## 3 Results  
### Embedded Toxicity  
The experimental setup yielded data that revealed a release of 9 substances from the recycled concrete samples and 10 substances released from the recycled wood samples. As presented in Tables 2 and 3, all chemicals released from concrete can be categorized as having been absorbed by and embedded in the concrete at some point along its value chain, since these chemicals are not naturally found in concrete [21]. The majority of chemicals released from wood are naturally occurring in the material apart from naphthalene and cyclohexene. Chemicals categorized as naturally occurring in wood can however also potentially affect human health. For instance, chronic exposure to hexanal, which is found in wood, can lead to organ impacts and failure [36]. Sources that contribute to the intentional or unintentional contamination of the wood with chemicals in the materials could include paints and other surface treatments during use cycles. Due to the low availability of chemical-specific human toxicological characterization factors in the most recent (at the time of calculation) version of USEtox 2.12 [30] and ILCD 2.0 2018 midpoint [28] characterization methods, it was only possible to characterize 5 of the 18 identified chemical compounds emitted from the material samples. These chemical compounds are benzene, benzaldehyde, hexane, naphthalene, and pyridine as shown in Table 4. These are marked with an * in Tables 2 and 3. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & & \multicolumn{3}{c}{**Sample Specific Concentrations**} \\ \multirow{2}{*}{**VOC Emitted**} & \multirow{2}{*}{**CAS No.**} & \multirow{2}{*}{**N/I**} & \multicolumn{3}{c}{**(ppm\({}_{\text{m}}\))**} \\ \cline{4-5}  & & & **1** & **2** & **3** \\ \hline
2-Norpinene, 3,6,6-trimethyl & 4889-83-2 & N & 1286.3 & 399.92 & 904.27 \\
3-carene & 13466-78-9 & N & 71.67 & - & 33.34 \\ \(\alpha\)-Longipinene & 5989-08-2 & N & - & - & 109.60 \\ \(\alpha\)-Pineine & 80-56-8 & N & 841.04 & 91.90 & 458.58 \\ \(\alpha\)-Terpinene & 99-86-5 & N & 122.33 & - & - \\ \(\alpha\)-Terpineol & 98-55-5 & N & 708.02 & - & - \\ Bornylacetate & 5655-61-8 & N & - & - & 20.26 \\ Cyclohexene & 110-83-8 & I & 767.47 & - & 493.94 \\ Hexanal & 66-25-1 & N & - & 50.21 & 34.63 \\ Naphthalene * & 91-20-3 & I & 76.98 & - & 287.87 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Identified VOCs emitted from three samples of recycled wood, categorized with CAS no., origin (N = naturally occurring/I = incorporated chemical) and concentration in ppm\({}_{\text{m}}\). * denotes the chemicals for which characterization factors exist. As presented in Tables 2 and 3, the concentration variations observed between the samples are considerable, which also causes the average embedded human toxicity impact per kg building material sample to exhibit significant variations. Figure 4 provides an illustration of the difference between the highest and lowest toxicity impact per kg of concrete and wood. Only a small variation is observed for the human toxicological impacts induced by 1 kg of the wood samples. One could postulate that this was a result of the surface properties of wood, relative to e.g., concrete, but it could just as easily be another property or simply the happenstance of sampling that resulted in this lower level of variation. Additionally, this could have resulted from the low percentage of total chemicals able to be characterized. Regardless, more testing would be required to arrive at a conclusion regarding this relative lack of variation.