Indoor dust samples were collected from homes (n = 45), offices (n = 20) and cars (n
= 20) within the West Midlands, UK. Dust was collected as described in chapter 2.
Generally domestic dust samples were collected from living rooms. However, in some cases, samples were collected from bedsits. The offices sampled ranged from closed single occupant office spaces, to open plan offices for up to 10 people. As described above for air samples, offices generally contained more electrical goods and foam chairs than homes, but fewer textiles and other consumer goods. The car samples varied greatly depending on the age and manufacturer of the car. There was a range across the samples from a 15 year old, 4 seater car, without carpet and a single analogue radio to a large people carrier, 2 years old, carpeted and upholstered throughout, and fitted with a DVD player, satellite navigation device, and digital stereo system. The differences are expected to provide large variance in compound detection and quantification.
Individual sample results and descriptive statistics for the three types of microenvironments are displayed in Table 43, Table 44, and Table 45. Results indicate the presence of PFCs in all samples, with PFOS (7400 ng g-1), PFOA (6000 ng g-1) and PFHxS (6100 ng g-1) present at some of the highest concentrations reported in this study as a whole. The persistent PFCs, which are also degradation products of the more volatile PFCs, are the predominant perfluorinated contaminants measured in dust, owing at least in part to their low vapour pressures and consequent preferential partitioning to dust. The more volatile compounds, EtFOSA, FOSA, MeFOSE and EtFOSE also had a high detection rate in the samples (> 80 %), whilst MeFOSA quantification was similar to the air samples, with sporadic detection in samples, leading to an overall < 40 % detection rate for the compound.
Table 43 UK home dust concentrations (ng g-1)
Table 44 UK office dust concentrations (ng g-1)
Table 45 UK car dust concentrations (ng g-1)
A comparison of the indoor microenvironment dust sample arithmetic mean dust concentrations are displayed in Figure 12. The ∑PFC concentrations are highest in office environments (2300 ng g-1), followed by homes (1900 ng g-1), yet concentrations from car environments were about half of the other two microenvironments (1200 ng g-1).
All indoor dust concentrations revealed positively skewed data (W < 0.885, p <
0.022), when subjected to the Shapiro-Wilk test for normality of data distribution;
therefore further statistical analysis was conducted on normalised (log-transformed) data. The arithmetic mean concentrations for each of the individual compounds and for ∑PFC in each microenvironment were compared, and significant differences were identified for FOSA in cars . The car dust samples reveal a significant difference (p <
0.001) when analysed (using the normalized data) via ANOVA for FOSA in car dust compared to both home and office dust. FOSA is a common intermediate degradation product of MeFOSE, EtFOSE (Plumlee et al., 2009) and other more volatile PFCs such as FTOH (Ellis et al., 2004).
Despite no other significant differences being identified between the microenvironments, trends are still noticeable within the data; this is particularly true of the ratios of PFOS:PFOA from the three dust microenvironments. In car and home dust, PFOS (mean, 450 ng g-1, 260 ng g-1, respectively) is more dominant; whereas PFOA (mean 550 ng g-1) is more prevalent in office dust. The presence of PFOA at higher concentrations could be indicative of the presence of precursor compounds such as FTOHs and PFOSEs (Jahnke et al., 2007b, D‘Hollander et al., 2010) in office equipment (Wallington et al., 2006).
For all compounds with the exception of FOSA, the car samples display the lowest mean concentrations (∑PFC = 1200 ng g-1). Vehicle concentrations are not
significantly different from the other microenvironments, but are generally less contaminated. However, the presence of FOSA in car samples (mean = 140 ng g-1) indicates opposite behaviour, with concentrations almost 3 times greater than in homes (mean = 54 ng g-1), and up to 7 times greater than offices (mean = 21 ng g-1).
FOSA in car samples contributes (on average) 10 % of the ∑PFC concentration, whilst in homes and offices this contribution, on average, is < 5 %. The removal of sample 13 (an outlier) from the analysis, the average contribution still remains above that of offices and homes (at 7 %). The presence of FOSA in cars is likely to originate from similar sources as other indoor environments, treated upholstery, leather treatments, electronic insulating wires etc. PFCs are also combined with many lubricants and surfactants used in the engine and mechanical parts (Drobny, 2005).
The car samples containing concentrations of FOSA were compared to their questionnaire data (see appendix), and no significant relationships were identified.
In comparison to concentrations found in dust samples from other countries (Table 46) the concentrations within this study are broadly similar to those reported in other studies. Comparisons of dust concentrations across different studies is complicated by various factors including analytical and sampling techniques, measurement of particulate and / or gaseous phase and identity of PFCs monitored. These parameters include whether the entire room, or a smaller area was sampled, or entire floor, or surface top dust was collected. The dust particle size range analysed is also an important parameter, as a negative relationship was identified between the particle size and the presence of PFCs by Fromme et al., (2008). Other parameters that would affect the results include the analytical methods employed. However, appropriate analytical QA/QC minimises the influence of this latter factor. Concentrations from the UK (this study) span a greater range for PFOS (3 – 7400 ng g-1) and PFOA (<DL -
4100 ng g-1) in homes compared to other studies (displayed in Table 46).
Concentrations from the UK (this study) span a greater range for PFOS (3 – 7400 ng g-1) and PFOA (<DL - 4100 ng g-1) in homes compared to other studies (displayed in Table 46). Removal of the extreme value for PFOS in sample 40 (7400 ng g-1) resulted in UK house dust PFOS concentrations remaining within the same range of those reported for Swedish, North American and Japanese homes (Björklund et al., 2009, Kato et al., 2009, Kubwabo et al., 2005 and Moriwaki et al., 2003). Despite the range of data being
Figure 12 Comparison of arithmetic mean concentrations of PFCs detected in home, office, and car dust (ng g-1, with error bars representing standard deviation)
similar to Sweden, the UK mean concentration considerably exceeds the Swedish results for PFOS and PFOA (Björklund et al., 2009) suggesting UK homes are more contaminated with PFCs.
The UK mean concentrations remain between results seen from two studies in the USA (Strynar et al., 2008 and Kato et al., 2009). Work by Kato et al. (2009) indicates USA PFC concentrations remain below that of the UK, but indicate similar concentrations for MeFOSA, where the majority of samples are below the LOQ values, with 29 % and 10 % of UK and USA samples containing quantifiable concentrations.
UK EtFOSA concentrations (98 ng g-1) are lower than those reported for the USA (201 ng g-1), (Kato et al., 2009), but are well above those reported for Canadian homes, in which EtFOSA was always not detected (Shoeib et al., 2005). The differences could be attributed to different use patterns of PFCs within these regions.
MeFOSE and EtFOSE concentrations measured by Shoeib et al., (2005) both exceed the range of concentrations identified in the UK, by 3.5 and 20 times for MeFOSE and EtFOSE respectively. This suggests that these two compounds have additional sources within Canadian homes. By comparison, UK concentrations display similar results to a USA study by Kato et al., (2009) for FOSA, MeFOSE and EtFOSE, suggesting that the increased concentrations seen in Canadian homes are not indicative of the whole North American region.
The UK dust concentrations analysed via PCA, along with classroom concentrations, are discussed in chapter 7, and home dust samples will be compared to other international samples collected and analysed according to the same protocol in chapter 9.
Table 46 Comparison of mean dust concentrations (and ranges) from this study and other international dust studies (ng g-1).
a 25th percentile – maximum concentration