Environ. Scl. Technol. 1901,25,1128-1133
has hydrogens on C5 and C6, and tN9, a nonachloro compound that has a fully chlorinated ring 2, are about the same. This observation suggests that the epoxidase can discriminate between the two sides of the methanoindane molecule and is configured to accept ring 1 but not ring 2. It is known that the two octachlorochlordanes, aCL and gCL, are metabolized to different products. The endo isomer, gCL, produces an optically active form of OXY, but the exo isomer, aCL, is metabolized to a racemic mixture of OXY isomers (13). aCL is also metabolized to relatively hydrophilic compounds that are excreted in the urine, but gCL is not (14). Remembering that compounds without a C2 hydrogen (such as MC6 and OXY) are poorly excreted, it is likely that the first step in the metabolism is a displacement of a hydrogen on C2 by an oxygen. The different metabolic pathways of aCL and gCL also suggest that the metabolic process is a stereospecific reaction, which is sensitive to the exo or endo position of the hydrogen on C2. The nonachlors are metabolized to OXY in a process that starts with dechlorination a t C3 to produce the corresponding octachloro compound. As a result of this dechlorination, the metabolic products from tN9 are the same as those produced from gCL (8, 9). The relatively long half-lives of the compounds with three chlorine atoms on ring 1suggest that dechlorination of this ring is the rate-limiting step in their metabolism. The stereochemistry of the enzyme/substrate interaction must be very specific to account for the large differences in depuration we have observed for the various chlordanes. The differential depuration of the various configurational isomers of ring 1, coupled with the apparent lack of metabolism of ring 2, strongly suggests that ring 1 (particularly carbons 2 and 3) is the critical site of interaction with the epoxidase.
Animal Research Facilities in Medical Sciences at Indiana University. Registry No. MC7, 31503-68-1; MC5, 31503-68-1; MC4, 133043-33-1;MC3,9831899-1; cN9,5103-73-1; MC6,130939-67-2; tN9,39765-80-5; aCL, 5566-34-7; OXY, 27304-13-8; HEP, 102457-3; gCL, 5103-71-9; chlordane, 12789-03-6.
Literature Cited (1) U.S. Environmental Protection Agency Fed. Regist. 1987, 52. 42145-42149. (2) Taguchi, S.;Yakushiji, T. Arch. Environ. Contam. Toxicol. 1988. 17. 65-71. (3) Dearth, 'M.; Hites, R. Environ. Sci. Technol. 1991, 25, 245-254. (4) Muir, D.; Norstrom, R.; Simon, M. Enuiron. Sci. Technol. 1988,22, 1071-1079. (5) Kawano, M.; Inoue, T.; Hidaka, H.; Tatsukawa, R. Enuiron. Sci. Technol. 1988, 22, 792-797. (6) Kramer, W.; Buchert, H.; Reuter, U.; Biscoito, M.; Maul, D.; Le Grand, G.; Ballschmiter, K. Chemosphere 1984,13, 1255-1267. (7) Brimfield, A.; Chatfield, D. Pestic. Biochem. Physiol. 1978, 9, 84-95. (8) Tashiro, S.; Matsumura, F. Arch. Environ. Contam. Toxicol. 1978, 7, 113-127. (9) Jackson, M.; Suggs, J.; Lewis, R. Abstracts of Papers, 170th National Meeting of the American Chemical Society, 1975; American Chemical Society: Washington, DC, 1975; PEST 84. (10) Miyazaki, T.; Yamagishi, T.; Matsumoto, M. Arch. Enuiron. Contam. Toxicol. 1985, 14, 475-483. (11) Jaffe, R.; Stemmler, E. A.; Eitzer, B. D.; Hites, R. A. J. Great Lakes Res. 1985, 11, 156-162. (12) Norstrom, R.; Simon, M.; Muir, D.; Schweinsburg, R. Enuiron. Sci. Technol. 1988, 22, 1063-1071. (13) Schwemmer, B.; Cochrane, W. P.; Polen, P. B. Science 1970, 169, 1087. (14) Balba, H. M.; Saha, J. G. J. Environ. Contam. Toxicol. 1978, B13, 211-233.
Acknowledgments We thank Ilora Basu for efforts contributing greatly to the success of this project. We also thank the staff of the
Received for reuiew October 8,1990. Accepted February 5,1991. This work was supported by Grant 87ER60530 from the U S . Dept. of Energy.
Lead Speciation of Particles on Air Filters Collected in the Vicinity of a Lead Smelter Thomas E. Clevenger,' Chlntana Salwan, and S. I?.Kolrtyohann
University of Missouri-Columbia, Columbia, Missouri 652 11
rn Various species of lead in particles on an air filter were quantitatively determined by selective extraction, Fourier transform infrared spectroscopy,and X-ray diffractometry. A selective extraction method was developed using known lead compounds and simulated samples. The developed procedure used the following reagents: 1.0 M MgCl, 0.5 M NH~OAC, 0.1 M NaPz07,O.l M EDTA, and 4 M "03 The lead particles had to be removed from the filter and preconcentrated by use of a density separation in order to prevent interference from the filter fibers and to concentrate the lead to a level high enough to be detected by instrumental methods. PbS04 and PbS were the major lead compounds on the filter. PbO may have been present at a lower concentration. Introduction With the lowering of the air lead standards, lead smelters are faced with the problem of reducing their air lead 1128 Envlron. Scl. Technol., Vol. 25,
No. 6, 1991
emissions. This can be difficult because of the many sources of lead emissions during the processing of the lead. These include transportation, storage, sintering, smelting, and refining of lead; all which are likely to contribute lead to the environment. Before a smelter can efficiently reduce lead emissions, the exact sources of lead need to be identified. Information concerning the lead compounds or species in which the lead is found might help in the source identification. Lead from concentrate haulage as well as dust from smelter storage piles would be unaltered galena (PbS). Concentrate roasting is likely to produce lead sulfates and oxides, while blast furnace emissions could contain lead metal and oxides. Speciation is the process of identifying the various chemical forms of an element. Different chemical forms of an element have different physical and chemical properties, and important processes such as environmental transport and bioavailability are species dependent. Se-
0013-936X/91/0925-1128$02.50/0
0 1991 American Chemlcal Soclety
"i""
Table I. Selective Extraction Scheme Chosen extractant
time, h
1.0 M MgClz (PH 7) 0.5 M NH~OAC (pH 7) 0.1 M Na4P20, (pH 7) 0.1 M EDTA (pH 7) 4.0 M HNO, at 100 OC
1.5 1.5 1.5 1.5 1.0
Acetone
7 Bulk Filter
Methods and Materials Chemicals. All chemicals were analytical grade (Fisher Scientific). Deionizedjdistilled water was used for preparation of reagent solutions and all glassware was cleaned by soaking in 3% HN03 (v/v). Selective Extraction. The extraction scheme listed in Table I was used for this study. The sample was placed into a 50-mL centrifuge tube (Oak Ridge polyallomer type) with 15 mL of the extraction reagent, shaken in a twist barrel shaker at maximum setting speed for 1.5 h, and centrifuged at 7000 rpm for 10 min. Supernatants were pipeted and kept for P b analysis. Residues were rinsed twice with a small volume of deionized water and the rinsing solution was discarded. All solutions were analyzed for Pb by atomic absorption spectrometer (Perkin-Elmer 703). Density Separation. A dense solution was made of methylene iodide and iodoform. This mixture had a density of 3.35 g/mL at room temperature. The sample was transferred into a centrifuge tube for the density separation. A 3-mL aliquot of the dense solution was added into the centrifuge tube, and the tube was shaken for 5 min and centrifuged a t 7000 rpm for 5 min. The residue was rinsed with acetone until the CH212and CHI3 were completely removed from the residue. This was indicated by the disappearance of the yellow-brown color in the acetone solution. The residue was dried in a desiccator and analyzed. FTIR. A pellet of 0.3% (1-mg sample in 300 mg of KBr) of the density-separated material in KBr was prepared. The mixture was ground in a vial shaken by a mechanical vibrator (Wig-L-Bug, Crescent Dental Manufacturing Co.) for 1 min, and one-third of the ground mixture was transferred to a 13-mm-diameter die and pressed by hydraulic pressure at 15000 lb of force for 10 min. A pellet was immediately mounted in a sample holder on the FTIR instrument for IR spectrum recording. The infrared spectrum was obtained at 4-cm-' resolution with 16 scans and a triglyceride sulfate detector. The spectrum was recorded from 4000 to 400 cm-' range. Identification of
I
I
4-l
AAS
lective extraction is one method currently being used to determine chemical forms. Selective extraction has been used extensively in metal speciation studies of soil (1-3), sludges (4, 6), and sediments (7-9). Although the extraction method provides valuable information as to chemical forms, there are questions as to its reliability (8-11). It is influenced by factors such as the choice of reagents, extraction sequence, time of extraction, and the ratio of extractant to sample. Inherent analytical problems exist, such as selectivity, readsorption, and incomplete distribution of a metal among various fractions. A thorough validation of extraction methods is necessary for each sample type. The purpose of this research was to develop a method to identify the species of lead in particles on air filters collected near a lead smelter. The speciation method chosen to be used for this study was sequential/selective extraction with confirmationby Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction.
Used Acetone
Residue
AAS
Separation
SelectiveExtraction (MgCh:h'&OAc;HNO,)
Heavy Fraction I
Selective Extraction
RIR
Light Fraction I
X-ray Diffraction
AAS
Flgure 1. Schematic diagram of air filter analysis.
the lead species was done by comparison with the infrared spectra of pure lead compounds, which were obtained under the same conditions as was the sample. For accurate quantitative analysis, an equal amount of ground mixture, applied pressure, and pressing time for both standard and sample were necessary. Quantitative analysis of lead species was obtained by the establishment of a calibration curve using the characteristic peaks for known amounts of the compounds. Samples were analyzed by use of a Nicolet Model 60SX FTIR. X-ray Diffraction. Grinding of the solid material was needed when a sample was not finely powdered. The material was ground with a mortar and pestle, mixed with xylene to form a slurry, and spread on a glass microscope slide as a thin smear, and diffraction patterns were recorded in a locally modified computer-controlled GE XRD-5 X-ray powder diffractometer. Patterns were recorded as step scans (0.4' 28 steps, 10 s/point) from 5 to 125O, and the data were stored on computer disks for later analysis. The diffraction patterns of the samples were identified by comparison of d spacing and relative intensity with Joint Committee on Powder Diffraction Standards (JCPDS) powder diffraction files (11). The identifications were also confirmed by matching diffraction patterns of the samples to the pure compound patterns. Air Filters. Air filters collected around a lead smelter, consisting of 8 in. X 10 in. type A/E glass fiber filters (Gelman Sciences Inc.), were provided by personnel from the AMAX lead smelter before its sale and subsequent closing. The particles were separated and analyzed in accordance with a schematic diagram in Figure 1. The particles on the filters were removed by rinsing them with a vigorous stream of acetone. The particles in the acetone solution were separated by centrifugation at 7000 rpm for 5 min. The acetone filtrate containing the suspended fine glass fibers of the filter was evaporated until dried, digested with "OB, and analyzed for P b by atomic absorption spectroscopy ( U S ) . After acetone rinsing, the remaining bulk filter was digested with HN03 and analyzed for the unremovable lead by flame AAS. The settled particles from the centrifugation were dried at room temperature and added to a methylene iodide solution for density separation. Since the particles were very fine, grinding waa not necessary. The particles having a density greater than 3.3 separated to the bottom, while the fine filter fibers and other impurities with a density less than 3.3 remained suspended in the solution. The heavier particles, "heavy fraction", including the lead species, were separated from the methylene iodide solution by centrifugation, rinsed Environ. Sci. Technol., Vol. 25, No. 6, 1991
1129
Table 11. Percent Extraction of P u r e Lead Compounds by Various Reagents" reagent 1.0 M MgCIz 0.5 M NH~OAC 0.1 M Na4P2O7 0.1 M EDTA
PbSO,
PbO
PbCO,
95 k 2 100 f 5 100 f 10 102 f 4
1 f 0.4 81 f 2
2 f 0.8 10 k 1 99 f 8 103 f 4
91 f 3 100 zt 4
Pb304 0 3 f 0.3
7ztl 102 f 5
PbOz 0 0 0
102 f 6
PbS 2 f 0.1 2 f 0.3 3 f 0.2 4 f 0.6
The standard deviation was calculated by using six replicates.
Table 111. Selective Extraction of Lead Compounds Mixture by Various Reagents with and without Glass Filter Present reagents
predicted Pb, mg actual Pb, mg
% diff
Control Mixture with No Filter 1.0 M MgClz 4.31 4.84 0.5 M NH40Ac 8.96 9.12 0.1 M Na4Pz07 14.08 13.17 0.1 M EDTA 26.08 24.92
20 10
O
M
0
WM
1.0 M MgCI, 0.5 M NH40Ac 0.1 M Na4P2O7 0.1 M EDTA
-
0
.
5.8
,
6.0
.
~
6.2
.
,
6.4
.
,
6.6
.
,
68
.
,
70
.
,
7.2
.
~
7.4
.
,
7.6
.
,
7.8
.
:
6.0
.
1
11 2
7 5
Mixture with Glass Filter 3.51 1.97 9.72 7.76 13.02 11.50 22.95 22.38
78 25 13 2
MG Lead
8.2
I
PH
i
-I
Flgure 2. Selective extraction of PbO and PbC03 by acetate as a function of pH.
with acetone several times to remove CHI,, dried, and kept in a desiccator for further analysis. The light particles, "light fraction", were also separated from the CH212solution, rinsed several times with acetone, digested with HNO,, and analyzed for Pb by AAS. Both the heavy and light fractions were analyzed by the selective extraction method, FTIR spectroscopy, and X-ray diffraction.
Results and Discussion Selective Extraction. After several different extractants were tried, those listed in Table I were selected Decause of their ability to separate the lead compounds of interest. These were tested by having each extract a mixture containing each of the six lead compounds listed in Table I1 (10 mg each). The results in Table I1 show that it was possible, using this extraction scheme, to differentiate between five of the six lead compounds by sequential extraction. The selective extraction of PbS04 by the 1 M MgCl, solution was due to the formation of PbCl, and higher complex species of chloride ions. O'Conner and Kester (12) reported that the desorption of metals by MgCl, increased with ionic strength and activities of chloride and magnesium ions. The extraction of lead with NH40Ac is sensitive to pH. Extraction conditions were studied by varying the concentration and the pH of the solution (Figure 2). The optimum condition was chosen at pH 7 in which 80% of PbO and 10% of PbC03 were separated. The carbonate fraction was determined by using 0.1 M Na4PzO7solution at pH 7. Approximately 90% of PbO and 100% of PbC03 were extracted in this solution. EDTA extraction showed that it was an excellent chelating agent for all of the lead compounds except PbS. Digestion with concentrated HN03 was added as step 5 in order to dissolve all of the lead compounds, including PbS. In order to validate the method for an air filter matrix, pieces of a new A/E high-volume filter were spiked with the six standard lead compounds being studied. Lead 1130 Environ. Scl. Technol., Vol. 25, No. 6, 1991
go
16
. . .
...
, . .
, PbSO4 , , PBO , , PBS , Flgure 3. Lead speciation by selective extraction of the heavy, light, and bulk fractions.
recovery in each fraction was less than predicted (Table 111). The control results, containing no filter, agreed with the predicted lead concentrations. In particular the MgClz extraction showed very poor agreement, 78% difference. Lead was being adsorbed by the borosilicate fibers in the solution after the extraction had taken place. The filters broke into fine microfibers under the extraction conditions. These fine borosilicate fibers were suspended and dispersed in the solution, which increased the filter surface area. The adsorption of lead particles could actually be seen in the extraction of the orange-red Pb304with the EDTA solution. In the absence of a filter, the red Pb304 was completely extracted by the EDTA solution within 15 min and the color of the Pb&4 changed from orange-red to colorless. In the presence of the fine fiber, only part of the Pb@4 was extracted, and the orange-red Pb,04 was still present over a 1.5-h extraction period. The selective extraction method does not appear feasible for the direct determination of lead in the particles on filters. Air Filters Using Density Separation. A density separation was used in order to overcome the following problems: (1) filter interferences with the selective extraction method, (2) the inability of X-ray diffractometry
?
2.
ST2(PbS04+L imes tone)
E!
-
? -0
?:
ST2-STL(PbS04)
PbS04 .m
AN$iW*-&.n
sb.00
Ibo.00
1’10.00
1‘20.00
ia.00
%-
8 8-
I L i m s tone
“0
Figure 4. X-ray diffraction of iimestone-spiked standards. (a) PbSO,; (b) PbS.
and FTIR spectroscopy to detect the lead because of high background scattering from filter material and dust particles, and (3) lead concentrations too low for detection by instrumental methods. Following the outline given in Figure 1,an air filter containing particles with 2.3% lead, collected near a lead smelter, was rinsed with acetone and the particles in the acetone were separated and transferred to a methylene iodide solution for density separation. The bulk filter, after removal of the particles (Table IV), contained only 15.6 mg of Pb or 26% of the original lead. Only 1% of the Pb was found suspended in the acetone solution. The heavy and light fractions from the density separation contained 61.5% and 7.8% of the original Pb, respectively. The bulk, heavy, and light fractions were analyzed by selective extraction to determine the lead species. The heavy fraction contained 61.5% of the original lead with a distribution of 37% PbS04, 1.3% PbO, and 61% PbS. The light fraction contained only 7.8% of the original lead with a distribution of 84% PbS04,0% PbO, and 16% PbS. The bulk filter, after the removal of the particles, still contained 26% of the original lead with the distribution of lead as 36% PbS04, 33% PbO, and 31% PbS. All of
the PbO was still on the filter and was not removed from the filter by the acetone rinse. If only the heavy fraction of the density separation had been analyzed, the PbO would have been overlooked. The light fraction preferentially retained the PbS04. None of the fractions taken alone truly represent the actual original lead on the filter. By adding the individual fractions, the original lead on the filter was 41.2% PbS04, 10.1% PbO, and 48.8% PbS (Figure 3). This assumed that there were no other P b compounds present except the six included in this study. Other lead compounds that might be in the air (lead metal, organic lead, lead silicates) need to be added to the extraction scheme in order to make it more comprehensive. The FTIR analysis gave no indication of PbS04 in the bulk filter or in the light fraction, but there was 14% PbS04 in the heavy fraction. This was calculated from absorbance of the 619-cm-’ peak and a calibration curve. Since the FTIR did not show the PbS04 in the light fraction, the concentration of PbS04 may be below the detection limit. There was only 0.3% sample in a KBr pellet. Raising the mass in the KBr pellet to improve the detection limit was unsuccessful, because the pellet became Environ. Sci. Technol., Voi. 25, No. 6, 1991
1131
0
H, LIGHT FRACTION
I ? O0.00
f0.W
i?O.OO
j0
W
4b.00
Sb.W
dO.00
ANGLE
7b.00
2-THETA
d0.00
