The Centers for Disease Control has released a fascinating (to me) national report on "human exposure to environmental chemicals." It contains good news about things we know alot about: lead and second-hand smoke. Blood and urine samples were taken to measure the presence of 148 different chemicals (pdf).
For the period 1999–2002, 1.6% of children aged 1–5 years had elevated blood lead levels. This percentage has decreased from 4.4% in the early 1990s.75% seems like quite a big decrease, a victory owing to the increase in no-smoking regulations. The bad news is that they show increased levels of chemicals whose effects are less certain to scientists. "Cadmium" and various "phthalates" (which come from plastic) have all seen increases in our bodies. We will have to stay tuned to find out just what havoc those wreak on us. You can read some or all of the report at the CDC website here.
Cotinine is a metabolite of nicotine, and serum cotinine levels track exposure to environmental tobacco smoke (ETS) in people who do not smoke. Higher cotinine levels indicate more exposure to ETS, which is a human carcinogen (cancer-causing agent). Serum cotinine data for the U.S. population are available for 1988–1991 from previous work at CDC, and with this Third Report, data are now available for 1999–2002. From 1988–1991 to 1999–2002, median cotinine levels in nonsmokers decreased 68% for children, 69% for adolescents, and about 75% for adults.