Decline in Extractable Veterinary Antibiotics in Chicken Manure-Based Composts during Composting

Release of veterinary antibiotics (VSs) to agricultural environment through application of animal manure and/or animal manure-based composts to soils is of concern. The current study was conducted to examine decline of VAs during composting the chicken manure. For this, antibiotics free chicken manure (20 kg) and sawdust (10 kg) were added to the bench-scale composting apparatus and then the mixed material was spiked simultaneously with three VAs (chlortetracycline, CTC; sulfamethazine, SMZ; tylosin, TYL) at two different levels (10 and ). Then the decline of VAs was determined using Charm II system during 53 composting period. For comparison, composting only chicken manure was included at VAs concentration of . During composting, the concentration of all three different VAs declined below the prospective guideline values ( for CTC, for SMZ, and for TYL) except CTC at spiking when the chicken manure was composted together with sawdust. Interestingly, CTC at spiking appeared to be declined under the guideline value without sawdust while SMZ was resistant to be declined without sawdust. Unlike CTC and SMZ, TYL showed immediate decline right after spiking TYL to composting materials regardless the spiking concentration and existence of sawdust. Appropriate composting procedure of chicken manure was able to decline the residual VAs in the manure below the prospective guideline value and the importance of organic substances on this decline was perceived.