Body burden refers to the total of chemical exposures in the body—and how and where chemicals enter the body. Steingraber compares this to the reading of seasonal growth rings on trees. Body burden measures cumulative exposure but requires extensive sampling and is best completed during autopsy or archived human tissues. Biomonitoring, which records the levels of contamination in humans through blood and urine, is effective because it doesn’t rely on questionnaires, surveys, interviews, or personal anecdotes. It’s the drug test of the ecological world. Its success depends on sampling a large enough representative population and sufficient time to detect trends. Biomonitoring of children with high levels of lead contamination from gasoline successfully led to the elimination of lead from gasoline in the 1970s. Eliminating smoke inhalation has also decreased toxins, though this has a long way to go.

In 1999, the Centers for Disease Control (CDC) examined a sampling of the US population. The results suggest that nearly all US residents have chemicals used in flame-retardant materials, which act like PCBs in their bodies, or similar chemicals that appear to be greater in children and women of reproductive age. The study suggested, however, that PCBs had declined and that persistent organic pollutants had declined in pregnant women as compared to 50 years earlier.