**2. Materials and method**

#### **2.1 The study area**

Samples were collected in eight regions of Ghana with the land cover ranging from 138 to 2950 km<sup>2</sup> . The rivers that were sampled in the mining areas are Nyam river, Subri river, Birim river, and river Bonsa. The nature and the location of the rivers demonstrate the presence of metal contamination due to mining activities. The rivers from the pristine areas are Oda river, Bosomkese forest river, Ankasa river, Atewa forest river, Kalakpa river, Kakum river, and Mole river. The pristine rivers were used as background checks in order to assess the extent of metal contamination.

#### **2.2 Sampling and sample collection**

Water samples were collected from four selected rivers around the gold mining areas and seven rivers from the pristine areas. Sample collection was undertaken from January 2015 to January 2016. A total of 44 composite samples of water were collected from both mining and pristine areas. The rivers were sampled 100 m apart at four different points. 1.5 L plastic bottles that had been prewashed with detergent and 1:1 concentrated nitric acid/distilled water solution and eventually rinsed with only distilled water were used. The samples for metal analysis were acidified to a pH of 2 at site using concentrated HNO3 before they were transported to the Chemistry Department laboratory of University of Cape Coast. The samples were kept in refrigerator at a temperature of 4°C for further analysis [28].

### **2.3 Digestion and analysis of water samples**

Chemicals and reagents for analysis were acquired from the Central Analytical Facility of Queensland University of Science and Technology. 70% Nitric acid (HNO3) was further distilled twice in Analab Sub-Boiling Distillation system. Water for the analysis was acquired from MilliQ water purification system (Millipore, Billerica, MA, USA). Water samples were analyzed in triplicates to check the efficiency of the analytical instrument. Centrifuge tubes were washed by rinsing three times in ultrapure water. They were then soaked in 3% analytical grade HCl and left on a hot plate for two days. The operating conditions for the instrument were the following parameters: Cell Gas flow rates: 5 ml/min; Carrier Gas Flow: 1.05 l/min; KED Voltage: 5 V; ICP RF Power: 1550 W; Octopole bias (V): �18, Octopole RF (V); 190: Spray Chamber t (C); 2: Sample depth (mm); 8.

The samples were digested by acidifying with 1 mL NHO3. They were later centrifuged at 3500 rpm for 15 min. The samples were then filtered through 0.45 μm pore size cellulose acetate filters.

They were then analyzed with Agilent 8800 Triple Quadrupole Inductively Coupled Plasma Emission Spectrometer (ICP-QQQMS) in the Central Analytical Research Facility (CARF) laboratory of Queensland University of Technology, Australia. The same digestion procedure was applied to the Quality Control (QC) samples and the blank. The analytes were acquired using He mode, and those elements that do not suffer from polyatomic interferences were acquired in no gas mode.

Some physicochemical parameters such as pH, conductivity, and turbidity were also determined. The pH was determined alongside the temperature using a precalibrated JENWAY 3310 and JENWAY 3510 pH meter. Conductivity was measured using a pre-calibrated PHYWE 13701.93 and WAGTECH 4510 conductivity meter. The turbidity was measured with a Hachturbidimeter.

#### **2.4 Recovery and reproducibility studies**

Calibration solution was prepared by using Choice Analytical ICV-1 Solution and a Standard Agilent Technologies Multi Element Reference Standard 2A. The Agilent Standard was analyzed as unknown to monitor the accuracy of analytic process. The percent recovery was computed to range from 99.5% to 103.8% with the relative standard deviation ranging between 0.38 and 2.23. The recovery results indicate that the error associated with the determination of concentrations of the metals was negligible.

#### **2.5 Data and statistical analysis**

IBM SPSS Statistics version 22 and the Excel Analysis ToolPak were used to analyze the data from the study. Basic statistics such as mean and standard deviation were computed along the multivariate statistics. Relationships associated with the variables were tested using correlation analysis with statistical significance at p < 0.05. Hierarchical Cluster analysis (HCA) was also employed to provide a visual summary of the clustering process unsupervised pattern recognition technique. Factor analysis (FA) and principal component analysis (PCA) were computed to identify significant principal components in the data. The PCA was carried out by the Promax normalized rotation method for the results [29, 30]. PROMETHEE, a multicriteria outranking method, was employed to rank objects on the basis of range of variables and GAIA to add descriptive complement to the PROMETHEE rankings.

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

#### **2.6 Human health risk assessment**

The risk estimation was based on the United States Environmental Protection Agency (USEPA) risk assessment method for ingestion and dermal contact [29, 31].

The average daily dose (ADD) for the heavy metals (**Eq. 1**) was calculated using the following modified equations from USEPA protocol 1989 and 2004.

$$\text{ADDing} = \frac{\text{Cx} \times \text{Ir} \times \text{Ef} \times \text{Ed}}{\text{Bwt} \times \text{At} \times \text{365}} \tag{1}$$

where Cx is the concentration of the metals in the drinking water (mg*/*L), Ir is the ingestion rate per unit time (L*/*day), Ed is the exposure duration (years), Ef is the exposure frequency (days*/*year), Bwt is the body weight of receptor (kg), and At is the average lifetime (years), which is equal to the life expectancy of a resident Ghanaian. In addition, ADDing is the quantity of heavy metals ingested per kilogram of body weight.

In this study, surface water ingestion is assumed to be the main pathway for risk assessment because the rivers are potential sources of drinking water. However, dermal contact is another important pathway, because residents sometimes swim in these rivers and thus may come into contact with the toxic metals through body contact.

Average daily dose for dermal contact was calculated using the formula in **Eq. 2** below:

$$\text{ADDTerm} = \frac{\text{Cr} \quad \times \text{Sa} \times \text{Pc} \times \text{Et} \times \text{Ef} \times \text{Ed} \times \text{Cf}}{\text{Bwt} \times \text{At} \times \text{365}} \tag{2}$$

where Sa is the total skin surface area (cm3 ), Cf is the volumetric conversion factor for water (1 L/1000 cm<sup>3</sup> ), Pc is the chemical-specific dermal permeability constant (cm/h).

The hazard for the metals was estimated as the ratio of the calculated dose to the reference dose (RfD) (mg/L/day) using **Eq. 3** below:

$$\text{HQ} = \frac{ADD}{\text{RfD}} \tag{3}$$

The chronic daily intake (CDI) of the metal was calculated using the **Eq. 4** below:

$$\text{CDI} = \text{C} \begin{array}{c} \text{DIing} \\ \text{Bwt} \end{array} \tag{4}$$

where C is the concentration of heavy metal in water, DI is the average daily intake rate (2 L).

The carcinogenic risks (CRs) of the metals were calculated using **Eq. 5 and 6** below for ingestion and dermal contact, respectively. The carcinogenic risk acceptable by USEPA ranges from 1x10�<sup>6</sup> to 1x10�<sup>4</sup> .

$$\text{CRing} = \frac{ADD \text{ing}}{\text{SFing}} \tag{5}$$

$$\text{CRdem} = \frac{ADDerm}{\text{SFing}} \tag{6}$$

where SF is the slope factor (mg/kg)/day. For As, Cd, and Cr, the slope factor values are 1.5, 6.1 � <sup>10</sup><sup>2</sup> , and 5.0 � <sup>10</sup><sup>2</sup> (mg/kg)/day, respectively.
