The increasing sulfonamide contamination in water worldwide has raised concerns due to its consequential ecological effects and related human health issues. Pollution by sulfonamides in groundwater, surface water, wastewater, and soil is common, as most of the antibiotics are excreted from the body through urine and feces without transformation. Bioremediation is an environmentally friendly and cost-effective alternative to physico-chemical cleanup options. Microalgae mediated bioremediation has gained research interests due to their endogenous catabolic systems, heterotrophic capabilities, role in the fixation and turnover of carbon, and their recovered biomass to produce bioenergy. This study investigated the environmental risks of two common emerging contaminants, sulfamethazine (SMZ) and sulfamethoxazole (SMX), and their mixture using a green microalga, Scenedesmus obliquus, as a test organism. The calculated EC50 values of SMZ, SMX, and their mixture (11:1wt/wt) after 96 h were 1.23, 0.12, and 0.89 mgL-1, respectively. The toxicity of the mixture could be better predicted using a concentration addition model than an independent action model. The risk quotients of SMZ, SMX, and their mixture were &gt;1 during the experiment, indicating their high potential risks on aquatic microorganisms. Despite their toxicity, S. obliquus exhibited 17.3% and 29.3% removal of 0.1 mg SMZ L-1 and 0.2 mg SMX L-1, respectively, after 11 days of cultivation. Substrate interaction was observed between SMZ and SMX, which showed a significantly improved removal of SMZ (up to 3.4 folds) when mixed with SMX (0.2 mg L-1). The metabolic pathways of SMZ and SMX were proposed according to mass spectroscopic analysis, which showed four common metabolites (4-nitroSMX, desmino-SMX, benzenesulfonamide, and toluene sulfonamide), formed because of hydroxylation, methylation, nitrosation, and deamination.

Environmental risks of sulfamethazine and sulfamethoxazole, and their preferential biodegradation from a mixture by a green microalga, Scenedesmus obliquus

256th National Meeting (2018)

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