Chapter 5 Results and Discussion
5.5. Comparison of the Palmiet and Sezela Rivers
A comparison between the two rivers is made to determine the activities which place a stress on the ecosystem. The Palmiet River is defined as an industrial-residential river whereas the Sezela River is defined as an agricultural-agricultural processing river. The Palmiet River is therefore expected to exhibit higher heavy metal concentrations while the Sezela River may be more prone to inorganic anion pollutants due to the nature of agricultural activities.
5.5.1. Anion Pollutants
A comparison of the average phosphate, nitrate and sulfate concentrations in both rivers was done (Table 5.8). All three anions are different to each other in the rivers. Phosphates and sulfates in the Palmiet River are lower than the Sezela River. These anions are deposited in the river via run-off from the fertilised sugarcane fields. However, the levels present in Sezela are not above the listed guideline values. Nitrate levels in the Palmiet River are higher than the Sezela River. Additionally, the levels exceed the stipulated guideline value. The influx of nitrates may be due to the use of nitric acid in industrial processing in the Pinetown area (Thambiran 2002).
Table 5.8: Average metal (sediment) and anion (water) concentrations of the Palmiet and Sezela Rivers.
River
Inorganic Element / mgkg-1 Anion / mgL-1
Cr Cu Ni Pb Zn PO43- SO42- NO3-
Palmiet 415.90 334.27 296.35 212.82 713.96 < DL 23.31 135.00 Sezela 147.48 87.80 110.83 124.79 123.04 2.65 64.27 34.02
Values in red indicate concentrations exceeding the ERM values (metals) and guideline values (anions)
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5.5.2. Metal Pollutants
The Palmiet River had higher average metal concentrations in sediment than the Sezela River (Table 5.8). The Palmiet River has metal, metal processing, paint and chemical manufacturing industries in the Pinetown area which contribute significantly to the metal concentrations in the river. Chromium, Cu, Ni and Zn exceed the ERM values which indicates that the risk of metal toxicity is greater. In comparison, metal concentrations in the Sezela River are significantly different to Palmiet (ANOVA, p >0.05) and are considerably lower. The effect of industrial activities on metal introduction into the environment can be clearly seen in these two river systems.
5.5.3. Comparison of Palmiet and Sezela Rivers to other South African (SA) Rivers
The two rivers studied were compared to a number of other SA rivers where significant research has been carried out. The Palmiet River is a tributary of the Umgeni River.
5.5.3.1. Anions
Other industrial rivers are compared with the Palmiet River (Table 5.9). No phosphates were detected in the Palmiet and Umgeni Rivers. The nitrate concentration in both these rivers are above the guideline value which suggests that nitrate contamination is a problem since the Jukskei River has comparatively lower concentrations. Sulfates are of concern with concentrations greater than 500 mgL-1 (WHO 2006). Sulfates are generally precipitates due to its solubility with cations particularly of Ba, Sr, Pb and Ca.
Sezela River has average anion concentrations below guideline limits (Table 5.9). Compared to other agricultural rivers, the Sezela River has elevated levels of anions. Fertilisers are primary input sources of anions into freshwater systems. The Sezela River flows through sugarcane plantations similar to the Umdloti River (Olaniran et al. 2013). This suggests that
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commercial fertilisers are being used excessively in these regions as other agricultural rivers have much lower concentrations.
Table 5.9: Comparison of average anion concentrations in this study and other South African rivers.
River Type of River
Anion / mg.L-1
Reference PO43- NO3- SO42-
Palmiet Industrial 0.00 135.00 23.31
Umgeni Industrial - 66.97 193.57 (Dikole 2014)
Jukskei Industrial 0.4 22.3 195 (Huizenga and Harmse 2005) Sezela Agricultural 2.65 34.02 64.27
Umdloti Agricultural 1.06 0.13 27.86 (Olaniran et al. 2013) Crocodile Agricultural 0.043 0.49 - (van der Laan et al. 2012)
Pongola Agricultural 0.034 0.45 - (van der Laan et al. 2012)
Values in red indicate concentrations exceeding the guideline values
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5.5.3.2. Metal Contaminants
Rivers with similar anthropogenic activities in South Africa were compared to the Palmiet and Sezela Rivers (Table 5.10). The Umgeni and Isipingo Rivers are well documented rivers for heavy metal pollution (Carnie 2014). Industrial effluent containing dissolved metals are released into rivers and waterways. These metals accumulate in sediment and begin to affect the environment. The Palmiet River, a tributary river, has higher concentrations in sediment than the major rivers which is of concern. Industrial rivers have higher concentrations of metals than the agricultural rivers. This suggests that toxicity is of concern particularly in industrial rivers.
The Sezela River has higher average metal concentrations in sediment than similar agricultural rivers (Table 5.10). Metal accumulation in the sediment may be due to the use of fertilisers and additives to the sugarcane fields. The geology of the region contributes to the total metal concentration of the area. The agricultural activity around the Sezela River is a larger scale activity compared to the Tyume and Mvudi regions which rationalises the higher concentrations as more fertiliser and resources are utilised.
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Table 5.10: Comparison of total heavy metal concentration (average concentration) in sediment from South African river studies River Type of River Cr / mg kg-1 Cu / mg kg-1 Ni / mg kg-1 Pb / mg kg-1 Zn / mg kg-1 Reference
Palmiet Industrial 415.9 334.27 296.35 212.82 713.96
Umgeni Industrial 82 85 - 172 145 (Dikole 2014)
Isipingo Industrial 248.44 195.75 32.76 228.75 1796 (Pillay 2011)
Vaal Industrial 68.77 32.27 71.27 9.4 46.27 (Pheiffer et al. 2014)
Orange Industrial 16.8 20.1 33.8 4.6 31.3 (Pheiffer et al. 2014)
Swartkops Industrial 20.3 6.8 - 33 36 (Binning and Baird 2001)
Sezela Agricultural 147.48 87.8 110.83 124.79 123.04
Tyume Agricultural - 0.279 0.6 0.052 0.329 (Awofolu et al. 2005)
Mvudi Agricultural 97.8 30.24 - 4.28 26.56 (Edokpayi et al. 2016)
Values in red represent concentrations greater than the ERM value
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