Sources of heavy metal contamination in a river-lake system

SOURCES OF HEAVY METAL C O N T A M I N A T I O N IN A RIVER-LAKE SYSTEM

TOGWELL A. JACKSON

Inland Waters Directorate, Freshwater Institute, 501 Unirersity Crescent, Winnipeg, Manitoba R3T 2N6, Canada

ABSTRACT

Sediments of the Wabigoon Rig'er, Ontario, are polluted with Hg from an &dustrial source at Dryden. Downstream from Dryden the river flows first through Clay Lake and then through Ball Lake. Hg, Cu, Zn, Cd and Fe concentrations in sediments of both lakes are correlated with organic C, but Hg content per unit concentration of organic C is higher, and increases more steeply with organic C, in Clay Lake than in Ball Lake; in contrast, the Cu, Zn, Cd, and Fe concentrations per unit concentration of organic C are nearly the same in both lakes. These results substantiate the conclusion that the Hg originated at a point upstream from the lakes and tended to accumulate in Clay Lake on its way downstream, whereas the other metals were leached into the two lakes from diffuse sources in the surrounding terrain. Accumulation of rirer-borne organic pollutants in Clay Lake was also demonstrated. Application of the methods employed to the general problem of recognising and locating element anomalies is discussed.

INTRODUCTION

Research on the dispersal of heavy metals through freshwater and terrestrial ecosystems, whether for the purpose of pollution control or geochemical prospecting, requires the capability of recognising and locating point-sources of these metals, in the case of heavy metal pollution of inland waters, the source of the metals may be an important legal issue: sometimes corporations responsible for such pollution attempt to evade responsibility by claiming that the metals come from natural sources (Azzaria & Habashi, 1976). In the Canadian Shield, where there has been widespread mineralisation of the bedrock, this can be a serious problem (Allan, 1975). 131 Era'iron. Pollut. (18) (1979)--c" Applied Science Publishers Ltd, England, 1979 Printed in Great Britain

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T O G W E L L A. J A C K S O N

The bottom sediments of lakes and streams are valuable indicators of the provenance and dispersal patterns of heavy metals (Allan, 1975~ F6rstner & Miiller, 1976). However, simply comparing the metal concentrations of sediment samples dredged from different localities is inadequate for detection of any but the most obvious anomalies. Inasmuch as metal concentrations in sediments depend not only on input from the source but also on such factors as the grain size, organic matter and sulphide content, mineral composition, and rate of deposition of the sediments, bulk analyses are of little use unless these factors are taken into account (Timperley & Allan, 1974; Allan & Brunskill, 1977; F6rstner, 1977). Thus, one sample might be richer in metals than another merely because it is finer grained and richer in organic matter, not because it represents a true metal anomaly. Various approaches to this problem have been proposed (Timperley & Allan, 1974; Allan, 1975; Allan & Brunskill, 1977; F6rstner, 1977). In the study reported here, which involved comparison of sediments from two lakes connected by a mercury-polluted river, concentrations of mercury and other metals were simply plotted against concentration of organic matter to determine whether samples from one lake had anomalously high metal concentrations per unit of organic matter relative to the other lake (cf. Timperley & Allan, 1974; Allan & Brunskill, 1977). The purpose was to confirm the suspected provenance of the metals, to test the usefulness of the methodology for finding point-sources of metal contamination in drainage systems and to investigate the fate of the mercury as it moved downstream through the two lakes. Evidence for the presence of river-borne organic pollutants was also sought.

FIELD AREA

The lakes, Clay Lake and Ball Lake, are situated in northwestern Ontario, Canada (Fig. 1), in a sparsely populated region largely covered with boreal forest and Pleistocene glacial deposits, and underlain by rocks of the pre-Phanerozoic Shield. The source of the mercury contamination was effluent from the chlor-alkali plant and pulp-and-paper mill of Reed Ltd (formerlY Dryden Chemicals Ltd, and the Dryden Paper Co.), in Dryden, Ontario (Armstrong & Hamilton, ! 973; Azzaria & Habashi, 1976; Bishop & Neary, 1976; Parks, 1976; Troyer, 1977). The mercury, together with organic wastes from the pulp-and-paper mill and from sewage (German, 1969), was dumped into the Wabigoon River, which flows into Clay Lake 85 km downstream from Dryden, and thence into Ball Lake, from which it emerges as the English River. The mercury has rendered fish in the English-Wabigoon system unfit to eat, and a number of Ojibway tribesmen living in the area have been found to have unacceptably high levels of mercury in their blood (Health & Welfare Canada, 1973; Troyer, 1977), and are reported to be suffering from the effects of mercury poisoning (Azzaria & Habashi, 1976; Troyer, 1977), owing to consumption

HEAVY METAL CONTAMINATION IN A RIVER--LAKE SYSTEM

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of contaminated fish. The waterway is not known to have been polluted appreciably by heavy metals other than mercury. Sedimentary copper, zinc, cadmium, and iron, which were included in the investigation for the sake of comparison with mercury, were presumed to have been derived chiefly from diffuse natural sources in the surrounding terrain.

MATERIALS A N D M E T H O D S

Bottom sediments varying from grey mud to grey or brown fine-to-medium-grained sand were dredged from different sites in Clay Lake and Ball Lake at depths of 0.3-17 m in August and September 1976. Hg was determined by extraction with hot 3:1 HC1/HNO 3 followed by flameless atomic absorption analysis employing a Perkin-Elmer 403 atomic absorption spectrophotometer. Cu, Zn, Cd, and Fe were determined by atomic absorption following digestion with hot 1: 3 HCIO4/HNO 3. The sediments were analysed for organic carbon (org. C) and total nitrogen (N) by Carlo-Erba CHN analyser. Non-volatile ('metal-bound') sulphide-sulphur (S 2-) was estimated by digesting dried sediment with boiling 6N HC1, trapping the expelled H2S in NaOH solution, and measuring the sulphide absorption maximum at 228nm using Na2S as a standard (Jackson, 1978). All analytical data were normalised to the oven-dry (105 °C) weight of the sediment. The data are recorded in Table 1.

RESULTS A N D DISCUSSION

A plot of metal concentrations against org. C content for Clay Lake and Ball Lake (Fig. 2) revealed that Hg differed dramatically from the other metals in its distribution pattern, even though all of the metals, as expected, were strongly correlated with org. C. Thus, the regression line for Hg in Clay Lake is much higher and steeper than the regression line for Hg in Ball Lake, indicating that Clay Lake has a considerably greater Hg concentration per unit concentration of organic matter. The two trends are so divergent that if the Clay Lake and Ball Lake samples are treated as a single population, the correlation between Hg and org. C is insignificant at the 5 ~ level. In contrast, the Cu, Zn, Cd, and Fe concentrations per unit concentration of org. C are practically the same in Ball Lake as in Clay Lake, and so the trend lines for the two lakes virtually coincide. Consequently, if the samples from Clay Lake and Ball Lake were lumped together as a single population, the correlation coetficients would be significant at the 1-0-1 ~ level. These results clearly reflect the fact that the Hg was introduced into the river from a point-source upstream from Clay Lake, while suggesting strongly that the other metals were, in large part, leached laterally into the lake-river system from scattered sources in the

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HEAVY METAL CONTAMINATION IN A RIVER-LAKE SYSTEM

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surrounding soil and bedrock. Evidently the Hg tended to accumulate in Clay Lake on its way downstream, thereby giving rise to anomalously high proportions of Hg relative to organic matter. Similarly, the S2-, N, and org. C data appear to indicate that appreciable quantities of organic wastes transported from Dryden have accumulated in Clay Lake (Fig. 3). A plot of S2- against either org. C or N gave a higher, steeper trend

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for Clay Lake than for Ball Lake, suggesting enrichment in oxygen-consuming, biodegradable organic matter (German, 1969) with resultant production ofbiogenic H2S. On the other hand, Clay Lake sediment tends to have a lower N/C ratio than that of Ball Lake, probably owing to C-rich, N-poor wastes such as wood fibre deposited in Clay Lake (German, 1969). These findings demonstrate that the methodology employed constitutes a simple but effective means of locating point-sources of heavy metals or other elements, or differentiating between a distant point-source and scattered local sources, in a drainage system. All that is required is to collect several samples of surface sediment at each of a number of different sampling stations going downstream and then to plot element concentrations against org. C or some other suitable quantitatively estimated sediment property such as grain size or Fe concentration to ascertain which sampling sites have anomalously high relative concentrations of the elements (cf. Timperley & Allan, 1974; Allan & Brunskill, 1977). This approach could be useful for both environmental research and geochemical prospecting. Furthermore, the observation that an appreciable amount of the Hg from Dryden was trapped in the bottom sediments of Clay Lake suggests that contamination of the river-lake system might have been prevented if Reed Ltd had passed its effluent through a series of metal-trapping anaerobic settling ponds instead of dumping it directly into the river. Such ponds could have been rendered perpetually anaerobic

138

TOGWELL A. JACKSON

by addition of municipal sewage--a cheap, abundant source of nutrients--to generate algal blooms which, on decomposing, would have consumed oxygen and produced H2S, resulting in precipitation of highly insoluble HgS in the sediments. Attention has been drawn to the possible efficacy of this approach in a report on the biogeochemistry of heavy metal pollutants in the vicinity of Flin Flon, Manitoba (Jackson, 1978). ACKNOWLEDGEMENTS

The Cu, Zn, Cd, Fe, and S 2 analyses were performed by R. Woychuk, and the Hg analyses were made in the laboratory of A. Lutz. B. Hauser did the org. C and N determinations. 1 thank F. A. J. Armstrong and G. McRae for furnishing the sediment samples together with helpful information and comments, and A. L. Hamilton for critical comments on the manuscript. The research was supported by the Department of the Environment, Federal Government of Canada. REFERENCES

ALLAN,R. J. (1975). Natural versus unnatural heavy metal concentrations in lake sediments in Canada. Int. Conf. on Heary Metals in the Enrironment, Toronto, Canada, 27-31 October, 1975, 785 808. ALLAN,R. J. & BRUNSKILL,G. J. (1977). Relative atomic variation (RAV) of elements in lake sediments: Lake Winnipeg and other Canadian lakes. In Interactions between sediments and fresh water, ed. by H. L. Golterman, 108-20. The Hague, Junk B. V. Publishers, and Wageningen, Centre for Agricultural Publishing and Documentation (Pudoc). ARMSTRONG,F. A. J. & HAMILTON,A. L. (1973). Pathways of mercury in a polluted northwestern Ontario lake. In Trace metals and metaLorganie interactions in natural waters, ed. by P. C. Singer, 131-56. Ann Arbor, Mich., Ann Arbor Science Publishers. AZZAmA, L. M. & HABASHI,F. (1976). Mercury pollution An examination of some basic issues. Can. Min. metall. Bull., Aug. 1977, 101 7. BISHOP, J. N. & NEARY, B. P. (1976). Mercury lerels in ]ish/rom Northwestern Ontario, 1971~1975. Toronto, Canada, Report, Inorganic Trace Contaminants Section, Laboratory Services Branch, Ontario Ministry of the Environment. FORSTNER, U. (1977). Metal concentrations in freshwater sediments--Natural background and cultural effects. In Interactions between sediments and#esh water, ed. by H. L. Golterman, 94-103. The Hague, Junk B. V. Publishers, and Wageningen, Centre for Agricultural Publishing and Documentation (Pudoc). FORSTNER,U. 8L M()LLER, G. (1976). Heavy metal pollution monitoring by river sediments. Fortschr. Miner., 53, 271 -88. GERMAN, M. J. (1969). Water pollution surrey of the Wabigoon Rirer. Toronto, Div. of Laboratories, Biology Branch, Ontario Water Resources Commission. HEALTH AND WELFARECANADA(1973). Final report, task /orce on organic mercury in the encironment, Grass), Narrows and White Dog, Ontario. Ottawa, Government of Canada (Mimeographed.) JACKSON,T. A. (1978). The biogeochemistry of heavy metals in polluted lakes and streams at Flin Flon, Canada, and a proposed method for limiting heavy metal pollution of natural waters. Enciron. Geol., 2, 173 89. PARKS, J. W. (1976). Mercury in sediment and water in the Wabigoon English River s)u'tem 1970 ~75. Toronto, Canada, Report, Technical Support Section, N.W. Region, Ontario Ministry of the Environment. TIMPERLEY, M. H. & ALLAN, R. J. (1974). The formation and detection of metal dispersion halos in organic lake sediments. J. geochem. E.vplor., 3, 167-90. TROYER, W. (1977). No safe place. Toronto & Vancouver, Clarke, Irwin & Co.