Lead behavior in abalone shell

No. 15,pp.3 183-3 189, 1994 Copyright 0 1994 ElsevierScience Ltd Printedin theUSA. All rightsreserved

Geochimica et Cosmochimica Acta, Vol. 58,

Pergamon

0016-7037/94 $6.00+ .oO

0016-7037(94)00113-8

Lead behavior in abalone shell* YOSHIMITSUHIRAO,‘.+AKKAZU MATSUMOTO,‘*$HIROSHI YAMAKAWA,’MASARUMAEDA,’ and KAN KIMURA' ‘College of Science and Engineering, Aoyama Gakuin University, 6-16-I Chitosedai, Setagayaku, Tokyo 157, Japan ‘Tokyo University of Fisheries, 4-5-7 Konan, Minatoku, Tokyo 108, Japan (Received June 15, 1993; accepted in revised form April 8, 1994)

Abstract-In order to gain information about the behavior of heavy metals in biological assimilation processes in a marine food chain and to investigate the possibility that lead pollution in a marine environment can be estimated by measurement of a small number of key materials from such a food chain, muscle and shell were analyzed from abalone (Huliutis) from a shallow water locality in a Japanese coastal region. Lead concentrations in muscle were about 26 ppb for abalone of approximately 3 years old and decreased systematically with increasing age of animals sampled, to about 3.3 ppb for a specimen approximately 8 years old. Lead concentrations in shell material gradually decreased also, from 150 ppb to 82 ppb in the oldest specimen. The decrease of concentration in tissues with increasing age indicates that a mechanism for exclusion of lead during tissue growth becomes more efficient with age. Along the food chain in which abalone is the final stage, lead was enriched at the first stage, from seawater to algae, by a factor of 100. Lead was diminished at all subsequent stages of the chain. Tissue of artificially cultured abalone had four times higher lead values compared to abalone grown in natural conditions, and this appears to reflect the fact that lead concentration was three times higher in seawater in the cultured environment. INTRODUCTION

higher, for comparable samples, than the values obtained by modem techniques by BURNETT and PATTERSON(1980b). The differences must be attributed to lead contamination during sampling and analysis in the older work, as discussed by PATTERSONand SETTLE (1976). Therefore, lead values that can be considered reliable for environmental samples are extremely restricted (further discussed in Participants of the Lead in Seawater Workshop, 1974, and PATTERSONand SETTLE, 1977). The purpose of this report is to discuss and clarify the behavior and movement of lead through the food chain of which abalone is taken as the final stage. Abalone has a relatively simple supporting food chain and is a large enough animal to allow collection of sufficiently large samples for reliable chemical analysis. Because of theoretical and observed chemical similarities, lead may be considered to accompany calcium in living matter (BURNETT, 1978; ELIASet al., 1982). The distribution, by tissue types, of the body burdens for the two metals may be compared. For instance, according to PATERSON and SETTLE (1977), fish bone contains about 70% of the total body burden of lead and 85% of the calcium, although bone constitutes only about 6% of the total body mass. Muscle constitutes 70% of the total mass but contains 3% of the lead burden. Concentration of lead in muscle is extremely low, 0.3 ng Pb/g fresh weight. In contrast to calcium and other alkaline earth metals, alkali metals are distributed relatively uniformly through different tissue types, with no specific abundance correlation between lead and alkali metals. In abalone, shell material accumulates 95% of the lead and 98% of calcium of the total body burden (BURNETTand PATTERSON,1980b). Because lead accompanies calcium through the food chain and concentrations of the two metals correspond by tissue types, lead concentration is in many cases normalized to calcium when reporting data in the present report.

AGAINST LEAD atsuccessivetrophic levels in the marine food chain has been demonstrated by SETTLE and PATTERSON (1980) and BURNETT and PATTERSON (1980a). It has also been clearly demonstrated in the terrestrial food chain by ELIASet al. (1982). BURNETTand PATTERSON (1980b) demonstrated that the lead depletion trend seen in other food chain systems is in effect in the seawater-algaeshell succession. However, they pointed out that whereas lead was diminished at every step in the terrestrial system, there was one step in the marine system, namely seawater-to-algae, where the lead concentration increased. This one exception may be explained by the extremely low concentration of lead in seawater. Those authors also attempted, by contrasting samples from both clean and polluted seawater environments, to characterize the degree to which lead pollution was recorded in the shell of the abalone (Halids). Coastal marine ecosystems are complicated because of the presence of large numbers of species of fauna and flora and the drastic changes of the growth characteristics of many of them in response to seasonal changes. Because of those complications, in order to make clear the lead distribution or lead pollution levels for coastal ecosystems, it would be necessary to accumulate a large number of systematic lead concentration data. Few reliable lead data are available for marine samples. Those summarized by PRESTON et al. (1972), BRYAN and HUMMERSTONE(1973), and BOWEN(1978) are 10 to 100 times DISCRIMINATION

* Paper presented at the symposium “Topics in GIobaI Geochemistry” in honor of Clair C. Patterson on 3-4 December 1993 in Pasadena, California, USA. +Present address: Tokyo National Research Institute of Cultural Properties, 13-27 Uenokoen, Taitoku, Tokyo 1 IO, Japan. * Present address: Geological Survey ofJapan, l-l-3 Higashi, Tsukubashi, Ibarakiken 305, Japan. 3183

3184

Y. Hirao et al. FIELD

AND SAMPLING

Table

1. Lead concentrations in seawater and algae in Am&u-Kominato nrer.

Field

Soluble Total (Pb “g 1 kg)

Seawater

The main field area for sample collection in the present study is the shore of Amatsu-Kominato of the Boso peninsula, Japan, about 100 km to the southeast of Tokyo, shown in Fig. 1. In AmatsuKominato village, the population is about 10,000 people, in a zone within 2 km of the coast. Economic activity centers on small farming and coastal fisheries. There is a small harbor for coastal fisheries on the opposite shore from the study area, about 1 km away. The shore of Amatsu-Kominato faces the Pacific ocean and is directly influenced by the open ocean. The shore of the study area is mainly covered with Tertiary sedimentary rock and breccia, and there is sandy bottom material to more than 30 m offshore. The ecosystem of the shore has been protected and reserved for research studies for the last 50 years, and algae and crustacean populations at the shore are very dense. Native abalone can be found even in shallow water in this area. The villages of Kasumi and Hamasaka are situated on the Sea of Japan side as shown in Fig. 1.The populations of Kasumi and Hamasaka villages are about 10,000 people each, and economic activity centers on coastal fisheries and small rice and fruit farming. No large factories are in the areas of the two villages. Unlike the case of Amatsu-Kominato, where Tokyo may contribute lead pollution, there is no large city near Kasumi and Hamasaka. The Tsushima current washes the north coastal area of Honshu Island, and Kasumi and Hamasaka areas are under the influence ofthis current. The lead pollution levels of Kasumi and Hamasaka areas are apparently similar to those of the Amatsu-Kominato area. Seawater

Seawater from the area inhabited by abalone and algae was collected from the shore in different seasons, and analyzed several times, to determine typical lead levels (HIRAO et al., 1986) as shown in Table 1.Seawater of a cultivation pool was also analyzed.

Several species of brown algae such as Eisenia bicyclis, Ecklonia cava, and Undria pinnatiJida were also collected in different seasons to allow assessment of variation of lead concentration (HIRAO et al., 1986) as shown in Table 1. These algae are the most abundant and largest species in this area and are confirmed by field observation to

Amatsu-Kominatoarea (1983) Near Ohsbima island (1976)

Average in

Akiya (Mica Peninsula) (1976) Tomiwa (outer part of Tokyo Bay) (1976) Inner Tokyo Bay (1980) Outer Tokyo Bay (1980)

z 46

40 $;

5?210 40

Species of Algae @pb. f:bsh weight) Mean Tidal Level (Infralittoral Zone) Sargassum rhunbergii Low Tidal Level Eiscnia bicyclis Undria pinnarifidn Ecklonia cow (1) Hirao eta/.(1986),

(2) Hirao e,a1.(1983).

200

Reference

(1)

25 :z

It; (1)

(3) Hirao et o/.(1979)

be the food for abalone. The same species of algae in a cultivation pool was collected as the same way and analyzed. Abalone

Four species of abalone (Haliotis discus, H. sieboldii, H. gigantea, and H. discus hannai) are found in coastal areas of Japan. There are some differences in their habitats, including the temperature zones in which they reside, resulting in differing activity and size (INO, 1952). In this study the most common species, H. discus and H. sieboidii were collected for study. Both species live in shallow water from 3 to 6 m depth near the shore and grow to around 20 cm at maximum after 10 years. Individuals of the same species were collected from different shores for comparison. ANALYTICAL

METHOD

Lead concentrations of abalone shell and muscle were determined by graphite furnace atomic absorption spectroscopy after removal of other metals by ion exchange and correction of chemical yield by *‘*Pb (MATSUMOTO et al., 1986). Calcium concentrations were obtained by inductively coupled plasma spectroscopy by a standard method. To avoid lead contamination during sample processing and analysis, special contamination control procedures were followed in preparation of laboratory environment, ware, and reagents, and in sample treatment, as detailed below. Pretreatment of Abalone

About thirty specimens of abalone of various size were caught for this research during the summer of I983 and spring of 1984. Abalone caught from the sea were immediately frozen in a polyethylene bag and carried to the laboratory in order to avoid contamination. Sea of Japan

Shell

1. AmatsuKominato

Pacific

2.

Kasumi

3.

Hamasaka

Ocean

FIG. 1. Map showing sampling locations. Collections were made in summer of 1983 and spring of 1984, for all three sampling sites, on both the Pacific and Sea of Japan sides of Honshu.

The shape and structure of abalone shell is shown in Fig. 2. The annual growth is represented by ring or rim structures 2-5 cm in width. These remain clearly visible on the shell, as it grows. The outermost annual ring from each individual was analyzed. The calcite and aragonite phases of the outermost layer of the shell, estimated to have grown within a year of sample collection, were separated and used for this analysis. The thickness of calcite layer is approximately VI0of aragonite layer. In order to compare lead concentration in different time-growth zones ofabalone shell, it is important that seawater conditions should be known to be uniform. Accordingly, only outermost shell rings, grown in the same seawater medium within a year of collection of samples, and taken from abalones of various sizes and ages, were used for analysis. This is one of the essential points of this report.

Geochemistry of Pb in abalone shells

3185

calculated from the sample weights and lead masses in its constituent subsamples (TATSUMOTOand PATTERSON, 1963; MATSUMOTOet al., 1986). Lead concentrations of muscle are presented in the present study on a wet-weight basis. Several analyses of calcite phase from the same individuals gave lead concentration values within the error range, confirming homogeneous concentration of lead in this phase. RESULTS AND DISCUSSION

The analyzed values for lead and calcium in abalone muscle and shell mater&I are shown in Table 2. Deviation of Lead Concentration in a Sample Group

J /

Shell

,

epidermis

Calcite ,

Cross

section

of

Aragonite

shell

FIG. 2. Structure of abalone shell.

The abalone was dissected using a stainless steel knife in a clean room, to separate the shell and soft tissue. Soft tissue was frozen again and stored until analysis. Shell material was washed with ethanol and acetone and then the outermost growth ring (Fig. 2) was cut away with a stainless steel saw, washed with ethanol, and finely crushed in an agate mortar. The powder was washed again with ethanol and acetone, and sieved # 120 to #240 mesh. Calcite and aragonite have different densities (2.71 and 2.95, respectively), and a heavy liquid method using bromoform gave good separation efficiency for both phases and from the organic materials (shell epidermis in Fig. 2). Separated calcite and aragonite phases of shell were subdivided into three or four independent subsamples of different graduated weights, from about IO to 50 mg to constitute a set for analysis. The samples were dissolved using constant amounts of 3 mL of nitric acid and 3 mL of perchloric acid for each subsample of the analytical set. The lead contents of both shell and muscle samples were separated from other components and determined by the method described below.

Deviation of lead concentrations of individual samples are shown in Table 2. Four cultivated abalone specimens of the same size from Ama~u-Kominato were analyzed to examine the concentration deviation among individuals. Four H. discus individuals ranging in size from 5.18 to 4.84 cm which were cultivated in the same pool for 3 years were used for this investigation. The analyzed values indicate that individuals of the same size have constant concentrations of lead in calcite and aragonite phases, and in muscle. This was also revealed by H. discus specimens from Kasumi that grew in natural conditions, where lead concentration in three individuals from 9.60 to 9.74 cm in size showed good agreement. These results confirm that same-sized, same-species individuals in identical environments have identical lead concentrations in their respective tissues. Differing lead concentrations between same-sized (same age) specimens must be linked to environmental differences.

Table 2. Concentratiaes of calcium and lead in abalone muscle and shelf tfwah weight basis).

Location

Muscle was separated from other soft tissues in a clean room after partial thawing using steel blades. Great care was taken to exclude any contamination from the other organs such as intestines, liver, and stomach. Separated muscle was su~ivided by cutting into three to four subsamples of different, graduated weights, from about I50 to 300 mg, to constitute a set for analysis. They were dried in quartz beakers, their dry weights were recorded, and they were dissolved using a constant 7 mL of nitric acid and 2.5 mL of perchloric acid for each subsample.

Lead Separation and ~termination

Lead in dissolved samples was purified by passing through an anion exchange column (AGlXI Br- form, 4 mm X 100 mm) using hydrobromic acid. The recovery of lead (yield) during this step was determined and corrected with using the “‘Pb method described by MATSUMOTO et al. (1986). The lead concentration in the purified solution was measured by graphite furnace atomic absorption spectroscopy. Lead concentration for an original undivid~ sample was

Shell*‘)

Muscle

H. discus

13.53

170

3.3

:: z:

12.53 11.52

160 190

7.2 4.6

;:

Muscle

Shell

a.7

130 120

120

140

140

150

10

770

320

11 ::

440 1;

210

170

zz 200

150 160 210

170 180 230

24 40

34 54 54 54

:::

z:

a.74 9.90

370 170

7.37

330

H. discus

5.61

320

H. discus

12.68

If:

H. discus H. d&clfs

12.35 5.18

150

H. discus H. discus

4.95 4.84 4.93

140 130 140

;A

H. sieboldii H. sieboldii H. sieboldii

14.33 13.69 10.57

1:;:

H. H. H. H.

12.70 9.74 9.62 9.60

H. discus H. discus

14.34 13.20

24 ;:

1.7 2.6 4.0

120

ml

11

420

9.0

-

a2 12

llfit 110

22

H. discus

discus discus discus discus

;:

-

190

3186

Y. Hirao et al.

2 5o

A.K

A

A.K

H. sieboldi

0

Kasuml

H.discus

0

5

10

15 cm

Shell length FIG. 3. Pb/Ca ratios in abalone muscle, in relation to shell length (shell length is an indicator ofage of individual). Lead concentrations consistently decrease with age. A * K: Amatsu-Kominato.

Lead in Abalone Muscle Lead concentration changes in muscles, relative to shell length as an indicator of age, of two species of abalone (H. discus and H. sieboldii), collected at Amatsu-Kominato, are shown in Fig. 3. Lead values are presented normalized to calcium. The gradients of curves for two species are somewhat different. Lead has been shown to be not only unnecessary to living matter but also harmful to it in general, so lead may be expected to be excluded from Ca-bearing matrices as a result ofdiscrimination during calcium uptake in the digestive systems and/or during the muscle formation (PATTERSON and SETTLE, 1977). The figure indicates that lead values in abalone muscle decrease systematically with the increase of shell length. The curve suggests that younger abalone contains

higher lead, indicating that lead absorption is greater in younger individuals. Muscle of abalone (H. discus) collected at Kasumi on the Sea of Japan side had lower Pb/Ca ratios than the sample taken at Amatsu-Kominato on the Pacific Ocean side. As growth rate and food type are similar at both locations, judging from the thickness of yearly growth ring of the shell and the similarity of algae which live in the two areas, the difference of lead concentrations in muscle for samples from the two locations can be attributed to different lead concentration levels in the two sites. This finding concerning lead concentration in soft tissue may be significant for the systematics of metal uptake by this organism. Lead in Abalone Shell

Data on concentration of lead in the main calcium reservoir (shell material) are also important for clarifying the distribution of lead in abalone. Lead concentration changes in

shell material in relation to shell size are presented in Fig. 4. The figure demonstrates that lead values in calcite and aragonite phases of the shell decrease as shell length increases, as is the case with muscle. Lead concentrations in shell material from different locations are also different. The same difference was observed for muscle. These findings indicate several important features, as follows. The first feature is that the systematic decrease of lead concentration with size of the individual animal, noted above, suggests that an organic control mechanism operates in the abalone. This may be explainable as follows: the urgency of rapid shell development during the rapid-growth stage of the early life of the abalone requires that calcium absorption in stomach or intestines minimize discrimination against lead, resulting in the “overlooking” of the bivalent lead ion that accompanies calcium. As the abalone grows larger and the rate of shell formation decreases, discrimination against lead in favor of calcium will become increasingly effective, as the slower absorption rates more closely approximate “equilibrium” conditions. Under those conditions, lead concentrations in both muscle and newly grown shell material decrease gradually as the animal moves into adulthood. The second feature is that different species of abalone, H. discus and H. sieboldii, show clear differences in lead concentration in shell and muscle even though they have similar diets (such as the algae Ecklonia cava, Undria pinnatifida, and Eisenia bicyclis) and reside in similar temperature zones in the shore environment. The fundamental physiological

0

5 Shell

10

15

cm

length

FIG. 4. Pb/Ca ratios in aragonite and calcite ofcurrent-year growth bands of abalone shell, in relation to shell length. Open symbols represent calcite, filled symbols aragonite, for both species and all three sample collection sites. Circles: Amatsu Kominato, H. discus; squares: Amatsu Kominato, H. sieboldii; triangles: Katsumi; stars: Hamasaka. Lead concentrations in both mineral phases decrease systematically with increasing age of individual, following the same trend shown by sofi tissue (muscle).

Geochemistry of Pb in abalone shells

differences that distinguish the separate species may control the differences observed for their lead concentration. DODD ( 1965) reported similar differences in magn~ium and strontium concentration for the shells of several species of bivalves. Other work (DODD, 1967; ZOLOTRAREV,1975) also suggests that the distribution of trace elements in the tissues of organisms may be distinctly different, according to their species as well as environmental circumstances. The third feature is that lead in abalone from various locations seems to fall on different lines (trends) in Fig. 4. From the observed values, it seems that the lead level of the collection site in Kasumi is cleaner than Hamasaka, and Hamasaka and Amatsu-Kominato appear similar to each other. The lead values recorded in the abalone shells of the same species from different locations may result from differences in tead polfution levels in their en~ronments. The fact that the abalone eat similar algae, reside in similar temperature zones, and show similar growth rates lends weight to this supposition. Alternatively, the most current annual-growth shell material of abalone can itself be considered representative as an indicator of the lead pollution level in a shore environment during a given year, because of the animal’s well-documented position in a well-documented food chain. In addition, the values recorded in annual shell growth layers are preserved in a readable sequenced order, allowing evaluation of successive changes of lead pollution levels of the shore environment, if appropriate corrections are developed and applied to account for the differing Ca-Pb discrimination in specimens of differing age (size). The main processes that exclude lead from the calcium reservoir may be different for tissues of different structural type, and the mechanisms may be fundamentally different. The Pb,fCa ratios in shell and muscle are 5.0 X LO-’ and 5.6 X 10e6, respectively. The difference is so large that it is reasonable to infer that the lead exclusion mechanisms may be very different for the two types of tissue, according to the capacities of the two material types to accommodate trace foreign ions. In addition to the above, the aragonite phase contains more lead than the calcite phase (Fig. 4). If the biologically

3187

ia4 Cultivated /-

Natural

/-

10-e

Seawater

Atgae

Abalone MUSCIE

Shell

FlG. 5. Lead concentrations, normalized to calcium, in components of the abalone food chain, for both natural (black bars) and cultivated (white bars) environments. The hatched areas represent the increased lead contribution estimated for the non-algae components of the total abalone diet in the natural environment (see discussion in text). In both environments, normalized lead concentrations increase in the step between the first two trophic levels of the food chain (seawater and algae), and subsequently decrease in the steps linking the abalone diet to the two tissue types (algae to muscle, and algae to shell). The ratios linking the normalized lead concentrations of the trophic levels are the same in both environments.

itated mineral matter of the abalone shell is similar to the same inorganically precipitated minerals, the larger crystal lattice sites in calcite could be expected to more readily admit larger ions such as lead. However, BURNETTand PATTERSON (1980b) also reported higher lead in aragonite phase than in calcite phase in abalone.

precip-

Lead Behavior in the Abalone Food Chain Tabie 3. Concentrations ofcalcium end lead in the food chain ofabaloae.

Sample

0.027”) 29’4)

1.4 x 10-n 2.3 x IO-6

369000”) 160

96 4.6

5.0 x 10-s 5.4 x 10.6

390 2720

0.081 600

4.0 x 10” 4.3 x 10-5

310 10

1.6 x lo-7 2.4 x 1P5

370 2400

369oo0’3) 85

*l) *2) *3) ‘4)

Tbc 6 year old abaknc of 143 g total weight and 12.55 cm length was used. The 6 year oki abalone of 186 g total weight and 12.68 cm kngtb was used. & in six11was confii to be constant50 tiat average value was cited. The vakes were cited from Tabk 1.

Aspects of the behavior of lead in the abalone food chain were studied as follows. The ecosystem of W. discus in the Amatsu-Kominato area has been studied extensively. Their main food is recognized to be a brown algae such as Ecklonia cuva, Undria pinnatifida, and Eisenia bicyclis, and the main food chain for abalone can be considered to be [seawater][brown algae]-[abalone (muscle or shell)]. Abalone are commonly raised as a mariculture food crop in the AmatsuKominato area, and both natural and cultivated ecosystems were studied to allow comparison of lead pollution levels in the two environments. Lead concentrations in seawater of natural and cultivated environments were determined. Natural-environment seawater was analyzed after several collections under ordinary calm conditions (HIRAO et al., 1986). The seawater from the cultivation pool is supplied through a water pipe constructed of lead many decades earlier, possibly

3188

Y. Hirao et al.

explaining at least part ofthe high seawater lead concentration listed in Table 3. Lead concentrations in the algae Ecklonia cava and Eisenia bicyclis in the natural environment, and the algae Eisenia bicyclis serving as abalone feed in the cultivation pool, were determined. The data are shown in Table 3. Lead in abalone was determined in muscle and shell for both environments and the data are tabulated in Table 3. The lead values are normalized to calcium and presented in the atomic ratio form in Fig. 5 for the abalone food chain. This figure shows that, at the first stage of the abalone food chain (from seawater to algae), lead is concentrated relative to calcium by factors of 200 and 1100 for natural and cultivated conditions, respectively. At the next step, from algae to shell, lead decreases by factors of 2.1 X IO-’ and 3.7 X 10e3. From algae to muscle for the cultivated environment, lead decreases by a factor of 0.57, but at the same transition in the natural condition it appears to increase slightly. The cultivated abalone clearly ingested only the fed algae, and these algae were analyzed for lead. Although the brown algae is proposed as the main food for the natural abalone, several other algae, plus organic films attached to rocks, and mosses may also be ingested, and lead values for abalone muscle in the natural environment suggest that the abalone eats rather “dirty” food compared to a hypothetical exclusive diet of the algae Ecklonia cava and Eisenia bicyclis. The cultivatedlnatural ratios of Pb/Ca ratios of seawater, muscle, and shell are 2.9, 4.3, and 3.2, respectively, in contrast to 18 for algae. It may be reasonable to take a factor of 3, as observed for Pb/ Cac,~~~~ cu,t,vated)lPblC~a,gae in natura~), as a representative value relating total lead contents for total ingested foods of the abalone in the two environments. This value is reasonable judging by the values for this factor that apply to the other trophic steps of the ecosystem. Following that assumption, the estimated Pb/Ca ratio in natural abalone food will be 1.4 X 10m5. This is the meaning of the hatched area in Fig. 5. If this is the effective Pb/Ca ratio in algae for natural abalone, the discrimination factor from algae to muscle is 0.4, and lead is in fact decreased from algae to muscle, by biopurification. BURNETT and PATTERSON (1980b) measured components of the food chain of abalone of different species in California, USA. They postulated lead concentrations in clean and polluted seawater of 25 and 50 ng Pb/kg, respectively, equivalent to 1.2 X lo-* and 2.4 X lo-* for Pb/Ca on an atomic ratio basis. Using the same molar ratio they got 3.3 X 10m6and 14 X 1Om6in algae, 18 X 10m6and 18 X 10m6 in abalone muscle, and 3.7 X lo-* and 4.1 X 10-s in abalone shell, respectively. The study by BURNETT and PATTERSON (1980b)

also faced the difficulty that the algae (considered by them as the sole abalone food) appears to be have a lower (Canormalized) lead value than the abalone muscle. It is probable that, in their study as well as the present one, the difficulty that muscle contains higher lead than algae may be explained by ingestion of other, higher-Pb food than the algae considered. The different lead levels in the seawater of the natural and cultivated environments are reflected in both abalone muscle and shell. This fact may be interpreted as strong support for the possibility of detection and evaluation of the lead pollution

levels in other districts, by analysis of shell and muscle, if species identity and similar growth rates can be established. CONCLUSION

Lead concentrations in muscle and in new-growth shell material of abalone decrease as the animals become older, indicating an increased ability by slower-growing mature individuals to discriminate against toxic lead during absorption processes. The effect is consistent despite interspecies variation in absolute concentrations in a given environment. Tissues of abalone raised for food in an artificial mariculture environment reflect the higher lead concentrations of the higherPb seawater introduced into the growth area, compared to natural specimens in a lower-Pb seawater environment adjacent to open ocean. Heavy metal concentrations in the clearly identifiable single-year growth bands of abalone shell materials may provide accurate time records of degree of pollution in growth environments. Acknowledgmenls-The authors wish to express their thanks to Dr. Todd K. Hinkley of the U. S. Geological Survey in Denver, who assisted in preparation of the paper and gave us constructive opinions throughout the submission. Edirorial handling: T. M. Church

REFERENCES BOWENH. J. M. (1978)Environmental Chemistry of the Elements, pp. 13-29. Academic Press. BRYANG. W. and HUMMERSTONE L. G. (1973) Brown seaweed as an indicator of heavy metals in estuaries in south-west England. J. Mar. Biol. Assn. U.K. 53, 705-720. BURNETTM. (1978) The occurrence and distribution of Ca, Sr, Ba and Pb in marine ecosystems. Ph.D. thesis, Caltech. BURNETTM. and PATTERSONC. C. (1980a) Analysis of natural and industrial lead in marine ecosystems. In Lead in the Marine Environment (ed. M. BRANICAand Z. KONRAD),pp. 15-30. Petgamon Press. BURNETTM. and PATTERSONC. C. (1980b) Perturbation of natural lead transport in nutrient calcium pathways of marine ecosystems by industrial lead. In Isotope Marine Chemistry (ed. E. D. GOLDBERG, et al.), pp. 4 13-438. Uchida-Rokkakudo. DODD J. R. (1965) Environmental control of strontium and magnesium in Mytilus. Geochim. Cosmochim. Acta 29, 385-398. DODD J. R. (I 967) Magnesium and strontium in calcareous skeletons; A review. J. Paleontology 41, 1313-1329. ELIASR. W., HIRAOY., and PATTERSONC. C. (1982) The circumvention of calcium along nutrient pathways by atmospheric inputs of industrial lead. Geochim. Cosmochim. Acta 46,256 l-2580. HIRAO Y., FUKUMOTOK., SUGISAKIH., and KIMURA K. (1979) Determination of lead in seawater by furnace atomic absorption spectrometry after concentration with vield tracer. Anal. Chem. g&651-653. HIRAOY., KOSHIKAWAM., SUGISAKIH., FUKUMOTOK., KIMURA K., and MATSUMOTOE. (1983)Lead, courier. and cadmium concentrations in the seawater of Tokyo Bay..Chrkyukagaku 17,4247 (in Japanese). HIRAOY., YAMAKAWAH., MAEDAM., MATSUMOTOA., NARAS., HANAMIH., KOMODAY., and KIMURA K. (1986) Distribution of lead in some algae. Chikyukaguku 20, 29-38 (in Japanese). IN0 T. (1952) Biological studies on the propagation ofJapanese abalone (genus Huliofis). Tokai Regional Fisheries Research Laboratory (in Japanese).

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