Sedimentary mercury stable isotope records of atmospheric and riverine pollution from two major European heavy metal refineries

Variations in sediment total mercury (Hg) concentrations and Hg stable isotopic compositions were investigated in the vicinity of two former non-ferrous metal (zinc) refineries in Lommel (Kempen, Belgium) and Viviez (Aveyron, France). Contaminated Kempen sediment Hg levels are up to 6.8 mg kg−1 corresponding to a peak in atmospheric Hg deposition of ~ 1.0 mg m−2 year−1 for the year 1968. Atmospheric and riverine Hg contamination from the zinc refinery point sources in Belgium and France present mass dependent (δ202Hg of −0.32 to + 0.71‰) and small mass independent Hg isotope signatures (Δ199Hg of −0.15 to − 0.04‰) that are significantly different from local geochemical background Hg (δ202Hg of − 1.44 to − 0.75‰; Δ199Hg of − 0.35 to + 0.06‰). In addition we found that selected sphalerite (ZnS) ore concentrates carry average δ202Hg of − 0.65 ± 1.33‰ (2σ, n = 4), similar to published Hg minerals (mainly HgS) with δ202Hg of −0.64 ± 1.82‰ (2σ, n = 125). Congolese ZnS ores from the Kipushi deposit show significant mass independent Hg isotope fractionation with average Δ201Hg of − 0.09 ± 0.02‰, and Δ199Hg of − 0.08 ± 0.01‰ (2σ, n = 3), possibly suggesting a partial atmospheric origin for trace Hg within the Kipushi ore deposit. Similar to Zn and Cd isotopes, high temperature non-ferrous metal refining processes appear to preferentially retain the heavy Hg isotopes in slag residues: Hg contaminated Cajarc (France) river sediment δ202Hg values of + 0.22 ± 0.52‰ (2σ, n = 17), considered to present an integrated picture of post-WWII 20th century slag tailing effluents, are significantly enriched in the heavier Hg isotopes relative to Kempen core B1 atmospheric Hg deposition with δ202Hg of −0.07 ± 0.34‰ (2σ, n = 10), as well as relative to Hg containing sulfide minerals with δ202Hg of −0.64 ± 1.82‰ (2σ, n = 125). The distinct Hg isotope signatures of natural and anthropogenic Hg suggest that tracing the various Hg emissions into regional Belgian and French ecosystems should be feasible. The highly elevated contamination of Hg in the Kempen warrants further study of local ecosystems including human exposure.

Research Highlights
► Congolese sphalerite ores from the Kipushi deposit show significant MIF.
► Non-ferrous metal refining appears to enrich slag material in heavy Hg isotopes.
► Hg contamination from European zinc smelters carries unique isotopic signatures.
► Pre-industrial French river sediments show significant non-zero MIF anomalies.