Spatial Distribution, Ecological Risk Assessment, and Source Identification of Metals in Sediments of the Krka River Estuary (Croatia)

Abstract

To evaluate the level of contamination and predict the potential toxicity risk, selected metal concentrations (Cd, Pb, Cr, Mn, Co, Ni, Cu, Zn, and As) were determined in 40 surface sediment samples from the stratified karstic Krka River estuary (Croatia). In addition, diffusive gradients in thin films (DGT) probes were deployed in situ to understand the mobilization mechanisms and bioavailability of metals in the sediment. The results show significant spatial differences between the upper and lower estuary, with the latter being more affected by anthropogenic pollution. The pollution assessment using the enrichment factor (EF), the geoaccumulation index (Igeo), and the pollution load index (PLI) showed a strong enrichment of metals in the lower part of the estuary, especially of Mn, Cu, Zn, Pb, and As. The statistical analysis (PCA) revealed the former ferromanganese factory and the port as major sources of pollution in the area. Nickel, Co, and Cr, although slightly elevated, may be attributed to the natural origin. The metal mobility in the estuarine sediment was primarily governed by early diagenetic processes (aerobic organic matter mineralization, Fe and Mn oxyhydroxide reduction), which caused the release of metals from the sediment into the pore water and subsequently into the overlying water column.

Early Diagenetic Processes in the Sediments of the Krka River Estuary

“…The possible sources of contamination in this part of the estuary are agricultural activities and nautical tourism. In the lower estuary, however, sediment contamination with metals was recorded, linked to the anthropogenic impact of the city of Šibenik [40,[43][44][45][46][47]. The major sources of contamination in the lower estuary were the Fe-Mn industry, the bulk cargo port (main cargo raw phosphates and artificial fertilisers), untreated wastewater discharge, and the repair shipyard [47].…”

“…In the lower estuary, however, sediment contamination with metals was recorded, linked to the anthropogenic impact of the city of Šibenik [40,[43][44][45][46][47]. The major sources of contamination in the lower estuary were the Fe-Mn industry, the bulk cargo port (main cargo raw phosphates and artificial fertilisers), untreated wastewater discharge, and the repair shipyard [47]. The Fe-Mn factory was operating for 50 years, until the mid-nineties, and during that time, no pollution control measures were implemented.…”

“…Industrial fumes and dust were emitted directly into the air while metallurgical slag was partially spread around or deposited near the smelter [48]. Although production stopped 30 years ago, and the remediation of the area was completed in 2013, the impact of factory activities can still be seen in the surface sediment [47]. Moreover, for many years, untreated communal and industrial wastewater was discharged into the estuary from 33 separate outflows along the waterfront.…”

“…This pronounced increase in Mn content in the sediment is a consequence of pollution from the electrode and ferroalloy factory. The factory has been closed for almost 30 years; nevertheless, its influence is still visible in the sediment [47]. At location K5, concentrations ranged from 0.065 to 0.126%.…”

Pollution Assessment and Spatial Distribution of Heavy Metals in Surface Waters and Bottom Sediments of the Krzna River (Poland)

“…They are classified as pollutants that pose a particularly serious threat to human health. The content of heavy metals in bottom sediments and surface waters is an important indicator of the state of the aquatic environment [4][5][6][7][8][9][10][11].…”