Dissolved gaseous mercury production and sea-air gaseous exchange in impacted coastal environments of the northern Adriatic Sea

Federico Floreani; Nicolò Barago; Katja Klun; Jadran Faganeli; Stefano Covelli

doi:10.1016/j.envpol.2023.121926

Dissolved gaseous mercury production and sea-air gaseous exchange in impacted coastal environments of the northern Adriatic Sea

Environ Pollut. 2023 Sep 1:332:121926. doi: 10.1016/j.envpol.2023.121926. Epub 2023 May 31.

Authors

Federico Floreani¹, Nicolò Barago², Katja Klun³, Jadran Faganeli³, Stefano Covelli²

Affiliations

¹ Department of Mathematics & Geosciences, University of Trieste, Via E. Weiss 2, 34128, Trieste, Italy; Department of Life Sciences, University of Trieste, Via L. Giorgieri 5, 34127, Trieste, Italy. Electronic address: federico.floreani@phd.units.it.
² Department of Mathematics & Geosciences, University of Trieste, Via E. Weiss 2, 34128, Trieste, Italy.
³ Marine Biology Station, National Institute of Biology, Fornace 41, 6330, Piran, Slovenia.

PMID: 37268218
DOI: 10.1016/j.envpol.2023.121926

Abstract

The northern Adriatic Sea is well known for mercury (Hg) contamination mainly due to historical Hg mining which took place in Idrija (Slovenia). The formation of dissolved gaseous mercury (DGM) and its subsequent volatilisation can reduce the amount of Hg available in the water column. In this work, the diurnal patterns of both DGM production and gaseous elemental Hg (Hg⁰) fluxes at the water-air interface were seasonally evaluated in two selected environments within this area, a highly Hg-impacted, confined fish farm (VN: Val Noghera, Italy) and an open coastal zone less impacted by Hg inputs (PR: Bay of Piran, Slovenia). A floating flux chamber coupled with a real-time Hg⁰ analyser was used for flux estimation in parallel with DGM concentrations determination through in-field incubations. Substantial DGM production was observed at VN (range = 126.0-711.3 pg L^-1) driven by both strong photoreduction and possibly dark biotic reduction, resulting in higher values in spring and summer and comparable concentrations throughout both day and night. Significantly lower DGM was observed at PR (range = 21.8-183.4 pg L^-1). Surprisingly, comparable Hg⁰ fluxes were found at the two sites (range VN = 7.43-41.17 ng m^-2 h^-1, PR = 0-81.49 ng m^-2 h^-1), likely due to enhanced gaseous exchanges at PR thanks to high water turbulence and to the strong limitation of evasion at VN by water stagnation and expected high DGM oxidation in saltwater. Slight differences between the temporal variation of DGM and fluxes indicate that Hg evasion is more controlled by factors such as water temperature and mixing conditions than DGM concentrations alone. The relative low Hg losses through volatilisation at VN (2.4-4.6% of total Hg) further confirm that static conditions in saltwater environments negatively affect the ability of this process in reducing the amount of Hg retained in the water column, therefore potentially leading to a greater availability for methylation and trophic transfer.

Keywords: Fish farm; Flux chamber; Idrija mercury mine; Mercury evasion; Water-air exchange.

MeSH terms

Environmental Monitoring / methods
Gases / analysis
Mercury* / analysis
Water
Water Pollutants, Chemical* / analysis

Substances

Mercury
Gases
Water Pollutants, Chemical
Water