Pergamon PII: S0045-6535(96)00228-7
Chemosphere, Vol. 33, No. 5, pp. 939-960, 1996 Copyright © 1996 Elsevier Science Ltd
Printed in Great Britain. All rights reserved 0045-6535/96 $15.00 + 0.00
TOXICITY IDENTIFICATION OF POCOMOKE RIVER POREWATER
GIAN GUPTA" and MAKESH KARUPPIAH Department of Natural Sciences
University of Maryland Eastern Shore Princess Anne, MD 21853
( R e c e i v e d i n U S A 2 4 F e b r u a r y 1 9 9 6 ; a c c e p ~ d 2 9 M a y 1 9 9 6 ) ABSTRACT
Toxicants associated with sediments affect many natural aquatic ecosystems. Pocomoke River (PR) is one of the 150 rivers and streams that feed its sediment into the Chesapeake Bay. The objective of this study was to use USEPA Toxicity Identification Evaluation (TIE) tests to identify toxicants in the sediment- porewater of PR. Samples from three depths (0-7.7, 7.8-15.4 and 15.5-23.1 cm) at four sites (1.6 km upstream of, adjacent to and 1.6 and 3.2 km downstream of the municipal sewage treatment plant (STP) outlet) were collected. The porewater samples were tested for toxicity (EC~) using the Microtox" marine luminescent bacteria (Vibrio fischeri), TOXITRAK TM toxicity test (Inhibition-%I), and Ceriodaphnia dubia (48-h survival-%S). High toxicity values (EC~ = 12.8%, % I = 93 and % S = 11) were observed for the samples collected at the site 1.6 km downstream of the STP outlet, which is near an intensive agricultural area including a poultry farm. Toxicity reduced significantly with increasing depth at every sampling site. Toxicity also decreased with distance from the most contaminated site both upstream and downstream. Qualitative MetPLATE TM analyses showed that toxic forms of metals were present in all the sampling sites except for the site 1.6 km upstream of the STP outlet. Phase I TIE tests suggested that the toxicity was due to oxidants, metals and organic compounds. Phase II TIE tests identified chlorine (total) and heavy metals [zinc (Zn), lead (Pb), copper (Cu), cadmium (Cd) and Arsenic (As)]. Polychlorinated biphenyls (PCBs) and organochlorine pesticides were found in PR porewater. Copyright © 1996 Eisevier Science Ltd
INTRODUCTION
The adsorption of biogenic and anthropogenic organic
chemicals onto particles and continuous deposition of pollutants
make sediments temporary or long-term sinks for many toxicants
(Knezovich et al., 1987). Agricultural runoff is a major source of
contaminants to the Chesapeake Bay and its tributaries (Helz and
Huggett, 1987). The quality of the Chesapeake Bay is being harmed
by the inflow of nutrients, sediments and toxic contaminants from
"Author for corresDondence
939
940
surrounding environments (USAEC, 1993). The sedimentation rate in
the Chesapeake Bay ranges from 1.6-12.6 mm/year (Kerhin et al.,
1988). The PR, a Chesapeake Bay tributary on the Eastern Shore of
Maryland, runs through the city of Pocomoke and is one of the 150
rivers and streams that feed into the Bay. Agricultural runoff is
the main source of contaminants along the Eastern shore of Maryland
(USGS, 1992). Herbicides, pesticides and heavy metals are the
important toxicants that contaminate the bay system due to
agricultural runoff (Buttleman and Lovejoy, 1987). The
concentrations of pesticides and metals in the sediments were
relatively high near the Chincoteague Inlet area (Morton and
Wolfin, 1993), located near our study site.
The PR receives runoff from extensive agricultural practices.
Along with non-point agricultural runoff, a small STP is another
source of contaminants into the PR. The STP began operating in 1971
and serves about 4,000 persons. The STP receives an average daily
inflow of 1.2 x 104 Lpd including effluents (i x 105 Lpd) from
poultry processing, food, gun manufacturing, plastic, wood and
other small scale industries.
TIE tests (USEPA 1989, 1991) can be used to characterize
classes of toxicants and identify specific toxic compounds in
porewaters or elutriates from contaminated sediments (USEPA 1991a;
Berigan and Ankley, 1991). These TIE tests include initial
toxicity, baseline toxicity, pH adjustment, aeration, filtration,
Cis-column solid phase extraction (Cls SPE), sodium thioeulfate
(Na2S203) addition, ethylenediaminetetraacetate ligand (EDTA
chelation), graduated pH and zeolite tests to identify the
toxicants in porewaters. No information is available in the
lite~rature on the toxicity of PR porewater.
OBJECTIVES
The objectives of this study were: i) to use USEPA (1989,
1991} approved TIE tests to identify toxic components in porewater
of PR, and 2) to determine the changes in toxicity with sediment
depth and distance from the municipal STP outlet and the poultry
farm discharge.
MATERIALS AND METHODS
STUDY SITE AND SAMPLE COLLECTION:
Fig. 1. Sampling sites in PR
941
Agricultural area
farm
Agricultural area
l ~ v e r
Origin - 1 6 k m
Residential a r e a
~-age treatment plant outlet
942
Four study sites (Fig. 1), 1.6 km upstream of the STP (PR1),
at the STP outlet (PR2), 1.6 km downstream of the STP (PR3;
adjacent to a poultry farm) and 3.2 km downstream of the STP (PR4;
receiving agricultural runoff) were selected for study. A Peterson
classmate dredge was used to collect the sediment samples. Sediment
samples were separated into 0-7.7, 7.8-15.4 and 15.5-23.1 cm
depths, stored in polythene ziplock bags and shipped on ice to the
University of Maryland Eastern Shore Environmental Sciences
Research Lab. Porewater was separated from the sediment by
centrifugation in an IEC (Needham Heights, MA) Model 2K centrifuge
at 5000G for 30 min using teflon centrifuge bottles. Porewater and
sediment samples were then stored in glass and plastic sample
bottles, respectively at 4°C. Microtox, Toxitrak, MetPLATE and
Ceriodaphnia dubia were used to measure the toxicity of PR
porewater.
MICROTOX R TOXICITY TEST:
Toxicity of porewater was measured using Microtox Toxicity
Analyzer 2055 (Beckman Instruments, Carlsbad, CA) (Bulich, 1984).
The ECs0 was calculated using the software Version 7.8 supplied by
Beckman.
TOXITRAK TM TEST:
Inhibition of dye reduction (Liu, 1989) with PR porewater was
measured.
METPLATE TM TEST FOR HEAVY METAL TOXICITY:
Presence of toxic heavy metals in the porewater was measured
qualitatively using microbial assay - MetPLATE, Group 206
Technologies, Gainesville, FL (Bitton et al., 1994).
ceri¢~aphnia dubia TEST:
Six animals (USEPA, Duluth, MN) grown in spring water using
Ward's (Rochester, NY) daphnia feed, were used for testing the
toxicity (survival - 48 h) of the porewater (30 mL) (hardness
1.84±0.67 mg/L of CaC03) (Mount and Norberg, 1984; USEPA 1989a). All
toxicity tests were done using the porewater without dilution, with
no change in pH (initial pH - 6.3±0.2) and at room temperature
(22±1°C) following the recommended standard procedures.
TIE TESTS:
The physico-chemical characteristics of PR porewater sample
from all sites and depths were measured using standard methods
(APHA, 1989). USEPA (1991) Phase I TIE test procedures were used to
determine the toxicity of the porewater using Microtox R and
Ceriodaphnia dubia. In Phase II TIE tests (USEPA, 1989), metal
concentrations in porewater were analyzed using a Perkin-Elmer
(Norwalk, CT) Atomic Absorption Spectrophotometer with graphite
furnace (detection limits for Pb, Cu, Cd and As were 0.05, 0.02,
0.003 and 0.2 ~g/L, respectively) or flame emission (detection
limit for Zn was 0.1 mg/L). Nitric acid digestion procedure was
used for preparing samples for analyzing heavy metals in the
por~aater (APHA, 1989; Hoke etal., 1993).
Organic compounds in PR porewater were analyzed using Hewlett
Packard 5890 A (San Fernando, CA) Gas Chromatograph (GC) with
Eleo~ron Capture Detector. A 50 ~L sample of surrogate was used as
internal standard (including blank). The surrogate was a mixture of
PCB #14 (3,5-dichlorobiphenyl) = 0.1698 ~g/mL + PCB #166
(2,3,4,4'5,6-hexachlorobiphenyl)= 0.146 ~g/mL. The oven conditions
943
944
were set at 100°C initially for 2 min then to 170°C at 4°C/min, then
to 280°C at 3°C/min; final holding time was 5 min at 280°C for PCBs.
A mixture of Alltech (Deerfield, IL) pesticide standards was used
for pesticide analyses (APHA, 1989). The oven conditions were set
at 50°C initially for 2 min then to 280°C at 10°C/min then to 310°C
at 4°C/min; final holding was 4 min for pesticides. A splitlees 5%
phenylmethyl silicon capillary (60 m length) column (DB-5, i.d.:
0.32 mm) and split/splitless 5% phenylmethyl silicon capillary (25
m length) column (i.d.: 0.2 mm) was used for PCB and pesticide
analyses, respectively. The carrier gas was hydrogen for PCBs and
helium for pesticides. The amount of sample injected was 2 #L
(APHA, 1989).
STATISTICAL ANALYSES
Randomized complete block (Gomez and Gomez, 1984) was used as
the experimental design. Analysis of Variance (ANOVA) and least
significant differences (LSD) were calculated (p~ 0.05) using SAS
(1985). All the experiments were replicated three times.
RESULTS AND DISCUSSION
Mean values of the porewater characteristics from different
sites are given in Table 1. The PR porewater was slightly acidic,
soft and had low dissolved oxygen. Total chlorine concentrations
ranged from 0.44-1.58 mg/L in the porewater.
TOXICITY TESTS:
The toxicity of PR porewater (7.7 cm depth), using various
tests, was highest at PR3 and lowest at PR1 (Table 2). Toxicity
(EC~%) to light emitting marine bacterium Vibrio fischeri at PR3
was 12.8%. Similar results have been reported on porewater toxicity
Table i: Physico-chemical characteristics of porewater (7.7 cm depth)
Site
Characteristic
PR1
PR2
PR3
PR4
(LSD)"
pH
6.1
6.0
Conductivity (mS/cm)
0.75
0.76
Turbidity (NTU)
2
3
Dissolved Oxygen (mg/L)
0.24
0.22
Salinity (%)
0.01
0.03
Nitrogen-ammonia (mg/L)
8 9
Nitrogen-nitrate (mg/L)
1.0
1.4
Oxid.Red. Potential (my)
89
90
Hardness (mg/L of CaCO3)
1.91
2.51
Total Chlorine (mg/L)
0.53
1.58
Sulfide (mg/L)
0.43
1.55
Phosphate (mg/L)
3.95
4.15
6.4
6
.5
(0.1
6)
0.74
0.74
(0.002)
4 4
(NV
")
0.1
8
0.2
0
(NV
)
0.0
7
0.0
9
(0.0
13
)
4
3
(3.77)
0.4
0
.4
(0.2
8)
85
84
(5.09)
1.5
1
.44
(0
.02
6)
0.7
8
0.4
4
(NV
)
0.3
8
0.3
7
(HV
)
3.0
1
3.0
0
(0.1
46
)
"Least significant differences (p~ 0.05)
"No value
946
Table 2: Toxicity (mean values) of PR porewater (7.7 cm depth)
Sampling Site
Toxicity test PR1 PR2 PR3 PR4 LSD"
Microtox (EC~%) 85 58 13 37 3.62
Toxitrak (% I) 14 58 93 66 7.11
C. dubia (48hr-%S) 94 55 11 39 12.84
MetPLATE P(-)'" Y(+) Y(+) Y(+)
" Least significant differences
°'P(-) Purple (negative), Y (+) Yellow (positive)
Table 3: Changes in porewater toxicity (Microtox EC~%, mean values')
with depth
Depth
(cm)
Site
PR1 PR2 PR3 PR4 LSD"
7.7 85 58 13 37 3.62
15.4 92 63 26 46 1.52
23.1 97 71 39 62 2.43
LSD 2.48 2.92 3.26 2.49
"All means are significantly different (PS 0.05) from one another
"'Least significant differences
(EC~ = 52.1-63.3%) of Lower Fox River, WI (Hoke et al., 1992) and
Grand Calumet River, IN, (EC~ = 0.3-93.8%) (Hoke et al., 1993). The
toxicity of all sites was significantly (p~ 0.05) different from
each other. Similar results were observed using Toxitrak TM (%
Inhibition) and Ceriodaphnia dubia (48 hr % survival) tests; both
these tests confirmed that PR3 was the most toxic and PR1 was the
least toxic site. MetPLATE TM tests were positive for all the sites
except for PR1 porewater showing thereby that the toxicity at this
site was not from heavy metals.
Mean values of EC~ (Microtox) ranged from 13-97% (Table 3).
The porewaters with EC~values ranging from 0-19, 20-39, 40-59, 60-
79, 80-99 and >100% have been classified as extremely toxic, very
toxic, toxic, moderately toxic, slightly toxic and non toxic,
respectively (Bennett and Cubbage, 1992). Since EC~ value for PR3
is 12.8%, it can be considered to be an extremely toxic site;
agricultural farm runoff including runoff from the poultry farm
were the main sources of pollutants at this site. The sites PR4 and
PR2 were less toxic than PR3 at the three depths studied and PRI
was the least toxic of all the four sites. The toxicity decreased
with increasing distance (in both directions because of the tides)
from PR3 and also with increasing depth indicating a reduction in
anthropogenic sources of pollution. The toxicity of the porewater
at PR2 was higher than the toxicity of the porewater at PR1 because
of tlhe discharge of pollutants from the STP at PR2. The PR4 is more
toxic than PR1 from the transport of pollutants from both PR2 and
PR3. The pollutants from point sources in the freshwater sediment
systems transport, disperse and dilute with increasing distance
947
948
from point of origin (Hellawell, 1988); the PR with a n average
salinity of 0.05±0.04 is a tidal river. Ankley etal., (1990) and
Dieter et al., (1994) reported some inconsistencies with theuse of
Microtox. However Microtox test (EC~) has been used in several
other sediment toxicity studies and was found to be highly
reproducible and less time consuming (Hoke et al., 1993 and
Toussaint et al., 1995); hence Microtox was used for further TIE
tests; Ceriodaphnia dubia was also used as an additional test.
TIE TESTS:
Phase I TIE test results for the most toxic sample (PR3 - 7.7
cm depth) are shown in Table 4. Reduction in toxicity (of the
porewater) was found with aeration (at initial pH), graduated pH
(11) test, sodium thiosulfate addition, EDTA chelation and C~s
column tests. These Phase I TIE test results suggest that the PR
porewater toxicity was due to pH sensitive toxicants/volatile
compounds and/or oxidants, heavy metals and organic compounds. The
Ceriodaphnia dubia test results were similar to that of Microtox i
test (Table 4). Hellawell (1988) reported that the toxicity of
metals is high in soft water than hardwater; the PR porewater is
very soft (CaCO 3 hardness - 1.84 mg/L, Table 1). Hoke et al., (1993)
found that water hardness (upto 3000 mg/L of Caco3) did not have any
effect on the Microtox test. Also the change in pH (6.8 - 8.4) does
not affect ~Microtox' toxicity significantly (Yates and Porter,
1984). Sodium thiosulfate addition decreased the toxicity possibly
because of the presence of oxidants or metals in the porewater.
Further, Phase II TIE tests revealed that the main toxicants
in PR porewater were total chlorine and heavy metals. The AAS
949
Table 4: Phase I TIE tests (site PR3)
Mlcrotox
Toxicity characterization tests EC~ %
Ceriodephnia
dubia
tS
Initial toxicity
Aeration (pH.._~.,)
Filtration (p . I -~)
EDTA chelation
Na2S~O 3 addition
Post Cil SPE test
Graduated pH test
p.3
pH~
PHIl
Zeolite
za (o .68 )"
49 ( 0 . 0 8 )
Z4 ( 0 . 2 3 )
88 (Z .63)
5? ( 0 . 2 0 )
?z (o.8z)
Z (NV")
z3 (o .68 )
27 (0.24)
z5 (o .zT)
zz (o .?z)
28 ( 0 . 3 7 )
22 ( 0 . 9 4 )
s3 ( z . ? 3 )
6? ( 0 . 6 3 )
?? (o.8e)
NS oel
11 (o.~z)
33 (1 .41 )
17 (1 .63 )
"Values in parentheses are standard deviations
"*No value
"*'No survival
950
analyses of the porewater showed high concentrations of Zn followed
by Pb, Cu, Cd and As (Table 5). The concentrations of Zn, Pb, Cu
and Cd were found to be significantly different (ps 0.05) at all
sites and depths. The metal concentrations in the porewater were
highest at the 7.7 cm depth and lowest at the 23.1 cm depth. The
porewater from PR3 had the highest metal concentrations (Table 5).
The concentrations of Zn, Pb, Cu and Cd ranged from 1.39 - 4.62,
0.57 - 0.74, 0.017 - 0.108 and 0.001 - 0.025 mg/L, respectively.
Arsenic was found in PR3 (7.7 and 15.4 cm depth) and PR4 (7.7 cm
depth) ranging from 0.004 - 0.007 mg/L. Arsenic is present both in
herbicides (Hellawell, 1988) and poultry litter (Gupta and Kelly,
1990). The site PR3 is 1.6 km downstream of the STP outlet but
adjacent to a poultry farm which appears to be the source of metals
into the river along with other agricultural runoff. Berndtsson
(1990) studied metal accumulation in sediments receiving sewage
effluents and extensive drainage from agricultural areas in River
Hoje, Sweden, and found high concentrations of Zn (1700 ppm), Pb
(180 ppm) and Cu (740 ppm). High concentration of Zn in PR
porewater can be both from agricultural runoff and from the
industries that contribute to the sewage influent. The Delmarva
Peninsula, where PR is located, is ranked 4th in the nation in
poultry and litter production (9,500 tons per day); land disposal
of large amounts of poultry litter can contribute heavy metals (Cu,
Cd and As) to waters and sediments after precipitation. A ton of
poultry litter contains approximately 320 ppm Cu, 35 ppm As and Pb
each and smaller amounts of Cd and Hg (Gupta and Kelly, 1990).
Cadmium tends to accumulate in sediments near sewage outfalls
951
Table 5: Porewater metal concentrations (mg/L)
METALS SITES
PR2 Depth PR1 ( c u )
7.7 2.12 ~
15.4 1.73 k
23.1" 1.39 ~
LSD 0.24
7.7 0.58 ~
15.4 0.57 k
23.1 0.57 ~
LSD 0.0076
7.7 0.026 ~
15.4 0.020 k
23.1 0.017 ~
LSD 0.002
7.7 0.001 ~
15.4 0.001"
23.1 0.001"
LSD 0.0001
7.7 ND °°
15.4 ND
23.1 ND
PR3 PR4 LSD °
3.05 ~ 4.62 p 3.18 ~ 0.87
Zn 2.61 = 3.51 M 2.73 ~ 0.12
1.91 ~ 2.892 2.56 ~ 0.14
0.02 0.12 0.08
0.59 e 0.74 p 0.58 b 0. 002
Pb 0.586 0.59 M 0.58 jr 0. 007
0.57 ~ 0.59 ~ 0.58 ~ 0. 002
0.0076 0.0037 0.0076
0.064 ~ 0.i08 ~ 0.070 ~ 0.006
Cu 0.035" 0.076 ~ 0.045 ~ 0.005
0. 022 ~ 0. 0552 0. 028 ~ 0. 002
0.004 0.006 0.008
0. 002 ~ 0. 025 ~ 0. 003 ~ 0. 0006
Cd 0. 0 0 2 ~ 0. 003 ~ 0. 002 ~ 0. 0002
0. 001 ~ 0. 002 ~ 0. 001 ~ 0. 0001
0. 0001 0.0047 0.0002
ND 0. 007 0. 004
AS ND 0. 005 ND
ND ND ND
~eaat significant differences
"Not detected
a d g J b e h k cfil
columnwiae comparisons within blocks; means with same letters a~e not significantly different (p~ 0.05)
m n o p rowwiae comparisons within blocks; means with same letters q r 8 t - are not significantly different (p~ 0.05) u v w x
952
(Swartz et al., 1985). Cadmium in PR porewater seems to be from the
sewage outfall and the poultry farm runoff.
The porewater from PR2 had higher concentrations of metals
than the porewater from PR1 but lower than the porewater from PR3.
This increase in the metal contents at PR3 can be from both the
transport of metals from PR2 (STP) and from the poultry and
agricultural farm runoff. The porewater from PR4 had higher
concentration of metals than the porewater from PR1. The
concentration of metals decreased with increasing depth at each of
the sites indicating a reduction in anthropogenic sources of
pollution with increasing time. High concentration of Cd at only
PR3 (7.7 cm depth) suggests point-sources of pollution of
relatively recent origin (Hershelman et al., 1981). The
concentration of all metals (Zn, Pb, Cu and Cd) exceeded the
freshwater acute criteria for protection of aquatic life (USEPA,
1991b) and also the range of the priority pollutants in porewater
(Straub, 1989)(Table 6). The mean concentration of Zn in the PR
porewater was higher compared with the EC~ (Microtox) value
reported for Zn by Chou and Hee (1994) (Table 6).
Phase I TIE tests suggested reduction in toxicity after Na~S203
addition; the PR porewater was analyzed for total chlorine. Even
though Na2S203 additions are designed to characterize the toxicity
of oxidants such as chlorine and its derivatives, this decrease in
the toxicity can also be from the removal of metals such as Cu and
Cd (USEPA, 1991). The total chlorine was found to be 0.53, 1.58,
0.78 and 0.44 mg/L at PR1, PR2, PR3 and PR4, respectively. Highest
concentration of total chlorine was found near the STP outlet
Table 6: Comparison of metal concentrations in PR porewater with Microtox "EC~"
concentration, EPA freshwater acute criteria and priority pollutant range in
porewater (#g/L)
Metal
Mean conc. of
Metal ion
Freshwater
Range
metals in PR
Microtox EC~ conc.
acute criteria
(Straub, 1989)
porewater
(Chou and Hee, 1994)
(USEPA, 1991b)
(7.7 cm depth)
Zn
3
24
0
10
00
1
20
9
0-3
30
Pb
6
00
6
00
8
3
30
-40
0
Cu
7
0
80
0
18
1
1-
49
Cd
8
20
00
0
4 2
- 7
954
(PR2), confirming the STP as a source of toxicity. The Pocomoke STP
uses only a primary settling tank and the effluent is then treated
with a large dose of chlorine. Total residual chlorine is toxic to
different organisms and the LC~of chlorine induced oxidants to mud
crab - Panopeus herbstii - is 10 mg/L (Breisch et al., 1984). over
140 STPs along the Chesapeake Bay use chlorine as disinfectant; the
total residual chlorine has been reported to be as high as 19 mg/L
in these effluents (Breisch et al., 1984).
Solid phase extraction (Cj8) test suggested that the toxicity
is from nonpolar organic compounds. The analysis of porewater (PR3,
7.7 cm depth) showed the presence of organochlorine pesticides
(Table 7). The concentration of heptachlor was higher than the
criteria for the freshwater aquatic life protection (Table 7). The
concentrations of other pesticides and PCBs found in PR porewater
were lower than the criteria for freshwater aquatic life
protection. Nearly 1.4 million kg of pesticides are used annually
for agricultural purposes on the Delmarva Peninsula (USGS, 1992).
Site PR3 is near an intensive agricultural area accounting for
these long term persistent pesticides in the porewater. Hoke et
al., (1993) reported lindane, chlordane and heptachlor
concentrations ranging from 0.1-0.7, 0.1-3.1 and 0.5-4.6 ~g/L in
porewater of Grand Calumet River, IN.
A total of 50 PCB congeners were found in the porewater (PR3,
7.7 cmdepth); the 10 congeners with the highest concentrations are
listed in Table 8. PCBs are ubiquitous in the environment and are
of anthropogenic nature (Potter and Pawliszyn, 1994). PCB
contamination in Michigan harbor has been attributed to non-point
Table 7: Pesticides and PCBs in PR porewater (PR3, 7.7 cm depth)
and comparison with freshwater aquatic life protection
criteria
955
Pesticides ng/L
Fresh water aquatic
life protection criteria
(ng/L) (Sittig, 1985)
Lindane 80
(B HCH 0.19
HCH) 0.17
Heptachlor 19.66 3.8
Chlordane 4
(t-Chlordane 0.21
c-Chlordane) 0.27
PCBs 12.88 14
Table 8: PCB congeners concentration in PR porewaters
Congener Name Mass (ng/L)
Number
105 2,3,3',4,4'-pentachlorobiphenyl 0.905
99 2,2',4,4',5-pentachlorobiphenyl 0.545
149 2,2',3,4',5',6-hexachlorobiphenyl 0.532
180 2,2',3,4,4',5,5'-heptachlorobiphenyl 0.445
28 2,4,4'-trichlorobiphenyl 0.289
182 2,2',3,4,4',5,6'-heptachlorobiphenyl 0.217
190 2,3,3',4,4',5,6-heptachlorobiphenyl 0.214
151 2,2',3,5,5',6-hexachlorobiphenyl 0.198
76 2',3,4,5,-tetrachlorobiphenyl 0.178
174 2,2', 3'3',4,5,6'-heptachlorobiphenyl 0.178
956
source pollution (Baudo and Muntau, 1990). PCBs were used as heat-
transfer fluids, hydraulic fluids, solvent extenders, plasticizers,
organic diluents and dielectric fluids (Abramowicz et al., 1993).
Polychlorlnated biphenyls might have been transported from other
sources such as leaking capacitor/transformer. Since the post-Cls
test showed a reduction in toxicity and the analyses of the
porewater revealed the presence of pesticides and PCBs, these
compounds may also be contributing to the toxicity of the
porewater.
The following conclusions can bemadebesed on the results of
this study:
1. The sampling site, 1.6 km downstream of the STP outlet had the
most toxic porewater compared to the other sites 1.6-3.2 km away
both downstream or upstream. The porewater from this site was
"extremely toxic"; sites 1.6 km upstream or downstream were
"very toxic" and the site 3.2 kmupetream was "sllghtly toxic".
2. Phase I and II TIE tests and porewater analyses for organic
compounds identified total chlorine and metals from STP, metals
and pesticides (from agrlcultural sources) as the contaminants
in the PR porewater.
3. The concentrations of heavy metals and the toxicity of the PR
porewater decreased with depth (7.7 > 15.4 > 23.1 cm) and with
increasing distance from the most polluted site.
ACKNOWLEDGEMENTS:
Thanks are due Dr. Joel Baker and Mr. Eric Nelson, CBL,
Solomons, MD, for their help with PCB and pesticide analyses.
957
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