Under the Clean Air Act, the EPA can regulate gasoline additions if they "endanger the public welfare." Scientific evidence showed that lead emissions from gasoline constituted 90 percent of all the lead in the air and that this lead could be absorbed into the body. The EPA promulgated regulations requiring a step-by-step reduction of the lead content of gasoline. Gasoline manufacturers challenged the EPA's rulemaking procedure, claiming that it was arbitrary and capricious because the evidence supporting the agency's decision was unsound.
They claimed that air was only one of several sources of the lead absorbed by the body. The EPA argued that the evidence it had marshaled was sufficient to justify the regulations. Who won this case and why?