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Fate of oxytetracycline in streams receiving aquaculture discharges: Model simulations

Authors

  • Peter E. Rose,

    1. River Studies Center, University of Wisconsin, La Crosse, Wisconsin 54601, USA
    2. Molecular and Environmental Toxicology Center and Department of Soil Science, University of Wisconsin, Madison, Wisconsin 53706, USA
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  • Joel A. Pedersen

    Corresponding author
    1. Molecular and Environmental Toxicology Center and Department of Soil Science, University of Wisconsin, Madison, Wisconsin 53706, USA
    • Molecular and Environmental Toxicology Center and Department of Soil Science, University of Wisconsin, Madison, Wisconsin 53706, USA
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Abstract

The potential aquatic fate of oxytetracycline (OTC) in streams receiving discharge from fish hatcheries was examined using the Water-Quality Analysis Simulation Program (WASP, Ver 6.1) model. The modeled 4.4-km stream network included a settling pond, a receiving segment, and two downstream segments. Attainment of quasi-steady state concentrations (concentration variation, <7.5 mg kg−1) in the sediment layers of the receiving segment and first downstream segment required several years. Median water-column concentrations (truly dissolved and colloid- and particle-associated) were 0, 0.57, 0.80, and 0.83 ng L−1 in the settling pond, receiving segment, first downstream segment, and second downstream segment. Truly dissolved fractions in the water column during dosing were 16% in the settling pond, 64% in the receiving segment, and approximately 78% in the river segments. Concentrations declined 20- to 400-fold, depending on the segment considered, within 1 d of dosing. Truly dissolved fractions in the water column after cessation of dosing were 96% in the settling pond and approximately 78% in the river segments. Expected sediment-bound concentrations were approximately 4 mg kg−1 in the receiving segment during dosing, with a median annual concentration of approximately 1.5 mg kg−1. Expected concentrations in downstream sediments were 0.2 mg kg−1 or less. Sensitivity analyses indicated the most important factors influencing fate under the hydrodynamic conditions simulated were settling-pond biosolids load, biosolids settling velocity, OTC depuration kinetics from biosolids, and OTC river particle-water distribution coefficient(s).

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