Monitoring heavy metal pollution in foraminifera from the Gulf of Edremit (northeastern Aegean Sea) between Izmir, Balıkesir and Çanakkale (Turkey)

Abstract

In this study, the populations and abnormal shell structures of Quaternary foraminifers in the sediments of the North-eastern Aegean Sea were examined. For this purpose, offshore drilling was carried out at three locations, and core samples were collected from 13 locations at Küçükkuyu (Çanakkale), Güre (Edremit-Balıkesir) and Dikili (İzmir). At these points, drilling reached depths ranging from 3.00 to 22.00 m beneath the seafloor; recent sediments were observed, but the bedrock was not reached. Examination of the faunal and sedimentological properties of the samples showed that the Gulf of Edremit is completely influenced by the sea and has rich foraminifers and ostracod populations.The abnormalities observed in the foraminifer shells, as well as the yellow- and/or black-coloured shells seen in both the foraminifer and ostracod populations, are due to natural and anthropogenic ecological pollution. The vertical (chronological) and horizontal (spatial) distributions of heavy metal concentrations in both the core and drill core samples were investigated to determine the causes of the morphological abnormalities observed in the foraminifers. In the present study, pollution index (PI) values were calculated to assess the degree of heavy metal pollution (Yümün 2017). The current land use status of the coastal areas corresponding to the measured PI values was investigated to identify the sources of the pollution. Especially in the Güre region, a large number of genera and species of benthic foraminifers showed overgrowth in the shell sizes of individuals, and the coloration of the shells is noteworthy.These changes in the shells are a result of thermal sources and agricultural activities in the region. Scanning electron microscopy (SEM) was used to perform an elemental analysis of the surfaces of dark yellow-orange foraminifers (Ammonia compacta and Elphidium crispum). The S, Fe and Mn concentrations in the shells were found to be high, based on the SEM analyses. This is similar to the high S and Fe contents of thermal waters. Thus, the main causes of the coloration of the shells have been accepted to be both thermal waters and fertilizers and pesticides that are used in agricultural activities.