Occurrence and risks of pharmaceuticals in Mahdia’s coastline (Tunisia): distribution, antibiotic resistance, and ecotoxicological impact

Pharmaceutical active compounds (PHACs) pose a significant risk to aquatic ecosystems due to their persistence and potential toxic effects. Despite their documented presence in various coastal environments, their occurrence along the Mahdia coastline remains largely unexplored. Using ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), we analyzed seawater and sediment samples collected over six consecutive months from Mahdia's marine environment. Results revealed that antibiotics were the most prevalent PHACs, with ofloxacin reaching 401 ng/L in seawater. Other consistently detected compounds included flumequine, nalidixic acid, oxytetracycline, and N4-acetylsulfamerazine, with maximum concentrations of 16 ng/L, 17.1 ng/L, 12.1 ng/L, and 59.2 ng/L, respectively. Additionally, carbamazepine was detected at 5.2 ng/L, while caffeine concentrations ranged from 12.6 ng/L to 638 ng/L in seawater and up to 6.87 ng/g in sediment. The study also assessed antibiotic resistance risks, expressed as resistance risk quotients (RRQs) and indicating that ofloxacin and flumequine pose a medium-risk threat to bacterial communities. Ecotoxicological evaluations through calculation of ecotoxicological risk quotient (ERQs) and hazard indexes (HI) classified ofloxacin as a low-to-moderate risk for fish populations. These findings provide the first comprehensive mapping of PHAC contamination and potential risks along the Mahdia coast, emphasizing the urgent need for improved wastewater treatment and monitoring programs to mitigate environmental risks.