The photolytic breakdown of caffeine and paracetamol residues in surface water

High concentrations of the most consumed pharmaceuticals, caffeine and paracetamol, have been observed globally in wastewater treatment plant discharge. Here, we assess the potential for photodegradation of caffeine and paracetamol residues at concentrations like those observed in treated wastewater discharges to the environment. Laboratory assays were used to measure rates of photodegradation of these two compounds both in distilled water and in natural river water with leaf litter leachate. When exposed to artificial light simulating natural sunlight, the half-life values of caffeine and paracetamol were significantly shorter than in the dark. The presence of organic matter increased caffeine and paracetamol half-life by lessening the photolytic effect. These results suggest that photolysis is a substantial contributor to the degradation of caffeine and paracetamol. The findings contribute to our understanding of persistence of pharmaceuticals in treated wastewater discharge. PRACTITIONER POINTS: The photodegradation of caffeine and paracetamol residues in surface water was examined. With leaf litter leachate, caffeine and paracetamol were photodegraded in distilled and natural river water in laboratory. Caffeine's half-life ranged from 2.3 to 16.2 days under artificial sunlight andparacetamols from 4.3 to 12.2 days. When incubated in the dark, the half-life for both compounds exceeded 4 weeks. Organic matter decreased the photolytic action of caffeine and paracetamol.