Talc in Atmospheric Dusts H. Windom, J. Griffin, and E. D. Goldberg Scripps Institution of Oceanography, University of California, San Diego, La Jolla, Calif.
The mineral talc has been observed in dusts recovered directly from the atmosphere and in the solid mineral phases of rain and snow. The talc, where detected, attains levels of the order of a per cent by weight in the solid phases. This talc probably arises from agricultural activity where the mineral is used as a carrier and diluent for pesticides. The amounts of talc found in atmospheric dusts appear to reflect a local introduction rather than a generalized global fallout.
T
he introduction of solid phases into the atmosphere from the continents and their subsequent dissemination about the earth’s surface has provided opportunities to study not only wind systems (Eaton, 1963), but also the compositions of the source areas (Delaney, Delaney, et al., 1967). Where such solid phases are sequentially recorded in sedimentary columns, such investigations can be extended over pSst times. For example, observations on the atmospheric fallout in the various strata of glacial snowfields allow the study of windtransported solids over time periods of years to hundreds of years (Windom, 1967). The contributions of eolian dusts to the marine sediments allow similar investigations to cover the time periods of thousands and millions of years (Rex and Goldberg, 1962). Finally, by recovering dust from the atmosphere through daily collections, the differential input of these solids to the atmosphere may be considered (Delaney, Delaney, et d., 1967). The atmosphere also receives solid phases created by man through his industrial, social, and agricultural activities. Such inputs are taking place with increasing intensity. Besides the more obvious introductions of debris from nuclear bomb detonations and of carbon and iron particles from industrial plants, there are the recently reported injections of pesticides in atmospheric dusts and rainwaters (Cohen and Pinkerton, 1966) and of lead oxides and halides into the atmosphere through the burning of lead tetraethyl in internal combustion engines (Tatsumoto and Patterson, 1963).
92037
The authors have discovered the atmospheric occurrence of another widely distributed solid phase introduced by mantalc. This mineral, quite rare in nature, has been observed in many samples of atmospherically transported materials. The initial results and their implications will be considered.
Sample Collections and Processing Techniques Table I gives the location, type of sample, and mineral composition of solid phases that have been subjected to atmospheric transport. The San Diego air samples were collected from heights of 100 to 200 meters using helium-inflated “kytoons” with a nylon-mesh collector suspended 25 meters below the kytoon. The meshes were sprayed with glycerol to retain the impinging dust particles. Similar techniques have been employed by other workers (Delaney el ai., 1967). The Nebraska dust samples were collected from a n airplane. The Bagdad dust was recovered from a second floor roof top during a storm, using a clean damp cloth as a collector. The Indian samples were recovered from a tower on the Island of Minicoy, about 500 km. off the coast of Cochin, India, with a nylonmesh collector as a part of a study of extraterrestrial dust. The glacial samples were obtained with precleaned stainless steel scoops or by direct coring of the snow fields. The samples were placed in one-gallon, large-mouthed, polyethylene bottles while in the frozen state. The bottles were kept in plastic bags before and after collection to reduce contamination by dust during transportation to and from the collection sites. The laboratory processing was carried out with a variety of precautions to minimize contamination with the ever prevalent laboratory dusts, whose sources may be the atmosphere or the equipment and reagents used in this work. Periodic blank runs were carried out o n the distilled water and nylon meshes to monitor the levels of contamination. Laboratory dust was collected in a n open glass beaker of distilled water placed on a laboratory bench top. Since most rubber laboratory equipment contains talc, only plastic, glass, and metal Volume 1, Number 11, November 1967 923
~~
Table I. Mineral Assembl Sample Rain
Atmospheric Dust
Location San Diego, Calif. 32' 50' N 117" 1 6 ' W
San Diego, Calif.
Scotts Bluff, Neb. 41 O 52' N 103" 40' W
Dust Storm a
Minicoy Island India 8" 20' N 73"Ol'E Bagdad, Iraq 33" 20' N 44' 26' E
Collection Date 7 Nov. 1966 7 Nov. 1966 5 Dec. 1966 13 March 1967 13 March 1967
Solid Phase Concn., MgJLiter 1.9 ...
17 Nov. 1966 15 Feb. 1967 16 Feb. 1967 17 Feb. 1967 21 Feb. 1967 22 Feb. 1967 23 Feb. 1967 24 Feb. 1967 27 Feb. 1967 28 Feb. 1967 6 March 1967 7 March 1967 8 March 1967 9 March 1967 28 April 1966 28 April 1966 10 May 1966 1963 1965 17 Feb. 1966
... 2.5 0.4
Talc
Quartz
Plagioclase
X
X
Mica
Amphibole
Chlorite
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
?
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
?
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
?
X
X
X
X
X
For the glacial materials, the collection date is the time of accumulation of the strata sampled.
apparatus were used. There is no evidence for any uncontrolled introduction of significant amounts of minerals during the processing or recovery of the samples. The nylon meshes used to collect the air samples were placed in Plexiglas columns and washed repeatedly with distilled water which was removed through a 0.45-micron Millipore filter disk. The solids were removed from the disk into distilled water by treatment with an ultrasonic generator. The removal efficiency was assumed to be high inasmuch as the filter disks were white following this treatment. The dusts were recovered by centrifugation. Sample sizes usually ranged from tens to hundreds of milligrams. Qualitative and semiquantitative mineral analyses were made using x-ray diffraction techniques that have been described previously (Goldberg and Griffin, 1964). There were no enrichment techniques applied to the solid phases recovered from the atmospheric samples. The lower limit for the unqualified detection of talc is OSZ by weight. Where there is some doubt as to the occurrence of talc, a question mark is used in the Table I. 924 Environmental Science and Technology
Results In general, the major minerals in these assemblages, with the exception of talc, can be characterized in two ways. They are among the more abundant minerals o n the crust of the earth, and they are refractory to chemical change through interactions with the air or hydrosphere. Quartz and plagioclase were present in all samples examined. Mica and amphibole were generally present, but in smaller amounts. Other minerals occasionally present were calcite, dolomite, chlorite, kaolinite, montmorillonite, pyroxene, anatase, rutile, cristobalite, and alunite. Often, these minerals resulted from a local source as opposed to a n introduction from a more distant area. For example, pyroxene, cristobalite, and alunite are sometimes found in glacial samples recovered from volcanic cones (Windom, 1967). Biological phases were often present and included spores, pollen, and diatoms in addition to the ever present disorganized organic phases. The presence of talc in the majority of the samples studied was unexpected. In reviewing potential sources among the
ages in Atmospheric Dusts
Sample Glaciera
Location
Yukon 60" 45' N 139" 30' W
Orizaba 19" 01 ' N 97" 1 5 ' W
Popocatepetl 19" 01' N 98" 37' W Washington 47" 52' N 123" 36' W
Snow Samples
Palomar 33" 24' N 116" 53' W Julian 33" 04' N 116" 36' W Mount Rainier 46' 51 ' N 121" 45' W Canadian Rockies 52" 55' N 118' 1 0 ' W
Collection Date
Solid Phase Concn., Mg./Liter
1967 1961 1955 1947 1936 1962-67 1957-62 1952-57 1942-47 1937-42 196Cb67 1949-53 1943-46 1967 1962 1950 1940 1932 1925 1916 1965
1965
1965
1967
0.8 0.5 0.5 0.3 0.5 89 734 17 19 49 302 38 159 1.8 1.9 2.4 1.8 9.9 3.7 10.1 2.2 1.4 2.9
30
2.7
Amphibole
Talc
Quartz
Plagioclase
Mica
X
X
X
X
X
X
? ?
X X X X X X X X X X
X
X X X
X X
X X
? X X
X X X X X X X X
?
X X X X X X X
X
X
X
X
X X X X X
X X
X X X X X X
X X X X X X X X
X
X X X
X
X
X
X
X
X
X
X
X
X
X
X X X X X X X X X X X X X X X X X
X X X X X X X X X X
X
X
X
X
X
X
Chlorite
X
X
X X
X X X X X
X X X X X
X
X
X
industrial and agricultural activities of man, the authors became aware of the utilization of talc as a carrier and diluent for pesticides. The extensive use of pesticides began in the late 1930's, a t which time pyrophyllite, talc, and soapstone were introduced as carriers for these synthetic materials (Figure 1). The earliest available data for the utilization of talc minerals as carriers and diluents for pesticides indicate about 10,500 tons per year o r about 2% of the total production of these minerals in 1941. The 1965 data show that 8% (68,000 tons per year) of the talc minerals mined were used in pesticide formulation. This represents about 30% of the total dry-solid carriers and diluents used in the pesticide industry. Fuller's earth commands a larger and increasing portion of the market with use of 45 to 59% as a granular dispersant. The utilization of talc leveled off in the 1950's when other methods of aerial dispersion became popular (Scotton, 1965). The application of the fine talc dusts (particle size with a range of 0.1 to 25 microns) provided poor geographical control because of wind drift (Scotton, 1965). To obtain proper coverage of a n area with the fine dusts such as talc, it was necessary Volume 1, Number 11, November 1967 925
IO 0 90
0
80
- 0
oou 0
0
0
o o
0 0
40
0 0
30
f
o .**.
70 60
.*
Figure 1. The use of talc as a pesticide carrier and diluent and the consumption of synthetic organic pesticides over the past 25 years in the United States Data from U. S. Department of Agriculture (1966) and U. S. Tariff Commission (1967). Note the continual rise in pesticide consumption and the leveling off of the use of talc
to apply the materials in far greater quantities than actually were needed for insect control, This resulted in costly operations as well as increased health hazards. The difficulty of wind drift has been partially avoided by the substitution of granular phases (particle size 200 to 600 microns) or the more recently introduced water or oil (light petroleum or xylene) base sprays. These latter methods have become widely adopted inasmuch as the size of the particle containing the pesticide can be controlled by the design and operation of the atomizer. The data clearly tend to substantiate the source of talc in these atmospheric dust ssmples as a result of pesticide dispersal. First, the glacier sample from Washington (Table I) shows a cut-off in talc at about 1940, the time a t which D D T became available as a broad spectrum insecticide. Second, the talc minerals used in agricultural dusts have a particle size range of roughly 0.1 to 25 microns with a n average size of 5 to 10 microns (Scotton, 1965). Analyses indicated that the talc occurs in less than 15-micron size fractions. Some most tentative and tenuous calculations can be made to ascertain the concord between the input and output of the talc used in agricultural dusting. The production of talc and soapstone as dry carriers for pesticides reached an annual level of 3.5 X 1010 grams in 1965 for the United States (U. S. Department of Agriculture, 1966), and one can assume that this was the amount dispersed. If 10% of this talc were dis926 Environmental Science and Technology
seminated in the mid-latitude westerlies about the northern hemisphere, and an area of 2.5 X lo1*sq. cm., before falling to the earth, the output is about 1.4 X 10-9 gram of talc per sq. cm. per year. Clearly, much of the talc probably stays within the latitudes of the U. S., say 30” to 60” N. The above figure would be increased then by a factor of two o r three. Semiquantitative analyses for talc were performed on the glacial samples of solid phases, the latter containing about 0.5% talc. Assuming an annual precipitation of about one meter of water per year, this is equivalent to 4 X 10-4 gram per sq. cm. for the total solids or about 2 X low6gram per sq. cm. per year for the talc. This lack of agreement strongly suggests that much of the talc is derived from local agricultural activity as opposed to fallout from the global wind systems. Clearly, a detailed analysis of the glacial record, coupled with the available data on pesticide utilization, will allow a more adequate elucidation of this problem. Nonetheless, talc appears to be a most promising tracer for the study of the dispersion of solids about the surface of the earth. Further, the translocation of pesticides (Cohen and Pinkerton, 1966) may be studied through the dissemination of their carriers and diluents. Acknowledgment
The kytoons were manufactured by Dewey and Almy, Cambridge, Mass.; the Nebraska samples were collected by J. P. Shedlovsky, National Center for Atmospheric Research, Boulder, Colo. ; the Bagdad sample by R. B. Berry, San Diego State College; and the Indian samples by D. Lal, Tata Institute, Bombay, India, and J. R. Arnold, University of California, San Diego, Calif. Literriture Cited
Cohen. L. M.. Pinkerton,, C.,. Adlances in Chem. Ser. No. 60,163-76 (1966). Delaney, A. C., Delaney, A. C., Parkin, D. W., Griffin, J. J., Goldberg, E. D., Reimann, B. E. F., Geochim. et Cosmochim. Acta 31, 885-909 (1967). Eaton, G. P., J . Geophys. Res. 68, 521-8 (1963). Goldberg, E. D., Griffin, J. J., J . Geophys. Res. 69, 4293309 (1964). Rex, R . R., Goldberg, E. D., “The Sea,” M. N. Hill, Ed., Vol. 1, pp. 295-304, Interscience, New York and London, 1962. Scotton, J. W., U. S. Department of Health, Education, and Welfare, Office of Pesticides, “Atmospheric Transport of Pesticide Aerosols,” 1965. Tatsumoto, M., Patterson, C. C., “Earth Science and Meteoritics,” J. Geiss and E. D . Goldberg, Eds., pp. 74-89, North Holland Publishing Co., Amsterdam, 1963. U. S. Department of Agriculture, Agriculture and Conservation Service, The Pesticide Review, 1966. U. S. Tariff Commission Reports, 1967. Windom, H., University of California, San Diego, Calif., unpublished results, 1967. Receicedfor reeiew July 10, 1967. Accepted October 12, 1967. This work was carried out under a contract with the Ofice of Nacal Research and the Unicersity of California.
