Ecotoxicological impacts of caffeine on Daphnia magna: insights from acute to chronic exposures.

Caffeine (CAF), a widely consumed central nervous system stimulant, has been detected in aquatic ecosystems, and several studies show that CAF affects non-target organisms. Although some ecotoxicological studies on CAF and aquatic organisms already exist, they mostly focus on marine organisms with concentrations relevant to those ecosystems. Thus, this study evaluated the ecotoxicological effects of CAF on Daphnia magna through four tests: acute exposure (48 h; 27–3000 mg/L; immobilization/mortality parameters), feeding inhibition assay evaluating immobilization/mortality parameters (24 h; 249–1000 mg/L), sub-chronic (10 days; 3.8–60 mg/L), and chronic (21 days; 4.6–35 mg/L) exposures, assessing life history parameters (age at first reproduction, fecundity, somatic growth rate, population growth rate, and reproductive output). In all assays, biochemical parameters like antioxidant defence biomarkers, lipid peroxidation, and cholinergic neurotransmission were evaluated. The results showed that CAF exposure caused feeding inhibition (EC50 = 323 mg/L), reduced somatic growth and fecundity (CAF ≥ 10 mg/L; p < 0.05), and induced changes in antioxidant defences (CAF ≥ 10 mg/L; p < 0.05) and acetylcholinesterase activity (CAF ≥ 60 mg/L; p < 0.05). These findings demonstrate that CAF induces toxic effects in D. magna, compromising key biological functions like growth, reproduction, and metabolic pathways, highlighting the need to monitor CAF residues found in aquatic environments. Moreover, these results offer critical data for environmental regulation, as the assessed parameters showed sensitivity in evaluating caffeine toxicity in freshwater organisms.