Environ. Sci. Technol. 1989, 23, 615-617
NOTES Container Adsorption of Tributyltin (TBT) Compounds: Implications for Environmental Analysis Rodney J. Carter,*,+ Nicholas J. Turocry,+ and Alan M. Bond’
Faculty of Applied Science and Technology, Warrnambool Institute of Advanced Education, Warrnambool, Victoria, Australia, and Division of Chemical and Physical Sciences, Deakin University, Waurn Ponds, 321 7 Victoria, Australia The polarographic response of tributyltin (TBT) as the chloride in 0.1 M NH4N03at pH 5.3 was examined in a number of cells constructed from materials commonly used in the collection, storage, and analysis of environmental samples. The response per unit concentration was greatest with polycarbonate and least with Perspex. This change is ascribed to significant adsorption of TBT onto the polarographic cell, electrodes, and stirrer. Graphite furnace atomic absorption spectrometry (GFAAS) was used to confirm the relative response for polycarbonate, glass, and Perspex. Adsorption was shown to take place on glass in less than 1 min after mixing.
Introduction Tributyltin (TBT) compounds, generally as the fluoride or oxide, are used as the active biocides in many marine antifouling paints. These paints are designed to continually release small amounts of the biocide into the water surrounding the structure or boat, thereby preventing attachment of fouling organisms. Recent publications (1-5) have demonstrated the extreme toxicity of TBT to estuarine organisms. The United Kingdom in 1985 established an environmental quality target (EQT) concentration of 20 ng dm-3. However, subsequent evidence suggests that an EQT lower than 2 ng dm-3 is required for environmental protection (1). At these very low levels it is paramount that contamination of samples or loss of TBT at any stage in the process of collection, storage, and analysis be guarded against. Work at the Warrnambool laboratories over the past few years suggested the possibility that TBT may adsorb strongly on container walls. This effect has been noted by previous workers (6-9).Despite this, the problem seems to have been ignored by many researchers. The technique of polarography, which has been used previously for determination of TBT in a variety of solvents (10-1 3), was adopted in its highly sensitive stripping form in order to evaluate the extent of adsorption. This paper briefly reports some surprising results obtained during an investigation into the adsorption properties of TBT on materials commonly used for collection, storage, and analysis of environmental samples. Experimental Section Polarographic cells were constructed from the materials under study. All were made with the same internal dimensions so that each presented the same surface area to Warrnambool Institute of Advanced Education.
* Deakin University.
0013-936X/89/0923-0615$01.50/0
a given volume of solution. Polarographic calibration curves for (TBT)Cl for each of the cells were determined over the range 1 X 104-5 X lo4 M. Solutions were prepared by successive 10-pL additions of a 2 X M stock (TBT)Cl solution (in methanol) to 20.00 mL of an aqueous 0.100 M NH4N03solution at its natural pH of 5.3. The solutions were thermostated at 20 f 1 “C during analysis. Solutions were purged with nitrogen for 5 min before analysis and for 5 min after each addition of (TBT)Cl in order to mix the solutions. Differential pulse anodic stripping analysis from a hanging mercury drop electrode was carried out using a Metrohm 646 VA Processor and 647 VA Stand. After a 20-s deposition the drop was stripped with a differential pulse scan (pulse height 75 mV) from -1.1 to -0.4 V at a rate of 10 mV/s (all potentials are given vs Ag/AgCl, 3 M KC1 electrode). Under these conditions, a peak for the oxidation of the reduction product of TBT deposited in mercury appeared at -0.77 V. The cells and the electrodes were soaked in a 1% solution of acetic acid in acetonitrile for 24 h before each calibration run in order to remove contamination from previous experiments. The extended soaking time was found necessary to ensure the reproducibility of calibration curves. A Hitachi 7000 Polarized Zeeman atomic absorption spectrophotometerfitted with a temperature controller and autosampler set to deliver 20 pL was used for graphite furnace (GFAAS) determinations of tin. The standard instrumental conditions in the 7000 program were used except that the wavelength was set to 286.3 nm and argon was “NOT interrupted” on atomization.
Results and Discussion The nonlinear calibration curves obtained for the polarographic stripping curves with different cells are reproduced in Figure 1. The wide variation in response from the different cell materials was not expected. The nature of the curves suggests that significant adsorption is taking place on the container surface, the glass electrodes, and the Teflon stirrer. Generally, the materials with the most organic character show the most adsorption. This is clearly seen in the sequence glass/silanized glass/waxed glass. This indicates that the adsorption involves the butyl groups of the TBT ion rather than the polar sites, as was expected. Teflon, which has long been used as a coating material because of its tendency to show little or no adsorption for many metal species, gave variable results but always adsorbed more than glass for comparable concentrations. This result supports work previously reported by Maguire (7). The work reported by Blair et al. (9) demonstrated adsorption of TBT in deionized water by
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0.09 0.08 0.07
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150
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-2 -
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c + m
E
.r
X W
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0 rn
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U
~
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1 perspex waxed g l a s s
Figure 1. Polarographic stripping calibration curves obtained for tributyltin chloride in 0.1 M NH,N03 as a function of cell material. There was no significant difference in performance for Teflon, polypropylene, and polyvinyl chloride and results are drawn as a single curve. In order to improve clarity, data points have been included on three curves only.
glass, Teflon, polycarbonate, and particularly by polyethylene. Differences in adsorption characteristics between the two reports may well be due to decreased ionization of the (TBT)Cl in the higher ionic strength NH4N03solutions. Blair et al. (9) maintain that there is little difference between glass and polycarbonate; however, the present report would suggest that polycarbonate is the preferred material. The shape of the calibration curves is not due to an unusual polarographic response since curves with related characteristics, shown in Figure 2, were obtained when the solutions in polycarbonate, glass, and Perspex cells were examined by graphite furnace atomic absorption spectrometry (GFAAS). For reasons of clarity, data points were not marked on Figure 2 until the signal for each calibration curve was significantly greater than the blank. The decreased adsorption observed with the GFAAS method a t low concentrations, when compared to the polarographic calibration curves, is attributable to the lack of glass electrodes and Teflon stirrer, which themselves adsorb a significant amount of TBT. The slight adsorption still suggested in the response with the polycarbonate container may represent adsorption by the material but also could be due to contact with materials present in the autosampling system of the GFAAS. The rate a t which adsorption takes place was investigated by measuring the atomic absorption signal of a 1 X lo4 M (TBT)Cl solution in a glass cell over a period of 3 days. After addition of (TBT)Cl, approximately 1 mL of the solution was poured into a polycarbonate vial in the autosampler and the tin concentration determined by GFAAS within 1 min of mixing. Aliquots (1 mL) were removed for analysis at various times over the next 3 days. There was no significant change in the signals over the time 616
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Figure 2. Calibration curves obtained by graphite furnace atomic absorption spectrometry for tributyltin chloride In 0.1 M NH,N03 as a function of cell material.
interval examined. Therefore for all practical analytical purposes, adsorption onto glass can be considered to occur instantaneously. No other materials were tested over the 3-day period since the changes in curvature and sensitivity demonstrated in Figure 1 by the different materials was sufficient to rank container materials for suitability. If significant adsorption occurs quickly, then the containers are unsuitable regardless of whether adsorption increases with time. Significant adsorption at a concentration of 1 X lo4 M (TBT)Cl takes place on all materials tested except polycarbonate. This concentration of approximately 0.3 mg dm-3 is lo4times higher than the EQT of 20 ng dms for the United Kingdom and lo6 times higher than that suggested by Waldock ( I ) . Since the materials tested represent those that are commonly used for collection and storage of environmental samples, reservations about the true environmental levels of TBT must be raised. Furthermore, many workers have not reported any concerns with adsorption during sample handling and analysis. The experiments conducted so far demonstrate that considerable care is necessary to reduce adsorption at all stages. Obviously polycarbonate is the preferred material of those tested to date. Results from static ecotoxicity testing-particularly any experiments that used Perspex tanks-must be treated with caution if adsorption was not considered in the calculation or determination of TBT levels. If polarographic methods are to be used for determination of TBT, then polycarbonate electrodes should be substituted for the usual glass system. The use of Perspex cells, frequently used for the polarographic determination of metal ions, is not recommended. Work is in progress to investigate the behavior of spiked natural samples and to determine whether commonly used nonaqueous extraction processes will remove the adsorbed TBT from the container surfaces. We recommend that all scientists working with environmental samples and low concentrations of TBT and other organometallic compounds seriously question their collection, storage, and analysis procedures in an endeavor to minimize adsorption processes. This aspect of analytical chemistry has received considerable attention for inorganic compounds but has been largely ignored in the past for the organometallic complexes.
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Envlron. Sci. Technol. 1989, 23, 617-618 Registry No. Tributyltin chloride, 1461-22-9; tributylstannylium,36643-28-4; water, 7732-18-5;polyethylene,9002-884; Teflon, 9002-84-0; polypropylene,9003-07-0;poly(viny1chloride), 9002-86-2; perspex, 9011-14-7.
Literature Cited Waldock, M. J.; Thain, J. E.; Waite, M. E. Appl. Organomet. Chem. 1987,1,287-301. Lawler, I. F.; Aldrich, J. C. Mar. Pollut. Bull. 1987,18, 274-278. Gibbs, P. E.;Bryan, G. W. J. Mar. Biol. Assoc. U.K. 1986, 66.767-777. Thain, J. E.; Waldock, M. J. Water Sci. Technol. 1986,18, 193-203. Matthias, C. L.; Bellama, J. M.; Olson, G. J.; Brinckman, F. E. Environ. Sci. Technol. 1986,20,609-615. Meinema, H. A.; Burger-Wiersma, T.;.Versluis-de Hann, G; Gevers, E. Ch. Environ. Sci. Technol. 1978,12,28&293.
(7) Maguire, R. J.; Carey, J. H.; Hale, E. J. J.Agric. Food Chem. 1983,31, 1060-1065. (8) Meador, J. P.;U’Ren, S. C.; Salazar, M. H. Water Res. 1984, 18, 647-650. (9) Blair, W.R.;Olson, G. J.; Brinckman, F. E.; Paule, R. C.; Becker, D. A. An International Butyltin Measurement Methods Intercomparison: Sample Preparation and Results of Analyses. National Bureau of Standards, NBSIR 863321,February 1986. (10) MacCrehan, W. A. Anal. Chem. 1981,53,74-77. (11)Hasebe, K.; Yamamoto, Y.; Kambara, T. Fresenius 2.Anal. .-., Chem. 1982,310,234-238. (12) Kenis, P.;Zirino, A. Anal. Chim. Acta 1983,149,157-166. (13) Bond, A. M.; McLachlan, N. M. Anal. Chim. Acta 1988, 204,151-159. I.
Received for review April 15,1988.Revised manuscript received September 13, 1988. Accepted February 8,1989.
CORRESPONDENCE Comment on “Occurrence and Bloaccumulation of Organochlorine Compounds in Fishes from Siskiwit Lake, Isle Royale, Lake Superlor” SIR Recently, Swackhamer and Hites reported (I) new results concerning bioaccumulation of organochlorine pesticides and selected polychlorinated biphenyl (PCB) congeners in fishes. Three comments should be made. First, as regards to Table 11, where selected PCB concentrations are shown, it is surprising that PCB congener 2,2’,4,4’,5,5’-hexachlorobiphenyl (IUPAC no. 153),which is known to exhibit a rather high log KO,(octanol-water partition coefficient) of 6.92 (2),is missing. PCB-153, as well as other diortho derivatives, is a very significant component of PCB residues. Other authors reported values for congener 153 in marine biota samples, e.g., Duinker et al. reported that this congener accounted for 25% of 17 PCB congeners quantified in porpoise tissues (3) and L. G. Hansen reported that this congener was 20% of 14-18 PCB congeners quantified in freshwater eel, deep-sea fish, and eagle liver (4). Another comment concerns the authors’ statement (I) that a quantitative comparison could not be made for PCBs because earlier studies measured total PCBs (usually expressed as Aroclor 1254) and in their paper the quantitation is based on selected PCB congeners. In regard to that point, we would like to note that our group (5) has recently published an intercomparison between quantitation of total PCBs (as Aroclor 1254)versus selected PCB congeners (28,52,101,118,138, 153,and 180) in several marine biota samples. A fador of 3.17 has been found that can be used for correlation purposes between new data calculated by using selected PCB congeners and old data which used total PCBs. This approach can be used for the values of congeners 52,101,118,138, and 180 of Table I1 (I) (a value of 20% has been estimated for congener 153, and congener 28 has not been considered because values are usually below 4% in fish). By using the factor of 3.17 (5)to the sum of these six selected PCB congeners of Table 0013-936X189/0923-0617$01.50/0
11, a total PCB value around 7 pg/g for white fish and lake trout will be obtained. Further, this value can be added to Table 111; therefore, an intercomparison with the PCB content from other data is feasible. Now it is obvious that the sentence of the authors (I) indicating that PCB concentrations have decreased with time, from 34 pg/g (indicated by the authors in Table 111) to 7 pg/g (our approach), is correct. A final comment is related to the model of BCF-log Kow applied by the authors ( I ) , who stated that it was only a rough approximation of bioaccumulation and had completely failed for PCBs. The reason why this happened is that most of the PCB congeners that bioaccumulate in fishes have log KO,above 6 (2) or (as DDE) close to 6 (6). It is quite evident that no linear correlation has been found by the authors (1) because the correlation between the bioaccumulation factor and the octanol-water partition coefficient losses its linearity above log KOw values of 5-6 (7). To overcome this problem, other correlations have been proposed, i.e., quadratic terms have been added to account for steric factors as well as terms of metabolism (7). To sum up, it can be stated that a correlation between physicochemical properties and bioaccumulation will only be feasible if different factors are considered. Registry No. 2,2’,4,4’,5,5’-Hexachlorobiphenyl, 35065-27-1; biphenyl, 92-52-4.
Literature Cited
0 1989 American Chemical Society
Swackhamer, D. L.; Hites, R. A. Environ. Sci. Technol. 1988, 22,543.
Hawker, D. W.; Connell, D. W. Environ. Sci. Technol. 1988, 22,382. Duinker, J. C.;Knap, A. H.; Binkley, K. C.; Van Dam, G .
H.; Darrel-Rew,A.; Hillebrand, M. T. J. Mar. Pollut. Bull. 1988,19,74.
Hansen, L. G. In Polychlorinated Biphenyls (PCBs): Mammalian and Environmental Toxicology; Safe, S., Ed.; Springer-Verlag: Berlin, 1987;pp 15-48. Porte, C.; BarcelB, D.; AlbaigBs,J. J. Chromatogr. 1988,442, 386.
Mackay, D.; Paterson, S.; Cheung, B.; Neely, W. B. Chemosphere 1985,14,335. Envlron. Sci. Technol., Voi. 23,
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