## 3 Results and Discussion
### Untargeted Analysis
#### 3.1.2 Industrial Compounds  
In sampling I and II, the screening in full-scan mode of the extracts allowed the detection of DPS and 2,4-DTBP. This untargeted procedure was employed also in sampling III, where, in addition to hydrocarbons, only 2,4-DTBP was found. Subsequently, semi-quantitative analysis was carried out in SIM mode. The ions at 125 \(m/z\) and 191 \(m/z\) were monitored for DPS and 2,4-DTBP, respectively. Analogously to hydrocarbons, the ratio between the analytes peak area in the sample and in a reference standard (concentration 1 mg L\({}^{-1}\)) was used to compare different POCIS extracts.  
DPS is a herbicide employed as ovicide and acaricide in the past. Today, it is mainly used as a monomer in the polymer industry and is a transformation product of phenols synthesis. It enters aquatic ecosystems through various sources and [PERSON] et al. affirmed that photochemical and chemical degradations are not significant in surficial water [25].  
DPS concentrations estimated in the sampling I extracts were approximately 1 mg L\({}^{-1}\), corresponding to 1 mg/POCIS. This value was comparable to that reported in one of our previous studies, where POCISs were deployed in Santa Margherita Harbor (Liguria) [9]. Furthermore, the detection of DPS at low concentrations in seawater was reported during a micro-pollutant monitoring campaign in a fish farm [17]. On the other hand, in sampling II and III, DPS was neither detected in the supply water nor in the treated water. This difference could be related to the sampling period of the last two deployments (winter).  
2,4-DTBP is a volatile organic compound used as intermediate for the preparation of UV stabilizers and antioxidants. Migration tests performed on high-density polyethylene pipes (HDPE) used in drinking water distribution networks showed 2,4-DTBP as the major migrating component from pipes into water [26]. It has fungicidal activity [27] and has shown potential endocrine disrupting effects and aquatic toxicity [28].  
Regarding first monitoring, higher levels of 2,4-DTBP in treated and shark tank waters were observed in sampling I compared to sampling II (mean value approximately 3 mg/POCIS and 1 mg/POCIS, respectively). Moreover, the concentration of 2,4-DTBP was approximately 6 mg/POCIS for supply water extracts obtained from sampling II, indicating strong abatement during water treatment (6 mg/POCIS and 1 mg/POCIS detected in supply and treated water, respectively).  
The second monitoring (sampling III) confirmed the good performances of the treatment system in pollutant removal. 2,4-DTBP was found in the sole supply water at a concentration around 4 mg/POCIS, while there was no evidence of the analyte presence in the treated water. The good performance of aquarium filtration and disinfection systems in 2,4-DTBP removal was an important result due to its endocrine disruptor effect and its aquatic toxicity.  
It is worth noting that a lower amount of 2,4-DTBP was sampled in winter (samplings II and III) compared to spring (sampling I), confirming the trend already observed for DPS, which was only detected in POCIS deployed in spring (sampling I).