Direct sampling measurements (at the time of exposure)
of the air we breathe, the water we drink, or the foods we eat are rarely done.
Instead, human exposure to toxic substances is often estimated from other data
by mathematical exposure modeling. Data
commonly used for exposure modeling include release data (e.g., TRI), ambient
environmental monitoring data (e.g. air quality), estimates of contam
A wide variety of factors (e.g., atmospheric conditions, distance from sources, time spent in various activities, etc.) are entered into exposure models to attempt to simulate conditions that accurately reflect what exposures actually occur for a given individual. Biology, chemistry, physics, and math may all play a role in developing models, and model equations are often quite complex with multiple variables. The validity of exposure estimates produced by model calculations thus depends on both (1), the quality of the data that enter the model, and (2), the accuracy and completeness of the model’s assumptions. A few examples of the uses of modeling to estimate exposure are CHAPIS (the Community Health Air Pollution Information System),[3] Scorecard,[4] and the Food Safety Risk Analysis Clearinghouse.[5]
Biomonitoring is the direct measurement of people's exposure to toxic substances in the environment by measuring the substances or their metabolites in human specimens, such as blood or urine. Biomonitoring measurements are the most health-relevant assessments of exposure because they indicate the amount of chemicals that actually get into people (from all environmental sources (e.g., air, soil, water, dust, food) combined. Biological samples that have been successfully used as biomarkers of exposure to environmental pollutants include blood, hair, fingernails and toenails, breast milk, bone, teeth, urine, and feces.[6]
Standard approaches to biomonitoring include blood
and urine screening for toxic substances. Common substances tested include PCBs, dioxins, furans (byproducts of
PVC production, industrial bleaching and incineration), heavy metals,
organochlorine insecticides, organophosphate insecticide metabolites,
phthalates (plasticizers), and volatile and semi-volatile organic chemicals
such as ethyl benzene. Biomonitoring of workers potentially exposed to harmful
chemicals in the workplace is required by law in many industries. Lead
screening is the most common form of community biomonitoring for environmental
exposures, but this section looks at other examples as well.
The CDC
Second National Report on Human Exposure to Environmental Chemicals presented
biomonitoring exposure data for 116 environmental chemicals in the civilian
The Body Burden Report by the Environmental Working Group[8] tested the blood and urine of 9 adults for even more chemicals than those investigated by the CDC (210) occurring in consumer products and industrial pollution. Of the 167 chemicals found, 76 cause cancer in humans or animals, 94 are toxic to the brain and nervous system, and 79 cause birth defects or abnormal development.
The Allegheny County Childhood Lead Poisoning
Prevention Program (CLPPP) conducts blood lead screening for children ages 0-6
door-to-door in high-risk communities and at fixed-site locations such as day
care facilities, head start programs, and health fairs. Laboratory testing services are provided by
the Allegheny County Division of Laboratories.
Screenings
are performed year round and are on-going.
Approximately 4000 screenings occurred last year and there were
approximately 300-400 cases identified as having a blood lead level in excess
of the guideline of 9mg/dl established by the CDC.[9] The population of children ages 0-6 is
approximately 72,000.[10] The coordinator identified several
difficulties in reaching children in this age group and stated that there is
still not enough screening going on in the county. Difficulties range from the ineffectiveness
and inefficiencies of the door-to-door screening method, problems in managing
identified cases, and the public’s lack of awareness about the effects of lead
on child development. Improvement in
monitoring blood lead levels in the county could be achieved by increasing the
number of screenings conducted by private physicians.[11]
Many
states, including
The PA State Department of Health maintains the Blood
Lead Surveillance System. Laboratories
approved to perform blood analysis for lead are required to report blood lead
levels for individuals up to the age of
16 and pregnant women. In 2002, the DOH
reports data for 71,776 children under age 16 screened out of an estimated
state population under age 16 of 2.5 million.
Other states (e.g.,
The future development of biomonitoring as a tool for
exposure assessment in community settings will depend on our ability to
accurately and cost-effectively test for substances of interest in the body as
well as the time, expense, and expertise needed to conduct such programs using
sound epidemiological methods. In
At
the 2004 annual meeting for the Society for Environmental Journalists (SEJ) at
·
27% of participants had Hg hair concentrations
that were greater than the 1 µg/g (1 ppm) level corresponding to the USEPA
reference dose (RfD) for methyl mercury, The USEPA defines the RfD as an “estimate
(with uncertainty spanning perhaps an order of magnitude) of a daily exposure
to the human population (including sensitive subgroups) that is likely to be
without an appreciable risk of deleterious effects during a lifetime.”
· The number of fish meals reported consumed was a strong predictor for mercury levels in hair, the lowest levels being generally found in vegetarians and vegans who ate no fish,
· Age was also found to be a statistically significant predictor of Hg levels, even after accounting for differences in fish consumption habits.
"What
awful choices,” said Dr. Spengler,
“we are being asked to make–lower your mercury
levels by switching away from beneficial fish, instead of reducing the source
of mercury with the currently
affordable control technologies for power plants. It is not just the
This study’s innovative approach appears to be a valuable way of increasing public awareness and involvement in monitoring human exposure to environmental toxins. Because hair sampling is relatively easy and non-invasive, participation rates for this type of study are generally high. Moreover, the study brought to light the lack of pre-existing data and public awareness about mercury exposures in the local population, provoking questions from participants such as: To what other toxic substances am I being exposed? How can I protect myself from being exposed to these substances? and Is my government doing enough to reduce the presence of these chemicals in my environment? Beyond the important information it can yield, the direct measurement of toxins in people can be a powerful impetus for increasing protective individual behaviors as well as more generating effective public health policy.