Evaluation of NHANES Biomonitoring Data for Volatile Organic Chemicals in Blood: Application of Chemical-Speciﬁc Screening Criteria

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Evaluation of NHANES biomonitoring data for volatile organic chemicals in blood: Application of chemical-speciﬁc screening criteria

CHRISTOPHER R. KIRMANa, LESA L. AYLWARDb, BEN C. BLOUNTc, DAVID W. PYATTd ANDSEANM.HAYSe aSummit Toxicology, Orange Village, Ohio, USA bSummit Toxicology, Falls Church, Virginia, USA cCenters for Disease Control and Prevention, Atlanta, Georgia, USA dSummit Toxicology, Superior, Colorado, USA eSummit Toxicology, Lyons, Colorado, USA

Available biomonitoring data for volatile organic chemicals (VOCs) in blood from the National Health and Nutrition Examination Survey (NHANES) (2003–2004) (CDC, 2009) were compared with recently derived screening biomonitoring equivalent (BE) values (Aylward et al., 2010). A BE is defined as the estimated concentration or range of concentrations of a chemical or its metabolites in a biological medium (blood, urine, or other medium) that is consistent with an existing health-based exposure guidance value. Blood concentrations of VOCs from the NHANES data set were compared with predicted screening BE values based upon a hazard quotient (HQ) for individual chemicals, and a hazard index (HI) approach for combined exposures. HI values for detected chemicals were generally at or below a value of 1, suggesting that the potential for deleterious effects is low. However, smokingwas an important determinant of HI and HQ values. Detected levels of benzene in non-smokers were within the range of BE values corresponding to a 1 Â 10À6–1 Â 10À4 range for upper-bound cancer risk; in smokers, levels of benzene were at the upper end of or exceeded this range. For VOCs that were not detected in the NHANES sampling, analytical detection limits were generally sufficiently sensitive to detect concentrations consistent with existing non-cancer and cancer risk-based exposure guidance values. Interpretations of measured blood concentrations of VOCs must be made with caution due to the substantial within-individual, within-day fluctuationsinlevelsexpectedduetotherapideliminationofVOCs. Journal of Exposure Science and Environmental Epidemiology (2012) 22, 24–34; doi:10.1038/jes.2011.37; published online 12 October 2011

Keywords: volatile organic compounds, VOCs, risk assessment, biomonitoring, biomonitoring equivalents.

Introduction to determine whether exposure levels are higher in specific subpopulations, such as minorities and children; The National Health and Nutrition Examination Survey to evaluate trends in levels of exposure over time; (NHANES) generates US population-representative biomo- to set priorities for research on human health effects; and nitoring data for many chemicals including volatile organic to determine the prevalence of people with levels above chemicals (VOCs) in blood (CDC, 2009). These biomonitor- established health-based levels (CDC, 2009). ing data have been considered by some to be the gold standard for exposure assessment (Sexton et al., 2005), and The last use requires availability of the ‘‘established health- provide valuable information to scientists, physicians, and based levels.’’ Development of epidemiologically based, health officials. The CDC lists a number of uses for the scientifically sound human health screening criteria for biomonitoring data: clinical use is a resource- and time-intensive effort that requires a biomarker for an established health endpoint to be to determine which chemicals get into the US population (1) reliable, reproducible across multiple laboratories, and at what concentrations; sensitive and specific, and (2) clearly and consistently to establish baseline values that can be used to determine associated with a clinical condition or disease (NRC, 2010). whether a person or group has an unusually high exposure; Scientific evidence demonstrating a cause and effect of to assess the effectiveness of public health efforts to reduce relationship of the kind needed to be a clinical biomarker, exposure of the Americans to specific chemicals; is lacking for exposures to most environmental chemicals. Until recently, health-based screening values for biomonitoring data were only available for a small number of 1. Address all correspondence to: Christopher R. Kirman, Summit chemicals (e.g., blood lead levels greater than or equal to 10 Toxicology, 29449 Pike Drive, Orange Village, Ohio 44022, USA. Z E-mail: [email protected] micrograms per deciliter ( 10 mg/dl)). As emphasized by the Received 24 February 2011; accepted 1 August 2011; published online 12 CDC, ‘‘[T]he presence of a chemical does not imply disease. October 2011 The levels or concentrations of the chemical are more important Screening BE evaluation for VOCs Kirman et al. determinants of the relation to disease, when established in adverse health effects in the population. The BE reflects a appropriate research studies, than the detection or presence of a conversion of toxicity values to a concentration (mg/l) in the chemical’’ (CDC, 2005). Thus, without quantitative criteria whole blood, serum, urine, or other biological matrix as for a screening-level evaluation of biomonitoring data in a appropriate, corresponding to a daily exposure to the risk assessment context, public health professionals cannot substance at an intake equal to the RfD. Then, in a manner assess the potential level of risk associated with specific analogoustohealthriskestimation based on intakes, human biomonitoring levels, nor the relative risks posed by different biomonitoring-measured results can be compared with the chemicals. BE to assess potential health hazards/risks. As an interim approach, the development of biomonitor- The BE values were previously derived for four trihalo- ing equivalents (BEs) has been proposed, and guidelines for methane (THM) compounds found as drinking water their derivation and communication have been developed disinfection byproducts (Aylward et al., 2008), and applied (Hays et al., 2007, 2008; LaKind et al., 2008). A BE is to evaluation NHANES 2003–2004 data for the THMs in defined as an estimate of the concentration or range of the the blood (LaKind et al., 2009). However, screening values concentrations of a chemical or its metabolites in a biological based on human clinical data are generally not available for medium (blood, urine, or other medium) that is consistent interpreting the health risk significance of the levels of the with an existing health-based exposure guidance value such other VOC compounds included in NHANES. Previously, as a reference dose (RfD) developed by USEPA, a minimal steady-state solutions to a generic VOC physiologically based risk level (MRL) developed by ATSDR, or tolerable daily pharmacokinetic (PBPK) model were used to estimate intake (TDI) developed by the Health Canada. Existing steady-state concentrations of VOCs in blood consistent chemical-specific pharmacokinetic data are used to estimate with existing cancer and non-cancer reference values (RfDs, biomarker concentrations that are consistent with the point RfCs, TDIs, and cancer risk-specific doses) (Aylward et al., of departure used in the derivation of an exposure guidance 2010). These screening-level BEs are consistent in concept value (such as the RfD, MRL, or TDI), and with the with the BEs, but unlike comprehensive BEs, detailed exposure guidance value itself. BEs can be estimated using consideration of the chemical-specific mode of action data available human or animal pharmacokinetic data (Hays and and relevance to screening-level derivation was not conducted colleagues, 2008), and have been derived for numerous in the analysis. The screening BE values can provide a basis compounds including acrylamide, cadmium, 2,4-dichloro- for an initial risk-based examination of the data on phenoxyacetic acid, toluene, and others (reviewed in Hays concentrations of VOCs in the blood collected in the and Aylward, 2009 and available at http://www.biomonitor NHANES program. ingequivalents.net). The BE values are intended to be used as This analysis presents a comparison of the available screening tools to allow the evaluation of biomonitoring data biomonitoring data for VOCs in the blood from NHANES in a risk assessment context. As such, BE values can be used (CDC, 2009) with these recently derived screening BE values to examine biomonitoring data to assess which chemicals (Aylward et al., 2010). For VOCs detected in the NHANES have large, small, or no margins of exposure compared with data set, blood levels were compared with the screening BE the existing exposure guidance values. BE values are only as values. This comparison allows for a prioritization among the robust as the underlying exposure guidance values and measured VOCs for a possible further risk assessment follow- pharmacokinetic data used to derive the values. The BE up (LaKind et al., 2008). For those VOCs that were not values are not intended to be diagnostic for potential health detected in the NHANES sampling, the analytical detection effects in humans, either individually or among a population. limits were compared with the screening BE values to assess The BEs can be used similar to the way the underlying whether the data are sufficiently sensitive to provide RfD, MRL, or TDI values are used. For example, to information that is relevant in the context of the existing evaluate potential risks in a population exposed to a risk assessments. Issues relevant to the interpretation of contaminant in drinking water, the risk assessors first measured blood concentrations of these transient, rapidly estimate the intake (exposure or dose) in the population of eliminated compounds (half-lives of elimination of less than concern (in mg/kg/day) and then compare that estimate with an hour to a few hours) and issues related to exposures to the RfD (mg/kg/day). USEPA defines the oral RfD as, ‘‘An multiple VOCs are also discussed. estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an Materials and methods appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with Biomonitoring Data uncertainty factors generally applied to reflect limitations of the Biomonitoring data for 28 VOCs in blood were obtained data used.’’ (USEPA, 2002). Therefore, if the dose (exposure from CDC’s 2003–2004 survey period (CDC, 2009), which level) falls below the RfD, there is little concern for any includes data from 1367 individuals. VOCs were measured in

Journal of Exposure Science and Environmental Epidemiology (2012) 22(1) 25 Kirman et al. Screening BE evaluation for VOCs the blood using isotope dilution, solid-phase microextraction, parameters (Aylward et al., 2010). Using steady-state gas chromatography, and mass spectrometry (Blount et al., solutions to a generic VOC PBPK model, chemical-specific 2006; Chambers et al., 2011). Laboratory measurements steady-state venous blood concentrations were estimated underwent extensive quality control and quality assurance across chemicals consistent with the existing exposure review, including tolerance limits for operational parameters, guidance values. These solutions permit an algebraic approach the measurement of quality control samples in each analytical to calculate the steady-state blood concentrations associated run to detect unacceptable performance in accuracy or with the steady-state exposure conditions for VOC com- precision, and verification of traceable calibration materials pounds, using a limited subset of chemical-specific parameters, (CDC, 2009). For the purposes of comparing results with the without necessitating the implementation of a full PBPK screening BE values, data for o-, m-,andp-xylenes were model for each chemical. Up to four screening BE values summed to determine the total xylene concentration for each (corresponding to oral non-cancer, inhalation non-cancer, individual, as the existing exposure guidance values do not oral cancer, and inhalation cancer assessments) were derived differentiate amongst the xylene isomers. In addition, for each VOC, depending upon the availability of appropriate because cigarette smoking can influence blood levels for a toxicity values and whether a chemical had been identified as a number of chemicals (e.g., benzene, toluene, ethylbenzene, carcinogen by a regulatory agency. No independent deriva- styrene, and xylenes), the concentrations of these chemicals in tions of exposure reference values were carried out. the blood were characterized separately based upon the The chemical-specific blood concentration screening values smoking status as determined by the presence of detectable for the VOCs of interest based on non-cancer reference levels of 2,5-dimethylfuran (DL ¼ 0.012 mg/l), a component values for both the oral and inhalation exposure range 0.01– of cigarette smoke, in blood (Ashley et al., 1996; Chambers 100 mg/l (Table 2), and the blood concentrations associated et al., 2011). with chronic exposure at cancer risk-specific doses at the Summary statistics for central tendency values (geometric 1 Â 10À5 risk level ranged 0.00009–0.06 mg/l (Table 2). BE mean (GM) and its 95% confidence interval) and range (5th values were not derived for 1,3-dichlorobenzene or 2,5- and 95th percentiles) are provided (Table 1). In calculating dimethylfuran due to the lack of available exposure guidance the summary statistics, samples with non-detects were values from a regulatory agency. The distribution of modeled imputed with a value equal to the detection limit divided by steady-state blood concentrations associated with unit the square root of 2. Although CDC does not typically exposure levels across the VOCs, may provide a basis for calculate and report GMs for chemicals with a detection estimating blood concentration screening values for VOCs frequency less than 60% (CDC, 2009), it was assumed here that lack chemical-specific pharmacokinetic data, as was that VOCs present in at least 5% of the samples could proposed for 1,2-dichloropropane, 1,2-dibromo-3-chloro- theoretically be present in the population at levels below the propane, chlorobenzene, nitrobenzene, and 1,4-dichloroben- detection limit. Thus, GM values for VOCs detected in zene (Aylward et al., 2010). less than 60% but greater than 5% of the samples were calculated here using this imputation, to permit a comparison Comparisons with the BE values. This approach results in some additional Biomonitoring data provide an internal dose measure that uncertainty in the calculated HQs for these compounds. reflects absorbed compound from multiple routes of exposure For VOCs detected in fewer than 5% of samples, (oral, inhalation, and dermal). Due to the inherent volatile summary statistics were not calculated here. It was assumed nature of the VOCs of interest in this work, it was expected that exposures to VOCs detected in fewer than 5% of the that inhalation would be the predominant route of exposure. samples are isolated in nature, and therefore comparison of However, uncertainty remains with respect to the degree to their intermittent concentrations to steady-state screening BE which other routes of exposures (e.g., oral or dermal values is inappropriate. However, detection limits for these exposures in drinking water) contribute. To address this chemicals were included in the evaluation (see section uncertainty, the biomonitoring data were compared with the Comparisons) to assess whether the analytical sensitivity of BE values for both the inhalation and oral exposures. the NHANES sampling program was sufficient to provide Toxicity values for dermal exposure are generally not meaningful information in the context of current risk available, and therefore corresponding screening BE values assessments for these compounds. were not derived. Due to the transient nature of VOCs in blood, the screening BE values are best applied to assess Biomonitoring Equivalents central tendency values for the biomonitoring data for the Screening BE values for VOCs were derived previously population (e.g., GM) (discussed in Aylward et al., 2010). To (Aylward et al., 2010). To support BE derivation for VOCs, facilitate comparisons, hazard quotient (HQ) values for non- two types of information were required: (1) existing exposure cancer endpoints (USEPA, 1989) were calculated for each guidance values such as RfDs, RfCs, TDIs, MRLs, cancer chemical and exposure route-specific screening BE value slope factors, and so on; and (2) key pharmacokinetic model using the GM concentration for detected VOCs (detection

26 Journal of Exposure Science and Environmental Epidemiology (2012) 22(1) Screening BE evaluation for VOCs Kirman et al.

Ta bl e 1 . VOC concentrations (mg/l) in human blood from NHANES survey years 2003–2004 (CDC, 2009).

Chemical Populationa Detection LOD Geometric mean 5–95th%-iles (mg/l) frequency (%) (mg/l) (95% CI) 5%-ile 95%-ile

Benzene Smokers 316/316 (100%) 0.024 0.136 (0.125–0.148) 0.046 0.44 Non-smokers 396/874 (45%) 0.024 0.024 (NC)b NC 0.06 Ethylbenzene Smokers 299/303 (99%) 0.024 0.067 (0.064–0.071) 0.031 0.16 Non-smokers 507/841 (60%) 0.024 0.028 (0.026–0.031) NC 0.071 Styrene Smokers 281/316 (89%) 0.03 0.068 (0.062–0.074) NC 0.18 Non-smokers 202/880 (23%) 0.03 0.026 (NC)b NC 0.068 Toluene Smokers 312/312 (100%) 0.025 0.324 (0.293–0.358) 0.11 0.99 Non-smokers 819/869 (94%) 0.025 0.082 (0.071–0.095) 0.023 0.34 o-xylene Smokers 184/316 (58%) 0.034 0.048 (0.045–0.051) 0.03 0.091 Non-smokers 274/893 (31%) 0.034 0.037 (NC)b NC 0.083 m-/p-xylene Smokers 314/314 (100%) 0.034 0.211 (0.198–0.225) 0.099 0.46 Non-smokers 865/876 (99%) 0.034 0.122 (0.109–0.136) 0.052 0.29 Total xylenes (sum of o-, m-,andp-) Smokers 314/314 (100%) 0.034 0.261 (0.246–0.276) 0.13 0.6 Non-smokers 865/876 (99%) 0.034 0.161 (0.146–0.178) 0.08 0.4 Carbon tetrachloride All 7/1362 (0.5%) 0.005 NC NC NC Chlorobenzene All 0/1366 (0%) 0.011 NC NC NC 1,2-dibromo-3-chloropropane All 0/1170 (0%) 0.1 NC NC NC Dibromomethane All 3/1355 (0.2%) 0.03 NC NC NC 1,2-dichlorobenzene All 0/1327 (0%) 0.1 NC NC NC 1,3-dichlorobenzene All 0/1334 (0%) 0.05 NC NC NC 1,4-dichlorobenzene All 716/1332 (54%) 0.12 0.194 (NC)b NC 3.3 1,1-dichloroethane All 0/1367 (0%) 0.01 NC NC NC 1,2-dichloroethane All 0/1346 (0%) 0.01 NC NC NC 1,1-dichloroethene All 0/1367 (0%) 0.009 NC NC NC Cis-1,2-dichloroethene All 0/1366 (0%) 0.01 NC NC NC Trans-1,2-dichloroethene All 0/1367 (0%) 0.01 NC NC NC Dichloromethane All 7/1165 (0.6%) 0.07 NC NC NC 1,2-dichloropropane All 0/1364 (0%) 0.008 NC NC NC 2,5-dimethylfuran All 317/1213 (26%) 0.012 0.0141 (NC)b NC 0.14 Hexachloroethane All 0/1366 (0%) 0.011 NC NC NC Methyl-tert-butylether (MTBE) All 1067/1307 (82%) 0.002 0.011 (0.006–0.020) NC 0.17 Nitrobenzene All 0/1066 (0%) 0.3 NC NC NC 1,1,2,2-tetrachloroethane All 2/1235 (0.2%) 0.01 NC NC NC Tetrachloroethylene (PCE) All 218/1317 (17%) 0.048 0.0422 (NC)b NC 0.14 1,1,1-trichloroethane All 2/1345 (0.1%) 0.048 NC NC NC 1,1,2-trichloroethane All 0/1354 (0%) 0.01 NC NC NC Trichloroethylene All 19/1228 (2%) 0.012 NC NC NC

NC, not calculated (proportion of results below limit of detection or LOD, 440%,wastoohightopermitavalidresult). aSmokers and non-smokers were designated by the presence or absence of detectable levels of 2,5-dimethylfuran (Ashley et al., 1996), and breakouts by smoking status were presented only for those compounds previously evaluated by Chambers et al., (2011) as being inﬂuenced by the smoking status. bCDC, (2009) does not present geometric mean calculations for compounds with detection rates o60%. However, for purposes of comparison with screening BE values, we estimated population-weighted geometric means for any compound with X5% detection rate in the NHANES sample assuming replacement of ND values by LOD/O2.

frequency greater than 5%), and the detection limit for all A hazard index (HI) approach was adopted to examine the VOCs using the following equation: potential hazards associated with combined exposures to VOCs. A detailed examination of the mode of action for each HQ GM or DL =BE ¼½ nc chemical was not conducted. Instead, chemicals were Where, grouped by the target organ system under a worst-case HQ ¼ hazard quotient; assumption of a common mode of action (USEPA, 2000, GM ¼ geometric mean (Table 1); 2007). This approach is expected to be a highly conservative, DL ¼ detection limit (Table 1); and screening-level method for assessing the potential impacts of BEnc ¼ screening BE value for non-cancer endpoints the low-level exposure to multiple chemicals, as different following inhalation or oral exposure (Table 2). toxicity endpoints in the same target organ system would not

Journal of Exposure Science and Environmental Epidemiology (2012) 22(1) 27 28 imne al. et Kirman

Table 2 . Toxicity values and corresponding BE values for VOCs (Aylward et al., 2010).

Chemical Oral non-cancer values Inhalation non-cancer values Oral cancer values Inhalation cancer values

Source Endpoint RfD, mg/kg/d BE (mg/l) Source Endpoint RfC, mg/m3 BE (mg/l) Source OSF BEa (mg/l) IUR BEa (mg/l)

Benzene i Hematologic 0.004 0.1 I Hematologic 0.03 0.1 i 0.015–0.055 0.001–0.1b 2.2E-06-7.8E-06 0.0008–0.08b Carbon tetrachloride i Hepatic 7.00EÀ04 0.01 i 0.13 0.0001–0.01 1.5EÀ05 0.0001–0.01 Chlorobenzene i Hepatic 0.02 0.2 h Renal, hepatic 0.02 0.03 1,2-dibromo-3-chloropropane i Repro/devel 0.0002 0.001 h 1.4 0.000009–0.0009 6.9EÀ07 0.005–0.5 Dibromomethane h Biochem 0.01 0.04 1,2-dichlorobenzene i Non-specific 0.09 0.7 h Body weight 0.2 0.7 1,3-dichlorobenzene 1,4-dichlorobenzene i Hepatic 0.8 3 1,1-dichloroethane h None observed 0.1 0.3 h Renal 0.5 0.9 1,2-dichloroethane i 0.091 0.0001–0.01 2.6EÀ05 0.0001–0.01 1,1-dichloroethene i Hepatic 0.05 0.06 i Hepatic 0.2 0.3 Cis-1,2-dichloroethene h Biochem 0.01 0.2 ora fEpsr cec n niomna Epidemiology Environmental and Science Exposure of Journal Trans-1,2-dichloroethene i Biochem 0.02 0.07 1,2-dichloropropane i Nasal 0.004 0.01 h 0.068 0.0002–0.02 2,5-dimethylfuran Ethylbenzene R Hepatic, renal 0.1 2 A Renal 1 4 Hexachloroethane I Renal 0.001 0.05 i 0.014 0.004–0.4 4.0EÀ06 0.002–0.2 Methyl-tert-butylether (MTBE) i Renal, hepatic 3 20 Methylene chloride I Hepatic 0.06 0.7 A Hepatic 1 3 i 0.0075 0.002–0.2 4.7EÀ07 0.006–0.6 Nitrobenzene I Biochem 0.002 0.02 i Respiratory 0.009 0.03 i 4.0EÀ05 0.00008–0.008 Styrene I Hematological, Hepatic 0.2 1 i Neuro 1 3 1,1,2,2-tetrachloroethane i 0.21 0.0004–0.04 Tetrachloroethene I Hepatic 0.01 1 HC 0.36 4 Toluene I Renal 0.08 0.9 i Neuro 5 20 1,1,1-trichloroethane I Body weight 2 100 i Neuro 5 20 1,1,2-trichloroethane I Biochem 0.004 0.05 i 0.057 0.0002–0.02 Trichloroethene R Kidney 0.54 8 R Renal, hepatic, neuro 1.9 6 Xylenes, mixed I Body weight 0.2 0.7 i Neuro 0.1 0.3 cenn Eeauto o VOCs for evaluation BE Screening Source: i, USEPA IRIS; HC, Health Canada; R, RIVM; h, USEPA HEAST; A, ATSDR MRL; OSF, oral slope factor; IUR, inhalation unit risk. aBE values for cancer endpoints reflect blood concentrations consistent with continuous exposure at the risk-specific doses or concentrations associated with 1 Â 10À6 –1 Â 10À4 for upper-bound cancer risks. bBE values for the cancer effects of benzene reflect the high end of the range of cancer potency estimates derived by USEPA. 21)22(1) (2012) Screening BE evaluation for VOCs Kirman et al. necessarily result in additive or cumulative toxicity. Within value was derived in Aylward et al., (2010) to allow a the context of the IPCS conceptual framework for the comparison. GM blood levels for benzene were generally combined exposures to multiple chemicals, this corresponds higher in the smokers (0.136 mg/l) than in the non-smokers to a conservative (health protective) ‘‘Tier 0’’ analysis that is (0.024 mg/l) (see Table 1). The GM for non-smokers falls ‘‘yconsidered to be conservative and protective, given the within the range of BE values that correspond to an upper- common underlying premise of being based on critical effects bound risk estimate of 1 Â 10À6–1 Â 10À4, while the GM for occurring at lowest dose.’’ (WHO, 2009). HI values were smokers slightly exceeds this range. The GM for benzene in calculated for each target organ system (i.e., the bases for the the non-smokers is driven by the imputed value for non- key toxicity values listed in Table 2) by summing HQ values detected concentrations, as detection frequency and levels across the chemicals sharing the same target organ system: were low in non-smokers (see Table 1). No cancer-based HI ¼ SHQ screening BE values were available for comparison for blood level data for the other frequently or moderately detected Where, VOCs (Aylward et al., 2010). HI ¼ target organ system-specific HI; and Analytical detection limits for the VOCs in the 2003–2004 HQ ¼ chemical-specific HQ. NHANES data set are generally lower than the non-cancer By convention, HQs and HI values are typically presented screening BE values for both the routes of exposure, with the with only one significant figure, reflecting the limited exception of nitrobenzene (inhalation and oral exposures) precision of the underlying screening values used in calculat- and 1,2-dibromo-3-chloropropane (inhalation exposure) ing these metrics. (Figure 2a and b). Detection limits for VOCs in blood are compared with the cancer-based BE values in Table 4. Detection limits for carcinogenic VOCs generally fall within Results the range of cancer-based BE values corresponding to a 1 Â 10À6–1 Â 10À4 risk level. For three of the carcinogenic Of the 28 VOCs analyzed in NHANES, 15 chemicals were VOCs (1,2-dibromo-3-chloropropane for oral exposures, detected (Table 1). Five VOCs were frequently detected 1,2-dichloropropane for oral exposures, and nitrobenzene (460% of samples for smokers and non-smokers combined: for inhalation exposures) detection limits exceed this range. benzene, ethylbenzene, toluene, xylenes, and methyl-tert- This indicates that the NHANES analytical methods and butylether). Four VOCs were moderately detected (5–60% of sample volumes are sufficiently sensitive to detect the blood samples for smokers and non-smokers combined: 1,4- concentrations of interest in a risk assessment context for dichlorobenzene, 2,5-dimethylfuran, styrene, and tetrachloro- mostoftheVOCsincludedinthesurvey. ethylene). Six VOCs were infrequently detected (o5% of the samples: carbon tetrachloride, dibromomethane, dichloromethane, 1,1,2,2-tetrachloroethane, 1,1,1-trichloroethane, Discussion and trichloroethylene). Based upon a comparison of the GM values, blood levels In this assessment, biomonitoring data for VOCs in the for benzene, ethylbenzene, styrene, toluene, and xylene were blood from NHANES (CDC, 2009) were compared with the generally higher in the smokers than in the non-smokers by screening BE values for non-cancer and cancer endpoints approximately two- to six-fold, resulting in higher HQ values (Aylward et al., 2010). An implicit assumption in this in smokers (Figure 1a and b). For non-smokers, HQ values evaluation is that the detected concentrations in blood for all detected chemicals were below 1. For smokers, HQ represent chronic blood concentrations in individuals (the values for oral and inhalation exposures to benzene were basis of the screening BE values). This is likely to be a highly approximately equal to 1. The HQ values for xylenes in conservative assumption for any given chemical and smokers approached a value of 1 for the inhalation route, but individual, given the biologically transient nature of these for all other chemicals were below 1. compounds (Sexton et al., 2005). However, this at least A target organ system-specific HI value of approximately 1 provides a basis for examination of the levels of detected was calculated for the blood system effects in smokers blood concentrations relative to levels of interest in a risk (inhalation exposure) (Table 3), which was almost entirely assessment context across thedifferentchemicalsinthe attributable to benzene. An HI value of 0.9 was estimated for NHANES data set. the neurological system in smokers, based principally on the For detected chemicals, using a health protective screening contribution of the HQ for xylene. The HI values for all the approach, HQ and HI values were generally at or below a other target organ systems in both smokers and non-smokers value of 1, suggesting that the potential for deleterious non- were below a value of 1 (Table 3). cancer effects is low. However, VOCs associated with Benzene was the only frequently detected VOC in the cigarette smoke were the most frequently detected VOC NHANES data set for which a cancer-based screening BE compounds in both smokers and non-smokers, and the

Journal of Exposure Science and Environmental Epidemiology (2012) 22(1) 29 Kirman et al. Screening BE evaluation for VOCs

Figure 1. Comparison of biomonitoring data for detected VOCs with screening BE values derived from exposure guidance values for non-cancer endpoints derived for (a) inhalation, and (b) oral routes of exposure. HQ values were calculated using the population-weighted GM concentrations (Table 1). *GM values used to calculate the HQ were heavily inﬂuenced by the large proportion (440%) of non-detected values (evaluated using DL/O2). calculated HQ and HI values were higher in the smokers than the basis of the cancer risk assessment for benzene from the in the non-smokers. With respect to cancer risk-based USEPA (which served as the basis for the derivation of the screening BE values, the GM of benzene concentrations screening BE values used here). The estimated lifetime risk of detected in the blood of smokers was slightly higher than the developing acute myeloid leukemia for an individual born range of screening BE values associated with a 1 Â 10À6– today is approximately 4 Â 10À3 (SEER, 2011). Thus, the 1 Â 10À4 cancer risk. However, if the screening BE had been theoretical cancer risks associated with the observed con- calculated using the lower end of the range of cancer potency centrations of benzene in the blood in NHANES data set in estimates derived by USEPA for benzene (Table 2), the smokers (based on the USEPA cancer slope factor and GM value in smokers would fall below the 1 Â 10À4 cancer corresponding screening BE values) fall approximately an risk level. order of magnitude below this level of lifetime risk. For Benzene exposure has been associated with the increased smokers, the potential risk of leukemia due to benzene is risk of acute myeloid leukemia in occupationally exposed likely to be small compared with the other cancer risks (e.g., populations. Occupational cohort data on total leukemia are lung cancer) associated with smoking in general.

30 Journal of Exposure Science and Environmental Epidemiology (2012) 22(1) Screening BE evaluation for VOCs Kirman et al.

Ta bl e 3 . Estimated hazard indices (HIs, rounded to 1 significant Blood concentrations would have to be maintained chroni- figure) by target organ system derived from chemical-specific hazard cally for a lifetime at those levels to result in the quotients (HQs) based on population geometric mean concentrations corresponding cancer risk levels. Furthermore, those risk- from NHANES for chemicals with detected concentrations. specific doses are based on upper-bound assessments of cancer potency; the true cancer potency for a given chemical Target organ sy stem and Chemical-specific HQs and summed HIs contributing chemicals is likely to be lower and may be zero, so while comparison of Smokers Non-smokers the measured blood concentrations with the cancer RSD- based screening BE values provides some information that is Evaluations based on screening BE values derived from oral reference values useful in comparing and prioritizing across chemicals, it Hepatic Styrene 0.07 0.03 cannot be used to estimate individual cancer risks, particu- Ethylbenzene 0.03 0.01 larly not for biologically transient compounds such as PCE 0.04 0.04 benzene and other VOCs. Sum, hepatic 0.1 0.07 Analytical detection limits for VOCs in blood are generally Renal sufficient to detect the blood concentrations of these Ethylbenzene 0.03 0.01 Toluene 0.4 0.09 compounds consistent with the existing non-cancer chronic Sum, renal 0.4 0.1 exposure reference values, and with the risk-specific exposure Body weight changes levels in the range of 1 Â 10À6–1 Â 10À4 cancer risk. Thus, Xylenes, mixed 0.4 0.2 the absence of any detectable levels of these compounds (with Sum, body weight changes 0.4 0.2 the few exceptions noted above in the results) should be Blood Styrene 0.07 0.03 interpreted in the context of existing risk assessments, as Benzene 1 0.2 providing clear information that exposures in the general Sum, blood 1 0.2 population as reflected in the NHANES sampling were below the levels of concern based on the current risk assessments. Evaluations based on screening BE values derived from inhalation The analytical detection limits for 1,2-dibromo-3-chloro- reference values Hepatic propane, 1,2-dichloropropane, and nitrobenzene in the 1,4-dichlorobenzene 0.06 0.06 NHANES program are above the risk-specific screening MTBE 0.0006 0.0006 BE values for the 1 Â 10À6–1 Â 10À4 cancer risk range, and Sum, hepatic 0.07 0.07 above the non-cancer screening BE values for 1,2-dibromo- Renal 3-chloropropane and nitrobenzene. However, this does not Ethylbenzene 0.02 0.007 MTBE 0.0006 0.0006 indicate the presence of risk to the population, as actual Sum, renal 0.02 0.008 concentrations of the VOCs in blood, if at all present, may be Blood considerably lower than the detection limits. If further Benzene 1 0.2 assessment of potential exposure levels is required for non- Sum, blood 1 0.2 detected compounds, other approaches may be useful. These Neurological Styrene 0.02 0.009 could include: (1) conducting a targeted study that collects Toluene 0.02 0.004 larger sample volumes than are available through NHANES; Xylenes, mixed 0.9 0.5 (2) development of refined analytical methods allowing Sum, neurological 0.9 0.5 greater sensitivity; (3) pooling of samples across individuals HIs are the sums of the HQs for all detected chemicals with exposure to obtain a higher sample volume for a population estimate reference values derived based on toxicological endpoints within a given (however, estimates of variation would no longer be target organ system. The HIs are estimated separately based on screening possible); and (4) exposure pathway characterization to BE values derived from inhalation and oral reference values. determine if the exposure pathways of potential concern as Italicized values are the endpoint-specific sums of the (non-italicized) chemical-specific HI values. identified by the risk assessments (oral exposure for 1,2- dibromo-3-chloropropane and 1,2-dichloropropane; inhalation exposure for nitrobenzene) are valid. The cancer risk-specific doses (RSDs), from which the Inter-individual variation in the blood VOC levels appears cancer-based BE values were derived, are estimates of the to be moderate for chemicals that were frequently detected, lifetime average daily exposure associated with a given cancer with the 95th percentile values approximately two- to seven- risk level for a chemical. Screening BE values for cancer fold higher than their corresponding GM values, reflecting RSDs provide an estimate of the steady-state blood skewness typically observed in lognormally distributed data concentrations that would result from chronic exposure at sets (Table 1). Greater inter-individual variation (95th those risk-specific doses. However, it isn’t possible to draw percentiles more than 10-fold above the limit of detection) conclusions regarding the lifetime cancer risks based on spot was noted for infrequently detected chemicals, which samples of transient compounds in blood of individuals. may reflect detection of isolated exposures or special

Journal of Exposure Science and Environmental Epidemiology (2012) 22(1) 31 Kirman et al. Screening BE evaluation for VOCs

Figure 2. Comparison of VOC detection limits with screening BE values for non-cancer endpoints derived from exposure guidance values for (a) inhalation and (b) oral routes of exposure. subpopulations rather than the upper tails of a continuous to be intermittent in nature and exhibit considerable temporal population distribution of levels. These data suggest that for variation. In children, temporal (intra-individual) variation some individuals, HQ and HI values may be higher than exceeded inter-individual variation for the blood levels of those calculated using the GM values. However, the screen- most the VOCs detected (Sexton et al., 2005, 2006). Based ing BE values derived herein correspond to predicted chronic upon the disparity between the exposure conditions under- steady-state blood levels resulting from the continuous lying the toxicity values (sustained and chronic) and the exposure at the cited exposure reference levels. Because exposures likely underlying the biomonitoring data (inter- VOCs are transient and rapidly eliminated, substantial mittent and short-term), central tendency estimates for blood variation in the blood concentrations would be expected concentrations of VOCs were considered to be an appro- among the individuals both within- and across- days. In the priate basis of comparison with the screening BE values for context of the chronic exposure reference values, concern VOCs. would arise only for the individuals with measured blood Toxicity values are not available for all VOCs and values in excess of the screening BE values occurring on a endpoints (Table 2). To address potential toxicity value continuous and/or frequent basis. Exposures to VOCs tend data gaps, additional toxicity values from non-federal or

32 Journal of Exposure Science and Environmental Epidemiology (2012) 22(1) Screening BE evaluation for VOCs Kirman et al.

Ta bl e 4 . Comparison of NHANES detection limits with screening BE values derived from cancer risk assessments.

Chemical Detection limit (mg/l) Screening BE (mg/l)a

Oral cancer Inhalation cancer

Benzene 0.024 0.001–0.1 0.0008–0.08 Carbon tetrachloride 0.005 0.0001–0.01 0.0001–0.01 1,2-dibromo-3-chloropropane 0.1 0.000009–0.0009 0.005–0.5 1,2-dichloroethane 0.01 0.0001–0.01 1,2-dichloroethane 0.01 0.0001–0.01 Dichloromethane 0.07 0.002–0.2 0.006–0.6 1,2-dichloropropane 0.3 0.0002–0.02 Hexachloroethane 0.011 0.004–0.4 0.002–0.2 Nitrobenzene 0.3 0.00008–0.008 1,1,2,2-tetrachloroethane 0.01 0.0004–0.04 1,1,2-trichloroethane 0.01 0.0002–0.02 aScreening BE value corresponds to estimated steady-state blood concentrations consistent with continuous exposure at the risk-speciﬁc dose or concentration corresponding to a range of 1 Â 10À6–1 Â 10À4 for upper-bound cancer risks.

non-published sources are available (USEPA, 2010), and blood system in smokers; xylene for the neurological system could be used to derive screening BE values using the steady- in smokers), further iteration (i.e., beyond the IPCS Tier 0) state solutions published in Aylward et al., (2010); however, of the analysis of combined exposures to multiple chemicals, such an approach was outside the scope of the current effort. using a more complex and accurate IPCS Tier 1–3 approach Two VOCs in the NHANES data set (1,3-dichlorobenzene, for VOCs does not appear to be warranted. 2,5-dimethylfuran) were lacking toxicity values for either The value of a screening risk assessment is the reduced level non-cancer or cancer endpoints. One possible approach for of effort and the ability to prioritize which chemicals warrant these chemicals would be to identify a toxicity surrogate further investigation, including a more robust risk assessment based upon a chemical with similar structure and mode of approach relying on a full BE, exposure pathway investiga- action. For example, use of BE values for 1,2-dichloroben- tions, examination of the risk assessment assumptions, and zene (0.7 mg/l; Table 2) to assess 1,3-dichlorobenzene, and BE other risk assessment and risk management approaches. The values for furan (0.04 mg/l; Aylward et al., 2010) to assess screening approach used here results in valuable perspectives 2,5-dimethylfuran would suggest that the potential for regarding the relative hazards of the VOC compounds deleterious non-cancer effects from these chemicals is low. examined in the NHANES in the general population. The This assessment includes a consideration of the potential findings that levels of VOCs in non-smokers are below the impacts of the presence of multiple VOCs in blood (1) across cancer and non-cancer regulatory exposure guidance values, the routes of exposure by relying upon internal dose-based using this conservative screening evaluation indicate that HQ values; and (2) across chemicals by segregating HQ additional, more detailed risk assessments for the VOCs values by the target organ system of the non-cancer toxicity included in this analysis are probably not warranted for the endpoint used as the basis of the risk assessment derivation. general population as a whole, although subpopulations with Inherent to this approach is an assumption that the dose of unusual exposures or other characteristics of interest may individual components are additive in producing a response warrant further study. For smokers, however, biomonitoring at the target tissue. Potential interactions leading to levels for specific smoking-related VOCs approach or exceed synergism (i.e., greater than additive) or antagonism (i.e., the non-cancer and cancer-based regulatory exposure gui- less than additive) were not addressed, nor could the dance values. potential contributions to risk from chemicals not measured In conclusion, for the small number of VOCs with or evaluated here be addressed. Alternative approaches to detectable blood concentrations in the NHANES data set, cumulative risk assessment include other component-based the potential for deleterious non-cancer effects appears low approaches (including response addition, relative potency but is affected by the smoking status of the participants. For factors, and interaction-based HI calculation), relying upon non-detected compounds, the analytical sensitivity of the whole mixture’s testing (USEPA, 2000, 2003), and account- NHANES program was generally sufficient to draw clear ing for interactions via metabolism when analytes compete conclusions that on a population basis, if exposures are for the same enzymes. However, based on the fact that the occurring, they are generally resulting in the blood levels that screening endpoint-specific HI values at or near 1 calculated are below levels of concern in the context of current risk herein are largely driven by a single chemical (benzene for the assessments.

Journal of Exposure Science and Environmental Epidemiology (2012) 22(1) 33 Kirman et al. Screening BE evaluation for VOCs

Conflict of interest Hays S.M., Aylward L.L., LaKind J.S., Bartels M.J., Barton H.A., Boogaard P.J., Brunk C., DiZio S., Dourson M., Goldstein D.A., Lipscomb J., Authors LLA, CRK, DWP, and SMH received funding Kilpatrick M.E., Krewski D., Krishnan K., Nordberg M., Okino M., Tan Y.M., Viau C., and Yager J.W. Guidelines for the derivation of from the American Chemistry Council (ACC) and the biomonitoring equivalents: report from the Biomonitoring Equivalents Expert American Petroleum Institute (API) to support preparation Workshop. Regul Toxicol Pharmacol 2008: 51: S4–S15. of the manuscript. The authors had complete freedom to LaKind J.S., Aylward L.L., Brunk C., DiZio S., Dourson M., Goldstein D.A., Kilpatrick M.E., Krewski D., Bartels M.J., Barton H.A., Boogaard P.J., design, implement, and report the analyses presented herein. Lipscomb J., Krishnan K., Nordberg M., Okino M., Tan Y.M., Viau C., Author BCB declares no conflict of interest. Yager J.W., and Hays S.M. 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