## 3 Results and Discussion
### Toxicity Studies
#### 3.7.2 Increment Life Cancer Risk  
The increment life cancer risk was evaluated for the PAHs with probable carcinogenic potentials to humans as listed by the International Agency for Research on Cancer (IARC) and U.S Environmental Protection Agency (US EPA), which include Benzo(k) fluoranthene (BkF) and Dibenz(a,h)anthracene (DahA) [50]. The BkF and DahA contributed 4.7% and 13%, respectively, with the highest concentration of DahA (730 \(\mathrm{\SIUnitSymbolMicro g}\)/kg) recorded at WH, while for sludge, the highest concentration of DahA was recorded at 7a (452 \(\mathrm{\SIUnitSymbolMicro g}\)/kg). Due to the high contribution of DahA to the total carcinogenic PAHs concentration, it was used in the calculation of ILCR. The model equation and parameters used for the evaluation of ILCR were taken from the literature and are tabulated in Table 4 The regulatory guidelines of the New York State Department of Health provided the classification of ILCR values where it was suggested that if the ILCR is less than \(10^{-6}\) it is very low or negligible risk, between \(10^{-6}\) to \(10^{-4}\) it is low risk, and when greater than \(10^{-4}\) to \(10^{-3}\) it is moderate risk, while greater than \(10^{-3}\) to \(10^{-2}\) is high risk and \(\geq 10^{-1}\) is classified as very high risk [51]. The ILCR\({}_{\mathrm{derm}}\) represents the increment life cancer risk via dermal contact (\(\mathrm{\SIUnitSymbolMicro g}\)/kg/day) and was calculated using Equation (3); the variables used are tabulated in Table 4.  
\[\mathrm{ILCRderm}=\frac{\mathrm{Ci}\times\mathrm{SA}\times\mathrm{Kp}\times \mathrm{ET}\times\mathrm{EF}\times\mathrm{ED}\times\mathrm{CF}}{\mathrm{BW} \times\mathrm{AT}} \tag{3}\] \begin{table}
\begin{tabular}{l c c} \hline \hline
**Variables** & **Child** & **Adult** & **Reference** \\ \hline Concentration, Ci (\(\mathrm{\SIUnitSymbolMicro g}\)/kg) & - & - & \\ \hline Skin area exposed, SA (\(\mathrm{cm}^{2}\)) & 2800 & 5700 & [38; 47] \\ \hline Exposure duration, ED (years) & 6 & 30 & [38] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameters used in the estimation of human cancer risk. \begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline \hline
**PAHs** & **Min** & **Max** & **Concentration** & **Mean** & **ERL** & **ERM** & **TEF** & **MEF** & **TEQ** & **CMEQ** & **Total** \\ \hline Naphthalene & 96.0 & 138 & 109 & 97.0 & 101 & 0.001 & - & 0.49 & - & 3.52 \\ Acenaphthylene & 112 & 213 & 140 & 113 & 117 & 0.001 & - & 0.64 & - & 4.60 \\ Acenaphthelene & 172 & 413 & 248 & 176 & 203 & 0.001 & - & 1.01 & - & 7.22 \\ Anthracene & nd & nd & nd & nd & nd & 0.01 & - & 16.0 & - & 11.4 \\ Fluoranthene & nd & nd & nd & nd & nd & 0.001 & - & 2.99 & - & 21.4 \\ Pyrene & 241 & 446 & 358 & 277 & 372 & 0.001 & - & 3.59 & - & 25.7 \\ Benzo(k)fluoranthene & nd & 787 & 738 & 679 & 761 & 0.1 & 0.11 & 66.0 & 72.6 & 4.72 \\ Benzo(ghi)perylene & 781 & 926 & 880 & 815 & 907 & 0.01 & 0.19 & 11.5 & 180 & 8.20 \\ Dibenz(ah)anthraacene & 186 & 229 & 212 & 193 & 222 & 1 & 0.29 & 1850 & 434 & 13.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Min, max, average concentrations, ERL, ERM, TEQ and MEQ. The ILCRderm values calculated with DahA concentrations for sludge and sediments were 1.01 \(\times\) 10\({}^{-1}\) and 1.92 \(\times\) 10\({}^{-1}\) for children and 2.62 \(\times\) 10\({}^{-1}\) and 4.98 \(\times\) 10\({}^{-1}\) for adults, correspondingly. Both the sites exhibited very high potential risk of cancer to the inhabitants of the area, suggesting that the study area is not entirely safe for use even for recreational purposes. An article titled \"uMsunduzi River being flushed ahead of Dusi marathon\" published by Mercury News also echoed the unsafeness of being exposed to the water of uMsunduzi river, where Henley dam water was released in order to flush toxins in the river water prior to the annual Dusi canoe marathon of 2022 [54]. It is worth noting that adults have a higher probability of being dermally exposed to these carcinogenic contaminants than children.