ABSTRACT
The.production.of.swine,.cattle,.and.poultry.raised.for.human.consumption.represents.a.significant.portion.of.the.U.S..agricultural.economy..To.maximize.production,.producers. regularly.use.antibiotics.as.supplements. in.animal. feed.and.water. to. increase.weight.gain.and.prevent.diseases.among. their. livestock.. In. swine,. for. example,.it.is.estimated.that.antibiotics.are.used.for.disease.prevention.and.growth. promotion.in.more.than.90%.of.starter.feeds,.75%.of.grower.feeds,.50%.of.finishing. feeds,.and.20%.of.sow.feeds,.and.equally.relevant.numbers.are.seen.in.beef.cattle. production.(Hayes.et.al.,.1999;.USDA.APHIS.Swine.2000.and.COFE)..It.has.been. well.documented.that.measurable.quantities.of.these.antibiotics.are.excreted,.often. in.original.form,.in.feces.and.urine.of.livestock.(FAO/WHO,.1991)..Livestock.waste,. containing.antibiotics,.is.often.used.as.fertilizer.for.farm.fields.or.pastures.and.may. result.in.nonpoint.source.pollution.of.ground.or.surface.waters.(Loke.et.al.,.2000).. Although.antibiotic.residues.have.been.studied.extensively.in.tissues.and.excrement,. we.are.only.beginning.to.understand.the.environmental.fate.of.antibiotics.and.their. metabolites.once.the.excreta.reaches.soil.and.water.environments.
