Physiological and biochemical tolerance responses of the estuarine saltmarsh plant Limbarda crithmoides L. under acetaminophen exposure: Insights into plant–pollutant interactions

Pharmaceutical contamination in estuarine and coastal environments is a growing concern due to continuous urban discharges and limited removal in conventional wastewater treatment. Acetaminophen, a frequently detected analgesic in surface and estuarine waters, was selected as a model compound to investigate its physiological effects on the native saltmarsh plant Limbarda crithmoides L. Rooted explants were exposed to acetaminophen (0.1, 1.0, and 2.0 mg/L) in liquid culture for 7, 14, and 21 days. Removal from solution was monitored by HPLC-DAD and GC–MS, while pigment levels, oxidative stress markers (MDA), osmoprotectants (proline, proteins, sugars), and secondary metabolites (phenolics, flavonoids, tannins, shikimic acid, PAL activity) were quantified in roots and shoots. L. crithmoides showed moderate tolerance to acetaminophen exposure, maintaining photosynthetic pigments and stable stress markers. Early responses involved osmoprotectant accumulation and controlled oxidative damage, followed by the activation of antioxidant and phenolic pathways at later stages, suggesting metabolic acclimation to sustained stress. Root tissues displayed lower oxidative damage and higher proline accumulation than aerial parts, indicating spatial differentiation of stress responses. Despite continuous exposure, plants preserved functional integrity and biochemical homeostasis. These results reveal key physiological and biochemical mechanisms underlying the tolerance limits of a native estuarine species to pharmaceutical stress, providing insight into plant–pollutant interactions and the potential role of saltmarsh vegetation in the functioning of contaminated coastal ecosystems.