Organic acid-induced release of lead from pyromorphite and its ...

F. Debela et al. / Chemosphere 80 (2010) 450–456 455tion water use, respectively) (CCME, 2005; Federal-Provincial-TerritorialCommittee on Drinking, 2008; WHO, 2008). For example,Pb released by 100 lM oxalic acid (17.6 lM Pb) > 350 times theCanadian standard for drinking water while the Pb released in50 lM acetic acid >40 times more. Soluble Pb in 50 lM mixed acidsolution was above the Canadian drinking water quality standardby a factor of at least 250.Other environmental concerns include potential P efflux togroundwater and eutrophication of water bodies because the Padded to form PY far exceeds amounts typically used for agriculturalpurposes (Singh et al., 2001; Chen et al., 2003; Pierzynskiand Gehl, 2004). The amounts of P released in the LMWOA solutionsare much higher compared to mQ water and may potentiallycontribute to eutrophication. However, the high P released in theLMWOA solution may benefit organisms in Pb-contaminated soilsbecause P is one of the three major elements needed by plants andsoil organisms along with N and K.Although Pb and P are released from PY reactions with LMWOA,the environmental fate of liberated Pb and P is subject to other processesin soils. Soluble Pb and P can adsorb on soil colloids (e.g.,negative and positive-charged soil organic matter) as well aschemisorb on the surface of oxides and oxyhydroxides. Researcheshave shown that PY formation in soil can be inhibited by the presenceof dissolved organic carbon (Lang and Kaupenjohann, 2003)and organic matter (Hashimoto et al., 2009) through organo-metalcomplex formation. It can be argued that even if LMWOA results inhigher release of Pb and P from PY, the fate of liberated Pb and Pfaces many complex processes (e.g., organo-metal complex formation)before they become bioavailable. In other words, the dissolutionof PY in natural soil systems and particularly in rhizospheresoil is much more complex than it is presented in a batch dissolutionexperiment, and therefore, our results are limited to just fewaspects of many complex processes in the environment.5. ConclusionsWe conclude that LMWOA are able to release more Pb from PYthan mQ water alone. One should be aware that under natural soilconditions, more dissolution of PY could be expected because severalLMWOA may occur in combination with many more acids(e.g., aromatic acids such as benzoic, p-hydroxybenzoic and protocatechuic)which have not been studied here. These acids may havehigher dissociation constants and may result in much higher levelsof soluble Pb 2+ released from PY than the LMWOA investigated inthis study. On the other hand, because of the incomplete understandingof the nature of soluble Pb (and P) and interaction withcomplex solid phases, care should be taken in the interpretationsof our results to assess the use of P amendment in remediationPb-contaminated soils.AcknowledgementsThis research was supported by the Canada Research Chair Programand the Natural Sciences and Engineering Research Council ofCanada. We would like to thank A. Esler and Q. Wu for their assistancein ICP analyses.ReferenceAdriano, D.C., 2001. Trace Elements in Terrestrial Environments: Biogeochemistry,Bioavailability, and Risks of Metals, second ed. Springer-Verlag, New York.Adriano, D.C., Wenzel, W.W., Vangronsveld, J., Bolan, N.S., 2004. Role of assistednatural remediation in environmental cleanup. Geodrema 122, 121–142.Banfield, J.F., Baker, W.W., Welch, S.A., Taunton, A., 1999. Biological impact onmineral dissolution: application of the lichen model to understanding mineralweathering in the rhizosphere. Proc. Natl. Acad. Sci. USA 96, 3404–3411.Cao, X., Ma, L.Q., Chen, M., Singh, S.P., Harris, W.G., 2002. Impacts of phosphateamendments on lead biogeochemistry at a contaminated site. Environ. Sci.Technol. 36, 5296–5304.CCME (Canadian Council of Ministers of the Environment), 2005. Canadian WaterQuality Guidelines for the Protection of Agricultural Water Uses: SummaryTable (updated October 2005). Canadian Council of Ministers of theEnvironment, Winnipeg.CEPA (Canadian Environmental Protection Agency), 1999. Canadian EnvironmentalProtection Act, 1999. Minister of Justice (accessed 1.02.10).Chen, M., Ma, L.Q., Singh, S.P., Cao, R.X., Melamed, R., 2003. Field demonstration ofin situ immobilization of soil Pb using P amendments. Adv. Environ. Res. 8, 93–102.Chrysochoou, M., Dermatas, D., Grubb, D.G., 2007. Phosphate application to firingrange soils for Pb immobilization: the unclear role of phosphate. J. Hazard.Mater. 144, 1–14.Dinkelaker, B., Romheld, V., Marschner, H., 1989. Citric acid excretion andprecipitation of calcium citrate in rhizosphere of white lupin (Lupins albus L.).Plant, Cell Environ. 12, 285–292.Drever, J.I., Stillings, L.L., 1997. The role of organic acids in mineral weathering.Colloids Surf., A 120, 167–181.Environment Canada, 2002. Children’s Environmental Heath. Envirozine(Environment Canada’s On-line Newsmagazine) Issue 20, Feature 2. (accessed 1.02.10).Federal-Provincial-Territorial Committee on Drinking Water, 2008. Guidelines forCanadian Drinking Water Quality Summary Table. Federal-Provincial-TerritorialCommittee on Health and the Environment. (accessed1.02.10).Fomina, M.A., Alexander, I.J., Hillier, S., Gadd, G.M., 2004. Zinc phosphate andpyromorphite solubilization by soil plant-symbiotic fungi. Geomicrobiol. J. 21,351–366.Fomina, M., Hillier, S., Charnock, J.M., Melville, K., Alexander, I.J., Gadd, G.M., 2005.Role of oxalic acid overexcretion in transformations of toxic metal minerals byBeauveria caledonica. Appl. Environ. Microbiol. 71, 371–381.Fox, T.R., Comerford, N.B., 1990. Low-molecular-weight organic acids in selectedforest soils of the southeastern USA. Soil Sci. Soc. Am. J. 54, 1139–1144.Gadd, G.M., 2004. Microbial influence on metal mobility and application forbioremediation. Geoderma 122, 109–119.Hashimoto, Y.M., Takaoka, M., Oshita, K., Tanida, H., 2009. Incompletetransformations of Pb to pyromorphite by phosphate-induced immobilizationinvestigated by X-ray absorption fine structure (XAFS) spectroscopy.Chemosphere 76, 616–622.Hettiarachchi, G.M., Pierzynski, G.M., Ransom, M.D., 2001. In situ stabilization of soillead using phosphorous. J. Environ. Qual. 30, 1214–1221.Jarosz-Wilkolazka, A., Gadd, G.F., 2003. Oxalate production by wood-rotting fungigrowing in toxic metal-amended medium. Chemosphere 52, 541–547.JCPDS-ICDD, 2001. PDF-2 Data Base (Sets 1-51 plus 70-89) JCPDS – InternationalCentre for Diffraction Data. Newtown Square, PA.Jones, D.L., 1998. Organic acids in the rhizosphere – a critical review. Plant Soil 205,25–44.Jones, D.L., Dennis, P.G., Owen, A.G., van Hees, P.A.W., 2003. Organic acid behavior insoils-misconceptions and knowledge gaps. Plant Soil 248, 31–41.Lang, F., Kaupenjohann, M., 2003. Effect of dissolved organic matter on precipitationand mobility of the lead compound chloropyromorphite in solution. Eur. J. SoilSci. 54, 139–148.Lindsay, W.L., 2001. Chemical Equilibria in Soils, second ed. The Blackburn Press,New Jersey.Ma, L.Q., 1996. Factors influencing the effectiveness and stability of aqueous leadimmobilization by hydroxyapatite. J. Environ. Qual. 25, 1420–1429.McBride, M.B., 1994. Environmental Chemistry of Soils. Oxford University Press,New York.Melamed, R., Cao, X., Chen, M., Ma, L.Q., 2003. Field assessment of leadimmobilization in a contaminated soil after phosphate application. Sci. TotalEnviron. 305, 117–127.Nriagu, J.O., 1973. Lead orthophosphates-II. Stability of chloropyromorphite at 25 C.Geochim. Coscmochim. Acta 37, 367–377.Pierzynski, G.M., Gehl, K.A., 2004. An alternative method for remediating leadcontaminatedsoils in residential areas: a decision case study. J. Nat. Resour. LifeSci. Ed. 33, 63–69.Robarge, W.P., 1999. Precipitation/dissolution reactions in soils. In: Sparks, D. (Ed.),Soil Physical Chemistry. CRC Press, Boca Raton, pp. 193–238.Ryan, P.R., Delhaize, E., Jones, D.L., 2001. Function and mechanism of organic anionexudation from plant roots. Annu. Rev. Plant Physiol. Plant Mol. Biol. 52, 527–560.Ryan, J.A., Scheckel, K.G., Berti, W.R., Brown, S.L., Casteel, S.W., Chaney, R.L.,Hallfrisch, J., Doolan, M., Grevatt, P., Maddaloni, M., Mosby, D., 2004. Reducingchildren’s risk from lead in soil. Environ. Sci. Technol. 38, 19A–24A.Sayer, J.A., Cotter-Howells, J.D., Watson, C., Hillier, S., Gadd, G.M., 1999. Leadmineral transformation by fungi. Curr. Biol. 9, 691–694.Scheckel, K.G., Ryan, J.A., 2002. Effects of aging and pH on dissolution kinetics andstability of chloropyromorphite. Environ. Sci. Technol. 36, 2198–2204.Scheckel, K.G., Ryan, J.A., 2003. In vitro formation of pyromorphite via reaction of Pbsources with soft-drink phosphoric acid. Sci. Total Environ. 302, 253–265.Shen, Y., Strom, L., Jonson, J., Tyler, G., 1996. Low-molecular organic acids in therhizosphere soil solution of beech forest (Fagus sylvatica L.) Cambisols