Adsorption/desorption and transport of sulfadiazine, sulfachloropyridazine, and sulfamethazine, in acid agricultural soils

1 Adsorption/desorption and transport of sulfadiazine, sulfachloropyridazine, and sulfamethazine, in 1 acid agricultural soils 2 3 Conde-Cid, M.1*, Nóvoa-Muñoz, J.C.1; Fernández-Sanjurjo, M.J.2, Núñez-Delgado, A.2, Álvarez-4 Rodríguez, E.2, Arias-Estévez, M.1,* 5 6 1Soil Science and Agricultural Chemistry, Fac. Sciences, Univ. Vigo, 32004 Ourense, Spain 7 2Dept. Soil Science and Agricultural Chemistry, Engineering Polytechnic School, Univ. Santiago de 8 Compostela, 27002 Lugo, Spain 9 10 *Corresponding author. E-mail address: [email protected] 11 12 Abstract 13 Batch-type experiments were used to study adsorption-desorption of three sulfonamides: sulfadiazine 14 (SDZ) sulfachloropyridazine (SCP), and sulfamethazine (SMT), in five crop soils, whereas laboratory soil 15 column experiments were employed to obtain data on transport processes. Adsorption results were 16 satisfactorily adjusted to Linear and Feundlich equations, with R2 values above 0.95. Adsorption followed 17 the sequence SDZ <SMT <SCP, showing higher values for soils with higher levels of organic carbon 18 (OC) content. Conversely, desorption was higher in soils with less OC, and lower in soils with higher OC 19 contents. The temporal moment analysis method gave values for the transport parameters τ and R which 20 were significantly correlated with soil parameters related to organic matter, specifically OC and N 21 concentrations. The higher retention of the three sulfonamides in soils with high organic matter content is 22 a relevant fact, with value when programming management practices in agricultural soils, and specifically 23 in relation to the spreading of animal manures, slurries, or waste containing these emerging pollutants. 24 25 Keywords: Antibiotics pollution; crop soils; soil columns; sorption/release; sulfonamides 26 27 1 Introduction 28 Non-point source pollution caused by the use of animal manures and slurries during farming activities 29 affects the sustainability of agricultural practices and is a matter of concern (Núñez-Delgado et al., 2002). 30 In recent years, special attention has been paid to diffuse pollution in relation to emergent contaminants, 31 as in the case of antibiotics. Among antibiotics, sulfonamides are one of the most consumed groups in 32 2 animal husbandry (Thiele-Bruhn, 2003), which is due to its low cost and relatively high efficacy in the 33 treatment of bacterial diseases. As indicated by Kumar et al. (2005), 30-90% of the doses of antibiotics 34 administered to animals are not absorbed. It means that these high percentages of antibiotic molecules 35 will be excreted and will reach soils when spread as organic amendments in form of solid manures or 36 pasty slurries. Once in the soil, sulfonamides suffer adsorption-desorption processes, which are dependent 37 on chemical characteristics of the antibiotics as well as on those of soil organic and inorganic 38 components. These adsorption-desorption processes affect the presence of sulfonamides in the soil 39 solution and their availability for plant uptake, as well as their eventual transport to water bodies (Conde-40 Cid et al., 2018a). 41 Sulfonamides were frequently detected in soils (between 1-11 ng kg-1), surface waters (up to 480 ng L-1), 42 groundwater (up to 410 ng L-1) and drinking waters (up to 200 ng L-1), due to their high solubility, their 43 low Koc values, and their low reactivity with soil particles, making them highly mobile (Hirsch et al., 44 1999; Sacher et al., 2001; Kemper, 2008; Díaz-Cruz et al., 2008; Cui et al., 2016). As a consequence, 45 these antibiotics are considered among those with higher risks of generating public health and 46 environmental hazards (De la Torre et al., 2012). Additionally, some authors have studied the adsorption 47 of sulfonamides to different soils (Figueroa-Diva, 2010; Pereira-Leal et al., 2013; Shen et al. al., 2018; 48 Rath et al., 2019), less frequently also focusing on desorption (Sukul et al., 2008; Doretto et al., 2014). 49 The results of these studies showed high mobility for sulfonamides, low adsorption, and a certain degree 50 of hysteresis between adsorption and desorption. The results also indicated that by lowering the pH and 51 increasing the content of carbon and clay, the adsorption of sulfonamides was increased (Pereira-Leal et 52 al., 2013; Lertpaitoonpan et al., 2009). 53 However, laboratory column experiments are considered a further step to approach field conditions, and 54 would provide complementary information, making data sets more realistic in order to assess the fate of 55 sulfonamides into the soil environment. Although some previous works used column experiments in this 56 way (for example, Unold et al., 2010; Wang et al., 2015), their number is clearly reduced as compared to 57 batch experiments. 58 In the present study, both batch-type and column experiments are addressed. Only few precedents can be 59 mentioned in this regard (for example, Maszkowska et al., 2013; Srinivasan and Sarmah, 2014). In view 60 or that, the main objectives of this work are: a) On the one hand, to increase knowledge on sulfonamides 61 adsorption-desorption processes taking place in soils with contrasting organic carbon (OC) contents, 62 which would be achieved by means of batch-type experiments. And b), on the other hand, to obtain data 63 3 on transport of sulfonamides in situations closer to field conditions, which would be achieved by means 64 of laboratory column experiments. The results obtained from both kinds of experiments would aid to 65 define ways to improve the management of agricultural soils receiving organic fertilizers or wastes 66 containing these antibiotics, which could prevent their entry into water bodies and the food chain. 67 68 2 Material and methods 69 2.1 Soil sampling and analyses 70 Five soils (soils 1, 2, 3, 4, and 5) were sampled in A Limia (Ourense province, NW Spain), a zone with 71 intensive farming activities, where slurries are usually spread on crop soils. Sampling was performed in a 72 zigzag manner, by means of an Edelman probe, taking 10-20 subsamples in each sampling point, at 0-20 73 cm depth. Then, subsamples were mixed for each sampling point to obtain a single representative sample 74 (≈2 kg). Once in the laboratory, samples were air dried, sieved by 2 mm, homogenized and stored in 75 polyethylene bottles until analyses. Standard methods (Tan, 1996) were used to quantify all parameters 76 indicated in Table 1. According to the IUSS-WRB (2014) all five soils are classified as Mollic Umbrisol 77 (Anthric). 78 Values of soil pH were measured in water and in 0.1 M KCl (soil:solution = 1:5 ratio), using a pH-meter 79 model 2001 (Crison, Spain). Elemental analysis was used to quantify organic carbon (OC) and total N 80 contents, by means of a ThermoFinnigan 1112 Series NC instrument (ThermoFinnigan, The Netherlands). 81 Exchangeable cations were extracted using 1 M NH4Cl and quantified by absorption/emission atomic 82 spectrometry (AAnalyst 200, Perkin Elmer, USA). The effective cation exchange capacity (eCEC) was 83 calculated as the sum of exchangeable Ca, Mg, Na, K and Al. Textural fractions were quantified by 84 means of wet sieving and the international method of the Robinson pipette: sand (2-0.05 mm), silt (0.05-85 0.002 mm), and clay (<0.002 mm). All determinations were made in triplicate. 86 As shown in Table 1, soil pHw was 5-5.1 for soils 1, 2 and 3, and somehow lower for soils 4 and 5 (4.7 87 and 4.5), while pHKCl was lower in all cases, indicating that negative charges are dominant. Soils 4 and 5 88 showed clearly higher values for eCEC compared to those of soils 1, 2, and 3, with also higher scores for 89 basic cations, especially Ca. In addition, OC and N contents were also clearly higher in soil 4, and 90 especially in soil 5, more than doubling the values of soils 1, 2, and 3. Finally, soils 4 and 5 showed 91 higher clay contents, whereas their silt and sand contents were similar or lower than those of soils 1, 2, 92 and 3. X-ray diffraction analyses were performed by means of a Philips PW1710 diffractometer (The 93 Netherlands). 94 4 95 96 2.2 Chemicals 97 All chemicals used were of high purity analytical grade, and were from Panreac (Barcelona, Spain), 98 unless acetonitrile, which was of HPLC grade, from Fisher Scientific (Madrid, Spain). The mobile phase 99 solution constituted by 0.02 mol L-1 phosphoric acid, as any other solutions used, were prepared with 100 milliQ water obtained by means of Millipore equipment (Millipore, Spain). The antibiotics SDZ (99.7% 101 purity), SCP (99.7% purity), and SMT (99.6% purity) were from Sigma-Aldrich (Madrid, Spain). 102 103 2.3 Batch-type experiments (sorption/desorption at equilibrium) 104 Adsorption and desorption in the equilibrium were studied for the three sulfonamides by means of batch-105 type experiments. Specifically, 2 g of soil were weighed in 15 mL polypropylene centrifuge tubes 106 (Deltalab, Spain), and suspended in 5 mL of solutions containing antibiotics individually (SDZ, SCP, or 107 SMT), at seven different concentrations (2.5, 5, 10, 20, 30, 40 and 50 μM), all of them containing 0.005 108 M CaCl2 as background electrolyte. Previous adsorption experiments performed for the three 109 sulfonamides (SDZ, SCP, and SMT), using NaCl and CaCl2 as background did not show significant 110 differences between both electrolytes (Table S1). These suspensions were shaken for 24 h in the dark, at 111 50 rpm, on a rotary shaker, and at room temperature (25 ± 1 °C). Previously, kinetic tests had indicated 112 that 24 h were sufficient to reach equilibrium. As next step, these suspensions were centrifuged for 15 113 min at 2665 x g in a Rotina 35R (Hettich Zentrifugen, Germany). The resulting supernatants were passed 114 through nylon syringe filters (0.45 μm pore size) (Fisherbrand, Spain), where antibiotic concentrations 115 were quantified by means of HPLC (see details below), and pH was measured using a combined glass 116 electrode pH-meter (Crison, Spain). The amount of each antibiotic adsorbed to the soil samples was 117 calculated as the difference between the amount of sulfonamides initially added and that remaining in the 118 solution at equilibrium, after 24 h of contact time. In two selected samples, adsorption was studied as a 119 function of pH (between 4-8) for two initial concentrations of SDZ, SMT and SCP. 120 To study desorption, soil samples previously subjected to the adsorption experiments were weighed to 121 quantify the amount of occluded solution, and then re-suspended in 5 mL of 0.005M CaCl2. Next, these 122 suspensions were shaken, centrifuged and analyzed in the same way as in the adsorption experiments. In 123 parallel, other experiments were performed using just antibiotic solutions (without soil), for each of the 124 three sulfonamides, and for each of the initial concentrations, in order to evaluate the eventual adsorption 125 5 of antibiotics to the tubes, or the eventual loss of antibiotic by abiotic degradation. As a result, it was 126 confirmed that in all cases the loss of antibiotic by these ways was negligible. The eventual loss of these 127 sulfonamides by biodegradation was also ruled out in a previous study (Conde-Cid et al., 2018b). 128 Soil samples were subjected to infrared (IR) spectroscopy before and after adsorption of each of the three 129 sulfonamides (Figs. S1 and S2), working with the highest antibiotics concentrations and in the same 130 conditions as in all other adsorption experiments. IR spectroscopy was carried out by means of a FTIR-131 Bomen MB102 equipment (ABB, Switzerland). The spectra were obtained by transmittance using KBr 132 pellets, performing determinations in the region between 400 and 4000 cm-1, with a resolution of 4 cm-1. 133 134 2.4 Transport experiments in laboratory soil columns 135 Column experiments were carried out at the laboratory, in order to study transport for each of the three 136 sulfonamides through each of the five soils. Specifically, vertically-oriented glass columns were used, 137 each of them being 80-mm long, and with 25 mm inner diameter. Each column was filled with soil (30-35 138 g), up to 5 cm (meaning a volume of 25.54 cm3), with progressive and incremental (each 1 cm) soft 139 compacting, gentle tapping to consolidate soil, also removing eventual air bubbles. Once filled, columns 140 were weighed to determine the exact mass of soil placed into each of them. At the lower side of the 141 columns (input), they were connected to a peristaltic pump (Gilson Minipuls 3, USA) by means of 1/16-142 inch (inner diameter) teflon tubing. In addition, a three-way valve was used to connect the pump to three 143 bottles containing distilled water, 0.005M CaCl2, or KBr at 10 mg L-1. At the upper side of the columns 144 (output), they were connected to a fraction collector (Gilson FC 203 B, USA), also by means of 1/16-inch 145 teflon tubing. 146 After that preparation phase, each soil column was slowly saturated (from the input, at the lower side) 147 with distilled water, for three days, with incoming flow of 1.5 mL h−1. After that, a solution containing an 148 inert tracer (Brat 10 mg L-1) was circulated through each column for 8 h, at a flow rate of 3 mL min-1, to 149 allow posterior calculation of retardation factors for each of the sulfonamides. The next step was passing 150 through each column a 0.005M CaCl2 solution, for 16 h, at a flow rate of 3 mL h-1. Then, dissolutions 151 containing each of the three sulfonamides individually, at concentration of 10 µM, as well as 0.005 M 152 CaCl2 as background electrolyte, were circulated through each column for 8 h, at a flow rate of 3 mL h-1. 153 After that, a 0.005M CaCl2 solution was passed through each column for 48 h, at a flow rate of 3 mL h-1, 154 allowing study release for each of the three antibiotics. At the end of the column experiments, all columns 155 were weighed again to determine pore volumes. At the outflow points, effluents were sampled every 30 156 6 min, for quantifying both the inert tracer and each of the three sulfonamides. Each outflow sample was 157 analyzed for each antibiotic by HPLC-UV (see details below), as well as for pH using a pH-meter 158 (Crison, Spain). A segmented flow analyzer (Bran Luebbe Auto Analyzer 3, Germay) was used to 159 quantify Brconcentration (Oosting and Reijnders, 1980; Trapp and Bell, 1989). All transport 160 experiments were carried out at 25 ± 1 ºC. All determinations were performed by triplicate. 161 Once all transport experiments were ended, breakthrough curves (BTC) were constructed. Each BTC 162 consists of the graphical representation of relative concentrations for each sulfonamide versus number of 163 pore volumes circulated through. Relative antibiotic concentrations (C/C0) were calculated as the ratio 164 between outflow antibiotic concentrations (C) and input antibiotic concentration (C0), with C0 being 10 165 µM for each of the three sulfonamides. 166 167 2.5 Modeling and statistics 168 Data from adsorption and desorption experiments were described by means of Linear (Eq. 1) and 169 Freundlich (Eq. 2) models: 170 𝑞𝑞𝑎𝑎= 𝐾𝐾𝑑𝑑𝐶𝐶𝑒𝑒𝑒𝑒 (Eq. 1) 171 𝑞𝑞𝑎𝑎= 𝐾𝐾𝐹𝐹𝐶𝐶𝑒𝑒𝑒𝑒 1/𝑛𝑛 (Eq. 2) 172 where qa (µmol kg-1) is the amount of antibiotic adsorbed on soil at the equilibrium; Ceq (µmol L-1) is the 173 concentration of antibiotic remaining in solution at equilibrium; Kd (L kg-1) is the coefficient of 174 distribution; KF (L1/n µmol1-1/n kg-1) and n (adimensional) are Freundlich’s parameters. 175 Breakthrough curves from transport experiments were described by means of temporal moment analysis, 176 as per Valocchi (1985), Stagnitti et al. (2000), and Kamra et al. (2001). The following parameters were 177 calculated to describe BTCs: 178 The first normalized moment (µ1 <𝑛𝑛>), which is the average time for output of each antibiotic under study 179 (mean breakthrough time) (τ), calculated as: 180 τ= µ1 <𝑛𝑛> = 𝑀𝑀1/𝑀𝑀0 181 where M0 and M1 represent zero and first moments. 182 A relative retardation factor (R) was calculated for each sulfonamide (SA) and for each soil with respect 183 to the inert tracer (Br): 184 𝑅𝑅= τ𝑆𝑆𝑆𝑆/τ𝐵𝐵𝐵𝐵 185 The second central moment (µ2) quantifies variance for BTCs, and standard deviation of the curve (σ) is 186 its square root: 187 7 𝜎𝜎= �µ2 188 Central moments (µ𝑝𝑝) are defined as: 189 µ𝑝𝑝= 1 𝑀𝑀0�(𝑡𝑡−µ1 <𝑛𝑛>)𝑝𝑝𝐶𝐶(𝑧𝑧,𝑡𝑡)/𝐶𝐶0𝑑𝑑𝑡𝑡 ∞ 0 190 where superscript p = 0; 1; 2; 3 … represents the successive zeroth, first, second, third, fourth moments, 191 etc.; C0 is the initial solution concentration at time t = 0; and z is the location. 192 Dispersivity (λ) indicates dispersion of a given substance within the column (Schoen et al., 1999; Stagnitti 193 et al., 2000), and is calculated as: 194 λ= (L/2) . (µ2/τ2) 195 where L is column length. 196 The third central moment (µ3) represents the asymmetry of the BTC, allowing calculation of a non-197 dimensional skewness parameter (S), as: 198 𝑆𝑆= µ3/µ2 3/2 199 The SPSS 15.0 software for Windows was used for fitting experimental adsorption/desorption data to the 200 Linear and Freundlich models, as well as for performing Pearson bivariate correlations. 201 202 2.6 Antibiotics analyses 203 The quantification of sulfonamides in the solutions was carried out following procedures previously 204 published (Conde-Cid et al., 2018a, b). Briefly, analyses were performed by means of a HPLC liquid 205 chromatograph (Dionex Corporation, USA) equipped with a P680 quaternary pump, an ASI-100 auto-206 sampler, a TCC-100 thermostatized column compartment, and a UVD170U detector. Chromatographic 207 separations were carried out in a Luna C18 column (150 mm long; 4.6 mm internal diameter; 5 µm 208 particle size) from Phenomenex (Spain) and a guard column (4 mm long; 2 mm i.d.; 5 µm particle size), 209 packed with the same material as the column. The injection volume was 50 µL and the flow rate was 1.5 210 mL min-1. The mobile phase consisted of acetonitrile (phase A) and 0.01 mol L-1 phosphoric acid (phase 211 B). A linear gradient elution program was run from 5 to 32% of phase A (and 95 to 68% of phase B) 212 within 10.5 min. The initial conditions were re-established in 2 min and held for 2.5 min. The total 213 analysis time was 15 min, with a retention time of 5.2 for SDZ, 7.0 for SMT and 9.6 for SCP, and the 214 wavelength used for detection was 270 nm. 215 216 217 8 218 219 3 Results and discussion 220 3.1 Batch Experiments: Adsorption-desorption of sulfonamides 221 Adsorption curves for SDZ (Fig. 1a), SMT (Fig. 1b), and SCP (Fig. 1c) were in all cases linear for the 222 different concentrations used (between 2.5 and 50μM), indicating a constant partition between 223 sulfonamides adsorbed and those in solution. This type of curves have been previously reported for 224 describing adsorption of sulfonamides (Doretto and Rath, 2013; Doretto et al., 2014; Pereira-Leal et al., 225 2013). 226 Table 2 shows that experimental data were satisfactorily modeled by the Freundlich and Linear equations, 227 with R2 values ranging 0.959-0.998 for the Linear equation, and 0.960-0.999 for the Freundlich equation. 228 The Kd values obtained from the adjustment of experimental data to the Linear equation were very similar 229 to those of the Freundlich's KF, mainly due to the fact that the values of the Freundlich's n parameter were 230 close to 1, circumstance in which the Freundlich equation is transformed into a linear one. Both Kd and KF 231 followed the sequence: SDZ <SMT <SCP, similarly to the sequence SDZ <Sulfamethoxazole <SMT 232 <SCP <Sulfathiazole, previously reported by Pereira-Leal et al. (2013) in soils from Brazil, and also to 233 the sequence: SDZ <SMT <Sulfadimethoxine <SCP <Sulfaquinoxaline, reported by Rath et al. (2019), 234 also for acid soils from Brazil, and to the sequence: Sulfanilamide <SDZ <Sulfadimethoxine <SMT 235 <Sulfapyridine, obtained by Thiele-Bruhn et al. (2004) for soils with pHs close to neutrality in Germany. 236 On the other hand, considering the different soils here studied, Table 2 also shows that the sequence from 237 lowest to highest Kd(ad) and KF(ad) was: Soil 1 <Soil2 <Soil 3 <Soil 4 <Soil 5. The values of Kd(ad), in the 238 case of SDZ were 0.9 ± 0.1 L kg-1 for soil 1, and 12.0 ± 0.6 L kg-1 for soil 5; whereas in the case of SMT 239 were 0.8 ± 0.0 L kg-1, and 14.2 ± 0.3 L kg-1, for soils 1 and 5, respectively; and in the case of SCP the 240 values of Kd(ad) were 1.5 ± 0.1 L kg-1, and 23.1 ± 2.1 L kg-1, for soil 1 and soil 5, respectively. The KF(ad) 241 values followed the same trend, also with similar values, as did adsorption percentages (Table 2). For the 242 three sulfonamides studied, the adsorption sequence coincides with that of total OC contents for the 243 different samples (Table 1); in fact, a positive and significant correlation was found between Kd(ad) and 244 OC for SDZ (r = 0.983, p <0.01), for SMT (r = 0.976, p <0.01), and for SCP (r = 0.983, p <0.01). The 245 correlations between KF(ad) and OC were similar to those of Kd(ad), with r values of 0.994 (p <0.01), 0.986 246 (p <0.01), and 0.992 (p <0.01), for SDZ, SMT and SCP, respectively. 247 9 Other authors previously found correlations between adsorption of sulfonamides and OC contents, such 248 as Srinivasan et al. (2014) in the case of SMT in 6 acid soils close to neutrality, and Pereira-Leal et al. 249 (2013) for acid soils in Brazil. Also, Vieira et al. (2017) found a correlation between SCP adsorption and 250 OC contents for acid soils in Brazil. 251 The lack of strong correlations between sulfonamides adsorption and clay content found for the studied 252 soils is related to mineralogy. Regarding primary minerals, the overall order of abundance is Muscovite > 253 Quartz > Albite (a sodic feldspar) > Microcline (a potassium feldspar). Among secondary minerals, the 254 most abundant is Kaolinite, followed by traces of 2:1 minerals or Gibbsite. In view of that, taking into 255 account the low content in secondary 2:1 minerals, the reactivity of the clay minerals in these soils would 256 be low, also in agreement with soil pH values (Supplementary Material, Figures S3S7 and Tables S2-257 S6). 258 Table 3 shows desorption results, indicating that SDZ, SMT and SCP desorption increased with the 259 amount of antibiotic added. On the other hand, the soil with the lowest OC content (soil 1), was the one 260 with the highest percentages of desorption, ranging 29-47% for SDZ, 14-30% for SMT, and 28-41% for 261 SCP, while the soil with the highest OC content (soil 5) showed the lowest percentages of desorption, 262 ranging 3-7% for SDZ, 1-4% for SMT, and 2-4% for SCP. In general, SMT was desorbed in smaller 263 proportion than SCP and SDZ. In a previous study, Chu et al. (2013) found desorption between 12% and 264 54% for SMT. In the present study, all three sulfonamides showed the desorption sequence: Soil 1> Soil 265 2> Soil 3> Soil 4> Soil 5 (Table 3), indicating that desorption is higher as lesser is the OC content of the 266 soils. 267 Although previous studies on desorption of sulfonamides are clearly lower in number than those on 268 adsorption, some of them have shown that lower desorption values are related to clay contents (Vieira et 269 al., 2017), or to organic carbon and fine texture fractions contents (Doretto and Ratth, 2013; Sukul et al., 270 2008). 271 In this study, as discussed above, due to the presence of clays of low reactivity (Supplementary Material, 272 Figures S3S7 and Tables S2-S6), these are not important variables in the process of adsorption-273 desorption of sulfonamides. However, a certain hysteresis can be observed when comparing desorption 274 with adsorption values, as desorption percentages are generally low. The hysteresis coefficient (H) was 275 calculated by means of the ratio KF(ad)/KF(des), with values in all cases close to 0 (between 0.1 and 0.5), 276 indicative of hysteresis for the physicochemical conditions of the study. On the other hand, both Kd(des) 277 and KF(des) (parameters that numerically are interpreted considering that their higher values indicate lower 278 16 References 420 Anskjær, G.G., Krogh, K.A., Halling-Sørensen, B. 2014. Dialysis experiments for assessing the pH-421 dependent sorption of sulphonamides to soil clay fractions. Chemosphere, 95, 116-123. 422 https://doi.org/10.1016/j.chemosphere.2013.08.048. 423 Carda-Broch, S., Berthod, A. 2004. Countercurrent Chromatography for the measurement of the 424 Hidrophobicity of Sulfonamide amphoteric Compounds. Chromatographia 59, 79-87. 425 https://doi.org/10.1365/s10337-003-0140-5. 426 Chu, B., Goyne, K.W., Anderson, S.H., Lin, C.H., Lerch, R.N. 2013. 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Main chemical characteristics of the five soils studied. pHw: pH in water; pHKCl: pH in KCl; Nae, 558 Ke, Cae, Mge and Ale: exchangeable cations; eCEC: effective cation exchange capacity; N: Total 559 Nitrogen; OC: Total organic carbon 560 561 562 pH w pH KCl Ca e Mg e Na e K e Al e eCEC N OC Sand Silt Clay cmol c kg-1 % Soil 1 5.1 4.5 2.17 0.99 0.23 0.64 0.22 4.25 0.1 1.1 67 14 19 Soil 2 5.0 4.4 2.48 0.51 0.29 1.25 0.76 5.29 0.2 2.1 61 16 23 Soil 3 5.1 4.6 3.67 0.71 0.12 1.22 1.10 6.82 0.3 3.8 48 27 25 Soil 4 4.7 4.5 5.91 1.68 0.57 2.96 0.52 11.65 0.5 5.3 41 26 34 Soil 5 4.5 4.0 5.94 1.48 0.42 1.14 2.66 11.64 0.8 10.9 49 19 32 22 Table 2. Adsorption parameters from adjustments to the Linear and Freundlich models, and maximum 563 and minimum adsorption percentages (% ad) for the five soils studied. SDZ: sulfadiazine; SMT: 564 sulfamethazine; SCP: sulfachloropyridazine; Kd(ad): coefficient of distribution obtained from adjustment 565 to the Linear equation (L kg-1). KF(ad): Freundlich constant (L1/n µmol1-1/n kg-1); n(ad): Freundlich parameter 566 (dimensionless) 567 Linear Freundlich % ad SDZ K d(ad) R2 K F(ad) n (ad) R2 Soil 1 0.9±0.1 0.984 1.0±0.3 1.0±0.3 0.983 23-51 Soil 2 1.3±0.0 0.994 1.7±0.3 1.1±0.1 0.992 34-55 Soil 3 1.9±0.1 0.991 2.4±0.6 1.1±0.1 0.988 43-71 Soil 4 4.5±0.1 0.995 4.3±0.6 1.0±0.1 0.995 57-66 Soil 5 12.0±0.6 0.989 9.2±1.3 0.9±0.1 0.995 80-87 SMT Soil 1 0.8±0.0 0.992 1.3±0.3 1.1±0.1 0.989 25-46 Soil 2 1.1±0.0 0.998 2.0±0.2 1.2±0.0 0.998 32-55 Soil 3 1.7±0.1 0.993 3.4±0.2 1.2±0.0 0.999 41-59 Soil 4 4.4±0.2 0.992 5.5±0.9 1.1±0.1 0.993 64-76 Soil 5 14.2±0.3 0.998 16.0±0.9 1.1±0.0 0.998 85-87 SCP Soil 1 1.5±0.1 0.975 2.8±0.2 1.2±0.1 0.986 36-49 Soil 2 2.7±0.1 0.996 3.5±0.4 1.1±0.0 0.997 52-64 Soil 3 3.6±0.1 0.994 5.8±0.6 1.2±0.1 0.996 59-76 Soil 4 11.1±0.4 0.995 11.2±1.2 1.0±0.1 0.995 81-88 Soil 5 23.1±2.1 0.959 21.8±5.6 1.0±0.2 0.960 90-92 568 569 23 Table 3. Desorption results (µmol kg-1, and %) for the five soils and for the various initial concentrations 570 studied. Co: initial concentration. SDZ: sulfadiazine; SMT: sulfamethazine; SCP: sulfachloropyridazine; 571 nd: not detected 572 Soil C o SDZ SMT SCP µmol L-1 µmol kg-1 % µmol kg-1 % µmol kg-1 % 1 5 1.3 33 0.7 14 1.7 33 10 2.5 29 2.1 24 4.2 41 20 4.8 47 4.7 30 6.0 28 30 5.9 30 6.0 28 10.3 32 2 5 1.2 27 nd nd 1.8 24 10 3.1 28 0.7 7 1.9 14 20 5.7 37 1.2 6 5.9 22 30 7.9 29 1.9 6 8.6 21 3 5 1.5 22 0.1 1 1.0 11 10 3.1 22 0.6 4 1.8 11 20 5.2 26 2.2 8 4.0 13 30 6.5 19 nd nd 5.6 12 4 5 1.1 12 0.1 1 0.7 6 10 2.5 14 0.1 0 0.8 4 20 5.1 18 0.3 1 3.4 8 30 7.5 15 0.5 1 7.3 12 5 5 0.6 5 0.1 1.0 0.5 4 10 0.8 3 1.1 4 0.8 3 20 2.5 7 1.3 3 1.0 2 30 4.4 7 nd nd 1.9 3 573 574 24 Table 4. Sulfonamides retention (% and µmol kg-1) and transport parameters derived from column 575 experiments; τ: mean concentration breakthrough time; R: retardation compared to Br-; σ: standard 576 deviation for the curve; λ: dispersivity; S: skewness; PV: number of pore volumes. SDZ: sulfadiazine; 577 SMT: sulfamethazine; SCP: sulfachloropyridazine 578 SDZ % retained Amount retained (µmol kg-1) τ (PV) R σ (PV) λ (cm) S Soil 1 0.00 0.00 3.20 1.59 1.32 0.42 1.19 Soil 2 0.00 0.00 3.88 1.94 1.90 0.60 1.18 Soil 3 0.00 0.00 4.46 2.41 2.01 0.51 1.38 Soil 4 0.00 0.00 5.91 3.23 2.53 0.46 1.00 Soil 5 47.90 5.70 7.00 3.60 3.14 0.50 0.49 SMT % retained Amount retained (µmol kg-1) τ (VP) R σ (VP) λ (cm) S Soil 1 8.30 0.70 3.30 1.64 1.64 0.62 1.65 Soil 2 2.70 0.23 4.23 2.12 2.57 0.92 1.53 Soil 3 13.00 1.25 4.41 2.39 2.30 0.68 1.75 Soil 4 32.10 4.07 5.88 3.21 2.53 0.46 1.06 Soil 5 63.30 8.40 9.17 4.72 2.68 0.21 -0.04 SCP % retained Amount retained (µmol kg-1) τ (VP) R σ (VP) λ (cm) S Soil 1 0.00 0.00 5.13 2.55 2.71 0.70 1.11 Soil 2 0.00 0.00 6.12 3.06 3.22 0.69 0.63 Soil 3 10.10 0.92 8.01 4.33 2.59 0.26 0.40 Soil 4 45.70 4.93 7.55 4.12 3.26 0.47 0.26 Soil 5 84.40 10.45 9.08 4.67 2.87 0.25 -0.03 579 580 25 581 Fig. 1. Adsorption curves for SDZ (sulfadiazine) (a), SMT (sulfamethazine) (b), and SCP 582 (Sulfachloropyridazine) (c) 583 0 30 60 90 120 150 010 20 30 40 50 q a (µmol kg-1) C eq (µmol L-1) Soil 1 Soil 2 Soil 3 Soil 4 Soil 5 a) 0 30 60 90 120 150 010 20 30 40 50 q a (µmol kg-1) C eq (µmol L-1) b) 0 30 60 90 120 150 010 20 30 40 50 q a (µmol kg-1) C eq (µmol L-1) c)