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Potential underestimation of chlorinated hydrocarbon concentrations in fresh water
Chemosphere, Vol.19, Nos.8/9, pp 1277-1287, 1989 Printed in Great Britain
0045-6535/89 $3.OO + .00 Pergamon Press plc
POTENTIAL UNDERESTIMATION OF CHLORINATED HYDROCARBON CONCENTRATIONS IN FRESH WATER
R. James Maguire* and Richard J. Tkacz Rivers Research Branch, National Water Research Institute Department of Environment, CanadaCentre for Inland Waters Burlington, Ontario, Canada L7R 4A6
ABSTRACT Significant concentrations of PCBs and other chlorinated hydrocarbons have been found in dichloromethane extracts of f i l t e r e d Niagara River, Canada, water at pH 12 after the water had been thoroughly extracted at pH 1. In samples from 43 dates in 1985/86, the contribution of the basic extract to the total concentration derived from acidic, basic and suspended solids extracts ranged from 0% for 31 of these chemicals to 100% for PCBs 15, 114 and 201, aldrin and p,p'-DDT. When the sums of concentrations of each chemical found in Niagara River water in the acidic, basic and suspended solids extracts over the 43 sampling dates were themselves summed, the basic fraction contributed 40% to the total concentrations of a l l chemicals, and 48% i f only PCBs were considered. Experiments with water from another source showed that some PCBs were recovered in dichloromethane extracts of basic f i l t e r e d water which had previously been thoroughly extracted under either acidic or neutral conditions. These results indicate that concentrations of chlorinated hydrocarbons in Niagara River water determined by extraction solely at neutral pH, the usual technique, may be underestimated. This finding, which may have general a p p l i c a b i l i t y to fresh waters, may be the result of a strong association between a fraction of the dissolved l i p o p h i l i c chemicals and dissolved organic matter in fresh water, an association that is resistant to organic solvent extraction at acidic or neutral pH, but which is at least p a r t i a l l y disrupted by extraction at high pH. INTRODUCTION
The contamination of Lake Ontario by chemicals in the Niagara River is a serious problem which has been studied intensively over the past twenty years (1-3).
Chlorinated hydrocarbons
such as PCBs, organochlorine pesticides and dioxins have been a focus of concern because of the r e l a t i v e l y long environmental persistence of these chemicals. The standard procedure for the determination of PCBs and other chlorinated hydrocarbons in water involves extraction at neutral pH, with or without pH adjustment (4-6).
Average recoveries of chlorinated hydrocar-
bons by solvent extraction from natural waters and wastewaters at reported in the range 63-86% (3,6-8).
neutral pH have been
Recent observations of PCBs and other chlorinated
hydrocarbons in dichloromethane extracts of f i l t e r e d Niagara River water at pH 12 after the water had been thoroughly extracted at p H I have indicated that standard methods used for the
1277
1278
extraction of chlorinated hydrocarbons from natural water may not be adequate. T h i s a r t i c l e describes those observations as well as experiments in which such chemicals were recovered from natural water samples and spiked natural water samples at pH 12 after the water had been extracted at either acidic or neutral pH. EXPERIMENTAL SECTION Materials Standards of chlorinated pesticides and hydrocarbons were obtained from chromatographic supply companies. Sets of PCB congeners were obtained from the National Research Council of Canada, Halifax, NS.
These PCB congeners represent, by weight, 3Z of Aroclor 1221, 44% of
Aroclor 1242, 48% of Aroclor 1248, 38% of Aroclor 1254 and 60% of Aroclor 1260, and thus the total of the PCB congeners reported in this study should not be regarded as "total PCBs". Pesticide grade dichloromethane and other solvents were obtained from different suppliers and their purity at lO00x concentration was checked before use.
The sodium sulfate, aluminum
f o i l , glass fibre f i l t e r s and disposable pipets were heated to 500°C for 24 h before use. All glassware was rinsed with pesticide grade solvents before use. Hydrochloric acid and sodium hydroxide solutions used for pH adjustment were prepared from reagent grade chemicals, but were extracted with pentane before use to eliminate contamination. Burlington Ship Canal Samples F o r t y - l i t r e water samples were collected on two dates in July and August, 1988, from the Burlington Ship Canal, which connects Hamilton Harbour with Lake Ontario. collected in modified stainless steel beverage containers (7).
The samples were
The samples were treated in
two different ways, as follows. Neutral-then-Basic extractions The sample c o l l e c t e d
in
July
1988 was d i v i d e d
d e t e r m i n a t i o n o f ambient PC8 c o n c e n t r a t i o n s experiment.
One sub-sample was f i l t e r e d
freeze-dried.
After
dichloromethane f o r steel
The f i l t e r
freeze-drying,
24 h w i t h
two 20 L sub-samples so t h a t
steel
a
as a PCB s p i k e - r e c o v e r y
through a 0.45 IJm glass f i b r e f i l t e r
n i t r o g e n and the m o d i f i e d p r e s s u r i z e d s t a i n l e s s and Teflon t r a n s f e r l i n e s ( 7 ) .
into
could be done as w e l l
beverage c o n t a i n e r s ,
using compressed pressure f i l t e r s
c o n t a i n i n g the suspended s o l i d s was frozen and then the
occasional
filter
was
shaking.
beverage c o n t a i n e r and e x t r a c t e d t w i c e by s t i r r i n g
1 h ( w a t e r / d l c h l o r o m e t h a n e r a t i o 40/1, v / v ) .
extracted
The f i l t r a t e
in
a
test
was t r a n s f e r r e d
tube
with
to a 40 L
w i t h 500 mL o f dichloromethane f o r
The pH of the sample was 7.4.
After extraction
at n e u t r a l pH, the aqueous phase was made basic to pH 12 by the a d d i t i o n o f concentrated NaOH, All
dichloromethane e x t r a c t s
were d r i e d and concentrated w i t h s o l v e n t changing to 1 mL of hexane.
and the w a t e r was e x t r a c t e d t w i c e more w i t h d i c h l o r o m e t h a n e .
The 1 mL hexane e x t r a c t s
were cleaned up by l o a d i n g on 20 cm x 1 cm i . d .
columns of a c t i v a t e d s i l i c a
gel and e l u t i o n
w i t h 60 mL of hexane f o l l o w e d by 60 mL o f 20Z dichloromethane - 80Z hexane ( v / v ) . PCBs and c h l o r i n a t e d
insecticides
eluted with
Most of the
hexane, but o c c a s i o n a l l y t r a c e s were found in
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the dichloromethane-hexane fraction.
The two fractions were combined, dried and concentrated
with solvent changing to 1.0 mL hexane with a toluene "keeper". The other sub-sample was spiked with 14 PCB congeners at concentrations of 1-40 ng/L. After a 16 h aging period the sample was f i l t e r e d , extracted and cleaned up as described above.
An aging period of 16 h, which corresponds to the t r a n s i t time of the Niagara River
from Lake Erie to Lake Ontario, was chosen so that the spiking experiment would have relevance to the Niagara River results (cf. below). Acidic-then-Basic extractions The sample collected in August 1988 was also divided into two 20 L sub-samples so that a determination of ambient PCB concentrations could be done as well as a PCB spike-recovery experiment.
One sub-sample was f i l t e r e d as described above. The f i l t r a t e was transferred to
a 40 L container, i t s pH was adjusted to 1 with concentrated HCI, and i t was extracted twice by s t i r r i n g with 500 mL of dichloromethane for 1 h.
After the extraction at pH I , the aqueous
phase was made basic to pH 12 by the addition of extracted twice more with dichloromethane.
concentrated NaOH, and the water was
A11 dichloromethane extracts were then cleaned up
as described above in the neutral-then-basic extraction experiment. The other sub-sample was spiked with 14 PCB congeners at concentrations of 1-40 ng/L. After a 16 h aging period the sample was f i l t e r e d and extracted under acidic-then-basic conditions.
The extracts were cleanup as described above.
Recoveries from D i s t i l l e d Water
In addition to the experiments with Burlington Ship Canal water, recovery experiments with
14
PCB congeners spiked
neutral-then-basic containers.
conditions
at and
1 - 4 0 ng/L in
distilled
acidic-then-basic
water were performed under
conditions
in
The spikes were aged for 30 min before extraction.
primarily conducted to determine i f
the
steel
beverage
These experiments were
any PCBs could be found in basic extracts of spiked
d i s t i l l e d water a f t e r extraction under either neutral or acidic conditions. Niagara River Samples
Water samples were collected at 43 dates between August 1985 and August 1986 near the mouth of
the Niagara River at
Niagara-on-the-Lake,
Ontario.
Twenty-litre samples were
collected 3-5 m from shore at a depth of 0.5 m in the modified pressurized beverage containers described above.
In order to avoid contamination by the surface mlcrolayer, the tops of the
containers were always removed under water. Within 2 h of collection the water samples were f i l t e r e d and were being extracted under acidic-then-neutral conditions as described for
the Burlington Ship Canal samples.
The
dichloromethane extracts were dried, solvent-changed to hexane with a toluene "keeper", and concentrated.
Extracts of suspended solids were concentrated to 1 mL, while extracts of water
were concentrated to 10 mL.
In contrast to the Burlington Ship Canal samples, the Niagara
River samples did not require clean-up.
1280
The Niagara River samples were only extracted under acidic-then-basic conditions since the purpose was to determine basic chemicals such as amines, and the f i r s t extraction under acidic conditions was intended to act as a clean-up step by removing acidic and neutral interferents.
The subsequent finding of chlorinated hydrocarbons in basic extracts prompted the
experiments with Burlington Ship Canal water and d i s t i l l e d water described above. Analyses Analyses of the sample extracts were performed with a Hewlett-Packard 5890A capillary column gas chromatograph with a single injector-dual column-dual electron capture detector technique.
One column was Ultra-2 and the other was 0V-17.
0.2 mm i . d . x 25 m in length, with 0.17 1~n film thickness. were 250 and 350°C, respectively.
Column dimensions were
Injector and detector temperatures
The i n i t i a l column temperature was 60°C, and the program
rate was 3°/min to 280°C, with an 8 min final hold.
The analyses were performed in 8:1 s p l i t
mode. The carrier gas flow rate was 1.0-1.5 mL/min (50-80 cm/s) and the make-up gas flow rate was 20 mL/min. For the Burlington Ship Canal samples, 14 PCB congeners were sought, while for the Niagara River samples, 89 chlorinated benzenes, alkanes, alkenes, insecticides and PCB congeners were sought. Standardmixtures of a11 of these compounds in the expected concentration
ranges were prepared and used to calibrate retention times and detector responses.
Chromatographic "windows" were typically 0.04 min at most at 80 min retention time. presence of a compound was taken to be tentatively confirmed i f appropriate chromatographic window on both columns, ( i i )
(i)
The
i t occurred within the
the concentrations determined with
each column were within 50% of each other (in which case the lower of the two concentrations was reported), and ( i i i )
the concentrations were above the l i m i t of quantitation for the
particular sample, as opposed to the l i m i t of detection (g).
The limits of quantitation for
the 89 compounds sought were f a i r l y conservative, being at least about 10 times the limits of detection for similar sizes of water samples in two previous studies of contaminants in the Niagara River (3,10).
Measurementprecision near the l i m i t of quantitation was about 15-20%.
Solvent and reagent blanks were performed routinely, and procedural blanks were performed three times during the course of the study.
At no time was contamination evident.
RESULTS D i s t i l l e d Water PCBs spiked into d i s t i l l e d water at
1-40 ng/L concentrations
in the steel beverage
containers and a11owed to age for 30 min were only recovered in the f i r s t of the duplicate 1 h extractions carried out under either neutral or acidic conditions, and not at a l l second extraction or in subsequent extractions of basic d i s t i l l e d water.
in the
The recoveries were
similar to those observed for the steel containers in an e a r l i e r study, in which 17 chlorinated hydrocarbons including chlorobenzenes, PCBs, octachlorostyrene and Mirex spiked into d i s t i l l e d water at fractional ng/L concentrations were recovered with efficiencies of 86-130% (average 102 ± 12%) with dichloromethane in t r i p l i c a t e extractions with s t i r r i n g for 10 min (7).
The water/dichloromethane ratio in that study was 30/I (v/v) for the f i r s t extraction,
1281
which saturated the water with dichloromethane, and 180/1 for the second and t h i r d extractions.
The aging time of the spike was 5 min in that study.
The extraction efficiencies
using the steel containers in this study and the e a r l i e r study are similar to those observed for chlorobenzenes with an a l l - g l a s s system (11).
Spikes of a l l
twelve possible chloroben-
zenes in d i s t i l l e d water in the range of 0.1-25700 ng/L were recovered with efficiencies of 80-96% (average 85 ± 5%) with hexane in a single extraction in a l l - g l a s s containers (water/ hexane r a t i o 54/1, v/v) with s t i r r i n g for 4 hr (11).
The aging time of the spike in this
l a t t e r study was not stated. Burlington Ship Canal Water Table 1 shows recoveries of 14 PCBs spiked into Burlington Ship Canal water at concentrations
of
1-40 ng/L and extracted under d i f f e r e n t
corrected for PCBs present before spiking.
conditions.
The concentrations were
The r a t i o of spiked to ambient concentrations was
in the range 1.0-48~5, with most ratios greater than 3.
I t is probable that there was signi-
ficant error in those few cases in which the spiked-to-ambient concentration ratio was less than 2.
Nevertheless, the data demonstrate that some PCBs were recovered in basic extracts of
f i l t e r e d water a f t e r the water had been extracted at either neutral or acidic pH. menon did not appear to be the result of conditions.
This pheno-
incomplete extraction under acidic or neutral
Extraction of acidic or neutral water samples, which had already been extracted
twice, one more time yielded no traces of PCBs.
In addition, there were no differences found
in extraction efficiency between glass and metal containers.
The contribution to the recovery
from the basic extracts was small, in the range 0-5.6% i f
water and suspended solids were
considered or
0-12.5% i f
only the dissolved phase were considered.
The average total
recoveries were similar under the two sets of extraction conditions, 71 and 77%. The overall recoveries determined in this work are similar to those of two e a r l i e r studies in the same area, but with extraction at neutral
pH only.
In one of
these studies, the extraction
efficiencies into dichloromethane from Niagara River water of many of the compounds sought in this study, at ng/L concentrations in a l l - g l a s s containers a f t e r overnight aging of the spike, were in the range 50-86%, with a mean of 63% (3).
In the other study using steel containers,
the extraction efficiencies of these or similar chlorinated hydrocarbons into dichloromethane from Lake Ontario water, at fractional ng/L concentrations a f t e r a 16 h aging of the spike, were in the range 56-118%, with a mean of 86% (7). Table 2 shows ambient concentrations of the 14 PCB congeners sought in Burlington Ship Canal water samples collected on the two dates in question.
In some cases these PCBs were
either not found at a l l or found only in the suspended solids fraction.
Under neutral-then-
basic extraction conditions 8 of the 14 PCBs sought were found in the basic extract, while under acidic-then-basic conditions on another date only 1 of the 14 PCBs sought was found in the basic extract. extracts in
The contribution to the concentration for each PCB congener from the basic
the two samples was in
the
range 0-33% i f
water and suspended solids were
considered or 0-50% i f only the dissolved phase were considered.
1282
Table 1.
Percentage recoveries of PCB congeners spiked into Burlington Ship Canal water.*
Chemical
Spiking Level (ng/L)
PCB 15 PCB 101 PCB 151 PCB 118 PCB 153 PCB 141 PCB 138 PCB 187 PCB 180 PCB 170 PCB 201 PCB 196 PCB 195 PCB 194
38.8 4.5 2.6 2.0 1.7 1.4 2.1 1.7 1.5 1.6 2.2 1.8 1.3 1.2
Experiment 2
Experiment I N 65 84 69 101 96 61 78 57 62 45 49 46 40 51
B
S
Total
A
3 2 6 2
5 5 8 13 4 3 7 13 5 5 5 2
65 92 76 115 111 65 81 64 76 50 56 51 42 53
53 49 48 75 59 51 68 56 56 32 49 46 40 42
I 2
2
Average total recovery
71 ± 22
B
3 4 6 5 6 4 3 4 1 3 3 4
S
Total
3 17 19 28 32 23 25 22 20 35 21 20 18 22
56 69 71 107 96 74 99 82 79 71 71 69 61 68
77 ± 15
*N and B or A and B refer to extracts made sequentially of f i l t e r e d water under neutral-thenbasic or acidic-then-basic conditions, respectively. S refers to the extract of the suspended solids. The chemicals are listed in order of elution from an Ultra-2 column. The numbering scheme for the PCB congeners is given in ref. 25. Table 2.
PCB concentrations (ng/L) in various extracts of Burlington Ship Canal water.*
Chemical
N
PCB 15 PCB 101 PCB 151 PCB 118 PCB 153 PCB 141 PCB 138 PCB 187 PCB 180 PCB 170 PCB 201 PCB 196 PCB 195 PCB 194
0.8 0.6 0.2 0.2 0.3 0.1 0.8 0.1 0.2 0.1
July 26, 1988 B S
0.4 0.1 0.3 0.1 0.7 0.1 0.2 0.1
0.8 0.4 0.4 0.7 0.2 0.6 0.3 0.6 0.4 0.3 0.2 0.1
Total 0.8 1.8 0.7 0.6 1.3 0.4 2.1 0.5 1.0 0.6 0.3 0.2 0.i
A
0.3 0.1
August 29, 1988 B S
0.i
Total
0.2 0.I
0.6 0.2
0.1
0.2
0.3
0.4
0.2 0.1 0.1 0.7
0.2 0.1 0.1 1.1
*N and B or A and B refer to extracts made sequentially of f i l t e r e d water under neutral-thenbasic or acidic-then-basic conditions, respectively. S refers to the extract of the suspended solids. To f a c i l i t a t e comparison, concentrations in S are given in units of ng of chemical associated with the suspended solids per l i t r e of water. Concentrations are not corrected for recovery. The limits of quantitation vary with each chemical and are in the range 0.04-0.8 ng/L for I mL extracts of water and for 1 mL extracts of suspended solids, each from a 20L sample. The compounds are listed in order of elution from an Ultra-2 column. The numbering scheme for the PCB congeners is given in ref. 25.
1283
Niaqara River Water As stated above, the Niagara River samples were only extracted under acidic-then-basic conditions.
Fifty-nine chemicals of the 89 sought were found at least once in water collected
at 43 dates during the period August 1985 - August 1986, and 28 of these 59 chemicals were found at least once in the basic extract.
There appeared to be no seasonal pattern for the
occurrence of chlorinated hydrocarbons in basic extracts of f i l t e r e d Niagara River water.
The
suspended solids, acidic and basic extracts accounted for 86%, 6% and 10%, respectively, of the total
number of times that chemicals were determined with confidence.
In a few cases
chemicals were only found in the basic extracts, and not in the p r i o r acidic extracts.
Those
chemicals found in basic extracts were occasionally found in r e l a t i v e l y high concentrations. Table 3 shows the sums of concentrations of each chemical found in the acidic, basic and suspended solids extracts over the 43 sampling dates.
The contribution from the basic extract
to the total concentration for a l l 43 sampling dates ranged from 0% for 31 of these chemicals to 100% for PCBs 15, 114 and 201, aldrin and p,p'-DDT. Table 3.
When the sums of concentrations of
Sums of concentrations (ng/L) of chlorinated hydrocarbons in various fractions of Niagara River water.*
Chemical
A
B
S
Total
1,3-dichlorobenzene
28
1,4-dichlorobenzene
28
28
1,2-dichlorobenzene
41
41
hexachloroethane
2
2
1,3,5-trichlorobenzene
1
1
1,2,4-trichlorobenzene
108
hexachlorobutadiene 1,2,3,5-tetrachlorobenzene
6
28
5
113
2
2
3
9
1,2,4,5-tetrachlorobenzene
5
5
1,2,3,4-tetrachlorobenzene
17
17 41
pentachlorobenzene
5
12
24
a-hexachlorocyclohexane
8
2
2
12
3
8
11
hexachlorobenzene pentachloroanisole
I
i
PCB 18
7
7
PCB 15
27
PCB 54
54
PCB 31 Heptachlor
13
9
4
Aldrin PCB 44
1
cont'd next page
10
53
53
23
37
59
85
15 8
57 22
I
PCB 52 PCB 49
27 3
18
15
1284
Table 3.
(cont'd)
Chemical PCB 40 Heptachlor epoxide y-Chlordane PCB 80 o,p'-DDE PCB 101 a-Endosulfan a-Chlordane Nonachlor PCB 87 Dieldrin p,p'-DDE PCB 77 PCB 154 o,p'-DDD Endrin PCB 151 B-Endosulfan PCB 118 p,p'-DDD PCB 114 o,p'-DDT PCB 153 PCB 105 PCB 141 PCB 137 p,p'-DDT PCB 138 PCB 159 PCB 182 PCB 187 PCB 183 PCB 180 PCB 191 PCB 201 PCB 209 Totals % PCB totals only %
A
B
5 3
11 21
2
8 8 34 54
12 2 i
3 3
8
35
S
Total
1 4 4 11 7 33 21 16 1 11 I 11 98 2 I 12 5 2 20 7
i 4 4 11 7 49 45 16 i 21 9 45 164 4 5 12 8 2 63 7 12 8 86 26 12 5 45 79 2 5 4 17 27 6 17 1 1445 100 908 100
12 10 5 2 1 13
3
52 21 8 4 45 64
14 12
8 24 2
2 2 5 4 15 6
17 220 15 88 10
576 40 433 48
1 649 45 387 42
*The data represent cumulative sums of concentrations in water samples collected on 43 dates between August 1985 and August 1986. A and B refer to extracts made sequentially of f i l t e r e d water under acidic followed by basic conditions. S refers to the extract of the suspended solids. To f a c i l i t a t e comparison, concentrations in S are given in units of ng of chemical associated with the suspended solids per l i t r e of water. Concentrations are not corrected for recovery. The l i m i t s of quantitation vary with each chemical, and are in the range 0.2-40 ng/L for 10 mL extracts of water and 0.02-4 ng/L for I mL extracts of suspended solids, each from a 20 L sample. The compounds are l i s t e d in order of elution from an Ultra-2 column. The numbering scheme for the PCBs is given in ref. 25.
1285
each chemical in the acidic, basic and suspended solids extracts in Table 3 were themselves summed, the basic fraction contributed 40% to the total concentrations of a l l chemicals, and 48% i f only PCBs were considered. DISCUSSION The spiking experiments described above provide evidence that the finding of l i p o p h i l i c chlorinated hydrocarbons in basic extracts of f i l t e r e d Niagara River and Burlington Ship Canal water after prior extraction at either acidic or neutral pH was not due to incomplete extraction.
Additional evidence against incomplete extraction is provided by the observation in
several Niagara River samples of (i) acidic extracts, and ( i i ) prior acidic extracts.
chemicals in the basic extracts but not in the prior
chemicals in basic extracts at higher concentrations than in the The observation of chemicals in basic extracts after extraction at
neutral pH also tends to discount the p o s s i b i l i t y that acidifying the f i l t e r e d water i n i t i a l l y to
pH 1 produced an a r t i f a c t
e f f i c i e n t l y extracted at
whereby chlorinated hydrocarbons which might
neutrality were only p a r t i a l l y extractable at
pH I,
have been and were
recovered more e f f i c i e n t l y at pH 12. The observation of l i p o p h i l i c chemicals in basic extracts of f i l t e r e d Niagara River water after the water had been extracted at acidic or neutral pH is of considerable significance since the Niagara River has been the major source of contamination of Lake Ontario (1-3).
It
may be that concentrations of l i p o p h i l i c chemicals in the Niagara River determined solely by extraction at neutral pH have been underestimated. generally applicable to fresh waters.
In addition, this phenomenon may be
We recommend that present methods of determination of
such chemicals in fresh waters be reviewed and, i f necessary, changed to take into account any fraction which is only extracted under basic conditions.
Although i t
is not widely used for
neutral chemicals, the U.S. Environmental Protection Agency base/neutral method (12) which employs i n i t i a l extraction at pH > 11 may be more appropriate than the more commonly used method of extraction at neutral pH. The presence of chlorinated hydrocarbons in basic extracts of Niagara River and Burlington Ship Canal water after extraction at acidic or neutral pH may be due to a strong binding between a fraction of the "dissolved" chemical and dissolved or colloidal organic matter, a binding which resists disruption by organic solvent extraction at low or neutral pH, but which is at least p a r t i a l l y disrupted by extraction under basic conditions.
There is a substantial
body of evidence for the association of l i p o p h i l i c chemicals and dissolved organic matter (DOM), in particular f u l v i c and humic acids in water (13-17, and references therein).
Lipo-
p h i l i c chemicals may bind to hydrophobic sites on DOM with the resulting complex held in solution or colloidal dispersion by polar hydroxyl, carboxyl and phenolic groups. Although binding to DOM appears to be the most plausible explanation for the observations reported here, this work offers no direct proof.
The proposed pH-dependent binding of lipophilic
chemicals to DOM is, however, supported by observations of decreasing binding of phthalates and DDT to f u l v i c and humic acids, respectively, with increasing pH (18,19).
I t is expected
that the amount of DOM-bound l i p o p h i l i c compound should decrease with increasing pH since the humic or f u l v i c acid polymers should be more hydrophilic at high pH~
Moreover, in Niagara
River water samples chemicals of log Kow < 4-5, such as the f i r s t 10 chemicals of Table 3, were not
found in
basic
extracts,
in
substantial agreement with e a r l i e r evidence from
1286
laboratory experiments that compounds with log Kow < 4 would probably not be bound to DOM to an appreciable extent (13).
I t should be noted that more severe conditions than pH adjustment
have been used to disrupt DOM-lipophilic chemical associations.
For example, a significant
fraction of f u l v i c acid-bound alkanes and dialkyl phthalates (all only extractable after methylation of the f u l v i c acid (18).
"naturally" present) was
This fraction was larger than
that fraction which was extractable by organic solvents from untreated f u l v i c acid. In spiked Burlington Ship Canal water samples, PCB concentrations in basic extracts relative to neutral or acidic extracts were not as high as was the case for unspiked samples. If
strong binding between PCBs and DOM were occurring, and i f
i t were subject to kinetic
control, the foregoing observation may have been a consequence of the shorter incubation period of the spiking experiment compared to the presumably much longer period of time that those PCBs were in unspiked water.
I f this were the case, i t would suggest the need for
further study of the variation of recovery of contaminants as a function of aging time in environmental matrices. A model of the d i s t r i b u t i o n of l i p o p h i l i c chemicals in natural waters has been proposed which includes the
"compartments":
t r u l y dissolved, adsorbed to
adsorbed to non-settling particulates or macromolecules (20).
suspended solids,
and
A study of the distribution of
PCB congeners in Lake Superior water using this model indicated that
colloid-associated
contaminants may be the dominant species in most surface waters, from the viewpoint of concentration (21).
I f our observations are of general significance, the "dissolved" fraction
may be even more important than is currently believed.
Binding of ] i p o p h i l i c chemicals to DOM
may be an important mechanism for their mobilization and transport in aquatic environments. The l i p o p h i l i c chemicals may be introduced to food chains and sediments as colloids aggregate and precipitate in the presence of larger particles, or, for example, in estuaries (22).
The
biological a v a i l a b i l i t y of the proposed DOM-bound chlorinated hydrocarbons in the Niagara River is unknown. However, both reduced and enhanced a v a i l a b i l i t y of DOM-bound chemicals to different organisms have been demonstrated (23,24). ACKNOWLEDGEMENTS We thank M.E. Fox, P.A. Thiessen, G.J. Pacepavicius and S.P. Batchelor for assistance. REFERENCES i.
Allan,
R.J.,
Mudroch, A. and Munawar, M., eds.,
Pollution Problem.
The Niagara River
Lake Ontario
J. Great Lakes Res. 9, 109-340 (1983).
2.
Oliver, B.G. and Charlton, M.N. Environ. Sci. Techno]. 18, 903-908 (1984).
3.
Oliver, B.G. and Nicho], K.D. Sci. Total. Environ. 39, 57-70 (1984).
4.
Environment Canada.
5.
U.S. Environmental Protection Agency. Guidelines establishing test procedures for the
Analytical Methods Manual Update, 1981.
Water Quality Branch,
Inland Waters Directorate, Department of Environment, Ottawa, Ontario, Canada KIA OE7. analysis of pollutants under the Clean Water Act. and PCBs. U.S. Fed. Reg. 49, 90-104 (1984).
Method 608 - Organochlorine Pesticides
1287
6.
P e l l i z z a r i , E.D., Sheldon, L.S., Bursey, J.T., Michael, L.C., Zweidinger, R.A. and Garrison, A.W. Project summary - master analytical scheme for organic compounds in water.
U.S. Environmental Protection Agency Report EPA/600/S4-85/O08, 9 pp., July
1985. 7.
Fox, M.E. A practical sampling and extraction system for the quantitative analysis of sub-ng/L organochlorine contaminants in f i l t e r e d water and suspended solids. "Methods for
Analysis
of
Organic Compounds in
Sonzogni, W.C. and Dube, D.J.,
eds., publ.
the
Great Lakes, Vol.
In II",
Univ. Wisconsin Sea Grant Institute,
Madison, WI, WIS-SG-86-244, pp. 27-34, 1986. Available from Communications Office, University of Wisconsin Sea Grant Institute, 1800 University Ave., Madison, WI 53705, USA. 8.
M i l l a r , J.D., Thomas, R.E. and Schattenberg, H.J.,
Ill.
Anal. Chem. 53, 214-219
9.
Keith, L.H., Crummett, W., Deegan, W., Libby, R.A., Taylor, J.K. and Wentler, G.
(1981). Anal. Chem. 55, 2210-2218 (1983). 10.
Kuntz, K.W. and Warry, N.D. J. Great Lakes Res. 9, 241-248 (1983).
11.
01iver, B.G. and Bothen, K.D. Anal. Chem. 52, 2066-2069 (1980).
12.
U.S. Environmental Protection Agency. Guidelines establishing test procedures for the analysis of pollutants. 153-174 (1984).
13.
Base/neutrals and acids - Method 625 U.S. Fed. Reg. 49,
Carter, C.W. and Suffet, I.H.
Interactions between dissolved humic and fulvic acids
and pollutants in aquatic environments.
In "Fate of Chemicals in the Environment",
Swann, RoL. and Eschenroeder, A., eds., Amer. Chem. Soc. Symp. Ser. 225, 215-229 (1983), American Chemical Society, Washington, DC 20036, USA. 14.
Wijayaratne, R.D. and Means, J.C.
15.
Carter, C.W. and Suffet, I.H.
16.
Caron, G., Suffet, I.H. and Belton, T.
17.
Landrum, P.F., Nihart, S.R., Eadie, B.J. and Gardner, W.S. Environ. Sci. Techno1. 18, 187-192 (1984).
18.
Matsuda, K. and Schnitzer, M. Bu11. Environ. Contamin. Toxico1. 6, 200-204 (1971).
19.
Carter, C.W. and Suffet, I.H. Environ. Sci. Techno1. 18, 735-740 (1982).
20.
Gschwend, P.M. and Wu, S.
21.
Baker, J.E., Capel, P.D. and Eisenreich, S.J. (1986).
22.
Sholkovitz, E.R., Boyle, E.A. and Price, N.B. Earth Planet. Sci. Lett. 40, 130-136 (1978).
23.
Boehm, P.D. and Quinn, J.G.
24.
Leversee, G.J., Landrum, P.F., Giesy, J.P. and Fannin, T. (Suppl.), 63-69 (1983).
25.
Ballschmlter, K. and Zell, M.
(Received
in Germany
iO May
Environ. Sci. Technol. 18, 121-123 (1984).
Org. Geochem. 8, 145-146 (1985). Chemosphere 14, 993-1000 (1985).
Environ. Sci. Technol. 19, 90-96 (1985). Environ. Sci. Techno1. 20, 1136-1143
Estuar. Coastal Mar. Sci. 4, 93-105 (1976). Can. J. Fish. Aquat. Sci. 4
Fresenlus Z. Anal. Chem. 302, 20-31 {1980).
1989;
accepted
21 June
1989)
0045-6535/89 $3.OO + .00 Pergamon Press plc
POTENTIAL UNDERESTIMATION OF CHLORINATED HYDROCARBON CONCENTRATIONS IN FRESH WATER
R. James Maguire* and Richard J. Tkacz Rivers Research Branch, National Water Research Institute Department of Environment, CanadaCentre for Inland Waters Burlington, Ontario, Canada L7R 4A6
ABSTRACT Significant concentrations of PCBs and other chlorinated hydrocarbons have been found in dichloromethane extracts of f i l t e r e d Niagara River, Canada, water at pH 12 after the water had been thoroughly extracted at pH 1. In samples from 43 dates in 1985/86, the contribution of the basic extract to the total concentration derived from acidic, basic and suspended solids extracts ranged from 0% for 31 of these chemicals to 100% for PCBs 15, 114 and 201, aldrin and p,p'-DDT. When the sums of concentrations of each chemical found in Niagara River water in the acidic, basic and suspended solids extracts over the 43 sampling dates were themselves summed, the basic fraction contributed 40% to the total concentrations of a l l chemicals, and 48% i f only PCBs were considered. Experiments with water from another source showed that some PCBs were recovered in dichloromethane extracts of basic f i l t e r e d water which had previously been thoroughly extracted under either acidic or neutral conditions. These results indicate that concentrations of chlorinated hydrocarbons in Niagara River water determined by extraction solely at neutral pH, the usual technique, may be underestimated. This finding, which may have general a p p l i c a b i l i t y to fresh waters, may be the result of a strong association between a fraction of the dissolved l i p o p h i l i c chemicals and dissolved organic matter in fresh water, an association that is resistant to organic solvent extraction at acidic or neutral pH, but which is at least p a r t i a l l y disrupted by extraction at high pH. INTRODUCTION
The contamination of Lake Ontario by chemicals in the Niagara River is a serious problem which has been studied intensively over the past twenty years (1-3).
Chlorinated hydrocarbons
such as PCBs, organochlorine pesticides and dioxins have been a focus of concern because of the r e l a t i v e l y long environmental persistence of these chemicals. The standard procedure for the determination of PCBs and other chlorinated hydrocarbons in water involves extraction at neutral pH, with or without pH adjustment (4-6).
Average recoveries of chlorinated hydrocar-
bons by solvent extraction from natural waters and wastewaters at reported in the range 63-86% (3,6-8).
neutral pH have been
Recent observations of PCBs and other chlorinated
hydrocarbons in dichloromethane extracts of f i l t e r e d Niagara River water at pH 12 after the water had been thoroughly extracted at p H I have indicated that standard methods used for the
1277
1278
extraction of chlorinated hydrocarbons from natural water may not be adequate. T h i s a r t i c l e describes those observations as well as experiments in which such chemicals were recovered from natural water samples and spiked natural water samples at pH 12 after the water had been extracted at either acidic or neutral pH. EXPERIMENTAL SECTION Materials Standards of chlorinated pesticides and hydrocarbons were obtained from chromatographic supply companies. Sets of PCB congeners were obtained from the National Research Council of Canada, Halifax, NS.
These PCB congeners represent, by weight, 3Z of Aroclor 1221, 44% of
Aroclor 1242, 48% of Aroclor 1248, 38% of Aroclor 1254 and 60% of Aroclor 1260, and thus the total of the PCB congeners reported in this study should not be regarded as "total PCBs". Pesticide grade dichloromethane and other solvents were obtained from different suppliers and their purity at lO00x concentration was checked before use.
The sodium sulfate, aluminum
f o i l , glass fibre f i l t e r s and disposable pipets were heated to 500°C for 24 h before use. All glassware was rinsed with pesticide grade solvents before use. Hydrochloric acid and sodium hydroxide solutions used for pH adjustment were prepared from reagent grade chemicals, but were extracted with pentane before use to eliminate contamination. Burlington Ship Canal Samples F o r t y - l i t r e water samples were collected on two dates in July and August, 1988, from the Burlington Ship Canal, which connects Hamilton Harbour with Lake Ontario. collected in modified stainless steel beverage containers (7).
The samples were
The samples were treated in
two different ways, as follows. Neutral-then-Basic extractions The sample c o l l e c t e d
in
July
1988 was d i v i d e d
d e t e r m i n a t i o n o f ambient PC8 c o n c e n t r a t i o n s experiment.
One sub-sample was f i l t e r e d
freeze-dried.
After
dichloromethane f o r steel
The f i l t e r
freeze-drying,
24 h w i t h
two 20 L sub-samples so t h a t
steel
a
as a PCB s p i k e - r e c o v e r y
through a 0.45 IJm glass f i b r e f i l t e r
n i t r o g e n and the m o d i f i e d p r e s s u r i z e d s t a i n l e s s and Teflon t r a n s f e r l i n e s ( 7 ) .
into
could be done as w e l l
beverage c o n t a i n e r s ,
using compressed pressure f i l t e r s
c o n t a i n i n g the suspended s o l i d s was frozen and then the
occasional
filter
was
shaking.
beverage c o n t a i n e r and e x t r a c t e d t w i c e by s t i r r i n g
1 h ( w a t e r / d l c h l o r o m e t h a n e r a t i o 40/1, v / v ) .
extracted
The f i l t r a t e
in
a
test
was t r a n s f e r r e d
tube
with
to a 40 L
w i t h 500 mL o f dichloromethane f o r
The pH of the sample was 7.4.
After extraction
at n e u t r a l pH, the aqueous phase was made basic to pH 12 by the a d d i t i o n o f concentrated NaOH, All
dichloromethane e x t r a c t s
were d r i e d and concentrated w i t h s o l v e n t changing to 1 mL of hexane.
and the w a t e r was e x t r a c t e d t w i c e more w i t h d i c h l o r o m e t h a n e .
The 1 mL hexane e x t r a c t s
were cleaned up by l o a d i n g on 20 cm x 1 cm i . d .
columns of a c t i v a t e d s i l i c a
gel and e l u t i o n
w i t h 60 mL of hexane f o l l o w e d by 60 mL o f 20Z dichloromethane - 80Z hexane ( v / v ) . PCBs and c h l o r i n a t e d
insecticides
eluted with
Most of the
hexane, but o c c a s i o n a l l y t r a c e s were found in
1279
the dichloromethane-hexane fraction.
The two fractions were combined, dried and concentrated
with solvent changing to 1.0 mL hexane with a toluene "keeper". The other sub-sample was spiked with 14 PCB congeners at concentrations of 1-40 ng/L. After a 16 h aging period the sample was f i l t e r e d , extracted and cleaned up as described above.
An aging period of 16 h, which corresponds to the t r a n s i t time of the Niagara River
from Lake Erie to Lake Ontario, was chosen so that the spiking experiment would have relevance to the Niagara River results (cf. below). Acidic-then-Basic extractions The sample collected in August 1988 was also divided into two 20 L sub-samples so that a determination of ambient PCB concentrations could be done as well as a PCB spike-recovery experiment.
One sub-sample was f i l t e r e d as described above. The f i l t r a t e was transferred to
a 40 L container, i t s pH was adjusted to 1 with concentrated HCI, and i t was extracted twice by s t i r r i n g with 500 mL of dichloromethane for 1 h.
After the extraction at pH I , the aqueous
phase was made basic to pH 12 by the addition of extracted twice more with dichloromethane.
concentrated NaOH, and the water was
A11 dichloromethane extracts were then cleaned up
as described above in the neutral-then-basic extraction experiment. The other sub-sample was spiked with 14 PCB congeners at concentrations of 1-40 ng/L. After a 16 h aging period the sample was f i l t e r e d and extracted under acidic-then-basic conditions.
The extracts were cleanup as described above.
Recoveries from D i s t i l l e d Water
In addition to the experiments with Burlington Ship Canal water, recovery experiments with
14
PCB congeners spiked
neutral-then-basic containers.
conditions
at and
1 - 4 0 ng/L in
distilled
acidic-then-basic
water were performed under
conditions
in
The spikes were aged for 30 min before extraction.
primarily conducted to determine i f
the
steel
beverage
These experiments were
any PCBs could be found in basic extracts of spiked
d i s t i l l e d water a f t e r extraction under either neutral or acidic conditions. Niagara River Samples
Water samples were collected at 43 dates between August 1985 and August 1986 near the mouth of
the Niagara River at
Niagara-on-the-Lake,
Ontario.
Twenty-litre samples were
collected 3-5 m from shore at a depth of 0.5 m in the modified pressurized beverage containers described above.
In order to avoid contamination by the surface mlcrolayer, the tops of the
containers were always removed under water. Within 2 h of collection the water samples were f i l t e r e d and were being extracted under acidic-then-neutral conditions as described for
the Burlington Ship Canal samples.
The
dichloromethane extracts were dried, solvent-changed to hexane with a toluene "keeper", and concentrated.
Extracts of suspended solids were concentrated to 1 mL, while extracts of water
were concentrated to 10 mL.
In contrast to the Burlington Ship Canal samples, the Niagara
River samples did not require clean-up.
1280
The Niagara River samples were only extracted under acidic-then-basic conditions since the purpose was to determine basic chemicals such as amines, and the f i r s t extraction under acidic conditions was intended to act as a clean-up step by removing acidic and neutral interferents.
The subsequent finding of chlorinated hydrocarbons in basic extracts prompted the
experiments with Burlington Ship Canal water and d i s t i l l e d water described above. Analyses Analyses of the sample extracts were performed with a Hewlett-Packard 5890A capillary column gas chromatograph with a single injector-dual column-dual electron capture detector technique.
One column was Ultra-2 and the other was 0V-17.
0.2 mm i . d . x 25 m in length, with 0.17 1~n film thickness. were 250 and 350°C, respectively.
Column dimensions were
Injector and detector temperatures
The i n i t i a l column temperature was 60°C, and the program
rate was 3°/min to 280°C, with an 8 min final hold.
The analyses were performed in 8:1 s p l i t
mode. The carrier gas flow rate was 1.0-1.5 mL/min (50-80 cm/s) and the make-up gas flow rate was 20 mL/min. For the Burlington Ship Canal samples, 14 PCB congeners were sought, while for the Niagara River samples, 89 chlorinated benzenes, alkanes, alkenes, insecticides and PCB congeners were sought. Standardmixtures of a11 of these compounds in the expected concentration
ranges were prepared and used to calibrate retention times and detector responses.
Chromatographic "windows" were typically 0.04 min at most at 80 min retention time. presence of a compound was taken to be tentatively confirmed i f appropriate chromatographic window on both columns, ( i i )
(i)
The
i t occurred within the
the concentrations determined with
each column were within 50% of each other (in which case the lower of the two concentrations was reported), and ( i i i )
the concentrations were above the l i m i t of quantitation for the
particular sample, as opposed to the l i m i t of detection (g).
The limits of quantitation for
the 89 compounds sought were f a i r l y conservative, being at least about 10 times the limits of detection for similar sizes of water samples in two previous studies of contaminants in the Niagara River (3,10).
Measurementprecision near the l i m i t of quantitation was about 15-20%.
Solvent and reagent blanks were performed routinely, and procedural blanks were performed three times during the course of the study.
At no time was contamination evident.
RESULTS D i s t i l l e d Water PCBs spiked into d i s t i l l e d water at
1-40 ng/L concentrations
in the steel beverage
containers and a11owed to age for 30 min were only recovered in the f i r s t of the duplicate 1 h extractions carried out under either neutral or acidic conditions, and not at a l l second extraction or in subsequent extractions of basic d i s t i l l e d water.
in the
The recoveries were
similar to those observed for the steel containers in an e a r l i e r study, in which 17 chlorinated hydrocarbons including chlorobenzenes, PCBs, octachlorostyrene and Mirex spiked into d i s t i l l e d water at fractional ng/L concentrations were recovered with efficiencies of 86-130% (average 102 ± 12%) with dichloromethane in t r i p l i c a t e extractions with s t i r r i n g for 10 min (7).
The water/dichloromethane ratio in that study was 30/I (v/v) for the f i r s t extraction,
1281
which saturated the water with dichloromethane, and 180/1 for the second and t h i r d extractions.
The aging time of the spike was 5 min in that study.
The extraction efficiencies
using the steel containers in this study and the e a r l i e r study are similar to those observed for chlorobenzenes with an a l l - g l a s s system (11).
Spikes of a l l
twelve possible chloroben-
zenes in d i s t i l l e d water in the range of 0.1-25700 ng/L were recovered with efficiencies of 80-96% (average 85 ± 5%) with hexane in a single extraction in a l l - g l a s s containers (water/ hexane r a t i o 54/1, v/v) with s t i r r i n g for 4 hr (11).
The aging time of the spike in this
l a t t e r study was not stated. Burlington Ship Canal Water Table 1 shows recoveries of 14 PCBs spiked into Burlington Ship Canal water at concentrations
of
1-40 ng/L and extracted under d i f f e r e n t
corrected for PCBs present before spiking.
conditions.
The concentrations were
The r a t i o of spiked to ambient concentrations was
in the range 1.0-48~5, with most ratios greater than 3.
I t is probable that there was signi-
ficant error in those few cases in which the spiked-to-ambient concentration ratio was less than 2.
Nevertheless, the data demonstrate that some PCBs were recovered in basic extracts of
f i l t e r e d water a f t e r the water had been extracted at either neutral or acidic pH. menon did not appear to be the result of conditions.
This pheno-
incomplete extraction under acidic or neutral
Extraction of acidic or neutral water samples, which had already been extracted
twice, one more time yielded no traces of PCBs.
In addition, there were no differences found
in extraction efficiency between glass and metal containers.
The contribution to the recovery
from the basic extracts was small, in the range 0-5.6% i f
water and suspended solids were
considered or
0-12.5% i f
only the dissolved phase were considered.
The average total
recoveries were similar under the two sets of extraction conditions, 71 and 77%. The overall recoveries determined in this work are similar to those of two e a r l i e r studies in the same area, but with extraction at neutral
pH only.
In one of
these studies, the extraction
efficiencies into dichloromethane from Niagara River water of many of the compounds sought in this study, at ng/L concentrations in a l l - g l a s s containers a f t e r overnight aging of the spike, were in the range 50-86%, with a mean of 63% (3).
In the other study using steel containers,
the extraction efficiencies of these or similar chlorinated hydrocarbons into dichloromethane from Lake Ontario water, at fractional ng/L concentrations a f t e r a 16 h aging of the spike, were in the range 56-118%, with a mean of 86% (7). Table 2 shows ambient concentrations of the 14 PCB congeners sought in Burlington Ship Canal water samples collected on the two dates in question.
In some cases these PCBs were
either not found at a l l or found only in the suspended solids fraction.
Under neutral-then-
basic extraction conditions 8 of the 14 PCBs sought were found in the basic extract, while under acidic-then-basic conditions on another date only 1 of the 14 PCBs sought was found in the basic extract. extracts in
The contribution to the concentration for each PCB congener from the basic
the two samples was in
the
range 0-33% i f
water and suspended solids were
considered or 0-50% i f only the dissolved phase were considered.
1282
Table 1.
Percentage recoveries of PCB congeners spiked into Burlington Ship Canal water.*
Chemical
Spiking Level (ng/L)
PCB 15 PCB 101 PCB 151 PCB 118 PCB 153 PCB 141 PCB 138 PCB 187 PCB 180 PCB 170 PCB 201 PCB 196 PCB 195 PCB 194
38.8 4.5 2.6 2.0 1.7 1.4 2.1 1.7 1.5 1.6 2.2 1.8 1.3 1.2
Experiment 2
Experiment I N 65 84 69 101 96 61 78 57 62 45 49 46 40 51
B
S
Total
A
3 2 6 2
5 5 8 13 4 3 7 13 5 5 5 2
65 92 76 115 111 65 81 64 76 50 56 51 42 53
53 49 48 75 59 51 68 56 56 32 49 46 40 42
I 2
2
Average total recovery
71 ± 22
B
3 4 6 5 6 4 3 4 1 3 3 4
S
Total
3 17 19 28 32 23 25 22 20 35 21 20 18 22
56 69 71 107 96 74 99 82 79 71 71 69 61 68
77 ± 15
*N and B or A and B refer to extracts made sequentially of f i l t e r e d water under neutral-thenbasic or acidic-then-basic conditions, respectively. S refers to the extract of the suspended solids. The chemicals are listed in order of elution from an Ultra-2 column. The numbering scheme for the PCB congeners is given in ref. 25. Table 2.
PCB concentrations (ng/L) in various extracts of Burlington Ship Canal water.*
Chemical
N
PCB 15 PCB 101 PCB 151 PCB 118 PCB 153 PCB 141 PCB 138 PCB 187 PCB 180 PCB 170 PCB 201 PCB 196 PCB 195 PCB 194
0.8 0.6 0.2 0.2 0.3 0.1 0.8 0.1 0.2 0.1
July 26, 1988 B S
0.4 0.1 0.3 0.1 0.7 0.1 0.2 0.1
0.8 0.4 0.4 0.7 0.2 0.6 0.3 0.6 0.4 0.3 0.2 0.1
Total 0.8 1.8 0.7 0.6 1.3 0.4 2.1 0.5 1.0 0.6 0.3 0.2 0.i
A
0.3 0.1
August 29, 1988 B S
0.i
Total
0.2 0.I
0.6 0.2
0.1
0.2
0.3
0.4
0.2 0.1 0.1 0.7
0.2 0.1 0.1 1.1
*N and B or A and B refer to extracts made sequentially of f i l t e r e d water under neutral-thenbasic or acidic-then-basic conditions, respectively. S refers to the extract of the suspended solids. To f a c i l i t a t e comparison, concentrations in S are given in units of ng of chemical associated with the suspended solids per l i t r e of water. Concentrations are not corrected for recovery. The limits of quantitation vary with each chemical and are in the range 0.04-0.8 ng/L for I mL extracts of water and for 1 mL extracts of suspended solids, each from a 20L sample. The compounds are listed in order of elution from an Ultra-2 column. The numbering scheme for the PCB congeners is given in ref. 25.
1283
Niaqara River Water As stated above, the Niagara River samples were only extracted under acidic-then-basic conditions.
Fifty-nine chemicals of the 89 sought were found at least once in water collected
at 43 dates during the period August 1985 - August 1986, and 28 of these 59 chemicals were found at least once in the basic extract.
There appeared to be no seasonal pattern for the
occurrence of chlorinated hydrocarbons in basic extracts of f i l t e r e d Niagara River water.
The
suspended solids, acidic and basic extracts accounted for 86%, 6% and 10%, respectively, of the total
number of times that chemicals were determined with confidence.
In a few cases
chemicals were only found in the basic extracts, and not in the p r i o r acidic extracts.
Those
chemicals found in basic extracts were occasionally found in r e l a t i v e l y high concentrations. Table 3 shows the sums of concentrations of each chemical found in the acidic, basic and suspended solids extracts over the 43 sampling dates.
The contribution from the basic extract
to the total concentration for a l l 43 sampling dates ranged from 0% for 31 of these chemicals to 100% for PCBs 15, 114 and 201, aldrin and p,p'-DDT. Table 3.
When the sums of concentrations of
Sums of concentrations (ng/L) of chlorinated hydrocarbons in various fractions of Niagara River water.*
Chemical
A
B
S
Total
1,3-dichlorobenzene
28
1,4-dichlorobenzene
28
28
1,2-dichlorobenzene
41
41
hexachloroethane
2
2
1,3,5-trichlorobenzene
1
1
1,2,4-trichlorobenzene
108
hexachlorobutadiene 1,2,3,5-tetrachlorobenzene
6
28
5
113
2
2
3
9
1,2,4,5-tetrachlorobenzene
5
5
1,2,3,4-tetrachlorobenzene
17
17 41
pentachlorobenzene
5
12
24
a-hexachlorocyclohexane
8
2
2
12
3
8
11
hexachlorobenzene pentachloroanisole
I
i
PCB 18
7
7
PCB 15
27
PCB 54
54
PCB 31 Heptachlor
13
9
4
Aldrin PCB 44
1
cont'd next page
10
53
53
23
37
59
85
15 8
57 22
I
PCB 52 PCB 49
27 3
18
15
1284
Table 3.
(cont'd)
Chemical PCB 40 Heptachlor epoxide y-Chlordane PCB 80 o,p'-DDE PCB 101 a-Endosulfan a-Chlordane Nonachlor PCB 87 Dieldrin p,p'-DDE PCB 77 PCB 154 o,p'-DDD Endrin PCB 151 B-Endosulfan PCB 118 p,p'-DDD PCB 114 o,p'-DDT PCB 153 PCB 105 PCB 141 PCB 137 p,p'-DDT PCB 138 PCB 159 PCB 182 PCB 187 PCB 183 PCB 180 PCB 191 PCB 201 PCB 209 Totals % PCB totals only %
A
B
5 3
11 21
2
8 8 34 54
12 2 i
3 3
8
35
S
Total
1 4 4 11 7 33 21 16 1 11 I 11 98 2 I 12 5 2 20 7
i 4 4 11 7 49 45 16 i 21 9 45 164 4 5 12 8 2 63 7 12 8 86 26 12 5 45 79 2 5 4 17 27 6 17 1 1445 100 908 100
12 10 5 2 1 13
3
52 21 8 4 45 64
14 12
8 24 2
2 2 5 4 15 6
17 220 15 88 10
576 40 433 48
1 649 45 387 42
*The data represent cumulative sums of concentrations in water samples collected on 43 dates between August 1985 and August 1986. A and B refer to extracts made sequentially of f i l t e r e d water under acidic followed by basic conditions. S refers to the extract of the suspended solids. To f a c i l i t a t e comparison, concentrations in S are given in units of ng of chemical associated with the suspended solids per l i t r e of water. Concentrations are not corrected for recovery. The l i m i t s of quantitation vary with each chemical, and are in the range 0.2-40 ng/L for 10 mL extracts of water and 0.02-4 ng/L for I mL extracts of suspended solids, each from a 20 L sample. The compounds are l i s t e d in order of elution from an Ultra-2 column. The numbering scheme for the PCBs is given in ref. 25.
1285
each chemical in the acidic, basic and suspended solids extracts in Table 3 were themselves summed, the basic fraction contributed 40% to the total concentrations of a l l chemicals, and 48% i f only PCBs were considered. DISCUSSION The spiking experiments described above provide evidence that the finding of l i p o p h i l i c chlorinated hydrocarbons in basic extracts of f i l t e r e d Niagara River and Burlington Ship Canal water after prior extraction at either acidic or neutral pH was not due to incomplete extraction.
Additional evidence against incomplete extraction is provided by the observation in
several Niagara River samples of (i) acidic extracts, and ( i i ) prior acidic extracts.
chemicals in the basic extracts but not in the prior
chemicals in basic extracts at higher concentrations than in the The observation of chemicals in basic extracts after extraction at
neutral pH also tends to discount the p o s s i b i l i t y that acidifying the f i l t e r e d water i n i t i a l l y to
pH 1 produced an a r t i f a c t
e f f i c i e n t l y extracted at
whereby chlorinated hydrocarbons which might
neutrality were only p a r t i a l l y extractable at
pH I,
have been and were
recovered more e f f i c i e n t l y at pH 12. The observation of l i p o p h i l i c chemicals in basic extracts of f i l t e r e d Niagara River water after the water had been extracted at acidic or neutral pH is of considerable significance since the Niagara River has been the major source of contamination of Lake Ontario (1-3).
It
may be that concentrations of l i p o p h i l i c chemicals in the Niagara River determined solely by extraction at neutral pH have been underestimated. generally applicable to fresh waters.
In addition, this phenomenon may be
We recommend that present methods of determination of
such chemicals in fresh waters be reviewed and, i f necessary, changed to take into account any fraction which is only extracted under basic conditions.
Although i t
is not widely used for
neutral chemicals, the U.S. Environmental Protection Agency base/neutral method (12) which employs i n i t i a l extraction at pH > 11 may be more appropriate than the more commonly used method of extraction at neutral pH. The presence of chlorinated hydrocarbons in basic extracts of Niagara River and Burlington Ship Canal water after extraction at acidic or neutral pH may be due to a strong binding between a fraction of the "dissolved" chemical and dissolved or colloidal organic matter, a binding which resists disruption by organic solvent extraction at low or neutral pH, but which is at least p a r t i a l l y disrupted by extraction under basic conditions.
There is a substantial
body of evidence for the association of l i p o p h i l i c chemicals and dissolved organic matter (DOM), in particular f u l v i c and humic acids in water (13-17, and references therein).
Lipo-
p h i l i c chemicals may bind to hydrophobic sites on DOM with the resulting complex held in solution or colloidal dispersion by polar hydroxyl, carboxyl and phenolic groups. Although binding to DOM appears to be the most plausible explanation for the observations reported here, this work offers no direct proof.
The proposed pH-dependent binding of lipophilic
chemicals to DOM is, however, supported by observations of decreasing binding of phthalates and DDT to f u l v i c and humic acids, respectively, with increasing pH (18,19).
I t is expected
that the amount of DOM-bound l i p o p h i l i c compound should decrease with increasing pH since the humic or f u l v i c acid polymers should be more hydrophilic at high pH~
Moreover, in Niagara
River water samples chemicals of log Kow < 4-5, such as the f i r s t 10 chemicals of Table 3, were not
found in
basic
extracts,
in
substantial agreement with e a r l i e r evidence from
1286
laboratory experiments that compounds with log Kow < 4 would probably not be bound to DOM to an appreciable extent (13).
I t should be noted that more severe conditions than pH adjustment
have been used to disrupt DOM-lipophilic chemical associations.
For example, a significant
fraction of f u l v i c acid-bound alkanes and dialkyl phthalates (all only extractable after methylation of the f u l v i c acid (18).
"naturally" present) was
This fraction was larger than
that fraction which was extractable by organic solvents from untreated f u l v i c acid. In spiked Burlington Ship Canal water samples, PCB concentrations in basic extracts relative to neutral or acidic extracts were not as high as was the case for unspiked samples. If
strong binding between PCBs and DOM were occurring, and i f
i t were subject to kinetic
control, the foregoing observation may have been a consequence of the shorter incubation period of the spiking experiment compared to the presumably much longer period of time that those PCBs were in unspiked water.
I f this were the case, i t would suggest the need for
further study of the variation of recovery of contaminants as a function of aging time in environmental matrices. A model of the d i s t r i b u t i o n of l i p o p h i l i c chemicals in natural waters has been proposed which includes the
"compartments":
t r u l y dissolved, adsorbed to
adsorbed to non-settling particulates or macromolecules (20).
suspended solids,
and
A study of the distribution of
PCB congeners in Lake Superior water using this model indicated that
colloid-associated
contaminants may be the dominant species in most surface waters, from the viewpoint of concentration (21).
I f our observations are of general significance, the "dissolved" fraction
may be even more important than is currently believed.
Binding of ] i p o p h i l i c chemicals to DOM
may be an important mechanism for their mobilization and transport in aquatic environments. The l i p o p h i l i c chemicals may be introduced to food chains and sediments as colloids aggregate and precipitate in the presence of larger particles, or, for example, in estuaries (22).
The
biological a v a i l a b i l i t y of the proposed DOM-bound chlorinated hydrocarbons in the Niagara River is unknown. However, both reduced and enhanced a v a i l a b i l i t y of DOM-bound chemicals to different organisms have been demonstrated (23,24). ACKNOWLEDGEMENTS We thank M.E. Fox, P.A. Thiessen, G.J. Pacepavicius and S.P. Batchelor for assistance. REFERENCES i.
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1989;
accepted
21 June
1989)