Sediment and salinity effects on the bioaccumulation of sulfamethoxazole in zebrafish (Danio rerio)

- Sulfamethoxazole bioaccumulation was quantified by direct concentration measurements.
- Sediment caused 13-28% reduction in sulfamethoxazole bioaccumulation.
- Salinity reduced sulfamethoxazole bioaccumulation to zebrafish.
- Equilibrium distribution of sulfamethoxazole was dominated by water.
- Sediment adsorption was most significant with small particles with large surface area.

The dynamic distribution of a widely used antibiotic sulfamethoxazole between water, sediment and aquatic organisms (zebrafish) was studied in microcosms. Sulfamethoxazole concentrations in water were gradually reduced, while in sediment and zebrafish gradually increased, suggesting active adsorption and bioaccumulation processes occurring. The presence of sediment particles and their interactions with water reduced the bioaccumulation of sulfamethoxazole in zebrafish by 13-28%. The sediment of smaller particle size with more organic carbon content and higher surface area, adsorbed sulfamethoxazole more extensively and decreased its bioaccumulation most significantly. The effect became more severe with increasing salinity in water due to the salting out of sulfamethoxazole, resulting in 24-33% reduction in bioaccumulation. At equilibrium, the distribution of sulfamethoxazole in different phases was quantified, with most sulfamethoxazole being associated with water (97.3%), followed by sedimentary phase (2.7%) and finally zebrafish (0.05%). The findings provided important data for further research into antibiotics fate and bio-uptake in aquatic organisms, and subsequent ecotoxicity.

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