Trace metals in Solway Firth sediments

creation of a competent international organization before implementation. Customary law is partial; it is directed at particular situations and it expresses national interests as they are perceived in a particular context without much opportunity for general forecasting or consideration. The protective measures which may be taken by states are only taken when the state sees a clear and imminent danger with regard to a particular substance or a particular event. There is also the consideration of whether a particular state, weighing economic costs, would act to prevent long-term consequences. Reviewing the entire international legal system, it can be said that it provides very few regulatory mechanisms to deal with the general quality of the marine environment which lies beyond national jurisdiction. What is now needed in the interests of conservation are:

1. A strong and unambiguous pollution control convention which includes provisions for international monitoring and enforcement; 2. A rational resource management plan for fisheries and mineral resources. Any plan to gain the support of the developing countries must include some idea of revenue sharing. In this context, the concept of the resources of the sea as the 'common heritage' of man must be supported as a legal principle; 3. The Canadian concept of 'residual coastal state jurisdiction', as embodied in the three principles on coastal state jurisdiction. BARBARA HOFFMAN

Sierra Club Office of International Affairs, 777 United Nations Plaza, New York, N Y 10017, USA.

Trace Metals in Solway Firth Sediments Although the hinterland of the Solway Firth contains deposits of a variety of non-ferrous metals, and coal and steel industries grew there during the industrial revolution, the trace metal content of sediments in the firth is low, and the Solway is the last major unpolluted estuary in Britain. The hinterland of the Solway Firth has been worked for non-ferrous metals, silver, lead and zinc, at least since medieval times. During the industrial revolution, the coast of Cumberland between Maryport and St Bees Head became important in the development of the coal and steel industries (Fig. 1). Indeed, Workington is notable since locally mined iron ore was particularly suitable for use in the Bessemer converter. Since 1945, these industries have declined in importance and other industries, which include such processes as the production of phosphoric acid and paperboard, have been introduced to the area. In the period 25 June-2 July, 1971 the opportunity was taken to sample the sublittoral sediments of this coast and determine their trace metal content. Comparative samples were taken on the shore at Allonby (R63) and Beckfoot (R103) on 7 September, 1971.

dried sub-samples which had first been treated with industrial spirit. These sub-samples were passed through a standard sieve series on the Udden-Wentworth scale agitated by an Endecott Test Sieve Shaker. No estimate of organic carbon content was attempted since sediments here have a substantial content of fine coal,

Results The trace metal concentrations of these sediments are given in Table 1 and compared with those from other areas. The most evident feature of these results is the low trace element content of the Solway sediments

KIRKCUDBRJGHT Pl~

BMILL PT.

a

,==~7 U

Methods At each of the sublittoral stations (Fig. 1), samples of sediment were taken by means of a 0.1 m s Van Veen grab, and a sub-sample of each was returned to the laboratory for trace metal and soil grade analysis. At Allonby and Beckfoot the sediment samples were collected from routinely worked transects. Sub-samples for trace elements were oven-dried at 100°C, and ground to pass through a 204 ~m nylon sieve. In the sublittoral sediments cadmium, copper, chromium, iron, lead, manganese and zinc were determined by atomic absorption spectrometry following a nitric and/perchloric acid digestion; cobalt, gallium, molybdenum, nickel, silver and tin were determined by optical emission spectrography. The littoral sediments were examined by atomic absorption spectrometry alone. At the 95 per cent confidence level the precision of atomic absorption analysis is + 15 per cent, and of optical spectroph analysis + 50 per cent. The soil grade analysis was performed upon oven-

S

O

SOLWAY FIRTH

CUMBERLAND

HITEHAVEN

S'[ BEES HEAD

59

when compared with the estuary a n d firth of the Clyde a n d with the Severn estuary, a difference which is generally significant at the 0.1 per cent level of probability when the results are subjected to the t-test. T h e only a p p a r e n t exception is c a d m i u m which is n o t significantly different in all three estuaries. C o m p a r e d with areas outside the British Isles, a similar picture pertains. Levels of silver, c h r o m i u m , copper a n d lead are m u c h lower t h a n those reported for the New York Bight area by Gross (1972); a n d of the comparative figures reported in T a b l e 1, the values reported for Gulf of Paria, Buzzards Bay, Saanich I n l e t a n d near shore sediments, are exceeded only by those of lead a n d zinc from the Solway sediments. This result is hardly surprising in view of the long history of the m i n i n g of these metal ores in the Solway hinterland. W h e n the concentrations of c a d m i u m , copper, iron, manganese, m o l y b d e n u m , lead a n d zinc in the sediments taken south of W o r k i n g t o n are c o m p a r e d with those from the shore at A l l o n b y a n d Beckfoot. there is either no difference or insufficient evidence for regarding the concentrations of c a d i m u m , copper, m o l y b d e n u m a n d zinc as different in the two areas. O n the other hand, the c o n c e n t r a t i o n s of iron, m a n g a n e s e a n d nickel were significantly lower at the u p s t r e a m stations, b u t the lead c o n c e n t r a t i o n was significantly higher (both at the 0.1 per cent level of p r o b a b i l i t y by the t-test) in the samples t a k e n at A l l o n b y a n d Beckfoot. P r e s u m a b l y , the differences in the c o n c e n t r a t i o n of these metals are a reflec-

tion of the influence of present a n d a b a n d o n e d iron a n d steel works on this part of the coast. T h e differing m a n g a n e s e levels may, in addition, be a reflection of the influence of water from the River D e r w e n t u p o n the sediments off W o r k i n g t o n . According to M r J. Patrick, high levels of m a n g a n e s e are k n o w n to occur in the sediments of Bassenthwaite Lake (an enlarged section of the R i v e r Derwent): this m a n g a n e s e m a y be released in periods of t u r b u l e n c e a n d cause corrosion p r o b l e m s in the public water supply system; d e a r l y , such a release will permit the metal to reach the sea off Workington. A closer inspection of the samples taken at A l l o n b y a n d Beckfoot suggested that two distinct groups of sediment of relatively high a n d low trace metal content were present, ie (1) those taken from the u p p e r shore level with m a r k e d d e v e l o p m e n t of flood c h a n n e l ' b a r b lets' a n d sand ridges, a n d (2) those from the levels of the Arenicola zone a n d below, respectively. Concentrations of copper, iron, m a n g a n e s e , m o l y b d e n u m , nickel, lead a n d zinc were significantly higher in the former group than in the latter. N o clear correlation with soil grade composition emerged from a consideration of these figures. A t this stage, too few results are available to do other t h a n note this difference. However, it should be recognized that the flood c h a n n e l system a n d flood c h a n n e l ' b a r b l e t s ' are strongly developed in this area. These systems are i m p o r t a n t to the transport of sedim e n t a r y materials and, without considering the relation-

TABLE 1 Concentration of trace elements in sediments of the Solway firth and other selected areas. (ppm with the exception of Fe, % dw Fe~(h.) ~"

_ -

Type of Sediment No. of samples Ag Cd Co Cr Cu Fe Ga Mn Mo Ni Pb Sn Zn

~

,~204 /, silts, clays

,~204 ~ silts, clays

.~204 l, silts, clays

58

10

52

Mean Range ~0.2 ND-~0.2 ~ 1 . 0 ND-2.4 16 8-50 35 12-80 l0 5-19 2.0 1.2-2.9 15 10-20 360 180-720 <'2 ND-2 38 20-85 37 ND-72 6.7 5-16 63 24-105

SD

~-~"

Mean Range 2.9 2.4-4.0 3.2 15 3.4 16 0.5-48 0.5 0.28 0.14-0.44 2.9 . . . 108 233 110-370 1 0.2-2.4 10 17 10-22 17 56 24-76 3.2 22 74 36-I 12

SD Mean Range ~0.2 . . 0.5 3.4 0-4 34 13-40 64 38-106 17 37 22-77 0.11 5.3 1.9-9.7 . . . . 104 I118 500-4000 0.79 0.3 0.1-0.4 3.6 50 19-62 16 86 48-134 19 5-30 33 165 7-244

SD

~

.~=

~

a' o

silt

-

1

7

Mean . 1.0 7 3.7 7 60 20 624 13 225 1.7 9.4 . . 950 1600 0.2 2.5 25 69 39 528 163 10 85 68 1680 470 .

mud - sandy silt 6-12 Range . 1.6-4.3 . 130-190 420-590

SD 1.1 25 66

NDND7.7 - 8.6 13 93 33 81 1 0 0 17 18 36 48 7.3 - 2.9 360 ND 31 55 30 22 - 9 -

1. Mackay, Halcrow and Thornton, 1972; 2. Butterworth, Lester and Nickless, 1972; 3. Hirst, 1962; 4. Moore, 1963; 5. Gross, 1967; 6. Chester, 1965. 60

-

55 20

89 -

ship of the trace metals content with any particular quality or grade of sedimentary material, it is implicit in these results that they are derived from a downstream

those reported by Perkins (1972b) and with the contention that the Solway Firth is Britain's sole remaining large estuary which is as yet unpolluted.

TABLE 2 Correlation coefficient of trace elements with the silt content of the sediments taken in Saltom and Parton Bays. Element

Cd

Co

Cr

Cu

Fe

Correlation Coefficient

0.128

0.88

-0.03

0.52

0.63

5

5

Level of Probability (%)

10

1

1

Ga

Mn

0.43 ~>5

Ni

Pb

Sn

Zn

0.63

0.24

0.58

0.04

0.74

5

>10

5

10

2

TABLE 3 Trace metal composition of Solway plain sandstones (after Davies, 1971). Element

Cr

Mn

Cu

Pb

Co

Ni

Mo

Zn

Concentration ppm

22

100

5

2(1

7

33

<~2

27

source. Such a conclusion is consistent with the view that estuaries like the Solway Firth have received continual supplies of sediment derived from material dumped in the Irish Sea during the Pleistocene Ice Age. Moreover, by use of Ru 1°6 and Zr~5/Nb 95 released from Windscale as a tracer, Perkins et al. (1964) and Perkins and Williams (1966) investigated the mechanism of transport of sedimentary materials from the bed of the north-east Irish Sea onto the salt marshes of the Solway Firth, and showed the importance of flood channel systems in this transport. Such a mechanism accounts also for the generally greater concentrations of trace metals found in the Solway Firth sediments than Davies (1971) recorded from the sandstones of the Solway Plain. The relationship between soil grade composition and the trace metal content of the sediments is more susceptible to examination in the greater number of samples taken from Saltom and Parton Bays. The strongest association between the silt/clay fraction (ie smaller than 0.0625 mm) and trace metal content occurred with respect to cobalt, iron, manganese, lead and zinc while there was either no, or only a weak, association with chromium, nickel and tin. In view of the strong association between organic matter, and chromium and tin reported by Mackay et al. (1972), such a weak relationship is perhaps to be expected. Nickel is apparently associated neither with the silt/ clay fraction nor organic matter, whereas lead may be associated with either, though more strongly with organic matter than with silt. To summarize, the hinterland of the Solway Firth contains a wide variety of metal ores which have been worked over wide areas for protracted periods, and which have made a contribution to the Firth itself through all the rivers which flow into the Firth (Perkins, 1972a). In addition, intensive working of iron has been pursued on the West Cumberland coast from the time of the industrial revolution. Bearing these facts in mind, it is of interest that the trace metal content of the Solway Firth sediments so far examined is so low. In this respect at least the results given are consistent with

The Applied Geochemistry Research Group's contribution forms part of a programme of work financed by a research contract from NERC awarded to the group under the direction of Professor John S. Webb. The assistance of the analytical staff of AGRG is gratefully acknowledged. E. J. PERKINS J. R. S. GILCHRIST O. J. ABaOTT

Marine Laboratory, University of Strathclyde, Dalandhui House, Garelochhead, Dunbartonshire, Scotland. W. HALCROW

Applied Geochemistry Research Group, Department of Geology, Imperial College, London, UK. Butterworth, J., Lester, P. & Nickless, G. (1972). Distribution of heavy metals in the Severn Estuary. Mar. Poll. Bull., 3(5): 72-74. Chester, R. (1965). Elemental geochemistry of marine sediments. In: Chemical Oceanography. Ed. by J, P. Riley & G. Skirrow (Academic Press), 2: 23-77. Davies, W. C. (1971). Regional geochemistry of stream sediments derived from an area underlain by the English Permo-Triassie. Ph.D. Thesis. University of London. Gross, M. G. (1967). Concentration of minor elements in diatomaceous sediments of a stagnant fjord. In: Estuaries. Ed. by G. H. Lauff, (AAAS Publ.), No. 83: 273-282. Gross, M. G. (1972). Marine waste deposits near New York. Mar. Poll. Bull., 3(4): 61-63. Hirst, D. M. (1962). Geochemistry of modern sediments from the Gulf of Paria. Geochim. et Cosmochim. Acta, 26: 1,147-1,187. Mackay, D. M., Halerow, W. & Thornton, E. (1972). Sludge dumping in the Firth of Clyde. Mar. Poll. Bull., 3(1): 7-11. Moore, J. R. (1963). Bottom Sediment studies, Buzzards Bay, Mass. Y. Sed. Petrol., 33: 511-558. Perkins, E. J. (1972a). Industry and the Solway Firth. The Environment this Month, 1(2): 47-54. Perkins, E. J. (1972b). Effects of steel works effluent. Mar. Poll. Bull., 3(6): 86-88. Perkins, E. J., Bailey, M. & Williams, B. R. H. (1964). The Biology of the Solway Firth in relation to the movement and accumulation of radioactive materials. IX. Seabed and sea-surface drifter releases--C. N.E. Irish Sea and Solway Firth, 1963. HMSO, UKAEA, PG Report 605 (CC). Perkins, E. J. & Williams, B. R. H. (1966). The Biology of the Solway Firth in relation to the movement and accumulation of radioactive materials. II. Distribution of Sediments and Benthos. HMSO, UKAEA, PG Report 587 (CC). 61