Using Drinking Water Treatment Residuals to Immobilize Tetracyclines in Manures and Manure-Amended Soils: Greenhouse Study.

Tetracyclines (TCs) are broad-spectrum antibiotics, which are extensively used for therapeutic purposes in livestock industry. Studies have shown that tetracyclines can enter the environment in significant concentrations via repeated land application of manure and accumulate in soil, generating potential environmental and human health risks. Our earlier batch sorption and incubation studies revealed high adsorption affinity of Al-based drinking water treatment residuals (WTRs) for tetracycline (TTC) and oxytetracycline (OTC). Based on the successful results from the sorption studies, we hypothesized that Al-WTR could be a promising green sorbent for TTC and OTC rich manure and manure amended soils. A greenhouse column study was set up to evaluate effectiveness of Al-WTR. Cattle manure and two physico-chemically variant soil types (from Immokalee and Belleglade series) were chosen based on their potential differences with regard to TCs reactivity. Bermuda grass (Cynodon dactylon) and corn (Zea mays L.) were used as control and test plants respectively. Manure and soil samples were spiked with various concentrations of TTC/OTC (0, 1, and 10 mM) and amended at three rates (0, 2.5 and 5%) of Al-WTR. Soil/manure and leachate samples were collected periodically; immediately after spiking (time zero), and after 1, 2, 3, and 4 months. Soil/manure samples were subjected to four different treatments; DI water, 1M KCl (competing ion effect), methanol (hydrophobicity), and 0.25M EDTA (chelating agent) followed by solid phase extraction (SPE) and analysis by HPLC. Results showed that compared to the unamended (no WTR) manure/soils, leaching and mobility of TTC/OTC significantly (p<0.001) decreased by 45-70% within 4 months across all the treatments tested. Leaching of TTC and OTC reduced significantly (p< 0.05) from manure and soils amended with 5% Al-WTR as compared to those with 2.5% Al-WTR. Presence of Bermuda grass and corn reduced leaching of TTC/OTC by 5-9% compared to columns with no plant cover. Highest total leaching (time zero to 4 months) was observed in Immokalee soil, followed by Belleglade soil and manure, showing physico-chemically dependent leaching behavior.  Solid phase extraction results showed less than 10% removal/desorption of the initial TTC/OTC concentration in both manure and soils in different phases tested (DI water (< 2%), 1M KCl (< 4%), methanol (< 5%), and 0.25M EDTA (<10%) after 3 months, indicating strong binding of TCs on Al-WTR. The desorption behavior observed is very encouraging with respect to stability of TTC/OTC sorbed to the retentive surfaces of the WTRs in amended soils and manure. This is the first greenhouse column study documenting WTR as an effective green sorbent for TCs rich manure and manure amended soils.

Keywords:  Tetracyclines, Remediation, Drinking Water Treatment Residuals, Greenhouse column study, Manure/Soils