## 3 Results and Discussion  
### PAH and Trace Metals Concentrations  
#### 3.1.1 PAHs  
Overall, the 25 PAHs were detected in all dust samples, except for perylene, which was not detected in six residences. The concentrations of all the individual PAHs are presented in Table 1. The total PAH concentration in indoor dust ranged between 1.4 and 7.3 \(\mathrm{\SIUnitSymbolMicro g}\), across the houses, with a median value of 2.2 \(\mathrm{\SIUnitSymbolMicro g}\), The house with the lowest total concentration was a recently renovated apartment, and its occupants had moved in about a month before the start of the campaign. This observation is consistent with previously conducted studies, where lower \(\mathrm{\SIUnitSymbolMicro PAH}\) concentrations in newly constructed or renovated houses have been reported [18,21]. The house with the highest \(\mathrm{\SIUnitSymbolMicro PAH}\) concentration was 10 years old, and the only distinct feature it had when compared to the other houses of the study was the presence of a large carpet in the living room. This finding is in agreement with the observations of [PERSON] et al. [18], who reported elevated total PAH concentration in a residence that was 90% carpeted. In general, the \(\mathrm{\SIUnitSymbolMicro PAH}\) concentrations in the present study were lower with respect to previous studies. Specifically, the mean levels of total PAHs in indoor dust in two studies that were conducted in China were much higher as follows: 21.9-329.6 and 30.9 \(\mathrm{\SIUnitSymbolMicro g}\)/g, respectively [2,9]. Similarly, higher concentrations were reported in USA (29.2 \(\mathrm{\SIUnitSymbolMicro g}\)/g) [28,29], Canada (12.9 \(\mathrm{\SIUnitSymbolMicro g}\)/g) [18] and Italy (5.11) [19]. Among the measured PAHs, phenanthrene was the most predominant, followed by fluorene, while perylene was the congener detected in the lowest concentrations in all the studied households. In terms of their molecular weight, PAHs are categorized in three main categories: PAHs with High Molecular Weight (HMW), Medium Molecular Weight (MMW) and Low Molecular Weight (LMW). HMW PAHs are in general more toxic and harmful with respect to the LMW, which are less toxic. In the present study, LMW PAHs were the predominant PAHs in indoor dust, accounting for 87.5 % of the total PAHs. Out of the 25 measured PAHs, 16 (naphthalene, acenapthylene, acenapthrene, fluorene, phenanthrene, anthracene, fluoranthrene, pyrene, bez(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, indeno(1,2,3-c,d)pyrene, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**PAH (ng/g)** & **Mean** & **Median** & **SD** & **Min** & **Max** \\ \hline Nap & 339 & 116 & 609 & 75.2 & 2479 \\
2M-Nap & 242 & 172 & 198 & 118 & 965 \\
1M-Nap & 126 & 91.6 & 107 & 61.1 & 518 \\ Acy & 15.7 & 13.2 & 7.82 & 8.24 & 39.4 \\
1,2 DM-Nap & 49.4 & 40.1 & 30.7 & 29.5 & 158 \\
2,6 DM-Nap & 11.7 & 9.08 & 7.04 & 6.43 & 33.2 \\ Ace & 94.6 & 78.0 & 69.0 & 60.8 & 353 \\
2,3,5-TM-Nap & 10.5 & 8.56 & 7.33 & 3.12 & 28.8 \\ FI & 421 & 424 & 207 & 221 & 1116 \\ DBT & 25.4 & 21.2 & 20.9 & 4.96 & 91.8 \\ Phe & 925 & 905 & 465 & 528 & 2525 \\
1M-Phe & 67.9 & 45.8 & 79.0 & 14.9 & 358 \\
3,6 DM-Phe & 42.3 & 21.5 & 75.7 & 7.59 & 334 \\ Ant & 22.6 & 19.4 & 12.7 & 10.3 & 57.3 \\ Flu & 99.0 & 86.0 & 61.8 & 30.2 & 308 \\ Pyr & 100 & 74.4 & 117 & 20.1 & 542 \\ BaA & 11.3 & 8.25 & 12.2 & 1.68 & 54.9 \\ Chr & 45.3 & 27.2 & 72.9 & 4.25 & 325 \\ BBr & 20.7 & 16.9 & 19.9 & 2.01 & 90.4 \\ BBr & 10.7 & 7.22 & 12.3 & 1.01 & 55.7 \\ Bep & 14.0 & 9.79 & 14.8 & 1.49 & 65.9 \\ Bap & 7.06 & 5.45 & 5.69 & 1.05 & 24.0 \\ Per & 1.02 & 1.08 & 1.06 & 0.00 & 3.39 \\ IndP & 11.1 & 8.39 & 10.8 & 1.05 & 49.2 \\ dBaAnt & 2.06 & 1.69 & 1.83 & 0.39 & 8.39 \\ BlghiIPer & 13.8 & 10.3 & 11.2 & 1.36 & 49.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Concentrations of polycyclic aromatic hydrocarbons (PAHs) in indoor dust samples (ng/g).