1

Contaminant concentrations in sport fish

from San Francisco Bay, 1997

A manuscript submitted to Marine Pollution Bulletin

by

Jay A. Davis *1, Michael D. May 1, Ben K. Greenfield 1,

Russell Fairey 2, Cassandra Roberts 2, Gary Ichikawa 3,

Matt S. Stoelting 4, Jonathan S. Becker 4, Ronald S. Tjeerdema 5

1. San Francisco Estuary Institute, Oakland, CA

2. Moss Landing Marine Laboratories, Moss Landing, CA

3. California Department of Fish and Game, Moss Landing, CA

4. Institute of Marine Sciences, University of California, Santa Cruz, CA

5. Department of Environmental Toxicology, University of California, Davis, CA

* Address for correspondence:

Jay Davis

San Francisco Estuary Institute7770 Pardee LaneOakland, CA 94621(510) 746-7368 phone(510) 746-7300 faxEmail: jay@sfei.org

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Abstract

In 1997, seven sport fish species were sampled from seven popular fishing areas in San

Francisco Bay. Mercury exceeded a human health screening value in 44 of 84 (52%)

samples. All collected samples of leopard shark and striped bass exceeded the mercury

screening value of 0.23 µg/g wet weight. PCBs exceeded the screening value in 51 of 72

(71%) samples. DDT, chlordane, and dieldrin had lower numbers of samples above screening

values: 16 of 72 (22%) for DDT, 11 of 72 (15%) for chlordanes, and 27 of 72 (37%) for dieldrin.

Concentrations of PCBs and other trace organics were highest in white croaker and shiner

surfperch, the two species with the highest fat content in their muscle tissue. Fish from one

location, Oakland Harbor, had significantly elevated wet weight concentrations of mercury,

PCBs, DDTs, and chlordanes compared to other locations. Removal of skin from white

croaker fillets reduced lipid concentrations by 27 to 49% and concentrations of trace organics

by 33 to 40%.

Keywords: fish tissue; mercury; PCBs; DDT; chlordane; dieldrin; estuaries; San Francisco

Bay

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Introduction

San Francisco Bay is a productive ecosystem with a densely populated periphery, and

supports a considerable amount of sport fishing. In 1994, Fairey et al. (1997) performed a

pilot study to measure concentrations of contaminants in muscle tissues of sport fish caught

in San Francisco Bay. The study indicated that there were six chemicals or chemical groups

that were of potential human health concern for people consuming Bay-caught fish: mercury,

PCBs, DDT, chlordane, dieldrin, and dioxins.

As a result of this pilot study, the California Office of Environmental Health Hazard

Assessment (OEHHA) issued an interim health advisory for people consuming fish from San

Francisco Bay (OEHHA, 1997, 1999). The interim advisory, which is still in place, states

that: 1) adults should limit consumption of Bay sport fish to, at most, two meals per month;

2) adults should not eat any striped bass over 35 in (89 cm); and 3) pregnant women or

women that may become pregnant or are breast-feeding, and children under 6 should not eat

more than one meal per month, and should not eat any meals of shark over 24 in (61 cm) or

striped bass over 27 in (69 cm). The advice was issued due to concern over human exposure

to residues of methylmercury, PCBs, dioxins, and organochlorine pesticides in Bay-caught

fish.In 1997, the San Francisco Estuary Regional Monitoring Program for Trace Substances

(RMP), which conducts long term monitoring of contaminants in the Estuary (SFEI, 2000),

incorporated a fish tissue monitoring element. The results of the first year of RMP fish

tissue monitoring are presented here. The objectives of this monitoring are: 1) to produce

information needed by regulatory agencies for updating human health advisories and

conducting human health risk assessments; and 2) to measure contaminant levels in fish

species over time to track trends and to evaluate the effectiveness of management efforts.

This monitoring is scheduled to be repeated once every three years. OEHHA is using the

presented in this article to meet the first objective. With data from only two rounds of

sampling it is premature to begin evaluating data to meet the second objective; this

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evaluation will only become meaningful after additional sampling rounds are conducted in

years to come.

The fish monitoring program targeted seven species that are frequently caught and

eaten by Bay fishers at seven popular fishing areas. Also included in the 1997 sampling

design was a study to determine the difference in contaminant concentrations of fillets of

white croaker with and without skin. This study was designed to determine whether

removing the skin from muscle fillets could significantly reduce exposure to organic

contaminants. White croaker were selected because they exhibited the highest

concentrations of trace organics in the 1994 study (Fairey et al., 1997).

In this paper, we summarize and interpret monitoring data from 1997 for the five

contaminants or contaminant classes and seven fish species examined. This paper also

evaluates: 1) the influence of length on mercury concentrations and lipid content on organic

contaminant concentrations; 2) the specific sites in San Francisco Bay where significantly

higher contaminant concentrations in muscle tissues were identified; 3) the fish species

exhibiting high between-site variability in contamination, which would be useful species for

future monitoring of spatial differences; and 4) the effect of skin removal on white croaker

tissue organic contaminant concentrations.

Methods

The species and fishing locations in the Bay were selected for sampling based on

available information on frequencies of catch and consumption by Bay fishers (Wade van

Buskirk, Pacific States Marine Fisheries Commission, personal communication), continuity

with the 1994 pilot study (Fairey et al., 1997), and to provide a broad geographic coverage of

the Bay. The species sampled included jacksmelt (Atherinopsis californiensis), shiner

surfperch (Cymatogaster aggregata), white croaker (Genyonemus lineatus), striped bass

(Morone saxatilis), California halibut (Paralichthys californicus), leopard shark (Triakis

semifasciata), and white sturgeon (Acipenser transmontanus). The seven sampling locations

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are distributed throughout the Bay (Figure 1). For each species, the distribution and number

of samples captured was influenced by natural distribution patterns and capture success in

the field (Table 1). Target size classes were based on legal limits (CDFG, 1997), guidance

presented in U.S. EPA (1995a), and growth curves where available. All fish collected were of

legal size (Table 1).

All species of fish were collected between May 27, 1997 and July 25, 1997. In addition,

sturgeon were captured in March and October of 1997. Collection gear included nylon stretch

mesh otter trawls, trammel nets, gill nets, and hook and line. Total length of each fish was

measured in the field to the nearest 1 cm. Heads and tails from the striped bass, leopard

sharks, and sturgeon were removed in the field. The intact body cavity was then wrapped in

Teflon before freezing. Fish were wrapped in chemically cleaned Teflon sheeting (cleaned

with detergent, acid, and petroleum ether) and frozen on dry ice for transportation to the

laboratory. Prior to dissection, all fish that were frozen whole (croaker, surfperch, and

jacksmelt) were remeasured to the nearest 0.5 cm and weighed to the nearest 0.1 gram. The

ranges of lengths of fish included in composites for each species are listed in Table 1.

Fish samples were dissected and composited in the same manner as in the pilot study

(SFRWQCB et al., 1995; Fairey et al., 1997). Dissection and compositing were performed

using non-contaminating techniques in a clean room environment. Fillets of muscle tissue

were removed in 5 to 10 g portions with Teflon forceps and stainless steel cutting utensils.

Equal weight fillets were taken from each fish to composite a total of at least 175 g. The

number of fish per composite varied by species and ranged between 1 and 20 (Table 1). All

samples were homogenized using a Brinkman Polytron. Aliquots were taken for each

analysis after homogenization.

In order to best represent human exposure, skin was removed from composites for those

species that typically have skin removed in food preparation (Table 1). Although the

of white croaker samples were analyzed with skin on, four white croaker muscle composites

were analyzed with skin removed in order to evaluate reductions in trace organic

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concentrations associated with skin removal. White croaker were selected for this evaluation

because they are a popular sport fish and they exhibited the highest organochlorine

concentrations in the 1994 sampling.

Samples were analyzed for mercury, PCBs, and organochlorine pesticides. The number of

composites analyzed varied by species and ranged between 4 and 15 (Table 2). Mercury was

analyzed in 18 individuals and 5 composites of striped bass. Limited analyses of mercury in

individual striped bass could be accommodated in the budget and were obtained because of

the well-established relationship of mercury concentrations with age and size. Analytical

methods were described in SFRWQCB et al. (1995) and Fairey et al. (1997). Briefly, aliquots

analyzed for PCBs and organochlorine pesticides were extracted with methylene chloride

and extracts cleaned and fractionated using silica/alumina and HPLC. Extracts were then

analyzed by dual column (DB-5 and DB-17) gas chromatography with electron capture

detection. Aliquots for mercury analysis were digested using nitric:perchloric acid and

analyzed by cold vapor flameless atomic absorption spectrometry. QA measures included

analysis of standard reference materials, lab duplicates, and matrix spikes. All data met the

data quality objectives specified in the RMP Quality Assurance Project Plan (QAPP) (Lowe et

al., 1999). For mercury, SRM (NIST oyster tissue 1566a) recoveries averaged 100.5%, and all

were within the 25% criterion established in the QAPP. For each individual PCB congener,

all SRM (Carp-1 from the National Research Council of Canada) analyses were within

acceptable range (±35%) of the certified concentrations. Similarly, for the organochlorine

pesticides all SRM (NIST mussel 1974a) analyses were within acceptable range (±35%) of the

certified concentrations.

PCBs were measured on a congener-specific basis. However, screening values for PCBs

are expressed as Aroclor equivalents. The method of Newman et al. (1998) was employed to

convert the congener data to Aroclor equivalent data. This method is based on comparing

ratios of 14 congeners in samples with their ratios in the commercial mixtures Aroclor 1248,

1254, and 1260. The concentrations of Aroclors 1248, 1254, and 1260 were estimated in this

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manner. As described by Newman et al. (1998), Aroclor estimates for biotic samples obtained

using the Newman method are rendered imprecise by the "weathering" (selective

degradation and metabolism of congeners) that occurs in the environment and in organisms,

making the fingerprint of biotic samples diverge from the fingerprints of Aroclors. The PCB

fingerprints observed in our fish samples did not exhibit significant weathering of the

patterns. Even in cases where weathering is observed, the Newman method is an

improvement over traditional methods of Aroclor determination because it minimizes

numerical biases introduced by overlapping Aroclor profiles while providing the advantage of

allowing quantification of the error in the calculation (Newman et al., 1998).

We define "sum of Aroclors" as the sum of Aroclors 1248, 1254, and 1260. The method

detection limit (MDL) for the congeners was 0.25 ng/g wet weight. This MDL was a

conservative estimate that encompassed the true MDLs for all congeners. Method detection

limits expressed on an Aroclor basis (calculated from the congener data) were 13 ng/g wet for

Aroclor 1254 and 1260 and 25 ng/g wet for Aroclor 1248. Unless otherwise indicated, PCB

data presented in this report are expressed as sum of Aroclors.

Screening values were calculated following U.S. EPA (1995a) guidance, as detailed in

SFRWQCB et al. (1995) and Fairey et al. (1997). U.S. EPA (1995a) defines screening values as

concentrations of target analytes in fish or shellfish tissue that are of potential public health

concern. Exceedance of screening values is an indication that more intensive site-specific

monitoring and/or evaluation of human health risk should be conducted. A consumption rate of

30 g fish/day (SFRWQCB et al., 1995) that applies to recreational fishers was used in

calculating screening values.

Within a given species, the older, and therefore larger, fish tend to accumulate higher

mercury concentrations (Huckabee et al., 1979). Since fish in this study were not aged,

was used as a correlate of age. To increase statistical power, length and mercury data were

pooled from this study and the samples collected in 1994 (SFRWQCB et al., 1995; Fairey et

al., 1997). The 1994 and 1997 datasets were generated by the same lab using the same

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methods. The effect of length or lipid concentration on contaminant levels was examined

using linear regression. Only samples with contaminant levels above the detection limit

used for these regression analyses. Statistical analyses were performed using SAS (SAS

Institute, 1990). Statistical significance for all tests was evaluated using = 0.05.

Comparison of differences in wet weight concentrations among locations provides an

indication of possible variation in human exposure to contaminants from consumption of fish

from different locations in the Bay. In order to have confidence that apparent differences

among locations accurately reflect conditions in the Bay, it is necessary to have consistent

results from replicate samples. Replicate sampling, with at least three composites consisting

of fish of uniform size, was performed at multiple locations for three species: jacksmelt,

shiner surfperch, and white croaker (Table 1). Comparisons among locations were made

using ANOVA and the Tukey-Kramer multiple comparison procedure. In these analyses,

samples with concentrations below detection limits were set to zero. Median concentrations

are presented with summary statistics (Table 2) as an unbiased indicator of central

tendency. Mean concentrations were used for spatial comparisons to allow calculation of

standard errors and to correspond with the use of parametric ANOVA.

The effect on trace organic concentrations of removing the skin from white croaker fillets

was examined using four pairs of composite samples. Each composite consisted of five

individual fish. Fillets without skin were taken from the other side of the same fish as fillets

with skin. Skin-on and skin-off samples were compared for percent lipid, dieldrin,

chlordanes, DDTs, and PCBs.

The complete dataset generated is provided in SFEI (1999).

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Results and Discussion

Mercury

Median mercury concentrations were highest in leopard shark, moderately high in

striped bass, and lowest in shiner surfperch and jacksmelt (Table 2). Mercury was measured

in a total of 84 samples, and 44 (52%) had concentrations higher than the screening value of

0.23 µg/g wet. Species with the highest median concentrations (leopard shark and striped

bass) always exceeded the screening value, while species with the lowest median

concentrations (shiner surfperch and jacksmelt) rarely or never exceeded the screening value

(Table 3).

Significant correlations of mercury with length were observed for jacksmelt (R2 = 0.46, p

= 0.016), leopard shark (R2 = 0.80, p < 0.0001), and white croaker (R2 = 0.80, p < 0.0001;

Figure 2). For halibut, the positive correlation between mercury and length was not

statistically significant (R2 = 0.20, p = 0.233; Figure 2). Composite samples of striped bass

did not show a significant correlation with length (R2 = 0.22, p = 0.094, Figure 2). Mercury

was not correlated with length in shiner surfperch (R2 = 0.007, p = 0.66; Figure 2) and

sturgeon were not examined because insufficient data were available (N = 4).

The lack of correlation between length and mercury concentration for shiner surfperch

may result from the fact that shiner surfperch are relatively small and generally live only 2 -

3 years (Anderson & Bryan, 1970; Odenweller, 1975). For this short-lived species, increased

length may indicate faster growth rate rather than increased age, causing growth dilution

and lower tissue concentrations (de Freitas et al., 1974; Huckabee et al., 1979). Additionally,

because shiner surfperch consume predominantly small epibenthic invertebrates throughout

their life history (Odenweller, 1975; Barry et al., 1996; K. Hieb, California Department of

Fish and Game, unpublished data), they probably do not increase in trophic position with

increasing size, weakening the correlation between size and bioaccumulation (Snodgrass et

al., 2000).

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The relationship between length and mercury was examined in more detail in striped

bass by measuring mercury concentrations in individual fish from two locations, Davis Point

(n = 10) and South Bay (n = 8). These data appear to support a hypothesis that two

subpopulations of striped bass were present in the Bay, one with a steeper slope for the

mercury:length regression line than the other (Figure 3). Collection location did not affect

which group a fish was in (Figure 3). In the Hudson River, analysis of PCBs in striped bass

muscle, combined with elemental analysis of otoliths, has identified migratory and non-

migratory subpopulations of striped bass with different PCB accumulation patterns

(Zlokovitz & Secor, 1999). Using tag-recapture methods, Calhoun (1952) demonstrated that

adult striped bass in Suisun Bay of the San Francisco Estuary exhibit both upstream and

downstream seasonal migration. Mercury concentrations in individual striped bass in the

50–60 cm size range were found to vary considerably, from 0.347 µg/g to 0.895 µg/g. The

wide range in mercury accumulation among similar sized striped bass and apparent bimodal

distribution might be explained by the presence of both migratory and non-migratory striped

bass in the Bay. Further sampling of individual striped bass would be needed to establish

whether subpopulations with different mercury accumulation patterns are indeed present in

the Bay.

Of the seven species evaluated in this study, leopard sharks exhibited the highest

median tissue mercury concentrations (Table 2). Previous studies have frequently found

elevated mercury levels in sharks, attributable to their slow growth, large size, and high

trophic position (Walker, 1976; Lyle, 1986; Walker, 1988; Huetter et al., 1995). Indeed,

leopard shark in this study were among the largest species sampled (Table 1) and of a size

corresponding to 11 years of age, according to the Von Bertalanffy growth function for this

species (Kusher et al., 1992). Additionally, their diet does include predatory crabs (e.g.,

Cancer spp.) and fish (Talent, 1976; Webber & Cech, 1998), providing some potential for high

trophic transfer.It is surprising that white sturgeon had much lower median mercury concentrations

leopard shark (Table 2). The sturgeon we sampled were larger and probably older than the

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leopard shark; the study mean sturgeon length (132 cm) corresponds to approximately 15

years of age (DeVore et al., 1995), whereas the mean leopard shark length (97 cm)

corresponds to 11 years of age (Kusher et al., 1992). Furthermore, their food consumption

patterns are thought to be similar, as both species consume predominantly benthic

invertebrates and augment these with fish. Although sturgeon appear to consume

predominantly bivalves (McKechnie & Fenner, 1971) and leopard sharks more frequently eat

decapod crustaceans and Urechis worms (Talent, 1976; Webber & Cech, 1998), mercury

concentrations among these different prey are similar in this region (G. Ichikawa, Moss

Landing Marine Lab, unpublished data). Future studies could evaluate the specific life

history or physiological differences that cause mercury in leopard shark to be four times as

high as in white sturgeon.

Wet weight mercury concentrations were elevated at the Oakland Harbor location in

shiner surfperch and jacksmelt (Table 4). In shiner surfperch, the samples from Oakland

Harbor were significantly higher than those from South Bay, Berkeley, and San Pablo Bay.

Jacksmelt at Oakland Harbor were significantly higher in mercury than jacksmelt from

Berkeley and were also higher than San Pablo Bay and the S.F. Waterfront, though these

latter differences were not statistically significant. Recent sampling also found high

concentrations of mercury in sediments of the Oakland Harbor area (Hunt et al., 1998; Daum

et al., 2000). It should be noted that only one sample of shiner surfperch and jacksmelt was

above the screening value of 0.23 µg/g wet.

Polychlorinated Biphenyls (PCBs)

Median sum of Aroclor concentrations were highest in white croaker and shiner

surfperch, and were substantially lower in the other species sampled, with the lowest

concentrations measured in California halibut and leopard shark (Table 2). For sum of

Aroclors, 51 of the 72 (71%) measured samples had concentrations higher than the screening

value of 23 ng/g wet weight (Table 3). All of the white croaker and shiner surfperch samples

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exceeded the screening value. Most of the jacksmelt (83%), striped bass (64%), and sturgeon

(75%) samples exceeded the screening value. Halibut (13%) and leopard shark (13%) had the

lowest incidence of concentrations above the screening value (Table 3).

Sum of Aroclor concentrations in the seven species sampled were significantly correlated

(R2 = 0.57, p < 0.0001) with lipid content (Figure 4a). The correlation with lipid was even

stronger (R2 = 0.69, p < 0.0001) for PCBs expressed as the sum of congeners. The fish species

with the highest lipid content in their muscle tissue had the highest PCB concentrations.

Some of the points that deviate from the regression line (Figure 4a) indicate other factors

controlling PCB concentrations. The plot indicates that the points for jacksmelt generally

have negative residuals (i.e., they fall below the regression line in Figure 4a). One possible

explanation for the relatively low concentrations of PCBs in jacksmelt is their different

trophic position. Jacksmelt feed at a lower trophic level and on pelagic prey, primarily

eating crustaceans, zooplankton, and algae (Boothe, 1967; Barry et al., 1996), while the other

species generally consume benthic prey at higher trophic levels. Persistent organochlorines

are known to accumulate to higher concentrations at higher trophic levels (Suedel et al.,

1994).

Jacksmelt, shiner surfperch, and white croaker had elevated PCB concentrations at the

Oakland Harbor location (Table 4). For jacksmelt and shiner surfperch, concentrations were

several-fold greater and significantly higher than at other sampling locations (Table 4).

PCBs in white croaker were significantly higher at Oakland than at Berkeley and San Pablo

Bay. None of the other sampling locations were significantly different from each other.

Overall, results from jacksmelt and shiner surfperch indicate distinctly elevated

concentrations of PCBs in the food web in Oakland Harbor relative to the other locations

sampled. These findings are consistent with observations of high concentrations of PCBs in

sediment in this area (Hunt et al., 1998; Daum et al., 2000). These findings suggest that

jacksmelt and shiner surfperch are capable of having sufficient site fidelity to exhibit

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significant spatial variation. PCB concentrations at the remaining locations were relatively

uniform.

In the skin removal comparison, for all four pairs of samples, lower concentrations of

sum of Aroclors were measured in the fillets with the skin removed (Table 5). These

reductions were associated with decreased amounts of lipid in the fillets without skin. Lipid

content was reduced by a mean of 33% in the fillets without skin (Table 5). Skin removal did

not reduce sum of Aroclor concentrations in these white croaker samples below the screening

value.

DDTs

Sum of DDT (sum of p,p’-DDT, o,p’-DDT, p,p’-DDE, o,p’-DDE, p,p’-DDD, and o,p’-DDD)

concentrations were highest in white croaker and shiner surfperch, intermediate in

jacksmelt and low in the larger species (striped bass, leopard shark, halibut, and sturgeon)

(Table 2). Sum of DDTs was above the screening value of 69 ng/g wet in 16 of 72 (22%)

samples (Table 3). All of the samples above the screening value were either white croaker or

shiner surfperch.

Sum of DDT concentrations in the seven species sampled were highly correlated (R2 =

0.85, p < 0.0001) with lipid content (Figure 4b). As observed for the other trace organics, the

fish species with the highest lipid content in their muscle tissue had the highest DDT

concentrations. The correlation of DDT with lipid was the strongest observed for all the trace

organics analyzed.

Wet weight DDT concentrations in shiner surfperch at Oakland Harbor were

significantly higher than at three of the other four locations where shiner surfperch were

collected (S.F. Waterfront, South Bay, and San Pablo Bay; Table 4). None of the other

sampling locations were significantly different from each other. Average DDT concentrations

in white croaker and jacksmelt from Oakland Harbor were also higher than at the other

locations, but the differences were not statistically significant (Table 4).

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Overall, results from shiner surfperch indicate elevated concentrations of DDTs in the

food web in Oakland Harbor relative to the other locations sampled. The relative degree of

contamination, with concentrations at Oakland Harbor up to two times as high as other Bay

locations, however, is lower than that observed for the PCBs. Excluding Oakland Harbor,

DDT concentrations at the other locations sampled were relatively uniform.

Skin removal from white croaker tissue samples caused an average 40% reduction in

concentration of DDTs (Table 5). The reductions were associated with decreased amounts of

lipid in the fillets without skin. Skin removal reduced the concentrations for samples from

S.F. Waterfront, Berkeley, and San Pablo Bay to below the screening value of 69 ng/g wet.

Chlordanes

Median concentrations of sum of chlordanes (sum of cis-chlordane, trans-chlordane, cis-

nonachlor, trans-nonachlor, and oxychlordane) concentrations were highest in white croaker,

intermediate in shiner surfperch, and lower in other species (Table 2). Sum of chlordanes

was above the screening value of 18 ng/g wet in 11 of 72 (15%) samples (Table 3). All of the

samples above the screening value were white croaker or shiner surfperch.

Sum of chlordane concentrations in the seven species sampled were significantly

correlated (R2 = 0.60, p < 0.0001) with lipid content (Figure 4c). As observed for the other

trace organics, the fish species with the highest lipid content in their muscle tissue had the

highest chlordane concentrations.

As with other contaminants, distinct spatial variation was observed for chlordane. The

strongest spatial variation was found for shiner surfperch, which had significantly higher

concentrations at Oakland Harbor than at the other four locations where shiner surfperch

were collected (Table 4). Excluding Oakland Harbor, none of the shiner surfperch samples

from other sampling locations were significantly different from each other. The average

concentration in jacksmelt from Oakland Harbor was also significantly higher than the

concentrations measured at all other locations (Table 4). For white croaker, Oakland Harbor

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was significantly higher than Berkeley and San Pablo Bay, but the magnitude of the

difference was not as great as observed for shiner surfperch and jacksmelt.

Overall, results from jacksmelt and shiner surfperch indicated elevated concentrations of

chlordanes in the food web in Oakland Harbor relative to the other locations sampled. The

degree of contamination was similar to that observed for the PCBs. Excluding Oakland

Harbor, chlordane concentrations at the other locations sampled were relatively uniform.

When skin was removed from white croaker tissue samples, the mean chlordane

concentration was reduced by 33% (Table 5). Skin removal reduced the concentrations for

samples from S.F. Waterfront and San Pablo Bay to below the screening value of 18 ng/g

wet.

Dieldrin

Dieldrin median concentrations were highest in white croaker, intermediate in

shiner surfperch, and 1.0 ng/g or less for all other species (Table 2). Dieldrin was above the

screening value of 1.5 ng/g wet in 27 of 72 (37%) samples (Table 3). The majority of these

were white croaker (100%) and shiner surfperch (60%). Dieldrin concentrations in the seven

species sampled were significantly correlated (R2 = 0.64, p < 0.0001) with lipid content

(Figure 4d). As observed for the other trace organics, the fish species with the highest lipid

content in their muscle tissue had the highest dieldrin concentrations. Unlike the other

contaminants discussed, distinct spatial variation was not observed for dieldrin. Average

dieldrin concentrations for jacksmelt, shiner surfperch, and white croaker were all highest at

Oakland Harbor, but Oakland was not significantly higher than any other location (Table 4).

The lack of significant spatial variation for dieldrin may be partially due to relatively low

measurement precision. For dieldrin, the concentrations measured (median = 1.2 ng/g) are

not much higher than the detection limit (0.25 ng/g). Overall, the data suggest that dieldrin

concentrations are slightly elevated at Oakland Harbor.

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When skin was removed from white croaker tissue samples, mean concentrations of

dieldrin were reduced by 34% (Table 5). Skin removal did not result in these white croaker

samples being below the screening value for dieldrin.

General Discussion

Comparisons to Screening Values

As found in the 1994 pilot study (SFRWQCB et al., 1995; Fairey et al., 1997), persistent

toxic chemicals in Bay fish were found at concentrations of potential human health concern

in 1997 RMP sampling. For all contaminants measured, at least some samples exceeded

screening values, with greater than 50% exceedance for mercury and PCBs. Mercury

exceeded a human health screening value in 44 of 84 (52%) Bay samples. All collected

samples of leopard shark and striped bass exceeded the mercury screening value. PCBs

exceeded the screening value in 51 of 72 (71%) Bay samples. All of the white croaker and

shiner surfperch samples exceeded the screening value for PCBs. Dieldrin, DDT, and

chlordane had lower numbers of Bay samples above screening values: 27 of 72 (37%) for

dieldrin, 16 of 72 (22%) for DDTs, and 11 of 72 (15%) for chlordanes.

Spatial Patterns

Significant variation in contaminant concentrations among locations was observed in the

three species (white croaker, shiner surfperch, and jacksmelt) employed to evaluate spatial

patterns. Spatial variation in wet weight concentrations was observed, indicating potential

spatial variation in human exposure to contaminants of concern. Oakland Harbor had

significantly elevated wet weight concentrations of mercury (in shiner surfperch and

jacksmelt), PCBs (shiner surfperch, white croaker, and jacksmelt), DDTs (shiner surfperch),

and chlordanes (shiner surfperch, white croaker, and jacksmelt). The observation of similar

spatial patterns in multiple species support the conclusion that the Oakland Harbor location

17

exhibits elevated concentrations of multiple contaminants. These findings are consistent

observations of high concentrations of mercury, PCBs, and organochlorine pesticides in

sediment at this location (Hunt et al., 1998; Daum et al., 2000). Overall, the results suggest

that shiner surfperch and jacksmelt are potentially useful indicators of spatial variation in

contamination in the Bay.

Of all species examined, shiner surfperch most often demonstrated significant spatial

differences. This species exhibits several life history attributes that appear to make it a

more sensitive indicator of spatial heterogeneity in contamination. First, shiner surfperch

are relatively small and short-lived (Anderson & Bryan, 1970; Odenweller, 1975), and may

be less likely to exhibit variability in contaminant concentrations due to differences in

growth rate and age (Huckabee et al., 1979). This can be observed in the absence of a

relationship between length and Hg concentration (Figure 2c). Additionally, because of its

small size, the shiner surfperch is likely to have a limited home-range. For example, Minns

(1995) demonstrated a highly significant positive relationship between body size and home-

range for 29 freshwater fish species. Another possible reason that shiner surfperch are

sensitive indicators of spatial heterogeneity in contamination is their preference for

consuming epibenthic invertebrates (Boothe, 1967; Barry et al., 1996), which ties them

closely to site-specific sediment contamination. A study of DDT in shiner surfperch at

Richmond Harbor in San Francisco Bay also found significant variation over a small spatial

scale, providing another example of the potential for spatial variability in this species

(Young et al., 2000).Jacksmelt also exhibited significant spatial pattern in mercury concentrations. This may

also result from a relatively small size and associated reduction in growth rate variability

and home range (Huckabee et al., 1979; Minns, 1995). However, jacksmelt forage

predominantly on pelagic zooplankton (Boothe, 1967; Barry et al., 1996), reducing the

potential impact of heterogeneity in benthic contamination. White croaker consume Crangon

sp. (bay shrimp) upon reaching larger sizes (K. Hieb, California Department of Fish and

Game, unpublished data) and may therefore display less site sensitivity due to the high

18

mobility of this prey taxon. White croaker themselves may also be more mobile than shiner

surfperch and jacksmelt.

Factors Influencing Contaminant Concentrations

Fish length and lipid content were identified as important factors influencing

accumulation of persistent contaminants. For most species, increasing length was

significantly correlated with increasing mercury concentrations, a pattern exhibited in many

previous studies (Huckabee et al., 1979; Wiener & Spry, 1996). Interspecific variation in

lipid content was significantly correlated with organic contaminant concentrations, a result

of the high lipid affinity of these compounds. Consistent with other studies (Stow et al.,

1997), intraspecific variation in organic contaminants was not clearly correlated with lipid.

Intraspecific correlations of organic contaminants with length, as observed by Stow et al.

(1997), were also inconclusive. Trophic position is probably also an important factor

accounting for some of the variation in these results, but the trophic positions of the species

sampled in the Bay are not well characterized. Understanding and accounting for the

influence of trophic position variation on contaminant levels will be essential to future

evaluation of spatial and temporal trends in contaminant concentrations.

The Effect of Skin Removal

Previous research has shown that removal of fatty tissue in fish preparation can reduce

organic contaminant concentration. However, the effectiveness of these preparation

techniques varies depending on the distribution of lipid for a given species (Reinert et al.,

1972). In our study, substantially lower concentrations of trace organics were measured in

white croaker fillets with the skin removed. These reductions often brought concentrations

below screening values. Therefore, removal of skin can result in meaningful reductions in

contaminant exposure for humans consuming white croaker captured in the Bay.

19

Acknowledgments

Members of the RMP Fish Contamination Committee provided guidance in all phases of

this monitoring. We particularly thank Karen Taberski (Committee Chair), who has been

instrumental in establishing and sustaining fish contamination monitoring in San Francisco

Bay. Other Committee members included Jon Amdur, Ray Arnold, Audrey Chiang, Bob

Fujimura, Margy Gassel, Jordan Gold, Erika Hoffman, Azibuike Lawson, Diana Lee, Brian

Sak, Alyce Ujihara, Dan Watson, Kristine Wong, and Steven Zeiger. We thank Stewart

Lamerdin, Ross Clark, James Downing, and Michele Jacobi for their field efforts, and the

Marine Science Institute in Redwood City for field support in the South Bay. John Newman

provided valuable advice on generating and interpreting the organochlorine data. We also

thank Adrienne Yang, Nicole David, and Patricia Chambers for help formatting the paper

and graphics and Jung Yoon and Samir Arora for data management. Kathy Hieb and the

Interagency Ecological Program provided unpublished data on foraging habits of bay fish

species. Gabriele Marek assisted with contract management. This is RMP Contribution #45.

20

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25

Table Captions:

Table 1. Sampled fish attributes and locations. Numbers in the location cells indicate

number of composite samples collected. When two numbers are present in a cell, the second

number indicates individual fish that were analyzed at that site for Hg.

Table 2. Summary statistics by species for mercury and organochlorines. Data are medians,

wet weight (ND = Not detected). For organics, ‘Σ’ indicates ‘sum of.’

Table 3. Summary of concentrations above screening values for each species. Numerator

indicates the number above the screening value, denominator indicates the number of

samples analyzed. All measurements are wet weight and ‘Σ’ indicates ‘sum of.’

Table 4. Contaminant concentrations (wet weight) at each sampling location for each

species in 1997. For each listing, mean values are presented, with standard error in

parentheses when more than two samples were collected. For multiple site comparisons for a

given contaminant, B sites are significantly higher than A sites; AB sites are not

significantly different from any other sites (ANOVA; Tukey-Kramer Multiple Comparison

Procedure; p<0.05). Listings with no letter do not have sufficient sample size for statistical

comparison (n < 3).

Table 5. Effect of skin removal on concentrations of lipid, PCBs (Σ Aroclors), DDTs,

chlordanes, and dieldrin in white croaker composites. Skin-on and skin-off composites were

comprised of tissue from the same set of fish. Within each site, a single composite of five fish

was compared. Concentrations in ng/g wet weight.

26

Figure Captions:

Figure 1. Sampling locations for 1997 RMP fish contamination monitoring.

Figure 2. Regressions of mercury concentrations and average fish length in composite

samples for each species. Data from 1994 and 1997.

Figure 3. Relationship between mercury concentrations and fish length in individual striped

bass from 1997. Fish were collected from two locations: Davis Point and South Bay.

Figure 4. Regressions of concentrations of PCBs (as sum of Aroclors), DDTs, chlordanes, and

dieldrin with lipid in all species in composite samples. For all linear regression

p < 0.0001.

Table 1:Number of composites analyzed

Species Number of

fish per

composite

Legal Size

(cm)

Size range collected

(cm)

Tissue

sampled a

SouthBay

BridgesO

aklandH

arborS.F.W

aterfrontBerkeley

SanPablo

Bay

DavisPoint

SuisunBay

Jacksmelt 5 No Limit 20–30 ms - 3 3 3 3 - -

Shiner Surfperch 20 No Limit 10–15 ms 3 3 3 3 3 - -

White Croaker 5 No Limit 20–30 ms - 4 3 4 3 - -

Striped Bass 2-3 > 45 45-82 m 2, 8 - - 2 3 3, 10 1

Leopard Shark 3 > 91 91-135 m 3 - - 2 3b - -

California Halibut 1 > 55 55-92 m 1 - - 4 3 - -

White Sturgeon 2-3 117 – 183 117-149 m 2 - - - 2 - -

a ms = muscle with skin; m = muscle without skin

b one of the samples collected was an individual, rather than a composite

Table 2:

N Length

(cm)

Mercury

(µg/g)

Lipid

(%)

Σ Aroclors

(ng/g)

Σ PCB Congeners

(ng/g)

Σ DDTs

(ng/g)

Σ Chlordanes

(ng/g)

Dieldrin

(ng/g)

Halibut 8 71 0.27 0.34 NDb 14 6.6 1.6 0.2

Jacksmelt 12 26 0.09 1.85 45 37 34 3.4 0.8

Leopard Shark 8 101 0.88 0.24 13 11 5.3 1.1 0.2

Shiner Surfperch 15 12 0.11 2.52 180 130 54 8.8 1.7

Striped Bass 11a 57 0.45 0.82 34 27 16 3.0 0.8

Sturgeon 4 132 0.27 1.30 33 35 17 4.1 1.0

White Croaker 14 25 0.19 7.04 310 240 85 18 4.5

a 18 individual and 5 composite striped bass were analyzed for mercury

b see Methods for Aroclor detection limits

Table 3:

Mercury

(µg/g)

Σ Aroclors

(ng/g)

Σ DDTs

(ng/g)

Σ Chlordanes

(ng/g)

Dieldrin

(ng/g)

Screening value 0.23 23 69 18 1.5

Halibut 5/8 1/8 0/8 0/8 0/8

Jacksmelt 1/12 10/12 0/12 0/12 1/12

Leopard Shark 8/8 1/8 0/8 0/8 0/8

Shiner Surfperch 0/15 15/15 4/15 3/15 9/15

Striped Bass 23/23 7/11 0/11 0/11 2/11

Sturgeon 3/4 3/4 0/4 0/4 1/4

White Croaker 4/14 14/14 12/14 8/14 14/14

All Species 44/84 51/72 16/72 11/72 27/72

Table 4:

Species

Site Jacksmelt Shiner Surfperch White Croaker Striped Bass Leopard Shark Halibut Sturgeon

Mer

cury

(g/

g)

South Bay - 0.106 (0.011) A - 0.456 (0.049) 0.906 (0.074) 0.251 0.299

Oakland 0.173 (0.040) B 0.165 (0.013) B 0.182 (0.013) A - - - -

S. F. Waterfront 0.086 (0.010) AB 0.111 (0.015) AB 0.225 (0.042) A - - - -

Berkeley 0.068 (0.003) A 0.093 (0.010) A 0.207 (0.018) A 0.308 0.879 0.254 (0.036) -

San Pablo Bay 0.094 (0.001) AB 0.106 (0.011) A 0.250 (0.051) A 0.502 0.922 (0.115) 0.356 (0.077) 0.257

Davis Point - - - 0.552 (0.055) - - -

Suisun Bay - - - 0.530 - - -

PCBs

(ng/

g)

South Bay - 190 (47) A - 34 27 (9.7) 59 23

Oakland 230 (50) B 740 (74) B 580 (100) B - - - -

S. F. Waterfront 34 (7.2) A 250 (27) A 350 (58) AB - - - -

Berkeley 25 (3.8) A 150 (13) A 260 (26) A 46 15 7 (3.9) -

San Pablo Bay 59 (9.2) A 100 (15) A 210 (35) A 30 0 (0) 0 (0) 33

Davis Point - - - 16 (16) - - -

Suisun Bay - - - 17 - - -

DD

Ts(n

g/g)

South Bay - 45 (12) A - 14 7.6 (2.1) 14 9.1

Oakland 41 (3.8) A 94 (1.6) B 140 (22) A - - - -

S. F. Waterfront 27 (7.4) A 48 (3.9) A 79 (6.3) A - - - -

Berkeley 34 (3.8) A 59 (7.6) AB 90 (16) A 34 5.4 6.2 (0.5) -

San Pablo Bay 31 (2.9) A 45 (8.8) A 76 (9.5) A 19 4.5 (0.7) 7.7 (1.3) 23

Davis Point - - - 19 (3.9) - - -

Suisun Bay - - - 14 - - -

Chlo

rdan

es(n

g/g)

South Bay - 11 (0.5) A - 2.8 2.5 (0.9) 2.8 2.5

Oakland 8.1 (1.4) B 41 (5.7) B 25 (2.9) B - - - -

S. F. Waterfront 3.5 (0.9) A 9.3 (1.7) A 19 (1.0) AB - - - -

Berkeley 2.3 (0.5) A 5.3 (2.0) A 15 (1.3) A 4.7 0.2 1.4 (0.4) -

San Pablo Bay 3.5 (0.2) A 5.2 (0.8) A 15 (2.1) A 3.4 0.8 (0.3) 1.1 (0.5) 5.9

Davis Point - - - 2.8 (0.6) - - -

Suisun Bay - - - 2.1 - - -

Die

ldri

n(n

g/g)

South Bay - 2.2 (0.3) A - 0.7 0.4 (0.2) 0.0 0.6

Oakland 1.5 (0.5) A 3.4 (0.9) A 5.1 (0.2) A - - - -

S. F. Waterfront 0.7 (0.2) A 1.5 (0.1) A 3.9 (0.4) A - - - -

Berkeley 0.6 (0.1) A 1.5 (0.7) A 4.5 (0.5) A 1.7 0.0 0.3 (0.1) -

San Pablo Bay 0.5 (0.3) A 1.2 (0.3) A 4.0 (0.6) A 1.1 0.3 (0.2) 0.2 (0.2) 1.5

Davis Point - - - 0.6 (0.3) - - -

Suisun Bay - - - 0.6 - - -

Table 5:

Site Treatment Lipid Σ Aroclors Σ DDTs Σ Chlordanes Dieldrin

Skin On 7.5 560 110 21 5.1

Oakland Skin Off 5.5 500 94 19 4.2

% Reduction 27 11 15 10 18

Skin On 7.3 430 87 20 4.3

S.F. Waterfront Skin Off 5.3 240 51 12 2.6

% Reduction 27 44 41 40 40

Skin On 6.4 330 140 15 3.6

Berkeley Skin Off 4.7 160 57 9.4 2

% Reduction 27 52 59 37 44

Skin On 9.3 280 94 18 5.2

San Pablo Bay Skin Off 4.7 150 53 10 3.4

% Reduction 49 46 44 44 35

Mean % Reduction 33 38 40 33 34