Common Blood Pressure Medication Losartan Breaks Down into Potentially Toxic Compounds in Sunlight, New research Finds
XIAMEN, CHINA – A widely prescribed medication for managing high blood pressure, losartan, degrades in sunlight-exposed water into byproducts exhibiting both high toxicity and resistance too biodegradation, according to a new study published in Frontiers in environmental Science & Engineering.Researchers investigated the environmental fate of losartan (LOS) through halogenation and photolysis, revealing concerning transformation pathways and potential risks to aquatic ecosystems.
The study, supported by the National Key R&D Program of China, the Natural Science Foundation of Xiamen, and the National Natural Science Foundation of China, details how losartan undergoes reactions with chlorine and bromine-common water disinfectants-accelerated by sunlight. These processes don’t simply eliminate the drug; instead,they create a complex mixture of compounds formed through halogen addition to the aromatic ring,hydroxylation,and even ring opening. While the initial breakdown appears rapid, some resulting products persist in the environment and pose a threat to aquatic life.
Researchers measured apparent rate constants (kapp) for chlorination and bromination of losartan. Chlorination rates, measured as kapp, HClO (LOS), ranged from 0.47 to 8.30 L/(mol·s) at pH levels between 5.0 and 8.0.Bromination proved significantly faster, with kapp, HBrO (LOS) values ranging from 8.38 × 103 to 1.55 × 105 L/(mol·s) over the same pH range. Losartan degradation occurs via direct photolysis, alongside reactions involving carbonate radicals and singlet oxygen when exposed to sunlight.The research team’s findings underscore the need for further investigation into the long-term ecological consequences of pharmaceutical runoff and the effectiveness of current water treatment methods in mitigating the formation of these potentially harmful degradation products. The full study is available at: https://journal.hep.com.cn/fese/EN/10.1007/s11783-025-1968-9.