Abstract:
The study evaluates artisanal gemstone mining contamination indices in soil and water of Ikinyinwa Community, Osun-State, Nigeria. Systematic grid sampling method was adopted to collect soil sample between the depths of 0-20 cm from mining area (MA) and non-mining areas (NMA) using spade. Water samples were taken from mining pits and surrounding streams using grab sampling methods. pH, particle sizes, organic carbon (OC), organic matter (OM), Nitrogen (N), phosphorus (P) and potassium (K) content in soil sample were determined. The dissolved oxygen (DO), total
solids (TS), total dissolved solids (TDS), chloride (Cl-), sulphate (SO4 -2) and nitrate (NO3 -) in water were also determined. Heavy metal in soil and water were determined using Atomic Absorption Spectrophotometer (AAS) while contamination indices were determined using standard equations. The descriptive statistical analyses of soil showed that pH has a mean value of 4.72±0.12. The values of organic carbon (OC) ranged from 0.18 - 0.73 % while that of organic matter (OM) ranged from 0.31–1.26. The mean values of N, P and K were obtained as 0.94±0.04 ppm, 19.96±0.14 ppm
and 66.80±0.43 ppm. The mean concentrations of heavy metal in soil ranged from 0.52±0.28 to 17.86±0.44. The average values of contamination factor (CF) and degree of contamination 𝐶𝑑𝑒𝑔of investigated heavy metal were within moderate contamination (1≤Cf<3) and (8≤𝐶𝑑𝑒𝑔<16) classifications respectively. Ten samples were contaminated with investigated heavy metals as their PLI values greater than one (PLI > 1). Consequently, the mean values of pH in water sample were obtained as 4.80±0.21 while that of Cl-, SO4 -2 and NO3 - were obtained as 84.42±0.07, 63.28±0.03
and 124.54±0.20. The accumulation of heavy metal in water sample were ranked in order of magnitude as Pb > Ni > Cd > Mn > Cu > Zn > Fe. The result revealed that the values of metal pollution index (MPI) in three water samples in respect to WHO standard were above the critical values of 100. The result of Heavy metal evaluation index (HEI) revealed that only Zn and Cu were within the low water quality pollution classification in respect to WHO (2011) and SON (2007) standards.
