{Arsenate and arsenite adsorption in relation with chemical properties of alluvial and loess soils} J. Serb. Chem. Soc. 82 (7–8) 943–954 (2017) UDC 549.73’755+544.723.2:504.53.054+ JSCS–5014 504.4.054 Original scientific paper 943 Arsenate and arsenite adsorption in relation with chemical properties of alluvial and loess soils SHAH RUKH1*, MOHAMMAD SALEEM AKHTAR1, AYAZ MEHMOOD2, SAYED HASSAN3, KHALID S. KHAN1, SYED M. S. NAQVI4 and MUHAMMAD IMRAN1 1Department of Soil Science & SWC, PMAS-Arid Agriculture University Rawalpindi-46000, Pakistan, 2Department of Agricultural Sciences, University of Haripur, Haripur-22620, Pakistan, 3Department of Crop and Soil Sciences, University of Georgia, Athens-30602, GA, USA and 4Institute of Biochemistry and Biotechnology, PMAS-Arid Agriculture University Rawalpindi-46000, Pakistan (Received 9 February, revised 18 March, accepted 20 March 2017) Abstract: Arsenic is one of the most toxic elements in the soil environment. Understanding of the arsenic adsorption chemistry is essential for evolving the extent of soil and groundwater contaminations. This research was conducted to determine the variation in adsorption behaviour of arsenite and arsenate with depth in different lithology soils. We sampled two parent materials at genetic horizons, and within a parent material, we selected two soils. Besides basic soil characterizations, a laboratory batch experiments were carried out to study the adsorption of arsenate and arsenite. Freundlich adsorption approaches were employed to investigate the adsorption of arsenate and arsenite in the soils. Freundlich isotherms fit arsenate and arsenite sorption data well with r2 values of 0.88–0.98 in most soils. Arsenate and arsenite adsorption varied with the soil properties, especially in clay composition and in the oxides of iron and alu- minum. Arsenic adsorption parameters also varied with depth in parent mat- erials, and loess derived soils had greater adsorption capacity as compared to alluvial soils in most of the adsorption parameters. This research concludes that the loess soils had higher arsenic adsorption capacity than the alluvial soils. Keywords: arsenic species; parent material; Freundlich isotherm. INTRODUCTION Arsenic is one of the most toxic trace element present in soil and water. Nat- urally As occurs in rocks and mineral weathering and it can contaminate soil and groundwater.1 Anthropogenic activities, including the application of agricultural pesticides, industrial waste and land filling of sewage sludge add As to soil and cause As mineral weathering. Mineralization of organic matter and cyclic oxid- * Corresponding author. E-mail: shahrukhshah86@hotmail.com https://doi.org/10.2298/JSC170209042R (CC) 2017 SCS. All rights reserved. _________________________________________________________________________________________________________________________Available on line at www.shd.org.rs/JSCS/ 944 RUKH et al. ation–reduction release As in the soluble form into the soil immediately after addition.2 Arsenic forms a variety of inorganic and organic compounds in soils.3 Inorg- anic As occurs dominantly as pentavalent arsenate (As(V)) and trivalent arsenite (As(III)). Arsenate species is predominant over As(III) and organic As and it may be up to 40 percent of total As content in contaminated soils.4 The inorganic As phases are hundreds times more toxic than the organic phases; and among the inorganic As forms, As(III) are twenty five to sixty times more toxic than As(V).5,6 Therefore, the correct estimation of As form in soil is important for understanding bioavailability of As and its effects on biota.7 The adsorption of As is probably initial on metal oxides especially iron oxides, i.e., goethite, lepidocrocite and less crystalline ferrihydrite. A large port- ion of As becomes adsorbed on metal oxides and only a small portion remains in soil water.8 The arsenic adsorption process controls the toxicity, fate, mobility and bioavailability of As in soils. Soil solution of As can be significantly differ- ent although the same amount of As exists in different soils due to its adsorption with the soil matrix. Therefore the understanding of the adsorption of As is imp- ortant for predicting the As behaviour in the soil environments.9 Arsenic adsorption on clay, metal oxides of iron and aluminum and organic matter is the most common process for As solid phase formation generally.10,11 It is reported that oxides and hydroxides of iron and aluminum are major con- stituents which controls As adsorption in soils.12,13 Calcite possibly has a role in the retention and the solubility of arsenic in carbonate rich environment. Phos- phate, organic matter and clay contents are the two important soil factors which significantly affect the adsorption of As in soils.14,15 Arsenate and As(III) adsorption studies used variety of adsorbents such as metal oxides, clays and soils. Studies was conducted on As(V) and As(III) ads- orption by amorphous iron and aluminum oxides, as well as on clay minerals, i.e., kaolinite and montmorillonite.16 For the modeling of As(V) and As(III) ads- orption the most widely used analytical isotherms are the Langmuir isotherm17 and the Freundlich isotherm.18 The studies on the arsenic adsorption in relation with lithology and development are scarce. We assumed that the adsorption behaviour of As(V) and As(III) may vary with the soil lithology and within a same lithology parent material, the soil development controls the arsenic forms adsorption. We sampled the two parent materials at genetic horizon level, and we selected two soils in each parent material. The objectives of the study were to evaluate the adsorption behaviour of As(V) and As(III) of different parent mat- erials soils and the effect of soil properties on As(V) and As(III) adsorption. (CC) 2017 SCS. All rights reserved. _________________________________________________________________________________________________________________________Available on line at www.shd.org.rs/JSCS/ ARSENATE AND ARSENITE ADSORPTION PARAMETERS 945 EXPERIMENTAL Soil sampling and characterization Soils were taken from the Pothwar Plateau, having different parent material, and we sel- ected alluvium and loess parent material for the present study. The GPS location and USDA taxonomy of selected soils is given in Table I. Triplicate profile for each soil was dug and soil samples were taken from each of the genetic horizon. Samples were air dried and crushed to pass through a 2-mm sieve. TABLE I. Selected soils loess and alluvium parent materials Soil Location USDA Classification Parent material Rawal 33o38’46.28’’N and 73o04’57.82’’E Fine silty, mixed, hyperthermic Typic Hapludalfs Alluvium Kotli 33o37’11.13’’N and 73o42’53.92’’E Fine, mixed, hyperthermic Entic Chromosterts Guliana 33°33’22.12’’N and 72°38’30.82’’E Silty, mixed, thermic Udic Haplustalfs Loess Mansehra 34o24’56’’N and 73o14’06’’E Fine loamy, mixed hyperthermic Typic Hapludalfs Each sample was analyzed for texture, pH, calcium carbonate, cation exchange capacity (CEC), Na2S2O4-extractable Fe and Al and dissolved organic carbon (DOC). The soil particle size distribution was determined by the dispersion in (NaPO3)6 solution and the soil pH of saturated soil paste was measured. Soil CaCO3 was determined by the acetic acid consumpt- ion.19 The DOC was extracted with K2SO4 and determined by consumption of K2Cr2O7. 20 Soil iron and aluminum oxides were dissolved in Na2S2O4 and C6H5Na3O7 and NaHCO3 buffer solution. The concentrations of Fe and Al in the extracts were measured by ICP-MS.21 Cation exchange capacity was determined by saturating soil with an index cation.22 Amorphous iron and aluminum were determined by extracting soil in acidified ammonium oxalate solution in dark.23 Batch experiment for arsenate and arsenite sorption Sorption isotherms for As(V) and arsenite were constructed to estimate Fruendlich model parameters employing the batch sorption experiments.24,25 In triplicate, 3.0 g of soil was equi- librated with 30 mL 0.01 M KNO3 solutions containing graded concentration of As(V) 0, 0.1, 2.5, 5, 8, 10, 15, 20, 25, 40 and 100 mg L-1 (Na2HAsO4). The suspension was shaken for 48 h at room temperature and centrifuged for 20 min at 3000 rpm. The supernatant was filtered through 0.45 µm cellulose membrane and analyzed for total arsenic. Separately, three g soil was equilibrated with 30 ml of 0.01 M KNO3 solution containing graded concentration of As(III) 0, 0.1, 0.5, 1, 3, 5, 7 and 8 mg L-1 from NaAsO2. The suspension was shaken for 48 h at room temperature and centrifuged for 20 min at 3000 rpm. The cellulose membrane of 0.45 µm was used to filter the supernatant and total arsenic was analyzed in the extract. Sorbed amount of As(V) and As(III) was calculated from the change in the solution phase concen- tration. The adsorption isotherm was fitted to the Freundlich equation:26 1/f w/x m K c β= (1) (CC) 2017 SCS. All rights reserved. _________________________________________________________________________________________________________________________Available on line at www.shd.org.rs/JSCS/ 946 RUKH et al. where x/m is the equilibrium concentration adsorbed by the soil (mg kg-1), cw is the equi- librium concentration in solution (mg L-1), β is an adsorption exponent related to adsorption intensity and Kf is the Fruendlich adsorption coefficient (L kg -1). Chemical analysis Soil pH and pH change for CaCO3 were determined by using Cole Parmer pH meter. For CEC analysis, NH4 + determination was carried out using shimadzu UV–Vis spectrophoto- meter. Elemental analysis of Fe, Al, and total arsenic were determined by using Perkin Elmer’s ICP-MS. Statistical analysis The variety of the adsorption parameters were ascribed to the soil parent material at different depths. The multivariate analysis was implemented using Proc General Linear Model in SAS version 9.4 (SAS Institute Inc., 2014).27 The parent material and soil (parent material) were class variable and the soil depths were multiple dependent variables. Stepwise multiple regression analysis was applied to correlate the adsorption parameters and the soil properties that determine adsorption of As(V) and As(III) in soils derived from loess and alluvium. RESULTS AND DISCUSSION Soil characteristics Soils varied in chemical and physical characteristics which are important for As(V) and As(III) adsorption (Table II). The soils were dominantly silt loam. Overall, the alluvium derived Kotli soil had larger clay content, followed by the Guliana, Mansehra and Rawal soils. Clay leaching and accumulation caused by the soil development processes was observed in Bt horizon of all the soils except for the Kotli, developed in clayey parent material. Most soils were non-cal- careous with lower DOC. Rawal soil under forest conditions showed higher DOC content. Dissolved organic carbon varied in most soils with higher contents in surface horizons and decreased with depth, in all the soils due to the accumul- ation of organic material at the surface horizons. Most of the soils were non-cal- careous except for the Rawal soil which had CaCO3 in the range of 35 to 100 g kg–1 and increased with depth. The similar values for CaCO3 were reported earlier.28 The CEC was in the range of 10 to 30 cmol+/kg. Higher CEC was obs- erved in the Guliana soil with the increasing trend with depth and seemed to increase at Bt horizon level in all the soils. Amount of citrate bicarbonate dithio- nate extractable iron seems increased with depth in all the soils. Overall, the Guliana soil showed greater amount of Fe due to soil development process which results in the iron release from primary mineral. In the Rawal, Guliana and Man- sehra soils high Fe content at Bt horizon was due to the translocation and the accumulation at Bt horizon level. Amount of citrate bicarbonate dithionate alu- minum was greater in the loess derived soils, as compared to alluvium derived soils indicating the significant change in Al with the change in parent material.29 Amount of citrate bicarbonate dithionate aluminum seems to be increased with the soil depth in all the soils. Loess derived Guliana and Mansehra were highly weathered soils, as supported by greater content of Fe and Al, compared to allu- (CC) 2017 SCS. All rights reserved. _________________________________________________________________________________________________________________________Available on line at www.shd.org.rs/JSCS/ ARSENATE AND ARSENITE ADSORPTION PARAMETERS 947 vium derived Rawal and Kotli soils. Oxalate-extractable iron also varied with parent material. The loess derived Guliana and Mansehra soils had higher con- centration of Fe compared to the alluvial Rawal and the Kotli soils. High Fe content was observed in soils at relatively higher stage of development and accu- mulated in Bt horizon, whereas in the Rawal and Kotli soils higher Fe was obs- erved in the surface horizons due to less leaching.30 High amorphous iron con- tents in Mansehra soils may attribute to high rainfall which reduces the crys- tallinity while dry climate promote crystallinity.31 Oxalate-extractable aluminum was higher in soils at higher stage of development since the weathering processes result in an increase in hydrolytic breakdown and release of iron and aluminum from the primary minerals. Oxalate-extractable aluminum content also increased with an increase in the depth. Overall iron and aluminum oxides were present in greater amount as a result of weathering in Guliana and Mansehra soils. Total As content varied between 3.4 to 6.92 mg kg–1 in most soil samples. In almost all the soils total As content increase with depth, which may indicate subsurface accu- mulation. TABLE II. Chemical properties of studied soils; CEC, cation exchange capacity; DOC, dissolved organic carbon; Fed, Ald, dithionate extractable Fe and Al; Feo, Alo, oxalate-extract- able Fe and Al; mean of n = 3; standard deviation in the parentheses Horizon Depth, cm pH Clay, g kg-1 CaCO3, g kg-1 CEC, cmol+/kg DOC, mg kg-1 Fed Ald Feo Alo Total As, mg kg-1 g kg-1 Rawal: Fine silty, mixed, hyperthermic, Typic Hapludalfs A 0–10 7.05 190 34(5.27) 9(0.60) 300(1.23) 5.0(0.33) 1.3(0.08) 0.10(0.02) 0.62(0.02) 3.52(0.05) Bw 10–18 7.35 215 35(3.50) 12(2.37) 170(0.40) 6.6(0.40) 1.7(0.10) 0.09(0.04) 0.82(0.07) 3.40(0.10) Bt 18–30 7.57 265 53(6.57) 14(1.19) 180(0.55) 9.4(0.33) 2.5(0.10) 0.09(0.00) 1.06(0.01) 3.57(0.13) Bk 30–46 7.63 215 102(24.7) 10(1.45) 160(0.41) 8.8(0.38) 2.3(0.06) 0.03(0.02) 0.83(0.04) 3.97(0.07) Kotli: Fine, mixed, hyperthermic Entic Chromostert Ap 0–10 7.93 345 5.9(0.30) 17(0.24) 150(0.78) 4.9(0.05) 1.4(0.02) 0.40(0.12) 0.69(0.04) 4.17(0.09) Bw 10–18 8.40 345 7.3(0.32) 16(2.46) 113(0.10) 5.8(0.29) 1.6(0.06) 0.51(0.02) 0.67(0.04) 3.75(0.20) C 18+ 8.20 445 5.6(0.24) 18(0.10) 46(0.36) 8.7(0.10) 2.6(0.02) 0.24(0.04) 0.79(0.05) 4.43(0.35) Guliana: Silty, mixed, thermic Udic Haplustalfs Ap 0–10 7.70 210 7.8(0.45) 26(0.65) 75(0.24) 8.0(0.41) 2.4(0.07) 0.21(0.02) 0.91(0.02) 5.21(0.04) Bw 1–20 7.37 210 7.8(0.70) 18(0.85) 70(0.48) 7.7(0.40) 2.4(0.10) 0.22(0.05) 0.96(0.05) 5.48(0.18) Bt1 20–30 7.48 295 6.4(1.05) 30(0.14) 60(0.08) 9.7(0.23) 3.3(0.06) 0.31(0.01) 1.25(0.04) 6.92(0.07) Bt2 30–50 7.50 320 6.1(1.35) 26(1.46) 60(0.67) 9.3(0.38) 3.5(0.15) 0.27(0.01) 1.39(0.10) 6.66(0.08) Mansehra: Fine loamy, mixed hyperthermic Typic Hapludalfs Ap 0–20 7.00 200 5.6(1.18) 17(0.60) 110 (0.40) 7.2(0.80) 2.0(0.62) 0.53(0.03) 0.91(0.03) 3.87(0.10) Bw 20–40 7.10 200 5.2(0.74) 13(0.60) 88(0.21) 5.8(0.29) 2.5(0.07) 0.56(0.04) 0.43(0.03) 3.50(0.05) Bt 40–70 7.08 310 6.2(0.17) 22(0.08) 66(0.75) 8.7(0.10) 4.0(0.10) 0.69(0.04) 1.48(0.06) 4.73(0.21) Arsenate and arsenite sorption isotherm The isotherms for As(V) and As(III) sorption depict variation in the shape of isotherms with the diversity in soil characteristics (Fig. 1). Overall, As(V) ads- (CC) 2017 SCS. All rights reserved. _________________________________________________________________________________________________________________________Available on line at www.shd.org.rs/JSCS/ 948 RUKH et al. orption was greater than As(III). Both As(V) and As(III) had fast rise in sorption, with a small increase in concentration in equilibrium solution. Several scientists reported a fast sorption initially and a moderate increase at the later part of the isotherm.9,18 Maximum sorption increase for As(V) was less than 150 mg kg–1. The Bt horizons, especially in the case of the Mansehra and the Guliana soils, had faster adsorption rise compared to Ap and Bw horizons. In case of As(III), where the concentration maxima was ≈ 30 mg kg–1 generally, had greater rise in the adsorbed concentration in case of Bt horizons of all the soils. It appears that the clay content had a stronger role in the adsorption of both As(V) and As(III). Several studies indicated a strong correlation of clay content with the adsorption of As(V) and As(III).32,33 Fig. 1. Adsorption isotherms for arsenate and arsenite constructed between adsorbed con- centrations at ordinate and solution concentration at abscissa in, indicating a fast initial rise especially in case of Bt horizon and the Bk horizon of Rawal had noteable low in adsorption. Freundlich equation sorption parameters Freundlich equation (Eq. (1)) fit the isotherms with most of the r2 > 0.95 (Fig. 2). Adsorption of As(V) and As(III) in these soils was well fitted by the Freundlich isotherm model.34 The maximum average adsorption intensity of As(III) (β) was lower than the adsorption intensity of As(V) in most soils, while the adsorption capacity (Kf) was greater for As(V) than As(III). It appears that As(V) had higher adsorption capacity than As(III), but with lesser binding int- ensity than most soils. The distribution of β and Kf for As(V) and As(III) rem- ained similar to the soil depth in both of the parent materials (Fig. 3), as the hypo- thesis of nonsignificant depth–PM interaction was accepted through MANOVA test criteria. Fruendlich adsorption parameters increased with soil depth in loess and alluvium. The loess derived soils had higher adsorption parameters (β and Kf) than alluvial soils at all soil depths. Variation in β and Kf of As(V) and As(III) with the soil depth in each parent material was also remained similar (Table III). (CC) 2017 SCS. All rights reserved. _________________________________________________________________________________________________________________________Available on line at www.shd.org.rs/JSCS/ ARSENATE AND ARSENITE ADSORPTION PARAMETERS 949 Fig. 2. Freundlich equation (Eq. (1)) fit for arsenate and arsenite isotherms in the selected soil horizons. Arsenate and arsenite adsorption parameters were calculated from the trendline. Fig. 3. Distribution of adsorption parameters (β and Kf) of arsenate and arsenite in each parent material (mean = 6, and bars show standard error). (CC) 2017 SCS. All rights reserved. _________________________________________________________________________________________________________________________Available on line at www.shd.org.rs/JSCS/ 950 RUKH et al. TABLE III. Fitted Freundlich sorption model parameters for arsenate and arsenite of each soil; adsorption intensity, β, and maximum adsorption capacity, Kf, both in L kg -1, were cal- culated from the respective regression equation. Values in parentheses are standard deviations Horizon Arsenate Arsenite β Kf β Kf Rawal: Fine silty, mixed, hyperthermic, Typic Hapludalfs A 1.43(0.06) 19(0.34) 2.20(0.02) 13(0.36) Bw 1.88(0.01) 35(0.55) 2.93(0.14) 24(0.70) Bt 1.82(0.02) 40(0.62) 2.77(0.35) 34(0.80) Bk 1.91(0.08) 38(0.76) 2.82(0.25) 29(0.10) Kotli: Fine, mixed, hyperthermic Entic Chromosterts Ap 1.80(0.06) 35(1.40) 2.07(0.04) 32(0.18) Bw 1.81(0.01) 36(0.45) 2.65(0.14) 32(0.29) C 2.18(0.05) 47(1.20) 3.43(0.21) 50(1.68) Guliana: Silty, mixed, thermic Udic Haplustalfs Ap 1.73(0.03) 34(0.59) 2.74(0.18) 27(2.29) Bw 1.90(0.11) 37(0.85) 2.98(0.04) 27(0.42) Bt1 2.03(0.11) 53(0.50) 3.43(0.10) 57(0.58) Bt2 2.22(0.02) 61(1.61) 3.31(0.13) 66(0.61) Mansehra: Fine loamy, mixed hyperthermic Typic Hapludalfs Ap 1.74(0.013) 36(0.24) 2.40(0.02) 27(0.20) Bw 2.01(0.031) 42(0.38) 3.11(0.12) 37(0.85) Bt 2.50(0.05) 75(1.96) 2.61(0.14) 76(1.80) The adsorption intensity ranged from 1.45 to 2.50 and Kf of As(V) ranged from 19 to 75 L kg-1 and. These results are in line with the findings of Roy et al.,35 Payne and Abdel-Fattah36 and Zeng et al.37 Arsenate β increased with depth in all the soils with the increase in clay content (r 0.48). As β is the intensity of adsorption, it is related to the abundance of metal oxides. It was evidenced that As(V) had high affinity for metal oxides from positive correlation of β with Fed (r 0.77), Ald (r 0.80), Feo (r 0.42) and Alo (r 0.71). Similarly, Kf, increased with depth with increase in clay content as evidenced by the positive correlation with clay (r 0.46). The CEC is largely related to clay content38 because there are more exchange sites for adsorption, so that As(V) Kf values positively correlated with CEC (r 0.59). The Kf had showed strong relation with iron (Fed (r 0.83) and Feo (r 0.50)) and aluminum (Ald (r 0.89) and Alo (r 0.87)) oxides as the increase in As(V) Kf and in the metal oxides with increase in soil depth. Several studies reported the role or iron and aluminum oxides in the As(V) adsorption.13,18 Over- all, As(V) β and Kf were increased linearly with the increase in metal oxide contents. Loess derived Guliana and Mansehra soils, which are more weathered soils, had greater amount of clay in Bt horizons and ultimately higher iron and aluminum oxides, resulted in greater adsorption of As(V) when compared to allu- vium derived Rawal and Kotli soils. The adsorption intensity, β, ranged from (CC) 2017 SCS. All rights reserved. _________________________________________________________________________________________________________________________Available on line at www.shd.org.rs/JSCS/ ARSENATE AND ARSENITE ADSORPTION PARAMETERS 951 2.07 to 3.43 and Kf ranged from 13 to 76 L kg–1. The adsorption parameters vary widely with the change in soil properties especially due to the differences in iron oxides.39 The β values showed non-significant relation with the metal oxides indicating the weak binding of As(III) on the metal oxide surfaces. However, As(III) β was positively related with clay content (r 0.38) and CEC (r 0.36). The adsorption capacity of As(III) was higher in weathered horizons of the Guliana and the Mansehra soils while β values are greater in Bw/Bt horizons of all the soils compared to remaining horizons. The Kf for As(III) increased with depth in all the soils except for the Kotli soil. Similar values for Kf of As(III) were obs- erved by Elkhatib et al.39 in loamy soils. Arsenite Kf showed similar behaviour as As(V) in the positive correlation with Fed (r 0.77), Ald (r 0.87), Feo (r 0.46) and Alo (r 0.82). The Bt horizons of the Guliana and the Mansehra soil had higher Kf values due to the higher clay and metal oxides content. Prediction of adsorption parameters We selected the soil properties (independent parameters) by the stepwise regression maximizing r2 and predicted the adsorption parameters of As(V) and As(III) obtained from the fitting of the isotherm to the Fruendlich equation. Soil was included as an independent parameter. Intercept differed with the soil type in case r2 improves significantly, due to the addition of a soil type as a variable. The multiple regression equations have more significance in the understanding of pro- cesses rather than as predictive tools. The regression equations for As(V) and As(III) adsorption parameters are given in the Table IV. It is apparent that β for As(V) is positively related with Ald while negatively correlated with CEC, CaCO3, which confirms the observation of Raven et al.18 that the adsorption int- ensity was more related to metal oxides. Freundlich coefficient related to the ads- orption capacity Kf in all soils was more related to Feo and Alo as compared to Fed and Ald.40 However, β for As(III) is suppressed by aluminum oxides (Ald and Alo) whereas it is increased in the presence of iron oxides and CEC related to clay content.38 The regression equation for As(III) Kf showed that the adsorption capacity of As(III) increases with the increase in Ald, whereas it was suppressed by the increase in CaCO3 and CEC. TABLE IV. Regression equations for different properties estimate for each adsorption parameter Arsenic form Regression equations r2 Arsenate β = 3.63 + 12.24Ald – 89.92CEC – 7.76CaCO3 – 0.26Clay 0.82 Kf = 236.33 + 17.80Feo – 72.44Alo 0.15 Arsenite β = 1.10 + 0.0055Feo – 0.052Alo – 0.021Ald + 0.23CEC 0.57 Kf = 21.77 + 8.66Ald – 66.50CEC – 5.21CaCO3 – 0.22Clay 0.82 (CC) 2017 SCS. All rights reserved. _________________________________________________________________________________________________________________________Available on line at www.shd.org.rs/JSCS/ 952 RUKH et al. CONCLUSIONS From our results, it can be concluded that As(V) adsorption was greater than As(III) in all the soils and varied with the soil properties, among which clay con- tent and iron and aluminum oxides exhibited the most important influence on As(V) and As(III) adsorption. Freundlich isotherms fit As(V) and As(III) sorp- tion data well with r2 values of 0.88–0.98 in most soils. Loess soils had higher adsorption capacity than alluvial soils. Metal oxides and clay contents are the major predictor for As(V) and As(III) adsorption parameters. This study may help to understand the soil and groundwater contamination phenomena. Acknowledgment. The authors thank the Higher Education Commission of Pakistan for financial assistance. И З В О Д УТИЦАЈ ХЕМИЈСКИХ СВОЈСТАВА ЛЕСНИХ И АЛУВИЈАЛНИХ ЗЕМЉИШНИХ НАСЛАГА НА АДСОРПЦИЈУ АРСЕНАТА И АРСЕНИТА SHAH RUKH1, MOHAMMAD SALEEM AKHTAR1, AYAZ MEHMOOD2, SAYED HASSAN3, KHALID S. KHAN1, SYED M. S. NAQVI4 и MUHAMMAD IMRAN1 1Department of Soil Science & SWC, PMAS-Arid Agriculture University Rawalpindi-46000, Pakistan, 2Department of Agricultural Sciences, University of Haripur, Haripur-22620, Pakistan, 3Department of Crop and Soil Sciences, University of Georgia, Athens-30602, GA, USA и 4Institute of Biochemistry and Biotechnology, PMAS-Arid Agriculture University Rawalpindi-46000, Pakistan Арсен је један од најтоксичнијих загађивача земљишта. Познавање адсорпционе хемије арсена је суштински важно за одређивање степена загађења земљишта и под- земних вода. Представљена су истраживања помоћу којих је одређена промена адсорп- ционог понашања арсената и арсенита са литосферном дубином. Узоркована су два матична материјала кроз различите типове земљишних наслага, а у оквиру та два ода- брана су по два узорка земљишта. Уз серијско лабораторијско испитивање адсорпције арсената и арсенита, урађена је и основна карактеризација земљишта. Примењен је Фројндлихов приступ анализи адсорпционих процеса. Фројндлихова изотерма задовоља- вајуће описује сорпционе податке за арсенат и арсенит, са r2 вредностима у опсегу 0,88– –0,98 за већину узорака земљишта. Адсорпциони параметри зависе од својстава зем- љишта, посебно од садржаја глине и оксида гвожђа и алуминијума. Ови параметри су се мењали и у зависности од дубине слоја у оквиру матичног материјала, и закључено је да лесно-заснована земљишта поседују већи адсорпциони капацитет од алувијалних. (Примљено 9. фебруара, ревидирано 18. марта, прихваћено 20. марта 2017) REFERENCES 1. H. Garelick, H. Jones, A. Dybowska, E. Valsami-Jones, Rev. Environ. Contam. Toxicol. 197 (2008) 17 2. E. Moreno-Jiménez, J. M. Peñalosa, E. Esteban, M. 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