Jatto S. Solomon, Aminu L. Ahmed, Ibrahim H. Adamu, Olugbenga O. Dimu
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Abuja, anthropogenic, magnetic susceptibility, superparamagnetic grains
Soil formed from lithological and weathering processes of parent rocks generally exhibit paramagnetic properties due to some minerals contained in the rocks and thus have significant value of magnetic susceptibility. This susceptibility arising from the influence of the parent rocks tend to mask anthropogenic grains pollutants released into the environment by human activities. Hence, it becomes difficult to identify the effect of the lithological and anthropogenic magnetic susceptibility in complex soil found in urban areas. The superparamagnetic effect of lithological soil, a single state domain and multi-domain state of anthropogenic grains can easily be investigated by frequency dependent measurements where readings between 0-2.0% indicates the absence of lithological influence, 2.0-8.0% indicates multi-domain grains or mixture of both single stage and multi-domian grains and 8.0-12% indicates the superparamagntic (SP) grain from lithological origin. In this work frequency dependent measurements were carried out along 5 selected road networks within the 5 districts of Abuja phase 1. Measurements were also carried out in 379 random points at the surface and depth of 40.0cm to investigate the distribution of anthropogenic grains in Abuja metropolis using the Bartington susceptibility meter. Frequency dependent measurements along the selected road networks indicate0-3.0% immediately after the roads pavement to a distance of about 3.0m from the road, indicating that the magnetic susceptibility arise mostly form anthropogenic influence rather than lithological processes. At the distance of 3.0-8.0m, frequency dependent values of about 3.0-8.0% were recorded, indicating mixture of both superparamagnetic and multi-domain grains. Beyond the distance of 8.0m, the frequency dependent values are mostly above 8.0.0%, indicating virtually all SP grains. The spatial distribution frequency dependent surface map shows the presence of anthropogenic grains in most part of the areas with frequency dependent values between 0-8.0% while at the depth of 40.0cm the lithological influence of the SP grains is evident with frequency dependent values above 8.0%. From the result, we conclude that the frequency dependent values obtained immediately after the road pavements and on the surface soil of Abuja arise mostly from anthropogenic dust falls of metallic pollutants released mostly from vehicular and industrial activities. While at a distance of about 8.0m and depth of 40cm most of the recorded frequency dependent values arise from the lithological processes of the parent rocks. We conclude that it is possible to identify the effect of lithological magnetic grains from anthropogenic grains using frequency dependent measurements.
