Environmental availability of sulfamethoxazole and its acetylated metabolite added to soils via sludge compost or bovine manure.

The fate of antibiotics and their metabolites in soils after application of organic waste depends on their environmental availability, which depends on the quality and biodegradability of the added exogenous organic matter (EOM). This study aimed at better understanding the fate of sulfamethoxazole (SMX) and N-acetyl-sulfamethoxazole (AcSMX) metabolite added to soils via sludge compost or cow manure application, during a 28-day incubation. Experimental results obtained for mineralized, extractable, and non-extractable fractions as well as EOM mineralization were used to couple SMX and AcSMX dynamics to the EOM evolution using the COP-Soil model. According to various mechanisms of extraction, CaCl2, EDTA and cyclodextrin solutions extracted contrasted available fractions (31-96% on day 0), resulting in different sets of parameter values in the model. CaCl2 extraction was the best method to assess the sulfonamide availability, leading to low relative root mean squared errors and best simulations of SMX and AcSMX dynamics. The decrease of SMX and AcSMX availability over time went with the formation of non-extractable residues, mostly of physicochemical origin. Using the COP-Soil model, the co-metabolism was assumed to be responsible for the formation of biogenic non-extractable residues and the low mineralization of SMX and AcSMX.

Explaining the accelerated degradation of ciprofloxacin, sulfamethazine, and erythromycin in different soil exposure scenarios by their aqueous extractability.

Antibiotics are frequently introduced into agricultural soils with the application of sewage sludge or farm organic fertilizers. Repeated exposure of soils to a pollutant can enrich for microbial populations that metabolize the chemical, reducing its environmental persistence. In London, Canada, soils from a long-term field experiment have received different concentrations of antibiotics annually for several years. The purpose of the present study was to assess the bioavailability of sulfamethazine, erythromycin, or ciprofloxacin through aqueous extractions with borax or EDTA solutions and their biodegradation following different soil exposure scenarios. Control soils and soils treated annually in the field with 10 mg antibiotics per kg were sampled, supplemented in the laboratory with radiolabeled antibiotic either added directly or carried in dairy manure. Sulfamethazine and erythromycin were initially more bioavailable than ciprofloxacin, with aqueous extractabilities representing 60, 36, and 8%, respectively. Sulfamethazine and erythromycin were degraded in soils, with a larger fraction mineralized in the long-term exposed soil (20 and 65%, respectively) than in control soil (0.4 and 3%, respectively) after 7 days of incubation. In contrast, ciprofloxacin was not mineralized neither in control nor long-term exposed soils. The mineralized fractions were similar for antibiotics added directly to soil or carried in dairy manure.

Development of a soft extraction method for sulfamethoxazole and transformation products from agricultural soils: Effects of organic matter co-extraction on the environmental availability assessment.

The recycling of biosolids and livestock manure in agriculture may lead to the introduction of antibiotic residues, i.e., parent molecule and transformation products, into amended soils. Their fate in soils can be approached through the assessment of their environmental availability. In this work, the environmental availability of sulfamethoxazole (SMX) and three transformation products (N4-acetyl-SMX, 3-amino-5-methylisoxazole, aniline) was assessed in soils amended with sludge compost or cow manure throughout a three-month incubation, using soft extractions with CaCl2, EDTA or cyclodextrin solutions. First, the freeze-storage of soil samples was shown to decrease the SMX extractability. The SMX extractability depended on the initial concentration, the amendment type and the extracting solution at day 0. From 1.9% up to 63% of the SMX total content was initially extractable. The lowest fractions were quantified in EDTA extracts in which the dissolved organic matter was the most complex and responsible for high matrix effects in mass spectrometry compared to CaCl2 extracts. The purification of cyclodextrin extracts highly reduced the matrix effects, but CaCl2 was considered as the most suitable extractant. SMX extractability strongly decreased after the first 8days of incubation to finally reach 0.4-0.8% after 84days, whatever the initial conditions. This high decrease could be related to humification observed through the increasing complexity of extracted dissolved organic matter. Very low levels of transformation products were quantified throughout the incubation period. The low environmental availability of SMX was mainly due to its sorption on soil organic matter and resulted in its low biotransformation in these amended soils.

A new extraction method to assess the environmental availability of ciprofloxacin in agricultural soils amended with exogenous organic matter.

Fluoroquinolone antibiotics such as ciprofloxacin can be found in soils receiving exogenous organic matter (EOM). Their long-term behavior in EOM-amended soils and their level of biodegradability are not well understood partly due to a lack of methods to estimate their environmental availability. We performed different aqueous extractions to quantify the available fraction of 14C-ciprofloxacin in soils amended with a compost of sewage sludge and green wastes or a farmyard manure contaminated at relevant environmental concentrations. After minimizing 14C-ciprofloxacin losses by adsorption on laboratory vessel tubes, three out of eleven different aqueous solutions were selected, i.e., Borax, Na2EDTA and 2-hydroxypropyl-ß-cyclodextrin. During 28 d of incubation, the non-extractable fractions were very high in all samples, i.e., 57-67% of the initial 14C-activity, and the availability of the antibiotic was very low, explaining its low biodegradation. A maximum of 6.3% of the initial 14C-activity was extracted from soil/compost mixtures with the Na2EDTA solution, and 7.2% from soil/manure mixtures with the Borax solution. The available fraction level was stable over the incubation in soil/compost mixtures but slightly varied in soil/manure mixtures following the organic matter decomposition. The choice of different soft extractants highlighted different sorption mechanisms controlling the environmental availability of ciprofloxacin, where the pH and the quality of the applied EOM appeared to be determinant.