Regasification terminals convert liquefied natural gas (LNG) transported by sea into natural gas (NG), which is subsequently injected into the national transmission network. At terminals located in the marine environment, seawater may be used in the regasification process, as it transfers heat to the liquefied gas and returns it to its gaseous state.

After use, the water is discharged back into the sea at a lower temperature, resulting in a negative temperature differential, and following treatment with chlorine as an antifouling agent. The main environmental impact potentially associated with the operation of offshore regasification terminals is therefore related to the discharge of this cold, chlorinated heat-exchange water.

The first offshore terminals to become operational in Italy, and for which historical process-water datasets suitable for assessing the environmental pressures exerted by these facilities are available, are the regasification terminals located off Porto Viro and Livorno.

For both terminals, during the 2014–2025 period, the temperature differential was closely correlated with the amount of natural gas injected into the network. Greater absolute negative values, of approximately −4°C, were recorded in years characterised by higher gas production. Nevertheless, the values always remained within the limits established by the relevant authorisation decrees.

The quantity of chlorine contained in the process water discharged into the sea also showed a strong correlation with the amount of natural gas injected into the network. At the Porto Viro terminal, active chlorine releases ranged from 10 to 50 tonnes per year, against natural gas injections ranging from 4 to 9 billion standard cubic metres (Sm³). At the Livorno terminal, chlorine releases ranged from 0.5 to 2.5 tonnes per year, against natural gas injections ranging from 1 to 4 billion Sm³.

In both cases, the release of chlorine in process water discharged into the sea consistently complied with the limits established by the applicable legislation and operating authorisations.

In Italian seas there are 138 offshore platforms; 42 of them—mostly located in the central and northern Adriatic and mainly used for natural gas extraction—are covered by an environmental monitoring plan. Among the monitored chemical substances are barium and polycyclic aromatic hydrocarbons (PAHs).

Barium is a metal used in the production of fluids required for drilling operations and it can be present in produced waters that are periodically discharged to the sea by platforms, while PAHs are chemical substances whose presence in the marine environment—besides natural factors—is linked to anthropogenic activities.

Barium and total PAH concentrations in surface sediments around platforms are environmental indicators of the pressure resulting from offshore gas field exploitation. Data available for 2008–2024 show a progressive decrease over time in the mean concentrations of these contaminants, with the highest concentrations generally detected close to the platforms.

Barium data are above the baseline reference value in the majority of sediment samples analysed in 2008–2014, whereas in 2015–2024 the share of exceedances is close to or below 50%. The percentage of sediment samples with total PAH concentrations above the limit value—an indicator of likely toxic effects on marine organisms—during 2009–2017 in some cases reaches 10–16% at stations 25 m from the platform, but decreases markedly at stations farther from the platform; during 2018–2024 exceedances of the reference value decrease further at all stations.

“Produced water” (also referred to as “formation water”) is one of the main effluents associated with the exploitation of hydrocarbon reservoirs in offshore marine environments and may potentially cause disruptive effects on ecosystems. The discharge of these effluents into the sea requires an authorisation, which is conditional upon the assessment of the results of annual monitoring of the environment surrounding the platform.

The number of platforms subject to environmental assessment of monitoring outcomes fluctuated between 2016 and 2024 due to variability in the number of discharge authorisation applications submitted, and it decreased in the most recent year. The number of platforms authorised each year declined from 2017 to 2021, then recovered up to 2023, before decreasing again in 2024 and dropping to zero in 2025; a similar trend is observed for the annual volume of produced water authorised for discharge into the sea.