(18) Hughes, M. M.; Natusch, D. F. S.; Taylor, D. R.; Zeller, M. V. In "Polynuclear Aromatic Hydrocarbons"; Bjorseth, A., Dennis, A. J., Eds.; Battelle Press: Columbus, OH, 1980; p 1-8. (19) Jager, J.; Hanui, V. J . Hyg., Epidemiol.,Microbiol., Zmmunol. 1980,24,1. (20) Moriconi, E. J.; Taranko, L. B. J . Org. Chem. 1963,28,1831. (21) Moriconi, E. J.; Taranko, L. B. J . Org. Chem. 1963,28,2526. (22) Pitts, J. N., Jr.; Lokensgard, D. M.; Ripley, P. S.; Van Cauwenberghe, K. A,; Van Vaeck, L.; Shaffer, S. D.; Thill, A. J.; Belser, W. L., Jr. Science 1980,210,1347. (23) Lee, F. S. C., presented at the 4th International Symposium on Liquid Chromatography, Boston, MA, May 7-10,1979. (24) Lee, F. S. C.; Pierson, W. R.; Ezike, J. In "Polynuclear Aromatic Hydrocarbons"; Bjorseth, A., Dennis, A. J., Eds.; Battelle Press: Columbus, OH, 1980; p 543-63. (25) Konig, J.; Juncke, W.; Balfanz, E., Grosch, B., Pott, F. Atmos. Enuiron. 1980,14, 609. (26) Miguel, A. H.; Korfmacher, W. A.; Wehry, E. L.; Mamantov, G.; Natusch, D. F. S. Enuiron. Sci. Technol. 1979,13, 1229.
(27) Miguel, A. H.; Natusch, D. F. S. Anal. Chem. 1975,47,1705. (28) Linton, R. W.; Loh, A.; Natusch, D. F. S.; Evans, C. A., Jr.; Williams, P. Science 1976,191, 852. (29) Linton, R. W.; Williams, P.; Evans, C. A., Jr.; Natusch, D. F. S. Anal. Chem. 1977,49,1514. (30) Keyser, T. R.; Natusch, D. F. S.; Evans, C. A,, Jr.; Linton, R. W. Enuiron. Sci. Technol. 1978,12, 768. (31) Griest, W. H.; Yeatts, L. B., Jr.; Corton, 3. E. Anal. Chem. 1980, 52,199. (32) Soltys, P. A. Masters Thesis, Colorado State University, Fort Collins, CO, 1980. (33) Jager, J. Cesh. Hyg. 1969,14, 135.
Received for review December 16,1980.Accepted July 17,1981. The research described herein was supported in part by Grants No. R803950030 from the U.S. Enuironmental Protection Agency, Duluth, M N , No. EE-77-S-02-4347from the U.S. Department of Energy, and No. NSF ENV 74-24276 from the U.S. National Science Foundation and by Contract No. RP-1307with the Electric Power Research Institute.
Determination of Polychlorinated Biphenyl Vapor Pressures by a Semimicro Gas Saturation Method John W. Westcott,? Charles G. Simon,? and Terry F. Bidleman" Department of Chemistry, Marine Science Program, and Belle W. Baruch Institute, University of South Carolina, Columbia, South Carolina 29208
being more effectively retained by foam than the lighter isomers (6, 7). Vapor pressures have been accurately determined for many types of high molecular weight organics including insecticides and herbicides (8-11), phthalate esters (121, and polycyclic aromatics (13).However, vapor pressures for PCB have been determined only for commercial Aroclor fluids, which contain many isomers of varying molecular weight, and not for their individual components. For example, Aroclor 1242 contains -20 components, mainly di-, tri-, and tetrachlorobiphenyls, while Aroclor 1254 is composed of 20 isomers containing 4-6 chlorines per molecule (14).For several reasons vapor-pressure data for these mixtures are uncertain indicators of the volatility of the individual isomers: there is no evidence that PCB isomer solutions exhibit ideal behavior (obey Raoult's Law); vapor pressures for PCB mixtures at 25 "C are extrapolated from data obtained at 100-250 "C higher than room temperature; and commercial PCB mixtures are liquids while most of the pure isomers are solids. This paper reports the use of a semimicro gas saturation method to determine the vapor pressures of three PCB isomers and two compounds of the DDT family.
Vapor pressures of three polychlorinated biphenyl (PCB) isomers and two compounds of the DDT family were determined by a semimicro gas saturation technique in which air was passed slowly through a glass column containing glass beads coated with 20-50 mg of the compound of interest. Effluent vapors from the column were trapped on Florisil, eluted, and determined by electron capture gas chromatography. Vapor pressures for tri-, tetra-, and pentachlorobiphenyl isomers were determined at 30,35, and 40 "Cand extrapolated to 25 "C by using the Antoine equation. Results obtained by gas saturation agreed well with vapor pressures measured by a gas-chromatographic technique. Vapor pressures for the solid PCB isomers were -5-10 times lower than values reported for the commercial Aroclor fluids 1242 and 1254. Henry's law constant ( H )for the isomers, calculated from the vapor pressure and the water solubility, were within the range of H values for the commercial mixtures.
Introduction Volatility is an important factor governing the transport of trace organics. Evaporation of industrial compounds such as polychlorinated biphenyls (PCB)from disposal sites and loss of pesticides from soils depends on vapor pressure, and their ultimate return to earth is also controlled by volatility. Less volatile organics are preferentially adsorbed to airborne particulate matter ( 1 , 2) and are more rapidly removed by rainfall and dry deposition ( 3 ) .The exchange rate of vapors across an air-water interface depends on the Henry's law constant, the ratio of vapor pressure to water solubility ( 4 , 5 ) . Finally, the collection of organic vapors on solid adsorbents is affected by vapor pressure. The movement of PCB isomers through a polyurethane foam column under high-volume sampling conditions parallels their order of elution from a gapchromatographic column, with the heavier PCB isomers + Department of Chemistry.
* Department of Chemistry, Marine Science Program, and Belle W. Baruch Institute. Address correspondence to this author a t the Department of Chemistry. 0013-936X/81/0915-1375$01.25/0
Experimental Section The organochlorine compound (20-50 mg) was dissolved in pentane and coated onto 1.3-mm diameter glass beads (cleaned by washing with pentane, drying, and baking overnight a t 400 "C).Attempts a t performing the coating in a beaker resulted in excessive loss of expensive PCB isomer on the beaker wall, so the following procedure was adopted. The beads were packed into a clean U-shaped glass column 80 cm long X 0.6-cm i.d. The required amount of organochlorine compound was added to one end of the column, and the column was filled from that end with pentane and gently agitated to mix the solution. The column was allowed to stand at room temperature with both ends open for 1-2 days to evaporate the solvent. The column was then placed in a thermostated water bath a t 30 "C,and dry cylinder air was passed through it slowly for an additional 2-3 days before vapor-pressure measurements were begun.
@ 1981 American Chemical Society
Volume 15, Number 11, November 1981 1375
Gas-saturation measurements were made by passing air at 0.1-0.4 mL/min through the column, thermostated a t 30,35, or 40 “C, and collecting the effluent on a 3-g Florisil trap (15). Tandem-trap experiments showed that the organochlorine vapors were quantitatively retained by this weight of Florisil. Flow rates were regulated by a double-needle valve (Nupro Model B-2SGD, Nupro Co., Willoughby, OH) and were measured with a soap-bubble flowmeter. The gas-pressure regulator, the Nupro valve, and the Florisil trap were a t ambient temperature. A schematic diagram of the experimental setup is shown in Figure 1. The Florisil trap was eluted with 6% ethyl ether in petroleum ether, and the eluate was adjusted to a suitable volume for gas-chromatographic analysis. Analyses were performed on a Varian 3700 chromatograph equipped with a 63Ni electron capture detector and a 180-cm long X 0.4-cm i.d. glass column packed with 3% OV-225, operated a t 180-200 “C and 40-60 mL/min nitrogen flow. Injector and detector temperatures were 220 and 350 “C, respectively. Quantitation was based on peak height. Individual PCB isomers were purchased from Analabs, Inc. (North Haven, CT); p,p’-DDE and o,p’DDT were obtained from the U.S. Environmental Protection Agency (Research Triangle Park, NC). Solvents were Mallinckrodt Nanograde or Baker Resi-analyzed brands.
Results and Discussion Saturation of a flowing gas stream has been used to determine the vapor pressures of several pesticides as well as to estimate the rate of volatilization from soils. In a typical experiment, nitrogen is passed through a sand or soil column coated with pesticide and the effluent vapor is trapped in hexane or on a solid adsorbent for analysis (8-10). The vapor pressure is calculated from the measured vapor density by using the ideal gas law: po = dRT/M
where po is the vapor pressure, d is the saturation vapor density, M is the molecular weight, T is the absolute temperature, and R is the gas constant. Vapor saturation experiments were carried out by using 2’,3,4-trichlorobiphenyl(2’,3,4-TCB), 2,2’,5,5’-tetrachlorobiphenyl (2,2’,5,5’-TCB), 2,2’,4,5,5’-pentachlorobiphenyl (2,2’,4,5,5’-PCB),p,p’-DDE, and o,p’-DDT. The latter two compounds were selected to test our system, since their vapor pressures have been determined by Spencer and Cliath ( 9 ) using a gas saturation technique. Their apparatus employed a large (6 X 43 cm) saturation column containing gram quantities of organochlorine compounds. The high cost of pure PCB isomers made it necessary to scale down the saturation column to the point where semimicro quantities of isomer AIR FLORlSiL TRAP
FNEEDLE VALVE
could be used. Experiments in which incremental amounts of PCB isomer were added to the same column showed that a minimum of -20 mg of compound was needed to obtain saturation of the airstream. Solid-vapor equilibrium for these organochlorines is established slowly. Figure 2 shows a plot of vapor density as a function of the residence time of air in the column for 2’,3,4-TCB and p,p’-DDE at 30 “C. It appears that vapor saturation is attained only after contact times in excess of 35-40 min. To achieve these long contact times, it was necessary to use a long column and to regulate the airflow a t a few tenths of a milliliter per minute. The double-needle valve proved very effective for regulating these low flow rates. Repeated measurements during the runs showed flows varying by less than 5%.In order to collect enough organochlorine on the Florisil for accurate GC analysis, experiments were run for 6-12 h. The results of the gas saturation experiments are summarized in Table I. For the three PCB isomers, vapor pressures were determined a t 30,35, and 40 “C, and Antoine plots of log po vs. 1/T were extrapolated to yield vapor pressures a t 25 “C (Figure 3). We also determined vapor pressures for these compounds with a capillary gas-chromatographic technique, by measuring the retention times of test compounds relative to that of a reference material of known vapor pressure (11, 16). The agreement between the gas saturation and GC values was good; our vapor pressures for p,p’-DDE and o,p’-DDT also agreed reasonably well with those determined by Spencer and Cliath (9) (Table 11). The solid PCB isomers 2’,3,4-TCB and 2,2’,5,5’-TCB are components of the commercial fluid Aroclor 1242, and 2,2’,4,5,5’-PCB is a component of Aroclor 1254 (17, 18). Reported vapor pressures for these fluids at 25 “C are 4.06 X and 7.71 X loW5torr, respectively (19). Vapor pressures for the solid PCB isomers are thus -5-10 times lower than for the commercial liquid mixtures. The Henry’s law constant ( H )may be calculated from the ratio of vapor pressure to water solubility, provided that both 2.3.4 - T C B
m
F
0
20
40
80
80
100
160
140
Figure 2. Vapor density of a trichlorobiphenyl isomer and p,p’-DDE as a function of the contact time of air in the coated bead saturation column.
Table 1. Organochlorine Vapor Pressures Determined by Gas Saturation Antolne constants
PO, a torr
30 ‘ C
25 OC
2’, 3,4-TCB
1.2 x 10-4
1.0 x 10-4
2,2‘,5,5’-TCB 2,2‘,4,5,5’-PCB p,p’-DDE
3.6 X 1.3 X 1.3 x 10-5
1.9 X 7.2 X
o,p‘-DDT
8.8 X
compd
COATED B E A D COLUMN
120
MINUTES
A
1.0s 11.8 11.1
B
1.51 x 103 4.92 X 4.84 X
lo3 lo3
The average coefficient of variation for determinations at 30 ‘C was 18%. Vapor pressures were based on experiments for which gas-solid contact times in the coated bead column exceeded 35-40 min. Constants for the equation log p o = A - B/T. a
Figure 1. Gas saturation apparatus.
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Environmental Science & Technology
Table 111. Vapor Pressures, Water Solubilities, and Henry’s Law Constants for Aroclor Mixtures and Individual PCB Isomers at 25 OC
2;3,4 - T C B -
PCB
Aroclor 1242
vapor pressure, a torr
2’,3,4-TCB
4.06 X ( 79) 7.71 X ( 79) 9.0 X
2,2’,5,5’-TCB
3.7 X
2,2‘,4,5,5’-PCB
8.2 X
Aroclor 1254
a
solublllt rng/m$
H, atm-m3/mo1
340-703 (20-22)
2.0 X 10-4-4.1 x 10-4
45-70 (20, 23) 78 (24)
4.7 X 10-4-7.3 x 10-4 3.9 x 10-4
3.1 X 10-4-5.3 27-46 x 10-4 (24, 25) 1.1 X 10-4-3.5 10-31 x 10-4 ~ 4 ~ 2 5 )
Vapor pressures for individual isomers are averages of the GS and GC values
in Table i l .
3.3
3.2
( 1 / T ) x 10
3
Antoine plots for tri-, tetra-, and pentachlorobiphenyl isomers. The vertical lines represent standard deviations of a single determination. Figure 3.
Table II. Comparison of Gas Saturation and Gas Chromatography for Determining Organochlorine Vapor Pressures PO, torr
compd
technique a
30 “C
2‘,3,4-TCB
GS
1.3 X
2,2‘,5, 5‘-TCB
GC GS
3.6 X
GC 2,2‘,4,5,5‘-PCB p,p‘-DDE
GS GC GS
13.0 X
GC
14.0 X
GS o,p’-DDT
a
1.3 X
GS GC GS
25 OC
ref
lop4
this work 0.8 x 10-4 16 1.9 X this work 5.5 x 10-5 16 7.2 X this work 9.2 X 76 this work 1.0 X
6.5 X 8.8 X 8.4 X 5.5 x 10-6
76 9
this work 76 9
GS = gas saturation, GC = capillary gas chromatography.
of these properties have been measured for the solute in the same physical state ( 5 ) . Vapor pressures (19) and water solubilities (20-23) have been determined for liquid PCB mixtures, and solubilities of several solid PCB isomers have also been determined ( 2 4 , 2 5 ) .With the availability of vapor pressures for the solids, it is now possible to calculate values of H for individual PCB isomers (Table 111).Differences in reported water solubilities for Aroclor mixtures or PCB isomers result in a corresponding 2-3-fold uncertainty in H values; however, the agreement between H for the liquid mixtures and the solid isomers is surprisingly good. Values of H for the tri-, tetra-, and pentachlorobiphenyl isomers range from ca. 1 x 10-4 to 5 x atm-m3/mol. Vapor transfer across an air-water interface is controlled by diffusive fluxes in air and water films a t the interface ( 4 , 5 ) . The exchange rate is limited by the resistance to mass transfer in the air and water films, with the ratio of the gasto-liquid resistance (RGL)given by ( 5 )
Here KG and K L are the gas- and liquid-phase exchange constants, R is the gas constant, T is the absolute temperature, and H is the Henry’s law constant. MacKay et al. ( 5 )calculated RGLas a function of H, K G ,and K L . For values of H > 5 x 10-3 atm-m3/mol, the resistance to vapor transfer is alatmmost entirely in the liquid phase. For H < 5 X m3/mol, gas-phase resistance dominates. The resistance to mass transfer in both phases is important in controlling the exchange rate for intermediate values of H . Accurate values of H are thus essential for predicting the exchange of pollutant vapors across an air-water interface. When one uses the model of MacKay et al. ( 5 )and the H values in Table 111,on the order of 10-80% of the resistance to PCB vapor transfer occurs in the air film, depending on the values chosen for K G and KL. Such predictions, of course, are valid only for a clean water surface and are likely to show deviations from reality if the surface is altered by the presence of particulate matter or surface-active organics. Literature Cited
(1) Cautreels, W.; Van Cauwenberghe, K. Atmos. Enuiron. 1978,12, 1133-41. (2) Junge, C. E. In “Fate of Pollutants in the Air and Water Envi-
ronm&ts”; Suffet, I. H., Ed.; Wiley-Interscience: New York, 1977; Vol. 8, pp 7-25. (3) Bidleman, T. F.; Christensen, E. J. J. Geophys. Res. 1979,84, 7857-62. (4) Liss, P. S.; Slater, P. G. Nature (London) 1974,247,181-4. (5) MacKay, D.; Shiu, W. Y.; Sutherland, R. P. Enuiron. Sci. Technol. 1979,13,333-7. (6) Simon, C. G.; Bidleman, T. F. Anal. Chem. 1979,51,1110-3. (7) Billings, W. N.; Bidleman, T. F. Enuiron. Sci. Technol. 1980,14, 679-83. ( 8 ) Spencer, W. F.; Cliath, M. M. Enuiron. Sci. Technol. 1969, 3 , 670-4. (9) Spencer, W. F.; Cliath, M. M. J . Agric. Food Chem. 1972, 20, 645-9. (10) Spencer, W. F.; Shoup, T. D.; Cliath, M. M.; Farmer, W. J.; Haque, R. J . Agric. Food Chem. 1979,27,273-8. (11) Hamilton, D. J. J. Chromatogr. 1980,195,75-83. (12) Small, P. A.; Small, K. W.; Cowley, P. Trans. Faraday SOC.1948, 44,810-6. (13) Pupp, C.; Lao, R. C.; Murray, J. J.; Pottie, R. F. Atmos. Enuiron. 1974,8,915-25. (14) Sawver, L. J . Assoc. Off. Anal. Chem. 1978.61.272-81. (15) Giam, C. S.; Chan. H:’S.; Neff, G. S. Anai. &em. 1975, 47, 2319-20. (16) Westcott, J. W.; Bidleman, T. F. J. Chromatogr. 1981, 210, 331-6. (17) Sissons, D.; Welti, D. J . Chromatogr. 1971,60, 15-32. (18) Webb, R. G.; McCall, A. C. J. Assoc. Off. Anal. Chem. 1972,55, 746-52.
Volume 15, Number 11, November 1981 1377
(19) MacKay, D.; Wolkoff, A. W. Enuiron. Sci. Technol. 1973, 7 , 611-4. (20) Lee, M. C.; Chain, E. S. K.: Griffin. R. A. Water Res. 1979.13, 1249-58. (21) Haque, R.; Schmedding, D. W.; Freed, V. H. Enuiron. Sci. Technol. 1974,8,139-42. (22) Lawrence, J.; Tosine, H. M. Environ. Sci. Technol. 1976, 10, 381-3. (23) Paris, D. F.; Steen, W. C.; Baughman, G. L. Chemosphere 1978, 4,319-25. (24) Wallnofer, P. R.; Koniger, N.; Hutzinger, 0.Analabs, Res. Notes
1973,13,14-6. Hutzinger, 0.;Safe, S.; Zitko, V. “The Chemistry of PCB’s”; CRC Press: Cleveland, OH; 1974, p 16. (25) Haaue. R.: Schmeddine. D. Bull. Environ. Contam. Toricol. ~... 1975, i 4 , i3-8. I
~
~
Receit~edforreuiew February 23,1981. Revised Manuscript Received July 1 , 1981. Accepted July 24,1981. This work was supported by the U.S. Enuironmental Protection Agency under grant no. 807048-01. Contribution number 416 of the Belle W . Baruch Institute.
Chemical Associations of Lead, Cadmium, Copper, and Zinc in Street Dusts and Roadside Soils Roy M. Harrison,* Duncan P. H. Laxen,?and Simon J. Wilson Department of Environmental Sciences, University of Lancaster, Lancaster LA 1 4YQ, England The chemical associations of Pb, Cd, Cu, and Zn in street dusts and roadside soils have been investigated by a sequential extraction procedure, which yields five fractions termed exchangeable, carbonate, Fe-Mn oxide, organic, and residual. In the soils and dusts examined which covered a pH range of 6.9-8.4, only in the case of cadmium is there any appreciable proportion of total metal in the exchangeable fraction. Lead and zinc are predominantly associated with carbonates and Fe-Mn oxides, whereas copper is largely in organic association. The results are interpreted in terms of the environmental mobility and bioavailability of the metals. Introduction
Street dusts often contain elevated concentrations of a range of toxic metals (1-4). In some instances the dusts may represent a significant pollutant source, especially when storm-water runoff removes a large part of the street dust and its associated metal from the roadway causing an increased metal input to rivers and/or sewage treatment works ( 5 , 6). I t has also been suggested that street dusts can be an important source of metal intake for young children due to inadvertent ingestion of the dust ( 7 ) .Roadside soils show considerable metallic contamination due both to direct deposition of vehicle-derived metal and to relocation of metals deposited on the road surface. In the case of both street dusts and roadside soils, the environmental mobility and bioavailability of the metal is dependent upon the physicochemical forms in which the metal is associated with the dust or soil. There is, however, little information available upon which to base an assessment of this question. Olson and Skogerboe (8) have used a preconcentration procedure in conjunction with X-ray powder diffraction (XRD) to study the crystalline forms of lead in street dusts and roadside soils. They concluded that PbS04 was the principal form of lead in the samples examined. More recently, Biggins and Harrison (9),using a similar approach, confirmed PbS04 to be the most commonly observed lead compound in street dusts but, in contrast to the earlier work of Olson and Skogerboe, concluded that only a few percent a t most of the lead was present as crystalline compounds amenable to XRD analysis. They concluded further that the lead added to street dust from automotive emissions was being converted to other noncrystalline physicochemical forms and that alternative approaches to speciation must be sought. The chemistry of + Present address: Grant Institute of Geology, -. University of Edinburgh, Edinburgh EH9 3JW, Scotland.
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Environmental Science & Technology
metals other than lead does not appear to have been studied in this type of sample. The present study reports results from the application of a sequential extraction procedure to the study of the chemical associations of four metals, lead, cadmium, copper, and zinc, in street dusts and roadside soils. Such procedures have been widely applied to the study of metals in soils and aquatic sediments (10-13). They are designed to remove metals selectively from the various components of the dust or soil with which they might be associated (Table I). Despite uncertainties as to the selectivity of the various extractants and to possible problems due to readsorption ( 1 4 ) , extraction procedures provide qualitative evidence regarding the forms of association of the metals and indirectly of their mobility and bioavailability ( 1 5 ) . A wide range of chemical extractants and sequential extraction schemes has been reported (10, 1 1 , 16, 17). The scheme of Tessier et al. (16)selected for the present study is one of the most thoroughly researched and, unlike many schemes, separately defines a carbonate fraction (Table 11). The terminology used to describe the separate fractions throughout this paper will be that of Tessier et al. ( 1 6 ) , although it must be borne in mind that the extractions are not entirely specific and there will be overlap between the fractions. Experimental Section
The sequential extraction scheme is summarized in Table
11. Extractions were performed on duplicate subsamples (ca. 1 g) which had been finely ground after passage through a 600-pm mesh to remove extraneous material. Duplicate sub-
Table 1. Classification of Metals Associated with Dusts, Sediments, and Soils classification
form of associatlon a
Extraction technique
soluble
metal ppt; pore water
release to pure water or river water
exchangeable
specifically adsorbed; ion exchangeable
exchange with excess cations
carbonate phase Fe-Mn oxide phase organic phase residual
ppt or co-ppt
release by mild acid
specifically adsorbed, co-ppt complexed; adsorbed in mineral lattices
reduction
a
oxidation digestion with strong acids
ppt = precipitate.
0013-936X/81/0915-1378$01.25/0
@ 1981 American Chemical Society
