Biogeochemistry of Environmentally Important Trace Elements

Chapter 10

Volatilization of Metals from a Landfill Site Generation and Immobilization of Volatile Species of Tin, Antimony, Bismuth, Mercury, Arsenic, and Tellurium on a Municipal Waste Deposit in Delta, British Columbia

Downloaded by CORNELL UNIV on May 21, 2017 | http://pubs.acs.org Publication Date: October 30, 2002 | doi: 10.1021/bk-2003-0835.ch010

Jörg Feldmann Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen, AB24 3UE Scotland, United Kingdom

In a landfill environment, many mainly main group elements, form volatile organometallic compounds (VMCs). This chapter focuses on the speciation of volatile metal compounds generated in a municipal waste deposit in Delta British Columbia, Canada. Mostly permethylated compounds of Sn, Bi, As, Sb, Se, Hg, and Te have been identified. When landfill gases percolated through the water column of a wetland, water -solublepolar organometallic compounds were identified in the water column as the degradation products of the volatile metal compounds. However, this effect is only marginal since the concentration of the volatile metal compounds above the wetland is not significantly different from the landfill gases in the gas wells in which landfill gas is collected. Stability tests on 12 different volatile species of arsenic, tin and antimony suggests that these compounds have an atmospheric half life, which allows them to volatilize from landfill sites and disperse in their vicinities.

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© 2003 American Chemical Society Cai and Braids; Biogeochemistry of Environmentally Important Trace Elements ACS Symposium Series; American Chemical Society: Washington, DC, 2002.


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In the biogeochemical cycle of heavy metals solubilization, sequestering and mobilization are key issues. Volatilization of metals is of importance when high temperature processes are considered. For example, volcanic exhalations or industrial processes such as waste incineration are significant sources of heavy elements. The most prominent element in this category is mercury as Hg°. Information about the volatilization process of heavy elements at ambient temperature i.e. 0-40°C is scarce since only a limited number of elements can form rather stable compounds which have a significant vapor pressure in this temperature range. A list of compounds with their boiling points is shown in Table I. Some of the listed volatile element species have been identified, and even quantified, in field studies to occur in the environment while others have been identified as volatile metabolites from pure bacteria and fungi cultures in laboratory experiments. The list is by far not complete. Biotransformation of TBT to DBT, MBT and eventually to inorganic tin is well accepted. However, only a few reports describe the occurrence of methylated butyltin compounds which point to biomethylation of the anthropogenic butylated tin compounds (/). Donard and coworkers (2) have reported the generation of methylated butyltins in polluted sediments in South west France. Although sediments are very good sinks for TBT, MeBu Sn has a significantly lower affinity to this phase (/). It could easily be released to the water column and consequently due to the high lipophilicity released to the atmosphere. Other studies have determined the generation of Me Hg in the mudflats of the heavy polluted River Elbe in northern Germany (3). Many volatile iodine compounds are known to be generated from marine macroalgae. Laturnus et ai (4) have shown that not only methyl-iodine but also ethyl-iodine, in addition to CH C1-I, CH2I2 » could be detected in the environment. Hansen et al (5) reported on a constructed wetland which was purpose-built to clean-up refinery process water containing 20-30 ug L' selenium. They have found that 10-30 % of the selenium was volatilized presumably as Me Se. The maximum flux was measured to be 190 μg of Se m" day" . We have found that arsenic and antimony have been generated by algal mats of geothermal waters in southern British Columbia (6). The water contained up to 300 μg L" arsenic and only 2 μgL" antimony, but a direct sampling of the algal mats using a flux chamber demonstrated that AsH , MeAsH , Me As and Me Sb were also generated from the algal mats. The number of field studies is however very limited and often restricted to special environments which are mostly anaerobic. One reason for this is that the volatile compounds are not persistent so they do not show significant concentrations in the atmosphere. In particular landfill gas contain many different VMCs. The aim of this paper is to show how volatile metal compounds, generated in a municipal waste deposit, react when they reach the landfill surface. Is a landfill site a significant source of volatile metal compounds or are these compounds too reactive to be volatilized into the atmosphere? 3

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Cai and Braids; Biogeochemistry of Environmentally Important Trace Elements ACS Symposium Series; American Chemical Society: Washington, DC, 2002.

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Table I: List of volatile compounds with their boiling points identified in the environment or in microorganism cultures in the laboratory Element

bp (°Q -55

Source (ind/bio) Industry

Field/Laboratory Reference

7 Reduced (electrolysis) LG, SG, HS Anaerobic (F/L) 6,8 MeAsH Anaerobic (F/L) 6 2 SG, HS Me AsH 36 6,8 Anaerobic (F/L) LG, SG, HS Me As Anaerobic, (F/L) 8 50 LG, SG, HS Aerobic (L) 9 Sb SbH 8 Anaerobic (F) -17 LG, SG Me Sb Anaerobic (F,L) 10,JJ 81 LG, SG, HS 12 Aerobic (L) Bi Me Bi Anaerobic (F,L) 13 109 LG, SG Sn Me SnH 14 Aerobic (L) 35 Me Sn Anaerobic 10, 11,15 78 LG, SG Bu SnMe Anaerobic (F,L) 1,2 Sediment Te Me Te Anerobic (F,L) 8, 11 83 LG, SG Se 8, 11 Me Se Anaerobic (F,L) 56 LG, SG Aerobic (F,L) 5 WL Aerobic (F,L) 3 Hg° Hg Me Hg 91 LG, SG Anaerobic (F) 8,3 Pb Me Pb Anaerobic (F) 16 100 LG,SG 16 Me PbEt Anaerobic (F) SG 16 Me PbEt Anaerobic (F) SG 16 Anaerobic (F) MePbEt SG, LG 16 Anaerobic (F) PbEt 200 SG, LG Ni Ni(CO) 17 Anaerobic (F) SG Mo Mo(CO) Anaerobic (F) 18 LG, SG W W(CO) Anaerobic (F) 18 LG, SG F field identification, L laboratory culture experiment, HS algal mats in hot springs, SG sewage gas, LG landfill gas, WL wetlands As


Species AsH

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Experimental Section This report will give some data on the process of volatilization on one particular municipal waste deposit in British Columbia (Delta, British Columbia). This site was still in operation in 1997, but older parts were already overgrown and due to the strong solidification through truck driving and the high annual precipitation level of the west coast of Canada, wetlands have been formed. Mainly municipal and similar industrial waste from Greater Vancouver was dumped here. Even when gas is pumped out of the landfill, some gas can easily reach the surface of the landfill after migration through the waste and soil. The gas that migrated through the landfill was visibly bubbling through the water of the wetland. A rich vegetation of typical wetland plants were growing in the water with a depth was about 30-50 cm.

Sampling and location

Gas samples Gas samples were taken directlyfromthe gas wells in which the landfill gas is collected and transported to the furnace. The gases in the gas wells were sampled directly into Tedlar bags by using a membrane pump (AirPro 6000D, Bios Instrument Corp., NJ). In addition gases which bubbled through the water of an overlying wetland on the landfill site was sampled by using afluxchamber, which was floating on the water surface. Basically the gas was collected under this device and pumped directly into the Tedlar bags. The flow rate was adjusted to 1 L min* . Five samples each (gas well and from different gas spurts on the wetland) were taken. The Tedlar bags were transported in black bags to the laboratory in order to prevent U V radiation destabilizing the VMCs. 1

Water samples The water of the wetland was also sampled into air-tight glass containers and subject to hydride generation methodology in order to identify degradation products of the volatile organometallic compounds, which percolated through the water. The samples (10 mL) were purged with helium (133 mL min" ) and cryotrapped (6 min) prior to the addition of 1 mL 6 % aqueous NaBH solution after acidification with 1 mL 1 M HC1. In order to distinguish between tri valent and pentavalent arsenic compound a second run used instead HC1 an ammonium 1

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132 acetate buffer. The volatile metal compounds generated were also cryotrapped and analyzed in the same way as the gas samples. No attempt was made to quantify how much of the VMCs are immobilized since it is not known how much gas has been percolated through this water. The emphasis was on the identification of methylated metal species in the water and their ratios. The intensities can directly be compared since the response of the ICP-MS is very similar for the individual species of one element.


Stability tests In order to test how stable the volatile metal compounds (VMCs) are in an oxic atmosphere, 12 different compounds were chosen to test in air at temperatures 20 and 50°C in the dark (5 replicates were made). The experimental set-up is described more thoroughly elsewhere (19). Briefly, SnH , Me SnH , Me SnH, BuSnH , SbH , MeSbH , Me SbH, Me Sb, AsH , MeAsH , Me AsH, Me As were generated using the appropriate involatile metal solutions and employing hydride generation methodology to generate the hydrides. The hydrides were purged by synthetic air into a 4 L Tedlar bag equipped with a septum. In addition the same set-up was done to test the influence of UV light. An ordinary UV lamp was placed so that the gas samples were exposed to approximately 5000 Lux and the temperature of 30°C. 50 mL were sampled from the gas standards and injected directly onto the U-trap, prior to GC-ICP-MS analyses. The gas standards stored in the dark were sampledfirston a daily basis for thefirstweek and then on a logarithmic time scale up to 6 months, while the standards exposed to UV light were sampled on an hourly basis. Most of the VMCs follow afirstor pseudo second order kinetic, but the study of the kinetics will be published in the near future (20). 4

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Analytical Procedure

The gas samples were analyzed within 24 hours by cryogenic trapping at 80°C using a packed column system filled with non-polar, chromatographic material (SP-2100 on Supelcoport). The trapped gases were deliberated and defocused on a second cryotrap with the same size and material as the previous one (length 22 cm, 6 mm diameter). The packed column was connected online to an ICP-MS (Plasmaquad PQ2+). Helium was used as a carrier gas (133 mL min" ') and mixed with 0.9 L min" nebulizer gas (Ar). This is thoroughly described elsewhere (J8). At this point the author takes the opportunity to thank Prof. W. R. Cullen for his permission to conduct this part of the study in his laboratory at UBC. A semi-quantitative method (21) was used to quantify the volatile metal 1


133 compounds in the gases. The intensities measured were normalized to the internal standard (10 ng L" Rh solution nebulized and mixed with the GC gas stream before entering the injector of the plasma torch of the ICP-MS). The analytical method used for the stability tests was slightly altered; instead of a packed column GC as described before, a capillary GC (CP-Sil 5CB Ultimetal capillary, 25 m χ 0.53 mm, i.d., d=l urn) was used along with a conventional GC (GC95 Ai Cambridge Ltd) and coupled to an ICP-MS (Spectromass 2000), which is also described in more detail elsewhere (19). 1


Results and Discussion The landfill gases which percolate through the wetland water contain numerous volatile metal species as shown in Table II. For mercury, Hg° was the main compound besides minor amounts of Me Hg. Me As and Me Sb dominate the element spectrum for arsenic and antimony, whereas for tin more than five different species have been identified with Me Sn being the main tin species. Other studies in which capillary GC was used more than eight different tin species have been recorded (22). The nature of the other tin species are still not very clear. Although we have identified the compound labeled U2 as Me SnEt (75), there are some indications for the occurrence of methylated butyltin species in landfill gases (Me Bu Sn, MeBu Sn) (23). Apartfromtin an ethylated arsenic compound Me AsEt was also identified. This is not unexpected since earlier results from a German landfill site have shown the occurrence of a late eluting peak with the an estimated boiling point of 87°C, the very same as the Me AsEt (10). Further, Me Te, Me Se and Me Bi have been recorded in addition to industrial Et Pb and small amounts of MeEt Pb. Relatively pure Et Pb was typically used in North America, but it cannot be excluded that small amounts of mixed ethyl-methyl lead have occurred in gasoline, which was eventually dumped on the landfill. In contrast, we have shown previously (8,16), that the main volatile lead compound in sewage gas from a sewage sludge fermentor in Germany was MeEt Pb. Although this points to the biomethylation of organolead by methanogenic compounds in a fermentor (tetraethyl lead gets de-ethylated and then eventually methylated), it is not unequivocal that a methylation of organolead takes place in this landfill site. All compounds have been identified by standard-addition with appropriate VMC standards. In addition Me Sn, Me Sb and Me Bi have been identified by the 2 dimensional GC-EI-MS (75). In addition to the gas samples, water samples were analyzed for the watersoluble degradation products of the VMCs. Hydride generation can volatilize most of the ionic organometallic species. Since the metal carbon bond is, for most compounds, robust enough to preserve the nature of the organometallic compound after hydride generation. The soluble metal species, which were 2

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Table II: Relative abundance of volatile metal species in landfill gas percolating through the water and their water-soluble degradation products in the water phase of the wetland. Element Gas sample VMCs As AsH MeAsH Me AsH Me As(III) Me AsEt Èb Me Sb(IIl) Sb (Ul)


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species 4.1 15.8 6.4 67.8 5.9 >98 2

Water sample Reaction % before HG species Oxidation and As(IIW) 48.3 1.1 limited MeAsO(OH) Me AsO(OH) 0.5 demethylation Me AsO 50.1 a

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Oxidation and Sb(IIW) 3.1 MeSbO(OH) 14.6 demethylation 40.8 Me SbO(OH) 41.5 Me SbO Sn Me Sn 87.8 Sn 16.4 Sn (Ul) Demethylation 4.7 MeSn 1.6 Sn (U2) 2.8 Me Sn 5.9 Sn (U3) 61.7 Debutylation ? 3.0 Me Sn Sn (U4) 1.7 Me Sn 3.8 BuSn 8.1 Bu Sn 2.5 Bi Me Bi Demethylation 97.1 100 Bi 2.9 MeBi Hg° Demethylation 95.7 39.8 Hg Hg Me Hg 4.3 Hg(Ul) 12.9 and Oxidation MeHg 39.8 Se Me Se 100 Me Se 100 Te Me Te 100 100 Me Te Pb Et PbMe 3.0 N.D. Et Pb 97 N.D. Mo Mo(CO) 100 N.D. W W(CO) 100 N.D. Sn (U1-U4): all R^n, Sb (Ul): unknown, N.D. not determined, HG hydride generation at pH 1, species show up as their hydrides so that the acid and oxide forms are only assumed. 3

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volatilized using the above-mentioned method and their relative amounts, are compared to the species identified in the gas samples (Table II) \ Figure 1 shows two examples for the element-specific detection (As and Sb) of volatile species in landfill gas and species, which were generated by hydride generation of the water samples. It can be seen that the volatile species are not the species dissolved in the water; thus transformation processes alter the species. In particular, oxidation and demethylation takes place when the volatile metal compounds percolate through the water column of the wetland. Interestingly, the different elements follow different reaction schemes: Me As tends to be oxidized to the pentavalent Me AsO which is soluble in water, while Me Sn is demethylated to Me Sn . The large amount of inorganic arsenic can be explained by the occurrence of large amount of arsine, which is not sufficiently trapped with the used method, so that the contribution of AsH is underestimated. Me Sb is oxidized from trivalent to pentavalent (Me SbO) but also to a much higher degree as arsenic demethylated. Thus, substantially more pentavalent dimethylated and monomethylated antimony compounds (e.g., Me SbO(OH, MeSbO(OH) ) occur in the water phase. Me Sn and other tetraalkyltin compounds are immobilized by demethylation or dealkylation. The Me Sn is more polar and therefore more water-soluble. Me Bi is completely demethylated to mostly inorganic bismuth. However, it should be noted that the hydride generations have not been sufficiently tested to conclude that only a minority of MeBi species had been in the water, since it is not known how ionic MeBi species react under the harsh condition for hydride generation. Mercury is immobilized by the demethylation of Me Hg to MeHg and by oxidation of Hg° to Hg . For selenium and tellurium compounds, the same compounds were detected in the gas sample as in the water after hydride generation. However, due to lack of knowledge about the behavior of these organometallic compounds using hydride generation, it can only be suggested that tellurium and selenium are maybe oxidized to their tetravalent forms. In general, oxidation can immobilize those metals, which can occur in the higher oxidation state, so that no M-C bonds have to be cleaved in order to form more polar organometallic compounds, while elements such as Sn or Hg have to be demethylated before a polar water-soluble compound can be formed. It is not known which proportion of VMCs are indeed immobilized by the reaction in the water phase. However a comparison of the gas, which percolated through the water-column, can be compared to the gas transported in the gas 3

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The water was also subject to hydride generation at neutral pH. Approximately 40% of the inorganic arsenic occurs as As(III), whereas most of the methylated species occur in their pentavalent forms as MeAsO(OH) and Me AsO(OH). 2

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Figure 1: GC-ICP-MS chromatograms of arsenic and antimony compounds in landfill gas and in the water after hydride generation.



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wells (see Figure 2). It can be seen that most compounds are in the same order of magnitude so that the immobilzation process by the water is not significant. This is unexpected in particular for those species which are known to be hydrolyzed and oxidized very quickly (e.g., MesBi). The reaction time in the water column is probably too short which enables the VMCs to reach the atmosphere in the bubbles without having contact with the water. Since no significant changes in the gas concentration of the gas in the wells, and that which percolated through the water have been determined, it can be concluded that volatile metal compounds generated in municipal waste deposits are released into the atmosphere. When those VMCs reach the atmosphere, how stable are they? Can they be transported over vast distances? We have determined the atmospheric half-life of twelve different volatile arsenic, antimony and tin compounds in air at a concentration of 10 μg m" , which can be seen in Figure 3 (19). The atmospheric half-life can be measured in hours and for some even in days rather than in seconds as suggested elsewhere (24), because of the low concentration of the compounds in the air. It should be noted that UV radiation has an enormous impact on the stability of these compounds in the atmosphere while the temperature effect is much smaller. 3

Conclusion In can be concluded that municipal waste deposits are significant sources of metal volatilization. Although this paper shows only data from one municipal waste deposit, it has been shown that landfill gas from other sites contain similar concentrations of VMCs. The generated VMCs are stable enough to diffuse through soil, waste and the overlying oxic water column of a wetland and can reach the atmosphere illustrated in Figure 4. Although degradation products of the VMCs have been identified in the water column, this "immobilization" seemed to have no significant effect on the flux out in the atmosphere. According to the estimated atmospheric half-life of VMCs, once in the atmosphere they are stable enough to dispersefromthe landfill site into the near vicinity. This might have toxicological implications. Since very limited knowledge is available about the toxicity of these compounds in very low concentrations, future studies are necessary to assess the chronic effects of VMCs to mammals.



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Figure 2: Comparison of volatile metal compounds in landfill gas sampled in the gas wells and above the wetland through which the gas percolated.

Figure 3 .Estimated atmospheric half-life ofselected volatile arsenic, antimony and tin compounds (each JO pm' ) measured in a synthetic air atmosphere at 20 and 50°C in the dark and at 3(fC with UV radiation (5000 Lux) (20). 3



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Figure 4. Percolation of landfill gas through the landfill sites and the overlaying wetland with the indication of the predominant species in each compartment.


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References 1. Vella, A.J.; Adami, J. P. T. Appl.Organomet.Chem. 2001, 15, 901-906. 2. Amouroux, D.; Tessier, E.; Donard, O. F. X. Environ. Sci. Technol. 2000, 34, 988-995. 3. Wallschläger, D.; Hintelmann, D.; Evans, R.D.; et al., Water Air Soil Poll. 1995, 80, 1325-1329. 4. Laturnus, F. Environ. Sci.Poll.Res. 2001, 8 103-108. 5. Hansen, D.; Duda, P. J.; Zayed, Α.; Terry, N. Environ. Sci. Technol. 1998, 32, 591-597. 6. Hirner, Α. V.; Feldmann, J.; Krupp, E.; Grümping, R.; Goguel, R.; Cullen, W. R. Org. Geochem. 1998, 29, 1765-1778. 7. Pedersen, B. Ann. Occup. Hyg. 1988, 32, 385-397. 8. Feldmann, J.; Hirner, A.V. Intern. J. Environ. Anal. Chem. 1995, 60, 339359. 9. Challenger, F. Chem. Rev. 1945, 36, 315-345. 10. Feldmann, J.; Grümping, R.; Himer, Α. V. Fresenius J. Anal. Chem. 1994, 350, 228-234. 11. Feldmann, J.; Haas, K.; Naëls, L.; Wehmeier, S. In Plasma Source Mass Spectrometry, Holland, G., Tanner, S.D., Eds.; Royal Society of Chemistry Proceedings, RSC, London, UK 2001; pp. 361-368. 12. Andrewes, P.; Cullen, W.R.; Feldmann, J.; Koch, I.; Polishchuk, E.; Reimer, K.J. Appl. Organomet. Chem. 1998, 12, 827-842. 13. Feldmann, et al. Appl. Organomet. Chem. 1999, 13, 739-748. 14. Donard, O. F. X.; Weber, J.H. Nature 1988, 332, 339-341. 15. Feldmann, J.; Koch, I.; Cullen, W.R. Analyst, 1998, 123, 815-820. 16. Feldmann, J.; Kleimann, J. Korrespondenz Abwasser, 1997, 44, 99-104. 17. Feldmann, J. J. Environ. Monit. 1999,1,33-37. 18. Feldmann, J.; Cullen, W. R. Environ.. Sci. Technol. 1997, 31, 2125-2129. 19. Haas, K.; Feldmann, J. Anal. Chem. 2000, 72, 4205-4211. 20. Haas, K.; Feldmann, J. J. Atmos. Environ, (in prep.) 2002. 21. Feldmann, J. J. Anal. At. Spectrom. 1997, 12, 1069-1076. 22. Haas, K.; Feldmann, J.; Wennrich, R.; Stärk, H. J. Fresenius J. Anal. Chem. 2001, 370, 587-596. 23. Cullen, W. R. personal. Comm. 2001. 24. Parris, G. E.; Brinckman, F. E. Environ. Sci. Technol. 1976, 10, 1128-1134.


Biogeochemistry of Environmentally Important Trace Elements

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