• I
~ j ~
C.M. 1989/E : 29
";
Marine Environmental Quality Committee
DISTRIBUTION OF ORGANOCHLORINE RESIDUES BETWEEN
DIFFERENT FRACTIONS OF SEDIMENTS AND BETWEEN DIFFERENT PLANKTONIC COMPARTMENTS IN THE SCHELDT ESTUARY AND THE BELGIAN COASTAL ZONE.
K. DELBEKE
TIIOMME,2.
1,
M. BOSSICART
1,
C. JOIRIS
1,
M. BOGAERT
2
and R. VAN-
ABSTRACT
PCB levels in sediments (bulk and
< 63/Lm), suspended matter and zooplank-
ton from the Belgian continental shelf and Scheldt cstuary are evaluated in relation
.'
to their organic carbon content, lipid content and for sediment 'also particle size distributions. Geographical and seasonal v~riations are discussed. A discussion is given
on the PCB accumulation mechanisms, considering passive (direct) contamination
routes (adsorption- partitioning) and for zooplankton also indire~t contamination
through food.
'1. INTRODUCTION
.
Thc ecotoxicological significance of organochlorine residues is a well-known
fact since
+/- 1960.
PCDs, still used in
i~dusti-ics
(Ascarel), are nowadays, in the
. Westerns countries, thc most important organochlorine residues to be studied.
The contamination mechllanisms of PCBs in marine and cstuarine environments have been investigated during the past few years by different research groups.
•
An equilibrium distribution of PCBs between the wat~r and the suspended matter was shown to be based on simple physicochemical adsorption and/or partition
mechanismS (ti. Bruggeman et al., 1985; Duursma et al., 1986, 1989; Delbeke arid'
J6iris, 1988). For the bulk sediments, adsorption on the organicand silt fraction
of sediments was demonstratcd (Simmons et al., 1980, Duinker 'et al., 1983). The
partitioning of PCBs into thc lipid fraction of sedimet:Its was furhtermore noted
during a preliminarY iIivcstigation of sediments' fr~m thc Belglan c6ntinerital sheif
1
2
Laboratorium voor Ecotoxicologie, V.U.B..
,
Laboratorium voor Ekologie en Systematiek, V.U.B., Pleinlaan 2,1050 Brussel.
(Delbeke and Joiris, 1988).
The aim of this study is therefore :
(1) to study the association of PCBs with the different fractions (day,organic
carbon, lipids) of the bulk sediments and of the silt and lutim fractions of the
sediments
«
63J.tm).
(2) to get a global image of the actual contaminant levels of the sediments from
the Belgian continental shelf and Scheldt estuary, considering spatial and temporal
variations and
(3) to compare PCB levels between different planktonic compartments and
sediments and interpret the results in a more general way.
•
2. MATER/ALS
SampIes were colleeted between February 1986 and March 1988, during different cruises with the R.V. Belgica in the Belgian coastal zone and the Scheldt
Estuary (Fig.l). Surface sediments (upper cm) were colleeted with a stainless steel
box corerj suspended matter was colleeted through pumping of sea water at 3m
depth and continuous centrifugation. Zooplankton was sampled on a 250J.tm or
a 500J.tm net with a "high speed" sampIer. The fresh sampIes were imrriediately
deep-frozen, on board.
•
.640
+630
Fig. 1. Sampllng stations and areas durlng different campaigns between 1986
..'ind 19ß8
.
;l
v
..
+ ,1..
w
i
•
a>
'"
...0:1
.. .
'::
1-
,\l
..,..,
...
1
...
..'"
1:
:!;
. . . . (l
a
.
a;
...
•
~
a>
~
~
•
t
.......
;::
....
~
..
":
;;:
,
~
1
.'
r·
•
.
....
.... ....
Fig.
2.
Comparlson of PCB patterns ln
(a)
~
;e
~
~
..,'"
:
sediments,
..... ...
~
~
~
:
;::
~
,
.....
...
'.
(b) Araclor 1254 and
(c) Aroclor 1260. (A-M: peaks used for calculation of ·"total PCB" values).
3. METHODS
The granulometrie distribution of the bulk sediments was analysed after an
ultrasonic treatment, on a sedimentation balance. The bulk sediments were wet
sieved on 63JLm to separate the sand from the silt and lutum fraction of the sediments. The bulk sediment, the fine sediment fraction, the suspended matter and
zooplankton were further analysed for the lipid contents (after extraction with hexane/acetone (9/1)), the organie carbon content (CH analyzer) and the PCB levels.
The latter was measured after soxhlet extraction with hexane/acetone (9/1), clean
up on a florisil column and gaschromatographie measurements with an electron
capture detector, a capillary column system, an automatie sampier and a plotter-
•
integrator. The conditions used are: splitless injection (splitter closing time: 0.5
min)j injector tO : 220°Cj oven tO : 90°C - 270°C in a temperature programj detector tO : 305° Cj column : fused silica CPsil8CB (25 m, 0.22 mm diameter, 0.12 JLm
film-thickness)j carrier-gas: 0.6 bar N2 j detector-gas : 20 ml N2/mini injection
volume IJLI. The quantitative determination of PCB levels is based on individual
PCB congeners (IUPAC nrs. 28, 52, 101, 118, 153, 138, 170 and 180) and on the
total PCB quantity as compared with the most similar standard mixture : Aroclor
1254 (Fig. 2) .
•
4. RESULTS AND DISCUSSION-
4.1. peB patterns in different sampie types.
A constancy in the PCB patterns (it is the relative abundance of the different congeners in the PCB mixture can be seen within a sampIe type for surface
sediments (upper cm.), the silt and lutum fraction of the surface sediments and suspended matter (r2
•
:
0.7-0.98) (Fig. 3). In zooplankton, being more heterogeneous,
the variations were somewhat bigger (r2 : 0.1-0.8).
A difference in the relative importance of each congener between the natural
sampIes (f.i. IUPAC nr. 138 in zc-oplankton, compared to the other sampIe types)
is noted. Higher chlorinated PCll congeners (IUPAC nr. 153 to 180) are more
important in natural sampIes than in Aroclor 1254 (Fig. 4).
Due to these differences in PCB patterns between different sampIe types and
•
eventually different regions it is important to compare PCB levels on the basis of
individual congeners, and to get a more global view of the PCB contamination, on
the sum of the individual congeners, even if they only represent a fraction of the
total PCB level. For the researches it is however nowadays not clear which congeners
ought to be used. Different teams use different
congen~rs
and the congeners used
change within one research team, according to the gained experience. It therefore
seems convenient to additionally express results as total PCB values (in compari,son
with standard mixtures), to enable the comparison of resuIts in course of time and
with literature, even if analyses were executed on glass column systems.
ta
I · "071x - "404, R-........ : .94'
6
'"
~
3
.
........
'g
...*
~
l/l
, • 1.036x - 1.919, R-s'lun4: .918
..
:I
Cl
~
.tb_
.
.
0
:;
/
3
2
V
0
...
5
'"...~
""'
'1"
I
II
2
Cl
.....
/8
0
,..0
"
)'
0
+ ++
+ ......:.
-I
-2
<",';I
-3
-4
. . . . . . .V
/1!
-'.)
..
2
3
W;,,) of PC9 (Il'iI/9 O-Y)
6
7
-3
-2
-I
1
0
2a
'.I
3:;;0
= .416)( -
..,)
m
6
4'
o
40
3:1
200
o
ISO
~
30
~
20
~
tl
o
o
E 100
".
:I
SO+----t--~--~-~----'"--~-__,.-_t
m
I
4
, ••158x + .486, R-.'l..rH: .967
3.932, R-s'lur": .856
2~0
0
3
2b
300
....
2
w:,,)or $Im 28-1 E:o("'l/9 D'w')
~
~
+
1:1
10
SO
+
:I
0
-50
-100
Ol--.ß:~---------------t
0
100
200
300
400
:lOO
-:I ~<:;--+---'-~-~-r-~--r---.-....,-.---r-~--r---.---f
-50
o
100
t 50
200
2:lO
300
m
JWIl28-I80/k
11m FtB(Il'iI/9 o-y)
Fig. 3. Pelatlon between (a) the 3um of the PCB congeners (IUPAC nrs. 28,
52, 101, 118, 138, 153, 170, 180) and the "total PCB" concentraUons in
comparison with Aroclor 1254 and (b) the relation between the peB congener
nr. 153 and the sum of the peB congeners (28 till 180) in f. i. (1) bulk
~ediments and (2) the silt and lutum fraction of the sediments (<. 63 ~m) (DW
= dry welght j .
•
The PCB results in the further study are esscntially compared as thc sum
of 8 congcncrs (IUPAC nrs. 28, 52, 101, 118, 138, 153, 170, 180) representing
respectively for total sediments, silt and lutum fraction of the sediments, suspended
matter and zooplankton: 31%, 43%, 34% and 28% of the total PCB contamination.
·"congener
30
I
•
20
". lh I I1h
o
28
S2
I!II Oll iI JIJI
101
118
153
01 1
1
I11 I
1111
•
•
138
180
170
relatlve centr~bljn,on of seme PCB congeners ~n the PCB
(.:i~ .;-um cf the l~cr~qener~}, ~n Aroclor 1:::54 •. total surface
.o~th~ent •. the :nlt L~nd 1IJtum fr,"lt"ltlon of the :>urface sedlment (frat1tlon <:
f<-; ~m~ A. Btlspended ID.Hter _and Zt)opL"nkton ... from theBeh.llan Contlnental
Shelf Imean values 3nd 3tandard dev~dt~on error ~~rs).
Y.lg
4
'The
;::ont,'iIDlfüUOn
4.2. Geographical and temporal variation of PCB levels in sediments.'
The studied sediments, from thc Scheldt estuary and the Belgian coastal zone,
have a broad range of geological characteristics (f.i. granulomctric distribution)
and of organic carbon and lipid contents. Large variations in PCB levels according
•
to the sampling station and sampling period are noted (Fig. 5).' It is therefore
important, in order to understand and evaluate the noted contaminant levels, to
study their association with the silt, the day, the organic carbon and the lipids of
the sediments and thus to standardize the measured PCB levels.
,
4.3. Association of PCBs with different sediment fractions.
~.
Comparison of the PCB conta.n:tination of 15 bulk surface sediments (2ng.gdry weight) versus their respective silt and lutum fraction (14 ng.g-
1
1
.l'
dry weight)
shows a higher affinity of PCB for the silt, the fine sediment fraction, than for sand
l,
,
.t
i',
Oetober 1gei
120
a
~
100
""
90
0
"-
""
.5
0
~
,
60
CD
N
~
40
III
20
0
n
.....
.....
-
..
.,N
......
-C
...
•
..
........
......
OO
,.,.-G.,.--oooO%., •
·_·-
.. .
UO
.
0
.,
000
•
.. 0
December 1987
190
160
~
c
b
140
-.."" 120
'" 100
.5
0
~
,
e
CD
('.
S
III
90
60
40
20
0
.
"
ft.
.....
. '" -..... ....~
1ft
•
Cl
.. 0
....
Februar/198e
3:50
~
000
1ft
·e
300
Cl
~~
0>
5
0
200
I
1:50
0>
CO
('~
E
100
:J
CI)
:50
•
nn
0
:::~:-::!~::;~ö~=:~
.. .
.;
~g--
n
......
000
•
.. 0
MarCh 1988
-----------'--....-.-"""'------_""---t
m,t--.......
d
200
~ 17'5
~Is)
.......
SIZl
g
cri
§
('~
(/)
100
7'5
:10
Zl
•::~;:=~::;3
; • ; ; • • • •• 01;:1°-=-:0"
• ~ g - - =: .. : • :. •
••
Fig. 5. PCB levels ln surface sediments (fraction .;:: 63 JLDl) from different
places in the Scheldt estuary and the Belgian Continental Shelf in different
periods in 1987 and 1988 (~g.g-2 dry weight) (see also Fig. 1).
on a lipid weighted base however the PCB levels are much more comparable (Table
1) suggesting already partitioning of PCBs into the lipid fraction of the sediments.
I
Both sediment fractions (bulk< 63Jlm) are therefore, in a first step, separated for
a more deeply investigation.
Comparing the geological and chemical characteristics of the bulk sediments,
high correlation coefficients are noted between the silt fraction (% < 63 Jlm), the
organic carbon content and the lipid contents of the sampIes (Fig. 6).
y - 2.1 .. 7. - .135. R-s,•• 114: .192
90
•
o
80
iO
60
~
50
~
30
.
40
v
20
10
0
-10
-s
".,,/
....
o
10
15
20
2S
30
35
40
45
50
POC mglg O'W
y - 82.299. - ."65. R-slIUre4: .716
90
//
.'
."
",'"
60
E
50
~
40
oe
~
0
./
0
70
•
//
0
80
///
I
I
30
//0
20
//
10
o
-10
-.2
..§2.
...&.~
/ . ,!
o
-
.4
.6
.8
liP(mgig O'W)
1.2
1.4
FlO. 6 FelatlC'n between silt and particulate organic carban i 6a i ar liPld
content:: (6b) ln bIll: '::llrface sedlment.:: fram the Scheldt E~tllary and BelgB.n
Contlnental stielf ln 1987 and 1988.
ccnt~mlnated =one {S18)
excluding one sample fram a
highly
TtiliLf: 1
Com~x~r~son
cf
of FCB levels ias sum of congenersl in different
~urf~c ~ediment ~amrle~'
fract~on
cf the
sed~ment
imedian levels, n
15
14
and lutum
28
y. 38.653x - 2.611,
20Q
180
160
>
co
140
'"
~
c;
100
aI
80
0;-
~
<n
6V
40
20
0
-20
-I
R~qu.,.ed:
.992
I
I
•
......,. 1:0
GI
N
fract~ons
and lutum
~g . g-1 11 pid
::ed~ment
Tot:ü
~ilt
and the
= 15),
ng.gr1 dry we~ght
Identltlc~t~on
~;ilt
~ed~ment~
total
~
/1
0
-7a
,
Z
3
LiplmQig DWI
S
4
.
6
-
y. 15.231x + .103, R-squared: .654
12
,.
~
co
a
c;
6
.....,.'"
~
9)
0;GI
N
•~
0
10
"
2
0
~~
,~
,..-
~-
0
,,~-
,,-
Cl!8 0,,-"0
&O~
:';;':-?-Q._ 0
°V . . . . I
-2
-.1
,~
0
.1
1Q..
0
-
0
...
.4
.3
LiP(1llC)!9 OW')
.s
.6
-
Fi~.
7:
Relation between peB and lipid contents of bulk sediments
e?cluding samples from a more contamlnated zone .
• : station 140 in February 1988.
(7b):
"Thc association betwcen silt and organic carbon and thc association bctween
silt or organic carbon and PCDs, indicates thc importance of adsorption of PCDs
onto sediments, a statement already noted during previous investigations, on bulk
sediment sampIes (Simmons et al., 1980j Duursma et al., 1989). Our study revealed
additionally a very high correlation between the PCD and the lipid content of the
bulk sediments indicating the importance of partitioning of PCDs into the sediment
particlcs (Fig. 7).
Similar assodations were invcstigated within thc silt and lutum frac~ion « 63
J-lm) of thc sediments : a positive relation bctween the organic carbon 'and lipid
contents was noted. Thc lipid and carbon contents of thc sediments are howcver
not rclated to thc prcsencc of day (%) (Fig.. 8). Thc PCDs of thc silt and lutum
fraction of the sediments, exduding somc sampIes from a particular zone in thc
Scheldt cstuary (sec later), are ~sociatcd with thc lipids in thc samplcs, lcss with
thc organic carbon and not at all with the day (Fig. 9). This dearly revcals the
association of PCDs with the lipids of thc sediments in an equilibrium state with
thc surrounding watcr. Thc non-association with thc day shows cvidence
ror thc
.
.
origin of the PCDs in thc sediment: sedimented biological material (cssentially
suspended phytoplankton).
The similar relationship (PCB-lipids), with siInilar regression coefficient, notcd
in rcspectivcly the bulk (Fig. 7) and the fine sedieinnt fraction
e·
« 63 J-lm) (Fig. 9)
can be understood considering the origin of the sediment lipids (biological material).
All sampIes can therefore be combined into onc general cquation and a PCD level
.
.
of +/- 20 J-lg. g-l lipid can than bc calculatcd as an acccptablc mean valuc for the
Belgian coastal zone and the Scheldt Estuary ror thc period Oetober 1987-March
1988 (Fig. 10). The zone Kalo-Doel needs special futur~ attention with sohle very
high, some very low and some "normal" PCB valucs. Possibly we are dealing with
.
'.
occasional dumping ofratty materials either with or without PCBs. The equilibrium
.
.
state, depending on the diffusion transport via interstitual water, resilspension of .
,,
,,
I
.f
~
i
r
sediment material, biotrubation etc., has in those "special" sampIes not yet becn
I
lr
1..
I
I
,I
t
I
f'
l
R~qu.red:
7S
70
0
0
65
......'"
'"lIt
.02 J
0
°
60
0
8
0
co,,"
"''''
0
0
50
0
00
4S
0
0 0 0
o 0
0
0
0
0°
0
40
0
0
0
0
0
~S
10
0
30
20
50
40
POC mg/g DW
R~qu.red:
60
.062
7S
70
65
.
....'"
'"
lIt
0
0
0
P
60 0
5S
50 0
00&
0
Q)
o
0
00
0
0
Cf:)
0
c)
0
4S
0
.;0
0
0
°
0
0
0
35
0
......
1.5
.5
2.5
3 3.5 4
liP{mg/g DW)
4.5
5
5.5
6
6.5
7
y - .086. - • J 78. R-squ.red: .629
7
6
,..
)0
0
4
~
3
r
•...
'0
5
2
0
-I
0
:5
10
1:5
:zo
~
:50
0
~
POC ITlCJ/II rJvI
40
4:5
:50
~
60
Fig. 8. Fielations between the geological and chemical characteristics of the
silt and lutum fraction of surface sediments from the Scheldt estuary and
the Belgian Continental Shelf in 1987-1988.
R~"".... tI:
.353
160
0
1040
s;-
120
Q
100
.....
~
~
,5
.
0
0
80
~
CD
N
l:
:>
'"
0
0
0
00
0
40
20
o
00
o 0
~.rt
6>0
0
~8r\.-
-
~
~f"\
0
9a
-
n
-20
0
10
20
y
30
POC mg/g DW
= 22.626x -
SO
40
60
1.745. R-squel"ed: .713
160
o
140
•
":>
<:0
.....
~
~
120
100
c
.....
0
80
CD
7
60
CD
N
E
:>
(/)
o
000
40
o
20
9c
0
-20
-1
0
2
3
~
7
Lip(mglg D'N)
F~g.
9. Relation between the PCB levels and the silt fraction (9a), the POC
(9hl, and the hp~d content (9c) of sed~Dlent sampIes from the
Scheldt estuary and the Belgian Continental Shelf in 1987-1988. Some sampIes
from the Scheldt estuarv w~th a very particular peB behaviour (see fig. 10)
are exc:Iuded from this graph.
t~ontent
reached.
Seasonal variations in PCB contents must also be considered, the highest levels
being noted in February (Fig. 5) (see also later) .
•
4.4. Distribution of PCBs between the different compartments of the water
column.
Comparing PCB levels between the different planktonic compartments and the
sediments from the Belgian coastal zone (1986-1988) shows on a dry weight base
increasing PCB levels: bulk sediment, silt and lutum, suspended matter, zooplankton. On a lipid weight base, PCB levels in sediments and suspended matter are
comparablej in zooplankton they are lower (Table 2). The similarity in PCB levels
(on lipid weighted base) between the sediments and the suspended matter clearly
shows the importance of a passive physicochemical equilibrium partitioning between
•
the water, the suspended matter and the sediments. For the sediments, one must
therefore consider sorption and desorption phenomenons of PCBs. A redistribution of the contaminants into the water-column in association with the breakdown
of organic material clearly exists in agreement with results during laboratorium
experiments (Wildish et al., 1980).
The sediments can thus not be considered as a "sink" for PCBsj the sediments
represent nevertheless an enormous "stock" of PCBs considering the large amount
of organic sediment material present at the bottom of the estuaries and seas.
-
----------
TABU: ::;
PCB levels (as sum of congeners ln different natural sampIes from the
Belgian coastal zone.
(median levels. n = nllmbers of samples) .
Identification
Period
Surface sediment (1987-1988 )
Silt and lutum
( 1987-1988)
Suspended matter 198ö
1987-1988
•
n
ng.g- 1 dry weight
IL9·g- 1 lipid
9
2
10
8
3
8
15
27
21
27
9
8
154
~
159
2
6
15
Zooplankton:
>- 250
;..
1986
1987-1988
J.1m
500 J.1m
,..
• • 21.715x - .67 ............. ::r.a
3'50
300
,
~
I
~ 200
.....
"" 1:50
""
.5
0
•
0
cu
100
...
:50
-;-
a>
§
~)
0
-so
- 1
~
~
1+
•
•
•
•
••
o
I!
!
o
6
7
tlg 10. Relation between PCB and lipid levels of sediments (bulk and silt
sediments) from the Scheldt estuary and the Belgian continental shelf (.
ZQIle Kalo-Doel alld 1 sampIe !rom Antwerp. -t: 140 February 1988).
4.5. pcn uptake mechanisms in suspended matter and zooplankton.
Considering the planktonic compartments, a positive tendency between pcn
levels and lipid contents can be noted for suspended matter, not for zooplankton
(Fig. 11).
This .again indicates the existence of a passive physicochemical adsorption/
paritioning mechnisms of pcn in suspended matter and the importance of biologically regulated uptake and elimination mcchnisms of pcns in zooplankton. In
.
.
suspended matter (and sediments) one must however also consider the dilution of
pcns into the available lipids and thus evaluate pcn levels considering the biomass
levels (Delbeke and Joiris 1988, Joiris et aL, 1987). lIighest pcn levels, in suspended
•
matter, zooplankton and also in sediments can therefore be noted during the winter
(February 1986 and 1987), when the amount of suspended matter is low (Fig. 12
and Fig. 5).
4.6 Geographical differences in pcn levels in the Belgian Continental Shelf.
The geographical comparison of PCB levels in suspended matter and zooplankton reveals, for the different periods considered, higher PCB levels in t~e near coast
area than in the open sea region (Fig. 12). This dilution of PCHs into the sea is
rlated to the transport mechanisms of PCBs : PCBs are, due to their low. water
solubility essentially associated with the particulate fraction of the water-column
(f.i. Verscheuren 1983 and f.i. Duursman et aL, 1989) and are therefore to a very
high extent deposited on and transported by the sediments. They are only, to a
.•
limited extent, transpo~ted with thc watter current, causing lower PCD levels, in
remote areas from the dumping origin.
CONCLUSION
The investigation of the pcn concentrations in sediments, suspended matter
and zooplankton from the Belgian Continental Shelf and Scheldt Estuary in com-· .
parison with chemical parameters (particulate organic carbon, lipid contents) and
for the sediments also geological parameters (particle size distribution) indicates
the existence of anequilibrium partition between the water, the suspendedmatter
R"1ö'lu.r.4: .669
300
0
,...
~
0
....
..s
...
~
~O
200
0
~
C1'
ISO
0
";'"
CD
N
§
100
~
0
:50
0
0
00
0
0
lla
0
.5
1.5
2
2.5
:3
lip(mglg DIN)
3.5
350
0
,..,
)Q
...
!...
.....
0
300
.!.!!!..
250
.
200
N
ISO
0
";'"
•
...~
0
0
0
100
0
0
SO
10
20
30
40
SO
60
70
!lO
90
100
110
LiP(rnq/Q OW)
F~g
11. Relation between PCB and lipid levels of suspended matter (11a) and
zooplankton (llb) from the Belgian Continental Shelf and Scheldt estuary in
1986
...------------
~
100
+'6311
~"'"
-
-
-
--
-
suspended aatter
1
~
--
:;300
...
Ü"'
>.«lO
e
Q, ~
........
.a=0
tlQ?lIl
-
":'2110
lZl I""
~ IOD
!IO
4
'01JI5O
::l
'uii:i
1
"-
2-lJ2
•
month
F~g.
200
tlO
~D1
0
0
suspended aatter
1
10
1
100
50
~_.2
0
12
0
•
•
1O
12
..onth
12. Seasonal and geographical differences in PCB levels (as total PCBs,
compared to Aroclor 1254) in suspended matter and zooplankton trom the
Belgian Continental SheH and Scheldt. estuary in 1986. - , 1: near coast
area; ---- 2; open sea area.
and the sediments.
The partitioning coefficient, being different for the different PCll congeners, ,
causes different pell concentration factors for the congeners in the natural sampIes. Differences in "PCll patterns" are thereforc encountered between standard
solutions, sediments, suspended matter, and zooplankton. PCll congeners with .
high chlorination (138, 153, 170, 180) are more important in natural sampIes compared to standard mixtures espccially in zooplankton. It thus seems important to·
compare PCll levels as sum of congeners. To be able to compare with literaturc it
is however still important to measure the "total PCll" concentrations, as compared
to the standard mixture. An estimation still valuablc within a compartment and
geographical region.
The pollutants are essentially associated with thc lipid fraction of thc partieu':'
lates, in an cquilibrium statc. Stable ratios can bc noted between the PCll levels
and thc lipid levels in suspended matter and sediments: """"",,20IJg PCll . g- 1 lipid
(as sum of the congeners, 28, 52, 101, 118, 138, 153, 170, 180) for the llelgian coastal'
zone and Scheldt Estuary during the period October 1987-March 1988. Thc similar
contaminant levels (on a lipid base) in sediments compared to suspended matter
indicatcs sorption and desorption phenomenons of PCBs in the sediments and redistribution of the contaminants in the water-column. Sediments can therefore not
be considered as a sink for PCll compounds.
The sorption and desorption speed of PClls in the sediment is however dependen~
on diffusion transport, rcsuspension of bottom material, bioturbation ....
Local dumping of PCll rieh and PCll poor silt could thus be noted in a particular '.
region of the Scheldt Estuary : between Antwerp and Doel. The elevated PCB levels
could nothe related to particle size or chemical characteristies (organie carbon and
lipid concentrations) of th~ sediments.
A dilution of PClls from the near- coast area into the open sea area is noted,
in different periods, for suspended matter and zooplankton. This transport phenomenon is related to the low water solubility
and therefore to the
.
. , association of
i
i
f•
pcns with the biological particlcs from the water-colwnn and sediments. The pcn
levels in zooplankton are superior on a dry weight base inferior on a lipid weight base
to thc ones in suspended matter and sediments and not related to the lipid contcnts
of thc zooplankton, indicating uptake of these organochlorine residucs through food
intake and dilution of these organoclorines in the autogenticaJly formed zooplankton
lipids.
Acknowledgement
The authors express their gratitude to the personnel of the R.V. "Belgica" for
their co-operation during the campaigns, to Mr. J. Nieuwenhuize (Delta Institute,
Yerseke), for the practical tips on gaschromatography with capillary colums and to
Ms. C. Van OngevaJlc for carcfully' typing tfiis manuscript. This researCh study
was cxecuted with the financial support of the Ministry of Public Health and Environment (Unit for the Mathcmatical Model of the North Sea and Scheldt Estuary) .
,and the conccrtcd actions (Ministry of Scicncc - V.U.B.).
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