Physico-chemical Properties and Heavy metal Contamination Levels of Soils from Riruwai Mining Area, North-western Nigeria

Mining activities, despite their economic importance, are well documented as one of the most significant sources of heavy metal pollution in the soil. In the present study, the physico-chemical properties and heavy metal contamination levels of the soils around the Riruwai mining area, in north-western Nigeria, were investigated. A total of 60 surface soil samples from four (4) sampling sites, which include 18 from active mine sites, 12 from abandoned mine sites, 21 from farmlands and 9 from control sites, were collected during the dry and rainy seasons. The physico-chemical properties such as pH, electrical conductivity (EC), soil organic matter (SOM), and cation exchange capacity (CEC) were determined using various analytical techniques. The concentrations of heavy metals were analyzed using a Microwave Plasma Atomic Emission Spectrometer (MP-AES), and the measured concentrations were used to evaluate the pollution load index (PLI). The findings of the study revealed that mining activities had a significant impact on the physicochemical characteristics of the soils, with lower pH, CEC, and SOM values in particular in active and abandoned mining sites. The physico-chemical characteristics of soil vary seasonally, with higher values typically reported during the rainy season, except for pH. The concentrations of arsenic, cadmium, lead, and zinc in the soils of the Riruwai mining area exceeded the threshold value recommended by WHO/FAO (2001) in all the sampling locations and seasons, with the exception of the control sites. The PLI values indicated that the soils in active and abandoned mining sites are strongly polluted by heavy metals, while farmland soils are moderately polluted and control site soils are unpolluted. The soils in the study area are significantly contaminated by heavy metals, particularly in active and abandoned mining sites, and the contamination has spread to farmland, suggesting a significant need for proper containment of heavy metal pollution levels in the area, particularly arsenic, cadmium, lead, and zinc.