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.

Regasification terminals convert liquefied natural gas (LNG) transported by sea into natural gas (NG), which is then fed into the national distribution network. For terminals located in marine environments, seawater can be used in the regasification process because it transfers heat to the liquefied gas, bringing it back to the gaseous phase. The seawater used is subsequently discharged back into the sea after undergoing a temperature decrease (negative thermal delta) and after being treated with chlorine as an anti-fouling agent. The main environmental impact that may occur during the operation of offshore regasifiers is therefore related to the discharge of these cold, chlorinated heat-exchange waters.

In Italy, the first offshore terminals to enter operation—and for which time series data on process water are available to assess the environmental pressure exerted by these facilities—are the regasification terminals located off Porto Viro and Livorno.

For both terminals, over the period 2014–2024, the thermal delta trend was closely correlated with the quantity of NG fed into the network, with larger absolute values and negative sign (around -4°C) in years with higher NG output, while always remaining within the limits set by the relevant authorisation decrees. The amount of chlorine contained in the process water discharged into the sea also showed good correlation with the quantity of NG fed into the network, with values between 10–50 tonnes/year for the Porto Viro terminal, with NG injected ranging between 4 and 9 billion standard cubic metres (Smc), and between 0.5–2.5 tonnes/year for the Livorno terminal, with NG injected ranging between 1 and 4 billion Smc. In both cases, chlorine releases in discharged process water always complied with the limits set by applicable legislation and operating permits.