A Preliminary Evaluation of Human Health Risk of Potentially Toxic Elements in Playground Soils from Selected Public Primary Schools in Minna, North-Central Nigeria

Abstract

The grain size distribution and concentration of some potentially toxic elements in playground soils in selected public primary schools in Minna metropolis, Nigeria has been investigated. This was aimed at assessing the risk of exposure of young, vulnerable children in the schools to toxic elements through hand-to-mouth habits and inhalation of soils and dusts. The schools selected for this study are located within the inner city area of the metropolis and is underlain mainly by Older Granites of the central Nigeria Basement Complex. Grain size analysis was conducted on soil samples from eight primary schools and a handheld X-ray fluorescence spectrometer (×-MET5100) was used to measure the concentration of some potentially toxic metals. The results show that these soils are predominantly composed of fine sand (40 to 66 %, with mean of 53.25 %), followed by medium sand (20 to 46 %, with mean of 35.63 %). The silt/clay fraction accounts for 3 to 14 % of soils, with an average of about 7.88 %. The abundance of the three fractions therefore is in the order Fine sand > Medium sand > Silt/clay respectively. The concentration of Zn, Cu, Pb, Cd and Mn in the surface soils was used to evaluate the health risks posed to children in the schools though the ingestion pathway. The Average daily dose (ADDi) for the elements are 6.61 x 10-4, 2.78 x 10-4, 4.32 x 10-4, 1.53 x 10-3 and 5.55 x 10-3 respectively. Their corresponding Hazard Quotient (HQi) were found to be 2.20 x 10-3 for Zn, 6.95 x 10-3 for Cu, 1.23 x 10-1 for Pb, 1.53 for Cd and 3.96 x 10-1 for Mn. The computed Hazard Index (HI) of 2.06 is greater than the threshold value of 1 and indicates the potential for adverse health effects to the children in those schools. A more detailed study, including larger sample size and the fractionation of potentially toxic elements in different grain sizes and mineralogical phases will be useful in further assessing the level of risk.