Mechanisms of toxicity and stress tolerance in aquatic plants under combined exposure to pharmaceuticals, personal care products, and eutrophication: A meta-analysis.
Given the increasing co-occurrence of pharmaceuticals and personal care products (PPCPs) and eutrophication in aquatic environments, it is crucial to understand PPCP-nutrient-plant interactions and their combined ecological impact. However, the literature regarding quantitative thresholds and metabolic trade-offs remain highly fragmented. In this meta-analysis, we compiled a dataset comprising 407 observations from 38 rigorously screened studies, covering various PPCP classes and floating, submerged, and emergent plant habitats. Remediation efficiency and physiological stress markers specifically enzymatic defense and oxidative damage were selected as informative endpoints for assessing plant responses to combined exposure. The combined stressors' phytotoxicity generally manifested as severe oxidative stress and metabolic exhaustion in submerged species, despite high apparent initial removal. However, the observed remediation phenotype was heavily influenced by experimental conditions, particularly exposure concentration, transitioning from a metabolic primer to an inhibitory stressor above a 10 mg/L threshold. Conversely, physiological stability and active removal efficiency were maintained in floating species and specific elite emergent candidates, particularly Vetiveria zizanioides, following exposure to co-contamination. Ultimately, this meta-analysis highlights the severe metabolic costs aquatic plants face in co-contaminated systems. We identified a critical toxicity tipping point at a 10 mg/L exposure concentration. Beyond this threshold, we observed a critical performance shift at a 10 mg/L exposure concentration. We hypothesize that beyond this threshold, plant defense systems are severely overwhelmed, and the observed removal of contaminants may transition from active biological degradation to passive physical sorption. These findings provide essential mechanistic insights into how combined chemical and nutrient stressors disrupt plant physiology, which is critical for understanding their broader ecological impact.