REMEDIATION OF TETRACYCLINES IN MANURE AMENDED SOILS: A LONG-TERM GREENHOUSE STUDY

Our previous batch sorption and incubation studies revealed high adsorption affinity of aluminum-based drinking water treatment residuals (Al-WTR) for veterinary antibiotics, tetracycline (TTC) and oxytetracycline (OTC). Scaling up, we conducted a long-term (2 years) greenhouse column study to evaluate the effectiveness of Al-WTR in immobilizing the antibiotics in soils amended with TTC/OTC-rich manures under dynamic flow conditions. Two physico-chemically variant soil types with vastly different organic matter contents – an Immokalee series Spodosol, and a Pahokee series Muck - were chosen based on their potential differences with regard to antibiotic reactivity. Bermuda grass (Cynodon dactylon) and corn (Zea mays L.) were used as cover plants. Soils were amended with manures that were spiked with various concentrations of TTC/OTC (0, 2.25, and 22.5 mg kg^-1) and subsequently treated with various rates (0, 25, and 50 g kg^-1) of Al-WTR. Control soils, manure amended soils, plants, and leachate samples were collected periodically for two years. Results showed that compared to the untreated (no Al-WTR) soils, leaching and mobility of TTC/OTC significantly (p<0.001) decreased by 43-75% within 24 months across all Al-WTR application rates. Leaching of TTC and OTC decreased significantly (p< 0.05) from manure amended soils treated with 50 g kg^-1 Al-WTR as compared to those treated with 25 g kg^-1 Al-WTR. Presence of plant cover reduced leaching of TTC/OTC compared to columns with no cover. Leaching (time zero to 24 months) of OTC/TTC was consistently high in unamended (no manure) and untreated (no Al-WTR) Immokalee soil, followed by Pahokee and manure amended soils, corresponding to various Al-WTR treatments. Results obtained from the greenhouse column study are encouraging, and an important step towards developing an inexpensive, “green” remediation method for soils amended with antibiotics-rich manures.