Heavy metals risk assessment of water and sediments collected from selected river tributaries of the Mara River in Tanzania

Mihayo Sahani Nkinda,Jasper Nathan Ijumba,Mwemezi Johaiven Rwiza,Karoli Nicholas Njau

doi:10.1007/s43832-021-00003-5

Mihayo Sahani Nkinda, Jasper Nathan Ijumba + Show 2 more

https://doi.org/10.1007/s43832-021-00003-5

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Abstract

This study investigated the levels of Pb, Hg, Cr, Cd, and As in water and sediments from the tributaries of the Mara River, Tanzania. Pollution risk of water and sediments was investigated using seven indices and five metals. During the dry period, the highest concentration of Pb, Hg, Cr, Cd, and As in sediments was 17.45 ± 1.22, 0.01, 1.56 ± 0.5, 1.3 ± 0.09, and 30.81 ± 0.02 mg/kg, respectively. During the wet period, the highest concentration of Pb, Hg, Cr, Cd, and As in sediments was 4.37 ± 0.28, 0.012, 2.58 ± 0.57, 2.25 ± 0.35, and 53 ± 0.02 mg/kg, respectively. For surface water, the respective highest concentrations of Pb, Hg, Cr, Cd, and As were 0.76 ± 0.09, 0.04, 0.68 ± 0.09, 0.74 ± 0.1, and 0.47 ± 0.06 mg/L for the dry period. The wet period max concentrations for Pb, Hg, Cr, Cd, and As in surface water were 0.56, 0.03, 0.55 ± 0.03, 0.48 ± 0.03, and 0.4 ± 0.03 mg/L, respectively. Principal component analysis results indicated dominant loadings for Pb and As in sediments during the dry period. Comparison of sediment concentrations with sediment quality guidelines revealed that As and Cd were enriched. Correlation coefficient results indicated that As had a strong negative correlation with the rest of the elements in sediments during the dry period. In the wet period, As had a significant correlation with Cd (r = 0.92, p < 0.01) in sediments. The analysis of environmental risks indicated significant enrichment of sediments with As and Cd. It is important to put in place relevant control mechanisms targeting metals in the studied tributaries, with a focus on As and Cd.

Highlights

In environmental studies, the phrase heavy metals is used to imply metals and metalloids with high atomic weight and whose specific gravity is five times the specific gravity of water at 4 °C [1]
The maximum temperature and electrical conductivity (EC) in the dry period were in accordance with the World Health Organization (WHO) recommended range of 20–35 °C and 100–2000 μS/cm, respectively
There is not much research related to water and sediment quality related to riverine ecosystems of sub-Saharan Africa

Summary

Introduction

The phrase heavy metals is used to imply metals and metalloids with high atomic weight and whose specific gravity is five times the specific gravity of water at 4 °C [1]. Heavy metals in the aquatic environment may have their source in either natural or anthropogenic activities. Human activities that may contribute to environmental heavy metals include but are not limited to the generation of domestic waste, mining operations, industrial activities, agricultural expansion, and fossil fuel applications. Natural processes such as volcanic activity and the weathering of rocks may contribute significant levels of heavy metals in the environment [2]. Heavy metals may occur in the environment in both elemental and compound forms. Some heavy metals may be found attached to fine particles, while others may exist in a labile form. Heavy metals are persistent and toxic to ecosystems, making their assessment and subsequent

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