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-β-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.

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 limitations and gaps. In the present study, [Ring-¹⁴C] acetyl sulfamethoxazole (¹⁴C-Ac-SMX) was used to investigate the fate of human metabolite of SMX during activated sludge process at environmentally relevant concentration. At the end of 216 h, 3.1% of the spiked activity in the initial aqueous phase was mineralized, 50% was adsorbed onto the solid phase, and 36.5% still remained in the aqueous phase, indicating that adsorption, not biodegradation, was the main dissipation pathway. In the existence of microbial activities, accumulation into the solid phase was much higher, which was less bioavailable by chemical sequential extraction. The multimedia kinetic model simultaneously depicted the fate of Ac-SMX in the gas, aqueous, and solid phases, and demonstrated that microbially accelerated accumulation onto the solid phase was attributed to lower desorption rate from the solid phase to the aqueous phase, where adsorption rate was not the key factor. Therefore, Ac-SMX cannot be efficiently mineralized and remain in the aqueous or the solid phases. The accumulation in the solid phase is less bioavailable and is hard to be desorbed in the existence of microbial activities, and should not be easily degraded, and may lead to the development of antibiotic-resistant bacteria and genes after discharge into the environment.

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.

Behaviour of S-metolachlor and its oxanilic and ethanesulfonic acids metabolites under fresh vs. partially decomposed cover crop mulches: A laboratory study

At the time of spring pre-emergent herbicide application, the soil surface in conservation agriculture is most of the time covered by cover crops (CC) mulches. The state of these mulches depends on their destruction date and on the selected species. Sorption and degradation of ¹⁴C-S-metolachlor on and within 8 decaying CC-covered (2 species × 4 initial decomposition state) soils corresponding to conservation agriculture were compared to its fate in bare soil (BS) corresponding to conventional agriculture. ¹⁴C-S-metolachlor and its metabolites distribution between mineralized, extractable and non-extractable (NER) fractions was determined at 5 dates during a 20 °C/84-d period. Herbicide mineralization was weak (<2%) for both CC and BS. Extractability of ¹⁴C in BS was intermediate between CC that were decomposed 28 or 56 days and 0 or 6 days before application. Degradates consisted in up to 43% of total radioactivity, with specificities according to the CC or soil compartment. NER formation was equivalent in BS and in the much decomposed CC-amended microcosms, and was stronger in less decomposed CC. S-metolachlor DT₅₀ was 23-d in BS, and 9, 15, 39 and 25-d for CC ordered by increased decomposition state at the time of application. These results were attributed to the proportion of ¹⁴C intercepted by CC, and to higher levels of organic matter and microbial activity in less decomposed CC as compared with more decomposed ones. Then the state of decomposition level of CC residues determines the behaviour of SMOC (S-metolachlor) sprayed on the mulch in the conditions of conservation agriculture.

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.

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-β-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 glyphosate and degradates in cover crop residues and underlying soil: A laboratory study

The increasing use of cover crops (CC) may lead to an increase in glyphosate application for their destruction. Sorption and degradation of (14)C-glyphosate on and within 4 decaying CC-amended soils were compared to its fate in a bare soil. (14)C-Glyphosate and its metabolites distribution between mineralized, water-soluble, NH4OH-soluble and non-extractable fractions was determined at 5 dates during a 20 °C/84-d period. The presence of CC extends (14)C-glyphosate degradation half-life from 7 to 28 days depending on the CC. (14)C-Glyphosate dissipation occurred mainly through mineralization in soils and through mineralization and bound residue formation in decaying CC. Differences in sorption and degradation levels were attributed to differences in composition and availability to microorganisms. CC- and soil-specific dissipation patterns were established with the help of explicit relationships between extractability and microbial activity.

Impact of liming and drying municipal sewage sludge on the amount and availability of (14)C-acetyl sulfamethoxazole and (14)C-acetaminophen residues

Acetyl Sulfamethoxazole (AC-SMX) and acetaminophen (ACM) can be found in municipal sewage sludge, and their content and availability may be influenced by sludge treatments, such as drying and liming. A sludge similarly centrifuged with/without a flocculant was spiked with (14)C-labelled AC-SMX or ACM. Then, it was either limed (20% CaO) or/and dried under different laboratory conditions (1 week at ambient temperature; and 48 h at 40 or 80 °C). The total amount and distribution of the (14)C-compounds among several chemical fractions, based on the sludge floc definition, were assessed at the end of the treatments. All the (14)C-activity brought initially was recovered in the limed and/or dried sludges for AC-SMX but only between 44.4 and 84.9% for ACM, with the highest rate obtained for the limed sludge. Drying at 80 °C or liming increased the percentage of the sludge total organic carbon recovered in the extracts containing soluble extracellular polymeric substances (S-EPS) and the percentage of the total (14)C-activity extracted simultaneously. The non-extractable residues represented only 3.9-11.6% of the total (14)C-activity measured in the treated sludges for AC-SMX and 16.9-21.8% for ACM. The presence of AC-SMX and ACM residues in the treated sludges, after liming and drying under different conditions, was shown using some (14)C-labelled molecules. At this time scale and according to the extraction method selected, most of the (14)C-residues remained soluble and easily extractable for both compounds. This result implies that certain precautions should be taken when storing sludges before being spread on the field. Sludge piles, particularly the limed sludge, should be protected from rain to limit the production of lixiviates, which may contain residues of AC-SMX and ACM.

Measuring Leaf Penetration and Volatilization of Chlorothalonil and Epoxiconazole Applied on Wheat Leaves in a Laboratory-Scale Experiment

Estimation of pesticide volatilization from plants is difficult because of our poor understanding of foliar penetration by pesticides, which governs the amount of pesticide available for volatilization from the leaf surface. The description of foliar penetration is still incomplete because experimental measurements of this complex process are difficult. In this study, the dynamics of leaf penetration of C-chlorothalonil and C-epoxiconazole applied to wheat leaves were measured in a volatilization chamber, which allowed us to simultaneously measure pesticide volatilization. Fungicide penetration into leaves was characterized using a well-defined sequential extraction procedure distinguishing pesticide fractions residing at different foliar compartments; this enabled us to accurately measure the penetration rate constant into the leaves. The effect of pesticide formulation was also examined by comparing formulated and pure epoxiconazole. We observed a strong effect of formulation on leaf penetration in the case of a systemic product. Furthermore, the penetration rate constant of formulated epoxiconazole was almost three times that of pure epoxiconazole (0.47 ± 0.20 and 0.17 ± 0.07, respectively). Our experimental results showed high recovery rates of the radioactivity applied within the range of 90.5 to 105.2%. Moreover, our results confirm that pesticide physicochemical properties are key factors in understanding leaf penetration of pesticide and its volatilization. This study provides important and useful parameters for mechanistic models describing volatilization of fungicides applied to plants, which are scarce in the literature.

Nature and decomposition degree of cover crops influence pesticide sorption: quantification and modelling

This study quantifies and models the influence of the type and the degree of decomposition of cover crops (CC) on three pesticides sorption: epoxiconazole (EPX), S-metolachlor (SMOC) and glyphosate (GLY). Residues of four cover crop species were incubated for 0, 6, 28 or 56 d in controlled conditions. For each incubation time, adsorption of pesticides on CC residues was measured in batch experiments. Additionally, the biochemical and elemental composition (Van Soest fractionation, C:N, (13)C NMR spectroscopy) of CC was characterized. Mineralization of CC residues was monitored at all incubation times using CO2 trapping. Results showed that the adsorption of pesticides differed significantly according to (i) the type of molecule, (ii) the type of CC, (iii) the degree of CC decomposition and the interaction CC×decomposition time. EPX and GLY were the most (Kd ranging from 188 to 267 L kg(-1)) and the least (Kd ranging from 18 to 28 L kg(-1)) sorbed pesticides respectively. With increasing decomposition of the CC residue, sorption increased by 1.6- to 4.7-fold according to the type of pesticide and cover crop. It was significantly correlated with the net cumulative mineralization (ρ>0.7) and other indicators of biochemical composition such as C:N ratio (ρ<-0.7), the Van Soest neutral detergent soluble fraction (ρ>0.5) and the alkyl/O-alkyl C ratio determined by NMR. An innovative model based on net cumulative mineralization of CC residues is proposed to describe the pesticide sorption and appears to be a promising approach to account for the effects of decaying plant residues on the environmental fate of pesticides.

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.

Water pressure head and temperature impact on isoxaflutole degradation in crop residues and loamy surface soil under conventional and conservation tillage management

Laboratory incubations were performed in order to evaluate the dissipation of the proherbicide isoxaflutole in seedbed layer soil samples from conventional and conservation tillage systems and in maize and oat residues left at the soil surface under conservation tillage. The effects of temperature and water pressure head on radiolabelled isoxaflutole degradation were studied for each sample for 21d. Mineralisation of isoxaflutole was low for all samples and ranged from 0.0% to 0.9% of applied (14)C in soil samples and from 0.0% to 2.4% of applied (14)C in residue samples. In soil samples, degradation half-life of isoxaflutole ranged from 9 to 26h, with significantly higher values under conservation tillage. In residue samples, degradation half-life ranged from 3 to 31h, with significantly higher values in maize residues, despite a higher mineralisation and bound residue formation than in oat residues. Whatever the sample, most of the applied (14)C remained extractable during the experiment and, after 21d, less than 15% of applied (14)C were unextractable. This extractable fraction was composed of diketonitrile, benzoic acid derivative and several unidentified metabolites, with one of them accounting for more than 17% of applied (14)C. This study showed that tillage system design, including crop residues management, could help reducing the environmental impacts of isoxaflutole.

Variability of retention process of isoxaflutole and its diketonitrile metabolite in soil under conventional and conservation tillage

BACKGROUND

Sorption largely controls pesticide fate in soils because it influences its availability for biodegradation or transport in the soil water. In this study, variability of sorption and desorption of isoxaflutole (IFT) and its active metabolite diketonitrile (DKN) was investigated under conventional and conservation tillage.

RESULTS

According to soil samples, IFT K(D) values ranged from 1.4 to 3.2 L kg(-1) and DKN K(D) values ranged from 0.02 to 0.17 L kg(-1) . Positive correlations were found between organic carbon content and IFT and DKN sorption. IFT and DKN sorption was higher under conservation than under conventional tillage owing to higher organic carbon content. Under conservation tillage, measurements on maize and oat residues collected from the soil surface showed a greater sorption of IFT on plant residues than on soil samples, with the highest sorbed quantities measured on maize residues (K(D) ≈ 45 L kg(-1) ). Desorption of IFT was hysteretic, and, after five consecutive desorptions, between 72 and 89% of the sorbed IFT was desorbed from soil samples. For maize residues, desorption was weak (<50% of the sorbed IFT), but, after two complementary desorptions allowing for IFT hydrolysis, DKN was released from maize residues.

CONCLUSION

Owing to an increase in organic carbon in topsoil layers, sorption of IFT and DKN was enhanced under conservation tillage. Greater sorption capacities under conservation tillage could help in decreasing DKN leaching to groundwater.

Pedotransfer functions for isoproturon sorption on soils and vadose zone materials

BACKGROUND

Sorption coefficients (the linear K(D) or the non-linear K(F) and N(F)) are critical parameters in models of pesticide transport to groundwater or surface water. In this work, a dataset of isoproturon sorption coefficients and corresponding soil properties (264 K(D) and 55 K(F)) was compiled, and pedotransfer functions were built for predicting isoproturon sorption in soils and vadose zone materials. These were benchmarked against various other prediction methods.

RESULTS

The results show that the organic carbon content (OC) and pH are the two main soil properties influencing isoproturon K(D) . The pedotransfer function is K(D) = 1.7822 + 0.0162 OC(1.5) - 0.1958 pH (K(D) in L kg(-1) and OC in g kg(-1)). For low-OC soils (OC < 6.15 g kg(-1)), clay and pH are most influential. The pedotransfer function is then K(D) = 0.9980 + 0.0002 clay - 0.0990 pH (clay in g kg(-1)). Benchmarking K(D) estimations showed that functions calibrated on more specific subsets of the data perform better on these subsets than functions calibrated on larger subsets.

CONCLUSION

Predicting isoproturon sorption in soils in unsampled locations should rely, whenever possible, and by order of preference, on (a) site- or soil-specific pedotransfer functions, (b) pedotransfer functions calibrated on a large dataset, (c) K(OC) values calculated on a large dataset or (d) K(OC) values taken from existing pesticide properties databases.

Selected pesticides adsorption and desorption in substrates from artificial wetland and forest buffer

Buffer zones such as artificial wetlands and forest buffers may help decrease non-point-source pesticide pollution from agricultural catchments. The present study focuses on understanding the role of the substrates mainly found in such buffer zones for pesticide adsorption and desorption. Radiolabeled [(14)C]isoproturon, [(14)C]metazachlor, and [(14)C]epoxiconazole were used to measure adsorption and desorption isotherms on wetland sediments and plants and forest soil and litter from two sites in France. Wetland sediments and forest soil exhibited the most important potential for pesticide adsorption. Wetland plants and forest litter also showed high adsorption coefficients and were associated with highly hysteretic desorption, particularly for the moderately mobile isoproturon and metazachlor. Adsorption of the highly hydrophobic epoxiconazole was strong and associated with weak desorption from all substrates. Calculated sorption coefficients were larger than those classically measured on soils. Isoproturon, metazachlor, and epoxiconazole K(OC) sorption coefficients ranged from 84 to 372, 131 to 255, and 1,356 to 3,939 L/kg, respectively. Therefore, specifically collecting buffer zone substrate sorption data is needed for modeling purposes. Results showed that forests and wetlands present potential for pesticide retention. This may be enhanced by planting vegetation and leaving dead vegetal material in buffer zone design.

Occurrence of estrogens in sewage sludge and their fate during plant-scale anaerobic digestion

Estrogens, which contribute greatly to the endocrine-disrupting activity in sewage, are partially sorbed onto particulate matter during sewage treatment. We thus investigated the occurrence of estrogens in different kinds of sludge and throughout a plant-scale anaerobic digestion process. The analytical method was first validated when sorption interaction between spiked estrogens and sludge could occur. Hence, the recovery ratio of estrone (E1), 17beta-estradiol (E2), estriol (E3) and 17alpha-ethinylestradiol (EE2) were determined when added to liquid sludge and mixed under various conditions. We show that minor non-extractable residues were formed (5-10%), suggesting that the sorption interaction established with sludge did not limit estrogen extraction. Estrogen concentrations measured in collected samples varied with sludge type. Secondary sludge showed higher E1 contents than primary sludge: respectively, 43 and 8 ng g(-1) dry weight (dw). Two pathways of E1 production during secondary treatment are proposed to explain such a result. Higher estrogen concentrations were found in secondary sludge from a conventional plant (55 ng g(-1)dw) compared to those from an advanced plant (13 ng g(-1)dw). Based on estimated estrogen concentrations in sewage, we conclude that operating parameters play a role in the sorption of estrogens during secondary treatment. Also, the hydrophobic properties of the estrogens influenced the individual adsorption of each molecule. Thus, E3 showed the highest estimated concentrations in sewage but very low concentrations in sludge. Finally, plant-scale anaerobic digestion showed low efficiency (<40%) for removing estrogens and, regarding the final dewatering process, concentrations increased for E2 and EE2.

Temperature and water pressure head effects on the degradation of the diketonitrile metabolite of isoxaflutole in a loamy soil under two tillage systems

Laboratory studies were conducted to evaluate the effects of temperature and water pressure head on the degradation of the diketonitrile metabolite (DKN) of isoxaflutole during 84d in samples collected in a loamy soil under conventional (CT) and conservation (MT) tillage systems. Soil temperature was the major factor controlling DKN degradation in the two tillage systems. The shortest half-lives (T(1/2)) were measured in the seedbed samples under MT at 25 degrees C and -33cm water pressure head. We found that mouldboard ploughing under CT was responsible for the spatial variability of herbicide degradation properties, whereas under MT herbicide degradation was associated to the vertical distribution of organic matter.

Effects of temperature and water content on degradation of isoproturon in three soil profiles

The phenylurea herbicide isoproturon, 3-(4-isopropylphenyl)-1,1-dimethylurea (IPU), is widely used to control pre- and post-emergence of grass and broad-leaved weeds in cereal crops. Its degradation in soils is a key process for assessing its leaching risk to groundwater resources. The degradation properties of various samples from surface and subsurface soil (down to 1m depth) of a heterogeneous agricultural field were studied using (14)C-IPU. Laboratory incubations were carried out at 22 and 10 degrees C and at water contents 90% and 50% of the estimated water holding capacity (eWHC) corresponding to water potentials between -56 kPa and -660 MPa. Degradation was found to be more sensitive to water content variations than to temperature variations in the ranges that we used. For surface layers, at 10 and 22 degrees C, the degradation half-life increased by a factor 10 and 15, respectively, when water content decreased from 90% to 50% eWHC. Under optimal degradation conditions (i.e. 22 degrees C and 90% eWHC), 3-(4-isopropylphenyl)-1-methylurea (MDIPU) was the main metabolite in surface samples. At subsurface depths, IPU half-lives were larger than 100 d, IPU was the main compound after 92 d of incubation and the main metabolite was an unidentified polar metabolite. These results suggest a metabolic pathway involving hydroxylations for subsurface materials. IPU degradation was largely affected by water availability in both surface and subsurface horizons. Clay content seemed to play a major role in degradation processes in subsurface soil by determining through sorption IPU availability in soil solution and/or by limiting water availability for microorganisms.