Lead levels in air vary from 0.17 micrograms per cubic metre in unpopulated rural areas through 4 micrograms per cubic metre in urban, densely populated areas. Values near freeways may reach 10 - 25 micrograms per cubic metre, and in a long highway tunnel, extreme values of 50 micrograms per cubic metre are possible. As environmental regulations have reduced or eliminated the use of lead in gasoline, these values have steadily dropped. Abnormal sources of lead intake for humans are primarily two. First, drinkers of large amounts of moonshine whisky drink in lead from the lead solders of stills.
Modern paints contain little or no lead.
Lead balance in the body is important. The maximum normal daily output of lead from the human body is about 2000 micrograms per day. The details of the normal or average input and output are as follows. Clearly, the average input and output are approximately in balance. It is only when a human body takes in a high level of lead that the lead accumulates in the body.