333

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Waste Management 28 (2008) 1518–1527 www.elsevier.com/locate/wasman

Organometals of tin, lead and mercury compounds in landfill gases and leachates from Bavaria, Germany G. Ilgen a, D. Glindemann

a,1

, R. Herrmann

b,z

, F. Hertel

a,2

, J.-H. Huang

c,*

¨ K), University of Bayreuth, D-95440 Bayreuth, Germany Central Analytic, Bayreuth Institute of Terrestrial Ecosystem Research (BITO b Department of Hydrology, University of Bayreuth, D-95448 Bayreuth, Germany ¨ K), University of Bayreuth, D-95440 Bayreuth, Germany Department of Soil Ecology, Bayreuth Institute of Terrestrial Ecosystem Research (BITO a

c

Accepted 4 June 2007 Available online 11 September 2007

Abstract Organo-Sn, -Pb and -Hg compounds were monitored in gases and leachates of 11 municipal waste landfills and one hazardous waste landfill from Bavaria, Germany, with the objectives to estimate the methylation of Sn, Pb and Hg and to assess the risk of their release into the adjacent environment. In the gases, tetramethyl Sn predominated (>80% of total gaseous Sn) with concentrations up to 160 lg Sn m3. Dimethyl-Hg and tetramethyl-Pb were only occasionally detected with concentrations up to 2.9 and 2.1 lg m3 as Hg or Pb, respectively. In all leachates, trimethyl-Sn dominated with a maximum concentration of 2100 ng Sn L1. No organo-Pb compounds were found, and monomethyl-Hg was detected in only one leachate. The concentrations of trimethyl-Sn were up to 100-fold higher in the condensate water than in leachates, and the concentrations of organo-Sn compounds were lower in the adjacent groundwater than in the corresponding leachates. The high abundance of methylated Sn species in the gases and leachates indicates Sn methylation, suggesting the landfill as a source for organo-Sn compounds. In comparison, methylation of Hg and Pb was of little importance, probably due to low Hg concentrations and low rates of Pb methylation in the landfill. The risks of organo-Sn compounds release to the adjacent air is low due to flaring of landfill gases. However, there is probable release of organo-Sn compounds, especially trimethyl-Sn, to the adjacent groundwater. Ó 2007 Elsevier Ltd. All rights reserved.

1. Introduction Organo-Sn, organo-Hg and organo-Pb compounds play an important role in the geochemical cycle due to their higher toxicity, volatility and/or lipophilicity as compared to their inorganic forms (Thayer, 1995). Tin has a larger number of organometallic derivatives in commercial use than any other element. This gave rise to a *

Corresponding author. Present address: Institute of Biogeochemistry and Pollutant Dynamics, Swiss Federal Institute of Technology Zurich (ETHZ), ETH Zentrum, CHN, CH-8092 Zu¨rich, Switzerland. Tel.: +41 44 632 88 19; fax: +41 44 63 11 18. E-mail address: [email protected] (J.-H. Huang). 1 Present address: Goettinger Bogen 15, D-06126 Halle, Germany. z Deceased. 2 Present address: Alnylam Europe AG/Chemische Synthese, FritzHornschuch-Str. 9, D-95326 Kulmbach, Germany. 0956-053X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2007.06.020

dramatic increase in the worldwide production of organoSn compounds from less than 5000 tons in 1955 up to 50,000 tons in 1992 (Hoch, 2001). Organo-Sn compounds are common industrial products which are used as biocides, as stabilizing additives in polyvinylchloride (PVC) and as antifouling agents. Peralkylated organo-Pb compounds like tetramethyl Pb and tetraethyl Pb have been used as antiknock additives in gasoline products for several decades (Łobin˜ski et al., 1994). Lead-containing antiknock additives have been terminated for several years in Northern and Central Europe but are still used in many countries of Eastern Europe. In addition to anthropogenic sources, organo-Sn and organo-Pb compounds can be formed or transformed by chemical and biological processes in the environment such as biomethylation and transalkylation (Hamasaki et al., 1995; Hempel et al., 2000). Unlike organo-Sn and organo-Pb compounds, organo-Hg com-

G. Ilgen et al. / Waste Management 28 (2008) 1518–1527

pounds in the environment are generally considered to originate from natural processes instead of anthropogenic emission, e.g., in situ Hg methylation in wetland soils and aquatic ecosystem (St. Louis et al., 1996) and in vivo methylation by organisms (Jereb et al., 2003). Landfills are waste disposal sites for the deposit of waste onto or into land, including domestic and industrial waste. The major environmental impact to the landfill is emission of pollutants via the leachate and gas pathway. The commercial use of Sn, Pb and Hg compounds reflects their occurrence in the landfill body (Kjeldsen et al., 2002). The anoxic conditions in the landfill may benefit the methylation of inorganic Sn, Pb and Hg (Lindberg et al., 2005). Nevertheless, the occurrence and fate of organo-Sn, organo-Pb and organo-Hg compounds in landfills has not been widely studied. Feldmann and Hirner (1995) identified tetramethyl-Sn, organo-Sn hydrides and five tetramethylethyl-Pb in landfill gases from central Germany. Neither Hg0 nor methylated Hg species could be identified. The concentrations of total gaseous Sn, Hg and Pb ranged over the intervals 8.6–35, 0.05–0.13 and 0.01–0.03 lg m3, respectively. However, much higher total gaseous Hg concentrations were observed in gases from the landfills in USA with concentrations up to 12 lg m3 (Lindberg et al., 2005). Furthermore, dimethyl Hg was the dominant organo-Hg compound in the landfill gases. Mersiowsky et al. (2001) found methyl-Sn, butyl-Sn and octyl-Sn species in the landfill leachates from eight European landfills. Monobutyl-Sn predominated with a maximum concentration of 4.1 lg L1. Recently, ethylated and propylated Sn species were found in landfill gases in Scotland and Germany (Mitra et al., 2005). In comparison with organo-Sn compounds, there is still very little knowledge about organo-Pb and organo-Hg in the landfill leachates. Therefore, the objectives of this study are: (1) to monitor gaseous and ionic organo-Sn, -Pb and -Hg compounds in a number of landfills from Bavarian, Germany; (2) to estimate the methylation of Sn, Hg and Pb in the landfills; and (3) to estimate the risks of release of organo-Sn, -Pb and -Hg compounds from the landfills to the adjacent environment.

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(Table 1). In comparison, the air in the vicinity of the landfill contains lower percentages of CO2 and CH4 (up to 3.6% and 1.2%, respectively). With the age of about 30 years old, the investigated landfills were in the stable methanogenic phase (CH4 concentrations higher than those of CO2 concentrations) (Barlaz et al., 1989; Kjeldsen et al., 2002). A raised waste temperature (up to 28 °C related to ambient air temperature <10 °C in February 2000) was due to microbial activity at all sites (Table 2). Leachates and condensates from most landfills were neutral or slightly alkaline as a consequence of microbial methane production (Barlaz et al., 1989). The conductivities (up to 17,000 lS cm1) and total organic and inorganic C and total N concentrations (up to 2200 mg L1) in leachates and condensates were much higher than in the groundwater. The various chemical parameters in the gases and leachates indicate different phases of decomposition and varying microbial activity at different landfills investigated. 2.2. Materials All ionic organometallic species in the form of chlorides and peralkylated organometallic species analyzed were purchased with purities between 95% and 99%. Sodium tetra(n-propyl)borate, 98%, was purchased from GALAB, Geesthacht, Germany. Individual stock solutions (10 lg mL1 as Sn, Pb or Hg) of ionic organometallic species (monomethyl Sn, monobutyl-Sn, monomethyl-Hg, monooctyl-Sn, dimethyl-Sn, dibutyl-Sn, dioctyl-Sn, trimethyl-Sn, tributyl-Sn, and trimethyl-Pb) and peralkylated organometallic species (dimethyl-Hg, tetramethyl-Pb, tetraethyl-Pb, tetramethyl-Sn and tetraethyl-Sn) were prepared in methanol and cyclopentane, respectively, and stored at 40 °C in the dark. Working solutions with a concentration of 0.1 lg mL1 as Sn, Pb and Hg were prepared before each use by dilution of the stock solutions with methanol or cyclopentane. All glassware and sampling bottles used were cleaned by rinsing with tap water followed by Milli-Q water and subsequently stored in a 10% nitric acid bath for at least 48 h. Before use, glassware was thoroughly rinsed with Milli-Q water.

2. Materials and methods 2.3. Instrumentation 2.1. Site descriptions for the investigated landfills The 12 investigated landfills (D1–D12) are located in Bavaria, Germany. All landfills are municipal sanitation facilities containing liners and leachate collection systems with two exceptions. The one denominated D12, which is used for deposition of hazardous waste, does not have a polyethylene liner but is instead sealed with clay. Landfill D2 is an old landfill still without a liner at the bottom. At all investigated landfills, deposition began in the period 1972–1976. The percentage of CO2 and CH4 in the landfill gases ranged between 5.9% and 39% and 12% and 71%, respectively

A double GC–ICP–MS coupling consists of two gas chromatographs (HP Model 5890 and 6890) and an ICP– MS (ELAN 5000, Perkin–Elmer SCIEX, Thornhill, ON, Canada). This design allows us to analyze gaseous species with the cryogenic trap method and to perform spitless injection with large volumes of solvent in order to analyze analytes with both low and high boiling points. The thin and flexible transfer line (1.5 m length, 1/1600 od, 0.0400 id, ‘‘Silcosteel’’ deactive stainless steel tubing, Restek) is heated by a combination of hot argon mixed with the GC effluent before passing the transfer line using a T-joint in the GC oven, and by electrical resistance heating. The

21–57 38–71 50 n.a. 39–59 32–61 48–56 57–64 12–44 49–69 25–43 0.23–1.2 5.9–30 25–37 32 n.a. 19–28 27–37 23–31 34–39 17–32 31–34 13–24 0.97–3.6 0.2–5.3


Range Range Range

2.4. Sampling of landfill gas and analysis of gaseous organometallic compounds

0.07–2.1

22–66 11–44 23–52 15–56 32–160 7.0–34 38–40 16–25 22–96




19–42 10–36 20–50 14–19 29–160 5.6–28 31–32 14–22 20–79

n.a., not analyzed. n, number of samples. Absolute detection limits (DL: pg): tetramethyl-Sn = 1.8,dimethyl-Hg = 45, tetramethyl-Pb = 1.7. a Air samples in the vicinity of the landfill.

Median Range Median

flow through the transferline can be reversed to eliminate the solvent peak and to prevent graphite deposition onto the ICP–MS cones after large volume splitless injection. Operation parameters of this system and further details of the coupling were described by Glindemann et al. (2002).

Range

Median Range Median Range

10 23 20 57 24 30 17 69 20 38 18 54

Median Range

4.3–43 6.4–34

9.3 19 19 41 20 28 16 64 16 32 15 47 D1 (n = 9) D2 (n = 3) D3 (n = 1) D4 (n = 3) D5 (n = 4) D6 (n = 4) D7 (n = 4) D8 (n = 5) D9 (n = 4) D10 (n = 3) D11 (n = 3) D12 (n = 3)a

Median

Total gaseous Hg (lg Hg m3) Dimethyl Hg (lg Hg m3) Total gaseous Sn (lg Sn m3) Tetramethyl Sn (lg Sn m3) Landfill

Table 1 Concentrations of carbon dioxide, methane, organometals of tin, mercury and lead compounds in the landfill gases

Tetramethyl Pb (lg Pb m3)

Total gaseous Pb (lg Pb m3)

CH4 (%)

G. Ilgen et al. / Waste Management 28 (2008) 1518–1527

CO2 (%)

1520

Sampling of landfill gases, leachates, condensates and groundwater was conducted in February 2000. Landfill gases were sampled at different places in each landfill using 1–10 L Tedlar bags (MKC/ANALYT) by pumping. To prevent organometallic compounds from photolytic degradation, the Tedlar bags were shielded by aluminium foil against UV radiation. Before each sampling, about 200 L of fresh air was pumped through the pump for cleaning. Clean-up of the Tedlar bag was conducted by evacuation and argon purging in turns at least three times. For speciation of gaseous organometallic species, 250 mL gas from the samples kept in the Tedler bags was transferred using a gas-tight syringe, and passed through a Pasteur pipette (150 mm length) filled with 2.0 g NaOH(s) to remove CO2 and water vapor. Samples were then twice trapped (ultimate tubing ID 0.53 mm and fused silica tubing ID 0.32 mm, both uncoated and methyl deactivated) at approximately 186 °C (cooled in liquid argon) and further measured by GC (HP 5890)–ICP–MS. This method allows analysis of analytes out of a boiling point ranging from 40 to 200 °C. Quantification was conducted with external standard mixture of 3.3 lg Sn, Hg and Pb m3 as dimethyl-Hg, tetramethyl-Sn and tetramethyl-Pb in nitrogen gas (Fig. 1a). Total gaseous Sn, Hg or Pb was defined as the sum of all identified and unknown gaseous Sn, Hg or Pb species in the GC–ICP–MS chromatogram. Using a similar analytical design, Feldmann et al. (2001) demonstrated >90% recoveries of gaseous Sn compounds from CO2-rich samples. 2.5. Sampling of aqueous samples and analysis of ionic organometallic compounds Landfill leachates were taken from wells, basins or pipes and then filled in 1 L evacuated glass flasks with a glass stopper and a hermetic polytetrafluoroethylene sealing ring. Groundwater samples were taken in the vicinity of the landfills. Condensate water was collected from the landfill gas flair station. The groundwater was sampled by pumping from the depth of 6–25 m at a distance of 50–600 m from the center of the landfills. The aqueous samples were filtered through 0.45 lm filter of cellulose acetate membrane for further analysis. All aqueous samples were then stored at 4 °C for no more than 2 weeks until analysis. Derivatization of the samples was done by 10 mg sodium tetra(n-propyl)borate in acetate buffer (pH was adjusted to 4), and extracted with 2 mL cyclopentane

G. Ilgen et al. / Waste Management 28 (2008) 1518–1527

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Table 2 Chemical parameters of landfill leachates, condensates and groundwater Landfill

Range Temperature (°C)

pH

Conductivity (lS cm1)

Total organic C (mg L1)

Total inorganic C (mg L1)

Total N (mg L1)

Leachate D1 (n = 5) D2 (n = 2) D3 D4 D5 D6 D7 (n = 2) D8 D9 D10 (n = 3) D11 (n = 4) D12

7.1–28 10–16 24 n.a. 6.2 12–18 5.2–18 7.1 18 6–11 7.7–15 12

7.1–8.5 7.2–7.3 7.4 n.a. n.a. 7.1–8.0 7.6–7.8 7.1 7.7 7.0–8.2 7.3–7.9 9.0

3500–10,000 3000–8500 13,000 n.a. 4200 2510–17,000 4800–5500 5000 3200 2620–5500 6200–8000 60,000

99–350 20–61 430 n.a. 127 18–760 210–260 120 160 220–550 230–280 1300

84–500 98–670 900 n.a. 210 1300–2200 130–160 160 110 380–490 600–730 840

83–480 64–210 550 n.a. 55 210–640 170–220 240 160 220–380 250–380 520

Condensate D9 D10

8.8 21

5.9 7.1

500 5600

230 180

65 580

100 580

Groundwater D2 D6 D12

9.2 12 12

6.6 7.1 6.5

2200 2500 1000

5.0 18
220 2200 27

58 210 10

n.a., not analyzed. n, number of samples; n = 1, if not otherwise mentioned.

containing tetraethyl-Sn in 10 ng Sn as internal standard by vigorous shaking for 10 min. The cyclopentane extract was cleaned-up with a Pasteur pipette (150 mm length) filled with 0.15 g Al2O3 (3% deactived with Milli-Q water) and was then analyzed with a coupling of a gas chromatograph (HP 6890) to an ELAN 5000 ICP–MS (Perkin–Elmer SCIEX, Thornhill, ON, Canada). A GC–ICP–MS chromatogram with propyl derivates of ionic organo-Sn standards is shown in Fig. 2a. 2.6. Further analysis Analysis of CO2 and CH4 in the landfill gas was carried out with GC (HP-6890)-TCD. Total inorganic and organic carbon was determined as CO2 after acidification of the sample with HCl and then combustion at 800 °C (Elementar, High TOC). Total N was detected as N2 after combustion. For analysis of total Sn, Hg and Pb in leachates, 15 mL samples were filtered to 0.45 lm. Total Sn and Pb were then directly determined by ICP–MS (PlasmaQuad II+ Turbo, VG Elemental) and total Hg by AAS (AAS 4100, FIAS 400, Perkin–Elmer). 3. Results 3.1. Organotin, organomercury and organolead compounds in landfill gases In all investigated landfills, gaseous Sn species were detected in the gas phase with the highest total gaseous Sn concentration up to 160 lg Sn m3 (Table 1). Tetramethyl-Sn was the dominant Sn species and occupied at

least 80% of the total concentrations of gaseous Sn (Fig. 1b). Additionally, several unidentified gaseous Sn species were detected in the landfill gases. Gaseous Hg and Pb species were only found in the landfill gases at three of the 12 investigated sites (D1, D4 and D12). Their concentrations were at least one order of magnitude lower than the concentrations of Sn species. The concentrations of dimethyl-Hg were up to 0.18 lg Hg m3 in landfill gases at sites D1 and D4, whereas the dimethyl-Hg concentrations reached a value of 2.9 lg Hg m3 in the landfill gases at site D12. Tetramethyl-Pb and some unidentified Pb species were detected in the landfill gases at site D12 with concentrations up to 2.1 lg Pb m3 for tetramethyl-Pb and 5.3 lg Pb m3 for total gaseous Pb. Unknown gaseous Pb species were also found in the landfill gases at site D04, however, with much lower concentrations (0.01 lg Pb m3) compared to those at site D12. 3.2. Organotin, organomercury and organolead compounds in landfill leachates, landfill condensates and adjacent groundwater Methyl-Sn (mono-, di- and trimethyl-Sn), butyl-Sn (mono-, di- and tributyl-Sn) and octyl-Sn species (monoand dioctyl-Sn) were identified in the landfill leachates (Fig. 2, Table 3). Among all organo-Sn compounds, trimethyl-Sn predominated with concentrations between 22– 480 ng Sn L1 in most cases. Dimethyl-Sn was the second abundant organo-Sn compound in the landfill leachates. The concentrations of dimethyl Sn ranged up to 430 ng Sn L1. At site D12, the concentrations of trimethyl-Sn and dimethyl-Sn in the leachates (2100 and 980 ng Sn

1522

a

G. Ilgen et al. / Waste Management 28 (2008) 1518–1527

a

50000

50000 Tetramethyl Sn

TTET

Tetramethyl Pb

40000

Intensity (cps)

Intensity (cps)

40000

30000

20000 Dimethyl Hg

30000

20000

TBT

TMT DBT TTPrT

10000

10000

DMT

0 0

50

100

150

200

DOT

MMT

0

250

200

300

400

Retention time (s)

b

MOT

MBT

120

Sn 202 Hg 208 Pb

500

600

700

Retention time (s )

b

1600000 Tetramethyl Sn

120000

TTET

MBT

1200000

Intensity (cps)

Intensity (cps)

DBT

80000

800000 Dimethyl Hg

400000

Tetramethyl Pb

40000 TMT

120

TTPrT

Sn 202 Hg 208 Pb

0

0

200

400

600

800

Retention time (s)

Fig. 1. (a) GC/ICP–MS chromatograms of gaseous organometals of Sn, Pb and Hg compounds standards with 0.1 lg as Sn, Hg and Pb. (b) GC/ ICP–MS chromatograms of gaseous organometals of Sn, Pb and Hg compounds from D12 landfill gas.

L1, respectively) were extraordinarily high compared to those from the other sites. The concentrations of monomethyl-Sn in the landfill leachates (up to 83 ng Sn L1) were much lower than trimethyl-Sn and dimethyl-Sn, so that the abundance of methyl-Sn species in the landfill lechates was in the order tri- > di-  monomethyl-Sn. The buthyl-Sn and octyl-Sn species were much less abundant than methyl Sn species in the landfill leachates. The concentrations of butyl-Sn and octyl-Sn species never exceeded 570 and 17 ng Sn L1, respectively. In contrast to methyl Sn species, the abundance of butyl Sn species in the landfill leachates was in the order mono- > di- > tri-butyl Sn. Organo-Hg compounds was detected only in one leachate (D1) as monomethyl-Hg with concentrations of 21 ng Hg L1. No organo-Pb compounds were detected in any of the investigated leachates. The concentrations of total Sn were generally higher than total Pb in the landfill leachates and were much higher than those of total Hg (Table 3). At site D12, the total Sn and Hg concentrations in the leachates (210 lg Sn L1 and 1.9 lg Hg L1) were much higher than those from the other sites. However, the concentration of total Pb in leachates at

DMT

TBT MMT MOT

DOT

0 200

300

400

500

600

700

Retention time (s)

Fig. 2. (a) GC/ICP–MS Sn120 chromatograms of (a) organo-Sn standards with 5 ng Sn of each species and (b) organo-Sn compounds in D06 landfill leachate. (Abbreviations used are TMT (propyl derivates of trimethyl-Sn), MMT (monomethyl-Sn), TTPrT (tetrapropyl-Sn), MBT (monobutyl-Sn), (DBT) dibutyl-Sn, (TBT) tributyl-Sn, (MOT) monooctyl-Sn, (DOT) dioctyl-Sn.)

site D12 was only slightly higher than those from the other sites. In condensate water, the concentrations of trimethyl-Sn (610 ng Sn L1 at site D9 and 2300 ng Sn L1 at D10) were much higher compared to those in the corresponding landfill leachates (29 and 28–98 ng Sn L1, respectively) (Table 2). In comparison, the concentrations of other organo-Sn compounds in the condensates were at a quite similar level to those in the leachates. No organo-Pb and organo-Hg compounds were found in the condensates. In the investigated groundwater, the concentrations of organo-Sn compounds were all below 60 ng Sn L1. The concentrations of methyl-Sn species in the investigated groundwater were much lower than those in the landfill leachates. Especially at site D12, the concentrations of trimethyl-Sn and dimethyl-Sn decreased largely from 2,100 and 980 ng Sn L1, respectively, in the landfill leachates to 0.7 ng Sn L1 respective below the detection limit in

Table 3 Concentrations of organo-Sn compounds (ng Sn L1) in landfill leachates, condensates and groundwater Landfill

Dimethyl Sn

Monomethyl Sn

Tributyl Sn

Dibutyl Sn

Monobutyl Sn

Dioctyl Sn

Monooctyl Sn

Total Organo-Sn

Median Range

Median Range

Median Range

Median Range

Median Range

Median Range

Median Range

Median Range

Range

Leachte D1 (n = 5) D2 (n = 2) D3 D4 D5 D6 D7 (n = 2) D8 D9 D10 (n = 3) D11 (n = 4) D12

41 245 220 140 130 68 27 65 29 58 170 2100

28–88 18 160–330 228 36 150 170 25 22–31

Condensate D9 D10

2300 610

Groundwater D2 54 D6 13 D12 0.7



9.0

8.4–110 19 33

3.1 0.9

95 25

7.0 1.8

120 6.3

2500 650

0.7

0.1

0.4

1.8 12 19

0.6

1.5 2.1 21

64 27 83

10–27



48–200 400–620 350 320 340 940 31–41 160 80
G. Ilgen et al. / Waste Management 28 (2008) 1518–1527

Trimethyl Sn

n, number of samples; n = 1, if not otherwise mentioned. Detection limits (ng Sn L1): trimethyl Sn = 0.01, dimethyl Sn = 0.08, monomethyl Sn = 0.02, tributyl Sn= 0.08, dibutyl Sn = 0.3, monobutyl Sn = 0.8, dioctyl Sn = 0.2, monooctyl Sn= 0.4.

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G. Ilgen et al. / Waste Management 28 (2008) 1518–1527

the groundwater. Conversely, butyl-Sn and octyl-Sn species, which were not found in the leachates, were detected in the groundwater at site D12. No organo-Pb or organo-Hg was observed in the investigated groundwater. The concentrations of total Sn, Hg and Pb in the groundwater were apparently lower than those in the leachtes at both sites and were mostly below detection limits. 4. Discussion The high percentages of CO2 and CH4 in the landfill gases indicate the anoxic conditions in the landfills. The generation of CH4 by anaerobic microorganisms suggests that landfills may act as a bioreactor for methylated heavy metals compounds (Lindberg et al., 2001, 2005). The high abundance and dominance of tetramethyl-Sn and trimethyl-Sn in the investigated landfill gases and leachates, respectively, compared to the other organo-Sn compounds support the methylation of inorganic Sn in the landfills. To our knowledge, there is no industrial use of trimethyl-Sn, and the anthropogenic organo-Sn compounds are mostly butyl-Sn species (Hoch, 2001). This is reflected by the much more abundance of butyl-Sn species than methyl-, octyland phenyl-Sn species in different environments where organo-Sn compounds are found, e.g., soils, sediments and natural waters (Wilken et al., 1994; Hoch, 2001; Jiang et al., 2001; Huang et al., 2004). Methyl-Sn species found in the environment may be partly originated from in situ methylation processes (Pecheyran et al., 1998; Tessier et al., 2002). In the environmental compartments without

Sn methylation processes, methyl-Sn species will degrade and no tetramethyl-Sn will be emitted (Huang and Matzner, 2004a). There are no significant correlations between concentrations of methyl Sn species and CH4 in gases and total Sn in leachates for the entire data set. This may be due to the different chemical and biological reactivity at each site and because the methylation of Sn and CH4 formation is controlled by different processes in landfills. In simulated landfills, the CH4 production started at 20 days and reached its maximum at 70 days after incubation (Barlaz et al., 1989). In comparison, the concentrations of methyl Sn species bloomed at the first 30 days and decreased dramatically after 56 days (Michalzik et al., 2007). In comparison with methylated Sn, methylated Hg and Pb species were only occasionally found in our landfill gases and leachates. Lindberg et al. (2001, 2005) have demonstrated the formation of dimethyl-Hg and monomethylHg in the landfills with highest concentrations of 100 ng m3. In contrast, methylated Hg could not be found in the landfill gases in central Germany (Feldmann and Hirner, 1995). The methylated Hg detected at sites D1, D4, D8 and D12 suggest a potential for methylation of Hg in these landfills. The Hg methylation process occurring in the landfills appears to be dependent on the Hg concentrations in the landfills. This is suggested by the very low total Hg concentrations in the leachates at the sites with methylated Hg below the detection limit (Table 4). The concentrations of Hg compounds in the landfill leachates may range up to 160 lg L1 (Christensen et al., 2001).

Table 4 Concentrations of total Sn, Hg and Pb in the landfill leachates, condensates and groundwater Landfills

Total Sn (lg Sn L1)

Total Hg (lg Hg L1)

Total Pb (lg Pb L1)

Median

Range

Median

Range

Median

Range

Leachate D1 (n = 5) D2 (n = 2) D3 D4 D5 D6 D7 (n = 2) D8 D9 D10 (n = 3) D11 (n = 4) D12

12 2.9 35 n.a.

1.8–53
0.09

8.2 7.7 11 n.a. 9.1 18 18 21

2.0–12.0 3.2–12

Condensate D9 D10

n.a.
n.a.
n.a.
Groundwater D2 D6 D12

16–17


n = 1, if not otherwise mentioned. n.a., not analyzed. Detection limits: 1 lg L1 for Sn and Pb, 0.04 lg L1 for Hg.

0.11–0.14

16–20


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The low concentrations of total Hg in our landfill leachates may be explained by strictly enforced limitation on Hg deposition on landfills in Germany. Subsequently, the concentrations of bioavailable Hg for methylation is low. Further explanation is the immobilization of Hg by precipitation with biogenic sulfide in the landfill body (Kjeldsen et al., 2002). Craig and Moreton (1986) postulated that S2 prevented methylation of Hg2+ by precipitation of very insoluble HgS. In addition, the presence of S2 aided the conversion of monomethyl-Hg into dimethyl-Hg (Weber et al., 1998). This may explain why dimethyl-Hg was more frequently found in our landfills than monomethyl Hg. The landfill deposition of Pb and Sn is not as strictly regulated as Hg in Germany. Lead and Sn may have been buried in a landfill as part of domestic waste in the form of metallic ingredients of common goods or as incineration ash. These deposited metals and ashes could undergo corrosion under landfill conditions and subsequently generate high concentrations of dissolved metals in leachates. The much higher concentrations of methylated Sn than methylated Pb might be explained by a higher rate of methylation of Sn compared to Pb. This may due to fact that the Pb–C linkage is more labile than Sn–C, which enhances the rates of dealkylation, and the extreme instability of monoalkylPb, which favors formation of inorganic Pb (Thayer, 1995). Several gaseous Sn species in our landfill gases could not be identified due to the lack of available standards. The chromatogram indicates higher boiling points for these unknown Sn species than for tetramethyl-Sn. Thus, they may be methylbutyl-Sn, butyl-Sn hydrides and methylbutyl-Sn hydrides instead of methyl-Sn hydrides. Feldmann and Hirner (1995) indicate higher boiling points for monobutyl Sn and dibutyl Sn hydrides with 98 and 204 °C, respectively, than for tetramethyl Sn (82 °C). The occurrence of methylbutyl-Sn and butyl-Sn hydrides has already been reported for the other landfills (Feldmann and Hirner, 1995; Mailefer et al., 2001). Leaching of organo-Sn compounds from the polyvinyl chloride (PVC) pipes into drinking water has been demonstrated (Sadiki et al., 1996, 1999). Nevertheless, Mersiowsky et al. (1999) indicated that leaching of organo-Sn compounds from PVC products under landfill conditions was found to be generally low. The occurrence of monoand dioctyl-Sn in the landfill leachates indicates PVC products as a source of organo-Sn compounds, since octyl-Sn species are employed solely as PVC stabilizers (Mersiowsky et al., 2001). For butyl-Sn species, there may be some additional sources. Butyl-Sn species are also applied for wood preservation, used in glass treatment, used in agrochemicals and used for material protection (Hoch, 2001). The apparent dominance of monobutyl-Sn among butyl-Sn species in the landfill leachates points out the dealkylation of butyl-Sn in the landfill. Interestingly, the concentrations of trimethyl-Sn in the condensates were up to 100-fold higher than in the corresponding leachates. To explain these high levels in the con-

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densates, we suggest that the gaseous tetramethyl-Sn is demethylated to trimethyl-Sn in the landfill gas pipes and adsorbed by the relatively small amount of condensed water to produce a high concentration of trimethyl-Sn in the condensate. Di- and monomethyl-Sn in the condensates may be the products of further demethylation of trimethylSn. Beside methyl-Sn species, monobutyl-Sn and monooctyl-Sn were found in the condensates, but less enriched. The occurrence of butyl-Sn and octyl-Sn species point out the probable release of ionic organo-Sn compounds to the gas phase as halides (Mester and Sturgeon, 2002; Saint-Louis and Pelletier, 2004). This can be true because the concentrations of chloride are usually very high in the landfill leachates (150–4500 mg L1, Kjeldsen et al., 2002). Also, the butyl-Sn and octyl-Sn may travel as their peralkylated or hydride derivates and did undergo subsequent degradation and condensation. It is not easy to evaluate the relevance of both pathways for the occurrence of ionic organo-Sn compounds in the condensates due to the limited knowledge. However, the low concentrations of gaseous butyl- and octyl-Sn derivates in the landfill gases suggest that the pathway of halide formation seems to be more important for butyl- and octyl-Sn species. Although the tetramethyl-Sn concentrations were at the same level in D9 and D10 gases, the concentration of trimethyl-Sn in the condensate of D9 (2300 ng Sn L1) was much higher than in that of D10 (610 ng Sn L1). Probably, the rate of demethylation differed among sites, which should be addressed in the further investigation. The organo-Sn compounds in the landfill leachates may have an impact on the adjacent groundwater, especially at the landfills without a liner system. For example, a high concentration of trimethyl-Sn was observed in the adjacent groundwater at site D2. Still, the concentration of trimethyl-Sn was high in the adjacent groundwater at a site with a liner system (D06). However, we do not know how the organo-Sn compounds penetrate the liner. Here, the soils play a role as filter reducing concentrations of organo-Sn compounds in the adjacent groundwater. There is a lowest decrease of concentrations from the landfill leachates to groundwater for trimethyl-Sn among all organoSn compounds, coinciding with the lowest affinity of trimethyl-Sn to organic and mineral soil materials (Huang and Matzner, 2004b). The concentrations of all organoSn compounds in groundwater at site D12 is low; probably the sealed clay is a more effective adsorbent than soils and polyethylene liner (Hermosin et al., 1993). There is little knowledge about the ecotoxicological effects of trimethyl-Sn in the environment. However, tributyl-Sn with a similar structure to trimethyl-Sn cases chronic and acute poisoning of the most sensitive aquatic organisms, such as algae, zooplankton, mollusks and the larval stage of some fish even at low nanomolar aqueous concentrations (1–2 ng L1) (Gibbs and Bryan, 1996). Lethal concentrations are in the range of 40–1600 ng L1 for short term exposure, depending on the aquatic species (Hoch, 2001). Generally, the toxicity of trimethyl-Sn seems to be

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higher than that of tributyl-Sn (Hoch, 2001). Therefore, the elevated concentrations of trimethyl-Sn in the groundwater indicate an increasing risk to the aquatic ecosystem in the vicinity of the landfill. Since June 2005, waste in Germany must be treated in such a way that it cannot degrade further or release pollutant (BMU, 2007). Much lower concentrations of organo-Sn compounds in gases and leachates may be thus expected from the future landfills. 5. Conclusion Landfills may serve as bioreactors for methylation of Sn species. The high concentrations of gaseous Sn species suggest the landfills as a possible anthropogenic source of organo-Sn compounds emission to air. However, generated landfill gases are generally flared in Germany, leading to decomposition of organo-Sn compounds to its less toxic inorganic form. Emissions of organo-Hg and organo-Pb compounds from the investigated landfills are low, probably due to the low Hg concentrations and low rates of Pb methylation in the landfills. The elevated trimethyl-Sn concentrations in the adjacent groundwater indicate a contamination potential of organo-Sn compounds from the landfills to adjacent groundwater from the landfills. Acknowledgements The authors thank the members of Central Analytic, Bettina Popp, Petra Dietrich and Yvonne Hoffmann, for their analytical support and help with sampling. We particularly acknowledge the GALAB, Geesthacht, for their assistance concerning this research. We appreciate also the help of the municipal authorities during the sampling events at the investigated landfills. Financial support of this study came from Bayerischer Forschungsverband Abfallforschung und Reststoffverwertung. Thanks also due to Dr. Bjo¨rn Berg for his comments on this manuscript and language editing. References Barlaz, M.A., Schaefer, D.M., Ham, R.K., 1989. Bacterial population development and chemical characteristic of refuse decomposition in a simulated sanitary landfill. Applied and Environmental Microbiology 55, 55–65. Christensen, T.H., Kjeldsen, P., Bjerg, P.L., Jensen, D.L., Christensen, J.B., Baun, A., Albrechtsen, H.-J., Heron, G., 2001. Biogeochemistry of landfill leachate plumes. Applied Geochemistry 16, 659–718. Craig, P.J., Moreton, P.A., 1986. Total methyl mercury and sulphide levels in british estuarine sediments-III. Water Research 20, 1111– 1118. Feldmann, J., Hirner, A.V., 1995. Occurence of volatile metal and metalloid species in landfill and sewage gases. International Journal of Environmental Analytical Chemistry 60, 335–359. Feldmann, J., Nae¨ls, L., Hass, K., 2001. Cryotrapping of CO2-rich atmospheres for the analysis of volatile metal compounds using capillary GC-ICP-MS. Journal of Analytical Atomic Spectrometry 16, 1040–1043. German Federal Environmental Ministry (BMU), 2007. A milestone for environmental protection: landfilling of untreated waste, consigned to

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