Chemosphere 91 (2013) 302–306

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Removal properties of dissolved boron by glucomannan gel

Kyoko Oishi ⇑, Yugo MaehataDepartment of Civil Engineering, Graduate School of Engineering, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan

h i g h l i g h t s

" The boron removal efficiency was compared between the gel and semi-gel of glucomannan." The semi-gel removed the boron at pH P 11, which boron species is present as BðOHÞ�4 ." The semi-gel retained the free diol group had a high boron removal capacity." The gel lost diol group in the gelation process was not able to remove the boron." The presence of metals did not effect to boron removal capacity.

a r t i c l e i n f o

Article history:Received 16 April 2012Received in revised form 7 November 2012Accepted 9 November 2012Available online 20 December 2012

Keywords:Boron removalGlucomannan gelDiol groupMetal hydroxideAdsorptionDesorption

0045-6535/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.chemosphere.2012.11.034

⇑ Corresponding author. Tel./fax: +81 92 802 3423.E-mail address: ohishi@civil.kyushu-u.ac.jp (K. Ois

a b s t r a c t

Boron ions have long been known to form complexes with the cis-diol group of a polysaccharide. Konjacglucomannan (KGM) which is one of polysaccharides was used to remove dissolved boron in this study.KGM forms a complex with boron, but does not remove boron from contaminated waters as well as otherpolysaccharides because of its high water solubility. Therefore, the removal efficiencies of dissolvedboron were examined using both an insoluble KGM gel and KGM semi-gel. The former did not removedissolved boron, but the latter did. The difference in the ability of boron removal was due to the presenceof diol group inside. KGM loses free diol group during the process of gelation. On the other hand, thesemi-gel gelated only surface layer in water has diol group inside. The boron removal capacity of thesemi-gel was highest at pHs P 11, when the boron species is present as BðOHÞ�4 . The capacity was slightlyincreased by the addition of Al, Ca and Mg under high pH conditions. This was due to co-precipitation ofboron with Ca dissolved from the semi-gel. The boron adsorbed to the semi-gel easily was desorbedunder low pH conditions and the hysteresis was not found.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Boron compounds have extensive industrial uses in the manu-facture of glass and porcelain, and the production of cosmetics, fer-tilizers, disinfectants, and weatherproofing of wood. Therefore,boron contamination is occurred in many natural and artificialwaters and brines at relatively low concentrations throughoutthe world. Boron is an essential element for the proper structureand function of plant cell walls, and may also be important for reg-ulating hormones in animals (Nielsen et al., 1987; Matoh et al.,1992; Naghii and Samman, 1996; Blevins and Lukaszewski, 1998;Matoh and Kobayashi, 1998). On the other hand, many studiesregarding the toxicity of borax, otherwise known as sodium borate,were reported (Weir and Fisher, 1972; Landolph, 1985; Moseman,1994; Nobel et al., 1997; Sylvain et al., 1998; Wester et al., 1998).Citrus plants and some other agricultural crops exhibit the effectsof boron poisoning, which include yellowish spots on the leaves

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hi).

and fruits, accelerated decay and ultimately plant expiration(Hatcher and Bower, 1958). The symptoms of borax toxicity in hu-mans include headache, fever, nausea, vomiting, and erythematouseyes. Nephrotoxicity is the most common type of organ toxicity, fol-lowed by fatty liver degradation, cerebral edema and gastroenteri-tis (Weir and Fisher, 1972). Borax also has reproductive anddevelopmental toxicities (Landolph, 1985; Moseman, 1994; Westeret al., 1998). In 1999, Thailand declared borax as a prohibited sub-stance in Thai food because of these toxicities to human (Pongsavee,2009). In Japan, the Environmental Quality Standard for water pol-lution of boron was declared to less than 1 mg/L and the Water Pol-lution Control Law regarding boron was revised to 10 mg B/L (forsea water 230 mg B/L) in 2001. Therefore, the concentration of bor-on in wastewaters must be reduced to permitted levels.

Separation technologies for the removal and recovery of dis-solved boron mainly employ coagulation–precipitation (Yilmazet al., 2005), adsorption on activated carbon (Choi and Chen,1979; Kluczka et al., 2007), clay mineral (Özt}urk and Kavak,2005), chelating resin (Kunin and Preuss, 1964), boron selectiveresins (Hicks et al., 1986; Tsuboi et al., 1990; Matsumoto et al.,

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1999), and solvent extraction (Hano et al., 1994; Matsumoto et al.,1997).

Borate ions have long been known to form complexes with asaccharide having co-planar cis-diol groups or polyhydroxy com-pounds (Cakmak and Römheld, 1997; Choi et al., 2001). Therefore,resins chemically modified by saccharides and insoluble supportmatrix cross-linked with polymer were proposed for the removalof dissolved boron (Hicks et al., 1986; Maeda et al., 1995; Matsum-oto et al., 1999). Polyvinyl alcohol (PVA) is one of the most typicalpolymers that can be cross-linked by various ions. Extensive stud-ies about a PVA/borate complex have been reported (Cheng andRodriguez, 1981; Ochiai et al., 1981; Shibayama et al., 1988; Koikeet al., 1995; Lin et al., 2000). However, the separation techniquesmay produce secondary waste because the support materials arenot always biodegradable. Large scale economical removal of bor-on from dilute solutions is also desirable as one method of boronremoval.

The application of KGM as a biodegradable material is proposedto recovery dissolved boron in this study. The KGM and its deriva-tives have been developed for uses in various fields such as phar-maceutical, biotechnological, and fine chemical areas (Nishinariet al., 1992; Zhang et al., 2005). Gao et al. (2008) reported the com-plexation between KGM and borax. KGM is a neutral polysaccha-ride isolated from the tubers of Amorphophallus konjac C. Koch. Itconsists of b-(1 ? 4) linked b-D-glucose and b-D-mannose units ina molar ratio of 1:1.6 (Kato and Matsuda, 1969; Maeda et al.,1980; Katsuraya et al., 2003). Bolanos et al. (2004) showed ascheme for the complexation between the cis-diol groups on themannose units of KGM and the borate ions. Two cis-diol pairs ofdifferent KGM molecules can be connected by a borate ion. Itwas also reported that divalent metal cations can form metal coor-dination complexes with a boron/saccharide (Yamauchi et al.,1986; O’Neill et al., 1996; Kobayashi et al., 1999). However, KGMis not able to recover dissolved boron because the boron/KGMcomplex is soluble in water.

In this study, the boron removal capacities of insoluble KGM geland the semi-gel coated surface by a hydrogel were examined un-der different pH values. Moreover, recovery from the boron ad-sorbed was examined by changing pH values. Boroncontamination is a widespread problem in agricultural and indus-trial wastewaters. Besides boron, many other kinds of metal ionsare commonly present in these waters. Therefore the effects ofmetals on boron removal by boron/diol group complex formationwere examined in the presence of AlCl3, CaCl2 and MgCl2.

2. Materials and methods

2.1. Materials

Pure KGM particles and PROPOL ISLB� were kindly supplied byShimizu Chemical Co., Hiroshima, Japan. The latter is a semi-gelcoated the surface only by hydrogel when placed in water.

2.2. Determination of boron and metals

The boron concentration was measured by the azometin Hmethod (Kluczka et al., 2007). Metals were measured by ICP–AES(Perkin-Elmer Optima 5300 DV) after pretreatment with 0.5 NHNO3 at the Center of Advanced Instrumental Analysis, KyushuUniversity.

2.3. Preparation of KGM gel

A 3% (w/v) solution of pure KGM was prepared in water. Aftermixing, Ca(OH)2 was added at 5% (w/w) of KGM into the KGM solu-

tion and mixed at room temperature for 1 h. The solution was thentransferred into a flat vessel. The vessel was kept in the water bathat 80 �C for 1 h. After cooling to room temperature, the KGM gelwas cut into a cube of 1 cm3. The gel was sufficiently rinsed in Mil-liQ water.

2.4. Removal of boron by KGM gel

The boron solutions were prepared at concentrations of 10 mgB/L, 50 mg B/L, 100 mg B/L, 500 mg B/L, and 1000 mg B/L. Each bor-on solution was adjusted to pH = 4, 9, or 11 by 1 N HCl or NaOH.The 100 cubes of the gel prepared as described in Section 2.3 wereadded to 300 ml of each solution. The 100 cubes of the gel containabout 3 g of KGM. From the preliminary examination, 4 h of incu-bation was enough time for the boron adsorption to reach equilib-rium. Therefore, the mixture was incubated at 20 �C for 4 h on anorbital shaker at 120 rpm for all experiments. After the incubation,the solution was centrifuged for 10 min at 3000 rpm and the boronconcentration in the supernatant was determined. The amount ofboron removed from each solution was calculated by comparingthe concentration of solution treated with the gel to the initial con-centration. All experiments were done in triplicate.

2.5. Removal of boron by KGM semi-gel

Boron solution was prepared under the same conditions as de-scribed for Section 2.4. A total of 15 g of the semi-gel powder wasadded to 300 ml of each solution. The mixture was incubated un-der the same conditions as described for Section 2.4. A 4 h incuba-tion was also enough time for adsorption equilibrium of boron bythe semi-gel. After the incubation, the solution was centrifuged for10 min at 3000 rpm. The boron concentration in the supernatantwas determined. The removed boron from each solution was calcu-lated as described for Section 2.4. All experiments were done intriplicate.

2.6. Effects of metals on boron removal by the KGM semi-gel

AlCl3, CaCl2 and MgCl2 were each added to 300 ml of 50 mg B/Lto give a metal/boron molar ratio of 10�2, 10�1 and 100. These solu-tions were adjusted to pH = 11 by 1 N NaOH. Then 15 g of the semi-gel powder was added to each solution. A reference solution wasprepared without these metals. After the incubation, the solutionwas centrifuged for 10 min at 3000 rpm and then the boron andmetal concentrations in the supernatant were determined.

2.7. Desorption of boron from the boron/KGM semi-gel complex

A total of 15 g of the semi-gel powder was added to 300 ml of50 mg B/L adjusted to pH = 11 by 1 N NaOH. The mixtures wereincubated under the same conditions as described in Section 2.4.After the incubation, a portion of the mixture was taken and theresidue was adjusted to pH = 9 or 4 with 1 N HCl. A sample wasimmediately taken and then the residue was incubated for 4 h.These samples were centrifuged for 10 min at 3000 rpm and theboron concentration in the supernatant was determined.

3. Results and discussion

3.1. Removal capacity of boron by the KGM gel and KGM semi-gel

The removal properties of the boron by the gel under the differ-ent concentrations of boron and pH values are shown in Fig. 1. Theremoval ratios of boron by the gel increased with increases in theinitial boron concentration at the same ratio independent of pH

Fig. 2. Boron removal abilities of glucomannan semi-gel at different pH values andboron concentrations.

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values. The complex formation between the boron and the diolgroup occur at a higher pH condition (Goldberg and Grieve,2003). These results indicate that the apparent decrease of boronin the mixture during the incubation is not due to adsorption tothe KGM molecule in the gel, but due to dilution by transformationof the boron into the gel matrix by simple diffusion. The 100 cubesof the gel prepared at Section 2.3 correspond to the addition ofwater of 100 cm3. Accordingly the transformation of boron intothe gel matrix indicates a so-called dilution effect.

On the other hand, the removal ratios of boron by the semi-gelincreased with increases in the initial concentration and pH values(Fig. 2). The difference between the gel and the semi-gel in terms ofthe boron removal capacity is due to the absence or the presence ofthe diol group in these gels. KGM has naturally large amounts ofdiol groups. The gelation of KGM solution by alkalis is attributedto the conformational transformation of KGM from an amorphousform to an ordered form (Maekaji, 1974, 1973). Accordingly, thegelation of KGM by alkaline treatment results in the loss of the diolgroups (Maekaji, 1974). Therefore, as shown in Figs. 1 and 2, thefree diol groups responsible for forming the complex with borondo not remain in the gel, but do in the semi-gel. Accordingly, thedecrease of boron in the mixture during the incubation is due toadsorption by the boron/KGM complex formation in the semi-gel.

The boron removal capacity of the semi-gel was the most effi-cient at pH = 11 (Fig. 2). Goldberg and Grieve (2003) also reportedthat the boron adsorption of maize cell walls increased withincreasing pH of solution in the range of 4.5–10. This is relatedto the species of boron at various pH values. Borax dissociates intoboric acid and monoborate ion and an acid-base equilibrium isestablished between boric acid and monoborate ions as shown inEqs. (1) and (2) (Sinton, 1987; Pezron et al., 1989)

B4O2�7 þ 7H2O! 2BðOHÞ3 þ 2BðOHÞ�4 ð1Þ

BðOHÞ3 þH2O �Ka

BðOHÞ�4 þHþ pKa ¼ 9:0� 9:2 ð2Þ

At pHs < 8, pH = 9, and pHs > 11, the following boron species arepresent: boric acid, boric acid: monoborate ion = 1:1, and monob-orate ion, respectively. To evaluate the effects of pH on the bor-on/KGM complex formation, the boron solution was adjusted topH = 4, 9, or 11 in this study. Only the boron species BðOHÞ�4 is suit-able for formation of a stable complex with a diol group. Therefore,a high pH value is a significant factor for boron removal by thesemi-gel.

3.2. Effects of metals on boron removal by the KGM semi-gel

The removal ratios of boron by the semi-gel in the absence andpresence of Al, Ca and Mg are shown in Fig. 3. The presence of these

Fig. 1. Boron removal abilities of glucomannan gelated completely at different pHvalues and boron concentrations.

metals slightly increased the boron removal. The difference amongthese metals was not significant. There are two possible explana-tions for the increase of boron removal in the presence of thesemetals. One is incorporation in the boron/KGM complex of a diva-lent and/or trivalent cation bridge. It is reported that boron/poly-saccharide complexes are stabilized by Ca bridges in plant cellwalls (Clarkson and Hanson, 1980; Kobayashi et al., 1999; Bolanoset al., 2004; O’Neill et al., 2004). The other is the co-precipitation ofboron and these metals by the formation of M[B(OH)4]2�2H2O. Bor-on and Ca reacts to form calcium diborate dehydrate as shown inEq. (3) (Simonov, 1979).

Ca2þ þ 2BðOHÞ02 þ 2OH� þ 2H2O! Ca½BðOHÞ4�2 � 2H2O ð3Þ

At higher pH values, Ca and Mg are also precipitated as Ca(OH)2

and Mg(OH)2, respectively. A portion of the boron may be co-pre-cipitated with these metals as shown at Eq. (3). The changes inconcentrations of Al, Ca, and Mg during incubation with thesemi-gel and boron solution containing each element were shownin Fig. 4. The Ca concentration was slightly increased in both caseswhich CaCl2 was added and no done after the incubation with thesemi-gel. Only Ca was detected in the reference solution. The con-centration was about 60 mg/L and corresponded to the concentra-tion increased during incubation in the presence of CaCl2 in Fig. 4.This was due to dissolution from the semi-gel surface. The surfaceof semi-gel is coated with hydrogel containing Ca(OH)2 to preventdissolution of the glucomannan in water. The Mg concentration de-creased during the incubation. The solubility of Mg(OH)2 in water

Fig. 3. Effects of Al, Ca, and Mg on boron removal by glucomannan semi-gel.

Fig. 4. Behaviors of Al, Ca and Mg in the boron removal process by glucomannansemi-gel in the presence of these metals.

Fig. 5. Desorption of boron adsorbed on glucomannan semi-gel by decrease of pHvalue.

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is about 200-fold less than that of Ca(OH)2. Therefore, Mg may beprecipitate as Mg(OH)2. The Al concentration was not changed dur-ing incubation with the semi-gel (Fig. 4). Al precipitates as Al(OH)3

from pH = 5–8 and is dissolved as AlðOHÞ�4 at pHs > 9. However, aslight increase of boron removal was observed by the addition ofAlCl3 at pH = 11 (Fig. 3). Therefore, the apparent boron removalin the presences of Al and Mg may not be also due to the adsorp-tion to KGM, but due to reaction with Ca dissolved from thesemi-gel.

3.3. Desorption of boron from the boron/KGM semi-gel complex

The boron adsorbed to the semi-gel at pH = 11 was rapidly des-orbed until each equilibrium concentration when pH was changefrom 11 to 9 or 4 (Fig. 5). The changing to pH = 4 completely des-orbed the boron adsorbed by the semi-gel (Fig. 5). The hysteresisbetween the adsorption and desorption of boron by change in pHwas not observed (Fig. 5). Therefore, the boron adsorbed thesemi-gel is easily able to be recovered by decreasing pH value.

4. Conclusions

The gel and the semi-gel produced with KGM were applied toremove dissolved boron. The former did not remove dissolved bor-on, because it was lost its diol groups by the gelation of KGM. Thelatter removed the boron because the diol groups remained partlyin the KGM molecules. The boron removal capacity of the semi-gel

increased with increasing pH values. It greatly increased atpHs P 11, when BðOHÞ�4 became the dominant species. The pres-ence of Al, Ca and Mg slightly increased the boron removal. Thiswas due to the reaction boron with Ca added and Ca dissolved fromthe semi-gel and not due to incorporation with the boron/diolgroup complex. The boron adsorbed to the semi-gel was easily des-orbed with a decrease of pH values. The hysteresis betweenadsorption and desorption of boron by pH changes was not ob-served. Biodegradable adsorbents such as KGM and its derivativesare useful for the recovery of boron from waters contaminatedwith boron and metals and possibly represent an environmentallysustainable application.

References

Blevins, D.G., Lukaszewski, K.M., 1998. Boron in plant structure and function. Annu.Rev. Plant Physiol. Plant Mol. Biol. 49, 481–500.

Bolanos, L., Lukaszewski, K., Bonilla, I., Blevins, D., 2004. Why boron? Plant Physiol.Biochem. 42 (11), 907–912.

Cakmak, I., Römheld, V., 1997. Boron deficiency-induced impairments of cellularfunctions in plants. Plant Soil 193, 71–83.

Cheng, A.T.Y., Rodriguez, F., 1981. Mechanical properties of borate crosslinked poly(vinyl alcohol) gels. J. Appl. Polym. Sci. 26, 3895–3908.

Choi, J.H., Kim, B.C., Blackwell, J., Lyoo, W.S., 2001. Phase behavior and physicalgelation of high molecular weight syndicotactic poly(vinyl alcohol) solution.Macromolecules 34, 2964–2972.

Choi, W., Chen, K.Y., 1979. Evaluation of boron removal by adsorption on solids.Environ. Sci. Technol. 13, 189–198.

Clarkson, D.T., Hanson, J.B., 1980. The mineral nutrition of higher plants. Annu. Rev.Plant Physiol. 31, 239–298.

Gao, S., Guo, J., Nishinari, K., 2008. Thermoreversible konjac glucomannan gelcrosslinked by borax. Carbohydr. Polym. 72, 315–325.

Goldberg, S., Grieve, C.M., 2003. Boron adsorption by maize cell wall. Plant Soil 251,137–142.

Hano, T., Matsumoto, M., Kokubo, S., Kai, H., Takita, Y., Kokubo, N., 1994.Development of an extraction system for the recovery of boric acid fromgeothermal waters. Solvent. Extr. Res. Dev. Jpn. 1, 146–153.

Hatcher, J.T., Bower, C.A., 1958. Equilbria and dynamics of boron adsorption by soils.Soil Sci. 85, 319–323.

Hicks, K.B., Simpson, G.L., Bradbury, A.G.W., 1986. Removal of boric acid and relatedcompounds from solutions of carbohydrate with a boron-selective resin (IRA-743). Carbohydr. Res. 147, 39–48.

Kato, K., Matsuda, K., 1969. Studies on the chemical structure of konjac mannan;Part I. Isolation and characterization of oligosaccharides from the partial acidhydrolyzate of the mannan. Agri. Biol. Chem. 33, 1446–1453.

Katsuraya, K., Okuyama, K., Hatanaka, K., Oshima, R., Sato, T., Matsuzaki, K., 2003.Constitution of konjacglucomannan: Chemical analysis and 13C NMRspectroscopy. Carbohydr. Polym. 53, 183–189.

Kluczka, J., Ciba, J., Trojanowska, J., Zolotajkin, M., Turek, M., Dydo, P., 2007. Removalof boron dissolved in water. Environ. Progress 26, 71–77.

Kobayashi, M., Nakagawa, H., Asaka, T., Matoh, T., 1999. Borate-rhamnogalacturonan II bonding reinforced by Ca2+ retains pecticpolysaccharides in higher-plant cell walls. Plant Physiol. 119, 199–203.

Koike, A., Nemoto, N., Inoue, T., Osaki, K., 1995. Dynamic light scattering anddynamic viscoelasticity of poly (vinyl alcohol) in aqueous borax solutions; 1.Concentration effect. Macromolecules 28, 2339–2344.

Kunin, R., Preuss, A.F., 1964. Characterization of a boron-specific ion exchange resin.Ind. Eng. Chem. Prod. Res. Dev. 3, 304–306.

Landolph, J.R., 1985. Cytotoxity and negligible genetoxity of borax and borax ore onvulture mammalian cells. Am. J. Ind. Med. 7, 31–43.

Lin, H.L., Yu, T.L., Cheng, C.H., 2000. Reentrant behavior of poly (vinyl alcohol)-boraxsemidilute aqueous solutions. Colloid Polym. Sci. 278, 187–194.

Maeda, M., Shimahara, H., Sugiyama, N., 1980. Detailed examination of thebranched structure of konjac glucomannan. Agr. Biol. Chem. 44, 245–252.

Maeda, H., Egawa, H., Jyo, A., 1995. Preparation of chelating resins selective to boricacid by functionalization of macroporous poly(glycidymethacrylate) with 2-amino-2 hydroxymethyl-1,3-propanediol. Sep. Sci. Technol. 30, 3545–3554.

Maekaji, K., 1973. Peptization of the gel of konjac mannan. Agr. Biol. Chem. 37, 433–2434.

Maekaji, K., 1974. The mechanism of gelation of konjac mannan. Agr. Biol. Chem. 38,315–321.

Matoh, T., Ishigaki, K., Mizutani, M., Matsunaga, W., Takabe, K., 1992. Boronnutrition of cultured tobacco BY-2 Cell. I Requirement for and intracellularlocalization of boron and selection of cells that tolerate low levels of boron.Plant Cell Physiol. 33, 1135–1141.

Matoh, T., Kobayashi, M., 1998. Boron and calcium, essential inorganic constituentsof picnic polysaccharides in higher plant cell walls. J. Plant Res. 111, 179–190.

Matsumoto, M., Kondo, K., Hirata, M., Kokubo, S., Hano, T., Takada, T., 1997.Recovery of boric acid from wastewater by solvent extraction. Sep. Sci. Technol.32, 983–991.

306 K. Oishi, Y. Maehata / Chemosphere 91 (2013) 302–306

Matsumoto, M., Matsui, T., Kondo, K., 1999. Adsorption mechanism of boric acid onchitosan modified by saccharides. J. Chem. Eng. Jpn. 32, 190–196.

Moseman, R.F., 1994. Chemical disposition of boron in animals and humans.Environ. Health Perspect. 102, 113–117.

Naghii, M.R., Samman, S., 1996. The effect of boron supplementation on thedistribution of boron in selected tissues and on testosterone synthesis in rats. J.Nutr. Biochem. 7, 507–512.

Nielsen, F.H., Hunt, C.D., Mullen, L.M., Hunt, J.R., 1987. Effect of dietary boron onmineral, estrogen, and testosterone metabolism in postmenopausal women.The FASEB J. 1, 394–397.

Nishinari, K., Williams, P.A., Phillips, G.O., 1992. Review of the physic-chemicalcharacteristics and properties of konjac mannan. Food Hydrocolloids 6, 199–222.

Nobel, R., Banuelso, G.S., Paull, J.G., 1997. Boron toxicity. Plant Soil 193, 181–198.Ochiai, H., Shimizu, S., Tadokoro, Y., Murakami, I., 1981. Complex formation

between poly (vinyl alcohol) and borate ion. Polymer 22, 1456–1458.O’Neill, M.A., Warrenfeltz, D., Kates, K., Pellerin, P., Doco, T., Darvill, A.G.,

Albersheim, P., 1996. Rhamnogalacturonan-II, a pectic polysaccharide in thewalls of growing plant cell, forms a dimer that is covalently cross-linked by aborate ester. In vitro conditions for the formation and hydrolysis of the dimer. J.Biol. Chem. 271, 22923–22930.

O’Neill, M.A., Ishii, N., Albersheim, P., Darvill, A.G., 2004. Rhamnogalacturonan-II;Structure and function of a borate cross-linked cell wall pectic polysaccharide.Annu. Rev. Plant Biol. 55, 109–139.

Özt}urk, N., Kavak, D., 2005. Adsorption of boron from aqueous solutions using flyash: Bach and column studied. J. Hazard. Mater. 127, 81–88.

Pezron, B., Leibler, L., Ricard, A., Lafuma, F., Audebert, R., 1989. Complex formation inpolymer-ion solution.1. Polymer concentration effects. Macromolecules 22,1169–1174.

Pongsavee, M., 2009. Genotoxic effects of borax on cultured lymphocytes. SoutheastAsian J. Trop. Med. Public Health 40, 411–418.

Shibayama, M., Sato, M., Kimura, Y., Fijiwara, H., Nomura, S., 1988. 11B n.m.r. studyon the reaction of poly (vinyl alcohol) with boric acid. Polymer 29, 336–340.

Simonov, M.A., 1979. The new mineral hexahydroborite, Ca[B(OH)4]2�2H2O. Inter.Geology Rev. 21, 491–496.

Sinton, S.W., 1987. Complextion chemistry of sodium borate with poly(vinylalcohol) and small diols: A boron-11 NMR study. Macromolecules 20, 2430–2441.

Sylvain, I.C., Berry, J.P., Galle, P., 1998. Ultranstructural apoptotic lesions induced inrad thymocytes after borax ingestion. Anticancer Res. 18, 2455–2461.

Tsuboi, I., Kunugita, E., Komasawa, I., 1990. Recovery and purification of boron fromcoal fly ash. J. Chem. Eng. Jpn. 23, 480–485.

Yamauchi, T., Hara, T., Sonoda, Y., 1986. Distribution of calcium and boron in thepectin fraction of tomato leaf cell wall. Plant Cell Physiol. 27, 729–732.

Yilmaz, A.E., Boncukcuoglu, R., Kocakerim, M.M., Keskinler, B., 2005. Theinvestigation of parameters affecting boron removal by electrocoagulationmethod. J. Hazard. Mater. 125, 160–165.

Zhang, Y., Xie, B., Gan, X., 2005. Advance in the applications of konjac glucomannanand its derivatives. Carbohydr. Polym. 60, 27–31.

Weir, R.J., Fisher, R.S., 1972. Toxicologic studies on borax and boric acid. Toxicol.Appl. Pharmacol. 23, 351–364.

Wester, R.C., Hui, X., Hartway, T., Maibach, H.I., Bell, K., Schell, M.I., Northington, D.J.,Strong, P., Culver, B.D., 1998. In vivo percutaneous absorption of boric acid,borax and disodium octaborate tetrahydrate in humans compared to in vitroabsorption in human skin from infinite and finite doses. Toxicol. Sci. 45, 42–51.