&EPA
United States
Environmental Protection
Agency
Office of Water EPA- 820-F-13-059
4305T
November 2013
Technical Fact Sheet: Trends in Blood Mercury
Concentrations among Women of Childbearing Age
Summary
One of the primary risks associated with eating
contaminated finfish and shellfish is exposure to
methylmercury (MeHg). EPA looked at data
from 1999-2010 from the Centers for Disease
Control and Prevention (CDC) National Health
and Nutrition Examination Survey (NHANES),
to see whether there was a trend in blood
mercury concentrations and in fish consumption
among women of childbearing age.
The data showed that mercury levels in women
of childbearing age dropped 34 percent from a
survey conducted in 1999-2000 to follow-up
surveys conducted from 2001 to 2010.
Additionally, the percentage of women of
childbearing age with blood mercury levels
above the level of concern decreased 65 percent
between the 1999-2000 survey and the follow-
up surveys from 2001-2010. During the survey
period there was very little change in the amount
offish consumed.
Background
People are exposed to mercury mostly through
the consumption of finfish and shellfish.
Mercury released into the environment is
converted to MeHG in soils and sediments, and
over time, bioaccumulates in finfish and
shellfish. MeHg exposure to infants before birth
is associated with adverse health effects, for
example, neuropsychological deficits in IQ and
motor function.
The EPA analyzed NHANES' 1999-2010 data to
investigate trends over time in blood mercury
concentrations and fish consumption in women
of childbearing age (16-49 years). Each two-
year NHANES survey is an independent sample
that is representative of the U.S. population.
EPA's analysis is described in detail in an EPA
report titled, Trends in Blood Mercury
Concentrations and Fish Consumption among
U.S. Women of Childbearing Age, NHANES,
1999-2010.
How was this study conducted?
EPA developed a methodology to consistently
assess trends over time in the NHANES blood
mercury data. The methodology was peer
reviewed, and then revised to reflect input from
the peer reviewers. This methodology was
applied consistently to the data over all six
survey cycles.
The Agency used multiple imputation to
calculate the values below the limit of detection
for both blood inorganic and blood total
mercury. EPA then calculated blood MeHg as
the difference between the two values.
NHANES collects 24-hour dietary recall data
and asks respondents how many times in the
past 30 days they consumed 31 varieties of
finfish and shellfish. EPA combined these data
to create an estimate of 30-day finfish/ shellfish
consumption in grams, and grams per kilogram
bodyweight, for each respondent.
Next, EPA gathered data on fish tissue mercury
concentrations from 20 sources, including the
U.S. Food and Drug Administration, State
Departments of Environmental Quality and
Health, and data presented in peer-reviewed
journals. The Agency used this data, combined
with dietary recall data also from NHANES, to
estimate 30-day mercury intake in micrograms
per kilogram bodyweight and the mercury
concentration in the fish consumed.
The Agency weighted all analyses using the
recommended statistical weights. The sampling
design variables were used in calculating the
variance of the estimates as described in the
NHANES Analytical Guidelines.
EPA modeled the relationship between mean
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blood MeHg, blood MeHg above 5.8 (ig/L, and
fish consumption and mercury intake variables
using regression analyses, adjusting for
differences by respondent age, race, income, and
time across NHANES releases.
What Were the Results of the Study?
Trends in Blood Mercury Concentrations
For blood MeHg, the geometric mean in 1999-
2000 was 1.51 times higher than the geometric
mean across the subsequent 10 years. This
represents a decrease of 34 percent between
1999-2000 and 2001-2010.
The percent of women of childbearing age with
blood MeHg over 5.8ug/L in 1999-2000 was
2.86 times higher than the percent of women in
2001-2010, representing a 65 percent decrease
between 1999-2000 and 2001-2010.
Associations between Fish Consumption
Frequency and Blood Mercury Concentrations
The study found a significant relationship
between mercury intake from fish consumption
and blood mercury. The analysis showed little
change in fish consumption and mercury intake
over the study period. There was a marginally
statistically significant decreasing trend across
NHANES survey releases in the ratio of mercury
intake to fish consumed.
Demographic characteristics were associated
with blood mercury as expected: higher
concentrations observed with increasing age and
income and higher concentrations observed in
the "other" race category and lower
concentrations observed in Latinos. Similar
patterns between fish consumption and
demographic characteristics were found.
What Actions is EPA Taking to Reduce
Mercury
In 2013, EPA took two significant actions
toward making fish and shellfish safer to eat. In
June, the Agency proposed new effluent
guidelines for steam electric power plants, which
would greatly reduce a major source of mercury
discharges. Currently, steam electric power
plants discharge 2,820 pounds of mercury into
the Nation's waterbodies every year. Without
the new guidelines, EPA has determined these
mercury wastes may be making fish unsafe for
human consumption in 65% of the waterbodies
where steam electric plants discharge. Second,
in April EPA issued the new Mercury and Air
Toxics rule, which sets emissions limitation
standards for mercury emitted from power
plants.
In support of these 2013 actions, EPA assessed
its progress by looking at the measurement of
blood mercury levels in women of childbearing
age reported via NHANES by the CDC.
Conclusions
The analyses found blood mercury
concentrations in NHANES survey release
1999-2000 to be significantly higher than the
mean of the remaining releases for both blood
total mercury and blood MeHg. Additionally,
the percent with MeHg greater than 5.8 (ig/L is
significantly higher in survey release 1999-2000.
The analysis also found a slight quadratic trend
in blood MeHg concentration since 1999-2000.
This trend indicates decreasing blood MeHg
concentrations between the initial sets of
NHANES survey releases, followed by
relatively small changes and a slight increase in
the last years.
There was a marginally statistically significant
decreasing trend across NHANES survey
releases in the ratio of mercury intake to fish
consumed that is consistent with women shifting
their consumption to fish with lower mercury
concentrations; however, other studies are
needed to determine 1) if there is a link between
changing consumption patterns and blood
mercury, and 2) if fish advisories have led to the
changing consumption patterns.
For More Information
Contact Jeff Bigler at bigler.jeff@epa.gov or
(202) 566-0389, or visit the EPA website at
http://www.epa.gov/hg/advisories.htm.
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