## 2 Methods
### Embedded Toxicity--Experimental Setup  
Recycled wood and concrete were collected, shredded and crushed, respectively, to fit into 250 mL DURAN(r) BlueCap flasks. A manual SPME holder was used to precondition the SPME fiber in the gas chromatography (GC) injector port for 0.5 h at 270 \({}^{\circ}\)C [16]. Triplicates of material batches were incubated at 70 \({}^{\circ}\)C for a total of 24 h in the 250 mL DURAN(r) BlueCap flasks equipped with septum caps following 30 min of SPME extraction of the head space/gaseous phase [16]. No considerable head space concentration changes were observed when prolonging incubation from 24 h to 48 h, indicating that (air/concrete) equilibrium was reached within 24 h, which was similarly observed by [PERSON] and [PERSON] [18]. The extracted analytes on the SPME fiber were desorbed into the GC injector port at 230 \({}^{\circ}\)C for qualitative and quantitative assessment in a gas chromatography-mass spectrometry (GC-MS) instrument with a DB-5 MS capillary column (Dimensions: 30 m, 0.25 mm, 0.25 \(\mu\)m, 7 inches) [16]. The initial temperature of the GC oven was set to 30 \({}^{\circ}\)C, and the temperature was subsequently ramped at 5 \({}^{\circ}\)C/min to 325 \({}^{\circ}\)C. The experimental setup is shown in Figure 2.  
Data acquired from the MS detection was analyzed using the Xcalibur Qual Browser and the National Institute of Standards and Technology (NIST) Mass Spectral Library [24] to identify the different VOC analytes extracted from the materials. The chemicals were identified by comparing the spectrum of each peak in the chromatograms to reference spectra in the library [25]. Contamination tests of the flasks were performed using triplicates of a blank sample. Between each extraction, the SPME fibers were stored in glass vials and cleaned in the GC injector port to avoid further contaminations. VOCs emitted from the \"clean\" SPME fibers, the GC column, and the glassware was identified and quantified. The chemical equipment \"contaminations\" are listed in Table 1 and were subtracted from the results used in further analysis. Therefore, if emitted by a material sample, these VOCs would not be included in further analysis and are thus subtracted from the results. The subtracted \"contaminations\" included for concrete is toluene; and for both wood and concrete, they include oleic acid, propanoic acid, and various types of cyclosiloxane that were identified. The areas under the identified peaks from the chromatograms were used in the quantification of the chemical compounds emitted from the material samples along with a standard curve of hexane (0.5 ppm, 1 ppm, 2 ppm, 4 ppm, 8 ppm, 16 ppm) providing a conversion factor and reference for the concentration (unit ppm\({}_{\rm m}\) or mg/kg) of chemicals emitted from the samples analyzed [26; 27]. Quantitative data of the chemicals emitted by the material samples (unit ppm\({}_{\rm m}\)) was used in combination with characterization factors \begin{table}
\begin{tabular}{c c} \hline \hline
**Compound** & **CAS No.** \\ \hline
1-(2,3-dimethyl-furan-3-yl)ethanoneone & 10599-70-9 \\
1-Hexanol & 111-27-3 \\
2,3-Dihydroxypropyllealidate & 25496-72-4 \\ Dodecane & 112-40-3 \\ Dronabinol & 1972-08-3 \\ Hexadecanoic acid & 10499-94-2 \\ Octadecanoic acid & 57-11-4 \\ Octane & 111-65-9 \\ Oleic acid & 112-80-1 \\ Oxime (Acetophenone) & 613-91-2 \\ Pentadecanoic acid & 1002-94-2 \\ Phenol & 108-95-2 \\ Propanoic acid & 79-09-4 \\ Toluene & 108-88-3 \\ Cyclosiloxane & N/A \\ \hline \hline \end{tabular}
\end{table} 
Table 1: VOCs were identified from the contamination test of the SPME fiber and the GC-MS column itself, as well as the blank samples. The compound is identified with a CAS number (CAS no.) from the National Institute of Standards and Technology (NIST) library. However, a CAS no. was not available (N/A) for the various types of cyclosiloxane. Figure 2: Experimental setup for analyzing the embedded toxicity of recycled wood and concrete.