,
,
,,,,"
"
INTERNATIONAL COUNCIL FOR THE
EXPLORATION OF TUE SEA,"
SURFACE
C.M. 1993/E:28
Marine Environmental
Quality Committee/
Ref.Theme Session Q.
MICROlAYER CONTAMINATION ANO TOXIClTY IN THE NORTH SEA
PLYMOUTH NEAR-SHORE l<1ATERS.
ANO
J.J.CLEARY,I.R.B.MCFADZEN ANO L.O.PETERS.
NERC Plymouth Marine Laboratory, Prospeet Plaee, l<1est
Plymouth, PLI 30H., U.K.
Hoe,
ABSTRACT
A variety of chemical contaminants accumulate in the surface microlayer at
concentrations sometimes orders of magnitude greater than in subsurface
waters.Biota resident in the surface waters whether permanent,(the neuston),or
temporary, (eg. eggs and larvae of fish and erustaceans) ,may therefore be
exposed to much greater concentrations of toxieants than biota resident in the
subsurfaee .Also organisms resident in the littoral may be exposed to
microlayer deposited by the ebbing tide.To determine the extent to which the
surface microlayer is toxie to these early life stages, water sampies were
collected and tested for toxicity using larval bioassay.Cryopreserved ve1iger
1arvae of the Manila c1am (TapesphUippinarum) and Pacific oyster
(Crassostrea gigas) and yolk sac turbot larvae (Scophthalmus maximus) were
used to assess the toxicity of North Sea (German Bight) and Plymouth nearshore waters respectively.Chemical analyses revealed enhanced levels of metals
(Cu, Pb) ,organotins and polyaromatic hydrocarbons in the surface microlayer
compared with
near-surface bulk seawater (0.5m) .Bioassay results indicated
greater toxicity in --the microlayer--.than--subsurface,and strong correlation
between chemica1 contaminants and larval toxicity.
•
Microlayer studies provide a useful input to environmental assessment ,and
indi'cate .that the potential effects of contaminants at the sea surface may
pose-a serious threat to larval surviva1 and fisheries recruitment .
INTROOUCTION
The wor1d's oceans cover 70% of the earth's surface.The sea-surface microlayer
which occurs at the air-sea interface is the region through which all gaseous
and particu1ate matter must pass when exchanging between the atmosphere and
the ocean.The surface miero1ayer is not a clear1y defined slice of water since
microlayer thickness varies with the samp1ing device used (Garrett &
Ouce,l980). It is composed of lipids and other macromolecular components such
as polysaccharides, proteins and fatty acids, and has the capacity to
accumulate enhanced concentrations of chemicals compared to subsurface water
(Garrett,l967;Baier et a1.,1974).
1
~.
Tbe sea surfa=~ ~~s an important eoncentration point for both natural biogenie
organle films ~d~ for organie and metal eontaminants(Hardy,1982).Compared to
the bulk wa::E::- conly .& few eentimetres deep, the sea-surfaee mierolayer orten
eontains hig..~1:.r -enriched eoneentrations of both natural and anthropogenie
ehemieals
i~l~uding
polyehlorinated
biphenyls
(PCB's),polyaromatie
hydroearbons !?AAH's),and'potentially toxie traee metals (eg.Cu,Pb) and
organometals s-..ch .. as "i'BT, (Hardy et a1. ,1985a,1987, 1990; Cleary,1991;Hardy and
Cleary,1992).
The sea surf.;.:a .ls also a biologieally a'etive interface inhabited by high
densities of ni~=ro-organisms (baeterioneuston and phytoneuston) , small
erustaeeans c=d the eggs and larvae of fish and shellfish (zooneuston)
(Hardy ,1982) .Pe:.1~gie fish eggs can eoncentrate at the surface by floatation
due to their 1:.i.?~~ lipid eontent and positive buoyancy,and fish eggs, ,larvae
and fry ean ::-ell:~ain in 'the surfaee layer even in waves 3-6 feet high
(Zaitsev:1971)_3i~ota resident at the surfaee may therefore be exposed to the
higher toxie..;..::::: ceoneentrations existing in the surface mierolayer and suffe'r
greater dele~e=iccus effects than biota resident in subsurface waters.
Demersal fis~ ~gg~s deposited intertidally, and other organisms resident in the
littoral zor.~,nay·· also have extensive eontact with the mlcrolayer during the
ebbing tide ~~:n ·they are exposed to the sea surfaee as the tide recedes.The
nature of e:xp:suI:re for littoral organlsms, partieularly those that graze on
surfaces on ~-b:'ch.. the microlayer may be deposited, is very different and may be
substantially ~i~bher than for organlsms in subsurface waters.
Tbe possibilit:y :therefore exists that toxieant accumulation in the surfaee
mierolayer codd
have serious detrimental effects on the reeruitment and
survival of ~o~ ~neus~onie and demersal populations.
In this pap.er ·..e.; deseribe some of our studies on microlayer toxicity. The
purpose of ~f;se
studies was to quantify toxicants that accumulate in the
surfaee miero:ayver and to assess its biologieal impact by determining
pathologieal ·:ffieets in larvae of marine organisms.Simple 'experimental
bioassay sys::ens ·.were used on water sampies fro lll . the North Sea and from sites
near Plymouth in Southwest England.Chemieal analyses were carried out on the
same sampies tc daeteruine toxieant eoneentrations. ',.
. t • '_ _
.•~'.,
MATERIALS AND METHODS
Sampie
collection~..
i) North Sea sa.Dlt:ples were colleeted during a eruise of the RV Valdivia in
March 1990 alo~ ~a transect in the German Bight (Fig.I).To avoid eontamination
from the ship ,samn:ples were colleeted from a small inflatable boat about 300
metres upwir~ of the ship.Mierolayer sampies were eolleeted using stainless
steel and nylon:', mesh Garrett screens for organie and metal analysis
respeetively. lCl~eary & Stebbing ,1987).Garrett screens eollect the top 200400 mierons of ct:ne surfaee mierolayer (Garrett,1965) .Near-surface bulk water
sampies were c:ll~eeted by opening a bottle 0.5 m below the surface.For trace
metal analyses s~les were collected in acid cleaned bottles ; for organotins
and bioassay. :at::~les were acid eleaned and solvent rinsed prior to sampling
(Hardy & Cleary,l1992).
2
•
•
' •. ' '.1·
•
11) Sampies from sitcs near Plymouth (Fig.l) were collected using an automated
rotating glass cylinder microlayer sampier which collccts the top 50-100
microns of the surface microlaycr (Carlson et a1., 1988). This differs from
conventional rotating drum micro1ayer sarnplers which are orientcd normal to
the dircction of travel (Harvey,1966;Daurnas et al.,1976;Sodergren,l987;Hardy
et a1:, 1988). The glass cylinder
is oriented parallel to the direction of
travel,and avoids the problem of materials accumulating aheadof the drum as
it is towed through the water. Adsorbed microlayer was transferred from the"
glass drum surface by a windscrceri wiper asscmbly
into a reservoir and
pumpcd directly into glass bottles ,cleaned as before. Garrett screen and
subsurface sampies were collccted in the usual manner.
Chemical
analyses.
The North Sea sampies were extractcd on board ship for subsequent analysis in
the laboratory.For organotins a 2 1 water sampie was acidifled with 50 ml of
glacial acetic acid and cxtractcd with 25 ml of toluene by mixing on a
platform shaker for 15 min.The sampie was transferred to aseparatory funnel
and the lower aqueous layer discarded. The to1uene extract was stored in a
glass vi al in a freezer until analysis. \\There necessary extracts were
prcconcentrated before analysing for organotins.Aliquots were treated with 1M
sodium hydroxide and reanalysed to determine tributyltin (Cleary,199l).
Trace metals were removed from seawater by solvent extraction (Danielsson et
al.,1982).Metal carbamate complexes were extracted from seawater (buffered to
pH 5) with ammonium pyreillidine dithiocarbamate (APDC) and diethylammonium
dicthyldithiocarbamate
(DDDC)
into
l,l,2-trich1oro-1,2,2-trifluoroethane
(Frcon TF) and back-extracted into 0.3 M nitric acid for analysis by graphite
furnace atomic absorption spectrophotometry.
Polyaromatic hydrocarbons
ml hexane in sealed glass
hexane was transferred by
f1uorescence spectroscopy
were determined by shaking 1 1 water samples with 10
sampling bott1es for 10 min on a platform shaker.The
pipette into glass storage vials and analysed by UV
(Law et a1.,1988).
Toxicity tests.
•
Bioassays were performed on the North Sea samplcs on board the RV Valdivia
using cryopreserved oyster (Crassostrea gigas) and clam (Tapes philippinarum)
ve1iger larvae.(For details of this technique see McFadzen,1992).Three hundred
larvae per rep1icate were'used,and exposed to the water sampies at the
incubation temperature of 20 degrees Centigrade for 48 hours. Each vial was
then treated with 4% buffe red formalin to preserve the larvae for subsequent
analysis.Microscopic examination of larvae was conducted at random with
survival assessed as the number of viable larvae observed in the first 50
cncountered.
Bioassays carried out at Plymouth Marine Laboratory on water sampies taken
locally used turbot larvae (Scophthalmus maximus) obtained from Golden Sea
Produce,Hunterston,Scotland.Static exposure tests,in triplicate, were carried
out at 15 degrees Centigrade using a 12 hour light/12 hour dark regime.Three
day old larvae were added to the sampies (100 larvae /250 ml) and mortalities
determined at 24 hour intervals by microscopic examination for the absence of
a heart-beat.Toxicity exposure results were compared to control seawater from
a clean offshore site.
3
c
RESULTS
a) In the German Bight area of the North Sea concentrations of
copper,lead,organotin and tributyltin were greater in the microlayer than in
near-surface bulkwater at all stations (Fig.2).Enhaneement was more marked for
organotins than for traee metals,and mean enriehment faetors (mlerolayer
concentration / O.Sm subsurface water concentration) were 2.3 (Pb),5.0
(Cu),6.3 (TBT) and 9.8 (organotins).Maximum concentrations occurred at nearshore sites and declined with dlstance from the' land in both the surface
microlayer and near-surface bulkwater. Tbe larval bioassay showed a similar
trend.Tbe survival of elam larvae exposed to both mierolayer and subsurface
water inereased with distance offshore,and larvae exposed to the surfaee'
microlayer showed significantly greater toxicity than those exposed to
bulkwater (Fig.3) .Oyster larvae also showed the greatest toxicity at the
nearshore site in both the microlayer and bulkwater,and declined with
distance from the coast (Fig. 3) .Clan larvae were more sensitive than oyster
larvae to microlayer samp1es,but both showed a simi1ar response to bulkwater
sampies.
~
~
A significant relationship was evident between biological and ehemical
toxicity.The correlation between 1a~'al toxicity and chemical contaminants was
more marked with clam than oyster. Survival of elain larvae deereased with
increasing concentrations of Cu, Pb, TBT and organotin (Fig.4) in both
microlayer and bulkwater .No correlation was evident between oyster larval
survival and TBT or organotin concentration, but a positive relationship was
found with Cu and Pb (Fig.5).
b) In the Plymouth study, microlayer and bulkwater samples collected near
Plymouth
were analysed for polyaromatic hydrocarbons (PAH's),widespread
eontaminants identified in other mierolayer studies (Cross et al. ,1987 ; Hardy
et al., 1987;Word et al., 1987 and shown to effect the growth of microlayer
phytoneuston (Riznyk et al.,1987).They were tested for toxicity using turbot
larvae, a speeies used at PML for toxiei ty s tudies. Enhanced mierolayer
concentrations of total PMl's occurred at the 4 sites sampled,Sutton marina,
Looe ,Devonport and Plymouth Sound (Fig.6). Enrichment ratios were 742, 34,
2.7 and 1. 2 respeetively. Larval mortality followed a similar trend with
greater mortality in the microlayer than subsurface (Fig. 6) .Mortality in the
microlayer screen sampies was intennediate between micro1ayer' drum and 0.5
metre subsurface;consistent with the greater thiekness of mierolayer sampled
with the screen (200-400um) cornpared with the glass drum (50-.100 um)
(Fig.7).The strong correlation between larval mortality and PAH concentration
(F1g.8) shows that a s1gnificant relationship exists between b1010g1cal
response and contaminant eoncentration.
DISCUSSION
Consistent features of these microlayer studies are:- 1) the ability of the
surface microlayer to accumulate a range of chemical contaminants
cg.metals,organometals and organic compounds;
ii) the greater toxicity shown
by the microlayer exposed to different speeies of marine organism; iii) the
4
..
•
signifieant eorrelations betwccn eontaminant eoneentration and toxieity.
Although such eorrelations do not prove eause nnd effeet,it is elear that the
mierolayer is more toxie than subsurfaee water, nnd ean neeumulate ehemieal
eontaminants to levels whieh exeeed aeeepted water qunlity eriteria.For
example mierolayer coneentrations of TBT and Cu exeeed both the U.K.EQS value
of 2 ng TBTfl and the U.S.EPA ehronie water quality limit of 2.9 ug Cu/I.
Clearly,mierolayer contamination is a potential threat to neustonic ,pelagie
and demersal organisms, partieularly to the early life stages when organisms
are most vulnerable. The .reasons for the high inc1denee (5-26%) of embryo
abnormality found in eod,whiting and plaiee from the North Sen (Dethlefsen et
al.,1985),and the even higher malformation rates (26-44%) in North Sea
plaiee,flounder· and dab found by Cameron et a1. , (1992) ,have not been
. identified, but suspieion falls on the surfaee mierolayer.lt seems likely that
the surfaee mierolayer eould have a strong influenee on fishcries survival and
reeruitment.
ACKNOWLEDGEMENTS
These studies formed part of the PML rcsearch programme on mierolayer toxicity
and part of the Bremerhaven Workshop on biologieal effects of contaminants in
the North Sea. Funding ,in part, was from the U. K. Departmcnt of the
Environment,PECD 7/7/359.
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•
Baier,R.E., Goupil,D.W., Perlmutter,S., King,R. (1974). Dominant chemiea1
eomposition of sea-surfaee films,natural slieks and foams.J.Reeh.Atmos.,
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,
Carlson,D.J.,Cantey.J.L.,Cu11en,J.J.(1988).Deseription of and resu1ts from a
new surfaee mierolayer sampling device.Deep Sea Res.,35:7,1205-1213.
Cameron,P., Berg,J., Dethlefsen,V., Westerhagen,H.von (1992). Deve10pmenta1
defects in pe1agie embryos of severa1 flatfish speeies in the southern North
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Cleary,J.J., Stebbing,A.R.D. (1987). Organotin in the surface miero1ayer and
subsurfaee waters of southwest England. Mar.Po1l.Bu11.,18,238-246.
Cleary ,J.J. (1991) .Organotin in the marine surfaee miero1ayer and subsurface
waters of southwest Eng1and:relation to toxicity thresholds and the UK
Environmental Qua1ity Standard. Mar.Env.Res.,32,213-222 .
Cross,J.N., Hardy,J.T., Hose,J.E., Hershelman,G.P., Antrim,L.D.;Gossett,R.W.,
Creeelius,E.A. (1987).Contaminant eoncentrations and toxieity of sea-surface
miero1ayer near Los Angeles,Ca1ifornia. Mar.Env.Res.,23,307-323.
Danielsson,L.D., Magnusson,B., Westerlund,S., Zhang,K. (1982). Traee meta1
determinations in estuarine waters by electrothermal atomie absorption
spectrometry after extraction of dithioearbamate comp1exes into Freon.
Anal.Chim. Acta. ,144:183-188.
Daumas ,R.A. ,Laborde. P. L. ,Marty ,J .C. ,Saliot,A. (1976). Influence
of
sampling
method
on
the
ehemieal
eomposition
of
water
surfaee
film.
Limnol.Oeeanogr.,21,3l9-326.
Dethlefsen,V., Cameron,P., Westernhagen,H von. (1985). Untersuchungen uber die
Haufigkeit von Mißbildungen in Fischembryonen der sudlichen Nordsee.
Inf. Fischwirtsch. 32: 22-27.
Garrett,W.D.(1965).Collection of slick forming materials from the sea
surfaee. Limnol.Oeeanogr.lO:602-605.
Garrett;W.D.(l967).The organie chemieal composition of the ocean surface. Deep
5
:
Sea Researeh,14,221-227.
Garrett,W.D. and Duee,R.A.(1980).Surfaee mierolayer samp1ers. In: Air-Sea
interaction:Instruments and methods, (ed.F.Dobson,L.Hasse and R.Davis).Plenum.
Hardy,J.T. (1982). The sea surface mierolayer,
biology,
chemistry, and
anthropogenie enrichment. Prog. Oceanogr., 11:307-328.
Hardy,J.T.,Apts,C.W.,Crece1ius,E.A., Bloom,N.S.(1985a). Sea-surface microlayer
metals enrichments in an urban and rural bay. Estuar.coast.Shelf Sci. 20:299312.
Hardy ,J . T. , Crecellus, E.A. , Apts, C. W. , . Gurtisen,J .M. (1987). Sea-surface
contamination in Puget Sound :Part II.Concentration of eontaminants and
relation to toxicity.Mar.environ.Res. 23:251-271.
Hardy ,J . T. ,Coley ,J .A. ,Antrim, L. D. ,Kiesser, S. L. (1988).A
hydrophobic
large
volume sampler for collecting aquatic surface microlayers: eharacterisation
and comparison to the glass plate method. Can.J.Fish.Aquat.Sci.45 (2) 822826.
.
Hardy,J.T.,Crecelius,E.A.,Antrim,L.D.,Kiesser,S.L., Broadhurst,V.L.Boehm,P.D.,
. Steinhauer,W.G.(1990).Aquatic surface contamination in Chesapeake Bay ..
Mar.Chem. 28:333-351.
Hardy,J.T.,Cleary,J.J.(1992). Surface microlayer contamination and toxicity in
the German Bight. Mar.Ecol.Prog.Ser.91:203-2l0.
Harvey,G.W.(1966).Microlayer collection from the sea surface:a new method and
initial resu1ts. Limnol.Oceanogr.l1,608-6l3.
Law,R.J.,Fileman,T.W.,Portmann,J.E.(1988).Methods of analysis of hydrocarbons
in marine and other samples.In:Aquatic environment protection:Analytical
methods,No.2.MAFF,Directorate of Fisheries Research.
McFadzen,I.R.B.(1992).Growth and survival of cryopreserved oyster and clam
larvae along a pollution gradient in the German Bight. Mar Ecol. Prog. Ser.
91:215-220.
Riznyk,R.Z.,Hardy,J.T.,Pearson,W.Jabs,L.(1987).Short term effects of
polynuclear aromatic hydrocarbons on sea-surface microlayer phytoneuston.
Bull.Environ.Contam.Toxicol.38:1037-1043.
Sodergren,A.(1987).Origin and composition of surface slicks in lakes of
differing trophic status.Limnol.Oceanogr.32,1307-1316.
Word,J .Q. ;Hardy ,J. T. ,Crecelius, E.A. ,Kiesser, S. L. (1987).A laboratory' study of
the accumulation and toxicity of contaminants at the sea-surface from
sediments proposed for dredging. Mar.Env.Res.23:325-338.
Zaitsev,Y.P.(1971).Marine neustonology.(K.A,Vinogradov,ed.). Israel programmes
for scientific trans1ations,Jerusalem.
~
•
6
.,
A
DEVON
Exeter
7'[
"[
P'E
B
•
54'N
54 'N
6'E
a'E
7'[
Fig.l.Sampling sites: A) near Plymouth ~n southwest England,l) Sutton
marina,2) Plymouth Sound,3) Devonport,4)
Lccee
and B) in the German Bight.
-
__ 10
---
. l.
~
8
0
-.§
6
C
4
.
-;
...c
ll;
e
Fce
I-
- ; 4000
s~ic
con
5000
--§ 3000
c
\
''':;
...f
~
.-
...c
_______e,
2
I
bulk
o
1
o
~ 1000
U
....................
.'..• _ -
o t-------.-.+-------+---.--.. -.---.. - .....-------::..
3
2
2000
bulk
50
---
s~ic
. l.
on
-=-c
-=.
C 30 .
...f
-
<J
c~
C
20
~
o
...o
Oll
J:l
Q..
.
; 10 .
o
bulk
•
e--__
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..---.------+-------I-----t-----I
o
2000 .
.51
~
o
4
Station
.§ 40
..:;
3
3000
Oll
o
•
' ........
o --. ------.-.---+----.---+
o
2
4
60
~
.---- -------.
•~"
Station
J5
.s
\~
1
2
Station
3
4
•
1000
bulk
."",-
0
"
o
'e----
_e----,.
-----+-----+---.
o
1
2
Station
Fig.2 Contaminant concentrations in the surface microlayer
and bulkwater (0.5m subsurface) in the German Bight in March 1990
3
4
110
ii 100
>
110
TSurface microlayer
;;
> 100
.~
.~
.,
:l
•
"I"
.,
V 80
.,
~
~
70
E
Ü
.,
:::l
90
~
.3
Surface microlayer
••
I
2
3
"I"
60
•
50
------+----
,
90
"I"
80
3...
70
Vi
60
•
•-
IJ
6-
50
------t
.,::l
~
I
110
v
Oll
C
..!! 70
] 100
.~
"I"
-•
90
80
i
I
.,
:::l
~
~
C
!
..!!
Oll
Bulkwater
90
80
...
70
Vi
60
IJ
E
Ü
4
Station
;; 100 Bulkw.t«
>
.~
3
2
4
Station
110
•"I"
60
6-
50
---.
···t····· ._-- .,.• " .•. .•••.••
2
3
.....
..-.-- ---f
4
50 _...-
T
"I"
!
•.1
I
.,.
T
T
•
•...
._.-----_._--+---.~
._--_.+-
Station
Fig.3 Toxie responses of c1am larvae (Tapes philippinarum) aud oyster
larvae (Crassostrea gigas) to surfaee mierolayer aud
bulkwater (O.5m subsurface) from the German Bight
.. -------- ----------t
3
2
Station
4
'i
...
100
·E
'"=
90
~
Cl
•
80
=
e
• •
elS
Gof
"
~
elS
C
60
eelS
50
Ci
40
~
90
~
Cl
=
e
..
'~
_·_-t
2
•
:-----
..-.
80
elS
Gof
~
elS
"-..
IV= -4.69 X + 87.55 R2= 0.88 p= 0.003"
0
oE
'"=
•
.---~~
70
100
...
..
~,.---,
'i
.-t---.
4
-
6
-
i:
•
~
eco:
.'f--
-----------f
8
70
60
Iv
50
Ci 40
10
= -0.008X + 86.4 R2= 0.81 P = 0.0131
. -r--
0
1000
TBT (ng Sn 1-1)
'i 100
...
·E
'"=
~
Cl
=
co:
e
<lo'
~
CIl
C
~
eelS
Ci
90
80
..
·E
'i
'"=
•
........
70
--
t
C
~o
Gof
-----
---------
e
---..
~
•
-'-
CIl
i:
'~
~
•
-~.
IV= -0.68 X + 82.59 R2= 0.84 p= 0.0071
40
i
I
0
10
2000
i-------i
3000
4000
5000
100
•
90
80
elS
•
60
-t-
Cu (ng 1-1)
I
I;..--- •--
•
20
30
40
.' ······1
50
70
••
60
e
50
Ci
40
IV = -0.02X + 91.8 R2= 0.82 P = 0.01l1
CIl
._ ....
_,
60
'~
---+
--t-
0
500
Organotin (ng Sn 1-1)
Fig.4 Relationship between contaminant concentrations
in surface microlayer and bulkwater (O.5m subsurface)
and survival of c1am larvae (Tapes philippinarum)
1000
I~OO
Pb (ng I-I)
..
-
--+--------1
2000
2500
100
..~
=
co:
90
•• !IIl
80
""E~
~
.::
t
.! ~
100
• •
.-.-----
----•
•
70
..
~
•
r..
~
....
'"
0
=-,"
C =
Q; ,
."I
---------.
~'"
70
'"
60
-""
;"
0
IV= -0.34 X + 86.66 R2= 0.57 P= 0. 1331
50
I
o
10
20
30
40
50
•
IV= -0.004X + 89.77 R2= 0.64 p=o.081
0
60
.--------
.
80
.~
I.
•
60
50
~
eo:l
4J
---~--.._----
•
•
90
=
1000
2000
3000
4000
5000
Cu (ng 1-1)
Organotin (ng Sn 1-1)
100
100
..
~
=
90
.. "
=-
80
-
70
eo:l
4J
4J ~
eo:l":-
+
• •
••
••
i: ,
70
1 •
•
:: ~--2.26~+.8.• ~ 0.58 1'" 0.1271~~
o
2
4
6
8
10
eo:l
I.
~
'"; "
0
::l
'"
•
•
60
IV = -0.014X + 94.9 R2= 0.77 P= 0.0221
50
0
500
TBT (ng Sn 1-1)
Fig.5 Relationship between contaminant concentrations
in surface microlayer and bulkwater ,(O.5m subsurface)
and survival of oyster larvae (Crassostrea gigas)
1000
1500
Pb (ng 1-1)
2000
2500
... ..
10‫סס‬oo
A
1‫סס‬oo
-
~ 1000
:I:
-<
D..
100
n
~
10
1
Looe
Sutton marina
Devonpon
B
100
80
~
60
~
40
1
~
20
0
Looe
Sutton-marina
•
Mkrolalu
Devonpon
[J O.5m
Plymouth sound
•
A. Total PAR levels in microlayer and O.5m salnples, at 4 .
sites near Plymouth.
B. Mortality responses in turbot larvae after exposure to
thc above sampIes for 96 hours.
FrG.6.
Comparison between the effects of microlayer (drum and screen), O.5m and control sea
water sampIes from 4 sites near Plymouth, using a turbot larvae bioassay.
100
Sutton marlna
I
I
•
100
Looe
I
80
80
,/
I
I
I
I
I
I
I
I
,/
,,'
, '"
,"
I
,"
0
24
48
72
96
0
--e--
Houn
•
r-
Dn-
48
72
96
Houn
Sawa
--0100
24
o.s.
c-...a
100
Devonport
Plymouth
sound
80
SO'"
?;-
?;-
~0
60
1/
40
~0 60
~
~
11
20
.... --....
(1
0
..
.
t
---
________ t--
------~
.. -------~
"
...I
48
24
72
96
0
Houn .
.
40
48
24
Houn
FrG.7.
72
96
"
.
Correlation between total PAH (Jlg/L) and percentage mortality
of turbot (Sc. maximus ) larvae exposed for 96 hours.
100000
10000
~
2; 1000
::r:
<
0..
y =0.73 + 0.03x
R"2=0.90
P =0.0003
"3 100
o
f-I
10
1
, 0
o
20
40
60
% Mortality (96 hours)
FIG.8.
80
100