Contrasting persistence and sediment retention of pharmaceuticals in aquaculture systems

The use of pharmaceuticals in aquaculture, together with diffuse anthropogenic inputs, raises concerns regarding their persistence and accumulation in water–sediment systems of fish farms. In this study, the fate of three model pharmaceuticals with contrasting properties, namely acetaminophen (APAP), sulfamethoxazole (SMX), and ciprofloxacin (CIP), was investigated in water-sediment microcosms derived from six aquaculture sites with different physicochemical characteristics in Italy and Thailand. Experiments were conducted under sterilized and non-sterilized conditions to qualitatively distinguish biotic and abiotic contributions to dissipation. Concentration trends in the water phase were combined with sequential sediment extraction and high-resolution mass spectrometry (HRMS) suspect screening to support fate interpretation. Results demonstrated highly compound-specific dissipation pathways. APAP underwent rapid biotic turnover (>80% loss within 7 days) with negligible sediment accumulation (<5%), whereas SMX exhibited moderate, site-specific aqueous persistence (20–40% loss over 21 days). Crucially, HRMS analyses linked these aqueous attenuations to the generation of transformation products, which preliminary in silico screening suggests may possess higher ecotoxicity than their parent molecules. Conversely, CIP rapidly partitioned into strongly bound sediment fractions without detectable metabolites, confirming a purely retention-driven removal. The results highlight the necessity of integrating water-phase monitoring with sediment-resolved approaches and high-resolution structural elucidation. These findings provide practical insights into the environmental behavior of pharmaceuticals in aquaculture ponds, emphasizing that apparent aqueous dissipation does not necessarily equate to ecological risk mitigation, and confirming sediments as potential long-term reservoirs for specific antibiotic classes.