Chemical Exposures

Exposure to carcinogens that exist as pollutants in our air, food, water, and soil, also influence the incidence of cancer. Most exposure to toxic substances and hazardous wastes results from human activities, particularly through agricultural and industrial production. Chemicals were selected for inclusion in this report based on the following set of criteria: (1) likely or probable carcinogen as classified by IARC classification (Group 1 or 2A), (2) available biomarker data from the National Health and Nutrition Examination Survey (NHANES) since 2004, and (3) ubiquitous (i.e. >50% with detectable levels) in the U.S. general population (based on NHANES data).


The R function “svyquantile” from the R Package “survey” was used to estimate the percentiles and their confidence limits. The “betaWald” interval option was chosen, which was computed by adapting the method proposed by Wooddruff (1952) and the method proposed by Korn & Graubard (1998). The R function “svyranktest” from the same package was used to test whether there is statistically significant difference between the estimated percentiles obtained from different survey years. For more details on the R functions used, see The R functions were chosen in order to perform the desired significance tests.


  • Korn EL, Graubard BI. (1998). Confidence Intervals For Proportions With Small Expected Number of Positive Counts Estimated From Survey Data. Survey Methodology, 23, 193-201.
  • Woodruff RS (1952). Confidence intervals for medians and other position measures. JASA, 57, 622-627.