Disturbed Soil Columns Research Articles

Effect of the phosphate and mineralogical composition on the movement and mineralization of glyphosate in clay soils

Glyphosate is one of the most used herbicides worldwide. In rice paddy fields, it is usually applied for weed control during the pre-planting stage. Phosphate fertilizers may enhance herbicide displacement in the soil matrix. The objective of this study was to assess the effect of monoamoniun phosphate and the mineralogical composition on the movement and mineralization of glyphosate in clay soils (CS1; CS2 and CS3) in Colombia. Glyphosate miscible displacement experiments were performed in disturbed soil columns, with and without the addition of phosphate after the application of a pulse of N-(phosphonomethyl-14C) glycine. Simultaneously, 14C-glyphosate mineralization was measured indirectly by quantifying the amount 14C–CO2 released daily. At the end of the experiment, the columns were divided into six horizontal sections and glyphosate-bound residues were determined in the soil. The addition of phosphate decreased glyphosate retention time (in CS1 and CS2) and increased the total leached amount only in CS1 soil. Overall, more than 95% of the applied glyphosate was retained in the soil columns. Glyphosate mineralization half-life adjusted to a bi-exponential model, implying that one fraction degrades rapidly due to being more bioavailable, and the other fraction presents a slow rate of degradation and, that although high contents of kaolinite clays are important in the adsorption and translocation of the herbicide, the presence of calcites and divalent cations modify this process, favoring the persistence of the molecule in the soil. Glyphosate partitions into an easily degradable fraction and a more recalcitrant fraction adsorbed to kaolinite clays, calcites, and divalent cations. This fraction is less available for biodegradation thus favoring glyphosate persistence in soil.

Soil column-experimental research on the migration pattern of petroleum pollutant in the soil

In the process of oilfield exploitation and production, harmful pollutants, such as Crude oil that falls to the ground (generally refers to crude oil that leaks to the ground during oil production or transportation), production wastewater and oil-bearing mud are produced. In this contribution, the soil and crude oil from Daqing area are adopted as experimental materials to make a soil column-experimental device. The results show that the maximum migration depth of petroleum pollutants is 25 cm, most of the pollutants exist above 10 cm. The components of pollutants in disturbed soil column are complex, and the peak area of each component is large, mainly distributed in C12–C28, while in undisturbed soil column, the content of pollutants is small, and the peak area of each component is also small, mainly distributed in C12–C22. With the increase of depth, the relative content of aromatic hydrocarbons increases. The migration ability of low carbon component is weaker than the other components in crude oil. The components with high carbon number are significantly higher in shallow part. The relative contents of each component from high to low are saturates, aromatic hydrocarbons, resin and asphaltene in the soil. Compared with disturbed soil columns, the structure of undisturbed soil is complex, and the migration rate of pollutants in undisturbed soil is slower than that in disturbed soil. With the increase of depth, the light components of disturbed soil columns gradually decrease, and the relative content of heavy components changes little. The light components of the undisturbed soil column also gradually decreased, and the heavy components greater than C22 did not migrate to the depth of the soil column.

Unsaturated transport of Escherichia coli through disturbed soil column: effect of natural zeolite and cow manure addition

Organic and inorganic amendments are routinely applied to ameliorate soil conditions in semi-arid regions. This study aimed to examine the unsaturated transport of nalidixic acid-resistance Escherichia coli (E. coli NAR) in soil amended by cow manure (CM) and natural zeolite (NZ). Two levels of NZ (5 and 15% w/w) were added to a loam soil containing 5% w/w CM and incubated for 60 days. Then, the soil mixtures were poured into cylinders (3.6 × 15 cm) and a pulse (0.1 pore volume) of bacteria suspension (106 Cell mL−1) was added on top of the soil columns and leaching experiments were conducted at a steady-state, unsaturated flow condition and filtration coefficient (λf ), relative adsorption index (SR ), maximum depth of bacteria transport (Zmax ), average (Cav ) and cumulative cell density (Ccum ) were calculated. CM and NZ application significantly increased the peak density, Z max , C av , and C cum of E. coli NAR. The Cav , and Ccum of E. coli NAR in both 5 and 15% NZ containing mixtures were about 1 and 2-fold higher compared to the control. CM and NZ addition to soil decreased the filtration coefficient (λf ) and relative adsorption index (SR ) compared to the control. According to our results, we should conclude that the presence of NZ and CM, separately or together, can significantly increase the risk of groundwater contamination and it should be used with prudence.

Quantifying preferential flows on two farmlands in the North China plain using dual infiltration and dye tracer methods

Preferential flow, as a significant part of soil water infiltration, affects crop water use efficiency and pollutant transport in soil. Although it is important to properly assess the effect of preferential flow on soil water infiltration, there is a lack of widely accepted methods to quantify preferential flow. In this study, a new dual infiltration method (DI method) was used to quantify the contribution of preferential flow at two farmlands in the North China plain. The experiments were performed at two field sites (LY and SZ). To apply the new method, a double-ring infiltrometer was used to measure the steady-state infiltration rate (i.e., when infiltration rate becomes constant or stable with time, SIR) at the field sites, while a constant-head infiltrometer was used to measure the saturated hydraulic conductivity of packed soil columns consisting of disturbed soil obtained from each field site. Water flow in the disturbed soil columns was used to approximate the matrix infiltration rate (MIR), and the difference between SIR and MIR represented the preferential flow infiltration rate (PFIR). A dye tracer was also applied to the infiltrometers to quantify the proportion of preferential flow. For the LY site, the DI method found that the PFIR was 68 times larger than the MIR, while, based on the dye tracer method, the PFIR was only 2 times larger than the MIR. The DI and dye tracer method derived values of PFIR were similar for the SZ site, with MIR accounting for 61% (DI method) and 67% (dye tracer method) of the SIR. Wormholes were an important factor in the preferential flow generated in the LY site. The total areas of wormholes visible at the surface and the PFIR values were significantly positively correlated, r = 0.79 (P < 0.05). The DI method reasonably quantified preferential flow at the field sites, while the dye tracer method might underestimate preferential flow in soil with abundant macropores.

Atrazine behavior in an agricultural soil: adsorption–desorption, leaching, and bioaugmentation with Arthrobacter sp. strain AAC22

PurposeTo evaluate atrazine behavior in an agricultural soil (adsorption–desorption, leaching) and the effects of bioaugmentation with the Arthrobacter sp. strain AAC22, as a soil remediating strategy.Material and methodsAn agricultural soil with a history of atrazine application was used. Equilibrium batch experiments allowed the investigation of the adsorption–desorption of atrazine at different soil depths, while the atrazine leaching potential was assessed using disturbed soil columns. Arthrobacter sp. strain AAC22 was selected for bioaugmentation, to remove atrazine in soil microcosms. Removal efficiency was determined by a bioassay with oat seeds.Results and discussionAdsorption and desorption isotherms of atrazine at different soil depths were well described by the Freundlich equation (R2 > 0.99 and R2 > 0.98, respectively). The Freundlich constant (Kf) and desorption coefficient (Kfd1–3) decreased and increased, respectively, as soil depth increased. The Kf and Kfd1–3 values were correlated positively to organic carbon (r = 0.97) and negatively to pH (r = − 0.93). In this soil, 70.2% of atrazine applied (2.5 kg ha−1) was recovered in the leachate and 7.6% remained in the soil column. The higher atrazine concentration leached can be explained by the negative hysteresis of adsorption–desorption in this soil. Bioaugmentation with AAC22 enhanced atrazine removal being nearly 70% after 2 days of treatment, and it was almost complete (> 99%) after 8 days. A bioassay demonstrated that bioaugmentation was successful and toxic by-products were not detected.ConclusionThe adsorption–desorption and leaching experiments demonstrated the high mobility of the atrazine in the study soil. The bioaugmentation using the AAC22 strain is an effective strategy for atrazine removal in polluted soils.

Impact of olive mill wastewater (OMW) on the soil hydraulic and solute transport properties

The Mediterranean area concentrates the world’s largest production area of olive oil. The olive oil industry represents, in this basin, one of the leading sectors of the agri-food economy. Olive mill water (OMW) is the principal waste effluent produced by the olive oil industry. Due to its high pollution load, this aqueous by-product cannot be directly disposed of in domestic wastewater treatment plants (especially those with a biological treatment unit). Untreated OMW is currently used for agronomic purposes in several countries, mainly because it is rich in valuable plant nutrients. However, OMW is characterized by toxic phenols, high organic matter, high salinity, suspended solids and several other components that may have possible negative effects on chemical and physical soil properties, as well as soil biological activities. In the present research, we focused on the effects of OMW application on transport and hydraulic soil properties. Three distinct soils from a pedological point of view were selected and a series of laboratory steady-state miscible flow tests were conducted under saturated conditions, on both OMW-treated and -untreated soil columns. Tests were conducted on disturbed and undisturbed soil columns. The approach proposed by Kachanoski, based on soil impedance (Z) measurements via the time domain reflectometry (TDR) technique, was used to monitor the leaching experiments. The breakthrough curves (BTCs) exhibited different shapes that allowed the repercussions of OMW applications on soil transport behaviour to be distinguished. Several additional tests conducted on OMW-treated and -untreated soil cores to determine water retention curves (SWRCs) and saturated hydraulic conductivity Ks allowed us to infer the probable mechanisms involved in soil hydrological behaviour changes under OMW treatments. The results show that when OMW leaches into the soil immediately after its disposal there is little effect on the evaluated hydraulic and hydrodispersive properties. By contrast, we demonstrated that a short incubation period (i.e. a short contact time between OMW and soil) of 10 days is enough to exert a great influence on all the values determined (e.g. soil pore velocity v and Ks reduced by up to one order of magnitude). These effects were especially evident in undisturbed soil samples.Graphic

Mobility of insecticide residues and main intermediates in a clay-loam soil, and impact of leachate components on their photocatalytic degradation

This work assesses the behavior (adsorption, degradation and leaching) of four insecticides (chlorantraniliprole, thiametoxam, imidacloprid and pirimicarb) and their main reaction intermediates in a clay-loam textured soil (1.6% OM). Following the batch equilibrium method, the KOC (as log values) ranged from 1.2 to 3.9 (thiametoxam and pirimicarb, respectively). All the insecticides were moderately persistent (t½ = 39–100 days) in the following order: thiametoxam > imidacloprid > pirimicarb > chlorantraniliprole. Two major transformation products, desmethyl-formamido pirimicarb and desmethyl pirimicarb, were formed as consequence of dealkylation of the parent compound. Using disturbed soil columns only thiametoxam (93% of the initial amount) and imidacloprid (42% of the initial amount) were recovered from leachates. In the case of pirimicarb and chlorantraniliprole, 74% and 30%, respectively, were recovered from the soil. Thiametoxam and imidacloprid can be catalogued as mobile compounds, while pirimicarb and chlorantraniliprole are classified as immobile according to the screening indices used (GUS and ELI). Leachates containing thiametoxam and imidacloprid were subjected to photocatalytic treatment for 240 min using TiO2/Na2S2O8 with the help of a photochemical reactor equipped with LED lamp. Both compounds had a very fast degradation rate (half-lives ≤ 0.5 min) in deionized water, while their half-lives were 112 min and 178 min, respectively, in leaching water. This implies a strong effect of the water matrix composition, mainly due to organic matter dissolved (quenching). Only traces of thiametoxam urea and hydroxy imidacloprid were detected during the photocatalytic experiment.

THE USABILITY OF HYDROGEL IN INCREASING THE EFFICIENCY OF GYPSUM APPLIED TO SALINE-SODIC SOILS

This study aimed at the assessment of the usability of hydrogel in increasing the efficiency of gypsum applied to saline-sodic soils. The experiment was conducted under laboratory conditions in disturbed soil columns and was set-up in a completely randomized design with six hydrogel application rates (Control, 0.05%, 0.10%, 0.15%, 0.20% and 0.25% weight/weight (w/w) basis) and with three replications. Hydrogel application to saline-sodic soil had significant effects on leachate pH. The highest leachate pH’s were found in the final leachates in the order of 0.05%&gt;0.10%&gt;0.15%, as 9.12, 9.09, and 9.03, respectively. In all of the application rates tested, the highest electrical conductivity (EC) and Na+ leachate losses were obtained after first pore volume of leaching and then decreased gradually with further leaching. Relative to the control, hydrogel application in the rate of 0.05% increased the leaching of Na+ by 8.1% on total. However, due to the absence of statistically significant effects of the treatments on Na+ leaching, an improvement in soil exchangeable sodium percentage (ESP) and pH in saturation extract (pHe) values as an indicator of reclamation was not proven. Use of gypsum together with hydrogel increased saturated hydraulic conductivity of soils in the rates of 28.6%-42.6%, which is especially important for reducing the duration for amelioration of saline-sodic soils. Application of hydrogel to saline-sodic soils along with gypsum can be an efficient management option not only for reducing the risk of physiological drought, but also for reducing the amount of time to reclaim saline-sodic soils.

Physical disturbance accelerates carbon loss through increasing labile carbon release

Labile carbon (C) is a major source of C loss because of its high vulnerability to environmental change. Yet its potential role in regulating soil organic carbon (SOC) dynamics remains unclear. In this study, we tested the effect of physical disturbance on SOC decomposition using soils from two abandoned farmlands free of management practice for more than 28 years. The soil respiration rate was measured in undisturbed and disturbed soil columns and was inversely modeled using the two-compartment model. We found that the C loss was 16.8~74.1% higher in disturbed than in undisturbed soil columns. Physical disturbance increased the total amount of labile C (C&lt;sub&gt;1&lt;/sub&gt;) loss by 136~241%, while had no effect on the kinetic decomposition rate constants of both labile (k&lt;sub&gt;1&lt;/sub&gt;) and stable (k&lt;sub&gt;2&lt;/sub&gt;) SOC decomposition. Physical disturbance fragmented the large macroaggregates into small macroaggregates, microaggregates, and free silt and clay-sized fractions. This indicates that C loss was derived from the initially protected labile C, and there was no change of SOC fraction being decomposed. Our results give insights into the understanding of the extent of labile C loss to physical disruption and demonstrate the potential effect of physical disturbance on SOC dynamics.

Use of Index-Based Screening Models to Evaluate the Leaching of Triclopyr and Fluroxypyr Through a Loam Soil Amended with Vermicompost.

The effect of vermicompost added to a loam soil on the leaching behaviour of two herbicides (triclopyr and fluroxypyr) was examined. Mobility of the herbicides was assessed using disturbed soil columns under laboratory conditions. In both cases, the addition of vermicompost significantly increased the sorption of the compounds. For both, DT50 values were slightly higher in the amended soil, due to the increased adsorption. Rate constants (k) calculated according to pseudo-first order model were significantly lower in the case of triclopyr (very persistent), which led to a much lower degradation rate compared to fluroxypyr (persistent) in both unamended and amended soils. Values calculated for the experimental leaching index (ELI) in unamended and amended soils showed medium and high leachability for fluroxypyr (0.31 and 0.29) and triclopyr (0.72 and 0.70), respectively. Other index-based screening models (GUS, RLPI, LIX) also catalogue both herbicides as potential leachers. Results confirm that triclopyr and fluroxypyr may contaminate groundwater resources.

EFFECT OF WATER IONIC STRENGTH ON SODIUM DESORPTION FOR SOME CALCAREOUS SOILS IN NINEVEH PROVINCE

A laboratory study was conducted to determine sodium desorption behavior from exchange positions of soil solid phase because of a quiet water flow. Using sulfuric water collected from a sulfuric spring and a chlorine water from Tigris river. The flow was through two disturbed soil columns. Soils were sampled from Fadhlia and Hamdania locations in Nineveh province/ northern Iraq. Waters flow were persisted for 240 minutes with 4 cm highness over soils surface was maintained. Leachates were collected every 10 minutes for a total ten extracts which analyzed for Na+. Three mathematical kinetic description were considered as an accumulative soluble Na+, Na+ expressed by SAR and ESP concepts , sequences as parabolic diffusion, zero order, 1st order, Elovitch and power function (poly ordered) models were applied. Mathematical descriptions revealed succession of 1st order and power function models. Na+ desorption coefficient rate values by 1st order model were ranged from 96 ×10-3 - 185 × 10-3 minute for chlorine water, for sulfuric water were from 10 ×10-3 - 34×10-3 minute for both locations respectively, while desorption coefficient rate values according to power function model were 686 ×10-3 , 683×10-3 , 634×10-3 mg.kg-1.min..-1 respectively. Results referred also that Na+ desorption coefficient rate values was proportionally increased with waters ionic strength.

EFFECT OF WATER IONIC STRENGTH ON CALCIUM AND MAGNESIUM DESORPTION FROM SOME CALCAREOUS SOILS IN NINEVEH PROVINCE

A laboratory study was conducted to determine desorption behavior of Ca+2 and Mg+2 from of solid phase and dissolution of their holding minerals by using quiet water flow of different ionic strength and SAR constructed by miscible displacement technique via two Aridisols disturbed soil columns sampled from Fadhlia and Hamdania locations in Nineveh province northern of Iraq for 10 irrigation cycles elongated for 240 minute, and also to determine Ca+2&Mg+2 and desorption coefficient rates at 298˚ Kelvin. Results referred two desorption process pathways. First denoted to contributing of exchangeable phase in desorption process and enrichment of soil solution with a highly desorption rate. Second stage denotes to dissolution of minerals holding Ca+2&Mg+2 which supply soil solution for long period by water ionic strength action in presence of in common ion. Parabolic diffusion and power function models appeared high significant of desorption process. Water of high ionic strength 11.2×10-5 mole.L-1 gave highest desorption capacity 456.4 c.mole.kg-1 in comparison with that of low ionic strength 1.12×10-5 mole.L-1 24.9 c.mole.kg-1. Highest desorption coefficient rate 35.51 mg. kg-1.mint-½ in Fadhlia location for water of high ionic strength while it reduced to 2.225 mg. kg-1.mint-½ for low water ionic strength. Desorption coefficient rate in Fadhlia was higher than that in Hamdania location due to difference of waters ionic strength.

Simulating Zn, Cd and Ni Transport in Disturbed and Undisturbed Soil Columns: Comparison of Alternative Models

This study compared four solute transport models for three heavy metals, i.e. Zn, Cd and Ni, in two disturbed and undisturbed loamy soil columns. The models include convection–dispersion equation (CDE), mobile–immobile model (MIM), fractional advection–dispersion equation (FADE) and the continuous time random walk model (CTRW). The experiments were carried out for each metal at three initial concentrations (C0 = 50, 100 and 150 mg L−1) and three replications in both soil columns. The results indicated that CDE, MIM, FADE and CTRW, with r2 > 0.98 and RMSE Ni > Cd. The hydrodynamic dispersion coefficient (D) in the undisturbed soil was higher than the disturbed soil. The spreading parameter (β) of CTRW and the fractional differentiation orders (α) in FADE were approximately 1.0 and 1.7, respectively. Consequently, the heavy metal transport within both soil columns were anomalous or non-Fickian transport. However, CDE and MIM, which are based on Fickian diffusion law, were more appropriate for simulating heavy metal transport through two soil columns in comparison with CTRW and FADE.

Mobility of Cadmium in Distributed Desert Soil Column Amended by Sewage Sludge

The main aim of this research is to predict the movement of cadmium (Cd) ions in sewage sludge-amended soil columns. Sewage sludge impact on the mobility of cadmium was studied using disturbed soil columns, to assess the vertical movement of Cd in desert soil treated with different rates of sewage sludge, i.e., (T1= 0, T2= 20, T3=40, and T4= 60 ton/hectare). The obtained results showed that the physiochemical properties of the studied soil had improved significantly due to sewage sludge addition. Soil organic matter and porosity increase the water-holding capacity and structure of studied soil. Sewage sludge had the ability to increase soil fertility.&#x0D; In contrast, the excess of some heavy metals in the amended soil is the negative impact of using sewage sludge. Cadmium concentrations were greater at a higher rate (T4) of sludge treatment (14.2 mg/kg). According to the findings, the sewage sludge addition to the tested columns yielded considerable Cd concentrations in their leachates. Whereby, leachates of the soil column amendment with 60 ton/hectare contained higher Cd concentration (3.03 mg/l).&#x0D; Moreover, after leaching the soil cadmium concentration differ according to the addition rate, leading to this trend: (T1) &lt; (T2) &lt; (T3) &lt; (T4). Distribution of Cd in soil columns after the leaching process distributed on the soil layers. Overall, Cd movement in sludge-amended soil was correlated with organic matter and pH with r= (0.71439 and 0.0.94886) and r= (0.70965 and 0.99047) respectively.

The Effect of Salinity of Water Irrigation and Manure on Leaching Escherchia coli in Disturbed Soil Columns

The Effect of Salinity of Water Irrigation and Manure on Leaching Escherchia coli in Disturbed Soil Columns

Mechanisms of biochar effects on thermal properties of red soil in south China

Soil thermal properties play crucial roles in governing heat storage and conduction across soil profiles and affect various soil processes by determining soil microclimate. Biochar has gained wide attention as a soil amendment to affect a series of soil physiochemical properties. However, little information is available on the integrated effects of biochar application on soil thermal properties. Disturbed soil columns with consistent bulk density (1.3 g cm−3) were packed using clayey red soil and wheat straw biochar at application rates (w/w) of 0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%. Besides, a 2-year field experiment of biochar application at the same application rates with crop rotation was performed in a red soil region in south China. Soil thermal properties, i.e. thermal capacity, conductivity and diffusivity, were measured with heat pulse method for disturbed soil columns and undisturbed soil cores from the field at controlled soil water contents ranging from 0% to 40% at an interval of 5%. Furthermore, soil thermal properties were measured in situ for different biochar treatments under field conditions. For the disturbed soil columns, no significant effect of biochar application on soil thermal properties was detected at most of the soil water content levels. Additionally, it indicated that biochar application cannot directly affect soil thermal properties by changing soil solid substances composition at application rates up to 2.5% w/w. The results from undisturbed soil cores showed significant decreasing effects of biochar application on soil thermal capacity and diffusivity at most of the soil water content levels. The results from in situ measurement showed significant decreasing effect of biochar application on soil thermal capacity, conductivity and diffusivity. Two main underlying mechanisms were identified for the effects of biochar application on soil thermal properties. One is the negative effect of biochar application on soil thermal capacity and conductivity by increasing the soil total porosity, mainly by increase in the meso- and macro-porosity. The other is the positive effects of biochar application on soil thermal properties by increasing the soil water content through improved soil water retention ability. The negative effects through change in the soil structure were the dominant effect under field condition.

Valorization of Organic Wastes to Reduce the Movement of Priority Substances Through a Semiarid Soil

In this work, we examined the effect of two different organic wastes, composted sheep manure and coir, on the sorption, persistence, and mobility of three pesticides (alachlor, chlorfenvinphos, and chlorpyrifos) included as priority substances in European Directive 2013/39/EU. With this aim, leaching studies were conducted using disturbed soil columns filled with a typical agricultural soil (hipercalcic calcisol) from a semiarid area (southeastern Spain) to determine their potential for groundwater pollution. The three compounds were found in leachates of unamended soil although in different proportions: 53% (alachlor), 9% (chlorfenvinphos), and 6% (chlorpiryfos). The addition of organic wastes significantly increased the sorption of the studied pesticides. As a consequence, the half-lives of the studied pesticides were higher in amended than in unamended soils. A marked reduction of the amount recovered in leachates was observed in the amended soils, except for chlorpiryfos, whose recoveries barely changed. According to their potential groundwater pollution calculated as the groundwater ubiquity score (GUS) index, alachlor and chlorfenvinphos show medium leachability while chlorpiryfos is unlikely to leach.

Enhanced degradation of spiro-insecticides and their leacher enol derivatives in soil by solarization and biosolarization techniques

The leaching potential of three insecticides (spirodiclofen, spiromesifen, and spirotetramat) was assessed using disturbed soil columns. Small quantities of spirodiclofen and spiromesifen were detected in leachate fraction, while spirotetramat residues were not found in the leachates. In addition, the transformation products (enol derivatives) are relatively more mobile than the parent compounds and may leach into groundwater. Moreover, the use of disinfection soil techniques (solarization and biosolarization) to enhance their degradation rates in soil was investigated. The results show that both practices achieved a reduction in the number of juvenile nematodes, enhancing in a parallel way degradation rates of the insecticides and their enol derivatives as compared with the non-disinfected soil. This behavior can be mainly attributed to the increase in soil temperature and changes in microbial activity. All insecticides showed similar behavior under solarization and biosolarization conditions. As a consequence, both agronomic techniques could be considered as suitable strategies for detoxification of soils polluted with the studied pesticides.

Effect of pH and soil structure on transport of sulfonamide antibiotics in agricultural soils

We investigated the effect of solution pH and soil structure on transport of sulfonamide antibiotics (sulfamethoxazole, sulfadimethoxine and sulfamethazine) in combination with batch sorption tests and column experiments. Sorption isotherms properly conformed to Freundlich model, and sorption potential of the antibiotics is as follows; sulfadimethoxine > sulfamethoxazole > sulfamethazine. Decreasing pH values led to increased sorption potential of the antibiotics on soil material in pH range of 4.0–8.0. This likely resulted from abundance of neutral and positive-charged sulfonamides species at low pH, which electrostatically bind to sorption sites on soil surface. Due to destruction of macropore channels, lower hydraulic conductivities of mobile zone were estimated in the disturbed soil columns than in the undisturbed soil columns, and eventually led to lower mobility of the antibiotics in disturbed column. The results suggest that knowledge of soil structure and solution condition is required to predict fate and distribution of sulfonamide antibiotics in environmental matrix.

Sulfadimethoxine transport in soil columns in relation to sorbable and non-sorbable tracers.

In this study, miscible displacement experiment and batch sorption experiments were performed with sulfadimethoxine, dye tracer, Brilliant Blue FCF (BB) and a conservative tracer (bromide) to depict, analyse and interpret transport paths of sulfadimethoxine in undisturbed and disturbed soil columns. Batch sorption experiment revealed that sorption potential increased in the order: Brilliant Blue FCF > sulfadimethoxine > bromide. The horizontal spatial patterns of sulfadimethoxine and the tracers were analysed in each depth, and selective samples were taken in horizontal cross-section. Non-adsorbable and conservative tracer, bromide spread more widely into longitudinal and horizontal direction than sulfadimethoxine and Brilliant Blue FCF, since adsorption reduced transversal dispersion of the sulfadimethoxine and dye. In non-stained area, residual concentrations of sulfadimethoxine were relatively lower than in stained areas. Therefore, Brilliant Blue FCF distribution can be used to approximate sulfadimethoxine movement in soil. However, presence of preferential flow networks found in undisturbed soil cores can enhance mobility of sulfadimethoxine and the tracers, due to faster flow velocities and non-equilibrium adsorption. Our findings showed that other dye tracers may also be applicable to identify transport pathways of various organic contaminants, of which physico-chemical properties are similar to those of the dye tracers. Preferential flow should be considered for drinking water managements and transport modelling, since this allows faster pollutants transport from their sources, and create critical consequences for groundwater quality and solute transport modelling.