- Email: [email protected]
Atmospheric deposition as a source of trace elements in soils
Palaeogeography, Palaeoclirnatology, Palaeoecology (Global and Planetary Change Section), 82 (1990): 141-148 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
141
A t m o s p h e r i c deposition as a s o u r c e of trace e l e m e n t s in soils * A.L. P A G E 1 a n d E. S T E I N N E S
2
1Department of Soil and Environmental Sciences, University o[ Cali[ornia, Riverside, CA 92521 (U.S.A.) 2 Department ol Chemistry, University of Trondheirn, AVH, 7055 DragvoU (Norway)
(Received February 20, 1989; revised and accepted September 20, 1989)
1. I n t r o d u c t i o n
2. T r a c e e l e m e n t c o n c e n t r a t i o n s
T h e c o n c e n t r a t i o n s of t r a c e e l e m e n t s in soils a r e d e t e r m i n e d b y t h e a m o u n t s p r e s e n t in t h e parent materials, plus the amounts added through wind, water, and human activities, minus the amounts removed through leaching, surface runoff, and volatilization, and by vegetation. As the more soluble trace elements are r e m o v e d b y l e a c h i n g , t h e less s o l u b l e a c c u m u l a t e in soils. T h e p a r e n t m a t e r i a l s for soils a r e c r u s t a l ign e o u s , s e d i m e n t a r y , a n d m e t a m o r p h i c r o c k s exp o s e d t o w e a t h e r i n g a t t h e s u r f a c e of t h e e a r t h . In the igneous group, the basic igneous rocks (e.g., b a s a l t ) , in g e n e r a l , c o n t a i n h i g h e r conc e n t r a t i o n s of Fe, Cd, Cr, Co, M n , Ni, V, a n d Zn t h a n d o t h e a c i d i g n e o u s r o c k s (e.g., g r a n i t e ) . C o n c e n t r a t i o n s of Be, P b , Li, M o , Re, T h a n d U, on t h e o t h e r h a n d , a r e c o n s i s t e n t l y h i g h e r in g r a n i t e s t h a n in b a s a l t s ( T a b l e I). E x c e p t for M n a n d Hg, s h a l e s c o n t a i n h i g h e r c o n c e n t r a t i o n s of m e t a l s (A1, Fe, Be, Cd, Cr, Co, Cu, P b , Li, M o , Ni, Sin, T h , U, V, Zn) t h a n d o t h e s a n d s t o n e s a n d c a r b o n a t e s . C o n c e n t r a t i o n s of Fe, A1, Cr, Co, Cu, a n d Li in s a n d s t o n e s a r e g r e a t e r on t h e a v e r a g e t h a n t h o s e o b s e r v e d in c a r b o n a t e s .
T y p i c a l r a n g e s of m e t a l c o n c e n t r a t i o n s f o u n d in soils a c c o r d i n g t o d a t a c o m p i l e d b y M a t t i g o d a n d P a g e (1983) a r e i l l u s t r a t e d in Fig. 1. T h e
* Position paper prepared for the IUGS Workshop on Past Global Changes, Interlaken, Switzerland, April 24-28, 1989. 0921-8181/90/$03.50 © 1990 - Elsevier Science Publishers B.V.
in soils
TABLE I Typical levels of trace elements in igneous and sedimentary rocks a Ele-
Igneous rocks
Sedimentary rocks
ment Granite Basalt Shales Sandstones Carbonates In% Al Fe
7.5 2.0
8.4 2.8
8.4 4.8
3.4 1.5
0.7 1.0
<1 0.05 35 0.3 30 10 25 460 0.3 0.2 5 0.5 2.5 0.5 20 18
<1 0.05 11 0.1 5 8 6 850 0.2 0.2 15 0.5 1.7 2.2 30 20
In mgkg -1 Be Cd Cr Co Cu Pb Li Mn Hg Mo Ni Sn Th U V Zn
4.0 0.1 12 6 13 35 25 300 0.1 4 0.8 3 40 4 45 50
0.5 3 0.1 0.3 100 90 40 19 100 40 5 2O 12 70 1400 850 0.2 0.3 0.8 2.6 113 68 2 6 2.0 12 0.5 4 260 130 90 100
" Authors' estimates from data of Mason and Moore (1982) and Bowen (1979).
142
A.L. P A G E A N D E. S T E I N N E S
d a t a based upon the compilation of Bowen (1979) exclude soils t h a t are near ore bodies and those t h a t have been contaminated from point or mobile sources. Elevated concentrations of m a n y trace elements can occur naturally in soils. These high concentrations are due either to parent materials t h a t are ore bodies or due to secondary dispersion. Soils t h a t are highly elevated with trace elements under natural conditions have been observed in Norway (Lag and Bolviken, 1974), England and Wales (Thornton, 1982) and elsewhere. Table II lists levels of Cd, Cu, Ni, Pb and Zn found in surface soils from six different localities in Norway. According to Lag and Bolviken (1974) varying degrees of phytotoxicities due to Pb and Cu were observed in some of these soils. No phytotoxicity due to high concentrations of Cd and Zn in soils, however, was observed by T h o r n t o n (1982). Quite comprehensive data for the trace elem e n t concentrations in soils from the United States (Pierce et al., 1982; Logan and Miller, 1983; Holmgren et al., 1989), Canada (Frank, 1976), Germany (Kloke, 1982), Italy (Bini et al., 1988), United Kingdom (McGraph, 1986), and the Eastern Bloc countries (Kabata-Pendias and Pendias, 1984) have been published.
1.000,000 100.000 10.000
3. Atmospheric deposition of trace e l e m e n t s onto soils Trace elements enter the atmosphere as gases, aerosols, and particulates derived from a wide variety of natural and anthropogenic sources. Once airborne, the trace elements are transported through wind m o v e m e n t and deposited onto land or water surfaces some distance from the source. T h e distance of t r a n s p o r t depends on the nature of the emitting source, the size and density of the particles and changes in their physical characteristics a n d / o r chemical composition during transport, adsorption and solution processes, and meteorological conditions. Natural processes contributing trace elements to the atmosphere include chemical and biological volatilization, volcanic and geothermal activity, wind entrainment, forest fires, and spontaneous combustion. Anthropogenic processes include the combustion of fossil fuels, mining and smelting, industrial and urban activities. The extent to which atmospheric deposition may contribute to the total metal concentrations in soils depends on the a m o u n t s deposited, differences between the chemical composition of the deposited material and t h a t of the soil on
!! U!H.
E
[ ] MAJOR PLANT NIJTRIENT [~]MINOR PLANT NUTP~ENT I ~ E S S E N T I A L ~O1~ S O M E SPECIES ~T'-,~POTENTIALt. 'V TOXIC E L E M E N T
1000
1O0 10 1
0.1 00.1 Cd
5e
Fig. 1. Ranges and median values of metal concentrations found in uncontaminated soils (in mg kg-i). From Mattigod and Page (1983) and based on data from Bowen (1979).
ATMOSPHERIC DEPOSITION AS A SOURCE OF TRACE ELEMENTS IN SOILS
•
. - e
25 39 ~
e
e
0
143
0
I00 ~80 2 S 0 ~ 9 0
~90
Fig. 2. Lead in h u m u s (ppm); strong c o n t r i b u t i o n from long-range a i r pollution.
A.L. PAGE AND E. STEINNES
144 T A B L E II N a t u r a l surface soils ( 2 - 5 cm) with highly elevated concentrations of trace elements (mg k g - 1 ) Area
Cd
Cu
Ni
Pb
Zn
Snertingdal Gala Skavern Krokvann Hjerkin Karasjok
0.9 0.7 0.9 1.8 1.3 0.6
15 6 126 260 785 7400
12 9 37 48 18 32
24500 6400 97000 10400 57 18
44 40 416 860 232 36
a From: M a t t i g o d a n d Page (1983) a n d based on d a t a from L a g a n d Bolviken (1974).
which the material is deposited, and the depth to which the deposited metal is mixed with the soil. Amounts deposited are measured by summing deposition collected in wet and dry fall. Both measurements are subject to a considerable degree of uncertainty due mainly to seasonal and short-term variations in the meteorological conditions at the collection site. Deposition of metals, for example, varies with intensity and duration of a rainfall event, the nature and extent of the canopy, wind direction and velocity, re-entrainment, particle size distribution, etc. Another technique to obtain values for amounts of metals deposited onto soils is to estimate them from air concentrations and deposition velocities (Sposito and Page, 1984). Although this technique is subject to similar degrees of uncertainty discussed above, because a more extensive data base is available for air concentrations, it is possible to obtain more widespread estimates of deposition. Estimates of amounts of trace elements deposited onto soils in remote, rural, and urban regions of the United States and Europe are presented in Table III. Values for amounts deposited in Europe and rural and urban regions in the United States were computed from air concentrations and an assumed deposition velocity of 5 mm s-1. Because the size of air-borne particulates is smaller in remote regions, we have assumed a deposition velocity of 2 mm sec -1 to compute deposition for this region. According to data presented by Lannefors and Hansen (1983), a deposition velocity of 2 mm s - 1
would correspond to a particle diameter of about 0.06-0.5 ~m, while t hat of 5 mm s -1 would correspond to particle diameters of 1-2 /zm. These particle diameters are in the general ranges of air-borne particles. Deposition in a remote region of the U.S. was computed from air concentrations reported for Northern Michigan by Alkezweeny et al. (1982); those in rural and urban regions from air concentrations reported by the U.S. Environmental Protection Agency (1979). Deposition in Europe was computed from median air concentrations compiled by Bowen (1979) and is considered by the authors to be more or less representative of deposition in urban regions. In general, the data show deposition of Cu, Fe, Mn, Ni and V in urban regions of Europe and the United States to be somewhat similar. In the United States, deposition of the industrial metals (Fe, Pb and Zn), as expected, show a rather dramatic increase in urban regions compared to rural and remote regions (Table III). 4. I n f l u e n c e o n s o i l t r a c e e l e m e n t c o n c e n t r a tions
Although the data presented in Table III provide estimates of amounts of trace elements deposited from air onto the surface of soil, they do not relate directly to the extent to which trace element concentrations in soil may increase as a result of atmospheric deposition. Conditions may differ considerably between disturbed soils (e.g., agricultural soils), where the supplied trace elements will be mixed within the surface layer, and where in undisturbed natural soils the elements deposited in most cases tend to concentrate in the uppermost few cm of the soil. Moreover, the surface layer of natural soils may often have a high content of organic matter, in which case it may serve as a very efficient trap for some trace elements. 4.1. Disturbed soils
Estimated increased concentrations of trace elements in soil resulting from atmospheric deposition assuming t h a t the trace elements de-
ATMOSPHERIC DEPOSITION AS A SOURCE OF TRACE ELEMENTS IN SOILS TABLE III Levels of trace e l e m e n t s deposited onto soils (in g ha - I y r ~) Element
United States " Remote ¢
Be Cd Cu Fe Pb Mn Mo Ni V Zn
1.4 2.4 78 6.3 2.4 0.5 0.5 20
Europe b
Rural
Urban
< 0.3 < 1.1 508 552 381 < 2.5 <4 < 4 25 161
< 0.3 6.3 573 3345 1815 110 <4 35 83 525
536 2208 189 68 39 47 1900
a Levels for r u r a l an d u r b a n areas in t h e U n i t e d S t a t e s are der ived from 90th percentile air c o n c e n t r a t i o n s (U.S. Env i r o n m e n t a l P r o t e c t i o n Agency, 1979) a s s u m i n g a deposition velocity of 5 m m s-1. b Der ived from m e d i a n values for air (Bowen, 1979) assuming deposition velocity of 5 m m s-1. c Der ived from air c o n c e n t r a t i o n s for n o r t h e r n M i c h i g a n (Alkezweeny et al., 1982) a s s u m i n g a deposition velocity of 2 r a m s -1.
posited would be mixed in the surface horizon (0-0.15 m) of soil with a bulk density of 1.5 × 103 kg m -3 are presented in Table IV. Compared with typical soil concentrations, the annual increase in metal concentrations in soil resulting from deposition from air with a composition
T A B L E IV Increase in trace e l e m e n t c o n c e n t r a t i o n s in the u p p e r 0.15 m of soil from a t m o s p h e r i c deposition in remote, rural, and u r b a n regions of the U n i t e d S t a t e s ( i n / ~ g kg -1) a
Element
Be Cd Cu Fe Pb Mn Mo Ni V Zn
C o n c e n t r a t i o n arising from depositio n
T y p i c a l soil concentration
Remote
Rural
Urban
0.6 1.1 35 2.8 1.1 0.2 0.2 8.9
< 0.1 < 0.5 225 245 169 < 1.1 < 1.8 < 1.8 11 72
< 0.1 2.8 255 1487 808 49 < 1.8 16 39 233
145
comparable to t hat occurring in remote regions, e.g., northern Michigan, is extremely small and except for Cd, is less than 0.02% of the typical soil concentrations. Likewise the annual increase in the concentrations of Fe, Mn, Ni, and and V in soil arising from deposition from air having a composition comparable to t hat in rural regions are less than 0.02% of the typical soil concentration. In rural regions the estimates indicate t hat atmospheric deposition would increase the typical concentration of Be, Cd and Zn by < 0.15% each year; Cu and Pb would increase by 0.75 and 1.1%, respectively. In the case of metal deposition from air considered to have a composition comparable to an urban region, based upon typical soil levels, the predicted annual increases of Mn and Fe are less than 0.005%, whereas those of Ni and V are 0.03 and 0.04%, respectively; Zn, Cu and Cd range from about 0.5 to 0.9%, and Pb at a value of 5.4% shows the greatest increase above typical soil concentrations. Data presented for Pb are for the 1979 year and since t hat time in the United States the concentration of Pb in gasoline has been either drastically reduced or eliminated. Based upon data presented by the U.S. Environmental Protection Agency (1986), deposition of Pb in urban areas of the United States would be about one-half of those presented in this report. For some elements not included in Table IV (e.g., As, Sb, Se and the halogens C1, Br and I), air-borne supply from natural and anthropogenic sources may be more significant than for most of the above elements (Lag and Steinnes, 1976; Allen and Steinnes, 1979). 4.2. Undisturbed natural soils
300 350 30,000 40 x 106 15,000 1 × 106 1200 50,000 90,000 50,000
C o m p u t e d from d a t a presented in T a b l e I I I a s s u m i n g a b u l k d e n s i t y for soil of 1.5 × 103 kg m 3.
Studies carried out in Norway may illustrate that under certain conditions long-range atmospheric transport over a long period of time may cause very significant increases of some anthropogenic trace elements in the surface horizon of natural soils. The deposition rates of volatile trace elements such as Pb, Cd, Zn, As and Sb are about ten-fold higher in the southernmost area of the country than in some more northerly
146 A.L.
/
i
•
•
oeee
e
•
•
•
•
~:........: ..~ •
•.~~,,.
ee
! ~i..-..~ i.
•.
e a
~
r
."
~.._ '
" ,
•
•
*
• -..-.~. •
•
°Qe°
• oo¢
•
•
•
o
o
•
•
•
j
.)
•
I e
•
•
•
O
•
oO0
25 59 65 t00 t60 250 590 ~90 Fig. 3. Lead in C horizon (ppm); mainly influenced by bedrock geology.
PAGE
AND
E. STEINNES
147
A T M O S P H E R I C D E P O S I T I O N AS A SOURCE OF T R A C E E L E M E N T S IN SOILS
regions (Steinnes, 1980). Studies of air particulate samples at Birkenes, S. Norway, in conjunction with air trajectory data show t hat the supply of the above elements occurs with winds from the sector SE SW to at least 80% (Pacyna et al., 1984; Amundsen et al., 1987). Furthermore, precipitation events occur mainly with the same wind directions. The atmospheric supply of these pollutants to this area is therefore considerable in spite of the fact that the main source regions are located at distances of 1000 km or more. A national survey of natural surface soils in Norway revealed th at the southern soils had many-fold higher contents of Pb, Cd, As and Sb in the humus layer than soils from Central and Northern Norway. Also for Zn and S e a distinct N S gradient was evident, while for Cu there were no strong regional differences (Allen and Steinnes, 1979). The correspondence with the present geographical deposition pattern for these elements was remarkable. In a similar, more recent survey samples at different depths in the soil profile were collected (Bolviken and Steinnes, 1987). In Figs. 2 and 3 results for HNO3-extractable Pb in the humus layer (3-5 cm depth) and C-horizon (60 cm), respectively, are shown. The very distinct Pb excess evident in areas near the southern coast in the humus samples is not at all evident in the mineral subsoil, which strongly indicates that what is observed is a large-scale contamination from long-range atmospheric transport, probably over a long period of time. Investigations of peat cores from ombrotropic bogs in different parts of the country (Hvatum et al., 1983, 1987) provides strong support to the above conclusion. Relative depth profiles from a bog in S. Norway (Fig. 4) indicate that the air-borne supply of Pb, Cd, As and Sb has increased by at least a factor of 20 since pre-industrial time in Europe, and further indicate t h a t the four elements have a similar origin. Studies of Se (Lag and Steinnes, 1974, 1978) and C1, Br, and I (Lag and Steinnes, 1976) show t h a t atmospheric supply from natural sources may also be important in determining surface soil concentrations. For the halogens, surface
1.0
Z O F--Z~ Z L~ Z
0
.........
AS
- -
Pb
......
Cd
----
Sb
0.5
LJ
J L~
I, X
5
I I0
Y'.
I 20
7 50
)
DEPTH, cm Fig. 4. C o n c e n t r a t i o n s of t r a c e e l e m e n t s i n p e a t p r o f i l e s , n o r m a l i z e d t o t h e level in t h e s u r f a c e l a y e r ( o m b r o t r o p h i c b o g in s o u t h e a s t e r n N o r w a y ) .
soil levels vary in a very consistent and systematic manner with the distance from the ocean. In the case of Se, which is in general present at very low levels in the underground mineral soil in Norway, the geographical distribution indicates airborne supply both from the marine environment (coastal regions all over the country) and with long-range transported pollution aerosols (southernmost regions). The data from the ombrotrophic peak profiles provide additional support to these interpretations.
Summary Regional air pollution is not a major contribution to the trace element content of disturbed remote, rural and urban soils. Trace elements deposited are diluted by mixing with underlying mineral soil of high bulk density ( - 1.25 1.75 kg m 3). On the contrary, long-range transport and subsequent deposition onto the surface humus
148
layer of undisturbed soils may substantially increase the trace element content of the humus layer. Trace elements deposited are not subject to subtantial mixing and essentially remain in the humus layer of low bulk density ( - 0.2-0.5 kg m-a). Low bulk density and minimal dilution through mixing account for the high enrichment in the undisturbed soil humus layer. In conclusion, although in general regional and long-range transport is not a major contributor to the trace element content of most soils, there are important exceptions which should not be overlooked. Reterences Alkezweeny, A.J., Laulainen, N.S. and Thorp, J.M., 1982. Atmos. Environ., 16: 242. Allen, R.O. and Steirmes, E., 1979. In: Heavy Metals in the Environment. CEP Consultants, Edinburgh, p. 271. Amundsen, C.E., Rambaek, J.P., Semb, A. and Steinnes, E., 1987. J. Radioanal. Chem., 114: 5. Bini, C., Dall'Aglio, M., Ferretti, O. and Gragnani, R., 1988. Environ. Geochem. Health, 10: 63. Bowen, H.J.M., 1979. Environmental Chemistry of the Elements. Academic Press, London. Bolviken, B. and Steinnes, E., 1987. In: Heavy Metals in the Environment. CEP Consultants, Edinburgh, 1, p. 291. Frank, R., Ishida, K. and Suda, P., 1976. Can. J. Soil Sci., 56: 181. Hawkes, H.E. and Webb, J.S., 1962. Geochemistry of Mineral Exploration. Harper and Row, New York, N.Y. Holmgren, G.G.S., Meyer, M.W., Daniels, R.B., Chaney, R.L. and Kubota, J., 1989. J. Environ. Qual., in press. Hvatum, O.O., Bolviken, B. and Steinnes, E., 1983. Ecol. Bull. Stockholm, 35: 351.
A.L. PAGE AND E. STEINNES Hvatum, O.O., Steinnes, E. and Bolviken, B., 1987. In: Heavy Metals in the Environment. CEP Consultants, Edinburgh, 1, p. 201. Kabata-Pendias, A. and Pendias, H., 1984. Trace Elements in Soils and Plants. CRC Press, Boca Raton, Fla. Kloke, A., 1982. Wat. Sci. Technol., 14: 61. Lannefors, H. and Hansen, H.C., 1983. Atmos. Environ., 17: 87. Logan, T.J. and Miller, R.H., 1983. Ohio State Univ. Agric. Res. Dev. Res. Circ., 275. Lag, J. and Bolviken, B., 1974. Nor. Geol. Unders. Bull., 23: 73. Lag, . and Steinnes, E., 1974. Ambio, 3: 237. Lag, J. and Steinnes, E., 1976. Geoderma, 16: 317. Lag, J. and Steinnes, E., 1978. Geoderma, 20: 3. Mason, B. and Moore, G.B., 1982. In: Principles of Geochemistry. Wiley, New York, N.Y., 4th ed. Mattigod, S.V. and Page, A.L., 1983. In: I. Thornton (Editor), Applied Environmental Geochemistry. Academic Press, London, p. 355. McGrath, S.P., 1986. In: D.D. Hemphill (Editor), Trace Substances in Environmental Health, Univ. Missouri, Columbia, Mo., p. 242. Pacyna, J.M., Semb, A. and Hanssen, J.E., 1984. Tellus, 36B: 163. Pierce, F.J., Dowdy, R.H. and Grigal, D.F., 1982). J. Environ. Qual., 11: 416. Sposito, G. and Page, A.L., 1984. In: H. Sigel (Editor), Metal Ions in Biological Systems. Marcel Dekker, New York, N.Y., p. 287. Steinnes, E., 1980. J. Radioanal. Chem., 58: 387. Thornton, I., 1982. In: D.D. Hemphill (Editor), Trace Substances in Environmental Health-XVI. Univ. Missouri, Columbia, Mo., p. 57. U.S. Environmental Protection Agency, 1979. Air Quality Data for Metals: 1977-1979. U.S. Environ. Prot. Agency, Research Triangle Park, N.C. U.S. Environmental Protection Agency, 1986. Air Quality Criteria for Lead. EPA-600/8-83/028aF. U.S. Environ. Prot. Agency, Research Triangle Park, N.C.
141
A t m o s p h e r i c deposition as a s o u r c e of trace e l e m e n t s in soils * A.L. P A G E 1 a n d E. S T E I N N E S
2
1Department of Soil and Environmental Sciences, University o[ Cali[ornia, Riverside, CA 92521 (U.S.A.) 2 Department ol Chemistry, University of Trondheirn, AVH, 7055 DragvoU (Norway)
(Received February 20, 1989; revised and accepted September 20, 1989)
1. I n t r o d u c t i o n
2. T r a c e e l e m e n t c o n c e n t r a t i o n s
T h e c o n c e n t r a t i o n s of t r a c e e l e m e n t s in soils a r e d e t e r m i n e d b y t h e a m o u n t s p r e s e n t in t h e parent materials, plus the amounts added through wind, water, and human activities, minus the amounts removed through leaching, surface runoff, and volatilization, and by vegetation. As the more soluble trace elements are r e m o v e d b y l e a c h i n g , t h e less s o l u b l e a c c u m u l a t e in soils. T h e p a r e n t m a t e r i a l s for soils a r e c r u s t a l ign e o u s , s e d i m e n t a r y , a n d m e t a m o r p h i c r o c k s exp o s e d t o w e a t h e r i n g a t t h e s u r f a c e of t h e e a r t h . In the igneous group, the basic igneous rocks (e.g., b a s a l t ) , in g e n e r a l , c o n t a i n h i g h e r conc e n t r a t i o n s of Fe, Cd, Cr, Co, M n , Ni, V, a n d Zn t h a n d o t h e a c i d i g n e o u s r o c k s (e.g., g r a n i t e ) . C o n c e n t r a t i o n s of Be, P b , Li, M o , Re, T h a n d U, on t h e o t h e r h a n d , a r e c o n s i s t e n t l y h i g h e r in g r a n i t e s t h a n in b a s a l t s ( T a b l e I). E x c e p t for M n a n d Hg, s h a l e s c o n t a i n h i g h e r c o n c e n t r a t i o n s of m e t a l s (A1, Fe, Be, Cd, Cr, Co, Cu, P b , Li, M o , Ni, Sin, T h , U, V, Zn) t h a n d o t h e s a n d s t o n e s a n d c a r b o n a t e s . C o n c e n t r a t i o n s of Fe, A1, Cr, Co, Cu, a n d Li in s a n d s t o n e s a r e g r e a t e r on t h e a v e r a g e t h a n t h o s e o b s e r v e d in c a r b o n a t e s .
T y p i c a l r a n g e s of m e t a l c o n c e n t r a t i o n s f o u n d in soils a c c o r d i n g t o d a t a c o m p i l e d b y M a t t i g o d a n d P a g e (1983) a r e i l l u s t r a t e d in Fig. 1. T h e
* Position paper prepared for the IUGS Workshop on Past Global Changes, Interlaken, Switzerland, April 24-28, 1989. 0921-8181/90/$03.50 © 1990 - Elsevier Science Publishers B.V.
in soils
TABLE I Typical levels of trace elements in igneous and sedimentary rocks a Ele-
Igneous rocks
Sedimentary rocks
ment Granite Basalt Shales Sandstones Carbonates In% Al Fe
7.5 2.0
8.4 2.8
8.4 4.8
3.4 1.5
0.7 1.0
<1 0.05 35 0.3 30 10 25 460 0.3 0.2 5 0.5 2.5 0.5 20 18
<1 0.05 11 0.1 5 8 6 850 0.2 0.2 15 0.5 1.7 2.2 30 20
In mgkg -1 Be Cd Cr Co Cu Pb Li Mn Hg Mo Ni Sn Th U V Zn
4.0 0.1 12 6 13 35 25 300 0.1 4 0.8 3 40 4 45 50
0.5 3 0.1 0.3 100 90 40 19 100 40 5 2O 12 70 1400 850 0.2 0.3 0.8 2.6 113 68 2 6 2.0 12 0.5 4 260 130 90 100
" Authors' estimates from data of Mason and Moore (1982) and Bowen (1979).
142
A.L. P A G E A N D E. S T E I N N E S
d a t a based upon the compilation of Bowen (1979) exclude soils t h a t are near ore bodies and those t h a t have been contaminated from point or mobile sources. Elevated concentrations of m a n y trace elements can occur naturally in soils. These high concentrations are due either to parent materials t h a t are ore bodies or due to secondary dispersion. Soils t h a t are highly elevated with trace elements under natural conditions have been observed in Norway (Lag and Bolviken, 1974), England and Wales (Thornton, 1982) and elsewhere. Table II lists levels of Cd, Cu, Ni, Pb and Zn found in surface soils from six different localities in Norway. According to Lag and Bolviken (1974) varying degrees of phytotoxicities due to Pb and Cu were observed in some of these soils. No phytotoxicity due to high concentrations of Cd and Zn in soils, however, was observed by T h o r n t o n (1982). Quite comprehensive data for the trace elem e n t concentrations in soils from the United States (Pierce et al., 1982; Logan and Miller, 1983; Holmgren et al., 1989), Canada (Frank, 1976), Germany (Kloke, 1982), Italy (Bini et al., 1988), United Kingdom (McGraph, 1986), and the Eastern Bloc countries (Kabata-Pendias and Pendias, 1984) have been published.
1.000,000 100.000 10.000
3. Atmospheric deposition of trace e l e m e n t s onto soils Trace elements enter the atmosphere as gases, aerosols, and particulates derived from a wide variety of natural and anthropogenic sources. Once airborne, the trace elements are transported through wind m o v e m e n t and deposited onto land or water surfaces some distance from the source. T h e distance of t r a n s p o r t depends on the nature of the emitting source, the size and density of the particles and changes in their physical characteristics a n d / o r chemical composition during transport, adsorption and solution processes, and meteorological conditions. Natural processes contributing trace elements to the atmosphere include chemical and biological volatilization, volcanic and geothermal activity, wind entrainment, forest fires, and spontaneous combustion. Anthropogenic processes include the combustion of fossil fuels, mining and smelting, industrial and urban activities. The extent to which atmospheric deposition may contribute to the total metal concentrations in soils depends on the a m o u n t s deposited, differences between the chemical composition of the deposited material and t h a t of the soil on
!! U!H.
E
[ ] MAJOR PLANT NIJTRIENT [~]MINOR PLANT NUTP~ENT I ~ E S S E N T I A L ~O1~ S O M E SPECIES ~T'-,~POTENTIALt. 'V TOXIC E L E M E N T
1000
1O0 10 1
0.1 00.1 Cd
5e
Fig. 1. Ranges and median values of metal concentrations found in uncontaminated soils (in mg kg-i). From Mattigod and Page (1983) and based on data from Bowen (1979).
ATMOSPHERIC DEPOSITION AS A SOURCE OF TRACE ELEMENTS IN SOILS
•
. - e
25 39 ~
e
e
0
143
0
I00 ~80 2 S 0 ~ 9 0
~90
Fig. 2. Lead in h u m u s (ppm); strong c o n t r i b u t i o n from long-range a i r pollution.
A.L. PAGE AND E. STEINNES
144 T A B L E II N a t u r a l surface soils ( 2 - 5 cm) with highly elevated concentrations of trace elements (mg k g - 1 ) Area
Cd
Cu
Ni
Pb
Zn
Snertingdal Gala Skavern Krokvann Hjerkin Karasjok
0.9 0.7 0.9 1.8 1.3 0.6
15 6 126 260 785 7400
12 9 37 48 18 32
24500 6400 97000 10400 57 18
44 40 416 860 232 36
a From: M a t t i g o d a n d Page (1983) a n d based on d a t a from L a g a n d Bolviken (1974).
which the material is deposited, and the depth to which the deposited metal is mixed with the soil. Amounts deposited are measured by summing deposition collected in wet and dry fall. Both measurements are subject to a considerable degree of uncertainty due mainly to seasonal and short-term variations in the meteorological conditions at the collection site. Deposition of metals, for example, varies with intensity and duration of a rainfall event, the nature and extent of the canopy, wind direction and velocity, re-entrainment, particle size distribution, etc. Another technique to obtain values for amounts of metals deposited onto soils is to estimate them from air concentrations and deposition velocities (Sposito and Page, 1984). Although this technique is subject to similar degrees of uncertainty discussed above, because a more extensive data base is available for air concentrations, it is possible to obtain more widespread estimates of deposition. Estimates of amounts of trace elements deposited onto soils in remote, rural, and urban regions of the United States and Europe are presented in Table III. Values for amounts deposited in Europe and rural and urban regions in the United States were computed from air concentrations and an assumed deposition velocity of 5 mm s-1. Because the size of air-borne particulates is smaller in remote regions, we have assumed a deposition velocity of 2 mm sec -1 to compute deposition for this region. According to data presented by Lannefors and Hansen (1983), a deposition velocity of 2 mm s - 1
would correspond to a particle diameter of about 0.06-0.5 ~m, while t hat of 5 mm s -1 would correspond to particle diameters of 1-2 /zm. These particle diameters are in the general ranges of air-borne particles. Deposition in a remote region of the U.S. was computed from air concentrations reported for Northern Michigan by Alkezweeny et al. (1982); those in rural and urban regions from air concentrations reported by the U.S. Environmental Protection Agency (1979). Deposition in Europe was computed from median air concentrations compiled by Bowen (1979) and is considered by the authors to be more or less representative of deposition in urban regions. In general, the data show deposition of Cu, Fe, Mn, Ni and V in urban regions of Europe and the United States to be somewhat similar. In the United States, deposition of the industrial metals (Fe, Pb and Zn), as expected, show a rather dramatic increase in urban regions compared to rural and remote regions (Table III). 4. I n f l u e n c e o n s o i l t r a c e e l e m e n t c o n c e n t r a tions
Although the data presented in Table III provide estimates of amounts of trace elements deposited from air onto the surface of soil, they do not relate directly to the extent to which trace element concentrations in soil may increase as a result of atmospheric deposition. Conditions may differ considerably between disturbed soils (e.g., agricultural soils), where the supplied trace elements will be mixed within the surface layer, and where in undisturbed natural soils the elements deposited in most cases tend to concentrate in the uppermost few cm of the soil. Moreover, the surface layer of natural soils may often have a high content of organic matter, in which case it may serve as a very efficient trap for some trace elements. 4.1. Disturbed soils
Estimated increased concentrations of trace elements in soil resulting from atmospheric deposition assuming t h a t the trace elements de-
ATMOSPHERIC DEPOSITION AS A SOURCE OF TRACE ELEMENTS IN SOILS TABLE III Levels of trace e l e m e n t s deposited onto soils (in g ha - I y r ~) Element
United States " Remote ¢
Be Cd Cu Fe Pb Mn Mo Ni V Zn
1.4 2.4 78 6.3 2.4 0.5 0.5 20
Europe b
Rural
Urban
< 0.3 < 1.1 508 552 381 < 2.5 <4 < 4 25 161
< 0.3 6.3 573 3345 1815 110 <4 35 83 525
536 2208 189 68 39 47 1900
a Levels for r u r a l an d u r b a n areas in t h e U n i t e d S t a t e s are der ived from 90th percentile air c o n c e n t r a t i o n s (U.S. Env i r o n m e n t a l P r o t e c t i o n Agency, 1979) a s s u m i n g a deposition velocity of 5 m m s-1. b Der ived from m e d i a n values for air (Bowen, 1979) assuming deposition velocity of 5 m m s-1. c Der ived from air c o n c e n t r a t i o n s for n o r t h e r n M i c h i g a n (Alkezweeny et al., 1982) a s s u m i n g a deposition velocity of 2 r a m s -1.
posited would be mixed in the surface horizon (0-0.15 m) of soil with a bulk density of 1.5 × 103 kg m -3 are presented in Table IV. Compared with typical soil concentrations, the annual increase in metal concentrations in soil resulting from deposition from air with a composition
T A B L E IV Increase in trace e l e m e n t c o n c e n t r a t i o n s in the u p p e r 0.15 m of soil from a t m o s p h e r i c deposition in remote, rural, and u r b a n regions of the U n i t e d S t a t e s ( i n / ~ g kg -1) a
Element
Be Cd Cu Fe Pb Mn Mo Ni V Zn
C o n c e n t r a t i o n arising from depositio n
T y p i c a l soil concentration
Remote
Rural
Urban
0.6 1.1 35 2.8 1.1 0.2 0.2 8.9
< 0.1 < 0.5 225 245 169 < 1.1 < 1.8 < 1.8 11 72
< 0.1 2.8 255 1487 808 49 < 1.8 16 39 233
145
comparable to t hat occurring in remote regions, e.g., northern Michigan, is extremely small and except for Cd, is less than 0.02% of the typical soil concentrations. Likewise the annual increase in the concentrations of Fe, Mn, Ni, and and V in soil arising from deposition from air having a composition comparable to t hat in rural regions are less than 0.02% of the typical soil concentration. In rural regions the estimates indicate t hat atmospheric deposition would increase the typical concentration of Be, Cd and Zn by < 0.15% each year; Cu and Pb would increase by 0.75 and 1.1%, respectively. In the case of metal deposition from air considered to have a composition comparable to an urban region, based upon typical soil levels, the predicted annual increases of Mn and Fe are less than 0.005%, whereas those of Ni and V are 0.03 and 0.04%, respectively; Zn, Cu and Cd range from about 0.5 to 0.9%, and Pb at a value of 5.4% shows the greatest increase above typical soil concentrations. Data presented for Pb are for the 1979 year and since t hat time in the United States the concentration of Pb in gasoline has been either drastically reduced or eliminated. Based upon data presented by the U.S. Environmental Protection Agency (1986), deposition of Pb in urban areas of the United States would be about one-half of those presented in this report. For some elements not included in Table IV (e.g., As, Sb, Se and the halogens C1, Br and I), air-borne supply from natural and anthropogenic sources may be more significant than for most of the above elements (Lag and Steinnes, 1976; Allen and Steinnes, 1979). 4.2. Undisturbed natural soils
300 350 30,000 40 x 106 15,000 1 × 106 1200 50,000 90,000 50,000
C o m p u t e d from d a t a presented in T a b l e I I I a s s u m i n g a b u l k d e n s i t y for soil of 1.5 × 103 kg m 3.
Studies carried out in Norway may illustrate that under certain conditions long-range atmospheric transport over a long period of time may cause very significant increases of some anthropogenic trace elements in the surface horizon of natural soils. The deposition rates of volatile trace elements such as Pb, Cd, Zn, As and Sb are about ten-fold higher in the southernmost area of the country than in some more northerly
146 A.L.
/
i
•
•
oeee
e
•
•
•
•
~:........: ..~ •
•.~~,,.
ee
! ~i..-..~ i.
•.
e a
~
r
."
~.._ '
" ,
•
•
*
• -..-.~. •
•
°Qe°
• oo¢
•
•
•
o
o
•
•
•
j
.)
•
I e
•
•
•
O
•
oO0
25 59 65 t00 t60 250 590 ~90 Fig. 3. Lead in C horizon (ppm); mainly influenced by bedrock geology.
PAGE
AND
E. STEINNES
147
A T M O S P H E R I C D E P O S I T I O N AS A SOURCE OF T R A C E E L E M E N T S IN SOILS
regions (Steinnes, 1980). Studies of air particulate samples at Birkenes, S. Norway, in conjunction with air trajectory data show t hat the supply of the above elements occurs with winds from the sector SE SW to at least 80% (Pacyna et al., 1984; Amundsen et al., 1987). Furthermore, precipitation events occur mainly with the same wind directions. The atmospheric supply of these pollutants to this area is therefore considerable in spite of the fact that the main source regions are located at distances of 1000 km or more. A national survey of natural surface soils in Norway revealed th at the southern soils had many-fold higher contents of Pb, Cd, As and Sb in the humus layer than soils from Central and Northern Norway. Also for Zn and S e a distinct N S gradient was evident, while for Cu there were no strong regional differences (Allen and Steinnes, 1979). The correspondence with the present geographical deposition pattern for these elements was remarkable. In a similar, more recent survey samples at different depths in the soil profile were collected (Bolviken and Steinnes, 1987). In Figs. 2 and 3 results for HNO3-extractable Pb in the humus layer (3-5 cm depth) and C-horizon (60 cm), respectively, are shown. The very distinct Pb excess evident in areas near the southern coast in the humus samples is not at all evident in the mineral subsoil, which strongly indicates that what is observed is a large-scale contamination from long-range atmospheric transport, probably over a long period of time. Investigations of peat cores from ombrotropic bogs in different parts of the country (Hvatum et al., 1983, 1987) provides strong support to the above conclusion. Relative depth profiles from a bog in S. Norway (Fig. 4) indicate that the air-borne supply of Pb, Cd, As and Sb has increased by at least a factor of 20 since pre-industrial time in Europe, and further indicate t h a t the four elements have a similar origin. Studies of Se (Lag and Steinnes, 1974, 1978) and C1, Br, and I (Lag and Steinnes, 1976) show t h a t atmospheric supply from natural sources may also be important in determining surface soil concentrations. For the halogens, surface
1.0
Z O F--Z~ Z L~ Z
0
.........
AS
- -
Pb
......
Cd
----
Sb
0.5
LJ
J L~
I, X
5
I I0
Y'.
I 20
7 50
)
DEPTH, cm Fig. 4. C o n c e n t r a t i o n s of t r a c e e l e m e n t s i n p e a t p r o f i l e s , n o r m a l i z e d t o t h e level in t h e s u r f a c e l a y e r ( o m b r o t r o p h i c b o g in s o u t h e a s t e r n N o r w a y ) .
soil levels vary in a very consistent and systematic manner with the distance from the ocean. In the case of Se, which is in general present at very low levels in the underground mineral soil in Norway, the geographical distribution indicates airborne supply both from the marine environment (coastal regions all over the country) and with long-range transported pollution aerosols (southernmost regions). The data from the ombrotrophic peak profiles provide additional support to these interpretations.
Summary Regional air pollution is not a major contribution to the trace element content of disturbed remote, rural and urban soils. Trace elements deposited are diluted by mixing with underlying mineral soil of high bulk density ( - 1.25 1.75 kg m 3). On the contrary, long-range transport and subsequent deposition onto the surface humus
148
layer of undisturbed soils may substantially increase the trace element content of the humus layer. Trace elements deposited are not subject to subtantial mixing and essentially remain in the humus layer of low bulk density ( - 0.2-0.5 kg m-a). Low bulk density and minimal dilution through mixing account for the high enrichment in the undisturbed soil humus layer. In conclusion, although in general regional and long-range transport is not a major contributor to the trace element content of most soils, there are important exceptions which should not be overlooked. Reterences Alkezweeny, A.J., Laulainen, N.S. and Thorp, J.M., 1982. Atmos. Environ., 16: 242. Allen, R.O. and Steirmes, E., 1979. In: Heavy Metals in the Environment. CEP Consultants, Edinburgh, p. 271. Amundsen, C.E., Rambaek, J.P., Semb, A. and Steinnes, E., 1987. J. Radioanal. Chem., 114: 5. Bini, C., Dall'Aglio, M., Ferretti, O. and Gragnani, R., 1988. Environ. Geochem. Health, 10: 63. Bowen, H.J.M., 1979. Environmental Chemistry of the Elements. Academic Press, London. Bolviken, B. and Steinnes, E., 1987. In: Heavy Metals in the Environment. CEP Consultants, Edinburgh, 1, p. 291. Frank, R., Ishida, K. and Suda, P., 1976. Can. J. Soil Sci., 56: 181. Hawkes, H.E. and Webb, J.S., 1962. Geochemistry of Mineral Exploration. Harper and Row, New York, N.Y. Holmgren, G.G.S., Meyer, M.W., Daniels, R.B., Chaney, R.L. and Kubota, J., 1989. J. Environ. Qual., in press. Hvatum, O.O., Bolviken, B. and Steinnes, E., 1983. Ecol. Bull. Stockholm, 35: 351.
A.L. PAGE AND E. STEINNES Hvatum, O.O., Steinnes, E. and Bolviken, B., 1987. In: Heavy Metals in the Environment. CEP Consultants, Edinburgh, 1, p. 201. Kabata-Pendias, A. and Pendias, H., 1984. Trace Elements in Soils and Plants. CRC Press, Boca Raton, Fla. Kloke, A., 1982. Wat. Sci. Technol., 14: 61. Lannefors, H. and Hansen, H.C., 1983. Atmos. Environ., 17: 87. Logan, T.J. and Miller, R.H., 1983. Ohio State Univ. Agric. Res. Dev. Res. Circ., 275. Lag, J. and Bolviken, B., 1974. Nor. Geol. Unders. Bull., 23: 73. Lag, . and Steinnes, E., 1974. Ambio, 3: 237. Lag, J. and Steinnes, E., 1976. Geoderma, 16: 317. Lag, J. and Steinnes, E., 1978. Geoderma, 20: 3. Mason, B. and Moore, G.B., 1982. In: Principles of Geochemistry. Wiley, New York, N.Y., 4th ed. Mattigod, S.V. and Page, A.L., 1983. In: I. Thornton (Editor), Applied Environmental Geochemistry. Academic Press, London, p. 355. McGrath, S.P., 1986. In: D.D. Hemphill (Editor), Trace Substances in Environmental Health, Univ. Missouri, Columbia, Mo., p. 242. Pacyna, J.M., Semb, A. and Hanssen, J.E., 1984. Tellus, 36B: 163. Pierce, F.J., Dowdy, R.H. and Grigal, D.F., 1982). J. Environ. Qual., 11: 416. Sposito, G. and Page, A.L., 1984. In: H. Sigel (Editor), Metal Ions in Biological Systems. Marcel Dekker, New York, N.Y., p. 287. Steinnes, E., 1980. J. Radioanal. Chem., 58: 387. Thornton, I., 1982. In: D.D. Hemphill (Editor), Trace Substances in Environmental Health-XVI. Univ. Missouri, Columbia, Mo., p. 57. U.S. Environmental Protection Agency, 1979. Air Quality Data for Metals: 1977-1979. U.S. Environ. Prot. Agency, Research Triangle Park, N.C. U.S. Environmental Protection Agency, 1986. Air Quality Criteria for Lead. EPA-600/8-83/028aF. U.S. Environ. Prot. Agency, Research Triangle Park, N.C.