Paraquat Adsorption Characteristics of Some Malaysian Soils

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Pertanika 10<2), 119-124(1987) Paraquat Adsorption Characteristics of Some Malaysian Soils MARCUS JOPONY Jabatan Kimia, UKM Kampus Sabah, Beg. Berkunci No. 62, 88996 Kota Kinabalu, Sabah.

1 Pertanika 10<2), (1987) Paraquat Adsorption Characteristics of Some Malaysian Soils MARCUS JOPONY Jabatan Kimia, UKM Kampus Sabah, Beg. Berkunci No. 62, Kota Kinabalu, Sabah. Key words: Paraquat; adsorption; organic matter. ABSTRAK Kajian jerapan ini menunjukkan bahawa jerapan paraquat berbeza di antara sampel tanah kajian. Jerapan tersebut dikaitkan dengan kandungan bahan organik sampel tanah. Walau bagaimanapun komponen bukan organik bagi tanah juga memberi sumbangan kepada jerapan, maka keduadua komponen organik dan bukan organik bagi tanah adalah terlibat dalam jerapan paraquat pada tanah tersebut. Jerapan paraquat ini mengikut isoterma jerapan Langmuir dan Freundlich. ABSTRACT This adsorption study showed that adsorption oj paraquat varied between the t soil samples studied. The adsorption was related to the organic matter content of the samples. However, the inorganic components of the soil also contributed to the adsorption. Hence, both the inorganic and organic components of the soils were involved in the paraquat adsorption. The adsorption followed both the Langmuir and Freundlich adsorption isotherms. INTRODUCTION 1, l'-dimethyl 4, 4-bipyridylium ion, commonly known as paraquat, is available commercially as dichloride salt and is a widely used herbicide in Malaysia. In aqueous solution, this pesticide exists as divalent cations with their positive charges distributed around the molecules (Hayes etal, 1975; Buidon et al., 1977). Interaction, particularly adsorption, of a pesticide with soil is an important factor affecting the fate of pesticides in the soil environment, and the organocation paraquat is no exception. Adsorption will control the quantity of the pesticide in soil solution and thus determine its persistence, mobility and bioavailability. The extent of adsorption depends on the chemical nature of the soil environment. Adsorption of paraquat by soil is related to soil components. The clay and organic components have a major contribution towards the adsorption (Knight and Tomlinson, 1967). The role of organic matter in the soil is quite significant. Paraquat is known to become inactivated in high organic soils (Khan et ai, 1976; Damanakis et al., 1970; Calderbank, 1968). Reviews by Burns and Hayes (1974) and Khan (1974^, stated that humic substances have a high affinity for paraquat. The adsorption is however influenced by the resident inorganic charge balancing cations in the humic polymer. Specific studies showed that clay minerals also have a high affinity for paraquat (Haque et al., 1970; Hayes et at., 1975). Adsorption affinity is in the order vermiculite > montmorilonite > illite > kaolinite (Hayes et al., 1975). The oxide component also contribute towards paraquat adsorption in soil (Oladimeji, 1976). This paper describes some paraquat adsorption characteristics of six Malaysian soils, with particular emphasis on the contribution of the organic and inorganic components of the soils towards the adsorption.

$Only the < lmm fraction of the air-dried soil samples were used in the chemical and adsorption analyses.$

2 MARCUS JOPO NY MATERIALS AND METHODS Six Malaysian soil samples were used in this study and the source of each soil is given in Table 1. Only the < lmm fraction of the air-dried soil samples were used in the chemical and adsorption analyses. Samples SI S2 S3 S4 S5 S6 TABLE 1 Sources of soils under investigation Sources Danum Valley rainforest Forest plantation Secondary forest Tin mining area Mangrove swamp Podzol (B horizon) The ph of each soil sample was measured in a 1:2 suspension using distilled water. Organic carbon content was determined by the Walkley- Black method (1934), while the cation exchange capacity was determined by the ammonium acetate method (Chapman, 1965). For the adsorption studies, 2g of soil sample was equilibrated for 12 hours with 25ml of paraquat solution with concentrations ranging from mg/ml. The paraquat solutions were prepared from paraquat dichloride (ICI Malaysia Ltd). After equilibration, the paraquat solution was separated from the soil residue by centrifugation and then filtration. The absorbance of the aliquot was determined at 640nm in a UV spectrophotometer. The absorbance values for paraquat solutions of known concentrations were also determined in order to obtain a calibration curve. The final solution concentrations of the added paraquat were determined from the calibration curve. The difference between the initial and final concentrations gave the amount of paraquat adsorbed. The same procedure was used with S5 and S6 samples pretreated to remove the organic matter by heating at 550 C for 5 hours. The treated samples were designated S5-Tr and S6-Tr, respectively. Ignition of soil at high temperature can cause destruction of organic matter (Nelson and Sommers, 1982), and infact has been used to estimate soil organic matter (Davies, 1974). RESULTS AND DISCUSSIONS Table 2 shows some chemical properties of the soil samples. Basically the soils varied in ph, organic carbon content and cation exchange capacity (CEC). Organic carbon or organic matter content was highest in the mangrove soil sample (S5) while the lowest value was found in the soil sample from a tin mining area (S4). The organic carbon contents of the treated S5 and S6 samples were not determined. However, since the ignition process is capable of destroying soil organic matter (Nelson and Sommers, 1982) they should differ significantly from the original samples in organic carbon content. The cation exchange capacities of the soils were poorly correlated (r = ) to their organic matter contents. This indicated that other components present in the soil also contributed to the CEC of the soils. The calibration curve of paraquat is shown in Figure 1. Within the concentration range studied, the a bsorbance values were directly proportional to concentrations. The paraquat adsorption data and isotherms are shown in Table 3 and Figure 2 respectively. Five levels of paraquat were added to TABLE 2 Some chemical properties of the soil samples SI S2 S3 S4 S5 S6 ph(h 2 O) Organic C (%) CEG (mcq/100g) PERTANIKA VOL. 10 NO. 2, 1987

PARAQUAT ADSORPTION CHARACTERISTICS OF SOME MALAYSIAN SOILS R: (19989 sodium hypochlorite have been obtained by Knight and Tomlinson (1967) and Oladimeji (1976) respectively.

3 PARAQUAT ADSORPTION CHARACTERISTICS OF SOME MALAYSIAN SOILS R: (19989 sodium hypochlorite have been obtained by Knight and Tomlinson (1967) and Oladimeji (1976) respectively. Organic matter or humic substances are known to have a high affinity for paraquat (Burns and Hayes, 1974; Khan, 1974; Khan, 1973.; Burns et al, 1973). This is mainly due to the presence of functional groups like COOH and OH. The paraquat cation can react with more than one of these functional groups (Stevenson, 1976). The mechanism of adsorption is predominantly ion exchange (Burns et at., 1973; Best et al, 1977; Schnitzer and Khan, 1972). The treated S5 and S6 samples were still capable of adsorbing 4-6% of the added para- K> 20 Paraquat Concentration, mg ml Fig. 1: Paraquat calibration curve at 640 nm the soils and the amount adsorbed varied between samples. The amount adsorbed also depended on the initial concentration of paraquat. For each level of paraquat addition, the amount adsorbed was in the order S5 > S6 > SI > S3 > S4 > S2, and was least in samples with low organic matter content. Comparison of untreated and treated S5 and S6 samples is given in Figure 3. The treated samples showed a significant reduction ( > 50%) in the amount of paraquat adsorbed. This suggests that the organic matter component of the soils contributed considerably to paraquat adsorption. Similar adsorption characteristics following organic matter removal by hydrogen peroxide and Paraquat equilibrium concentration, mg ml Fig. 2: Paraquat adsorption isotherms of the soil samples TABLE 3 Paraquat adsorption data for the soil samples Paraquat added (mg g "! ) SI S2 Paraquat adsorbed IJ m gg S3 S4 S5 ') S5-Tr S6 S6-Tr PERTANIKA VOL. 10 NO. 2,

MARCUS JO PONY quat. The removal of organic matter from the soils would normally leave behind the more resistant inorganic component of the soil.

4 MARCUS JO PONY quat. The removal of organic matter from the soils would normally leave behind the more resistant inorganic component of the soil. This component, therefore, most likely gave a major contribution to paraquat adsorption on the treated samples. The studies by Knight and Tomlinson (1967) and Oladimeji (1976) also showed that paraquat was still adsorbed after removal of the S5 organic component. The amount of paraquat adsorbed by the treated S5 and S6 samples were comparable to the amount adsorbed by sample S4 which had the least organic matter. These results showed that both the organic and inorganic components in the soil contributed to the paraquat adsorption. The paraquat adsorption on the soil samples followed both the Langmuir (except S2) and Freundlich adsorption isotherms. The respective correlation coefficients are given in Table 4. The values of the adsorption maxima, that is the maximum amount of paraquat that can be adsorbed on the soil samples, were o R* Paraquat equilibrium concentration, mg ml Fig. 3: Paraquat adsorption isotherms for the treated and untreated S5 and S6 samples LO Organic carbon (%) Fig. 4: Relationship between organic carbon content and paraquat adsorption maximum TABLE 4 Correlation coefficients for Langmuir and Freundlich adsorption isotherms for the paraquat adsorption Correlation coefficient Sample Langmuir Freundlich SI S2 S3 S4 S5 S5-Tr S6 S6-Tr 0.99! 0.55 ns ' 0.99 ' ' 0.99 :i 0.99 s p < 0.001; >0.001; 2 p >0.05; p > PERTANIKA VOL. 10 NO. 2, 1987

PARAQUAT ADSORPTION CHARACTERISTICS OF SOME MALAYSIAN SOILS 10 20 30 Cation exchange capacity, meq loog Fig.

5 PARAQUAT ADSORPTION CHARACTERISTICS OF SOME MALAYSIAN SOILS Cation exchange capacity, meq loog Fig. 5: Relationship between cation exchange capacity and adsorption maximum calculated from the Langmuir isotherms. The relationship between the adsorption maximum and the organic carbon content of the soil samples is shown in Figure 4. There was a good linear relationship (r = ) between the two parameters. Such relationship indicated that organic matter played an important role in the paraquat adsorption. There was a positive correlation (r = ) between the adsorption maximum and the cation exchange capacity (Figure 5). This was an indication of the possibility of ion exchange mechanism for the paraquat adsorption. CONCLUSION This study indicates that the amount of paraquat adsorbed by the Malaysian soils studied varies between samples. The inorganic component and particularly the organic component in the soil samples contribute towards the adsorption, and the adsorption generally follow both the Langmuir and Freundlich adsorption isotherms. ACKNOWLEDGEMENT The author wishes to thank Mr. Gires U. for his constructive comments on the statistical analyses using the ABC programme as well as in the preparation of this manuscript. REFERENCES BEST, J.A., J.B. WEBER and S.B. WEED. (1977): Competitive adsorption of diquat, paraquat and Ca on organic matters and exchange resins. Soil Sci. 114: BURDON, J., M.H.B. HAYES and M.E. PICK. (1977): The electron density distribution in pyridinium compounds and its relevance to their adsorption by expanding lattice clays. J. Environ. Set. Health. B12:37~51. BURNS. I.G. and M.H.B. HAYES. (1974): Some physicochemical principles involved in the adsorption of the organic cation paraquat by soil humic materials. Residue Rev. 52: BURNS, I.G., M.H.B. HAYES and M. STACEY. (1973): Spectroscopic studies on the mechanisms of adsorption by humic acid and model compound. Pestic. Set. 4: CALDERBANK, A. (1968): Adv. Pestic. Control Res. 8: CHAPMAN, H.D. (1965): Cation Exchange Capacity. In: Methods of Soil Analysis. Black, C.A., Evans, D.D., White, G.L., Ensminger, L.E. and Clark, F.E. (eds.). Am. Soc. of Agron., Inc. Madison Wis. DAMANAKIS. M. t D.S.H. DRENNAN, J.D. FRYER and K. HOLLEY.(1970): Weed Res. 10: DAVIES, B.E. (1974): Loss on ignition as an estimate of soil organic matter. Soil Sci. Soc. Am. Proc. 38: HAQJJE, R., S. LILLEY and W.R. LOSHAW. (1970): Mechanisms of adsorption of diquat and paraquat on montmorilonite surface. /. Colloid Interface Sci. 27: HAYES. M.H.B., M.E. PICK and B.A. TOMS. (1975): Interactions between clay minerals and bipyridylium herbicides. Residue Rev. 57: KHAN, S.U. (1973): Humic substances reactions involving bipyridylium herbicides in soil and aquatic environment. Residue Rev. 52: KHAN, S U. (1974): Interaction of humic substance with bipyridylium herbicides. Can.]. Soil Sci. 55: KHAN, S.U., A. BELANGER, E.J. HOGUE and H.A. HAMILTON. (1976): Can. J. Soil Sci. 56: KNIGHT, B.A.G. and T.E. TOMLINSON. (1967): The interaction of paraquat with mineral soils. J. Soil Sci. 18: NELSON, D.W. and L.E. SOMMERS. (1982): Total Carbon, Organic Carbon and Organic Matter. In: Methods of Soil Analysis Part 2. Page, A.L., Miller, R.H. and Keeney, D.R. (eds.) Am. Soc. of Agron., Inc. Madison Wis. OLADIMEJI. O.M. (1976): Mineralogical and chemical studies of tropical soils. Ph.D. Thesis, University of Birmingham. SCHNITZER, M. and S.U. KHAN. (1972): Humic Substances in the Environment, Dekker, New York. pp PERTANIKA VOL. 10 NO. 2,

6 MARCUS JOPONY STEVENSON, F.J. (1976): In: Bound and Conjugated tion of the Degtjareff method for determining soil Pesticides Residues. Kaufman, D.D. G.G. Still, organic matter and a proposed modification of G.D. Paulson and S.K. Bandal. (eds.). ACS the chromic acid titration method. Soil. Sc. 37: Symp. Ser. 29: WALKLEY, A. and I.A. BLACK. (1934): An examina- /D., in r,,«o >7i v ' (Received 19 February, 1987) 124 PERTANIKA VOL. 10 NO. 2, 1987

Solution Properties of Marine Humic Acid. II. Formation and Effects of Metal Ions on Solution Properties

Solution Properties of Marine Humic Acid. II. Aggregate Formation and Effects of Metal Ions on Solution Properties Noriko SHINOZUKA, Osamu SHINJI, and Shigeo HAYANO Institute of Industrial Science, University