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Journal of Environmental Science and Health, Part B
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Sensory properties of thio‐ and alkyl‐ phenolscausing flavor tainting in fish from the upperWisconsin River
Timothy P. Heil , Nancy A. Lane & Robert C. Lindsay
To cite this article: Timothy P. Heil , Nancy A. Lane & Robert C. Lindsay (1989) Sensoryproperties of thio‐ and alkyl‐ phenols causing flavor tainting in fish from the upper WisconsinRiver, Journal of Environmental Science and Health, Part B, 24:4, 361-388
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J. ENVIRON. SCI. HEALTH, B2A(4), 361-388 (1989)
SENSORY PROPERTIES OF THIO- AND
ALKYL- PHENOLS CAUSING FLAVOR TAINTING IN FISH FROM
THE UPPER WISCONSIN RIVER
KEY WORDS: Rainbow t r o u t , Sensory a n a l y s i sAlkylphenols, Thiophenol, Off-flavors
Timothy P. Heil , Nancy A. Laneand Robert C. Lindsay
Environmental Toxicology Center (T.P.H., R.C.L.)2
Department of Food Science (N.A.L., R.C.L)University of Wisconsin-Madison
Madison, Wisconsin 53706
ABSTRACT
A mixture of 10 ppb thiophenol, 1 ppb
3-isopropylphenol, 1 ppb 2,4-diisopropylphenol and 1
ppb carvacrol had nearly the same flavor quality as
environmentally tainted northern pike when added to the
flesh of untainted northern pike. Trout exposed to a
1 Current address: Radian Corporation, Box 13000,Research Triangle Park. N.C. 27709
2 Contribution No. 206 of the Environmental ToxicologyCenter.
361
Copyright © 1989 by Marcel Dekker, Inc.
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2362 HEIL, LANE, AND LINDSAY
mixture of alkylphenols and thiophenol (1-2 ppb each)
in water did not become flavor tainted, but trout fed a
formulated feed (2% body weight/day) containing 100 ppb
added alkylphenols and thiophenol became strongly
flavor tainted. Results suggest tainting via the food
chain is important with these compounds. Tainting
caused by thiophenol and isopropylphenols in tank-held
trout was removed by holding the fish in clean water
for 5 days.
INTRODUCTION
The coincidence of flavor tainting in fish with
industrial discharges into water has been reported
frequently in the literature (Boetius, 1954;
Krishnaswami and Kupchanko, 1969; Motohiro, 1983).
Fetterolf (1964), Baldwin et_ L^ (1961, 1970), Berg
(1983), Cook e_t a l ^ (1973), and Calbert et a l ^ (1974)
all have reported that fish caught or held downstream
of pulp and/or papermills were significantly more
off-flavored compared to fish caught or held in
upstream waters. However, confirmation of tainting
through laboratory studies has been d i f f i c u l t , and fish
have become flavor-impaired only when exposed to
untreated effluents (Liem & Naish, 1973; Farmer e_t al. ,
1973) or to very high concentrations of treated
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 363
e f f l u e n t (Tamura e_t a l . , 1954; Shumway & Chadwick,
1971; Shumway & Palensky, 1973; W h i t t l e and Flood,
1977; P a a s i v i r t a et^ a l . , 1983). Shumway and Palensky
(1973) exposed freshwater fish to individual compounds
that were often present in Kraft Mill effluents and
municipal sewage treatment effluents, and determined
tainting flavor thresholds for cresols, mono-, di-, and
trichlorophenols, ethanethiol, butanethiol and
guaiacol. However, even though many of these compounds
caused significant tainting in exposure studies, their
association with tainting of wild fish has not been
established.
More recently, Berg (1983) reported significant
concentrations of terpenes, alkylbenzenes, and
alkenylbenzenes in flavor tainted salmon (Salmo solar)
captured near pulp mills. Low levels of unidentified
chlorinated and sulphated organics were also found, but
the flavor tainting was attributed to the terpenes and
benzene derivatives. In studies on flavor tainted fish
from the Wisconsin River, Lane (1981) and Heil and
Lindsay (1988a) identified several phenolic compounds
with intense offensive aromas in fish downstream of
pulp and paper mills including a variety of
isopropylphenols, thiophenol and thiocresol.
The purpose of this investigation was to determine
some flavor tainting properties of selected
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364 HEIL, LANE, AND LINDSAY
isopropylphenols and thiols in fish and to investigate
the contributions of direct absorbtion and feed routes
for inducing these taints in fish.
MATERIALS AND METHODS
Wild-caught Fish Samples for Assessment of Tainting
Walleye pike (Stizostedion vitreum), northern pike
(Esox l u c i u s ) , black crappie (Promoxis nigromaculatus),
yellow perch (Perca f l a v e s c e n s ) , and bullhead
(Octalurus sp.) were collected from the Wisconsin River
by fyke nets or electroshocking by the State of
Wisconsin Department of Natural Resources from a
control s i t e in the Rainbow Flowage headwaters and at
downstream study s i t e s in Lake Wausau and the Mosinee
Flowage. These s i t e s were chosen to determine the
extent and type of tainting flavors present in fish
populations located below paper mills. These fish were
also used to document across-species flavor
characteristics. All fish were iced immediately upon
capture, and were filleted, skinned, vacuum packaged,
and frozen. No attempt was made to segregate fish
within a species according to size or sex. Preliminary
sensory analysis of cooked walleye fi l l e t s and minced
tissue containing added tainting compounds was
performed by the authors. Walleye f i l l e t s from the
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 365
control sampling site (Rainbow Flowage) were defrosted,
minced, and spiked with a tainting compound dissolved
in 1 ml ethanol. The mince was mixed thoroughly and
allowed to equilibrate at 5° C for 1 hr prior to
cooking in a microwave oven for 30 seconds. Samples
were coded before flavor assessments.
Static Exposures of Trout to Tainting Compounds in
Water
Aquacultured rainbow trout (Salmo gaidneri; UW Sea
Grant Institute Aquaculture Laboratory) were placed in
fiberglass tanks (220 1) filled with dechlorinated
water containing the appropriate amount of tainting
compound. These fish were 2 to 3 yr old, and weighed
from 1.4 to 2.7 kg. Tanks were previously filled with
water for 7 days before samples of water were extracted
with ether for GC analysis to verify that detectable
leaching of compounds from the fiberglass into the
water did not occur. Tanks were also tested to confirm
that only minimal amounts (less than 5%) of the test
compounds adsorbed to the walls of the tank. The water
was well aerated during tests to maintain dissolved
oxygen at saturation levels. Water temperatures were
kept at 12 +/- 1° C. All trout were fasted for at
least 12 hours prior to exposure. A stock solution of
an alkylphenol mixture contained 25 mg each of phenol,
2-methylphenol, 2-isopropylphenol, 4-isopropylphenol,
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366 HEIL, LANE, AND LINDSAY
and thymol; and 50 mg each of thiophenol,
2,4-diisopropylphenol, and 2,6-diisopropylphenol in 10
ml ethanol. One-tenth ml of the stock was introduced
into a tank to yield a concentration of 1 to 2 ppb for
each compound. The level of ethanol was below the
concentration necessary to affect the flavor of the
fish.
Trout were exposed in pairs with one fish removed
from the tank at 2 and at 24 hr. Fish were killed with
a stunning blow and were transported to the University
of Wisconsin, Department of Food Science, where they
were filleted, skinned, vacuum packed in oxygen barrier
polymer bags (Freshtuff , American Can Co., Neenah,
WI) and stored at -15° C.
Flow-through Depuration of Trout
For these studies trout were subjected to static
exposure of tainting compounds for 24 hr. Fish were
then transferred to a tank (220 1) equipped with a
stand pipe overflow and a clean water flow rate of one
1/min. After 5 days trout were killed with a stunning
blow, filleted, skinned, vacuum packed and stored at
-15 C prior to sensory analysis.
Exposure of Trout Via the Food Chain
Rainbow Trout (1 yr old; UW Sea Grant Institute
Aquaculture Laboratory) were weighed and placed
eighteen to a tank in 3 tanks (220 1 each) under
flow-through water (15° C) conditions of three 1/min.
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 367
Fish received either tainted or untainted formulated
feed (Silver Cup trout feed; Murray Elevators, Murray
UT) at 2% body weight each day for 4 weeks. Feed was
tainted by placing pellets in a 3-liter beaker, and
covering them with a solution of 100 ppb each
carvacrol, 2-isopropylphenol, 4-isopropylphenol,
3,5-diisopropylphenol, and thiophenol in ethanol (1
part ethanol/1 part pellets, w/w). Then the ethanol
was evaporated under a hood fan at 21° C for 24 hr.
Fish were withdrawn from each tank at weekly
intervals for assessment of off-flavors in order to
follow development of tainting off-flavors. These fish
were killed by stunning and then were filleted,
skinned, broiled and assessed for flavors. At the end
of 4 weeks, half of the remaining fish was processed
and vacuum packed at -10° C. The other half was
placed on a non-tainted feed diet for 7 days prior to
similar processing for sensory analysis.
Estimation of Octanol/Water Partition Coefficients for
Alkylphenols and Aromatic Thiols
Unreported octanol/water partition coefficients
(expressed as log P) were estimated from substituent
constants provided by Hansch and Leo (1979) according
to the equation:
log P = log P(structurally related chemical) +
substituent fragments (f) + spatial factors (F).
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368 HEIL, LANE, AND LINDSAY
Alternatively, published partition coefficients for
cyclohexanol/water (Kc/w) were used to estimate log P
according to the regression equation of Seiler (1974) :
log P = log Kc/w + hydrogen bond correction + 0.16
Finally, log P's were estimated from HPLC retention
times on a reversed phase column according to the
procedure of Veith et al. (1979). A solvent mixture of
water and methanol (30:70, v/v) was pumped (ISCO model
2300 HPLC pump; Lincoln, NE) through an analytical
TMuBondapak /C,o column (Waters Associates; Milford,
J-O
MA) at 2.0 ml/min. at approximately 800 psi. Chemicals
to be tested were dissolved in methanol (10 mg/1) and
20 ul were introduced to the column via a sample loop.4
An UV-Vis variable wavelength detector (ISCO V ,
Lincoln, Ne) with a 3.5 ul cel l volume (5 mm path
length) set at 270 nm was used to record retention
times. Seven chemicals for which log P has been
reported (Chou and Jurs, 1979) were used to calibrate
the elution time in units of log P. These chemicals
and th e i r log P were benzene (2.13), phenol (1.46),
thymol (3.30), thiophenol (1.46), thiazole (0.44),
4-methylphenol (1.96), and anthracene (4.45).
Preparation of Fish F i l l e t s for Sensory Analysis
Frozen fish f i l l e t s were thawed 2 hr (21° C)
prior to broiling. Broiled f i l l e t s were flaked and
portions (30 g) were served to panelists in coded
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 369
paper cups. Sensory analyses were carried out
according to procedures described by Amerine ej: al.,
(1965) and Larmond (1977). Panel evaluations were
conducted in individual booths equipped with running
water, and the room was illuminated with fluorescent
lighting (ca. 78 ft-c). A desriptive analysis ballot
(Stone e_t al., 1974) containing semi-structured seven
point linear scales was employed. Descriptors (Mahoney
et al., 1957) included intensity of difference (no
differnce to pronounced difference), off-flavor
intensity (none to extremely pronounced), and overall
preference (dislike extremely to like extremely).
In order to determine similarities in quality and
intensity of tainted flavors between different fish
samples, a ballot based on degree of difference
measurement principles (Mahoney e_t al., 1957) was
employed. Panelists were served an identified
reference sample, and were asked to compare each coded
sample served to the reference sample. Responses were
recorded on a structured continuous similarity scale
(see Table 2 for descriptors), and these data were
coded on a 7-point basis as described for the
off-flavor intensity and overall preference
determination.
Panels were composed of 26 to 30 members
experienced in the sensory analysis of foods.
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370 HEIL, LANE, AND LINDSAY
Panelists were not selected to recognize specific
t a i n t i n g flavors, and thus would not be expected to be
more discriminating than the general public.
Measurement of Thiophenol and Alkylphenols in Wild Fish
A quantitative analysis for the alkylphenols and
thiophenol (Heil and Lindsay, 1988b) was performed on a
portion (40 g) of minced f i l l e t s from walleye pike
taken from several downstream locations in l a t e winter
and spring of 1985. The remaining portions of these
f i l l e t s were broiled and used for q u a l i t a t i v e
off-flavor assessments by the authors.
RESULTS AND DISCUSSION
Flavor-Tainting in Wild-Caught Fish
The r e s u l t s of descriptive sensory analyses for
the wild-caught fish species from the 3 study s i t e s on
the Upper Wisconsin River (Table I) showed that a l l
tested species of fish in the downstream study areas
(Lake Wausau and Mosinee Flowage) exhibited pronounced
degrees of flavor impairment compared to the headwaters
control fish from the Rainbow Flowage. Each study s i t e
was separated from others by impassable dams which
served to prevent the mixing of the fish populations
(Heil and Lindsay, 1988b).
Similar off-flavor q u a l i t i e s were noted among a l l
of the fish which indicated that the offending t a i n t i n g
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 371
TABLE 1
Descriptive sensory analysis of fish captured in the early sumnerfrom Upper Wisconsin River s i t e s . Rainbow Flowage is a controls i t e above industrial and municipal a c t i v i t i e s on the river.
Samples inPanel Sessions
Walleye pikeRainbow FlowageLake Wausau
Rainbow FlowageMosinee Flowage
Northern pikeRainbow FlowageLake Wausau
Rainbow FlowageMosinee Flowage
Black crappieRainbow FlowageLake Wausau
Rainbow FlowageMosinee Flowage
Yellow perchRainbow FlowageLake Wausau
BullheadRainbow FlowageLake Wausau
Sample
Off-FlavorIntensity
Mean
2-76K5.50°
2.81*4.27b
2.79a4.62b
2.78?4.66°
2.34a5.19°
2.71a4.86°
2.43a4.31°
3.06a4.94°
Attributes
OverallPreference
Scores
4.37?2.30°
4.67?3.25b
4-39u2.91°
4.64a2.77°
5.02a2.25°
4.66a2.53°
4.83a3.13°
3.95a2.46°
Rainbow FlowageMosinee Flowage
3.60°5.15b
3.63a2.25"
Scale: 1 = None; 7 = Extremely pronounced.
Scale: 1 = Dislike extremely 7 = Like extremely.3n = 29
a,b,Mean scores in same column with same superscript within acomparison pair are not significantly different at 0.1% level.Comparison valid between members of pairs in sessions only.
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372 HEIL, LANE, AND LINDSAY
compounds were distributed over the entire downstream
study section. Flavor terms frequently associated with
fish containing alkylphenols were medicinal, phenolic,
chemical-like and petroleum-like. Paper-like, pulp
mill, cardboard-like descriptors were also used by
panelists, and these terms were associated with fish
containing both aromatic thiols and alkylphenols.
Flavor Tainting Caused by Thiophenol and Alkylphenols
added to Fish Tissue
Flavor evaluations of cooked minced walleye
intentionally tainted with alkylphenols and thiophenol
were carried out to develop initial data on the sensory
properties of these compounds. 2,4-Diisopropylphenbl
present at 3 ppb (based on weight of mince before
cooking) was perceived as smokey and phenolic, but at
30 ppb, it became sharp, petroleum-like and anise-like.
Petroleum-like flavors were also produced by
3-isopropylphenol (100 ppb) and carvacrol (100 ppb).
Paper-like, and cardbord-like descriptors were
associated with thiophenol (20 ppb), 2-isopropylphenol
(100 ppb) and 3-isopropylphenol (10 ppb). Metallic
descriptors were used for 2,4-diisopropylphenol (10
ppb) and carvacrol (1 ppb).
A mixture of 100 ppb each of carvacrol,
3-isopropylphenol and 2,4-diisopropylphenol in fish
mince gave flavors of paper-like, wet wool-like, and
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 373
sharp phenolic-like. A mixture of 10 ppb thiophenol
and 50 ppb 3-isopropylphenol gave a papery, cardboardy
flavor that was similar to the flavor of strongly
tainted wild fish from the Upper Wisconsin River.
Thiophenol acted to blend and smooth-out the sharp,
medicinal and phenolic notes from the phenols, and
caused contributions suggestive of wet papery notes.
The results of a taste panel that compared the
flavor types of northern pike mince prepared three ways
are shown in Table 2. Most panelists perceived the
broiled fish mince containing 1 ppb 3-isopropylphenol,
1 ppb 2,4-diisopropylphenol, 1 ppb carvacrol, and 10
ppb thiophenol; and the fish mince containing 2.5 ppb
3-isopropylphenol, 2.5 ppb 2,4-diisopropylphenol, 2.5
ppb carvacrol, and 10 ppb thiophenol to be
qualitatively similar to the coded reference Mosinee
Flowage tainted northern pike mince. The effects of
individual perception of tainting flavors in Wisconsin
River fish were illustrated in the results for the
coded naturally-tainted fish (Table 2) where a number
of panelists found the sample only vaguely similar to
the identical reference (R) sample that was used in the
test structure.
The frequency of panelist responses for the
Mosinee Flowage northern pike sample was very similar
to those for the spiked samples and a large number of
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374 HEIL, LANE, AND LINDSAY
TABLE 2Frequency of responses and mean flavor identity scores in comparison oftainting flavors in northern pike
Flavor IdentityDescriptors
Assigned Naturally Spiked SamplesValue Tainted 1 2
Definitely the same typeflavor as R , but muchstronger in intensity.
Definitely the same typeflavor as R, and nearlythe same intensity
Definitely the same typeflavor as R, but lessintense than R.
Probably the same typeflavor as R, but differsin intensity and/orflavor quality.
Undecided; not sure oneway or the other.
Probably not the same typeflavor as R; Can onlyperceive some similarites.
Definitely not the same typeflavor as R.
Flavor Identity Mean Score .
—Frequency of Responses-
3 6 1
4.00c 4.13C 4.07c
Naturally tainted Mosinee Flowage northern pike.bR = Reference: Naturally tainted Mosinee Flowage northern pike.cMean scores with the same superscript are not different from each otherat the 5% level.
dn = 30.
Rainbow Flowage (control site) northern pike containing 1 ppb3-isopropylphenol; lppb 2,4-diisopropylphenol; 1 ppb carvacrol; 10 ppbthiophenol.
Rainbow Flowage northern pike containing 2.5 ppb 3-isopropylphenol;2.5 ppb 2,4-diisopropylphenol; 2.5 ppb carvacrol; 10 ppb thiophenol.
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 375
panelists (18-19 of 30) perceived distinctly similar
flavor qualities and intensities for each of the
samples. Thus, these sensory data support the chemical
data (Heil and Lindsay, 1988b) in establishing a
cause-effect relationship between tainting flavors and
the presence of alkylphenols and thiophenol in
Wisconsin River fish.
Flavor-tainting of Trout Caused by Thiophenol
Sensory evaluation of trout exposed to 20 ppb
thiophenol in water for 24 hr showed that these fish
were much more intensely off-flavored than those which
were not exposed to thiophenol (Table 3). Trout
exposed to 100 ppb thiophenol in water for 24 hr became
too strongly off-flavored for submitting to sensory
evaluation panels. Thiophenol produced a slight meaty
flavor at 3 ppb, but had a strongly disagreeable
sulfur-like, burnt rubber flavor over the 15 to 30 ppb
range. While hydrogen sulfide, methyl mercaptan,
dimethyl sulfide and dimethyl disulfide have been
considered the primary odorous constituents in Kraft
mill odor emissions, thiophenol has apparently been
overlooked as a component of North American pulp mill
effluents. Thiophenol has been reported to be present
in paper mill operations in Europe (Metelev, 1983).
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376 HEIL, LANE, AND LINDSAY
TABLE 3
"lean scores for the descriptive sensory analysis of broiledrainbow trout exposed to water containing 20 ppb thiophenol for 24hr.
Sample Attributes
Off-Flavor OverallSamples Intensity1 Preference
Mean Scores
20 ppb Thiophenol 4.39 3.26a
in water
No Thiophenol 2.66° 4.89b
in water
Scale: 1 = Absent; 7 • Pronounced.
Scale: 1 = Dislike extremely; 7 • Like extremely.
3n = 14.
' Mean scores in same column with same superscript are notsignificantly different at The 5% level.
Tank Exposure and Depuration of 4-Isopropylphenol from
Trout
4-Isopropylphenol was chosen as a representative
of the isopropylphenol group for the exposure study
because it is the most toxic alkylphenol tested (Heil
and Lindsay, 1989). Trout receiving exposure to 50 ppb
to 4-isopropylphenol in water for 24 hr were
substantially more off-flavored than untainted trout or
trout subjected to a 5-day depuration period after
exposure to 4-isopropylphenol (Table 4). In fact, the
trout subjected to a 5-day depuration period received
lower off-flavor intensity scores than the control
fish, though the overall preference expressed for these
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 377
TABLE 4
Mean scores for the descriptive sensory analysis of rainbow troutexposed to water containing 50 ppb 4-isopropylphenolphenol for 24hr.
Samples
50 ppb 4-Isopropylphenolin water
Ho 4-Isopropylphenolin water
50 ppb 4-Isopropylphenol,then 5 day depuration
Sample
Off-FlavorIntensity1
Mean
4.41a
3.34b
2.72b
Scale: 1 - Absent; 7 - Pronounced.
Scale: 1 > Dislike extremely; 7 •3n - 28.
• Like extrer
Attributes
OverallPreference2
Scores 3
3.20a
4.16b
4.13°
nely.
scores in same column with same superscript are notsignificantly different at 1% level.
two samples was essentially equal. At this high level
of exposure trout were observed to become
flavor-tainted within 5 min. This observation is
similar to that of From and Horlyck (1984) who found a
very rapid uptake of geosmin by rainbow trout.
Octanol/Water Partition Coefficients
Literature and estimated values of log P for
thiophenol, 4-thiocresol and the alkylphenols are
presented in Table 5. The calibration data for log (P)
values estimated from HPLC retention times are
presented in Figure 1. The values range from a log P
of 2.52 for thiophenol to a log P of 4.28 for
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TABLE 5Octanol/water Partion C o e f f i c i e n t s Estimated by FragmentMethod (F), Solvent Regression Method (R) and by HPLC Method
Chemical Log(P)
Carvacrol
Thymol
Thiophenol
4-Thiocresol
4-Isopropylphenol
2-Isopropylphenol
3-Iaopropylphenol
2,5-Diisopropylphenol
2,6-Diisopropylphenol
3,5-Diisopropylphenol
2,4-Diisoprpylphenol
3.44(R) a, 3.52(C)
3.30 (actual v a l u e ) b
2.52(F)
3.18(F)
3.08(F), 3.54(R) C, 3.17(C)
2.64(F), 3.22(R) C, 3.17(C)
3.B8(F)
4.BKF), 4.28(C)
4.0KF) , 4.14(C)
4.<J1(F), 3.35<C)
4.0KF), 4.06(C)
£ Seller, 1974.Hansch and Anderson, 1967.Sana et a l . , 1963.
oo
ANTHRACENE.
LOG(P)=11.44LOG(RT) + 0.40r = 0.96
ATHYMOL
THIOPHENOL
BENZENE
4-METHYLPHENOL
PHENOL
THIAZOLE
0.1 0.2 0.3 0.4 0.5LOG RETENTION TIME (MIN)
FIGURE 1C a l i b r a t i o n Curve f o r Estimation of Log (P)
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 379
2,5-diisopropylphenol. Compounds noted for their
ability to bioconcentrate in the aquatic environment
via the water-to-organism pathway generally have a log
P > 5.5 (Chiou e_t al., 1977). Conversely, compounds
with a log P < 5 do not generally bioconcentrate to
significant levels. However, Gobas e_t al., (1988) has
shown that dietary absorption in fish is most efficient
for compounds with a log P < 6. The potential for
these compounds to accumulate over short periods of
time via the food chain exists, although they may not
partition strongly enough pose a long term
bioaccumulation threat.
Alkylphenol Supplemented Feed
Rainbow trout fed (2% body weight/day) a diet
supplemented by 100 ppb each 2-isopropylphenol,
4-isopropylphenol, 3,5-diisopropylphenol, carvacrol and
thiophenol exhibited significantly more pronounced
off-flavors than the control trout (Table 6). These
fish were criticized as containing medicinal,
petroleum-like, and phenolic-like off-flavors. Trout
taken off the tainted diet for 7 days were not
significantly more off-flavored than control fish
(Table 6).
The detection threshold of alkylphenols and
thiophenols in water are generally very low and
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380 HEIL, LANE, AND LINDSAY
TABLE 6
Mean scores for the descriptive sensory analysis of rainbow trouton feed containing a mixture of alkylphenols and thiophenol.
Samples
Trout on feed containingalkylphenols4
Trout taken off of feedfor 7 days
Trout on feed containingno alkylphenols(control)
Scale: 1 = Absent; 7 = Pronounced
Scale: 1 = Dislike extremely; 7 =
3n = 29.
Sample
Off-FlavorIntensity
-Mean
4.19a
3.00b
3.47b
Attributes
OverallPreference
Scores3
3.25a
4.42b
4.09b
Like extremely.
4100 ppb each of 2-isopropylphenol, 4-isopropylphenol,3,5-diisopropylphenol, carvacrol, and thiophenol.
' Mean scores in same column with same superscript are notsignificantly different at 1% level.
2-isopropylphenol, 3-isopropylphenol,
2,4-diisopropylphenol, and carvacrol are in the 0.1-5
ppb range (Lane, 1981). Water from the Wisconsin River
did not exhibit an odor reminiscent of the alkylphenols
at any time of the year, but during sporadic periods in
the early spring a distinct thiophenol-like aroma was
associated with the river especially in the vicinity of
dam spillways where opportunities for volatilization
existed. Lane (1981) reported an odor threshold for
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 381
thiophenol of 50 ppb in water. While the basis for
these occurrences of thiophenol-like aromas in the
river was not established, the sporadic nature of their
appearance indicates they are correlated with
industrial discharges into the cold ice-covered river.
These occurrences are accompanied by complaints of
strongly off-flavored fish in the river and suggest
that the thiophenol-like taint is transferred to fish
directly from the water. When subthreshold
concentrations of thiophenol and alkylphenols were used
in water exposures of trout, off-flavors were not
perceived in the fish (Table 7). This indicates that
fish do not strongly bioconcentrate the tainting
alkylphenols from the water.
With the exception of thiophenol, the results
suggest that the alkylphenol tainted sportsfish in the
Wisconsin River are more likely tainted via the food
chain than via direct exposure to tainting compounds in
the water. The experiments show that the tainting
phenolics are readily purged by rainbow trout within a
few days of termination of exposure, even though the
compounds were observed to be quickly taken up by the
fish upon direct exposure in water. The ability of
trout to rapidly purge the taint is similar to
observations by Shumway (1966) for rainbow trout and
Coho salmon exposed to chemical plant effluent and by
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3 8 2 HEIL, LANE, AND LINDSAY
TABLE 7
Mean scores for the descriptive sensory analysis of rainbow trouton exposed to water containing a mixture of alkylphenols andthiophenol.
Sample Attributes
Intensity of Off-Flavor OverallSamples Difference1 Intensity^ Preference3
Mean Scores4
Alkylphenols and 3.03a 3.09a 4.22a
Thiophenol exposure5
(1 to 2 ppb each)
No exposure (Reference) 2.70a 3.27a 4.28a
Scale: 1 = No difference; 7 = Extreme difference.
Scale: 1 = Absent; 7 = Pronounced.
Scale: 1 = Dislike extremely 7 = Like extremely.
4n = 28.
1 ppb each phenol, 2-methylphenol, 2-isopropylphenol,4- i sopropylphenoland thymol; 2 ppb each thiophenol, 2,4-diisopropylphenol and2,6-diisopropylphenol.
scores in same column with same superscript are notsignificantly different at 5% level .
Iredale and York (1976) for muddy-earthy flavors in
trout. However, Korschgen ej al . (1970) were unable to
readily purge off-flavors from carp that had been
obtained at sites downstream from municipal waste
effluents.
The data for the thiophenol-alkylphenol mixture
exposure studies show that the concentration of
alkylphenols in water that cause tainting in fish must
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SENSORY PROPERITIES CAUSING FLAVOR TAINTING 383
be greater than 2 ppb even when several phenols are
present at this concentration. The threshold for the
transfer of tainting compound from water to fish
appears to be between 2 and 20 ppb for thiophenol and
between 2 and 50 ppb for 4-isopropylphenol in water.
As noted, such levels have not been found in Wisconsin
River water, but ppb levels of the alkylphenols have
been found in Wisconsin River sediments (Heil and
Lindsay, 1988c)• The food chain route of transferring
off-flavor compounds into Wisconsin River fish is
attractive because i t explains why individual fish of
the same species captured in the same part of the river
have been observed on occasion to differ widely in
off-flavor intensity.
Measurement of Thiophenol and Alkylphenols in Wild Fish
Off-flavors in f i l l e t s from walleye pike collected
at several downstream river locations during the late
winter and spring were evaluated by the authors, and
subsequently, a quantitative analysis for the
alkylphenols and thiophenol (Heil and Lindsay, 1988a)
was performed on a portion of each f i l l e t (Table 8).
Fish described as exhibiting alkylphenol-like flavor
taints contained over 2 ppb 2-isopropylphenol and
varying amounts of diisopropylphenols (0.3 to 4.2 ppb).
Thiophenol was present in only one sample at a level of
0.9 ppb and this sample was particularly offensive
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384 HEIL, LANE, AND LINDSAY
TABLE 8
Concentrations (ppb; w/w)a of Tainting Compounds in Wisconsin RiverWalleye Pike Collected in Late Winter and Spring.
Tainting Compound
2-Isopropylphenol
2,4-Di isopropylphenol
2,5-Di isopropylphenol
3,5-Di isopropylphenol
Thymol
Carvacrol
Thiophenol
General FlavorAssessment
1
2.0
0
4.2
0
0.6
4.5
0
AlkylPhenol
2
2.9
0
0.3
0
0.5
0
0
AlkylPhenol
Location of i3 4
0.8
0
0
0
0
0
0
Good
8.2
1.5
0
3
0
13.0
0.9
Alkyl,Thio-Phenol
Collect]5
0.5
0
0
0
0
4.0
0
MuddyEarth}
on b
6
0.8
0
0
0
0.6
0.8
0
GoodT
7
1.3
0
0
0
0
1.5
0
Goo<
aStandard deviation of method +_ 2% at 50 ppb; +_ 20% a t 1 ppb. Based onlaboratory spikes.
1 : Prairie du Sac (March 14); 2 : Lake Wausau (April 18); 3 : WisconsinDells' (April 26); 4 : Below Plover Dam (May 15); 5 : Prair ie du Sac (June
6); 6 : Below Nekoosa Dam (June 19); 7 : Below Petenwell Flowage (June 19).
which was attributed to a combination effect of both
alkylphenol and thiophenol taints. Samples containing
isopropylphenol levels below 2 ppb and levels of
carvacrol below 4 ppb did not exhibit off-flavors
(Table 8) .
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SENSORY PROPERTIES CAUSING FLAVOR TAINTING 385
SUMMARY
A mixture of 10 ppb thiophenol, 1 ppb
3-isopropylphenol, 1 ppb 2,4-diisopropylphenol and 1
ppb carvacrol had nearly the same flavor quality as
environmentally tainted northern pike when added to the
flesh of untainted northern pike. Trout exposed to a
mixture of alkylphenols and thiophenol (1-2 ppb each)
in water did not become flavor tainted, but trout fed a
formulated feed (2% body weight/day) containing 100 ppb
2-isopropylphenol, 100 ppb 4-isopropylphenol, 100 ppb
3,5-diisopropylphenol, 100 ppb carvacrol and 100 ppb
thiophenol became strongly flavor tainted. Tainting
caused by thiophenol and isopropylphenols in tank-held
trout was removed by holding the fish in clean water
for 5-7 days.
Wild fish caught from the Wisconsin River in late
winter and spring of 1985 and described as exhibiting
alkylphenol-like flavor taints contained over 2 ppb
2-isopropylphenol and varying amounts of
diisopropylphenols (0.3 to 4.2 ppb). Thiophenol was
present in one sample at a level of 0.9 ppb and this
sample was particularly offensive. Samples containing
isopropylphenol levels below 2 ppb and levels of
carvacrol below 4 ppb did not exhibit off-flavors.
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386 HEIL, LANE, AND LINDSAY
ACKNOWLEDGMENTS
Research supported by the College of Agricultural and
Life Sciences, University of Wisconsin-Madison, the
University of Wisconsin Sea Grant I n s t i t u t e under a
grant from the National Sea Grant College Program,
Federal Grant No. NA84-D-0065, Project AS/A-8, and the
Wisconsin Department of Natural Resources.
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388 HEIL, LANE, AND LINDSAY
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