Munyaradzi Manjoro

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.

Fans, in association with hillslope gullies and badlands and their impact on the catchment sediment cascade, slope‐channel connectivity and local landscape evolution, have been reported in diverse geomorphic environments. However, research on the development and morphodynamics of gully fans is still in its infancy in South Africa. An investigation was undertaken in mid‐slope discontinuous gullies in the Eastern Cape Province of South Africa using field surveys and sediment source fingerprinting techniques to establish the dynamics of fan systems and their impacts on‐slope sediments. Findings showed that a sediment core collected from the upper region of the fan was composed mainly of sediment mobilised from subsurface sources, whereas that from the lower region of the fan consisted mostly of sediment from surface sources. ¹³⁷Cs data were consistent with the sediment source fingerprinting results, confirming the respective surface and subsurface origins of the sediment in the sampled cores. Additionally, ¹³⁷Cs pointed to the recent formation of the fan. Geomorphic reconstruction of the fan did not support a cut and fill mode of gully fan development. Rather, the fan formed as a consequence of discontinuous gullies in the mid‐slope leading to on‐slope sediment deposition and slope‐channel decoupling. It was also observed that hillslope sediment storage in the gully fan is temporally variable. Changes in the balance of morphodynamic processes may lead to sediment flushing and slope‐channel coupling. Copyright © 2012 John Wiley & Sons, Ltd.