A review of the potential risks associated with mercury in subsea oil and gas pipelines in Australia

Abstract

Environmental context The oil and gas industry has a significant liability in decommissioning offshore infrastructure. Following decommissioning, subsea pipelines could be left on the seabed to provide artificial reefs. Mercury is a contaminant of concern which could remain within pipelines. There are gaps in our knowledge on how mercury moves through the marine environment. We review the current science and identify future research needs to understand potential impacts from mercury in subsea pipelines which will better inform decommissioning activities globally. Abstract In the coming years, the oil and gas industry will have a significant liability in decommissioning offshore infrastructure such as subsea pipelines. The policies around decommissioning vary depending on regional policies and laws. In Australia, the ‘base case’ for decommissioning is removal of all property and the plugging and abandonment of wells in line with the Offshore Petroleum and Greenhouse Gas Storage (OPGGS) Act 2006. Options other than complete removal may be considered where the titleholder can demonstrate that the alternative decommissioning activity delivers equal or better environmental outcomes compared to complete removal and meets all requirements under the OPGGS Act and regulations. Recent research has demonstrated that decommissioning in situ can have significant environmental benefits by forming artificial reefs, increasing marine biodiversity, and providing a potential fishery location. An issue, which has been given less attention, is around contaminants remaining within decommissioned infrastructure and their potential risks to the marine environment. Mercury is a contaminant of concern known to be present in some oil and gas pipelines, but the potential long-term impacts on marine ecosystems are poorly understood. We present a synthesis of information on mercury cycling in the marine environment including key drivers of methylation in sediments and ocean waters, existing models to predict methylmercury concentrations in sediments, and toxicological effects to marine biota. We discuss the applicability of existing water and sediment quality guidelines, and the associated risk assessment frameworks to decommissioning offshore infrastructure contaminated with mercury. Globally, research is needed to provide a comprehensive risk assessment framework for offshore infrastructure decommissioning. We recommend future areas of research to improve our understanding of the potential risks associated with mercury in subsea oil and gas pipelines.

An approach to assessing subsea pipeline-associated mercury release into the North Sea and its potential environmental and human health impact

“…With decommissioning being in its infancy, all current proposals and conducted projects are executed in accordance with best practices and current scientific knowledge [119]. The present study, along with previous works [15,16,19], has highlighted gaps in the understanding of how contaminants associated with offshore infrastructures behave in the marine environment over time. With mercury having been associated with offshore oil and gas installations, the resulting potential environmental release in the case of in situ decommissioning could be a serious threat to the ecosystem and human health [15,16,19].…”

“…Only a few publications examine whether environmental mercury exposure affects the development or behaviour of wild organisms [90,91]. Similarly, limited data are available on mercury and methylmercury toxicity of marine species, a shortcoming recently highlighted by Gissi et al [19]. This highlights that although we are capable of modelling mercury in marine ecosystems and understanding the lethality in wild animals, we still lack the translation of what impact exposure to sub-lethal concentrations has outside of laboratory conditions.…”

“…However, little focus is currently placed on the effects of residual contaminants potentially associated with the infrastructure, even after cleaning [15][16][17]. One contaminant of concern is mercury, a naturally occurring heavy metal that is extracted alongside the hydrocarbon from offshore reservoirs [18,19]. Mercury is known to associate with the internal pipeline surfaces owing to rapid changes in temperature and pressure [20,21].…”

Offshore Decommissioning Horizon Scan: Research Priorities to Support Decision-Making Activities for Oil and Gas Infrastructure

“…Current knowledge of these contaminant sources and their ecotoxicological impacts on marine organisms following exposure is in its infancy (Melbourne-Thomas et al, 2021;Schläppy et al, 2021;Gissi et al, 2022;Koppel et al, 2022). Furthermore, the spatial extent and temporal legacy of such contaminants has not often been studied, although there is evidence of drill cuttings impacting biological communities over 1 km away, and over timescales of decades (Henry et al, 2017).…”

Foreword to the tribute issue for Dr Graeme Batley

“…Trace element speciation and its influence on bioaccumulation is a theme explored by five papers (Boily et al 2022;Cheng et al 2022;Cossart et al 2022;Glabonjat et al 2022;Hourtané et al 2022). The topics of water quality guideline development, risk assessment and regulatory science are covered by Fox and Batley (2022), Yeung et al (2022), Price et al (2022), Golding et al (2022) and Bowles and Beyer (2022) and finally, applied environmental chemistry exploring real world problems is represented by four papers (Gissi et al 2022;Kong et al 2022;Maher et al 2022;Yan et al 2022).…”