Fate of sulfamethoxazole in compost, manure and soil amended with previously stored organic wastes.

Application of organic wastes as soil fertilizers represents an important route of agricultural soil contamination by antibiotics such as sulfamethoxazole (SMX). Soil contamination may be influenced by the storage time of organic wastes before soil spreading. The objective of this work was to study the fate of SMX in two organic wastes, a co-compost of green waste and sewage sludge and a bovine manure, which were stored between 0 and 28 days, then incorporated in an agricultural soil that has never received organic waste and monitored for 28 days under laboratory conditions. Organic wastes were spiked with 14C-labelled SMX at two concentrations (4.77 and 48.03 mg kg-1 dry organic waste). The fate of SMX in organic wastes and soil-organic waste mixtures was monitored through the distribution of radioactivity in the mineralised, available (2-hydroxypropyl-ß-cyclodextrin extracts), extractable (acetonitrile extracts) and non-extractable fractions. SMX dissipation in organic wastes, although partial, was due to i) incomplete degradation, which led to the formation of metabolites detected by high performance liquid chromatography, ii) weak adsorption and iii) formation of non-extractable residues. Such processes varied with the organic wastes, the manure promoting non-extractable residues, and the compost leading to an increase in extractable and non-extractable residues. Short storage does not lead to complete SMX elimination; thus, environmental contamination may occur after incorporating organic wastes into soil. After addition of organic wastes to the soil, SMX residues in the available fraction decreased quickly and were transferred to the extractable and mostly non-extractable fractions. The fate of SMX in the soil also depended on the organic wastes and on the prior storage time for manure. However the fate of SMX in the organic wastes and soil-organic waste mixtures was independent on the initial spiked concentration.

Adsorption and degradation of the herbicide nicosulfuron in a stagnic Luvisol and Vermic Umbrisol cultivated under conventional or conservation agriculture.

The main goals of conservation agriculture are to enhance soil fertility and reduce soil degradation, especially through erosion. However, conservation agriculture practices can increase the risk of contamination by pesticides, mainly through vertical transfer via water flow. Better understanding of their sorption and degradation processes is thus needed in conservation agriculture as they control the amount of pesticide available for vertical transfer. The purpose of our study was to investigate the sorption and degradation processes of nicosulfuron in soil profiles (up to 90 cm deep) of a Vermic Umbrisol and a Stagnic Luvisol managed either in conventional or in conservation agriculture. Two laboratory sorption and incubation experiments were performed. Low sorption was observed regardless of the soil type, agricultural management or depth, with a maximum value of 1.3 ± 2.0 L kg-1. By the end of the experiment (91 days), nicosulfuron mineralisation in the Vermic Umbrisol was similar for the two types of agricultural management and rather depended on soil depth (29.0 ± 2.3% in the 0-60-cm layers against 7.5 ± 1.4% in the 60-90 cm). In the Stagnic Luvisol, nicosulfuron mineralisation reached similar value in every layer of the conservation agriculture plot (26.5% ± 0.7%). On the conventional tillage plot, mineralisation decreased in the deepest layer (25-60 cm) reaching only 18.4 ± 6.9% of the applied nicosulfuron. Regardless of the soil type or agricultural management, non-extractable residue formation was identified as the main dissipation process of nicosulfuron (45.1 ± 8.5% and 50.2 ± 7.0% under conventional and conservation agriculture respectively after 91 days). In our study, nicosulfuron behaved similarly in the Vermic Umbrisol regardless of the agricultural management, whereas the risk of transfer to groundwater seemed lower in the Stagnic Luvisol under conservation agriculture.

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.

Fate of sulfamethoxazole, its main metabolite N-ac-sulfamethoxazole and ciprofloxacin in agricultural soils amended or not by organic waste products.

Spreading organic waste products (OWP) issued from sewage sludge or manures into soil may disseminate antibiotics with unknown risks for human health and environment. Our objectives were to compare the fate of two sulfonamides, sulfamethoxazole (SMX) and its metabolite N-acetyl-sulfamethoxazole (N-ac-SMX), and one fluoroquinolone, ciprofloxacin (CIP), in an unamended soil, and two soils regularly amended since 1998 with a sewage sludge and green waste compost and with farmyard manure respectively. Incubations of soil spiked with 14C labelled SMX or N-ac-SMX (0.02 mg kg-1) or CIP (0.15 mg kg-1) allowed a quantification of radiolabeled molecules in the mineralized, easily, hardly and non-extractable fractions after 3 and 156 days. Nature of 14C molecules was also analyzed by HPLC in extractable fractions after 3 and 156 days. SMX and N-ac-SMX dissipation was fast and due to i) mineralization (∼10% of recovered 14C after 156 days) or incomplete degradation (production of metabolites), ii) adsorption, even if both sulfonamides present low Kd (<3 L kg-1) and iii) formation of non-extractable residues (NER), representing more than 50% of recovered radioactivity. N-ac-SMX was more mineralized than SMX, and formed more progressively NER, after a step of deacetylation. Adsorption of CIP was fast and formed mainly NER (>72%) whereas its mineralization was negligible. Repeated applications of OWP tend to enhance adsorption of antibiotics and lower their degradation, through the quantity and quality of the built up soil organic matter. If applications of sewage sludge compost favor adsorption and inhibit mineralization, applications of manure boost the formation of non-extractable residues.

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.

Fate of (14)C-organic pollutant residues in composted sludge after application to soil.

Organic micropollutants may be present in biosolids, leading to soil contamination when they are recycled in agriculture. A sludge spiked with (14)C-labelled glyphosate (GLY), sodium linear dodecylbenzene sulphonate (LAS), fluoranthene (FLT) or 4-n-nonylphenol (NP) was composted with green waste and the fate of the (14)C-micropollutant residues remaining after composting was assessed after the compost application to the soil. (14)C-residues were mineralised in the soil and represented after 140d 20-32% of the initial activity for LAS, 16-25% for GLY, 6-9% for FLT and 4-7% for NP. The (14)C-residues at the end of composting that could not be extracted with methanol or ammonia were minimally remobilised or even increased for FLT. After 140d, non-extractable residues represented 38-52% of all of the (14)C-residues remaining in the soil for FLT, 50-67% for GLY, 91-92% for NP and 94-97% for LAS and in most cases, less than 1% of the (14)C-residues were water soluble, suggesting a low direct availability for leaching and microbial or plant assimilation. FLT was identified as the main compound among the methanol-extractable (14)C-residues that may be potentially available. The fate of the (14)C-organic pollutant residues in composts after application to soil could be assessed through a sequential chemical extraction scheme and depended on the chemical nature of the pollutant.