Heavy metal pollutants in the sediments of the Rhone River

Proceedings Chapter

Reference

Heavy metal pollutants in the sediments of the Rhone River

VERNET, Jean-Pierre, JOHNSTON, Laura Margaret

Abstract

Une première étude de la distribution du Hg dans les sédiments du Rhône a été publiée en 1972. Par la suite, les mêmes points ont été échantillonnés annuellement. En 1971 et 1972, la centaine d'échantillons récoltés a été analysée pour déterminer la teneur en: Hg, Pb, Cr, Cd, Co, Sn, V, Ni, Zn et Cu. La contamination principale est due au Hg, puis vient le Cr et épisodiquement d'autres métaux lourds. Un certain nombre de sources de rejets industriels ont pu être localisées. Les rapports parviennent au Rhône généralement par les canaux et la contamination s'attenue vers l'aval par dilution.

VERNET, Jean-Pierre, JOHNSTON, Laura Margaret. Heavy metal pollutants in the sediments of the Rhone River. In: Proceedings of the International Conference on Transport of

Persistent Chemicals in Aquatic Ecosystems = Comptes rendus de la Conférence internationale sur le transport des produits chimiques persistants dans les

écosystèmes aquatiques . Ottawa : National Research Council of Canada, 1974. p. I-79-I-81

Available at:

http://archive-ouverte.unige.ch/unige:146007

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HEAVY METAL POLLUTANTS

I N THE S EOIMEN'.l'S OF TllE n110NE RIVEn by J.-P. VERNET and L.M. JOHNSTON University of Geneva, Dept. Earth Sciences, 13, rue des Maraichers, 1211 Geneva 4, Switzerland

Une ^premi~re etude de la distribution du Hg dans les sediments du RhOne a ete publiee en 1972.

Par la suite, les memes points ant ete echantil- lonnes annuellement. En 1971 et 1972, la centaine d'echantillons recoltes a ete analysee pour deter- miner la teneur en : Hg, Pb, er, Cd, co, Sn,

v ,

Ni, Zn et Cu. La contamination principale est due au Hg, puis vient le Cr et episodiquement d'autres metaux lourds. Un certain nombre de sources de re-

jets industriels ant pu etre localisees. Les rap- ports parviennent au RhOne gencralement par les canaux et la contamination s'attenue vers l'aval par dilution.

A preliminary study of the distribution of Hg in the sediment of the Rhone was published in 1972. Subsequently, samples rueJ>e taken f:rom the same Zoaations annuaity. ^In 1971 and 1972, the hundred or so samples colleated were analysed to detennine their Hg, Pb, Cr, Cd, Co, Sn, V, Ni, Zn and Cu oontent. The pollution is due mainly to Hg, to a lesse:r extent to C:r, and only to a minor extent to otheJ> heavy metals. A number of industrial waste soUJ>ces were pinpointed. The Bubstanoes usually enter the Rhone by way of the canals and the pollution deoreases downstream by dilution.

Introduction

The distribution of mercury in the sediments of the Rhone River and several Swiss lakes was stu- died during 1970 and 1971, and the results reported by Vernet and Thomas (1972a). The present note gi- ves additional data available from a continuation of this study and its expansion to include other trace elements (notably Pb, er, Cd, Co, Sn, v, Ni, Zn, Cu) of interest to environmental geochemists.

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During 1971 and 1972 sediment samples were taken in the Rhone River, major influent rivers and canal systems from Naters to Lake Geneva (fig.

1) . The samples were collected using plastic bot- tles as scoops in low water level stream banks and sieved as soon as possible to pass a 175 µ nylon screen (80 mesh). The fine fraction was dried at 40°c, lightly ground in a agate mortar and analy- zed at the facilities of the Bureau des Recherches Geologiques et Mini~res at Orleans (B.R.G.M.).

Mercury was determined after a nitric-hydrochlo- ric acid attack using a cold vapour atomic absor- ption technique. The remaining trace elements were determined by emission spectrography.

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Sample locations along the Rhone River system.

Results

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For each element a background level was cal- culated using the sample values upstream from the first indication of possible contamination toge- ther with unpolluted influent river samples. These values · along with the average values for all the Rhone River samples are reported in Table 1. There is a danger in this approach as local background levels may vary with.differing source rocks resul- ting in possibly erroneous results.

TABLE l

AVERAGE VALUES FOR TRACE METALS IN SEDIMENTS FROM THE RHONE RIVER

Element

Hg Pb er Cd Co Sn l.Ni

v

2. Zn Cu y B

Average of Rhone samples

690 60 65 5 10 8 55 60 60 20 35 45

Background*

55 (6) 55 (12) 35 (5)

5 **

10 (7) 8 **

so

25 (5) 60 (15) 55 (20) 12 (8) 25 (ll)

*Calculations based on (n) non-polluted samples.

-

**all samples used.

Local input sources and the impact on river sediments are summarized in fig. 2. To avoid com- plications arising from the different background values for each element the values are reported as "quantity of element X at a given point divided by the background for element X calculated from unpolluted s11mples". A log scale is used to permit the differing degrees of contamination to be indi- cated in a single diagram. The values above the abcissa are for the Rhone River samples and show the state of the sediments in the river itself.

Below the abcissa the results for the rivers and canals are given. A value of twice that of the background was considered significant.

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INFLUENT CANALS AND RIVERS

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Fig. 2 1972. Trace metal pollution of the Rhone River (upper axis) and asso- ciated canal systems and rivers

(lower axis). Values in parantheses exceed the scale factor of 100.

Numbers along the horizontal axis correspond to those in Fig. 1.

Discussion

It is evident from the diagram that mercury is the principal pollutant of the Rhone. The ma- jor portion comes from the large industrial che- mical complexes of Viege, Martigny and Manthey.

The effluents from these and other sources give values 100 to 1000 times the background levels.

The distribution of mercury in the river samples is summarized in Table 2. As can be seen in 1971-72 the mercury added to the envi- ronment by industrial activity accounts for grea- ter than 90% of total in the river system. Con- trol sediment samples taken at •Porte du Scex"

from 1964 to 1972 (fig •. 3l show that mercury con-

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tamination increased dramatically from 1965 to 1967 with the trend continuing through to 1971 (Vernet and Thomas, l972a). Mercury loss to the river system does not appear to have decreased between 1971 and 1972 and in fact the levels have marginally increased,

TABLE 2

MERCURY POLLUTION OF THE RHONE RIVER*

1971-72

Average value of polluted samples Average value of all samples Average value of non-polluted samples

• all values in ppb.

!21.!

780 600 60

1972

885 690 55

Based on the available data a mo~e realis- tic background for mercury in the Rhone River se- diments was determined (50-60 ppb) than that used by Vernet and Thomas (1972a) , The background le- v'el used by the latter authors (200 ppb) erred on the high side in order to assess merc~ry con- tamination in many Swiss lakes. It is now evi- dent that for the Rhone River this background was too high by a factor of four.

1500

I

~ 1000

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.c a.

500

PORTE DU SCEX

1964 66 68

SAMPLE YEAR

Fig. 3 Increase in mercury levels at the Porte du Scex, 1964-1972.

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Nickel is the next most abundant trace me- tal contaminant. Its distribution is more diffi- cult to interpret but it appears to be directly related to bedrock type. Rivers draining the Pennique (roches vertes, crystallin schists) such as the Saltina, Gamsa and Viege are generally hi- gher in nickel than the Rhone in the "llelvetique"

(limestones, marles). Once the influence of the tributary rivers ·is taken into consideration a second background level can be established (Ta- ble 1) • A minor decrease in nickel is evident in samples taken in the area dominated by gra- nites "Aiguilles Rouges". Shortly after the re- entrance into the "Helvetique" region the back- ground should fall towards its original value.

Any further deviations from the original back- ground should then be attributed to man-made sour- ces. The length of river course required to ef- fect this decrease is not known but an estimate might be made by comparing the levels found for the . Saltina, Gamsa and Viege. These rivers show nickel contents decreasing roughly in proportion to the amount of calcareous rock traversed.

Chromium is the next most frequent pollutant and shows a distribution similar to that of nickel from samples one to 23. Beyond this point man-made pollution becomes much more evident with definite source(s) between samples 24 and 28. This may be partially due to material introduced from canal Y but the major portion must be attributed to an as yet, unidentified source. Beyond this point va- lues return to near background levels.

Copper appears as a pollutant in the sedi- ments near station 18 and is likely attributable to the vinyards of the surrounding area. The peak at station 26 is due to a carryover from high le- vels in canal Y.

Zinc and lead are detected at stabion 26 and again are attributed to canal Y. Zinc levels re- main relatively high for several stations but re-

~urn to background level before the Rhone reaches Lake Geneva.

Lead is high in the samples near the upstream part of the study area due to an unknown source beyond the range of the study rather than any dif- ferences in the distribution of rock types.

Cadmium in the study area is almost always present in levels below the detection limit of the analysis. Cobalt, tin and vanadium are usual- ly present in low concentrations and show minimal variations.

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Conclusions

Based on this and previous studies mercury is the primary trace metal contaminant in the Rhone River system.

Nickel may be considered as a natural pol- lutant in the upper reaches of the Rhone but sources of man-made pollution ate evident in the area near Lake Geneva.

Copper, zinc and lead show very localized elevated levels which in most cases may be attri- buted to specific sources.

Pollution in the individual canal systems is extensive but except in the instances discus- sed above carryover into the main river system is negligible.

Acknowledgments

The authors wish to thank Dr. G. Scolari for his friendly scientific collaboration.

Thanks are also expressed to the Swiss National Fund for scientific research for the fi- nancial support .of the current limnogeological investigations of Swiss lakes and rivers.

The assistance and analytical support of the B.R.G.M. within the body of the Franco- Swiss group for the geology of the environment GEOLEM are gratefully acknowledged.

BIBLIOGRAPHY

VERNET, J.-P., and THOMAS, R.L,; l972a: Levels of mercury in the sediments of some Swiss Lakes including Lake Geneva and the Rhone River. - Eclogae Geol. Helv., vol. 65, p. 293-306.

id. 1972b : The occurence and distribution of Mercury in the sediments of the Petit Lac (Western Lake Geneva) •. - Eclogae Geol. Hel v.

V~l. 65, p. 307-316.

id. 1972c : Le Mercure dans l'Environnement et le rOle de la Geologic sedimentaire. - Bull. du B.R.G.M. (deuxi~me s~rie) Sec- tion 3, p. 43-61.