Impact of sludge treatments on the extractability and fate of acetyl sulfamethoxazole residues in amended soils

Sludge recycled in agriculture may bring antibiotics into cropped soils. The nature, total amount, and availability of the antibiotics in soil partly depend on the sludge treatments. Our paper compares the fate of N-acetyl sulfamethoxazole (AC-SMX) residues between soils incubated with the same sludge but submitted to different processes before being added in soil. The fate of C-14-AC-SMX residues was studied in mixtures of soil and sludges at different treatment levels: 1) activated and 2) centrifuged sludges, both enriched with C-14-AC-SMX, and 3) limed and 4) heat dried sludges obtained by treating the previously contaminated centrifuged sludge. The evolution of the extractability of C-14 residues (CaCl2, methanol) and their mineralization were followed during 119 days. More than 80% of the initial C-14-activity was no longer extractable after 14 days, except in soil with limed sludge. Liming and drying the centrifuged sludge decreased the mineralized C-14 fraction from 5.7-6.4% to 1.2-1.8% and consequently, the corresponding soils contained more C-14 residues after 119 days. Although C-14 residues were more CaCl2-extractable in soil with limed sludge, they seemed to be poorly bioavailable for biodegradation. For all solid sludges, the mineralization rate of C-14-AC-SMX residues was strongly correlated to that of sludge organic carbon, with a coefficient three times lower for the limed and dried sludges than for the centrifuged sludge after 14 days. (C) 2017 Elsevier Ltd. All rights reserved.