text: In 2006 the U.S. National Research Council published a report, Human Biomonitoring for Environmental Chemicals. The report recognized the value of biomonitoring for better understanding exposure to environmental chemicals, and included several findings and recommendations to improve the utility of biomonitoring data for health risk assessment. In summary, the report called for more rigorous health-based criteria for selecting chemicals to include in biomonitoring studies; the development of tools and techniques to improve risk-based interpretation and communication of biomonitoring data; integration of biomonitoring into exposure assessment and epidemiological research; and exploration of bioethical issues around biomonitoring, including informed consent, confidentiality of results, and others.
  The issue of exposure to environmental chemicals has received attention as a result of televised reports by Bill Moyers for PBS and Anderson Cooper for CNNs "Planet in Peril" series. The book Our Stolen Future', with a foreword by former Vice President Al Gore, also raised awareness by focusing on endocrine disruption.
  Surveys of human exposure to chemicals do not usually integrate the number of chemical compounds detected per person and the concentration of each compound. This leaves untested relevant exposure situations; e.g., whether individuals with low concentrations of some compounds have high concentrations of the other compounds. Analyses of the concentrations of a given compound usually show that most citizens have much lower concentrations than a certain minority. A study based on a representative sample of the population of Catalonia (Spain), which integrated the number of compounds detected per person and the concentration of each compound, found that more than half of the population had concentrations in the top quartile of 1 or more of the 19 persistent toxic substances (PTS) (pesticides, PCBs) analyzed. Significant subgroups of the population accumulated PTS mixtures at high concentrations. For instance, 48% of women 60–74 years had concentrations of  6 or more PTS in the top quartile; half of the entire population had levels of 1 to 5 PTS above 500 ng/g, and less than 4% of citizens had all PTS in the lowest quartile. Thus, PTS concentrations appear low in most of the population only when each individual compound is looked at separately. It is not accurate to state that most of the population has low concentrations of PTS. The assessment of mixture effects must address the fact that most individuals are contaminated by PTS mixtures made of compounds at both low and high concentrations.