Study of heavy metal pollution and speciation in Buyak Menderes and Gediz river sediments

Abstract

In this study, two economically important rivers of Turkey, Gediz and Buyuk Menderes (BM) are studied to determine their environmental pollution levels. An old analytical procedure involving sequential chemical extraction is improved and used for the partitioning of particulate trace metals (Cu, Co, Cr, Mn, Fe, Zn, Pb and Ni). Cationic and anionic Mn and Cr species with different phases are also determined by using leaching, extraction and ion exchange speciation processes.

The sediment samples are analysed using graphic-furnace atomic absorption spectroscopy and differential pulse anodic stripping voltammeter. Experimental results obtained on five replicate samples of fluvial bottom surface sediments at the sampling points demonstrate that the relative standard deviation of the sequential extraction procedure is generally better than ±10%. The accuracy, determined by comparing total metal concentrations with the sum of the five sequential chemical extractions, is proved to be satisfactory. The detection limits established for three standard deviations of blank for different metals are identical and found to be 0.1 mg/kg for sediment samples and 1 ppb for water samples. The results show that the pollution levels are significant especially for Pb, Cr, Mn and Zn in the Gediz river and Co, Mn, and Zn in the BM river. Comparison between our results and the measurements outlined before industralization and the beginning of the intensive pesticide applications in agricultural fields (In: Broekaert et al., editors, Metal speciation in the environment, vol. 23. 1989. p. 601–11; A research on the environmental pollution in the agricultual fields and watering in the Aegean region, Ege University Research Project, No. 127 1988 (in Turkish); DSI Water Analyses Report, Ankara, 1985 (in Turkish)) show that the pollution in these rivers is probably originated from industrial, agricultural and domestic waste discharges.

Introduction

The determination of extractable trace metals in soil or sediment is often used to gain an insight into chemical speciation. The toxicity of metals depends especially on their chemical forms rather than on their total elemental contents, and therefore, speciation studies increasingly gain importance. Examination of toxic heavy metals, i.e. Cu(II), Pb(II), Mn(II) and Cr(VI), have special importance in environmental samples [1], [2]. Thus, there is a crucial need to develop trace element analysis methods that allow separation of the different element species prior to trace element analysis.

River sediments are basic components of our environment as they provide nutrients for living organisms and serve as sinks for deleterious chemical species. Unfortunately, industrial and household waste discharges—directly or indirectly,through leakages in the sewage systems—into water sources cause excessive pollution of surface and underground water. Consequently, water quality and irrigation value are lost. It is necessary to know the mechanisms of the trace metals transportation and their complexes in rivers to understand their chemical cycles in nature.

A number of studies on the metal distributions in river sediments and suspended particles, and on speciation of metals have been performed [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13].

In this work, two economically important rivers of Turkey, Gediz and Buyuk Menderes (BM), are studied to establish their environmental pollution levels for some major trace elements. Tessier's extraction procedure is improved to determine the distribution of trace metals as exchangeable, bound to carbonates, bound to Fe–Mn oxides, bound to organic sulphurs and bound to residue. A three steps extraction and ion-exchange method is used for the partitioning of Cr(III) and Cr(VI) species. The Mn species are measured as well.