Geochemical characterisation of soil of Beira city, Mozambique: Geogenic origin and relation with land cover

Abstract

Beira city and Dondo district in Mozambique were studied with the purpose of evaluating the environmental quality of soil and to relate its quality with land cover and geology. This study revealed, by means of statistical tools, such as principal component analysis and multidimensional scaling, geochemical signatures of geogenic and anthropogenic origin in top- and sub-soil samples. Elements present in detrital minerals, deposited in recent geological formations of sedimentary origin (Ba, Cr, Hf, Ti, Th, U and REE), are related to the erosion products of mafic and orthogneissic formations derived from the upstream reaches of Pungwe River. Shallow coastal areas, where tropical climate (mean annual temperature of 24.5°C) facilitate oxidation and deposition of iron oxides on the surface of particles in soil/sediment, have a characteristic element association, comprising Al, Br, Co, Fe, K, Mg, Mn, Na, Ni, Rb and Sc. Anthropogenic influence in overpopulated areas, identified with discontinuous urban fabric, is characterised by Cu, Pb, P and Zn, and is considered as potential hazardous because of unpaved roads, an unprotected urban waste dump, and inexistent sewage network, thus, increasing the risk of exposure to the population. A comparison of the potentially hazardous elements in the soil of Beira with other cities from around the world shows that Beira has lower concentrations in these elements. This is because the historical industry that has given rise and development to many world cities is absent in Beira.