Mercury is routinely detected in offshore gas production facilities and infrastructure. Over the production life, mercury can precipitate onto the internal surfaces of equipment including subsea flow lines and gas export pipelines. As these facilities are decommissioned, effective risk management is required to ensure there is no impact from mercury on the marine environment. This is particularly crucial where in situ decommissioning options could be considered.
Previous work at ANSTO analysed pigging dust collected from a gas export pipeline offshore Australia. While concentrations of mercury were high (~ 1.7% dry mass), the dominant species was metacinnabar (b-HgS, >99%). The scientific literature generally reports HgS to be relatively low risk, i.e., limited solubility and bioavailability. However, few studies have investigated the fate and transport of HgS under Australian marine conditions.
Using radioisotope tracers of mercury (203Hg), we have synthesised metacinnabar and commenced investigations into its solubility and transformations in seawater under varying conditions of light (representing depth), temperature and dissolved oxygen. The range of conditions represented the offshore marine environment around Australia. Improving our understanding of the solubility of HgS in seawater will aid our ability to effectively manage and assess any potential risks of mercury in subsea gas pipelines.