Abstract
The cycling of metal(loid)s at the sediment–water interface (SWI) was evaluated at two selected sites (VN1 and VN3) in an active fish farm in the Grado Lagoon (Northern Adriatic, Italy). In situ experiments using a transparent benthic chamber and the collection of short sediment cores were performed, to investigate the behavior of metal(loid)s in the solid (sediments) and dissolved (porewaters) phases. Total and labile concentration of metal(loid)s were also determined in sediments, to quantify their potential mobility. Comparable total concentrations were found at both sites, excluding As, Mn, Pb and V, which were higher at VN3. Metal(loid) porewater profiles showed a diagenetic sequence and a close dependence with redox (suboxic/anoxic) conditions in the surface sediments. Positive diffusive fluxes along with benthic fluxes, particularly at the more oxic site, VN1, were found for almost all metal(loid)s, indicating their tendency to migrate towards the overlying water column. Despite sediments at two sites exhibiting high total metal(loid) concentrations and moderate effluxes at the SWI, the results suggest that they are hardly remobilized from the sediments. Recycling of metal(loid)s from the SWI would not constitute a threat for the aquatic trophic chain in the fish farm.
Highlights
Sediments are a critical compartment of aquatic ecosystems where natural and anthropogenic chemical substances accumulate
The total dissolved Hg (DHg) determination was conducted via a pre-reduction, using NH2 OH-HCl (30%, 0.25 mL), until the yellow colour disappeared, followed by a reduction with SnCl2 2% (Sigma-Aldrich) in HCl 4%, as in the EPA Method 1631e [22] and Atomic Fluorescence Spectrometry (AFS) detection (Mercur, Analytik Jena GmbH, Jena, Germany) coupled with a gold trap pre-concentration system
The rather constant trend with depth at both sites (Supplementary Materials Table S2), as well as the high logKD values estimated for Al, Fe and Hg, likely reflects the scarce mobility of metal(loid)s from the fish farm sediments to the water column, as confirmed by the results obtained by the weak extraction procedure (Table 2)
Summary
Sediments are a critical compartment of aquatic ecosystems where natural and anthropogenic chemical substances accumulate. Metal(loid)s represent a serious threat to the marine environment due to their potential toxicity, relative abundance, persistence and bioaccumulation throughout the whole trophic chain The study of their behavior and cycling at the sediment–water interface (SWI) is of great importance and allows for the planning of possible mitigation actions. The. SWI plays an important role in the assessment of metal contamination in aquatic environments, especially in the transitional systems such as lagoons. Plays an important role in the assessment of metal contamination in aquatic environments, The Marano and Grado Lagoon (Northern Adriatic Sea, Italy) is affected by a high especially in the transitional systems such as lagoons. Degree of mercury (Hg) contamination in sediments originating from the Idrija mine (NW previous studies reported an evident accumulation of other metal(loid)s in the lagoon subtidal sediments caused by industrial, urban and tourist activities [9,10,11]. The can be useful compartment providing useful information to improve the environmental quality of in understanding the mobility of the metal(loid)s in this compartment providing this modified aquatic system. the environmental quality of this modified aquatic system
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