In 2001, the US Centres for Disease Control (CDC) release its first exposure report of 27 environmental toxins measured in human bodies of a sample of the US population. (In the past, the CDC estimated population exposures to certain chemicals by measuring air, water or soil samples. But due to advances in biomonitoring techniques, it measured the chemicals directly from subjects' blood and urine In the past, the CDC estimated population exposures to certain chemicals by measuring air, water or soil samples. But due to advances in biomonitoring techniques, it measured the chemicals directly from subjects' blood and urine samples.) Each year it will add another 25 chemicals to record trends and establish baselines adequate to suggest public health interventions.