When pharmaceuticals go down the drain—often in people’s waste—they can persist through wastewater treatment, reaching waterways and posing harm to fish and other aquatic creatures. Researchers have been working on ways to remove these micropollutants from wastewater, and now one team introduces a new approach: design replacement drugs that biodegrade once they reach the environment. The researchers modified a drug commonly used to treat high blood pressure into a form that should still be pharmacologically active but that breaks down more easily in wastewater treatment (Environ. Sci. Technol. 2015, DOI: 10.1021/acs.est.5b03051).
Klaus Kümmerer of Leuphana University of Lüneburg, in Germany, came up with the idea while testing methods to remove micropollutants from wastewater. One method is exposure to ultraviolet light, which can transform compounds into more biodegradable products. He realized that this approach might also be used to synthesize more biodegradable alternatives to current drugs.
So he and his team tested the idea on propranolol, a beta blocker used to treat high blood pressure. Propranolol is toxic to some aquatic creatures when they’re chronically exposed at concentrations found in wastewater effluent, and the drug does not biodegrade in the environment. The researchers first dissolved the drug in pure water and exposed it to UV light for about four hours, yielding 16 derivatives that they identified using liquid chromatography with tandem mass spectrometry. Then they tested these compounds’ biodegradability by incubating them with effluent from a local sewage treatment plant and measuring consumption of oxygen and organic carbon over time by the microbes present.
They found that the most biodegradable derivatives were hydroxylated on one of propranolol’s aromatic rings. This change makes the ring more likely to open up, allowing easier access for microbes to digest the drug. The most promising derivative, 4-hydroxypropranolol, biodegraded by 23% into inorganic components such as carbon dioxide and water after one month. Some 48% of the derivative was at least partially degraded into other organic compounds that computer models predict to be low in toxicity.
Using computer modeling and a cell culture binding assay, the researchers predicted that 4-hydroxypropranolol should have similar drug activity to propranolol, as well as low toxicity and good absorption. These findings are corroborated by an earlier study showing that the two compounds have similar activity in rats, cats, dogs, and guinea pigs.
Kümmerer says the photochemical approach could be used to explore biodegradable alternatives for most drugs and other micropollutants, such as those found in personal care products. He and his team hope to improve the biodegradability of the propranolol derivative, and to investigate other methods to enhance drug decomposition.
“I’m overwhelmed with the innovativeness of the idea,” says Susan D. Richardson, an environmental chemist at the University of South Carolina. She says the researchers have cleverly used a simple method to produce an alternative compound with promising biodegradability.
For their next steps, she says the researchers should study the toxicity of the derivative and its degradation products in living organisms. They should also test whether drinking water treatment, such as chlorination, would transform these compounds into toxic by-products. If these hurdles are cleared, she says, this method “could be a revolutionary way to lower our load of drugs to the environment.”