recovery of 0.005 mg L-l of arsenic(II1) added t o the environmental samples which also contained 18.0 mg L-l of interfering ions appears satisfactory. The information presented here suggests that arsenic in water samples can be successfully concentrated and isolated from the interfering metal ions by the use of the anion exchange technique before its determination by the standard method (SDDC). The amount of resin used for this process depends on the extent of pollutants expected in wastewater. However, 5.0 g of the Amberlite resin appears to be sufficient for the routine elimination of interfering ions as well as for the concentration of arsenic from the environmental samples. The maximum desirable limit of arsenic in drinking water is 0.01 mg L-1 and the maximum safe limit is 0.05 mg L-I; the minimum detectable limit of the SDDC method is 0.5 wg ( 1 4 ) . Consequently, the ion exchange technique can be effectively applied to facilitate the concentration of arsenic from drinking water, even below the desirable limit, before its determination by the SDDC method (IO).
Acknouledgment The authors are grateful to Dr. H. V. Manning, President, Dr. B. L. Gore, Dean, and Dr. N. Smith, Department Chairman, all of Claflin College, for their encouragement in undertaking this work. Literature Cited (1) Lee, H . K. D., “Metallic Contamination and Human Health”, Academic Press, New York, N.Y., 1972. (2) United States Department of Health Education and Welfare, Public Health Service, “Drinking Water Standards”, Public Health
Service Publication No. 956, U S . Government Printing Office, Washington, D.C., 1972. ( 3 ) Subcommittee on Air and Water Pollution of the Committee on Public Works. US.Senate. “Water Pollution”, Part 4, U S . Senate, 91st Congress, 2nd Session, U S . Government Printing Office, Washington, D.C., 1970. (4) Caldwell. J. C.. Lishka. R.. McFarren. E., J Am. Water Works Assoc., 65,’731-5 (1973): (5) Chaney, A. L., Harold, J. M., Ind. Eng. Chem. Anal. Ed., 12,691-3 (1940). (6) Kolthof, I. M., Elias, A., Ind. Eng. Chem. Anal. Ed., 12, 177-9 ( 1940). ( 7 ) Liederman, D., Brown, F. E., Milmer, 0. I., Anal Chem., 30, 1543-6 (1958). ( 8 ) Powers, G. W., Jr., Martin, R. L., Piehl, F. ,J,, Griffin, J. M., Anal. Chem., 31,1589-93 (1959). (9)Ballinzer. D. C.. Lishka. R. J., Gales, M. E., J Am. Water Works Assoc., 54,1424-8 (1962). (10) American Public Health Association, American Water Works Association, and Water Pollution Control Federation, “Standard Methods for the Examination of Water and Waste Water”, 13th ed., American Public Health Association, Washington, D.C., 1971. (11) Tam, K. C., Enuiron. Sci. Technol., 8, 734-6 (1974). ( 1 2 ) Kopp, J. F., Anal. Chem., 45, 1786-7 (1973). (13) Sandhu, S. S., Analyst, 101,856-61 (1976). (14) Sandhu, S. S., Nelson, P., Anal. Chem., 50,322-5 (1978). (15) Farkas, E. J., Griesbach, R. C., Schachter, D., Hutton, M., EnL’iron.Sci. Technol., 6, 1116-7 (1972). (16) Balint-Ambro, J., J . Chrornatogr., 120,457-60 (1974). (17) Kunin, R., Percival, R. W., Kneip, T. J . , Dean, W. K., “Experiments in Ion Exchange”, 2nd ed., Mallinckrodt Chemical Works, St. Louis, Mo., 1965. (18) Kleinberg, J., Argersinger, W. J., Jr., Griswold, E., “Inorganic Chemistry”, D.C. Heath, Boston, Mass., 1960.
Receiced for reuieu March 27, 1978. Accepted Nocember 13, 1978. This iuork tuas supported by EPA Grant N o . R801164OlO.
CORRESPONDENCE
SIR: In the 1976 volume of ES&T, Edgington and Robbins ( I ) have modeled a relationship between the lead concentration in Lake Michigan sediments and the annual emission of lead into the atmosphere using the following assumptions: (a) The published data for the emission of lead from the combustion of coal prior to 1960 underestimates the actual emission by a factor h . The total atmospheric emission rate is taken to be: where J a c ( t )and Jag(t)are the data for the emission due to the combustion of coal and gasoline, respectively. (b) The sedimentation rate a t each point in the lake does not change with time and can be derived from 210Pbmeasurement by assuming a constant initial concentration of unsupported (excess) 210Pba t each stage in sediment accumulation (2). (c) The total flux of anthropogenic lead to the lake waters is a constant proportion of the annual atmospheric emission. (d) The spatial pattern of the flux of lead into the sediments does not change with time. (e) The outflow of lead from the lake is negligible. Hence, all the lead entering the lake waters is transferred to the sediments. Under these assumptions, Edgington and Robbins derive a relationship between the lead concentration in the sediments and the atmospheric emissions involving two undetermined parameters. These parameters were varied to give a leastsquares fit of the data to the model. Edgington and Robbins observe that certain cores have a more uniform lead concentration in the upper portions of the 478
Environmental Science & Technology
core, and attribute this to sediment mixing. They derive a modification to their model assuming homogeneity in the zone of mixing. In evaluating the above assumptions and procedures the following points may be noted. (a) Where a model has so many unverified assumptions, the validity of attempting to correct data, in this case the lead emission values due to the combustion of coal, is questionable. (b) Alternative calculation of the *IOPbchronology assuming a constant net rate of supply of unsupported 210Pbto the sediment surface (c.r.s. model, see ref 3 and 4 ) provides ample evidence for considerable variation in the sedimentation rate through time. (c) I t is unnecessary, and as we shall see, incorrect, to assume a constant ratio between the atmospheric lead emissions rate and the lead flux rate to the sediments. The zloPb age/ depth curves allow direct calculation of the relation between them. The total lead flux rate F ( t ) to the sediments of age t and depth x in a dated core is calculated by( means of the formula: where r ( t ) is the sedimentation rate a t time t and c ( x ) is the total lead concentration at depth x. Figure 1 compares graphs of total lead fluxhime derived from Edgington and Robbins chronology and from our c.r.s. based calculations for cores 17, 31, and 105. Using the mean sedimentation rate derived from the thickness of the Waukegan member, Edgington and Robbins calculate a mean “natural” (Le., preindustrial) lead flux of 0.16 pg/(cm2.year). By contrast, the lead fluxhime curves obtained using their
0013-936X/79/0913-0478$01 .OO/O @ 1979 American Chemical Society
L A K E MICHIGAN 17 31 105. Pb F l u x / T i m e
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Figure 1. Lake Michigan. Total Pb flux vs. time, 1750 to 1970 for cores 17, 31, and 105. Figure l a plots the values obtained using the measurements and models summarized in Robbins and Edgington (2)and Edgington and Robbins (7). Figure l b plots the values obtained using the total Pb concentrations reported by Edgington and Robbins and the c.r.s. model of *lOPbdating (3, 4). In both graphs, the dashed horizontal line represents Edgington and Robbins' estimate of the mean preindustrial total Pb flux. For core 31, an alternate profile of total Pb flux is graphed, assuming sediment mixing
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sedimentation rate figures indicate natural lead fluxes ranging from 0.26 pg/(cni2.year) to 0.43 pg/(cm2.year). Further, their curves date the initial increase above the natural flux to times ranging from 1830 to 1900. Curves derived from c.r.s.-based calculations indicate natural lead fluxes of 0.17,0.16,and 0.18 rg/(cm2.year), and all date the onset of increasing anthropogenic lead flux to the period immediately after 1860. Thus, in terms of internal consistency, comparison with preindustrial flux values and dating of the onset of increasing anthropogenic influence, the c.r.s.-based calculations appear to be valid. Edgington and Robbins ( I , Table I) derive present day anthropogenic flux rates for cores 17,31, and 105 of 1.5,4.4, and 2.8 kg/(cm2-year),respectively. The mean value is 2.9 wg/(cm2.year). Our calculations for 1965 indicate anthropogenic flux rates for these three cores of 1.4, 2.1, and 2.2 pg/ (cm2.year),with a mean value of 1.9 pg/(cm2-year). If, as Edgington and Robbins infer, sediment mixing has taken place, there is a more complicated relation between the rate of emission of lead to the atmosphere and the lead concentration in the sediments. Assuming that the rate of flux of lead to the sediments a t time t in the past is F ( t ) pg/(cm2.year), the total amount m ( t ) (wg/cm2) of lead in the zone of mixing a t this time satisfies the relation:
-&(t) = F ( t ) - rl(t)c(
