Heavy metals pollution and ecological risk assessment around artisanal gold mines in Zamfara, Nigeria

Abstract

Heavy metals pollution and potential ecological risk index were assessed in artisanal gold mining areas of Zamfara state, Nigeria. Soil samples were collected from three mines namely Kwali (05°45.49'E–11°59.66'N), Duke (06°19.56'E–12°21.45'N) and Maraba (06°22.43'E–12°20.26'N) while a non–mining area; Kadauri (06°08.71'E–12°13.56'N) was also chosen as a control. Samples were analysed using atomic absorption spectrophotometer and the results obtained showed that; the most abundant metal was Pb (148.59 mg/kg) in Kwali and the least was Ni (1.25 mg/kg) in Kadauri while the metals generally occurred in the order; Pb > Fe > Au > Al > Zn followed by other metals in an unspecified manner. All metal concentrations differed significantly (P<0.05) across sampling stations except Mn and Zn and they were all above the WHO limit which portrays a health risk. A strong positive correlation was found between metal pairs with r ≥ 0.5 (*p<0.05) in about 70% of them indicating commonality of source. Pb, Cd, Al and Au had contamination factors > 1in all sampling locations indicating increment in their concentrations above the pre–anthropogenic activities reference levels. Geoaccumulation index showed concentrations above background values of Pb, Cd, Al and Au while potential ecological risk index was highest (782.79) in Kwali and lowest (142.15) in Kadauri. Two principal components accounted for about 99.64% of the total variation in metals concentration with PC1 (95.21%) and PC2 (4.43%). This study showed the influence of artisanal gold mining on heavy metals concentration and suggested regulation of these practices.