Effects of the Antibiotic Sulfamethazine on DNA damage in Daphnia pulex embryos

Farmers commonly use an inexpensive veterinary drug with a high percentage sulfamethazine to prevent an array of bacterial infections and diseases in cattle, sheep, pigs, and chickens. Residue of sulfamethazine is usually passed through an animal’s system and excreted with the animal’s waste material. When cattle and sheep are free-ranged, they may release their waste in or near natural water sources, introducing sulfamethazine residue into fresh water ecosystems. Daphnia pulex, a local keystone plankton species, is a model organism for evaluating ecotoxicity. In this study, I have assessed toxicity of sulfamethazine residue by measuring its effect on levels of DNA damage in Daphnia pulex embryos using a Comet Assay. Daphnia were exposed to three different concentrations of sulfamethazine, spanning concentrations of the drug found in fresh water exposed to free-range livestock. The Daphnia were exposed to the drug for 30 minutes. Daphnia embryos were then extracted, lysed, electrophoresed, and analyzed under a fluorescent microscope. The results show a positive correlation between DNA damage and concentration of sulfamethazine, indicating genotoxicity of this compound at ecologically relevant doses