Abstract

Heavy metals (i.e. Cr, Co, Ni, Cu, Zn, Rb, Sr, Ba, Pb, V and Ga) distribution and their correlation with clay fraction were investigated. Fifteen samples of stream sediments were collected from the Lesser Zab River (LZR), which represent one of three major tributaries of the Tigris River at north-eastern Iraq. Grain size distributions and textural composition indicate that these sediments are mainly characterized as clayey silt and silty sand. This indicates that the fluctuation in the relative variation of the grain size distribution in the studied sediments is due local contrast in the hydrological conditions, such as stream speed, energy of transportation and geological, geomorphological and climatic characterizations that influenced sediments properties. On the other hand, clay mineral assemblages consist of palygorskite, kaolinite, illite, chlorite and smectite, which in turn reveals that these sediments were derived from rocks of similar mineralogical and chemical composition as it is coincided with other published works. The clay mineral assemblages demonstrate that major phase transformations were not observed except for the palygorskite formation from smectite, since the minerals pair exhibit good negative correlation (-0.598) within the Lesser Zab River (LZR) sediments. To determine interrelation between the heavy metals and the clay fractions in the studied samples, correlation coefficients and factor analysis were performed. Heavy metals provide significant positive correlation with themselves and with Al2O3, Fe2O3 and MnO. In addition, the results of factor analysis extracted two major factors; the first factor loading with the highest percent of variation (60%) from the major (Fe2O3, Al2O3 and MnO in weight %), heavy metals and clay fraction. While the second factor with the (14%) of variance includes Cr and silt fraction, which indicate the affinity of the heavy metals being adsorbed onto solid phase like clay particles. These observations suggest that a common mechanism regulates the heavy metal abundance, and that their concentrations are significantly controlled by fine clay fractions, clay mineral abundance and ferro manganese oxides-hydroxides.

Highlights

  • Fluvial sediments are sourced from the exposed rocks, among these, the crystalline rocks, which are influenced by streams under surface conditions

  • Grain size distributions and textural composition indicate that these sediments are mainly characterized as clayey silt and silty sand

  • Clay mineral assemblages consist of palygorskite, kaolinite, illite, chlorite and smectite, which in turn reveals that these sediments were derived from rocks of similar mineralogical and chemical composition as it is coincided with other published works

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Summary

Introduction

Fluvial sediments are sourced from the exposed rocks, among these, the crystalline rocks, which are influenced by streams under surface conditions. Sediments include different grain sizes (i.e. coarse sandstone to colloidal grains). Studying resent sediments offer insight on the physiochemical and environmental regimes in shallow marine and fluvial conditions which are influenced greatly by the changes of earth and human activities [2] [3], and sediments are used, usually, as pollution monitor in different aquatic regimes. Colloidal grains are greatly influenced by various parameters and hardly to provide accurate analysis results. While fine grain sediments are less influenced and used frequently as chemical and biochemical pollution indicators [4]

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