Literature Cited
(2) Bradford, G. R., et al. J . Enuiron. Qual. 1975,4,120. (3) Nielson, S. E.; Wium-Anderson, S. Physiol. Plant 1971, 24, 480. (4) Gross, R. E.; Pugno, P.; Dugger, W. M. Plant Physiol. 1970,46, 183. (5) Allen, H. E.; Hall, R. H.; Brisbin, T. D. Enuiron. Sci. Technol. 1980,14,441. (6) Sunda, W. G.; Engel, D. W.; Thuotte, R. M. Enuiron. Sci. Technol. 1978,12,409. (7) Chakoumakos, C.; Russo, R. C.; Thurston, R. V. Enuiron. Sei. Technol. 1979,13,213. (8) Frey, R. A,; Crist, R. H.; Oberholser, K. M. Proc. Pa. Acad. Sei. 1977,52,179. (9) Sailer, D.; Shellenberger, D.; Crist, R. H.; Oberholser, K. M. Proc. Pa. Acad. Sei. 1980,54, 85. (10) Siegel, B. Z.; Siegel, S. M. CRC Crit. Reu. Microbiol. 1973,lO. (11) Huang, C.-P.; Stumm, W. J . Colloid lnterfuce Sei. 1973, 43, 409. (12) Davis, J. A.; James, R. 0.;Leckie, James 0. J . Colloid Interface Sei. 1978,63,480. (13) Davis, J. A.; Leckie, J. 0. J . Colloid Interface Sei. 1980, 74, 32. (14) Stumm, W.; Morgan, J. J. “Aquatic Chemistry”; Interscience: New York, 1970; p 455. (15) Dodson, J. K., Jr.; Aronson, J. M. Bot Mar. 1978,21,241. (16) Elliot, H. A,; Huang, C.-P. Enuiron. Scz Technol. 1980, 14, 87. I (17) Hohl, H.; Stumm, W. J Colloid Interface Sei. 1976,55,281. (18) Davis, J. A.; Leckie, J. 0. J . Colloid Interface scz. 1978, 67, 90. (19) Davis, J. A,; Leckie, J. 0. Enuiron Sei. Technol. 1978, 12, 1309. (20) Elliot, H. A.; Huang, C.P. J . Colloid Interface Sei. 1979, 70, 29. (21) Davis, J. A.; Leckie, J. 0. Enuiron Sei. Technol. 1979, 1 3 , 1290. (22) S i l l h , L. B.; Martell, A. E. Spec. Publ.-Chem. Soc. 1971, No. 25, Supplement No. 1. (23) Ringbom, A. “Complexation in Analytical Chemistry”; Interscience: New York, 1979; Appendix. (24) Butler, J. N. “Ionic Equilibrium, a Mathematical Approach”; Addison-Wesley: Reading, MA, 1964; Chapter 7.
(1) Mortvedt, J. J.; Giordano, P. M.; Lindsay, W. L. “Micronutrients in Agriculture”; Soil Science Society of America: Madison, WI, 1972.
Received for review September 30,1980. Revised manuscript received May 18,1981. Accepted J u n e 15,1981.
the effect of Na+ on the adsorption of complexes of unlike charge. The species distribution values, a, for pH 7 are listed in Table 11. Results of the leaching experiments performed to explore further the bonding character are shown in Figure 8. Here, aqueous NaCl is more effective than water, as expected. Copper is retained in both cases while strontium is almost completely removed by NaC1, with zinc showing intermediate behavior.
Conclusion It has been demonstrated that the alga Vuucheria s. has a proton equivalence of -1000 pmol g-l, that metallic ion adsorptions range from -500 pmol g-1 for Cu2+to 100 for Na+, that metals displace each other in the order Cu > Sr > Zn > Mg > Na and they also displace protons, and that Na+ decreases adsorption of positive metallic ion complexes and enhances negative complexes. Most of these observations can be understood in the light of the protein and polysaccharide composition of the algal cell wall where one would expect covalent bonding amino and carbonyl groups and ionic charge bonding carboxyls and sulfates. Cu2+and Na+ then represent extremes in the bondings to these two types of functions. As found by Liecke, Davis, Stumm, and co-workers (22,17,18, 21) for inorganic colloids, bonding of a complexing agent directly to the surface with its attached metal must also be considered here. This could provide an alternate explanation for the observation that the aquo copper ion and the triethanolamine copper complex are about equally adsorbed. Acknowledgment We acknowledge the help of Mr. Charles Zercher with the experiments on proton displacements and p H titrations.
Identification and Determination of Individual Tetraalkyllead Species in Air Walter R. A. De Jonghe, Dipankar Chakraborti,?and Fred C. Adams+ Department of Chemistry, University of Antwerp (U.I.A,), B-2610 Wilrijk, Belgium
Introduction Several investigations have been undertaken in recent years to determine the contribution of gaseous tetraalkyllead compounds to the lead burden of our environment (1-5). One major focus of attention is the occurrence and fate of these pollutants in ambient air. As automotive emissions are the main source for both organic and inorganic atmospheric lead, lead levels rise with increasing traffic density. In urban areas, tetraalkyllead (TAL) compounds are generally believed to be present a t a concentration in the range 10-200 ng of P b m-3, which represents typically 1-10% of the total lead concentration (6-13). These data do not suffice for a full assessment of the health hazard associated with airborne alkylleads in view of the dissimilar toxic properties of different TAL species (14,15).
T o date, no comprehensive surveys have been performed regarding the discrimination of atmospheric TAL concenPresent address: Department of Chemistry, Texas A&M University, College Station, TX 77843. +
0013-936X/81/0915-1217$01 25/0 @ 1981 American Chemical
Society
trations into specific compounds. The available information is restricted to a few rather occasional measurements, intended to demonstrate the practical applicability of newly developed analytical techniques. Laveskog ( 1 6 ) determined tetramethyllead (TML) and tetraethyllead (TEL) separately in automobile exhaust gases and found a dependence of the concentration ratio TML/TEL on the driving mode of the car. Data on the other tetraalkyllead species were not reported. Similarly, some determinations of TML and TEL in city air were recently reported (17). In the air in the vicinity of a highway, Corrin (18) detected only TML, whereas, in air samples taken close to a car-repair shop, Rohbock et al. (13) found TML and TEL. The low analytical sensitivity of their method probably did not allow them to detect trace quantities of the lead alkyls with mixed ethyl-methyl groups, Le., TMEL (trimethylethyllead), DMDEL (dimethyldiethyllead), and MTEL (methyltriethyllead). The presence of these alkyllead species in city air, however, has been demonstrated by other workers (19,20).Furthermore, it was observed that all TAL compounds mentioned can be found in the atmosphere even Volume 15, Number 10, October 1981
1217
Air samples from a variety of sites in the surroundings of Antwerp, Belgium, have been analyzed to evaluate the nature and extent of environmental air pollution by gaseous tetraalkyllead compounds. Simultaneously, the inorganic lead present in the particulate phase was monitored. Measured alkyllead concentrations vary between 0.3 ng m-3 in a rural environment and 400 ng m-3 near a gasoline station. In ambient city air they,typically amount to 5-13% of the inorganic lead levels. Speciation of the organic lead concentrations by gas chromatography/atomic absorption spectrometry revealed
that all five tetraalkyllead compounds with ethyl and methyl groups are present in the atmosphere and that the average tetraalkyllead composition of the gasoline used in the area of investigation is reflected in the atmospheric alkyllead pattern. Inside-air alkyllead concentrations were found to correspond closely with those of outside air. The main reason for their occurrence in the environment appears to be both evaporative losses and exhaust gases from automotive traffic. No indications for the existence of a large-scale natural organolead source were encountered.
when the gasoline used in the area of investigation only contains tetraethyllead, as a result of chemical rearrangement reactions (20). A study of the nature of the tetraalkyllead content of ambient air therefore should include all five lead alkyls containing methyl and ethyl. In this work we present the results of the determination and chemical speciation of tetraalkyllead compounds in air samples taken in or near the city of Antwerp, Belgium, between March 7 and August 22,1980. The TAL composition of the different air samples is compared with that obtained from direct analysis of gasolines used in the same area and can be interpreted as a function of the relative stability of the different species. In addition, we report air concentration data for inorganic lead in the particulate matter, as the ratio of organic to inorganic lead is valuable for the comparison of results from different sampling sites.
along the wall, -25 m from the exit. The airflow inside the tunnel was from entrance to exit. Another sampling position was situated -5 m from a highway crossing in a very open environment, with traffic moving a t -60 km 11-l. Measurements were also performed ca. 10 m from two filling stations supplying gasoline with a known distinct TAL-composition and inside a large car-repair workshop (2500 m2) adjacent to one o f the gasoline stations. Finally, air samples were collected a t two relatively nonpolluted sites. One location was situated within the University campus, which represents a residential area with little traffic movement. The other was a position in the middle of a grassland in a rural environment -10 km from the city center, with the nearest, countryside-like road situated a t a distance of 500 m. All samples were taken in duplicate to minimize the possibility of artifacts. The air was collected -0.5 m above ground level, and the position was always chosen such that the dominating wind direction was perpendicular to the collection apparatus. T o compensate the diurnal fluctuations of the airborne lead concentrations, sampling was performed a t various times during the day. At the residential and rural areas, the air volume was increased from 360 to 500 L to enhance the sensitivity. Thus, for these sites the detection limits were lowered to -0.1 ng of Pb m-3 for TAL and 0.2 pg Pb m-J for inorganic lead.
Experimental Section For the present investigation the method described by De Jonghe et al. (21) was applied to a number of specific sites in the city and surroundings of Antwerp. The gaseous alkyllead compounds were collected from the air by cryogenic trapping a t -130 "C. Separation and analysis of the lead alkyls was accomplished by using a gas chromatograph with flameless atomic absorption spectrometric detection (GC-AAS). This combination allows the specific measurement of the individual tetraalkyllead compounds, TML, TMEL, DMDEL, MTEL, and TEL. In general, air samples were taken for a period of 1 h a t a sampling flow rate of 6 L min-l. Under these conditions the lowest detectable quantity amounts to -0.2 ng of P b m+. The precision of the measured concentrations is of the order of 13%,whereas the collection efficiency ranges between 90% for T E L and 100%for TML. Simultaneously with the lead alkyl compounds, inorganic lead present in the particulate phase was collected on 0.4-pm Nuclepore filters and analyzed by energy-dispersive X-ray fluorescence, using an adapted version of a previously elaborated method (22, 23). The detection limit for the 360-L samples is of the order of 0.3 pg m-3, The precision of the inorganic lead concentration data averages 14%. As the face velocity a t the filter amounted to -8 cm s-l, the collection efficiency exceeds 90% for all aerosol particles with a radius above 0.25 pm and below 0.01 pm ( 2 4 ) . Only in the range 0.01-0.25 pm is the efficiency lower, with a minimum of ca. 46% for particles of -0.05-pm radius. The different locations chosen for the measurements are such that typically encountered organic and inorganic airborne lead concentrations were likely to be detected and each site was expected to give rise to a characteristic atmospheric TAL pattern. One sampling point was located on the curb of a 10-m wide street, with buildings of 20-m height and a high traffic density in the business center of Antwerp. Samples were also taken inside an underground one-direction tunnel, 690 m long with three lanes and with heavy traffic (averaging 30 000 vehicles day-l, ca. 50% of which powered by diesel engines); the sampling point was situated on a small curb 1218
Environmental Science & Technology
Results and Discussion A number of results are summarized in Table I. The total alkyllead content of the air samples ranges between a minimum of 0.3 ng of Pb m-3 at the rural location and a maximum of 400 ng of P b m-3 near one of the filling stations. The highest levels for particulate lead, on the contrary, were observed in the tunnel. Although the TAL/inorganic lead concentration ratio is often used as a meaningful figure for comparing results from different sampling sites (I), Table I shows that they should be handled with caution. Despite the large difference in lead burden, the ratio of organic to inorganic lead is similar in the tunnel and a t the more remote places. In city air the TAL/inorganic lead ratio is typically of the order of 5-13%. Extremely high ratios were found in the air near the gasoline stations, as could be expected. For an interpretation of the speciation data, information is required on the ratio of the five TAL compounds present in the gasoline used in the area of investigation. Samples of leaded gasoline from six of the major distributors were analyzed by utilizing GC/AAS. This should give some rough idea about the average TAL in gasoline composition. The results are summarized in Table 11. Repetitive measurements over a 6-month period of four of the brands indicate that the TAL pattern remains stable. The data show that each brand of gasoline studied contains all five tetraalkyllead compounds and that the TAL distribution may vary drastically from one brand to another. This is in agreement with other investigations (19,25) although the average TAL composition obtained is somewhat different in this study. The predominant species are TML, TMEL, and TEL, with a mean ratio of TML to TEL
Table 1. Atmospheric Organic and Inorganic Lead Concentrations at the Different Measuring Sites site (no. of measurements)
gasoline station A (10) gasoline station B (11) car-repair workshop (6) underground tunnel (15) highway crossing (10) central-city street (9) residential area (7) rural area (6) a
org Pb concn, ng range
17-223 38-4 1o 100-290 12-162 14-44 49- 109 3.2-14 0.3-3.9
m-3
loa
inorg Pb concn, pg m-3 range av
av
205 f 72 39 f 38 24 f 9 a3 f 19 7 f 4 2 f l
2.7-35.4 6.3-19.9 5.9-14.2 0.2-1.4 0.8-3.0 4.6-12.7 0.6-3.4a 0.1-0.7a
1.0 f 0.5 1.6 f 1.1 2.2 f 1.4 7.6 f 2.9 1.5 f 0,5 1.1 f 0 5 0.3 f O.la 0.3 f 0.1 a
0.4-2.1 0.4-3 6 1.O-4.9 4.1-12.2 0.9-2.0 0.7-2.2 0.2-0.5a 0.2-0.5a
75
iaa f 112
orgllnorg Pb ratio, Yo range av
11.2 f 9.5 13.1 f 4.8 9.9 f 2.7 0.5 f 0.3 1.7 f 0.7 7.9 f 2.7 1.9 f 1.1a 0.5 f 0.3a
Semiquantitative.
Table II. Tetraalkyllead Distribution in Gasoline Samples brand of fuel a
total TAL concn, ppm Pb
regular premium B regular premium C regular premium D regular premium E regular premium F regular premium av regular premium
349 450 539 528 399 410 486 419 355 478 439 416 428 450
A
a
TML
MEL
1.3 0.7 26 25 99 99 27 a3
0.1 0.1 47 47 0.2 0.2 0.1 0.1 0.1 0.1 46 45 16 15
0.8
0.6 26 27 30 39
% of total TAL contents DMDEL
0.1 0.1 22 23 0.1
MTEL
TEL
0.2 0.2 3.9 4.7 0.1 0.1 0.4 0.1 0.2 0.2 4.8 4.6 1.6 1.7
0.1
0.1 0.1 0.1 0.1 21 22 7.2 7.6
98 99 1.7 1.1 0.7 0.5 73 17 99 99 2.0 1.9 46 36
Gasoline types A and B were obtained from the filling stations indicated A and B in Table I.
Table 111. Speciation of the Atmospheric Tetraalkyllead Concentrations at the Different Measuring Sitesa slte
TML
TMEL
gasoline station A gasoline station B car-repair workshop underground tunnel highway crossing central-city street residential areab rural area
ia f io 4 6 f 11 53 f 5 6 9 f 10 3 5 f 14 61 f 7 7 6 f 16 a 5 f 12
1242 9 31f 5 27f 4 13f 4 25f 3 13f 2 1 5 f 10 20f 6
a
Average of all measurements.
Two values
% of total TAL contents DMDEL
5 f 4 12 f 5 11 f 2 5 f 3 13f3 5 f l 6 f 2 nd
for MTEL and TEL above the detection limit not included.
of nearly 1.0.The other two species, DMDEL and MTEL, are present only in smaller quantities. On the average, the gasoline samples contained -0.44 g L-l organic lead. With the exception of gasoline type D, there is no systematic difference in TAL composition between the regular and premium brands. The differentiation of the atmospheric TAL into its component parts is given in Table 111. The patterns can be classified in three different types. One type is formed by the samples taken close to the gasoline stations and inside the car-repair workshop. It is typical for air pollution resulting from one single brand of gasoline. Another type is related to the samplings close to the traffic emission and groups the data from the tdnnel, the highway crossing and the downtown locations. The residential and rural areas constitute a third type. The handling of gasoline at the filling stations inevitably presents a number of alkyllead emission sources (26):direct
MTEL
2 f 2 7 f 6 1.8 f 0.5 2 f 2 4 f 3 1.2 f 0.4 nd nd
TEL
66 f 21 5 f 3 7 f 4 1 2 f 10 2 4 f 12 19 f 6 nd nd
nd = not detected.
evaporation, displaced fuel-tank vapors, entrained fuel droplets in the displaced vapors, liquid gasoline spillage, car exhaust gases, etc. Thus, it might be anticipated that the atmospheric TAL pattern which is obtained in the vicinity of a particular station shows a fairly good resemblance with the TAL composition of its gasoline. A qualitative agreement is indeed obtained but with a relative enhancement of the TML coritribution. This must be attributed to the higher vapor pressure and chemical stability of TML. Furthermore, the measurements are influenced by the motor traffic in the adjacent streets, which generates TAL patterns where the TML species is the dominant component. A nearly quantitative similarity of the TAL distribution in the gasoline and in the air is found during the filling up of the fuel reservoirs (Table IV). In these circumstances the emission of lead alkyls into the air is mainly the result of spillage. Consequently a complete evaporation can take place, whereby all constituents of the gasoline, including the TAL’S,volatilize. During the norVolume 15, Number 10, October 1981
1219
Table IV. Atmospheric TAL Concentrations Observed Near a Gasoline Station on the Occasion of the Filling Up of the Fuel Reservoirsa
a
gasollne station
amount of fuel added to the reservoir, L
total TAL concn /.4g In-5
A B
ca. 8000 ca. 9000
1.8 2.4
TML
TMEL
2.8
0.4
23
49
% of total TAL concn DMDEL
MTEL
0.2 23
TEL
96
0.7 4.1
1.5
30-min samples.
mal working conditions of a gasoline station, on the other hand, there is, in addition to this source, the evaporation resulting from the venting to the atmosphere of the gases which have accumulated in the empty fuel tanks or in other parts of the vehicles. As these have been in equilibrium with the liquid gasoline, the gaseous TAL composition can be expected to exhibit a strong enrichment of the more volatile species according to their higher partial vapor pressure. The equilibrium TAL vapors over type-A and type-B gasoline samples were analyzed in a laboratory experiment. For type A the vapor-phase composition was 54% TML, 2% TMEL, 0.6% DMDEL, 0.4%MTEL, and 43% TEL, whereas for type-B gasoline 55%, 37%, 6%, 0.8%, and 0.4% were obtained respectively. The actual TAL pattern which is observed near the gasoline stations is the result of spillage and evaporation emissions and exhaust fumes, with, in addition, a variable contribution from the surrounding, traffic-generated TAL. It is important to note that, despite the safety precautions taken, unexpectedly large amounts of lead alkyls are emitted into the atmosphere during the filling of the gasoline reservoirs. At a distance of 2 m from the site of handling, the air contains up to 2 pg mF3organic lead. As filling stations in densely populated areas are frequently situated at the ground floor of apartment buildings, these findings may well be of epidemiological importance. To the general public, the hazard from filling stations appears to be rather small, as the TAL levels around these sites are of the same order of magnitude as those encountered in a city street. The car-repair workshop is commercially related to the gasoline station, but a fraction of cars do not use gasoline of type B. Therefore a less pronounced similarity between the atmospheric and gasoline TAL spectra is observed. There was very little traffic in and out of the garage, so that exhaust gases probably have a rather small contribution. Further, little interference has to be expected from the ingress of outside air as the wind predominantly flowed in a direction away from the workshop entrance. Similarly, the effect of the filling station should be small. The elevated TAL levels in the air should therefore be mainly attributed to evaporative emissions. This shows the importance of evaporative emission as a pollution source for organic lead. The high inorganic lead levels are probably not resulting from automotive emissions but rather from redispersion of lead-containing dust particles. The atmospheric TAL pattern of type I1 can be compared with the average distribution of the five tetraalkylleads in gasoline. In general, the same predominance of TML, TMEL, and TEL, together with a negligible quantity of MTEL, is observed. There is, however, a shift of the relative contribution of TML and TEL. Whereas in the gasoline a ratio was found of -1.0, here a TML/TEL value of 1.5-5.8 is encountered. This is not unexpected in view of the physicochemical properties of these compounds, On account of a vapor pressure which is -100 times higher, TML is preferentially lost during evaporation of gasoline, while TEL tends to concentrate in the residue (27).In addition, the greater thermal stability of TML will favor its passage through the engine uncombusted (281, 1220
Environmental Science & Technology
SO that the TML/TEL ratio increases as the engine warms up from being cold (16).Finally the rate of TEL breakdown in the atmosphere is greater than that of TML (29). There are no indications for a gradual increase of the ratio TML/TEL during the day, because the variability of any given moment prevents any quantitative estimates of the extent of a possible effect. The tunnel is a special sampling site, and the tetraalkyllead concentrations found there deserve closer consideration. Vehicles normally travel at high speeds (ca. 100 km h-l), and large quantities of particulate lead are exhausted (30).Settled particulate matter is in addition continuously resuspended, which explains the high and extremely variable lead concentrations measured. The fast driving conditions also result in hot engines and thus provide a nearly complete combustion of the lead alkyls (13, 16). Similarly, the contribution of evaporative losses of gasoline from the fuel tanks and the carburetors should be negligible, since at high speeds the residence time of the cars inside the tunnel is limited. Under such high-speed conditions a TAL concentration of -15 ng of P b m-3 is measured. This value appears to be nearly independent of the number of cars that pass through the tunnel during sampling, as follows from Figure 1. This indicates clearly that with warmed-up engines and high speeds, vehicles are minor contributors of atmospheric organolead. The reason for the independency of the TAL levels as a function of traffic density probably lies in a compensation of higher lead levels by higher amounts of outside air, sucked into the tunnel by fast-moving cars. Consequently, only a "background" concentration characteristic for the site is present, which is probably generated for a large part outside the tunnel. When the traffic intensity exceeds 2500 cars h-l, a sharp increase in the airborne TAL level is observed. This must be related to the reduction of the average car speed for increasing traffic intensities, a phenomenon which can be observed from this traffic flux onwards. As the cars slow down, the airflow through the tunnel is reduced and a lesser degree of dilution by outside air occurs. Further, the residence time of a car inside the tunnel is extended, and the effect of the automotive
I
L 0
I
1
1000
I
I
23CG
1
1
I
3c3c
LOO0
1 10 5000 cars hour-I
Flgure 1. Lead content of the air inside an underground tunnel for road traffic: ( 0 )TAL concentration data: (X) inorganic lead concentration data.
emissions becomes more prominent. The high traffic intensities eventually lead to occasional jam formations with TAL concentrations above 150 ng of P b m-3. It appears that the relative contribution of the five TAL species to the total organic lead level is quite similar between the measurements at high speeds and low car density and the ones at lower speeds and high car density, as appears from Table V, where a number of measurements are listed, Each of the data points is the average of paired determinations. I t has been reported (31-33) that organolead compounds may be adsorbed onto dust particles. The adsorption was claimed to be reversible, so that subsequent desorption could contribute to observed gaseous TAL levels (13, 33). In view of the high amounts of particulate matter inside the tunnel, we have investigated whether airborne particulates and deposited soot contained significant amounts of TAL. For this purpose a technique of leaching the TAL from the samples into an organic solvent and analyzing them by GCIAAS was utilized (34). The method was found to give essentially quantitative recovery of TAL from dosed samples of air particulate matter. In the actual samples, the observed TAL levels in the air particulate matter were well below 1%of those in the gaseous phase. In none of the soot samples could TAL be detected. The fact that earlier analyses revealed significantly higher amounts of organic lead in particulate matter and street dust (31,32)should be attributed to the analytical methodology employed. In those cases “total organic lead” was determined, whereas in our work it specifically concerned TAL. Possibly this could indicate the presence of measurable quantities of the TAL-degradation products, i.e., PbR3X and PbRZXZ in the atmosphere. Up to now, no direct information on the presence of these compounds in air has been obtained, although the possibility of their existence has been postulated earlier (1,17). It is worth noting that the inorganic lead levels are much less affected by the differences in driving mode and by the air dilution and that only a moderate, linear increase of the airborne particulate lead concentration occurs for higher traffic intensities. Also, the traffic intensity-reduced speed relation only holds for intensities above 2500 cars h-l and below the practical saturation point of the tunnel (ca. 6000 cars h-l). I t is difficult to ascertain whether the presence of TAL compounds in ambient air results mainly from losses via the exhaust fumes or from evaporation losses. Harrison et al. (8) and Radziuk et al. (20) suggest evaporative emission as the main source. By simultaneous measurements of TML, CO, and inorganic particulate lead as a function of the off-highway distance, Corrin (18) arrives at the same conclusion. Other workers (23, 26, 291, on the contrary, assume that, in the presence of slow moving and cold-choked vehicles, incomplete combustion is the main source of atmospheric TAL. Directly behind the tailpipe of an idling car, we measured TAL concentrations of the order of 67 ng of P b m-3, with a TALhnorganic lead ratio of ca. 1 2 4 000. These results can be compared with those obtained by Radziuk et al. (20) but are markedly lower than the values reported by Laveskog (16).
In view of the large volumes of exhaust gases emitted (ca. 200 m3 h-l), even the lower concentrations are important. On the other hand, our findings in the workshop appear to indicate that evaporative emission can also constitute an important source. Probably the occurrence of TAL in ambient air is the combined result of both emission sources. The TAL pattern obtained in the central-city street resembles very well that from the tunnel. There seems to be no ready explanation for the discrepancy of the TAL pattern near t‘ e highway crossing compared to that of the other sites. There has been some controversy in the last few years as to whether the methylation of inorganic lead could provide an additional source of organic lead, especially TML, in the atmosphere (35-39). Evidence for methylation processes of lead was claimed by Harrison and Laxen (39) in view of their findings of elevated organidinorganic lead concentration ratios at rural locations. When the sampled air had passed over sea and coastal areas, organic to inorganic lead ratios of up to 50% were reported. Unfortunately, the method of analysis used by these authors could not discriminate between the different alkyllead species. It is therefore impossible to determine whether such elevated ratios are accompanied with exceptionally high TML contributions. The results presented in this work do not reveal considerable quantities of atmospheric lead alkyls in the rural environment. The observed concentrations are very similar to those reported for a rural environment in the hills surrounding Frankfurt/Main in Germany, where the gaseous lead concentration averaged 3 f 2 ng m-3 (13).Also, the average organolead concentration decreases smoothly from the city center, over the highwaycrossing sampling site, to those of the residential and rural areas. In addition, the TML/TMEL ratio closely resembles that found in central-city air (4.3 and 4.7, respectively), so that there are no indications of a large-scale natural source, and the advection of polluted urban air appears to be the only reason for the occurrence of these compounds at the locations investigated. As could be expected, the residential air has an intermediate organic lead content with a similar TML/TMEL ratio of 5.1. The absence of DMDEL, MTEL, and TEL in the pattern of the rural air should be attributed to a lack of sensitivity, since, if the TAL composition from city air were preserved, these compounds would be present only in amounts on the order of the limit of detection of the method. Chemical degradation could even further reduce this part of the alkyllead content of the rural air. In the air of the residential site, the presence of TEL and MTEL could be detected only on two occasions when the total alkyllead concentration exceeded 8 ng m-3. The relative concentration amounted to 1.4% and 19% of the total organolead concentration. The indication “not detected” in Table I11 was given, however, to indicate the average composition observed. From the above discussion it can be deduced that atmospheric pollution by alkyllead compounds is only important in the immediate vicinity of the source (gasolinestation, motor traffic). However, the lead alkyl vapors have a low removal rate from the atmosphere and are therefore present in nearly
Table V. Composition of the TAL Content of the Air inside the Underground Tunnel for Various Traffic Intensities traffic Intensity, cars h-‘
TML
TMEL
587 1844 2223 2700 3380 3859 4678
72 52 73 53 72 75 62
19 12 17 11 16 9.9 6.8
Oh
of total TAL concn DMDEL
2.3 6.2 2.0 5.6 8.4 3.1 3.5
MTEL
2.3 6.2 2.0 0.8 0.9 1.6 0.9
TEL
5.4 25 4.7 31 2.2 11 27
Volume 15, Number 10, October 1981
1221
Table VI. Comparison of Results of Air Samplings at Gasoline Stations alkyllead concn found, ng of Pb m-3 direct AAS GCAAS
260 210 1903 248
245 168 1786 223
GCAASIAAS, %
94.2 80.0 93.9 89.9
the same concentration in inside air as in the corresponding outside air. Even in the air inside a room of a building located in the residential area, TAL could be detected. The concentration averaged -6 ng of P b m-3 and was composed of 70% TML, 2870 TMEL, and 2%DMDEL. So, even in the more remote locations, the TAL concentration cannot be completely overlooked. Although the observed alkyllead levels are probably far too small to cause acute toxic effects in a city population, health hazards from long-term effects cannot be ruled out completely (40). In this context, it is relevant to note the determination of alkyllead in brain tissue of urban residents a t concentration levels similar to those which gave rise to strong inhibitory effects in in vitro experiments ( 4 , 4 1 ) . The results of this study could be compared with those obtained earlier for the total organic lead concentration determined by AAS using the iodine monochloride method (12). Slightly but significantly higher organic to inorganic concentration ratios were found with the latter procedure. Also, a third procedure (42) based on cryogenic trapping of the volatile compounds, desorption into a nitric acid solution, followed by a determination by graphite furnace atomic absorption spectrometry provides slightly higher results for organolead compounds. For samples taken in parallel near a gasoline filling station, the results obtained with both methods are compared in Table VI. These discrepancies cannot be entirely explained by the inaccuracies of both methods, namely, interferences due to inorganic lead in the total organolead procedures and an efficiency of somewhat less than 100%for the GC/AAS procedure. Again, it could partly result from the presence of nonnegligible concentrations of tri- and dialkyllead compounds in the atmosphere. Conclusions The atmospheric tetraalkyllead pattern reflects the average TAL composition of the gasoline used in the area of investigation. Tetramethyllead is relatively enriched in the air with respect to tetraethyllead, and this probably arises from a higher volatility and chemical stability. Both evaporation losses and exhaust fumes appear to be major sources for the emission of gaseous lead alkyls into the atmsophere. The contribution of gasoline stations to general environmental TAL levels can be considered small. No indication of a large-scale natural source for TAL compounds was found. The indirect evidence for the possible existence of ionic organolead species in the atmosphere deserves some further attention. Acknowledgment We are grateful to Dr. H. Robberecht for assistance in the XRF analysis of the filters and to Dr. P. Ashworth of the Associated Octel Co. (London) for the supply of organolead standards. We acknowledge helpful discussions with Dr. R. M. Harrison of the University of Lancaster and Mr. A. Slater of the Associated Octel Co. (London). This work was carried out within the framework of the National Research and Development Program on Environment of the Interministrial Commission for Science Policy, Belgium. 1222
Environmental Science & Technology
Literature Cited 1. Harrison, R. M.: Perrv. R. Atmos. Enuiron. 1977.11.847-52. 2. Potter, H. R.; Jarvie, A: W. P.;Markall, R. N. WateiPollut Control (Maidstone, E n d 1 1977, 76,123-8. 3. Sirota, G. R.; Uthe, J. F..Anal. Chem. 1977,49,823-5. 4. Nielsen, T.; Jensen, K. A.; Grandjean, P. Nature (London) 1978, 274,602-3. 5. Chau, Y. K.; Wong, P. T . S.; Bengert, G. A.; Kramar, 0. Anal. Chem. 1979,51, 186-8. 6. Snyder, L. J. Anal. Chem. 1967,39,591-5. 7. Purdue, L. J.; Enrione, R. E.; Thompson, R. J.; Bonfield, B. P,. Anal. Chem. 1973,45, 527-30. 8. Harrison, R. M.; Perry, R.; Slater, D. H. Atmos. Enuiron. 1974,8, 1187-94. 9. Lekkas, T. D. M.Sc. Thesis, Department of Civil Engineering, Imperial College of Science and Technoloav. London. 1974. 10. Rabinowitz, M. B.; Wetherill, G. W.; Ko&le, J. D. 3. Lab. Clin. Med. 1977,90,238-48. 11. Birch, J.; Harrison, R. M.; Laxen, D. P. H. Sci. Total Enuiron. 1980,14,31-42. 12. De Jonahe. W. R. A,: Adams. F. C. Atmos. Enuiron. 1980. 14. 1177-80. 13. Rohbock, E.; Georgii, H. W.; Muller, J. Atmos. Enciron,. 1980,14, 89-98. 14. Waldron, H. A,; Stofen, D. “Sub-Clinical Lead Poisoning”; Academic Press: New York, 1974. 15. Maddock, B. G.; Taylor, D. Proc. Int. Exp. Disc. Lead-Occurrence, Fate and Pollution in the Marine Environment, 1977, in press. 16. Laveskog, A. Proc. Int. Clean Air Congr.,2nd 1970,549-57. 17. Nielsen, T.; Egsgaard, H.; Larsen, E.; Schroll, G. Anal. Chim. Acta 1981,124, 1-13. 18. Corrin, M. L. In “Environmental Contamination Caused by Lead, Final Report”; Edwards, H. W., Ed.; Colorado State University: Fort Collins, CO, 1977; pp 179-200. 19. Reamer, D. C.; Zoller, W. H.; O’Haver, T. C. Anal. Chem. 1978, 50,1449-53. 20. Radziuk, B.; Thomassen, Y.; Van Loon, J. C.; Chau, Y. K. Anal. Chim. Acta 1979.105,255-62. 21. De Jonghe, W. R. A.; Chakraborti, D.; Adams, F. C. Anal. Chem. 1980,52,1974-7. 22. Van EsDen. P.: Adams. F. Anal. Chirn. Acta 1974.75.61-85. 23. Van Espen, P . Ph.D. Thesis, Department of Chemistry, University of Antwerp (U.I.A.), 1978. 24. Spurn?, K. R.; Lodge, J. P.; Frank, E. R.; Sheesley, D. C. Enuiron. Sci. Technol. 1969.3,453-64. 25. Robinson, J. W.; Vidauretta, L. E.; Walcott, D. K.; Goodbread, J. P.; Kiesel, E. L. Spectrosc. Lett. 1975,8.491-507. 26. National Research Council. “Lead-Airborne Lead in PersDective”; National Academy of Sciences: Washington, DC, 1977; pp 192-7. 27. Robinson, J. W.; Kiesel, E. L. J . Enuiron. Sci. Hpalth, Part A 1977,12,411-22. 28. Ryason, P . R. Combust. Flame 1963,7,235-43. 29. Harrison, R. M.; Laxen, D. P . H. Enuiron. Sci. Technol. 1978,12, 1384-92. 30. Hirschler, D. A,; Gilbert, L. F.; Lamb, F. W.; Niebylski, L. M. Ind. Eng. Chem. 1957,49,1131-42. 31. Harrison, R. M. J . Enuiron. Sci. Health, Part A 1976,11,41723. 32. Harrison, R. M.; Laxen, D. P. H. Atmos. Enuiron. 1977, 11, 201-3. 33. Edwards, H. W.; Rosenvold, R. J. Proc. Annu. NSF-RANN Trace Contam. Conf.,Z n d , 1974,59-63. 34. Surkyn, P. M S c . Thesis, Department of Chemistry, University of Antwerp (U.I.A.), 1980. 35. Wong, P. T. S.; Chail, Y. K.; Luxon, P. L. Nature (London) 1975, 253.263-4. 36 Jarvie, A. W. P.; Markall, R. N.; Potter, H. R. Nature (London) 1975,255, 217-8. 37. Schmidt. U.: Huber. F. Nature (London) 1976,259,157-8. 38. Ridley, W. P.; Dizikes, L. J.; Wood, J. M. Science 1977, 197, 329-32. 39. Harrison, R. M.; Laxen, D. P . H. Nature (London) 1978,275, 738-40. 40. Ahlberg, J.; Ramel, C.; Wachtmeister, C. A. Ambio 1972, I , 2931. 41. Grandjean, P.; Nielsen, T. Residue Rev. 1979, 72,97-148. 42. Jiang, S. G.; Chakraborti, D.; De Jonghe, W.; Adams, F. Fresenius’ Z. Anal. Chem. 1980,305,177-80. I
.
I
,
Receiued for revieu November 10,1980. Revised manuscript received May27,1981. Accepted June 16,1981.
