Table 1 shows the mean levels for the analysed water quality parameters. These results were compared against the EMA’s surface water and effluent quality classifications (Table 2). The analysed parameters are discussed below
Table 1: Surface water quality parameters.
Table 2
EMA classification of hazards
Classification
|
Risk
|
Reason of classification
|
Blue
|
Safe
|
Complies with blue standards
|
Green
|
Low Hazard
|
Waste meets green standard or blue license conditions not being meet
|
Yellow
|
Medium Hazard
|
Waste meets yellow standard, or green license conditions not being met
|
Red
|
High Hazard
|
Waste meets red standard or yellow license conditions not being met
|
3.1 Turbidity
During the dry season, turbidity in the upstream of the river averaged 4.87 NTU, 9.8 NTU in the mining area, and 6.25 NTU downstream. Turbidity was lowest in the wet season at the upper stream with a mean value of 3.47 NTU, illegal gold mining area with a value of 221 NTU, and downstream after illegal gold panning with a value of 17.7 NTU. The turbidity concentration in river water differed considerably across seasons, with a P value of 0.004. The EMA danger categorization for the upstream for both seasons was acceptable to standard blue, while the illegal gold panning region during the rainy season was acceptable to standard red, and there was standard yellow downstream. The EMA danger classification for the upstream for both seasons was standard blue class, while the illegal gold panning region during the rainy season was standard red class, and there were standard yellow and green classes downstream.
There was low turbidity in the upper stream of the River during both the rainy and dry seasons, owing to the lack of illegal gold panning activities and restricted siltation, which can turn water brown or muddy. In general, high turbidity at sampling point three during the wet season can be linked to high rainfall, which causes increased runoff and, as a result, water erosion in the river and within the river beds, increasing sediment load, as evidenced by the reddish colour of river water after rainfall events (Diamant et al, 2013). As a result, when water is supplied for drinking reasons, it is frequently subjected to water treatment due to the risk of turbidity. For example, mud and silt are washed into rivers and streams during the rainy season. The high turbidity at sampling site two is linked to a large amount of sediment being carried into the river by illegal gold panners in the form of gold-rich soil as they separate the mineral from the soil. Turbidity is a concern because it promotes siltation of water sources, resulting in limited river storage capacity and a higher risk of flooding (Mudyazhezha and Kanhukamwe,2014). As a consequence, water with high sedimentation poses a health risk to many water consumers who rely on chlorination to disinfect water with high turbidity, lowering chlorination's efficiency. Sediment settling can clog or block conveyance and storage systems, resulting in expensive maintenance costs.
3.2 PH
The graph below, shows reduction in the pH to acidic from the mining area up to the downstream of the River during drying season, hence having mean values of 6.37 and 6.10. The wet season showed a high pH with the mining area having the lowest mean of 7.31. The rest of the sampling sites in the wet season was alkaline with a significant difference of P value at -0.19. According to the EMA hazard classification standard, the upper stream, illegal gold panning area and the downstream, had figures within the blue safe class.
The pH results were underlined in blue, indicating that they were safe. During the wet season, these values were more neutral to alkaline, but during the dry season, they were more alkaline. This was linked to high levels of erosion in red clay and sandy soils, which contain basic chemicals such as iron oxide, iron hydroxide, and copper oxide, causing water to become alkaline (Environmental Impacts, 2002). More specifically, acidity of water in the dry season from the mining area upstream was caused by acid waste that was frequently released when illegal gold miners pumped water from the river into their buckets to access gold seams and then disposed of the contaminated water back into the river while it was contaminated or polluted. During the dry season, however, the pH lowering at sample sites two and three may have been caused by natural purification of water, which takes up more ambient oxygen, resulting in the supply of hydrogen ions, thereby neutralizing the acidity. Changes in pH have a negative impact on a variety of industries. It has the potential to lower aquatic biodiversity because these organisms took a long time to form and adapt to normal settings, and a sudden shift in these parameters can result in the death or migration of certain species (Shoko, 2002). In agriculture, pH extremes can induce nutrient deficits and toxicities due to nutrient imbalances. Acidic water, which corrodes the conveyance system and finds its way into human bodies, can induce heavy metal poisoning (Nyakungu and Mbera, 2013).
3.3 Iron
Iron concentrations declined at the upstream and downstream of the River during the dry season, with values of 0.405 mg/l and 11.95 mg/l, respectively, followed by a rise at the illegal gold panning region, with a value of 1035 mg/l. During the wet season, the values for upstream, mining region, and downstream were 0.62mg/, 8.63mg/l, and 5.63mg/l, respectively, compared to 0.62mg/, 8.63mg/l, and 5.63mg/l during the dry season. With a P value of 0.005, the iron concentration in river water varies considerably among seasons.
Iron (Fe) concentrations at unlawful gold panning spots were substantially higher than WHO limits as well as effluent regulations S.I.106 of 2007 (EMA) for both the dry and rainy seasons, and were classed as yellow and red standard classes. Higher concentrations of iron may have been released by illegal gold panning, which allows for the leaching of rocks containing iron into the River, as opposed to upstream where illicit gold panning is limited due to high water depths and infrastructure such as bridges. Local communities are at risk of iron poisoning, which an iron overload is produced by excessive iron intake, due to the high content of iron. As the stomach lining gets ulcerated, the first signs of iron poisoning via ingestion are stomach pains. Nausea and vomiting are common side effects. As the iron goes further into the body, damaging internal organs, mainly the brain and liver, and metabolic acidosis develops, the pain subsides for 24 hours. Thus, the findings of the study demonstrate that water pollution kills life that depends on water bodies, such as fish, crabs, birds, and a variety of other species that often end up on river banks or coasts.
3.4 Copper
During the dry season, copper concentrations drop to 0.22 mg/l and 0.53 mg/l at sample sites one and three, respectively. The copper concentration in the illegal mining region increased to 3.82 mg/l, 3.08 mg/l, 7.44 mg/l, and 4.02 mg/l, respectively, for upstream, mining area, and downstream. Copper's results were divided into three standard classes: green, red, and yellow. All of the study sites had significant differences in concentrations, with a P value of 0.001.
The presence of copper in water is due to its natural presence in water, which happens when flowing water comes into touch with copper-bearing rock or soil (Salem et al., 2000). The illegal gold panners dumped copper-bearing soils directly into the river, resulting in high copper levels at site two. The majority of copper in soil is contained in the form of silicates, which give soil its reddish colour, and these silicates are hydrolysed to release copper ions into water (Schulte, 2004). During the rainy season, there was an even higher concentration of copper, which could be due to natural processes such as high rates of water erosion, which result in more silt from red clay soils rich in copper ions being deposited into the river. Copper is necessary in the body in small amounts, but excessive amounts can have major health consequences, such as immune system breakdown and lowered susceptibility to opportunistic illnesses (Salem et al., 2000). This puts the people of Umzingwane River ward four villagers' health at risk because they don't have a consistent clean source of water for agriculture, irrigation, home usage, or livestock. Copper has a severe impact on agriculture because it destroys plant roots in high concentrations and is rarely translocated by plants, interfering with plant osmosis.
3.5 Chemical oxygen demand
The results for chemical oxygen demand, showed that sampling points 1, 2 and 3 in the wet season had extremely high COD values of 751mg/l (upper stream), 626mg\l (illegal gold panning area) and 459mg/l (downstream. There was a decrease of chemical oxygen demand from the upstream up to the downstream of the River in the wet season with values of 749mg/l, 342mg/l and332mg/l. The chemical oxygen demand, in the river water was significantly different between the seasons at P value 1.42.
Chemical oxygen demand values were in the red category (Tables 1 and 2). The data demonstrated that organic and inorganic pollution loads in water elevate COD levels from upstream, meaning that there is also an increase in organic and inorganic content in surface water from chemicals, which is consistent with earlier study (Ghorbani and Salem, 2021). As a result, excessive chemical oxygen demand levels from upstream were blamed for the organic and inorganic composition of chemicals produced by copper and iron in the river during the illegal gold panning activity. Higher COD levels imply more oxidizable organic material in the sample, lowering dissolved oxygen levels. When there is no light for photosynthesis, fish and crustaceans acquire oxygen through their gills, whereas aquatic plant life and phytoplankton require dissolved oxygen for respiration (Purcell and Kotz, 1987).
3.6 Electrical conductivity
Conductivity values were in blue categories for both dry and wet season at all sampling points with values ranging from 36.1 to 17.2µS/cm. The lowest value was recorded at sample site three during the wet season. The concentration of conductivity in the river water, were significantly different between the seasons at P value − 7.18.
A major increase of conductivity was noted at the illegal gold panning zone in the dry season as a result of high concentration of pollutants into the River and in the wet season were attributed to runoff from the illegal gold mining zone up to the downstream. Duncan (2020) claims that the higher the ion concentration, the larger the electrical current that may be conducted, and the fewer the ions, the lower the electrical currents. According to Rezania et al (2016), excessive high electrical conductivity levels cause stunted growth of aquatic vegetation, which is linked to leaf damage, the mortality of aquatic organisms such as fish, and eventually the death of aquatic vegetation.
3.7 Total suspended solids
The suspended solids at the upper stream of the River, had a mean value of 62mg/l, mining area 1050mg/l and downstream 47mg/l. In the wet season, values were 42.5mg/l at the upper stream, mining area 1000mg/l and 25.5mg/l downstream. The EMA hazard classification for the upstream for both seasons were acceptable to standard yellow class while as on illegal gold panning area were acceptable to standard red class and at downstream of the River, standard green class. The suspended solids, in the river water was significantly different between the seasons at P value 0.006.
High concentration of suspended solids were attributed to illegal mining as sediments and soils were released into the water during the mining process. According Chapman (2017), in some rivers, concentrations of suspended solids are influenced to a large degree by the chemistry of water. Therefore, a slight increase of suspended solids in the wet season compared to dry season were due to high River competence which had the capacity to erode every waste from the illegal gold mining zone up to the downstream.
3.8 Total dissolved solids
The summary of TDS concentration at all the three sampling sites, were presented in Table 1. The average values of the three sampling points for both the dry and wet seasons, ranged from 148.5mg/l up to 75.1mg/l and these values were in yellow categories thus below the WHO guidelines for surface water quality, except for sample site three during the dry season which were in standard green class. The dissolved solids, in the river water was significantly different between the seasons at P value 5.06.
During the dry season, TDS levels increased from upstream to downstream, owing to illicit gold panning activity, which deposited mineral rocks, organic debris, and salts into the water. During the wet season, there were larger concentrations of dissolved solids than during the dry season, which was attributable to high runoff dissolving every solid particle from sampling site two to three. Increased dissolved solids levels in public drinking water, according to (Bhojwani et al., 2019), can raise water treatment costs, force the development of alternative water sources, and shorten the life spans of water-using household equipment. During the wet season, a low concentration of dissolved solids was recorded upstream of the River, which was due to a limited depth of water to assist runoff as well as a restriction on unlawful panning activity. The Umzingwane River, which runs through Umzingwane district ward 4, is used for irrigation and serves as an agricultural land use. According to Gondeck et al., (2020) as well as Alam et al., (2021) high soluble salt accumulation in the soil produces water stress for crops by clogging soil pores with clay and humus, limiting the ability of plants to draw water from the soil. TDS of 75.1 mg/l is considered to be very low risk and does not cause salt build-up in the soil, whereas TDS of more than 148.5 mg/l is considered to be very high risk and is generally unacceptable for irrigation, with the exception of very salt-tolerant plants that require excellent drainage, frequent leaching, and intensive management. Findings of this study resonate with those of Duta et al., (2020) and Hirwa (2019) who in their studies conducted in India and Rwanda respecttively detected higher concentrations of TDS in water samples collected from Gold mining areas. Gold mining areas are therefore prone to elevated TDS levels.
Potential sources of detected surface water contamination in Umzingwane River
50% of questionnaire respondents indicated that, illegal gold panning is the major potential source of detected surface water contamination in Umzingwane River and concluded the illegal gold panners of using ancient methods when extracting gold rather than mercury and cyanide since they lack capital, (Table 3).
Table 3
Potential sources of detected surface water contamination in Umzingwane River
Sources of contaminates
|
Frequency
|
Percentage of respondents
|
Formal gold mining
|
10
|
25%
|
Agriculture
|
5
|
12.5%
|
Washing/ Bathing
|
5
|
12.5%
|
Informal gold panning
|
20
|
50%
|
Total
|
40
|
100%
|
Masiya et al (2012), stated that in Zimbabwe, the illegal gold panners (Makorokoza) use simple tools such as shovels because their mining methods are derived from ancient methods of mining, and their operations are small scale and do not have capital to buy modern tools. According to the Environmental officer from EMA, illegal gold panning often entails digging along riverbanks and riverbeds, resulting in fine soil, or silt, being discharged into the river system, a process known as siltation; the river become clogged with silt over time, distorting surface water quality. In addition, the water quality technician stated that illegal gold panning results in erosion of the exposed earth which carry substantial amounts of sediments into the river and excessive sediments has so much implications leading to high water turbidity. The 5% of the questionnaire respondents indicated that, agriculture and washing respectively are also the potential sources of detected pollutants in Umzingwane River, even though they constituted the lowest percentages. According to a representative from Umzingwane RDC, in order to protect their crops from bacteria and insects, farmers in Umzingwane often use chemicals and pesticide and these substances can be washed into the river through sedimentation and siltation. He also stated that, when it rains, these chemicals mix with rain water which then follows into Umzingwane River causing water pollution. According to Daramola et al (2022), sediments are naturally found in water surfaces, but they are produced in vast quantities as a result of land use change and agriculture, farming, deforestation, road construction among others. 25% of questionnaire respondents indicated that mining activities such as gold leaching is also a potential source of contaminates in Umzingwane River where cyanide chemicals are discharged in the river causing it to be overburdened with soils and particle matter. These findings concur with the findings by Duri (2020), found that gold panning activities along rivers are the major sources of contaminants.
Health risks associated with contaminated surface water
Thirty-eight percent of the questionnaire respondent, indicated that they suffer from diarrhoea. whilst, 25%, 17.5%, 12.5% and 7% of questionnaire respondents, indicated that, they face dysentery, cholera, hepatitis and typhoid respectively.
According to Umzingwane hospital nurse in charge, diarrhoea is the major health risk associated with contaminated surface water use and it is the most widely known diseases linked to contaminated water. She further revealed that, diarrhoea, typhoid patients at Umzingwane hospital are as a result of drinking contaminated water. EMA environmental officer explained that, bacteria’s found in contaminated surface water, are responsible for diarrhoea, cholera, dysentery, typhoid and hepatitis. These findings are in line with the findings by WHO (2018) which stated that contaminated water pose a serious diarrhoea and typhoid problems.
Effects of contaminated surface water on aquatic vegetation
Fifty percent (50%) of respondents indicated that contaminants in surface water cause poor growth of algae, thirty-seven percent (37%) said it resulted in low oxygen levels whilst 13 percent indicated eutrophication to be the effect of contaminated surface water.
The Environmental officer from EMA stated that, build-up of contaminants in water affects the amount of oxygen in the water and this complicates breathing for aquatic vegetation. She further stated that, turbidity can be caused by impurities and impacts the development rate of algae and other aquatic plants in the river, therefore increasing turbidity reduces the quantity of light available for photosynthesis. A representative from Umzingwane RDC, also confirmed that, contaminants can cause eutrophication and this can be a problem to aquatic vegetation as it can cause algal blooms. The representative from Umzingwane RDC revealed that eutrophication is as a result of stream bank cultivation as well as Umzinyathi irrigation scheme disposing agricultural chemicals directly or indirectly. For instance, the chemicals can be discharged through siltation and sedimentation as well as through disposing of used empty chemicals containers as well as washing used agricultural tools and chemical container such as fertilizer sacks. Oxygen depletion caused by water pollution disrupts aquatic ventilation, causing suffocation and disturbance among aquatic life. In some circumstances, smaller creatures die off instantly, and dissolved oxygen levels drop, resulting in the release of carbon dioxide, which depletes aquatic plants (Jaiswal et al., 2019).