THE APPLICATION OF REGIONAL GEOCHEMICAL RECONNAISSANCE SURVEYS IN THE

ASSESSMENT OF WATER QUALITY AND ESTUARINE POLLUTION

SIMON R. ASTOY and IAN THORSTON

Applied Geochemistry Research Group. Imperial College. London SW7, U.K.

(Rewired 15 November 1973)

h-i-RODUCI-ION

Regional geochemical reconnaissance data have been applied successfully to various aspects of environmen- tal research including agriculture, pollution, estuarine, fisheries and medical geography [I]. Recent studies have shown that geochemical data, and the methods employed in regional reconnaissance studies, are effec- tive in the prediction of water quality from the heavy metal aspect [Z]. Similarly, research into heavy metal pollution in estuaries and the establishment of baseline data for heavy metal occurrences in estuaries has been aided by regional geochemical data [3]. Present research into the use of regional geochemical data as an ancillary aid in the assessment of heavy metal con- tamination and surface water quality is primarily con- cerned with developing the application of regional geo- chemical data to the appraisal of broadscale water quality and as a guide to the selection of sites for the more costly and time consuming operation of water monitoring itself. This paper discusses the application and interpretation of regional geochemical data to water quality and pollution problems and illustrates the applications with examples of recently completed and continuing research.

THE RECIOSAL DISTRIBUTION OF TRACE ELEMENTS

Regional geochemical maps for England and Wales have recently been prepared by the Applied Geoche- mistry Research Group, Imperial College, with finan- cial aid from the Wolfson Foundation. These geo- chemical maps are based on data obtained by the

This paper was received for the Paris Conference, but together with several more wasaccepted for Wuter Research as there was no room for it on the Conference Programme.

multi-element analysis. by direct reading spec- trographic and calorimetric techniques. of the 204 pm fraction of 50,000 active stream sediment samples col- lected at road-tributary intersections. giving a sample density of approximately I sample mile-?. The choice of active stream sediment as a sampling medium for the construction of trace element maps is based on the premise that such sediments are nature’s closest approximation to a composite sample of the weathered products of rock and soil upstream from the sampling site. The maps reflect,. on a regional basis, the natural composition of both rocks and soils, thus providing baseline information on the occurrence and distribu- tion of trace elements. Patterns of trace element distri- bution shown by the maps at the same time reflect trace element contamination from mining. urban and industrial sources. Figure I illustrates a provisional map for the distribution of arsenic in England and Wales, produced by the overprinting of characters on a computer line printer. The computer programme has been designed to plot a symbol corresponding to the concentration level of the geometric mean of all data points falling within a “map cell” of nine adjacent sam- ples [4]. The resulting maps describe regional patterns of metal distribution, but do not represent point source data.

The background of normal level of arsenic in stream sediments in England and Wales lies in the con- centration range O-7 ppm, while the greatest con- centrations in anomalous areas can be in excess of 150 ppm (Fig. 1). Two main types of high concentration or anomalous areas can be resolved:

(1) Areas of sulphide mineralization such as in South-West England, North Wales, and the Lake Dis- trict of North-West England.

(2) Areas contaminated by recent and present day industrial activities, especially operations such as the smelting of metalliferous ores in parts of Cornwall and

W.R. 9/2--E

Arsenic

Fig. I. Pro\ Gsional map showing the distribution of arsenic in stream sediment in England and Wales.

Scale m miles

Devon adjacent to the areas of sulphide mineraliza- which are influenced by natural and contaminated

tion. Discrete areas of contamination also occur in runoff. They do not however indicate point source con-

areas of industrialization such as the West Midlands tamination of river or estuary due to input of local in-

and Northern central England. dustrial effluent. sewage, etc.

Thus provisional data available on the regional dis- tribution of toxic trace elements including arsenic, cad- mium. zinc, lead, copper and nickel on a national scale provide two main forms of information with obvious application in environmental studies:

WATER QUALITY !TI’lJDIES

(I) Data on the natural variations in the regional distribution of the elements.

(2) Data on the contamination of the environment by man’s activities and the re-distribution of trace ele- ments on a regional scale by the contaminating pro- cesses.

On this basis regional geochemical maps have been shown to highlight potential problem areas wherein anomalously high concentrations of potentially toxic elements may adversely affect the quality of potable water supply, and to provide information for the eva- luation of the background concentrations of trace ele- ments in tributary and river waters. and estuaries

The concept has recently been introduced of apply- ing regional geochemical reconnaissance data to the prediction of the trace metal status of surface drainage waters abstracted for potable water supplies [-?I. The fundamental purpose of using regional patterns of trace metal distribution is in the selection of areas and actual sites for more detailed programmes of water sampling and analysis. If the trace element content of stream and river sediments underlying waters of poten- tial use as potable water supplies can be used as a more stable index of the range of trace element con- centrations likely to be found in the waters themselves, then regional geochemical data will provide a very use- ful ancillary aid to water quality prediction. One of the major problems encountered in the monitoring of

Geochemical reconnaissance survqs 191

Table 1. Ranges and average values for trace element concentrations in 4 rivers and tributaries and their sediments

River gdiments (ppm)

Range Average Water (pg I- ‘)

Range Average

Fowe!

Red

Carnon

Gannel

CU Zn Pb cu Zn Pb CU Ztl Pb cu Ztl Pb

3370 50 31-370 150 3-t-384 100 56-1650 590 69-2800 605 101032 295 12-6500 I650

IjO-7000 1080 48-1440 470 X-520 100

150-7000~ 1000 43-4410 605

‘-‘I

tii9

ST35 35-260

5-25 960-l I60

1520-10.000 25-55 420

26-420 8-530

7 25

5 I7

I30 II

1080 4950

-II 12

310 I-IO

natural surface waters for their trace metal composi- tion is the high degree of fluctuation of trace metal levels on both a high frequency (diurnal). and long period (seasonal), basis. Sudden changes in precipi- tation. soil conditions, etc., can produce significant changes in the trace metal content of drainage waters. Any programme ofwater sampling and analysis for the monitoring of abstracted waters must be of sufficient intensity to indicate the short and long term fluctua- tions which can occur. As it is primarily the range, and in particular the upper limit, of trace element con- centrations in abstracted waters which is significant in establishing whether the medically recommended limits of trace metal concentrations are exceeded. it is important to establish whether the-trace metal content of drainage sediments is a stable guide of the range of concentrations found in waters.

Preliminary studies on the trace metal content of the sediments and waters of four rivers in Cornwall have demonstrated that tributary drainage sediments are a guide to the range of trace element concentrations in the overlying tributary and the main river itself [2]. Table I shows the range and average trace metal con-

tents in the four Cornish rivers and their tributaries. The catchments selected for study were those of the Fowey, Gannel, Carnon and Red Rivers, draining dif- ferent types of mineralization and catchment areas. Natural weathering processes, together with past and present mining activities. have given rise to high levels of metals such as copper. lead. zinc, cadmium tin and arsenic in the waters and sediments of these catchments, except for the Fowey which was included as a baseline catchment. Table I shows that there are significant differences between the trace metal content of the waters and sediments of the mineralized catchments and those of the unmineralized Fowey catchment. The average trace metal concentrations in the Fowey and its tributaries are of the same order of magnitude as the world averages for streams [S]. On the other hand, the average trace metal levels in the Carnon, Gannel and Red Rivers and their tributaries are higher and have wide concentration ranges because some of their tributaries drain mineralized areas while others do not. Table 2 provides a comparison of the trace metal content of tributary waters and sediments in mineralized and unmineralized areas. The reflection

Table 2. A comparison of the average trace element concentrations in the waters and sediments of mineralized and un- mineralized catchments

River Sediment (ppm)

Contaminated Uncontaminated Water (jig I- ‘)

Contaminated Uncontaminated

CU 706 563 9 25 Red Zn 1590 358 I80 70

Pb 775 133 18 7 cu 3000 416 1080 I080

Carnon Zn I839 391 8150 3060 Pb 540 402 44 37 cu 313 46 16 II

Gannet Zn 3995 255 800 59 Pb 2670 89 250 21

of the differences m the trace metal levels of the waters

from these areas in their associated sediments drmon-

strates the potential usefulness of yeochcmical rscon-

naissance based on stream sediment sampling in pre-

dieting water quality. It can be seen from Table 1 that

there is a considerable variation in the degree of conta-

mination of the waters from the different river systems.

In the Carnon River the uncontaminated waters have

higher copper and zinc concentrations than those of

the Red and Cannel Rivers: this is a result of the

extreme contamination of the Carnon River system in-

cluding those tributaries which do not directly drain

mineralized areas. The abnormally high trace element

contents in the Carnon waters are also probably due

to their low pH. while the Red and Gunnel catchments

have similar sediment trace element contents. but

lower water contents due to their higher pH regimes.

In the Gannel the lead content of both waters and sedi-

ments is very high as a result of the lead (galena) miner-

alization in the catchment.

The seasonal and diurnal Huctuations which occur

in the trace metal composition of drainage waters have

already been mentioned and these variations provide

a problem in the interpretation of trace element distri-

butions in stream sediments in terms of the range of

concentrations in the waters. At present studies on the

seasonal variations in the trace metal contents of the

waters and sediments of the four Cornish rivers above

are being monitored to relate these variations to

catchment characteristics such as topography.

drainage and soil type. It is--the intention of these

studies to provide a systemized and empirical method

for the interpretation of regional geochemical patterns

based on stream sediment sampling in terms of

catchment characteristics.

In addition to the studies in the specific river

catchments outlined above, more widescale investiga-

tions have been carried out on the regional reconnais-

sance of arsenic in stream waters and sediments

throughout the county of Cornwall. Arsenic was stud-

ied because of its abundance in South-west England

(Fig. I) and because of its potentially toxic nature. The

occurrence of arsenic mineralizations in South-west

England is well established, and the production of

arsenic from mispickel, its principle ore. has fluctuated

considerably reaching a maximum towards the end of

the 19th century. Further geochemical reconnaissance

based on stream sediment sampling showed that in

areas where adit drainage from old mines leads to the

direct input of arsenopyrite-rich waters in streams. the

associated sediments could often achieve peaks of

> 5000 ppm arsenic and the waters themselves contain

LIP to 3000 /ig I- ’ of soluble arsenic. The “normal” or

background levels in the non-mineralized areas were

O- 10 ppm in sediments and Ii) ~18 I-’ rn waters. the

LVorld Health Organization recommended limit for

drinking waters being 50 jog I-‘. Prsliminarv results

are encouraging. showing a direct empirical relation-

ship between the arsenic content of the sediments and

the upper range contents in associated waters.

ESTL .ARIUE POLLLTIOS .A\D CEOCHEZIIC.-\L RECOUS;\ISS.A\CE

Since the waters and sediments in estuaries are com-

posed to varying degrees of the runoff from river and

tributary drainage systems. it is reasonable to suppose

that the trace metal contents of tributary drainage

sediments (and thus regional geochemical data) will

give information on the tmce metal content of sedi-

ments and waters in associated estuaries. Recent

studies have demonstrated a good degree of correla-

tion between land-based geochemical patterns and

trace metal concentrations measured in selected

estuaries [6].

initial interest in the possible role that geochemical

studies could have in the investigation of estuarine

aquaculture problems arose from the suggestion that

zinc may be a possible cause of the intermittent failure

of oyster larvae at a hatchery in the Conway estuary,

North Wales. The metal contamination of the Conway

cdtchment had been previously established by a geo-

chemical reconnaissance of the area [7]. This recon-

naissance. based on the analysis of stream sediments,

indicated high levels of zinc and lead in part of the

Conway catchment which were traced to contamina-

tion from mill tailings and mine adit drainage, Elder-

field or trl. [S] sampled the tributary drainage, river and

estuarine waters and sediments of the Conway, and

provided evidence that the oyster hatchery in the estu-

ary was subjected to high loads of zinc in the fresh

water input due to the past mining activities in the

catchment. The zinc content of the estuarine water

showed marked seasonal and tidal fluctuations (Fig. 2),

ranging up to 370 /[g I- ’ Zn. i.e. nearly 50 times the

zinc concentration found in normal river and marine

waters [j]. Recent beaker trials using both zinc con-

taminated water from the Convvay and zinc sulphate

solutions have shown that larval development is inhi-

bited and the mortality rate increased over the range

IO@-500 /tg I-’ Zn. thus confirming that the con-

centrations of zinc observed in the hatchery waters

could inhibit the efficient development of larvae on a

periodic basis [9] (Fig. 3).

With an increasing awareness of the potential trace

metal problem in estuarine culture of economic species

of shellfish. a further four estuaries were selected for

geochemical investigation each being of shellfish pro-

duction potential. The estuaries selected were those of

Geochemical reconnaissance surveys I93

35,. Saltnlty

10.0 Sodium

oh 90

8.0 iI-_

Jonuary February March April May June

Fig. 2. The temporal variation of high water, salinity and some elemental concentrations in Conway water.

I20

0.0 ZnSO4 Treoiment

110 A.* Mine water treatment

g BO-

ki E 70-

f P 5 sa

40- End of zinc treoTmem

30. 1 1 I 1 1 1 1 1 1 J 0 I 2 3 4 5 6 7 6 9 IO

Time, days

Fig. 3. The relationship between mean size of larvae (Crassostrea yigus) and zinc concentrations in water.

the River Helford and Restronguet Creek in Cornwall. both known to have a history of base metal mining in their catchments and thus to be contaminated, and those of the River Colne and Poole Harbour. both thought to be relatively uncontaminated. The trace metal content of the sediments and waters from the selected estuaries were determined. and the observed inter-estuary differences clearly reflected in the analy- ses of the sediments sampled from the major tributary drninuge in the respective catchments (see Table 3).

These preliminary investigations into the appli- cation of geochemical data and methods to problems of estuarine pollution and aquaculture indicate a potential usefulness of such data in the selection of rstuarics for the cultivation of economic species. As in the case of rivers. there are very significant variations in the trace metal content of estuarine waters and sedi- ments on a short term (tidal) and long term (seasonal) basis. These variations must be taken into account when interpreting data on the-trace element chemistry of estuarine systems. but there are indications that readily available reconnaissance data may be a vdllb able ancillary aid in the selection of estuaries before embarking on the much more expensive and time con- suming exercise of water monitoring.

SL hIMARY

Preliminary studies on the application of regional, geochemical reconnaissance data, based on stream sediment sampling, to the assessment of water quality and estuarine pollution are encouraging. The use of the trace metal composition of tributary drainage sedi- ments for the prediction of the upper limits of the trace metal concentration ranges in associated waters has been demonstrated. suggesting that the already avail- able reconnaissance data may be a useful ancillary aid in the location of water monitoring sites in potential problem areas for potable water abstraction. The close association between the trace metal status of estuarine waters and sediments and their respective tributary drainage sediments allows the use of regional geo-

chemical reconnaissance data in the selection of estuaries for aquaculture and other amenities.

It must be emphasized that regional geochemical reconnaissance data. although a useful guide to the trace metal status ofpotable and estuarine waters. does require more detailed follow-up studies in selected areas. This is especially true for temporal studies to establish the seasonal variations in surface drainage systems. The present investigations in the United Kingdom involve areas of fairly well known character- istics and relatively small climatic and environmental scope; the extension of such studies to lesser known areas and regions of greater natural variations could well prove useful.

Ackr~owlrt~~r~nrnts-The research was financed by the Natural Environment Research Council and forms part of a continuing programmt under the overall direction of Pro- lessor J. S. Webb. Water quality studies in Cornwall have been carried out in collaboration with the Cornwall River Authorit).

REFEREXCES

[I] Thornton I. and Webb J. S. (1973) Environmental geo- chemistry: some recent studies in the United Kingdom. Proc. 7th Am~tra/ Con&rerlce on Trace Sub- statlces in Etrrirorzmetltal Henlth. University of Mis- souri, 1973. (In press).

[Z] Aston S. R.. Thornton I.. Webb J. S.. Purves J. B. and Milford B. L. (1973) The application of regional geo- chemical reconnaissance data to waler quality studies. J. LVot. Treat. Exam. (In press).

[3] Thornton I.. Brereton A. and Lord H. (1973) Geo- chemical stud@ in selected rivers and estuaries. (In press).

[4] Howarth R. J. (1971) Fortran IV program for %rey level mapping of spatial data. Mat&. G;ol. 3, 9%r21.

T51 Rilev J. P. and Chester R. t 19711 fnnoducriorl to Slur- &., . ,

irle Chemisrr!. Academic Press. London. [6] Thornton I. (1973) Geochemical parameters in the

assessment of estuarine pollution. Proc. British Eco- logical Sot. International Symposium 011 Degraded

Encironmellts and Resource Renewal. Leeds, 1973. (In press).

[7] Nichol 1.. Thornton I.. Webb J. S.. Fletcher W. K.. Horsnail R. F.. Khaleelee J. and Taylor D. (1970) Regional geochemical reconnaissance of the Denbigh- shire area. Report No. 70/B. Institute of Geological Sciences. London.

Geochemical reconnaissance surveys 195

[Y] Elderfield H.. Thornton 1. and Webb J. S. (1971) Heavy metals and oyster culture in Wales. Mur. PO/~. Bull. 2. 44-17.

[9] Btereton A.. Lord H.. Thornton I. and Webb J. S. (1971) Effect of zinc on growth and development of larvae of the Pacific oyster Crassosrreu yips. Mark

Biol. 19. 96- IO I.