Evaluation Of Trace Elements In The Environment Around The Lejweleputswa Area Of The Free State, South Africa

Abstract

Trace elements were evaluated in the soil, leaves, water and sediments in six towns of Allenridge, Odendaalsrus, Welkom, Virginia, Theunissen and Brandfort in the Lejweleputswa Municipal District of the Free State, South Africa in light of the extensive mining activities taking place in the area. Samples of soil, leaves, water and sediments were collected on monthly basis over a period of 3 months (October, November and December, 2012 and April, May and June, 2013) to cover both the dry and wet seasons. The sampled environmental samples were analyzed for trace elements using an ICP-OES, model ICPS – 7510 (Shimadzu), sequential plasma spectrometer. Soil samples were collected within 25 cm depth of soils and leaves collected from Acacia Karroo plants in the same vicinity at which the soil was collected. Water and sediment samples were also collected from streams in the same area from which the soil and leaves were collected. The reason for collecting all the different samples – soil, leaves, water and sediment samples from the same area for each location at a given sampling period, was to ensure proper comparison of trace elements content variation in the different media over the period of the study in a comparable environment. Soil trace elements variations in the six studied towns over the paired 3 months period of the study, in the Lejweleputswa District Municipality (LMD) of the Free State, South Africa, suggested that the highly concentrated trace elements of the soil were calcium, followed by iron and magnesium. The excessive concentration of calcium and magnesium in the soil, other than their natural occurrence, is attributed to the regular liming exercise in which calcium hydroxide (Ca(OH)2)and magnesium hydroxide (MgOH) are used to neutralize the excessive sulphuric acid (H2SO4) in the soil due to Acid Mine Drainage (AMD) caused by the dissolution of the sulphur occurring together with pyrite (FeS2) in water. This often leads to the formation of low pH-value (high concentration) of sulphuric acid. Calcium was the predominant trace element in leaves obtained from Lejweleputswa District Municipality. In Allenridge, the highest calcium concentration occurred in April, 2013 at above 100 ppm (2.12%). In Brandfort and Theunissen their highest calcium concentrations of above 100 ppm occurred in June 2013. The highest calcium concentration in Welkom above 100 ppm occurred in October, 2012 (2.10 %) and June, 2013 (2.08 %) respectively. For Virginia and Odendaalsrus, their highest calcium concentrations occurred in November, 2012 at about 1.50 % (>10 ppm) and December, 2012 at about 1.95 % (> 10 ppm). The highest mean concentration and distribution of calcium in the leaves was observed from Lejweleputswa District Municipality area of the Free State, South Africa. The calcium versus magnesium (Ca-Mg) ratio in leaves was statistically insignificant for all the towns. The second most abundant element in the leaves was magnesium, occurring at concentrations greater than 1.0 ppm. Sulphur and phosphorous also occurred mostly at concentrations greater than 1.0 ppm in the leaves. In the water bodies in Lejweleputswa District Municipality, the most dominant trace element was calcium in the environment. Sulphur showed great prominence especially in Allenridge where they occurred above 100 ppm most of the time. The highest occurrence of calcium by far was in Allenridge at about 1262 with drastic decrease in April, 2013 culminating in a relatively low calcium concentration in May, 2013. For other towns, the calcium concentration remained generally low except for Odendaalsrus where calcium concentration elevated to approximately 123.33 and 126.32 for the months of May and June, 2013 respectively. Welkom had the third highest concentration of calcium in the water surpassing Odendaalsrus only in October, 2012 and April, 2013. Allenridge recorded the highest concentration of magnesium in the water during October, November and December, 2012 at 195, 278 and 249 % respectively and 142 % in June, 2013. For other towns, magnesium concentrations remained generally moderate except for Welkom where it remained in the region of 60 % for most of the time. In the sediment, calcium and iron were the predominant trace elements in all the studied towns with sulphur, magnesium and aluminum showing significant prominence. The highest occurrence of calcium in sediment was in Welkom with least occurrences in Odendaalsrus and Virginia. However, in general, calcium occurrence in the sediment in all the studied towns appears relatively uniform. The highest occurrence of magnesium in sediment was recorded in Branfort, followed respectively by Theunissen and Welkom. Allenridge, Odendaalsrus and Virginia had even occurrence of magnesium in sediment.