Agric. Biol. Chem., 47 (6), 1219-1228, 1983 1219

Heavy Metal Concentrations in Muscle, Liver and KidneyTissue of Striped Dolphin, Stenella coeruleoalba,

and Their Variations with Body Length,Weight, Age and Sex

Katsuhisa Honda, Ryo Tatsukawa, Kazuomi Itano,*Nobuyuki Miyazaki** and Toraya Fujiyama***

Department of Environment Conservation, Ehime University,Tarumi 3-5-7, Matsuyama 790, Japan

*Department of Food Chemistry, Osaka City Instituteof Public Health and Environmental Sciences,

Tojo-cho 8-34, Tennoji-ku, Osaka 543, Japan**National Science Museum,Hyakunin-cho 3-23-1,

Shinjuku-ku, Tokyo 160, Japan

***Department of Marine Science, University of the Ryukyus,Nishibara-cho, Senbara 1, Okinawa 903-01, Japan

Received July 26, 1982

The concentrations of Fe, Mn, Zn, Cu, Pb, Ni, Cd and Hg in the muscle, liver and kidney offifty nine striped dolphins captured during 1977~ 1980 were determined by atomic absorptionspectrophotometry. The levels of most the metals examined were higher in the liver than the othertissues, except for the highest renal Cd. The frequency distribution of the metal concentrations wasmostly log-normal. For all of the organs, correlation of the metal concentrations to the body length,weight and age was positive for Fe, Pb, Ni, Cd and Hg, and negative for Mn, Zn and Cu. A highercorrelation of the concentrations of Fe, Mn, Zn and Cu to the body length and weight than to theage indicates that the metabolic turnover is more important than age or exposure time in

determining the levels of those metals. Whilst the concentration of Pb, Ni, Cd and Hg correlatedclosely with the age of dolphins, and this suggests that the age or exposure time is a dominant factorfor accumulation of these metals.

The concentrations of Pb, Ni, Cd and Hg in the muscle, liver and kidney increased with ageuntil 1 year, leveled off through 1 to 18 years by physical dilution with increased body weight, andthereafter steadily increased year by year, but in case of Hg such physical dilution effects were notsignificant. Relatively wide variation of the metal concentrations in the pup and 8 ~ 25 years femaleswas probably due to the effects of suckling, and of parturition and lactation, respectively.

The accumulation of heavy metals in marineorganisms has increasingly drawn attention

because of heavy metal pollution in the marineenvironment. In particular, mercury whichcaused "Minamata disease" is known to behighly concentrated in top predators in the

marine food chain such as seal, dolphin, tuna,swordfish and shark. It is one of the mainconcerns among environmental scientists to

elucidate the origin and mechanism of mercuryaccumulation in these species. The mercury

and the other heavy metal concentrations inmarine mammals have been extensively

studied by many workers for various speciesin different localities.1 ~17) The nature of tissueor organs, size and age of animals, and seasonor locality for sample collection are very criti-cal for the investigation of large animals suchas marine mammals.However, a detailedanalysis of tissue and organ distribution ofmetals and their variation with age, sex, re-productive activities and season largely re-mained to be studied.Among marine mammals, the striped dol-phin, Stenella coeruleoalba, which predomi-nantly feed on squid, myctophid fishes and

1220 K. Honda et al.

shrimp, is an abundant and important com-ponent of the upper part of the pelagic foodweb surrounding Japan.18) Since it is a long-

living marine mammal, i.e. more than 40 years,the animal is useful as an "indicator species"to learn complex long-term accumulation

characteristics of heavy metals in the marineenvironment.

Wehave already reported the distribution

characteristics of heavy metals in bone, blub-ber and skin of the striped dolphin, and the

nature of the organ(s) of dolphins to be selec-ted for ecological and hygienic comparisonwas discussed.23)

The main objectives of this paper, therefore,are as follows: (1) the measurement of metallevels in muscle, liver and kidney, (2) thevariation and frequency distribution of these

metal concentrations and (3) the relationshipbetween metal concentration, body length,

weight, age and sex. The heavy metals studiedwere Fe, Mn, Zn, Cu, Pb, Ni, Cd and Hg.

MATERIALSANDMETHODS

Fifty nine striped dolphins were captured alive atKawanaon the east coast of the Izu Peninsula in

December 1977, and at Taiji on the southern tip of the KiiPeninsula during the winter open seasons in December1978 ~ 1980. Since the animals are seasonal migrators, theopen season in these areas is between October and

January.19) All specimens appeared to be in a good healthycondition, with no macroscopic pathological symptoms.The animals were frozen at -20°C as soon as field

conditions permitted (1 ~ 8 hr).Body length, weight, sex and basic morphometric datawere recorded for all specimens. The mandibular teethwere taken from each animal and were aged from thedentinal growth layers following the methods of Kasuya etal.20) After detailed anatomy, the weight of various organsand tissues was measured and recorded, and these datawith the relevant biometrics have already been reported byMiyazaki et al.22) Representative muscle samples for metaldetermination were taken from a site about 10 cm in widthunder the dorsal fin, as described by Honda et al.23) Liversamples were excised from the medio-lateral lobe; samplesof kidney were from medio-lateral region of the leftkidney. These samples were packed in polyethylene bagsand kept frozen at -20°C until analysis.

One to ten grams of tissue from each sample weredigested with a concentrated sulfuric, nitric and perchloricacid mixture. Measurements of the heavy metals (Fe, Mn,

Zn, Cu, Pb, Ni and Cd) were performed by atomicabsorption spectrophotometry, and the concentration ofHg was determined by flameless atomic absorptionspectrophotometry.

RESULTS AND DISCUSSION

Metal levels in muscle, liver and kidneyTable I shows the meanconcentration ofheavy metals (jug/wet g) in muslce, liver andkidney of the striped dolphin. The level of themetals examined was generally higher in theliver than the other tissues, and markedly sofor Hg. The highest level of Cd, however, wasin the kidney where the meanconcentration(24.8 jug/wet g) was approximately four timeshigher than that in the liver (6.26/ig/wet g).

The characteristics accumulation of Hg in liverand Cd in kidney has been reported by manyworkers for other species of marine mammalsfrom different localities.1 ~6))9 ~17) Correlationcoefficients among the metals in all the threetissues were calculated to see if there was anyrelationship between the metals, and the re-sults are shown in Table II. The concentrationsof Fe, Pb, Ni, Cd and Hg gave a positivecorrelation and these concentrations gave anegative one to the concentration of Mn, Znand Cu except for the positive correlationbetween Cd and Zn in the kidney.

The literature concerning heavy metals,particularly Hg, in seals is exten-sive,1~<M5~i7,26,37) but information on the

levels in small toothed cetacean is verysparse. The levels of Fe and Hg in stripeddolphin from Kawana, Japan,37) West

Indies,34) and Western Mediterranean33* arein a similar range to ours. Most of the metallevels in striped dolphin also agree withthose of harbour porpoises, a beluga whaleand a bottlenose whale.6'26) However, Cd

levels in the muscle, liver and kidney of strip-ed dolphins were one or two orders higherthan those of harbour porpoises and a belugawhale, and also significantly higher compar-

ed with those (<0.2^g/wet g) in seals such asharbour seal,4) common seal25) and ringed

seal.7) Such a high Cd level in the striped dol-phin is explained by the fact that they feed

Heavy Metals in Striped Dolphin 1221

Table I. Heavy Metals (^g/wet g) in Muscle, Liver and Kidneyof Striped Dolphin, S. coeruleoalba

蝣 M uscle 蝣 L iver K idney

(N YRange yMean V /o

(N YR ang eM ean

c v %(N Y

R angeMean ^V/o

F e (59) 47 - 2221 59 20.8 (57) 55.8 - 95.5 2 15

44.4 (30)39. 6 - 26 714 3 30. 3

M n (59)0. 15 -0. 460 .27 23. 0

(57) 1.30-6.713.18

31.9 (30) 0.45- 1.320.82 26.7

Z n (59)6. 86 -20 .41 1.4 21. 5

(57) 26.5- 10944.5

29.7 (30)22.8-41. 230.1 15.5

C u (59)1.28 - 3.372.04 17.5

(57) 3.57 - 15.28.09

23.1 (30)1.46 -6.053.13 40.0

P b (59)0. 04- 0.2 60 .18 40. 1

(57) 0.03-0.640.22 65.9 (30) 0.01 -0.710.17 99.4

N i (59)0. 04- 0.2 50 .14 36. 3

(57)0.05 -0.49

0.2247.4 (30)

0.07 -0.630.22 76.3

C d (59)0.01 -0.250. 10 64 .2

(57)0.04-ll.1

6.2637.0 (30)

0.0 6-69.6 24.8 65.2

H g (5 1)0.46- 15.77. 02 57 .9

(45)1.70 - 4 85

20 567.5 (20)

0.91 -17.68.71 69.7

a Numberof samples analyzed.

on squid in which the Cd concentration is

extraordinarily high.32'35)Moreover, Pb (>2iug/wet g) in the liver ofCalifornia sea lion,3) elephant seal7) and com-mon seal,24) and Fe (200 ~ 5000 /xg/wet g) in theliver of weddell seal, leopard seal, crabeaterseal and dugong exceeded significantly theconcentrations in our striped dolphins.Hepatic Fe in marine mammalsis stored ashemosiderin which is considered to accumulateas a result of excessive Fe intake.7'38) Seals liveinshore where occasional exposure to high Pbpollution will accumulate a high level of Pb,and conversely, striped dolphins live offshorein a low level ofPb.

Frequency distribution of metal concentrationsin muscle, liver and kidneyA wide variation (CV%) in all metal con-centrations of striped dolphins was observed inthe liver and kidney, and Pb, Ni, Cd and Hgconcentrations in the muscle also varied widely(Table I). The frequency distribution of themetal concentrations in the muscle, liver andkidney are shown in Fig. 1. Here the data arecombined for both males and females, the

skewness of concentration distribution being

measured by Fisher's measure (g).The pattern of frequency distribution differsslightly from an ordinary bell-shaped normaldistribution, has a tailing to the right for mostof the metals, and to the left for both themuscular Fe and hepatic Cd. To examine thefrequency distribution pattern, cumulative fre-quency was plotted on probability paper (Fig.2). A straight line was obtained on logarithmicprobability paper and this indicates that theconcentrations of most the metals examinedobey a log-normal distribution. Plots of Cdconcentrations in the muscle are shown in Fig.2, as an example.The frequency distribution of heavy metalconcentrations in marine mammalshas notbeen previously reported. Ting et al.29) havereported that the frequency distribution oftrace elements in two species of marine fishand one marine algae was long-normal. Giesey etal.30) have examined the frequency distributionof concentrations of Cd, Cr, Cu, Fe and Zn inthe whole bodies of five fresh water species offish taken from an inpoundment in SouthCarolina, USA, and demonstrated that the

1222 K. Honda et al.

Table II. Correlation Matrix of: Age, Body Length and Weight vs.Metal Concentration; Metal vs. Metal in the Muscle, Liver

and Kidney of Striped Dolphin, S. coeruleoalbaI F e M n Z n C u P b N i C d H g

M 0 .53 4* 0 .0 97 - 0.375fl 0. 05 7 0.630fc 0 .4 80* 0 .78 06 0. 817 *

A g e L 0 .2 77 - 0. 406 * - 0 . 5 82 * - 0 .4 3 2 * 0.4 92" 0 .4 855 0 .39 86 0. 8236

K 0 .2 99 - 0 . 5 1 6* - 0 . 0 9 7 - 0.4 46* 0. 1 17 0 . 10 7 0 .24 5 0.687ft

B o d y

len g th

M

L

K

0 .77 5*

0 .3 75-

0 .54 25

0 .1 50

- 0 . 5 3 0*

- 0 . 5 9 1*

- 0. 464 *

- 0 . 7 2 15

- 0 .12 9

0. 03 3

- 0. 14 4- 0 .5 6 9 *

0.3 86a

0.3 86*

0. 10 4

0 .4 53*

0.3 28a

0 .1 5 7

0 .54 8*

0 .36 9*

0 .3 00

0. 736 *

0. 72 2*

0. 610 *

B o d y

w eig h t

M

L

K

0 .71 7*

0 .2 85

0 .49 3b

0 .1 34

- 0 . 5 0 3*

- 0 . 5 4 8b

- 0 . 4 0 8"

- 0. 706 *

- 0 . 2 0 2

- 0 . 0 2 9

- 0. 1 18- 0 .5 6 5 "

0.3 88-

0.3 97*

0.0 68

0 .4 66*

0 .3 97*

0.1 1 5

0 .57 9*

0 .38 0*

0 .2 94

0.793fc

0. 732 *

0. 641 6

M 0 .2 33 - 0 . 2 9 2 0. 17 6 0.1 5 9 0 .2 89 0. 412 a 0. 666 *

F e L - 0 .40 0* - 0 . 3 0 5 - 0 . 0 5 5 0. 204 0 .0 09 0 .1 39 0. 17 0

K - 0 . 3 59 - - 0 . 0 7 8 - 0.4 24* 0.1 1 5 0 .32 2- 0 .14 8 0. 363*

M 0 .21 2 0.4 306 - 0.0 49 - 0 .1 1 0 - 0 .1 39 - 0. 12 9

M n L 0. 611 * 0.3 53* - 0 . 2 2 9 - 0 . 0 3 1 - 0 .10 4 - 0 . 2 9 5

K 0. 325 a 0.6 056 - 0.1 1 9 - 0 .1 2 9 - 0 .14 2 - 0 . 65 6 6

M 0. 13 7 - 0 .1 5 5 - 0 .0 20 - 0 .2 1 7 - 0 . 2 3 0

Z n L 0.4 73- - 0 .3 90* -0 . 2 9 1 - 0 . 3 4 3 - - 0. 459 *

K 0. 203 0.2 43 - 0 .0 0 7 0 .52 8* - 0 . 0 4 9

M - 0 . 0 8 2 - 0 . 0 6 0 - 0 .2 2 6 - 0 . 0 5 4

C u L - 0 .1 8 0 - 0 .0 62 - 0 .1 82 - 0 . 0 2 5

K 0 .2 92 -0 . 5 01 * - 0 .0 4 2 - 0 .6 2 5 6

M 0 .2 65 0. 49 2* 0. 432 *

P b L 0 .5 10 0 .2 42 0.5 816

K 0 .35 7- 0 .1 54 0.0 51

M 0 .2 94 0.4 446

N i L 0 .2 62 0.4 69 "

K 0. 12 9 0. 01 7

M 0.6 86 *

H g L 0.258fl

K 0.3 91-

a Significant level, p<0.05.b Significant level, p<0.001.

M, muscle; L, liver; K, kidney.

log-normal, normal, Weibull and exponentialdistributions had a best fit to 57, 17, 26 and 0%of the species-element groupings respectively.Taguchi et al.28) have also reported that thefrequency distribution of concentrations of Fe,Zn, Cd and Cu in the muscle of dogfish waslog-normal.

Our results, examined for eight metals in themuscle, liver and kidney of striped dolphinsalso showed a log-normal distribution similarto those of the other marine organisms.

Therefore, positive or negative skewnesscauses some discrepancy in the confidencelimits for the mean. To avoid a large error inconfidence limits for populations in which theprimary deviation from normality is a stronglypositive or negative skew, Cochron36) has sug-gested that the sample size (n) must be largeenough so that n>25g2, where g is Fisher's

measure of skewness. In accordance with thisrule, the numberof our samples analysed waslarge enough for most of the metals, but Pb

Heavy Metals in Striped Dolphin 1223

g=-1.32 g=0.541 g=1.02 g=1.41 g=0.481 g=0.301 g=0.802 g=0.730

»å  \ . r 2 j26 j

g=0.933 g=1.41 g=2.47 g=0.996 g=0.675 g=0.756 g=-0.599 g=0.85920- i24. 25S24 525

l. å  L I I . Llver

20 å  g=0.086 g=0.729 g=0.569 g=0.406 g=2.03 g=2.19 g=0.906 g=0.064i/jdngw

Fe Mn Zn Cu Pb Ni Cd Hg

Metal concentration

Fig. 1. Frequency Distribution of Fe, Mn, Zn, Cu, Pb, Ni, Cd and Hg Concentration in the Muscle, Liverand Kidney of Striped Dolphin.

The data for males and females are combined.

«. 80

0.05 0.10 0.20

Cd concentration

Fig. 2. Cumulative Frequency: Cd Concentration

(fig/wet g) in the Muscle, Liver and Kidney of StripedDolphin.

I-#, normal scale; O-O> logarithmic scale.

and Ni in the kidney showed high skewness(<?2=4.12 for Pb and 4.80 for Ni). When thedistribution of heavy metal concentrations inbiology is non-normal and highly skewed, the

sample size should be sufficiently large.

Changes of metal concentrations with age andsex

Significant positive correlation of the metalconcentrations with age for striped dolphinwas found in the muscular Fe, Pb, Ni, Cd andHg, in the hepatic Pb, Ni, Cd and Hg, and inthe renal Hg, whilst the hepatic Mn, Zn and Cuand the renal Mn and Cu were negativelycorrelated with age (/?<0.001, Table II). Theconcentrations of metals in the muscle, liverand kidney are plotted against age (Figs. 3(a)and 3(b)), with the data for males and femalesbeing separately plotted.Remarkable differences in most of the metalconcentrations in the muscle, liver and kidneywere observed between the ages of 0~ 1 year(pup) and the older specimens (immature andmature). The concentrations of Fe, Pb, Ni, Cdand Hg were higher in the latter than theformer, and those of Mn, Zn and Cu, exceptfor Mn and Cu in the muscle and Zn in the

1224 K. Honda et al.

Fe Muscle * ° MnMuscle

^ » o O à"^ 00 «

600r _ 7.Or ..

Fe Liver f Mn Liver

à".°à" *à"à" "à"# à" Vv .°. %à"» °

01 30°f o Fe Kidney 2°°r MnKidney

\ - o \t^ A«. ^ o \

( oà" . o *

à"H I < 1 à" 1 I 1 1 1 1

* 30r 4.0r-

£ ZnMuscle o CUMuscleCa) 0

i I . , , , I 1 . . .

200r ^ 20 r r å 

Zn Liver Cu Liver

50_ 7 -

Zn Kidney , Cu Kidney1%>,; - : i.0å # °i*°#r * 5y\°°-. o °

. % ..s à"

10 20 30 40 10 20 30 40

Age in years Age in years

Fig. 3(a). Relationships between the Concentration of Fe, Mn, Zn and Cu in Muscle, Liver and Kidney,and the Age for Striped Dolphin.#, male; O, female.

kidney, were higher in the pup. After the rapidchange of metal concentrations in pups, thevalues of Mn, Zn and Cu in immature andmature dolphins remain relatively unchanged,but those ofFe, Pb, Ni, Cd and Hg character-istically change with age.The concentration of Fe in the muscle in-

creased with age until 8 years and thereafterremained constant. A similar tendency alsowas observed with Fe in the liver and kidney.The concentrations of Pb, Ni and Cd in themuscle, liver and kidney increased with ageuntil 1 year, and then remained constantthrough 1 to 18 years. After about 18 years,

Heavy Metals in Striped Dolphin 1225

"MusclePb ' Z* ' "Muscle Cd à"". OOVà" à" à"à"j^^ O* /

Liver Pb £ ' Liver Cd

jj .70r o 70r ^. o

<o Kidney Pb Kidney Cd

(T3 ' ' ' ' ' * ' ' * " '

-P .25r à" 2O'r

g Muscle Ni . Muscle Hg° à" à"*S *^^6C à" * à" «^- o

8 :-^-r^ro -a à" à" .

fO *5^* °à" ° * °o ° * o^"-"^ ° à"*

S o ° /^

"50["Liver Ni * > Liver Hg

* KidneyNi KidneyHg à"

à" .

à"à"/^~- °

å ;..à". :^^-^ y ***r °,* 9à"-s 5^ o J

10 20 30 40 10 20 30 40

Age in years Age in years

Fig. 3(b). Relationships between the Concentration ofPb, Ni, Cd and Hg in Muscle, Liver and Kidney, andthe Age for Striped Dolphin.

), male; O, female.

the concentration of Pb, Ni and Cd furtherincreased with age. A steady increase of Hgconcentration in the liver against age duringthe whole life span was observed, whereas Hgin the muscle and kidney reached a plateauafter about 18 years.

The increase of body length and weight of

the striped dolphin ceases at about 8 and 18years respectively (Fig. 4, discussed in detail

later), the weaning and maturity ages being0~ l and 8 years respectively.21*A fast change of metal concentration frombirth up to 1 year indicates that particularmetals such as Pb, Ni and Cd are transferred via

1226 K. Honda et al.

300p

I . M' offi^t 'g«»**u.*à" *

I 150fi

oi ' ' ' '10 20 30 40

2OO.r

£loo- o^/ à"

0L 1 1 1 1

10 20 30 40

Age in years

Fig. 4. Relationships between the Body Length and

Weight, and the Age for Striped Dolphin.#, male; O, female.

milk from the mother to her pup. The plateauof the concentrations of Pb, Ni and Cd during1 ~ 18 years is explained by physical dilutionfrom the increase in body weight. Hg did notshow such similar dilution effects as Pb, Niand Cd and this implies a higher absorptionrate of Hg in the digestive tract of stripeddolphin and a larger persistence of Hg thanthose of other metals. Moreover, a plateau inthe concentration of Hg in the muscle andkidney comes earlier than that in the liver. Thisindicates a longer biological half-life of Hg inthe liver.

Sexual differences in the metal concen-

tration of striped dolphins are not particularlygreat (Figs. 3(a) and 3(b)). The concentrationsof muscular Pb and Ni and hepatic Fe, Zn, Cu,Pb and Ni were higher in mature male than inmature female, although the hepatic Mncon-centration in female was higher than that inmale. Furthermore, the concentration of met-als in 8~25 year females varied more widelythan that in males and this probably reflectssuch reproductive activities as parturition andlactation.

Relationships between body length, weight andmetal concentration

There were also some significant positive ornegative correlations for metal levels againstbody length and weight. The concentrations ofFe, Mn, Zn and Cu in the muscle, liver andkidney showed a high correlation with bodylength, high with body weight and slight withage. In the case of Pb, Ni, Cd and Hg,

however, the correlation with age was alwaysstronger than those with body length andweight (Table II).The concentration of Fe in the muscle wasproportional to the body length, roughly to thecube root of the body weight, and slightlyhigher in female than male (Fig. 5). Similarresults wereobtained on the concentrations ofFe, Mn and Zn in the liver and kidney. This isunderstandable by the regression equation be-tween the body length and weight which showsBW=2.19x l0~5BL2-88 (r2=0.968).38) The

concentration of Hg in the muscle, liver andkidney also correlated with the body lengthand weight, higher in female than in male,although it showed strong positive skewnesswith larger size. Similar results (not shown)were found for Pb, Ni and Cd in the muscleand liver. Plots of Hg concentration in the liverto the body length and weight are shown inFig. 6, as an example.Although Hg concentration in marine mam-mals as well as many fish is knownto increasewith age and size, clear tendencies for othermetals have not been established. The cor-relation of Fe, Mn, Cu and Cd concentrationsto the age and size of harbour seal4) and

dugong7) agree well with our results for stripeddolphin.

However, no significant correlation of Pband Ni concentrations with age and size wasobserved for harbour seal4) and dugong.7)These papers also showed that the concen-tration of Zn in the liver and kidney of dugongpositively correlated with the age, while aspecific increase of Zn concentration in har-bour seal was not found. In our striped dol-phins, Pb and Ni correlated with age and Znshowed a negative correlation against age.

Heavy Metals in Striped Dolphin 1227

300 r-^. y=0.826X-24.0 r=0.795

$ : Y=0.869X-22.0 r=0.786 ~

a 150 - 0,0^^^^ "

0I 1 1 1 1 1 '

100 200 300

Body length in cm

300r n odc o$: Y=28.5X°*i4b r =0.903% : Y=35.2X°*320 r2=0.892

l150' c^^^*^^ *

0 100 200

Body length in kg

Fig. 5. Relationships between the Concentration of Fein Muscle and the Body Length and Weight for StripedDolphin.

#, male; O, female.

- 500r j:Y=2.24xl03e°-050X r2=0.96lo|;|*

jjj ?:Y=l.OlxlO4e°-°64X r2=0.920 W

250 - W*

qI i :-i e-o-i a^m ' ' '100 200 300

Body length in cm

» 5OOh:Y=l.O2e°-O38Xr2=0.930 ° f/ *

^ ?:Y=0.78e°-041Xr2=0.883 j*J

t .yv-250 " ocb7/

J/*à"

^ °°^* *à"

0 ' '**^ {^ ' ^o

Body weight in kg

Fig. 6. Relationships between the Concentration of Hgin Liver and the Body Length and Weight for StripedDolphin.

#, male; O» female.

This difference may be due to the smallersample sizes of young harbour seals anddugongs compared with ours, because the pupof striped dolphin contained relatively high Znin the liver and low Pb and Ni in the muscle,

liver and kidney.Studies by Olsson37) on northern pike, Esoxlucius L., are of interest since he found that fishof the same size but of different ages (as ameasure of exposure time) had similar Hg

levels. He found also that males had signifi-cantly greater Hg levels than females. Gaskinet al.6) have found clear correlations of Hgconcentration with age in the muscle, kidney,cerebrum and liver of harbour porpoises. Theyalso found that Hg levels, except in the liver,were less well-correlated with weight and bodylength than with age, and not significantlycorrelated with weight and length within thesameage classes. Our results here agree wellwith the results on harbour porpoises6) but notwith those on the northern pike.37) Such cor-relation of metal concentration to body length,weight and age indicates that the metabolicturnover (correlated with size) is more impor-tant than age or exposure time in determingthe levels ofFe, Mn, Zn,, and Cu, and that theage or exposure time is a dominant factor foraccumulation of Pb, Ni, Cd and Hg in marinemammals.

Acknowledgments.Specimens were collected throughthe cooperation of the fishermen's unions at KawanaandTaiji. Weare greatly indebted to Messrs. Y. Torikai andK. Kouno for helping in the dissection of samples andanalysis, and to Mr. N. Oka for helping with computationand statistical analysis. This work was supported in partby Grants-in-Aid for Scientific Research (Project No.343056) from the Ministry of Education, Science and

Culture of Japan and by the Toyota Foundation (80-1-123).

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