Exposure assessment of veterinary medicines in aquatic systems

The release of veterinary medicines into the aquatic environment may occur through direct or indirect pathways. An example of direct release is the use of medicines in aquaculture (Armstrong et al. 2005; Davies et al. 1998), where chemicals used to treat fish are added directly to water. Indirect releases, in which medicines make their way to water through transport from other matrices, include the application of animal manure to land or direct excretion of residues onto pasture land, from which the therapeutic chemicals may be transported into the aquatic environment (Jørgensen and Halling-Sørensen 2000; Boxall et al. 2003, 2004). Veterinary medicines used to treat companion animals may also be transported into the aquatic environment through disposal of unused medicines, veterinary waste, or animal carcasses (Daughton and Ternes 1999, Boxall et al. 2004). The potential for a veterinary medicine to be released to the aquatic environment will be determined by several different criteria, including the method of treatment, agriculture or aquaculture practices, environmental conditions, and the properties of the veterinary medicine.