Assessment of heavy metals and radionuclides in dust fallout in the West Rand mining area of South Africa

Abstract

Windblown dust can contain radioactive materials from mining. These radionuclides when inhaled in dust produce ionizing radiation which damages the cells and tissues in the body. The aim of this study was to assess dust fallout radionuclides in the West Rand mining area of South Africa. Dust fallout monitoring was done using the method (ASTM) D-1739 of 1998 employing multi-directional buckets. Results show that all 9 locations investigated in the different seasons recorded dust fallout rates within stipulated residential limit according to the National Dust Control Regulations (NDCR) (Government Gazette 36974, 1 Nov 2013). Locations 3 in spring (301.93 mg/m²/day) and 6 in winter (589.8 mg/m²/day) recorded dust fallout rates with values above the target value of 300 mg/m²/day according to guidelines by South African Standards (SANS 1929:2011). The ANOVA tests (p-value < 0.05) indicate that the mean dust fallout rate is significantly different across the seasons, mean dust fallout rate in summer is significantly (p-value < 0.05) more than the autumn by 103.15 mg/m²/day. Moderate, positive correlations (0.4 ≤ r < 0.7) exist between average dust fallout rate and wind speed. A weak, negative correlation exist between average dust fallout rate and rainfall with a value of -0.393. All the investigated elements had Enrichment Factor (EF) greater than 1. Cadmium (Cd) and lead (Pb) were extremely enriched (68.36 and 43.48, respectively), whereas Thorium (Th) (7.26) and Chromium (Cr) (9.79) had significant enrichment. Activity concentrations obtained for ²²⁶Ra, ²³⁸U, ²³²Th and ⁴⁰K were 53.59 ± 20.45 Bq/kg, 15.20 ± 6.74 Bq/kg, 6.62 ± 2.76 Bq/kg and 278.51 ± 84.39 Bq/kg, respectively. Activity concentrations were within world averages except ²²⁶Ra which exceeded the 32 Bq/kg world average. Statistically significant (p-value < 0.05), strong (0.7≤ r< 0.9) and positive correlation exists between ²²⁶Ra and ⁴⁰K. A moderate, positive correlation (0.4 ≤ r < 0.7) exist between ²³⁸U and ²³²Th. Since EF values showed that the elements in the dust had anthropogenic influence, further studies should look at contributions of different sources to the elements found in dust.