Degradation of Gemfibrozil and Naproxen in a river water ecosystem

摘要

Pharmaceuticals are nowadays generally recognized to be environmental micropollutants owing to their ubiquitous occurrence in water bodies at concentrations ranging from ng to μg/L. Since they are molecules designed to be biologically active at very low concentrations, their presence is a source of concern for both human and ecosystem health and the ecological effects on receiving ecosystems remain largely unknown. Incomplete removal during biological wastewater treatments is the main source of surface water contamination. Some of the molecules detected are reported to be persistent in surface water while others, although they are not intrinsically persistent (being rapidly degraded), are being continuously introduced into the aquatic ecosystem, so that they can be considered pseudo-persistent compounds. Degradation of a chemical in the aquatic ecosystem depends on a variety of factors, including the compound's properties, environmental factors and above all the presence of a natural microbial community able to degrade it via metabolic and/or co-metabolic pathways. Naproxen, a non-steroidal anti-inflammatory drug and Gemfibrozil, a fibrate drug used as a lipid regulator, have been found in several natural EU and Italian surface waters, including the River Tiber (Rome). In this context, the present work aims to evaluate if the natural bacterial community of the Tiber was able to degrade Naproxen and Gemfibrozil. Moreover the effects of these chemicals on the bacterial community structure in terms of live bacterial abundances and composition were also assessed. For this purpose, different river water microcosms were set up (in the presence/absence of the natural microbial community) and treated with 100μg/L of Naproxen or Gemfibrozil in order to evaluate the disappearance time of 50% of the initial concentrations (DT_(50)). The overall results show that Gemfibrozil (DT_(50)>70days) was more persistent than Naproxen (DT_(50)=27days) and that the autochthonous microbial community had a key role in their degradation. The fact that Naproxen was found in river samples analyzed in a greater concentration was therefore due not to its persistence, but to its pseudo-persistence linked to the spread in its use among the population.