Ecological risk assessment of caffeine in global aquatic ecosystems: From land to sea

Caffeine, as a marker of human activity, has been widely detected in aquatic environments worldwide. This study analyzed caffeine concentrations in aquatic environments across 85 countries/regions to evaluate its ecological risks to freshwater and marine species. Based on species sensitivity distribution (SSD) curves, a chronic freshwater predicted no-effect concentration (PNEC) of 0.052 μg/L was derived, which may serve as a useful screening benchmark for global ecological risk assessment, pending further refinement with expanded chronic toxicity datasets. The derived chronic seawater PNEC (0.14 μg/L) in this study was only used as a preliminary screening threshold for caffeine risk. A multi-dimensional quantitative assessment of global ecological risks was performed via integrated application of risk quotient (RQ) based on PNEC, potentially affected fraction (PAF) and joint probability curve (JPC). Results showed 83.67% of global freshwater monitoring sites posed high risks (RQ > 1). PAF analysis indicated caffeine concentrations in 71.95% of freshwater monitoring sites might adversely affect over 5% of freshwater species, while JPC revealed a 13.29% risk probability to 5% of freshwater species. Based on Monte Carlo predictions, the median RQ for caffeine in pore water of freshwater sediment was 0.051, indicating the low risk (RQ < 0.1). In coastal monitoring sites, 50.52% of global coastal monitoring sites posed high risks. PAF analysis showed 32.99% of coastal monitoring sites threatened over 5% of marine species and JPC demonstrated a 34.16% risk probability to 5% of marine species. High-risk areas seem to be coupled with high coffee/tea consumption and limited wastewater treatment, implying that improving the treatment efficiency of WWTPs is crucial for lowering risks.