The formation of bioavailable Hg in a pipeline: An initial investigation into Hg bioaccumulation resulting from oil and gas decommissioning

Mercury (Hg) released during offshore pipeline decommissioning may pose ecological risks, yet little is known about its chemical form and biological impact. We examined how Hg⁰ can react on and subsequently be released from laboratory-generated steel pipeline material to interact with marine algae, focusing on chemical speciation, transformation, and cellular uptake. Laboratory exposures of the marine algae, Isochrysis galbana, to pipeline-derived Hg showed accumulation up to 109 mg kg^-1 dry weight, as determined by cold vapour atomic fluorescence spectrometry (CV-AFS). Single-cell inductively coupled plasma mass spectrometry (SC ICP-MS) confirmed substantial cell-associated Hg, with bimodal distributions suggesting distinct uptake or surface-association pathways. Although classical growth and photosynthetic parameters did not consistently reveal toxicity, Hg exposure altered cell populations and aggregation behaviour, indicating sublethal but ecologically relevant effects. Our findings demonstrate that through interactions with pipeline material Hg⁰ can be transformed into species which have an increased likelihood of bioaccumulation.