Origin and partitioning of mercury in the polluted Scheldt Estuary and adjacent coastal zone

Vincent Perrot; Tianhui Ma; Delphine Vandeputte; Vendula Smolikova; Arne Bratkic; Martine Leermakers; Willy Baeyens; Yue Gao

doi:10.1016/j.scitotenv.2023.163019

Origin and partitioning of mercury in the polluted Scheldt Estuary and adjacent coastal zone

Sci Total Environ. 2023 Jun 20:878:163019. doi: 10.1016/j.scitotenv.2023.163019. Epub 2023 Mar 29.

Authors

Vincent Perrot¹, Tianhui Ma¹, Delphine Vandeputte¹, Vendula Smolikova¹, Arne Bratkic², Martine Leermakers¹, Willy Baeyens¹, Yue Gao³

Affiliations

¹ Vrije Universiteit Brussel (VUB), Analytical and Environmental Geochemistry (AMGC), Pleinlaan 2, Ixelles 1050, Belgium.
² Universitat de Lleida, Chemistry Department, Environmental Physical Chemistry group, Av. Rovira Roure 191, 25198 Lleida, Spain.
³ Vrije Universiteit Brussel (VUB), Analytical and Environmental Geochemistry (AMGC), Pleinlaan 2, Ixelles 1050, Belgium. Electronic address: yue.gao@vub.be.

PMID: 36996990
DOI: 10.1016/j.scitotenv.2023.163019

Abstract

Estuaries and coastal zones are areas with complex biogeochemical and hydrological cycles and are generally facing intense pollution due to anthropogenic activities. An emblematic example is the Scheldt Estuary which ends up in the North Sea and has been historically heavily contaminated by multiple pollutants, including mercury (Hg). We report here Hg species and their levels in surface waters of the Scheldt Estuary and the Belgian Part of North Sea (BPNS) from different sampling campaigns in February-April 2020 and 2021. Along the estuary, Hg concentration on suspended particles ([Hg_SPM]) progressively decreased with increasing salinity and was strongly correlated with organic matter content (%C_org) and origin (identified with δ¹³C_org). While [Hg_SPM] drives total Hg concentration in the estuary (total dissolved Hg, Hg_TD is only 7 ± 6 %), annual and daily variations of total Hg levels were mostly attributed to changes in SPM loads depending on river discharge and tidal regime. In the BPNS, a significant fraction of total Hg occurs as Hg_TD (40 ± 21 %) and the majority of this Hg_TD was reducible (i.e. labile Hg), meaning potentially available for microorganisms. Compared to the '90s, a significant decrease of [Hg_SPM] was observed in the estuary, but this was not the case for [Hg_TD], which can be due to (1) still significant discrete discharges from Antwerp industrial area, and (2) higher Hg partitioning towards the dissolved phase in the water column relative to the '90s. Our results highlight the important contribution of the Scheldt estuary for the Hg budget in North Sea coastal waters, as well as the need for seasonal monitoring of all Hg species.

Keywords: Belgian part of the North Sea; Mercury (Hg) speciation; Organic matter; Scheldt Estuary; Suspended particles.