPA notes that between 1970 and 1979 a 41% drop in the composite maximum quarterly average of ambient air-lead concentrations at 105 sites across the nation was accompanied by a 40% drop in the amount of lead consumption in gasoline, excluding sales to the military. (Pirkle Et al 1983)

1983 June - The Second National Health and Nutrition Examination Survey (NHANES II) reveals a precipitous decline in blood lead levels in all segments of the US population, a drop of 37% (from 14.6 to 9.2, a drop of 5.4 micrograms per deciliter) between Feb 1976 and Feb 1980, closely paralleling the contemporaneous decline in the amount of lead added to gasoline. [See graph above.] (Pirkle et al 1983)

1984 - City of Chicago first to order end of all leaded gasoline sales since New York City ended ban on leaded gasoline in 1928. (Kovarik 2011)

1985 – US EPA’s estimates based on Pirkle et al (1983) indicate that lead in gasoline in the United States may be responsible for well over one million cases of hypertension per year and for over 5,000 deaths from heart attacks, strokes, and other diseases related to blood pressure. Moreover, these estimates cover only males aged 40 to 59 and, in the case of heart attacks, strokes, and deaths, only white males in that age group. In their estimation of the total benefits of a phase down of gasoline some other impacts were also addressed, for example Children’s Health Effects. US EPA’s estimation of the total benefit of a phase down of leaded petrol was: “7.9 billion, while the estimated cost is only $607 million, resulting in net benefits of $7.3 billion”. (Schwartz et al 1985)

1986 – Japan (probably due to its Minamata mercury tragedy and high value placed on IQ and longevity, or perhaps due to pressure from its auto-makers to be able to include catalytic converters on all new vehicles) became the first nation to fully phase-out leaded petrol.

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