Materials and Method

3.1: Description of study areas

Matla power plant is located in Mpumalanga Province (26.28249ºS 29.14072°E). The plant has the capacity of generating 3600 MW installed capacity and it has been in operation since 1983. Lethabo power plant is located in the Free State Province (26.74194°S 27.9775°E) and has been in operation since 1985. It has a generating capacity of 3708 MW of electricity. Rooiwal power plant is located in Gauteng Province (25.55580°S 28.23834°E). The plant has been in production since 1963 and has an installed capacity of 300 MW of electricity. In all three plants combustion gases are released through two stacks and local sub-bituminous coal is used in all of them (Fig 1.2).

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Fig 3.1. Picture of power plant showing two stacks where emission is released and four coolants

3.2: Materials and reagent

PAHs considered in this study included naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[e]acephenantrylene, benzo[k]flouranthene, benzo[a]pyrene, perylene, and indeno[1,2,3-cd] pyrene). All PAH standards were of 98.0 to 99.5% purity and were purchased from Sigma (Seelze, Germany). The solvents used for the extractions and clean-up were of analytical grade (99.5 %). Solvents were also from Sigma-Aldrich and included hexane, acetone, methanol, dicholoroethene,

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dichloromethane and chloroform. Acetonitrile (MeCN) was purchased from Romil (Waterbeach, Cambrigde, UK). Silica gel used in column clean-up was purchased from Merck (Darmstadt, Germany). Standard reference material soil from Industrial Analytical Ltd (Midrand, South Africa) Ltd with Catlog No: CRM 142-100 and Lot No: 014105 was used.

3.3: Soil samples

About 500 g of surface soil (0–5 cm depth) samples were collected with the aid of a stainless steel trowel in the predominant wind direction, 0 to 30 km from the coal power plant for Matla and Lethabo and 0 to 20 km for Rooiwal coal power plant. Plant samples were also collected at the same point where the soils were taken. The plant was washed thoroughly in distilled water so as to remove superficial dust. The samples were allowed to dry in an oven at a temperature of 60 °C for a period of 48 h. Samples were collected six times between August 2010 and June 2011 with the aid of the global positioning system (GPS) to ensure sampling from the same area. In each sampling site, seven composite samples were collected. The control samples were collected from the greenhouse at the University of South Africa. It is a controlled area with reduced human activities. All soil samples were air-dried, pulverised and stored in amber bottles at 0–4 °C until chemical analysis (Okedeyi et al., 2012).

Digitaria is a genus of about 300 species of grass (family Poaceae) native to tropical and warm temperate regions. Common names include crabgrass, finger-grass, and fonio. They are slender monocotyledonous annual and perennial lawn, pasture, and

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forage plants; some are often considered lawn pests. Digitus is the Latin word for "finger", and they are distinguished by the long, finger-like inflorescences they produce. Crabgrasses have uses despite being classified by many as weeds. The seeds, most notably those of fonio, can be toasted and ground into a flour, which can be used to make porridge or fermented to make beer. Fonio has been widely used as a staple crop in parts of Africa. It also has decent nutrient qualities as a forage for cattle.

85 3.4: Soxhlet extraction procedure

Soxhlet extraction was used for the extraction of PAHs from soil according to the recommended US Environmental Protection Agency Method 3540C (Lauet al., 2010). . Air-dried soil samples were sieved through a 600 micron mesh sieve; 10 g was weighed into an extraction thimble and the PAHs were extracted with (1:1) hexane/acetone mixture for 6 hours. The extracts were transferred to a rotary evaporator and pre- concentrated to a volume of 2 mL with a vacuum rotary evaporator from Buchi R-200 (Flawil, Switzerland). The concentrated extracts were cleaned up using column chromatography (silica gel). PAHs were eluted with acetone and concentrated to 1.5 mL under a gentle stream of nitrogen (Crnkovic et al., 2007; Olajire et al., 2007).

3.5: GC-MS of PAHs

Stock standard solutions of concentrations of 100 µg mL-1 were prepared in acetone and stored at 4 0C. The determination of PAHs was on Agilent GC-MS consisting of a 7890A GC equipped with a splitless injector, 5975C mass selective detector (MSD) and 7693 autosampler from Agilent Technologies (Santa Clara, California, USA). Data acquisition was achieved using Agilent MSD ChemStation. A sample of 1 µL was injected into a capillary column DB-1HT 30 m × 0.25 mm i.d. with 0.1 μm film thickness (Agilent Technologies, Santa Clara, California, USA). A splitless injection mode was used. Temperature programming was as follows; initial temperature was at 60 0C held for 4 minutes, followed by an increase to 310 0C at 7 0C/minutes and held for 20 min at the maximum set temperature. Ultra-high purity helium (99.999 %) gas was used as the carrier gas at a flow rate of 1 mL min-1 (Afrox (Johannesburg, RSA). An external

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standard calibration method based on a four-point calibration curve (concentration levels of 0.5 to 4 µg mL-1) was used.

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Fig 3.3 Typical chromatogram of 15 PAHs standards. Peak ID: a = Nap, b = Ace, c =

Flo, d = Phe, e = Anth, f = Flan, g = Pyr, h = B[a]a,i = Chry, j = B[b]f,k = B[e]a, l = B[k]f, m = B[a]p, n = Pery and o = Ind