Applicability of the Charm II system for monitoring antibiotic residues in manure-based composts

The effluence of veterinary antibiotics (VAs) to aquatic and terrestrial environments is of concern due to the potential adverse effects on human health, such as the production of antibiotic resistant bacteria. One of the main pathways for antibiotics to enter the environment is via the application of manure and/or manure-based composts as an alternative organic fertilizer to agricultural lands. While a wide diversity of manure-based composts are produced in Korea, there is currently no regulatory guideline for VA residues. Hence, monitoring and limiting the concentration of VA residues in manure and/or manure-based composts prior to application to the lands is important to mitigate any environmental burden. The current study was conducted to examine the applicability of the Charm II antibiotic test system for monitoring tetracyclines, sulfonamides and macrolides in manure-based composts. The Charm II system was a highly reproducible method for determining whether VA residue concentrations in manure-based compost exceeded specific guideline values. A wide range of manure-based composts and liquid fertilizers commercially available in Korea were examined using the Charm II system to monitor the residues of the target VAs. For this, the guideline concentrations of VA residues (0.8 mg kg⁻¹ for tetracyclines, 0.2 mg kg⁻¹ for sulfonamides, and 0.1 mg kg⁻¹ for macrolides) stated in ‘Official Standard of Feeds’ under the ‘Control of Livestock and Fish Feed Act’ in Korea were adopted to establish control points. Of the 70 compost samples examined 12 exceeded 0.8 mg kg⁻¹ for tetracyclines and 21 exceeded 0.2 mg kg⁻¹ for sulfonamides. Of the 25 liquid fertilizer samples examined most samples exceeded these prospective guidelines.