METAL POLLUTION HISTORY OF THE GOLDEN HORN SEDIMENTS (1912 – 1987)

Gaye Tuncer, Gurdal Tuncel, Turgut I. Balkas

Middle East Technical University, Dept. Environmental Engineering, 06531 Ankara, Turkey

ABSTRACT.

The Golden Horn is a heavily polluted water body in a large metropolitan with a population of approximately 10 million. A 3-m long undisturbed core sample was collected in the Golden Horn, from research vessel RV Knorr, during the third leg of the joint Turkish – American Black Sea expedition in 1989. The core was sliced and dated using 210Pb isotope technique. The bottom of the core corresponds to year 1912. Each slice was analysed for major, minor and trace elements by inductively coupled plasma emission spectrometry (ICP). Although, anthropogenic elements Mo, Zn, Cr, Cu, Ag, and Cd accounts for a minute fraction of the elemental mass, their concentration increase along the core, signifying human influence on chemical composition of the Golden Horn Sediments. Concentrations of pollution-derived elements do not change significantly between 1912 and 1950, but their concentrations increase sharply in the second half of the century.

INTRODUCTION

Concerns on environmental degradation by human activities have resulted accumulation of large volumes of data on current levels of contaminants in various environmental compartments including sediments. However, information about evolution of environmental contamination is not as abundant. Cores collected from estuaries and coastal seas (Szefer et al., 1998), in lakes (Wei et al., 1997) at polar ice caps (Crozaz et al., 1964), oceans (Ohkouchi et al., 1997) and high mountain glaciers (Windom, 1969) have shown that the environmental pollution by human activities has started at the beginning of the 20^th century. However, pollution chronology for individual water bodies may vary depending on the population growth and industrialisation in that particular area.

The Golden Horn is a popular water body in Turkey. It was a famous recreational area at the time of Ottomans. It also served as the most important port of the region at that time. Golden Horn suffered from heavy pollution due to extensive industrialisation and rapid population growth in Istanbul in the 20^th century. This manuscript describes how metal pollution have evolved in the Golden Horn between 1912 and 1987, by analysing ²¹⁰Pb dated slices of a 3 m long core collected close to Galata bridge in 1989.

METHODS

A 3-m long gravity core and three box cores were collected from the Golden Horn (41°01.41’ N, 28°57.92’ E) during the Black Sea Expedition, Cruise-3, onboard the R.V. Knorr, at June 1988. The core was sliced into 2 – 5 cm long layers, dated by ²¹⁰Pb technique and each layer was analysed for Zn, Cd, Cr, Cu, Ni, Co, V, La, Mn, Fe, Ag, Li, Na, K, Be, Mg, Ca, Sr, Al, Ti, Rb, La, Mo and Pb using an ARL, model 3410 Inductively Coupled Plasma Emission Spectrometer (ICP). Details of the experimental methods are given elsewhere (Teksoz et al., 1991)

RESULTS AND DISCUSSION

Sediment accumulation rate in the Golden Horn, which was calculated as 3.5 cm y^-1 using ²¹⁰Pb dating technique (Teksöz et al., 1991) is significantly higher than accumulation rates reported for various bays and estuaries in the literature, which are typically close to, but smaller than 1.0 cm y^-1.

There are two main streams, namely Alibeyköy and Kagithane, flowing to the Golden Horn. These streams have a total drainage area of 380 km² and they discharge approximately 50 x 10⁶ m³ of water and 59 x 10³ m³ of sedimentary material every year. In addition to river discharges, approximately 1.9 x 10⁶ tons of liquid and 4.9 x 10⁴ tons of solid wastes are being discharged to the Golden Horn, resulting in rapid accumulation of solid material at the bottom of the watershed. The core sample covers a period between 1912 and 1987, based on ²¹⁰Pb geochronology, which is long enough to understand how pollution in the Golden Horn evolved in the 20^th century. Since most industrial and domestic discharges to the Golden Horn are confined to the second half of the century, one would expect significant differences in the compositions of sediment at the top and bottom layers of the core.

Concentrations of soil-related elements such as Al, Mn, V and Fe are comparable at the top and bottom slices of the core as expected. However, concentrations of pollution-derived elements such as Pb, Ni, Cu, Cr, Ag, Cd and Zn approximately a factor of two higher in top slices indicating that their abundance in the Golden Horn sediments are significantly altered in the last century due to anthropogenic activities.

The ratios of elements, Li, Na, K, Rb, Mg, Ca, Sr, Ba, Al, La, Ti, V, Mn, Fe and Co - to - Al in both the top and bottom slices of the core are comparable to the corresponding ratios in the average soil indicating that their source is the earth’s crust and their concentrations are not affected from anthropogenic sources around the Golden Horn.

The ratios of Zn, Mo, Ni and Cr - to - Al in the bottom slices of the core are also comparable to the corresponding ratios in the continental soil, but, Zn/Al, Mo/Al, Ni/Al and Cr/Al ratios at the top layers are significantly higher than both the corresponding ratios in the global soil and bottom layers, indicating that the Golden Horn was not polluted by these elements in the beginning of the century, but later chemical composition of the sediment is modified due to anthropogenic inputs.

The ratios of the third group of elements, which included Pb, Cu, Ag and Cd – to – Al are higher than corresponding ratios in the average soil both in the top and bottom layers of the core, suggesting that the chemical composition of the Golden Horn sediments was different from typical crustal composition even in the beginning of this century.

The elemental profiles obtained in this study also revealed how the change discussed in the previous sections evolved in time. Concentrations of litophilic elements Al, Co, La, Mn, Fe, Li, K, Rb, Be, Ba, Ti, V, and P do not change significantly along the core. Typical concentration profiles for this group of elements are given in Figure 1, for Fe. Concentration profiles for remaining elements included in the litophilic component are similar. Lack of significant variation in the concentrations in these lithophilic elements along the core confirms the previous conclusion that composition of the crustal component did not change between the bottom and top layers of the core.

Concentrations of marine elements Na, Mg, Sr and Ca gradually increase along the core as depicted in Figure 2 for Mg. The increase observed in the concentrations of marine elements is similar to the increase in the porosity along the core. The porosity of the sediments increases from 60% at the bottom of the core to 80% at the top due to compaction of the bottom layers. When the samples were dried, seawater evaporated leaving the sea salt behind. Since top layers of the core have more seawater than compacted bottom layers, higher quantities of sea salt and elements associated with it are deposited on the sediment surface upon drying, resulting in the observed profiles of Na, Mg, Sr, and Ca.

Unlike litophilic elements, concentration profiles of elements with anthropogenic origin reflect the increase in the urbanization and industrialization around the Golden Horn. Profiles for Zn and Cd are depicted in Figure 3 together with their crustal enrichment factors.

Concentrations of Zn, Cd, Cu and Cr followed approximately identical increasing trend in the 20^th century. Their concentrations did not change significantly in the first half of the century, but increased steadily after 1950. Enrichment factors of Zn, Cd, Cu, Ag and Cr were close to unity suggesting that observed concentrations of these elements between 1912 and 1950 are accounted for by the crustal component and there are no sign of anthropogenic contribution on their concentrations in this period. However the enrichment factors increase from unity to 20 for Zn and Cu, to 50 for Cd and to 5 for Cr in the second half of the century indicating a perturbation of natural levels between 1950 and 1988 by human activities in the region.

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