## 3 Results and Discussion
### PAHs Concentration Detected in uMsunduzi River Sediment Samples  
The optimised MAE and UE conditions were also applied in sediment samples collected from uMsunduzi River at four different sampling sites, namely: CD, CR, WH and BS. The samples from both the microwave and ultrasonic extraction methods were either filtered only or filtered then passed through SPE for further sample purification. The extraction methods and the effects of filtering and SPE cleaning of samples were then compared to determine their efficiency. All the studied PAHs were detected in all the collected sediment samples at varied concentrations, except for phenanthrene and fluorene (Figure 6). Pyrene, a four-ring PAH, showed high total concentration dominance at 24%, followed by a five-ring (Dibenz (ah) anthracene) at 17%, and then fluoranthene, another four-ring PAH at 13%. All the PAH concentrations obtained were within the maximum allowable concentration of 3.0 \(\times\) 10\({}^{3}\)\(\mathrm{\SIUnitSymbolMicro g}\)/kg (for naphthalene, acenaphthylene, acenaphthrene, fluorene, phenanthrene, anthracene, pyrene and benzo[ghi]perylene), except for dibenz (ah) anthracene, which showed concentrations above the limit of 300 \(\mathrm{\SIUnitSymbolMicro g}\)/kg in all four sampling sites. The anticipated dominance of these high-molecular-weight PAHs suggests the predominance of pyrolytic (incineration processes) contamination sources [32]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**PAH Compound (\(n\) = 5)** & \begin{tabular}{c} **LOD (\(\mathrm{\SIUnitSymbolMicro g}\)/kg)** \\ **MAE** \\ \end{tabular} & \begin{tabular}{c} **LOQ (\(\mathrm{\SIUnitSymbolMicro g}\)/kg)** \\ **UE** \\ \end{tabular} & \
\begin{tabular}{c} **\%Recovery \(\pm\) \%RSD** \\ **MAE** \\ \end{tabular} &
\begin{tabular}{c} **R\({}^{2}\) Values** \\ \end{tabular} \\ \hline Naphthalene & 0.162 & 0.095 & 0.434 & 0.245 & 92.3 \(\pm\) 0.04 & 121 \(\pm\) 0.02 & 0.9992 \\ Acenaphthylene & 0.113 & 0.051 & 0.323 & 0.136 & 98.1 \(\pm\) 0.03 & 97.2 \(\pm\) 0.01 & 0.9970 \\ Acenaphthrene & 0.034 & 0.145 & 0.080 & 0.394 & 98.1 \(\pm\) 0.01 & 107 \(\pm\) 0.04 & 0.9969 \\ Fluorene & 0.762 & 0.084 & 1.238 & 0.234 & 88.4 \(\pm\) 0.21 & 96.7 \(\pm\) 0.02 & 0.9969 \\ Phenanthrene & 1.211 & 0.960 & 3.536 & 1.259 & 101 \(\pm\) 0.33 & 94.9 \(\pm\) 0.02 & 0.9988 \\ Anthracene & 0.138 & 0.019 & 0.310 & 0.049 & 113 \(\pm\) 0.21 & 96.1 \(\pm\) 0.004 & 0.9970 \\ Fluoranthene & 0.964 & 0.093 & 2.795 & 0.266 & 79.1 \(\pm\) 0.26 & 93.7 \(\pm\) 0.02 & 0.9991 \\ Pyrene & 0.968 & 0.091 & 2.814 & 0.259 & 81.9 \(\pm\) 0.26 & 93.9 \(\pm\) 0.02 & 0.9993 \\ Benzo(k)fluoranthene & 0.058 & 0.183 & 0.118 & 0.546 & 81.3 \(\pm\) 0.29 & 96.0 \(\pm\) 0.05 & 0.9982 \\ Benzo(ghi)perylene & 0.025 & 0.215 & 0.445 & 0.642 & 87.9 \(\pm\) 0.26 & 96.6 \(\pm\) 0.06 & 0.9989 \\ Dibenz(a,h)anthracene & 0.062 & 0.127 & 0.245 & 0.382 & 122 \(\pm\) 0.13 & 118 \(\pm\) 0.04 & 0.9977 \\ \hline \end{tabular}
\end{table} 
Table 1: Recoveries, LOD and LOQ for MAE and UE, and correlation coefficient R\({}^{2}\). Figure 6: Concentrations of PAHs in uMsounduzi river sediments. The highest pyrene concentrations were obtained in sampling site CD, followed by WH, CR and BS, which is expected since CD is the industrial hub of Pietermaritzburg and WH is close to the New England dumpsite and Willowtown factories. The HWM-PAHs are more hydrophobic than those with low molecular weight, which allows them to be adsorbed in a soil matrix easily since they do not dissolve in water [33]. The results obtained when using MAE and UE with the same purification technique (filtering or SPE-cleaning) were comparable, while the results with the same extraction but different purification technique were different. The SPE-cleaned results gave high concentrations compared to the concentrations obtained when filtering only. The MAE-F + SPE gave concentrations ranging from 95.96 to 919.0 \(\upmu\)g/kg while the UE-F + SPE gave concentrations at ranges of 96.26-926.0 \(\upmu\)g/kg.