**1. Introduction**

South Africa as a country is regarded as one of the richest countries with abundance of mineral resources such as gold, platinum, coal, cobalt and many more [1, 2]. The exploration of gold started in the country in the 19th century [3], when the world largest gold deposit was discovered in the Witwatersrand Basin, South Africa [4]. The discovery of gold has contributed to the development of South Africa as one of the most developed and largest economy in the African continent [5]. However, the mining of gold and other minerals has led to the increase in the concentrations of toxic heavy metals in the biosphere, atmosphere, and hydrosphere [6–10]. Heavy metals are found naturally in all spheres of life at a minimal concentration. Natural sources include bedrock weathering, volcanic activities, and atmospheric fallout.

However, these concentrations have been increased due to anthropogenic activities for example, exploration of mineral deposits [11, 12].

Heavy metals are classified as metals with specific density more than 5 g/cm3 which negatively impact the environment and living organisms [13]. Heavy metals can be classified into two types; essential heavy metals and non-essential heavy metals [14]. Essential heavy metals such as iron and zinc are important for human metabolism at low concentrations; however at higher concentrations, they are toxic [15]. For example, iron is a type of needed protein for the red blood cells that carries oxygen from the lungs to all parts of the human body [16, 17]. However, at high concentrations, iron becomes toxic to humans leading to hemochromatosis which can cause serious damage to the human heart, liver and pancreas [18, 19]. Zinc is a major player in the development of DNA, growth of the body cells, building proteins and healing damaged body cells at low concentrations [20, 21]. At high concentrations, it causes nausea, vomiting, loss of appetite, stomach cramps, diarrhea, and headaches [22–24].

The non-essential heavy metals, for example, cadmium (Cd), arsenic (As), lead (Pb), uranium (U), are toxic to humans even at low concentrations [14, 25, 26]. Cadmium is known to cause lung damage, kidney damage and fragile bones which can result in death [27, 28]. Exposure to arsenic from food and water leads to cancer, skin lesions, cardiovascular disease, and diabetes [29–32]. Lead reduces brain development, causes anemia, body weakness, kidney, and brain damage [33–35]. Uranium can cause lung cancer, liver and kidney damage [36, 37]. Most of these non-essential heavy metals are carcinogenic; they could lead to the development of cancer of vital human organs which can eventually lead to death [14, 38]. This is even worse when these toxic heavy metals are ingested indirectly by immuno-deficient humans [39].

There are several pathways for heavy metals such as through air, water, and sediments [40, 41]. While some of these heavy metals are highly mobile, such as uranium (U), arsenic (As), some are of less mobility like lead (Pb), and cadmium (Cd). Depending on the mobility of the heavy metals, high concentration of the metal can be found several miles away from the mining environment. High concentrations of heavy metals have been recorded in sediments within and outside the perimeter of a mining area in South Africa. Fashola et al. [42] reported concentrations of As, Cd, Pb and Zn above the recommended levels by South African guidelines for soils and sediment qualities guidelines from abandoned gold mining sites. In the study of the spatial assessment of heavy metals contamination in household soils in rural Limpopo Province, South Africa, Kapwata et al. [43] reported high concentration of Pb, Cd, As and mercury (Hg), exceeding the Canadian reference levels of these heavy metals in soils characterized by abandoned mines and artisan mining activities in Limpopo Province, South Africa.

Concentrations of heavy metals have also been reported in plants around a mining environment. Flefel et al. [44] reported high concentrations of Cd, 0.85– 30.30 mg/kg and Pb, 21.50–68.00 mg/kg in aquatic plants higher than the sampled water. The researchers concluded that the concentrations of heavy metals in plants were above the acceptable limits of Cd, 0.02 mg/kg, Pb, 2 mg/kg set by World Health organization (WHO). In the study by Kausar et al. [45] high concentrations of Cd, Pb, and Zn were recorded in crops irrigated by heavy metal polluted water. The accumulation of Cd, Pb and Zn was recorded in the crops' leaves and root of carrot and spinach. While some of these plants are consumed directly by humans, some are used to feed animals such as cattle which exposes humans to direct and indirect carcinogenic health risks.

### *Toxic Heavy Metals in Soil and Plants from a Gold Mining Area, South Africa DOI: http://dx.doi.org/10.5772/intechopen.109639*

In mines nearby streams, high concentration of heavy metals has been recorded by several researchers [10, 46, 47]. Shapi et al. [46] reported heavy metal concentrations from water samples that have accumulated in wetlands due to the past gold mining operations in Krugersdorp, South Africa. The maximum concentrations recorded for As, Pb and Zn are 32.20 mg/L, 6.30 mg/L and 783 mg/L respectively [46]. In the study by Chetty et al. [47] on the transportation and accumulation of heavy metals in the Klip River's catchment, elevated concentrations of different heavy metals were recorded which included As, Cd, Pb. The authors concluded that the extensive accumulation of these heavy metals in the water body is the legacy of past and extensive gold mining in the Witwatersrand Basin [47]. Raji et al. [10] reported high concentration of uranium and other heavy metals in Rietspruit system because of gold mining activities that was operation at the headwater of the Rietspruit, Far West Rand goldfield. Residents of informal settlements that depend on nearby surface water from streams and dams polluted by heavy metals for their basic domestic needs eventually ingest dissolved heavy metals. The availability of these heavy metals will continuously pose an enormous health risk to downstream water users.

Many researchers have also reported high concentrations of heavy metals in air around the mining environment. Mining wastes such as unrehabilitated tailingdams are rich in heavy metals which are fine-grained. The top-layers of these tailing-dams can be transported by wind. Local residents within close proximity inhale this air which can lead to different respiratory diseases [48, 49]. Residents of Soweto, South Africa, residing near tailing-dams have reported several respiratory illnesses which has been linked to the presence of tailing-dams close to their community [50]. Heavy metals in air in due course settle down on land and plants. Plants uptake these heavy metals and bio-accumulate the toxic elements in their leaves, stems, and roots [51–53]. These plants are later consumed by humans either directly or indirectly through cattle that fed on those plants. In all the findings, the general conclusion was that there is an obvious decrease in the concentration of the heavy metals as the distance from the source pollutant (mining site) increases.

In this study, the concentrations of As, Cd, Pb, and Zn within a 1 km radius of a gold mining environment in North-West Province, South Africa was studied. These heavy metals are some of the most toxic heavy metals highlighted by the World Health Organization, WHO, [54–56] and they have been associated with gold mining operations [42, 57–59]. This study is important because there is currently limited published literature about the concentration of these heavy metals from the gold mine located in the North-West Province of South Africa. Considering the several agricultural activities within the proximity of the mines such as maize plantation and cattle husbandry, it is very important to determine the concentration of these selected heavy metals within a 1 km radius of the gold mine if crop safety measures need to be implemented.

The main objective of this study is to determine the concentrations of As, Cd, Zn and Pb in soils and plants within the 1 km radius of a gold mine. The specific objectives are highlighted below.


### **1.1 Study area**

The study area is in the Ratlou Local Municipality, North-West Province, South Africa surrounding an open pit mine (**Figure 1**). The gold mine was established in 1996 and gold is mined from the gold bearing ore in a banded ironstone formation of the Kraaipan Greenstone Belt. North-West Province is a water scarce Province because of the high-water demand and low precipitation. The rate of evaporation is more than double the rate of precipitation [58]. An extreme drought is experienced in the province.

The North-West Province is dominated by the Savannah Biome and the rest falls in the Grassland Biome. The climate of the Province is categorized by hot temperature reaching about 38°C in the summer and cold sunny winter.

Besides mining, agriculture is another mainstay of the economic activities in this region, hence, the province is regarded as the food basket of the nation. Large maize plantation and sunflowers are located within the 2 km radius of the gold mine. Grazing cattle and ranches were witnessed during fieldwork. The studied plant (*Eragrostis hypnoides*) is among the observed plants that the cattle fed on.

This study site was selected because it characterizes distinct land use landscapes. With the gold mine within proximity of established commercial farmlands, it is crucial to examine the concentrations of As, Cd, Pb and Zn in the soil and plant found within 1 km of an active gold mine.

**Figure 1.**

*Map of the study area showing the sampled sites.*

*Toxic Heavy Metals in Soil and Plants from a Gold Mining Area, South Africa DOI: http://dx.doi.org/10.5772/intechopen.109639*
