simultaneous extraction of organotin, organolead and organomercury species from soils and litter

Analytica Chimica Acta 493 (2003) 23–34

Simultaneous extraction of organotin, organolead andorganomercury species from soils and litter

Jen-How Huanga,∗, Gunter Ilgenb, Egbert Matzneraa Department of Soil Ecology, Bayreuth Institute for Terrestrial Ecosystem Research (BITÖK),

University of Bayreuth, D-95440 Bayreuth, Germanyb Department of Central Analytics, Bayreuth Institute for Terrestrial Ecosystem Research (BITÖK),

University of Bayreuth, D-95440 Bayreuth, Germany

Received 24 April 2003; accepted 3 July 2003

Abstract

Extracting organotin compounds (OTC) from soils is difficult due to the high cation exchange and complexation capacityof soils, and little information about OTC in soils is available. In this study, a new extraction method, combining 1 M CaCl2,0.1% tropolone, and glacial acetic acid was developed. Recoveries of mono-substituted OTC from spiked plant litter, andsoil samples were improved substantially to 40% compared to classical glacial acetic acid extraction commonly used insedimentology, yielding<10% recovery in C-rich soil samples. Simultaneously, the recovery of other OTC, trimethylleadand monomethylmercury was satisfactory. The recoveries of most species from the spiked litter, upland and wetland soilsexceeded 70%. The new method extracted much more organometallics from unspiked organic soils and litter than microwave-and ultrasound-assisted extraction and accelerated solvent extraction, most likely due to exchange of organometallics fromthe solid phase by Ca2+. The method is simple, highly efficient and with low contamination. Together with GC–ICP–massspectrometry, the method allows the detection of these organometallics in the pg g−1 range and it is particularly suitable forsoil and plant materials with low organometallics contents.© 2003 Elsevier B.V. All rights reserved.

Keywords:Organotin; Organolead; Organomercury; Soil extraction method; Organic soil; Mineral soil; Litter

1. Introduction

Organotin (OTC), organolead (OLC) and organo-mercury compounds (OMC) are all highly toxicorganometallics in the environment. They occur in thesoils mainly through the emission, atmospheric trans-port, and deposition[1–4]. Methylation in the soil canplay an additional important role as a source of theseorganometallics, like in the case of monomethylmer-

∗ Corresponding author. Tel.:+49-921-55-57-61;fax: +49-921-55-57-99.E-mail address:[email protected] (J.-H. Huang).

cury (MMM) [5]. With the exception of MMM, littleinformation about other organometallics, especiallyOTC and OLC, in soils is available. They absorbstrongly on organic matter and clay minerals[6,7]and thus may be accumulated in soils. Sorption ofionic organometallics by soils occurs dominantlyby electrostatic interaction between organometallicsand the negative charges on the surface of mineralparticles, and complexation of the organometallicsby negatively charged ligands (e.g. carboxylate andphenolate) of the soil organic matter (SOM)[7]. Incomparison with mineral phases, sorption of OTC onan organic phase is significantly larger[8]. Therefore,

0003-2670/$ – see front matter © 2003 Elsevier B.V. All rights reserved.doi:10.1016/S0003-2670(03)00861-4

24 J.-H. Huang et al. / Analytica Chimica Acta 493 (2003) 23–34

recovering organometallics from soils is more diffi-cult than from sediments, especially from forest floorsand wetland soils with high SOM content and cationexchange capacity (CEC).

In the past, most efforts were concentrated in devel-oping extraction methods for OTC from sediments, butrarely from soils. Common extraction methods used insedimentology, like acid extraction (e.g. glacial aceticacid) and solvent extraction could well recover di- andtri-substituted organotin compounds from sediments,but seldom mono-substituted organotin (MSOT) com-pounds [9]. Recently, several methods have beendeveloped to recover all OTC from sediments, likeaccelerate solvent extraction[10], ultrasound-assistedextraction [11] and microwave-assisted extraction[12]. However, these methods can contribute to degra-dation of organometallics during extraction[11,12].

The goal of this study was (1) to develop a methodfor simultaneous and quantitative recovery of OTC,especially MSOT, TML and MMM from litter and soilsamples; and (2) to evidence the necessary applicationof different extraction strategies for organometallicsfrom soils, especially organic soils, and litter was nec-essary.

2. Experimental

2.1. Reagents

Monomethyltin (MMT), 98%, chloride was ob-tained from Strem. Dimethyltin (DMT), 95%,dibutyltin (DBT), 97%, tributyltin (TBT), 97%, chlo-rides were purchased from Fluka, trimethyltin (TMT),99%, chloride from ABCR, monobutyltin (MBT),95%, chloride from Aldrich. MMM, 95%, Trimethyl-lead (TML), and dioctyltin (DOT), 95%, chlorideswere obtained from Alfa Aesar, monooctyltin (MOT),95%, chloride from Gelest. Triethyltin (TET), 98%chloride was purchased from Merck.

De-ionized water was purified in a Milli-Q system(Milli-Q system Millipore, Milford, MA). Sodiumtetra(n-propyl)borate (NaBPr4), 98%, was synthesizedby Dümichen, Halle. The derivatization reagent, 2%NaBPr4 solution, was prepared before each usage bydissolving reagent in water. The acetic buffer was pre-pared by dissolving 1 M sodium acetate in 1 l of waterfollowed by adjusting pH to 4 with glacial acetic acid.

Individual stock solutions (10�g ml−1 as Sn, Pband Hg) of MMM, MMT, MBT, MOT, DMT, DBT,DOT, TML, TMT, TBT were prepared in methanoland stored at−40◦C in the dark. A multi-compoundworking solution with concentration of 0.1�g ml−1 asSn, Pb and Hg was prepared before each use by dilu-tion of the stock solutions with methanol (Merck, p.a.grade). TET used as internal standard was prepared inthe same way.

Calibration curves for each species were con-structed in the range 0.01–100 ng l−1, as tin, leadand mercury using TET as internal standard. Typicalregression coefficients were of the order of 0.99.

Glassware used for the all analysis was cleaned byrinsing with tap water and Milli-Q water, and left ina 10% nitric acid bath for at least 48 h. It was finallythoroughly rinsed with Milli-Q water before use.

2.2. Samples and certified reference materials

Soil samples were taken at the forested catchmentLehstenbach in the Fichtelgebirge area of northeasternBavaria/Germany. Prevailing soil types are DystricCambisols and Haplic Podzols (FAO classification),developed from deeply weathered granitic bedrockand Histosols. Soil samples were taken from a HaplicPodsol from the forest floor and from different layersof the mineral soil. Furthermore, samples were takenfrom a Histosol profile.

Litter samples were collected in litter traps underthe Norway spruce (Picea abies(L.) Karst.) stand.

The Soil samples were passed through a 2 mm(mineral soils) and a 5 mm (organic soils) sieve,homogenized and freeze-dried, since drying athigher temperatures may possibly cause losses oforganometallics. Litter was directly freeze-dried. Af-ter freeze-drying, the samples were ground and storedat 2◦C in the dark for long-term usage.Table 1givesinformation about chemical parameters of the samples.

CRM-462 certified reference coastal sediment con-taining butyltin species was obtained from the Institutefor Reference Materials of the European Commis-sion (Gheel Belgium). IAEA-356 certified referencecoastal sediment containing MMM was obtained fromInternational Atomic Energy Agency. Both sedimentmaterials were stored at−40◦C in the dark for thelong-term usage. Both reference sediments were cho-sen because of the lowest contents of butyltin species

J.-H. Huang et al. / Analytica Chimica Acta 493 (2003) 23–34 25

Table 1Carbon contents, cation exchange capacity (CEC), pH and textures of soils

Depth (cm) C (%) CEC (mmolc kg−1) pH (H2O) Sand (%) Silt (%) Clay (%)

Hoplic PodsolOi 8.5–8 47.8 245.8 4.50Oe 8–3 37.2 237.4 3.80Oa 3–0 37.6 274.2 3.50Ah 0–10 3.89 97.6 3.70 51.6 38.0 10.4Bh 10–12 9.05 246.3 3.80 34.0 49.6 16.4Bhs 12–30 5.36 137.5 4.40 44.7 44.8 10.4BvCv 30–55 0.84 42.5 4.50 45.8 43.4 10.8Cv 55–70 0.22 31.8 4.50 56.4 34.0 9.6

Histosol1 0–10 39.10 59.6 4.552 10–20 44.30 106.5 4.633 20–30 42.60 112.8 4.864 30–40 37.10 118.4 5.035 40–50 38.90 113.1 5.016 50–60 38.30 155.0 5.20

Litter 42.45 120.1CRM-462 1.66 638.2 n.d. n.d. n.d.IAEA-356 8.55 1265 n.d. n.d. n.d.

n.d.: not determined.

and MMM among all reference sediments, whichwere possibly close to contents in remote soils.

2.3. Apparatus

A GC–ICP–MS coupling consists of a gas chro-matograph (HP Model 6890) and a ICP–MS (ELAN5000, Perkin-Elmer SCIEX, Thornhill, Ont., Canada).Operation parameters of the GC–ICP–MS system arelisted in Table 2. More details of the coupling weredescribed by Glindemann et al[13].

2.4. Extraction procedures

For the classical extraction with glacial acetic acid,we used standard addition with 1, 2 and 5 ng of eachspecies to 1 g of mineral soil and to 0.5 g of litter andforest floor samples.

Since no reference soils for OTC, OLC and OMCwere available, a forest floor sample (Oe layer mainlycomposed of partly decomposed litter) was used to op-timize the extraction recoveries. Spiked samples werenot considered while the adsorption behavior couldbe in some degree different from the real samples.

Table 2GC–ICP–MS operation parameters

Gas chromatograph HP 6980 seriesColumn HP-1, 30 m× 0.25 mm i.d.,

film thickness: 0.25�mInjection port temperature 250◦CInjection volume 20�lInjection mode SplitlessCarrier gas flow Helium, 2 ml min−1

Oven program Initial temperature: 50◦C;initial time: 5 min; rate:30◦C min−1; finaltemperature: 320◦C; finaltime: 1 min

Transfer lineTransfer line column Silcosteel tubing, 1.02 mm

i.d., 1.59 mm o.d.Temperature 140◦C

ICP–MS instrument Perkin-Elmer SCIEX ELAN5000

rf power 1050 WPlasma gas flow rate 15 l min−1

Intermediate gas flow rate 0.85 l min−1

Nebulizer gas flow rate 0.70 l min−1

Oxygen flow rate 15 l min−1


MSOT, which is the most difficult recovered species,was used as criteria for optimizing the recoveries ofOTC. As solvents, Milli-Q water, 1 M HCl in methanoland glacial acetic acid was applied with 4 ml to eachsample. Na+, K+, Ca2+ and Al3+ as chlorides andCu2+ as sulfate were added to the solvents mentionedabove in 1 M concentrations. Tropolone was addedin concentrations of 0.05–0.4% only to glacial aceticacid with 1 M CaCl2. Samples were mixed with 5 ngSn internal standard as TET, which does not occurin the environment. The glass tubes were shaken hor-izontally in the dark for 24 h. All extractions weredone with three replicates. After extraction, the sam-ples were centrifuged for 10 min (1300× g). The sol-vents were transferred into glass volumetric flasks anddiluted with Milli-Q water to about 85 ml.

For testing the recovery quality of the new method,1 g of mineral soil and 0.5 g of litter and forest floorwas spiked with 5 ng of each species in 10 ml glasscentrifuge tubes. The samples were then stored in thedark and at the room temperature overnight.

Recoveries of the added organometallics were cal-culated by subtracting the original contents in eachsample.

2.5. Extraction with the commonly used methods

Commonly used extraction methods such asmicrowave-assisted extraction, ultrasound-assisted ex-traction and accelerate solvent extraction (ASE) wereoptimized to recover all OTC close to 100% fromsediments in the past studies[10,27,28]. To investi-gate the validity of these methods and our method fororganic soils and litter, unspiked three representativesamples, Oe and Fen soil and litter, were extractedwith these methods and our method.

For microwave-assisted extraction, 0.2 g of sam-ple spiked with 5 ng of Sn internal standard (TET)was extracted by 10 ml of 50% acetic acid and ex-posed to microwave at 60 W power for 3 min[27]. Forultrasound-assisted extraction, 0.2 g of sample spikedwith 5 ng of Sn internal standard (TET) was extractedby 5 ml of glacial acetic acid and placed in an ultra-sound bath for 4 min[28]. ASE was conducted with1 M acetic acid and 1 M acetate in methanol. 0.5 gof sample spiked with 5 ng of Sn internal standard(TET) was filled in die extraction cells with solventand heated within 5 min to 100◦C. The soils were ex-

tracted with five static cycles of 5 min each. Betweeneach cycle, 4 ml of solvent was renewed. At die endof the extraction, the cells were rinsed with 4 ml ofsolvent and purged with nitrogen[10].

After extraction, each supernatant solution (per cen-trifuge) was removed to 100 ml volumetric glass flask.After adjusting with acetate buffer to pH 4, the flaskwas then filled up to 85 ml with Milli-Q water. Fur-ther analysis was done with the procedures describedin the Section 2.6.

2.6. Analytical procedures

Derivatization of the extracts was done by 0.5 mlof NaBPr4 solution in the flasks adjusting pH withthe acetic buffer, and extracted with 1 ml of cy-clopentane by vigorous shaking for 10 min. Thecyclopentane extract was afterwards centrifuged(8800 × g) and cleaned-up with a pasteur pipette(150 mm length) filled with approximately 0.15 g ofsilica gel (0.063–0.2�m, heated at 500◦C overnight,5% deactived with water) and analyzed by couplingof GC–ICP–MS.

2.7. Determination of CEC and carbon content

Two grams of sediments and 4 g of soils and lit-ter were extracted with 30 ml of 1 M NH4Cl(aq) with5 min mechanical shaking and then 5 min centrifuga-tion (1200× g). After three replicates, all the solutionwas filtered and diluted with Milli-Q water to 100 mlin 100 ml glass volumetric flasks. The amounts of K,Na, Ca, Mg, Al, Mn, Fe in solution was analyzed byICP–AES.

For analysis of carbon contents, 5 mg of litter and30 mg of soil and sediment material was analyzedfor carbon content by CHN-O Rapid, Elementar,Germany.

3. Results and discussion

Specific soil layers often have higher contents of or-ganic matter (SOM) as compared to sediments. Thisis especially the case for the soil samples investigatedin this study. Even the Podsol soil has a C content ofmore than 5% up to a depth of 30 cm and the Histosolhas C contents of around 40%. The SOM is composed


dominantly of humic substances with very high CEC.Additionally to the exchangeable binding on SOM andclay minerals, organometallics might be complexed bythe SOM[7]. The stronger complexation mechanismmight play a more important role than exchangeablebinding, especially in C-rich forest floors and wetlandsoils [8]. In sediments, cation exchange process ofOTC at permanently negative charged surfaces of claysand at deprotonated surface hydroxyl groups are sup-posed to be the main adsorption mechanism of OTC[14,15]. For sediments, the binding or organometallicsmight also occur by hydrophobic interaction with pre-viously attached molecules, but this mechanism re-sults in a much weaker binding strength in compari-son to the electrostatic interactions[6]. In conclusion,adsorption of ionic organometallics in soils should bestronger than in sediments, especially if forest floorsand wetland soils with high CEC and carbon contentsare considered.

3.1. Optimization of extraction solvents

In comparison to pure glacial acetic acid, extrac-tion of MMT and MBT from the forest floor sam-ples was enhanced by addition of Ca2+ and tropolone(seeFig. 1a). Tropolone addition yielded the high-est amounts. Surprisingly, extraction with A13+ andCu2+ in glacial acid could not improve the extractionof three-charged MSOT from organic soil in compar-ison to pure glacial acetic acid. Extraction of MMMand TML was significantly improved by addition ofNa+, K+ and Ca2+ while the addition of tropoloneonly increased their yields slightly. Cu2+ was not ef-

0

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Fig. 1. Effect of different cation and tropolone on extraction of MMT, MBT, TML, and MMM from Oe horizon soil with extracts based onglacial acetic acid. (*) Without any addition, cation concentration: 1 M; Tp: 0.1% tropolone; St: glacial acetic acid extraction combiningstandard addition. Mean values and S.D. (n = 3) are presented. (a) Left axis: MMT; right axis: MBT; (b) left axis: TML; right axis: MMM.

fective, but A13+ increased the extraction of TML andMMM.

Extract based on Milli-Q water and salt solutions didnot extract MSOT and most of the other species (datanot shown). Solvents combining 1 M HCl and metha-nol also failed to extract MSOT (data not shown).

Addition of Ca2+ in the glacial acetic acid was mosteffective for MSOT extraction at 1 M (seeFig. 2). Therecovery of MSOT from organic soils decreased withfurther increase in the concentration of Ca2+. For bothTML and MMM, the highest recoveries were between1 and 2 M Ca2+.

The concentration of tropolone also effected the ex-traction yield of MMT and MBT: a maximum was ob-served at 0.1% (seeFig. 3a). However, the tropolonehad no effect on the extraction of MMM and TML(seeFig. 3b).

We found glacial acetic acid-based solvent moreuseful for the extraction of organometallics from soilsas compared to water and HCl (data not shown) for thefollowing reasons: (1) partial digestion of soil organicmatter and complexing with organometallics, (2) pro-viding milder digestion as HCl and avoiding poten-tial degradation of OTC during long-term extraction,(3) protonation of negative charges and release of ex-changeable organometallics.

A13+, Cu2+ and Ca2+ are known to form com-plexes with SOM, and might thereby decomplex andrelease organometallics. However, this was only foundin case of Ca2+. The failure of A13+-assisted extrac-tion might be attributed to concurrent complexing ofA13+ with acetate instead of SOM[16]. Most extractstested here, including glacial acetic acid and A13+,


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(b)

Fig. 2. Effect of different Ca2+ concentrations on extraction of MMT, MBT, TML, and MMM from Oe horizon soil with extracts based onglacial acetic acid. Mean values and S.D. (n = 3) are presented. (a) Left axis: MMT; right axis: MBT; (b) left axis: TML; right axis: MMM.

exhibited typical yellow color after extraction of or-ganic soils, whereas the solvent containing Ca2+ re-sulted in extract with a dark brown color, indicatinghigher solubility of SOM. Only the addition of Ca2+seemed to release organometallics into the solutionphases by exchange reaction. Extraction with Cu2+ inall solvents was not successful, possibly because Cu2+hindered the further derivatization with NaBPr4. Thiswas proven with the internal standard TET, which wasalso not detectable in the presence of Cu2+ duringderivatization.

The extraction efficiency of Ca2+ followed an op-timal function (Fig. 2), reaching a maximum at 1 Mconcentrations in case of MMT and MBT but at higherCa2+ concentration in case of MMM and TML. Highconcentrations of Ca2+ will affect the colloidal prop-erties of the SOM and clay minerals in that the elec-

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Fig. 3. Effect of different % of tropolone on extraction of MMT, MBT, TML, and MMM from Oe horizon soil with extracts based on1 M Ca2+ and glacial acetic acid. Mean values and S.D. (n = 3) are presented. (a) Left axis: MMT; right axis: MBT; (b) left axis: TML:right axis: MMM.

trical double layer will decrease and flocculation isenhanced. The latter might lead to the occlusion oforganometallics in newly formed structures. Higherthan 1 M Ca2+ concentration is also not favorable be-cause of technical reasons, since for the separation ofsoil and solvent the high viscosity of such solutions isunfavorable.

The extraction of MMM and TML was also im-proved by adding 1 M Na+ and K+ in glacial aceticacid, which are not complexing cations to SOM.The extraction of MMM and TML was also slightlyimproved by addition of A13+. This suggested thatthe binding of MMM and TML in soils is basedon different mechanisms as compared to MMT andMBT. The improved extraction of MMM and TMLby monomeric cations indicated the exchangeablebinding of these.


We used chlorides as salts for the addition ofcations. Formation of chlorides of MMM can occur[17], which might additionally improve the extractionfrom the soil.

The extraction of MMT and MBT was remark-ably improved by adding tropolone, because of itsspecific complexation capability toward OTC[18].Improvement of extraction with tropolone was alsofound, but to a lesser extend, for MMM and TML.Complexation of MMM and TML with tropolone isless compared to OTC. Decrease of the extractionefficiency for MMT and MBT with tropolone over0.1% could be associated with interference with theCa2+–acetic acid–tropolone extraction system byforming tropolone dimer[19] and tropolone acetate[20].

3.2. Validation of the methods

Concentrations of DBT and TBT in the referencesediments CRM-462 and IAEA-356 were in agree-ment with the certified values (seeFig. 4a). The con-tent of MBT, which was not certified, was determinedin agreement with Abalos et al[11]. Content of MMMdetermined in IAEA-356 were lower than certified val-ues, but in agreement with the results of other authors(seeFig. 4b) [22–24].

3.3. Recovery of spiked organometallics from soils

Comparing our new extraction method with the re-sults obtained from the classical glacial acetic acid

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Bloom et al. Qian et al. this studyHintelmann et al.

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Fig. 4. (a) Results of determination of butyltin species in certified reference sediment CRM-462 [11,21]. The reference sediment wasrecertificated in 1998. The content of MBT was not certified. Mean values and S.D. (n = 3) are presented. (b) Result of determination ofMMM in certified reference sediment IAEA-356 [22–24]. Mean values and S.D. (n = 3) are presented.

extraction (see Fig. 5) shows a significant improve-ment for all organometallics considered. Generally, thegreatest improvement occurred in the C-rich upper soillayers of the upland and wetland soil. Improvementswere less pronounced in deeper mineral soil layers.

With regard to Sn, MSOT was most improved.Glacial acetic acid recovered only 0–30% of MMTfrom the spiked soil samples while the new methodyielded 60–100% depending on depth. Similar rela-tion was found in case of MBT and to a less extentfor MOT.

Glacial acetic acid totally failed to extract MMMfrom upland and wetlands soils (see Fig. 5) and recov-eries of TML were in the range of 20–60%. The newmethod improved the recovery of MMM and TMLfrom both soil profiles to 70–100%.

The extraction of litter samples resulted in similarpatterns as compared to the soil samples. The newmethod yielded recoveries of MSOT close to 100%,the glacial acetic acid method yielded <10% (seeTable 3). The relations of the different Sn speciesduring recovery also changed with the extractionprocedure: the old method suggests that recovery ofMMT < DMT < TMT. The new method indicatedon the contrary TMT < DMT < MMT.

The difficulty to satisfactorily recover organometa-llics with classic glacial acid extraction from soils,especially organic soils, has been demonstrated. How-ever, even with the new method, we observed a rela-tive low recovery of MMT and DMT species in bothspiked upland and wetland soils reaching 40–90%with higher recoveries in the deeper mineral soil layers


Fig. 5. Recoveries of OTC, TML and MMM from upland and wetland soils extracted with method G: glacial acetic acid extraction; methodC: 1 M Ca2+ and 0.1% tropolone in glacial acetic acid. For method C, n = 3, all S.D. were under 5%. All soil samples were spiked with5 ng Sn, Pb, Hg of each species.

J.-H.

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Table 3Recoveries of OTC, TML and MMM from the litter samples (in %)

Methods TMT DMT MMT TBT DBT MBT MOT DOT TML MMM

Glacial acetic acid 66.5 33.3 1.40 94.9 91.1 7.58 22.3 108.3 104.3 56.3CaCl2, tropolone,

glacial acetic acid81.4 ± 5.25 94.7 ± 2.63 104 ± 6.84 101 ± 3.60 97.2 ± 5.97 97.9 ± 5.54 93.9 ± 3.09 102 ± 2.29 96.4 ± 1.82 96.7 ± 3.59

Recoveries with glacial acetic acid extraction were determined by standard addition. For CaCl2, tropolone, and glacial acetic acid extraction, mean values and S.D. (n = 3)are presented.

32J.-H

.H

ua

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et

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na

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)2

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34

Table 4Contents of methyltin and butyltin compounds (in pg Sn g−1), trimethyllead (TML) (in pg Pb g−1) and monomethylmercury (MMM) (in pg Hg g−1) in litter, Oe and Fen soilsdetermined with different extraction methods

TMT DMT MMT TBT DBT MBT TML MMM

OeCaCl2, Tp, HOAca 6.3 ± 0.2 907 ± 141 3350 ± 858 68.0 ± 8.1 616 ± 8.0 21500 ± 4610 14.8 ± 4.4 222 ± 65.8Microwave-assisted n.d. 313 ± 12.3 180 ± 2.6 64.5 ± 2.5 517 ± 32.2 830 ± 11.3 n.d. n.d.Ultrasound-assisted n.d. 82.9 ± 7.8 187 ± 2.2 69.1 ± 12.1 548 ± 18.9 1280 ± 6.8 n.d. 64.3 ± 7.7ASE n.d. 17.7 ± 1.1 n.d. 58.7 ± 4.0 414.5 ± 17.0 208 ± 36.7 15.7 ± 2.7 178 ± 9.2

Fen-1CaCl2, Tp, HOAca 5.7 ± 1.6 352 ± 32.9 962 ± 5.5 93.7 ± 11.1 604 ± 23.5 7190 ± 16.3 41.2 ± 6.5 27200 ± 927Microwave-assisted n.d. 290 ± 66 n.d. 89.6 ± 13.9 569 ± 47.3 n.d. 41.2 ± 1.9 50.6 ± 7.7Ultrasound-assisted n.d. 79.7 ± 5.2 12.5 ± 1.0 97.1 ± 8.3 646 ± 95.0 458 ± 11.7 20.0 ± 6.3 21.8 ± 0.9ASE n.d. 16.1 ± 4.7 5.7 ± 0.4 83.6 ± 4.9 99.3 ± 6.91 n.d. 42.5 ± 1.8 27800 ± 995

LitterCaCl2, Tp, HOAca 4.8 ± 0.9 24.4 ± 1.3 62.9 ± 4.2 41.4 ± 2.2 1670 ± 226 3780 ± 41.8 15.3 ± 0.7 243 ± 13.7Microwave-assisted n.d. 21.3 ± 3.0 n.d. 36.3 ± 3.7 1440 ± 72.1 n.d. n.d. 78.3 ± 3.8Ultrasound-assisted n.d. n.d. n.d. 42.8 ± 5.7 1490 ± 213 245.2 ± 11.6 n.d. 138.4 ± 9.19ASE n.d. n.d. n.d. 29.1 ± 3.3 n.d. n.d. 15.7 ± 2.5 157.6 ± 15.4

Mean values of three replicates and S.D. are shown; n.d.: not detected.a Extraction by 1 M CaCl2, 0.1% tropolone in glacial acetic acid.


of the Podsol soil and low recoveries in the Histosoland upper Podsol soil. The reasons for that remainhighly speculative. In case of DMT, one might thinkof the disproportion to MMT and TMT through thecomplexation with tropolone [25]. In case of MMT,the strong binding of the trivalent and small ion toSOM seems to be relevant. The lower recovery ofTMT from spiked litter with new method than glacialacetic acid extraction might contribute to dismutationof TM–tropolone complex during extration [26].

3.4. Comparison with the other modern extractionmethods

TBT and DBT were satisfactorily extracted from allorganic samples with all commonly used methods incomparison to our method (Table 4). MBT, DMT andMMT were either not detected or poorly extracted bythe commonly used methods and TMT was not foundat all. ASE extracted similar amounts of TML andMMM from organic samples. The microwave- andultrasound-assisted extraction recovered little TMLand MMM compared to our method.

The disability of the commonly used methods toextract TMT in trace amounts from all soil samplesmight he due to TMT losses during extraction. Extrac-tion of methyltin compounds and MBT from organicsoils and litter was not satisfying, although these meth-ods were shown to recover them satisfactorily fromsediment samples [10,27,28]. None of the commonlyused methods can extract all OTC, OLC and OMCsimultaneously with high efficiency.

In summary, satisfactory and simultaneous extrac-tion of all OTC, TML and MMM species from C-richsoils should combine different extraction mechanisms.Solvents consisted of CaCl2, tropolone and glacialacetic acid could recover organometallics through thefollowing mechanism: (1) glacial acetic acid digest-ing sample materials, (2) Ca2+ complexing SOM andexcluding organometallics from the adsorption sites,(3) tropolone selectively complexing OTC, (4) Ca2+cationic exchange TML and MMM, and (5) formationof metalloid chlorides and acetates.

4. Conclusions

In this study, we have demonstrated the capabilityof a new method for extraction and detection of OTC,

TML and MMM in litter, upland and wetland soils.The major advantages over established techniques forsediments are the higher recoveries of OTC, OLCand OMC from C-rich soils and litter. It provideshigher analytical accuracy, lower uncertainty anddetection limits than the method combining glacialacetic acid extraction and standard addition. Be-sides, the method is simple and time-effective. Unlikemicrowave- and ultrasound-assisted extraction, thepossibility of degradation of organometallics duringextraction with this method is very low. This methodis suitable for determination of samples with verylow contents of OTC, OLC and OMC in the range ofpicogram per gram, for example in remote terrestrialecosystems.

Acknowledgements

We want to thank Frank Hertel and Petra Dietrich,central analytics, for technical support. This workwas financially supported by the German AcademicExchange Service (DAAD) and the German Min-istry for Education and Research (BMBF), PT BEO-51-0339476D.

Appendix A

Abbreviation of organometallics.

Abbreviation Full name

DBT DibutyltinDMT DimethyltinDOT DioctyltinMBT MonobutyltinMMM MonomethylmercuryMMT MonomethyltinMOT MonooctyltinMSOT Mono-substituted organotinOTC OrganotinOLC OrganoleadOMC OrganomercuryTBT TributyltinTET TriethyltinTML TrimethylleadTMT Trimethyltin


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