Scientific registration n : 727 Presentation : poster Extraction of Mobile Forms of Nutrients and Heavy Metal Pollutants in Soil Using Ion Exchange Membranes Extraction dans les sols des formes mobiles de nutriments et de métaux lourds polluants, en utilisant les membranes d échange d ions NIKOLOV Nikolay Pushkarov Institute of Soil Science and Agroecology, Shosse Bankia 7, Sofia 1080, Bulgaria, Fax (359) (2) 248937 ABSTRACT The use of ion exchange membranes for the extraction of the mobile forms of a number of nutrients and pollutants in soils of different properties has been studied. The amounts of Ca, Mg, K, Mn, Cu, Zn, Pb, Cd, NO 3 -N and P extracted by ion exchange membranes are in good correlation with the amounts extracted by some commonly used methods. It is suggested that ion exchange membranes may give a satisfactory assessment of the mobile forms of a large number of elements in soils. INTRODUCTION Plants and related living systems can exist and achieve optimal development within certain limits of concentrations of chemical elements and their available forms in the soil. These concentrations must be controlled because as a result of both genetic processes and anthropogenic activities they can vary from extreme deficiency to high toxicity. This requires soil tests able to measure a large number of elements in soils of different properties. Considerable research has been devoted to chemical extractants for simultaneous extraction of a larger number of elements. Mehlich (1953) developed the Double Acid method for P, Ca, Mg, K, Na and NH 4 +. The same author (Mehlich, 1978) suggested a new extractant for P, K, Mg, Ca, Na, Mn and Zn which was later modified into Mehlich 3 (Mehlich et al., 1984) to include also Cu. Soltanpour and Schwab (1977) published the AB-DTPA test for extraction of NO 3 -N, P, K, Zn, Fe, Cu and Mn in alkaline soils. Van Lierop (1986) reported a simultaneous extraction of NO 3 -N, P, K, Ca, Mg, Na and S using the Kelowna extractant. Van Raij et al. (1986 developed a method for extraction of P, K, Ca and Mg based on ion exchange resins. Scogley et al. (1990) published the Phyto Availability Soil Test designed to assay plant available nutrient quantity as a function of diffusive ion movement to a spherical, mixed bed ion exchange resin sink. Somasiri and Edwards 1
(1992) developed an ion exchange resin method for nutrient extraction of advisory soil samples which covers Al, Ca, Mg, K, Na, P and S. The objectives of the present research were to study the use of ion exchange membranes (IEM) as an universal and applicable to soils of different properties multielement soil test, able to measure the basic nutrients as well as some pollutants and other ions that the soil can release. Conceptually the method is designed to extract water soluble and exchangeable forms of the elements as well as elements that plants can use from certain compounds of limited solubility in the solid phase of the soil. By measuring these forms of the elements one can asses the fertility and environmental status of the soil and predict the necessary amendments. MATERIALS AND METHODS Extraction sets of ion exchange membranes (ESIEM). A MK-40 cation exchange membrane (CEM) and a MA-40 anion exchange membrane (AEM) produced by Shtchekinskoe Obedinenie Azot (former USSR) were used. Each extraction set consists of 10 meq CEM (6 strips 22 mm by 65 mm wet) and 10 meq AEM (5 strips 22 mm by 65 mm wet). Preparation of new membranes. Before use each ESIEM (saturated initially with 1 N NH 4 CL) was shaken for 30 minutes successively with 50 ml 1 N HCl., 50 ml 1N NaOH, saturated again with 1N NH 4 CL and then washed with distilled water. After that each ESIEM was treated with a "cation" and an"anion" solutions so as to saturate some sites which may cause irreversible sorption and to check the purity of the blanks after such a treatment. For this purpose ESIEM were shaken16 hr. with 50 ml the following concentration in mg/liter: Ca-800 as CaCl 2.2H 2 O, Mg-240 as Mg(NO3) 2.6H 2 O, K-400 as KCL, Na-240 as NaCl, Mn-20 as manganous chloride BDH standard solution for AAS, Fe-100 as FeCl 3.6H 2 O, Cu-20 as Cu(NO 3 ) 2.3H 2 O, Zn-20 as Zn(NO 3 ) 2.4H2O, Cd-10 as CdCl 2.2.5H 2 O, Pb-10 as Pb(NO 3 ) 2. After this treatment the ESIEM were saturated again with 1N NH 4 CL and washed with distilled water. This was followed by shaking the ESIEM for 16 hr. with 50 ml of an "anion" solution of the following concentrations (in mg/liter):no3-n-100 as NH 4 NO 3, P-100 as KH 2 PO 4, Cl- 2000 as NaCl, S- 320 as Na 2 SO 4. Finally ESIEM were shaken 15 times for 30 min. with 50 ml solution (ph 7) which is 0.35 N ammonium acetate, 0.02 M EDTA and after that 15 times for 30 min. with 50 ml distilled water. The results of the analysis show that the blanks are good and the ESIEM can be used for the extraction of soils. When not in use ESIEM are kept in plastic bottles in distilled water. Extraction of soils. Ten grams (10 g) of air dry soil ground to pass 2 mm sieve was shaken for 16 hours in a 150 ml wide mouth plastic bottle with an ESIEM and 75 ml distilled water on an end-to-end shaker at 23 0 C. The strips were separated from the soil, washed in distilled water and transferred into a plastic bottle. After that 50 ml of a solution (ph 7) 0.9 N ammonium acetate, 0.1N ammonium malate, 0.001M EDTA was added and the bottle was shaken for 30 minutes. This desorption was applied one time for all soils, but for 14 selected soils (4 soils polluted with heavy metals and 10 not polluted) it was repeated 4 times in order to study the recovery of the elements from the ESIEM. The resulting solution was used to measure the extracted elements, and the ESIEM were regenerated. 2
Regeneration of used membranes. Each ESIEM is regenerated by shaking it 15 times for 30 minutes with 50 ml solution (ph 7) 0.35N ammonium acetate, 0.02M EDTA, and after that 15 times for 30 min. in 50 ml distilled water. After this ESIEM can be used for extraction of soils. Soils. The method was applied to samples of the surface horizon of 35 representative soils of Bulgaria. Fourteen soils out of them were from polluted areas near Cu, Zn and Pb smelters, and 21 soils were not polluted but two of them had salinity and several contained up to 12 meq/100 g exchangeable Al. The 35 samples were used to measure all elements subject to this study except NO 3 -N. Twenty other samples from field experiments using four rates of application of N on five different soils were used to measure NO 3 -N. Analytical methods. A Perkin Elmer 2100 instrument for atomic absorption spectroscopy (AAS) was used to measure Ca, Mg, Cu, Zn, Mn, Al, Fe, Cd and Pb. K and Na were measured by flame photometry and P by the molybdenum blue method (Murphy and Riley, 1962). For the NO 3 -N determination a 15 ml aliquot was boiled with 5 ml 5 N NaOH until half of the volume was evaporated in order to remove NH 3 and then NO 3 -N was measured by steam distillation. Sulfur was measured using Twin 80 (Garrido, 1964). RESULTS AND DISCUSSION Desorption of the elements from the ion exchange membranes. The results of four successive desorptions of the elements from the ESIEM after their reaction with 14 soils show (on the average for all soils and elements) that the largest part (70.9 %) of the total amount of an element extracted by ESIEM was found in the first desorption, a smaller part (18.4 %) in the second desorption, 7.4 % in the third desorption and 3.3 % in the fourth desorption.. The sum of the first and the second desorptions accounts for a high recovery (89.3 %). The percentage of recovery, however. may be a subject to some variation depending on the element and on the soil. Comparison of IEM-extraction with some commonly used methods. The amounts of the elements extracted by some commonly used methods and by IEM (the sum of four desorptions of ESIEM) from 6 soils of contrasting properties are shown in Table 1. The correlation coefficients between the commonly used methods and the IEM (Table 2) are calculated for all 35 soils and separately for the groups of polluted (with the particular element) and not polluted soils using the data of the first desorption of ESIEM as it was found that the correlation coefficients did not vary considerably when the amounts of the elements in the first, the sum of the first two, or the sum of all four desorptions of ESIEM were used to correlate with the "commonly used " methods. Calcium. IEM extracts almost completely (average value 91.2%) exchangeable calcium; in soils containing CaCO 3 it extracts some additional amounts. The correlation between IEM and AA is high for both not polluted and polluted soils. Magnesium. The average value of IEM-extracted exchangeable Mg is 73.9%; in two soils, containing 6.0 and 12.0 meq exchangeable Al/100 g, it extracts respectively 66% and 55% of exchangeable Mg. The correlation with AA is high for the 35 soils and for the not polluted soils, but no correlation was found for the polluted soils. 3
Potassium. The average percentage of IEM -extracted exchangeable K is 74.1% but it varies from 58.8% in a vertisol to 88.9% in a light textured soil. High correlation exists between IEM and AA for both polluted and not polluted soils. Sodium. IEM extracted 58.2% of the large amount AA extractable water soluble and exchangeable Na in a saline soil. IEM distinguished the saline soil from soils low in Na. Aluminum. The sorption distribution of Al 3+ between the soil and the IEM is much in favor of the soil. IEM extracted only about 10% of exchangeable Al in the soil. Iron. IEM extracted less Fe than DTPA especially in a very acid and high in humus soil. In the alkaline soil IEM extracted more Fe than DTPA, mainly as a complex anion. IEM was correlated better with AA than with DTPA. Manganese. IEM -extractable Mn is slightly higher than DTPA-extractable and AAextractable Mn. High correlation is found between IEM and DTPA- extractable Mn for both polluted and not polluted soils and also between IEM and AA for polluted soils. Copper. The amount of Cu extracted by IEM is larger than the amount extracted by AA and smaller than that extracted by DTPA and by EDTA. In soils not polluted with Cu IEM is best correlated with EDTA, followed by AA. For the soils polluted with Cu, IEM is highly correlated with EDTA, AA and DTPA. Zinc. IEM extracts more Zn than AA and less than EDTA or DTPA. In soils not polluted with Zn IEM correlates best with EDTA, then comes DTPA, but no correlation was found with AA. In Zn- polluted soils IEM correlates well with (in decreasing order) EDTA, DTPA and AA. Cadmium. Only EDTA extracts enough Cd which can be measured by AAS in soils not polluted with Cd. The amounts of cadmium extracted by IEM and AA from these soils are low and require flameless AAS. In soils polluted with Cd IEM extracted somewhat smaller amounts than AA, DTPA, and EDTA. The correlation of IEM with EDTA, AA and DTPA is high. Lead. IEM extract more Pb than AA but less than EDTA in soils polluted with Pb. There was no correlation between IEM and EDTA for soils not polluted with Pb. A high coefficient of correlation was found between IEM and EDTA for soils polluted with Pb. Phosphorus. There is some positive correlation between IEM and Olsen P but not all soils behave in the same way. IEM extractable P in soils which are polluted with cation pollutants like Cu, Zn, Cd, Pb, Mn, Na and water soluble salts does not correlate with Olsen's P, while in those soils which are not polluted, the correlation is quite good. The presence of pollutants decreased the extractability of P by IEM. Sulfur. IEM distinguishes the salt affected soil containing large amount of S from the soils which are not salt affected. Nitrate-nitrogen. IEM extract practically the same amounts of NO 3 -N as the KCL extraction does. High correlation exists between the two methods. CONCLUSION IEM can distinguish the soils containing high concentration of mobile forms of some elements from the soils having low concentration. Extraction with ion exchange membranes gave a satisfactory correlation with other commonly used methods of extraction for a large number of elements.on the basis of these preliminary results it is concluded, that ion exchange membranes may give satisfactory assessment of the mobile 4
forms of a large number of elements including not only basic nutrients but also some heavy metals and other pollutants. ACKNOWLEDGMENT The author would like to thank Dr. V. I. Savitch for the provision of ion exchange membranes, and The National Research Fund of The Ministry of Education, Science and Technology in Bulgaria for financing part of this study. REFERENCES 1. Bremner, J. M. 1965. Inorganic forms of nitrogen. In: C.A. Black et al. (ed.). Methods of soil analysis. Part 2. Agronomy 9: 1179-1237. Am. Soc. of Agron., Inc., Madison, Wis. 2. Garrido, L. M. 1964. Determination of sulfur in plant material. Analyst 89, 61-66. 3. van Lierop, W. 1986. Soil nitrate determination using the Kelowna multiple element extractant. Commun. Soil Sci. Plant Anal. 17(12), 1311-1329. 4. Lindsay, W. L. and W. A. Norvell. 1978. Development of a DTPA soil test for zinc, iron, manganese and copper. Soil Sci. Soc. Am. J. 42, 421-428. 5. Mehlich, A. 1953. Determination of P, Ca, Mg, K, Na and NH 4. North Carolina Soil Testing Division, Mimeo, N. C. Dept. Agr., Raleigh. 6. Mehlich, A. 1978. New extractant for soil test evaluation of phosphorus, potassium, magnesium, calcium, sodium, manganese and zinc. Commun. Soil. Sci. Plant. Anal. 9(6), 477-492. 7. Mehlich, A. 1984. Mehlich 3 soil test extractant: a modification of Mehlich 2 extractant. Commun. Soil Sci. Plant Anal. 15(12), 1409-1416. 8. Ministry of Agriculture, Fisheries and Food. 1986. Reference book 427. The analysis of Agricultural materials. HMSO, London. 9. Murphy, J. and J. P. Riley. 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta. 27, 31-36. 10. Olsen, S. R., C.V. Cole, F. S. Watanabe and L. A. Dean. 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate. US Dep. Of Agr. Circ. 939. 11. van Raij, B., J. A. Quaggio, and N. M. da Silva. 1986. Extraction of phosphorus, potassium, calcium and magnesium from soils by an ion- exchange resin procedure. Commun. Soil Sci. Plant Anal. 17(5), 547-566. 12. Skogley, E. O., S. J. Georgitis, J. E. Yang and B. E. Schaff. 1990. The phyto availability soil test PST. Commun. Soil Sci. Plant Anal. 21(13-16), 1229-1243. 5
13. Soltanpour, P. N. and A. P. Schwab. 1977. A new soil test for simultaneous extraction of macro- and micro- nutrients in alkaline soils. Commun. Soil Sci. Plant Anal. 8(3), 195-207. 14. Somasiri, L. L. W. and A. C. Edwards. 1992. Anion exchange resin method for nutrient extraction of agricultural advisory soil samples. Commun. Soil Sci. Plant Anal. 23(7-8), 645-657. Keywords : ion exchange resins, mobile forms of N, P, K, Ca, Mg, Cu, Zn, Pb, Cd, soil pollution, soil nutrients Mots clés : résines d échange d ion, formes mobiles de N, P, K, Ca, Mg, Cu, Zn, Pb, Cd, pollution du sol, éléments nutritifs 6
Table 1. Mobile forms of the elements extracted by commonly used methods and by ion exchange membranes (IEM) from soils of contrasting properties Element and method of extraction Calcaric chernozen 2.7 % Humus 1.8 % CaCO 3 ph H2O 8.0 Eutric planosol 1.9 % Humus 62 % Base Satur. ph H2O 5.1 Soil Humic cambisol 20% Humus 12 % Base Satur. ph H2O 4.5 meq/100g Solonetzsolonchak 2 % Humus ph H2O 9.0 Fluvisol 2.2 % Humus ph H2O 4.7 Polluted: 620 mg Cu /kg Ca AA 39.7 7.9 2.2 14.0 16.6 40.5 Calcaric Fluvisol 2.0 % Humus ph H2O 7.5 Polluted: 2656 mg Pb 1338 mg Zn 22 mg Cd /kg Ca IEM 43.93 6.64 2.6 9.01 13.81 39.15 Mg AA 3.1 1.8 1.0 16.0 2.8 1.87 Mg IEM 2.39 1.11 0.66 13.88 1.9 0.96 mg/kg K AA 179.3 102.9 152.7 149.4 195.9 224.1 K IEM 120.3 78.8 128.7 101.7 155.9 133.2 Na AA 3.0 25.0 31.0 6000 n.d. n.d. NA IEM 5.0 14.0 6.0 3626 44.0 20.0 Mn DTPA 23.0 124.0 3.0 32.0 116.0 11.2 Mn IEM 42.4 146.3 45.9 217. 8 135.5 22.6 Fe DTPA 15.0 92.0 304.0 12.0 160.0 6.34 Fe IEM 14.4 8.3 34.9 24.9 6.7 4.9 Cu EDTA 7.5 4.05 2.45 4.80 347.5 66.5 Cu IEM 3.6 1.9 0.3 3.0 75.5 5.3 Zn EDTA 1.8 1.25 4.55 0.65 17.0 335.0 Zn IEM 1.6 1.0 3.3 0.1 7.7 244.9 Cd EDTA 0.1 0.1 0.1 0.05 0.35 19.75 Cd IEM n.d.* n.d.. n.d n.d. n.d. 7.0 Pb EDTA 2.9 3.50 9.70 7.85 18.20 1087.5 Pb IEM n.d. n.d. n.d. n.d. n.d. 526.3 P Olsen 13.1 6.3 13.5 3.4 49.4 45.7 P IEM 15.7 12.2 26.7 1.0 80.4 39.0 S IEM 20.9 24.7 68.3 3180 70.5 23.1 n.d.* not determined 7
Table 2. Correlation between the amounts of elements extracted by the commonly used methods and the amounts extracted by ion exchange membranes (IEM) Element and commonly used method of extraction Number of soils Coef. of correlation between the commonly used metho d and IEM Element and commonly used method of extraction Number of soils Coef. of correlation between the commonly used metho d and IEM r r Ca-AA 21 n.p.* 0.988 Cu-EDTA 7 p. 0.979 Ca-AA 14 p.** 0.950 Cu-EDTA all 35 0.939 Ca-AA all 35 0.967 Cu-AA 28 n.p. 0.734 Mg-AA 21 n.p. 0.990 Cu-AA 7 p. 0.972 Mg-AA 14 p. 0.018 Cu-AA all 35 0.970 Mg-AA all 35 0.977 Zn-DTPA 23 n.p. 0.839 K- AA 21 n.p. 0.943 Zn-DTPA 12 p. 0.818 K- AA 14 p. 0.912 Zn-DTPA all 35 0.921 K- AA all 35 0.940 Zn-EDTA 23 n.p. 0.894 Mn-DTPA 21 n.p. 0.893 Zn-EDTA 12 p. 0.858 Mn-DTPA 14 p. 0.945 Zn-EDTA all 35 0.938 Mn-DTPA all 35 0.859 Zn-AA 23 n.p. 0.369 Mn-AA 21 n.p. 0.692 Zn-AA 12 p. 0.759 Mn-AA 14 p. 0.936 Zn-AA all 35 0.877 Mn-AA all 35 0.735 Cd-DTPA 12 p. 0.818 Fe-DTPA 21 n.p. 0.574 Cd-EDTA 12 p. 0.858 Fe-DTPA 14 p. 0.204 Cd-AA 12 p. 0.852 Fe-DTPA all 35 0.533 Pb-EDTA 23 n.p. 0.036 Fe-AA 21 n.p. 0.782 Pb-EDTA 12 p. 0.809 Fe-AA 14 p. 0.617 Pb-EDTA all 35 0.872 Fe-AA all 35 0.725 Pb-AA 12 p. 0.476 Cu-DTPA 28 n.p. 0.574 NO 3 N (KCl) 20 n.p. 0.985 Cu-DTPA 7 p. 0.979 P-Olsen 18 n.p. 0.776 Cu-DTPA all 35 0.973 P-Olsen 17 p. 0.184 Cu-EDTA 28 n.p. 0.797 P-Olsen all 35 0.621 n.p.* not polluted p.** polluted 8