Column studies to investigate the fate of veterinary antibiotics in clay soils following slurry application to agricultural land.

The environment may be exposed to veterinary medicines administered to livestock due to the application of organic fertilisers to land. For other groups of substances that are applied to agricultural land (e.g. pesticides), preferential flow in underdrained clay soils has been identified as an extremely important pathway by which pollution of surface waters can occur. Three soil column leaching experiments have therefore been carried out using a clay soil to investigate the fate of a range of antibiotics from the sulphonamide, tetracycline and macrolide groups. These column studies complemented a range of other experiments at the field and semi-field scales, as well as modelling studies which are being reported in separate papers. Each column study had a different objective. The first examined the effect of pig slurry on the mobility of antibiotics in clay loam soil. The second experiment investigated changes in soil water pH due to the application of slurry. The final experiment quantified the extent to which soil tillage prior to slurry application can reduce the leaching of antibiotic residues found in slurry. It was found that slurry had no impact on the leaching of oxytetracycline although soil water pH was affected significantly by slurry application. It was also shown that pre-tillage can substantially reduce the leaching of antibiotic residues through macroporous clay soils.