# Speciation of the Removed Pollutants in Bioremediation of Hydrocarbon-Contaminated Soil
## 3 Results  
### Residual Concentration of the Diesel Oil Hydrocarbons  
The results for the mesocosoms at the start and end of the run, as average values on the total mesocosom soil, are reported in Table 5.  
At a glance, the very limited removal of diesel oil hydrocarbons for the NA mesocosm as supported by the geophysical monitoring is evident [8], whereas in the others, the values show degradation of the pollutants, even if to a different extent by the number of carbon atoms.  
To better manage the data, the composition of the residual diesel oil was expressed by clusters of isomeric alkanes and aromatics. To this aim, it was decided to cluster the alkanes and aromatic according to the following ranges:  
* C8-C11;
* C12-C15;
* C16-C19;
* C20-C24;
* Aromatics.  
For the NA mesocosm, this analysis was not carried out due to its near-zero removal efficiency.  
As for the removal efficiency, speciation was carried out on two kinds of soil samples: samples collected by mixing the whole mesocosm, and samples taken just at the bottom.  
Composition by cluster is also interesting from the applicative point of view when the legislation on soil pollution imposes concentration limits linked to the number of carbon atoms. The current Italian legislation is an example of this, even if not unique. The concentration limits present in the current legislation are given in Table 6[15].  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**Maximum Allowed Concentration**} \\ \cline{2-3}  & \multicolumn{2}{c}{**Site for Public Use**} & **Site for Industrial and Commercial Use** \\  & **(g\(\cdot\)kg\({}^{-1}\) of Soil)** & **(g\(\cdot\)kg\({}^{-1}\) of Soil)** \\ \hline Light hydrocarbons (C \(\leq\) 12) & 0.010 & 0.25 \\ Heavy hydrocarbons (C \(>\) 12) & 0.050 & 0.75 \\ Pyrene & 0.0050 & 0.050 \\ Benzo(\(\alpha\))anthracene & 0.00050 & 0.010 \\ \hline \hline \end{tabular}
\end{table}
Table 6: The maximum concentration of hydrocarbons given by the Italian legislation.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**No. of**} & \multicolumn{4}{c}{**Composition (g\(\cdot\)kg\({}^{-1}\) of Soil)**} \\ \cline{2-5}  & **At t = 0** & **At t = 193 Days** & **At t = 228 Days** & **At t = 228 Days** \\  & **Days** & **NA Mescosom** & **BS Mescosom** & **BS + IN Mescosom** \\ \hline C8 & 0.8 & 1.7 & 0.3 & 0.4 \\ C9 & 1.7 & 1.5 & 0.2 & 0.1 \\ C10 & 4.0 & 1.4 & 0.4 & 0.4 \\ C11 & 5.3 & 4.5 & 1.4 & 1.2 \\ C12 & 4.9 & 4.1 & 1.9 & 1.5 \\ C13 & 5.6 & 4.6 &  
Tables 7 and 8 show the chemical composition of diesel oil by clusters for the biostimulated mesocosom, analyzed on the total soil and at the bottom.  
In both cases, except for the aromatics, the concentration of residual diesel oil on the bottom is always much higher than the value of the total mesocosms.  
Moreover, comparing our findings with the maximum allowed limits given by the current Italian legislation, the biological process did not sufficiently remove the pollution to leave the site suitable for reuse; this is to say, additional treatment for soil clean-up is compulsory.