###### Abstract  
The determination of trace pollutants in seawater is challenging, and sampling is a crucial step in the entire analytical process. Passive samplers combine in situ sampling and preconcentration, thus limiting the tedious treatment steps of the conventional sampling methods. Their use to monitor water quality in confined marine environment could bring several advantages. In this work, the presence of organic contaminants at trace and ultra-trace levels was assessed in the Genoa Aquarium supply-and-treated water using Polar Organic Integrative Samplers (POCIS). Both untargeted gas chromatography-mass spectrometry and targeted liquid chromatography-tandem mass spectrometry were employed. The untargeted approach showed the presence of hydrocarbons, diphenyl sulfone and 2,4-di-tert-butyl-phenol. Only hydrocarbons were detected in all the samples. Nineteen emerging contaminants, belonging to different classes (pharmaceuticals, UV-filters, hormones and perfluorinated compounds), were selected for the target analysis. Thirteen analytes were detected, mainly in supply water, even though the majority of them were below the quantitation limit. It is worthy to note that two of the detected UV-filters had never been reported in seawater using the POCIS samplers. The comparison of the analytes detected in supply and treated water indicated a good performance of the Aquarium water treatment system in the abatement of seawater contaminants.  
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the Polar Organic Chemical Integrative Sampler (POCIS) was designed to sample polar compounds [5]. However, POCIS was applied to the sampling of chemicals characterized by a logKow comprised between 0 and 5 [6]. It consists in a sorbent phase sandwiched between two microporous membranes, usually made of polyethersulfone (PES), which are kept together by two stainless rings.  
POCIS devices generally show low affinity for highly hydrophobic and ionic compounds [7]. Indeed, low diffusion through the membranes was found for hydrophobic substances because the PES polymer can act as the primary receiving sorption phase for these compounds [8]. Nevertheless, the detection of some lipophilic substances using these samplers is reported [9; 10]. The introduction and testing of new sorption materials and membranes in passive techniques are aimed at increasing the range of chemicals that can be sampled [6].  
POCIS are mainly employed to monitor contaminants in freshwater and wastewater [10; 11; 12; 13; 14], while their use for seawater monitoring remains limited [9; 15; 16]. Furthermore, the use of this device in a confined marine environment was only reported for the detection of micro-pollutants in a Spanish fish farm located in a coastal area [17]. Nevertheless, their use to monitor water quality of circumscribed environments (such as swimming pools or aquarium tanks) could bring several advantages. Aquarium water is generally collected from the coastal zone and subjected to treatments. Then, renewal water systems allow the water in fish tanks to be replaced to some extent every day, thus making the passive sampling approach useful for verifying water quality over time.  
The aim of this work was to identify the presence of polar organic contaminants in Aquarium water (Genoa, Liguria, Italy). POCIS samplers were employed to continuously monitor the quality of supply water (withdrawn from the sea), of treated water (filtered and disinfected) and of shark tank water, verifying the efficacy of the treatment system used before tank filling. Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were employed to detect the presence of classical and emerging contaminants.