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

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 N4-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 ?g 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, intI1 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 intI1 gene was found throughout the entire experimental period. Finally, SMX did not cause evident inhibition or suffering symptoms for the plant.