About the biomonitoring data

Information on this page:

What do these data tell us?

  • For cotinine, the percentage of nonsmokers exposed to environmental tobacco smoke (ETS) in a representative sample of the U.S. population.
  • For all other chemicals, the median and upper percentiles of blood or urine levels in a representative sample of the U.S. population.
  • Data broken down by age, race/ethnicity, sex, and year.

How can we use these data?

  • Track trends in exposure to chemicals over time.
  • Show exposure levels that may be harmful to health.
  • Learn which groups of people are more highly exposed than others.
  • Target highly exposed or vulnerable groups for policies or programs to reduce exposures.
  • Evaluate whether exposure reduction efforts were effective.
  • Identify communities with high exposures that are not seen in national data.

What can these data not tell us?

  • The specific sources of exposure to the chemical being measured.
  • Finding a chemical in blood or urine does not mean the exposure causes a health effect; it only tells us that a person was exposed to the chemical. Looking at biomonitoring data and health effects studies together can help us determine levels of chemical exposures that cause health effects.
  • For some chemicals, such as mercury, enough research on possible health effects has been done that public health scientists have determined a reference for safe and unsafe levels in blood or urine. For other chemicals, we do not yet know enough to determine a reference level.

What is the source of the data?

  • The U.S. Centers for Disease Control and Prevention's National Biomonitoring Program measures chemicals in the blood and urine of a representative sample of the U.S. population through the National Health and Nutrition Examination Survey (NHANES). NHANES is an ongoing survey of the U.S. population.
  • Data are made publicly available in two-year cycles, and can be found on the CDC's National Report on Human Exposure to Environmental Chemicals web page.
  • Some of the data shown are from peer-reviewed published papers that used NHANES data or from Morbidity and Mortality Weekly Reports from the CDC. Links to the sources of data are provided on the Facts & Figures pages.

What are the units used for biomonitoring? What is a mcg/L?

  • Chemicals are usually measured in blood and urine as the mass of the chemical (such as a microgram (mcg), or one-millionth of a gram) per volume (such as a liter (L)) of blood or urine. The units most commonly seen are mcg/L. Cotinine is measured as nanograms (ng) per milliliter (mL) of serum.
  • For some chemicals, such as arsenic and cadmium, data are presented as either mcg/L of urine or mcg/g of creatinine. Creatinine-corrected data (presented as mcg/g of creatinine) take into account the variable dilution of spot urine samples.

What are the limitations of the data?

  • A single urine or blood measurement may not reflect a person's ongoing exposure, particularly for chemicals cleared quickly from the body.
  • Many factors such as genetics, diet, and biological characteristics can influence how an individual metabolizes and clears a chemical from the body, and thus their urine and blood levels.
  • National biomonitoring data from NHANES do not necessarily reflect chemical levels and trends in exposure among Minnesota residents. There may be reasons why exposures are different at the state or local level, including localized sources of pollution, climate patterns, and differences in lifestyle factors such as diet.

Where can I find more technical information related to the data?