Chromium Distribution and Spatial Variations in the Finer Sediment Grain Size Fraction and Unfractioned Surficial Sediments on Nyanza Gulf, of Lake Victoria (East Africa)

Job Mwamburi

doi:10.1155/2016/7528263

Abstract

Surficial sediments collected from the Nyanza Gulf of Lake Victoria (East Africa) were used to determine spatial concentrations of Cr and determine differences in contents of the unfractioned (whole sediment) and the finer grain size sediments, establishing any changes in Cr enrichment and potential ecological risks using sediment quality guidelines. A single pollution index was also used to evaluate level of Cr contamination. The spatial mean Cr contents in the <63 µm (silt-clay) fraction were found to be significantly lower than those in the unfractioned sediments, but with a strong linear positive correlation. The study results show decreasing spatial amounts of Cr in surficial sediments of the Nyanza Gulf, when compared to a study done 20 years earlier. However, the 95% confidence limits of the overall mean Cr in unfractioned sediments exceed the threshold effect concentration (TEC), indicating the potential for Cr remobilization from sediments. In general the sediment enrichment is evidence of possible dominance of lithogenous sources of Cr in the surface lake sediments, with potential anthropogenic sources from the drainage system and nearshore urban areas. The sediments are unpolluted with respect to geoaccumulation index, and sediment enrichment factors suggest a minor to moderate enrichment of Cr in surficial sediments of three sites around the Nyanza Gulf zones and around the river mouth in the main lake.

Highlights

Metals, being recalcitrant to biodegradation process pose a persistent threat to human health and environment
This study provides the spatial distribution of Cr in the unfractioned and finer sediments of the Nyanza Gulf, with an evaluation of the changes in concentrations, sediment quality, and ecological risks
Levels of Cr in surficial sediments are within ranges reported for major soils in sub-Saharan Africa

Summary

Introduction

Metals, being recalcitrant to biodegradation process pose a persistent threat to human health and environment. Emissions of metals result from fossil fuels combustion, industrial process, and solid waste incineration. Increasing anthropogenic sources of metals often leads to increased enrichments in lake sediments. Lake sediments are regarded as important sinks and secondary sources of metal contaminants, which range from essential or beneficial to detrimental metals. The most important industrial sources of chromium in the atmosphere are those related to ferrochrome production. Chemical and refractory processing, cement-producing plants, automobile brake lining and catalytic converters for automobiles, leather tanneries, and chrome pigments contribute to the atmospheric burden of chromium [2, 3]. Hexavalent chromium (Cr VI), along with the less common metallic chromium (Cr0), is most commonly produced by industrial processes

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Conclusion