2.3 ENVIRONMENTAL POLLUTION BY POTENTIALLY TOXIC ELEMENTS
2.3.1 Potentially toxic elements in river water
Water is important for the existence of life on earth. All organisms require it and aquatic plants and animals live their life in water hence making water their direct source of life.
The contamination of water bodies such as rivers, oceans and lakes in which pollutants are directly or indirectly discharged into water bodies without sufficient treatment to remove harmful particles or substances is termed water pollution (Agrawal et al., 2010). Human development has partially contributed to the deterioration of water quality. Water quality is referred by the physical, chemical and biological characteristics of water in relation to their existence of life and especially human activities (Lamb, 1985).
The effect of water pollution damages not only individual species and population, but also the natural biological communities. Water pollution is a major global problem, which requires continuous assessment and modifications of water resource policies at all levels from international to individual aquifers and wells. It has been suggested that water pollution is the leading worldwide cause of deaths and diseases, and that it accounts for the deaths of more than 14,000 people daily as reported by West (2006).
Water pollution is often linked to heart diseases, poor blood circulation, nervous system and skin lesion. Cholera and diarrhoea are among the common problems caused by the accumulation of bacteria and metal poisoning in water (Khan and Ghouri, 2011). The future human and aquatic generation face a threat of alteration in the chromosomal makeup, as a result of uncontrollable water pollution (Nazir et al., 2015). This is caused by toxic effluents from different sources which reduce the availability of oxygen in the water body, when they are directly disposed as wastes in the water system.
As such, the flora and fauna of rivers, seas and oceans is adversely affected by water pollution. Thus, poses as a direct threat to the human health via the food chain (Asfaw et al., 2013).
13 The water quality guidelines where classified on their usage such as agricultural, aquatic, domestic and industrial use. Water quality guideline values are used for the relevant and specified activities associated with the water use. Industrial water refers to the different uses of water in industrial under process types, such as cooling water, steam generation, process water, production water and utility water (DWAF, 1996b).
Industries have been popularly identified as the main contributors to elevated levels of chemical deposits in the environment and water bodies (DWAF, 1996b). The untreated water disposed into rivers and streams after industrial productions, may cause corrosions, abrasions and aquatic deaths which through a food chain may cause irreversible damages to human health over long exposure (DWAF, 1996b).
Domestic water refers to water that is used in a domestic environment and also refers to all uses water can be put to in this environment. These include water for drinking, cleaning, cooking and handling food and beverage preparations, bathing and personal hygiene, recreational activities such as swimming, laundry and gardening. Commonly, domestic water users experience impacts such as bad health due to the poor water quality (DWAF, 1996a). The presence of potentially toxic elements in the water systems and water bodies, lead to detrimental health effects due to both short and long-term exposure based on the type of constituents found in the water course (Bernhoft, 2013).
Irrigation water refers to water which is used to supply the water requirements of crops and plants which are not provided by rain and refers to all uses water may be put to in this environment. This include water for the plantation of commercial crop irrigation water application and distribution systems, small scale home gardening and potted plants sold in flea markets (DWAF, 1996c). Equally important, untreated water used for irrigation can leave detrimental impacts such as the reduction in the yield of crops due to salinity or constituents that are harmful to the proper growth of the plants.
Accumulation of potentially toxic elements in the crops lead to corrosion of the planting equipment and toxicity in humans through food chains (DWAF, 1996c).
Although South Africa has made substantial progress in shifting policy bodies to address mine closure and mine water management, and the mining industries have changed their practices to adhere to new laws and regulations, irregularities in the system still remain.
14 South Africa is one of the few countries in the world that cherish the basic right to sufficient and clean water in its constitution. This is implemented by the existence of water bodies, which are bulk water supply agencies that operate pipelines, dams, waste water systems and sell water from reservoirs to municipalities. Despite the efforts, availability of water in South Africa varies with space and time commonly favouring urban places and excluding rural settlements.
Activities in the mining industries are one of the setbacks that environmental policy makers need to address as an ongoing assessment to minimise the deterioration of water quality.
Disturbance to the food chain is one of the major effects of water pollution. When toxins are present in water they are conveyed to higher level organisms through the food chain. As such, these hazardous wastes are passed on to humans and animals.
Potentially toxic elements like Pb, Hg, Fe, Cd, Al and Mg are mostly present in water.
If these metals are present in the sediments, they reach the food chain through plants and aquatic animals (Cheng and Hu, 2010; Hosono et al., 2011). This then causes accumulation of heavy metal poisoning in the human bodies and aquatic animals.
Poor blood circulation, vomiting, skin lesions and damage to the nervous system are few of the many other health issues related to polluted or untreated water (Ashraf et al., 2011). Water pollution is considered to be a major cause of death of the population across the world. Water pollutants modify the overall chemistry of the water, causing changes in acidity, conductivity and temperature. These in turn have an effect on the marine life (Ashton and Dabrowski, 2011).
Marine food sources are contaminated or eliminated by water pollution and disturb the vulnerable ecological balance of marine life. Dead fish, birds, dolphins, and many other animals often wind up on beaches, killed by pollutants in their habitat. Heavy rains carry up dirt and silt, and then deposit them into the water. If the dirt and silt settle in the water body, then the sediments prevent sunlight from reaching aquatic plants.
If the sunlight can’t reach the plants, they will die. The sediments also clog up fish gills and suffocate organisms that live on the bottom body of the water (Hosono et al., 2010).
15 Additionally, pollution affects and modifies the chemistry of water. The pollutants, including toxic chemicals, can alter the acidity, conductivity and temperature of water.
Drastic killing of fish and aquatic plants in rivers, oceans and seas is an after-effect of water contamination. Addo-Bediako et al. (2014) reported that the metal concentrations in the muscle tissue of fish (Schilbe intermedius) appear to have increased at Flag Boshielo Dam and the Phalaborwa Barrage over the past 20 years.
They further reported that the concentrations of Al, Cu, Fe and Cr were high in the muscle tissues of the fish. Studies by Addo-Bediako et al. (2014) have been done at the Phalaborwa Barrage where it was reported that almost all fish sample analysed from the river exceeded the recommended level for Pb and more than 50% exceeded the permissible level of As.
2.3.1.1 The effect of pH on the environment and water
There are many contributing factors that can affect the pH of water. These factors are both natural and man-made. Natural changes in pH can result from the existence of carbonate materials and limestone. When carbonate minerals are present in the soil and sediments at the bottom of streams, rivers and seas, the alkalinity of water increases, keeping the pH of water close to neutral even when acids or bases are added (Utah State University, 2013).
Carbonate materials beyond the neutral limits can increase the basicity of water.
Volcanic ash, sulphate-reducing bacteria in wetlands, airborne particulates from wildfires and even lightning are some of the additional natural modifications of pH levels in water bodies (NADP, 2013). Low pH levels can influence the solubility of potentially toxic elements. The elevated levels of hydrogen ions influence metal cations such as Al, Pb, Cu and Cd to be easily discharged into the water instead of being absorbed into the sediments (USGS, 2013).
Pollution is one of the anthropogenic activities that can also change a water's pH, which in turn can harm animals and plants living in the water (USGS, 2013).
According to the APHA (1998) the pH range of 6.0-9.0 appears to provide a good protection for aquatic organisms such as fish and the bottom dwelling invertebrates like corals and snails.
16 Susceptibility of aquatic species determines the degree of damage caused by the changes in pH values. Apart from aquatic species being at risk of being affected by the changes in water pH, humans are also at risk due to the direct and indirect use of river and stream water. In a thesis submitted by borosilicate (2005), he emphasised that although humans have higher pH level tolerance ranging from 4-11 with minimal gastrointestinal irritation, values greater than 11 can cause skin and eye irritations.
Furthermore, pH values below 2.5 will cause irreversible damage to skin and organ linings.
Lower pH levels increase the risk of mobilised toxic metals that can be absorbed, even by humans while levels above 8.0 cannot be effectively disinfected with chlorine, causing other indirect dangers to the human health (USEPA, 2012).
The pH levels below and above 6.5-9.5 range can cause damage and corrosion to pipes and other water systems, hence increasing heavy metal toxicity in the environment (WHO, 2003).
Active and abandoned mining and power stations have an equal share in the contributions towards the acidity of the surrounding environment which also affect the pH of water. These industries release chemical emissions during coal burning for coal- fired powered stations and automobiles during transportations (Osmond et al., 1995).
Mine acid runoffs lower pH values below the accepted levels. This may be tolerable for some aquatic species such as frogs but not for most fish. Potentially toxic elements can accumulate on the gills of fish or cause deformities in young fish, reducing their chance of survival (Pandey and Madhuri, 2014). Agricultural activities also release chemicals such as pesticides and herbicides, which alter the pH levels of water (Morakinyo et al., 2013).