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The Influence of Physicochemical Properties on the Internal Dose Of Journal of Exposure Science and Environmental Epidemiology (2013) 23, 39 -- 45 & 2013 Nature America, Inc. All rights reserved 1559-0631/13 www.nature.com/jes ORIGINAL ARTICLE The influence of physicochemical properties on the internal dose of trihalomethanes in humans following a controlled showering exposure Lalith K. Silva1, Lorraine C. Backer2, David L. Ashley1, Sydney M. Gordon3, Marielle C. Brinkman3, John R. Nuckols4, Charles R. Wilkes5 and Benjamin C. Blount1 Although disinfection of domestic water supply is crucial for protecting public health from waterborne diseases, this process forms potentially harmful by-products, such as trihalomethanes (THMs). We evaluated the influence of physicochemical properties of four THMs (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) on the internal dose after showering. One hundred volunteers showered for 10 min in a controlled setting with fixed water flow, air flow, and temperature. We measured THMs in shower water, shower air, bathroom air, and blood samples collected at various time intervals. The geometric mean (GM) for total THM concentration in shower water was 96.2 mg/l. The GM of total THM in air increased from 5.8 mg/m3 pre shower to 351 mg/m3 during showering. Similarly, the GM of total-blood THM concentration increased from 16.5 ng/l pre shower to 299 ng/l at 10 min post shower. THM levels were significantly correlated between different matrices (e.g. dibromochloromethane levels) in water and air (r ¼ 0.941); blood and water (r ¼ 0.845); and blood and air (r ¼ 0.831). The slopes of best-fit lines for THM levels in water vs air and blood vs air increased with increasing partition coefficient of water/air and blood/air. The slope of the correlation plot of THM levels in water vs air decreased in a linear (r ¼ 0.995) fashion with increasing Henry’s law constant. The physicochemical properties (volatility, partition coefficients, and Henry’s law constant) are useful parameters for predicting THM movement between matrices and understanding THM exposure during showering. Journal of Exposure Science and Environmental Epidemiology (2013) 23, 39--45; doi:10.1038/jes.2012.80; published online 25 July 2012 Keywords: trihalomethane exposure; water disinfection by-products; human blood; showering; partition coefficients; Henry’s law constants INTRODUCTION by which DBPs might cause adverse health effects are not well Water disinfection is important to control infectious disease understood, a more accurate assessment of exposure will improve outbreaks such as typhoid, hepatitis, Giardia infection, and cholera the precision of epidemiological studies by reducing exposure arising from the public water supply. However, potentially harmful misclassification. chemicals, such as trihalomethanes (THMs), can be formed as The presence of THMs in the domestic water supply leads to 8--13 by-products. THMs are halogenated organic compounds formed exposure to THMs from daily water-related activities, such as during disinfection by the reaction of chlorine with naturally drinking and bathing/showering. THMs in tap water are inhaled occurring organic matter such as humic and fulvic acids. Chloro- following aerosolization or vaporization during showering. In form, bromodichloromethane (BDCM), dibromochloromethane addition, THMs are absorbed dermally during showering and (DBCM), and bromoform are the primary THMs found in tap bathing. Because THMs are lipophilic and metabolized rapidly, the water in the United States.1 levels in blood may vary depending on the time of sample col- 14 Epidemiological studies suggest that exposure to THMs increases lection after exposure. the risk of various adverse health outcomes in humans. Long-term Because of prevalent exposure to THMs from the use of tap 15 exposure to THMs may lead to increased risk of cancers in the water, the US Environmental Protection Agency (US EPA) bladder, stomach, pancreas, kidney, and rectum.2--4 THM expo- established regulatory limits for THM levels in tap water. These sure may also increase the risk of Hodgkin’s and non-Hodgkin’s regulatory changes appear to have resulted in decreased THM lymphoma.2--5 Furthermore, exposure to disinfection by-products levels in both domestic water supply and in US residents using (DBP), including THMs, may be associated with adverse reproduc- that water.16 Estimating human exposure to THMs is complicated tive outcomes such as reduced gestational age, intrauterine owing to variation in routes of exposure (e.g. ingestion, inhalation, growth retardation, and birth defects.6,7 Although the mechanisms and dermal), absorption, distribution, metabolism, and excretion. 1Division of Laboratory Sciences, Centers for Disease Control and Prevention, Atlanta, Georgia, USA; 2Division of Environmental Hazards and Health Effects National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia, USA; 3Battelle Memorial Institute, Columbus, Ohio, USA; 4Department of Environmental & Radiological Health Sciences, Colorado State University, Fort Collins, Colorado, USA and 5Wilkes Technologies, 10126 Parkwood Terrace, Bethesda, Maryland, USA. Correspondence to: Dr. Lalith K. Silva, Division of Laboratory Sciences, National Center for Environmental Health, CDC, 4770 Buford Highway, NE, Mail Stop F47, Atlanta, GA 30341, USA. Tel.: þ 770 488 3559. Fax: þ 770 488 0181. E-mail: [email protected] The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention. Received 17 October 2011; accepted 8 May 2012; published online 25 July 2012 Blood and air trihalomethane levels after showering Silva et al 40 Measuring metrics of internal dose (e.g. THM concentrations in 25 min after the end of the total exposure period, which is the same as 10 blood) is therefore a useful approach for assessing recent human and 30 min, respectively, after showering ended. It is important to note exposure to THMs.17 Internal dose of THMs is related to many that both the 10- and 30-min post-shower samples were collected during factors, including tap water THM levels; duration and frequency of the elimination phase for THMs, and thus the samples do not represent the water use activity; route of exposure; genetics; metabolic factors; peak blood concentrations but rather occur in the downslope of the blood and THM physicochemical properties (e.g. volatility, partition concentration vs time curve.20 Samples were analyzed for THM levels using coefficient, half-life in blood). headspace solid-phase micro-extraction (SPME) coupled with gas chroma- To better understand how physicochemical properties affect tography (GC) and high-resolution mass spectrometry (MS). Analyte THM uptake during showering, we evaluated THM levels in shower quantification was based on stable isotope dilution.21 water, shower air, and blood of 100 study participants who showered under controlled conditions (e.g. 10-min shower, shower temperature, shower water flow). A summary of our findings Air Samples has been published.10 In this paper, we examine the relationships We collected three air samples near the subject’s breathing zone: a pre- between THM physicochemical properties (Henry’s law constant, exposure instantaneous sample collected in the bathroom (hereafter volatility, and partition coefficients) and post-showering blood referred to as the ‘‘pre-shower’’ air samples), a 10-min time-integrated THM levels. sample collected in the shower stall during the entire 10-min showering period (hereafter referred to as the ‘‘during shower’’ air samples), and a 5-min time-integrated post-shower sample collected in the unventilated METHODS bathroom, starting immediately after the shower ended (hereafter referred Human Subjects to as the ‘‘post-shower’’ air samples). Air samples were collected remotely The institutional review boards of the Centers for Disease Control and using evacuated stainless steel canisters and a continuously flowing 100 Prevention (CDC), the National Institutes of Health, the General Clinical sampling line (copper tubing, 4 outer diameter). Filled canisters were Research Center (GCRC) at the University of Pittsburgh, and Battelle Memorial sealed and shipped to Battelle (Columbus, OH, USA) for analysis. We Institute approved this study protocol. We complied with all applicable analyzed the samples for THMs by automated GC/MS using a modified 22 requirements for protection of human subjects. Study participants gave version of US Environmental Protection Agency method TO-14. Full 23 written informed consent before the study. details of air sampling and analysis procedures are available elsewhere. Study Design and Participants Water Samples Pittsburgh was chosen for this study, because the tap water there typically The shower head was modified to allow remote water sampling. Duplicate contains measurable levels of the four DBPs of interest. Brominated DBPs samples were collected 5 min after each shower began. Participants were can form during disinfection of water containing natural organic material instructed to set the shower water temperature between 40 and 41 1C. and bromide. Significant levels of bromide are typically found in the Shower water temperature was monitored by the participant via a digital Allegheny River in Western Pennsylvania, possibly because of a combina- thermometer in the shower stall, and remotely by the study staff via 18 tion of natural and anthropogenic sources. The Allegheny River was the wireless transmission
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