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 14C-AC-SMX residues was studied in mixtures of soil and sludges at different treatment levels: 1) activated and 2) centrifuged sludges, both enriched with 14C-AC-SMX, and 3) limed and 4) heat-dried sludges obtained by treating the previously contaminated centrifuged sludge. The evolution of the extractability of 14C residues (CaCl2, methanol) and their mineralization were followed during 119 days. More than 80% of the initial 14C activity was no longer extractable after 14 days, except in soil with limed sludge. Liming and drying the centrifuged sludge decreased the mineralized 14C fraction from 5.7-6.4% to 1.2–1.8% and consequently, the corresponding soils contained more 14C residues after 119 days. Although 14C 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 14C-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

Fate of 14C-acetyl sulfamethoxazole during the activated sludge process

Compared to antibiotic parent molecule, human metabolites are generally more polar and sometimes not less toxic in wastewater.However, most researches focus on the fate of parent molecule. Therefore, behaviors of human metabolites are little known.Moreover, though much has been done on the fate of antibiotics during activated sludge process, there are still some limitationsand gaps. In the present study, [Ring-14C] acetyl sulfamethoxazole (14C-Ac-SMX) was used to investigate the fate of humanmetabolite of SMX during activated sludge process at environmentally relevant concentration. At the end of 216 h, 3.1% of thespiked activity in the initial aqueous phase was mineralized, 50% was adsorbed onto the solid phase, and 36.5% still remained inthe aqueous phase, indicating that adsorption, not biodegradation, was the main dissipation pathway. In the existence of microbialactivities, accumulation into the solid phase was much higher, which was less bioavailable by chemical sequential extraction. Themultimedia kinetic model simultaneously depicted the fate of Ac-SMX in the gas, aqueous, and solid phases, and demonstratedthat microbially accelerated accumulation onto the solid phase was attributed to lower desorption rate from the solid phase to theaqueous phase, where adsorption rate was not the key factor. Therefore, Ac-SMX cannot be efficiently mineralized and remain inthe aqueous or the solid phases. The accumulation in the solid phase is less bioavailable and is hard to be desorbed in the existenceof microbial activities, and should not be easily degraded, and may lead to the development of antibiotic-resistant bacteria andgenes after discharge into the environment

The COP-SOIL model for mineralization and bioavailability of organic micropollutants during composts decomposition in soil

UMR INRA EGC et PESSAC, Véolia EnvironnementThe COP-SOIL model for mineralization and bioavailability of organic micropollutants during composts decomposition in soil. 15. International Conferences of RAMIRAN (Network on Recycling of Agricultural, Municipal and Industrial Residues in Agriculture