Light and microbial effects on the transformation of four sulfonamides in eel pond water and sediment

Sulfonamides (SAs) are one of the most widely used antimicrobials for human and veterinary medication. The purpose of this study was to further understand the fate of SAs in eel (Anguilla japonica) pond water and sediment slurry in a laboratory-scale experiment. Four SAs were used in this experiment: sulfadiazine (DIA), sulfadimethoxine (SDM), sulfamethazine (SMZ), and sulfamethoxazole (SMX). The effects of light and microbial activities on the transformation of these four SAs in pond water and sediment slurry were investigated. Results indicate that the four SAs were all phototransformed in both the pond water and sediment slurry. The transformation processes of these four SAs can also be enhanced by biological activities in the light aside from the sole effect of light itself. The ranges of the half-lives (t1/2) of the four SAs were 1.7–7.3 and 0.7–7.9 days in illuminated, non-sterile water and in the sediment slurry, respectively. The t1/2 values were higher in the sterile water and sediment slurry at 8.0–48.9 and 6.5–47.3 days, respectively. The synergetic effects of microbial activity on the transformation of DIA, SDM, and SMZ only occurred in the light and were hindered under dark conditions. Only SMX was slowly biotransformed in the dark. However, transformation rates of SMX were 2.06–6.49 times slower in the dark than in the light.