Evaluation of the sulfonamide antibiotic persistence in the presence of the aquatic plant Lemna minor

Sulfonamide antibiotics are currently prescribed to treat urinary infections in human and veterinary therapeutics. Following administration, they are only partially metabolized and, therefore, a large amount is excreted unaltered or as active metabolites via urine and faeces; in the case of human administration, the antibiotic residues can reach wastewater treatment plants and, through effluents, the receiving waterbodies. Currently, there is little known about the fate and effects on health ecosystem of these compounds. Among Sulfonamides, sulfamethoxazole (SMX) is one of the most detected antibiotics in river waters. SMX disrupts the folate biosynthetic pathway in bacteria, which is identical to that of plants, raising concerns about toxicity effects on non-target organisms. Therefore, improving our knowledge on the persistence of SMX, especially in natural water ecosystems, is particularly needed. In this framework, macrophyte aquatic plants, such as Lemna minor L, growing in wetlands and contaminated water bodies, can be a useful tool to evaluate the interaction between aquatic plants and organic pollutants. Moreover, the plant-natural microbial community interactions on the antibiotics biodegradations have to take into accounts. In this context, the aim of this study was to improve our knowledge on the biodegradability of SMX in river water, focusing on the effect of the antibiotic on both the natural microbial community and plants. Lab-scale experiments were set up by using microcosms containing river water treated with 500 ug/L of SMX both in the presence/absence of the plant L. minor and in presence/absence (sterilized river water) of the natural microbial community. Other microcosms (Controls) were set up with no-treated river water (without the antibiotic). The experimental set was kept in a growth chamber under controlled conditions. Water samples were collected at fixed times and the SMX residual concentrations were measured over time, by a chromatographic method (HPLC-UV). The effects of the antibiotic on the natural microbial community were assessed in terms of cell vitality, abundance and phylogenetic diversity. Moreover, physiological and biochemical determinations were performed on plants. SMX residual concentrations in plants were also analyzed at the end of the experiment; in this case, Accelerated Solvent Extraction (ASE) followed by Solid Phase Extraction (SPE) purification methods were used.