Environment International 75 (2015) 166–171 Contents lists available at ScienceDirect Environment International journal homepage: www.elsevier.com/locate/envint Occurrence of perchlorate in indoor dust from the United States and eleven other countries: Implications for human exposure Yanjian Wan a,b,1, Qian Wu a,1, Khalid O Abualnaja c, Alexandros G Asimakopoulos a, Adrian Covaci d, Bondi Gevao e, Boris Johnson-Restrepo f, Taha A Kumosani g, Govindan Malarvannan d, Hyo-Bang Moon h, Haruhiko Nakata i, Ravindra K Sinha j, Tu Binh Minh k, Kurunthachalam Kannan a,c,⁎ a Wadsworth Center, New York State Department of Health, and Department of Environmental Health Sciences, School of Public Health, State University of New York at Albany, Empire State Plaza, P.O Box 509, Albany, New York 12201-0509, United States b CDC of Changjiang River Administration and Navigational Affairs, General Hospital of the Yangtze River Shipping, Wuhan 430019, China c Biochemistry Department, Faculty of Science, Experimental Biochemistry Unit, King Fahd Medical Research Center and Bioactive Natural Products Research Group, King Abdulaziz University, Jeddah 21589, Saudi Arabia d Toxicological Center, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Antwerp, Belgium e Environmental Management Program, Environment and Life Sciences Center, Kuwait Institute for Scientific Research, P.O Box 24885, Safat 13109, Kuwait f Environmental and Chemistry Group, Sede San Pablo, University of Cartagena, Cartagena, Bolívar 130015, Colombia g Biochemistry Department, Faculty of Science, Experimental Biochemistry Unit, King Fahd Medical Research Center and Production of Bioproducts for Industrial Applications Research Group, King Abdulaziz University, Jeddah, Saudi Arabia h Department of Marine Sciences and Convergent Technology, College of Science and Technology, Hanyang University, Ansan, South Korea i Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan j Department of Zoology, Patna University, Patna 800 005, India k Faculty of Chemistry, Hanoi University of Science, Vietnam National University Hanoi, 19 Le Thanh Tong, Hoan Kiem, Hanoi, Viet Nam a r t i c l e i n f o Article history: Received 17 September 2014 Accepted 11 November 2014 Available online xxxx Keywords: Perchlorate Indoor dust Human exposure Global survey a b s t r a c t Perchlorate is a widespread environmental contaminant and potent thyroid hormone disrupting compound Despite this, very little is known with regard to the occurrence of this compound in indoor dust and the exposure of humans to perchlorate through dust ingestion In this study, 366 indoor dust samples were collected from 12 countries, the USA, Colombia, Greece, Romania, Japan, Korea, Pakistan, Kuwait, Saudi Arabia, India, Vietnam, and China, during 2010–2014 Dust samples were extracted by 1% (v/v) methylamine in water Analyte separation was achieved by an ion exchange (AS-21) column and analysis was performed by high performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) The overall concentrations of perchlorate in dust were in the range of 0.02–104 μg/g (geometric mean: 0.41 μg/g) The indoor dust samples from China contained the highest concentrations (geometric mean: 5.38 μg/g) No remarkable differences in perchlorate concentrations in dust were found among various microenvironments (i.e., car, home, office, and laboratory) The estimated median daily intake (EDI) of perchlorate for toddlers through dust ingestion in the USA, Colombia, Greece, Romania, Japan, Korea, Pakistan, Kuwait, Saudi Arabia, India, Vietnam, and China was 1.89, 0.37, 1.71, 0.74, 4.90, 7.20, 0.60, 0.80, 1.55, 0.70, 2.15, and 21.3 ng/kg body weight (bw)/day, respectively Although high concentrations of perchlorate were measured in some dust samples, the contribution of dust to total perchlorate intake was b 5% of the total perchlorate intake in humans This is the first multinational survey on the occurrence of perchlorate in indoor dust © 2014 Elsevier Ltd All rights reserved Introduction Perchlorate is both a naturally occurring (Rao et al., 2010; Urbansky et al., 2001) and man-made chemical, widely used as an oxidant in rocket fuel, missiles, flares, fireworks, and automobile air bag inflators ⁎ Corresponding author at: Wadsworth Center, Empire State Plaza, P.O Box 509, Albany, NY 12201-0509, United States E-mail address: kkannan@wadsworth.org (K Kannan) Co-first author contributed to this study equally http://dx.doi.org/10.1016/j.envint.2014.11.005 0160-4120/© 2014 Elsevier Ltd All rights reserved (Motzer, 2001) Anthropogenic sources are thought to be the major sources of perchlorate in the environment Perchlorate has been reported to occur in human bodily fluids, such as saliva, breast milk, serum, and urine (Blount et al., 2009; Eguchi et al., 2014; Oldi and Kannan, 2009) Perchlorate has the ability to inhibit the uptake of iodide at 30 times greater affinity than iodine itself by the sodium/iodide symporter (NIS) (Tonacchera et al., 2004), which results in the disruption of thyroid hormone production in animals and humans (Blount et al., 2006; Chen et al., 2014; Dohán et al., 2007; Gilbert and Sui, 2008; Wu et al., 2010; York et al., 2003) A decreased thyroid hormone level has been Y Wan et al / Environment International 75 (2015) 166–171 shown to adversely affect neurodevelopment in mammals, human fetuses, infants, toddlers, and children (Charatcharoenwitthaya et al., 2014; Mendez and Eftim, 2012; Wu et al., 2012; York et al., 2003) Perchlorate is also recognized as a persistent and pervasive contaminant (Fisher et al., 2000; Motzer, 2001) It can accumulate in leafy vegetables and reach humans through the food chain (Lee et al., 2012; Sanchez et al., 2006; Voogt and Jackson, 2010) The United States Environmental Protection Agency (USEPA) has proposed an oral reference dose (RfD) of 0.7 μg perchlorate/kg body weight (bw)/day (Greer et al., 2002; Zewdie et al., 2010) Assessing sources of human exposure to perchlorate is a subject of considerable interest among various environmental and public health agencies throughout the world Thus far, perchlorate has been reported to occur in drinking water (Blount et al., 2010; Kannan et al., 2009; Wu et al., 2010), foodstuffs (Lee et al., 2012; Wang et al., 2009), and outdoor dust particles (Gan et al., 2014) The current estimates of exposure to perchlorate, extrapolated from blood or urine biomonitoring studies in the USA and China, suggested values that exceed the RfD in many cases, especially for infants and toddlers (Zhang et al., 2010) Because perchlorate is a water-soluble contaminant present in fertilizers, it was believed that agricultural produce was the major source of human exposure to this chemical However, perchlorate is also used in many products in the indoor environment, including bleach, matches, and pharmaceutics (Zewdie et al., 2010) Despite this, no earlier studies have reported the occurrence of perchlorate in indoor dust Indoor dust can be a significant source of human exposure to contaminants such as polybrominated diphenyl ethers (PBDEs) (Rudel et al., 2003; Lorber, 2008; Wu et al., 2007) and ingestion of indoor dust has been shown to be an important exposure pathway to environmental chemicals, especially for infants and toddlers (Johnson-Restrepo and Kannan, 2009; Guo and Kannan, 2011; Liao et al., 2012) Determination of perchlorate levels in indoor dust and the assessment of human exposure doses through the ingestion of dust are imperative to the assessment of risks and for the development of strategies to mitigate exposures In this study, we conducted a multinational survey of perchlorate levels in 366 indoor dust samples collected from 12 countries (two American, two European, and eight Asian countries) Perchlorate exposures via dust ingestion for various age groups (infants, toddlers, children, teenagers, and adults) were calculated on the basis of the measured concentrations This is the first study to report the occurrence of perchlorate in indoor dust from several countries Materials and methods 2.1 Chemicals Ammonium perchlorate (N99.9%) and methylamine (40 wt.% solution in water) were purchased from Sigma-Aldrich (St Louis, MO, USA) Isotope-labeled sodium perchlorate (Cl18O− , N 90%) was purchased from Cambridge Isotope Laboratories (Andover, MA, USA) Milli-Q water was obtained from an ultrapure water system (Barnstead International, Dubuque, IA, USA) All other reagents used in the study were analytical grade 2.2 Sample collection From 2010 to 2014, 366 dust samples were collected from single or multiple cities in 12 countries, including Athens, Greece (2014, n = 30); Iasi, Romania (2012, n = 23); Albany, New York, USA (2014, n = 30); Cartagena, Colombia (2014, n = 39); Kumamoto, Nagasaki, Fukuoka, Saitama, and Saga, Japan (2012, n = 22); Ansan and Anyang, Korea (2012, n = 40); Faisalabad, Pakistan (2011–2012, n = 24); Kuwait City (2013, n = 34); Jeddah, Saudi Arabia (2014, n = 31); Patna, India (2014, n = 30); Hanoi, Thai Binh, and Hungyen, Vietnam (2014, n = 33); and Beijing, Guangzhou, and Shanghai, China (2010–2011, n = 30) 167 Bedrooms and living rooms of homes and apartments (all countries), offices (Korea, Vietnam, and Japan), laboratories (Korea and Vietnam), and cars (Kuwait) were selected for sampling Floor dust samples were obtained from vacuum cleaner bags in each of the sampling sites, with the exception of samples from China and India, which were obtained by sweeping the floor All samples were sieved through a 150 μm sieve, homogenized, packed in clean aluminum foil, and stored at °C until analysis 2.3 Sample preparation Dust samples were extracted and analyzed by following the method described elsewhere, with some modifications (Gan et al., 2014) Briefly, 50 mg of sample was accurately weighed and transferred into a 15 mL polypropylene (PP) conical tube Samples were then spiked with ng of 18O-perchlorate, as an internal standard The dust samples were extracted with 5.0 mL of 1% methylamine in water by shaking in an orbital shaker (Eberbach Corp., Ann Arbor, MI, USA) for 30 The mixture was centrifuged at 4,500 ×g for (Eppendorf Centrifuge 5804, Hamburg, Germany), and the supernatant was transferred into a new PP tube The extract was purified by passage through an Envi-Carb cartridge (250 mg/3 mL; Supelclean, Bellefonte, PA, USA), preconditioned with mL of water The purified extract was filtered through a 0.2 μm regenerated cellulose membrane filter (Phenomenex, Torrance, CA, USA) prior to analysis by liquid chromatography–tandem mass spectrometry (LC–MS/MS) 2.4 Instrumental analysis Samples were analyzed with a Waters 2695 high performance liquid chromatograph (HPLC) (Waters Corporation, Milford, MA, USA) and Micromass Quattro tandem mass spectrometer (MS/MS) in the negative electrospray ionization mode with multiple reaction monitoring Chromatographic separation was achieved with a 250 mm × mm IonPac AS-21 anion-exchange column (Dionex, Sunnyvale, CA, USA) An isocratic mobile phase of 20 mM aqueous methylamine was used at a flow rate of 300 μL/min Perchlorate was monitored by the mass transition of m/z 99 → m/z 83 for 35ClO4 and m/z 101 → m/z 85 for 37 37 ClO4 The ratio of the peak areas of 35ClO− ClO− to was monitored, and a ratio of 3.12 ± 25% was considered acceptable The cone voltage and the collision energy were 40 V and 22 V, respectively The perchlorate internal standard (Cl18O− ) was monitored by a mass transition of m/z 107 → m/z 89 Limit of quantitation (LOQ) for perchlorate in indoor dust was 0.02 μg/g, which was calculated based on the lowest concentration in the calibration that produced a signal-to-noise ratio of 10; the average weight of samples taken for analysis and the concentration/dilution factors were included in the calculation of LOQ 2.5 Quality assurance and quality control Quantification was performed by two internal calibrations, which were established at six low concentrations of perchlorate standard solutions ranging from 0.2 to 10 μg/L, and at six high concentrations ranging from 10 to 500 μg/L The correlation coefficient of the calibration (r) curve was 0.999 Calibration standards were injected daily before and after the injection of a batch of samples For samples with responses greater than the linear range, extracts were diluted with water and reanalyzed All of the standard solutions were prepared in water, and the spiked concentration of the internal standard (18O-ClO4) was 1.0 μg/L The injection of 10 μL of 0.2 μg/L standard yielded a signal-tonoise ratio of 10 Recoveries and the presence of matrix effects for dust samples were tested in triplicate by spiking the native perchlorate standard at three different levels (1.0, 10, and 100 μg/L), and the results are presented in Table S1 The recoveries of perchlorate spiked into each of the samples ranged from 89% to 101% 168 Y Wan et al / Environment International 75 (2015) 166–171 Procedural blanks, spiked blanks, and matrix spike samples were included in each batch of 30 samples analyzed Perchlorate was not detected in procedural blanks A mid-point calibration standard and water blank were injected after every 10 samples to monitor for drift in instrumental response and carry-over from previous injections 2.6 Calculation of daily exposure doses Based on the median and 95th percentile concentrations of perchlorate measured in indoor dust samples, daily intake (EDIing; ng/kg bw/day) doses of perchlorate through dust ingestion were estimated as shown in Eq (1) (Guo and Kannan, 2011; USEPA, 2011): EDIing ¼ C Â DIR=BW ð1Þ where C is the concentration of perchlorate in dust samples (ng/g), DIR is the dust ingestion rate (g/day), and BW is the body weight (kg) We assumed an absorption efficiency of 100% for perchlorate from dust to systemic blood circulation Details of the parameters used in EDIing calculation are shown in Table S2 Estimated daily intakes (EDIdermal; ng/kg bw/day) of perchlorate through dermal absorption of dust were calculated as shown in Eq (2) (USEPA, 2011; Gan et al., 2014; Guo and Kannan, 2011): EDIdermal ¼ ðC Â SAR Â FÞ=BW ð2Þ where SAR is the skin adherence rate (g/day), and F is the dermal absorption factor (Table S2) 2.7 Statistical analysis Statistical analysis was performed with SPSS 18 Concentrations below the LOQ were substituted with a value equal to LOQ divided by the square root of for the calculation of geometric mean (GM) Measured concentration values were not normally distributed and, therefore, were log-transformed for the analysis of variance (ANOVA) or t-test Differences between groups were compared by a one-way ANOVA with the Tukey test All statistical tests were considered significant if the two-tailed p-value was b0.05 Table Concentrations of perchlorate (μg/g) in indoor dust collected from twelve countries Country n Sampling year Geometric mean Median Mean Range Greece Romania USA Colombia Japan Korea Pakistan Kuwait Saudi Arabia India Vietnam China All countries 30 23 30 39 22 40 24 34 31 30 33 30 366 2014 2012 2014 2014 2012 2012 2011–2012 2013 2014 2014 2014 2010–2011 2010–2014 0.42 0.18 0.29 0.09 1.16 1.34 0.10 0.20 0.32 0.24 0.68 5.38 0.41 0.37 0.16 0.41 0.08 0.98 1.44 0.12 0.16 0.31 0.14 0.43 4.25 0.30 0.69 0.29 0.46 0.20 7.48 3.21 0.13 0.37 0.47 1.24 4.61 9.45 2.31 0.08–4.67 0.03–1.83 0.03–1.18 0.02–1.79 0.11–104 0.06–47.0 0.03–0.29 0.04–2.07 0.02–3.11 0.04–19.1 0.05–34.6 0.88–60.7 0.02–104 than those found for homes (Table S4) Perchlorate concentrations in dust collected from offices in Korea and Vietnam were similar to the concentrations found for homes (p N 0.05), but lower than the concentrations measured for environmental analytical laboratories (p b 0.05; Table S4) The higher concentrations of perchlorate in dust samples collected from laboratories may be associated with the use of chemicals and reagents that contain perchlorate in laboratories (Hseu, 2004) The ubiquitous occurrence of perchlorate in indoor dust suggests the existence of sources of this compound in the indoor environment The measured concentrations are remarkably high and comparable to those reported for widely studied compounds, such as polybrominated diphenyl ethers (PBDEs) and phthalates (Rudel et al., 2003; Guo and Kannan, 2011) The source of perchlorate in the indoor environment is not well known and is a subject for future investigation However, perchlorate and its salts are used in many products, including batteries, bleach, and leather products, and these may contribute to the sources in the indoor environments (Zewdie et al., 2010) This is the first report that shows widespread occurrence of perchlorate in indoor dust 3.2 Perchlorate exposure through dust ingestion Results and discussion 3.1 Concentrations Perchlorate was found in all 366 dust samples collected from the 12 countries at concentrations ranging from 0.02 to 104 μg/g (GM: 0.41 μg/g) The GM concentrations of perchlorate in indoor dust samples were found, in the decreasing order, as: China (GM: 5.38 μg/g) N Korea (1.34) N Japan (1.16) N Vietnam (0.68) N Greece (0.42) N Saudi Arabia (0.32) N the USA (0.29) N India (0.24) N Kuwait (0.20) N Romania (0.18) N Pakistan (0.10) N Colombia (0.09) (Table 1) The median concentrations for China, Korea, Japan, Vietnam, the USA, Greece, Saudi Arabia, Kuwait, Romania, India, Pakistan, and Colombia were 4.25, 1.44, 0.98, 0.43, 0.41, 0.37, 0.31, 0.16, 0.16, 0.14, 0.12 and 0.08 μg/g, respectively The highest GM and median concentrations of perchlorate from China were significantly higher than the concentrations determined for any other country studied The measured perchlorate concentrations in dust from China were four times higher than the concentrations found for Korea (second highest), and 60 times higher than the concentrations found for Colombia (lowest) (p b 0.05; Fig 1, Table 1, and Table S3) The highest concentration measured in China can be related to their high volume of production and usage of fireworks (Gan et al., 2014; Wu et al., 2010) Among various microenvironments studied, perchlorate concentrations in dust collected from cars in Kuwait were not significantly higher The significance of indoor dust ingestion as a pathway for human exposure to PBDEs (Rudel et al., 2003) and phthalates (Guo and Kannan, 2011) has been highlighted recently Sources of human exposure to perchlorate have not been fully characterized, and the contribution of indoor dust to perchlorate exposure was not known prior to this study Humans can be exposed to perchlorate via dust ingestion, dermal absorption, and inhalation In comparison with ingestion, exposure through dermal absorption and inhalation of dust is two to three orders of magnitude lower (Table S5) (Guo and Kannan, 2011) Therefore, no further discussions were conducted with regard to exposure calculations based on dermal absorption and inhalation of indoor dust Several factors, such as age, time spent in indoor microenvironments (i.e., home, office/laboratory, and car), and amount of dust ingestion, can influence exposure doses (Geens et al., 2009) For the EDI of perchlorate through dust ingestion, we categorized the population into five age groups: infants (b year), toddlers (1–3 years), children (4–11 years), teenagers (12–21 years), and adults (≥21 years) according to the U.S Environmental Protection Agency's Exposure Factors Handbook (USEPA, 2011) The body weights for various age groups in China were adopted from a previous study (Guo and Kannan, 2011), and these values were also applied in the calculation of EDI for the populations in other Asian countries The median and 95th percentile values of perchlorate concentrations measured in indoor dust in this study were used in the calculation of EDI for median and high exposure scenarios, respectively Y Wan et al / Environment International 75 (2015) 166–171 169 Fig Spatial distribution of perchlorate (median; μg/g) in indoor dust from 12 countries studied Infants and toddlers experienced higher doses of perchlorate exposure through dust ingestion than did the other age groups for all of the countries studied (Table 2) The median daily perchlorate intakes via indoor dust ingestion in China were up to 0.018 and 0.015 μg/kg bw/day for toddlers and infants, respectively; the intake values estimated for adults (0.003 μg/kg bw/day) in China were approximately 5–6 times lower than those found for infants and toddlers (Table 2) A similar intake pattern was found for various age groups in the other countries Among countries investigated, Colombia had the lowest exposure dose, approximately 40–60 times lower than the exposure doses estimated for China (Table 2) The EDI values calculated for toddlers and infants in China through dust ingestion were one order of magnitude lower than the USEPA's RfD (0.7 μg/kg bw/day) It should be noted that exposure doses estimated for some dust samples from Korea and Vietnam, which were collected in laboratories, may overestimate the actual exposure doses for the general populations in these two countries A few samples from laboratories in these countries had elevated levels of perchlorate 3.3 Perchlorate exposure doses through indoor dust compared with other sources of exposures Diet and drinking water are considered significant sources of human exposure to perchlorate (Huber et al., 2011) A few studies have extrapolated biomonitoring studies of perchlorate in urine or blood to assess total daily intake (Valentín-Blasini et al., 2011; Zhang et al., 2010) Among the 12 countries studied here, the EDI of perchlorate through diet and water was characterized for the USA Based on the total daily perchlorate intake values reported for the USA (calculated based on urinary concentrations as shown in Table 3; median, 0.160 and 0.066 μg/kg bw/day for infants and adults, respectively; data for toddlers are not available) (Huber et al., 2011; Valentín-Blasini et al., 2011), the percentage of exposure contributed by indoor dust ingestion (this study, median, 1.76 and 0.15 ng/kg bw/day for infants and adults, respectively) were 1.1% and 0.2% for infants and adults, respectively Thus, despite high concentrations of perchlorate found in dust samples, the contribution of dust to daily intake is small Table Estimated daily intakes (EDIing, ng/kg bw/day) of perchlorate by ingestion of indoor dust for various age groups in twelve countries Country Greece Romania USA Colombia Japan Korea Pakistan Kuwait Saudi Arabia India Vietnam China All countries Median 95th percentile Infants Toddlers Children Teenagers Adults Infants Toddlers Children Teenagers Adults 1.59 0.69 1.76 0.34 5.88 8.64 0.72 0.96 1.86 0.84 2.58 25.5 1.80 1.71 0.74 1.89 0.37 4.90 7.20 0.60 0.80 1.55 0.70 2.15 21.3 1.50 0.82 0.36 0.91 0.18 2.35 3.46 0.29 0.38 0.74 0.34 1.03 10.2 0.72 0.35 0.15 0.38 0.08 1.11 1.63 0.14 0.18 0.35 0.16 0.49 4.81 0.34 0.14 0.06 0.15 0.03 0.47 0.69 0.06 0.08 0.15 0.07 0.20 2.02 0.14 4.45 1.93 2.53 1.36 104 34.1 0.98 3.19 4.07 16.0 46.7 88.2 19.0 4.79 2.07 2.72 1.46 86.8 28.5 0.82 2.66 3.39 13.3 38.9 73.5 15.8 2.31 1.00 1.31 0.71 41.7 13.7 0.39 1.28 1.63 6.41 18.7 35.3 7.58 0.97 0.42 0.55 0.30 19.7 6.44 0.19 0.60 0.77 3.02 8.82 16.6 3.58 0.39 0.17 0.22 0.12 8.27 2.71 0.08 0.25 0.32 1.27 3.71 7.00 1.50 170 Y Wan et al / Environment International 75 (2015) 166–171 Table Estimated daily intakes (EDI) of perchlorate calculated through dust ingestion pathway in comparison with several other pathways Location Group EDI (ng/kg/day) Route USA Median, 160 Median, 66.0 GM, 119 GM, 57.0 Median, 1.76 Median, 1.89 Median, 0.15 Mean, 2220 Mean, 1550 Mean, 1120 Mean, 1050 Mean, 340 Mean, 80.0 Median, 25.5 Median, 21.3 Median, 2.02 Median, 17.0 Median, 110 Median, 40.0 Median, 8.64 Median, 7.20 Median, 0.69 Urine Valentín-Blasini et al (2011) Urine Blount et al (2007) Food & water Huber et al (2011) China Korea Infants Adults Children Adults Infants Toddlers Adults Infants Toddlers Adults Hengyang Nanchang Overall Infants Toddlers Adults Ages 1–2 Ages 3–6 Adults Infants Toddlers Adults New York State Department of Health, where the study was conceived and performed Its contents are solely the responsibility of the authors and not necessarily represent the official views of the CDC Reference Appendix A Supplementary data Indoor dust Supplementary data to this article can be found online at http://dx doi.org/10.1016/j.envint.2014.11.005 This study References Blood Zhang et al (2010) Water Wu et al (2010) Indoor dust This study Food Lee et al (2012) Indoor dust This study In China, rice and dairy milk have been analyzed for perchlorate (Shi et al., 2007) Further, a mean EDI of perchlorate in tap water in China was reported as 0.08 μg/kg bw/day (Table 3) (Huber et al., 2011; Wu et al., 2010) Thus, the EDI of perchlorate through dust ingestion was 2.5% of that reported for tap water in China In comparison with the total EDI of perchlorate (Table 3; median 1.55 and 1.12 μg/kg bw/day for toddlers and adults, respectively) calculated based on blood concentrations in Nanchang, China, indoor dust ingestion (median 0.022 and 0.002 μg/kg bw/day for toddlers and adults in China, respectively) contributed to 1.4% and 0.2%, respectively, of perchlorate intake for toddlers and adults (Zhang et al., 2010) In Korea, the daily perchlorate exposure dose through domestic food consumption (Lee et al., 2012) (0.17 μg/kg bw/day for toddlers and 0.04 μg/kg bw/day for adults) was similar to the values reported for the USA (Table 3; GM 0.12 μg/kg bw/day for children and 0.06 μg/kg bw/day for adults) (Huber et al., 2011) In general, the daily intake of perchlorate through indoor dust ingestion in Korea was 6.5% (toddlers) and 1.7% (adults) of the values reported for dietary intakes in Korea In summary, high concentrations of perchlorate, on the order of several micrograms per gram, were detected in indoor dust collected from several countries Concentrations of perchlorate in dust samples from China (GM: 5.38 μg/g) were significantly higher than those from Korea (1.34 μg/g), Japan (1.16 μg/g), Vietnam (0.68 μg/g), Greece (0.42 μg/g), Saudi Arabia (0.32 μg/g), the USA (0.29 μg/g), India (0.24 μg/g), Kuwait (0.20 μg/g), Romania (0.18 μg/g), Pakistan (0.18 μg/g), and Colombia (0.09 μg/g) Although high concentrations of perchlorate were measured in some dust samples, the contribution of dust to total perchlorate intake is minor (b 5% of the total perchlorate intake) To our knowledge, this is the first study to describe the widespread occurrence of perchlorate in indoor dust The sources of high levels of indoor concentrations of perchlorate need further investigation Acknowledgments The authors thank Pierina Maza-Anaya, a youth research fellow supported by the Colombian National Science and Technology System, for helping 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Determination of perchlorate levels in indoor dust and the assessment of human exposure doses through the ingestion of dust are imperative to the assessment of risks and for the development of strategies... chemicals and reagents that contain perchlorate in laboratories (Hseu, 2004) The ubiquitous occurrence of perchlorate in indoor dust suggests the existence of sources of this compound in the indoor. .. calculation of EDI for the populations in other Asian countries The median and 95th percentile values of perchlorate concentrations measured in indoor dust in this study were used in the calculation