Desorption kinetics of ciprofloxacin in municipal biosolids determined by diffusion gradient in thin films

In-situ measurement of dissolved sulfide in surface sediment porewater using diffusive gradients in thin films (DGT) coupled with digital imaging

Dissolved sulfide in sediment porewater significantly influences aquatic ecosystems. Conventionally, sulfide determination in sediment porewater relies on ex-situ analytical methods, susceptible to measurement errors due to sulfide oxidation and volatilization during sample analysis. In this study, we introduced an innovative in-situ method for assessing dissolved sulfide in surface sediment porewater, leveraging the integration of diffusive gradients in thin films (DGT) with digital imaging. The DGT device effectively concentrates sulfide in sediment porewater, inducing observable color changes in the binding gel. Recordings of these changes, captured by imaging equipment, facilitated the establishment of calibration curves correlating grayscale value alterations in the binding gel to sulfide concentrations. Under optimal conditions, the developed method demonstrated a linear detection range of 3.0-200 μmol L-1 at 20 °C, particularly when the exposure time exceeded 180 min. The developed method is insensitive to salinity and suitable for measuring sulfide concentrations in various natural water environments. Compared to traditional ex-situ methods, our approach circumvents challenges linked to intricate pre-treatment, prolonged analysis duration, and significant systemic errors. This proposed method presents a real-time solution for sulfide concentration assessment in surface sediment porewater, empowering researchers with an efficient means to monitor and study dynamic sulfide levels.

Calibration comparison between two passive samplers -o-DGT and POCIS- for 109 hydrophilic emerging and priority organic compounds

The Polar Organic Chemical Integrative Samplers (POCIS) is the most widely used passive sampler for hydrophilic compounds, but unsuitable for certain ionic organic contaminants. The Diffusive Gradient in Thin-Film technique (o-DGT) has shown positive results for both ionic and hydrophilic compounds. However, a calibration step is now needed to evaluate kinetic constant of accumulation for a wide range of molecules. In this study, o-DGT and POCIS were compared for the sampling of three families of micropollutants of potential risk to aquatic environments: 53 pesticides, 36 pharmaceuticals and 20 hormones. A calibration experiment was conducted to compare the kinetic models and constants from a scientific and practical perspective. The results are discussed in a single table that summarizes the performance of both passive samplers for the 109 compounds of interest. The advantage of o-DGT is that it allows linear accumulation for 72 compounds versus only 33 with POCIS. The mean times to equilibrium obtained with o-DGT are higher than those obtained with POCIS. These results confirm that the presence of a diffusion gel delays the achievement of equilibrium during compound accumulation. Therefore, o-DGT can be considered for situations where POCIS cannot be used due to non-linear accumulation over a typical 14-day deployment period. However, overall sampling rates and mass transfer coefficients also appear reduced with o-DGT, which is explained by the smaller exchange surface area, as well as the consideration of an additional diffusive layer in this device. This paper also showed that the most appropriate membrane to sample polar compounds with o-DGT was a polyethersulfone polymer with a pore size of 5 μm.

DGT method for the in situ measurement of triazines and the desorption kinetics of atrazine in soil

Triazines are frequently detected in nature water and agricultural soils worldwide. They are considered harmful to plants, animals, and the human health. In this study, diffusive gradients in thin films (DGT) method was developed for the assessment of several triazines. DGT device was used for the in situ measurement of atrazine in a pesticide factory and obtained reliable data. The atrazine concentrations measured by DGT, and solvent extraction method was in a constant ratio. The DIFS model was coupled with DGT technique to study the desorption kinetics of atrazine in four kinds of different soils. The yellow-brown soil was more inclined to adsorb atrazine than other three soils. 2_D DIFS model was used to obtain the partition coefficient for labile atrazine (K_dl), the values of the response time (T_c), and desorption/adsorption rates (k₁ and k_-1). The yellow-brown soil has a larger labile pool size, and a faster resupply speed of atrazine. The 1_D DIFS model was used to simulate the profiles of atrazine concentrations in soil solution and solid phase. The results show that the desorption of atrazine in soil was limited by kinetic limitation at short time, and was limited by the solid phase reservoir at long time.

Desorption kinetics of antipsychotic drugs from sandy sediments by diffusive gradients in thin-films technique

Dynamic processes of organic contaminants in sediments can have important toxicological implications in aquatic systems. The current study used diffusive gradients in thin-films (DGT) devices in sandy sediments spiked with nine antipsychotics and in field sandy sediments. Samplers were deployed for 1 to 30 days to determine the flux of these compounds to DGT devices and the exchange rates between the porewater and sediment solid phase. The results showed a continuous removal of antipsychotics to a binding gel and induced a mobile flux from the DGT device to the adjacent sediment solution. A dynamic model, DGT-induced fluxes in soils and sediments, was used to derive rate constants of resupply of antipsychotics from solid phase to aqueous phase (response time, T_c) and distribution coefficients for labile antipsychotics. The largest labile pool was found for lamotrigine and carbamazepine in spiked sediments. Carbamazepine, clozapine, citalopram, and lamotrigine were resupplied rapidly by sediments with T_c (25-30 min). T_c values of bupropion and amitriptyline were the longest (≈5 h), which exhibited slow desorption rates in sediments. In field sediments, high resupply was found for carbamazepine and lamotrigine, which did not show higher labile pool. The T_c values were obviously higher in the filed sediments (52-171 h). Although the adsorption process is dominant for most studied antipsychotics in both spiked sediments and field sediments, the kinetic resupply of antipsychotic compounds may not be accurately estimated by laboratory-controlled incubation experiments. More studies are needed to explore the mechanisms of desorption kinetics by using in situ DGT technique in the field.

Determination of diffusion coefficients in agarose and polyacrylamide gels for 112 organic chemicals for passive sampling by organic Diffusive Gradients in Thin films (o-DGT)

The diffusive gradient in thin film technique was recently adapted to organic compounds. The diffusional coefficient (D) is a key parameter needed to calculate the time-weighted average concentration. In this study, two methods are used for D measurement in two gels (agarose and polyacrylamide): the diffusion cell method (D_cell) and the slice stacking method (D_stack). Thus, D were discussed and compared for 112 organic compounds, including pesticides, hormones, and pharmaceuticals. D_stack tends to be higher than D_cell. It could be explained by the presence of a non-negligible diffusive boundary layer thickness in diffusion cell. Consequently, the use of sampling rates (R_S) should be more adequate to determine water concentration, for a given bulk flow velocity. D_stack also corresponds to the diffusion in gel only, allowing the determination of the maximal R_S, and would be considered as a reference value that can be adjusted to in situ conditions, by applying the appropriate DBL thickness. The range and variability of D values found in the literature and obtained in this work were discussed. Relationships between D and compound physicochemical properties (molecular mass, log Dow, polar surface area, van der Waals volume) were investigated. We did not find clear and robust correlation between D and any single physicochemical property, for the set of compounds tested.

In situ application of the diffusive gradients in thin film technique in aquaculture ponds for monitoring antibiotics, hormones, and herbicides

In recent years, as the abuse of antibiotics, hormones, and herbicides has worsened in aquaculture industry, it is important to monitor the concentrations of those trace contaminants in aquaculture water more effortlessly. The aim of this study was to develop a reliable sampling method for chemical monitoring in aquaculture ponds based on the technique of diffusive gradients in thin films (DGT). A binding material (XDA-1 resin) with high adsorption capacity for antibiotics, hormones, and herbicides was selected. In laboratory, the diffusion coefficients of 11 antibiotics, 3 hormones, and 3 herbicides of the XDA-1-DGT devices were tested and ranged from 1.0×10-6 to 8.7×10-5 cm2/s. During the in situ application of XDA-1-DGT devices in different aquaculture ponds, concentrations of 11 antibiotics, 3 hormones, and 3 herbicides in aquaculture water (CSOLN) via grab sampling were also analyzed and found ranging from 0.03 to 6.3 ng/L, lower than the results based on DGT (CDGT) (1.2-1.3×102 ng/L). The values of CDGT/CSOLN were larger than one unit, suggesting that the rates of resupply of target chemicals (antibiotics, hormones, and herbicides) by the desorption and diffusion of pond water were higher than the rates of uptake by XDA-1-DGT, and pond water was proved a sufficient reservoir of antibiotics for DGT application. The value of Log (CDGT/CSOLN) of 1.1 derived from the application in the aquaculture ponds of 14 regions in Eastern China can be a reference value for future chemical monitoring based on DGT technique. And the accuracy of this value was found hardly affected by the physical and chemical properties of chemicals with pKa ranging from -1 to 12, Log Kow ranging from 0 to 4.5, and Log solubility ranging from 0.0 to 4.0.

A critical review of diffusive gradients in thin films technique for measuring organic pollutants: Potential limitations, application to solid phases, and combination with bioassays

Diffusive gradient in thin films (DGT) for organics has received considerable attention for studying the chemical dynamics of various organic pollutants in the environment. This review investigates current limitations of DGT for organics and identifies several research gaps for future studies. The application of a protective outer filter membrane has been recommended for most DGT applications, however, important questions regarding longer lag times due to significant interaction or adsorption of specific groups of compounds on the outer membrane remain. A modified DGT configuration has been developed that uses the diffusive gel as the outer membrane without the use of an extra filter membrane, however use of this configuration, while largely successful, remains limited. Biofouling has been a concern when using DGT for metals; however, effect on the performance of DGT for organics needs to be systemically studied. Storage stability of compounds on intact DGT samplers has been assessed in select studies and that data is synthesized here. DGT has been used to describe the kinetic desorption of antibiotics from soils and biosolids based on the soil/biosolid physical-chemical characteristics, yet applications remain limited and requires further research before wide-scale adoption is recommended. Finally, DGT for organics has been rarely, albeit successfully, combined with bioassays as well as in vivo bioaccumulation studies in zebrafish. Studies using DGT combined with bioassays to predict the adverse effects of environmental mixtures on aquatic or terrestrial biota are discussed here and should be considered for future research.

Effect of biosolids characteristics on retention and release behavior of azithromycin and ciprofloxacin

Azithromycin (AZ) and ciprofloxacin (CIP) are commonly prescribed antibiotics frequently detected in municipal biosolids and identified by the USEPA as contaminants of emerging concern. The land application of municipal biosolids is an agronomically beneficial practice but is also a potential pathway of CIP and AZ release into the environment. Understanding retention-release behavior is crucial for assessing the environmental fate of and risks from land-applied biosolids-borne target antibiotics. Here, we used batch equilibrations to assess retention and release of environmentally relevant concentrations of CIP and AZ in ten different biosolids. The biosolids included Class A and Class B materials with a range of physiochemical characteristics (e.g. pH, cation exchange capacity (CEC), organic matter content (OM), and iron (Fe) and aluminum (Al)) expected to influence retention and release of AZ and CIP. Retention was linear (R² > 0.99 for AZ and >0.96 for CIP) and sorption coefficients (K_d) ranged from 52 to 370 L kg^-1 for AZ and 430-2300 L kg^-1 for CIP. Desorption also varied but was highly hysteretic, with hysteresis coefficients (H) ranging 0.01 to 0.15 for AZ and ≤0.01 for CIP, suggesting limited bioaccessibility. The penalized and shrinkage method least absolute shrinkage and selection operator (LASSO) was used to produce models describing AZ and CIP sorption behavior based on any given biosolids physiochemical characteristics. Multiple linear regression analysis linked AZ sorption behavior to total Fe content, likely due to a predisposition of AZ to participate in reactions with in situ Fe species. CIP sorption behavior was linked to oxalate extractable Al and total phosphorus (P) content, suggesting CIP bonding with amorphous forms of Al and a potential relationship between CIP sorption to biosolids and biosolids production processes, as manifested by correlation of CIP sorption with total P content.

Desorption kinetics of tetracyclines in soils assessed by diffusive gradients in thin films

Tetracyclines (TCs) are frequently detected in agricultural soils worldwide, causing a potential threat to crops and human health. In this study, diffusive gradients in thin films technique (DGT) was used to measure the distribution and exchange rates of three TCs (tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC)) between the solid phase and solution in five farmland soils. The relationship between the accumulated masses with time suggested that TCs consumption in soil solution by DGT would induce the supply from the soil solid phase. The distribution coefficient for the labile antibiotics (K_dl), response time (T_c) and desorption/adsorption rates (k_b and k_f) between dissolved and sorbed TCs were derived from the dynamic model of DIFS (DGT induced fluxes in soils). The K_dl showed similar sizes of labile solid phase pools for TC and OTC while larger pool sizes were observed for CTC in the soils. Although the concentrations of CTC were lowest in soil solution, the potential hazard caused by continuous release from soil particles could not be ignored. The long response time (>30 min in most cases) suggested that the resupply of TCs from soil solids was limited by their desorption rates (1.26-121 × 10^-6 s^-1). The soils in finer texture, with higher clay and silt contents (<50 μm) showed a greater potential for TCs release.

Adaptation of diffusive gradients in thin films technique to sample organic pollutants in the environment: An overview of o-DGT passive samplers

The adaptation of the diffusive gradients in thin films technique (DGT) to sample organic pollutants in the environment, called o-DGT has been performed since 2011 for various types of organic compounds (e.g. pesticides, pharmaceuticals, hormones, endocrine disrupting chemicals, household and personal care products). To sample these different compounds, configuration of the samplers (mainly receiving phase and diffusive gel) has to be adapted. Up-to-date, sampling of 142 organic compounds by this passive sampler have been tested. This review provides the state-of-art of o-DGT passive sampler development, describing theory and modelling, calibration, configuration of the devices, and field applications. The most used configurations were agarose-XAD-18 and agarose-HLB configuration. o-DGT can be used to sample soils and most of natural waters (range of pH 4-9 and ionic strength 0.001-0.1 M). This review discusses current limitation of o-DGT in light of the feedback of DGT use to sample inorganic contaminants. It mainly concern the low sampling rates currently obtained by o-DGT compared to other passive samplers. This weakness could be compensated in the future with new sampler's design allowing an increase in exposure area.

Bacteria-assisted removal of fluoroquinolones from wheat rhizospheres in an agricultural soil

Extensive fluoroquinolone antibiotics use results in their widespread occurrence in various environments including soil, which threatens the soil ecology and public health. The fate of fluoroquinolones in agricultural soil and the efficacy of enhanced degradation in the presence of an agricultural crops and antibiotic degrading bacteria could be better understood. The current study examined ciprofloxacin (CIP), enrofloxacin (ENR), and levofloxacin (LEV) biodegradation in a Maury Silt Loam soil in greenhouse conditions by bacterial-assisted removal of individual and mixed antibiotics in wheat rhizospheres. Fluoroquinolones were added at rates of 5, 50, and 100 mg kg^-1. Three bacterial isolates were applied at 10⁶ CFU g^-1 soil individually and in consortium. Antibiotics appeared in wheat tissue, with more accumulation in roots than shoots. Low recoveries (<50%) of CIP, ENR, and LEV were observed at all levels and treatments in a bacteria and wheat-free control compared to the initial concentrations applied Contaminated soil with wheat had greater antibiotic recovery than the wheat-free control. Antibiotic recovery with bacterial inoculum was less than that of the indigenous bacteria. The least antibiotic recovery occurred with wheat and bacterial inoculum together. At concentrations of 5 and 50 mg kg^-1, but not at 100 mg kg^-1, CIP, ENR, and LEV were below detection limits in soil after 30 days through the combination of wheat and bacteria compared to the control. This synergistic removal of the fluoroquinolone antibiotics is proposed to be due to enhanced antibiotic bioavailability, which suggests it as an environment-friendly approach to biodegradation.

Risk assessment of biosolids-borne ciprofloxacin and azithromycin

Ciprofloxacin (CIP) and azithromycin (AZ) are commonly prescribed antibiotics for various infections in humans and are frequently detected in biosolids. Ecological and human health risks from biosolids-borne CIP and AZ are not well understood, but necessary for formulating policies on safe use and management of biosolids. A tiered integrated risk assessment (IRA), based on the World Health Organization (WHO) framework and the USEPA Part 503 Biosolids Rule, was conducted to assess human and ecological health risks from biosolids-borne CIP and AZ. The IRA utilized the hazard quotient (HQ) approach to evaluate risks to various receptors of concern (including humans, animals, and birds) in sixteen exposure pathways and three conservative biosolids land application scenarios. The scenarios consisted of (i) single-heavy (100 Mg ha^-1) land application of biosolids containing 95th percentile concentrations of CIP or AZ (USEPA, 2009), (ii) long-term (annual for 40-y) land application of biosolids containing typical (median; USEPA, 2009) CIP or AZ concentrations, and (iii) long-term (annual for 40-y) land application of biosolids containing the 95th percentile concentrations of CIP or AZ. The unrealistically conservative screening level (Tier 1) assessment identified three pathways of potential concern: biosolids → soil → plant (CIP); biosolids → soil → soil organism (CIP and AZ); and biosolids → soil → soil organism → predator (CIP and AZ). Subsequent tier (refined; more realistic) assessments and pollutant limits (calculated based on the USEPA Part 503 Biosolids Rule) suggested negligible human and ecological health risks from biosolids-borne CIP and AZ under real-world biosolids application scenarios. Pollutant concentration limits were 12 mg CIP kg^-1 and 2.2 mg AZ kg^-1; suggesting that pollutant load tracking is not needed for the majority (75% for CIP and 90% for AZ) of USA biosolids. Biosolids-borne antibiotic resistance (currently not addressed in any risk assessment model) is the principal uncertainty limiting risk assessment of biosolids-borne antibiotics including CIP and AZ.

Retention-release of ciprofloxacin and azithromycin in biosolids and biosolids-amended soils

Ciprofloxacin (CIP) and azithromycin (AZ) are commonly prescribed antibiotics, often found at elevated concentrations in treated sewage sludge (biosolids), and could pose human and ecological risks when land applied. Limited retention-release data preclude assessing potential risks from the target antibiotics in biosolids and biosolids-amended soils. The present work assessed sorption-desorption of CIP and AZ in biosolids and biosolids-amended soils using the "traditional" batch equilibration method. The batch equilibration method also included un-amended soils for comparison. Release potentials of the biosolids-borne antibiotics were assessed via multiple desorption equilibrations in the presence of CaCl₂, soils, PbCl₂, or competing antibiotic (CIP versus AZ) solutions. Desorption kinetics of CIP from biosolids were also evaluated by the diffusive gradient in thin films technique (DGT), coupled with a diffusion transport-exchange model available in 2D-DIFs. Sorption of both antibiotics followed linear models with partitioning coefficient (K_d) values for CIP ranging between 40 and 334 L kg^-1 in soils and 357 L kg^-1 in biosolids, and values for AZ ranging between 11 and 202 L kg^-1 in soils and 428 L kg^-1 in biosolids. Antibiotic desorption from the biosolids was highly hysteretic (hysteresis coefficients < 0.003) and desorption of the biosolids-borne chemicals was extremely small (<3%) using any of the various desorption equilibration approaches. Desorption was hysteric in soils too; where desorption percentages were 4, 5, and 26% for CIP and 6, 32, and 50% for AZ in the silt loam soil, manured sand, and sand, respectively. CIP release from biosolids determined by DGT was also small (<1%), ascribed to low dissolved and labile concentrations in the solid phase and a small effective diffusion coefficient. Results obtained using equilibrium and dynamic approaches suggest that the target antibiotic bioaccessibilities from biosolids and finer-textured (typical agricultural) soils would be minimal and that biosolids (not soils) control desorption of the two biosolids-borne chemicals.

Abiotic, biotic and photolytic degradation affinity of 14 antibiotics and one metabolite - batch experiments and a model framework

In this study, degradation affinities of 14 antibiotics and one metabolite were determined in batch experiments. A modelling framework was applied to decrypt potential ranges of abiotic, biotic and photolytic degradation coefficients. In detail, we performed batch experiments with three different sewages in the dark at 7 °C and 22 °C. Additionally, we conducted further batch experiments with artificial irradiation and different dilutions of the sewage at 30 °C - de novo three different sewages were used. The batch experiments were initially spiked with a stock solution with 14 antibiotics and one metabolite to increase background concentrations by 1 μg L^-1 for each compound. The final antibiotic concentrations were sub-inhibitory with regard to sewage bacteria. The here presented modelling framework based on the Activated Sludge Model No. 3 in combination with adsorption and desorption processes. The model was calibrated with monitored standard sewage compounds before antibiotic degradation rates were quantified. The model decrypted ranges of abiotic, biotic and photolytic degradation coefficients. In detail, six antibiotics were not abiotic degradable at 7 °C, five antibiotics not at 22 °C and only 2 antibiotics at 30 °C. Finally, nine antibiotics were not significantly biodegradable at 7 °C and 22 °C. The model determined the link between adsorption characteristics and biodegradation rates. In detail, the rate was significantly affected by the bio-solid partition coefficient and the duration until adsorption was balanced. All antibiotics and the metabolite were photolytic degradable. In general, photolytic degradation was the most efficient elimination pathway of presented antibiotics except for the given metabolite and penicillin antibiotics.

Tetracycline desorption kinetics in municipal biosolids and poultry litter amendments determined by diffusive gradients in thin films (DGT)

Tetracycline (TET) is commonly used to treat bacterial diseases in humans and chickens (Gallus gallus domesticus), is largely excreted, and is often found at elevated concentrations in treated sewage sludge (biosolids) and poultry litter (excrement plus bedding materials). Land spreading of these materials is practiced worldwide to improve soil fertility, but the practice raises questions about whether TET could be released to the environment and cause adverse effects. Hazard risks largely depend on the concentration in the solid phase that can be released to the solution phase (labile TET), it's desorption rate constant, and diffusion rate of dissolved TET in amendments. In this study, these quantities were evaluated in biosolids and three types of litter amendments by combinations of equilibrium sorption-desorption isotherm and desorption kinetic studies using diffusive gradient in thin films (DGT) samplers. Results from isotherm experiments showed that TET partitioning was inhibited at the high dissolved organic carbon (DOC) concentrations in amendments (6-15% of dry mass). Despite low partition coefficients determined at high particle/DOC concentrations of amendments (K_d = 9-46 mL g^-1), results from DGT experiments revealed that TET release by desorption and diffusion would be slow and short-lived (<3 d) due to small effective diffusion coefficients (<8 × 10^-8 cm² s^-1) and low concentrations of labile TET in amendments (<5% of total TET). Despite this, evaluations of antibiotic uptake during microbial colonization and plant root interception of amendment surfaces are highly warranted.

Sewer sediment-bound antibiotics as a potential environmental risk: Adsorption and desorption affinity of 14 antibiotics and one metabolite

In this study, 14 antibiotics and one metabolite were determined in sewages and size-dependent sewer sediments at three sampling sites in the city of Dresden, Germany. Adsorption and desorption experiments were conducted with fractionated sediments. All antibiotics and the metabolite investigated were determined in the sewages; 9 of 14 antibiotics and the metabolite were adsorbed to sewer sediments. The adsorbed antibiotic loads in ng of antibiotic per g of sediment correlated with antibiotic concentrations in ng of antibiotic per litre of sewage. The size fractions <63 μm, 63-100 μm and 100-200 μm had significantly higher loads of adsorbed antibiotics than bigger size fractions. In general, the adsorbed load decreased with an increasing size fraction, but size fractions >200 μm had similar levels of adsorbed antibiotic loads. An antibiotic-specific adsorption coefficient, normalized to organic content, was calculated: four antibiotics exceeded 10.0 L g^-1, three antibiotics fell below 1.0 L g^-1 and all residual antibiotics and the metabolite were in the range of 1.0-10.0 L g^-1. The adsorbed antibiotic load and the organic matter increased with time, generally. The mineral composition had a minor effect on the adsorption coefficients. Desorption dynamics of five antibiotics and the metabolite were quantified. Regardless of the size fraction, the predominant part of the equilibrium antibiotic concentration was desorbed after 10 min. The calculated desorption distribution coefficient indicated adsorption as irreversible at the pH investigated (7.5 ± 0.5).

Sorption-desorption equilibrium and diffusion of tetracycline in poultry litter and municipal biosolids soil amendments

Tetracycline (TET) is commonly used to treat bacterial diseases in humans and chickens (Gallus gallus domesticus), is largely excreted, and is found at elevated concentrations in treated sewage sludge (biosolids) and poultry litter (excrement plus bedding materials). Routine application of these nutrient-and carbon-enriched materials to soils improves fertility and other characteristics, but the presence of antibiotics (and other pharmaceuticals) in amendments raises questions about potential adverse effects on biota and development of antibiotic resistance in the environment. Hazard risks are largely dictated by sorption-desorption and diffusion behavior in amendments, so these processes were evaluated from sorption-desorption equilibrium isotherm and diffusion cell experiments with four types amendments (biosolids, poultry manure, wood chip litter, and rice hull litter) at three temperatures (8 °C, 20 °C and 32 °C). Linear sorption-desorption equilibrium distribution constants (Kd) in native amendments ranged between 124-2418 L kg^-1. TET sorption was significantly increased after treatment with alum, and there was a strong exponential relationship between Kd and the concentration of bound Al³⁺ in amendments (R² = 0.94), which indicated that amendments contained functional groups capable of chelating Al³⁺ and forming metal bridges with TET. Effective diffusion coefficients of TET in amendments ranged between 0.1 and 5.2 × 10^-6 cm² s^-1, which were positively related to temperature and inversely related to Kd by a multiple regression model (R² = 0.86). Treatment of organic amendments with alum greatly increased Kd, would decrease D_s, and so would greatly reduce hazard risks of applying these organic amendments with this antibiotic to soils.

A diffusive gradients in thin-films technique for the assessment of bisphenols desorption from soils

Desorption/adsorption of bisphenols (BPs) in soils affects their mobility and availability. However, the kinetics of these processes have not been well studied, due to the lack of appropriate means of measurement. Diffusive gradients in thin-films (DGT) technique can assess kinetic processes in soils and have recently been developed for measuring three BPs (BPA, BPB and BPF). DGT was deployed for 2.5h to 20 d in five soils with different soil properties. Non-linear increase in mass accumulation by DGT with time indicated poor resupply of BPs from soil solid to solution phase. By fitting the data with DIFS (DGT-induced fluxes in soils) model, values for the labile partition coefficient (K_dl), response time (t_c) and rates of exchange (k₁ and k_-1) of BPs between soil solid and solution phases were obtained. The derived values of K_dl showed that most of the BPs in the soil could participate in labile exchange. Average response times of 1-2h implied that the supply of BPs to DGT was limited by their desorption rate. Soils with more binding sites (higher DOM, CEC and Fe oxides) could resupply BPs more quickly, highlighting the danger of just considering partition effects.