## 2 Results and Discussion
### The Headspace C. erythraea _VOC Composition_  
Two fibers (PDMS/DVB and DVB/CAR/PDMS) were selected for HS-SPME after preliminary research with respect to overall number of isolated compounds. Both fibers showed qualitatively similar chemical profiles of the extracted compounds, but individual compound percentages varied (Table 1). A total of 52 VOCs were identified and reported for the first time in _C. erythraea_ headspace. \begin{table}
\begin{tabular}{l l c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Compound**} & **RI** & **RI** & **Area percentage (\%)** \\  & & **HP-5 MS** & **HP-FFAP** & **A** & **B** \\ \hline
1. & 2-Methylpentane \({}^{*}\) & \(<\)900 & / & 0.5 & 0.6 \\
2. & 3-Methylpentane \({}^{*}\) & \(<\)900 & / & 1.1 & 1.7 \\
3. & Hexane & \(<\)900 & \(<900\) & 0.6 & 2.0 \\
4. & Ethyl acetate & \(<\)900 & 901 & - & 0.8 \\
5. & Methylcyclopentane & \(<\)900 & / & 1.7 & 1.9 \\
6. & Cyclohexane & \(<\)900 & / & 0.5 & 0.8 \\
7. & Pentanal & \(<\)900 & / & - & 0.8 \\
8. & Toluene & \(<\)900 & 1067 & 4.5 & 18.0 \\
9. & Hexanal & \(<\)900 & 1105 & 1.5 & 4.8 \\
10. & 1,4-Dimethylbenzene \({}^{*}\) & \(<\)900 & / & - & 0.4 \\
11. & Heptanal & 905 & / & - & 0.4 \\
12. & \(a\)-Thujene & 933 & / & - & 0.6 \\
13. & \(a\)-Pinene & 941 & 1040 & - & 1.0 \\
14. & Propylbenzene (Isocumene) & 960 & / & - & 0.6 \\
15. & \(m\)-Ethyltoluene \({}^{*}\) & 968 & / & 0.9 & 1.7 \\
16. & 1,2,4-Trimethylbenzene (Pseudocumene) & 976 & / & 0.9 & 1.0 \\
17. & Sabinene & 982 & 1140 & 0.6 & 1.3 \\
18. & \(\beta\)-Pinene & 984 & 1130 & - & 1.1 \\
19. & \(o\)-Ethyltoluene \({}^{*}\) & 987 & / & 0.8 & 0.8 \\
20. & 2-Pentylfuran & 996 & 1249 & 1.0 & 2.4 \\
21. & 1,2,3-trimethylbenzene (Hemimellitene) & 1002 & / & 1.8 & 2.5 \\
22. & \(p\)-Cymene & 1032 & 1293 & 2.8 & 3.5 \\
23. & Limonene & 1036 & 1220 & 1.5 & 1.8 \\
24. & 1,8-Cineole & 1039 & 1231 & 1.1 & 0.9 \\
25. & \(\gamma\)-Terpinene & 1066 & / & 2.2 & 2.2 \\
26. & \(a\)-Terpinolene & 1094 & / & - & 0.5 \\
27. & Undecane & 1100 & 1100 & - & 0.7 \\
28. & Linalool & 1107 & 1560 & 2.8 & 0.9 \\
29. & Nonanal & 1109 & / & 2.9 & 1.8 \\
30. & \(\beta\)-Thujone & 1112 & 1450 & 2.8 & 1.2 \\
31. & Camphor & 1152 & 1548 & 5.1 & 2.0 \\
32. & Menthone & 1162 & 1490 & 6.1 & 4.3 \\
33. & Isomenthone & 1172 & 1519 & 0.9 & 1.6 \\
34. & Menthol & 1183 & 1658 & 2.9 & 6.7 \\
35. & Terpinen-4-ol & 1186 & 1623 & 10.3 & 6.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The headspace volatiles of _C. erythraea_ obtained by HS-SPME with the fibers:Aliphatic and aromatic hydrocarbons were abundant, particularly toluene (4.5%; 18.0%) and naphthalene (8.2%; 1.8%) followed by _o_- and _m_-ethyltoluene (0.8-1.7%). The trimethylbenzenes pseudocumene (0.9%; 1.0%) and hemimellitene (1.8%; 2.5%) were also present, but were not found in the oil composition (Table 2). Although benzene derivatives are usually considered as compounds of possible anthropogenic origin, new results indicate possible other pathways of their natural biogenesis. Namely, the emission of toluene from different plants was observed, although no biochemical pathway for toluene production is known [11]. Trace naphthalene amounts are produced by magnolias and flower extracts from gynoecia of five taxa (_Magnolia denudata, Magnolia liliiflora, Magnolia tomentosa, Magnolia praecocissima_ var. _praecocissima_ and var. _borealis_) contained naphthalene as main component [12]. Furthermore, Formosan subterranean termite [13] and some strains of the fungus _Muscodor albus_ naturally produce naphthalene, while _Muscodor vitigens_ produces naphthalene almost exclusively [14]. Therefore natural origin of the benzene derivatives found in _C. erythraea_ oil could be similar, and they can be excluded as pollutants since the plant was collected from ecologically pure area. Aliphatic hydrocarbons and carbonyls up to C18 were present as minor constituents (probably originated from fatty acids catabolism) and those up to C6 were only found in _C.