In this study, the stability of 124 target analytes in influent and effluent wastewater samples during short-term (4°C) and long-term (-18°C) storage was assessed. The most common storage scenario was considered, in which samples were frozen immediately after sampling without any pre-treatment. During short-term storage more analytes remained stable (concentration during storage was in the range of 60-120% of the initial concentration) at 4°C than at -18°C. During long-term storage (-18°C), three types of behavior were observed: constant concentrations throughout the experimental period, decreasing concentrations with time, and loss of the compound from the sample after freezing. Differences between effluent and influent samples were observed for 50 out of 124 tested PPCPs. The amount of stable analytes decreased with time during long-term storage. 72% and 56% of the target compounds in the effluent and influent wastewater, respectively, remained stable during 60days of storage. The number of stable compounds decreased to 57 (46%) and 46 (37%) in the effluent and influent, respectively, over 120days. 15 Pharmaceuticals were lost after freezing/thawing cycle. The results stress the importance of storage factors during analysis of pharmaceuticals in wastewater. The stability of target compounds in the samples under the planned storage conditions should be checked before starting the experiment to obtain reliable data.

University of South Bohemia in Ceske Budejovice Faculty of Fisheries and Protection of Waters South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses Research Institute of Fish Culture and Hydrobiology Zátiší 728 2 389 25 Vodňany Czech Republic

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