Surface Deposition of Lead and Cadmium from the Atmosphere in the Detroit River—Lake St. Clair Region

J. Great Lakes Res. 11(3):305-312 Internat. Assoc. Great Lakes Res., 1985

SURFACE DEPOSITION OF LEAD AND CADMIUM FROM THE ATMOSPHERE IN THE DETROIT RIVER-LAKE ST. CLAIR REGION

M. Sanderson, D. Marchand, and P. McQuarrie Great Lakes Institute University of Windsor Windsor, Ontario N9B 3P4 ABSTRACT. The research reported here forms part of a large multidisciplinary study offour toxic contaminants-lead, cadmium, PCBs, and octachlorostyrene in the Essex region of southwestern Ontario. The purpose ofthis part of the project is to quantify the atmospheric loading of the metallic contaminants. A bulk precipitation sampler, wet-only precipitation sampler, and recording rain gauge were installed at an urban and rural site. Results from 2 years ofdata indicate that atmospheric loading of lead is 40-50 times that of cadmium in the city and 16-40 times that of cadmium in the rural areas. Lead loadings in the city were found to be 2-4 times higher than in the rural areas, while cadmium loadings appeared to be similar in both areas. Concentrations of the metals are higher in winter than in summer, but because of higher summer precipitation surface loadings are similar in both seasons. Preliminary statistical analysis indicates that concentrations of the metals are related to intensity and amount of precipitation but not usually to wind direction. ADDITIONAL INDEX WORDS: Trace metals, atmospheric pollution.

INTRODUCTION The research reported here forms part of a multidisciplinary research project of the Great Lakes Institute, University of Windsor, entitled "A Case Study of Selected Toxic Contaminants in the Essex Region." The four contaminants studied are two trace metals, lead and cadmium, and two organics, octachlorostyrene and polycWorinated biphenyls. The purpose of the present report is to examine seasonal differences in the concentrations of the two metals in the precipitation, to compare rural and urban concentrations, to attempt to relate the concentrations to meteorological variables, and finally to estimate surface loadings of the contaminants. This paper is an expanded version of a paper presented at a conference on the Hydrochemical Balances of Freshwater Systems, held in Uppsala, Sweden, in 1984 (Sanderson and Marchand 1984). Heavy metals have been found in all of the Great Lakes and are of concern since they bioaccumulate in fish and wildlife. In addition, the surface loadings of these contaminants to land areas may result in their uptake by crops and natural vegetation. Human consumption can cause a variety of health

problems. Lead causes anemia, fatigue, and brain damage, especially in children, while cadmium can cause kidney damage and metabolic disturbances. The Great Lakes are susceptible to atmospheric contamination because their very large surface areas permit the addition of a large pollution load directly to the lakes. It has been found that on a global scale, atmospheric loadings represent 121 % of stream loadings for lead and 42070 for cadmium (Allen and Halley 1980). The source of lead and cadmium in the atmosphere is primarily anthropogenic through the combustion of fossil fuels, and especially the burning of gasoline. It is estimated that 70-90% of atmospheric lead comes from leaded gasoline exhaust (NRCC 1978). The presence of lead and cadmium in the atmosphere is the result of both local sources and long range transport depending on particle size (Rohbock 1982). Large particles tend to settle near the source, as in industrialized urban areas, while small particles can be transported in the atmosphere long distances and are more likely to be cleansed from the atmosphere by wet deposition (Struempler 1976). The standard for drinking water set by the Cana305

306

SANDERSON et al.

dian government is 50 p,g L-l for lead and 2 p,g L-l for cadmium, while the International Joint Commission objectives for Great Lakes waters are 10-35 p,g L-l for lead (depending on lake) and 0.2 p,g L-l for cadmium. Present average concentrations of the metals in the waters of Lake St. Clair are 2 p,g L-l for lead and not detectable for cadmium (Allen and Halley 1980). Testing the precipitation in the Great Lakes area for trace metal content began in the 1970s and sampling procedures have been found to vary widely. A bulk sampler which collects both wet and dry depositions was the more common instrument used in the earlier days while more recently, automatic samplers which collect precipitation only have been used. A recent literature survey of trace metals in precipitation in the Great Lakes area gave average concentrations of 28 p,g L-l for lead and 1.2 p,g L-l for cadmium for bulk samples (Allen and Halley 1980). It is expected that concentrations of the contaminants in precipitation are higher in urban than in rural areas. A perusal of the literature indicated that, in North America, concentrations of lead in urban precipitation range from 5-50 p,g L-l and from 3-15 p,g L-l for rural precipitation (Van Loon 1973). Similarly, cadmium concentrations in urban precipitation vary from 1-5 p,g L-l (Shiomi and Kuntz 1973) and ND-7 p,g L-l in the country (Jeffries and Snyder 1981, Van Loon 1973). Using data on average precipitation, the loadings estimates for Lake Erie thus vary widely, from 40-850 g ha-1yr- 1 for lead and 2-60 g ha-1yr-1for cadmium (Allen and Halley 1980). Some researchers have concluded that wet deposition is more important than dry in surface loading of lead and cadmium (Ter Haar et af. 1967, Jeffries and Snyder 1981, Georgii and Pankrath 1982, Nurnberg et af. 1982, Rohbock 1982). For example, in rural New Jersey the ratio of wet/dry deposition of lead was estimated at 2: 1 (Knuth et af. 1983). Others have found that surface loading of the two metals is equally the result of wet and dry deposition (Pattenden et af. 1982). For forested areas in Germany it was found that dry deposition of lead was of the same order of magnitude as wet deposition, and in the case of cadmium, exceeded wet deposition (Hafken et af. 1983). Some of the uncertainty regarding the proportionalloading by wet and dry fallout is due to the fact that dry deposition appears to vary with surface cover and a simple accurate method of monitoring dry deposition is not yet available (Sickles et af. 1983).

RESEARCH METHODS Several precipitation sampling stations were installed in the region (see Fig. 1): at West Windsor Water Pollution Control Plant in a higWy industrialized area near the Detroit River in October 1982; at the Agriculture Canada Research Station at Woodslee in a rural district approximately 35 km SE of Windsor in May 1983; and at St. Joachim in a rural setting 40 km E of Windsor in January 1984. The site at St. Joachim is not ideal and not as "rural" as that at Woodslee since it is closer to a highway. However, it was a necessary choice for the wet-only sampler because it is a well supervised site and there were problems of maintenance at Woodslee. Each site has a Belfort rain gauge to measure precipitation depth, intensity, and duration, a bulk precipitation sampler (Fig. 2), and a precipitation sampler for collection of wet-only samples (Fig. 3). Meteorological data are available from the Ontario

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FIG. 1. Location of the sampling sites.

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LEAD AND CADMIUM FROM THE ATMOSPHERE BIRD PRONGS - -....

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FIG. 2. Bulk Precipitation Sampler. The orifice remains uncovered and sampler collects both wet and dry fallout. Sample bottle is changed after each precipitation event.

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FIG. 3. MIC Wet-Only Precipitation Sampler. This sample collects precipitation only. The lid opens only during the precipitation event.

307

Ministry of the Environment's weather station 1 km NW of the West Windsor site, and from the Institute's meteorological tower at Woodslee. Sample collection and analysis are in accordance with the Canadian Department of Environment practices. Plastic collection bottles were soaked overnight with Alconox soap and water, rinsed with tap water, soaked in 5070 solution of RN0 3 (Baker instra analyzed) for 2 weeks and rinsed three times with distilled, deionized water to remove potential contaminants. Pure (100%) RN0 3 was added to the collection bottles at the ratio of 2 mL: 1 L of storage capacity to prevent the adherence of contaminants to the sides of the bottles. The bottles were then placed within the bulk samplers. The same pure RN0 3 acid was added to plastic collection bags at the same ratio and these bags placed in the wet collection bucket of the wetonly samplers. Samples were collected as soon after a precipitation event as possible. The samples were then stored in pre-washed, pre-acidified storage bottles for analysis. Analysis of lead and cadmium content was carried out using an Instrumentation Laboratory (lL) 351 flame Atomic Absorption Spectrophotometer (AA) (detection limit 30 p.g VI for lead, and 4p.g L-I for cadmium) and a Scintrex AAZ-2 Zeeman Modulated flameless Atomic Absorption Spectrophotometer with tungsten filament (detection limits 4 p.g L-I for lead, 0.1 p.g L-I for cadmium). The surface loading of lead and cadmium in g ha- I was calculated for the sample periods by multiplying the concentrations (p.g L-I) by the precipitation depth obtained from the Belfort rain gauges. Statistical tests were also performed to determine the correlation between concentration levels and precipitation amount, duration, and intensity, and wind direction. RESULTS AND DISCUSSION During the period October 1982-August 1984, a total of 98 bulk and 77 wet-only samples from the West Windsor site were analyzed. There were approximately equal numbers of cold season (16 October-IS April) and warm season (16 April-IS October) samples. At the Woodslee site, the period yielded 57 bulk but only 28 wet-only samples because of problems with the automatic sampler. At the St. Joachim site, 23 bulk samples and 18 wet-only samples have been analyzed. A summary of the observed concentrations of lead is seen in Table 1. From the table it is apparent

SANDERSON et a/.

308

TABLE 1. Lead in precipitation-Essex County (p,g L-l). Bulk Samples

Wet Only Samples

Mean

#Samples

Range

Mean

#Samples

Range

URBAN WEST WINDSOR October-April 1982-83 1983-84

81.8 83.8

(29) (18)

9-250 11-270

29.9 30.0'

(22) (13)

9-237 8-101

April-October 1983 1984 1st Year 2nd Year TOTAL PERIOD

58.3 67.3 69.9 74.9 71.8

(30) (21) (59) (39) (98)

3-300 10-233 3-300 10-270

15.0 25.4 22.3 27.3 24.4

(23) (19) (45) (32) (77)

3-58 4-77 3-237 4-101

RURAL WOODSLEE October-April 1983-84

25.6

(18)

8-96

10.7

(7)

7-20

April-October 1983 1984 2nd Year TOTAL PERIOD

16.8 15.4 20.2 19.1

(19) (20) (38) (57)

4-55 3-37 3-96

7.0

(21)

1-20

7.9

(28)

ST. JOACHIM October-April 1983-84

45.0

(7)

16-108

6.0

(1)

April-October 1984 TOTAL PERIOD

34.4 37.6

(16) (23)

6-323

25.6 24.5

(17) (18)

that bulk precipitation in West Windsor contains 3.5 times the lead concentration of bulk precipitation in the Woodslee area, and approximately twice as much as in 81. Joachim. This is to be expected as a result of greater automobile traffic in the city. In the precipitation-only samples from West Windsor, lead concentrations were three times greater than in Woodslee but similar to those in 81. Joachim. This may be explained by the proximity of the 81. Joachim sampler to a busy roadway. The bulk precipitation samples had approximately three times the lead concentrations of the wet-only samples in both West Windsor and Woodslee. It is not understood why the situation at 81. Joachim is different, with a ratio of 38:24 for bulk/wet concentrations. At all locations, it is

7-126

noted that lead concentrations in the cold season were considerably higher than in the warm season of the year. The mean lead concentration of 72 p,g L-I for urban bulk precipitation exceeds the Canadian drinking water standard of 50 p,g L-I. However, the concentrations of lead in the wet-only precipitation samples were less than the drinking water standard - approximately 25 p,g VI in the city and 8-25 p,g L-I in the country. Concentrations of cadmium in precipitation are seen in Table 2. In the city the concentrations of cadmium in the bulk precipitation samples were approximately two times those in Woodslee but the same as those in 81. Joachim (although the number of samples at the latter site was relatively few). This difference between concentrations at

309

LEAD AND CADMIUM FROM THE ATMOSPHERE TABLE 2. Cadmium in precipitation - Essex County (p,g L-l). Bulk Samples

Wet Only Samples

Mean

#Samples

Range

Mean

#Samples

Range

URBAN WEST WINDSOR October-April 1982-83 1983-84

1.37 1.47

(29) (18)

0.2-4.7 0.3-4.6

0.88 1.05

(22) (13)

0.3-3.0 0.01-5.4

April-October 1983 1984 1st Year 2nd Year TOTAL PERIOD

0.80 1.37 1.08 1.42 1.22

(30) (21) (59) (39) (98)

0.2-2.5 0.4-3.9 0.2-4.7 0.3-4.6

0.36 0.74 0.62 0.87 0.72

(23) (19) (45) (32)

0.1-1.5 0.06-1.8 0.1-3.0 0.01-5.4

RURAL WOODSLEE October-April 1983-84

0.44

(18)

nd-1.1

0.38

(7)

0.11-0.5

April-October 1983 1984 2nd Year TOTAL PERIOD

0.51 0.84 0.65 0.61

(15) (20) (38) (53)

nd-4.1 0.2-4.6 nd-4.6

0.19

(23)

nd-1.7

0.23

(30)

ST. JOACHIM October-April 1983-84

2.49

(7)

1.1-44

nd

(1)

April-October 1984 TOTAL PERIOD

2.80 1.60

(16) (23)

0.3-14.3

1.46 1.06

(17) (18)

Woodslee and St. Joachim may be attributed again to the proximity to automobile traffic at the St. Joachim site. The cadmium concentrations in the bulk samples averaged approximately two times those of the wet-only samples. Concentrations of cadmium, as for lead, were higher during the colder than the warmer season of the year. The mean cadmium concentration in urban as well as rural precipitation is below the Canadian drinking water standard of 2 JLg L-l. SURFACE LOADINGS To obtain the atmospheric loadings of the two pollutants to the surface of the land or the lake, the concentrations were multiplied by the depth of precipitation, with the results shown in Table 3.

(77)

0.07-6.9

Averaging all the data from the West Windsor bulk samples gives an estimate of 360 g ha-'yr for ' surface lead loading - about 35 times the loading of cadmium (7 g ha-'yr ' ). For Woodslee the proportional (lead/cadmium) loading is 40: 1 and for St. Joachim 16:1. The lead/cadmium proportional loadings at Windsor and Woodslee are considerably higher than the 25:1 average figures quoted in Allen and Halley for the Great Lakes region as a whole. For the West Windsor site (where the most data are available), it is apparent (Table 3) that atmospheric lead and cadmium loadings in the colder part of the year are similar to those in the warm season, the increased precipitation compensating for the lower concentration in the warmer season.

310

SANDERSON et al.

TABLE 3. Atmospheric loading of lead and cadmiumEssex County. Lead

Cadmium

Bulk Wet-Only Bulk Wet-Only WEST WINDSOR

October-April (g ha-1mo- l )

1982-83 1983-84 April-October

27.8 33.8

11.3 12.6

0.5 0.7

0.4 0.4

37.8 26.1 AVERAGE ANNUAL 360

10.6 11.7 138

0.5 0.5 7.0

0.2 0.3 4.0

7.6

6.6

0.2

0.1

14.4 5.5 AVERAGE ANNUAL 80

7.6

0.7 0.1 2.0

0.2

15.8

11.4

1.0

0.6

11.1 AVERAGE ANNUAL 160

9.1 120

0.6 10.0

0.5 7.0

(g ha-1mo- l )

1983 1984 (est)

(g ha-1yr l )

WOODSLEE

October-April (g ha-1mo- l )

1983-84 April-October (g ha-1mo- l )

1983 1984 (est)

(g ha-1yr l )

ST. JOACHIM

October-April 1983-84 April-October 1984 (est) (g ha-1yr l )

If we assume that the difference between bulk and wet-only loading equals dry fallout, the ratio of wet:dry deposition for lead in the urban area is approximately 1:2 and for cadmium 1: 1. This proportion of wet/dry deposition of lead differs from those quoted earlier for New Jersey (2:1) and for Germany (l :1). It would appear that the differences are due to the actual siting of the collectors as well as to the surface cover. However, it is realized that the above assumption is probably incorrect because of the uncertainty of the catch efficiency of the bulk collectors.

STATISTICAL ANALYSIS AND CONCLUSIONS Kendall-Tau correlation coefficients were obtained between the four classes of concentrations and the duration, intensity, and amount of precipitation and wind direction (Table 4). The correlation coefficients indicated that there is a significant inverse relationship between the four concentration parameters and the amount of precipitation. In other words, the larger precipitation events resulted in lower concentrations of the metals. The intensity of the precipitation was also significantly correlated with all four concentration parameters, but not so strongly as precipitation amount. The duration of the precipitation event was significantly correlated only with metal concentrations in the bulk samples. No significant relationship was found between any of the concentrations and wind direction, either preceding or during a precipitation event at West Windsor. Shown in Table 4 were the correlations with wind direction immediately before the precipitation event and the first hour of precipitation. Other wind parameters were tested but no significant correlations were obtained. This is probably the result of the proximity of this site to the multiple sources of lead in the urban industrial complex, or the fact that near surface wind direction is a very poor indicator of storm trajectories. Kendall-Tau correlation coefficients were similarly obtained for the lead and cadmium concentrations and various climatic factors at the rural site at Woodslee (Table 5). As in West Windsor, the highest correlations were obtained between metal concentrations in the bulk samples and precipitation amounts. The correlations between concentrations in the wet-only samples and amount of precipitation were not significant. Precipitation intensity and the duration of the precipitation event were not significant in all cases in explaining the metal concentrations. Unlike at West Windsor, wind direction at Woodslee, both in the hour preceding and the first hour of the precipitation event, was significantly correlated with the metal concentration in the bulk samples. This indicates a localized source of the pollutants which is presumably the urban DetroitWindsor complex. Similar statistical tests will be carried out for the rural St. Joachim site when more data become available. Data collection will be continued until the summer of 1985, and also some models will be used to estimate dry deposition of the two metals in order

311

LEAD AND CADMIUM FROM THE ATMOSPHERE

TABLE 4. Kendall-Tau correlation coefficients between lead and cadmium concentrations in precipitation and various climatic factors (West Windsor).

Bulk Pb Bulk lead Wet-only lead Bulk cadmium Wet-only cadmium

1.0

Wetonly Pb 0.43* 1.0

Bulk Cd 0.68* 0.44* 1.0

Wind direction I

Precipitation

Wetonly Cd

Amount

Duratn.

Int.

Hr. Preceding

1st hour

0.36* 0.57* 0.46* 1.0

-0.48* -0.36* -0.52* -0.33*

-0.20* -0.04 -0.21 * 0.08

-0.35* -0.42* -0.39* -0.43*

0.07 0.00 0.03 0.09

0.07 -0.04 -0.07 -0.01

'significant at the 0.05 confidence level. lwind directions grouped into 8 classes 45° each.

TABLE 5. Kendall-Tau correlation coefficients for Woodslee precipitation samples.

Bulk Pb Bulk lead Wet-only lead Bulk cadmium Wet-only cadmium

1.0

Wetonly Pb 0.18 1.0

Bulk Cd 0.31 * -0.01 1.0

Precipitation

Wind direction

Wetonly Cd

Amount

Duratn.

Int.

Hr. Preceding

1st hour

-0.02 0.40* 0.26 1.0

-0.42* -0.10 -0.32* -0.17

-0.28* 0.17 -0.14 0.04

-0.25* -0.18 -0.30* -0.40*

0.29* 0.36 0.45* 0.03

0.33* 0.36 0.50* 0.20

'significant at the 0.05 confidence level.

to clarify the relationship of wet:dry fallout. It is also hoped that upper air data can be used in connection with specific precipitation events which resulted in large surface loadings, to gain more knowledge of the sources of the pollutants. ACKNOWLEDGMENTS

This research was supported by contract UP-6-175 from the Department of Supply and Services, Canada. REFERENCES Allen, H. E., and Halley, M. A. 1980. Assessment of airborne inorganic contaminants in the Great Lakes. Report to the International Joint Commission, Appendix B. Windsor, Ontario. Georgii, H. W. and Pankrath, J. (eds). 1982. Deposition of Atmospheric Pollutants. Holland: D. Reidel Publishing Co. Hafken, K. D., Meixner, F. X., and Ehnalt, D. H. 1983. Deposition of atmospheric trace constituents onto different natural surfaces. In Precipitation Scavenging, Dry Deposition and Resuspension, Pruppacher et al., pp. 825-836. New York: Elsevier Science Publishing Co.

Jeffries, D. S., and Snyder, W. R. 1981. Atmospheric deposition of heavy metals in Central Ontario. Water, Air and Soil Pollution 15:127-152. Knuth, R. H., Knutson, E. D., Feely, H. W., and Volchuk, H. L. 1983. Size distribution of atmospheric Pb and 2lOPb in rural New Jersey: Implications for wet and dry deposition. In Precipitation Scavenging, Dry Deposition and Resuspension, Pruppacher et al., pp. 1325-1336. New York: Elsevier Science Publishing Co. National Research Council Canada. 1978. Effects of lead in the environment: Quantitative aspects. NRCC No. 16736. Nurnberg, H. W., Valenta, P., and Nguyen, U. D. 1982. Wet deposition of toxic metals from the atmosphere in the Federal Republic of Germany. In Deposition of Atmospheric Pollutants, H. W. Georgii and J. Pankrath (eds). Holland: D. Reidel Publishing Co. Pattenden, N. G., Branson, J. R., and Fisher, E. R. 1982. Trace element measurements in wet and dry deposition and airborne particulates at an urban site. In Deposition of Atmospheric Pollutants, H. W. Georgii and J. Pankrath (eds). Holland: D. Reidel Publishing Co. Rohbock, E. 1983. Atmospheric removal of airborne metal by wet and dry deposition. In Deposition of Atmospheric Pollutants, H. W. Georgii and J. Pankrath (eds). Holland: D. Reidel Publishing Co.

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Sanderson, M. E., and Marchand, D. 1984. Lead and cadmium in precipitation in the Essex region of Southwestern Ontario. In Hydrochemical Balances of Freshwater Systems, pp. 215-222. Uppsala Symposium. IAHS Publication 50. Shiomi, M., and Kuntz, K. W. 1973. Great Lakes precipitation chemistry, Part 1. Lake Ontario basin. In Proc. 16th Con! Great Lakes Res., pp. 581-602. Internat. Assoc. Great Lakes Res. Sickes, J. E., Bach, W. D., and Spiller, L. L. 1983. Comparison of several techniques for determining dry deposition flux. In Precipitation Scavenging, Dry

Deposition and Resuspension, Pruppacher et al., pp. 979-990. New York: Elsevier Science Publishing Co. Struempler, A. W. 1976. Trace metals in rain and snow during 1973 at Chandran, Nebraska. Atmospheric Environment 10:33-37. Ter Harr, G. L., Holtzman, R. B., and Lucas, H. F. 1967. Lead and lead-21O in rainwater. Nature 216:353-355. Van Loon, J. C. 1973. Toronto's precipitation analyzed for heavy metal content. Water Pollution Control 1Il :38-41.