## 4 Conclusions  
In this anthropogenically modified lagoon environment, notable differences in terms of concentration and trends in sediment profiles were not observed between the two sites. Cadmium and Hg showed high EF values at both sites (5-20), thus indicating a \"significant enrichment\", as compared to the local background. Mercury contamination is mainly due to the legacy of the past extraction activity at the Idrija mining district (NW Slovenia), whereas Cd enrichments are attributed to more recent undefined anthropogenic sources. Excluding Cd and Hg, low enrichment factors (EF) were found at both sites; however, slightly higher EF values were observed at VN3 (EF up to 2.27), with respect to VN1 (EF up to 1.44). Except for Mn, the labile percentage of metal(loid)s was low or absent, thus suggesting that the amount of elements in association with Fe and Mn oxides and hydroxides was scarce. The results from porewaters showed the highest concentration of Al, Cd, Cu, Fe, Pb and Zn at VN3 and, in general, the metal(loid)s roughly followed the H\({}_{2}\)S trend. The adsorption/release of some metal(loid)s associated with Fe and Mn oxy-hydroxides and FeS/FeS\({}_{2}\) or precipitation as sulphides govern their mobility. The logK\({}_{\text{D}}\) values at the two sites did not differ significantly and were found to be comparable with values reported in the literature. A positive diffusive flux was found for almost all metal(loid)s, thus indicating a tendency to migrate from porewaters to the overlying water, especially with regard to Fe and Mn. However, during the benthic chamber experiment, high metal(loid) concentrations and great variability over time were observed at the more oxic site, VN1, compared to the anoxic site, VN3. The benthic fluxes, mostly effluxes, showed significant differences between the two sites, with the highest values estimated for Fe at VN1 and Mn at VN3, indicating of a release from the sediment to the overlying water column. Effluxes for all metal(loid)s, excluding Cr, and H\({}_{2}\)S were estimated at VN3 and associated with the anoxic conditions that characterised this site. Conversely, the influxes of Cr, Cu, Hg and Mn estimated at VN1 could be the consequence of the immobilisation of Mn and concomitantly other involved metals. However, the highest benthic effluxes, except for As and Pb, were observed at this oxic site (VN1), thus indicating a major release from the sediment to the water column of Al, Fe, Ni, V, Cd and Zn. A possible explanation could be the intense bioturbation produced by benthic organisms that plays a major role in the significant variability of the metal benthic fluxes in the lagoon. Overall, the mobility of metal(loid)s from the sediment to the porewaters and to the overlying water column, although driven by an intense remineralisation of the organic matter and bioturbation, appears to be limited and related to the specific environmental conditions of the experimental site. Therefore, it seems that the presence of metal(loid)s in fish farm sediments, excluding Hg, for which this semi-confined environment was found to be a potential bioreactor for MeHg production, [12] do not represent a severe risk for the aquaculture activity. The following are available online, at [[https://www.mdpi.com/2076-3417/11/5/2350/s1](https://www.mdpi.com/2076-3417/11/5/2350/s1)]([https://www.mdpi.com/2076-3417/11/5/2350/s1](https://www.mdpi.com/2076-3417/11/5/2350/s1)). Figure S1: Metal(loid) profiles in VN1 and VN3 sediment cores. Table S1: Enrichment factors (EFs) calculated for all metal(loid)s for each level of the sediment cores (VN1 and VN3). Table S2: Log K\({}_{\text{D}}\) values for all metal(loid)s in each level of cores VN1 and VN3. **Author Contributions:** Data curation, conceptualisation, methodology, writing--original draft and writing--review, [PERSON] ([PERSON]), E.P. ([PERSON]), J.F. and S.C.; analyses, [PERSON] ([PERSON]), E.P. ([PERSON]) and M.C.