Ecological assessment of heavy metal pollution and acidification in surface soil around Kangal Lignite-Burning

Lignite coal is an important energy source in Turkey's electrical energy production due to the available in abundance, domestic and economic. However, the use of lignite coal as fuel in thermal power plants leads to major environmental problems such as the generation of acid gases (SO2, SO3, NO and NO2) and fly ash. Heavy metals contained in fly ash have potential risks for human health and soil and water ecosystems. Therefore, it is of great importance to study the heavy metal contamination and acidification of agricultural soil around the coal-fired thermal power plants. In this study, the heavy metal concentrations of 140 surface soil samples from the area around the Kangal lignite-fired thermal power plant were analysed by using energy dispersive X-ray fluorescence spectrometer to assess the contamination level of soils. pH values of soil samples were determined to assess the acidification of soils. The average concentration of iron (Fe), aluminium (Al), titanium (Ti), manganese (Mn), chromium (Cr), nickel (Ni), strontium (Sr), zinc (Zn), zirconium (Zr), cobalt (Co), rubidium (Rb), copper (Cu), lead (Pb), arsenic (As), tin (Sn) and mercury (Hg) metal analysed in soil samples were measure as 39064.8±430.7 mg/kg, 37813. 9± 1134.3 mg/kg, 2261.7 ± 62.4 mg/kg, 720.8 ± 10.0, 713.2 ± 19.9, 610.1 ± 16.8, 410.8 ± 14.4, 81.8 ± 3.1, 65.3 ± 2.2, 63.9 ± 1.6, 34.5 ± 1.0 mg/kg, 28.8 ± 0.3 mg/kg, 17.0 ± 0.6 mg/kg, 9.0 ± 0.8 mg/kg, 3.3 ± 0.1 mg/kg and 1.7 ± 0.1 mg/kg, respectively. In general, the metal concentrations of the soil samples taken from dominant wind direction were higher than the others. The values of pH varied from 7.5 (slightly alkaline) to 8.2 (moderately alkaline) with an average value of 8.0 ± 0.1 (moderately alkaline). Ecological risk parameters or indicators such as the geo-accumulation index (IGA), enrichment factor (EF), contamination factor (CF), contamination degree (CD), modified contamination degree (mCD), and pollution load index (IPL) were estimated to assess the heavy metal soil contamination of each soil sample. The IGA, EF and CF results reveal that the study area are heavily or very highly contaminated with Cr, Ni and Hg. Based on the IPL value, the soil samples are polluted with heavy metals. However, the mCD indicates a moderate heavy metal contamination of the soil samples.