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Envlron. Sci. Technol. 1988, 20, 171 174
Response of Atmospheric Lead to Decreased Use of Lead in Gasoline Steven J. Elsenrelch,' Nancy A. Metrer, and Noel R. Urban Environmental Engineering Program, Department of Civil and Mineral Engineering, University of Minnesota, Minneapolis, Minnesota 55455
John A. Robblns Great Lakes Environmental Research Laboratory, NOAA, Ann Arbor, Michigan 481 04
rn Wet-only precipitation collected in urban Minneapolis, MN, and rural, northcentral Minnesota (Marcell) has been analyzed for P b since the late 1970s. Annual volumeweighted mean concentrations of Pb in precipitation have decreased from 29 to 4.3 pg/L a t the urban site and from 5.7 to 1.5 pg/L at the rural site in the years 1979-1983. Annual Pb fluxes in precipitation have decreased from 1979 to 1983: 2000 to 370 (ng/cm2)/year at the urban site and 430 to 100 (ng/cm2)/year at the rural site. Decreases in atmospheric P b fluxes are closely correlated with decreases in P b used in gasoline in Minnesota and nationally and with a recently constructed atmospheric P b source function for the Great Lakes region. Introduction The atmosphere is recognized as an important if not major contributor to the geochemical cycling of many major and trace elements (e.g., 1,2). The primary sources of inorganic atmospheric aerosols are wind-blown continental dust, sea spray, volcanism, biological activity, and anthropogenic emissions (1-4). The first four represent primarily natural sources of metals to the atmosphere. The ratio of anthropogenic emissions to total natural emissions is the highest for the atmophilic elements Sn, Cu, Cd, Zn, As, Se, Mo, Ag, Hg, and P b (1). The importance of anthropogenic sources to atmospheric burdens is best demonstrated for P b for which combustion of gasoline and smelter operations contribute most of the atmospheric emissions (5, 6 ) . Significant attention has been focused on the health effects of lead in urban areas, in continental North America, and globally (2, 7-11). The geochemical cycling of lead in urban areas (6, 8, 12), forest and bog ecosystems (13-18), lakes (1+22), oceans (e.g., 23-26), and atmosphere has been studied extensively. These studies conclude that atmospheric P b is derived largely from combustion of leaded gasoline, occurs primarily attached to aerosol smaller than 0.2 pm in diameter, is efficiently scavenged by precipitation, has an atmospheric residence time on the scale of days, and may be transported long distances from emitting sources. Wet removal processes are more important then dry deposition except near heavily traveled roadways and in urban and industrial centers (11,301. Since 1968-70, the lead content in gasoline has decreased steadily (32)and may be eliminated by 1990. Profiles of P b in dated sediment cores (21,33-38) and Pb in atmospheric aerosol (39) suggest that the environment is responding to decreasing use of leaded gasoline. The objectives of this paper are to document the response of atmospheric lead to decreased use of leaded gasoline and to compare atmospheric trends to an updated atmospheric P b source function applicable to the Great Lakes region. Experimental Section Wet-only precipitation has been collected over the last 5 years at the University of Minnesota (45O N, 93O20' W) and for 3 years a t a National Atmospheric Deposition 0013-936X/86/0920-0171$01.50/0
Program (NADP) site near Marcell, MN (47'32' N, 93'28' W), the location of an in-depth study on the biogeochemistry of a Sphagnum bog. Marcell is located approximately 320 km north of Minneapolis, MN, and 160 km northwest of Duluth, MN. The area is forested primarily with spruce, aspen, and birch and is remote from major local atmospheric P b sources. Previous studies in northeastern Minnesota provide additional precipitation data in 1977 and 1979 at nearby sites (4, 40). Weekly integrated, wet-only precipitation was collected at both sites by using automatic sensing wet/* Aerochem Metric samplers. Samples were collected in polyethylene buckets previously rinsed and leached for 3 weeks with distilled, deionized water. Samples were acidified to 1% (volume) with redistilled, concentrated nitric acid once transferred out of the sampling bucket and were then stored in acid-washed polyethylene bottles at 4 OC in the dark until analyzed. All concentrations represent acidsoluble lead. Lead was determined by flameless atomic absorption using a Perkin-Elmer Model AAS with Model 400 graphite furnace. Snow cores were collected about 2 weeks prior to snowmelt at the Marcell site to determine P b loading rates between November and April in 1981-83. Before snowfall commenced, three 1-m2 plots were covered with polyethylene sheets to serve as a clean sampling base in late winter. In late March or early April each year, several snowcores were obtained from each plot using plexiglass tubes that had been soaked and rinsed with distilled, deionized water. The snow was transported to the laboratory in clean plastic bags where the snow was melted slowly and treated as described above. The plastic bags did not contribute to analytical blanks above 0.1 pg/L. The wet-only automatic sampler dt the urban site operated through the winter months. Analytical blanks were typically below the working detection limit of 0.1 pg/L. Uncertainty in the analytical measurement was *27% at the detection limit and f 6 % at 26 pg/L, typical of high values encountered. In all cases, propagation of error in the calculation of annual atmospheric loading rates resulted in error estimates of less than 10%. Results and Discussion The last 40 years have seen lead released into the environment in quantities far greater than any previous emissions. The primary source of atmospheric P b is exhaust from automobiles using leaded gasoline. However, lead alkyls used as antiknock additives in gasoline were not the first source of anthropogenic lead. Widespread atmospheric P b contamination occurred in Southeast Asia 4500 years ago when methods for the smelting of lead sulfide ores and cupellation of silver were developed (41, 42). The Romans increased environmental P b concentrations to about 5 times background 1800-2000 years ago. The next major increase occurred about 250 years ago at
0 1986 American Chemical Society
Envlron. Sci. Technol., Vol. 20, No. 2, 1986
171
30
1
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Table 11. Atmospheric Pb Fluxes to Urban and Rural Sites in Minnesota
year
Pb loading, (ng/cm2)/rear urban rural
Figure 1. Average lead content of regulargrade gasoline used in the United States (47).
1977 1979 1981 1982 1983
2000 640 480 370
Table I. Pb Concentrations in Precipitation at Urban and Rural Sites in Minnesota
year
15 + Summer -A- Winter
10 0.5
I
-/
v
1950
year 1979 1981 1982 1983
year 1979 1981 1982 1983
1960
1970
1980
Pb concn ranges, p g / L urban rural 1.3-193 1.1-109 0.6-39.9 0.1-16.7
0.2-20.8 0.5-6.1 0.1-8.4
volume-weightedmean Pb concn, pg/L urban rural 29 9.5 6.6 4.3
5.7 2.3 1.5 1.5
the onset of the Industrial Revolution when P b concentrations increased to 10 times background (41). In the mid-l940s, atmospheric P b concentrations increased sharply due to massive increases in P b emissions from automobiles (42, 43). Since that time, increased P b emissions to the atmospheric have matched trends in gasoline Pb content (Figure 1) and consumption. Passage of the Clean Air Act in 1972 decreased lead usage substantially. Nevertheless, P b inputs to a subalpine ecosystem in the late 1970s were still 20 times the background levels of a few centuries ago (43). The ranges and volume-weighted mean concentrations of Pb in annual precipitation have decreased substantially since 1979 at both the urban and forested, rural sites (Table I). Lead concentrations have decreased at the urban site from a volume-weighted mean of 29 pg/L in 1979 to 4.3 pg/L in 1983 and from 5.7 to 1.5 pg/L at the rural site. These data show that 1983 concentrations are less than 20% of their 1979 values. Decreased P b concentrations in precipitation may be due to increased precipitation volume with no change in P b emissions (i.e., dilution), altered weather patterns, analytical problems, and/or decreased emissions. Table I1 shows that annual precipitation was relatively constant at the urban site but decreased by about 40% at the rural site from 1979 to 1983. Thus changes in annual rainfall cannot explain decreased concentrations and loading rates. There is no suggestion that atmospheric weather patterns in the Midwest have changed izl the last several years either. Although P b represents well-known analytical difficulties (42), measures were taken to minimize conm i n a t i o n and loss while applying sensitive measurement tools. Techniques used to avoid contamination were not changed over the span of this study and thus are not responsible for decreased P b concentrations. We conclude that decreased Pb emissions are the cause of decreased Pb concentrations in precipitation. Atmospheric P b fluxes were calculated by multiplying volume-weighted mean concentrations by annual precip172
Environ. Sci. Technol., Vol. 20, No.
2, 1986
1977 1979 1981 1982 1983
700 430 340 120 100
precipitation, cm urban rural 88.6 78.9 71.1 81.0 87.9
94.5 83.3 83.3 66.0 56.6
Table 111. Recent Precipitation Fluxes of Pb location
flux, (ng/ cm*)/year
yeads)
ref
Minnesota, urban S. Lake Michigan Minnesota, rural N. Lake Michigan N. Wisconsin, rural S. Pacific easterlies N. Pacific easterlies N. Atlantic westerlies
400-2000 970 100-300 240 600 4 10 270
1979-1983 1975-1976 1979-1983 1975-1976 1979-1980 1978-1979 1978-1979 1978-1979
this study 31
this study 31 30 11 11 11
itation measured at the urban site. At the Marcel1 site, the annual atmospheric flux was computed as the summation of weekly deposition plus the amount in the snowpack. Snowpack loading rates were 178,21, and 13 (ng of Pb/cm2)/year for 1981-1983, respectively. During the period from 1981 to 1983, P b loading rates decreased from 640 to 370 (ng/cm2)/year at the urban site and from 340 to 100 (ng/cm2)/year at the rural site. These values are placed in perespective by comparison to recent P b fluxes measured in different environments (Table 111). Lead fluxes for the forested site in northcentral Minnesota from 1981 to 1983 bridge those for the North Atlantic westerlies reported by Settle et al. ( 1 1 ) and represent values about 20 times background. Talbot and Andren (30) estimated a net P b flux to a forested area of northern Wisconsin of 600 (ng/cm2)/year for 1979-80. Wet deposition accounted for 75% of the total flux at that site. If precipitation fluxes at the Marcel1 rural site are assumed to be 75% of total fluxes (30),total Pb deposition may be 130-450 (ng/cm2)/year for the years 1983-1981. Atmospheric fluxes at the rural site of 130-450 (ng/cm2)/year are in good agreement with recent Pb accumulation rates in a nearby Sphagnum bog that receives only atmospheric inputs (400f 120 (ng/cm2)/year) integrated over 10 years of moss accumulation (15)). Decreasing atmospheric deposition rates of Pb reflect decreasing usage of leaded gasoline. Changes in the amount of P b added to the atmosphere via gasoline use in the United States (32) and State of Minnesota (44) in recent years are comparable to trends in atmospheric P b loading rates to the urban and rural sites (Figure 2). In the U.S., the total amount of Pb used in gasoline decreased from 12.95 X 1O1Og in 1979 to 5.66 X 1O1Og in 1983. For Minnesota, total P b use fell from 3.17 X lo9 g in 1979 to 1.4 x IO9 g in 1983. In both cases, the reduction in Pb use from 1979 to 1983 was 56%,and Minnesota’s use was 2.5%
.
T 800 %
5’ .
1977.
N’
.
600
{
1982
1979
1983
1981
3 J
1600
1981 1200
800
2oot1982 19838
I 0
I
I
I
I
i400 I
50 100 150 0 50 LEAD USED IN GASOLINE
I
-
I
100 150 US (Gg)
I
200
Flgure 2. Comparison of lead In gasoline use In the United States to wetonly atmospheric lead fluxes at the Marcell (rural) and Minneapolis (urban) sites.
of the national total, proportional to population. Figure 2 shows that atmospheric P b fluxes decreased by about 80% a t the urban and rural sites from 1979 to 1983 but more slowly since 1981 as P b usage leveled off. The fact that atmospheric P b fluxes have decreased more (80%) than has Pb-additive usage (56%)may indicate that more efficient controls on P b emissions may have been implemented on other P b sources. Since atmospheric P b is derived largely from anthropogenic sources and mostly from combustion of gasoline, Edgington and Robbins (33)constructed an atmospheric P b source function for 1972 based on gasoline and coal combustion nationally and normalized to the relative proportion of the national population residing in the Chicago, IL-Gary, IN, area. The magnitude of the atmospheric P b deposition was scaled to the atmospheric P b data derived from Winchester and Nifong (45). The P b source function predicted accurately the time-dependent accumulation of excess or anthropogenic Pb in sediment cores from the southern basin of Lake Michigan. An updated P b source function has been constructed (46)that is applicable to the entire Great Lakes region. The updated P b source function originally included gasoline and coal contributions to atmospheric emissions, with the coal needed to predict adequately the early tail on the sediment profiles. The P b source function presented in Figure 3 includes only gasoline contributions to P b emissions. Coal contributions are a negligible fraction of the total (46). The updated P b source function predicts accurately the time-dependent accumulation of P b in sediment cores taken in 1981 from the eastern basin of Lake Ontario and in 1982 from Lake Erie. Figure 3 shows the P b source function for the period of 1920-1983. Emissions of P b from the combustion of leaded gasoline peaked in the late 1960s through 1972 and have decreased dramatically since. The units of the P b source function or regional atmospheric loading rate (lo6 g/year) apply to the entire Great Lakes region. Superimposed on the loading function are a series of atmospheric P b measurements made in the period from the early 1960s through 1983. Measurements of aerosol P b at Argonne National Laboratory south of Chicago (39)made from 1965 through 1981 coincide with the P b source function as do aerosol measurements reported for 46 sites as part of the National Air Quality and Emissions Trends from 1975 through 1981 (47). The trends in wet atmospheric P b fluxes observed at the urban Minneapolis, MN, site and the rural Marcell site also follow the source function. The previous data demonstrate clearly the relationship between atmospheric P b burdens, wet deposition, and P b emissions derived from the combustion of leaded gasoline in automobiles. The response time of the atmosphere to changes in Pb emissions is dramatic and, of course, entirely
,OOt
I/ 1920
/ I
I
I
1940
5
1960
lvv 1950
YEAR
Flgure 3. Atmospheric lead source function compared to measurements of atmospheric lead concentrations In aerosol and precIpb%on: (0)Argonne National Laboratory (39);(0)Argonne National Laboratory Health and Safety Laboratory (HASL) Reports (48);(0)Natlonal Air Quality and Emlsslons Trends (NAQE) Reports, 46 sites (49);(V) atmospheric Pb precipitation fluxes, Marcell (rural site); (A)atmospheric Pb precipitation fluxes, Minneapolls (urban site). Regional atmospheric Pb loading rates (y-axis) are based on data collected in 1970 by Winchester and Nlfong (46). Arrows denote data for normalizationof HASL and NAQE data sets.
predictable. Since P b has an atmospheric half-life on the order of days due ita efficient removal by precipitation (301, atmospheric fluxes of P b to lakes, forests, and urban areas decrease rapidly in response to decreased emissions. This is one of the clearest examples of the response of an environmental contaminant to regulatory action via the Clean Air Act of 1972. Patterson and co-workers (11,29)point out, however, that P b fluxes remain 10-100 times background levels. Away from urban and industrial centers, the atmospheric P b burden still is derived primarily from gasoline combustion. Other emission sources such as coal-fired power plants, waste incineration, and wind-eroded soil will become more important in the future. As demonstrated by these data, atmospheric Pb concentrations and fluxes will continue to decrease substantially if use of P b in gasoline is further decreased. Acknowledgments
Our appreciation is extended to E. S. Very and A. Elling who provided assistance in obtaining precipitation samples at the NADP site near Marcell. We also wish to acknowledge the assistance of K. A. Johansen in constructing the atmospheric P b source function. Registry No. Pb,7439-92-1.
Literature Cited Lantzy, R. J.; Mackenzie, F. T. Geochim. Cosmochim. Aqta 1979, 43, 511. Galloway, J.; Thornton, J. D.; Norton, S. A.; Volchok, H. L.; McLean, R. A. Atmos. Enuiron. 1982, 16, 1647-1700. Rahn, K. A. T h e Chemical Composition of the Atmospheric Aerosol”; University of Rhode Island Technical Report: Kingston, RI, 1976. Thornton, J. D.; Eisenreich, S. J. Atmos. Enuiron. 1982, 8,1945-1955. Settle, D. M.; Patterson, C. C. Science 1980,207,1167-1176. Huntzicher, J. J.; Friedlander, S. K.; Davidson, C. I. Enuiron. Sci. Technol. 1975, 9, 448-457. Needleman, H. L.,Ed. “Low Level of Lead Exposure; the Clinical Implications of Current Research”; Raven: New York, 1980. National Research Council “Lead in the Environment”; Washington, D.C., 1980; 524 pp. Nriagu, J. O., Ed. “The Biogeochemistry of Lead in the Environment. Part A: Ecological Cycles”; Elsevier-North Envlron. Sci. Technol., Vol. 20, No. 2, 1986
173
Holland Biomedical Press: New York, 1978. (10) Munger, J. W.; Eisenreich, S. J. Environ. Sci. Technol. 1983, 17,32-40A. (11) Settle, D. M.; Patterson, C. C.; Turekian, K. K.; Cochran, J. K. J . Geophys. Res. 1982, 87, 1239-1245. (12) Brown, R. G. “Atmospheric Deposition of Selected Chemicals and Their Effect on Non-point Source Pollution in the Twin Cities Metropolitan Area, Minnesota”; U.S. Geol. Survey, Water-Res. Invest. Rept. 83-4195: St. Paul, MN, 1984; 24 pp. (13) Van Hook, R. I.; Harris, W. F.; Henderson, G. S. Ambio 1977, 6, 281-286. (14) Smith, W. H.; Siccama, T. G. J . Environ. Qual. 1981, 10, 323-333. (15) Schurr, K. A. “Biogeochemistry of Selected Metals in a Forested Sphagnum Bog in Minnesota”; M.S. Thesis, University of Minnesota, Minneapolis, MN, December 1983; 341 pp. (16) Livett, E. A,; Lee, J. A.; Tallis, J. H. J . Ecol. 1979, 67, 865-89 1. (17) Aaby, B.; Jacobsen, J.; Jacobsen, 0. S. Dan. Geol. Unders. Arbog 1979, 45-68. (18) Pakarinen, P.; Tolonen, K. Oikos 1977,28, 69-73. (19) Hesslein, R. H.; Broecker, W. S.; Schindler, D. W. Can. J . Fish. Aquat. Sci. 1980, 37, 378-386. (20) Elzerman, A. W.; Armstrong, D. E. Limnol. Oceanogr. 1979, 24, 133. (21) Heit, M.; Tan, Y.; Klusek, C., Water,Air, Soil Pollut. 1981, 15, 441-464. (22) Talbot, R. W.; Andren, A. W. Geochim. Cosmochim. Acta 1984, 48, 2053-2063. (23) Craig, H.; Krishnaswami, S.; Somayajulu, B. L. Earth Planet. Sci. Lett. 1973, 17, 295-305. (24) Turekian, K. K.; Kharkar, D. P.; Thompson, J. J . Rech. Atmos. 1974,8, 639-646. (25) Bacon, M. P.; Brewer, P. G.; Spencer, D. W.; Murray, J.; Goddard, W. Deep-sea Res. 1980,27A, 119-135. (26) Spencer, D. W.; Bacon, M. P.; Brewer, P. G. J. Mar. Res. 1981,39,119-138. (27) Lazrus, A. L.; Lorange, E.; Lodge, J. P. Environ. Sci. Technol. 1970, 4, 55. (28) Lindberg, S. E.; Harriss, R. C. J . Geophys. Res. 1983,88, 5091-5100. (29) Settle, D. M.; Patterson, C. C. J. Geophys. Res. 1982,87, 8857-8869. (30) Talbot, R. W.; Andren, A. W. J . Geophys. Res. 1983,88, 6752-6760. (31) Eisenreich, S. J. Water,Air, Soil Pollut. 1980,13,287-301.
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(32) U.S. Environmental Protection Agency, Technical Report, Fuel Additives Division, Washington, D.C., 1984. (33) Edgington, D. N.; Robbins, J. A. Environ. Sci. Technol. 1976,10,266-274. (34) Robbins, J. A. “Sediments of Lake Huron: Elemental Composition and Accumulation Rates”; EPA Technical Report EPA-600/3-80-080, August 1980; 310 pp. (35) Norton, S. A.; Hess, C. T.; Davis, R. B. In ”Atmospheric Pollutants in Natural Waters”, Chapter 20, Eisenreich, S. J., Ed.; Ann Arbor Science Publ.: Ann Arbor, MI, 1981; pp 409-421. (36) Galloway, J. N.; Likens, G. E. Limnol. Oceaogr. 1979,24, 427-433. (37) Evans, R. D.; Rigler, F. H. Enuiron. Sci. Technol. 1980,14, 216-218. (38) Dillon, P. J.; Evans, R. D. Hydrobiol. 1982, 91, 121-130. (39) Nelson, D., Argonne National Lab., Argonne, IL, personal communication, 1982. (40) Eisenreich, S. J.; Hollod, G:J.; Langevin, S. A. “Precipitation Chemistry and Atmospheric Deposition of Trace Elements in Northeastern Minnesota”; Technical Report to Minnesota Environmental Quality Board, 1978; 149 pp. (41) Patterson, C. C. Amer. A iqu. 1971, 36, 286-321. (42) Murozomi, M.; Chow, T. .; Patterson, C. C. Geochim. Cosmochim. Acta 1969, 33, 1247-1294. (43) Shirahata, H.; Elias, R. M.; Patterson, C. C.; Koide, M. Geochim. Cosmochim. Acta 1980,44, 149-162. (44) Minnesota Department of Revenue and Energy, and the Pollution Control Agency, personal communication, 1984. (45) Winchester, J. W.; Nifong, G. D. Water, Air, Soil Pollut. 1971, 1, 50-64. (46) Rossman, R.; Robbins, J. A. Ocean Sciences Mtg., Amer. Geophys. Union and the Amer. Soc. Limnol. Oceanogr., New Orleans, LA, Jan 1984. (47) Shelton, E. M.; Whisman, M. L.; Woodward, P. W. “Trends in Motor Gasolines: 1942-1981”; U S . Department of Energy Report DOE/BETC/RI-82/4, Bartlesville, OK, 1982. (48) Argonne National Laboratory, Health and Safety Laboratory (HASL) Reports, Argonne, IL, 1967-81. (49) U.S. Environmental Protection Agency, National Air Quality and Emissions Trends (NAQE), Washington, D.C., 1982.
9
Received for review March 25,1985. Accepted July 29,1985. This research was funded in part by a grant from the National Science Foundation (NSFIDEB 7922142) to E. Gorham, H. Wright, D. Grigal, and S. Eisenreich.
