Concentrations of Cr, Ag, Mo, Ni, Co, and Mn in Suspended Material in Streams Karl K. Turekian and Martha R . Scott‘ Department of Geology, Yale University, New Haven, Conn. 06520
There are regional differences in the concentrations of chromium, silver, molybdenum, nickel, cobalt, and manganese in suspended sediments of streams. The sediments of the Mississippi, and the rivers west of it draining into the Gulf of Mexico, as well as the Rhone River resemble average shale in composition, while the rivers of the United States east of the Mississippi are considerably higher in concentration. This difference is not due to differences in cationexchange capacity but rather perhaps to a greater amount of a trace-element rich soil component and industrial contamination in the eastern rivers. The Susquehanna River alone is supplying about 45 tons of silver a year as possibly recoverable detrital material.
T
his study grew out of the authors’ work o n the traceelement composition of stream waters (Turekian et al., 1967; Kharkar et al., 1967). Stream water samples contain suspended mineral and organic material of both natural and human origin. Before determining the composition of trace elements “dissolved” in river water, each sample was filtered through a 0.45-micron Millipore filter. In this note, the results obtained from the spectrographic analyses of the ashed residues caught by the filters are reported. The elements chosen for determination were those for which the stream waters Present address, Department of Geology, Florida State University, Tallahassee. Fla. 940 Environmental Science and Technologj
were analyzed by neutron activation and manganese because of interest to deep-sea sedimentation studies. These results, although preliminary, have been useful in this work in determining the modes of transport of trace elements to the oceans, and may be of interest to other investigators. Figure 1 shows the sample locations for the 18 U. S. rivers sampled in June 1966; samples from the Rhone River (France) and the Rio Maipo (Chile) were also analyzed. The spectro-analytical method, similar to the technique for the analysis of deep-sea sediments, has been described by Turekian and Schutz (1965). A 5-mg. sample was arced using direct current arc excitation. Each determination was made in duplicate, and an error of approximately 20 to 15 coefficient of variation is assigned to each element. Standards, with a matrix composition similar to deep-sea clays, were run on each plate. The elements determined were chromium, silver, molybdenum, nickel, cobalt, and manganese. The trace-element concentrations reported in Table I may be due to a combination of factors: industrial or other human contamination, the percentage of certain trace-element rich minerals such as chromite or amphibole, different cationexchange capacities of the different materials, organically associated metals, or manganese and iron oxide particles and coatings on clays. The authors cannot delineate uniquely the role of each type of association from the data obtained but can make some reasonable statements about the importance of some modes of transport. The Mississippi River and those west of it draining into the Gulf of Mexico differ in several respects from the rivers of the eastern United States (Kennedy, 1965). The Mississippi River and central United States rivers have higher suspended loads and sediments rich in montmorillonite; the eastern rivers are characterized by lower suspended loads, larger proportions of kaolinite, illite, and “aluminum-interlayered
clay” than the more western rivers, and sediments containing significantly more organic carbon than the average for United States streams. Kennedy (1965) reports that the cation exchange capacity of the clay fraction from eastern U. S. streams is 14 t o 28 meq. per 100 grams, while that of central and west central U. S. stream clays is 25 t o 65 meq. per 100 grams. Although there may be higher silt and sand contents of the western streams, the cation-exchange capacity of the total suspended load is still higher for the Mississippi and rivers west of it than for the eastern ones (Kennedy, 1965, Table 12). The cation exchange capacity of the sediment of each stream does not appear to vary with rate of discharge o r concentration of suspended sediment. The trace-element concentration data of Table I show that the eastern U. S. streams are higher in the concentration of most elements than the western U. S. streams even though the cation-exchange capacities of the eastern U . S. stream sediments are the lowest of the rivers sampled. Hence: the major trace-element transport mode cannot be simple cation exchange. Qualitative spectrographic analyses of Brazos River bottom sediment shswed no significant differences in the trace-element contents of the 2- to 20-, 0.2- to 2-, and less than 0.2-micron size fractions, indicating that the fine fraction of this stream sediment does not contain a large amount of trace elements relative to the coarser fraction despite a generally higher cation-exchange capacity of finer material. When the trace element concentration averages for the suspended load of the rivers west of the Mississippi and the Rhone River in France are compared with the average shale, except possibly for silver and molybdenum, the concentrations are similar, seeming to indicate that these rivers are essentially transporting material equivalent to shales that have been eroded without much chemical modification. The rivers of the eastern U. S. and possibly the Rio Maipo, draining the Andes, have much higher trace-element concentrations indicating other sources of trace elements. The trace-element composition of the dissolved trace elements is not reflected in the compositon of the detrital load. Therefore, the trace elements carried by the stream sediments to a large degree are probably in inert positions. The strong correlation of the trace elements with manganese may mean either coprecipitation of trace elements with iron and manganese oxides in weathering profiles, association with organic material from soils, or possibly industrial contam-
Figure 1. Location of United States rivers sampled Numbers correspond to those of Table I
Volume 1, Number 11, November 1967 941
River and State 1 Brazos, Tex. 2 Colorado, Tex. 3 Red, La. 4 Mississippi, Ark. 5 Tombigbee, Ala. 6 Alabama, Ala. 7 Chattahoochie, Ga. 8 Flint, Ga. 9 Savannah, S. C. 10 Wateree, S. C. 11 Pee Dee, S. C. 12 Cape Fear, N. C. 13 Neuse, N. C. 14 Roanoke, N. C . 15 James, Va. 16 Rappahannock, Va. 17 Potomac, Va. 18 Susquehanna, Pa. Rhone, France Avignon, June 1966 Rio Maipo, Chile Puente Alto, S. of Santiago, September 1966 Shales (Turekian and Wedepohl, 1961)
Table I. Trace-Element Composition of Suspended Material in Rivers Suspended Parts per Million Load, Mg./L. Ag Mo Ni Cr 954 100 0.4 11 30 150 82 0.6 IO 40 436 37 0.3 5 6 185 150 0.7 18 100 25 220 1 .o 22 200 54 150 4.0 19 100 71 190 7.0 20 100 12 210 1 .o 28 100 30 460 2.0 35 250 37 1.5 200 24 100 188 150 0.4 15 100 61 130 0.7 16 70 36 380 4.0 22 70 33 240 4.9 21 100 41 290 7.0 29 300 28 140 1. o 31 80 34 1.5 170 23 400 290 15.0 54 32 > 1000 296 150 0.7 14 60 41
68
1. o
90
0.1
ination. For normal stream concentration of trace elements, aged iron and manganese oxides are not good cation absorbers, but fresh precipitates of iron oxide (hydroxide)either in soil profiles or as the result of acid industrial wastes being neutralized-act as excellent scavengers. The suspended sediments of the Susquehanna River and to a lesser degree the James River are extremely high in most of the trace elements even when compared with the other eastern rivers. Therefore, at first view, the Susquehanna data represent industrial contamination in part, but such an explanation is less probable for the James River. Future work should show the sources of the trace elements in stream sediments. Preliminary work seems t o indicate that criteria such as uranium-234 to uranium-238 ratio of the sediments should be an index of soil derivation, while a search
44
2.6
co 20 17 7 33 31 34 35 39 36 34 23 21 30 45 60 46 94 >500 29
690 780 320 2,300 5.900 3,700 2 400 5.100 4.400 7,000 1.300 1.700 3 .000 7,900 15,000 2.200 7.700 12,000 820
40
76
2,400
68
19
850
41n
~
for manganese and iron minerals or coatings will help decide whether the soil-derived trace elements have been concentrated by organic or inorganic materials. Industrial contamination will be more difficult to identify because of the range of types of trace metal injection into a stream, but knowledge of location of each type of contaminant should be coupled with a systematic sampling of the suspended load of the stream to test the industrial effect adequately. The annual transport of trace elements by the Susquehanna River as suspended material (Table 11) is sufficiently large to be of possible economic interest if demand for some of these metals increases, and the metals are present in an easily recoverable form. Some other rivers such as the James River also may be of interest in this context. Literature Cited
~~
Table 11. Trace Element Transport by the Susquehanna River Tonslyear Transporteda Chromium Silver Molybdenum Nickel Cobalt Manganese
870 45 97 3,000 1,500 120,000
Assuming 300 X 103 tons per year of suspended sedimen-nirasured for the Juniata River.
942 Environmental Science and Technology
Kennedy, V. C., Geol. Suru. Profess. Puper433-D, D-13 (1965). Kharkar, D. P., Turekian, K . K., Bertine, K . K.. Geochim. Cosnzochim. k c f a , in press (1967). Turekian, K. K., H a r r i s , R . C., Johnson, D . G.. Limnol. Oceanog., in press (1967). Turekian. K. K.. Schutz. D. F.. Proc. Unic. Rhode Island Symp. 'Marine Geochem: (October 1964) Occasionul Publ. 3, 41-89 (1965). Turekian, K . K., Wedepohl, K. H., Geol. Soc. Am. Bull. 12, 175-92 (1961). Receiced for review September 1 , 1967. Accepted October 26, 1967. Work supported by the Atomic Energy Commission through Grant AT(30-1)-2912. One of the authors (M.R.S.) was a National Science Foundation Post- Doctoral Fellow while engaged in this research.
