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Speciation and Degradation of Triphenyltin in Typical Paddy Fields and Its Uptake into Rice Plants Fabiane G. Antes,† Eva Krupp,*,‡,§ Erico M. M. Flores,† Valderi L. Dressler,*,† and Joerg Feldmann‡ †
Departamento de Química, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil Department of Chemistry, University of Aberdeen, Meston Building, Meston Walk, AB24 3TU, Aberdeen, United Kingdom § ACES Aberdeen Centre for Environmental Sustainability, University of Aberdeen, AB23 3UU, Aberdeen, United Kingdom ‡
bS Supporting Information ABSTRACT: Triphenyltin (TPhT) is a biocide used worldwide in agriculture, especially in rice crop farming. The distribution and dissipation of TPhT in rice fields, as well as uptake of TPhT and other phenyltin compounds (monophenyltin, MPhT, and diphenyltin, DPhT) is still unknown at present. In this study, speciation analysis of phenyltin compounds was carried out in soil and water from a rice field where TPhT was applied during rice seeding according to legal application rates in Brazil. The results indicate the degradation of biocide and distribution of tin species into soil and water. To evaluate whether TPhT is taken up by plants, rice plants were exposed to three different TPhT application rates in a controlled mesocosm during 7 weeks. After this period, tin speciation was determined in soil, roots, leaves, and grains of rice. Degradation of TPhT was observed in soil, where DPhT and MPhT were detected. MPhT, DPhT, and TPhT were also detected in the roots of plants exposed to all TPhT application rates. Only TPhT was detected in leaves and at relatively low concentration, suggesting selective transport of TPhT in the xylem, in contrast to DPhT and MPhT. Concentration of phenyltin species in rice grains was lower than the limit of detection, suggesting that rice plants do not have the capability to take up TPhT from soil and transport it to the grains.
’ INTRODUCTION Triphenyltin (TPhT) is widely used in agriculture as a biocide.1 In Brazil, this compound is regularly used in rice (Oryza sativa L.) farming. TPhT can be applied directly to the soil or leaves during plant growth, playing the function of molluscicide and fungicide, respectively.2 Brazilian legislation recommends that the maximum residue of TPhT in commercial rice should be below 0.1 mg 3 kg 1.3 However, this limit is not routinely controlled. TPhT is also registered with the U.S. Environmental Protection Agency (EPA), and its use is allowed as a fungicide on pecans, potatoes, and sugar beet crops.4 Among organotin compounds, the trisubstituted compounds are the most toxic, while the nature of the anion group has little or no effect on the biocide activity, except that this anion itself is a toxic component (general formula R3SnX, where R is an alkyl or aryl group and X is an anion such as hydroxide, acetate, etc.1 The toxicity and cardiovascular activity of organotin compounds has been recently reviewed by Nath.5 Experimental studies have shown that TPhT may have endocrine-disrupting capabilities resulting in adverse effects on the reproductive system of mollusks and mammals. 2,6,7 These endocrine-disrupting effects include the development of imposex in gastropods and changes in reproductive organs as well as alterations in sexual hormone levels in rats.8,9 Other studies also showed highly toxic effects of r 2011 American Chemical Society
TPhT on fish, such as suppression of number of eggs and egg quality, causing a decrease in the fecundity of females, and induced teratogenesis such as eye defects, morphological malformation, and conjoined twins.10 12 Due to food exposed to TPhT, especially fish and fishery products, humans are indirectly subject to this compound and its toxicological effects. According to Hoch,1 TPhT has a relatively low stability in the environment, and ultraviolet irradiation or biological or chemical cleavage could be responsible for progressive loss of aryl groups from the Sn-organo cation. Consequently, diphenyltin (DPhT), monophenyltin (MPhT), and inorganic tin (Sn) can be formed. Dubascoux et al.13 studied the kinetics of degradation of TPhT in soil spiked with contaminated sewage sludge. According to this study, TPhT degradation occurred very quickly at the beginning of the experiment. Over 85% of TPhT was degraded after 53 days (total experiment time) and the calculated TPhT half-life was 6 ( 1 days. However, DPhT and MPhT showed higher persistence in soil. The degradation of TPhT (as triphenyltin acetate) in selected soil types was studied by Yen et al.14 They found that temperature was the most important factor that contributed to Received: August 13, 2011 Accepted: November 11, 2011 Revised: November 5, 2011 Published: November 11, 2011 10524
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Environmental Science & Technology the TPhT degradation rate and that soil moisture content and microbial activity did not significantly affect the degradation of this compound. The authors observed high degradation rates in soil, with half-lives between 8.3 and 19.4 days, depending on temperature and kind of soil. Little is currently known about the uptake of phenyltin compounds by plants. A study about TPhT uptake from soil by lettuce showed that most of the TPhT that was absorbed remained in roots and only a low amount was transported to the shoots (less than 2%). Additionally, relatively high degradation of TPhT in soil was observed, where only about 20 30% of the initially introduced TPhT was detected after 54 days.15 In some crops, instead of applying the TPhT to the soil, the biocide is applied over the plant leaves. In an experiment performed to evaluate TPhT and its degradation products’ assimilation in leaves and soil from sprayed pecan orchards, it was concluded that TPhT was rapidly degraded to DPhT and mainly to MPhT, probably due to photocatalytic reactions.16 In spite of the use of TPhT in rice crops in many countries, no reports were found in the literature about TPhT or its degradation products’ uptake by rice plants. Here we determined TPhT and its degradation products DPhT and MPhT in soil and water of a paddy field that received the routine TPhT application employed in southern Brazil. Additionally, in order to evaluate the extent of TPhT uptake and transportation to different parts of rice (roots, grains, and leaves), a study was conducted where rice plants were exposed to different concentrations of TPhT added to the irrigation water, in a controlled mesocosm experiment. Speciation analysis of MPhT, DPhT, and TPhT was performed in soil, roots, leaves, and grains via gas chromatography coupled to inductively coupled plasma mass spectrometry (GC-ICP-MS).
’ MATERIALS AND METHODS Sampling of Soil and Water in a Rice Field. Soil samples were collected in a rice farm from Brazil where TPhT hydroxide was applied to the field during rice seeding. Samples (soil volumes of 20 20 20 cm) were collected at five points in a paddy field of 2.5 km2, three days after the application of TPhT hydroxide. Soil samples were dried by lyophilization, ground with mortar and pestle, sieved to obtain particle size lower than 200 μm, and stored at 20 °C. The superficial water layer was also collected in the same rice field. This sample was maintained at 20 °C until speciation analysis. Controlled Mesocosm Experiments. After germination on vermiculite, 30-day-old rice (Oryza sativa L.) plants were transplanted to 1 L plastic pots packed with dry clay-rich soil. The plant pots were placed in a greenhouse with temperature and light simulating tropical conditions (temperature between 22 and 35 °C). Daylight was supplemented with sodium lamps, which were on during 8 h per day. Plants were grown under irrigated conditions by permanent immersion of the pots, in individual trays where water and nutrient solution were added three times a week. Nutrients were supplied through addition of Yoshida solution. A description of this procedure and also the composition of the Yoshida solution is given in Supporting Information. Experiments were performed with 12 plants that were divided into four groups (i.e., three plants/dose): one was the control group and three groups were exposed to three different concentrations of TPhT. The treatment consisted of addition of TPhT in 50 mL of Yoshida solution. The concentration of TPhT in
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these solutions was 20, 100, and 1000 μg 3 kg 1 (as Sn), identified as low, medium, and high TPhT concentration, respectively. The medium concentration was chosen to simulate the amount usually applied in rice fields in Brazil.3 The addition of TPhT solutions was performed during 7 weeks and finished 7 days before rice was ready for harvesting. Total mass of TPhT (as Sn) added to the soil during the whole experiment is described in Table S2 (Supporting Information). Harvesting Rice Plants and Sample Preparation for Speciation Analysis. Rice plants were taken out of the pot and the whole plant plus soil mass was weighed. Plants were then carefully separated from soil, and roots were washed with water to remove the soil completely. Roots were separated from shoots by cutting out a piece of 4 cm between roots and shoots, to avoid intercontamination of both parts. Panicles were removed from the leaves, and rice spikelets were removed from panicles manually. The mass of soil, roots, leaves, and spikelets was recorded. Rice grains were separated from their husks by use of a mortar and pestle, and the mass of all grains of each plant was recorded. Rice parts and soil were stored in zip-lock bags at 80 °C before sample preparation for speciation analysis. Evaluation of Sample Preparation Procedures for Speciation Analysis. For the purpose of quality control, the extraction procedure was evaluated using spiked soil and plant material samples due to the lack of certified reference materials for phenyltin compounds. In the case of plant material, the extraction procedure was evaluated by use of rice grains, which were ground in a mortar and pestle under liquid N2, and about 1 g of material was transferred to a glass vial. Soil samples were homogenized with a spatula and also weighed into glass vials. For tin species extraction, two procedures, adapted from Lespes et al.15 and Monperrus et al.,17 were used for soil and plant material. These procedures were evaluated by use of plant material and soil samples spiked with MPhT, DPhT and TPhT. The procedure adapted from Lespes et al.15 showed the best analyte recovery and therefore it was used for MPhT, DPhT, and TPhT speciation analysis. A brief description of sample preparation procedures evaluated is given below. Procedure A: One gram of material (soil or plant) was transferred to a 20 mL glass vial, and 3 mL of methanol + ethyl acetate (1:1) solution was added. The vial was maintained under mechanical shaking for 1 h. Then 5 mL of 0.035 mol 3 L 1 HCl solution prepared in methanol + ethyl acetate (1:1) was added and the vial was shaken for 1 h and then centrifuged at 5000 rpm for 5 min. Procedure B: This was similar to procedure A, except 5 mL of 0.1 mol 3 L 1 HCl plus 1 g of NaCl was used instead of 0.035 mol 3 L 1 HCl. This procedure was evaluated only for soil. Procedure C: One gram of dry material (soil or plant) was transferred to a 20 mL glass vial, and 2 mL of methanol and 5 mL of acetic acid were added. The vial was agitated for 12 h and centrifuged at 5000 rpm for 5 min.Blank samples were prepared in the same way but without the addition of phenyltin compounds. After extractions, 4 mL of supernatant was transferred to a clean glass vial and 50 μL of tripropyltin (TPrT) solution (50 μg 3 L 1 as Sn) was added as internal standard (IS). The pH of this solution was adjusted to 4.9 by use of an acetic acid/sodium acetate buffer. This mixture was then submitted to ethylation by the addition of 1 mL of isooctane and 1 mL of 2% (m/v) sodium tetraethylborate solution. The vial was immediately capped and vigorously shaken for 5 min. The solution was centrifuged at 3000 rpm for 10525
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Environmental Science & Technology 5 min to help phase separation and the organic layer was transferred to a 2 mL amber autosampler vial. Samples from the mesocosm experiments were analyzed in duplicate, and samples collected in the rice field were analyzed in triplicate. For analysis of water collected in the rice field, 10 mL of sample was derivatized following the same procedure described above. The derivatization was performed in triplicate and extracts were kept at 80 °C until analysis by GC-ICP-MS. Quantification was performed via standard addition calibration with IS, and at least two measurements were done per sample. Spiked soil and plant material samples were also prepared by the addition of MPhT, DPhT, and TPhT standard solutions in order to submerge 5 g of soil or plant material (rice grains), which were collected in a place where TPhT had never been applied. After equilibration during 48 h in the dark, the solvent was eliminated with a gentle stream of argon. The concentrations of MPhT, DPhT, and TPhT were 33.4, 30.1, and 71.1 ng 3 g 1 in spiked soil and 65.0, 55.2, and 50.5 ng 3 g 1 in spiked plant material, respectively. Spiked samples were stored at 20 °C before extraction and analysis. Blank samples were prepared in the same way but without the addition of phenyltin compounds. The commercial product Mertin 400, a suspension containing 400 g 3 L 1 TPhT hydroxide used in rice fields, was also analyzed by GC-ICP-MS in order to evaluate the purity of this product. Therefore, the biocide was weighed and diluted in water and derivatized by the same procedure as applied for the water samples. Soil samples collected in the rice field were digested for total tin determination. Digestion was performed with an Ethos II microwave oven (Milestone, Bergamo, Italy) where 0.25 g of dry soil sample was transferred to poly(tetrafluoroethylene) (PTFE) vessels and 5, 2, and 2 mL of HNO3, HF, and HCl, respectively, were added. Digestion program consisted of two steps: a ramp of 10 min up to 200 °C, followed by 30 min at this temperature. Total tin was determined by ICP-MS at m/z 120, by use of Perkin-Elmer-SCIEX model Elan DRC II equipment (Thornhill, Canada). Tin Speciation Analysis. An Agilent 6890 gas chromatograph (Palo Alto, CA) was coupled to an Agilent ICP-MS 7500c via a homemade heated transfer line. Dry plasma conditions were used because in this case better species transport was obtained. The GC-ICP-MS operating conditions are described in Table S3 (Supporting Information). Chromatographic signals obtained were processed on the basis of peak area by the WinFAAS 1.0 software. Standards and Reagents. MPhT, DPhT, TPhT, and TPrT stock standard solutions were prepared by dissolving appropriate amounts of the respective compounds (PhSnCl3, Ph2SnCl2, and Ph3SnCl, Sigma Aldrich, Dorset, England; Pr3SnCl, Strem Chemicals, Newburyport, MA) in methanol (Mallinckrodt, Phillipsburg, NJ). Intermediate standard solutions were prepared weekly by dilution of stock solutions in methanol, and work standard solutions were prepared daily in 0.1 mol 3 L 1 HCl. All solutions were maintained in the dark at 20 °C. Methanol, ethyl acetate, NaCl, and HCl (high purity, Merck, Darmstadt, Germany) were used for preparing extraction solutions. A 2% (m/v) NaBEt4 (Sigma Aldrich) solution, prepared in water, was used for ethylation. Adjustment of pH was performed with a 1.0 mol 3 L 1 acetic acid/sodium acetate buffer (pH 4.90). After ethylation, tin species extraction was performed with isooctane (Mallinckrodt). Yoshida’s nutrient solution was prepared from respective analytical-grade salts (see Supporting Information).
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Figure 1. Chromatograms obtained by GC-ICP-MS. (a) Standards (20 μg 3 L 1) of MPhT, DPhT, and TPhT (as Sn); (b) soil sample exposed to high TPhT concentration; (c) roots sample exposed to high TPhT concentration. Peak 1, inorganic Sn; peak 2, TPrT; peak 3, MPhT; peak 4, DPhT; peak 5, TPhT; peak 6, Me3Sn+ (suggested); peak 7, Me2Sn2+ (suggested); peak 8, PhMe2Sn+ (suggested); peak 9, PhMeSn2+ (suggested); peak 10, Ph2MeSn+ (suggested).
’ RESULTS AND DISCUSSION Tin Speciation Analysis and Its Improvement. Due to the relatively low stability of TPhT,18,19 the use of microwave- or ultrasound-assisted extraction procedures is usually not recommended.20 However, considering that extraction by microwave radiation is usually faster than other extraction methods, a procedure using microwave radiation (5 min, 60 °C) was also evaluated (results not presented); however this procedure yielded low recoveries for TPhT and recoveries higher than 100% for DPhT and MPhT. These results indicate species degradation and interconversion, and therefore microwave extraction was not used for further investigations. Therefore, in this study only extraction procedures using mechanical shaking were evaluated. Recoveries obtained for MPhT, DPhT, and TPhT in plant material (using procedures A and C) and in soil (using procedures A, B, and C) are shown in Table S4 (Supporting Information). Recoveries obtained by procedures A and C were lower than 90% and 75%, respectively, for all species in soil samples. Low recoveries were also obtained for procedure C for phenyltin extraction from plant material. On the other hand, recoveries higher than 94% were obtained for plant material and soil by extraction procedures 10526
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Environmental Science & Technology A and B, respectively. Therefore, procedure A was used for phenyltin extraction from plant material, and procedure B was used for soil samples. Extraction procedures A and B were subsequently applied for phenyltin compound speciation analysis in enriched soil and plant material samples. The recoveries obtained in soil were 79%, 97%, and 95% for MPhT, DPhT, and TPhT, respectively, while the recoveries in plant material were 86%, 95%, and 96% for MPhT, DPhT, and TPhT, respectively. Although relatively lower recovery has been observed for MPhT in enriched soil and plant material samples, the obtained results could be considered suitable when the difficulties usually described for phenyltin compound speciation analysis are taken into account.20 Chromatograms obtained for enriched soil and plant material are shown in Figure S1 (Supporting Information). The limits of detection (LOD), calculated following the signal at intercept and 3 times the standard deviation about regression of the calibration curve, for MPhT, DPhT, and TPhT were 0.5, 0.66, and 0.72 μg 3 L 1, respectively (as Sn). The LOD values for 1 g of sample used for extraction were 1.0, 1.3, and 1.4 ng 3 g 1 for MPhT, DPhT, and TPhT, respectively (as Sn). Chromatograms obtained by GC-ICP-MS for standard, soil, and rice (roots) samples are shown in Figure 1a, b, and c, respectively. It is possible to observe a similar peak shape for samples and standard solution and good peak resolution for all species. The peak that corresponds to TPhT is relatively broad due to the high boiling point of ethyl-TPhT (close to 300 °C).21 The transfer line used in this experiment is homemade and has a heating limit of 220 °C. Therefore, the transport of TPhT through the transfer line to the ICP torch is not optimal and causes peak broadening due to insufficient heating. Nonetheless, the triphenyltin compound can be quantified, even though detection limits are compromised. Other not-identified peaks can be observed in Figure 1b and c with retention times that do not correspond with retention times of the standards. These peaks were also not observed in chromatograms obtained for enriched soil and plant material (Figure S1, Supporting Information). These peaks are discussed in the next section. Phenyltin Compounds in Soil and Water from a Rice Field. The commercial biocide was analyzed and TPhT was established to be the main organotin compound. Only traces of DPhT had been found, while MPhT was below the detection limit and no other unknown tin species were recorded. Results obtained for phenyltin species for diluted sample are shown in Table S5 (Supporting Information). In general, TPhT is added directly into the irrigation water when the rice is seeded to kill mollusks that could destroy the seeds. However, due to dissipation of TPhT and its degradation in the environment, which leads to formation of the still-toxic MPhT and DPhT compounds, the consequences and damages to other aquatic living organisms could have a serious environmental impact.11 Additionally, the potential of TPhT to contaminate groundwater has to be considered.14 However, very few studies reporting the effects of TPhT use in rice fields are available, and this compound is still used in indiscriminate ways in many places around the world.22 To evaluate the contamination with phenyltins in a rice field, soil and water samples were analyzed by GC-ICP-MS. It is important to mention that the application of TPhT hydroxide in this field was done 3 days before sampling. However, this field has been used for more then 10 years for rice crops, and TPhT is applied at least once a year. The results obtained are presented in Table 1.
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According to the results shown in Table 1, it can be observed that the distribution of phenyltin compounds is different in soil samples from the same field collected at different points. Phenyltin species were detected in concentrations above LOD in soil samples 3 and 5 (LOD 1.1, 1.3, and 1.4 ng 3 g 1 for MPhT, DPhT, and TPhT, respectively, as Sn). This behavior can be explained by TPhT hydroxide not being homogenously applied in the field. Additionally, in this case, rice cultivation is performed in irrigated fields and the water can be responsible for transportation and dissipation of the biocide. In the water sample that was analyzed, only TPhT was detected, at relatively low concentrations. It is also important to consider the presence of MPhT and DPhT in the soil samples. The analysis of a commercial TPhT hydroxide (Mertin 400) product indicated that the concentration of DPhT was lower than 0.5% of the concentration of TPhT, while MPhT was not detected. This suggests that MPhT and DPhT detected in soil samples were from degradation of TPhT after its application and not from contamination of the commercial biocide used. Triphenyltin Uptake by Rice Plants. The application of TPhT in rice crops in Brazil is usually performed with a commercial suspension of triphenyltin hydroxide (Mertin 400). According to the guidelines on the product, 1 L of a 400 g 3 L 1 suspension is applied to 4 ha of rice field. If it is taken into account that rice is cultivated in irrigated fields, with a water layer of approximately 10 cm, the concentration of triphenyltin hydroxide is expected to be approximately 100 μg 3 L 1. Therefore, the experiment conducted in this work was performed under similar conditions. No phenyltin species were detected in roots, leaves, and grains in control rice samples. In the same way, these species were not detected in control samples of soil. However, MPhT, DPhT, and TPhT species were detected in soil that was exposed to low, medium, and high concentrations of TPhT. Table 2 shows the concentration of phenyltin species in soil and roots from plants exposed to different TPhT levels. As can be observed from the results shown in Table 2, TPhT in soil is degraded to DPhT and MPhT species. Apparently, the degradation of TPhT to DPhT and MPhT depends on the amount of TPhT added to soil. The concentration of TPhT in soil exposed to high TPhT concentration is significantly lower than those of MPhT and DPhT, indicating that the degradation of TPhT was higher compared to the other two levels. For medium and low concentrations of TPhT added to soils, the concentration is similar for all phenyltin species. The reason for this behavior was not investigated in this study, but it may be related to the different stabilities of each species in soil or possible stabilizing effects of substances present in soil that can form complexes preferentially with one of the phenyltin species. The presence of MPhT, DPhT, and TPhT was also detected in the roots. These results are shown in Table 2 for three different TPhT levels of concentration. In general, the distribution of phenyltin species in roots for the different initial concentrations of TPhT is similar to that observed in soil samples. It is possible to observe an increasing of all phenyltin species concentration in roots with increased TPhT added. Regarding phenyltin species uptake from soil, we postulate some possibilities that could be considered to explain this behavior. The rice plant may have taken up preferentially TPhT, and DPhT and MPhT species could be formed in roots, as a consequence of the plant metabolism. On the other hand, plants could take up the three species from the soil. Another possibility is that both effects could occur simultaneously, that is, the plant could take up the three 10527
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phenyltin species from soil, and species interconversion and degradation could occur, even in the roots. According to TPhT concentration in roots and soil shown in Table 2, the calculated roots/soil uptake ratio is 6.25, 3.44, and 13.3 for low, medium, and high concentration exposed plants, respectively. In this way, it could be suggested that plant uptake ratio would be higher for plants exposed to higher TPhT levels. In contrast to what was observed for roots, for leaves of plants exposed to low and medium TPhT content, the concentration of MPhT, DPhT, and TPhT was lower than the LOD. Only TPhT was detected (1.33 ( 0.49 ng 3 g 1, as Sn) in leaves of plants treated with high TPhT concentration. DPhT and MPhT concentration was lower than their respective LODs. A chromatogram obtained for leaves exposed to high TPhT level is shown in Figure 2, where a small peak corresponding to TPhT can be observed but no MPhT or DPhT. It is also possible to see an unknown peak with retention time of 200 s, with a relatively high intensity. This peak also appears in chromatograms b and c in Figure 1 and could be related to other tin species, as will be explained afterward. Only a low concentration of TPhT was detected in the leaves, although the concentration of DPhT and MPhT was higher in the roots than TPhT. This would point to preferential TPhT translocation from the roots through xylem sap into the leaves. No phenyltin species were found in the rice grain. According to these results, it seems that rice plants do not easily take up phenyltins and transport them from soil to leaves and grains. Additionally, although relatively high degradation of TPhT has been observed in soil and all phenyltin species were detected in roots and at similar levels, DPhT and MPhT were not transported to the shoots. Probably phenyltin molecules are not easily translocated to the shoots of rice plants, similar to the effect observed for lettuce by Lespes et al.15 These results indicate that rice consumption does not imply risks to health regarding contamination with TPhT and other tin species, although a
thorough field study needs to confirm the mesocosm experiments. Although the mesocosm experiment has been performed trying to simulate field condition, some factors such as microorganisms, environmental effects like rain, etc., could not be reproduced. Therefore, additional experiments in the field would be necessary to confirm the obtained results. As the total amount of TPhT that each plant was exposed to is known (Table S2, Supporting Information) and the mass of each part of plant and soil at the end of the experiment was also known, it was possible to calculate how much was taken up by the plants, by use of the absolute values of phenyltin species found in each plant as listed in Table 3. In this sense, for plants exposed to low TPhT level, the content of TPhT found in the roots after the experiment was only 0.13% ( 0.05% of the amount of TPhT to which the plants were exposed (8 μg). Similarly, for plants exposed to medium and high TPhT levels (72 and 373 μg, respectively), the content of TPhT determined in the roots was 0.09% ( 0.05% and 0.19% ( 0.04% of the amount of TPhT to which plants were exposed. The percentage of TPhT that remained in soil for plants exposed to low, medium, and high levels of TPhT was 1.94% ( 0.07%, 2.41% ( 0.68%, and 1.40% ( 0.38%, respectively. The low recoveries could be attributed to degradation of TPhT to DPhT and MPhT and even to inorganic tin. Although inorganic tin was not quantified, a peak corresponding to this species with a retention time of about 160 s was observed in all samples. Additionally, losses by volatilization through bioalkylation by formation of volatile tetraalkyltin species may have occurred during the experiment. The formation of tetraalkyltin through Sn methylation is a well-established process that occurs naturally in the environment.23,24 Krupp et al.23 estimated 2 4 μg of Sn 3 (m 3 of landfill gas) in two landfill sites in
Table 1. Results for Mono-, Di-, and Triphenyltin in Soil and Water Samples from a Rice Fielda sample
MPhT
DPhT
TPhT
(ng 3 g 1, as Sn)
(ng 3 g 1, as Sn)
(ng 3 g 1, as Sn)
soil 1
