The Science of the Total Environment, 97/98 (1990) 673-684 Elsevier Science Publishers B.V., Amsterdam

673

ARSENIC IN BENTHIC BIVALVES OF SAN FRANCISCO BAY AND THE SACRAMENTO/SAN JOAQUIN RIVER DELTA

CAROLYN JOHNS* and SAMUEL N. LUOMA

U.S. Geological Survey, Mail Stop 465, 345 Middlefield Road, Menlo Park, CA 94025 (U.S.A.)

ABSTRACT

Arsenic concentrations were determined in fine-grained, oxidized, surface sediments and in two benthic bivalves, Corbicula sp. and Macoma balthica, within San Francisco Bay, the Sacramento/ San Joaquin River Delta, and selected rivers not influenced by urban or industrial activity. Arsenic concentrations in all samples were characteristic of values reported for uncontaminated estuaries. Small temporal fluctuations and low arsenic concentrations in bivalves and sediments suggest that most inputs of arsenic are likely to be minor and arsenic contamination is not widespread in the Bay.

INTRODUCTION

The aqua t i c chemis t ry , geochemis t ry , and b i o a c c u m u l a t i o n of an th ropogen- ical ly mobi l ized a r sen ic have been the focus of m u c h r e s e a r c h because of the es tab l i shed tox ic i ty of this e l emen t (Ferguson and Gavis , 1972; Crecel ius , 1975; Crece l ius et al., 1975; Pen rose et al., 1975; Andreae , 1978; Fowler and Unlu, 1978; W a s l e n c h u k and Windom, 1978; Un lu and Fowler , 1979; W r e n c h et al., 1979; Klumpp, 1980; Langs ton , 1980, 1983, 1984; Sanders and Windom, 1980; Phi l l ips and Depledge, 1985, 1986). This pape r repor t s the spa t ia l d i s t r ibu t ion of a r sen ic in two species of ben th ic b iva lves and in fine, oxidized sur face sed iments of San F ranc i sco Bay. The ma jo r goal was to de te rmine if a r sen ic c o n t a m i n a t i o n is common in b iva lves and sediments in the es tuary , wi th a p a r t i c u l a r focus on the n o r t h e r n reach, which shows reg iona l e n r i c h m e n t wi th se len ium ( Johns et al., 1988). S t rong seasona l v a r i a t i o n s of r ive r ine t r ace e lement inpu ts and sed iment cha rac t e r i s t i c s con t r ibu te to f luc tua t ions in levels of b io log ica l ly ava i l ab l e t r ace e lements wi th in the San F ranc i sco Bay e s t u a r y (Luoma and Phil l ips, 1988). These f luc tua t ions can cause t r ace e lement c o n c e n t r a t i o n s wi th in ben th ic b iva lves to f luc tua te as well (Luoma et al., 1985; L u o m a and Phil l ips, 1988). In order to s e p a r a t e possible n a t u r a l f luc tua t ions f rom a n t h r o p o g e n i c a l l y caused e n r i c h m e n t of a rsenic in b iva lves and

*Present address: Environmental Studies Program, St. Lawrence University, Canton, NY 13617, U.S.A.

0048-9697/90/$03.50 © 1990 Elsevier Science Publishers B.V.

674

sediments, temporal variability in tissue and sediment concentrations of arsenic was also considered.

San Francisco Bay is a large, urbanized estuary which has been extensively altered by human activity (Nichols et al., 1986). The sediments and biota reflect trace element inputs from both local and regional sources (Luoma and Cain, 1979; Luoma and Cloern, 1982; Thomson et al., 1984; Johns et al., 1988; Luoma and Phillips, 1988; Luoma et al., 1990). However, data are limited for the concentrations of arsenic in sediments and bivalves. Previous studies in San Francisco Bay focused on effects of dredging a naval shipyard (Anderlini et al., 1975) and determining concentrations in sediments and several bivalve species in the more saline portions of the Bay, prior to recent increased urbanization and industrial activity (Risebrough et al., 1977). No studies have examined arsenic concentrations in bivalves or sediments in the northern reach of the estuary.

Arsenic may enter the estuary in the effluents of a number of municipal and industrial discharges (Luoma and Cloern, 1982; Moore and Ramamoorthy, 1984). Another potential source of arsenic to the estuary is the San Joaquin River. In the western San Joaquin Valley, natural weathering of soils derived from arsenic-rich marine shales has been accelerated by irrigation and artificial drainage of saline soils. Some of the agricultural drainage water enters the San Joaquin River and may reach the head of the estuary.

METHODS AND MATERIALS

Sampling design

Arsenic concentrations were determined in two species of benthic bivalves, Corbicula sp. and Macoma balthica, and in fine-grained, oxidized, surface sediments. Arsenic concentrations in bivalves and sediments from the agricul- tural region of the lower San Joaquin River and Delta (C7, Cll ; Fig. 1) were compared with arsenic concentrations at stations in the northern reach of San Francisco Bay, a heavily urbanized and industrialized area (C1-C7, C8). Stations C1-C7 were sampled repeatedly from September 1984 through September 1986 to examine temporal variability.

Several more stations were sampled once each, concurrently with C7. Arsenic concentrations in the sediments and bivalves at C7 were compared with areas known to receive agricultural drainage return water from saline soils (C12), and with two stations which did not receive significant runoff from saline soils, C9 on the Sacramento River and C10 on the Tuolumne River (Fig. 1). Station Cll , also in the lower San Joaquin region, was sampled once to compare the representativeness of Station C7 in this hydrologically complex area.

A small sampling effort examined potential enrichment of arsenic in sediments and bivalves (Macoma balthica) in the more saline portions of San Francisco Bay. Samples were collected twice a t one location in North Bay

~',~ Big

.4

Ocean ~ ,

San Francisco

/

! (drquine: Strait .

01 \ - ' ~ C2 C3 C4 Delta

C5

Vernal!s !

West San Joaquin O 20 40 km

River (

Cl l

C10

C12

675

Fig. 1. Locat ions of sampl ing s ta t ions and designated geographical areas. 'M' indicates s ta t ions where M a c o m a b a l t h i c a was sampled; 'C' indicates s ta t ions where C o r b i c u l a sp. was sampled.

676

(M1), o n c e a t o n e l o c a t i o n in C e n t r a l B a y (M2), a n d t w i c e a t one s t a t i o n in S o u t h S a n F r a n c i s c o B a y (M3). F r o m F e b r u a r y 1986 t h r o u g h M a y 1987, m o n t h l y s a m p l e s w e r e c o l l e c t e d a t a f i f th S o u t h B a y l o c a t i o n (M4) w h i c h h a s s h o w n c o n t a m i n a t i o n o f s e d i m e n t s a n d b i v a l v e s w i t h s e v e r a l m e t a l s ( L u o m a a n d C a i n , 1979; T h o m s o n e t al . , 1984; F ig . 1). A r s e n i c c o n c e n t r a t i o n s in Macoma a t t h e s e s t a t i o n s w e r e c o m p a r e d w i t h o n e c o l l e c t i o n f rom t h e e s t u a r y a t B ig R i v e r on t h e N o r t h e r n C a l i f o r n i a C o a s t (M5, F ig . 1). B ig R i v e r h a s no k n o w n a n t h r o p o g e n i c s o u r c e o f a r s e n i c .

Sample collection, preparation, and analysis

B i v a l v e s w e r e s a m p l e d , d e p u r a t e d , d i v i d e d i n t o s ize c l a s ses , h o m o g e n i z e d , l y o p h i l i z e d , a n d p r e p a r e d for a r s e n i c a n a l y s i s by a d r y a s h m e t h o d as p r e v i o u s l y d e s c r i b e d ( J o h n s et al . , 1988). T h e 4 M HC1 s o l u t i o n s o f s a m p l e s w e r e t r e a t e d w i t h a n e x c e s s o f p o t a s s i u m i o d i d e to e n s u r e r e d u c t i o n of a l l a r s e n a t e to a r s e n i t e p r i o r to a n a l y s i s by h y d r i d e g e n e r a t i o n a t o m i c a b s o r p t i o n s p e c t r o - s copy , e m p l o y i n g 3% NaBH4 (in 1% N a O H ) as t h e r e d u c t a n t .

R e a g e n t b l a n k s a n d s t a n d a r d r e f e r e n c e m a t e r i a l s (NBS S R M 1566 O y s t e r T i s sue , R M 50 A l b a c o r e T i s sue , a n d S R M 1572 C i t r u s L e a v e s ) w e r e a n a l y z e d a t r e g u l a r i n t e r v a l s . R e c o v e r i e s o f a r s e n i c f rom t h e b i o l o g i c a l r e f e r e n c e m a t e r i a l s a r e r e p o r t e d in T a b l e 1.

S e d i m e n t s a m p l e s w e r e c o l l e c t e d a n d p r e p a r e d for a r s e n i c a n a l y s i s by t h e s a m e m e t h o d s as p r e v i o u s l y d e s c r i b e d for s e l e n i u m ( J o h n s et a l . , 1988). R e c o v e r i e s o f a r s e n i c f rom s e d i m e n t r e f e r e n c e m a t e r i a l s a r e r e p o r t e d in T a b l e 1. A l i q u o t s o f w e t - s i e v e d s e d i m e n t s w e r e e x t r a c t e d w i t h 0.5 M HC1 as d e s c r i b e d by L a n g s t o n (1980).

TABLE 1

Recoveries of total arsenic from standard reference materials

Material Certified value a Recovered value

Oyster Tissue (NBS SRM 1566) 13.4 + 1.9 Albacore Tuna (NBS RM 50) 3.3 + 0.4 c Citrus Leaves (NBS SRM 1572) 3.1 + 0.3 Estuarine Sediment (NBS SRM 1646) 11.6 ÷ 1.3 River Sediment (NBS SRM 1645) 66 d Urban Particulate (NBS SRM 1648) 115 + 10 USGS Standard MAG-1 (Marine Mud) 10.0

13.0 (n = 13; SD = 0.90) b 3.1 (n - 24; SD - 0.20) 3.3 (n - 6; SD = 0.10)

10.4 (n = 6; SD = 0.4) 68.7 (n = 6; SD = 2.1) 122 (n = 2; SD = 2.1) 9.3 (n - 3; SD = 0.6)

a Concentrations in micrograms arsenic per gram, dry weight. b n = number of separate samples processed; SD is the standard deviation of the mean. ¢ Not certified. Value given as the probable mean. a Only reported values (not certified) are obtainable.

677

RESULTS

Arsenic concentrations in Corbicula

Mean arsenic concentrations in Corbicula ranged from 5.4 to 11.5#g g 1 among all stations. Temporal variability in mean arsenic concentrations was slight at most stations and showed no consistent seasonal trends (Fig. 2, Station C5).

Arsenic concentrations in animals from the San Joaquin River were signifi- cantly (P ~ 0.05) lower than in animals from the Sacramento and Tuolumne (Fig. 3). Grand mean arsenic concentrations were not significantly different (P > 0.05) at C7 and Cll , in the lower San Joaquin River (Fig. 3). Arsenic concentrations at C7 and Cl l were also similar to those at C12 on the mid-San Joaquin River, which receives agricultural return water.

The strategy of repeatedly sampling Stations C1-C7 allowed sensitive resolution of spatial distributions of arsenic. The grand mean concentrations in Corbicula (aggregated data, all collections) were significantly (P ~< 0.05) higher from stations in the estuary (C1-C6, C8) than in the lower San Joaquin River (C7, Fig. 3); but concentrations in clams from the estuary were not different than in clams from the Sacramento and Tuolumne Rivers. Some significant, but small, differences in mean arsenic concentrations in tissues occurred among Stations C1-C6 as well (P ~< 0.05; Fig. 3). However, there was no discernible spatial trend in arsenic concentrations among these stations.

Animal size showed no consistent influence on arsenic concentrations in tissues of Corbicula. Significant (P ~< 0.05) positive relationships between shell length and tissue concentration of arsenic occurred in 39% of the collections.

1984 J 1985 1986 I

20 J I

] 10.1 11 --

sis ~s I s , 6

9 11 1 3 5 7 9 11 1 3 5 7 9

M o n t h of Co l lec t ion

Fig. 2. Mean arsenic concentrations in Corbicula from Station C5 as observed from September 1984 through September 1986. Vertical bars represent 95% confidence intervals for the means. The mean arsenic concentration (#g g-1 dry weight) is listed above each bar. The number of composited samples analyzed is designated at the bottom of the figure. Values for means and confidence limits have been back-transformed from log10.

678

15

ab t abc O~ bc [ 1 0 2 bcd 10.7 abc

to - +,.of o i,.6od . ~1o. , . . -1

67 64 71 62 77 75 84 20 5 11 13 13 J

I 1 I I [ [ I i [ I I I ~ 1 2 3 4 5 6 7 8 9 10 11 12

Corbicuta S t a t i o n

Fig. 3. Grand mean arsenic concentrations in Corbieula sp. from northern San Francisco Bay and the lower San Joaquin River (C1-C8) collected between September 1984 and September 1986, compared with mean concentrations in animals collected in November 1985 from the Sacramento River (C9), and in September 1986 from the Tuolumne (C10), the lower San Joaquin at Mossdale (Cll), and the middle San Joaquin River (C12). Vertical bars represent 95% confidence intervals for the means. The number of composited samples analyzed for each mean is shown above the station designation. Bars are labelled by the same letter when means are not significantly different (P > 0.05; analysis of variance and T-K method for testing differences among means; Sokal and Rohlf, 1981). Two sets of ANOVA and range tests were performed; one compared grand means at C1-C8 and the other compared means for C7 and C~C12. Tests are differentiated by locating one set of letters above and the other below the 95% confidence limits (respectively).

S lopes of t hese r e g r e s s i o n s a n d t he p o r t i o n of t he v a r i a n c e in a r s e n i c con-

c e n t r a t i o n s a c c o u n t e d for by a n i m a l size v a r i e d m a r k e d l y a m o n g s a m p l i n g da t e s a t e ach s t a t i o n . Size i n f l u e n c e did n o t a p p e a r to b i a s c o m p a r i s o n s a m o n g s t a t ions . M e a n shel l l e n g t h s of Corbicula f rom S t a t i o n s C7, C l l , a n d C12 were s i m i l a r to e a c h o t h e r a n d s i g n i f i c a n t l y (P ~< 0.05) g r e a t e r t h a n the o t h e r Corbicula s t a t i o n s ( J o h n s et al., 1988). Howeve r , l owes t m e a n a r s e n i c con- c e n t r a t i o n s were f o u n d a t C7 a n d C l l . H i g h e s t m e a n a r s e n i c c o n c e n t r a t i o n s were f o u n d in a n i m a l s f rom C1-C6 a n d C8, e v e n t h o u g h m e a n she l l l e n g t h s

were s m a l l e r a t t hese s t a t i ons .

Arsenic concentrations in M a c o m a

No s i g n i f i c a n t , pos i t i ve r e l a t i o n s h i p s b e t w e e n size of Macoma a n d a r s e n i c c o n c e n t r a t i o n were obse rved w i t h i n i n d i v i d u a l c o l l e c t i o n s a t M4. Howeve r , i n a l i n e a r r e g r e s s i o n of a l l a r s e n i c c o n c e n t r a t i o n s on she l l l e n g t h s a t M4, a n i m a l size a c c o u n t e d for a sma l l p o r t i o n of t he v a r i a b i l i t y i n t i s sue a r s e n i c c o n c e n t r a - t i o n (P < 0.05; coeff ic ient of d e t e r m i n a t i o n = 0.124). S i g n i f i c a n t , pos i t i ve l i n e a r r e l a t i o n s h i p s b e t w e e n she l l l e n g t h a n d t i s s u e a r s e n i c c o n c e n t r a t i o n

o c c u r r e d o n l y tw ice a m o n g 23 c o l l e c t i o n s a t five Macoma s t a t i o n s (M5, r = 0.661, P ~< 0.05; M3, r = 0.863, P ~< 0.01).

679

I I i i I i i I i 1 1 i i I i i i i i i l l

14

~ - " 10.

,~ 8 9.4 1 4 " " 1 • | . .8 .

7 t 6 - - 7.0

4 - - S.S

7.0

I I I H I I i , , I I , , t I [ t I I , , I 9 " 2 3 4 I / 5 / I 6 7 8 9 I0 II 12 I 2 3 4 " 5

1985 1986 1987 M o n t h of C o l l e c t i o n

Fig. 4. M e a n a r sen ic c o n c e n t r a t i o n s in Macoma balthica from s ta t ions in San F ranc i sco Bay a t sampl ing dates be tween Sep tember 1985 and May 1987:M1 ( e ); M2 (o); M3 (a); M4 (o), and Big River: M5 (@). Ver t i ca l bars r ep re sen t 95% confidence in te rva l s for the means . M e a n a r sen ic c o n c e n t r a t i o n (pg g ~) is l is ted b e n e a t h each bar. The n u m b e r of composi ted samples analyzed is des igna ted a t the bo t tom of the figure.

- !

8 l

12

:=,10

w a

- - ab 12.1

-- t 1°2 ab 10.,

9.0 e

-- t7.6

M1 M2 M3 M4 M5

Macoma S t a t i o n

Fig. 5. G r a n d mean a r sen ic c o n c e n t r a t i o n s in Macoma balthica from s t a t ions in San Franc i sco Bay (M1-M4) and Big River (M5). The n u m b e r of composi ted samples analyzed for each m e a n is shown above the s t a t i on des ignat ion . Ver t ica l bars r ep re sen t 95% confidence in te rva l s for the means. Bars are label led wi th the same le t te r when means are no t s igni f icant ly different (P > 0.05; ana lys i s of v a r i a n c e and T-K method for t e s t ing differences among means; Sokal and Rohlf, 1981).

680

M e a n a rsen ic c o n c e n t r a t i o n s in Macoma balthica at M4 ranged f rom 5.8 to 11.7 pg g 1 wi th a g rand m e a n of 9.0 pg g 1 among the 17 col lect ions. M e a n a rsen ic levels in the M4 b iva lves f luc tua ted a m o n g col lect ions , bu t did not show cons i s t en t s easona l i ty (Fig. 4). The g rand m e a n a rsen ic c o n c e n t r a t i o n (7.6 gg g 1) was lowest a t M2 (P ~< 0.05; Fig. 5). This s t a t ion is loca ted in the well-flushed cen t ra l por t ion of the e s tua ry and an ima l s a t this s t a t ion p robab ly r ep re sen t a r ecen t r eco lon iza t ion of the si te (Luoma, unpub l i shed data) . Otherwise , g rand m e a n arsenic c o n c e n t r a t i o n s in Macoma were s imi la r a m o n g mos t s t a t ions in Cen t ra l and South San F ranc i sco Bay and did not differ f rom the m e a n a rsen ic c o n c e n t r a t i o n at M5, where no a n t h r o p o g e n i c sources of a r sen ic inpu t a re known.

Arsenic concentrations in fine sediments

Tota l a r sen ic c o n c e n t r a t i o n s of all fine sed iment samples r anged f rom 6 to 16 #g g 1 and typ ica l ly a v e r a g e d 10-12 #g g-1 a t mos t s t a t ions (Fig. 6). Con- cen t r a t i ons in the lower San Joaqu in , the S a c r a m e n t o and the T u o l u m n e were s l ight ly lower t h a n in the es tuary , a l t h o u g h the s t a t ions were s imi la r in anc i l l a ry cha rac t e r i s t i c s of the sed iments (% carbon, to ta l i ron, to ta l manganese , fine par t i c les abundance ; L u o m a et al., 1990). Grand m e a n HC1- e x t r a c t a b l e a r sen ic c o n c e n t r a t i o n s r anged be tween 2.0 and 4.0 #g g 1 and differed less a m o n g s t a t ions t h a n did to ta l concen t ra t ions . Sl ight a r sen ic e n r i c h m e n t was ev ident in N o r t h Bay compared wi th Sou th Bay sediments . The

18

16

14

12

8

- - 13.4

_ 12.3 11,9 11.9 /

11.8 - - 0

10.2

- - 6 8.3 12 8~)5

-

14 7~

o 2., 11 14

4

I 1 I I I I I I I 1 I C1 C2 C3 C4 C5 C6 C7 C8 cg C10 C12

Station

? _ 12

6.0 605 0

0O 2.5

1.8 • 16 ~ -

I I I l I M1 M2 M3 M4 M5

Fig. 6. Mean total arsenic (O) and mean extractable (0.5 N HC1) arsenic ($) in fine ( < 100 ttm) oxidized surface sediments from stations in San Francisco Bay (M1-M4, C1-C6, C8), Big River (M5), the lower San Joaquin (C7), Sacramento (C9), Tuolumne (C10), and middle San Joaquin Rivers (C12). Vertical bars represent 95% confidence intervals for the means. The number of samples analyzed is given below each bar or circle.

681

mean concentration of arsenic for all sediments from North Bay (C1-C8; 3.5 + 0.17 pg g 1) was higher than the mean concentration from all South Bay sediments (M1-M4; 2.2 + 0.38, mean + one standard error). Differences in sediment arsenic concentrations between C7 and C1-C6 were similar to dif- ferences in arsenic concentration in Corbicula at these stations.

Neither HCl-extractable arsenic nor total arsenic in sediments correlated significantly with arsenic in Corbicula or Macoma. The range of values was small and variances were similar in sediments and animals. The ratio of HC1- extractable arsenic to HCl-extractable iron has proved a useful predictor of arsenic availability to the bivalve Scrobicularia plana (Langston, 1980). Ratios calculated for Stations C1 C8 were very low (0.40~).65) compared with those observed by Langston (1980), reflecting both low concentrations of total arsenic in the sediments and low concentrations of potentially biologically available arsenic.

DISCUSSION

Arsenic concentrations in whole soft tissues of both Corbicula and Macoma, and in fine sediments, appeared comparable to concentrations in bivalves and sediments from uncontaminated estuaries. Scrobicularia plana from United Kingdom estuaries not influenced by metalliferous mining wastes contained from 13 to 24 pg g 1 arsenic in whole soft tissues (Langston, 1980). Similar concentrations of arsenic, 6.~16.6 ttg g 1, were found in Macoma balthica in uncontaminated estuaries (Bryan et al., 1985; Langston, 1985). In contaminated estuaries, arsenic concentrations as high as 65.5 pg g-1 were observed in Macoma balthica (Langston, 1986).

Langston (1980) reported near-total arsenic concentrations ranging from 2 to 16 gg g- 1, similar to observations in this study, in sediments of uncontami- nated estuaries in the United Kingdom. Offshore sediments from Lake Michigan contained from 5.2 to 9.2 #g g 1 arsenic (Christensen and Chien, 1979). Similarly, total arsenic concentrations in sediments of 10 Saskatchewan lakes ranged from 2.7 to 13.2 #g g- ' (Huang and Liaw, 1978).

Studies conducted more than 10 years ago in San Francisco Bay also show arsenic concentrations similar to those found here. Macoma balthica near naval shipyards in North Bay contained arsenic concentrations ranging from 8.9 to 16.3 ~g g-l, with most values between 10 and 13 #g g-1 (Anderlini et al., 1975). Mytilus edulis in central and southern San Francisco Bay contained from 5 to 12 ttg g 1 arsenic in whole soft tissues (Anderlini et al., 1975; Risebrough et al., 1977). Sediment samples from several South San Francisco Bay sites contained 5-7.9 #g g-1 arsenic (Risebrough et al., 1977). Arsenic concentrations in sediments collected near naval shipyards were typically 10-14 #g g-l, but reached 26 pg g-1 (Anderlini et al., 1975; Risebrough et al., 1977). Total arsenic at C7 was similar to concentrations reported more recently for fine ( < 63 pm) bed sediments of the San Joaquin River (median value, 9.8 gg g 1; Clifton and Gilliom, 1989). These data suggest, unlike other trace elements

682

(Luoma and Phillips, 1988), large inputs of biologically available arsenic do not appear to be common within San Francisco Bay. Slight arsenic enrichment was indicated in both sediments and animals in Suisun Bay (Fig. 1). This enrichment appears to be local in origin. Low arsenic concentrat ions at stations on the San Joaquin (C12), Sacramento (C9), and Tuolumne (C10) Rivers also suggest a lack of significant arsenic inputs from agricultural re turn water and small r iverine inputs of bioavailable arsenic in general.

Temporal fluctuations in arsenic of Corbicula and Macoma were small, but showed some similarities to biologically-driven fluctuations of other metals (Cain and Luoma, 1986; Luoma et al., 1990). Animals size explained only a small portion of variance in arsenic concentrat ions in Macoma, probably reflecting a lack of significant levels of bioavailable arsenic at the Macoma stations. In the nor thern reach of the estuary where tissue arsenic concentrat ions in Corbicula suggest slight arsenic enrichment, animal size may have more importance, as reflected in the increased occurrence, although variable in magnitude, of positive relationships between Corbicula animal size and arsenic concentrat ion in tissues.

A second possibility for the small temporal fluctuations relates to seasonal reproductive cycles. In Scrobicularia, arsenic was rapidly incorporated into gonadal tissues and shed during spawning, al though in Mytilis gonadal de- velopment diluted total arsenic concentrat ions (Langston, 1984). Arsenic content of gonadal tissue as a percentage of total body arsenic in Scrobicularia ranged from 6.4 to 20.5% over a season. If fluctuations of the same magnitude occur in Macoma or Corbicula, this might contribute to the fluctuations of tissue arsenic concentrat ion observed in these species.

SUMMARY

Arsenic concentrat ions in Corbicula and Macoma balthica in San Francisco Bay and the Sacramento/San Joaquin Delta are generally consistent with concentrat ions found in uncontaminated systems, despite the occurrence of arsenic-rich marine shales in the watershed. Lower arsenic concentrat ions occur in both Corbicula and fine sediments in the lower San Joaquin River stations than in the urbanized Suisun Bay/Delta. However, the generally low arsenic concentrat ions in bivalves and fine sediment indicate that local and regional inputs of arsenic are minor at the head of this estuary and do not measurably influence the distribution of arsenic in bivalves or fine sediments throughout the Bay and delta.

REFERENCES

Anderlini, V.C., J.W. Chapman, D.C. Girvin, S.J. McCormick, A.S. Newton and R.W. Risebrough, 1975. Heavy metal uptake study. Appendix H. Pollutant uptake. Dredge Disposal Study, San Francisco Bay and Estuary, submitted to U.S. Army Corps of Engineers, October, 1975.

Andreae, M.O., 1978. Distribution and speciation of arsenic in natural water and some marine algae. Deep-Sea Res., 25: 391~402.

683

Bryan, G.W., W.J. Langston, L.G. Hummerstone and G.R. Burt, 1985. A guide to the assessment of heavy metal contaminat ion in estuaries using biological indicators. Occas. Publ. 4, Mar. Biol. Assoc. U.K., Plymouth, Uni ted Kingdom, 92 pp.

Cain, D.J. and S.N. Luoma, 1986. Effect of seasonally changing tissue weight on trace metal concentrat ions in the bivalve Macoma balthica in San Francisco Bay. Mar. Ecol. Prog. Ser., 28: 209-217.

Christensen, E.R. and N.K. Chien, 1979. Arsenic, mercury, and other elements in dated Green Bay sediments. In: Proc. Int. Conf. Heavy Metals in the Environment, London. CEP Consultants Ltd, Edinburgh, pp. 373 376.

Clifton, D.G. and R.J. Gilliom, 1989. Trace elements in bed sediments of the San Joaquin River and its t r ibutary streams, California. U.S. Geological Survey, Water Research Investigations Rep. 88-4169.

Crecelius, E.A., 1975. The geochemical cycle of arsenic in Lake Washington and its relat ion to other elements. Limnol. Oceanogr., 20: 441451.

Crecelius, E.A., M.H. Bothner and R. Carpenter, 1975. Geochemistries of arsenic, antimony, mercury and related elements in sediments of Puget Sound. Environ. Sci. Technol., 9: 325-333.

Ferguson, J.F. and J. Gavis, 1972. A review of the arsenic cycle in na tura l waters. Water Res., 6: 1259-1274.

Fowler, S.W. and M.Y. Unlu, 1978. Factors affecting bioaccumulat ion and el imination of arsenic in the shrimp Lysomata seticaudata. Chemosphere, 7: 711-720.

Huang, P.M. and W.K. Liaw, 1978. Distr ibut ion and fract ionat ion of arsenic in selected fresh water lake sediments. Int. Rev. Gesamten. Hydrobiol., 63: 533-543.

Johns, C., S.N. Luoma and V. Elrod, 1988. Selenium accumulat ion in benthic bivalves and fine sediments of San Francisco Bay, the S a c r a m e n t ~ S a n Joaquin Delta, and selected tributaries. Estuar ine Coastal Shelf Sci., 27:381 396.

Klumpp, D.W., 1980. Accumulat ion of arsenic from water and food by Littorina littoralis and Nucella lapillus. Mar. Biol., 58:265 274.

Langston, W.J., 1980. Arsenic in U.K. estuarine sediments and its availabil i ty to benthic organisms. J. Mar. Biol. Assoc. U.K., 60: 869-881.

Langston, W.J., 1983. The behaviour of arsenic in selected United Kingdom estuaries. Can. J. Fish. Aquat. Sci., 40(Suppl. 2): 143-150.

Langston, W.J., 1984. Availabil i ty of arsenic to estuarine and marine organisms: a field and laboratory evaluation. Mar. Biol., 80: 143-154.

Langston, W.J., 1985. Assessment of the distr ibution and availabil i ty of arsenic and mercury in estuaries. In: J.G. Wilson and W. Holcoow (Eds), Estuar ine Management and Quality Assessment. Plenum Press, New York, pp. 131-146.

Langston, W.J., 1986. Metals in sediments and benthic organisms in the Mersey estuary. Estuar ine Coastal Shelf Sci., 23: 239-261.

Luoma, S.N. and D.J. Cain, 1979. Fluctuat ions of copper, zinc, and silver in tellenid clams as related to freshwater discharge~South San Francisco Bay. In. T.J. Conomos (Ed.), San Francisco Bay: The Urbanized Estuary. Pacific Division, AAAS, San Francisco, pp. 231 246.

Luoma, S.N. and J.E. Cloern, 1982. The impacts of waste-water discharge on biological com- munities in San Francisco Bay. In: H.J. Kockelman, T.J. Conomos and A.E. Leviton (Eds), San Francisco Bay, Use and Protection. Pacific Division, AAAS, San Francisco, pp. 137 160.

Luoma, S.N. and D.J.H. Phillips, 1988. Distribution, variabili ty, and impacts of trace elements in San Francisco Bay. Mar. Pollut. Bull., 19: 413-425.

Luoma, S.N., D. Cain and C. Johansson, 1985. Temporal fluctuations of silver, copper, and zinc in the bivalve Macoma balthica at five s tat ions in South San Francisco Bay. Hydrobiologia, 129: 109-120.

Luoma, S.N., R. Dagovitz and E. Axtmann, 1990. Temporally intensive study of trace metals in sediments and bivalves from a large r iver-es tuar ine system: Suisun Bay/Delta in San Francisco Bay. Sci. Total Environ., 97/98: 68~712.

Moore, J.W. and S. Ramamoorthy, 1984. Heavy Metals in Natual Waters - - Applied Monitor ing and Impact Assessment. Springer-Verlag, New York, 268 pp.

684

Nichols, F.H., J.E. Cloern, S.N. Luoma and D.H. Peterson, 1986. The modification of an estuary. Science, 231: 567-573.

Penrose, W.R., R. Black and M.J. Hayward, 1975. Limited arsenic dispersion in seawater, sediments, and biota near a continuous source. J. Fish. Res. Board Can., 32: 1275-1281.

Phillips, D.J.H. and M.H. Depledge, 1985. Metabolic pathways involving arsenic in marine organisms: a unifying hypothesis. Mar. Environ. Res., 17: 1-12.

Phillips, D.J.H. and M.H. Depledge, 1986. Distr ibution of inorganic and total arsenic in tissues of the marine gastropod Hemifusus ternatanus. Mar. Ecol. Prog. Ser. 34: 261-266.

Risebrough, R.W., J.W. Chapman, R.K. Okazaki and T.T. Schmidt, 1977. Toxicants in San Francisco Bay and Estuary. Report to The Association of Bay Area Governments, Berkeley, California.

Sanders, J.G. and H.L. Windom, 1980. The uptake and reduction of arsenic species by marine algae. Estuar ine Coastal Shelf Sci., 10: 555-567.

Sokal, R.R. and F.J. Rohlf, 1981. Biometry. W.H. Freeman and Co., New York, 2rid edn, 859 pp. Thomson, E.A., S.N. Luoma, C.E. Johansson and D.J. Cain, 1984. Comparison of sediments and

organisms in identifying sources of biologically available trace metal contamination. Water Res., 18: 755-765.

Unlu, M.Y. and S.W. Fowler, 1979. Factors affecting the flux of arsenic through the mussel Mytilis galloprovincialis. Mar. Biol., 51: 209-219.

Waslenchuk, D.G. and H.L. Windom, 1978. Factors controll ing the estuarine chemistry of arsenic. Estuarine Coastal Mar. Sci., 7: 455-464.

Wrench, J.J., S.W. Fowler and M.Y. Unlu, 1979. Arsenic metabolism in a marine food chain. Mar. Pollut. Bull., 10: 18-20.