HEAVY METALS IN CLAMS AND SEDIMENTS FROM MORRO BAY

Masters Thesis Presented to the faculty of

California Polytechnic State University, San Luis Obispo

In partial fulfillment Of the requirements for the degree of

Masters of Science in Civil and Environmental Engineering

By Jennifer Pehaim

June 2004

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© 2004 Jennifer Pehaim

ALL RIGHTS RESERVED

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APPROVAL PAGE

Title: Heavy Metals in Clams and Sediments from Morro Bay

Author: Jennifer Pehaim

Date Submitted: June 2004

Dr. Yarrow Nelson, Advisor

Dr. Samuel A. Vigil, Committee Member

Dr. Tom Ruehr, Committee Member

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ABSTRACT Heavy Metals in Clams and Sediments from Morro Bay

Morro Bay on the Central Coast of California is an impacted estuary, currently listed by

the State Water Resources Control Board under the Clean Water Act as a 303(d) – Impaired Water Body for metals, pathogens, and sedimentation and siltation (SWRCB 2002 Staff Report). Although the sediment concentrations of some metals are elevated in the Morro Bay estuary, the bioavailability of these metals to aquatic organisms living in the estuary is unknown.

A study of metal contamination of clams and the surrounding sediments collected from the estuary was conducted to evaluate the potential impacts and bioavailability of these metals. An additional purpose of this study was to determine if sediment metal concentrations could be used as a reliable predictor of metal concentrations in clams. From the metal concentrations measured, acceptable consumption levels for five metals (As, Cd, Cr, Pb, and Ni) were calculated from the Food and Drug Administration (USFDA) Guidance Documents for Metals in Shellfish.

The two clam species found in the bay were Macoma secta and Macoma suda. The clams and surrounding sediments were collected in the bay over three days at five different sites and were analyzed for nine different elements (As, Cd, Cr, Cu, Pb, Ni, V, Zn, and Fe) using inductively coupled plasma (ICP) analysis (EPA Method 6010).

Of the metals tested, total chromium and nickel are of greatest concern. Total chromium sediment concentrations (average 62.8 mg/kg) exceeded the NOAA Threshold Effects Level (TEL) of 52.3 mg/kg, and clam concentrations (average 37.0 mg/kg) greatly exceeded the Median International Standards (MIS) of 1.0 mg/kg. No correlation was found between total chromium concentrations in clams and total chromium concentrations in sediments. For some of the sampling sites, the total chromium concentrations were higher in the clams than in the sediments, and at other sites the opposite was true. Nickel sediment (average 79.9 mg/kg) and clam concentrations (average 25.6 mg/kg) exceeded NOAA benchmark values for sediments, but no tissue benchmark value could be found for nickel. Nickel did not bioaccumulate in the clams as evidenced by considerably lower concentrations in the clams compared to the sediments.

Clam tissue concentrations of total arsenic exceeded both the USFWS limit of 0.25 mg/kg and the OEHHA 1.0 mg/kg benchmark. However, measured total arsenic concentrations were very close to the detection limit, therefore arsenic is probably not a concern in Morro Bay. The concentration of zinc in clams was higher than the MIS (70 mg/kg) at the mouth of Chorro Creek site (Site 2). However, sediment and tissue zinc concentrations were below the TEL and MIS values for zinc at all other sites. Higher zinc concentrations were observed in the clam tissues compared to the zinc concentrations in the sediments, indicating zinc might bioaccumulate in these two species of clams.

Tissue metal concentrations for clams collected near the mouth of Chorro Creek (Site 2) were high for cadmium, total chromium, nickel, and zinc. Clam tissue metal concentrations for South Middle Bay (Site 5) appear to be unusually high for total chromium, nickel and vanadium. Sediment and clam metal concentrations were low at all sites for total arsenic, copper, lead, and

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vanadium. Metal concentrations were lower in clams than in sediments at all sites for total arsenic, cadmium, copper, nickel, lead, and vanadium.

Consumption of clams from Morro Bay at normal consumption rates should be safe with regards to total arsenic, cadmium, lead, and nickel concentrations. However, total chromium measured in the clam tissue may not be safe to eat at the USFDA Levels of Concern if clams from Morro Bay are consumed at normal shellfish consumption levels. Consumption of more than 25 g per week of clams in Morro Bay could place a 60 kg person over the USFDA Level of Concern for chromium consumption.

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ACKNOWLEDGMENTS

I would like to express my deepest gratitude to my thesis advisor and professor Dr.

Yarrow Nelson in the Environmental Engineering Department for his expertise and immense

patience with me through the course of this project. His hard work and diligence made this

project possible. A special thanks to Dr. Tom Ruehr in the Soil Science Department for his

insightful discussions and for his different approach to my project. Thank you to my professor

and thesis board advisor, Dr. Sam Vigil, for his work in this project.

A special thanks to the Morro Bay National Estuary Program (NEP) for their generous

mini-grant, which made this project possible.

Thank you to the staff at Department of Fish and Game, Moss Landing, especially Gary

Ichikawa for answering my relentless questions and opening their facilities for my use.

I would also like to express my deepest gratitude to my parents and husband for their

vigilance, guidance, and support. All of you are my rock in the turbulent seas of life and you all

played an important role in my achievements and success in life. Thank you.

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TABLE OF CONTENTS

List of Tables ................................................................................................................................ ix

List of Figures ..................................................................................................................................x

List of Abbreviations ..................................................................................................................... xi

Chapters

Chapter 1. Introduction..............................................................................................................1

Chapter 2. Background..............................................................................................................3

Bioaccumulation Factors .........................................................................................4

Competitive Metal Sorption.....................................................................................4

Colloid Influences on Metal Transport ....................................................................5

Colloid Influences on Bioavailability ......................................................................7

Soil Amendments and Chelating Agents .................................................................8

Chapter 3. Procedures..............................................................................................................10

Sample Collection..................................................................................................12

Sample Preparation ................................................................................................12

Sample Homogenization and Digestion.................................................................13

Sample Analysis.....................................................................................................13

Sample Calculation ................................................................................................14

Quality Assurance..................................................................................................14

Chapter 4. Results....................................................................................................................16

Sampling Site Characteristics and Observed Clam Populations............................16

Metal Concentrations in Clams and Sediments .....................................................17

Spatial Variation of Metal Concentrations in Clam Tissue and Sediments...........24

Human Consumption Levels..................................................................................35

Bioaccumulation Concentration Factor .................................................................39

Chapter 5. Conclusion .............................................................................................................40

Chapter 6. Works Cited ...........................................................................................................43

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APPENDICES

A1 Sample Collection Method

A2 California Department of Fish and Game (CADFG) Sample Collection

and Preparation Procedure

B1 Sample Preparation and Digestion Methods

B2 California Department of Fish and Game (CADFG) Methods

C Results from Creek Environmental Laboratories

D Detailed Description of Sampling Sites

E National Oceanic Atmospheric Administration (NOAA) Screening

Quick Reference Tables (SQuIRT)

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TABLES

Table 1. Sampling Locations by Number ............................................................................10

Table 2. Quality Control Duplication Analysis ...................................................................15

Table 3. Sample Composite Preparation..............................................................................18

Table 4. Clam Tissue Metal Concentrations measured by ICP ...........................................19

Table 5. Sediment Metal Concentrations measured by ICP ................................................20

Table 6. Clam Tissue and Sediment Metal Concentrations Averaged by Site ....................21

Table 7. Summary of Clam Tissue (wet) and Sediment (dry) Metal Concentrations..........23

Table 8. NOAA SQuIRT Marine Sediment Increasing Predicted Toxicity Gradient ........24

Table 9. Recommended Human Consumption Levels.........................................................36

Table 10. Quantity of Clams Safe for Consumption Below USFDA Levels of Concern......37

Table 11. Bioaccumulation Concentration Factors................................................................39

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FIGURES

Figure 1. Map of Moro Bay Sampling Sites .........................................................................11

Figure 2. Metal Concentrations Averaged by Metal Over All Sites .....................................22

Figure 3. Total Arsenic Concentration in Clam Tissues and Sediment ................................25

Figure 4. Cadmium Concentration in Clam Tissues and Sediment ......................................26

Figure 5. Total Chromium Concentration in Clam Tissues and Sediment ...........................28

Figure 6. Copper Concentration in Clam Tissues and Sediments.........................................29

Figure 7. Iron Concentration in Clam Tissues and Sediments ..............................................30

Figure 8. Lead Concentration in Clam Tissues and Sediments.............................................31

Figure 9. Nickel Concentration in Clam Tissues and Sediments ..........................................32

Figure 10. Vanadium Concentration in Clam Tissues and Sediments ....................................33

Figure 11. Zinc Concentration in Clam Tissues and Sediments .............................................34

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LIST OF ABBREVIATIONS

AET Apparent Effects Threshold (NOAA)

DDWQA Decision Document of Water Quality Assessment

CADFG California Department of Fish and Game

ERL Effects Range – Low (NOAA)

ERM Effects Range Median (NOAA)

USFDA Food and Drug Administration

ICP Inductively Coupled Plasma

MIS Median International Standards

MRCA Market Research Corporation of America

MTRL Maximum Tissue Residue Level(s) (State Mussel Watch Program, 2000)

NOAA National Oceanic Atmospheric Administration

OEHHA California Office of Environmental Health Hazard Assessment

PEL Probable Effects Level (NOAA)

RWQCB Regional Water Quality Control Board

SQuIRT Screening Quick Reference Tables

SWRCB State Water Resources Control Board

TEL Threshold Effects Level (NOAA)

USFW U.S. Fish and Wildlife

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CHAPTER 1 INTRODUCTION

Morro Bay on the Central Coast of California is an impacted estuary, currently listed by

the State Water Resources Control Board (SWRCB) under the Clean Water Act as a 303(d) –

Impaired Water Body for metals, pathogens, and sedimentation and siltation (SWRCB 2002

Staff Report). Recent analyses by the Regional Water Quality Control Board (RWQCB) indicate

concentrations of several toxic metals in Morro Bay sediments are considerably higher than the

National Oceanic and Atmospheric Administration (NOAA) Apparent Effects Threshold (AET)

(Duffield, 2001, personal communication). The sediment concentrations of nickel (Ni), total

chromium (Cr) and aluminum (Al) are up to six times higher than the AET values for these

metals.

Although the sediment concentrations are elevated, the bioavailability of these metals to

aquatic organisms living in the estuary is unknown. Since clams are benthic filter feeders, they

are a meaningful indicator of the bioavailability of toxic metal contamination in the estuary

(Luoma et al., 1983). These animals ingest metal-enriched particles directly (Luoma et al.,

1983), thereby giving an indication of the bioaccumulation ability of metals. Therefore, a study

of metal contamination of clams and the surrounding sediments collected from the estuary was

conducted as an appropriate means of evaluating potential impacts of metal loadings from the

watershed plus residual metal contaminants in sediments. An additional purpose of this study

was to determine if sediment metal concentrations could be used as a reliable predictor of metal

concentrations in clams. Clams and surrounding sediments collected in the bay over three days

at five different sites were analyzed for nine different elements (As, Cd, Cr, Cu, Pb, Ni, V, Zn,

and Fe) using Inductively Coupled Plasma (ICP) analysis (EPA Method 6010). The clam and

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sediment results were compared to NOAA metal standards. From the metal concentrations

measured in clams, an acceptable consumption levels for five metals (As, Cd, Cr, Pb, and Ni)

were calculated from the Food and Drug Administration (FDA) Guidance Documents for Metals

in Shellfish.

Oysters were originally considered for this study due to their ease in collection.

However, because the only oysters in the bay are located in an oyster farm, their spatial

distribution in Morro Bay is limited. Since a spatial relationship of metals was desired in this

study, it was decided native clams found in the bay would satisfy the necessary components for

this study. The two species found in the bay and used in the analyses were Macoma secta and

Macoma suda.

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CHAPTER 2 BACKGROUND

Marine sediments of the world are increasingly contaminated with heavy metals and

other contaminants due to a history of industrial discharges and urban runoff. Marine sediments

are an important environmental component when considering the fate and transport of metals

within a watershed. The behavior and distribution of metals in marine sediments is influenced

by hydrodynamics, anthropogenic discharges, and biogeochemical processes (Zwolsman et al.,

1997). Marine bivalves (clams and mussels) have long been employed as pollution biomonitors

in coastal environments. This is due to their intimate contact with the contaminated sediments

and exceedingly high pumping activity and their responses are often proportional to ambient

pollutant concentrations (Wang and Guo., 2000).

Numerous factors need to be considered in marine environments when assessing

bioaccumulation of metals in bivalve animals. Various conditions (organic content, pH, and

presence of sulfide) are considered potential metal sinks. An important sink of metals are

hydrous iron oxides (a large part of oxidized sediments) acting by binding heavy metals to the

surface of sediments (Luoma and Bryan, 1978). The strength of metal binding to the particulates

contributes to the availability of the metal. Strongly bound metals are less available, and weakly

bounded metals are more available (Luoma, 1983). However, bound metals may be bioavailable

depending on the feeding and biogeochemical characteristic of the organism. No universal way

to assess the bioconcentration factors to benthic organisms exists for several reasons. The two

most important factors include differences between organisms and inconsistent chemistry

between metals and metal interactions. Redox cycles, such as those caused by tidal action

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increased the metal availability to organisms by interfering with the metal species equilibrium

(Simpson et al., 2002).

Bioaccumulation Factors

Several studies have developed mathematical relationships to predict bioaccumulation of

metals in benthic organisms. In one recent experiment, the influences of metal bioavailability of

natural colloids to marine bivalves were studied using artificially contaminated sediments radio-

labeled metals (Wang and Guo, 2000). Their accumulation index was defined as the

radioactivity of metals in whole individual bivalve (dpm) divided by radioactivity of metals in

the water column (dpm/L). This index includes shell uptake by adsorption or absorption and

cannot be used to indicate the absolute uptake of metals to the tissues. Assimilation efficiencies

were calculated by Griscom et al. 2000, but were not clearly defined. Assimilation efficiencies

differed more widely between metals than among geochemical conditions for a single metal.

The maximum differences in metal assimilation efficiencies were approximately two-fold from

high organic content and low organic content. In addition, the direction (positive or negative) of

influence total organic content had on bioavailability assimilation efficiencies was not consistent

among metals or among species tested (Griscom et al., 2000).

Competitive Metal Sorption

Competitive sorption between different metals was observed in several studies. In one

recent study, zinc limited the uptake of cadmium in plants and animals (Brown et al., 2002a,

Brown et al., 2002b). This was due to the excessive amounts of zinc compared to cadmium

found at mine waste sites in ratios greater than 100 to 1 (Brown et al., 2002a). These high levels

of zinc created iron deficiencies in plants, causing yellowing of young leaves. Similar levels of

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zinc created copper deficiencies in ruminant animals (cow, goat, deer, elk), but the deficiencies

were easily reversed during the span of the study with no apparent injury to the animal (Brown et

al., 2002b). Copper and chromium uptake from wastewaters by biomass consisting of the algae

from C. vulgaris were mutually inhibited by the presence of the other metals (Aksu and Açikel,

1998). Uptake inhibition was a function of pH; removal of copper was maximized at higher pH

(pH = 4) for copper and maximized at lower pH (pH = 2) for chromium (Aksu and Açikel,

1998). Such competitive sorption is likely to occur in marine sediments. The presence of one

metal in excess over the other metals will influence to some degree the uptake of each metal in

benthic organisms. For instance, the presence of iron may compete with lead in binding or

transport sites, thus decreasing the uptake of lead (Luoma and Bryan, 1978). Therefore,

comparing the concentration between all metals will yield an additional component needing to be

included in any bioaccumulation model.

Colloid Influences on Metal Transport

Metals are generally considered to be immobile in most soils due to various metal

binding processes (Luoma, 1983). However, the presence of colloid-bound metals as

resuspended soil particles is related to the soil metal concentrations and is an important factor for

metal transport. The presence of colloids enhances metal transport between 50 and 90 %, mainly

due to colloid-metal binding, and secondly due to cotransportation mechanisms (Karathanasis,

1999). Metal cotransport is dependent on the colloidal composition and the characteristics of the

metal (Karathanasis, 1999). An inverse relationship exists between sorption energy and surface

coverage (Karathanasis, 1999). Given this relationship, sorption affinities can be higher for the

colloids than for the soil matrix. Therefore, increased metal transport by preferentially sorbing

or desorbing metals from colloids is expected. Another study supported this relationship by

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reporting the colloidal desorption was the primary process responsible for metal concentration

increase (Cantwell et al., 2002).

Several geochemical factors need to be considered when addressing the influence of

colloids on metal transfer. Factors include soil characteristics, colloid characteristics, pH,

organic carbon (OC), redox potential (Eh), tidal action, the presence of organisms in the

sediments, acid volatile sulfides (AVS), and dissolved oxygen (DO) (Karathanasis, 1999; Wang

and Guo, 2000; Simpson et al., 2002; Griscom et al., 2000; and Cantwell et al., 2002). Increased

colloidal surface area and charge, pH, and OC generally increase metal transport (Karathanasis,

1999 and Wang and Guo, 2000). In contrast, large colloid size and Fe- and Al-oxyhydroxides

present in the sediment were generally inhibiting for metal transport (Karathanasis, 1999). Grain

size regulated the amount of sediment resuspended to the water column, with the finer particles

(silt and clay fraction) increasing metal transport (Cantwell et al., 2002). Anaerobic and aerobic

cycles under simulated tidal action increased the flux of zinc to the overlying water due to

increased colloidal concentrations (Simpson et al., 2002). In addition, disturbances from benthic

organisms increased the colloidal concentration, thus increasing the zinc flux (Simpson et al.,

2002). Bioturbation of sediments can remove surface bacterial coatings and expose new surface

sites for adsorption of metals (Griscom et al., 2000). Acid volatile sulfides (AVS) react strongly

with metals to form insoluble metal sulfides, thus removing them from the water column (Lee et

al., 2000). Colloids with a high AVS concentration will increase metal transport due to the

increased mobility of the colloids. Dissolved oxygen and redox potential generally limit metal

transport. Various properties are influenced by dissolved oxygen concentrations, such as AVS

and redox potential. Therefore, DO is an important component to consider when determining

metal transport.

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Colloid Influences on Bioavailability

The presence of colloids can increase the bioavailability of the metals to organisms

through two possible mechanisms. The first involves direct ingestion of the colloids. Colloidal

particles represent an important food source for deposit and suspension feeding benthic

organisms (Griscom et al., 2000). Uptake of metals from these particles is a function of the

particle metal concentration, feeding rates, and biogeochemical factors (Griscom et al., 2000).

The geochemical composition of the colloid amplifies the bioavailability of silver to deposit-

feeding clams. Manganese oxides increased the accumulation of silver 100 times more rapidly

than amorphous iron oxides (Luoma and Jenne, 1977). In addition to direct metal ingestion of

metal-bound colloids, colloids have the potential to release metals into the dissolved phase.

Uptake of metals from the dissolved phase is the second possible method. Aquatic colloids were

operationally defined as particles in the size fraction between 1 nm and 0.2 µm by Wang and

Guo, (2000) but Cantwell et al. (2002) defined colloids as particles retained on a one-micron

filter (≥ 1 µm). As illustrated by the differing definition of colloids, inaccurate recognition of

colloidal phase could be credited with the observed increase in bioavailability, the dissolved

metal phase or the colloid-bound metal phase.

Benthic organisms bioaccumulated substantial amounts of Cd, Ni, and Zn from sediments

when simultaneous extracted metals (SEM) were only a fraction of AVS, most notably for

cadmium (Lee et al., 2000). Although sulfide binds with metals to form insoluble metal sulfides,

feeding characteristics of the organism can increase the bioaccumulation from direct ingestion of

the colloids. Bioavailability of metals to benthic organisms followed changes in particulate

metal concentrations. However, metal concentration will not always predict bioavailability in

nature, as cautioned by Lee et al (2000). In addition, acid solubility alone was an inadequate

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predictor of the bioavailability of metals in the gut of bivalves (Griscom et al., 2000; Luoma,

1983). In contrast to the study by Lee et al. (2000), cadmium uptake was not significantly

increased by colloidal concentration (Wang and Guo, 2000), because most Cd was partitioned

into the dissolved phase. In contrast to conventional thinking, anoxic conditions did not

significantly reduce metal uptake. Metals were bioavailable to benthic organisms under anoxic

conditions (Wang and Guo. 2000). The differences may be due to the different feeding methods

of the bivalves studied. Therefore, simple SEM/AVS correlations are not likely to be adequate

for predicting metal uptake by different species of benthic organisms in different environments.

Soil Amendments and Chelating Agents

Soil amendments (in-situ) and chelating agents (ex-situ) influence the availability of

metals for uptake by organisms. Biosolid amendments (municipal wastewater sludge) with

added alkaline byproducts significantly reduced metal availability and toxicity to organisms

(Brown et al., 2002a, Brown et al., 2002b). Metal availability in the soils decreased sufficiently

to be safe for plant and animal habitation (Brown et al., 2002a, Brown et al., 2002b). The

addition of capping materials over marine sediments reduced the zinc flux compared to no

application (control) samples (Simpson et al., 2002). The clean native sediment cap was the

most effective in reducing zinc flux. Capping materials were recommended to control metals

due to metal sulfide formation (Simpson et al., 2002). Four ex-situ extraction agents were

investigated for their ability to remove metals from contaminated sites (Steele and Pichtel, 1998).

Using EDTA (ethylenediaminetetraacetic acid) as an extraction species yielded better lead

removal rates than did ADA (N-2(acetamido)-iminodiacetic acid), PDA (pyridine-2,6-

dicarboxylic acid), and HCl for lead. However, HCl was a more efficient extractant for cadmium

(Simpson et al., 2002). Chelating agents have the added bonus of allowing recovery of the

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metals for reuse or sale and the chelating reagent can be recovered for reuse in the process. In

addition, bioavailability was independent of the concentration of metals complexed with EDTA

or NTA compared to uptake from free metal ion concentrations. Depending on the extent and

characteristics of contamination in marine sediments, these and other methods may be a feasible

method for remediation of contaminated sediments by decreasing bioavailability of metals.

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CHAPTER 3 PROCEDURES

The sampling locations were in Morro Bay estuary in Central California. Five sampling

sites were chosen for clam and sediment collection to correspond to the same sites of previous

sediment sampling by Shanta Duffield at the RWQCB (Figure 1). The original sites included

Site 1 - Front Bay, Site 2 - Chorro Creek Mouth, Site 3 - Los Osos Creek Mouth, Site 4 - Back

Bay, and Site 5 - South Middle Bay. During collection, the Back Bay was determined to be

unsafe for collection because of deep mud, resulting in its abandonment as a collection site. A

second site in the middle of the bay (Site 4 - North Middle Bay) was chosen to maintain the

number of sites to five. The site numbers and locations are noted in Table 1 below. The days

chosen for sampling were April 29, May 4, and May 5, 2002, to take advantage of the negative

tides during daylight hours. Kayaks were used for transportation across the main channel and up

tributaries in the bay.

Table 1: Sampling Locations by Number

Site Number Site Location

1 Front Bay

2 Chorro Creek Mouth

3 Los Osos Creek Mouth

4 North Middle Bay

5 South Middle Bay

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Figure 1: Map of Morro Bay Sampling Sites*

*Map of Morro Bay Sampling Sites: This map shows the clam and sediment sampling locations in Morro Bay. Sites labeled with an “X” are the sites used previously for RWQCB sediment sampling. Circled numbers are the sampling sites used in this study.

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Sample Collection

The clams analyzed were collected using hand methods (gloved hands, plastic spades,

and digging). Approximately 50 grams of surrounding sediment was collected from the same

depth the clams were collected. The sediment and clams were double-bagged separately in

gallon-sized Ziploc™ bags and labeled with site name and the date of collection. Contamination

sources were minimized as much as possible through the practice of cleaning the collection

equipment with 10% nitric acid, detergent, and deionized water between sampling sites. After

collection, the samples were transported to the laboratory in coolers with ice. After collection

and initial rinsing of the clams, the clam and the sediment samples were frozen until digested and

analyzed. Refer to Appendix A1 for the complete Sample Collection Method as amended from

the California Department of Fish and Game’s (CADFG) procedure Sample Collection and

Preparation Procedure, Appendix A2.

Sample Preparation

Inside the clean room laboratory at Moss Landing, CADFG, individual clams were

separated into three groups by species for each sampling site, as the sample allowed. Due to the

variations in the collection of individuals, the number and weight of each of the composites

differed. The total tissue weight collected in each composite was not critical because an equal

amount of homogenized tissue was used in the digestion step. The objective was to collect

sufficient tissue to obtain a representative sample for each population. The clams were rinsed

with deionized water to remove any remaining sediment outside or inside the shell. All of the

soft tissue was scraped out of the shell with a scalpel and placed into pre-weighed labeled jars.

Each shell length was measured by closing the clamshell around a ruler and recording the widest

length. The equipment was washed between each group with soap, tap water rinse, and a

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deionized water rinse. The clams were frozen until the homogenization step. The shells from

the individuals used and any remaining individuals were bagged, labeled, and frozen.

Sample Homogenization and Digestion

The frozen clams were homogenized using a hand-held Tissue TearorTM homogenizer

Model 398 (Biospec Products, Inc.) to a smooth consistency with no chunks. Between each

sample, the hand-held homogenizer was washed using a six-step process (Appendix B).

Approximately equal amounts of homogenized clam paste were digested in concentrated nitric

acid in a microwave digester. The digestion program consisted of a 15 minute controlled warm

up to 195 ºC, 20 minutes at this temperature, and with a 20 minute cool down process at the end.

Once the microwave digested samples cooled and returned to surrounding pressure, each sample

was placed into pre-weighed, labeled, and acid-cleaned plastic bottles. Care was taken to entrain

droplets on the walls of the digestion vessels to ensure complete recovery of the sample. Each

bottle was diluted with MiliQ water to a volume of approximately 20 mL. Refer to Appendix B1

for the complete Sample Preparation and Digestion Methods as amended from the CADFG at

Moss Landing Methods, Appendix B2.

Any remaining samples not digested or used were kept frozen and saved for future

reference. The digested clam solutions produced from the week spent in Moss Landing were

stored in the refrigerator until analyzed.

Sample Analysis

A selected number of these clam digestion solutions, along with the corresponding

sediment sample, were sent to Creek Environmental Laboratory (Creek) in San Luis Obispo in

June 2002, for Inductively Coupled Plasma (ICP) analysis using EPA Method 6010. Both the

clam and sediment results were reported on a wet basis from Creek Environmental Laboratory.

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Blind duplicates of one clam sample and one sediment sample were sent to Creek Environmental

Laboratory for quality control purposes.

Sample Calculation

Two sample calculations are shown below. The first calculation demonstrates how to

calculate metal concentrations in clam tissue using the metal concentration measured. The

second calculation demonstrates the conversion of the sediment metal concentration on a wet

basis to sediment metal concentration to on a dry basis. Sediment results were changed from a

wet basis to a dry basis using reported moisture content to correlate comparisons with threshold

values.

Clam Metal Conc = (metal concentration measured)(volume of digested sample) (composite body mass)

Clam Metal Conc = (0.011 mg Cd/L)(20.254 mL)(1 L/1000 mL) = 0.172 mg Cd (1.293 g body mass)(1 kg/1000 g) kg body mass

Sediment Metal Conc (dry) = (Metal Conc (wet)) / (1 - % Moisture/100)

Sediment Metal Conc (dry) = (47 mg Cr/kg sediment) / (1 – 0.26) = 63.5 mg Cr kg sediment

Quality Assurance

Duplication of analysis was performed for Site 4 (North Middle Bay) for quality

assurance purposes. All of the duplicate analyses matched closely (Table 2), except the duplicate

for vanadium in clam tissues. The values reported for clam tissue vanadium concentrations were

2.07 and 22.3 mg/kg, a factor of ten difference. All other metals were within 1% for clam tissue

concentrations and within 15% for sediment concentrations.

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Table 2: Quality Control Duplication Analysis

Clam Results Percent Difference

Sediment Result (dry)

Percent DifferenceMetal

mg/L % mg/kg %

Cadmium ND ND

Cadmium (duplicate) ND 0

ND 0

Total chromium 1.1 52

Total chromium (duplicate) 1.1 0

54 4

Nickel 0.85 64

Nickel (duplicate) 0.86 1

75 15

Vanadium 0.13 22

Vanadium (duplicate) 1.4 90

22 0

Iron 48 9,000

Iron (duplicate) 48 0

10,000 11

* ND – no detect

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CHAPTER 4 RESULTS AND DISCUSSION

Sampling Site Characteristics and Observed Clam Populations

During sampling, a variety of conditions were encountered at the five sampling sites.

Chorro Creek (Site 2) and Los Osos Creek (Site 3) mouths were similar in the type of sediment

observed. Both had gray sandy material with little or no surrounding vegetation. The surface of

the sediment above the riverbed on Los Osos Creek was softer compared to the same area on

Chorro Creek, but both were firm compared to the three other sites. The clams were collected at

a depth between 6 to 8 inches and no other marine life was observed in the vicinity. However,

the number and species of clams found at both creek mouths differed greatly (Table 3). Chorro

Creek had a large concentration of the smaller (approximately 26 mm) clam M. secta, whereas

the clams collected from Los Osos Creek mouth were the larger (approximately 36 mm) clam M.

suda and occurred in smaller clusters.

Site 1 (Front Bay) and Site 4 (North Middle Bay) were similar in the type of sediment

observed and clams collected. Both sites were soft, and appear to be high in organic content, and

had a very strong sulfur odor. Due to the softness of the sediment, walking upright was difficult

to the point where moving around on hands and knees in a wetsuit was required. The sediment

contained two layers within the depth the clams were collected. The top layer was

approximately one inch thick, brown in color, and contained a variety of vegetation. The second

layer appeared to have a higher organic content, was black in color and more viscous than the top

layer. At these two sites, other marine life was seen, including oysters, crabs, shrimp, snails, and

other bivalve species. At the Front Bay site, the large (36mm) clam M. suda was found in small

groups of 3 to 4 individuals at approximately 6 inches deep. Similarly, at the North Middle Bay

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site, the same species of clam was found in smaller quantities as Site 1 at approximately the same

depth. Broken shells of clam, oyster, and other bivalve organisms were found at Site 4.

Site 5 (South Middle Bay) is similar to the creek mouth sites (Site 2 and Site 3) in the

characteristics of the sediment. The firm brown sandy material was firm enough to walk on

above the level of the channel as it was for the creek mouth sites. In addition, the vegetation was

sparse, but contained small amounts of organic material below the surface. At this site, some

empty and broken clam, oyster, and other bivalve shells were found. This site is characterized

by a meager amount of clams, as demonstrated by the number of individuals collected (Table 3).

A detailed description of the sampling site conditions can be found in Appendix D.

The average body weight per individual for M. suda and M. secta was 2.12 and 0.82

grams with an average shell length at the widest point of 36 and 26 mm, respectively (Table 3).

Metal Concentrations in Clams and Sediments

The metal concentrations determined in clam tissue and sediment using ICP analysis by

Creek Environmental Laboratory is reported in Table 4 and Table 5. The results from Creek are

found in Appendix C. For calculation purposes, no detection values were entered as half of the

not detected levels. These values are marked with an asterisk to distinguish the no detection

values apart from the other results. Clam tissue metal concentration is expressed in mg of metal

per kg of body mass (wet) and the sediment results are expressed in mg of metal per kg of

sediment (dry). Sediment results were changed from a wet basis to a dry basis to correlate

comparisons with threshold values, as indicated on Figures 2-11.

Table 3: Sample Composite Preparation Composite #1 Composite #2 Composite #3 Composite #4 Composite #5 A B C A B C D A B A B C A

Species M.suda M.suda M.secta M.secta M.secta M.secta M.suda M.suda M.suda M.suda M.suda M.suda M.suda Number of individuals 10 10 11 27 27 26 4 6 6 9 8 8 4

Initial wt (g) 41.31 40.66 41.16 41.27 41.05 41.23 41.18 41.63 41.66 41.19 41.24 41.75 41.42 Final wt (g) 58.34 59.57 52.42 63.81 59.77 60.53 52.24 55.47 57.24 61.52 54.87 56.53 49.36

Net wt (g) 17.03 18.91 11.26 22.54 18.72 19.30 11.06 13.84 15.58 20.33 13.63 14.78 7.94 Ave wt/individual (g) 1.70 1.89 1.02 0.83 0.69 0.74 2.77 2.31 2.60 2.26 1.70 1.85 1.99

Ave shell length (mm) 33 32 27 26 25 26 32 40 41 37 34 36 38 Stdev shell length (mm) 9.1 6.7 2.6 2.0 1.6 1.3 19 12 12 10 8.7 4.8 6.8

Shell lengths (mm) 48 37 29 29 26 27 40 51 53 58 47 43 47 39 40 30 27 27 26 55 50 51 30 28 40 37 28 27 27 25 26 23 16 39 45 43 25 32 35 23 34 27 28 26 26 18 39 44 32 42 39 31 36 34 26 21 25 25 41 30 28 39 31 25 41 26 26 26 25 18 22 36 27 39 32 34 27 24 28 27 30 24 31 24 19 27 28 26 25 48 36 33 47 28 23 26 27 26 29 30 29 33 28 26 28 26 25 26 25 28 24 27 25 23 24 25 24 26 22 26 26 26 24 25 26 26 27 25 25 26 26 25 26 23 26 26 28 22 26 24 24 25 26 22 26 26 22 22 28 24 26 27 26 24 28 25

Average weight per individual for M. suda = 2.12 grams M. secta = 0.82 grams Average shell length per individual for M. suda = 36 mm M. secta = 26 mm

18

19

Table 4: Clam Tissue Metal Concentrations measured by ICP

Extract Conc (wet) Body Mass Final Volume

Metal Conc. in

tissue (wet)Species Site Sample Metal

mg/L g mL mg/kg M.secta Front Bay 1 Cadmium 0.011 1.293 20.254 0.172 M.secta Front Bay 1 Total chromium 0.91 1.293 20.254 14.3 M.secta Front Bay 1 Nickel 0.65 1.293 20.254 10.2 M.secta Front Bay 1 Vanadium 0.051 1.293 20.254 0.799 M.secta Front Bay 1 Iron 21 1.293 20.254 329 ִ M.suda Chorro Mouth 2 Total arsenic 0.11 1.265 20.000 1.74 M.suda Chorro Mouth 2 Cadmium 0.031 1.265 20.000 0.490 M.suda Chorro Mouth 2 Total chromium 6.6 1.265 20.000 104 ִ M.suda Chorro Mouth 2 Copper 0.18 1.265 20.000 2.85 M.suda Chorro Mouth 2 Lead 0.022 1.265 20.000 0.348 M.suda Chorro Mouth 2 Nickel 4.3 1.265 20.000 67.9 ִ M.suda Chorro Mouth 2 Vanadium 0.17 1.265 20.000 2.69 M.suda Chorro Mouth 2 Zinc 5.8 1.265 20.000 91.7 M.suda Chorro Mouth 2 Iron 75 1.265 20.000 1,186 ִ M.suda Osos Mouth 3 Total arsenic 0.097 1.341 19.984 1.45 M.suda Osos Mouth 3 Cadmium 0.0025* 1.341 19.984 0.0373M.suda Osos Mouth 3 Total chromium 0.40 1.341 19.984 5.96 M.suda Osos Mouth 3 Copper 0.25 1.341 19.984 3.73 M.suda Osos Mouth 3 Lead 0.010* 1.341 19.984 0.149 M.suda Osos Mouth 3 Nickel 0.43 1.341 19.984 6.41 M.suda Osos Mouth 3 Vanadium 0.11 1.341 19.984 1.64 M.suda Osos Mouth 3 Zinc 2.2 1.341 19.984 32.8 M.suda Osos Mouth 3 Iron 40 1.341 19.984 596 ִ M.suda N Middle Bay 4 Cadmium 0.0025* 1.256 20.011 0.0398M.suda N Middle Bay 4 Total chromium 1.1 1.256 20.011 17.5 M.suda N Middle Bay 4 Nickel 0.85 1.256 20.011 13.5 M.suda N Middle Bay 4 Vanadium 0.13 1.256 20.011 2.07 M.suda N Middle Bay 4 Iron 48 1.256 20.011 765 ִ M.suda S Middle Bay 5 Cadmium 0.0025* 1.246 19.976 0.0401M.suda S Middle Bay 5 Total chromium 3.9 1.246 19.976 62.5 M.suda S Middle Bay 5 Nickel 2.6 1.246 19.976 41.7 M.suda S Middle Bay 5 Vanadium 1.2 1.246 19.976 19.2 M.suda S Middle Bay 5 Iron 56 1.246 19.976 898 ִ M.suda N Middle Bay (Duplicate) 4 Cadmium 0.0025* 1.256 20.011 0.0398M.suda N Middle Bay (Duplicate) 4 Total chromium 1.1 1.256 20.011 17.5 M.suda N Middle Bay (Duplicate) 4 Nickel 0.86 1.256 20.011 13.7 M.suda N Middle Bay (Duplicate) 4 Vanadium 1.4 1.256 20.011 22.3 M.suda N Middle Bay (Duplicate) 4 Iron 48 1.256 20.011 765 ִ

*No detection are reported as half of the detection limit

20

Table 5: Sediment Metal Concentrations measured by ICP

Wet Conc Metal Conc. in Sediment

(dry wt basis) Site Sample Metal Percent Moisture

mg/kg mg/kg Front Bay 1 Cadmium 26 0.15* 0.203 Front Bay 1 Total chromium 26 47 63.5 Front Bay 1 Nickel 26 61 82.4 Front Bay 1 Vanadium 26 19 25.7 Front Bay 1 Iron 26 8,700 11757 ִ Chorro Mouth 2 Total arsenic 26 1.5* 2.03 Chorro Mouth 2 Cadmium 26 0.15* 0.203 Chorro Mouth 2 Total chromium 26 48 64.9 Chorro Mouth 2 Copper 26 6.9 9.32 Chorro Mouth 2 Lead 26 1.6 2.16 Chorro Mouth 2 Nickel 26 63 85.1 Chorro Mouth 2 Vanadium 26 19 25.7 Chorro Mouth 2 Zinc 26 18 24.3 Chorro Mouth 2 Iron 26 8,600 11622 ִ Osos Mouth 3 Total arsenic 23 1.5* 1.95 Osos Mouth 3 Cadmium 23 0.15* 0.195 Osos Mouth 3 Total chromium 23 40 51.9 Osos Mouth 3 Copper 23 4.1 5.32 Osos Mouth 3 Lead 23 0.5* 0.649 Osos Mouth 3 Nickel 23 44 57.1 Osos Mouth 3 Vanadium 23 16 20.8 Osos Mouth 3 Zinc 23 14 18.2 Osos Mouth 3 Iron 23 6,700 8701 ִ N Middle Bay 4 Cadmium 28 0.15* 0.208 N Middle Bay 4 Total chromium 28 52 72.2 N Middle Bay 4 Nickel 28 64 88.9 N Middle Bay 4 Vanadium 28 22 30.6 N Middle Bay 4 Iron 28 9,000 12500 ִ S Middle Bay 5 Cadmium 22 0.15* 0.192 S Middle Bay 5 Total chromium 22 34 43.6 S Middle Bay 5 Nickel 22 41 52.6 S Middle Bay 5 Vanadium 22 16 20.5 S Middle Bay 5 Iron 22 6,300 8077 ִ N Middle Bay (Duplicate) 4 Cadmium 33 0.15* 0.224 N Middle Bay (Duplicate) 4 Total chromium 33 54 80.6 N Middle Bay (Duplicate) 4 Nickel 33 75 112 ִ N Middle Bay (Duplicate) 4 Vanadium 33 22 32.8 N Middle Bay (Duplicate) 4 Iron 33 10,000 14925 ִ *No detection are reported as half of the detection limit

21

Metal concentrations for clam tissues and sediment, averaged over all sites are

summarized in Table 6 and shown in Figure 2. The highest metal concentrations in both

sediment and clams were observed for total chromium, nickel, vanadium, and zinc, excluding

iron. Total arsenic and cadmium concentrations were similar in clam tissue and sediment, all at

low concentrations. In contrast, total chromium, copper, lead, nickel, and vanadium exhibited

over twice the metal concentrations in the sediment compared to the clam tissue. In the reverse,

zinc had three times higher metal concentrations in the clam tissue compared to the sediment.

To achieve a useful representation of the relationships between averaged metal concentrations,

iron was not included in this figure due to the high values measured. The results as presented in

Figure 2 are averaged over all of the sites by metal, however the bar graph does not properly

address spatial variations or whether the measured concentrations are detrimental. The metal

concentrations for clams tissue and sediments are described in more detail in Table 7.

Table 6: Clam Tissue and Sediment Metal Concentrations Averaged by Site

Metal Clam Ave (mg/kg)

Clam Standard Deviation

Sediment Ave (mg/kg)

Sediment Standard Deviation

Total Arsenic 1.59 0.208 1.99 0.0558

Cadmium 0.137 0.181 0.204 0.0113

Total Chromium 37.0 38.5 62.8 13.4

Copper 3.29 0.622 7.32 2.83

Lead 0.248 0.141 1.41 1.07

Nickel 25.6 24.3 79.7 21.9

Vanadium 8.12 9.86 26.0 5.00

Zinc 62.2 41.7 21.3 4.34

Iron 756 ִ 287 ִ 11264 ִ 2531 ִ

62.8

79.7

62.2

21.326.0

1.41

7.32

0.2041.99

37.0

0.2

8.1

25.6

3.290.137

1.59

0

10

20

30

40

50

60

70

80

90

Arsenic Cadmium Chromium Copper Lead Nickel Vanadium Zinc

Met

al C

once

ntra

tion

(mg/

kg)

Sediment AverageClam Average

Figure 2: Metal Concentrations Averaged by Metal Over All Sites *Error bars are calculated using the Standard Error.

22

23

Table 7: Summary of Clam Tissue (wet) and Sediment (dry) Metal Concentrations

Clam Results Sediment Result (dry) Site Sample Metal

mg/kg mg/kg Chorro Mouth 2 Total arsenic 1.74 2.03 Osos Mouth 3 Total arsenic 1.45 1.95 Front Bay 1 Cadmium 0.172 0.203 Chorro Mouth 2 Cadmium 0.490 0.203 Osos Mouth 3 Cadmium 0.0373 0.195 N Middle Bay 4 Cadmium 0.0398 0.208 N Middle Bay (Duplicate) 4 Cadmium 0.0398 0.224 S Middle Bay 5 Cadmium 0.0401 0.192 Front Bay 1 Total chromium 14.3 63.5 Chorro Mouth 2 Total chromium 104 . 64.9 Osos Mouth 3 Total chromium 5.96 51.9 N Middle Bay 4 Total chromium 17.5 72.2 N Middle Bay (Duplicate) 4 Total chromium 17.5 80.6 S Middle Bay 5 Total chromium 62.5 43.6 Chorro Mouth 2 Copper 2.85 9.32 Osos Mouth 3 Copper 3.73 5.32 Chorro Mouth 2 Lead 0.348 2.16 Osos Mouth 3 Lead 0.149 0.649 Front Bay 1 Nickel 10.2 82.4 Chorro Mouth 2 Nickel 68.0 85.1 Osos Mouth 3 Nickel 6.41 57.1 N Middle Bay 4 Nickel 13.5 88.9 N Middle Bay (Duplicate) 4 Nickel 13.7 112 ִ S Middle Bay 5 Nickel 41.7 52.6 ִ Front Bay 1 Vanadium 0.799 25.7 Chorro Mouth 2 Vanadium 2.69 25.7 Osos Mouth 3 Vanadium 1.64 20.8 N Middle Bay 4 Vanadium 2.07 30.6 N Middle Bay (Duplicate) 4 Vanadium 22.3 32.8 S Middle Bay 5 Vanadium 19.2 20.5 Chorro Mouth 2 Zinc 91.7 24.3 Osos Mouth 3 Zinc 32.8 18.2 Front Bay 1 Iron 329 . 11757 ִ Chorro Mouth 2 Iron 1,186 . 11622 ִ Osos Mouth 3 Iron 596 . 8701 ִ N Middle Bay 4 Iron 765 . 12500 ִ N Middle Bay (Duplicate) 4 Iron 765 . 14925 ִ S Middle Bay 5 Iron 898 . 8077 ִ

24

Spatial Variation of Metal Concentrations in Clam Tissue and Sediments

The spatial variability in metal concentrations for both clams and sediments are shown

for each metal in Figures 3 through 11. The values for clam tissue and sediment metal

concentrations are plotted by the sampling location for each metal separately with no-detect

levels expressed as half of the detection limit and are italicized for reference. Results for each

metal are described individually. Observed metal concentrations at each site are compared to

benchmark values. Sediment values were compared to standards reported by NOAA (page 2 in

the Screening Quick Reference Tables (SQuiRT), Appendix E). Clam tissue values were

compared to benchmarks reported by the FDA’s Center for Food Safety and Applied Nutrition

Study (1993) and from pages 11 and 12 of Part H: Decision Document of Water Quality

Assessment for San Diego Creek and Newport Bay (DDWQA).

Table 8: NOAA SQuIRT Marine Sediment Increasing Predicted Toxicity Gradient

Abbreviation Effect Level

TEL Threshold Effects Level

ERL Effects Range – Low

PEL Probable Effects Level

ERM Effects Range Median

AET Apparent Effects Threshold

Total arsenic concentrations in the clam tissue and sediment were similar at the two creek

mouth sites (Figure 3). Total arsenic concentrations were only determined by ICP at these two

sites due to budget constraints. The sediment concentrations were both below the detection

level, and therefore below all of the NOAA benchmark levels. The clam tissue total arsenic

25

concentrations exceeded the U.S. Fish and Wildlife (USFW) benchmark of 0.25 mg/kg (page 11

of Part H), and slightly exceeded the California Office of Environmental Health Hazard

Assessment (OEHHA) value of 1.0 mg/kg (page 12 of Part H). However, since the arsenic

concentrations measured are near the detection limit (0.05 mg/L), this is probably not

meaningful. Sediment total arsenic concentrations were always slightly larger than the tissue

arsenic concentrations, signifying arsenic may not bioaccumulate for the two clam species

studied.

1.95

2.03

1.45

1.74

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Metal Concentration (mg/kg)

SedimentClam

Sediment Limits(NOAA Values)TEL = 7.24ERL = 8.2PEL = 41.6ERM = 70

Tissue Limits:OEHHA Value1.0 mg/kgUS Fish & Wildlife0.25 mg/kg

Chorro Creek

Osos Creek

USFW OEHHA TEL

Figure 3: Total Arsenic Concentration in Clam Tissues and Sediment

26

Cadmium concentrations were analyzed at all five sites (Figure 4). All of the sediment

values and most of the clam tissue values were below the detection limit. Cadmium was

detected above the detection limit in only two clam tissue samples, at Front Bay (Site 1) and at

Chorro Creek (Site 2). The cadmium concentration in clam tissue at the mouth of Chorro Creek

(Site 2) of 0.490 mg/kg was considerably higher than the cadmium concentrations of the other

samples, but was below the 1.0 mg/kg Maximum Tissue Residue Level (MTRL) from State

Mussel Watch Program, 2000 value for cadmium in seawater (on page 12 of Part H).

0.203

0.195

0.192

0.490

0.203

0.224

0.2080.03980.0398

0.0373

0.172

0.0401

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Metal Concentration (mg/kg)

SedimentClam

Sediment Limits(NOAA Values)TEL = 0.676ERL = 1.2PEL = 4.21ERM = 9.6

Tissue Limits:MTRL1.0 mg/kg

Chorro Creek

Osos Creek

Front Bay

N Middle Bay

S Middle Bay

TEL

Figure 4: Cadmium Concentration in Clam Tissues and Sediment

27

Total chromium distribution in tissue and sediment samples for all five sites is shown in

Figure 5. The sediment chromium concentrations are in the range of the two lowest benchmark

limits. The mouth of Chorro Creek sediment chromium value is above the ERL (81 mg/kg), Site

5 sediment concentration was above the TEL (52.3 mg/kg), and the remaining three sites had

sediment chromium concentrations below the TEL (Figure 5). All of the tissue chromium

concentrations were above the 1.0 mg/kg Median International Standards (MIS), indicating the

observed metal concentrations in the tissues might be a problem with regards to total chromium

loading on the estuary with the highest tissue concentration at the mouth of Chorro Creek (Site

2). No apparent correlation was observed between total chromium concentrations in clams and

total chromium concentrations in sediments. For some sites, sediment concentrations were

higher, while for other sites, the clam tissues had higher total chromium concentrations (Figure

5).

28

63.5

64.9

51.9

80.6

62.5

72.2

43.6

17.5

14.3

104

5.96

17.5

0.0 20.0 40.0 60.0 80.0 100.0 120.0

Metal Concentration (mg/kg)

SedimentClam

Chorro Creek

Osos Creek

Front Bay

N Middle Bay

S Middle BaySediment Limits(NOAA Values)TEL = 52.3ERL = 81PEL = 160.4ERM = 370

Tissue Limits:MIS Value1.0 mg/kg

TEL ERLMIS

Figure 5: Total Chromium Concentration in Clam Tissues and Sediment

29

The copper values measured are low for both tissue and sediment (Figure 6). The largest

sediment value (9.32 mg/kg) was approximately half of the TEL for this metal (18.7 mg/kg).

Likewise, the tissue values were a fifth of the USFW benchmark of 15 mg/kg. Copper values

were determined by ICP only at two sites for budgetary reasons. Sediment copper

concentrations were always larger than the tissue copper concentrations, signifying copper may

not bioaccumulate for the two clam species studied.

9.32

5.32

2.85

3.73

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0

Metal Concentration (mg/kg)

SedimentClam

Chorro Creek

Osos Creek

Sediment Limits(NOAA Values)TEL = 18.7ERL = 34PEL = 108.2ERM = 270

Tissue Limits:USFW Value15 mg/kg

USFW

Figure 6: Copper Concentration in Clam Tissues and Sediment

30

Iron concentrations in the clams and sediments were consistently lower than the NOAA

value (Figure 7). The iron concentrations were much higher in the sediments than in the clams,

as expected. A large portion of soil is composed of iron oxides, as clearly shown in Figure 7.

Since iron is not considered toxic, only guidelines can be found from NOAA for sediments and

no tissue limits could be found. Sediment iron concentrations were always larger than the tissue

iron concentrations, signifying iron may not bioaccumulate for the two clam species studied.

11757

11622

8701

12500 14925

8077

329

596

765

898

1,186

765

0 5000 10000 15000 20000

Metal Concentration (mg/kg)

SedimentClam

Chorro Creek

Osos Creek

Front Bay

N Middle Bay

S Middle Bay

Sediment Limits(NOAA Values)AET 220,000 N

Tissue Limits:None found

Figure 7: Iron Concentration in Clam Tissues and Sediment

31

Figure 8 shows the spatial variations for lead at the two creek mouth sites. The lead

concentrations at Los Osos Creek (Site 3) for both sediment and clam tissue were below the

detection limits. The sediment lead concentration was well below all of the NOAA limits. The

tissue value measured at the mouth of Chorro Creek (Site 2) was below the MIS limit of 2.0

mg/kg. It appears lead may not bioaccumulate in the two clam species studied (apparent from

the sediment lead concentrations were always higher than the tissue lead concentrations). Note,

only two sites were sampled for lead with ICP. Based on previous sediment analyses, lead was

not expected to be notable and was not considered critical. Consequently, only two samples

were analyzed.

0.649

2.16

0.149

0.348

0.0 0.5 1.0 1.5 2.0 2.5

Metal Concentration (mg/kg)

SedimentClam

Chorro Creek

Osos Creek

Sediment Limits(NOAA Values)TEL = 30.24ERL = 46.7PEL = 112.18ERM = 218

Tissue Limits:MIS Value2.0 ppm

MIS

Figure 8: Lead Concentration in Clam Tissues and Sediment

32

Overall, the sediment nickel concentrations were higher than in the clam tissue (Figure

9). For the sediment nickel concentrations, all of the values were above the ERM of 51.6 mg/kg.

The highest nickel concentration for clam tissue was 68.0 mg/kg for clams collected at the mouth

of Chorro Creek (Site 2). This is well above the NOAA Effects Range Median (ERM) for

sediments, however no tissue benchmark limit could be found for comparison. Three of the clam

tissue values were below the NOAA Threshold Effects Level (TEL) for nickel in sediments. The

South Middle Bay clam tissue value was close to the NOAA Probable Effects Level (PEL) at a

value of 41.7 mg/kg for sediment. Nickel appears not to bioaccumulate in the two species of

clams studied (as apparent from the sediment concentrations being larger than the tissue

concentrations).

57.1

88.9

52.6

68.0

112

85.1

82.4

13.5

10.2

13.7

6.41

41.7

0.0 20.0 40.0 60.0 80.0 100.0 120.0Metal Concentration (mg/kg)

SedimentClam

Chorro Creek

Osos Creek

Front Bay

N Middle Bay

S Middle Bay

Sediment Limits(NOAA Values)TEL = 15.9ERL = 20.9PEL = 42.8ERM = 51.6

Tissue Limits:None Found

PEL ERMERLTEL

Figure 9: Nickel Concentration in Clam Tissues and Sediment

33

No correlation existed between clam tissue and sediment concentration for vanadium

(Figure 10). The sediment vanadium concentrations were clustered together with values between

19.2 to 32.8 mg/kg. The vanadium clam tissue values were highest at Site 5 (South Middle Bay)

and Site 4 (North Middle Bay). The other three sites had small clam tissue concentrations

compared to the sediment values. Note, one vanadium value was a factor of ten larger than the

other in the duplicate clam tissue concentrations at Site 4 (Table 2). Similar to iron, only

guidelines were given by NOAA, and not benchmark limits because vanadium is a natural

component of soil. All tissue and sediment vanadium concentrations were below the lowest

NOAA benchmark. No tissue guidelines or benchmark limits could be found.

25.7

25.7

20.8

20.5

0.799

2.69

1.64

22.330.6

32.82.07

19.2

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0

Metal Concentration (mg/kg)

SedimentClam

Chorro Creek

Osos Creek

Front Bay

N Middle Bay

S Middle Bay

Sediment Limits(NOAA Values)AET = 57 N

Tissue Limits:None Found

Figure 10: Vanadium Concentration in Clam Tissues and Sediment

34

Sediment zinc concentrations were well below the sediment limits for zinc by a factor of

six for both sites. The tissue zinc concentration at Chorro Creek mouth (91.7 mg/kg) was above

the MIS tissue value (70 mg/kg), however the zinc tissue concentration was below the MIS limit

at Osos Creek mouth (32.8 mg/kg). Zinc may bioaccumulate in these two species of clams as

indicated by the considerably higher metal concentration in the clam tissues compared to the

metal concentrations in the sediments. Unfortunately, only samples from two sites were

analyzed by ICP, making it difficult to confirm this observation. Only two samples were

analyzed by ICP for zinc since it was not considered to be notable at the onset of the study, and

due to budget constraints.

24.3

18.2 32.8

91.7

0 20 40 60 80 100Metal Concentration (mg/kg)

SedimentClam

Chorro Creek

Osos Creek

Sediment Limits(NOAA Values)TEL = 124ERL = 150PEL = 271ERM = 410

Tissue Limits:MIS Value70 mg;kg

MIS

Figure 11: Zinc Concentration in Clam Tissues and Sediment

35

The mouth of Chorro Creek (Site 2) tissue metal concentrations was high for cadmium,

total chromium, nickel, and zinc. These high metal concentrations could be caused by

discharges into the watershed upstream of the estuary. Runoff from Camp San Luis Obispo, the

state penitentiary, or other anthropologic activities are possible sources of the metals observed

(Duffield, 2000). The SWRCB cites the sources of metal contamination to be surface mining,

nonpoint sources, boat discharge, and vessel wastes.

Human Consumption Levels

To determine safe levels of consumption of these clams for the general public, Table 9

was created to summarize background and maximum consumption levels from the Guidance

Documents for Metals in Shellfish (Guidance Documents) from the Center for Food Safety &

Applied Nutrition at the FDA (USFDA, 1993a, 1993b, 1993c, 1993d). Guidance Documents

have been published for five out of the nine metals considered in this study (As, Cd, Cr, Pb, and

Ni). Consumption guidelines from the World Health Organization (WHO) are included in Table

9 for comparison. For additional information consult WHO (1983) and WHO/FAO (1989).

36

Table 9: Recommended Human Consumption Levels

Background Consumption

Level

WHO/FAO 1989

WHO tolerable daily

intake

USFDA Levels of Concern Metal

µg/person/day* µg/kg/week mg µg/person/day*

Other Entity Recommendations

As 30 15 130 130 WHO 1983 Tolerable Daily Intake = 0.05 mg/kg

Cd 10 7 55 55

Cr 30 -100 ? ? 200 National Academy of Science Cr(III) = 50 - 200 µg/person/d

Pb 5 - 10 ? ? 6, 15, 25, 75**

Ni 120 no set limit no set limit 1200 EPA Oral Dose of 20 µg/kg/d and NOAEL of 5 mg/kg/d

* for a 60 kg person ** depending on population 6 µg/person/d ages 0 - 6 15 µg/person/d children over 7 25 µg/person/d pregnant women 75 µg/person/d adults

The frequency of shellfish consumption was characterized by the Market Research

Corporation of America (MRCA) 14-Day Survey (5 Year Menu Census, 1982-87) (MCRA,

1988). The MRCA reported 4.8% of the surveyed population consumed molluscan bivalves.

Calculated within the Guidance Documents, the average intake of molluscan bivalves is

estimated to be 12 grams/day for adults (male and female) between 18 and 44 years of age. This

equals approximately 84 grams/week for an average adult who eats shellfish. For the average

clam size in this study, this was approximately 40 M. suda clams and 102 M. secta clams per

week.

Table 10 summaries the FDA Levels of Concern, average tissue concentration, and the

maximum number of clams eaten per week to exceed the Levels of Concerns for each metal.

Example calculations used to find the Level of Concern and Threshold Consumption Levels are

listed in Table 10. Level of Concern was calculated using the USFDA Level of Concern value

37

and subtracting the USFAD Background Level to obtain a metal concentration value accounting

for the metal exposure not from food sources. This value was then used to calculate a Threshold

Consumption Level appropriate for the metal concentrations measured in the clams from Morro

Bay.

Level of Concern = [(130 µg As/person/day) – (30 µg As/person/d)](7 d/wk) = 700 µg As person/wk

Threshold = (700 µgAs/person/wk)(kg clam/1.59 mg As)(mg/1000 µg)(1000g/kg) = 440 g clam person/wk

Table 10: Quantity of Clams Safe for Consumption Below USFDA Levels of Concern

Metal USFDA Levels of Concern

USFDA Background

Level

Average Tissue

Concentration

Threshold Consumption

Level

µg/person/day* µg/person/day* mg/kg g clam/week

As 130 30 1.59 440

Cd 55 10 0.137 2,300

Cr 200 65 37.0 25.5

Pb 75 7.5 0.248 1,900

Ni 1200 120 25.6 295

* for a 60 kg person

Total Arsenic was treated as all inorganic arsenic in the Guidance Document due to the

high toxicity of inorganic arsenic compared to organic arsenic. This was considered to be a

conservative assumption with regards to the toxicity of arsenic. The total arsenic measured in

the clams from Morro Bay was 1.59 mg As/kg clam body weight. Using the USFDA Level of

Concern for arsenic (subtracting out the USFDA Background arsenic level) the threshold amount

38

for a 60 kg person to eat was calculated to be 440 grams of clams per week. Since this quantity

greatly exceeded the average consumption of 84 grams of clams per week a person consumes

each week, consumption of clams from Morro Bay should be safe with regards to arsenic

concentration.

The cadmium measured in the clams from Morro Bay was 0.137 mg Cd/kg clam body

weight. Calculating the USFDA Level of Concern for cadmium, the threshold amount for a 60

kg person to eat was calculated to be 2,300 grams of clams per week. This quantity of clams

exceeds by more than two orders of magnitude the average personal consumption of 84 grams

per week. Therefore, consuming clams from Morro Bay at the average consumption rate should

be safe with regards to cadmium concentrations.

With a measured total chromium value of 37.0 mg Cr/kg clam body weight, the

calculated weekly threshold amount a 60 kg person could eat is approximately 25.5 grams of

clams. This quantity of clams is below the 84 grams/week an average person consumes each

week. Therefore, caution should be exerted when considering consuming clams from Morro

Bay; it may not be safe to eat with regards to chromium concentration.

The lead measured in the clams from Morro Bay was 0.248 mg Pb/kg clam body weight.

Using the USFDA Level of Concern for lead and subtracting out the USFDA Background lead

level, the threshold amount a 60 kg person could eat was calculated to be 1,900 grams of clams

per week. Since this quantity far exceeds by two orders of magnitude the amount the average

person consumes each week, consumption of clams from Morro Bay should be safe with regards

to lead concentration.

The last metal listed in Table 10 (nickel) had an average concentration of 25.6 mg Ni/kg

clam body weight. The calculated weekly threshold value for a 60 kg person is 295 grams of

39

clams. Since this quantity of clams exceeds the amount the average person consumes each week

(84 grams of clams per week), consuming clams from Morro Bay may be safe with regards to

nickel concentration.

Bioaccumulation Concentration Factor

Bioaccumulation concentration factors (BCFs) shown in Table 11 were calculated from

dividing tissue metal concentrations by the corresponding sediment metal concentrations. BCFs

for all metals (except for zinc) were less than 1, indicating these metals may not bioaccumulate

under the conditions found in Morro Bay for the clams species studied. Zinc has a BCF of

almost three (BCF = 2.93), indicating zinc bioaccumlates three fold for the species studied from

Morro Bay.

Table 11: Bioaccumulation Concentration Factors

Tissue Metal Concentration

Sediment Metal Concentration Metal

mg/kg mg/kg

Bioaccumulation Concentration Factor

Total Arsenic 1.59 1.99 0.80

Cadmium 0.137 0.204 0.67

Total Chromium 37.0 62.8 0.59

Copper 3.29 7.32 0.45

Lead 0.248 1.41 0.18

Nickel 25.6 79.7 0.32

Vanadium 8.12 26.0 0.31

Zinc 62.2 21.3 2.93

Iron 756 ִ 11264 ִ 0.07

40

CHAPTER 5 CONCLUSION

Of all of the metals tested, total chromium, nickel, and zinc are of greatest concern

according to clam and sediment benchmarks established by NOAA, OEHHA, USWFS, FDA,

WHO, and others.. With chromium, sediments exceeded NOAA benchmark value and clam

concentrations greatly exceeded the MIS value. Additionally, nickel sediment and clam

concentrations exceeded NOAA benchmarks value, although no tissue benchmark value could be

found for nickel. The clam concentration of zinc was higher than the MIS at one site (the sample

collected at the mouth of Chorro Creek). For arsenic, clam tissue concentrations exceed both the

USFW and OEHHA benchmark values. However, all measured arsenic concentrations were

near the detection limit, and are therefore, probably not a concern.

Three-fold higher zinc concentrations were observed in the clam tissues compared to the

zinc concentrations in the sediments, indicating zinc might bioaccumulate in these two species of

clams. However, sediment and tissue zinc concentrations were below the TEL and MIS values

for zinc. Simulated tidal action increased the zinc flux to the overlying water column due to

increased colloidal concentration (Simpson et al., 2002). In addition, benthic organisms

increased the zinc flux (Simpson et al., 2002). Therefore, zinc likely bioaccumlates in the

conditions found in Morro Bay. The clam concentrations of cadmium, copper, lead, and

vanadium were below relevant benchmark values.

Risk associated with the consumption of these two clam species with regards to the five

metals (As, Cd, Cr, Pb, and Ni) based on published values in the Guidance Documents for metals

in Shellfish by the FDA is minimal at average molluscan bivalve consumption levels, except for

total chromium. An average person (60 kg) consuming clams from the Bay would consume a

41

quantity of total chromium possibly posing a health threat. In addition to the average population,

total chromium levels in the clams represent a health risk to high-risk populations (fishermen and

their families) who consume larger quantities of shellfish. Chromium (III) has been documented

as an essential trace element for humans. The National Academy of Sciences recommends a

daily intake level of Cr (III) of 50-200 µg/day. This upper value is the Level of Concern used for

the calculations. However, levels of total chromium measured in clams from Morro Bay exceed

this health level. Therefore, the average person should exercise caution when consuming clams

from Morro Bay with regards to the person’s total chromium consumption.

Both chromium and nickel are contained in serpentine geological formations common in

the Morro Bay watershed. Erosion of these formations (natural and unnatural) is likely to

contribute to high nickel and chromium concentrations.

Uptake of metals by benthic organisms is influenced by many factors (metal chemistry,

sediment chemistry, type of organism, colloid concentrations, chelating agents, and others), and

it is nearly impossible to predict bioaccumulation using simple models with a single or few

indicators. The results in this study support this. No correlation was discovered between

sediment concentration and clam tissue concentration in Morro Bay.

All of the metals studied did not appear to bioaccumulate, except with zinc. Sediment

metals concentrations, such as chromium, nickel, and vanadium, were higher than the tissue

concentrations. In contrast, zinc tissue metal concentrations were almost three times higher

compared to the sediment metal concentration.

Spatial relationships existed within this study (the mouth of Chorro Creek had higher

values). With added data on metal concentrations for both the clam tissue and for the sediments,

42

more detailed descriptions could be made concerning the relationships between each metal, the

site location, and the benthic organism.

With more data, a bioaccumulation factor measuring the weight of metal(s) per kg of

clam body mass can be attempted for the species studied from Morro Bay. Additional studies

recommended are to compare metal concentrations in the shell of the organism to the soft tissues

and sediments. A complete study would entail the collection and measurement of metals in the

water column, sediments, soft and hard tissues of the benthic organisms studied.

43

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