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detoxlcation reactions: oolvmerization. dechlorination
...
Flgure 3. Detoxication scheme based on the use of Cu(I1)-smectite as a catalyst.
PCP reaction product was highly colored (purple) and because dimerization previously observed in Cu(I1)smc Aite occurred at the para position, as in the case of anisole which formed 4,4'-dimethoxybiphenyl (5). HPLC analysis of the PCP reaction products showed no peaks corresponding to the retention time of an authentic standard of octachlorodibenzo-p-dioxin.The masses at mle 424 ( A 2), 390 ( A + 2), and 356 ( A + 2) correspond to PCP dimers having seven, six, and five chlorine atoms, respectively. The relative intensities of the A , A + 2, A + 4, A + 6, and A + 8 masses were consistent with these numbers of chlorine atoms. It is not clear whether the lower chlorinated dimers were separate reaction products or if they appeared as fragmentation products from the molecular ion at mle 460. A visible spectrum'of 3-chloroanisole radical cations formed on Cu(I1)-smectite showed two main peaks, one in the red region at 625 nm and the other at 465-475 nm in the blue. These two peaks represent two species, the one at 625 nm being the monomer radical cation and the one at 465-475 nm a dimer radical cation. The rationale for this statement is that the clay initially turns blue which suggests an absorption band in the red region. This would be the first reaction to occur. Then with time the color changes to more green, which would signal the dimerization process.
+
Discussion The results demonstrate that chlorinated phenols and anisoles form radical cations and polymerize upon refluxing in hexane together with Cu(I1)-smectite. Thus, the presence of chlorine on the aromatic ring does not prevent the oxidation reaction from occurring. For phenol, this is true even when the ring is fully chlorinated as demonstrated for PCP. In addition to the polymerization reaction, the observation of a dechlorination reaction taking place, as in the case of PCP going to a tetrachlorophenol, is of interest. Both dechlorination and polymerization
reactions may be important steps in the ultimate detoxication of organochlorine pollutants. The work reported here suggests the possibility of using Cu(I1)-smectite as a catalytic material to alter or degrade chlorinated aromatic molecules that may be present in industrial wastes or elsewhere. This material could easily be reused by oxidation of Cu(1) to Cu(I1) with air (Figure 3). This work supports the earlier observation of radical cation formation and polymerization of some dioxins (9) via the same reaction. Once the reactive radical cation is formed, it may be subject to a variety of detoxication reactions (e.g., polymerization, dechlorination) resulting in the formation of less toxic products (Figure 3). Advantages of this system are that the Cu(I1)-smectite is easily prepared from natural products such as Wyoming bentonite, the reaction temperature is low (69 "C, the boiling point of hexane), and the process is relatively inexpensive compared with other disposal operations (e.g., incineration). Registry No. PCP, 87-86-5;p-HOCsH4CI,106-48-9; 3935-95-5. chloroanisole, 2845-89-8;2,3,5,6-tetrachlorophenol,
Literature Cited (1) Doner, H.E.;Mortland, M. M. Science (Washington,D.C.) 1969, 166, 1406. (2) Mortland, M. M.; Pinnavaia,T. J. Nature Phys. Sci. 1971, 229, 75. (3) Pinnavaia, T.J.; Mortland, M. M. J. Phys. Chem. 1971,75, 3957. (4) Rupert, J. P.J. Phys. Chem. 1973, 77,784. (5) Fenn, D.; Mortland, M. M.; Pinnavaia, T. J. Clays Clay Miner. 1973,21, 315. (6) Pinnavaia,T.J.; Hall, P. L.; Cady, S. S.; Mortland, M. M. J. Phys. Chem. 1974, 78,994. (7) Mortland, M. M.;Halloran, L. J. Soil Sci. SOC.Am. Proc. 1976, 40, 367.
(8) Sawhney, B.L.;Kozloski, R. K.; Jackson, P. J.; Gent, M. P. N.Clays Clay Miner. 1985, 32, 108. (9) Boyd, S. A,; Mortland, M. M. Nature (London) 1985,316, 532. (10) Tomita, M.; Ueda, S. Chem. Pharm. Bull. 1964, 12, 33. (11) Shine, H.J.; Piette, L. J. Am. Chem. SOC.1962,84, 4798. (12) Yang, G.C.; Pohland, A. E. In Chlorodioxins-Origin and Fate; Blair, E., Ed.; American Chemical Society: Washington, DC, 1973; pp 33-43. (13) March, J. Advanced Organic Chemistry; McGraw-Hill: New York, NY, 1977; Chapter 9.
Received for review October 30, 1985. Accepted May 9, 1986. Contribution of the Michigan Agricultural Experiment Station, East Lansing, MI, 48824-1114. MAES J. Ser. No. 12028. This work was supported by a Toxicology Research Grant from the MAES and the Michigan State University Center for Environmental Toxicology and the U S . Environmental Protection Agency (Grant CR813215).
Platinum and Palladium in Roadside Dust Vernon F. Hodge" and Martha 0. Stallard
Scripps Institution of Oceanography, University of California-San
converters significant quantities of platinum and palladium to the roadside environment. Dust samples collected from broad-leaved plants contained as high as 0.7 ppm of platinum and 2.5 times less palladium. Rains may wash this concentrate into local water systems or the ocean.
Diego, La Jolla, California 92093 brication of catalytic converters has approximately doubled the use of metals in the United States, and consequently, the autOIIIobile industry consumes as rf~uch of these rare metals as all other industries combined ( I ) . In 1977, researchers at General Motors reported that Platinum was emitted at the rate of 1-3 pgfmile (0.8-1.9 .ualkm) in the exhaust from cars equipped with catalytic converters (2). On the basis of thismeasurement, the authors of an excellent report on the platinum group I,
Since 1975, the exhaust systems of millions of new cars have been equipped with catalytic converters. The fa1058
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Table I. Platinum and Other Metals (Concentrations in ppm Dry Weight Except Iron) in Roadside Dust i n San Diego, California collection no. 1
2 3
location
date 1985
Interstate 5, Mission Bay (on ocean side) July 16 July 17 Interstate 5IInterstate 8 overpass July 18 Interstate 5, near airport turnoff
distance vehicle count from edge average daily’ of road, ft Major Freeways 110 156 000 -2 154000 96000 -2
collected from
Pt, Pd, Pb, Fe, Pt/ ppm ppm ppm % Pd
Pb/ Pt
Agapanthus sp. 0.10 0.68 Hedera sp. 0.25 Hedera sp.
0.038 1060 3.3 2.6 10600 0.28 2850 4.5 2.4 4200 0.19 2660 4.3 1.3 10600
Agapanthus sp. 0.26 Agapanthus sp. 0.30
0.081 0.15
Residential Streeta 4 5 6 l
heavy traffic La Jolla Shores Drivec La Jolla Shores Drivec light traffic 47th StreetlLandis Bellaire Court
Feb 1 June 25
14 000 14000
July 17
b
July 17
b
-2 -2
Washington 0.060 0.024 Navel Orange Myoporum sp. 0.037 0.015
880 3.1 3.2 940 3.3 2.0
3400 3100
890 2.9 2.5 14800 490 3.4 2.5 13200
Source: California Transportation Department. *Not available. In front of Scripps Institution of Oceanography.
metals, also published in 1977, estimated that it would take over 1000 years for platinum metal concentrations in roadside topsoil to reach the concentrations observed in the rich ores in South African mines (4-10 ppm) (3). While this conclusion may be true for topsoils, we recently analyzed dust from the leaves of roadside plants and found concentrations of platinum as high as 0.7 ppm and palladium as high as 0.3 ppm (Table I). The highest concentrations of both metals were found in dust collected from plants growing at the edge of heavily trafficked streets and highways and the lowest in samples collected from plants growing in the yards of houses located on lightly trafficked streets. The concentrations of both metals in the dust samples are much higher than the reported natural abundances of these elements. Thus, it appears that widespread use of the catalytic converter, which contains platinum and palladium, makes it possible for these rare metals and their compounds to enter the environment in a dispersive manner.
Sampling and Analysis Dust, which is ubiquitous in San Diego, was gathered from the surfaces of broad-leaved plants with a pure bristle brush. Ivy and agapanthus leaves, from which collections 2-5 were derived (Table I), carried such high dust burdens (1-5 mg/cm2) that it was easy to obtain more than 1 g of sample at these locations. The samples were mixed thoroughly, subsampled, and dissolved by wet ashing techniques. Platinum and palladium were isolated by anion exchange and assayed by graphite furnace atomic absorption spectroscopy (AA) (4). For comparison, lead and iron were determined by flame AA in the dissolved sample prior to ion exchange. Values reported in Table I are the average of two or more analyses of dust from the same collection. Results and Conclusions Not surprisingly, the samples that have the highest concentrations of platinum and palladium also have the highest concentrations of lead, and indicator of automobile emissions (Table I). Moreover, while the iron concentrations of the samples vary by less than a factor of 2, from 4.5% to 2.9%,the platinum and palladium concentrations vary by a factor of 20. This observation suggests artificial enrichment of the noble metals in road dust. The natural abundances of the platinum group metals are not well-known but appear to be very low. Crustal data support values of about 0.005 ppm for platinum and 0.010 ppm for palladium (5). Recently, the platinum concen-
tration in 24 oceanic sediments was found to average 0.0038 ppm ( 4 ) , close to the estimated crustal abundance. Therefore, the concentrations of platinum and palladium in road dust are anomalously high. The high-platinum dust samples in Table I are comparable to relatively rich ores. Platinum is mined in South Africa where the ores have platinum group metal concentrations of 4-10 ppm, the richest in the world, while in Sudbury, Ontario, Canada, platinum is a byproduct from processing ores with less than 1 ppm of this precious metal (3). The highest platinum values thus far reported in the oceans are in manganese nodules (6). In some shallow depth nodules, platinum concentrations approach 1 PPm. The average Pt/Pd ratio in Table I is 2.5. Catalytic converters have been reported to contain platinum and palladium in this proportion ( 2 , 3 ) . This ratio is typical of ores mined in South Africa and quite different from the ratios of 1.0 and 0.5 of ores mined in Canada and the U.S.S.R., respectively (3). The Pb/Pt ratios of the seven samples in Table I vary by a factor of 5, from 3100 to 14800. The high concentrations of the two metals in roadside dust apparently result from the combined fallout of particles emitted in the exhaust from vehicles burning leaded gasoline and those burning unleaded gasoline which are equipped with catalytic converters. The observed spread in the ratio in this limited number of samples is not surprising because of the large number of factors that can influence the distribution of these two elements. These factors include the complex vehicular mix which may vary from location to location, the particle-size distribution of the metals as they are emitted in the exhaust, particle-particle interactions in the air, driving conditions, meteorological conditions, and many other factors. Thus, the Pb/Pt ratio is most likely site dependent and could vary from time to time at the same site. However, the Pb/Pt ratios of 3400 and 3100 for samples 4 and 5, collected at the same site 5 months apart, suggest that the traffic mix and other conditions at this site may lead to an averaging effect which produces a characteristic Pb/Pt ratio. A simple calculation can be performed that suggests that the observed Pb/Pt ratio is reasonable in magnitude. Due to extensive inventories on vehicle types in San Diego County, it is possible to calculate that, out of a total of 838 million gallons (3.17 billion L) of unleaded and leaded gasoline delivered to the county gasoline stations in 1984, 623 million gallons (2.36 billion L) were consumed by automobiles equipped with catalytic converters (7), or 3 times more gasoline was consumed by automobiles with catalytic Envlron. Scl. Technol., Vol. 20, No. 10, 1986
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converters. If we assume (A) that all vehicles in the county system average 15 miles/gal of fuel (6.4 km/L), (B)that each vehicle equipped with a catalytic converter emits 2 pug of platinum/mile (1.3 pg of Pt/km) (2),(C) that each vehicle burning leaded gasoline emits 100% of the lead in the fuel it consukes or approximately (0.8 g of Pb/gal)/(l5 miles/gal) = 53 000 pg of Pb/mile (33 000 pg of Pb/km), and (D) that all of the emitted metals end up in road dust, a Pb/Pt ratio of (53000 pg of Pb/mile)/[(Bpg of Pt/mile) X 31 or 9O00 results. This value is roughly the average ratio observed for the seven environmental road dust samples in Table I (8600) and suggests that the complex set of factors perturbing this ratio are interacting to produce a range of at least a factor of 5. In conclusion, dust accumulating along freeways and busy streets can concentrate upwards to 1ppm of platinum and half as much palladium. It is probable that the first rains after long periods of dry weather, which are common in southern California, will concentrate platinum and palladium from rooftops and streets and send relatively large amounts of both soluble (in laboratory conditions approximately 10% of the platinum emissions was water soluble (2))and insoluble forms of these rare metals into storm drains leading to the Pacific coastal waters. Thus, the release of platinum and palladium into the environment from auto emissions may not only impact the environments close to streets and highways but also the local ocean waters where the platinum and palladium concentrations are very low, approximately 150 pg of P t / L and 40 pg of Pb/L (4, 8), as well as other open water systems. There is one report of an increase in palladium concen-
trations in the most recently deposited sediments in the moat that surrounds the Emperor’s Palace in Tokyo (8). This may indeed be due to runoff from adjacent streets traveled by automobiles equipped with catalytic converters.
Acknowledgments We thank Edward D. Goldberg of Scripps Institution of Oceanography and Robert J. Mross and Virginia Bigler-Engler of the San Diego County Air Pollution Control District for the data on gasoline consumption by vehicle types. Registry No. Pt, 7440-06-4; Pd, 7440-05-3; Pb, 7439-92-1; Fe, 7439-89-6.
Literature Cited (1) Young, G. Nl. Geogr. 1983, 164, 686-706. (2) Hill, R. F.; Mayer, W. J. IEEE Trans. Nucl. Sci.
1977
NS-24, 2549-2554. (3) Platinum Group Metals; The National Research Council, National Academy of Sciences: Washington, DC, 1977. (4) Goldberg, E. D.; Hodge, V.; Kay, P.; Stallard,S.; Koide, M. Appl. Geochem. 1986, I, 227-232. (5) Mason, €3. Principles of Geochemistry,2nd ed.; Wiley: New
York, 1958. (6) Hodge, V.; Stallard,M.; Koide, M.; Goldberg, E. D. Earth Planet. Sci. Lett. 1985, 72, 158-162. (7) Mross, R. J., San Diego County Air Pollution Control (8)
District, personal communication, 1985. Lee, D. S. Nature (London) 1983, 305, 47-48.
Received for review October 7, 1985. Accepted May 12, 1986.
Using UNIFAC To Calculate Aqueous Solubilities Wllllam Brian Arbuckle Department of Civil Engineering, University of Akron, Akron, Ohio 44325
Several problems have been noted in the literature when UNIFAC has been used to calculate environmental parameters. This article evaluates UNIFAC to aid those interested in applying the technique. The original UNIFAC calculation procedure should be used with the most recent (1982) interaction parameters. When organic solid solubilities are calculated, fugacity corrections should not be made, even though theory requires them, because poorer estimates result. Within a family of compounds systematic errors may result, but they can be corrected. Missing interaction parameters can be estimated if sufficient data are available. UNIFAC’s accuracy for solubility estimates could be improved if a new set of interaction parameters were developed on the basis of infinite-dilution activity coefficients of compounds in aqueous solution.
Introduction UNIFAC-calculated infinite-dilution activity coefficients (7”) can be used to calculate the aqueous solubility (Cs, mol/m3) of immiscible organic compounds using (1, 2) C, = 55556/y” (1) where 7”is greater than 1000 for liquid solutes and greater than 100 for solid solutes (3, 4 ) . This technique underestimates solubility for many compounds ( I ) ,so regression equations have been proposed to improve solubility estimates (5). Others have used UNIFAC to calculate activity coefficients and state “UNIFAC results in very inaccurate 1060
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activity coefficients” (6). To aid those interested in applying UNIFAC, this article evaluates (1) UNIFAC interaction parameter data bases (7, 8) (2) standard and modified calculation procedures (9, IO) (3) solid solubility and indicates UNIFAC accuracy. In addition, systematic errors and missing interaction parameters are discussed.
Data Sets UNIFAC calculates activity coefficients (y)by dividing them into two parts: log y = log yc + log Y R (2) Both are calculated on the basis of the molecule’s functional groups (CH2, C=C, OH, COOH, etc.), and the combinatorial fraction (yC)is based on the functional group surface area and volume; these values are available in a table (7). The residual fraction (yR) is calculated by considering interaction energies between functional groups within the mixture; again the values are in a table (7),but many values are missing, indicating that insufficient data were available for determining the interactions between those functional groups. The original UNIFAC article identified 18 functional groups with their assaociated interaction parameters (9);these parameters worked well for vapor-liquid equilibria (VLE) but did not perform satisfactorily for liquid-liquid equilibria (LLE) calculations (8). This LLE weakness resulted in the development of an additional set of interaction parameters (8). Later, the
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