Distribution of Copper, Nickeland Zinc in the Thames EstuaryCHRISTOPHER STEVENSON  and BETTY NGà* The Environment Agency, Thames Region, KingsMeadow House, Kings Meadow Road, Reading RG18DQ, UKàThe Environment Agency Wales, Rivers House, St.Mellons Business Park, St. Mellons, Cardi� CF3 0LT,UK

In the United Kingdom, considerable work has beenreported on the fate of heavy metals in the North Sea(Burton et al., 1994), the Tamar Estuary (Morris,1986; Ackroyd et al., 1986), the Humber Estuary(Turner et al., 1993; Comber et al., 1995), and theMersey Estuary (Campbell et al., 1988; Comber et al.,1995). However, the same cannot be said for the pol-lution levels and geochemical behaviours of heavymetals in the Thames Estuary. Heavy metal concen-trations in suspended sediments (Turner, 1990) andbed sediments (Attrill and Thomas, 1995) of theThames Estuary have been recorded, but only fromone-o� studies. This paper provides additional data onthe temporal and spatial distributions of copper, nickeland zinc in the Thames Estuary, and on the majorsources of these pollutants.The Environment Agency and one of its predecessor

bodies, the National Rivers Authority, carry out rou-tine monitoring of the Thames Estuary, its tributaries,industrial e�uents and the discharges of major sewagetreatment works (STWs; see Fig. 1). The monitoredparameters include salinity; suspended solids; total anddissolved copper, nickel and zinc; and concentrationsof these metals in sediment samples. Salinity (aschloride) is either measured in the ®eld using titrationwith silver nitrate and lead chromate as an indicator,or in the laboratory. Suspended solids levels are de-termined by ®ltration using GF/C membranes of 1.2lm pore size. Metal concentrations in the water col-umn are measured by anodic stripping voltametry, thedissolved fraction being separated in the ®eld by ®l-tering through 0.45 lm membrane ®lters. Sedimentsare prepared by acid digestion, and analysed for metalsby inductively coupled plasma-atomic emission spec-troscopy.Data for salinity, suspended solids, and total and

dissolved metal in samples collected from 1990 to 1995

at the locations shown in Fig. 1 are reported in thispaper. Metal concentrations in sediments at a number oflocations are also reported.To estimate the loads of heavy metals emanating from

the various sources in the Thames Estuary, ¯ow datawere required. For the river tributaries, ¯ow records (forthe period from 1990 to 1995) at the gauging stationsnearest to their con¯uence with the Thames Estuarywere retrieved from the data archive of the EnvironmentAgency. For sewage treatment works, ¯ow data for thesame period from Thames Water Utilities were used.Maximum consented discharge ¯ows were used for in-dustrial e�uents. The annual average loads from eachsource were calculated by multiplying the average ¯owand the average total metal concentration, assuming the¯ow and metal concentrations to be statistically inde-pendent.Tables 1±3 show annual mean concentrations of

dissolved copper, nickel and zinc along the ThamesEstuary. At the sampling sites from Barnes to Green-hithe, concentrations of dissolved copper decreasedfrom 1990 to 1994, but increased in 1995. At ChapmanBuoy and No. 2 Sea Reach, dissolved copper concen-trations increased from 1992 to 1995. Dissolved nickelexhibited general reductions with time at most sam-pling sites, as did concentrations of dissolved zinc, ex-cept at Mucking, Chapman Buoy and No. 2 SeaReach. Seasonal variations in dissolved metal concen-trations were also studied. Higher concentrationstended to occur in the Autumn, with lower values atthe start of each year.Metal concentrations measured during various sur-

veys of sediments are given in Table 4. The concentra-tions reported by Attrill and Thomas (1995) for samplestaken during 1989 are also given for comparison.Beckton is in the Upper-Mid Estuary. West Thurrockand Gravesend are in the Outer-Mid Estuary and all theother sites noted in Table 4 are in the Outer Estuary.The 1989 and 1992 data suggest a general decrease withtime of metal concentrations in sediments along thewhole estuary. However, as shown by the 1994 and 1995data, there is signi®cant annual variation in the copperand zinc concentrations in sediments.The freshwater ¯ow in the Thames Estuary is domi-

nated by inputs from the River Thames itself; BecktonSTW; Crossness STW; Modgen STW; and the River Lee(see Table 5). Hence, it is not surprising that the majorloads of copper, nickel and zinc also come from thesesources. However, the relative contributions of heavymetals to the tidal Thames from these sources di�erfrom the relative contributions they make to the fresh-water ¯ow. Table 5 shows the relative annual averagecontributions of the tributaries, STWs and industriale�uents of copper, nickel and zinc into the tideway. Onaverage, the River Thames accounts for 30±40% of theheavy metal input into the tideway, while Modgen STW,Beckton STW and the River Lee each contribute at least10%.

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After this work was completed, a related study byPower et al. (1998) came to the attention of the au-thors. Power et al. (1998) ®tted temporal functions toobserved concentrations of cadmium, copper, mercury,nickel, lead and zinc at a single site (Erith), and pre-dicted the concentrations of these metals at that site

for the year 2000. We did not adopt such an approachto study temporal trends of metal concentrationsalong the Thames Estuary, as we believe that a single-variate description is not adequate and that otherfactors such as the loads from point discharges areimportant.

Fig. 1 Sampling sites in the Thames Estuary, its tributaries, sewageworks and industrial e�uents. The symbols d, n, D, and m rep-resent, respectively, STWs, industrial e�uents, sampling locationsin the tributaries, and in the estuary. River labels: 1 ± RiverThames, 2 ± River Crane, 3 ± River Brent, 4 ± River Lee, 5 ± RiverRoding, 6 ± River Beam, 7 ± River Ingrebourne, 8 ± Ravensbo-urne River, 9 ± River Wandle, 10 ± Beverley Brook. STWs: A ±Mogden, B ± Kew, C ± Beckton, D ± Crossness, E ± Long Reach,F ± North¯eet, G ± Tilbury, H ± Gravesend, I ± Basildon, J ±Canvey Island, K ± Southend. Industrial e�uents: L ± Pur¯eetBoard Mills, M ± Empire Paper Mill, N ± Brittania Metals, O ±Cleanaway, P ± Shell UK. Sampling locations in tributaries: a ±Thames at Teddington Weir, b ± Crane at Northcote Road,Isleworth, c ± Brent/GUC at Lock 100, Brentford, d ± BeverleyBrook at Priests Bridge, e ± Wandle at the Causeway, Wands-worth, f ± Ravensbourne at Deptford Bridge, g ± Lee at Car-penters Road, h ± Roding at Woodford Bridge, i ± Beam atHavering Sluice, j ± Ingrebourne at A13 Bridge. Sampling loca-tions in the estuary: k ± Barnes, l ± London Bridge, m ± Erith, n ±Greenhithe, o ± Gravesend, p ± Mucking, q ± Chapman Buoy, r ±Southend, s ± No. 2 Sea Reach.

TABLE 1

Mean values (lg lÿ1) of dissolved Copper in the Thames Estuary for the years 1990±1995a.

Sampling locations 1990 1991 1992 1993 1994 1995

Barnes 24.25 (12) 7.07 (8) 6.56 (9) 4.55 (12) 4.52 (11) 6.29 (12)London Bridge 18.63 (12) 9.97 (9) 8.10 (10) 4.68 (12) 4.02 (12) 5.07 (11)Erith 9.25 (10) 9.68 (6) 6.38 (8) 3.86 (10) 1.94 (12) 3.82 (10)Greenhithe No data No data No data 4.42 (7) 2.43 (11) 4.63 (10)Gravesend No data No data No data 3.75 (8) 3.28 (11) 2.42 (8)Mucking 8.20 (10) 7.59 (8) 3.7 (10) 3.29 (11) 4.53 (11) 4.40 (11)Chapman Buoy 8.25 (10) 6.81 (8) 1.89 (9) 2.84 (12) 3.98 (10) 6.10 (5)Southend No data No data No data 1.70 (1) No data No dataNo. 2 Sea Reach 13.58 (6) 4.64 (7) 1.25 (8) 2.48 (11) 3.74 (8) 8.18 (5)

a The number of samples taken is shown in parentheses. Figures in italics indicate compliance failures with the 5 lg lÿ1 standard of the 76/454/EECDangerous Substances Directive. See Fig. 1 for sampling locations.

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TABLE 2

Mean values (lg lÿ1) of dissolved Nickel in the Thames estuary for the years 1991±1995a.

Sampling locations 1991 1992 1993 1994 1995

Barnes 7.33 (6) 8.68 (5) 4.58 (10) 4.65 (11) 4.83 (12)London Bridge 13.49 (7) 7.99 (7) 5.10 (11) 4.54 (12) 4.84 (12)Erith 9.10 (5) 5.61 (6) 5.28 (11) 4.86 (12) 5.23 (11)Greenhithe No data No data 5.01 (8) 5.50 (11) 4.63 (10)Gravesend No data No data 4.63 (8) 5.40 (11) 4.02 (8)Mucking 4.88 (5) 5.25 (8) 3.87 (10) 5.66 (12) 3.48 (11)Chapman Buoy 4.10 (5) 4.49 (5) 2.73 (10) 2.66 (9) 2.69 (4)Southend No data No data 2.70 (1) No data No dataNo. 2 Sea Reach 3.00 (5) 4.02 (4) 1.88 (10) 1.84 (7) 1.33 (5)

a The number of samples is shown in parentheses The compliance standard of the 76/454/EEC Dangerous Substances Directive is 30 lg lÿ1. See Fig. 1for sampling locations.

TABLE 3

Mean values (lg lÿ1) of dissolved Zinc in the Thames Estuary for the years 1991±1995a.

Sampling locations 1991 1992 1993 1994 1995

Barnes 96.50 (6) 19.51 (9) 13.67 (12) 17.66 (10) 14.70 (12)London Bridge 44.43 (7) 20.56 (9) 16.92 (12) 15.97 (12) 16.08 (12)Erith 44.42 (4) 27.56 (9) 22.73 (11) 19.98 (12) 22.77 (10)Greenhithe No data No data 23.00 (8) 20.60 (11) 19.45 (10)Gravesend No data No data 17.00 (8) 17.92 (11) 16.19 (7)Mucking 20.40 (5) 17.14 (11) 15.08 (12) 20.14 (11) 22.54 (11)Chapman Buoy 12.63 (4) 11.44 (9) 10.67 (12) 20.81 (10) 23.72 (5)Southend No data No data 11.00 (11) No data No dataNo. 2 Sea Reach 6.66 (5) 11.13 (8) 7.64 (11) 32.47 (8) 15.23 (6)

a The number of samples taken is shown in parentheses. Figures in italics indicate compliance failures with the 40 lg lÿ1 standard of the 76/454/EECDangerous Substances Directive. See Fig. 1 for sampling locations.

TABLE 4

Concentrations of Copper, Nickel and Zinc (mg kgÿ1 dry weight) in sedimentsa.

Site Distance (km) fromTeddington Weir

Date Copper Nickel Zinc

Beckton 48.7 24/11/92 37.2 21.5 142West Thurrock 66.1 08/03/94 43.2 30.2 168

23/05/95 95.2 36.9 99.8Gravesend 72.7 24/11/92 36.5 19.6 132Mucking 82.1 21/03/94 15.2 13.0 72.8

06/06/95 21.1 14 107Blythe Sands 86.5 04/11/92 37.2 23.3 155Chapman Buoy 92.7 04/11/92 32.0 24.6 180Grain Flats 98.5 04/11/92 43.6 30.2 176Southend 99.9 04/11/92 21.7 17.6 135Upper-Mid Estuary 1989 70 36 244Outer-Mid Estuary 1989 50 31 185Outer-Estuary 1989 24 21 115

aWest Thurrock is an intertidal site, while all the other sites are subtidal. The 1989 data are all from Attrill and Thomas (1995).

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The authors would like to thank the Environment Agency for thepermission to use and publish the data. The authors would also like toexpress their sincere thanks to Tony Place and Sta�ord Cross for theiradvice on European Directives and laboratory analyses of ®eld data.This work was carried out as part of CS's M.Sc. project under BN'ssupervision while she was working in the Thames Region of the En-vironment Agency. The opinions stated in the paper are those of theauthors and not necessarily those of the Environment Agency.

Ackroyd, D. R., Bale, A. J., Howland, R. J. M., Knox, S., Millward,G. E. and Morris, A. W. (1986) Distributions and behaviour ofdissolved Cu, Zn and Mn in the Tamar Estuary. Estuarine,Coastal and Shelf Science 23, 621±640.

Attrill, M. J. and Thomas, R. M. (1995) Heavy metal concentrations insediment from the Thames Estuary, UK.Marine Pollution Bulletin30, 742±744.

Burton, J. D., Althaus, M., Millward, G. E., Morris, A. W., Statham,P. J., Tappin, A. D. and Turner, A. (1994) Processes in¯uencingthe fate of trace metals in the North Sea. In Understanding theNorth Sea System eds. H. Charnock, K. R. Dyer, J. M.

Huthnance, P. S. Liss, J. H. Simpson and P. B. Tett, pp. 179±190.Chapman Hall, London.

Campbell, J. A., Whitelaw, K., Riley, J. P., Head, P. C. and Jones, P.D. (1988) Contrasting behaviour of dissolved and particulatenickel and zinc in a polluted estuary. Science of the TotalEnvironment 71, 141±155.

Comber, S. D. W., Gunn, A. M. and Whalley, C. (1995) Comparisonof the partitioning of trace metals in the Humber and Merseyestuaries. Marine Pollution Bulletin 30, 851±860.

Morris, A. W. (1986) Removal of trace metals in the very low salinityregion of the Tamar Estuary, England. Science of the TotalEnvironment 49, 297±304.

Power, M., Attrill, M. J. and Thomas, R. M. (1998) Heavy metalconcentration trends in the Thames Estuary (unpublished).

Turner, A. (1990) Chemical dynamics in North Sea estuaries andplumes. Ph.D. Thesis, Polytechnic South West, Plymouth, UK.

Turner, A., Millward, G. E., Bale, A. J. and Morris, A. W. (1993)Application of the KD concept to the study of trace metal removaland desorption during estuarine mixing. Estuarine, Coastal andShelf Science 36, 1±13.

TABLE 5

Average (1990±1995) inputs of Copper, Nickel, Zinc and freshwater into the Thames Estuarya

Sources Copper (kg dayÿ1) Nickel (kg dayÿ1) Zinc (kg dayÿ1) Freshwater Inputs (Ml dayÿ1)

River Brent 0.99 (1.4) 0.54 (0.8) 3.04 (0.9) 81.15 (1.0)River Crane 0.47 (0.7) 0.23 (0.3) 1.26 (0.4) 43.20 (0.5)River Beam 0.20 (0.3) 0.33 (0.5) 1.06 (0.3) 26.37 (0.3)R. Ingrebourne 0.35 (0.5) 0.28 (0.4) 1.29 (0.4) 27.27 (0.3)River Lee 5.96 (8.4) 7.37 (10.4) 31.57 (9.0) 565.12 (6.8)River Roding 2.84 (4.0) 0.76 (1.1) 4.82 (1.4) 138.55 (1.7)River Wandle 1.47 (2.1) 0.89 (1.3) 9.13 (2.6) 157.32 (1.9)Beverley Brook 0.45 (0.6) 0.29 (0.4) 2.42 (0.7) 49.80 (0.6)Ravensbourne R. 0.33 (0.5) 0.19 (0.3) 1.17 (0.3) 34.42 (0.4)River Thames 29.35 (41.5) 26.20 (37.1) 106.52 (30.3) 4,544.61 (54.9)Mogden STW 6.47 (9.2) 9.30 (13.2) 57.93 (16.5) 469.36 (5.7)Kew STW 0.20 (0.3) 0.22 (0.3) 1.69 (0.5) 33.26 (0.4)Beckton STW 9.48 (13.4) 10.04 (14.2) 67.52 (19.2) 1,121.07 (13.5)Crossness STW 3.33 (4.7) 6.84 (9.7) 32.41 (9.2) 626.73 (7.6)Long Reach STW 2.11 (3.0) 1.12 (1.6) 14.33 (4.1) 181.92 (2.2)North¯eet STW 0.43 (0.6) 0.17 (0.2) 0.87 (0.2) 12.93 (0.2)Tilbury STW 0.26 (0.4) 1.84 (2.6) 1.36 (0.4) 31.31 (0.4)Gravesend STW 1.74 (2.5) 0.24 (0.3) 1.95 (0.6) 17.59 (0.2)Basildon STW 0.24 (0.3) 0.35 (0.5) 2.72 (0.8) 25.78 (0.3)Canvey Island STW 0.18 (0.3) 0.46 (0.7) 0.79 (0.2) 12.53 (0.2)Southend STW 3.25 (4.6) 2.42 (3.4) 6.35 (1.8) 51.61 (0.6)Brittania Metals 0.06 (0.1) 0.20 (0.3) 0.49 (0.1) 0.20 (0.0)Shell Green Yd. 0.53 (0.8) 0.23 (0.3) 0.79 (0.2) 10.80 (0.1)Empire Paper Mills No data (0.0) No data (0.0) No data (0.0) 8.11 (0.1)Pur¯eet Mills No data (0.0) No data (0.0) No data (0.0) 6.00 (0.1)Cleanaway 0.06 (0.1) 0.22 (0.3) 0.36 (0.1) 1.00 (0.0)

Total 70.74 (100.0) 70.72 (100.0) 351.85 (100.0) 8,278.00 (100.0)

a The percentage contributions are shown in parentheses. See Fig. 1 for locations of sources.

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