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Lead and other elements in house dust of Japanese residences – Source of lead and health risks due to metal exposure
Environmental Pollution 189 (2014) 223e228
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Lead and other elements in house dust of Japanese residences e Source of lead and health risks due to metal exposure Jun Yoshinaga a, *, Kumiko Yamasaki a, Ayumi Yonemura a, Yuri Ishibashi b, Takaya Kaido b, Kodai Mizuno b, Mai Takagi c, Atsushi Tanaka c a b c
Department of Environmental Studies, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8563, Japan Kitasato University, Kitasato 1-15-1, Sagamihara, Kanagawa 228-8555, Japan National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-8506, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 December 2013 Received in revised form 3 March 2014 Accepted 8 March 2014
The levels of 25 elements in house dust collected from 100 general Japanese residences were measured. Factor analysis was applied on the multi-element data to explore source of Pb (median concentration 49.1 mg/kg) in house dust. Six factors were extracted and Pb was found to have great loading on the fifth factor with Sb and Sn, suggesting solder (Sn), and plastic and metals (Sb) may be the sources of Pb in the house dust of Japanese residences. No significant loading was found on soil-related factors indicating non-significant contribution of Pb in track-in soil. Seven heavy metals (Cd, Cu, Mo, Pb, Sb, Sn, and Zn) were found in house dust at >10 times more condensed than crustal abundance. Health risk of these elements to children via the ingestion of house dust was estimated based on the comparison with tolerable daily intake and found to be non-significant for most of the elements. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: House dust Pb (lead) Factor analysis Sb (antimony) Sn (tin) Health risk
1. Introduction Adverse effect of Pb on children’s health has become a matter of worldwide public health concern because it has been shown that even a low level exposure could result in deficit in cognitive development, which could subsequently result in massive economic loss at nation level (Landrigan et al., 2002; Grosse et al., 2002; Gould, 2009). House dust has long been recognized as major source of Pb for children (Lanphear et al., 1998) and concern has been raised particularly in the United States where Pb-based paint was in use for residence until late 1970s. Paint chips from inside the residence could directly contaminate house dust. Paint chips from outside of residence, as well as contaminated residential soil, could indirectly contaminate house dust by track-in of soil particles. Contaminated house dust could be ingested by infants and children by normal hand-to-mouth activity resulting in Pb poisoning (Su et al., 2002). However, house dust was the major source of Pb for children where residential Pb-based paint had not been used: for instance, in Japan, people do not have custom to paint their residence not
* Corresponding author. E-mail address: [email protected] (J. Yoshinaga). http://dx.doi.org/10.1016/j.envpol.2014.03.003 0269-7491/Ó 2014 Elsevier Ltd. All rights reserved.
only present days but also in the past but house dust was still found to be a significant source of Pb for children. Aung et al. (2004) estimated that 50% of daily Pb exposure of Japanese children was from house dust based on the analyses of Pb in house dust, soil and duplicated diet. Takagi et al. (2011) demonstrated that isotope ratios of Pb in children’s blood and those in house dust were close to each other based on high-precision Pb isotope analysis. Although Pb exposure level of Japanese children has been among the lowest in the world (Yoshinaga et al., 2012), identification of source of Pb in house dust and subsequent risk reduction may be desirable because threshold for deleterious effect of Pb for cognitive development of children was postulated to be absent (Lanphear et al., 2005). In this study, multi-element analysis of house dust samples collected from 100 residences of the general Japanese was carried out and factor analysis was applied to the multi-element data to find elements that have close association with Pb. This information will help to get insight into the source of Pb in house dust in residences in Japan and other countries where no particular source(s), such as Pb-based paint and gasoline additives, is known. Additionally, general profile of element composition of house dust of Japanese residence was presented and their associated health risk for children was estimated.
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2. Materials and methods The house dust samples analyzed in this study were prepared from vacuum cleaner dust collected from the general households in Japan. Four separated samplings were carried out during 2006e2012 (Table 1) from the households in residential areas with no known Pb point sources. Staffs and students of the authors’ laboratory asked their acquaintances for cooperation for vacuum dust sampling. In some sampling, vacuum cleaner dust sampling period was specified to be 30 days but sampling period was not specified in the other. Thus, the samples of this study were not randomly collected but were obtained by ad-hoc manner. Cadmium and Pb results for some samples were published in Ishibashi et al. (2008) and multielement data of 27 sampled in 2007 were published in Kaido et al. (2009). Vacuum dust was passed through stainless-steel 250 mm-mesh using a mechanical shaker (AS-200, Retsch, Haan, Germany) and the passed fraction was used for analysis because it was likely to adhered on children’s hands (Yamamoto et al., 2006). An aliquot (100 mg) of the house dust sample was digested with HNO3/HF/ HClO4 in a Teflon beaker on a hot plate. After digestion, acid was evaporated to dryness and the residue was re-dissolved in 50 g of 0.14 mol/L HNO3. Acids used were of the purest grade commercially available (AA series, Tama Chemical Co. Ltd, Kawasaki, Japan) and Millipore (Waters, Tokyo, Japan) purified water was used throughout. The concentration of Al, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, Sr, Ti, V and Zn were determined by ICP atomic emission spectrometry (ICAP-750, Nippon JarrellAsh, Tokyo, Japan) from the digested sample. Spectroscopic interferences from major element (Al, Ca, and Fe) to Ni, P, and V were corrected. The sample solution was further diluted 20 times and Cd, Co, Cs, Mo, Pb, Sb, Sn, and U concentrations were determined by ICP mass spectrometry (7500ce, Agilent Technologies Japan, Tokyo, Japan) using Rh (1 ppb) as internal standard. Moisture content of house dust sample was measured separately from the sample for digestion. Weight loss after 110 C heating for 2 h was regarded as moisture. A certified reference material (CRM) of house dust matrix (NIST SRM 2598 Indoor Dust) was concurrently analyzed with house dust samples for analytical quality assurance throughout the whole study period. In Table 2 presented the results of our CRM analyses. Note that certified value was given only for Cd, Cr, and Pb of our analytes and the mean values for these three elements agreed well with the certified values. Although relative standard deviations of element concentrations were larger than expected from the concentration level and measurement precision of ICP atomic emission spectrometry or ICP mass spectrometry, it might be due to sample inhomogeneity of this CRM; this may be justified by the large uncertainty attached to the certified values. Element concentrations were converted to dry-weight basis and distribution was tested for normality. All of the element concentrations were not normally distributed and log-transformation was needed to approximate them to normality. Factor analysis using principal component method as extraction with Varimax rotation was applied to log-transformed element concentrations. SPSS for Windows ver 19.0 (IBM, Tokyo, Japan) was used for statistical analyses. In order to characterize element profile in house dust, enrichment factor (EF) was calculated by the following equation: EF ¼
EHD =AlHD ECR =AlCR
where E indicates element concentration (median) and subscripts HD and CR indicate house dust and abundance of element in earth’s crust (crustal abundance), respectively. Crustal abundance of element was adopted from Rudnick and Gao (2004). Daily exposure of children to potentially toxic metals through unintentional house dust ingestion was estimated by multiplying median concentration obtained in the present study and ingestion rate of house dust to be 100 mg/day (Recommended value for daily dust ingestion, general population upper percentile value) (US EPA, 2011). The estimated exposure level was compared with dietary intake (Aung et al., 2006; Oguri and Yoshinaga, 2013) and their ratios to tolerable intakes (WHO Provisional Tolerable Weekly Intake (PTWI) for Sn and EPA Reference Dose for
Table 1 Location and period of house dust samplings and number of samples included in this study. Location
Period
Number of samplesa
Reference
19 Prefectures of Japan Metropolitan Tokyo & Hiroshima Metropolitan Tokyo Metropolitan Tokyo (Chiba) Total
2006 2007 2009 2012
38 (38) 27 (2) 15 (9)b 20 (2) 100
Ishibashi et al., 2008 Kaido et al., 2009 Takagi, 2010 None
a Number of samples from detached housing was shown in parenthesis; others were from collective housings. b Information of two households on detached/collective was missing.
Table 2 Analytical results of NIST SRM 2583 Indoor Dust.
Al Ba Ca Cd Co Cr Cs Cu Fe K Mg Mn Mo Na Ni P Pb S Sb Sn Sr Ti V U Zn
Unit
Measured (n ¼ 17)a
% mg/kg % mg/kg mg/kg mg/kg mg/kg mg/kg % % % mg/kg mg/kg % mg/kg % mg/kg % mg/kg mg/kg mg/kg % mg/kg mg/kg mg/kg
1.94 259 3.12 6.86 6.17 65.8 0.96 242 0.950 0.836 0.883 222 3.55 9.53 91.2 0.207 83.4 4.52 9.42 21.3 102 0.210 23.1 1.09 906
0.05 9 0.23 1.16 0.28 9.1 0.12 20 0.022 0.050 0.042 7 0.28 0.28 11.2 0.011 5.9 0.16 0.55 3.5 7 0.010 4.3 0.15 30
Certified
7.3 3.7 80 22
85.9 7.2
a Arithmetic mean standard deviation of measured values obtained from replicated analyses.
others) were calculated for the evaluation of health risks of children associated with house dust ingestion (WHO PTWI for Sn is available at http://www.inchem.org/ documents/jecfa/jecmono/v46je12.htm#_46125000 and Reference Doses for others are available at http://www.epa.gov/IRIS/). A 5-years-old child with 18.7 kg body weight consuming 1281 kcal/day of energy was assumed (Ministry of Health, Labor and Welfare of Japan, 2012)).
3. Results Table 3 shows dry weight element concentrations in house dust samples analyzed in this study. Among the elements determined, Ca was the most abundant followed by Al, Fe, Na, K, and S in this order. Median and geometric mean concentration of Pb was 49.1 and 57.9 mg/kg, respectively, with a large variation (up to 0.373%) (Table 3). Fig. 1 shows EF of elements in house dust samples of Japanese residences. The EF was around 1 for many elements but EF of Pb along with that of Cd, Cu, Mo, P, S, Sb, Sn and Zn exceeded 10 indicating that the abundance of these elements was more condensed in house dust than natural occurrence. Note that we did not carry out statistical analyses examining variation in element concentrations due to 4 sampling occasions, difference in element concentrations between detached and collective housings, or correlation of element concentrations with age of residence because of our ad-hoc sampling designs and unsuitability for such statistical analyses. Table 4 shows the result of factor analysis. Six factors were extracted with initial eigenvalue >1.0, by which 71.4% of total variance was explained. Factor loadings of Al, Fe, Mn, Ti, V and alkaline earth metals were great on Factor 1 and thus it indicated that the factor was soil-related. On Factor 2, loading of Al was moderately high (0.581) and that of alkali metal and U was the highest: thus Factor 2 was also considered soil or other geogenic material related but more association with alkali metals than Factor 1 was noted. On Factor 3, Cd, Cu, and Zn showed great loading indicating that this factor was common heavy metal-related. This could be inferred as airborne particulate-related because abundances of these elements in atmospheric particles were known to
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Table 3 Element concentrations in house dust samples collected from Japanese residences (n ¼ 100, dry weight basis).
Al Ba Ca Cd Co Cr Cs Cu Fe K Mg Mn Mo Na Ni P Pb S Sb Sn Sr Ti V U Zn a
Unit
Mean (SD)a
Min
5th
25th
50th
75th
95th
Max
% mg/kg % mg/kg mg/kg mg/kg mg/kg mg/kg % % % mg/kg mg/kg % mg/kg % mg/kg % mg/kg mg/kg mg/kg % mg/kg mg/kg mg/kg
1.57 208 2.25 1.02 4.69 67.8 0.711 304 1.00 0.687 0.400 226 2.11 0.827 59.6 0.110 57.9 0.552 10.1 18.4 66.8 0.152 24.7 0.401 920
0.328 31.9 0.397 0.175 0.794 14.8 0.137 66.8 0.161 0.279 0.0742 38.6 0.501 0.368 13.2 0.0347 11.9 0.258 1.93 3.13 12.0 0.0342 3.79 0.094 188
0.525 75.4 0.940 0.277 1.84 34.6 0.241 87.9 0.337 0.354 0.141 80.5 0.847 0.465 25.1 0.0544 17.7 0.307 4.31 6.58 28.5 0.0745 7.31 0.172 434
1.05 132 1.56 0.61 3.15 50.3 0.463 181 0.676 0.523 0.271 165 1.28 0.651 38.7 0.0852 33.0 0.446 6.62 11.4 47.4 0.119 15.6 0.232 644
1.62 207 2.33 1.04 4.43 66.3 0.716 266 1.01 0.666 0.379 224 2.03 0.807 56.5 0.104 49.1 0.533 8.85 17.3 69.2 0.150 24.6 0.381 896
2.43 282 2.93 1.64 6.88 93.0 1.06 511 1.60 0.836 0.575 327 2.99 1.06 89.4 0.142 86.3 0.687 13.4 25.8 87.8 0.191 43.1 0.625 1.22 103
3.88 719 6.29 3.46 12.1 161 1.97 1.61 103 3.06 1.47 1.05 551 10.4 1.43 173 0.243 267 0.926 22.7 87.3 156 0.269 76.7 1.31 3.50 103
4.88 3.51 13.2 5.62 18.5 285 3.75 7.72 4.01 2.17 4.17 679 78.7 3.20 390 2.29 3.73 3.89 439 170 227 0.529 92.2 1.66 5.92
(1.80) (2.05) (1.77) (2.01) (1.80) (1.60) (1.85) (2.30) (1.85) (1.51) (1.82) (1.77) (2.13) (1.45) (1.80) (1.64) (2.50) (1.45) (2.06) (2.13) (1.62) (1.50) (2.04) (1.87) (1.79)
103
103
103
103
Geometric mean and geometric standard deviation in parenthesis.
be inter-related each other. On Factor 4, loading of Cr, Ni, and Mo was great indicating that this factor is related to stainless-steel. On factor 5, loading of Pb was great along with Sb and Sn. Figs. 2 and 3 presents scatter plot of the log-transformed concentrations of Sn and Pb and those of Sb and Pb, respectively. Highly significant correlation was observed for these pairs (r ¼ 0.465, p < 0.001 for SnePb; r ¼ 0.405, p < 0.001 for SbePb). Factor 6 was considered biological material-related because of great loading of biogenic elements S and P. Estimated maximum daily exposure levels of toxic metals, of which EF was >10 (Fig. 1), through ingestion of house dust was shown in Table 5 along with dietary intake for reference. All of the ratios of exposure level from house dust to tolerable intake were less than 5%.
4. Discussion 4.1. Element concentrations in house dust of Japanese residences This was the first study to present multi-element profile of house dust collected from Japanese households except for our previous small-scale study in which results for a part of samples of this study (27 samples from Metropolitan Tokyo and Hiroshima in Table 1) was reported (Kaido et al., 2009). Table 6 compared geometric mean concentrations of multi-elements in house dust obtained in this study with reported values in Canada (Rasmussen et al., 2001), Australia (Chattopadhyay et al., 2003) and UK (Turner and Simmonds, 2006). It must be noted that comparison may not be appropriate because particulate diameter of sample and
Fig. 1. Enrichment factor (EF) of elements in house dust collected from general Japanese residences. For definition of EF, see text.
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J. Yoshinaga et al. / Environmental Pollution 189 (2014) 223e228
Table 4 Result of factor analysis after principal component extraction and Varimax rotation. Factor 1
Factor 2
Factor 3
Factor 4
Factor 5
Factor 6
Eigenvalue
6.607
3.432
2.238
2.077
1.760
1.735
Cumulative %
26.43
40.16
49.11
57.41
64.46
71.40
Al Ca Co Fe Mg Mn Sr Ti V Ba K Na U Cd Cu Zn Cr Mo Ni Pb Sb Sn P S
0.695 0.549 0.842 0.862 0.840 0.865 0.721 0.771 0.902 0.304 0.239 0.353 0.341 0.105 0.079 0.057 0.171 0.125 0.389 0.236 0.067 0.038 0.105 0.285
0.581 0.037 0.212 0.281 0.065 0.379 0.437 0.230 0.182 0.447 0.842 0.557 0.735 0.234 0.038 0.035 0.048 0.329 0.082 0.212 0.202 0.177 0.035 0.223
0.006 0.122 0.125 0.078 0.064 0.008 0.059 0.204 0.111 0.360 0.001 0.256 0.167 0.588 0.786 0.804 0.079 0.121 0.370 0.269 0.132 0.018 0.022 0.229
0.030 0.122 0.286 0.242 0.108 0.174 0.044 0.141 0.047 0.037 0.060 0.113 0.209 0.294 0.037 0.069 0.824 0.555 0.554 0.389 0.097 0.289 0.028 0.292
0.008 0.122 0.095 0.055 0.088 0.080 0.061 0.102 0.071 0.143 0.004 0.138 0.044 0.136 0.233 0.085 0.064 0.300 0.132 0.637 0.794 0.644 0.061 0.104
0.280 0.431 0.037 0.032 0.127 0.010 0.231 0.011 0.064 0.266 0.171 0.011 0.234 0.070 0.072 0.100 0.193 0.145 0.083 0.139 0.026 0.016 0.848 0.635
Maximum loading was denoted in italic.
digestion method was different from study to study. The digestion employed in Canadian study (HNO3/HF) was the most similar to ours (HNO3/HClO4/HF) in that silicate was destroyed by HF and may allow us to compare with. Generally, element concentration was higher in the Canadian study than in ours except for Ni and V which exhibited similar to ours and Cu, Sb, and Zn concentrations which were higher in ours. Higher concentrations of Al, Fe, Mn, alkali and alkaline earth elements in Canadian house dust might be ascribed to greater abundance of track-in soil particles than in Japanese residences where people take off shoes at the entrance. 4.2. Source of Pb in house dust The present EF calculation indicated that the abundance of Pb and other elements (Cd, Cu, Mo, P, S, Sn, Sb, and Zn) were >10 times condensed in house dust than natural occurrence (Fig. 1). This indicated that Pb and these elements in house dust were anthropogenic contamination origin. It is possible that track-in of soil particles and outdoor dust, that were contaminated with
Fig. 3. Scatter plot of the concentrations of Sb and Pb in house dust.
anthropogenic Pb, were the source of metals in house dust, however it would not be the case. The result of our factor analysis indicated that Pb and these metals had greater loading on other factors than soil-related Factors 1 and 2 (Table 4). Moreover, with regard to Pb, the results of our previous studies support the idea that Pb in house dust was not primarily from soil. Ishibashi et al. (2008) have examined the relationship between Pb concentration in house dust and those in garden soil for 41 households in Japan, and found only a weak correlation with marginal significance between the two. They inferred this result that track-in of soil was not at least major source of Pb in house dust. Kaido et al. (2009) compared intra-collective housing variation in Pb concentration in house dust with inter-collective housing variation in Tokyo Metropolitan area and Hiroshima Prefecture, Japan. The result showed that intra-collective housing variation, i.e., inter-household variation in a collective housing, was larger than inter-collective housing, i.e., geographic variation, indicating that indoor factor(s) was a major contributor to house dust Pb concentration. The result of the present factor analysis and other previous findings of ours indicated that Pb in house dust in Japanese households largely came from indoor environment though a minor contribution from soil cannot be ruled out (Ishibashi et al., 2008).
Table 5 Comparison of estimated daily exposure to metals through house dust ingestion of children with median dietary intake of the Japanese and tolerable intakes.
Cd Cu Mo Pb Sb Sn Zn
Fig. 2. Scatter plot of the concentrations of Sn and Pb in house dust.
House dusta (mg/day)
Dietb (mg/day)
Tolerable intakec (mg/person/day)
House dust/ Tolerable intake
0.10 27 2.0 4.9 0.89 1.7 90
13 5.7 1.0 5.3 1.2 1.6 4.9
19 (10 103) (5.4 102) e 7.5 37 103 (40 103)
0.005 0.003 0.004 e 0.12 0.00005 0.002
102 102
102 103
a Estimated maximum daily exposure level: [median concentration] [house dust ingesttion rate 100 mg/day]. b Duplicated diet data of 5-yrs old children from Aung et al. (2006) except for Sb that was estimated from adult intake (1.7 mg/day) reported by Oguri and Yoshinaga (2013) and average daily calory intake of children and adult Japanese (MHLW, 2012). c Reference dose for Cd and Sb from US EPA, and tolerable daily intake for Sn from JECFA. Tolerable upper limit intake for essential trace element Cu, Mo and Zn from Ministry of Health, Labor and Welfare (MHLW) of Japan was given for children but only for adult, which is in the parenthesis. All of the values are converted to mg/ person/day unit by assuming 18.7 kg body weight of 5-years-old child (MHLW, 2012). Tolerable intake for Pb is still under discussion in health authorities and not yet determined at present.
J. Yoshinaga et al. / Environmental Pollution 189 (2014) 223e228 Table 6 Comparison of geometric mean elemental concentration in house dust reported in the present and previous studies.
Al Ba Ca Cd Co Cr Cs Cu Fe K Mg Mn Mo Na Ni P Pb S Sb Sn Sr Ti V U Zn a b c
Unit
This study N ¼ 100
Canadaa N ¼ 48
% mg/kg % mg/kg mg/kg mg/kg mg/kg mg/kg % % % mg/kg mg/kg % mg/kg % mg/kg % mg/kg mg/kg mg/kg % mg/kg mg/kg mg/kg
1.57 208 2.25 1.02 4.69 67.8 0.711 304 1.00 0.687 0.400 226 2.11 0.827 59.6 0.110 57.9 0.552 10.1 18.4 66.8 0.152 24.7 0.401 920
2.43 454 4.67 4.42 8.40 75.4 171 1.32 1.00 0.944 260 1.96 2.04 53.6 0.134 233
Australiab N ¼ 82
0.795
1.9
1.2
64.3 103 0.274
54.0
15.6 85.2
5.54 21.9 242 23.7 0.55 628
UKc N ¼ 32
301 0.874
524
53.1 150
23.9
437
622
Rasmussen et al. (2001): 100e250 mm, HNO3/HF digestion. Chattopadhyay et al. (2003): <100 mm, HNO3 digestion. Turner and Simmonds (2006): <63 mm, HCl/HNO3 digestion.
Pb exhibited great loading on Factor 5 along with Sb and Sn (Table 4). This result suggested that mechanism of house dust contamination by Pb is different from that of typical heavy metals, such as Cd, Cu, and Zn that showed great loading on Factor 3, a tentatively designated as atmospheric particle factor. It’s rather surprising because close correlation has often been seen between the concentrations of Pb and these heavy metals (particularly Cu and Zn) not only in the urban atmosphere but also in soil environment of various countries (e.g., Marcazzan et al., 2001; Manta et al., 2002; Balasubramanian and Qian, 2004; Li et al., 2004; Möller et al., 2005) including Japan (Sakata et al., 2000; Takaoka et al., 2007). The source of Pb and Zn or Cu in atmosphere and soil has often been considered traffic and waste incineration. Thus Pb in house dust was not considered primarily originated from atmospheric particles from the present factor analysis. This is partly in accordance with the result of Ishibashi et al. (2008) who found only marginally significant correlation between Pb in house dust and in outdoor dust (exterior windowsill dust) in 41 households in Japan. Instead, the result suggested that Pb share a common mechanism of house dust contamination with Sb and Sn; Figs. 2 and 3 visually indicate close relationships between Sn and Pb, and between Sb and Pb in house dust. Pb and Sn were common components of solder though non-Pb solder has been in wide use today. However, there still may be products such as cans and electronic devices, manufactured in the past and SnePb solder was applied, in indoor environment and these may be ascribed to coexistence of these two elements in house dust (Fig. 2). It has been recognized that Pb and Sb were often detected at elevated levels in various toys and others made of plastic and cheap jewelries made of metals (Guney and Zagury, 2013; Korfali et al., 2013). The debris from worn out such products may be related to highly significant correlation between Sb and Pb concentrations in house dust (Fig. 3). However, there is no idea regarding how common mechanism(s) involving all of the three metals (Pb, Sn, and Sb) works. It is
227
possible that Factor 5 reflects separate two different relationships i.e., PbeSn and PbeSb, were coincided by chance. Anyway, it was indicated that identification of the sources of Sb and Sn in house dust would be useful for source identification of Pb. 4.3. Element contamination of house dust Apart from Pb, the factor analysis of the present study suggested sources of element contamination of house dust. With regard to Factor 4, loading of Cr, Mo and Ni was noted (Table 4). These elements are major components of stainless steel. Therefore, it is speculated that stainless steel debris is a common constituent of house dust. Other possibility is that contamination of samples during analytical procedure of our house dust sample took place; use of stainless steel mesh to prepare house dust sample from vacuum cleaner dust might be the contamination source. The fact that Cr or Ni concentrations in house dust samples of the present study was not higher than the literature values (Table 6) suggested that the analytical contamination was unlikely the case. Factor 6 had high loadings of P and S. These were biogenic elements and this factor suggested that biological material, such as food debris and small insects, was one of major constituents of house dust. 4.4. Health risk of children associated with unintentional house dust ingestion Although some metals were found at more condensed levels in house dust than the natural occurrence by >10 times (Fig. 1), estimated exposure of children to those metals via the unintentional ingestion of house dust were lower than the average dietary intake levels except for Pb and Sb that were estimated to be the same levels with dietary intake (Table 5). It must be noted that bioaccessibility/bioavailability of metals in house dust was not considered in this estimation but only the total concentration was used for calculation; in this sense, the estimate was upper bound. In any cases, exposure levels through house dust ingestion were less than tolerable intake levels (0.00004 for Sn to 0.12 for Sb) and the associated health risks were found to be minimal. Since tolerable intake level of Pb is currently under consideration in international authorities such as EFSA, it is premature to conclude if Pb in house dust is at risk for general Japanese adult or not. 5. Conclusion Factor analysis based on multi-element data of house dust, collected from general Japanese residences, indicated that 1) soil was not a major source of Pb in house dust, 2) Pb did not share common contamination mechanism with Cd, Cu or Zn, which have been indicated to have close relationships in soil and atmospheric particles in the previous studies, and 3) instead Pb had close relationship with Sb and Sn in house dust. The present study offered an important clue to identify the source of Pb in house dust of Japanese residences and, consequently, to further lower Pb exposure level of Japanese children. Health risk of Japanese children due to exposure to potentially toxic metals (Cd, Cu, Mo, Pb, Sb, Sn, and Zn) through unintentional ingestion of house dust may not be problematic except for Pb for which tolerable daily intake information is lacking and thus assessment was not possible. Abbreviations Al Ba Ca
aluminum barium calcium
228
Cd Co Cr Cs Cu Fe K Mg Mn Mo Na Ni P Pb S Sb Sn Sr Ti U V Zn
J. Yoshinaga et al. / Environmental Pollution 189 (2014) 223e228
cadmium cobalt chromium cesium copper iron potassium magnesium manganese molybdenum sodium nickel phosphorus lead sulfur antimony tin strontium titanium uranium vanadium zinc
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Landrigan, P.J., Schechter, C.B., Lipton, J.M., Fahs, M.C., Schwartz, J., 2002. Environmental pollution and disease in American children: estimates of morbidity, mortality, and costs for lead poisoning, asthma, cancer, and developmental disabilities. Environ. Health Perspect. 110, 721e728. Lanphear, B.P., Matte, T.D., Rogers, J., Clickner, R.P., Dietz, B., et al., 1998. The contribution of lead-contaminated house dust and residential soil to children’s blood lead levels. Environ. Res. 79, 51e68. Lanphear, B.P., Hornung, R., Khoury, J., Yolton, K., Baghurst, P., et al., 2005. Low-level environmental lead exposure and children’s intellectual function: an international pooled analysis. Environ. Health Perspect. 113, 894e899. Li, X., Lee, S., Wong, S., Shi, W., Thornton, I., 2004. The study of metal contamination in urban soils of Hong Kong using GIS-based approach. Environ. Pollut. 129, 113e124. Manta, D.S., Angelone, M., Bellanca, A., Neri, R., Sprovieri, M., 2002. Heavy metals in urban soils: a case study from the city of Palermo (Sicily), Italy. Sci. Total Environ. 300, 229e243. Marcazzan, G.M., Vaccaro, S., Valli, G., Vecchi, R., 2001. Characterization of PM10 and PM2.5 particulate matter in the ambient air of Milan (Italy). Atmos. Environ. 35, 4639e4650. Ministry of Health, Labour and Welfare of Japan, 2012. National Health and Nutrition Examination Survey in 2011. http://www.mhlw.go.jp/bunya/kenkou/eiyou/ h23-houkoku.html (in Japanese). (Accessed 01.11.13.). Möller, A., Müller, H.W., Abdullah, A., Abdelgawad, G., Utermann, J., 2005. Urban soil pollution in Damascus, Syria: concentrations and patterns of heavy metals in the soils of the Damascus Ghouta. Geoderma 124, 63e71. Oguri, Y., Yoshinaga, J., 2013. Market basket survey of trace metal intake in Shizuoka City, Japan. Biomed. Res. Trace Elem. 24, 13e22 (in Japanese with English abstract). Rasmussen, P.E., Subramanian, K.S., Jessiman, B.J., 2001. A multi-element profile of housedust in relation to exterior dust and soils in the city of Ottawa, Canada. Sci. Total Environ. 267, 125e140. Rudnick, R.L., Gao, S., 2004. The curst. In: Rudnick, R.L. (Ed.), Treatise on Geochemistry, vol. 3. Elsevier, Oxford, pp. 1e64. Sakata, M., Kurata, M., Tanaka, N., 2000. Estimating contribution from municipal solid waste incineration to trace metal concentrations in Japanese urban atmosphere using lead as a marker element. Geochem. J. 34, 23e32. Su, M., Barrueto Jr., F., Hoffman, R.S., 2002. Childhood lead poisoning from paint chips: a continuing problem. J. Urban Health 79, 491e501. Takagi, M., 2010. Exposure of Children to Chemicals Through House Dust Ingestion. University of Tokyo (Doctoral thesis). Takagi, M., Yoshinaga, J., Seyama, H., Tanaka, A., 2011. Isotope ratio measurement of lead in blood and environmental samples by multi-collector inductively coupled plasma mass spectrometry. Anal. Sci. 27, 29e35. Takaoka, M., Yoshinaga, J., Tanaka, A., 2007. Relationship between heavy metal concentrations in playground soil in Tokyo. J. Environ. Chem. 17, 629e634 (in Japanese with English abstract). Turner, A., Simmonds, L., 2006. Elemental concentrations and metal bioavailability in UK household dust. Sci. Total Environ. 371, 74e81. US EPA, 2011. Exposure Factors Handbook: 2011 Edition (EPA/600/R-090/052F) Washington DC. Yamamoto, N., Takahashi, Y., Yoshinaga, J., Tanaka, A., Shibata, Y., 2006. Size distribution of soil particles adhered on children’s hands. Arch. Environ. Contam. Toxicol. 51, 157e163. Yoshinaga, J., Takagi, M., Yamasaki, K., Tamiya, S., Watanabe, C., Kaji, M., 2012. Blood lead levels of contemporary Japanese children. Environ. Health Prev. Med. 17, 27e33.
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Lead and other elements in house dust of Japanese residences e Source of lead and health risks due to metal exposure Jun Yoshinaga a, *, Kumiko Yamasaki a, Ayumi Yonemura a, Yuri Ishibashi b, Takaya Kaido b, Kodai Mizuno b, Mai Takagi c, Atsushi Tanaka c a b c
Department of Environmental Studies, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8563, Japan Kitasato University, Kitasato 1-15-1, Sagamihara, Kanagawa 228-8555, Japan National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-8506, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 December 2013 Received in revised form 3 March 2014 Accepted 8 March 2014
The levels of 25 elements in house dust collected from 100 general Japanese residences were measured. Factor analysis was applied on the multi-element data to explore source of Pb (median concentration 49.1 mg/kg) in house dust. Six factors were extracted and Pb was found to have great loading on the fifth factor with Sb and Sn, suggesting solder (Sn), and plastic and metals (Sb) may be the sources of Pb in the house dust of Japanese residences. No significant loading was found on soil-related factors indicating non-significant contribution of Pb in track-in soil. Seven heavy metals (Cd, Cu, Mo, Pb, Sb, Sn, and Zn) were found in house dust at >10 times more condensed than crustal abundance. Health risk of these elements to children via the ingestion of house dust was estimated based on the comparison with tolerable daily intake and found to be non-significant for most of the elements. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: House dust Pb (lead) Factor analysis Sb (antimony) Sn (tin) Health risk
1. Introduction Adverse effect of Pb on children’s health has become a matter of worldwide public health concern because it has been shown that even a low level exposure could result in deficit in cognitive development, which could subsequently result in massive economic loss at nation level (Landrigan et al., 2002; Grosse et al., 2002; Gould, 2009). House dust has long been recognized as major source of Pb for children (Lanphear et al., 1998) and concern has been raised particularly in the United States where Pb-based paint was in use for residence until late 1970s. Paint chips from inside the residence could directly contaminate house dust. Paint chips from outside of residence, as well as contaminated residential soil, could indirectly contaminate house dust by track-in of soil particles. Contaminated house dust could be ingested by infants and children by normal hand-to-mouth activity resulting in Pb poisoning (Su et al., 2002). However, house dust was the major source of Pb for children where residential Pb-based paint had not been used: for instance, in Japan, people do not have custom to paint their residence not
* Corresponding author. E-mail address: [email protected] (J. Yoshinaga). http://dx.doi.org/10.1016/j.envpol.2014.03.003 0269-7491/Ó 2014 Elsevier Ltd. All rights reserved.
only present days but also in the past but house dust was still found to be a significant source of Pb for children. Aung et al. (2004) estimated that 50% of daily Pb exposure of Japanese children was from house dust based on the analyses of Pb in house dust, soil and duplicated diet. Takagi et al. (2011) demonstrated that isotope ratios of Pb in children’s blood and those in house dust were close to each other based on high-precision Pb isotope analysis. Although Pb exposure level of Japanese children has been among the lowest in the world (Yoshinaga et al., 2012), identification of source of Pb in house dust and subsequent risk reduction may be desirable because threshold for deleterious effect of Pb for cognitive development of children was postulated to be absent (Lanphear et al., 2005). In this study, multi-element analysis of house dust samples collected from 100 residences of the general Japanese was carried out and factor analysis was applied to the multi-element data to find elements that have close association with Pb. This information will help to get insight into the source of Pb in house dust in residences in Japan and other countries where no particular source(s), such as Pb-based paint and gasoline additives, is known. Additionally, general profile of element composition of house dust of Japanese residence was presented and their associated health risk for children was estimated.
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2. Materials and methods The house dust samples analyzed in this study were prepared from vacuum cleaner dust collected from the general households in Japan. Four separated samplings were carried out during 2006e2012 (Table 1) from the households in residential areas with no known Pb point sources. Staffs and students of the authors’ laboratory asked their acquaintances for cooperation for vacuum dust sampling. In some sampling, vacuum cleaner dust sampling period was specified to be 30 days but sampling period was not specified in the other. Thus, the samples of this study were not randomly collected but were obtained by ad-hoc manner. Cadmium and Pb results for some samples were published in Ishibashi et al. (2008) and multielement data of 27 sampled in 2007 were published in Kaido et al. (2009). Vacuum dust was passed through stainless-steel 250 mm-mesh using a mechanical shaker (AS-200, Retsch, Haan, Germany) and the passed fraction was used for analysis because it was likely to adhered on children’s hands (Yamamoto et al., 2006). An aliquot (100 mg) of the house dust sample was digested with HNO3/HF/ HClO4 in a Teflon beaker on a hot plate. After digestion, acid was evaporated to dryness and the residue was re-dissolved in 50 g of 0.14 mol/L HNO3. Acids used were of the purest grade commercially available (AA series, Tama Chemical Co. Ltd, Kawasaki, Japan) and Millipore (Waters, Tokyo, Japan) purified water was used throughout. The concentration of Al, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, Sr, Ti, V and Zn were determined by ICP atomic emission spectrometry (ICAP-750, Nippon JarrellAsh, Tokyo, Japan) from the digested sample. Spectroscopic interferences from major element (Al, Ca, and Fe) to Ni, P, and V were corrected. The sample solution was further diluted 20 times and Cd, Co, Cs, Mo, Pb, Sb, Sn, and U concentrations were determined by ICP mass spectrometry (7500ce, Agilent Technologies Japan, Tokyo, Japan) using Rh (1 ppb) as internal standard. Moisture content of house dust sample was measured separately from the sample for digestion. Weight loss after 110 C heating for 2 h was regarded as moisture. A certified reference material (CRM) of house dust matrix (NIST SRM 2598 Indoor Dust) was concurrently analyzed with house dust samples for analytical quality assurance throughout the whole study period. In Table 2 presented the results of our CRM analyses. Note that certified value was given only for Cd, Cr, and Pb of our analytes and the mean values for these three elements agreed well with the certified values. Although relative standard deviations of element concentrations were larger than expected from the concentration level and measurement precision of ICP atomic emission spectrometry or ICP mass spectrometry, it might be due to sample inhomogeneity of this CRM; this may be justified by the large uncertainty attached to the certified values. Element concentrations were converted to dry-weight basis and distribution was tested for normality. All of the element concentrations were not normally distributed and log-transformation was needed to approximate them to normality. Factor analysis using principal component method as extraction with Varimax rotation was applied to log-transformed element concentrations. SPSS for Windows ver 19.0 (IBM, Tokyo, Japan) was used for statistical analyses. In order to characterize element profile in house dust, enrichment factor (EF) was calculated by the following equation: EF ¼
EHD =AlHD ECR =AlCR
where E indicates element concentration (median) and subscripts HD and CR indicate house dust and abundance of element in earth’s crust (crustal abundance), respectively. Crustal abundance of element was adopted from Rudnick and Gao (2004). Daily exposure of children to potentially toxic metals through unintentional house dust ingestion was estimated by multiplying median concentration obtained in the present study and ingestion rate of house dust to be 100 mg/day (Recommended value for daily dust ingestion, general population upper percentile value) (US EPA, 2011). The estimated exposure level was compared with dietary intake (Aung et al., 2006; Oguri and Yoshinaga, 2013) and their ratios to tolerable intakes (WHO Provisional Tolerable Weekly Intake (PTWI) for Sn and EPA Reference Dose for
Table 1 Location and period of house dust samplings and number of samples included in this study. Location
Period
Number of samplesa
Reference
19 Prefectures of Japan Metropolitan Tokyo & Hiroshima Metropolitan Tokyo Metropolitan Tokyo (Chiba) Total
2006 2007 2009 2012
38 (38) 27 (2) 15 (9)b 20 (2) 100
Ishibashi et al., 2008 Kaido et al., 2009 Takagi, 2010 None
a Number of samples from detached housing was shown in parenthesis; others were from collective housings. b Information of two households on detached/collective was missing.
Table 2 Analytical results of NIST SRM 2583 Indoor Dust.
Al Ba Ca Cd Co Cr Cs Cu Fe K Mg Mn Mo Na Ni P Pb S Sb Sn Sr Ti V U Zn
Unit
Measured (n ¼ 17)a
% mg/kg % mg/kg mg/kg mg/kg mg/kg mg/kg % % % mg/kg mg/kg % mg/kg % mg/kg % mg/kg mg/kg mg/kg % mg/kg mg/kg mg/kg
1.94 259 3.12 6.86 6.17 65.8 0.96 242 0.950 0.836 0.883 222 3.55 9.53 91.2 0.207 83.4 4.52 9.42 21.3 102 0.210 23.1 1.09 906
0.05 9 0.23 1.16 0.28 9.1 0.12 20 0.022 0.050 0.042 7 0.28 0.28 11.2 0.011 5.9 0.16 0.55 3.5 7 0.010 4.3 0.15 30
Certified
7.3 3.7 80 22
85.9 7.2
a Arithmetic mean standard deviation of measured values obtained from replicated analyses.
others) were calculated for the evaluation of health risks of children associated with house dust ingestion (WHO PTWI for Sn is available at http://www.inchem.org/ documents/jecfa/jecmono/v46je12.htm#_46125000 and Reference Doses for others are available at http://www.epa.gov/IRIS/). A 5-years-old child with 18.7 kg body weight consuming 1281 kcal/day of energy was assumed (Ministry of Health, Labor and Welfare of Japan, 2012)).
3. Results Table 3 shows dry weight element concentrations in house dust samples analyzed in this study. Among the elements determined, Ca was the most abundant followed by Al, Fe, Na, K, and S in this order. Median and geometric mean concentration of Pb was 49.1 and 57.9 mg/kg, respectively, with a large variation (up to 0.373%) (Table 3). Fig. 1 shows EF of elements in house dust samples of Japanese residences. The EF was around 1 for many elements but EF of Pb along with that of Cd, Cu, Mo, P, S, Sb, Sn and Zn exceeded 10 indicating that the abundance of these elements was more condensed in house dust than natural occurrence. Note that we did not carry out statistical analyses examining variation in element concentrations due to 4 sampling occasions, difference in element concentrations between detached and collective housings, or correlation of element concentrations with age of residence because of our ad-hoc sampling designs and unsuitability for such statistical analyses. Table 4 shows the result of factor analysis. Six factors were extracted with initial eigenvalue >1.0, by which 71.4% of total variance was explained. Factor loadings of Al, Fe, Mn, Ti, V and alkaline earth metals were great on Factor 1 and thus it indicated that the factor was soil-related. On Factor 2, loading of Al was moderately high (0.581) and that of alkali metal and U was the highest: thus Factor 2 was also considered soil or other geogenic material related but more association with alkali metals than Factor 1 was noted. On Factor 3, Cd, Cu, and Zn showed great loading indicating that this factor was common heavy metal-related. This could be inferred as airborne particulate-related because abundances of these elements in atmospheric particles were known to
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225
Table 3 Element concentrations in house dust samples collected from Japanese residences (n ¼ 100, dry weight basis).
Al Ba Ca Cd Co Cr Cs Cu Fe K Mg Mn Mo Na Ni P Pb S Sb Sn Sr Ti V U Zn a
Unit
Mean (SD)a
Min
5th
25th
50th
75th
95th
Max
% mg/kg % mg/kg mg/kg mg/kg mg/kg mg/kg % % % mg/kg mg/kg % mg/kg % mg/kg % mg/kg mg/kg mg/kg % mg/kg mg/kg mg/kg
1.57 208 2.25 1.02 4.69 67.8 0.711 304 1.00 0.687 0.400 226 2.11 0.827 59.6 0.110 57.9 0.552 10.1 18.4 66.8 0.152 24.7 0.401 920
0.328 31.9 0.397 0.175 0.794 14.8 0.137 66.8 0.161 0.279 0.0742 38.6 0.501 0.368 13.2 0.0347 11.9 0.258 1.93 3.13 12.0 0.0342 3.79 0.094 188
0.525 75.4 0.940 0.277 1.84 34.6 0.241 87.9 0.337 0.354 0.141 80.5 0.847 0.465 25.1 0.0544 17.7 0.307 4.31 6.58 28.5 0.0745 7.31 0.172 434
1.05 132 1.56 0.61 3.15 50.3 0.463 181 0.676 0.523 0.271 165 1.28 0.651 38.7 0.0852 33.0 0.446 6.62 11.4 47.4 0.119 15.6 0.232 644
1.62 207 2.33 1.04 4.43 66.3 0.716 266 1.01 0.666 0.379 224 2.03 0.807 56.5 0.104 49.1 0.533 8.85 17.3 69.2 0.150 24.6 0.381 896
2.43 282 2.93 1.64 6.88 93.0 1.06 511 1.60 0.836 0.575 327 2.99 1.06 89.4 0.142 86.3 0.687 13.4 25.8 87.8 0.191 43.1 0.625 1.22 103
3.88 719 6.29 3.46 12.1 161 1.97 1.61 103 3.06 1.47 1.05 551 10.4 1.43 173 0.243 267 0.926 22.7 87.3 156 0.269 76.7 1.31 3.50 103
4.88 3.51 13.2 5.62 18.5 285 3.75 7.72 4.01 2.17 4.17 679 78.7 3.20 390 2.29 3.73 3.89 439 170 227 0.529 92.2 1.66 5.92
(1.80) (2.05) (1.77) (2.01) (1.80) (1.60) (1.85) (2.30) (1.85) (1.51) (1.82) (1.77) (2.13) (1.45) (1.80) (1.64) (2.50) (1.45) (2.06) (2.13) (1.62) (1.50) (2.04) (1.87) (1.79)
103
103
103
103
Geometric mean and geometric standard deviation in parenthesis.
be inter-related each other. On Factor 4, loading of Cr, Ni, and Mo was great indicating that this factor is related to stainless-steel. On factor 5, loading of Pb was great along with Sb and Sn. Figs. 2 and 3 presents scatter plot of the log-transformed concentrations of Sn and Pb and those of Sb and Pb, respectively. Highly significant correlation was observed for these pairs (r ¼ 0.465, p < 0.001 for SnePb; r ¼ 0.405, p < 0.001 for SbePb). Factor 6 was considered biological material-related because of great loading of biogenic elements S and P. Estimated maximum daily exposure levels of toxic metals, of which EF was >10 (Fig. 1), through ingestion of house dust was shown in Table 5 along with dietary intake for reference. All of the ratios of exposure level from house dust to tolerable intake were less than 5%.
4. Discussion 4.1. Element concentrations in house dust of Japanese residences This was the first study to present multi-element profile of house dust collected from Japanese households except for our previous small-scale study in which results for a part of samples of this study (27 samples from Metropolitan Tokyo and Hiroshima in Table 1) was reported (Kaido et al., 2009). Table 6 compared geometric mean concentrations of multi-elements in house dust obtained in this study with reported values in Canada (Rasmussen et al., 2001), Australia (Chattopadhyay et al., 2003) and UK (Turner and Simmonds, 2006). It must be noted that comparison may not be appropriate because particulate diameter of sample and
Fig. 1. Enrichment factor (EF) of elements in house dust collected from general Japanese residences. For definition of EF, see text.
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J. Yoshinaga et al. / Environmental Pollution 189 (2014) 223e228
Table 4 Result of factor analysis after principal component extraction and Varimax rotation. Factor 1
Factor 2
Factor 3
Factor 4
Factor 5
Factor 6
Eigenvalue
6.607
3.432
2.238
2.077
1.760
1.735
Cumulative %
26.43
40.16
49.11
57.41
64.46
71.40
Al Ca Co Fe Mg Mn Sr Ti V Ba K Na U Cd Cu Zn Cr Mo Ni Pb Sb Sn P S
0.695 0.549 0.842 0.862 0.840 0.865 0.721 0.771 0.902 0.304 0.239 0.353 0.341 0.105 0.079 0.057 0.171 0.125 0.389 0.236 0.067 0.038 0.105 0.285
0.581 0.037 0.212 0.281 0.065 0.379 0.437 0.230 0.182 0.447 0.842 0.557 0.735 0.234 0.038 0.035 0.048 0.329 0.082 0.212 0.202 0.177 0.035 0.223
0.006 0.122 0.125 0.078 0.064 0.008 0.059 0.204 0.111 0.360 0.001 0.256 0.167 0.588 0.786 0.804 0.079 0.121 0.370 0.269 0.132 0.018 0.022 0.229
0.030 0.122 0.286 0.242 0.108 0.174 0.044 0.141 0.047 0.037 0.060 0.113 0.209 0.294 0.037 0.069 0.824 0.555 0.554 0.389 0.097 0.289 0.028 0.292
0.008 0.122 0.095 0.055 0.088 0.080 0.061 0.102 0.071 0.143 0.004 0.138 0.044 0.136 0.233 0.085 0.064 0.300 0.132 0.637 0.794 0.644 0.061 0.104
0.280 0.431 0.037 0.032 0.127 0.010 0.231 0.011 0.064 0.266 0.171 0.011 0.234 0.070 0.072 0.100 0.193 0.145 0.083 0.139 0.026 0.016 0.848 0.635
Maximum loading was denoted in italic.
digestion method was different from study to study. The digestion employed in Canadian study (HNO3/HF) was the most similar to ours (HNO3/HClO4/HF) in that silicate was destroyed by HF and may allow us to compare with. Generally, element concentration was higher in the Canadian study than in ours except for Ni and V which exhibited similar to ours and Cu, Sb, and Zn concentrations which were higher in ours. Higher concentrations of Al, Fe, Mn, alkali and alkaline earth elements in Canadian house dust might be ascribed to greater abundance of track-in soil particles than in Japanese residences where people take off shoes at the entrance. 4.2. Source of Pb in house dust The present EF calculation indicated that the abundance of Pb and other elements (Cd, Cu, Mo, P, S, Sn, Sb, and Zn) were >10 times condensed in house dust than natural occurrence (Fig. 1). This indicated that Pb and these elements in house dust were anthropogenic contamination origin. It is possible that track-in of soil particles and outdoor dust, that were contaminated with
Fig. 3. Scatter plot of the concentrations of Sb and Pb in house dust.
anthropogenic Pb, were the source of metals in house dust, however it would not be the case. The result of our factor analysis indicated that Pb and these metals had greater loading on other factors than soil-related Factors 1 and 2 (Table 4). Moreover, with regard to Pb, the results of our previous studies support the idea that Pb in house dust was not primarily from soil. Ishibashi et al. (2008) have examined the relationship between Pb concentration in house dust and those in garden soil for 41 households in Japan, and found only a weak correlation with marginal significance between the two. They inferred this result that track-in of soil was not at least major source of Pb in house dust. Kaido et al. (2009) compared intra-collective housing variation in Pb concentration in house dust with inter-collective housing variation in Tokyo Metropolitan area and Hiroshima Prefecture, Japan. The result showed that intra-collective housing variation, i.e., inter-household variation in a collective housing, was larger than inter-collective housing, i.e., geographic variation, indicating that indoor factor(s) was a major contributor to house dust Pb concentration. The result of the present factor analysis and other previous findings of ours indicated that Pb in house dust in Japanese households largely came from indoor environment though a minor contribution from soil cannot be ruled out (Ishibashi et al., 2008).
Table 5 Comparison of estimated daily exposure to metals through house dust ingestion of children with median dietary intake of the Japanese and tolerable intakes.
Cd Cu Mo Pb Sb Sn Zn
Fig. 2. Scatter plot of the concentrations of Sn and Pb in house dust.
House dusta (mg/day)
Dietb (mg/day)
Tolerable intakec (mg/person/day)
House dust/ Tolerable intake
0.10 27 2.0 4.9 0.89 1.7 90
13 5.7 1.0 5.3 1.2 1.6 4.9
19 (10 103) (5.4 102) e 7.5 37 103 (40 103)
0.005 0.003 0.004 e 0.12 0.00005 0.002
102 102
102 103
a Estimated maximum daily exposure level: [median concentration] [house dust ingesttion rate 100 mg/day]. b Duplicated diet data of 5-yrs old children from Aung et al. (2006) except for Sb that was estimated from adult intake (1.7 mg/day) reported by Oguri and Yoshinaga (2013) and average daily calory intake of children and adult Japanese (MHLW, 2012). c Reference dose for Cd and Sb from US EPA, and tolerable daily intake for Sn from JECFA. Tolerable upper limit intake for essential trace element Cu, Mo and Zn from Ministry of Health, Labor and Welfare (MHLW) of Japan was given for children but only for adult, which is in the parenthesis. All of the values are converted to mg/ person/day unit by assuming 18.7 kg body weight of 5-years-old child (MHLW, 2012). Tolerable intake for Pb is still under discussion in health authorities and not yet determined at present.
J. Yoshinaga et al. / Environmental Pollution 189 (2014) 223e228 Table 6 Comparison of geometric mean elemental concentration in house dust reported in the present and previous studies.
Al Ba Ca Cd Co Cr Cs Cu Fe K Mg Mn Mo Na Ni P Pb S Sb Sn Sr Ti V U Zn a b c
Unit
This study N ¼ 100
Canadaa N ¼ 48
% mg/kg % mg/kg mg/kg mg/kg mg/kg mg/kg % % % mg/kg mg/kg % mg/kg % mg/kg % mg/kg mg/kg mg/kg % mg/kg mg/kg mg/kg
1.57 208 2.25 1.02 4.69 67.8 0.711 304 1.00 0.687 0.400 226 2.11 0.827 59.6 0.110 57.9 0.552 10.1 18.4 66.8 0.152 24.7 0.401 920
2.43 454 4.67 4.42 8.40 75.4 171 1.32 1.00 0.944 260 1.96 2.04 53.6 0.134 233
Australiab N ¼ 82
0.795
1.9
1.2
64.3 103 0.274
54.0
15.6 85.2
5.54 21.9 242 23.7 0.55 628
UKc N ¼ 32
301 0.874
524
53.1 150
23.9
437
622
Rasmussen et al. (2001): 100e250 mm, HNO3/HF digestion. Chattopadhyay et al. (2003): <100 mm, HNO3 digestion. Turner and Simmonds (2006): <63 mm, HCl/HNO3 digestion.
Pb exhibited great loading on Factor 5 along with Sb and Sn (Table 4). This result suggested that mechanism of house dust contamination by Pb is different from that of typical heavy metals, such as Cd, Cu, and Zn that showed great loading on Factor 3, a tentatively designated as atmospheric particle factor. It’s rather surprising because close correlation has often been seen between the concentrations of Pb and these heavy metals (particularly Cu and Zn) not only in the urban atmosphere but also in soil environment of various countries (e.g., Marcazzan et al., 2001; Manta et al., 2002; Balasubramanian and Qian, 2004; Li et al., 2004; Möller et al., 2005) including Japan (Sakata et al., 2000; Takaoka et al., 2007). The source of Pb and Zn or Cu in atmosphere and soil has often been considered traffic and waste incineration. Thus Pb in house dust was not considered primarily originated from atmospheric particles from the present factor analysis. This is partly in accordance with the result of Ishibashi et al. (2008) who found only marginally significant correlation between Pb in house dust and in outdoor dust (exterior windowsill dust) in 41 households in Japan. Instead, the result suggested that Pb share a common mechanism of house dust contamination with Sb and Sn; Figs. 2 and 3 visually indicate close relationships between Sn and Pb, and between Sb and Pb in house dust. Pb and Sn were common components of solder though non-Pb solder has been in wide use today. However, there still may be products such as cans and electronic devices, manufactured in the past and SnePb solder was applied, in indoor environment and these may be ascribed to coexistence of these two elements in house dust (Fig. 2). It has been recognized that Pb and Sb were often detected at elevated levels in various toys and others made of plastic and cheap jewelries made of metals (Guney and Zagury, 2013; Korfali et al., 2013). The debris from worn out such products may be related to highly significant correlation between Sb and Pb concentrations in house dust (Fig. 3). However, there is no idea regarding how common mechanism(s) involving all of the three metals (Pb, Sn, and Sb) works. It is
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possible that Factor 5 reflects separate two different relationships i.e., PbeSn and PbeSb, were coincided by chance. Anyway, it was indicated that identification of the sources of Sb and Sn in house dust would be useful for source identification of Pb. 4.3. Element contamination of house dust Apart from Pb, the factor analysis of the present study suggested sources of element contamination of house dust. With regard to Factor 4, loading of Cr, Mo and Ni was noted (Table 4). These elements are major components of stainless steel. Therefore, it is speculated that stainless steel debris is a common constituent of house dust. Other possibility is that contamination of samples during analytical procedure of our house dust sample took place; use of stainless steel mesh to prepare house dust sample from vacuum cleaner dust might be the contamination source. The fact that Cr or Ni concentrations in house dust samples of the present study was not higher than the literature values (Table 6) suggested that the analytical contamination was unlikely the case. Factor 6 had high loadings of P and S. These were biogenic elements and this factor suggested that biological material, such as food debris and small insects, was one of major constituents of house dust. 4.4. Health risk of children associated with unintentional house dust ingestion Although some metals were found at more condensed levels in house dust than the natural occurrence by >10 times (Fig. 1), estimated exposure of children to those metals via the unintentional ingestion of house dust were lower than the average dietary intake levels except for Pb and Sb that were estimated to be the same levels with dietary intake (Table 5). It must be noted that bioaccessibility/bioavailability of metals in house dust was not considered in this estimation but only the total concentration was used for calculation; in this sense, the estimate was upper bound. In any cases, exposure levels through house dust ingestion were less than tolerable intake levels (0.00004 for Sn to 0.12 for Sb) and the associated health risks were found to be minimal. Since tolerable intake level of Pb is currently under consideration in international authorities such as EFSA, it is premature to conclude if Pb in house dust is at risk for general Japanese adult or not. 5. Conclusion Factor analysis based on multi-element data of house dust, collected from general Japanese residences, indicated that 1) soil was not a major source of Pb in house dust, 2) Pb did not share common contamination mechanism with Cd, Cu or Zn, which have been indicated to have close relationships in soil and atmospheric particles in the previous studies, and 3) instead Pb had close relationship with Sb and Sn in house dust. The present study offered an important clue to identify the source of Pb in house dust of Japanese residences and, consequently, to further lower Pb exposure level of Japanese children. Health risk of Japanese children due to exposure to potentially toxic metals (Cd, Cu, Mo, Pb, Sb, Sn, and Zn) through unintentional ingestion of house dust may not be problematic except for Pb for which tolerable daily intake information is lacking and thus assessment was not possible. Abbreviations Al Ba Ca
aluminum barium calcium
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Cd Co Cr Cs Cu Fe K Mg Mn Mo Na Ni P Pb S Sb Sn Sr Ti U V Zn
J. Yoshinaga et al. / Environmental Pollution 189 (2014) 223e228
cadmium cobalt chromium cesium copper iron potassium magnesium manganese molybdenum sodium nickel phosphorus lead sulfur antimony tin strontium titanium uranium vanadium zinc
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