A coupled-enzyme equilibrium method for measuring urea in serum: optimization and evaluation of the AACC study group on urea candidate reference method

We describe a coupled-enzyme equilibrium method for measuring urea in serum, which is performed on supernates prepared by treating each specimen with Ba(OH)2 and ZnSO4 (Somogyi reagent). Analytical recovery of [14C]urea added to a variety of matrices was essentially complete (mean, 100.6%) for the supernates after precipitation. Nine variables were univariately examined in arriving at the reaction conditions for the method: glutamate dehydrogenase, urease, 2-oxoglutarate, ADP, Tris . HCI, NADH, EDTA, pH, and temperature. The reagent is stable for at least 48 days at--20 degrees C and for 23 days at 4 degrees C. Mean analytical recovery of urea (14 mmol/L) added to seven different specimens (three different matrices) was 100.8%. The analytical linear range of the method extends to 30 mmol of urea per liter. Of 22 potential interferents, only bilirubin at 1 mmol/L (580 mg/L), hemoglobin at 10 g/L, and hydroxyurea at 6 mmol/L showed more than 2% interference. We discuss precision and effects of specimen dilution, and compare results for 100 human serum specimens with those measured for the same specimens with four other urea methods. We examined the effects of measuring a blank, consisting of sample and reagent without urease, with each specimen.

Strategies for biological monitoring of exposure for contemporary-use pesticides

Pesticides are used on a massive scale in the United States. The widespread use of these pesticides has made it virtually impossible for the average person to avoid exposure at some level. Generally, it is believed that low-level exposure to these pesticides does not produce acute toxic effects; however, various cancers and other noncancer health endpoints have been associated with chronic exposure to several groups of pesticides. Therefore, it is imperative that well-designed studies investigate the potential relationship between contemporary pesticide exposure and health effects. For these studies to be accurate, reliable methods for determining individual exposure must be used. Biological monitoring is a useful tool for assessing exposure to some contemporary pesticides. As with any analytical method, biological monitoring entails many difficulties, but, in many instances, they can be overcome by the logical use of available information and information acquired in carefully designed studies. At the Centers for Disease Control and Prevention (CDC), we have acquired extensive experience in the development and application of specific techniques for biological monitoring of a variety of toxicants, including many of the contemporary-use pesticides. We have used these methods to measure the internal dose of pesticides received by people in acute and chronic incidents resulting from both environmental and industrial exposure. Additionally, we have established normative values, or reference ranges, of several pesticides based on measurements of their metabolites in the urine of randomly selected adults in the US population. These data have been successfully used to distinguish overt exposures from `background' exposure. In this paper, we present several examples of the usefulness of biological monitoring in urine and blood and describe the difficulties involved with developing methods in these matrices. We also present a general strategy, considerations, and recommendations for developing biological monitoring techniques for measuring the internal dose of contemporary-use pesticides.

Urine concentrations of a tobacco-specific nitrosamine carcinogen in the U.S. population from secondhand smoke exposure

BACKGROUND

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and its reduction product in the body, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), are potent pulmonary carcinogens. We have measured total NNAL in the U.S. population of tobacco users and nonsmokers exposed to secondhand smoke.

METHODS

We measured total urinary NNAL (free NNAL plus its glucuronides following hydrolysis) by using a sensitive and specific high-performance liquid chromatography/tandem mass spectrometry method. We calculated the percentage above the limit of detection, the 50th through 95th percentiles, and in some cases, geometric means for groups classified by age, gender, and race/ethnicity.

RESULTS

Total urinary NNAL was measureable at or above its limit of detection (0.6 pg/mL) in 55% of the study participants, including 41% of nonsmokers. The population distribution of urinary NNAL included smoker and nonsmoker regions similar to the bimodal distribution of serum cotinine, and serum cotinine and total urinary NNAL were strongly correlated (r = 0.92; P < 0.001). Among nonsmokers, children had significantly higher concentrations of NNAL than did adults with the age of ≥20 years (P < 0.001).

CONCLUSIONS

Among National Health and Nutrition Examination Survey participants, total NNAL was found at measurable levels in the urine of 41% of nonsmokers and in 87.5% of those with substantial secondhand-smoke exposure (with serum cotinine concentrations of 0.1-10 ng/mL). Children with the age of 6 to 11 years had the highest NNAL concentrations among all nonsmokers.

IMPACT

We describe for the first time the distribution of total urinary NNAL in the entire U.S. population, including smokers and nonsmokers. NNAL was detected in 41% of all nonsmokers.

Increases in tobacco exposure biomarkers measured in non-smokers exposed to sidestream cigarette smoke under controlled conditions

National surveys of the exposure of non-smokers to secondhand smoke based on serum cotinine analyses have consistently identified certain groups within the population including children, males and non-Hispanic Blacks as having relatively greater exposure. Although these differences in mean serum cotinine concentrations probably represent differences in exposure of individuals in their daily lives, it is also possible that metabolic or other differences in response might influence the results. To better define the nature of those findings, we have examined the response of 40 non-smokers including both men and women and African-Americans and whites to sidestream (SS) cigarette smoke generated by a smoking machine under controlled conditions. In this study, participants were exposed to aged, diluted SS smoke (ADSS) generated in an environmental chamber with a mean air nicotine concentration of 140 microg m(-3) and 8.6 ppm CO for 4 h. Salivary cotinine was measured every 30 min, and serum cotinine samples were taken prior to, and 2 h after exposure. Urinary nicotine metabolites and NNAL, a tobacco-specific nitrosamine, and 4-aminobiphenyl (4-AB) haemoglobin adducts were also measured prior to and 2 h following the exposure. Under these uniform, controlled conditions, we found a similar response to ADSS smoke exposure among all the participants. In all cases a significant increase in biomarker concentration was noted following exposure, and the short-term increases in salivary cotinine concentration were quite similar at approximately 12 pg ml(-1) min(-1) among the groups. In this small study, no significant differences by gender or race were seen in the mean increases observed in cotinine, NNAL or 4-AB adducts following 4 h of exposure. Thus, our results are most consistent with a relatively uniform response in tobacco biomarker concentrations following short-term exposure to ADSS tobacco smoke, and suggest that biomarker measurements are capable of effectively indicating increases in exposure among groups of non-smokers.

Levels in the U.S. population of those persistent organic pollutants (2003-2004) included in the Stockholm Convention or in other long range transboundary air pollution agreements

We report human serum levels of selected persistent organic pollutants (POPs) categorized by age, sex, and race/ ethnicity from a statistically representative sampling of the U.S. population during 2003 and 2004. The serum levels are for several chemicals listed in the Stockholm Convention on Persistent Organic Pollutants, in the Geneva Convention on Long-Range Transboundary Air Pollution, or in both. Population data for each chemical are described by geometric means and percentiles and are categorized by age, sex, and race/ ethnicity. At the 90th and 95th percentile, the dioxin total toxic equivalency (TEQ), using the 2005 toxic equivalency factors (TEFs) for all persons 12 years of age and older was 30.9 pg/g lipid (95% confidence interval (CI): 28.2-33.9 pg/g lipid) and 37.8 pg/g lipid (95% CI: 35.3-43.4 pg/g lipid), respectively. At both the 90th and 95th percentiles total TEQ increased significantly with increasing age. The population geometric mean (GM) for the total PCB concentration (sum of 35 congeners) for all persons 12 years of age and older was 0.820 ng/g whole-weight (95% CI: 0.782-0.863 ng/g whole-weight) and 134.4 ng/g lipid (95% CI: 128.9-140.0 ng/g lipid). The population 95th percentile for the total PCB concentration for all persons 12 years of age and older was 3.53 ng/g whole-weight (95% CI: 3.23-3.92 ng/g whole-weight) and 531 ng/g lipid (95% CI: 498-570 ng/g lipid). The concentrations of aldrin, endrin, gamma-HCH, and o,p'-DDT were <limit of detection for all strata in the U.S. population. Hexachlorobenzene was detected in 99.9% of the persons aged 12 years and older (GM: 15.2 ng/g lipid, 95% CI: 14.5-15.9 ng/g lipid). beta-HCH was detected in 69.5% of the persons aged 12 years and older (75th percentile: 14.0 ng/g lipid, 95% CI: 12.1-16.5 ng/g lipid). p,p'-DDT was detected in 73.8% of the persons aged 12 years and older (90th percentile: 11.9 ng/g lipid. 95% CI: 9.9-14.9 ng/g lipid). The DDT metabolite p,p'-DDE was detected in 99.7% of persons aged 12 years and older (GM: 238.4 ng/g lipid, 95% CI: 194.6-292.2 ng/g lipid). Oxychlordane(GM: 9.4 ng/g lipid, 95% CI: 8.7-10.1 ng/g lipid);transnonachlor (GM: 14.6 ng/g lipid, 95% CI: 13.1-16.5 ng/g lipid); and heptachlor epoxide (90th percentile: 13.4 ng/g lipid, 95% CI: 11.1-15.9 ng/g lipid) were detected in 82.9, 92.6, and 60% of persons aged 12 years and older, respectively. Mirexwas detected in 40.7% of persons aged 12 years and older (90th percentile: 8.3 ng/g lipid, 95% CI: <LOD-13.0 ng/g lipid). Dieldrin was detected in 87.2% of persons aged 12 years and older (95th percentile: 18.9 ng/g lipid, 95% CI: 15.8-24.5 ng/g lipid).

Dioxin exposure, from infancy through puberty, produces endocrine disruption and affects human semen quality

BACKGROUND

Environmental toxicants are allegedly involved in decreasing semen quality in recent decades; however, definitive proof is not yet available. In 1976 an accident exposed residents in Seveso, Italy, to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

OBJECTIVE

The purpose of this study was to investigate reproductive hormones and sperm quality in exposed males.

METHODS

We studied 135 males exposed to TCDD at three age groups, infancy/prepuberty (1-9 years), puberty (10-17 years), and adulthood (18-26 years), and 184 healthy male comparisons using 1976 serum TCDD levels and semen quality and reproductive hormones from samples collected 22 years later.

RESULTS

Relative to comparisons, 71 men (mean age at exposure, 6.2 years; median serum TCDD, 210 ppt) at 22-31 years of age showed reductions in sperm concentration (53.6 vs. 72.5 million/mL; p = 0.025); percent progressive motility (33.2% vs. 40.8%; p < 0.001); total motile sperm count (44.2 vs. 77.5 x 10(6); p = 0.018); estradiol (76.2 vs. 95.9 pmol/L; p = 0.001); and an increase in follicle-stimulating hormone (FSH; 3.58 vs. 2.98 IU/L; p = 0.055). Forty-four men (mean age at exposure, 13.2 years; median serum TCDD, 164 ppt) at 32-39 years of age showed increased total sperm count (272 vs. 191.9 x 10(6); p = 0.042), total motile sperm count (105 vs. 64.9 x10(6); p = 0.036), FSH (4.1 vs. 3.2 UI/L; p = 0.038), and reduced estradiol (74.4 vs. 92.9 pmol/L; p < 0.001). No effects were observed in 20 men, 40-47 years of age, who were exposed to TCDD (median, 123 ppt) as adults (mean age at exposure, 21.5 years).

CONCLUSIONS

Exposure to TCDD in infancy reduces sperm concentration and motility, and an opposite effect is seen with exposure during puberty. Exposure in either period leads to permanent reduction of estradiol and increased FSH. These effects are permanent and occur at TCDD concentrations < 68 ppt, which is within one order of magnitude of those in the industrialized world in the 1970s and 1980s and may be responsible at least in part for the reported decrease in sperm quality, especially in younger men.

Identification and Quantification of Diethylene Glycol in Pharmaceuticals Implicated in Poisoning Epidemics: An Historical Laboratory Perspective

Over the last several decades, mass poisonings of diethylene glycol (DEG), usually ingested as an unintended component of pharmaceutical preparations, have occurred. In order to promptly halt the rise in deaths due to ingestion of these pharmaceuticals, laboratory analysis has often been employed to identify and quantify the etiologic agent after the medications have been tentatively implicated. Over the past 15 years, the Centers for Disease Control and Prevention has been involved in identifying DEG in implicated pharmaceutical products during three poisoning epidemics that occurred in Nigeria (1990), Haiti (1995), and, most recently, in Panama (2006). In each case, the timeliness of the identification was paramount in reducing the mortality involved in these mass poisonings. Using state-of-the-art analytical technology, we were able to provide initial identification of DEG within 24 h of receiving samples for each epidemic, allowing a timely public health response. However, over the past 15 years, the analytical instrumentation available and the laboratory responses undertaken have changed. In addition, the type of information and the degree of confirmation of results requested during each epidemic varied based upon the number of individuals involved and the political tenor involved with the outbreak. We describe our historical approach to identifying and quantifying DEG during each of these outbreaks. Furthermore, the reoccurrence of outbreaks has prompted us to establish standard technology to use in potential future outbreaks to allow an even more timely response. This methodology includes the development of biomarkers of DEG exposure, which would be extremely useful in instances where pharmaceuticals are not clearly implicated.

Genetic studies of a cluster of acute lymphoblastic leukemia cases in Churchill County, Nevada

OBJECTIVE

In a study to identify exposures associated with 15 cases of childhood leukemia, we found levels of tungsten, arsenic, and dichlorodiphenyldichloroethylene in participants to be higher than mean values reported in the National Report on Human Exposure to Environmental Chemicals. Because case and comparison families had similar levels of these contaminants, we conducted genetic studies to identify gene polymorphisms that might have made case children more susceptible than comparison children to effects of the exposures.

DESIGN

We compared case with comparison children to determine whether differences existed in the frequency of polymorphic genes, including genes that code for enzymes in the folate and purine pathways. We also included discovery of polymorphic forms of genes that code for enzymes that are inhibited by tungsten: xanthine dehydrogenase, sulfite oxidase (SUOXgene), and aldehyde oxidase.

PARTICIPANTS

Eleven case children were age- and sex-matched with 42 community comparison children for genetic analyses. Twenty parents of case children also contributed to the analyses.

RESULTS

One bilalleleic gene locus in SUOX was significantly associated with either case or comparison status, depending on which alleles the child carried (without adjusting for multiple comparisons).

CONCLUSIONS

Although genetic studies did not provide evidence that a common agent or genetic susceptibility factor caused the leukemias, the association between a SUOXgene locus and disease status in the presence of high tungsten and arsenic levels warrants further investigation.

RELEVANCE

Although analyses of community clusters of cancer have rarely identified causes, these findings have generated hypotheses to be tested in subsequent studies.

Reference range levels of polycyclic aromatic hydrocarbons in the US population by measurement of urinary monohydroxy metabolites

We developed a gas chromatography isotope-dilution high-resolution mass spectrometry (GC/ID-HRMS) method for measuring 14 polycyclic aromatic hydrocarbon (PAH) metabolites representing seven parent PAHs in 3 mL of urine at low parts-per-trillion levels. PAH levels were determined in urine samples collected in 1999 and 2000 from approximately 2400 participants in the National Health and Nutrition Examination Survey, and, for the first time, reference range values were calculated for these metabolites in the US population. Using this GC/ID-HRMS method, we found detectable concentrations for monohydroxy metabolite isomers of fluorene, phenanthrene, fluoranthene, pyrene, and chrysene, benzo[c]phenanthrene, and benz[a]anthracene. Some monohydroxy metabolite isomers of benzo[c]phenanthrene, chrysene, and benz[a]anthracene exhibited low detection frequencies that did not allow for geometric mean calculations. Our study results enabled us to establish a reference range for the targeted PAHs in the general US population.

Urinary tobacco‐specific nitrosamines and 4‐aminobiphenyl hemoglobin adducts measured in smokers of either regular or light cigarettes

Cigarette brands may differ in their reported yields of "tar" as determined by the Federal Trade Commission smoking-machine method. Brands with relatively lower tar and nicotine yields often are described as light cigarettes. Smokers of light cigarettes generally maintain a nicotine intake comparable to that of smokers of regular cigarettes through compensatory smoking behaviors, but similar data have not been reported for carcinogen biomarkers. In the present study we measured serum cotinine concentrations (a marker of nicotine exposure), urinary levels of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL, a tobacco-specific nitrosamine [TSNA]), and hemoglobin adducts of 4-aminobiphenyl (4-ABP) in 150 smokers of either regular or light cigarettes. The TSNA and aromatic amines are known carcinogens in tobacco smoke. Multiple regression models were developed for each of the analytes and used to calculate adjusted geometric means. We found no significant differences in the levels of these biomarkers between customary users of light and regular cigarettes. Thus the concentrations of the carcinogen biomarkers NNAL and 4-ABP in the smokers who regularly smoked light cigarettes were essentially the same as those in the smokers who chose regular cigarettes.

Biochemical indicators of B vitamin status in the US population after folic acid fortification: results from the National Health and Nutrition Examination Survey 1999-2000

BACKGROUND

Mandatory folic acid fortification of cereal-grain products was introduced in the United States in 1998 to decrease the risk that women will have children with neural tube defects.

OBJECTIVE

The objective was to determine the effect of folic acid fortification on concentrations of serum and red blood cell (RBC) folate, serum vitamin B-12, and plasma total homocysteine (tHcy) and methylmalonic acid (MMA) in the US population.

DESIGN

Blood was collected from a nationally representative sample of approximately 7300 participants aged > or = 3 y in the National Health and Nutrition Examination Survey (NHANES) during 1999-2000 and was analyzed for these B vitamin-status indicators. The results were compared with findings from the prefortification survey NHANES III (1988-1994).

RESULTS

The reference ranges (5th-95th percentiles) were 13.1-74.3 nmol/L for serum folate, 347-1167 nmol/L for RBC folate, and 179-738 pmol/L for serum vitamin B-12. For plasma tHcy and MMA, the reference ranges for serum vitamin B-12-replete participants with normal serum creatinine concentrations were 3.2-10.7 mumol/L and 60-210 nmol/L, respectively. The prevalence of low serum folate concentrations (<6.8 nmol/L) decreased from 16% before to 0.5% after fortification. In elderly persons, the prevalence of high serum folate concentrations (>45.3 nmol/L) increased from 7% before to 38% after fortification; 3% had marginally low serum vitamin B-12 concentrations (<148 pmol/L) and 7% had elevated plasma MMA concentrations (>370 nmol/L). Seventy-eight percent of the US population had plasma tHcy concentrations <9 micromol/L.

CONCLUSIONS

Every segment of the US population appears to benefit from folic acid fortification. Continued monitoring of B vitamin concentrations in the US population is warranted.

National exposure measurements for decisions to protect public health from environmental exposures

Protecting public health from environmental exposures requires four steps: detection of exposures known or expected to cause disease, assessment of health risk from exposure, implementation of an exposure intervention, and assurance that the exposure intervention is effective. To prioritize efforts in these four areas one must consider the size of the population affected, the seriousness of health effects, and the availability of cost-effective exposure interventions. Population exposure data is critical to each of these steps for protecting health. Biomonitoring data for the US population is now available to assist public health scientists and physicians in preventing disease from environmental exposures, and it complements that available for levels of chemicals in environmental media. The Second National Report on Human Exposure to Environmental Chemicals provides for the US population serum, blood and urine levels for 116 environmental chemicals over the years 1999 and 2000, with separate analyses by age, sex, and race/ethnicity. This national exposure information identifies which chemicals get into Americans in measurable quantities; determines whether exposure levels are higher among population subgroups; determines how many Americans have levels of chemicals above recognized health threshold levels (for chemicals with such threshold levels); establishes reference ranges that define general population exposure so unusual exposures can be recognized; assesses the effectiveness of public health efforts to reduce population exposure to selected chemicals; and tracks over time trends in US population exposure. Blood lead measurements in the population were important in identifying lead in gasoline as a significant source of human lead exposure and documenting the reduction in blood lead levels in the population as a result of removing lead from gasoline and other products in the United States. Serum cotinine levels in the early 1990s found more widespread exposure to environmental tobacco smoke (ETS) in the United States than previously thought and additional measurements in 1999 and 2000 documented major declines in exposure to ETS as a result of public health actions in the 1990s. A new biomonitoring assessment of the exposure of the US population will be released every 2 years as the "National Report on Human Exposure to Environmental Chemicals." These reports will include the current 116 chemicals and new chemicals added to monitor priority exposures of the population.

Concentrations of environmental chemicals associated with neurodevelopmental effects in U.S. population

Humans are exposed to many environmental chemicals, some of which can potentially affect neurodevelopment. Fetuses, infants, and young children are the most susceptible to the effects of these chemicals. As part of the National Health and Examination Survey, 1999-2000, the Centers for Disease Control and Prevention analyzed biological samples for many of these chemicals in a representative sampling of the U.S. population. Concentration data of selected metals, persistent organic pollutants, organophosphorus and carbamate insecticides, and cotinine are presented. For example, the 95th percentile estimates for serum total PCBs (whole weight) in the population aged 20 years and older is about 2.7 ng/g. The 95th percentile estimates for serum dioxin total toxic equivalence in the U.S. population aged 20 years and older is between 40 and 50 pg/g lipid basis. In general, human levels of these chemicals are decreasing over time in the U.S. population. This reflects the effects of legislation, industry efforts, and changes in lifestyle/activity patterns in the U.S. population. These data will continue to be collected in 2-year cycles and thus allow changes in human levels to be followed.

Comparison of 1-hydroxypyrene exposure in the US population with that in occupational exposure studies

Urine samples collected in 1999 and 2000 as part of the National Health and Nutrition Examination Survey (NHANES) were analyzed for 14 monohydroxy polycyclic aromatic hydrocarbons (PAHs), and, for the first time, reference range values were calculated for these metabolites in the US population. Pyrene is a major component of most PAH mixtures and often is used as a surrogate for total PAH exposure. We detected 1-hydroxypyrene (1-OHpyrene), a metabolite of pyrene, in more than 99% of the samples. The overall geometric mean concentration for 1-OHpyrene in the USA was 79.8 ng/l, with a 95% confidence interval (CI) of 69.0-92.2 ng/l. The overall geometric mean creatinine-adjusted urinary 1-OHpyrene levels in the USA was 74.2 ng/g creatinine (0.039 micromol/mol), with a 95% CI of 64.1-85.9 ng/g creatinine (0.034-0.046 micromol/mol). There were no statistically significant differences among age, gender, or race/ethnicity groups. Adult smokers in the USA have urinary 1-OHpyrene levels three times higher than those of non-smokers. This difference was statistically significant. In this paper, we compare the reference range of urinary 1-OHpyrene levels with levels reported from various occupations by other researchers.

Concentrations of dialkyl phosphate metabolites of organophosphorus pesticides in the U.S. population

We report population-based concentrations, stratified by age, sex, and racial/ethnic groups, of dialkyl phosphate (DAP) metabolites of multiple organophosphorus pesticides. We measured dimethylphosphate (DMP), dimethylthiophosphate (DMTP), dimethyldithiophosphate (DMDTP), diethylphosphate (DEP), diethylthiophosphate (DETP), and diethyldithiophosphate (DEDTP) concentrations in 1,949 urine samples collected in U.S. residents 6-59 years of age during 1999 and 2000 as a part of the ongoing National Health and Nutrition Examination Survey (NHANES). We detected each DAP metabolite in more than 50% of the samples, with DEP being detected most frequently (71%) at a limit of detection of 0.2 microg/L. The geometric means for the metabolites detected in more than 60% of the samples were 1.85 microg/L for DMTP and 1.04 microg/L for DEP. The 95th percentiles for each metabolite were DMP, 13 microg/L; DMTP, 46 microg/L; DMDTP, 19 micro g/L; DEP, 13 microg/L; DETP, 2.2 microg/L; and DEDTP, 0.87 microg/L. We determined the molar sums of the dimethyl-containing and diethyl-containing metabolites; their geometric mean concentrations were 49.4 and 10.5 nmol/L, respectively, and their 95th percentiles were 583 and 108 nmol/L, respectively. These data are also presented as creatinine-adjusted concentrations. Multivariate analyses showed concentrations of DAPs in children 6-11 years of age that were consistently significantly higher than in adults and often higher than in adolescents. Although the concentrations between sexes and among racial/ethnic groups varied, no significant differences were observed. These data will be important in evaluating the impact of organophosphorus pesticide exposure in the U.S. population and the effectiveness of regulatory actions.

Serum selenium levels in the US population: Third National Health and Nutrition Examination Survey, 1988-1994

The published literature on serum selenium levels in the US population describes studies on small samples that may not be representative of the US population. This analysis provides the first nationally representative serum selenium levels in the US population by age group, sex, race-ethnicity, poverty income ratio (PIR), geographic region, and urban status. The Third National Health and Nutrition Examination Survey (NHANES III) is a national population-based cross-sectional survey with an in-person interview and serum selenium measurements. For the 18,597 persons for whom serum selenium values wereavailable in NHANES III, the mean concentration was 1.58 nmol/L and the median concentration was 1.56 nmol/L. Mean serum selenium levels differed by age group, sex, race ethnicity, PIR, and geographic region. The US population has slight differences in serum selenium levels by demographic factors.

Measurement of p-nitrophenol in the urine of residents whose homes were contaminated with methyl parathion

During the last several years, illegal commercial application of methyl parathion (MP) in domestic settings in several U.S. Southeastern and Midwestern States has affected largely inner-city residents. As part of a multiagency response involving the U.S. Environmental Protection Agency (U.S. EPA), the Agency for Toxic Substances and Disease Registry (ATSDR), and state and local health departments, our laboratory developed a rapid, high-throughput, selective method for quantifying p-nitrophenol (PNP), a biomarker of MP exposure, using isotope dilution high-performance liquid chromatography-tandem mass spectrometry. We measured PNP in approximately 16,000 samples collected from residents of seven different states. Using this method, we were able to receive sample batches from each state; prepare, analyze, and quantify the samples for PNP; verify the results; and report the data to the health departments and ATSDR in about 48 hr. These data indicate that many residents had urinary PNP concentrations well in excess of those of the general U.S. population. In fact, their urinary PNP concentrations were more consistent with those seen in occupational settings or in poisoning cases. Although these data, when coupled with other MP metabolite data, suggest that many residents with the highest concentrations of urinary PNP had significant exposure to MP, they do not unequivocally rule out exposure to PNP resulting from environmental degradation of MP. Even with their limitations, these data were used with the assumption that all PNP was derived from MP exposure, which enabled the U.S. EPA and ATSDR to develop a comprehensive, biologically driven response that was protective of human health, especially susceptible populations, and included clinical evaluations, outreach activities, community education, integrated pest management, and decontamination of homes.

Prevalence of C282Y and H63D mutations in the hemochromatosis (HFE) gene in the United States

CONTEXT

Population-based estimates of the prevalence of disease-associated mutations, such as hemochromatosis (HFE) gene mutations, are needed to determine the usefulness of genetic screening.

OBJECTIVE

To estimate the prevalence of the HFE mutations C282Y and H63D in the US population.

DESIGN

Cross-sectional population-based study of samples in the DNA bank from phase 2 of the Third National Health and Nutrition Examination Survey conducted from 1992 to 1994.

SETTING AND PARTICIPANTS

Genotyped samples of cells from a total of 5171 participants, cross-classified by sex, age, and race/ethnicity in the analysis.

MAIN OUTCOME MEASURES

Estimates of the prevalence of C282Y and H63D mutations.

RESULTS

The prevalence of C282Y homozygosity is estimated to be 0.26% (95% confidence interval [CI], 0.12%-0.49%); 1.89% (95% CI, 1.48%-2.43%) for H63D homozygosity; and 1.97% (95% CI, 1.54%-2.49%) for compound heterozygosity. The prevalence estimates for C282Y heterozygosity (C282Y/wild type) are 9.54% among non-Hispanic whites, 2.33% among non-Hispanic blacks, and 2.75% among Mexican-Americans. The prevalence estimates of the C282Y mutation in the US population are 5.4% (95% CI, 4.7%-6.2%) and 13.5% (95% CI, 12.5%-14.8%) for the H63D mutation.

CONCLUSIONS

Estimates of prevalence of HFE mutations are within the expected range for non-Hispanic whites and blacks but the estimated prevalence of the C282Y mutation among Mexican-Americans is less than expected. Mutation data now need to be linked to clinically relevant indices, such as transferrin saturation level.

Analysis of factors influencing the comparison of homocysteine values between the Third National Health and Nutrition Examination Survey (NHANES) and NHANES 1999+

Two important changes occurred in the time between the Third National Health and Nutrition Examination Survey (NHANES III) (1991-1994) and the later survey (NHANES 1999+) regarding total homocysteine (tHcy), i.e., a change in matrix from serum to plasma and a change in analytical methods. The goals of this study were to determine the magnitude of potential differences between plasma and serum with regard to tHcy concentrations, and between the two analytical methods used in these surveys. Optimally prepared plasma, serum allowed to clot for 30 and 60 min at room temperature and serum allowed to clot for 30 and 60 min and subjected to four freeze-thaw cycles, prepared from blood samples collected from 30 healthy people, were analyzed by both methods. Serum samples had significantly higher tHcy concentrations than plasma samples, and the difference increased with longer clotting time. Freeze-thaw cycles had little or no effect on the variability or bias in the serum sample results. The tHcy results produced by the two analytical methods were significantly different, but consistent across sample types. On average, the results of the method used in NHANES III were lower by 0.64 micromol/L; however, the relative bias varied with tHcy concentration. The tHcy results determined in surplus serum from NHANES III overestimated tHcy concentrations by approximately 10% compared with optimally prepared plasma. The average method bias was 6% between the two analytical methods. On the basis of changes in matrix and methodology, direct comparison of tHcy results between the two surveys is inappropriate.

A reference method laboratory network for cholesterol: a model for standardization and improvement of clinical laboratory measurements

BACKGROUND

Accurate and precise measurement of blood cholesterol plays a central role in the National Cholesterol Education Program's strategy to reduce the morbidity and mortality attributable to coronary heart disease. Matrix effects hamper the ability of manufacturers to adequately calibrate and validate traceability to the National Reference System for Cholesterol (NRS/CHOL). CDC created the Cholesterol Reference Method Laboratory Network (CRMLN) to improve cholesterol measurement by assisting manufacturers of in vitro diagnostic products with validation of the traceability of their assays to the NRS/CHOL.

METHODS

CRMLN laboratories established the CDC cholesterol reference method (modification of the Abell-Levy-Brodie-Kendall chemical method) and are standardized using CDC frozen serum reference materials. CRMLN laboratories use common quality-control materials and participate in monthly external performance evaluations conducted by CDC. The CRMLN performance criteria require member laboratories to agree with CDC within +/-1.0% and maintain a CV < or =2.0%.

RESULTS

From 1995 to 200 the CRMLN laboratories met the accuracy criterion 97% of the time and the precision criterion 99% of the time. During this time period, the CRMLN maintained an average bias to CDC of 0.01% and an average collective CV of 0.33%.

CONCLUSIONS

CDC established the CRMLN as the first international reference method laboratory network. The CRMLN assists manufacturers in the validation of the calibration of their diagnostic products so that clinical laboratories can measure blood cholesterol more reliably. The CRMLN can serve as a model for other clinical analytes where traceability to a hierarchy of methods is needed and matrix effects of the field methods with processed calibrators or reference materials are present.

A Reference Method Laboratory Network for Cholesterol: A Model for Standardization and Improvement of Clinical Laboratory Measurements

Background: Accurate and precise measurement of blood cholesterol plays a central role in the National Cholesterol Education Program’s strategy to reduce the morbidity and mortality attributable to coronary heart disease. Matrix effects hamper the ability of manufacturers to adequately calibrate and validate traceability to the National Reference System for Cholesterol (NRS/CHOL). CDC created the Cholesterol Reference Method Laboratory Network (CRMLN) to improve cholesterol measurement by assisting manufacturers of in vitro diagnostic products with validation of the traceability of their assays to the NRS/CHOL.

Methods: CRMLN laboratories established the CDC cholesterol reference method (modification of the Abell-Levy-Brodie-Kendall chemical method) and are standardized using CDC frozen serum reference materials. CRMLN laboratories use common quality-control materials and participate in monthly external performance evaluations conducted by CDC. The CRMLN performance criteria require member laboratories to agree with CDC within ± 1.0% and maintain a CV ≤2.0%.

Results: From 1995 to 2000, the CRMLN laboratories met the accuracy criterion 97% of the time and the precision criterion 99% of the time. During this time period, the CRMLN maintained an average bias to CDC of 0.01% and an average collective CV of 0.33%.

Conclusions: CDC established the CRMLN as the first international reference method laboratory network. The CRMLN assists manufacturers in the validation of the calibration of their diagnostic products so that clinical laboratories can measure blood cholesterol more reliably. The CRMLN can serve as a model for other clinical analytes where traceability to a hierarchy of methods is needed and matrix effects of the field methods with processed calibrators or reference materials are present.

Levels of seven urinary phthalate metabolites in a human reference population

Using a novel and highly selective technique, we measured monoester metabolites of seven commonly used phthalates in urine samples from a reference population of 289 adult humans. This analytical approach allowed us to directly measure the individual phthalate metabolites responsible for the animal reproductive and developmental toxicity while avoiding contamination from the ubiquitous parent compounds. The monoesters with the highest urinary levels found were monoethyl phthalate (95th percentile, 3,750 ppb, 2,610 microg/g creatinine), monobutyl phthalate (95th percentile, 294 ppb, 162 microg/g creatinine), and monobenzyl phthalate (95th percentile, 137 ppb, 92 microg/g creatinine), reflecting exposure to diethyl phthalate, dibutyl phthalate, and benzyl butyl phthalate. Women of reproductive age (20-40 years) were found to have significantly higher levels of monobutyl phthalate, a reproductive and developmental toxicant in rodents, than other age/gender groups (p < 0.005). Current scientific and regulatory attention on phthalates has focused almost exclusively on health risks from exposure to only two phthalates, di-(2-ethylhexyl) phthalate and di-isononyl phthalate. Our findings strongly suggest that health-risk assessments for phthalate exposure in humans should include diethyl, dibutyl, and benzyl butyl phthalates.

Serum dioxin levels in Seveso, Italy, population in 1976

On July 10, 1976, an explosion at a chemical plant near Seveso, Italy, released a mixture of chemicals, including 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2,4,5-trichlorophenol. As a result, several thousand people in the Seveso area may have been exposed to those chemicals. At that time, human exposure assessment was based primarily on soil levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Medical examinations of this potentially exposed population and control subjects were begun in 1976 and in some cases continued until 1985. In 1988, we began assessing human exposure in this population by measuring 2,3,7,8-tetrachlorodibenzo-p-dioxin in small volumes of serum specimens remaining from the medical examinations. As expected, we found that the median serum dioxin levels were highest among people who lived closest to the explosion and were progressively lower among groups living farther away. These measurements have allowed us to assess exposure more accurately among individuals in this population and to relate exposure to various health effects. We found that some individuals in the exposed population had among the highest serum dioxin levels ever reported, yet chloracne was the only unequivocal effect found; cancer risks are still being investigated. We also found that other individuals with as high or higher serum dioxin levels did not develop chloracne. We also found that the serum half-life of dioxin in this population was 7-8 years, which agrees with other findings although we do report some differences in the serum half-life of TCDD for women and children. We also observed an increase in the percentage of female newborns to parents who resided in Zone A at the time of the explosion, and we also report on the 1976 serum dioxin levels in people who later developed cancer.

Paternal concentrations of dioxin and sex ratio of offspring

BACKGROUND

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD or dioxin), is commonly considered the most toxic man-made substance. We have previously shown that high serum concentrations of TCDD in parents from Seveso, Italy, were linked to their having a relative increase in the number of female births after the parents exposure to a release of dioxin in 1976. We have continued the study to determine whether the parents' sex and/or age at exposure affected the sex ratio of their children.

METHODS

We measured the TCDD concentrations in serum samples from potentially exposed parents collected in 1976 and 1977, and investigated the sex ratio of their offspring.

FINDINGS

Serum samples were collected from 239 men and 296 women. 346 girls and 328 boys were born to potentially exposed parents between 1977 and 1996, showing an increased probability of female births (lower sex ratio) with increasing TCDD concentrations in the serum samples from the fathers (p=0.008). This effect starts at concentrations less than 20 ng per kg bodyweight. Fathers exposed when they were younger than 19 years of age sired significantly more girls than boys (sex ratio 0.38 [95% CI 0.30-0.47]).

INTERPRETATION

Exposure of men to TCDD is linked to a lowered male/female sex ratio in their offspring, which may persist for years after exposure. The median concentration of dioxin in fathers in this study is similar to doses that induce epididymal impairments in rats and is about 20 times the estimated average concentration of TCDD currently found in human beings in industrialised countries. These observations could have important public-health implications.

Levels of methyleugenol in a subset of adults in the general U.S. population as determined by high resolution mass spectrometry

We developed a sensitive and accurate analytical method for quantifying methyleugenol (ME) in human serum. Our method uses a simple solid-phase extraction followed by a highly specific analysis using isotope dilution gas chromatography-high resolution mass spectrometry. Our method is very accurate; its limit of detection is 3.1 pg/g and its average coefficient of variation is 14% over a 200-pg/g range. We applied this method to measure serum ME concentrations in adults in the general U.S. population. ME was detected in 98% of our samples, with a mean ME concentration of 24 pg/g (range < 3.1-390 pg/g). Lipid adjustment of the data did not alter the distribution. Bivariate and multivariate analyses using selected demographic variables showed only marginal relationships between race/ethnicity and sex/fasting status with serum ME concentrations. Although no demographic variable was a good predictor of ME exposure or dose, our data indicate prevalent exposure of U.S. adults to ME. Detailed pharmacokinetic studies are required to determine the relationship between ME intake and human serum ME concentrations.

Exposure of the U.S. population aged 6 years and older to cadmium: 1988-1994

Cadmium was measured in urine specimens from 22,162 participants in the Third National Health and Nutrition Examination Survey (NHANES III 1988-1994). Urine cadmium, expressed either as uncorrected (microg/L) or creatinine corrected (microg/g creatinine) increased with age and with smoking. The arithmetic mean value for urine cadmium in the U.S. population was 0.57 microg/L or 0.48 microg/g creatinine. Based on our estimates, about 2.3% of the U.S. population have urine cadmium concentrations greater than 2 microg/g creatinine, and 0.2% have concentrations greater than 5 microg/g creatinine, the current World Health Organization health-based exposure limit.

Uranium and thorium in urine of United States residents: reference range concentrations

We measured uranium and thorium in urine of 500 U. S. residents to establish reference range concentrations using a magnetic-sector inductively coupled argon plasma mass spectrometer (ICP-MS). We found uranium at detectable concentrations in 96.6% of the urine specimens and thorium in 39.6% of the specimens. The 95th percentile concenetration for uranium was 34.5 ng/L (parts per trillion); concentrations ranged up to 4080 ng/L. Thorium had a 95th percentile concentration of 3.09 ng/L; concentrations ranged up to 7.7 ng/L.

Exposure assessment: serum levels of TCDD in Seveso, Italy

Accurate exposure assessment is an important step in both risk assessment and epidemiologic studies involving potential human exposure to environmental toxicants. Various methods have been used to assess human exposure. These methods include models based on one's temporal and spatial nearness to the source, environmental levels of toxicant, and biological measures. We believe that the latter measure is the "gold standard." In this article we present the serum 2,3,7,8-tetrachlorodibenzo-p-dioxin levels in residents of the contaminated zones in Seveso, Italy, in 1976, and delineate these data by age and gender. Some of these serum levels are among the highest ever reported and thus this population serves as a benchmark for comparison of human exposure and potential adverse health effects. One such potential population is that population consuming potentially contaminated fish.

Strategies for biological monitoring of exposure for contemporary-use pesticides

Pesticides are used on a massive scale in the United States. The widespread use of these pesticides has made it virtually impossible for the average person to avoid exposure at some level. Generally, it is believed that low-level exposure to these pesticides does not produce acute toxic effects; however, various cancers and other noncancer health endpoints have been associated with chronic exposure to several groups of pesticides. Therefore, it is imperative that well-designed studies investigate the potential relationship between contemporary pesticide exposure and health effects. For these studies to be accurate, reliable methods for determining individual exposure must be used. Biological monitoring is a useful tool for assessing exposure to some contemporary pesticides. As with any analytical method, biological monitoring entails many difficulties, but, in many instances, they can be overcome by the logical use of available information and information acquired in carefully designed studies. At the Centers for Disease Control and Prevention (CDC), we have acquired extensive experience in the development and application of specific techniques for biological monitoring of a variety of toxicants, including many of the contemporary-use pesticides. We have used these methods to measure the internal dose of pesticides received by people in acute and chronic incidents resulting from both environmental and industrial exposure. Additionally, we have established normative values, or reference ranges, of several pesticides based on measurements of their metabolites in the urine of randomly selected adults in the US population. These data have been successfully used to distinguish overt exposures from 'background' exposure. In this paper, we present several examples of the usefulness of biological monitoring in urine and blood and describe the difficulties involved with developing methods in these matrices. We also present a general strategy, considerations, and recommendations for developing biological monitoring techniques for measuring the internal dose of contemporary-use pesticides.

Current activities at the Centers for Disease Control and Prevention's National Diabetes Laboratory

In 1997, the Centers for Disease Control and Prevention established the National Diabetes Laboratory in order to help prevent and treat type 1 diabetes. This state-of-the-art laboratory collaborates with research scientists and key national and international organizations throughout the world to identify and study risk factors for type 1 diabetes by developing measurements for glycosylated proteins, developing and evaluating technology for measuring genetic risk factors for the disease, and working to standardize autoantibody measurements. Developing improved technologies for diagnosing and managing diabetes and developing reference materials for properly calibrating and standardizing blood glucose meters are also critical aspects of the laboratory's work. In addition, the laboratory provides quality storage for valuable collections of biologics and other materials and facilitates sharing of specimens, associated epidemiologic data, and test results. Working with our partners in diabetes research, we are improving the diagnosis, treatment, and prevention of type 1 diabetes.

Trace metals in urine of United States residents: reference range concentrations

We measured 13 metals in the urine of 496 United States residents to establish reference range concentrations using inductively coupled argon plasma mass spectrometry and Zeeman graphite furnace atomic absorption spectrometry. We frequently found 8 of these analytes at detectable concentrations in urine specimens: molybdenum (in 99.8%); lead (98.8%); tin (89%); thallium (77%); antimony (73.5%); manganese (73%); cesium (71%); tungsten (70%); and platinum (69.7%). The 95th percentile concentration for molybdenum was 168 micrograms/L; concentrations ranged up to 688 micrograms/L. Lead concentrations ranged up to 67 micrograms/L, and the 95th upper percentile was 6.4 micrograms/L. Tin had 95th upper percentile of 20.1 micrograms/L. Other analytes measured at detectable concentrations included barium (in 67% of the specimens); beryllium (67%); chromium (54%); thorium (44%); and cobalt (43%). In almost every case, the 95th upper percentiles of these analytes were less than 15 micrograms/L.

Development and validation of sensitive method for determination of serum cotinine in smokers and nonsmokers by liquid chromatography/atmospheric pressure ionization tandem mass spectrometry

We describe a sensitive and specific method for measuring cotinine in serum by HPLC coupled to an atmospheric pressure chemical ionization tandem mass spectrometer. This method can analyze 100 samples/day on a routine basis, and its limit of detection of 50 ng/L makes it applicable to the analysis of samples from nonsmokers potentially exposed to environmental tobacco smoke. Analytical accuracy has been demonstrated from the analysis of NIST cotinine standards and from comparative analyses by both the current method and gas chromatography/high-resolution mass spectrometry. Precision has been examined through the repetitive analysis of a series of bench and blind QC materials. This method has been applied to the analysis of cotinine in serum samples collected as part of the Third National Health and Nutrition Examination Survey (NHANES III).

Development and validation of sensitive method for determination of serum cotinine in smokers and nonsmokers by liquid chromatography/atmospheric pressure ionization tandem mass spectrometry

We describe a sensitive and specific method for measuring cotinine in serum by HPLC coupled to an atmospheric pressure chemical ionization tandem mass spectrometer. This method can analyze 100 samples/day on a routine basis, and its limit of detection of 50 ng/L makes it applicable to the analysis of samples from nonsmokers potentially exposed to environmental tobacco smoke. Analytical accuracy has been demonstrated from the analysis of NIST cotinine standards and from comparative analyses by both the current method and gas chromatography/high-resolution mass spectrometry. Precision has been examined through the repetitive analysis of a series of bench and blind QC materials. This method has been applied to the analysis of cotinine in serum samples collected as part of the Third National Health and Nutrition Examination Survey (NHANES III).

Results of an international round robin for serum and whole-blood folate

Because of the increasing significance of folate nutriture to public health, a "round robin" interlaboratory comparison study was conducted to assess differences among methods. Twenty research laboratories participated in a 3-day analysis of six serum and six whole-blood pools. Overall means, SDs, and CVs derived from these results were compared within and across method types. Results reported for serum and whole-blood folate demonstrated overall CVs of 27.6% and 35.7%, respectively, across pools and two- to ninefold differences in concentrations between methods, with the greatest variation occurring at critical low folate concentrations. Although results for serum pools were less variable than those for whole-blood pools, substantial intermethod variation still occurred. The overall results underscore the urgent need for developing and validating reference methods for serum and whole-blood folate and for properly characterized reference materials. For evaluating study or clinical data, method-specific reference ranges (established with clinical confirmation of values for truly folate-deficient individuals) must be used.

Isotope dilution--mass spectrometric quantification of specific proteins: model application with apolipoprotein A-I

An enzymatic hydrolysis isotope dilution-mass spectrometric method was developed for reference quantification of specific proteins. The analytical procedure involved measuring a reproducibly hydrolyzed peptide (serving as the primary standard) unique to a specific protein. This new mass spectrometric method was evaluated by assessing the concentration of apolipoprotein (apo) A-I in the European Community Bureau of Reference (BCR) lyophilized Certified Reference Material (CRM 393). We used the method to make 96 measurements (4 replicate analyses of 4 enzymatic digests of 6 vials of BCR-CRM 393), which gave an average total protein mass of 1.048 mg (+/- 1.0% at 99% confidence limits). The total overall analytical CV was 3.95%. The results of this evaluation of our model approach to determine the concentration of a specific protein in a purified preparation demonstrated that our new mass spectrometric method can be used to measure apolipoproteins and other specific proteins without the use of epitopic immunoassay methods.

Results of an international round robin for serum and whole-blood folate

Because of the increasing significance of folate nutriture to public health, a "round robin" interlaboratory comparison study was conducted to assess differences among methods. Twenty research laboratories participated in a 3-day analysis of six serum and six whole-blood pools. Overall means, SDs, and CVs derived from these results were compared within and across method types. Results reported for serum and whole-blood folate demonstrated overall CVs of 27.6% and 35.7%, respectively, across pools and two- to ninefold differences in concentrations between methods, with the greatest variation occurring at critical low folate concentrations. Although results for serum pools were less variable than those for whole-blood pools, substantial intermethod variation still occurred. The overall results underscore the urgent need for developing and validating reference methods for serum and whole-blood folate and for properly characterized reference materials. For evaluating study or clinical data, method-specific reference ranges (established with clinical confirmation of values for truly folate-deficient individuals) must be used.

Isotope dilution--mass spectrometric quantification of specific proteins: model application with apolipoprotein A-I

An enzymatic hydrolysis isotope dilution-mass spectrometric method was developed for reference quantification of specific proteins. The analytical procedure involved measuring a reproducibly hydrolyzed peptide (serving as the primary standard) unique to a specific protein. This new mass spectrometric method was evaluated by assessing the concentration of apolipoprotein (apo) A-I in the European Community Bureau of Reference (BCR) lyophilized Certified Reference Material (CRM 393). We used the method to make 96 measurements (4 replicate analyses of 4 enzymatic digests of 6 vials of BCR-CRM 393), which gave an average total protein mass of 1.048 mg (+/- 1.0% at 99% confidence limits). The total overall analytical CV was 3.95%. The results of this evaluation of our model approach to determine the concentration of a specific protein in a purified preparation demonstrated that our new mass spectrometric method can be used to measure apolipoproteins and other specific proteins without the use of epitopic immunoassay methods.

Analysis of benzoylecgonine in dried blood spots by liquid chromatography--atmospheric pressure chemical ionization tandem mass spectrometry

Residual samples from blood spots (i.e., whole blood spotted onto filter paper) are a useful source for epidemiological screening studies involving newborns. However, the small volume of blood available from residual blood spots complicates the assay. A method for analyzing benzoylecgonine (BZE; the primary metabolite of cocaine) in blood spots, in which the blood spot is eluted with aqueous ammonium acetate-methanol containing N-methyl trideuterated-BZE as an internal standard, followed by high-performance liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry using multiple reaction monitoring, has been developed. This approach provides a rapid, direct, sensitive (limit of detection, approximately 2 ng/mL, based on a 12-microL sample size), and highly specific means of determining BZE concentrations in blood spots. We have applied this method for confirmatory analyses in a large epidemiological study of the prevalence of cocaine use during late pregnancy.

Recommendations for the selection and use of protocols for assignment of values to reference materials

It is essential that testing of patient samples give values that are traceable to those in a recognized, authorizative reference material. In addition, samples used for laboratory proficiency testing must have values assigned from such a reference material if results are to be comparable among materials and laboratories. As a result, the assignment of values to secondary and tertiary reference materials, calibrants, controls, and proficiency samples should be performed as precisely as possible, within reasonable limits. The intent of this document is to give guidelines for assignment of values at three levels of transfer. 1) from primary to secondary reference, materials, such as international or national references; 2) from secondary to tertiary reference materials, such as manufacturers' in-house calibrants and controls; and 3) from tertiary reference materials, such as manufacturers' in-house calibrants and controls; and 3) from tertiary reference materials to working calibrants and controls. It is hoped that these guidelines will facilitate the selection and utilization of an appropriate value transfer protocol for each level of value assignment. Because of the wide variety and nature of analytes, however, the guidelines are intentionally broad and may require revision for specific analytes.

Pesticide residues in urine of adults living in the United States: reference range concentrations

We measured 12 analytes in urine of 1000 adults living in the United States to establish reference range concentrations for pesticide residues. We frequently found six of these analytes: 2,5-dichlorophenol (in 98% of adults); 2,4-dichlorophenol (in 64%); 1-naphthol (in 86%); 2-naphthol (in 81%); 3,5,6- trichloro-2-pyridinol (in 82%); and pentachlorophenol (in 64%). The 95th percentile concentration (95th PC) for 2,5-dichlorophenol (indicative of p-dichlorobenzene exposure) was 790 micrograms/liter; concentrations ranged up to 8700 micrograms/liter. 2,4-Dichlorophenol concentrations ranged up to 450 micrograms/ liter, and the 95thPC was 64 micrograms/liter. 1-Naphthol and 2-naphthol (indicative of naphthalene exposure) had 95thPCs of 43 and 30 micrograms/liter, respectively; concentrations of 1-naphthol ranged up to 2500 micrograms/liter. Chlorpyrifos exposure was indicated by 3,5,6-tricholoro-2-pyridinol concentrations of 13 (95thPC) and 77 micrograms/liter (maximum observed). Pentachlorophenol had a 95thPC of 8.2 micrograms/liter. Other analytes measured included 4-nitrophenol (in 41%); 2,4,5-trichlorophenol (in 20%); 2,4,6-trichlorophenol (in 9.5%); 2,4-dichlorophenoxyacetic acid (in 12%); 2-isopropoxyphenol (in 6.8%); and 7-carbofuranphenol (in 1.5%). The 95thPCs of these analytes were < 6 micrograms/liter. p-Dichlorobenzene exposure is ubiquitous; naphthalene and chlorpyrifos are also major sources of pesticide exposure. Exposure to chlorpyrifos appears to be increasing. Although pentachlorophenol exposure is frequent, exposure appears to be decreasing. These reference range concentrations provide information about pesticide exposure and serve as a basis against which to compare concentrations in subjects who may have been exposed to pesticides.

Relation of a seafood diet to mercury, selenium, arsenic, and polychlorinated biphenyl and other organochlorine concentrations in human milk

Human transition milk was sampled from 88 mothers at the Faroe Islands, where the seafood diet includes pilot whale meat and blubber. Milk mercury concentrations (median, 2.45 micrograms/liter) were significantly associated with mercury concentrations in cord blood and with the frequency of pilot whale dinners during pregnancy. Milk selenium concentrations (mean, 19.1 micrograms/liter) correlated significantly with concentrations in cord blood but not with seafood consumption. Arsenic concentrations were very low. Twenty-four of the milk samples were separated into four pools based on fish intake and milk mercury concentrations. The polychlorinated biphenyl (PCB) concentrations (1.8-3.5 micrograms/g lipid) were high and mainly due to congener numbers 153, 180, and 138. One pool contained a congener 77 concentration of 1380 ppt, which is the highest ever reported in a human specimen for a coplanar PCB. The highest PCB concentrations were seen in the pools from women who had eaten frequent whale dinners and whose milk contained high mercury concentrations. The concentrations of chlorinated dibenzo-p-dioxins and furans were not similarly elevated. Given the advantages associated with breast-feeding, advice to nursing mothers in this population should take into regard the possible risks associated with long-term exposure to milk contaminants.

Using biological monitoring to assess human exposure to priority toxicants

Scientifically valid exposure assessment is crucial to risk assessment, risk management, and prevention of environmental disease. Scientists have used three tools to assess exposure: exposure history/questionnaire, environmental monitoring (including personal monitoring), and biological monitoring. Combinations of these tools usually provide the exposure information needed to meet objectives of human studies evaluating the exposure-health effect relationship. Biological monitoring is a capable exposure assessment tool that has provided important information used in public health decisions. We briefly describe how risk assessment and risk management decisions for lead, dioxin, and volatile organic compounds have substantially benefited from exposure information obtained from biological monitoring.

The priority toxicant reference range study: interim report

The relationship between human exposure to environmental toxicants and health effects is of utmost interest to public health scientists. To define this relationship, these scientists need accurate and precise methods for assessing human exposure and effects. One of the most accurate and precise means of assessing exposure is to measure the level of the toxicant or its primary metabolite in a biologic specimen; this has been defined as measuring the internal dose. This measurement must be quantitative to best study the dose-response relationship. Pertinent questions asked during an exposure assessment include "How do the levels of a given toxicant in a particular population compare with the levels of that toxicant in other populations?" and "What is the prevalence of exposure to that toxicant in other populations?" To answer these questions for two chemical classes of environmental toxicants, we developed state-of-the-art analytic methods and then applied them to measure the levels of 44 environmental toxicants in biologic specimens from 1000 United States residents who participated in the Third National Health and Nutrition Examination Survey (NHANES III). These 1000 people are a cross-sectional subset of the NHANES III population and were selected from urban and rural communities in four regions of the United States; all were between 20 and 59 years of age. This subset is not a probability-based sample.(ABSTRACT TRUNCATED AT 250 WORDS)