Monday, November 13, 2006

Emerging Contaminants in the Environment: Biosolids-Borne Antibiotics.

Kiera Coffin and Mary Stromberger. Colorado State Univ, Dept of Soil & Crop Sciences, Fort Collins, CO 80523

Biosolids are a nutrient rich organic matter that is a result ing from the physical and biological treatments of wastewater. They can be used as a slow release fertilizer when used in land application, and they provide low concentrations of many useful plant nutrients. Biosolids as an additive also add structure and water retention to soil. An emerging concern about biosolids is that they might be a source of therapeutic agents including antibiotics.  Six biosolids samples were collected from locations around the country. These samples were analyzed for the various classes of antibiotics (macrolides, sulfonamides and tetracyclines) and percentage of antibiotic-resistant microorganisms. We found tetracycline concentrations to be the highest in the samples at a range of 3-15,000 ppb. Within the tetracycline class, oxytetracycline, meclocylcine, and tetracycline were the most concentrated. Large percentages (17%-35%) of bacterial isolates from the biosolids were resistant to 1.0 mg L-1 of the antibiotic oxytetracycline, and less than 1% of bacterial isolates were resistant to 5.0 mg L-1 of oxytetracycline. Biosolids have the potential to add antibiotics, mainly tetracyclines, and antibiotic-resistant organisms into the environment. However, despite longterm applications of biosolids to two Colorado field sites, detectable quantities of tetracyclines were not measureable. Laboratory studies are being conducted to determine tetracycline concentrations required to impact soil microbial communities. Additional experiments are being conducted to determine potential effects of copper on microbial antibiotic resistance patterns.