Degradation, Fate and Bioavailability of Sulfamethazine in Pond Water and Sediment

Antibiotics from animal agriculture are found in surface waters and stream sediments. We investigated the degradation and fate of sulfamethazine in small pond water and sediment microcosms. Sulfamethazine [¹⁴C-phenyl] was added to the water phase directly, or in a dilute swine manure solution that simulated runoff from manured land. Sulfamethazine dissipated rapidly with a 2.7-d half-life in pond water and 4.2-d half-life when applied with the swine manure. Sulfamethazine in the sediment accounted for 10 to 15% of the applied antibiotic within 14 days, and then declined thereafter. Non-extractable sediment-bound residue accounted 40% (water and sediment) to 61% (water, sediment and manure) of applied ¹⁴C. Two photodegradation products were recovered from both water and sediment. Biodegradation, as indicated by metabolite formation and ¹⁴CO₂ evolution, was less significant than photodegradation. Manure input increased sorption of sulfamethazine to sediment , with k_d ranging from 1.7 to 2.8 L/kg. The bioavailability of sulfamethazine in pond water microcosms was evaluated using the aquatic worm Lumbriculus variegatus, resulting a log BCF of 1.89 (bioconcentration factor) following sediment exposure.