Concentrations of chemicals found in participants of this project were compared to data from the National Health and Nutrition Examination Survey (NHANES) conducted by the CDC. The NHANES is an ongoing project of the CDC that aims to gather baseline information about the health of the U.S. population. The most recent published data from NHANES at the time of the Mind, Disrupted project (2009) was employed at all times.
When possible, reference data from the NHANES 2003–2004 data collection period were used. The reference data for PFCs (perfluorinated compounds) and perchlorate is from NHANES 2001–2002. The reference data for mercury included data collected as recently as 2006, while the reference data for lead was collected no later than 2000.
“CDC average” is the average (geometric mean) concentration in the total NHANES study population. “CDC 95th percentile” is the average (geometric mean) concentration of the chemical in the 5% of the NHANES population with the highest concentrations.
Data not found in graphs
Concentrations that were below the limit of detection (LOD) are graphically reported as zero. Chemicals below the limit of detection are not necessarily absent from the sample; they could be present at levels below those that the present technology can detect.
Some chemicals were detected, but at concentrations too low to accurately quantify. Concentrations detected below the limit of quantification (LOQ) were graphically reported as zero in graphs including all of the study participants. Some of the chemicals analyzed were below the LOD or LOQ in all participants. Data for those chemicals were not included in the graphs. Any data not included in the graphs may be found in the data tables.
Testing chemicals in urine
The analysis of chemical data from urine testing is more complicated than the analysis of chemical data from blood testing. The concentrations of both natural substances and toxins in urine change based on how hydrated a person is, what time of day it is, or what he or she ate recently. To account for this difference, a naturally occurring chemical called creatinine, which is present in all urine, is measured along with the other chemicals being studied. Knowing the concentration of creatinine in the urine makes it easier to compare the results of different people.
The process of using creatinine to standardize urine results is called “creatinine adjustment.” When creatinine adjustment has been used, it is indicated on the graph.