Agency for Toxic Substances and Disease Registry conducted a study to evaluate body burden levels of volatile organic compounds (VOCs) among residents of highly industrialized Calcasieu Parish, LA, USA, in 2002. Blood VOC levels in a representative sample of participants in Calcasieu Parish were compared with a similar group of participants in the less-industrialized Lafayette Parish. Participants’ ages ranged from 15 to 91 years, 46% were men, and 89% were Caucasian. VOC levels in these two populations were also compared at the national levels. Solid-phase microextraction coupled with gas chromatography mass spectrometry was used to measure levels of 30 VOCs in blood samples collected from 283 self-described non-smoking study participants. Of the 30 VOCs, 6 had quantifiable levels in at least 25% of the blood samples analyzed. The frequency of detection was >95% for benzene and m-/p-xylene, >60% for 1,4-dichlorbenzene and toluene, 27% for ethylbenzene, and 39% for styrene. Calcasieu and Lafayette Parish participants had similar distributions for six VOCs in key percentiles and geometric means. When compared with a representative sampling of the 1999–2000 US general population, no significant differences were found between the parish data and the US general population.
Volatile organic compounds (VOCs) are ubiquitous contaminants released into the environment by natural and manmade sources. The most common sources of VOC exposure include tobacco smoke, petroleum products, chlorinated water, and synthetic products such as paints, lubricants, and insecticides.1, 2, 3 Exposure to VOCs is more common indoors than outdoors, with concentrations of many VOCs up to 10 times higher indoors than outdoors.4, 5 Exposure to VOCs occurs through inhalation, ingestion, and dermal contact.6, 7 VOCs have a relatively short biological half-life (4 h) and are rapidly eliminated from the body. However, repetitive or ongoing exposures can lead to an increase in VOCs in the body.8, 9 Long-term exposure to VOCs may increase risk for certain types of cancers10 and birth defects.11
Calcasieu Parish is a heavily industrialized area in southwest LA, USA. This Parish has an area of 1071 square miles and a population of ∼188,000. The discovery of petroleum and gas reserves in the early 1900s led to the growth of many petrochemical and agrochemical manufacturing and processing plants in Calcasieu Parish, particularly in the Lake Charles area. These manufacturing plants produce chemicals such as chlorinated solvents, petroleum-based chemicals, and commercial chemical feedstock. In 2000, the US Environmental Protection Agency’s (USEPA) Toxic Release Inventory ranked Calcasieu Parish sixth in the state, with 31 industries reporting releases of more than 14 million pounds of environmental contaminants, with petroleum, chemical, and solvent recovery industries being the largest contributors to the total release. In 2002, stationary point source VOC emissions in Calcasieu Parish were 22.3 tons per day (tpd) and the total VOC emissions from all source categories (stationary point, non-point, non-road mobile, and on-road mobile) was ∼49.6 tpd.12
Calcasieu Parish residents expressed concern about the adverse health effects that may result from exposure to chemical contaminants released into the environment from emissions by these industrial sources. In 1998, at the request of the USEPA, the Agency for Toxic Substances and Disease Registry (ATSDR) assessed dioxin exposure among a small sample of Calcasieu Parish residents by measuring it in their serum. The results showed that the mean and median dioxin toxic equivalent concentrations exceeded the 95th percentile of a reference sample, which was calculated from data reported in national studies that were compiled by ATSDR and the National Center for Environmental Health (NCEH).13 These findings provided the basis for a broader investigation of residential exposure to dioxins and VOCs in Calcasieu Parish.
In 2002, ATSDR initiated a parish-wide exposure study to evaluate blood VOC levels among residents of heavily industrialized Calcasieu Parish. The study was designed to recruit a representative sample of Calcasieu Parish residents, age 15 years or older, mostly in residential areas around the petrochemical and agrochemical industries in Calcasieu Parish, along with a similar group of residents of Lafayette Parish (Figure 1). Lafayette Parish was chosen as the comparison population because it is demographically and geographically similar to Calcasieu Parish and has fewer industrial facilities. Lafayette Parish was ranked 48th in the state for emissions with 10 industries reporting releases of more than 11,000 pounds of environmental contaminants. The stationary point source VOC emissions and the total VOC emissions in Lafayette Parish were much lower than that in Calcasieu Parish in 2002, which were 0.54 tpd and 27.2 tpd, respectively.14
The objective of this study is to characterize human blood VOC levels in a population-based sample of Calcasieu Parish residents living within few miles to the industries and to compare their levels with residents in nearby, less-industrialized Lafayette Parish. In addition, participants were classified into risk zones, defined as being in one of the four geographic groups: industrial corridor (1 to 6 miles), industrial buffer (7 to 8 miles), and outer zone (9 to 25 miles) in Calcasieu Parish and Lafayette Parish (Figure 1). To determine whether there were regional differences in VOC levels, blood VOC levels of residents in each parish were compared. In addition, blood VOCs from both parishes were combined and then compared with the national background levels that were reported in the 1999–2000 National Report on Human Exposure to Environmental Chemicals, which is an ongoing assessment of the US population’s exposure to chemicals in the environment.15
The details of the study design, target and comparison area, sampling design, and selection criteria for the study participants were described in previous publications.16, 17 In summary, a multistage cluster probability sample was taken of Calcasieu and Lafayette Parishes for the purpose of comparing dioxin levels between residents of the two parishes. Participants in the present study were selected from among the same people who were chosen for the dioxin study, and included persons who were non-smokers and who had lived in Calcasieu Parish the 5 years preceding both of these studies and who were at least 15 years of age. The comparison group consisted of persons who resided in Lafayette Parish for the past 5 years, had never resided in Calcasieu Parish, and were at least 15 years of age. A total of 297 participants were randomly selected to participate in the VOC study. Of the 297 participants, 204 were Calcasieu Parish participants and 93 were Lafayette Parish participants.
Each participant received information about the study, including their rights, and was required to sign a consent form approved by the Centers for Disease Control and Prevention’s (CDC) Human Subjects Institutional Review Board. Participants under the age of 18 years signed a participant assent form and their parents or guardian signed a parental permission form. Each participant was asked to complete a questionnaire. A trained interviewer administered the questionnaire that was designed to collect information regarding demographics (e.g., age, race, gender, and length of parish residency), lifestyle (e.g., smoking status, source of water used for cooking and drinking, and frequency of chemical use), and occupational exposure to VOCs. Data were collected on the use of VOC containing products, such as deodorizers, paints, weed killers, diesel fuel, kerosene, and gasoline. The study was designed to exclude smokers and people who had laboratory evidence of an elevated smoking biomarker, 2,5-dimethylfuran. This smoking biomarker was used to differentiate smokers and non-smokers because the whole blood concentration of 2,5-dimethylfuran is an excellent predictor of smoking when compared with responses about smoking on questionnaires.18 Smoking is a major contributor to the internal dose levels of many VOCs and it is difficult to assess other VOC exposures among smokers.19 In this study, the blood VOC reference values were taken from CDC’s 1999–2000 National Health and Nutrition Examination Survey (NHANES). The NHANES measures the health and nutritional status of the non-institutionalized US population.
Collection and Preparation of Blood Samples
In May 2002, a trained phlebotomist collected 10 ml of whole blood from participants for the VOC analysis, according to procedures established by the NCEH laboratory. Blood samples were collected via venipuncture into blood collection vials (10 ml draw, Vacutainers, Becton-Dickinson, Franklin Lakes, NJ, USA) that were specially treated to remove residual VOCs.20 Participants’ blood samples were analyzed for VOCs at CDC’s NCEH laboratory. Documentation and chain-of-custody methods were used to ensure the integrity of the biological specimens during transport and the pre-analytical phase. The blood samples were subsequently stored chilled (4 °C) in the dark until analysis. Established quality assurance/quality control (QC) procedures were followed during collection, transport, storage, and analysis of the specimens to ensure sample integrity. Contamination from external VOCs was prevented by carefully pre-screening all sample-handling materials. The absence of contamination was confirmed by testing both storage blanks and analytical batch blanks. The analytical method and storage conditions were characterized and validated as described in a previous report Blount et al.17 Specifically, analysis of QC materials indicated adequate method interday precision for analytes measured in both the low QC pool (coefficient of variation=11%) and the high QC pool (coefficient of variation=7%). To confirm that participants were not recently exposed to tobacco smoke, all blood samples were tested for 2,5-dimethylfuran, an indicator of tobacco smoke exposure.
Analysis of VOCs in Blood Samples
Blood VOCs were quantified using solid-phase microextraction gas chromatography–mass spectrometry (SPME–GC–MS) as described by Blount et al.17 Briefly, blood (3 ml) was spiked with a mixture of stable isotope-labeled internal standards, heated to 40 °C, extracted using headspace SPME, and analyzed by GC–MS. VOCs were quantified using relative ion ratios of native analytes to stable isotope analogs; calibration curves were prepared daily to minimize bias. The resulting data were subjected to rigorous QC procedures to confirm the accuracy and precision of analysis.21
Statistical analyses were performed using Statistical Analysis System (SAS) software (SAS Institute, Version 9.1.3). SAS software’s SurveyFREQ, SurveyMEANS, and SurveyLOGISTIC procedures were used to produce population-weighted estimates for means, SDs, and parameter estimates, and to investigate associations between blood VOC levels and various demographic and exposure variables. These procedures account for the multistage cluster design that was used for sample selection. Specification of the study design parameters (strata, primary sampling units, and weights) is described in earlier publications.16, 17
If blood VOC levels were below the limit of detection (LOD), the levels were reported as the LOD divided by the square root of 2, a standard method of imputation for laboratory data that are below the LOD.22 As many blood VOC distributions are highly skewed, they were log-transformed (base e) for calculation of geometric means (GMs). In addition, bivariate categorical variables were created for each blood VOC variable, indicating whether or not a particular value was in the upper decile of the combined data from Calcasieu and Lafayette Parishes.
Descriptive and analytical methods were used to compare VOC blood levels between the Calcasieu and Lafayette Parishes. Arithmetic and GMs, quartiles, and selected percentiles were calculated to describe blood VOC distributions. Cross-tabulations were calculated by parish for both demographic and exposure variables. The Rao–Scott χ2-test23 was used to assess statistical significance of results. This test is a design-adjusted version of the usual χ2-test and takes into account the complex sample design employed in this study. Both bivariable and multivariable logistic regression analyses were conducted to investigate associations between blood VOC levels, parishes, and various demographic and exposure variables. Odds ratios (ORs) were calculated and Wald’s confidence intervals (CIs) were used to assess statistical significance. Results of all analyses were considered to be statistically significant when the P-values for test statistics were <0.05. CIs of ORs were considered to indicate statistical significance when the interval did not contain the null value.
The participant response rates were 87.7% from Calcasieu Parish and 72% from Lafayette Parish. The data on self-reported characteristics are shown in Table 1. Comparison of information collected from Calcasieu Parish participants and Lafayette Parish participants showed very similar demographic characteristics such as race and gender, age category, smoking history, and occupational exposure to VOCs. The study participants ranged in age from 15 to 91 years old, 46% of the participants were men, and 89% were Caucasian. Participants from both parishes reported similar use of city water as a source for drinking and cooking. Participants from Calcasieu Parish were more likely to have lived in their parish for a longer duration than participants from Lafayette Parish. This was the only statistically significant demographic difference (P<0.0007; Table 1).
The frequency of self-reported use of VOC-containing products in the last 3 days before the study is presented in Table 2. Participants in both parishes reported a history of using VOC-containing chemicals in the last 3 days before specimen collection. Analysis of the data showed similar use of chemicals between parishes with the exception of diesel fuel and kerosene. Diesel fuel or kerosene was used more frequently among residents of Calcasieu Parish (P<0.0001). However, these fuels typically contain different VOCs than gasoline. Kerosene and diesel fuel typically have fewer of the lower molecular weight VOCs of interest and are not likely to be significant sources of the six VOCs that we examined in this study.
The study was designed to exclude current smokers and people who had elevated 2,5-dimethylfuran for recent smoking behavior. Smoking questionnaire data showed 92% of Calcasieu participants and 89% of Lafayette Parish participants reported that they had not smoked in the past 5 years (Table 1). To confirm whether a participant was recently exposed to tobacco smoke, we measured levels of 2,5-dimethylfuran, a biomarker for recent tobacco smoke exposure, in the blood samples collected from each study participant. Measurable levels of this chemical are associated with significant exposure to tobacco smoke. The data showed that 13 participants (about 4%) had elevated levels (>0.012 ng/ml) of 2,5-dimethylfuran present in their blood. As a result, these 13 participants were excluded from the study along with one participant who acknowledged smoking on the day that the blood specimens were drawn. Thus, the final sample size was 283: 192 Calcasieu Parish participants and 91 Lafayette Parish participants.
We tested the blood samples of 283 participants for 30 VOCs. Of the 30 VOCs, 17 were undetected in 99% of the samples and 7 were undetected in 75% of the samples. As these 24 VOCs were not detected at the lowest detection limits in most samples, no further assessments were conducted on them. The final analysis included six VOCs that were detected in at least 25% of the blood samples. They were benzene, ethylbenzene, m-/p-xylene, 1, 4-dichlorobenzene, styrene, and toluene. The detection frequencies above LOD were >95% for benzene and m-/p-xylene, and >60% for 1,4-dichlorbenzene and toluene. The detection frequencies for ethylbenzene and styrene were 27% and 39%, respectively (Table 3). The LOD is used for analytic detection and this value is not related to or above a health-based standard.
ORs for being in the top tenth percentile of blood VOC levels were calculated for the six VOCs (Table 4). The crude OR for, m-/p-xylene, (OR=1.69; 95% CI=1.02–2.80), was the only statistically significant result. We adjusted the ORs for age, gender, race, occupational exposure status, risk zones, and source of drinking and cooking water. After adjustment, the OR for m-/p-xylene (OR=2.10; 95% CI=0.094–4.70) was no longer statistically significant. Overall, blood levels of m-/p-xylene were lower in Calcasieu Parish participants than that in the Lafayette Parish participants. Crude ORs and adjusted ORs of the other five VOCs in both parishes were also not statistically significant. When we analyzed the blood VOC levels of participants in the risk zones (industrial corridor, industrial buffer, and outer zone), we found no association between risk zones and blood VOC levels.
The GMs of benzene, ethylbenzene, toluene, 1, 4-dichlorobenzene, and styrene were compared between Calcasieu Parish and Lafayette Parishes and they were not statistically different between the two parishes (Table 5). The GM for m-/p-xylene, however, was statistically higher for Lafayette Parish when compared with Calcasieu Parish. In addition, we compared the GMs of the six VOCs and various percentiles of the distribution in Calcasieu and Lafayette Parishes, and the mean levels of both parishes combined with the US general population, 1999–2000 NHANES for non-smokers. We found blood levels of benzene, ethyl benzene, m-/p-xylene, and toluene were lower in Calcasieu Parish, Lafayette Parish, and both parishes combined for key percentiles and GMs with the reference range values reported in the 1999–2000 NHANES (Table 6). Blood levels of styrene were not available at the 25th and 75th percentiles in the 1999–2000 NHANES survey, but the GM of styrene in Calcasieu Parish, Lafayette Parish, and both parishes combined were similar and comparable to NHANES. Blood levels of 1,4-dichlorobenzene were higher in Calcasieu Parish, Lafayette Parish, and both parishes combined at key percentiles and the GM when compared with NHANES (Table 6). However, the differences were not statistically significant.
DISCUSSION AND CONCLUSION
The goal of this study was to determine whether people living in a community with residential areas in close proximity to petrochemical and agrochemical manufacturing industries had higher blood VOC levels than people living in a community with less industrial manufacturing activity. The study design recruited a representative sample of Calcasieu Parish residents, age 15 years and older, living mostly within 1 to 8 miles to the industries in Calcasieu Parish. A small group of Calcasieu Parish residents living 9 to 25 miles from the industries was also included from the towns of Vinton, Iowa, and DeQuincy. A similar group of residents of the less-industrialized Lafayette Parish was selected for comparison. The study participants included non-smokers and persons who did not have laboratory evidence of elevated 2,5-dimethylfuran, a biomarker for recent smoking behavior. Therefore, the results are applicable to non-smokers. The demographics, lifestyle, and occupational characteristics data indicated that the residents in Calcasieu Parish were less mobile and lived longer in the parish when compared with Lafayette Parish residents.
According to the 2002 Louisiana VOC emissions data, Calcasieu Parish had ∼2-fold higher total VOC emissions and 41-fold higher stationary point source VOC emissions when compared with Lafayette Parish.12, 14 Testing of 283 blood samples for 30 different VOCs revealed that blood levels of 24 of the VOCs were so low that they were not detected at the lowest detection limit. The limits of detection relate to sample analysis and do not relate to health. As VOCs do not persist in the body, this study does not reflect past exposures.
Despite having higher industrial emissions in the environment, as well as higher total and stationary point source VOC emissions in Calcasieu Parish, analytical results indicated that Calcasieu Parish participants did not have elevated blood VOC levels for the six VOCs analyzed when compared with Lafayette Parish participants. When Calcasieu Parish participants were further analyzed by risk zones (industrial corridor, industrial buffer, and outer zone), no differences were noted in the blood VOC levels within the risk zones. Both Calcasieu and Lafayette Parish participants had similar distributions for the six blood VOCs. One probable explanation could be that VOCs emitted through industrial processes were diluted in the air. Therefore, outdoor environmental exposure of the six VOCs to the general public was minimized and may not have been as high when compared with indoor exposure sources. Calcasieu Parish participants lived within 1 to 25 miles of the industries and the wind direction may have been a contributing factor. Typically, human exposures to volatile environmental contaminants via air occur more often downwind from emitting sources.24 Depending on the wind direction, some Calcasieu Parish residents may have been exposed to VOCs more frequently and some less frequently than others. However, the study design did not account for meteorological conditions (e.g., prevailing winds and precipitation) and thus does not assess this potential confounder that could modify how outdoor air VOCs relate to blood VOC levels of participants in this study. In addition, most of the internal doses of VOCs that result from environmental exposures have a short half-life and are eliminated from blood in a matter of hours.9
Blood VOC levels of Calcasieu Parish participants were compared with those of Lafayette Parish participants, and blood VOC levels of participants from both parishes were combined and compared with national sampling results. Environmental toxicants were measured in blood and urine samples obtained from a random sample of participants in the 1999–2000 NHANES. NHANES is designed to obtain information on the health and nutritional status of the non-institutionalized US population. The NCEH laboratory at CDC conducts all laboratory tests for environmental contaminants in samples collected for NHANES. Measuring internal dose is often the best method for assessing the nature and extent of human exposure to environmental toxicants. The six blood VOC levels analyzed in this study were either lower than or comparable to the national reference range values for the US population. Although the GM for m-/p-xylene was statistically higher in Lafayette Parish compared with Calcasieu Parish, the GM for m-/p-xylene in both parishes were lower than the national sampling results (1999–2000 NHANES). People living in close proximity to the industrial plants that emit VOCs in the environment did not have blood VOCs at levels to cause health concern.
This study had several strengths. Biomonitoring was used to assess participant’s exposure to VOCs. Biomonitoring is considered the gold standard for assessing human exposure to toxic substances. Instead of estimating how much of a toxic substance gets into people from measured environmental concentrations, biomonitoring measures contaminant levels that are actually in a person’s body. Two different comparison populations were used, one regional and one national, to evaluate VOC levels in the target population. Out of 30 VOCs analyzed, 24 were below detection limits leaving 6 VOCs detected in high-enough concentrations to enable comparison with national sampling results. An additional strength was the strong support from the community and their active involvement in the development of this study.
The study also had some limitations. The study design did not account for meteorological conditions (e.g., prevailing winds and precipitation) that can modulate exposure to airborne pollutants. The analysis of the blood samples for the VOC levels reflects current exposure and do not reflect past exposures. In addition, some potential physiological modifiers of blood VOC levels were not assessed that could affect blood VOC concentrations (e.g., blood lipids, obesity, and genetic polymorphisms). However, these limitations did not significantly affect the overall objective of assessing blood VOC levels in this population.
In summary, there were no statistically significant and consistent differences in the levels of the six VOCs in the blood samples collected from Calcasieu and Lafayette Parish residents even though Calcasieu Parish residents live in close proximity to several petrochemical and agrochemical industries. In addition, the blood VOC levels in Calcasieu Parish residents did not exceed reference range values for the US population. The results of this study suggest that living in close proximity to industries in Calcasieu Parish, a parish with high VOC production and release in the environment, does not necessarily equate to elevated blood VOC levels when compared with national sampling results.
Ashley DL, Bonin MA, Cardinali FL, McCraw JM, Wooten JV . Blood concentrations of volatile organic compounds in a nonoccupationally exposed US population and in groups with suspected exposure. Clin Chem 1994; 40: 1401–1404.
Wallace L, Buckley T, Pellizzari E, Gordon S . Breath measurements as volatile organic compound biomarkers. Environ Health Perspect 1996; 104 (Suppl 5): 861–869.
Lin YS, Egeghy PP, Rappaport SM . Relationships between levels of volatile organic compounds in air and blood from the general population. J Exp Sci Environ Epidemiol 2008; 18: 421–429.
Adgate JL, Church TR, Ryan AD, Ramachandran G, Fredrickson AL, Stock TH et al. Outdoor, indoor, and personal exposure to VOCs in children. Environ Health Perspect 2004; 112: 1386–1392.
United States Environmental Protection Agency (USEPA). An Introduction to Indoor Air Quality. Volatile Organic Compounds (VOCs) 2010. http://www.epa.gov/iaq/voc.html Accessed: 14 December 2010.
Hodgson M, Levin H, Wolkoff P . Volatile organic compounds and indoor air. J Allergy Clin Immunol 1994; 94: 296–303.
Churchill JE, Ashley DL, Kaye WE . Recent chemical exposures and blood volatile organic compound levels in a large population-based sample. Arch Environ Health 2001; 56: 157–166.
Ashley DL, Prah JD . Time dependence of blood concentrations during and after exposure to a mixture of volatile organic compounds. Arch Environ Health 1997; 52: 26–33.
Sexton K, Adgate JL, Church TR, Ashley DL, Needham LL, Ramachandran G et al. Children's exposure to volatile organic compounds as determined by longitudinal measurements in blood. Environ Health Perspect 2005; 113: 342–349.
Cohn P, Klotz J, Bove F, Fagliano J . Drinking water contamination and the incidence of leukemia and non-Hodgkin’s lymphoma. Environ Health Perspect 1994; 102: 556–561.
Berry M, Bove F . Birth weight reduction associated with residence near a hazardous waste landfill. Environ Health Perspect 1997; 105: 856–861.
Calcasieu Parish: VOC Emissions Inventory Baseline (2002) and Projections (2008, 2011, and 2014) in Tons per Day (Table 3–2). Accessed: 14 December 2010, http://www.deq.louisiana.gov/portal/Portals/0/AirQualityAssessment/Planning/SIP/Calcasieu-table3.2&3.3-final.pdf.
Agency for Toxic Substances and Disease Registry. Exposure Investigation, Calcasieu Estuary. Department of Health and Human Services: Atlanta, 1999.
Lafayette Parish: VOC Emissions Inventory Baseline (2002) and Projections (2008, 2011, and 2014) in Tons per Day (Table 3–2) http://www.deq.louisiana.gov/portal/LinkClick.aspx?link=AirQualityAssessment%2FLafa-table3.2%263.2-final.pdf . Accessed: 14 December 2010.
CDC 2003 Second National Report on Human Exposure to Environmental Chemicals. Centers for Disease Control and Prevention; National Center for Environmental Health; Division of Laboratory Sciences, Atlanta, GA (http://www.cdc.gov/exposurereport).
Agency for Toxic Substances and Disease Registry 2005 Serum dioxin levels in residents of Calcasieu Parish, Louisiana. Department of Health and Human Services: Atlanta.
Wong LC, Millette MD, Uddin MS, Needham LL, Patterson DG, Turner W . Serum dioxin concentrations in residents of Calcasieu and Lafayette Parishes, Louisiana with comparison to the U. S. population. J Exp Sci Environ Epidemiol 2008; 18: 1–10.
Ashley DL, Bonin MA, Hamar B, McGeehin M . Using the blood concentration of 2.5-dimethylfuran as a marker for smoking. Int Arch Occup Environ Health 1996; 68: 183–187.
Ashley DL, Bonin MA, Hamar B, McGeehin M . Removing the smoking confounder from blood volatile organic compound measurements. Environ Res 2005; 71: 39–45.
Cardinali FL, McCraw JM, Ashley DL, Bonin MA, Wooten JV . Treatment of vacutainers for the analysis of volatile organic compounds in human blood at the low parts-per-trillion level. J. Chromatogr Sci 1995; 33: 557–560.
Blount BC, Kobelski RJ, McElprang DO, Ashley DL, Morrow JC, Chambers DM et al. Quantification of 31 volatile organic compounds in whole blood using solid-phase microextraction and gas chromatography-mass spectrometry. 2006 J Chromatogr B Analyt Technol Biomed Life Sci. 7 832: 292–301.
Hornung RW, Reed LD . Estimation of average concentration in the presence of nondetectable values. Appl Occup Environ Hygiene 1990; 5: 46–51.
Rao JNK, Scott AJ . On simple adjustments to chi-square tests with survey data. Ann Stat 1987; 15: 385–397.
Agency for Toxic Substances and Disease Registry, 2005. Public Health Assessment Guidance Manual (2005 update), Chapter 6: Evaluating Exposure Pathways. Department of Health and Human Services: Atlanta. http://www.atsdr.cdc.gov/hac/PHAManual/ch6.html.
We acknowledge the contributions of the Calcasieu Community Study Work Group, Section of Epidemiology and Environmental Toxicology, Office of Public Health, Louisiana Department of Health and Hospitals and the National Opinion Research Center.
The authors declare no conflict of interest.
About this article
Cite this article
Uddin, M., Blount, B., Lewin, M. et al. Comparison of blood volatile organic compound levels in residents of Calcasieu and Lafayette Parishes, LA, with US reference ranges. J Expo Sci Environ Epidemiol 24, 602–607 (2014). https://doi.org/10.1038/jes.2013.94
- volatile organic compounds
Journal of Exposure Science & Environmental Epidemiology (2018)