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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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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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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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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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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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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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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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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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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


Black crappieRainbow FlowageLake Wausau


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°


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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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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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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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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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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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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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



2,4-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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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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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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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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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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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



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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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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Baldwin, R.E., Strong, D.H. and Torrie, J.H., Trans.Am. Fish. S o c , 90, 175-180 (1961).

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Cook, W.H., Farmer, F.A., K r i s t i a n s e n , O.E., R e i d , K.,Re i d , J . and Rowbottom, R., P u l p P a p e r Mag. Can.74C, 97-106, T 113-122 ( 1 9 7 3 ) .

F a r m e r , F.A., N e i l s o n , H.R. and E s a r , D., Can. I n s t .Food S c i . Tech. J . 4, 12-16 ( 1 9 7 3 ) .

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SENSORY PROPERTIES CAUSING FLAVOR TAINTING 387

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Lane, N.A. " I s o l a t i o n of V o l a t i l e Compounds andEvaluation of P o t e n t i a l Roles of SelectedCompounds in the Flavor Tainting of UpperWisconsin River F i s h . " 1981. U. of Wisconsin,Madison. Master of Science t h e s i s .

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Received: February 20, 1989

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