Heavy metal contamination of brown seaweed and sediments from the UK
coastline between the Wear river and the Tees river
Lorenzo Giusti*
Department of Environmental Sciences, Faculty of Applied Sciences, University of the West of England, Frenchay Campus, Coldharbour Lane,
Bristol BS16 1QY
Received 1 December 1999; accepted 23 November 2000
Abstract
The concentration of Fe, Mn, Zn, Cu, Pb, Ni, Cr, Cd, and Ag were determined in the brown alga Fucus vesiculosus and intertidal surface
sediments from coastal locations of northeast England. Levels of heavy metals similar to those of polluted areas of the British coastline were
detected. There is evidence of contamination (especially with Zn and Pb) in sediments from sites affected by colliery spoil and from the Wear
estuary. The pelitic fraction ( < 63 mm) is usually more enriched in heavy metals, but it represents a very small percentage of the bulk samples.
The fine-grained sand is a very important repository of contaminants especially where particles of colliery spoil, secondary mineral, and
amorphous phases are present. Aqua regia-extracted Zn, Cu, and Pb in sediments are significantly correlated with those in seaweed. Despite
the closure of all base metal and coal mines, and the cessation of many industrial activities in the region, sediments and brown algae are
contaminated with heavy metals. The control site (Holy Island) and the Tees estuary appear to be the least affected. D 2001 Elsevier Science
Ltd. All rights reserved.
Keywords: Heavy metals; Seaweed; Sediment; Estuarine and coastal pollution
1. Introduction
For many centuries, the economic development of the
northeast of England has been strongly linked to base
metal mining in the Pennines and to coal mining in the
Durham and Northumberland Coalfields. Urbanised indus-
trial centres grew mainly around the estuaries of the Tyne
River, the Wear River, and the Tees River (Fig. 1). The
production of iron and steel, and shipbuilding, were
located on the Tyne and Wear estuaries, whereas the
petrochemical industry developed on the Tees mouth. All
coal mining, heavy metal mining, and shipbuilding activ-
ities have now ceased, and steel production has been
scaled down. As a result, there has been a significant
reduction in industrial discharges into the local estuaries
and coastal waters. Domestic sewage, previously dis-
charged untreated into the rivers, has been largely diverted
to treatment plants located on or near the coast.
With the exception of Holy Island, which consists of
sandstone intruded by a quartz±dolerite dyke, the coastline
sampled in this study is characterised by magnesian lime-
stone cliffs of Permian age overlain by Pleistocene glacial
deposits. The beaches are mostly composed of relatively
coarse material (boulders, cobbles, gravel, pebbles, and
sand). Natural clastic material eroded from the cliffs is mixed
with alluvium carried by the local rivers and drifted south-
ward by tidal currents. At sites such as Horden, Easington,
and Blackhall Rocks, millions of tonnes of coal waste were
dumped along the coast (Norton, 1985). In some cases, the
colliery spoil has been reworked into terraces where weath-
ering processes have produced clay minerals and iron oxide
coatings on sand particles (Humphries, 1996).
Large volumes (presently about 300,000 m3 day ÿ 1) of
minewater are still being pumped into the River Wear and its
tributaries in order to prevent groundwater rebound
(Younger, 1995). This is equivalent to about 15% of the
average Wear River flow. The alluvium of the main river
systems of this region has been contaminated by historic
mining, especially of minerals such as galena (PbS), spha-
lerite (ZnS), cerussite (PbCO3), smithsonite (ZnCO3), pyrite
(FeS2), fluorite (CaF2), and baryte (BaSO4; Dunham, 1934).
0160-4120/01/$ ± see front matter D 2001 Elsevier Science Ltd. All rights reserved.
PII: S0 1 6 0 - 4 1 2 0 ( 0 0 ) 0 0 11 7 - 3
Tel.: +44-117-344-2487; fax: +44-117-344-2904.
E-mail address: [email protected] (L. Giusti).
www.elsevier.com/locate/envint
Environment International 26 (2001) 275±286
The aim of this work was to find out whether changes in
economic development and recent cleanup measures have
produced an improvement in environmental conditions in
the marine environment. The main objective was an assess-
ment of the present heavy metal concentration in sediments
and in the brown alga Fucus vesiculosus. Signs of recovery
Fig. 1. Map of the northeast of England and sampling sites.
L. Giusti / Environment International 26 (2001) 275±286276
of macroalgal populations in the Tyne, Wear, and Tees
estuaries have recently been reported (Hardy et al., 1993).
Sediment samples have been traditionally used in sedi-
mentological and geochemical exploration studies, and over
the past few decades they have also been extensively
analysed to assess anthropogenic impacts in the aquatic
environment. Unpolluted marine and freshwater sediments
from many sites around the world generally contain less
than 50 mg kgÿ 1 Zn, up to 20 mg kgÿ 1 Cu, between 2
and 50 mg kgÿ 1 Pb, up to about 100 mg kgÿ 1 Ni, less
than 60 mg kgÿ 1 Cr, and less than 1 mg kgÿ 1 Cd (Moore
and Ramamoorthy, 1984; Bryan and Langston, 1992).
Typical background Ag concentration in surface sediments
is about 0.1 mg kgÿ 1 and in polluted estuaries this metal
normally ranges up to 5 mg kgÿ 1 (Luoma et al., 1995).
Unfortunately, the concentration of trace metals in sedi-
ments does not provide sufficient information on metal
availability to the biota living in it or in the overlying water
column. Nonetheless, trace metals present in the water
column are transferred to the sediments especially by
adsorption onto suspended material and deposited to the
seabed. Estuaries and coastal areas are thus the largest
repositories of contaminants. Detritus-feeding organisms
are directly exposed to sediment-bound metals. Many
workers have assessed environmental conditions and metal
bioavailability by means of biomonitors such as seaweed
and mussels.
Some of the lowest heavy metal concentrations (in mg
kgÿ 1 dry weight) found in F. vesiculosus were reported by
Riget et al. (1997) for the GodthaÊbs Fjord of west Green-
land, with particular reference to Zn (7.2±17.3 mg kgÿ 1),
Pb (0.3±0.4 mg kgÿ 1), and Fe (33±77 mg kgÿ 1). Other
elements reported in their study included Cr (0.6 mg kgÿ 1),
Cu (2.1±5.3 mg kgÿ 1), and Cd (0.5±3.9 mg kgÿ 1). These
values are quite low in comparison to those of F. vesiculosus
from other sites in North America and Europe not signifi-
cantly affected by local sources of metals. For example, up
to 400 mg kgÿ 1 Zn were found in the southern North Sea
(Dutton et al., 1973), and up to 514 mg kgÿ 1 Zn in the
Sannager Fjord of Norway (Pedersen, 1984). Iron is nor-
mally up to about 100±250 mg kgÿ 1 (Lunde, 1970; Preston
et al., 1972; Fuge and James, 1974; Phillips, 1979; SoÈder-
lund et al., 1988), but average Fe values of up to about 600
mg kgÿ 1 can be expected in the North Sea (Struck et al.,
1997); Pb is often more than 10 mg kgÿ 1, but it can be as
low as 0.1±0.2 mg kgÿ 1 in uncontaminated areas with low
Pb background values (Dutton et al., 1973; Stenner and
Nickless, 1975; Phillips, 1979). Cu is rarely found to be
more than about 50 mg kgÿ 1 (e.g. Preston et al., 1972;
Fuge and James, 1974; Forsberg et al., 1988). The few Cr
determinations reported in the literature for uncontaminated
locations are usually less than 1 mg kgÿ 1 (Forsberg et al.,
1988; Riget et al., 1997). Higher Cr levels (about 10 mg
kgÿ 1) were found by Jayasekera and Rossbach (1996) in F.
vesiculosus from the North Sea. British coastal areas in the
North Sea do not normally exceed 1 mg kgÿ 1 Ag, and most
of the reported values are in the range of 0.1±0.7 mg kgÿ 1.
Similar Ag values were given by Preston et al. (1972) for
coastal sites on the Atlantic side of the British Isles. The
latter study also gave a range of about 1±20 mg kgÿ 1 Ni
for selected locations around the British coastline, with a
geometric mean of about 6 mg kgÿ 1.
There is evidence of seasonal variations of trace metal
concentration in macroalgae (Bryan and Hummerstone,
1973; Fuge and James, 1973, 1974; Young, 1975), espe-
cially for Mn, Fe, Zn, Cu, Cd, Co, and Al. The general trend
appears to be an increase in concentration in the winter and
early spring, and minimum concentrations in the summer
and autumn.
Samples of mussels from Tees mouth and Holy Island
have been analysed during a survey of the UK coastline of
the North Sea (Widdows et al., 1995), but there is limited
published information on heavy metals in seaweed from the
stretch of coastline comprised between the Wear River and
the Tees River. Also, the author is not aware of any
published report on combined studies of local biomonitors
and sediments. This paper reports the trace metal concentra-
tions in the seaweed F. vesiculosus and in sediments from
coastal sites of northeast England. The data on seaweed are
also compared with information about the common mussel
Mytilus edulis obtained in a parallel investigation (Giusti et
al., 1999).
2. Materials and methods
2.1. Sampling methods
Seaweed samples were collected during the winter
1997±1998 from the upper to middle tidal area at 17 sites
(Fig. 1): Roker North Pier, Roker estuary, Easington,
Horden, Blackhall Rocks, Middleton, North Gare, five sites
at Bran Sands, and four sites at Holy Island. Holy Island
was chosen as a control location as the main activities on
this island are fishing and tourism, and because it is
situated off the coast of a rural part of Northumberland.
The beaches of Whitburn, Easington, Horden, and Black-
hall Rocks have been heavily impacted by coal waste
dumping until 1993, when mining activities ceased. Bran
Sands was chosen because it is located downstream of a
very industrialised area.
At each site, a composite sample of seaweed was
obtained by combining the most recent 8±10 cm of fronds
removed from 20±30 randomly chosen plants. Metal con-
centrations in F. vesiculosus have been reported to be
normally lower in the growing tips than in older stalky
growth (e.g. Bryan and Hummerstone, 1973; Forsberg et al.,
1988). If typical growth rates of 2±3 cm month ÿ 1 are
assumed (Knight and Parke, 1950), the samples collected in
this study would give an integrated concentration of heavy
metals for a time span of about 3±5 months. The seaweed
was cleaned in the field as much as possible with marine
L. Giusti / Environment International 26 (2001) 275±286 277
water, placed in polyethylene bags containing seawater from
the local environment, and taken to the laboratory after a
few hours.
Intertidal surface (top 5 cm) sediments were collected at
eight of the above sites, namely: Holy Island (Site 1), Roker
estuary, Easington, Horden, Blackhall Rocks, Middleton,
North Gare, and Bran Sands (Site 13). At each site, three
samples were taken within an area of about 10 m2. They
were removed with a polyethylene scoop and immediately
wet-sieved with marine water to separate the pelite ( < 63
mm) and the fine-grained sand (more than 63 mm to less than
180 mm). Large detritus was separated by sieving through 2-
mm sieves. The sediment fractions were transferred to
polyethylene bottles and carried to the laboratory together
with the bags of seaweed. Additional samples were sieved
to determine the sediment grain size distribution.
The pelitic fraction is usually the main scavenger of
heavy metals. However, heavy metals can be present in
more coarse-grained sediment fractions, especially in
regions heavily impacted by human activities. Microscopic
observations of our samples have shown that oxide coatings
and particles of coal and shale are often present in the fine-
grained sand. Also, as indicated in Table 1, fine-grained
sand represents about 35±49% by weight of each sample,
whereas the pelite is in the range of 0±6.5%.
2.2. Analytical methods
2.2.1. Seaweed
On arrival to the laboratory, the seaweed was briefly
washed with deionised water, dried at 105°C for 48 h,
cooled, weighed, and ashed at 475°C in a muffle furnace
for 24 h (Fuge and James, 1973). From each sample, three
5-g aliquots of the ashed material were kept in 50-ml glass
beakers with 20 ml aqua regia (5 ml of 16 M HNO3 and 15
ml of 16 M HCl) for 48 h. They were later refluxed on a hot
plate, and diluted to 50 ml with deionised water.
2.2.2. Sediment
Sediments were dried in the oven at 105°C for 48 h.
Three aliquots of 1 g of each dry sediment fraction were
separated. The sediment aliquots were prepared for diges-
tion by grinding them to a fine powder with an agate mortar
and pestle, and ashed at 475°C in a muffle furnace for 2 h.
This step allowed the determination of the organic content
Table 2
Average recovery of metals in Standard Reference Material NIES No. 9 Sargasso seaweed
Element
NIES 9
(certified value) This study
Recovery
(%) n
Fe 187 � 6 172 � 4 92.0 6
Mn 21.2 � 1.0 20.4 � 0.5 96.2 6
Zn 15.6 � 1.2 13.1 � 0.7 84.0 6
Cr 0.2a 0.27 � 0.06 6
Cu 4.9 � 0.2 4.8 � 0.2 98.0 6
Pb 1.35 � 0.05 1.40 � 0.04 103.7 6
Ni b
Cd 0.15 � 0.02 0.17 � 0.02 113.3 6
Ag 0.31 � 0.02 0.33 � 0.05 106.5 6
Concentrations are quoted as mg/g dry weight.
n = number of replicates.a Reference value (not certified).b No reference or certified value reported.
Table 1
Grain size distribution (in wt.%) of sediment from coastal sites of northeast England
Site
% gravel
( > 2 mm)
% coarse/
medium sand
( < 2 mm, > 180 mm)
% fine sand
( < 180 mm, > 63 mm)
% pelite
( < 63 mm)
Holy Island 1.4 55.0 38.2 5.4
Whitburn 2.0 60.3 34.8 2.9
Roker (North Peer) 5.9 52.0 40.1 2.0
Roker (estuary) 4.6 40.4 48.5 6.5
Easington 23.2 38.2 38.6 0
Horden 15.7 35.0 49.3 0
Blackhall Rocks 5.4 50.0 42.6 2.0
Middleton 1.7 51.8 40.8 5.7
North Gare 2.2 51.9 41.5 4.4
Bran Sands 4.1 55.7 37.2 3.0
L. Giusti / Environment International 26 (2001) 275±286278
as percentage loss on ignition (% LOI). The aqua regia
digestion method was used on 0.500 � 0.002 g of the ashed
aliquots. Aqua regia digestion of sediments extracts only a
fraction of the major elements because silicates are not
completely dissolved with this method. However, most
heavy metals not bound to silicates are efficiently dissolved
(Ure, 1990). The method of standard addition was used to
correct for matrix effects. Salt matrix effects for Ag, Cd, Ni,
Pb, and Cu were overcome by using matrix modifiers.
All digest solutions were analysed, at least in duplicate,
by flame atomic absorption spectrophotometry (Varian
SpectrAA-10Plus) and by graphite furnace atomic absorp-
tion spectrophotometry (Varian SpectrAA-300 with GTA96
graphite tube atomiser). Metals analysed included Fe, Mn,
Zn, Cu, Pb, Ni, Cr, Cd, and Ag.
2.3. Quality control
The precision and recovery of the procedures were
checked using the following certified standard reference
materials: NIES No. 9 Sargasso seaweed, GBW07302
stream sediment, GBW07313 marine sediment, and
SRM2711 Montana soil. Blanks were run with each batch
of samples. All reagents were ultrapure and glassware/
plasticware/filters cleaned according to the method of Laxen
and Harrison (1981). Blank values were negligible in
comparison to the sample concentrations.
A comparison between certified values of Sargasso sea-
weed and those found in this study (Table 2) indicates that Fe,
Mn, Zn, and Cu concentrations in our samples may have been
underestimated by about 8%, 4%, 16%, and 2%, respectively,
whereas Pb, Cd, and Ag may have been overestimated by
about 4%, 13%, and 7%, respectively. No correction was
applied to our data. Replicate analyses gave coefficients of
variation of less than 5% for all elements except Cr, Cd, and
Ag for which variations were up to 11%. The seaweed fronds
from each location were manually mixed, and the resulting
composite sample was separated into three subsamples before
ashing took place. The standard deviations listed in Table 4
refer to these three subsamples. Therefore, the values of
standard deviation are a combination of analytical error and
of the natural variability in metal concentration at a specific
Table 4
Concentration of metals (mg kgÿ 1 dry weight) and percentage ash (at 450°C) of F. vesiculosus
No SITE Fe Mn Zn Cu Pb Ni Cr Cd Ag
%
ash
1 Holy Island 65.0 � 4.1 276.2 � 21.6 14.9 � 1.1 5.7 � 1.2 0.1 0.3 � 0.1 0.8 � 0.1 0.28 � 0.06 1.1 � 0.4 20
2 Holy Island 94.7 � 6.2 479.4 � 32.0 17.7 � 2.4 5.6 � 0.8 0.3 0.4 1.1 � 0.1 0.45 � 0.05 1.0 � 0.1 21
3 Holy Island 273.0 � 12.0 353.9 � 24.3 12.9 � 0.8 4.8 � 2.0 0.6 � 0.1 0.4 1.2 � 0.2 0.33 � 0.12 0.9 � 0.2 22
4 Holy Island 616.1 � 8.6 778.4 � 38.8 16.9 � 2.0 9.4 � 1.3 1.1 � 0.1 0.7 � 0.2 1.8 � 0.3 0.22 � 0.07 1.4 � 0.5 23
5 Whitburn 636.5 � 14.5 490.6 � 22.0 560.2 � 17.4 29.6 � 4.6 3.6 � 0.4 3.0 � 0.4 5.0 � 0.6 2.53 � 0.18 2.6 � 1.3 20
6 Roker 300.3 � 16.6 360.0 � 36.1 511.4 � 25.3 23.3 � 2.2 5.9 � 0.4 20.2 � 1.9 3.0 � 0.4 2.41 � 0.31 1.6 � 0.4 22
7 Roker 490.6 � 41.2 176.0 � 12.6 740.0 � 20.7 30.7 � 1.3 7.8 � 2.5 30.6 � 2.4 3.6 � 1.1 2.02 � 0.81 1.8 � 0.8 22
8 Easington 1208.9 � 98.2 80.6 � 4.2 1015.5 � 54.4 50.6 � 10.6 12.1 � 4.0 36.0 � 5.1 3.8 � 2.3 10.03 � 4.12 4.2 � 0.6 20
9 Horden 920.1 � 51.3 105.4 � 18.6 904.8 � 33.3 35.9 � 6.8 8.4 � 4.1 70.5 � 8.9 3.5 � 2.2 9.18 � 2.06 3.8 � 1.5 20
10 Blackhall Rock 815.1 � 64.6 107.9 � 15.3 140.3 � 16.7 20.2 � 4.8 5.7 � 3.2 32.1 � 3.2 2.6 � 0.4 2.16 � 1.14 3.0 � 1.4 21
11 Middleton 1027.0 � 81.2 83.0 � 9.9 45.4 � 2.2 9.7 � 4.7 0.6 � 0.2 0.4 � 0.1 1.1 � 0.2 0.14 � 0.05 1.8 � 0.3 28
12 North Gare 80.4 � 3.8 31.6 � 3.9 23.6 � 2.6 8.4 � 2.5 4.9 � 0.8 0.7 � 0.1 2.1 � 0.2 0.21 � 0.03 1.2 � 0.4 23
13 Bran Sands 658.8 � 28.9 136.2 � 14.4 62.9 � 3.1 15.8 � 2.4 3.2 � 1.0 2.9 � 0.3 2.4 � 0.2 0.06 � 0.01 1.3 � 0.9 22
14 Bran Sands 123.2 � 16.2 118.1 � 9.1 46.8 � 5.8 12.3 � 1.1 1.1 � 0.5 2.1 � 0.1 1.2 0.04 � 0.01 1.1 � 0.1 28
15 Bran Sands 130.9 � 9.1 93.5 � 6.1 42.1 � 6.8 10.0 � 0.7 2.0 � 0.7 1.6 1.2 � 0.1 0.04 � 0.01 1.3 � 0.2 26
16 Bran Sands 95.6 � 8.1 55.2 � 3.0 36.2 � 2.3 13.9 � 1.2 0.7 � 0.1 1.5 1.0 � 0.1 0.03 1.1 � 0.1 26
17 Bran Sands 67.5 � 6.1 18.8 � 2.2 41.8 � 4.9 10.2 � 0.8 0.5 � 0.1 0.6 � 0.1 0.9 � 0.2 0.02 0.9 � 0.2 29
Table 3
Average recovery of metals in standard reference sediments GBW07302 (stream sediment), GBW07313 (marine sediment), and SRM2711 (Montana soil)
Element
GBW07302
(certified value) This study
Recovery
(%)
GBW07313
(certified value) This study
Recovery
(%)
SRM2711
(certified value) This study
Recovery
(%) n
% Fe a 1.29 � 0.02 a 3.82 � 0.02 2.89 � 0.06 2.94 � 0.16 101.7 8
Mn 240 210 � 0.01 87.5 a 638 � 28 580 � 11 90.9 8
Zn 44 41.3 � 2.6 93.9 160 120 � 13 75.0 350.4 � 4.8 351.0 � 0.2 100.2 8
Cr 12.2 13.7 � 2.1 112.3 58.4 46.2 � 5.3 79.1 a 8
Cu 4.9 5.3 � 0.3 108.2 424 367 � 12 86.6 114 � 2 132 � 3.2 115.8 8
Pb 32 30.9 � 3.1 96.6 29.3 30.9 � 3.2 105.5 1162 � 31 1149 � 15 98.9 8
Ni 5.5 4.3 � 0.3 78.2 150 140 + 2 93.3 20.6 � 1.1 14.7 � 3.3 71.4 8
Cd 0.065 0.021 � 0.011 32.3 a 41.70 � 0.25 45.60 � 2.40 109.4 8
Ag 0.066 0.052 � 0.012 78.8 a 4.63 � 0.39 3.15 � 0.78 68.0 8
Concentrations are quoted as mg kgÿ 1, with the exception of Fe for which a percentage value is given.
n = number of replicates.a No certified value reported.
L. Giusti / Environment International 26 (2001) 275±286 279
geographical location. For the most abundant elements (Fe,
Mn, Zn) the coefficients of variation were up to 18% and
usually less than 10%, whereas larger coefficients (up to 40±
67%) were typical of less abundant trace elements.
The recovery of metals in standard reference sediments by
the aqua regia digestion method was normally in the range of
78±116% of the certified total concentrations (Table 3). The
most notable exception was that of Cd as only 32% was found
for GBW07302. However, the Cd recovery in SRM2711 was
109.4%. This points to some problems in the detection of the
low Cd levels present in the former standard and explains the
poor Cd detection in some of our samples.
3. Results and discussion
3.1. Seaweed
The most abundant elements found in the seaweed
material analysed are Fe, Mn, Zn, and Cu, and the least
Table 5
Concentration of metals (in mg kgÿ 1 dry weight, except for Fe, which is expressed as percent) and % LOI in sediments
No Site and size fraction Fe Mn Zn Cu Pb Ni Cr Cd Ag % LOI
1 Holy Island
< 180 mm 1.04 � 0.13 172 � 30 40.7 � 9.7 34 � 7 10 � 3 15 � 2 18 � 4 nd 13.3 � 1.9 1.06 � 0.19
< 63 mm 1.26 � 0.16 207 � 40 11.3 � 2.0 12 � 3 20 � 2 23 � 3 15 � 2 nd 16.9 � 1.8 0.49 � 0.03
7 Roker
< 180 mm 3.14 � 0.86 1787 � 259 527 � 75 54 � 22 653 � 58 40 � 5 58 � 15 3.1 � 0.6 6.6 � 0.6 0.76 � 0.07
< 63 mm 4.46 � 0.30 2597 � 258 1284 � 272 110 � 30 1137 � 197 75 � 9 87 � 12 5.3 � 0.9 7.5 � 0.9 0.92 � 0.03
8 Easington
< 180 mm 3.36 � 1.79 578 � 203 2230 � 496 230 � 57 643 � 133 61 � 16 13 � 2 11.2 � 2.9 5.6 � 1.3 2.53 � 0.40
9 Horden
< 180 mm 4.47 � 2.02 625 � 192 1962 � 279 172 � 75 880 � 272 77 � 22 16 � 3 6.1 � 3.5 3.8 � 0.7 1.17 � 0.22
10 Blackhall Rock
< 180 mm 4.25 � 0.47 993 � 117 496 � 155 209 � 60 414 � 69 51 � 6 20 � 5 2.2 � 0.82. 4.7 � 1.1 2.38 � 1.11
< 63 mm 3.08 � 0.41 1209 � 256 560 � 111 113 � 27 628 � 79 66 � 10 43 � 9 3 � 0.4 4.2 � 1.4 1.48 � 0.13
11 Middleton
< 180 mm 2.78 � 0.66 879 � 151 327 � 76 25 � 9 226 � 55 60 � 19 35 � 5 2.2 � 0.4 4.8 � 0.9 0.53 � 0.03
< 63 mm 4.30 � 0.74 1271 � 195 301 � 97 161 � 28 286 � 60 105 � 20 52 � 10 2.8 � 0.9 7.5 � 1.6 0.59 � 0.08
12 North Gare
< 180 mm 1.10 � 0.27 317 � 45 52 � 10 9 � 2 25 � 4 12 � 4 10 � 2 nd 4.0 � 1.1 0.43 � 0.02
< 63 mm 1.56 � 0.56 393 � 80 151 � 35 141 � 20 47 � 6 19 � 7 18 � 3 nd 4.9 � 1.8 1.68 � 0.21
13 Bran Sands
< 180 mm 1.77 � 0.21 394 � 44 116 � 49 28 � 9 41 � 4 14 � 3 12 � 2 nd 15.0 � 2.7 0.59 � 0.08
< 63 mm 3.24 � 0.45 1126 � 141 113 � 68 99 � 11 156 � 13 27 � 4 35 � 5 nd 19.3 � 5.7 1.07 � 0.09
Tyne estuarya ( < 100 mm) 2.82 395 421 92 187 34 46 2.17 1.55
Continental crustb 4.32 716 65 25 14.8 56 126 0.01 0.07
Guideline valuesc 150± 410 34± 270 46.7±218 20.9± 51.6 81± 370 1.2± 9.6 1.0±3.7
nd = not detected.a Bryan and Langston, 1992 (HNO3 digestion).b Wedepohl, 1995 (HNO3/H2O2 digestion).c Long et al., 1995.
Fig. 2. Relationship between the concentration of (a) Pb and Cu, and (b) Zn and Cu in F. vesiculosus. For n = 17 at P < .01, the critical r is .606. The error bars
combine analytical error and natural variations of sample concentration at each site.
L. Giusti / Environment International 26 (2001) 275±286280
abundant are usually Cd and Ag (Table 4). However, Cd and
Ag appear quite concentrated in samples from Easington
and Horden (about 9±10 and 4 mg kgÿ 1, respectively), and
Ni (about 20±70 mg kgÿ 1) in samples from Roker and
Blackhall Rocks. The concentration sequence of the most
abundant elements is usually Fe > Mn > Zn > Cu. However,
at Holy Island, Mn > Fe, and at Whitburn, Roker, Easington,
Blackhall Rock, and one site at Bran Sands (No. 17),
Zn > Mn. The highest Mn enrichment in seaweed is at Holy
Island (276±778 mg kgÿ 1), which is also characterised by
the lowest concentrations of Zn (13±18 mg kgÿ 1), Pb
(0.1±1.1 mg kgÿ 1), and Ni (0.3±0.7 mg kgÿ 1). At Bran
Sands, Fe and Mn enrichment in seaweed decreases sig-
nificantly from Sites 13 to 17, going downstream along the
southern part of the Tees estuary. There is also an apparent
parallel decrease in all other trace metals, though this is not
statistically significant.
A significant correlation ( P < .001) exists between Fe
and Ag (r =.826), Zn and Cu (r =.957), Zn and Pb (r =.887),
Zn and Cr (r =.830), Zn and Ag (r =.822), Cu and Pb
(r =.910), Cu and Cr (r =.839), Cu and Ag (r =.881), and Pb
and Cr (r =.780). No element was correlated with Mn or
with ash content. Fig. 2a,b illustrates examples of these
statistical relationships.
The possibility that seaweeds may have been contami-
nated with metals scavenged by iron oxyhydroxides present
in fine sediment particles was considered and tested in two
ways: (1) assuming that all the iron in the seaweed samples
originated from sediment contamination, and (2) comparing
metal/Fe ratios in sediment and seaweed. Potential contam-
ination from sediment particles appears theoretically possi-
ble only for Pb.
3.2. Sediment
Observations of sediment samples with a binocular
microscope revealed that the sediments were largely com-
posed of quartz, carbonates, and feldspars, some coated by
oxides, and mixed with shell debris. Opaque minerals
(mostly pyrite) were present. Coal particles were also
common in all sediments. Very small grains could not be
identified. The fine sand fraction of surface sediments was
available from eight of the sites investigated, whereas the
pelitic fraction was available in sufficient amount only at six
of the sites sampled: At Easington and Horden, only sand
and gravel were present in the sediment (Table 1).
The concentrations (mean � S.D.) of heavy metals in
sediments are given in Table 5. Iron is the most abundant
(about 1±4.5 wt.%) of the metals analysed, and, exception
made for Blackhall Rocks, it is more enriched in the pelitic
fraction. Manganese is always the most abundant of the
trace metals in the pelite, with mean values ranging from
207 mg kgÿ 1 at Holy Island to 2597 mg kgÿ 1 at Roker. In
most cases, the least abundant elements are Ag and Cd.
For comparative purposes, Table 5 lists also the heavy
metal concentrations in sediments of the Tyne estuary (Bryan
and Langston, 1992) and in the continental crust (Wedepohl,
1995). Unfortunately, data sets cannot be readily compared
as different digestion methods were used on different sedi-
ment fractions. More meaningful estimates of sediment
contamination can be made with reference to background
values from the same area investigated. Rowlatt and Lovell
(1994) reported median values of Pb (11 mg kgÿ 1), Zn (15
mg kg ÿ 1), and Cr (18 mg kg ÿ 1) for < 2-mm seabed
sediments analysed in the Joint Monitoring Group Sediment
Baseline study. They studied the shelf region of the North
Atlantic and its marginal areas, including the North Sea. Pb,
Zn, and Cr background values from a sediment core taken 16
km off the Tyne estuary were 12, 38, and 45 mg kgÿ 1,
respectively (Rowlatt and Lovell, 1994). In general, these
authors found that the seabed sediments of Tyneside and
Teesside were above these background values. Even though
a direct comparison with our data cannot be made due to the
different size range of the sediment fraction analysed, these
values can be referred to as baseline concentrations.
The sediment quality guideline values proposed by Long
et al. (1995) are also listed in Table 5, as they can be used to
estimate the probability that adverse effects to the local biota
may occur. These effects are possible within the concentra-
tion range indicated, and frequently observed at higher
concentrations. These values refer to bulk sediments
digested with strong reagents and cannot be compared with
Table 7
Correlation coefficient matrix for heavy metals in aqua regia-digested
sediments ( < 63 mm fraction)
Fe Mn Zn Cu Pb Ni Cr Cd Ag % LOI
Fe .864 .666 .515 .689 .813 .784 .716 ÿ .152 .184
Mn .916 .322 .921 .612 .926 .910 ÿ .228 ÿ .084
Zn .232 .982 .516 .856 .801 ÿ .395 .045
Cu .212 .491 .253 ÿ .110 ÿ .545 .395
Pb .549 .868 .762 ÿ .386 .032
Ni .685 .000 ÿ .400 ÿ .300
Cr .740 ÿ .332 ÿ .173
Cd .460 ÿ .268
Ag ÿ .472
% LOI
Critical r = .468 at P < .05, or r = .590 at P < .01 (n = 18).
Table 6
Correlation coefficient matrix for heavy metals in aqua regia-digested
sediments ( < 180 mm fraction)
Fe Mn Zn Cu Pb Ni Cr Cd Ag % LOI
Fe .538 .649 .761 .833 .871 .247 .358 ÿ .425 .539
Mn .089 .141 .548 .401 .881 ÿ .370 ÿ .329 .055
Zn .793 .826 .761 ÿ .134 .900 ÿ .394 .579
Cu .716 .706 ÿ .205 .651 ÿ .369 .901
Pb .829 .308 .581 ÿ .510 .453
Ni .207 .469 ÿ .567 .468
Cr ÿ .430 ÿ .145 ÿ .228
Cd .134 .000
Ag ÿ .228
% LOI
Critical r = .404 at P < .05, or r = .515 at P < .01 (n = 24).
L. Giusti / Environment International 26 (2001) 275±286 281
our data listed in Table 5. However, it is possible to calculate
minimum bulk metal concentration, taking into account the
percentage of fine-grained sand and pelite, and assuming no
metal contribution from gravel and coarse/medium sand.
This means a dilution effect of about 50±60%. The recal-
culated sediment levels of Zn, Pb, Ni, Cd, and Ag for Roker,
Easington, Horden, Blackhall Rocks, and Middleton are
either within or higher than the guideline values of Long
et al. (1995).
In our study, the surface sediment at control Site 1
(Holy Island) has lower or similar Pb, Zn, and Cr con-
centrations than the background values of Rowatt and
Lovell (1994). Background Cr is exceeded only at Roker
and Middleton. All other sites show Zn and Pb contamina-
tion. Iron is significantly ( P < .01) correlated with many
elements in the fine-grained sand, including Mn, Zn, Cu,
Pb, and Ni, and with Mn, Zn, Pb, Ni, Cr, and Cd in the
pelitic fraction (Tables 6 and 7). Some of the deviations
from a linear trend are due to metal enrichment of sedi-
ments at some of the sites investigated. More specifically,
Pb contamination in the pelitic and sand fractions can be
inferred for Roker, Easington, Horden, and only for the
pelitic fraction at Blackhall Rocks. Both fractions are
enriched in Ag at Holy Island and Bran Sands. Examples
of scatter plots of Fe concentration (expressed as percent)
vs. the concentration of other metals (in mg kgÿ 1) are
shown in Fig. 3. The scatter found for the fine-grained
sand fraction is usually due to high metal values (espe-
cially Zn, Pb, and Cd) at Easington and Horden. Similar
trends were observed when these metals are plotted against
Mn (Fig. 4). Zinc enrichment at Easington and Horden is
also shown by the trends in the Zn vs. Pb and Zn vs. Cr
scatter diagrams (Figs. 5 and 6, respectively). If the
samples from Horden and Easington are excluded from
the correlation calculations, a highly significant ( P < .001)
correlation would be observed between Fe and Zn
(r =.872), Mn and Zn (r =.874), Mn and Pb (r =.968),
and Mn and Cd (r =.714) in the sand fraction. Silver is
negatively correlated to all elements except Cd. This may
be partially due to the similar speciation of these two
metals in aquatic environments.
The organic matter content (as % LOI) in sediments is
generally in the range 0.4±3.6%. The relatively higher
percentage found at Easington, Horden, North Gare, and
Fig. 4. Scatter plot of (a) Mn vs. Pb and (b) Mn vs. Zn concentration in sediment fractions (pelite and fine sand) from the coast of northeast England.
Fig. 3. Scatter plot of (a) Fe vs. Pb and (b) Fe vs. Zn concentration in sediment fractions (pelite and fine sand) from the coast of northeast England.
L. Giusti / Environment International 26 (2001) 275±286282
especially at Blackhall Rocks are partly due to the presence
of small particles of coal, especially in the sand fraction.
Copper shows the highest positive correlation with %
LOI (r =.901, P < .01) in the fine-grained sand (Fig. 7 and
Tables 6 and 7). The strong affinity of Cu for organic
material in sediments is quite well known (e.g. Luoma
and Bryan, 1981; Davies-Colley et al., 1984; Borg and
Jonsson, 1996), although other phases such as Fe±Mn
oxides and hydroxides can also be good Cu scavengers.
Other metals positively correlated with organic matter in the
sand fraction are Fe, Zn (both at P < .01), Pb, and Ni (both at
P < .05).
3.3. Comparison between heavy metal concentrations in
sediments and marine organisms
The aqua regia-extracted Zn, Cu, and Pb in sediments
are positively correlated ( P < .05) with those of F. vesicu-
losus, as shown for example in Fig. 8 for Zn. A sig-
nificant correlation ( P < .05) was also found for Ni
extracted from the sand fraction. These relationships
indicate that some of the metals held in the sediment
may become available to the seaweeds. This may occur,
for example, when Fe and/or Mn are remobilised (together
with the scavenged trace metals) from anoxic sediments
back into the water column. The biodegradation of organic
material will also cause a release of heavy metals to
marine water. Even though Ag is widely distributed in
all sediments, and especially those of Holy Island and
Bran Sands, this metal is more accumulated in F. vesicu-
losus at sites affected by mining activity.
Metal concentrations in surface sediments (Table 5) and
in the soft tissue of the mussel M. edulis (Giusti et al., 1999)
appear to be generally unrelated. It is possible that although
Fe oxides/hydroxides and organic matter can bind high
Fig. 7. Relationship between Cu concentration and organic matter content
(as % LOI) in marine sediments from the northeast coast of England. The
regression line and the correlation factor (r =.901) refer to the sand fraction
(full circles). The empty circles represent the pelitic fraction.
Fig. 8. Relationship between Zn concentrations in F. vesiculosus and Zn in
aqua regia extracts of sediment fractions from the same sites in northeast
England (n = 14, P < .05).
Fig. 6. Plot of Zn vs. Cr concentration in sediments from the coast of
northeast England, showing the Zn enrichment of sand samples from
Easington and Horden.
Fig. 5. Plot of Zn vs. Pb concentration in sediment fractions from the coast
of northeast England. The pelite is represented by empty circles, the fine
sand by full circles. The regression line and the correlation factor (r =.965)
refer to the pelitic fraction only (n = 18). For n = 18, at P < .01, the critical r
is .590.
L. Giusti / Environment International 26 (2001) 275±286 283
concentrations of trace metals, they also cause a reduction in
trace metal bioavailability in the digestive tract of mussels
(Luoma and Bryan, 1978; Langston, 1980). This is more
likely to result in a correlation of heavy metals in mussels
with the ratio metal/Fe in sediment. In our study, we found a
significant positive correlation (at P < .01) between Pb in
mussels and the Pb/Fe ratio in the aqua regia extracts of
surface sediments.
3.4. Metal pollution index (MPI)
The overall metal burden of F. vesiculosus was compared
with the total aqua regia-extracted metal content in sedi-
ments, using the MPI calculated with the formula (Usero et
al., 1996, 1997):
MPI � �M1 �M2 �M3 � . . .�Mn�1=n
where Mn is the concentration of metal n expressed in mg
kgÿ 1 of dry weight.
Lower MPI in algal material is to be expected, as
accumulated heavy metals derive only from dissolved
species present in marine water. Sediments are normally
larger repositories of contaminants. However, the variations
in algal MPI between sites appear to be similar, though of a
different order of magnitude, to the variations of sediment
(fine sand) MPI. Fig. 9 shows that the two sets of MPI are
significantly correlated (r =.959, n = 8). The correlation
between pelite MPI and algal MPI (n = 6) is not significant.
Both monitoring methods (i.e. with sediment and with
algae) have thus proved to be quite effective in highlighting
metal concentration gradients.
3.5. Comparison between heavy metal concentrations in
seaweeds and mussels
Along the coastline studied, the concentration of Cu, Zn,
Pb, Cd, and Ag in seaweed is usually lower than in soft
tissue of mussels (Giusti et al., 1999) from the same sites.
Only at Roker was the Zn accumulated by F. vesiculosus
higher than in M. edulis. Nickel is more abundant in
seaweeds than in mussels from Holy Island, Roker, and
Blackhall Rocks, and Cr levels are higher in seaweeds at
Holy Island and Middleton.
Our seaweed samples showed a more pronounced accu-
mulation of Mn than the mussels from the same sites (Giusti
et al., 1999). This appears to be quite commonly observed
elsewhere. For example, the average North Sea and Baltic
Sea Mn concentration in F. vesiculosus is 356 and 748 mg
kg ÿ 1 dry weight, respectively, which is one order of
magnitude higher than in mussels from the same areas, i.e.
29.7 and 47.2 mg kgÿ 1, respectively (Struck et al., 1997).
High levels of Mn or Zn in water are known to suppress
the accumulation of trace amounts of dissolved Cd, Co, Ni,
Zn, or Mn in seaweed as a result of competition for
available binding sites (Bryan et al., 1985). It is thus
possible that the low Zn, Ni, and Cd values in seaweeds
at Holy Island might be caused by the high accumulation of
Mn. Also, the general lack of a significant correlation
between Mn and any of the other metals analysed in
seaweed may be partially due to the same reason. In our
study, the significant positive correlation between Zn and
Cu in seaweed rules out large competition effects between
these two metals.
4. Conclusions
Given the seasonal and short-term variability of estuar-
ine and coastal environments, large variations in dis-
solved and particulate metal concentrations should be
expected, thus making the interpretation of heavy metal
distribution gradients quite problematic. Nonetheless,
some conclusions can be drawn based on the combina-
tion of information obtained from seaweed, sediment, and
previously published data on heavy metals in mussels
from the same sites.
(i) Seaweeds from Whitburn, Roker, Easington, and
Horden, have a relatively high burden of Zn (511±1016
mg kgÿ 1), Cu (23±51 mg kgÿ 1), Cr (3.0±5.0 mg kgÿ 1),
and, at the latter three sites, of Ni (20±71 mg kgÿ 1) and Pb
(6±12 mg kgÿ 1). Also, Cd (6±10 mg kgÿ 1) and Ag (4 mg
kgÿ 1) are high at Easington and Horden. In general, these
Cd and Ag levels are comparable to those of contaminated
estuarine and coastal sites around the UK. Seaweed at Holy
Island and Bran Sands appears to be the least enriched in
trace metals.
(ii) Concentrations of Pb, Zn, Cu, Cd, and Ag in F.
vesiculosus are usually lower than in M. edulis from the
same area, whereas Mn is normally an order of magnitude
higher in seaweed.
(iii) The fact that aqua regia-extracted Zn, Cu, and Pb in
sediments are positively correlated with the concentrations
of these metals in seaweed, but not to those in mussels,
suggests that metal uptake from ingested sediment is less
important than ingestion of dissolved metal species. This
conclusion can also be inferred on the basis of theFig. 9. Scatterplot of correlation between MPI of fine-grained sand and MPI
of F. vesiculosus.
L. Giusti / Environment International 26 (2001) 275±286284
significant correlation between MPI in sediment and MPI
in algae.
(iv) Sediments from Roker, Easington, Horden, Blackhall
Rocks, and Middleton have concentrations of Zn, Pb, Ni,
Cd, and Ag likely to cause adverse biological effects.
(v) The pelitic fraction is usually more enriched in heavy
metals, but it represents a very small portion of the sediment
samples (0±6.5% by weight). The fine-grained sand is also
a very important repository of contaminants, especially
when mixed with particles of colliery spoil and secondary
mineral and amorphous phases. Therefore, the normalisation
of bulk sediment composition based on the percentage of
pelite is not applicable to sediments of the area studied. This
is likely to be the case at other sites contaminated with waste
from mining activity or where secondary accumulation of
Fe and Mn compounds are common. Coatings of oxides,
hydroxide, or of organic matter can increase significantly
the concentration of heavy metals of particles larger than 63
mm. In this study, a stronger affinity of most metals for Fe
was found in the fine-grained sand fraction and for Mn in
the pelitic fraction. In both fractions, Cr is more strongly
correlated with Mn. The negative correlation between Ag
and Fe and between Ag and Mn reflects the affinity of silver
for organic fractions such as humic acids, and its tendency
to form chlorocomplexes in marine water.
(vi) Despite the closure of all base metal mines and coal
mines in the region studied, sediments are still contaminated
with heavy metals. The heavy metal burden of seaweed (and
mussels) at the sites investigated is similar to those of other
polluted areas of the British coastline. Silver enrichment in
seaweed is more pronounced at sites affected by past mining
activities, whereas the highest Ag concentrations in sedi-
ments were found at Holy Island and Bran Sands. It is
difficult at this stage to point to specific sources of Ag at
these two sites, but sewage is a likely source.
(vii) Our monitoring took place over a short period of
time and although seaweed samples give information relat-
ing to a number of months before sampling, further work is
necessary before firm conclusions can be drawn on the
apparent reduction of anthropogenic impact on the marine
environment at Teesside. As sedimentation rates can vary
considerably over the year, and dredging is routinely carried
out in the Wear and Tees estuaries, more systematic sam-
pling is necessary to confirm our preliminary conclusions.
One of the limitations of environmental impact studies
based on the analysis of tissue of biomonitors is the fact
that a significant proportion of the dissolved metals present
in surface water may be present as nonbioavailable organic
complexes, especially in estuarine areas and near industrial
and sewage outfalls. Iron is the only metal which is known
to become increasingly available to phytoplankton when
chelating agents such as ethylenediaminetetraacetate
(EDTA) are present (Luoma, 1983). If complexation with
strong organic ligands takes place, the metal burden found
in seaweed may not be proportional to the dissolved fraction
of metals in seawater. Other information such as salinity,
pH, concentration of humic and fulvic acids, and concentra-
tion of synthetic chelating agents is required to be able to
interpret more precisely any data of metal uptake from
solution by aquatic organisms.
Acknowledgments
The author is indebted to Arun Mistry and Peta Carter for
their technical support.
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