**3.4 PROMETHEE and GAIA analysis of the heavy metals**

Contamination of the rivers by heavy metals was ranked and recognized from site to site by simultaneously and systematically subjecting the concentrations to PROMETHEE and GAIA analysis. PROMETHEE II complete ranking of the sites (**Figure 3)** from least polluted to the highest polluted is shown as follows: CK ˃ AOD ˃ NM ˃ EA ˃ VKP ˃ WA ˃ BB ˃ WTB ˃ AOB ˃ BAM ˃ EAM.

The ranking shows that the pristine sites are less contaminated by the metals compared with the mining sites. The site with the least metal contamination is Kakum River (pristine site), and the highest contaminated river is the Birim River (mining site). GAIA, which is a pattern recognition tool, indicates that approximately 81.90% of the variance is explained by the first two principal components (PCs). The GAIA plot

**Figure 3.** *Component plot showing metal loadings on components from pristine and mining sites.*

**Figure 4.**

*PROMETHEE 2 outflow ranking of sampling sites based on heavy metals concentration in water samples from mine sites.*

(**Figure 4)** identified similar groupings and trend as obtained from the PCA analysis. GAIA plot of the sampling sites (**Figures 5** and **6**) showed the decision axis (Pi) pointing toward the pristine sites. The PROMETHEE and GAIA analysis clearly indicates that the pristine sites are the least contaminated, while the mining sites are the most contaminated with the metals. The results also showed that anthropogenic activities such as mining may be impacting heavily on heavy metal contamination of the rivers.

*Effect of Mining on Heavy Metals Toxicity and Health Risk in Selected Rivers of Ghana DOI: http://dx.doi.org/10.5772/intechopen.102093*


#### **Table 7.**

*Carcinogenic and non-carcinogenic assessment.*

#### **3.5 Carcinogenic risk assessment**

Using the Central Tendency Exposure scenario (CTE) for child and adults, carcinogenic risks associated with ingestion and dermal contact with heavy metals (As, Cr, Ni, and Pb) were determined. For ingestion of water, the highest cancer risks for child and adult were measured from river EAM, a mining site for Cr as 3.45 x 10<sup>1</sup> and 3.70 x 10<sup>1</sup> , respectively. The highest cancer risks were measured for child and adult residents from river WA for Cr as 2.19 x 10<sup>2</sup> and 2.35 x 10<sup>2</sup> , respectively. Chromium posed the highest cancer risks in river EAM and WA for adult and child residents (**Table 7**). Chromium concentration from all the sites posed serious carcinogenic risk to both adult and child residents ranging from 9.39 x 10<sup>2</sup> to 1.35 x 10<sup>1</sup> and 8.77 x 10<sup>2</sup> to 1.26 x 10<sup>1</sup> , respectively. The carcinogenic risks for Ni, As, and Pb are within the USEPA risk limit (1.0 <sup>10</sup><sup>6</sup> to 1.0 <sup>10</sup><sup>4</sup> ) [30, 31] except for As (3.35 <sup>10</sup><sup>3</sup> and 3.12 <sup>10</sup><sup>3</sup> ) at site AOB and Pb (2.10 <sup>10</sup><sup>3</sup> and 1.96 <sup>10</sup><sup>3</sup> ) at site EAM for resident adult and child, respectively. This implies that for As and Pb, there is a likelihood that up to 2–3 adults, out of 1000 and 1–3 children out of 1000 respectively if equally exposed continuously for 70 years would contract cancer. The carcinogenic risk via dermal contact **(Table 7)** or As, Ni, and Pb in the pristine and mining sites for adult and child is almost within the USEPA risk assessment guideline limit. However, the carcinogenic risks for Cr from all rivers in the mining sites were higher, ranging from 7.37 x 10<sup>3</sup> to 1.31 x 10<sup>2</sup> and 3.90 x 10<sup>3</sup> to 1.07 x 10<sup>2</sup> for child and adult residents,

respectively. The risk values in this study are comparable with values obtained by other researchers [19, 32, 42]. The high carcinogenic risk values for As and Cr raise carcinogenic concerns for the local residents in the catchment areas. The method of risk estimation employed in this study provides ways to screen those pollutants that are of public health concern in order to prioritize research and policy interventions.
