Investigating how H2S can alter the interactions between Hg0 and corroded steel surfaces to guide future decommissioning projects

Abstract

Many oil and gas developments will soon be decommissioned and, knowledge on the accumulation of mercury (Hg), throughout offshore infrastructure is limited. Any release of Hg could have a detrimental impact on marine ecosystems. To bridge this knowledge gap, a fractionation approach was taken on steel samples exposed to Hg⁰ and H₂S, separating Hg compounds removed from the surface into polar, non-polar and insoluble fractions. Hg⁰ reacted on corroded surfaces to form several compounds, over 50% of which were removed by seawater. This suggests that pipelines on the seabed could release a dramatic amount of Hg into the sea if they are left in place. Furthermore, a Cu-Hg amalgam, was identified to be a dominant species, by a combination of XFM, XANES and LA-ICP-TOFMS. Seawater-soluble and amalgam-bound Hg were present regardless of co-exposure to H₂S. When H₂S was present Hg nanoparticles accounted for up to 1% of the total Hg on the steel. This investigation has shown that the Hg speciation on the surfaces of pipelines is complex and future decommissioning strategies should consider a range of Hg species beyond only Hg⁰ and metacinnabar (β-HgS), all of which could interact with biota and impact Hg biomagnification through the marine the food web.