Sulfamethoxazole persistence in a river water ecosystem and its effects on the natural microbial community and Lemna minor plant

Abstract Sulfamethoxazole (SMX) is a sulfonamide antibiotic commonly used in human and veterinary medicine and frequently detected in surface water as a micro-contaminant. The presence of this antibiotic and its main transformation product N 4 -acetyl-sulfamethoxazole (Ac-SMX) was evaluated in an Italian river water by Solid Phase Extraction (SPE) and subsequent LC MS/MS determination. River water microcosm experiments were set up in the presence and absence of duckweed ( Lemna minor L.) adding SMX (500 μg L −1 ) with the aim of evaluating the persistence of antibiotic and its effects on both the microbial community naturally occurred in a river and the plant . The concentrations of SMX and Ac-SMX were measured at fixed times over a period of 28 days. The microbial abundance, intI 1 gene and plant morpho-physiological analyses were also conducted. In the river water samples, SMX was not detected as a parent compound, but its acetylate metabolite Ac-SMX was found as a micro-contaminant. The results of the microcosm experiment showed that SMX did not substantially degrade, except in the presence of L. minor where a slight decrease (17%) was observed. The river residual concentration of Ac-SMX remained quite constant during the experimental period. The river microbial community was initially affected by adding the antibiotic with a decrease in its abundance; however, although it was not able to degrade SMX, it displayed an overall antibiotic resistance. In fact, the intI 1 gene was found throughout the entire experimental period. Finally, SMX did not cause evident inhibition or suffering symptoms for the plant.