Anthropogenic mercury contamination in sediments of Krka River estuary (Croatia)

Coastal and estuarine sediments play an important role in the biogeochemical cycle of mercury (Hg) in the aquatic environment. When contaminated, sediments can act as a potential source of Hg and may pose a long-term risk to aquatic biota. The aim of this research was to assess spatial and historical distribution of Hg in the sediments of the Krka River estuary, an environment that so far has been regarded as relatively unpolluted. To achieve this goal, 40 surface sediment samples and 7 sediment cores were collected along the entire estuary. Hg concentrations in the surface and deep sediments of the Krka River estuary were found in a broad range 0.042-57.8 mg kg^-1, demonstrating significant spatial and temporal differences in Hg input to the estuarine sediments. Two distinct areas were distinguished; upper estuary where the Hg content was comparable to other unpolluted Adriatic sediments, and the lower estuary where sediment profiles reflected the history of anthropogenic Hg input associated with the city of Šibenik. The vertical Hg profile from the most affected area of the estuary, combined with ²¹⁰Pb and ¹³⁷Cs dating, demonstrated that a significant increase of Hg input started in late 1940s/early 1950s, mainly related to shipyard activities. This study provided more insight on the Hg concentration in the Krka River estuary, demonstrating that the high values obtained, although localized, were comparable to the ones found in some of the most contaminated sites in the Mediterranean.