At a glance
- Persistent chemicals are usually measured in serum, whereas non-persistent chemicals are typically assessed by measuring their metabolites in urine.
- The higher percentiles (75th, 90th, 95th) provide information on the upper range of levels in the population and help identify unusual levels in public health investigations or studies.
Persistent and non-persistent chemicals
In the Report, most measurements in urine quantify chemical metabolites of non-persistent chemicals (those that do not stay in the body a long time). Metals and some tobacco biomarkers (e.g., heterocyclic amines) measured in urine are exceptions for they are not metabolites. Persistent chemicals (those that stay in the body for a long time) are usually measured in serum as the parent chemical.
Use of percentiles
The higher percentiles (75th, 90th, 95th) provided for each chemical convey useful information about the upper distribution and range of levels in the population. The 95th percentile is helpful when determining whether levels observed in separate public health investigations or other studies are unusual.