There has to be some level of scale involved... I googled for lead emissions and found a nice graph showing a quarter of a billion tons in 1972 dropping to basi

There has to be some level of scale involved... I googled for lead emissions and found a nice graph showing a quarter of a billion tons in 1972 dropping to basically nothing now, around 500 tons or so. The graph links from here http://faculty.cua.edu/forbes/environment.htm http://faculty.cua.edu/forbes/environment.htm