## 3 Results and Discussion
### Toxicity Studies  
#### 3.7.1 Risk Assessment  
To characterize and assess the toxicity of PAHs, a number of factors were evaluated, which included the effects range low (ERL), effects range median (ERM) and the benzo(a)pyrene toxic equivalency quotient (TEQ), together with mutagenic equivalency quotient (MEQ) and the increment life cancer risk (ILCR). The concentrations of PAHs in soil obtained from MAE-F + SPE were used to assess the toxicity of PAHs, since it was found to be the most efficient method. The ERL, which corresponds to the 10 th percentile of data (concentration below with which effects that infrequently occur), and the effects range ERM, corresponding to the 50 th percentile of data (effects that frequently occur), were used ([PERSON] et al., 2020). The ERL and ERM values (Table 3) were used as guidelines on where the average acceptable concentration levels of total PAH in sediments should be below the ERL, while the unacceptable concentration levels were the ones above the ERM. Average concentrations above ERM are indicative of toxic effects relative to the area of investigation ([PERSON] et al., 2020). The TEQ and MEQ were calculated using Equations (1) and (2), where Ci is the PAH concentration, TEF is the toxic equivalency factor and MEF is mutagenic equivalency factor ([PERSON] et al., 2020). The ILRC was evaluated based on the dermal exposure risk (Equation (3)) since the uMsunduzi river is used for recreational purposes, such as the Dusi canoe marathon, and the sludge landfill is used for planting landscaping grass (lawns). The contamination by the PAHs in the studied sites was classified into three different groups: (1) not contaminated when the total PAH concentration of a site was less than 200 ug/kg, (2) weakly contaminated when the total concentration was between 200-600 ug/kg and (3) heavily contaminated when it was greater than 1000 ug/kg ([PERSON] et al., 2020).  
\[\text{TEQ}=\sum\text{Ci}\times\text{TEF} \tag{1}\]  
\[\text{MEQ}=\sum\text{Ci}\times\text{MEF} \tag{2}\]  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Sampling Point** & **CD** & **CR** & **WH** & **BS** & **14A** & **7A** \\ \hline Fl/(Fl + Py) & 0.45 & 0.47 & 0.45 & 0.45 & 0.46 & 0.45 \\ \hline LMW/HMW & 0.29 & 0.29 & 0.43 & 0.37 & 0.30 & 0.21 \\ \hline \end{tabular}
\end{table}
Table 2: Diagnostic ratios.  
The average concentration levels were between the ERL and ERM for all PAHs in uMsundizi river sediments except for naphthalene, acenaphthylene and acenaphthelene, which had values above ERM, indicating that mild toxic effects to the organisms are likely to occur and indicative of toxic effects to the surrounding environment. The TEQ and MEQ were calculated by multiplying the PAH compound concentration with their corresponding TEF and MEF values, respectively [49]. The PAH TEQ and MEQ average ranged from 0.49 to 1850 \(\mathrm{\SIUnitSymbolMicro g}\)/kg and 72.6-434 \(\mathrm{\SIUnitSymbolMicro g}\)/kg, respectively. The sum of toxic equivalency quotient (STEQ) of all PAH compounds was below the safe level of 600 \(\mathrm{\SIUnitSymbolMicro g}\)/kg, except for the \(\mathrm{\sum}\)TEQ of dibenz(ah)anthracene, indicating its high toxicity potency in the study area [49]. Therefore, consideration of regulating combustion and ensuring all activities that cause these contaminants in the environment are controlled to ensure the safety of human and aquatic lives is vital. All the sites investigated were heavily contaminated, with concentrations ranging from 2909 \(\mathrm{\SIUnitSymbolMicro g}\)/kg (CD)-4326 \(\mathrm{\SIUnitSymbolMicro g}\)/kg (14a).