The effect of diethylene glycol on pollution from offshore gas platforms Michela Mannozzi, A Giorgio Famiglini, B,D Achille Cappiello, B Chiara Maggi, A Pierangela Palma, B Maria Teresa Berducci, A Veronica Termopoli, B Andrea Tornambe ` A and Loredana Manfra A,C A ISPRA – Institute for Environmental Protection and Research, Via Brancati 60, I-00144 Rome, Italy. B University of Urbino Carlo Bo, Department of Pure and Applied Sciences, LC-MS Laboratory Piazza Rinascimento 6, I-61029 Urbino, Italy. C Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn Villa Comunale, I-80121 Naples, Italy. D Corresponding author. Email: giorgio.famiglini@uniurb.it Environmental context. Marine mining activities are potential sources of environmental pollution. Diethylene glycol used in offshore platforms has been suspected to facilitate the release of toxic substances into the sea. The results obtained elucidate that this release is not significant for the metals examined here, apart from iron, nor for polycyclic aromatic hydrocarbons, even at very high diethylene glycol concentrations. Abstract. The role of diethylene glycol (DEG) as a co-solvent for selected organic and inorganic pollutants adsorbed onto the particulate matter in produced formation water (PFW) from offshore gas platforms is thoroughly evaluated. Artificial seawater samples were spiked with certified sediments containing several polycyclic aromatic hydrocarbons (PAH) and metals. Aliquots (1 L) containing no DEG and DEG at 3500 and 5000 mg L À1 were kept in static and dynamic modes for 24 h before analysis to allow sufficient partitioning time between solid and liquid phases for the selected analytes. The Italian legislation on this matter sets 3500 mg L À1 as the highest concentration for DEG in PFW. In our experiments, concentrations equal to and above the set limit were chosen to enhance any possible co-solvent effect. Real PFW samples were also analysed, both with and without DEG. The analyses were conducted by using GC-MS for the PAH, and ICP-MS for the metals. A minor co-solvent effect was observed for low-molecular-weight PAH in the artificial seawater in static mode. Among metals, only iron showed an increase in solubility in the presence of DEG, demonstrating the co-solvent effect of DEG. The experiments in dynamic mode revealed no increase in the solubility of any other analytes in the liquid phase compared with static mode. Additional keywords: GC-MS, heavy metals, ICP-MS, polycyclic aromatic hydrocarbons, produced formation water. Received 7 November 2017, accepted 15 December 2017, published online 24 April 2018 Introduction During the production of natural gas from offshore platforms, wastewater is commonly generated. This wastewater is com- monly called produced formation water (PFW) and is a het- erogeneous aqueous mixture that can contain chemicals such as aromatic and aliphatic hydrocarbons, metals, sands, salts, and other additives used to optimise the gas platform efficiency. [1] These chemicals can be found either dissolved in the PFW or adsorbed in the particulate fraction. The term PFW can also refer to water trapped in deep impermeable geological formations, including reservoirs of oil and natural gas. During the extraction process, PFW can mix with the oil and natural gas that is extracted. PFW can also be intentionally injected into the gas reservoir to maintain sufficient pressure during the extraction process. Such injection is regulated by law. [2] PFW can also mix with the chemicals involved in the production process. PFW represents the main liquid waste from offshore gas platforms and may be discharged into the ocean after being suitably treated to remove gaseous hydrocarbons. [3,4] Glycols, such as diethylene glycol (DEG), are highly hygroscopic, and are therefore typi- cally used in the water-stripping process from natural gas in off- and on-shore gas platforms. DEG is used to prevent the formation of gas hydrates and to inhibit the corrosion of gas lines during the gas dehydration process. [5] After use, it is recovered and regenerated for both economic and environmental purposes. However, it could enter the environment in the case of leaks or spills. Furthermore, DEG can also be injected downstream of the wellheads and added to the extracted flows from the gas reser- voirs to avoid freezing or formation of gas hydrates. In these cases, it can be found in PFW at high concentration. In Italy, a Decree of the Ministry of Environment sets 3500 mg L À1 as the maximum concentration of DEG in PFW that can be discharged directly into the sea. From ecotoxicological studies, DEG-effect concentrations (EC 50 ), at which 50 % of its maximal effect is observed, have been derived for different organisms; EC 50 values were found to vary between 500 and 90 000 mg L À1 , most CSIRO PUBLISHING Environ. Chem. 2018, 15, 74–82 https://doi.org/10.1071/EN17198 Journal compilation Ó CSIRO 2018 www.publish.csiro.au/journals/env 74 Research Paper