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Hair mercury levels in U.S. children and women of childbearing age: reference range data from NHANES 1999-2000.

Exposure to methyl methyl (mĕth`əl), CH3, organic free radical or alkyl group derived from methane by the removal of one hydrogen atom.  mercury, a risk factor for neurodevelopmental toxicity, was assessed in U.S. children 1-5 years of age (n = 838) and women 16-49 years of age (n = 1,726) using hair mercury analysis during the 1999-2000 National Health and Nutrition Examination Survey (NHANES NHANES National Health and Nutrition Examination Survey (US CDC) ). The data are nationally representative and are based on analysis of cross-sectional data Cross-sectional data in statistics and econometrics is a type of one-dimensional data set. Cross-sectional data refers to data collected by observing many subjects (such as individuals, firms or countries/regions) at the same point of time, or without regard to differences in time.  for the non-institutionalized, U.S. household population. The survey consisted of interviews conducted in participants' homes and standardized standardized

pertaining to data that have been submitted to standardization procedures.

standardized morbidity rate
see morbidity rate.

standardized mortality rate
see mortality rate.
 health examinations conducted in mobile examination centers. Distributions of total hair mercury levels expressed as micrograms per gram hair Hg and the association of hair Hg levels with sociodemographic characteristics and fish consumption are reported. Geometric mean (mathematics) geometric mean - The Nth root of the product of N numbers.

If each number in a list of numbers was replaced with their geometric mean, then multiplying them all together would still give the same result.
 (standard error of the geometric mean) hair mercury was 0.12 [micro]g/g (0.01 [micro]g/g) in children, and 0.20 [micro]g/g (0.02 [micro]g/g) in women. Among frequent fish consumers, geometric mean hair mercury levels were 3-fold higher for women (0.38 vs. 0.11 [micro]g/g) and 2-fold higher for children (0.16 vs. 0.08 [micro]g/g) compared with nonconsumers. The NHANES 1999-2000 data provide population-based data on hair mercury concentrations for women and children in the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. . Hair mercury levels were associated with age and fish consumption frequency. Key words: blood, child, diet, female, hair, mercury, NHANES, preschool. Environ Health Perspect 112:1165-1171 (2004). doi:10.1289/ehp.7046 available via[Online 27 May 2004]


Mercury is a naturally occurring heavy metal whose presence in the environment is widespread and persistent [Agency for Toxic Substances and Disease Registry The United States Agency for Toxic Substances and Disease Registry, (ATSDR) is an agency for the U.S. Department of Health and Human Services that is directed by a congressional mandate to perform specific functions concerning the effect on public health of hazardous  (ATSDR ATSDR Agency for Toxic Substances & Disease Registry ) 1999; National Research Council (NRC NRC
1. National Research Council

2. Nuclear Regulatory Commission

Noun 1. NRC - an independent federal agency created in 1974 to license and regulate nuclear power plants
) 2000]. Hg occurs in metallic or elemental elemental

emanating from or pertaining to elements.

elemental diet
see elemental diet.
, inorganic inorganic /in·or·gan·ic/ (in?or-gan´ik)
1. having no organs.

2. not of organic origin.

, and organic forms (ATSDR 1999). When elemental Hg is emitted as a combustion by-product by·prod·uct or by-prod·uct  
1. Something produced in the making of something else.

2. A secondary result; a side effect.


 of fossil fuels fossil fuel: see energy, sources of; fuel.
fossil fuel

Any of a class of materials of biologic origin occurring within the Earth's crust that can be used as a source of energy. Fossil fuels include coal, petroleum, and natural gas.
, it becomes methylated meth·yl·ate  
An organic compound in which the hydrogen of the hydroxyl group of methyl alcohol is replaced by a metal.

tr.v. meth·yl·at·ed, meth·yl·at·ing, meth·yl·ates
 in the environment and accumulates in animal tissues, including fish. Methyl mercury (MeHg) in the aquatic food chain contributes to higher tissue Hg levels among fish consumers (Boening 2000). Total Hg in the hair of fish eaters correlates with Hg in the target tissue, the brain (Cernichiari et al. 1995).

The mammalian mammalian

emanating from or pertaining to mammals.
 nervous system is highly vulnerable to MeHg (Castoldi et al. 2001). Exposure to high levels of MeHg during the last two trimesters of pregnancy produces documented neurodevelopmental problems, including language, attention, and memory problems [Marsh et al. 1987; NRC 2000; U.S. Environmental Protection Agency Environmental Protection Agency (EPA), independent agency of the U.S. government, with headquarters in Washington, D.C. It was established in 1970 to reduce and control air and water pollution, noise pollution, and radiation and to ensure the safe handling and  (EPA EPA eicosapentaenoic acid.

eicosapentaenoic acid

EPA, See acid, eicosapentaenoic.

) 1997]. Accidental poisoning incidents in Japan (Harada 1995) and Iraq (Amin-Zaki et al. 1974) demonstrated the pronounced neurologic neurologic /neu·ro·log·ic/ (-loj´ik) pertaining to neurology or to the nervous system.
Having to do with the nervous system.
 injuries that result from high-level MeHg exposures, particularly in children who were exposed in utero in utero (in u´ter-o) [L.] within the uterus.

in u·ter·o
In the uterus.

in utero adv.

More recent prospective epidemiologic data from New Zealand New Zealand (zē`lənd), island country (2005 est. pop. 4,035,000), 104,454 sq mi (270,534 sq km), in the S Pacific Ocean, over 1,000 mi (1,600 km) SE of Australia. The capital is Wellington; the largest city and leading port is Auckland. , the Faroe Islands Faroe Islands
 or Faeroe Islands

Group of islands in the Atlantic Ocean that form a self-governing region of Denmark. Area: 540 sq mi (1,399 sq km). Population: (2002 est.) 47,400.
, and the Seychelles assessed developmental effects of lower level MeHg exposure in fish-consuming populations resulting from maternal and fetal exposures to MeHg (Cernichiari et al. 1995; Grandjean et al. 1999). The U.S. EPA MeHg exposure reference dose (RfD) of 0.1 [micro]g/kg body weight/day was based on data from the Faroes and New Zealand, with supporting analyses from all three major prospective cohort studies A cohort study is a form of longitudinal study used in medicine and social science. It is one type of study design.

In medicine, it is usually undertaken to obtain evidence to try to refute the existence of a suspected association between cause and disease; failure to refute
 (Rice et al. 2003). The assessments of Hg exposure for the U.S. population have included regional biomonitoring studies conducted by state and federal agencies (Pellizzari et al. 1999) and assessments of population subgroups, including sport fishermen and their families (Burge and Evans 1994; Kosatsky et al. 2000), pregnant women in selected geographic areas (Bjornberg et al. 2003; Stern et al. 2001), high-end fish consumers (Hightower and Moore 2003), and American Indian American Indian
 or Native American or Amerindian or indigenous American

Any member of the various aboriginal peoples of the Western Hemisphere, with the exception of the Eskimos (Inuit) and the Aleuts.
 and Alaskan Native groups (Rothschild and Duffy 2001).

Total blood and hair Hg are indicators of MeHg exposure in fish consumers and others who are not exposed to inorganic and elemental Hg occupationally or incidentally (Carrington and Bolger 2002; Mahaffey 2000; NRC 2000). Exposure to MeHg increases with fish consumption [International Programme on Chemical Safety The International Programme on Chemical Safety (IPCS) is a collaboration between three United Nations bodies—the World Health Organization, the International Labour Organization and the United Nations Environment Programme.  (IPCS See AS/400 Integrated PC Server. ) 1990; Yamaguchi et al. 1975]. Once consumed, 90% of MeHg is absorbed in the human gut (Miettinen 1973). Approximately 95% of measurable Hg in blood is the methylated form (Sherlock A Macintosh utility starting with Version 8.5 of the operating system that provides a common facility for searching the local hard disk, the local network and the Internet.  et al. 1984). After absorption, MeHg is distributed throughout the body within hours (Clarkson 1997). Peak MeHg blood levels in human subjects fed fish containing known concentrations of MeHg occurred within 4-14 hr of ingestion ingestion /in·ges·tion/ (-chun) the taking of food, drugs, etc., into the body by mouth.

1. The act of taking food and drink into the body by the mouth.

 (Kershaw et al. 1980). The mean [+ or -] SE half-life of blood MeHg reported from a study with 20 adults whose diet included halibut halibut: see flatfish.

Any of various flatfishes, especially the Atlantic and Pacific halibuts (genus Hippoglossus, family Pleuronectidae), both of which have eyes and colour on the right side.
 with measured MeHg was 50 [+ or -] 1 days (range, 42-70 days) (Sherlock et al. 1984).

Hair Hg concentration is the preferred biomarker biomarker /bio·mark·er/ (bi´o-mahr?ker)
1. a biological molecule used as a marker for a substance or process of interest.

2. tumor marker.

 for evaluating Hg exposure for extended periods of time such as periods of weeks or months (NRC 2000). Hair incorporates Hg present in circulating cir·cu·late  
v. cir·cu·lat·ed, cir·cu·lat·ing, cir·cu·lates

1. To move in or flow through a circle or circuit: blood circulating through the body.

 blood during hair formation in the hair follicle hair follicle
A deep narrow pit that is formed by the tubular invagination of the epidermis and corium and encloses the root of the hair.

Hair follicle 
 (Clarkson 1983). Hair growth and analysis studies assessed hair growth rates Growth Rates

The compounded annualized rate of growth of a company's revenues, earnings, dividends, or other figures.

Remember, historically high growth rates don't always mean a high rate of growth looking into the future.
 and the relationship between MeHg intake and hair levels (Clarkson 1992; Grandjean et al. 1994). Hair growth averages 1-1.5 cm per month and provides a time record of previous Hg exposure depending on the length of the hair (Suzuki et al. 1984). Approximately 80% of hair Hg is MeHg (Cernichiari et al. 1995; Phelps et al. 1980). Total Hg and MeHg levels in hair are linearly related (Pellizzari et al. 1999), with total Hg concentrations in hair thought to average 150- to 200-fold higher than Hg concentrations in blood (Gill et al. 2002).

The Centers for Disease Control and Prevention Centers for Disease Control and Prevention (CDC), agency of the U.S. Public Health Service since 1973, with headquarters in Atlanta; it was established in 1946 as the Communicable Disease Center.  (CDC See Control Data, century date change and Back Orifice.

CDC - Control Data Corporation
), the U.S. EPA, U.S. Food and Drug Administration, Department of Energy, and the National Oceanographic and Atmospheric Administration funded a comprehensive Hg assessment component as part of the 1999-2001 National Health and Nutrition Examination Survey (NHANES). The NHANES Hg assessment component targeted children 1-5 years of age and women 16-19 years of age. Preliminary blood and hair Hg results from NHANES 1999 were reported in 2001 (CDC 2001). A detailed analysis of NHANES 1999-2000 blood Hg data was published in 2003 (Schober et al. 2003). Blood Hg levels were examined by race/ethnicity, maternal education level, and fish consumption frequency. Blood Hg levels were low overall in children and adults, but approximately 8% of women had levels > 5.8 [micro]g/L, a level that corresponds to the U.S. EPA's RfD. At the time, geometric mean (GM) total hair Hg values were not computed for the NHANES 1999 data. This report on hair Hg describes hair Hg levels in U.S. children and women of childbearing child·bear·ing
Pregnancy and parturition.

childbearing adj.
 age by race/ethnicity, fish consumption frequency level, pregnancy status, and education level (females 20-49 years of age) and examines the relationship between total blood and hair Hg.

Materials and Methods

Survey description. The NHANES survey is conducted to provide continuous health and nutrition data on the U.S. population for all ages [National Center for Health Statistics National Center for Health Statistics (NCHS) is part of the Centers for Disease Control and Prevention (CDC), which is part of the United States Department of Health and Human Services.

NCHS is the United States' principal health statistics agency.
 (NCHS NCHS National Center for Health Statistics
NCHS Naperville Central High School (Illinois)
NCHS North Central High School
NCHS Natrona County High School (Wyoming)
NCHS National Center for Health Services
) 2002b]. Standardized interviews and examination methods are administered by trained staff, including physicians, dentists, health technologists, interviewers, and laboratory technicians. Health examinations are conducted in mobile examination centers that travel to 15 geographic sites per year.

Sample design. The NHANES survey design is a stratified stratified /strat·i·fied/ (strat´i-fid) formed or arranged in layers.

Arranged in the form of layers or strata.
, multistage mul·ti·stage  
1. Functioning in more than one stage: a multistage design project.

2. Relating to or composed of two or more propulsion units.
, national probability sample of the civilian, noninstitutionalized U.S. population; regional estimates are not produced (NCHS 2002). One or more participants within the eligible households sampled are included in the survey. Annual samples are nationally representative and include approximately 6,000 interviewed and 5,000 examined persons. NHANES 1999-2001 included expanded samples of Mexican Americans This is a list of notable Mexican-Americans. Athletes
Baseball players
  • Arturo Stenger- MLB Roadie?
  • Hank Aguirre - MLB pitcher
  • Frank Arellanes - First Mexican American MLB player
  • Eric Chavez - MLB third baseman
, non-Hispanic blacks, pregnant females, adolescents 12-19 years of age, and adults [greater than or equal to] 60 years of age.

Data collection for the Hg assessment component. The NHANES 1999-2000 Hg assessment component included a dietary interview and blood, hair, and urinary Hg assessments. Venipuncture venipuncture /veni·punc·ture/ (ven?i-pungk´chur) surgical puncture of a vein.

ve·ni·punc·ture or ve·ne·punc·ture
 blood collection was conducted on persons [greater than or equal to] 1 year of age, hair collection on children 1-5 years of age and women 16-49 years of age, and urine collection on persons [greater than or equal to] 6 years of age. The NHANES dietary assessment component included a 24-hr dietary recall interview on all examined persons and fish and shellfish shellfish, popular name for certain edible mollusks (see Mollusca), e.g., oysters, clams, and scallops, and for certain edible crustaceans, e.g., crabs, lobsters, and shrimps. All are aquatic invertebrates with shells; they are not fish.  consumption frequency questions on persons [greater than or equal to] 1 year of age. All survey examination protocols, questionnaires, and reporting criteria were approved by the NCHS institutional review board; total hair Hg values of [greater than or equal to] 15 [micro]g/g or total blood Hg values of [greater than or equal to] 200 [micro]g/L were reported to participants. Signed informed consent was obtained for all survey participants. Participants or their guardians provided consent for participants < 18 years of age. Examined persons received remuneration REMUNERATION. Reward; recompense; salary. Dig. 17, 1, 7.  for their participation in the survey ranging from $30 to $100, depending on their age and examination content; transportation and child care expenses were also compensated.

Hair specimen collection. A minimum of 5-10 mg of hair was required for the hair analysis assay. Approximately 100 strands of hair (~ 50 mg) were gathered and cut from the occipital occipital /oc·cip·i·tal/ (ok-sip´i-t'l) pertaining to the occiput; located near the occipital bone.

Of or relating to the occipital bone.

 region of the scalp (approximately the diameter of a pencil eraser). A 1.5 x 2 in. Post-it (adhesive paper square; 3M, St. Paul St. Paul

as a missionary he fearlessly confronts the “perils of waters, of robbers, in the city, in the wilderness.” [N.T.: II Cor. 11:26]

See : Bravery
, MN) was placed over the end of the hair strands closest to the scalp; the paper was marked with an arrow indicating the end of hair closest to the scalp. A plastic clip was placed over the paper to secure the hair sample. The samples were placed in a resealable plastic bag and shipped to the Research Triangle Institute The Research Triangle Institute (RTI) is a non-profit research organization based in the Research Triangle Park (RTP) of North Carolina. RTI is the oldest tenant of this major research park, and the sister organization to the Research Triangle Foundation.  for analysis. Respondents or proxies for children were asked if the respondent's hair had been given a permanent or been treated with a hair dye or a hair relaxer re·lax·er  
One that relaxes, as a chemical solution used on tightly curled hair to soften or loosen the curls.

Noun 1. relaxer - any agent that produces relaxation; "music is a good relaxer"
 product within the last month. The analysis compared total hair Hg in persons with treated hair (any of the products listed) to those with untreated hair.

Hair Hg analysis. Hair segments of 0.4 in. (1.0 cm) closest to the scalp, approximately 1 month's growth, were analyzed for total Hg concentration using a cold vapor atomic fluorescence spectroscopy Fluorescence spectroscopy or fluorometry or spectrofluorimetry is a type of electromagnetic spectroscopy which analyzes fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain  method (Pellizzari et al. 1999). The method involves digestion of the analyte from hair samples using a 30:70 mixture of sulfuric sul·fu·ric  
Of, relating to, or containing sulfur, especially with valence 6.


Containing sulfur, especially sulfur with a valence of 6. Compare sulfurous.

Adj. 1.
 and nitric acids nitric acid, chemical compound, HNO3, colorless, highly corrosive, poisonous liquid that gives off choking red or yellow fumes in moist air. It is miscible with water in all proportions.  and subsequent analysis by cold vapor atomic fluorescence fluorescence (flrĕs`əns), luminescence in which light of a visible color is emitted from a substance under stimulation or excitation by light or other forms of electromagnetic  spectrometry spectrometry /spec·trom·e·try/ (spek-trom´e-tre) determination of the wavelengths or frequencies of the lines in a spectrum.

. The analyte is identified by the presence of fluorescence signal from a Hg-specific detector. During NHANES 1999-2000, hair Hg was analyzed in batches of 20-40 samples, and quantification of the analyte was carried out using batch-specific standard calibration curves In analytical chemistry, a calibration curve is a general method for determining the concentration of a substance in an unknown sample by comparing the unknown to a set of standard samples of known concentration. . Linearity greater than 0.99 was confirmed for each curve using eight aqueous aqueous /aque·ous/ (a´kwe-us)
1. watery; prepared with water.

2. see under humor.

 calibration calibration /cal·i·bra·tion/ (kal?i-bra´shun) determination of the accuracy of an instrument, usually by measurement of its variation from a standard, to ascertain necessary correction factors.  standards (0, 5, 10, 30, 50, 80, and 85 pg/mL Hg) as previously described (Pellizzari et al. 1999). Daily quality control (QC) procedures included analysis in triplicate of a known human hair reference standard certified See certification.  at 4.42 [micro]g/g Hg (Pellizzari et al. 1999). QC standard checks were performed initially and after every 10th sample, and replicate measurements were performed (duplicate sample preparation with duplicate analysis of each preparation).

Percent recovery of the Hg analyte was monitored by analyzing hair samples spiked with a known Hg reference standard before the digestion process. Mean percent recovery of Hg ([+ or -] SD) in the spiked samples was 96.2 [+ or -] 12.1%]. The precision of analysis was assessed from duplicate extracts (i.e., reanalysis of the same extract at a later time) and from duplicate hair sample analyses (i.e., a second aliquot aliquot (al-ee-kwoh) adj. a definite fractional share, usually applied when dividing and distributing a dead person's estate or trust assets. (See: share)  of hair processed through the entire analysis process). The mean precision ([+ or -] SD) for duplicate extract and sample analyses was 5.4 [+ or -] 8.7% and 11.7 [+ or -] 14.4%), respectively. The limit of detection (LOD Lod (lōd), city (1994 pop. 51,200), central Israel. It is also known as Lydda. Its manufactures include paper products, chemicals, oil products, electronic equipment, processed food, and cigarettes. ) for total hair Hg varied by analytic batch because of the laboratory's batch-specific standardization standardization

In industry, the development and application of standards that make it possible to manufacture a large volume of interchangeable parts. Standardization may focus on engineering standards, such as properties of materials, fits and tolerances, and drafting
 methodology. Method detection limits ranged from 0.0006 to 0.06 [micro]g/g. Whenever the values for hair Hg were below a batch LOD, a fill value equal to the batch-specific LOD divided by the square root of 2 was used (Taylor 1987).

Fish and shellfish consumption frequency questionnaire. Fish and shellfish consumption frequency during the 30-day period before hair collection was reported. The fish and shellfish frequency questions were administered by bilingual interviewers in English or Spanish. A proxy respondent reported for children < 6 years of age and proxy-assisted interviews were conducted with children 6-11 years of age (NCHS 2002a). No information was obtained about portion sizes, recipes, or preparation methods. Fish frequency data were grouped into three categories: no fish consumed, fish consumed one or two times, and fish consumed three or more times during the past 30 days. Shellfish consumption was coded as either no shellfish consumed or shellfish consumed one or more times during the past 30 days. Weighted GM total hair Hg levels and percentiles were computed for each fish and shellfish consumption frequency category.

Covariates. Race and ethnicity were categorized cat·e·go·rize  
tr.v. cat·e·go·rized, cat·e·go·riz·ing, cat·e·go·riz·es
To put into a category or categories; classify.

 as non-Hispanic white, non-Hispanic black, and Mexican American Mexican American
A U.S. citizen or resident of Mexican descent.

 based on self-reported information provided by the survey participants. The sample size for the other race/ethnicity group that includes Asians and American Indians American Indians: see Americas, antiquity and prehistory of the; Natives, Middle American; Natives, North American; Natives, South American.  was too small to present separate estimates; the total population estimates include data for the other race/ethnicity group composed of 103 children and 195 women. Age in years at the time of the household interview was used. Pregnancy status was self-reported during private interviews administered to women [greater than or equal to] 12 years of age at the mobile examination center. Pregnancy status was confirmed with a urinary pregnancy test pregnancy test Any test used to detect or confirm pregnancy; in early pregnancy, all PTs measure hCG, the developing placenta's principal hormone, which is detectable as early as 6 days after fertilization; in clinical laboratories, serum levels of hCG are  in females [greater than or equal to] 18 years of age in NHANES 1999 and in females [greater than or equal to] 8 years of age in NHANES 2000.

Statistical methods. Weighted estimates were produced using NHANES mobile examination center-examined sample weight values. These NHANES 1999-2000 sample weights adjust for the differential probabilities of selection and nonresponse in the survey sample (NCHS 2002b). The sample weights were poststratified to the 1990 U.S. Census total population estimates. A second nonresponse adjustment was applied during the hair Hg analysis to adjust for the higher, nonrandom hair collection nonresponse rates among African-American and Mexican-American boys (Lohr 1999).

Distributions, extreme hair Hg values, influential observations based on an analysis of the survey sample weights and hair Hg data, laboratory QC data, and correlation analyses were examined initially (Korn and Graubard 1999). After the initial analyses demonstrated that the total hair Hg data were non-normally distributed, a logarithmic logarithmic

pertaining to logarithm.

logarithmic relationship
when the logs of two variables plotted against each other create a straight line.
 transformation of total hair Hg was applied to normalize normalize

to convert a set of data by, for example, converting them to logarithms or reciprocals so that their previous non-normal distribution is converted to a normal one.
 the distribution data. Outliers and influential points were detected using box plots, normal probability plots, and residual analysis, including studentized residuals In statistics, a studentized residual, named in honor of William Sealey Gosset, who wrote under the pseudonym Student, is a residual adjusted by dividing it by an estimate of its standard deviation.  for hair Hg and log of hair Hg, weighted and unweighted. Percentiles, means, and GMs were calculated to describe the distributions of hair Hg levels in children and women; arithmetic and GMs were included for comparison with other published reports. Standard errors (SEs) of the GMs and means and their confidence intervals confidence interval,
n a statistical device used to determine the range within which an acceptable datum would fall. Confidence intervals are usually expressed in percentages, typically 95% or 99%.
 (CIs) were computed using SUDAAN (Survey Data Analysis) weighted delete-1 jackknife jack·knife  
1. A large clasp knife.

2. Sports A dive in the pike position, in which the diver straightens out to enter the water hands first.

 (Research Triangle Institute 2001). Tests of statistical significance used [alpha] = 0.05. Weighted Pearson partial correlations Noun 1. partial correlation - a correlation between two variables when the effects of one or more related variables are removed
statistics - a branch of applied mathematics concerned with the collection and interpretation of quantitative data and the use of
 were used for bivariate bi·var·i·ate  
Mathematics Having two variables: bivariate binomial distribution.

Adj. 1.
 comparisons and to identify predictors for the multiple regression Multiple regression

The estimated relationship between a dependent variable and more than one explanatory variable.
 models. Correlations of total log blood and log hair Hg were performed using Pearson's method. Total hair to total blood Hg ratios were computed for children and women. The natural logarithm Natural logarithm

Logarithm to the base e (approximately 2.7183).
 of hair Hg was the dependent variable for all of the regression analyses. Multiple regression was performed using SUDAAN. Tests of differences among groups used regressions with groups defined by dummy variables This article is not about "dummy variables" as that term is usually understood in mathematics. See free variables and bound variables.

In regression analysis, a dummy variable
 described in multivariate analysis multivariate analysis,
n a statistical approach used to evaluate multiple variables.

multivariate analysis,
n a set of techniques used when variation in several variables has to be studied simultaneously.
, and detection of predictors through regression (Srivastava and Sen 1990).


Response rates. A total of 12,160 persons were selected to participate in NHANES 1999-2000; 9,282 completed the household interview and health examination components (76.3%). Of the 1,250 children 1-5 years of age selected for the survey, 1,013 (81%) were interviewed and examined. Hair specimens were obtained from 838 examined children (83% of examined children); hair collection response rates were lower among non-Hispanic black and Mexican-American males because of insufficient hair specimen collection. Hair samples were obtained from 44 and 82% of non-Hispanic black and Mexican-American males respectively, compared with 90% of non-Hispanic white males. This response was not random, and sample weight adjustments were applied during final data analysis. A total of 2,314 women 16-49 years of age were selected to participate; of these, 1,819 were interviewed and examined (79%). Hair specimens were obtained from 1,726 women (95% of the examined women). Fish and shellfish consumption data were obtained for 93% of children (n = 785) and 96% of women (n = 1,660) with hair Hg data. Detectable total hair Hg levels were measured in 84 and 89% of hair specimens obtained for children and women, respectively.

Outliers and influential points. Three data points were considered outliers and influential. The values for hair Hg were 109.8, 415.2, and 849.0 [micro]g/g for three Mexican-American participants who were 3, 1, and 37 years of age, respectively. Repeat hair Hg analyses confirmed the high hair Hg values, and laboratory QC specimens for the batches in which the specimens were analyzed were within specification. Blood Hg data were examined for the hair Hg outlier outlier /out·li·er/ (out´li-er) an observation so distant from the central mass of the data that it noticeably influences results.


an extremely high or low value lying beyond the range of the bulk of the data.
 subset; total and inorganic blood Hg levels for all three persons were elevated, suggesting significant exposure to organic and inorganic Hg sources. Appropriate follow-up notification measures were undertaken to inform survey participants of these findings. Multivariate The use of multiple variables in a forecasting model.  analyses with the outlier data did not alter the results appreciably ap·pre·cia·ble  
Possible to estimate, measure, or perceive: appreciable changes in temperature. See Synonyms at perceptible.
. GMs, means, and medians increased slightly when the outlier values were included. For the purpose of reporting national reference values ref·er·ence values
A set of laboratory test values obtained from an individual or from a group in a defined state of health.
 for total hair Hg, the hair Hg outlier values were excluded from further analysis.

GMs and percentiles. GMs, means, and percentiles of hair Hg levels for children and women, respectively, are presented in Tables 1 and 2. For children, data are presented by race/ethnicity, fish consumption, shellfish consumption, and hair treatment group (Table 1). For women, results are presented by race/ ethnicity, age, fish consumption, shellfish consumption, hair treatment, pregnancy status, and education group (Table 2).

Race/ethnicity. Among children, the overall GM total hair Hg was 0.12 [micro]g/g. Non-Hispanic black and Mexican-American children had higher hair Hg levels than non-Hispanic white children. Boys had higher (nonsignificant non·sig·nif·i·cant  
1. Not significant.

2. Having, producing, or being a value obtained from a statistical test that lies within the limits for being of random occurrence.
) hair Hg levels than girls in all race/ethnicity groups (not shown). For women, non-Hispanic white females had significantly higher GM hair Hg levels than did non-Hispanic blacks and Mexican Americans.

Hair treatment. The GM hair Hg level of children who received hair treatments during the past month did not differ from that of the untreated group. Thirty-seven percent of women reported using a hair treatment; the GMs total hair Hg levels of the treated and untreated hair groups were the same (0.20 [micro]g/g).

Fish consumption. GM hair Hg increased with increasing frequency of fish consumption for children and adults (Tables 1 and 2). The GM hair Hg level of children consuming fish three or more times during the past month was twice as high as for nonconsuming children (0.16 vs. 0.08 [micro]g/g). Frequent fish consumers 30-49 years of age had the highest GM hair Hg levels of the adult groups examined (0.41 [micro]g/g).

Pregnancy status. GM hair Hg levels of pregnant women (n = 292) did not differ from that in nonpregnant women. Analysis by race/ethnicity among the pregnant subsample sub·sam·ple  
A sample drawn from a larger sample.

tr.v. sub·sam·pled, sub·sam·pling, sub·sam·ples
To take a subsample from (a larger sample).
 was limited to comparisons of GM and median hair Hg values because of small sample sizes; race/ethnicity differences were not statistically significant among the pregnant women. Non-Hispanic white and Mexican-American women had higher hair Hg levels than did non-Hispanic black women. GM hair Hg levels among the pregnant, frequent fish consumers (n = 79) did not differ from that among nonpregnant frequent fish consumers (0.56 vs. 0.37 [micro]g/g, respectively).

Regression analysis In statistics, a mathematical method of modeling the relationships among three or more variables. It is used to predict the value of one variable given the values of the others. For example, a model might estimate sales based on age and gender. . Separate multiple linear regression Linear regression

A statistical technique for fitting a straight line to a set of data points.
 models were developed for children and women (Tables 3 and 4). The reference group for the regression models was the non-Hispanic white group. Log-transformed hair Hg was regressed on race/ethnicity, fish consumption, shellfish consumption, and hair treatment for children (Table 3). Among children, differences were observed by race/ethnicity and fish consumption status. Compared with non-Hispanic whites, non-Hispanic blacks and Mexican Americans had higher total hair Hg levels. The least-squares (LS) means and their SEs were computed using the regression model y = log (hair Hg). LS means for non-Hispanic blacks and Mexican Americans were 0.19 and 0.16 [micro]g/g, respectively, compared with 0.09 [micro]g/g for non-Hispanic whites. Children who consumed fish one or more times during the previous month had higher total hair Hg levels than did children who did not consume fish. LS means for children (Table 3) who consumed fish one to two and three or more times per month were the same (0.14 [micro]g/g) and can be compared with those of children who did not consume fish during the previous month (0.08 [micro]g/g).

A separate regression model was developed for women 16-49 years of age (Table 4). Pregnancy status, age group, race/ethnicity, fish consumption, shellfish consumption, and hair treatment were included in the model. Hair Hg levels differed by race/ethnicity, and fish consumption and shellfish consumption frequencies. Log hair Hg levels of non-Hispanic whites and Mexican Americans were similar. Non-Hispanic whites had higher hair Hg levels than did non-Hispanic blacks. There was a positive relationship between fish consumption frequency and log hair Hg; log hair Hg levels of persons who consumed fish three or more times had higher total hair Hg levels than did women who consumed zero or one to two servings of fish during the past 30 days. When age groups were compared, hair Hg levels among women 40-49 years of age were higher than the reference group (women 16-19 years of age); the 20- to 29-and 30- to 39-year-old groups were not different from the reference group. LS means and 95% CIs were computed using the multiple regression model (Table 4). A separate analysis (not shown) was completed on a subsample of women 20-49 years of age to test the effects of education level as a surrogate marker surrogate marker Lab medicine A parameter or measured to detect a pathologic condition when a more specific test doesn't exist, is impractical or not cost-effective; surrogate testing has been used for non-A, non-B hepatitis, measuring ALT and antibodies to HBV  for socioeconomic status socioeconomic status,
n the position of an individual on a socio-economic scale that measures such factors as education, income, type of occupation, place of residence, and in some populations, ethnicity and religion.
. Education level was not associated with total hair Hg levels and did not alter the relationship between hair Hg and the other covariates.

Hair-to-blood correlations and ratios. Weighted Pearson correlations between log blood and log hair Hg were 0.67 for children and 0.79 for women, respectively (both correlations were p < .0001). Hair-to-blood Hg ratios were computed using total hair Hg (ng/g hair) and blood Hg ([micro]g/L) data. The SUDAAN Proc Ratio procedure for correlated variables was used to compute the ratios (Research Triangle Institute 2001). Weighted delete-1 jackknife was used; the numerator numerator

the upper part of a fraction.

numerator relationship
see additive genetic relationship.

numerator Epidemiology The upper part of a fraction
 and denominators were weighted sums for nonmissing values. The total sample mean [+ or -] SE hair-to-blood Hg ratios were 342 [+ or -] 20 for children 1-5 years of age and 234 [+ or -] 15 for females 16-49 years of age.


The NHANES 1999-2000 total hair Hg data provide national hair Hg reference data for U.S. children 1-5 years and women 16-49 years of age, including three major race/ethnicity subgroups. These baseline data will be used to monitor hair Hg levels in the U.S. population over time. These results were compared with reports across studies that used different biologic matrices to estimate Hg exposure.

The total hair Hg levels of NHANES children and women were generally lower than the levels reported in other studies of U.S. and international populations. GM hair Hg level in fish-consuming children 7 years of age in the Faroes was 2.99 [micro]g/g (Grandjean et al. 1999) compared with a GM (SE) value of 0.16 (0.02) [micro]g/g among frequent fish consumers in the NHANES sample 1-5 years of age. The mean [+ or -] SD and median maternal hair Hg levels of women in the Seychelles where frequent fish consumption occurs were 6.85 [+ or -] 4.5 [micro]g/g and 5.94 [micro]g/g, respectively (Cernichiari et al. 1995). The median total hair Hg level of women in the Faroes birth cohort study was 4.5 [micro]g/g; 12% had levels > 10 [micro]g/g (Grandjean et al. 1992). Recent hair Hg data for Japanese adult females residing in five districts showed an overall total hair Hg GM of 1.43 [micro]g/g (range, 1.23-2.50 [micro]g/g; Yasutake et al. 2003). The GM (SE) and median values Noun 1. median value - the value below which 50% of the cases fall

statistics - a branch of applied mathematics concerned with the collection and interpretation of quantitative data and the use of probability theory to estimate population
 for frequent fish consumers among women of childbearing age in NHANES were 0.77 (0.09) [micro]g/g and 0.33 [micro]g/g, respectively. The arithmetic mean (mathematics) arithmetic mean - The mean of a list of N numbers calculated by dividing their sum by N. The arithmetic mean is appropriate for sets of numbers that are added together or that form an arithmetic series.  hair Hg level reported in a probability-based sample of U.S. Great Lakes region The Great Lakes region can refer to:
  • Great Lakes region (North America)
  • African Great Lakes region
 residents [greater than or equal to] 21 years of age was 0.29 [micro]g/g (Pellizzari et al. 1999), compared with an arithmetic mean [+ or -] SE hair Hg value of 0.47 [+ or -] 0.06 [micro]g/g for NHANES females 16-49 years of age.

We report that the GM total hair Hg among pregnant women was 0.21 [micro]g/g and did not differ from hair Hg levels of nonpregnant women (GM = 0.20 [micro]g/g). The mean [+ or -] SE hair Hg level reported in a study of 189 New Jersey pregnant women was 0.53 [+ or -] 0.07 [micro]g/g (range, < 0.2-9.1 [micro]g/g; Stern et al. 2001); the NHANES pregnant females had an arithmetic mean [+ or -] SE hair Hg of 0.43 [+ or -] 0.089 [micro]g/g. Median hair Hg levels for 127 pregnant Swedish women were 0.35 mg/kg (range, 0.07-1.5 mg/kg; Bjornberg et al. 2003). Prenatal prenatal /pre·na·tal/ (-na´tal) preceding birth.

Preceding birth. Also called antenatal.


preceding birth.
 assessments of women from the Seychelles women reported mean [+ or -] SD total hair Hg of 6.85 [+ or -] 4.5 ppm (Pages Per Minute) The measurement of printer speed. See gppm.

PPM - Portable Pixmap
 and a median value of 5.94 ppm (Myers et al. 2003).

These hair Hg values provide an estimate of exposure over an approximate 1 month period, as recent exposure is not yet incorporated into the hair growth outside of the scalp. The steady-state hair-to-blood MeHg concentration ratio reported by the World Health Organization for adults was approximately 250:1, compared with a total hair-to-blood Hg ratio of 234 for NHANES females (IPCS 1990). Values for NHANES children were higher (ratio value of 342 overall), and this may reflect the higher percentages of children with blood Hg levels below the LOD. The hair-to-blood ratios were highly variable, in part, because hair and blood measurements are not comparable regarding the time period of exposure. Additionally, Hg exposure in this study is low for most respondents, and these results may not be comparable with correlations and ratios predicted in groups with higher levels of Hg exposure.

The advantages of hair Hg assessment include the fact that hair collection is noninvasive non·in·va·sive
1. Not penetrating the body, as by incision. Used especially of a diagnostic procedure.

2. Not invading healthy tissue.
, and good response rates can be achieved in population subgroups that are difficult to obtain blood specimens from, such as children. For example, during NHANES 1999-2000, blood Hg data were collected on 56% of selected children, whereas hair collection was completed on 67% of selected children. Additionally, hair is a time record marker of MeHg exposure in individuals and can be used to estimate Hg exposure over extended periods of time such as fetal exposure during gestation GESTATION, med. jur. The time during which a female, who has conceived, carries the embryo or foetus in her uterus. By the common consent of mankind, the term of gestation is considered to be ten lunar months, or forty weeks, equal to nine calendar months and a week.  (Cernichiari et al. 1995).

Several considerations for interpreting the NHANES 1999-2000 hair Hg results are provided. The NHANES 1999-2000 sample, although nationally representative, does not permit estimation of MeHg exposure in population groups with potentially high dietary exposure such as subsistence subsistence,
n the state of being supported or remaining alive with a minimum of essentials.
 fishers, residents in specific geographic regions of the United States, sport fishers, and members of racial and ethnic population subgroups (e.g., Asians and Pacific Islanders Pacific Islander
1. A native or inhabitant of any of the Polynesian, Micronesian, or Melanesian islands of Oceania.

2. A person of Polynesian, Micronesian, or Melanesian descent. See Usage Note at Asian.
). These subgroups may consume more fish than the general U.S. population and have higher MeHg exposure. Seafood consumption among Asian Americans This page is a list of Asian Americans. Politics
  • 1956 - Dalip Singh Saund became the first Asian immigrant elected to the U.S. Congress upon his election to the House of Representatives.
  • 1959 - Hiram Fong became the first Asian American elected to the U.S. Senate.
 and Pacific Islanders (AAPI AAPI Asian Americans and Pacific Islanders (HHS BHPR; US government)
AAPI Association d'Aide aux Personnes Incontinentes
AAPI American Association of the Physicians of Indian Origin
AAPI Antique and Amusement Photographers International
) in King County, Washington “King County” redirects here. For other uses, see King County (disambiguation).

King County is located in the U.S. state of Washington. The population in the 2000 census was 1,737,034 and in 2006 was an estimated 1,835,300.
, averaged 117 g/day (Sechena et al. 2003), compared with mean intakes of 10-14 g/day for the total U.S. population [greater than or equal to] 20 years of age (U.S. Department of Agriculture 1999). Significant variation was observed in consumption rates and food preferences of the 10 AAPI groups. Second, three extreme hair Hg values were analyzed and confirmed in NHANES and were discarded dis·card  
v. dis·card·ed, dis·card·ing, dis·cards
1. To throw away; reject.

a. To throw out (a playing card) from one's hand.

 in developing the distributions because it was not possible to determine the contributing factors that resulted in these values. This underscores the complexity of Hg assessment and exposure in populations. Finally, the NHANES 1999-2000 sample design was composed of a small number of primary sampling units (PSUs; 26 unique PSUs total). This feature limits regional or geographic area comparisons and statistical comparisons between population subgroups.

The NHANES data may be useful for assessing the prevalence of health risks in the U.S. population when the associated risks of low-level Hg content are better defined and may be used to support diet and health research, policy, and monitoring activities. Diet remains the primary contributor to MeHg exposure in populations. More than 50% of NHANES participants consumed fish during a 30-day reference period. Annual seafood consumption projections for the U.S. population indicate that 75-93% of adult women and 58-72% of children 2-5 years of age consume seafood (Carrington and Bolger 2002).

Hair Hg analysis in national samples of U.S. children and women of childbearing age provide a useful biomarker for long-term Hg exposure. Acceptance of the hair collection procedure was high among survey participants and excellent method precision was achieved, allowing for of detection of hair Hg in approximately 84 and 89% of children and women, respectively. Total hair Hg is associated with age, race/ethnicity, and fish consumption frequency. Among women of childbearing age, total hair Hg levels of pregnant and nonpregnant women were the same.
Table 1. GM and selected percentile (95% CI) total hair
Hg ([micro]g/g): U.S. children 1-5 years of age, NHANES 1999-2000.

description                       No.       GM           Mean

Total                             838      0.12          0.22
                                        (0.10-0.13)   (0.18-0.25)

Race and ethnicity
  Non-Hispanic white              238      0.09          0.18
                                        (0.08-0.11)   (0.12-0.23)
  Non-Hispanic black              161      0.19          0.32
                                        (0.14-0.24)   (0.20-0.43)
  Mexican American                336      0.15          0.22
                                        (0.12-0.17)   (0.18-0.25)

Fish consumption frequency
    in past 30 days
  0                               354      0.08          0.13
                                        (0.07-0.10)   (0.11-0.14)
  1 or 2 times                    221      0.14          0.21
                                        (0.11-0.16)   (0.17-0.24)
  [greater than or equal to]      208      0.16          0.40
    3 times                             (0.11-0.21)   (0.24-0.55)

Shellfish consumption frequency
    in past 30 days
  0                               587      0.11          0.21
                                        (0.09-0.12)   (0.17-0.24)
  [greater than or equal to]      195      0.15          0.27
    1 time                              (0.11-0.19)   (0.17-0.36)

Recent hair color or treatment
  No                              798      0.12          0.22
                                        (0.10-0.13)   (0.18-0.25)
  Yes                             39       0.11          0.14
                                        (0.08-0.14)   (0.12-0.15)


description                             10th            25th

Total                                   0.03            0.06
                                    (0.01-0.05)      (0.05-0.07)

Race and ethnicity
  Non-Hispanic white                  0.03 (a)          0.05
                                    (0.02-0.03)      (0.04-0.06)
  Non-Hispanic black                  0.06 (a)          0.10
                                    (0.06-0.07)      (0.07-0.13)
  Mexican American                      0.05            0.09
                                    (0.04-0.06)      (0.08-0.10)

Fish consumption frequency
    in past 30 days
  0                                   0.03 (a)          0.05
                                    (0.02-0.03)      (0.04-0.06)
  1 or 2 times                          0.05            0.07
                                    (0.04-0.06)      (0.05-0.09)
  [greater than or equal to]            0.04            0.06
    3 times                         (0.01-0.06)      (0.03-0.09)

Shellfish consumption frequency
    in past 30 days
  0                                     0.03            0.05
                                    (0.02-0.04)      (0.04-0.07)
  [greater than or equal to]            0.05            0.07
    1 time                          (0.04-0.06)      (0.02-0.12)

Recent hair color or treatment
  No                                    0.03           0.06 (a)
                                    (0.01-0.05)      (0.05-0.06)
  Yes                                   0.04            0.08
                                  (-0.00-0.08) (b)   (0.05-0.10)


description                          50th          75th

Total                                0.11          0.21
                                  (0.10-0.13)   (0.15-0.27)

Race and ethnicity
  Non-Hispanic white                 0.09          0.17
                                  (0.07-0.10)   (0.14-0.20)
  Non-Hispanic black                 0.19          0.33
                                  (0.11-0.27)   (0.22-0.44)
  Mexican American                   0.15          0.27
                                  (0.12-0.17)   (0.20-0.34)

Fish consumption frequency
    in past 30 days
  0                                  0.08          0.14
                                  (0.07-0.09)   (0.11-0.18)
  1 or 2 times                       0.12          0.22
                                  (0.10-0.15)   (0.14-0.30)
  [greater than or equal to]         0.14          0.30
    3 times                       10.09-0.19)   (0.24-0.36)

Shellfish consumption frequency
    in past 30 days
  0                                  0.10          0.18
                                  (0.08-0.12)   (0.12-0.24)
  [greater than or equal to]         0.14          0.28
    1 time                        (0.10-0.18)   (0.22-0.33)

Recent hair color or treatment
  No                                 0.11          0.21
                                  (0.10-0.13)   (0.16-0.27)
  Yes                                0.10          0.13
                                  (0.07-0.13)   (0.10-0.16)


description                             90th            95th

Total                                   0.41            0.64
                                    (0.33-0.49)      (0.52-0.76)

Race and ethnicity
  Non-Hispanic white                    0.31            0.60
                                    (0.12-0.51)      (0.23-0.96)
  Non-Hispanic black                    0.58            0.81
                                    (0.15-1.00)      (0.44-1.19)
  Mexican American                      0.42            0.56
                                    (0.35-0.50)      (0.40-0.73)

Fish consumption frequency
    in past 30 days
  0                                     0.26            0.38
                                    (0.21-0.32)      (0.35-0.40)
  1 or 2 times                          0.39            0.60
                                    (0.34-0.44)      (0.24-0.97)
  [greater than or equal to]            0.91            2.00
    3 times                         (0.40-1.42)      (0.39-3.62)

Shellfish consumption frequency
    in past 30 days
  0                                     0.38            0.64
                                    (0.28-0.47)      (0.55-0.73)
  [greater than or equal to]            0.40            0.66
    1 time                          (0.26-0.55)      (0.24-1.08)

Recent hair color or treatment
  No                                    0.41            0.66
                                    (0.31-0.51)      (0.52-0.79)
  Yes                                   0.37            0.44
                                  (-0.22-0.97) (b)   (0.35-0.53)

(a) Bound of CI and percentile are equal because
of round-off error. (b) Jackknife estimate not stable.

Table 2. GM and selected percentile (95% CI) total hair Hg
([micro]g/g): U.S. females 16-49 years of age, NHANES 1999-2000.

description                         No.         GM           Mean

Total                               1,726      0.20          0.47
                                            (0.16-0.24)   (0.35-0.58)
Race and ethnicity
  Non-Hispanic white                  582      0.20          0.42
                                            (0.16-0.24)   (0.32-0.51)
  Non-Hispanic black                  356      0.14          0.48
                                            (0.11-0.17)   (0.04-0.91)
  Mexican American                    593      0.18          0.28
                                            (0.15-0.21)   (0.24-0.31)
Age group (years)                     516    0.13 (a)        0.29
                                            (0.13-0.20)   (0.21-0.36)
  20-29                               449    0.18 (a)        0.39
                                            (0.18-0.28)   (0.29-0.48)
  30-39                               408      0.21          0.57
                                            (0.13-0.20)   (0.33-0.80)
  40-49                               353      0.26          0.49
                                            (0.18-0.28)   (0.37-0.60)
Fish consumption frequency
    in past 30 days
  0                                   639      0.11          0.25
                                            (0.08-0.13)   (0.11-0.38)
  1 or 2 times                        573      0.20          0.36
                                            (0.16-0.25)   (0.28-0.43)
  [greater than or equal to] 3        447      0.38          0.77
    times                                   (0.28-0.48)   (0.59-0.94)
Shellfish consumption frequency
    in past 30 days
  0                                   878      0.13          0.26
                                            (0.10-0.15)   (0.20-0.31)
  [greater than or equal to] 1        782      0.31          0.64
    time                                    (0.25-0.36)   (0.50-0.77)
Pregnancy status
  Not pregnant                      1,429      0.20          0.47
                                            (0.16-0.24)   (0.35-0.58)
  Pregnant                            292      0.21          0.43
                                            (0.15-0.27)   (0.27-0.58)
Recent hair color or treatment
  No                                1,089      0.20          0.43
                                            (0.16-0.25)   (0.33-0.52)
  Yes                                 637      0.20          0.52
                                            (0.16-0.25)   (0.34-0.69)
Education (women [greater than or
    equal to] 20 years of age)
  < High school                       342      0.19          0.46
                                            (0.15-0.24)   (0.28-0.63)
  High school                         285      0.17          0.28
                                            (0.13-0.21)   (0.22-0.33)
  > High school                       580      0.24          0.58
                                            (0.19-0.30)   (0.42-0.73)


description                            10th          25th

Total                                  0.04          0.09
                                    (0.03-0.05)   (0.07-0.11)
Race and ethnicity
  Non-Hispanic white                   0.04          0.09
                                    (0.02-0.05)   (0.07-0.11)
  Non-Hispanic black                   0.04          0.07
                                    (0.02-0.05)   (0.05-0.08)
  Mexican American                     0.06          0.10
                                    (0.03-0.09)   (0.07-0.13)
Age group (years)                    0.03 (a)      0.06 (a)
                                    (0.02-0.03)   (0.05-0.06)
  20-29                                0.03          0.08
                                    (0.02-0.05)   (0.07-0.10)
  30-39                                0.04          0.09
                                    (0.03-0.05)   (0.08-0.10)
  40-49                                0.06          0.11
                                    (0.04-0.09)   (0.06-0.16)
Fish consumption frequency
    in past 30 days
  0                                    0.02          0.05
                                    (0.01-0.04)   (0.03-0.07)
  1 or 2 times                         0.05          0.10
                                    (0.04-0.06)   (0.07-0.13)
  [greater than or equal to] 3         0.09          0.17
    times                           (0.07-0.10)   (0.09-0.24)
Shellfish consumption frequency
    in past 30 days
  0                                    0.03          0.06
                                    (0.02-0.04)   (0.04-0.08)
  [greater than or equal to] 1         0.08          0.14
    time                            (0.06-0.10)   (0.12-0.17)
Pregnancy status
  Not pregnant                         0.04          0.09
                                    (0.03-0.05)   (0.07-0.11)
  Pregnant                             0.05          0.09
                                    (0.04-0.07)   (0.08-0.10)
Recent hair color or treatment
  No                                   0.04          0.09
                                    (0.02-0.06)   (0.07-0.11)
  Yes                                0.04 (a)        0.09
                                    (0.04-0.05)   (0.07-0.11)
Education (women [greater than or
    equal to] 20 years of age)
  < High school                        0.05          0.09
                                    (0.01-0.08)   (0.07-0.11)
  High school                          0.04          0.09
                                    (0.02-0.06)   (0.07-0.12)
  > High school                        0.04          0.10
                                    (0.03-0.06)   (0.08-0.12)


description                            50th          75th

Total                                  0.19          0.42
                                    (0.15-0.23)   (0.29-0.55)
Race and ethnicity
  Non-Hispanic white                   0.19          0.45
                                    (0.14-0.24)   (0.21-0.70)
  Non-Hispanic black                   0.13          0.27
                                    (0.10-0.16)   (0.23-0.30)
  Mexican American                     0.18          0.32
                                    (0.15-0.20)   (0.24-0.40)
Age group (years)                      0.12          0.27
                                    (0.09-0.15)   (0.23-0.31)
  20-29                                0.18          0.35
                                    (0.11-0.24)   (0.23-0.48)
  30-39                                0.19          0.40
                                    (0.12-0.26)   (0.31-0.48)
  40-49                                0.24          0.55
                                    (0.18-0.29)   (0.40-0.69)
Fish consumption frequency
    in past 30 days
  0                                    0.10          0.20
                                    (0.07-0.14)   (0.16-0.24)
  1 or 2 times                         0.19          0.39
                                    (0.13-0.25)   (0.33-0.45)
  [greater than or equal to] 3         0.34          0.81
    times                           (0.24-0.45)   (0.33-1.30)
Shellfish consumption frequency
    in past 30 days
  0                                    0.12          0.25
                                    (0.10-0.14)   (0.19-0.32)
  [greater than or equal to] 1         0.28          0.58
    time                            (0.24-0.32)   (0.46-0.70)
Pregnancy status
  Not pregnant                         0.19          0.42
                                    (0.15-0.23)   (0.28-0.57)
  Pregnant                             0.17          0.43
                                    (0.06-0.28)   (0.32-0.53)
Recent hair color or treatment
  No                                   0.19          0.43
                                    (0.16-0.23)   (0.27-0.58)
  Yes                                  0.18          0.41
                                    (0.16-0.21)   (0.32-0.51)
Education (women [greater than or
    equal to] 20 years of age)
  < High school                        0.17          0.34
                                    (0.13-0.21)   (0.24-0.43)
  High school                          0.16          0.31
                                    (0.11-0.21)   (0.17-0.44)
  > High school                        0.24          0.52
                                    (0.19-0.28)   (0.32-0.72)


description                               90th            95th

Total                                     1.11            1.73
                                       (0.54-1.68)     (1.44-2.02)
Race and ethnicity
  Non-Hispanic white                      1.17            1.84
                                       (0.38-1.96)     (0.82-2.86)
  Non-Hispanic black                      0.50            0.88
                                       (0.35-0.65)     (0.26-1.50)
  Mexican American                        0.50            0.78
                                       (0.46-0.54)     (0.51-1.05)
Age group (years)                         0.52            0.87
                                       (0.29-0.76)     (0.51-1.22)
  20-29                                   0.81            1.43
                                       (0.65-0.98)     (1.23-1.64)
  30-39                                   1.12            2.04
                                       (0.58-1.66)     (1.55-2.53)
  40-49                                   1.39            1.71
                                       (1.06-1.72)     (1.06-2.36)
Fish consumption frequency
    in past 30 days
  0                                       0.40            0.55
                                       (0.25-0.56)     (0.36-0.74)
  1 or 2 times                            0.79            1.26
                                       (0.76-0.81)     (0.74-1.78)
  [greater than or equal to] 3            1.75            2.75
    times                              (0.75-2.76)     (1.99-3.50)
Shellfish consumption frequency
    in past 30 days
  0                                       0.53            0.81
                                       (0.43-0.62)     (0.24-1.38)
  [greater than or equal to] 1            1.50            2.22
    time                               (1.29-1.70)     (1.62-2.83)
Pregnancy status
  Not pregnant                            1.11            1.71
                                       (0.50-1.73)     (1.18-2.25)
  Pregnant                                1.04            1.84
                                    (-1.09-3.19) (b)   (0.03-3.65)
Recent hair color or treatment
  No                                      1.12            1.70
                                       (0.57-1.67)     (0.90-2.49)
  Yes                                     1.10            1.94
                                    (-0.01-2.21) (b)   (0.74-3.14)
Education (women [greater than or
    equal to] 20 years of age)
  < High school                           0.80            1.73
                                       (0.00-1.60)     (0.95-2.51)
  High school                             0.61            1.09
                                       (0.23-0.99)     (0.60-1.57)
  > High school                           1.41            2.11
                                       (0.99-1.82)     (1.60-2.63)

(a) Bound of CI and percentile are equal because of round-off error.

(b) Jackknife estimate not stable.

Table 3. Regression model ([R.sup.2] = 0.15) and LS means for
y = log(hair Hg), U.S. children 1-5 years of age, NHANES 1999-2000.

                                                      Exp(LS means)
Characteristics                b(p-Value)      SE        (95% CI)

Intercept                    -2.64 (< 0.05)   0.09   0.11 (0.10-0.13)
  Non-Hispanic white               --                0.09 (0.08-0.11)
  Non-Hispanic black          0.69 (< 0.05)   0.15   0.19 (0.14-0.25)
  Mexican American            0.51 (< 0.05)   0.10   0.16 (0.14-0.18)
Fish consumption frequency
    in past 30 days
  0                                --                0.08 (0.07-0.10)
  1 or 2 times                0.57 (< 0.05)   0.11   0.14 (0.12-0.17)
  [greater than or equal      0.57 (< 0.05)   0.18   0.14 (0.11-0.19)
    to] 3 times
Shellfish consumption
    frequency in past 30
  0                                --                0.11 (0.10-0.13)
  [greater than or equal      -0.04 (0.74)    0.13   0.11 (0.08-0.14)
    to] 1 time
Recent hair color or
  No                               --                0.11 (0.10-0.13)
  Yes                         -0.19 (0.30)    0.18   0.09 (0.06-0.13)

--, Reference level.

Table 4. Regression model ([R.sup.2] = 0.27) and LS means for
y = log(hair Hg), U.S. females 16-49 years of age, NHANES 1999-2000.

                                                      Exp(LS means)
Characteristics                b(P-Value)      SE        (95% CI)

Intercept                    -2.64 (< 0.05)   0.11   0.19 (0.16-0.22)
  Non-Hispanic white               --                0.20 (0.16-0.24)
  Non-Hispanic black         -0.32 (< 0.05)   0.12   0.14 (0.12-0.17)
  Mexican American            0.07 (0.44)     0.10   0.21 (0.18-0.25)
Fish consumption frequency
    in past 30 days
  0                                --                0.11 (0.09-0.13)
  1 or 2 times                0.55 (< 0.05)   0.10   0.19 (0.6-0.23)
  [greater than or equal      1.05 (< 0.05)   0.14   0.32 (0.24-0.41)
    to] 3 times
Shellfish consumption
    frequency in past 30
  0                                --                0.14 (0.12-0.17)
  [greater than or equal      0.56 (< 0.05)   0.08   0.25 (0.21-0.29)
    to] 1 time
Recent hair color or
  No                               --                0.20 (0.16-0.24)
  Yes                        -0.11 (0.17)     0.08   0.18 (0.15-0.21)
  Not pregnant                     --                0.19 (0.16-0.22)
  Pregnant                    0.12 (0.31)     0.12   0.21 (0.17-0.26)
Age groups (years)
  16-19                            --                0.15 (0.12-0.19)
  20-29                       0.15 (0.19)     0.11   0.17 (0.14-0.21)
  30-39                       0.22 (0.05)     0.11   0.19 (0.15-0.23)
  40-49                       0.39 (< 0.05)   0.13   0.22 (0.18-0.28)

--, Reference level.


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Margaret A. McDowell, (1) Charles F. Dillon, (1) John Osterloh, (2) P. Michael Bolger, (3) Edo Pellizzari, (4) Reshan Fernando, (4) Ruben Montes de Oca Montes de Oca is the name of the 15th canton in the province of San José in Costa Rica. The canton covers an area of 15.16 km²[1], and has a population of 53,357[2]. The capital city of the canton is San Pedro. , (5) Susan E. Schober, (1) Thomas Sinks, (2) Robert L. Jones, (2) and Kathryn Ft. Mahaffey (6)

(1) National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD, USA; (2) National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia, USA; (3) Center for Food Safety and Applied Nutrition The Center for Food Safety and Applied Nutrition (CFSAN, pronounced sif'-san) is the branch of the Food and Drug Administration (FDA) which regulates food, dietary supplements, and cosmetics.

"Food" within the context of FDA is a very broad term with some limitations.
, U.S. Food and Drug Administration, College Park, Maryland College Park is a city in Prince George's County, Maryland, USA. The population was 24,657 at the 2000 census. It is best known as the home of the University of Maryland, College Park, and since 1994 the city has also been home to the "Archives II" facility of the U.S. , USA; (4) Research Triangle Institute, Research Triangle Park, NC, USA; (5) The Orkand Corporation, Falls Church, Virginia Falls Church is an independent city in Virginia, United States. The population was 10,377 at the 2000 census. This city is a part of the Washington Metropolitan Area. A much larger number of people reside in Greater Falls Church , USA; (6) The Office of Science Coordination and Policy, Office of Prevention, Pesticides, and Toxic Substances, U.S. Environmental Protection Agency, Washington, DC, USA

Address all correspondence to M.A. McDowell, National Center for Health Statistics, 3311 Toledo Rd., Room 4335, Hyattsville, MD 20782 USA. Telephone: (301) 458-4368. Fax: (301) 458-4028. E-mail: MMcDowell@cdc.gnv

References to sites of non-CDC organizations on the Internet are provided as a service to readers and do not constitute or imply endorsement of these organizations or their programs by the CDC or the U.S. Department of Health and Human Services Noun 1. Department of Health and Human Services - the United States federal department that administers all federal programs dealing with health and welfare; created in 1979
Health and Human Services, HHS
. The CDC is not responsible for the content of pages found at these sites.

The authors declare they have no competing financial interests.

Received 19 February 2004; accepted 27 May 2004.
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Date:Aug 1, 2004
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