NOAA Technical Memorandum NMFS-NWFSC-83

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

An Overview of Sensory Effects 

on Juvenile Salmonids Exposed 

to Dissolved Copper:

Applying a Benchmark Concentration 

Approach to Evaluate Sublethal

Neurobehavioral Toxicity

October 2007
NOAA Technical Memorandum

NMFS-NWFSC Series

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may be cited in the scientific and technical literature.

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Reference throughout this document to trade names does 

not imply endorsement by the National Marine Fisheries 

Service, NOAA.

This document should be referenced as follows:

Hecht, S.A., D.H. Baldwin, C.A. Mebane, T. Hawkes, S.J. 

Gross, and N.L. Scholz. 2007. An overview of sensory 

effects on juvenile salmonids exposed to dissolved copper: 

Applying a benchmark concentration approach to evaluate 

sublethal neurobehavioral toxicity. U.S. Dept. Commer., 

NOAA Tech. Memo. NMFS-NWFSC-83, 39 p.
NOAA Technical Memorandum NMFS-NWFSC-83

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

An Overview of Sensory Effects 

on Juvenile Salmonids Exposed 

to Dissolved Copper:

Applying a Benchmark Concentration 

Approach to Evaluate Sublethal

Neurobehavioral Toxicity

Scott A. Hecht,

1

 David H. Baldwin, Christopher A. Mebane,

2

Tony Hawkes,

1

 Sean J. Gross,

3

 and Nathaniel L. Scholz

Northwest Fisheries Science Center

Ecotoxicology and Environmental Fish Health Program

2725 Montlake Boulevard East

Seattle, Washington 98112

National Marine Fisheries Service

Office of Protected Resources, Endangered Species Division

510 Desmond Drive Southeast

Lacey, Washington 98506

U.S. Geological Survey

NMFS Liaison

10095 West Emerald Street

Boise, Idaho 83704

National Marine Fisheries Service

Washington State Habitat Office

7600 Sand Point Way Northeast

Seattle, Washington 98115

October 2007

1

2

3
Most NOAA Technical Memorandums

NMFS-NWFSC are available online at the 

Northwest Fisheries Science Center

web site (http://www.nwfsc.noaa.gov)

Copies are also available from:

National Technical Information Service

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phone orders (1-800-553-6847)

e-mail orders (orders@ntis.fedworld.gov)

ii
Table of Contents 

List of Figures...............................................................................................................................................v

List of Tables ..............................................................................................................................................vii

Executive Summary .....................................................................................................................................ix

Acknowledgments........................................................................................................................................xi

Introduction...................................................................................................................................................1

Previous Studies on the Effects of Copper....................................................................................................3

Application of the Benchmark Concentration Analysis................................................................................9

Results of the Benchmark Concentration Analysis.....................................................................................11

Discussion of Site Specific Considerations for Sensory System Effects....................................................14

Impairment from Short-term Increases of dCu.......................................................................................14

Calculating an Acute Criterion Maximum Concentration......................................................................14

Salmonids Are Typically Exposed to Multiple Stressors.......................................................................15

Bioavailability of dCu ............................................................................................................................15

Olfactory Toxicity in Saltwater..............................................................................................................16

Avoiding Short-term Increases in dCu ...................................................................................................17

Coho Salmon–derived BMCs Should Apply to Other Salmonids..........................................................17

Conclusions.................................................................................................................................................18

Glossary ......................................................................................................................................................19

References...................................................................................................................................................21

Appendix A: Other Salmonid Sensory Effects of dCu ...............................................................................27

Migratory Disruption..............................................................................................................................27

Laboratory Avoidance Studies ...............................................................................................................28

Other Adverse Effects ............................................................................................................................31

Appendix B: Supplementary Bibliography.................................................................................................33

Copper Sources.......................................................................................................................................33

Benchmark Concentration/Dose.............................................................................................................33

Copper and Neurobiology ......................................................................................................................33

Reviews ..................................................................................................................................................35

Studies with Other Metals ......................................................................................................................36

Selected Behavioral Studies ...................................................................................................................37

Recovery of Olfactory Epithelium after Damage...................................................................................38

Additional Endpoints..............................................................................................................................38

iii
iv
List of Figures 

Figure 1. Recording methods and features of the salmon peripheral olfactory system. ..............................6

Figure 2. Copper-induced reductions in juvenile salmonid olfactory response and behavior are 

significantly correlated..................................................................................................................................8

Figure 3. Using a benchmark concentration approach to estimate a threshold for dCu toxicity in the 

salmonid olfactory system. .........................................................................................................................12

Figure A-1. Reduction in downstream migration of yearling coho salmon following 6-days exposure 

to copper at various concentrations.............................................................................................................29

v
vi
List of Tables 

Table 1. Selected examples of adverse effects with copper to salmonids or their prey...............................4 

Table 2. Benchmark responses and benchmark concentrations for juvenile salmon 

exposed to dCu for 3 hours. ........................................................................................................................13

vii
viii
Executive Summary 

Dissolved copper (dCu) is a ubiquitous surface water pollutant that causes a range of 

adverse effects in fish as well as in aquatic invertebrates and algae. This technical memorandum 

is a summary and targeted synthesis regarding sensory effects to juvenile salmonids from lowlevel exposures to dCu. As such, the material presented here serves to summarize scientific 

research on dCu and its impacts on salmonid sensory systems. In addition, this document 

provides a benchmark analysis of empirical data generated in recent National Marine Fisheries 

Service investigations that have focused on salmon olfactory function. The review section, 

Appendix A, discusses peer reviewed and gray literature on the effects of dCu on salmonid 

sensory systems, associated sensory-mediated behaviors, and physiology. It is intended to 

facilitate understanding of the effects of dCu on sensory system–mediated behaviors that are 

important to survival, reproduction, and distribution of salmonids. The review does not address 

the effects of dCu on salmonid habitats, although copper is also highly toxic at low μg/L 

concentrations to aquatic primary producers and invertebrates (i.e., the aquatic food web). 

Undoubtedly, new information will become available that enhances our current understanding of 

copper’s effect on threatened and endangered salmonids and their supporting habitats. 

A large body of scientific literature has shown that fish behaviors can be disrupted at 

concentrations of dCu that are at or slightly above ambient concentrations (i.e., background). In 

this document, background is operationally defined as surface waters with less than 3 μg/L dCu, 

as experimental water had background dCu concentrations as high as 3 μg/L dCu. Sensory 

system effects are generally among the more sensitive fish responses and underlie important 

behaviors involved in growth, reproduction, and (ultimately) survival (i.e., predator avoidance). 

Recent experiments on the sensory systems and corresponding behavior of juvenile salmonids 

contribute to more than four decades of research and show that dCu is a neurotoxicant that 

directly damages the sensory capabilities of salmonids at low concentrations. These effects can 

manifest over a period of minutes to hours and can persist for weeks. 

To estimate toxicological effect thresholds for dCu in surface waters, benchmark 

concentrations (BMCs) were calculated using a U.S. Environmental Protection Agency 

methodology. This paper presents examples of BMCs for juvenile salmonid olfactory function 

based on recent data. BMCs ranged 0.18–2.1 μg/L, corresponding to reductions in predator 

avoidance behavior of approximately 8–57%. The BMC examples represent the dCu 

concentration (above background) expected to affect the ability of juvenile salmonids to avoid 

predators in freshwater. These concentration thresholds for juvenile salmonid sensory and 

behavioral responses fall within the range of other sublethal endpoints affected by dCu such as 

behavior, growth, and primary production, which is 0.75–2.5 μg/L. 

The paper also discusses the influence of water chemistry on the bioavailability and 

toxicity of copper to fish sensory systems. Studies exploring behavioral avoidance as well as 

representative studies of other effects to salmonids are also summarized. Salmon may be able to 

ix
avoid dCu in environmental situations where distinct gradients occur. However, avoidance of 

dCu originating from nonpoint sources appears unlikely. Given the large body of literature on 

copper and responses of aquatic ecosystems, we focused on a subset of fish sensory system 

studies relevant to anadromous salmonids. 

Point and nonpoint source discharges from anthropogenic activities frequently exceed 

these thresholds by one, two, and sometimes three orders of magnitude, and can occur for hours 

to days. The U.S. Geological Survey ambient monitoring results for dCu representing 811 sites 

across the United States detected concentrations ranging 1–51 μg/L, with a median of 1.2 μg/L. 

Additionally, typical dCu concentrations originating from road runoff from a California study 

were 3.4–64.5 μg/L, with a mean of 15.8 μg/L. Taken together, the information reviewed and 

presented herein indicates that impairment of sensory functions important to survival of juvenile 

salmonids is likely to be widespread in many freshwater aquatic habitats. Impairment of these 

essential behaviors may manifest within minutes and continue for hours to days depending on 

concentration and exposure duration. Therefore, dCu has the potential to limit the productivity 

and intrinsic growth potential of wild salmon populations by reducing the survival and lifetime 

reproductive success of individual salmonids. 

x
Acknowledgments 

The authors thank Jim Meador, Lyndal Johnson, and Karen Peck for insightful and 

critical reviews of prior versions of this document. We also thank Jenifer McIntyre, Neil 

Rickard, and Scott Anderson for fruitful discussions and comments. 

xi
xii
Introduction 

Copper, a naturally occurring element, is an essential micronutrient for plants and 

animals. However, copper is also recognized as a priority pollutant under the U.S. Clean Water 

Act. Historical and current anthropogenic activities have mobilized significant quantities of 

copper. Vehicle emissions and brake pad dust (Drapper et al. 2000), pesticides (USEPA 2005), 

industrial processes, municipal discharges, mining, and rooftops (Good 1993, Thomas and 

Greene 1993) are a few of the sources of copper in the environment. These various human 

activities may lead to the unintended and, in some circumstances, intended introduction of 

copper into aquatic ecosytems (Sansalone and Buchberger 1997, Wheeler et al. 2005). Once in 

the aquatic environment, copper is detected in multiple forms. It can be dissolved, or bound to 

organic and inorganic materials either in suspension or in sediment. This so called speciation of 

copper is dependent on site specific abiotic and biotic factors. As an element, copper will persist 

and cycle through ecosystems. Copper in its dissolved state is worthy of particular scrutiny as it 

is highly toxic to a broad range of aquatic species including algae, macrophytes, aquatic 

invertebrates, and fishes. The latter include anadromous salmon and steelhead within the 

Oncorhynchus and Salmo genera that are, in part, managed by the National Marine Fisheries 

Service. 

Currently, anadromous salmonid populations inhabit waters of Alaska, Oregon, 

Washington, California, Idaho (Oncorhynchus spp.), and Maine (Atlantic salmon [Salmo salar]). 

Dissolved copper (referred to as dCu herein) is consistently detected in salmonid habitats 

including areas important for rearing, migrating, and spawning (Alpers et al. 2000, Soller et al. 

2005). Dissolved copper is known to affect a variety of biological endpoints in fish (e.g., 

survival, growth, behavior, osmoregulation, sensory function, and others, as reviewed in Eisler 

1998). More than three decades of experimental results have shown that the sensory systems of 

salmonids are particularly vulnerable to the neurotoxic effects of dCu. Recent experimental 

evidence showed that juvenile sensory system–mediated behaviors are also affected by shortterm exposures to dCu. 

Given the ecological significance of these behaviors to salmonids, it is important to 

characterize the potential effects from dCu. The growing body of scientific literature indicates 

that dCu is a potent neurotoxicant that directly damages the sensory capabilities of salmonids at 

low concentrations (see the Previous Studies on the Effects of Copper section). These 

concentrations may stem from anthropogenic inputs of dCu to salmonid habitats. Salmonid 

sensory systems mediate ecologically important behaviors involved in predator avoidance, 

migration, and reproduction. Impairment of these behaviors can limit an individual salmonid’s 

potential to complete its life cycle and thus may have adverse consequences at the scale of wild 

populations. 

The purpose of this paper is to: (1) summarize information on the effects of dCu to the 

sensory systems of juvenile salmonids in freshwater (also see Appendix A), (2) conduct a 
benchmark concentration analysis to generate examples of dCu effect thresholds, and (3) to 

discuss site-specific considerations for sensory system effects. As such, it focuses on a single 

contaminant (dCu), two relevant sensory system endpoints (olfaction and alarm response 

behavior), and a single salmonid life stage (juvenile, <10 months old). 

2
Previous Studies on the Effects of Copper 

Examples of copper’s effects on a suite of selected biological endpoints from laboratory 

and field exposures are presented in Table 1. Additionally, Appendix A contains a targeted 

review and summary of some of the previous studies showing copper’s effect on salmonid 

behavior, including avoidance and migratory disruptions. Appendix B is a supplementary 

bibliography that provides further information sources on salmonid sensory systems. The 

following analysis of sensory effects on juvenile salmonids primarily emphasizes recent and 

ongoing research conducted at the National Marine Fisheries Service’s Northwest Fisheries 

Science Center. However, the phenomenon that copper and some other trace metals can interfere 

with chemoreception, alter behaviors, and influence the movements of fish was first described at 

least 40 years ago, and a large body of knowledge on the adverse effects of dCu has subsequently 

developed (Table 1). 

The salmonid olfactory sensory system relies on olfactory receptor neurons (ciliated 

ORNs) to detect and respond to cues in the aquatic environment. The receptors are in direct 

contact with the aqueous environment. Olfactory receptors detect chemical cues that are 

important in finding food, avoiding predators, navigating migratory routes, recognizing kin, 

reproducing, and avoiding pollution. The architecture of the salmon olfactory system consists of 

a pair of olfactory rosettes, each positioned within an olfactory chamber near the midline of the 

fish’s rostrum (Figure 1A). Each rosette contains ORNs that respond to dissolved odorants as 

water passes through the olfactory chamber (Figure 1B) and over the surface of the rosette in 

which the receptor neurons are embedded (Figure 1C). These chemical cues convey important 

information about the surrounding aquatic environment. 

Direct exposure to dCu can impair and destroy olfactory sensory neurons, although the 

precise mechanism by which dCu interferes with the normal function of ORNs remains unknown 

(Hansen et al. 1999b, Baldwin et al. 2003, Sandahl et al. 2006, Sandahl et al. 2007). Impairment 

of olfaction (i.e., smell) can be measured by an electrophysiological technique called the 

electro-olfactogram (EOG) (Figure 1) (Scott and Scott-Johnson 2002, Baldwin and Scholz 2005, 

Sandahl et al. 2006). The EOG measures olfactory response of a population of receptor neurons 

in fish. Reductions in the EOG amplitude of copper-exposed fish compared to unexposed fish 

reflect functional losses in sensory capacity. Dissolved copper’s toxic effect to olfactory sensory 

neurons is observable as a reduction in or elimination of the EOG amplitude to a recognizable 

odor (Figure 1D). 

Several recent studies highlight some important aspects of copper olfactory toxicity 

(Baldwin et al. 2003, Sandahl et al. 2004, 2007). Baldwin et al. (2003) found that the neurotoxic 

effects of copper in coho salmon (Oncorhynchus kisutch) manifest over a timescale of minutes. 

At 10 minutes, EOG amplitude reductions were observed in juvenile coho exposed to 2, 5, 10, 

and 20 μg/L dCu above experimental background (3 μg/L). After 30 minutes at 2 μg/L dCu 

above experimental background, the EOG amplitude from juvenile coho to odors was reduced by 

approximately 25% compared to controls; in 20 μg/L dCu after 30 minutes by approximately 

3
80%. Sandahl et al. (2004) found similar effects following 7 days of exposure (both in EOG 

reductions and copper concentrations). This result indicated that the juvenile olfactory system 

does not appear to be able to adapt or otherwise compensate for continuous copper exposure for 

durations up to 7 days. 

Table 1. Selected examples of adverse effects with copper to salmonids or their prey.a

Species 

(lifestage) Effect 

Effect 

concentration (μg/L)b

Effect 

statistic 

Hardness 

(mg/L)c

Exposure 

duration Source 

Sensory and behavioral effects

Coho salmon 

(juvenile) 

Reduced olfaction and 

compromised alarm 

response 

0.18–2.1 EC10 to 

EC50

120 3 hours Sandahl et al. 

2007 

Chinook salmon 

(O. tshawytscha)

(juvenile) 

Avoidance in laboratory 

exposures 

0.75 LOEC 25 20 minutes Hansen et al. 

1999a 

Rainbow trout 

(O, mykiss) 

(juvenile) 

Avoidance in laboratory 

exposures 

1.6 LOEC 25 20 minutes Hansen et al. 

1999a 

Chinook salmon 

(juvenile) 

Loss of avoidance ability 2 LOEC 25 21 days Hansen et al. 

1999a 

Atlantic salmon 

(juvenile) 

Avoidance in laboratory 

exposures 

2.4 LOEC 20 20 minutes Sprague et al. 

1965 

Atlantic salmon 

(adult) 

Spawning migrations in 

the wild interrupted 

20 LOEC 20 Indefinite Sprague et al. 

1965 

Chinook salmon 

(adult) 

Spawning migrations in 

the wild apparently 

interrupted 

10–25 LOEC 40 Indefinite Mebane 2000 

Coho salmon Delays and reduced 

downstream migration of 

dCu-exposed juveniles 

5 LOEC 95 6 days Lorz and 

McPherson 1976, 

1977 

Rainbow trout Loss of homing ability 22 LOEC 63 40 weeks Saucier et al. 

1991 

Ecosystem effects 

NAd Ecosystem function: 

Reduced photosynthesis 

2.5 LOEC 49 ≈ 1 year Leland and Carter 

1985 

NAd Ecosystem structure: loss 

of invertebrate taxa 

richness in a mountain 

stream 

5 LOEC 49 ≈ 1 year Leland et al. 1989

Other sublethal effects 

Chinook salmon Reduced growth 

(as weight) 

1.9 EC10 25 120 days Chapman 1982 

Rainbow trout Reduced growth 

(as weight) 

2.8 EC10 25 120 days Marr et al. 1996 

4
Table 1 continued. Selected examples of adverse effects with copper to salmonids or their prey.a

Species 

(lifestage) Effect 

Effect 

concentration (μg/L)b

Effect 

statistic 

Hardness 

(mg/L)c

Exposure 

duration Source 

Other sublethal effects (cont.)

Coho salmon Reduced growth 

(as weight) 

21–22 NOEC 24–32 60 days Mudge et al. 1993

Steelhead 

(O. mykiss) 

Reduced growth 

(as weight) 

45 to >51 NOEC 24–32 60 days Mudge et al. 1993

Direct lethalitye

Chinook salmon 

(fry) 

Death 19 LC50 24 96 hours Chapman 1978 

Coho salmon 

(fry) 

Death 28–38 LC50 20–25 96 hours Lorz and 

McPherson 1976 

Steelhead/rainbow trout (fry) 

Death 9–17 LC50 24–25 96 hours Chapman 1978, 

Marr et al. 1999 

Coho salmon 

(adult) 

Death 46 LC50 20 96 hours Chapman and 

Stevens 1978 

Steelhead 

(adult) 

Death 57 LC50 42 96 hours Chapman and 

Stevens 1978 

Coho salmon 

(juvenile) 

Death 21–22 NOEC 24–32 60 days Mudge et al. 1993

Steelhead 

(juvenile) 

Death 24–28 NOEC 24–32 60 days Mudge et al. 1993

Steelhead 

(egg-to-fry) 

Death 11.9 EC10 25 120 days Chapman 1982 

a

 Abbreviations: LOEC = Lowest observed adverse effect concentration (and most LOEC values given are not 

thresholds, but were simply the lowest concentration tested); NOEC = No observed adverse effect concentration; 

LC50 = the concentration that kills 50% of the test population; ECp = effective concentration adversely affecting (p) 

percent of the test population or percent of measured response, e.g., 10% for an EC10, etc.; and Indefinite = field 

exposures without defined starting and ending times. NA = not applicable. 

b

 Effects and exposure durations stem from laboratory and field experiments, therefore in some experiments multiple 

routes of exposure may be present (i.e., aqueous and dietary) and water chemistry conditions will likely differ (see 

reference for details).

c

 Hardness is reported, as it can influence the toxicity of copper. 

d

 This study examined ecosystems consisting of a number of species or unidentified species. e

 Acute sensitivity of salmonids to copper probably varies by life stage, and the swim-up fry stage is probably more 

sensitive than older juvenile life stages such as parr and smolts or adults.

5
Figure 1. Recording methods and features of the salmon 

peripheral olfactory system. A) Photograph 

showing the rostrum of a coho salmon during the 

recording of electro-olfactograms (EOGs). The 

mouthpiece provides chilled, anaesthetized water 

to the gills, while the perfusion tube delivers odorcontaining solutions to the olfactory chamber. 

The recording electrode in the olfactory chamber 

and reference electrode in the skin monitor the 

response of the olfactory system to an odor. B) 

Scanning electron micrograph showing a rosette, 

located within an olfactory chamber of a juvenile 

coho salmon. Each rosette consists of lamellae 

(lobes) covered by an epithelium containing 

regions of sensory neurons. The open circle 

denotes the location and approximate size of the 

tip of the recording microelectrode. C) Scanning 

electron micrograph showing a cross section from 

a region of sensory epithelium of a lamella. In the 

upper left is the apical surface containing the cilia 

and microvilli of the olfactory receptor neurons 

(ORNs). The dendrites and somata of the ORNs 

appear in the center within the epithelium, while 

the axons of the ORNs emerge from the basal 

surface at the lower right to produce the olfactory 

nerve. D) Typical odor-evoked EOGs obtained 

from a salmon before and after exposure to 

copper. A 10-second switch to a solution 

containing 10-5 M L-serine is shown with a 

horizontal bar. The EOG evoked by the odor 

pulse consists of a negative deflection in the 

voltage. A 30-minute exposure to copper reduced 

the amplitude of the EOG evoked in the same fish 

by 57%. (Photos courtesy of Carla Stehr. Figure 

adapted from Baldwin and Scholz 2005). 

6
Recently, using EOG measurements in combination with a predator avoidance assay, 

Sandahl et al. (2007) presented the first evidence that impaired olfaction (smell) resulted in a 

direct suppression of predator avoidance behavior (alarm response) by juvenile coho salmon at 

environmentally relevant dCu exposures (≥2.0 μg/L; 3 hr exposure). Unexposed juveniles 

(control treatment) reduced their swimming speed on average by 74% (alarm response) in 

response to an alarm odor (conspecific skin extract). A reduction in swimming speed is a typical 

predator avoidance response for salmonids and many other fish. In unexposed fish, the alarm 

odor elicited a mean EOG response of 1.2 mV. Juvenile coho salmon exposed to 2-20 μg/L 

copper exhibited measurable reductions in both EOG (50–92%) and alarm response (47 to 

>100%) (derived from data in Figure 2 of Sandahl et al. 2007). Juvenile coho exhibited 

statistically significant decline in antipredator behavior at 5, 10, and 20 μg/L dCu (Figure 2). 

Importantly, concentrations of dCu below 2 μg/L were not tested in Sandahl et al. (2007). 

This is notable because all concentrations tested (between 2 and 20 μg/L) significantly affected 

olfaction with reductions in EOG ranging ≈50–92%. Because individual juvenile coho were 

significantly affected at the lowest concentration tested (2 μg/L), uncertainty remains with 

respect to the precise threshold for olfactory impairment. The results of this last study provide 

evidence that juvenile salmon exposed to sublethal dCu concentrations at 2 μg/L (resulting in 

approximately 50% reductions in EOG), and likely even lower, might not recognize and respond 

to a predation threat, and therefore have an increased risk of being eaten by other fishes or birds 

(a form of ecological death, Kruzynski and Birtwell 1994).

Typically dCu concentrations in road runoff are well within the range affecting 

antipredator behavior, for example, 3.4–64.5 μg/L, with a mean of 15.8 μg/L (Soller et al. 2005). 

A 3 hour exposure is also likely to be environmentally relevant, as stormwater runoff durations 

from roads typically range from a few minutes to several hours (Sansalone and Buchberger 

1997). Fish may regain their capacity to detect odors fairly quickly in some cases; physiological 

recovery of olfactory neuron function is dose-dependent and occurs within a few hours at low 

copper concentrations (i.e., <25 μg/L dCu, Baldwin et al. 2003). However, long-term damage to 

the sensory epithelia has also been documented. Where cell death occurs (i.e., ≥25 μg/l copper, 

Hansen et al. 1999a, 1999b) recovery is on the order of weeks (Moran et al. 1992) and in some 

cases months (Evans and Hara 1985). 

Interestingly, another fish sensory system, the lateral line, is also a target for the 

neurotoxic effects of dCu. It is composed of mechanosensory neurons (hair cells) that respond to 

surface water vibrations, flow, and other types of mechanical cues in the aquatic environment. 

The lateral line system thereby mediates shoaling, pursuit of prey, predator avoidance, and 

rheotaxis (orientation to flow). In a recent study, dCu (i.e., ≥20 μg/L; 3 hour exposure) killed 

20% of hair cells in zebrafish (Danio rerio) (Linbo et al. 2006). As mentioned earlier, juvenile 

salmon ORNs may also be killed at higher concentrations of dCu, highlighting the similar 

sensitivity of olfactory and lateral line receptors to this toxic metal. Consequently, dCu may 

damage or destroy either or both of these important sensory systems. Currently, we are not 

aware of any research on the effects of dCu to the lateral line of salmonids, although the 

comparable sensitivity of the olfactory system across species suggests that the salmon lateral line 

is likely to be vulnerable as well. 

7
Figure 2. Copper-induced reductions in juvenile salmonid olfactory response and behavior are 

significantly correlated. Fish exposed to dCu (3 hours) showed reduced olfactory sensitivity and 

corresponding reduction in predator avoidance behavior. Values represent treatment means (with 

copper exposure concentration labeled to the right); error bars represent one standard error; 

n = 8–12 individual coho salmon; asterisk (*) represents a statistically significant difference in 

olfactory response (EOG data) compared to controls (one-way ANOVA with Dunnett post hoc 

test, p < 0.05); †

represents statistically significant difference in behavioral response to skin extract 

(% reduction in swimming) compared to controls (one-way ANOVA with Dunnett post hoc test, 

p < 0.05). The line represents a statistically significant linear regression based on treatment 

means (n = 5; p < 0.0001; r2

 = 0.94). 1 ppb = 1 μg/l. (Adapted from Figure 2C in Sandahl et al. 

2007.) 

In this paper, a benchmark dose (concentration) analysis (USEPA 1995) is applied to 

recent data from dose-response experiments on juvenile salmonids exposed to dCu (Sandahl et 

al. 2007) to determine the exposure concentrations that may adversely affect salmonid sensory 

systems. In previous studies, benchmark concentrations (BMCs) were determined for olfactory 

responses, however, concomitant behavioral responses were not measured (Baldwin et al. 2003, 

Sandahl et al. 2004). The BMC analysis conducted herein determined concentrations of dCu that 

could be expected to affect juvenile salmonid olfaction and, by extension, alarm response 

behavior involved in predator avoidance. 

8
Application of the Benchmark 

Concentration Analysis 

The BMC, also referred to as a benchmark dose, is a method that has been used since 

1995 by agencies such as the U.S. Environmental Protection Agency (EPA) to determine no 

observable adverse effect level (NOAEL) values. The method statistically fits dose-response 

data to determine NOAEL values (EPA 1995). This is in contrast to other methods (e.g., using 

an analysis of variance) that rely on finding a no observable effect concentration (NOEC) and 

lowest observable effect concentration (LOEC) to establish the NOAEL. Multiple difficulties 

arising from the traditional approach of selecting a NOAEL from dose-response data were 

previously identified by the EPA. Specific shortcomings associated with traditional methods 

included: 1) arbitrary selection of a NOAEL based on scientific judgments; 2) experiments 

involving fewer animals produced higher NOAELs; 3) dose-response slopes were largely 

ignored; and 4) the NOAEL was limited to the doses tested experimentally (EPA 1995). These 

as well as other concerns with selection of a NOAEL led to the development of an alternative 

approach, the BMC analysis. The BMC approach uses the complete dose-response data set to 

identify a NOAEL, thereby selecting an exposure concentration that may not have been tested 

experimentally. 

The BMC is statistically defined as the lower confidence limit for a dose that produces a 

predetermined adverse effect relative to controls. This effect is referred to as the benchmark 

response (BMR) (EPA 1995). Unlike the traditional method of selecting the NOAEL (e.g., 

establishing a NOEC), the BMC takes into account the full range of dose-response data by fitting 

it with an appropriate regression equation. These can be linear, logarithmic, sigmoidal, etc. The 

BMR is generally set near the lower limit of responses (e.g., an effect concentration of 10%) that 

can be measured directly in exposed or affected animals. 

In the present context, a BMC approach was used to estimate thresholds for dCu’s 

sublethal effects on the chemosensory physiology and predator avoidance behaviors of juvenile 

coho salmon (Sandahl et al. 2007). An example of this approach is shown in Figure 3. This 

methodology has been used previously to determine toxicity thresholds in Pacific salmon 

(Sandahl and Jenkins 2002, Baldwin et al. 2003, Sandahl et al. 2004). The dose-response 

relationship for copper’s effect on the EOG was described by fitting the data with a sigmoid 

logistic model: 

y = m/[1+(x/k)n] 

where m is maximum EOG amplitude (fixed at the control mean of 1.2 mV), y is EOG 

amplitude, x is copper concentration, k is copper concentration at half-maximum EOG amplitude 

(EC50), and n is slope. 

9
For this nonlinear regression, the average olfactory response of the control fish to a 

natural odor was used to constrain the maximum odor evoked EOG (m in the above equation). 

Consequently, the control fish were not used in the regression other than to set m. The 

regression incorporated the individual response of each exposed fish (n = 44 total) rather than the 

average values for each exposure group. As shown in Figure 3, the sigmoid logistic model was a 

very good fit for both the sensory and behavioral data (r2 = 0.94, p < 0.0001). Benchmark 

concentrations were then determined based on the concentration at which the estimated curve 

intersected benchmark responses. 

10
Results of the Benchmark 

Concentration Analysis 

Examples of benchmark concentrations and responses are presented in Figure 3 and 

Table 2. The EPA methodology recommends using the concentration that represents a 10% 

reduction in response compared to controls when limited biological effects data are available 

(EPA 1995). This is the BMC10 and is synonymous with the concentration producing an effect of 

10% (EC10), in this case a 10% reduction in the recorded amplitude of the salmon’s 

chemosensory response (EOG). Since the predicted fish EOG response at the BMC10 falls well 

within the olfactory response of unexposed juveniles, that is, 95% CI (control fish, Figure 3), it is 

more than likely that this individual response (1.08 mV) at the BMC10 (0.18 μg/L) would not be 

detectable or biologically significant as an adverse response. 

Other BMCs were derived using statistical criteria to determine benchmark responses. 

For example, Table 2 shows two BMCs that were determined using the statistical departure of 

the lower-bound confidence interval (CI) of the control mean (unexposed fish), 1.2 mV (either 

the 90 or 95% CI). The selection of different CIs results in different BMCs. The CI-derived 

BMCs represent a reasonable estimate of when an individual salmonid is likely to have a 

biologically significant reduction in olfaction and a concomitant reduction in predator avoidance 

behavior. The relative departures from controls in Table 2 are equivalent to effective 

concentrations for olfactory inhibition, that is, at the lower-bound 90% CI a BMC of 0.59 μg/L 

equates to a BMC24.2. Put another way, the BMC analysis predicts a substantial 24.2 % 

reduction in olfaction (i.e., EOG amplitude) at 0.59 μg/L dCu. At the lower-bound 95% CI a 

29.2% reduction in olfaction is predicted to occur at 0.79 μg/L. 

The BMC50 is equivalent to the EC50 for olfactory responses (2.1 μg/L) and is very 

similar to the lowest observable effect concentration (LOEC) of 2 μg/L. Since the EC50

approximately equals the LOEC, it is almost certain that effects to juvenile salmonid olfaction 

will occur at lower concentrations than those measured. Therefore it is appropriate and useful to 

apply a BMC analysis to these data to predict effects occurring between 0 and 2 μg/L dCu. The 

predicted effect thresholds for sensory responses in juvenile coho salmon ranged 0.18–2.1 μg/L, 

which corresponded to reductions in predator avoidance behavior (i.e., reduced alarm response) 

of 8–57%. Comparatively, the other two studies that conducted a BMC approach with salmon 

olfaction data sets (e.g., EOG measures) estimated dCu BMCs of 3.6–10.7 μg/L (BMC20–

BMC50) (Sandahl et al. 2004) and 2.3–3.0 μg/L (BMC25) (Baldwin et al. 2003). 

Together these three studies highlight that different experimental conditions including 

age of fish, exposure duration, and experimental background of dCu may influence BMCs. 

Importantly, of the three experiments that derived BMCs for olfactory impairment, the data set 

used in this technical memorandum from Sandahl et al. (2007) empirically linked impaired 

olfaction to an ecologically relevant behavior, that is, reduced alarm behavior (Figure 2). 

11
Therefore, we believe that the dCu BMC analysis herein is derived from the most ecologically 

relevant of the three studies. 

Figure 3. Using a benchmark concentration approach to estimate a threshold for dCu toxicity in the 

salmonid olfactory system. Filled circles represent treatment means; error bars represent the 95% 

confidence interval for each mean (n = 8–12 individual coho salmon). An asterisk (*) indicates a 

statistically significant difference in the size of the olfactory response (EOG data) compared to 

controls (one-way ANOVA with Dunnett post hoc test, p < 0.05). The line represents a 

statistically significant nonlinear regression based on individual fish (n = 44, p < 0.0001, 

r

2

 = 0.55). The gray shading shows the 95% confidence band for the nonlinear regression. The 

regression used a standard sigmoid function with the maximum constrained to the control mean 

(1.2 mV, indicated by the upper horizontal dashed line). Therefore, the control fish were not 

included in the nonlinear regression. The lower bound of the 95% confidence interval of the 

control mean (0.85 mV) is indicated by the lower horizontal dashed line and is an example of a 

BMR. The large open circle shows where the regression line crosses the BMR and denotes the 

corresponding BMC, which in this case is a dCu concentration of 0.79 μg/L. Horizontal and 

vertical lines through the open circle highlight the 95% confidence intervals for the BMC based 

on the results of the nonlinear regression. The small open circle shows where the regression line 

crosses the BMR (1.08 mV) and denotes the corresponding BMC10 (0.18 μg/L) at which a 10% 

reduction in olfactory capacity is expected. (Data from Sandahl et al. 2007.) 

12
Table 2. Benchmark responses and benchmark concentrations for juvenile salmon exposed to dCu for 

3 hours. Benchmark response values represent a reduction in olfactory response to an alarm 

pheromone as measured via EOG recordings. Behavioral impairment indicates a predicted 

decrease in predator recognition and avoidance as indicated by a reduced alarm response. CI = 

confidence interval; NA = not applicable. 

Benchmark responsesa

Benchmark 

concentrationsb

Behavioral impairment 

(predicted)c

Departure from mean of controls 

Departure from mean 

of controls 

Statisticald 

(CI of control 

mean) 

Relativee

(% reduction in 

olfactory response) 

Valuef

(μg/l) 

95% CIg

(μg/l) 

Relativeh

(% reduction in alarm 

response) 

NA 10.0 0.18 0.06–0.52 8.3 

Lower 90% 24.2 0.59 0.30–1.16 25.6 

Lower 95% 29.2 0.79 0.44–1.42 31.8 

NA 50.0 2.10 1.60–2.90 57.2 

a

 The predetermined level of altered response or risk at which the benchmark dose (concentration) is calculated 

(EPA/630/R-94/007, 02/1995). 

b

 The dose (concentration) producing a predetermined, altered response for an effect (EPA/630/R-94/007; 02/1995). 

c

 Based on the linear regression shown in Figure 2; note behavioral responses were determined by inputting the 

Benchmark response value (EOG, mV) into the regression equation. 

d

 Location of the value with respect to a confidence interval of the mean of the controls. 

e

 Amount of reduction in the olfactory response represented by the value relative to the mean of the controls. 

f

 Corresponding concentration; see Figure 3 and text for calculation method. 

g Confidence interval for the value based on the nonlinear regression. h

 Amount of reduction in alarm response represented by the value relative to the mean of the controls. 

13
Discussion of Site Specific Considerations 

for Sensory System Effects 

Below we identify several issues to consider when using the BMCs to evaluate dCu 

concentrations under natural conditions. 

Impairment from Short-term Increases of dCu 

These BMCs reflect expected impairment of chemosensory systems from short-term 

increases of dCu above ambient concentrations (defined here as < 3 μg/L) (Baldwin et al. 2003, 

Sandahl et al. 2004, 2007) and are not expected to be alleviated by homeostatic mechanisms. 

Specifically, the BMCs are predicated on increases of dCu in salmon habitats that result from 

specific human activities. Effects to juvenile salmonid olfaction are expected following a few 

minutes of exposure. Salmonids are capable of regulating the amount of internal copper via 

uptake and elimination processes. These so called homeostatic mechanisms (such as 

metallothionein induction) can reduce copper’s toxic effects and may result in acclimation. 

Consequently, fish may tolerate certain dCu exposures without showing overt toxicological 

responses; however, at higher levels these mechanisms could ultimately fail. 

Initial evidence indicates that homeostatic mechanisms are not likely to reduce copper 

toxicity to the olfactory sensory system for pulsed or short-term exposures lasting less than a 

week (Hansen et al. 1999a) or for chronically exposed fish (McPherson et al. 2004). Moreover, 

lateral line neurons exposed continuously to dCu for 72 hours showed no signs of acclimation 

within this exposure interval (Linbo et al. 2006). For other measures of copper toxicity from 

long-term exposures, evidence suggests that olfactory acclimation may not occur (Table 1, 

Appendix A). Fish exposed to higher dCu concentrations for longer periods may lose much of 

their olfactory function. For example, field evidence suggests that wild fish living in heavy 

metal contaminated lakes where total copper concentrations ranged 9.7–15 μg/L showed reduced 

olfactory-mediated predator avoidance behavior; that is, homeostatic mechanisms appeared 

insufficient to alleviate metal toxicity, including copper (McPherson et al. 2004). 

Calculating an Acute Criterion Maximum Concentration 

The EPA sets acute water quality criteria by calculating an acute criterion maximum 

concentration (CMC) (Stephan et al. 1985). The CMC is an estimate of the highest 

concentration of a substance in surface water to which an aquatic community can be exposed 

briefly without resulting in an unacceptable effect (EPA 2002).We calculated an acute CMC 

using the Biotic Ligand Model (BLM) (EPA 2007). Interestingly, the estimated acute CMC 

based on the BLM using measured and estimated water quality parameters from Sandahl et. al. 

(2007) was 0.63 μg/L with a range from 0.34 to 3.2 μg/L, while the EPA hardness-based acute 

CMC (EPA 2002) was 6.7 μg/L. Because the BLM-based acute criterion is sensitive to pH and 

14
DOC, the range of measured test pH values (6.5–7.1) and the range of estimated DOC values 

(0.3–1.5 mg/L) produced this range of BLM-based acute criterion values. It is also interesting 

that the acute CMC range (0.34–3.2 μg/L) overlapped with the olfactory-based BMC range 

(0.18–2.1 μg/L). 

Salmonids Are Typically Exposed to Multiple Stressors 

These BMCs are specifically focused on the impact of dissolved copper alone on 

olfaction and predator avoidance behavior. Salmonids are rarely exposed to dCu only under 

natural conditions. In fact, exposure to complex environmental mixtures of other toxic 

compounds (e.g., metals, pesticides, PAHs, etc.) in conjunction with other stressors (e.g., 

elevated temperatures, low dissolved oxygen, etc.,) is the norm for many salmonid-bearing 

habitats. Equally important are exposure routes other than the water column, such as 

consumption of contaminated prey items (dietary) or direct contact with contaminated sediments. 

Threshold examples (BMCs) presented here are based solely on juvenile salmonids exposed to 

dCu. Presently, these thresholds do not take into account multiple routes of exposure or the 

potential impacts of complex mixtures of contaminants on olfaction. That said, several studies 

have shown a greater than expected toxicity (i.e., nonadditive) to other fish endpoints from 

mixtures of metals (Sprague et al. 1965, Norwood et al. 2003). For example, mixtures 

containing zinc and copper were found to have greater than additive toxicity to a wide variety of 

aquatic organisms including freshwater fish (Eisler 1998). Other metal mixtures also yielded 

greater than additive toxic effects at low dissolved concentrations (Playle 2004). The toxic 

effects of metals to salmonids may also be exacerbated by other types of contaminants such as 

pesticides (Forget et al. 1999). While interactions among multiple stressors, including 

contaminant mixtures, are beyond the scope of this document, they warrant careful consideration 

in site-specific assessments. 

Bioavailability of dCu 

These BMCs were derived from experiments using a single freshwater source 

(dechlorinated, soft municipal water). Hardness, alkalinity, and dissolved organic carbon (DOC) 

are known to alter the bioavailability of dissolved copper in surface waters to ligands in the fish 

gill. These water chemistry parameters can therefore influence the potential for dCu exposure in 

the field to cause an acute fish kill. Acute copper lethality mediated via the gill route of 

exposure is typically estimated using the Biotic Ligand Model (BLM; reviewed by Niyogi and 

Wood 2004). However, recent unpublished research by McIntyre et al. (in press) suggest that 

these parameters may have less of an influence on salmonid olfactory function across 

environmentally realistic ranges of hardness, alkalinity, and DOC. 

To date, the U.S. Geological Survey (USGS) has monitored hardness, alkalinity, and 

DOC for more than 10 years in many West Coast river basins including the Willamette River 

basin, Puget Sound basin, Yakima River basin, and the Sacramento-San Joaquin River basin 

(USGS no date). Several at-risk species of anadromous salmonids inhabit these basins. The 

monitoring data indicate that surface waters within these basins typically have very low hardness 

and alkalinity and seasonally affected DOC concentrations. Hardness, alkalinity, and DOC 

levels found in most freshwater habitats occupied by Pacific salmonids would be unlikely to 

15
confer substantial protection against dCu olfactory toxicity (Winberg et al. 1992, Bjerselius et al. 

1993, Baldwin et al. 2003, McIntyre et al. in press). 

Recent experimental results suggest that significant amelioration of olfactory toxicity due 

to hardness is unlikely in typical Pacific salmonid freshwater habitats. The experiment showed 

that hardness at 20, 120, and 240 mg/L Ca (experimentally introduced as CaCl2) did not 

significantly protect juvenile coho salmon from olfactory toxicity following 30 minute laboratory 

exposures to 10 μg dCu/L above an experimental background of 3 μg/L (Baldwin et al. 2003). 

In another experiment, a 20 μg dCu/L exposure (30 minutes) in water with low hardness and 

alkalinity and no DOC produced an 82% inhibition in juvenile coho olfactory function (McIntyre 

et al. in press). A hardness of ≥82 mg/L Ca was needed to reduce the level of olfactory 

inhibition to ≤50% at 20 μg/L dCu ( McIntyre et al. in press). However, 82 mg/L was never 

exceeded in any of the surface water samples from USGS-sampled NAWQA basins (McIntyre et 

al. in press). 

Typical alkalinity values from Pacific Northwest and California freshwater surface waters 

are also unlikely to protect salmonids from olfactory toxicity (USGS no date). Some reduction 

in dCu olfactory toxicity was observed in a recent study (McIntyre et al. in press). However, 

only 0.4% of stream samples contained alkalinity levels sufficient to reduce olfactory toxicity of 

dCu by half (McIntyre et al. in press). Bjerselius et al. (1993) and Winberg et al. (1992) also 

found that hardness and alkalinity provided limited amelioration of olfactory responses in 

juvenile Atlantic salmon exposed to dCu. 

Increases in DOC showed greater protection to dCu compared to increases in alkalinity 

and hardness. Twenty-nine percent of USGS surface water samples from West Coast basins had 

a DOC concentration sufficient to limit olfactory impairment to 50% or less at 20 μg dCu /L 

(McIntyre et al. in press). Only a small fraction (6%) of all samples contained DOC levels 

(greater or equal to 6 mg/L) sufficient to completely protect the olfactory responses of juvenile 

coho salmon from the toxic effect of 20 μg dCu /L (McIntyre et al. in press). This information 

underscores the importance of evaluating site-specific DOC data to address the potential 

influence of this water quality parameter on olfactory toxicity. 

Because the typical range of hardness, alkalinity, and DOC concentrations are unlikely to 

confer substantial protection against dCu toxicity, we expect that the BMC thresholds presented 

in this document will be applicable for most of the freshwater environments that provide 

migrating, spawning, and rearing habitats for salmonids. 

Olfactory Toxicity in Saltwater 

Dissolved copper’s effect on salmonid olfaction in saltwater environments remains a 

recognized data gap and it is presently uncertain whether the BMC thresholds derived in this 

document apply to salt water environments. Estuarine and nearshore salt water environments, 

despite their higher salinity (in part due to increased cation concentrations) and hardness may or 

may not confer protection against dCu-induced olfactory toxicity. One source of this uncertainty 

is whether or not free copper (Cu2+) is the sole species of copper responsible for olfactory 

toxicity. In freshwater, evidence suggests that Cu2+ is not the only toxic species that adversely 

affects olfaction in fish (McIntyre et al. in press) as well as more conventional endpoints such as 

16
mortality (Niyogi and Wood 2004). Other copper species (e.g., CuOH; Cu1+) will also bind to 

the gill, thereby causing toxicity (Niyogi and Wood 2004). While the physiological basis for 

salmonid olfaction is well characterized, the transition to saltwater may involve important 

changes in olfactory receptor neuron function that ultimately influence the expression of the as 

yet unidentified ligands for dCu. 

Avoiding Short-term Increases in dCu 

Salmonids may or may not avoid short-term increases in dCu. Salmonids will actively 

avoid water containing dCu if they can detect it. As a consequence, fish may not use otherwise 

high quality rearing and spawning habitats. In addition, the presence of dCu may affect 

migratory routes of juveniles and adults. Smith and Bailey (1990) and Mebane (2000) derived 

regulatory “zones of passage” around wastewater discharges that were based on salmonid 

avoidance responses. However, in areas with diffuse, nonpoint source pollution, or multiple 

point source discharges, it may be difficult to apply “zones of passage”, and in some cases 

available zones of passage may not exist. Despite a fish’s preference to avoid dCu, 

circumstances may force migrating juveniles and adults to be exposed. For dCu contaminated, 

high quality rearing habitats, juveniles could either remain and be exposed or move to lower 

quality habitats. Juveniles could therefore suffer either reduced predator avoidance or reduced 

growth. For contaminated spawning habitats, adult salmon may either remain and be exposed as 

well as their offspring or move to lower quality habitats. Both of these scenarios result in 

potential reductions in reproductive success. 

Coho Salmon–derived BMCs Should Apply to Other Salmonids 

These BMCs were derived using data from juvenile coho salmon, but should apply to 

other fish species. The examples of BMC thresholds were derived from data based on juvenile 

coho salmon (4–5 month old, mean of 0.9 grams wet weight). However, we expect these BMC 

examples to be generally applicable to other species of salmon, trout, and steelhead in freshwater 

habitats. For example, 3 hour exposures of 4-month-old steelhead to a similar range of dCu 

produced comparable olfactory toxicity to that reported for 4-month-old coho salmon (Baldwin 

et al. in prep.). Studies on 10-month-old juvenile coho had similar reductions in olfaction 

compared to 4-month-old fish (Baldwin et al. 2003, Sandahl et al. 2004). Juvenile chum salmon 

(O. keta) (2–3 month old) also showed a dose dependent reduction in EOG amplitude following 

exposure to dCu (3–58 μg/L) (Sandahl et al. 2006). Taken together these findings suggest that 

the BMC threshold derived herein should be applicable to juvenile life stages of coho, Chinook, 

sockeye (O. nerka), and pink salmon (O. gorbuscha) as well as steelhead, bull trout (Salvelinus 

confluentus), and other members of the family Salmonidae. As noted earlier, the toxicity of dCu 

to other life stages (particularly marine phases of life) remains to be determined. 

17
Conclusions 

Dissolved copper (dCu) is a ubiquitous, bioavailable pollutant that can directly interfere 

with fish sensory systems and by extension important behaviors that underlie predator avoidance, 

juvenile growth, and migratory success (see Appendix A). Recent research shows that dCu not 

only impairs sensory neurons in a salmonid’s nose, but also impairs juvenile salmonids’ ability 

to detect and respond to predation cues. A juvenile salmonid with disrupted predator avoidance 

behaviors stands a greater risk of mortality and by extension a reduction in the likelihood of 

surviving to reproduce. The degree to which effects on individual behavior and survival impact 

a given population will depend in part on the number of the individuals affected and the status of 

the population (numbers, distribution, growth rate, etc.). 

In this report, BMCs were calculated using an EPA methodology to provide examples of 

effect thresholds of dCu’s impacts on salmonid sensory biology and behavior. The BMC 

examples represent increases in the dCu concentration above background or ambient levels 

(where background is less than or equal to 3 μg/L) expected to affect juvenile salmonid ability to 

avoid predators in fresh water. Benchmark concentrations ranged 0.18–2.1 μg/L, corresponding 

to reductions in predator avoidance behavior (alarm reaction) that ranged approximately 8–57%. 

Taking into account the olfactory responses of unexposed fish, a more biologically relevant 

range of BMCs is 0.59–2.1 μg/L (Table 2). This second range of BMC thresholds is similar to or 

slightly less than documented effects to other copper-affected sublethal endpoints such as 

behavior and growth that range 0.75–2.5 μg/L (see Table 1). 

The primary objective of this report was to present examples of threshold concentrations 

for effects of dCu on a critical aspect of salmonid biology: olfaction. A secondary objective of 

this paper was to summarize a selection of recent and historical information related to the effects 

of dCu on salmonid sensory systems. This document is based on the current state of the science. 

Importantly, this overview is not a comprehensive summary of the myriad effects of copper to 

anadromous salmonids. As such, new information will undoubtedly become available that 

enhances our understanding of copper’s effect on salmonid populations and their supporting 

habitats. The information reviewed and presented herein indicates that significant impairment of 

sensory functions important to survival of threatened and endangered juvenile salmonids is likely 

to be widespread in many freshwater aquatic habitats. Impairment of these essential behaviors 

may occur following 10 minutes of exposure and continue for hours to weeks depending on 

concentration and duration. 

18
Glossary 

Acute exposure. Short-term continuous exposure usually lasting 96 hours or less. 

BLM. Biotic Ligand Model 

Chronic exposure. Longer-term continuous or pulsed exposures generally lasting greater than 

96 hours. 

Confidence interval (CI). A random interval constructed from data in such a way that the 

probability that the interval contains the true value can be specified before the data are 

collected. 

dCu. dissolved copper. 

DOC. dissolved organic carbon. 

ECp. Effective concentration adversely affecting (p) percent of the test population or percent of 

measured response, for example, 10% for an EC10 and so forth. 

EOG. electro-olfactogram. 

LC50. The aqueous concentration of a substance that kills 50% of the test population. 

Lower-bound 90% confidence interval. The lower half of the 90% confidence interval of the 

mean. 

Lower-bound 95% confidence interval. The lower half of the 95% confidence interval of the 

mean. 

LOEC. lowest observable effect concentration. 

Mean. The average of the response values in a treatment population. Numerically the mean 

represents the sum of the individual response values divided by the number of individuals in 

a treatment. 

mV. millivolts. 

NOAEL. no observable adverse effect level. 

NOEC. no observable effect concentration. 

ORN. olfactory receptor neuron. 

ppb. part(s) per billion, equivalent to μg/L. 

19
Relative departure from control response. A user selected level of response compared to 

control response; for example, a 10% reduction from the control response (unexposed 

individuals). 

Statistical departure from control response. Uses statistical methods to select a response 

based on the distribution of responses seen in unexposed individuals. For example, the 95% 

lower bound confidence interval of the mean response from controls (unexposed individuals). 

20
References 

Alpers, C. N., R. C. Antweiler, H. E. Taylor, P. D. Dileanis, and J. L. Domagalski. 2000. Metals 

transport in the Sacramento River, California, 1996–1997, Volume 2: Interpretation of metal 

loads. U.S. Geological Survey water resources investigation report 2000–4002. 

Baldwin, D. H., J. F. Sandahl, J. S. Labenia, and N. L. Scholz. 2003. Sublethal effects of copper on coho 

salmon: Impacts on nonoverlapping receptor pathways in the peripheral olfactory nervous system. 

Environ. Toxicol. Chem. 22:2266–2274. 

Baldwin, D. H., and N. L. Scholz. 2005. The electro-olfactogram: An in vivo measure of peripheral 

olfactory function and sublethal neurotoxicity in fish. In G. K. Ostrander (ed.), Techniques in 

aquatic toxicology, Volume 2, p. 257–276. CRC Press, Inc., Boca Raton, FL. 

Baldwin, D.H., C. Tatara, and N.L. Scholz. In prep. Olfactory sensitivity and copper toxicity in 

steelhead salmon raised in natural and hatchery environments. (Available from D. Baldwin, 

NWFSC, 2725 Montlake Blvd. E., Seattle, WA 98112.) 

Bjerselius, R., S. Winberg, Y. Winberg, and K. Zeipel. 1993. Ca2+ protects olfactory receptor function 

against acute Cu(II) toxicity in Atlantic salmon. Aquat. Toxicol. 25:125–138. 

Chapman, G. A. 1978. Toxicities of cadmium, copper, and zinc to four juvenile stages of Chinook 

salmon and steelhead. Trans. Am. Fish. Soc. 107:841–847. 

Chapman, G. A. 1982. Chinook salmon early life stage tests with cadmium, copper, and zinc. Letter of 

December 6, 1982 to Charles Stephan, EPA Environmental Research Laboratory, Duluth. 

Environmental Protection Agency, Corvallis, Oregon. Online at http://www.epa.gov/ow/ 

docket.html [accessed 27 September 2007]. 

Chapman, G. A. Unpubl. data. Acclimation, life stage differences in lethality and behavioral effects of 

chronic copper exposures with steelhead. Letter of July 5, 1994 to Chris Mebane, NOAA liaison 

to EPA Region 10, Seattle, WA. (Available from EPA Coastal Ecosystems Team, Newport, OR.) 

Chapman, G. A., and D. G. Stevens. 1978. Acutely lethal levels of cadmium, copper, and zinc to adult 

male coho salmon and steelhead. Trans. Am. Fish. Soc. 107:837–840. 

Damkaer, D. M., and D. B. Dey. 1989. Evidence of fluoride effects on salmon passage at John Day 

Dam, Columbia River, 1982–1986. N. Am. J. Fish. Manag. 9:154–168. 

Drapper, D., R. Tomlinson, and P. Williams. 2000. Pollutant concentrations in road runoff: Southeast 

Queensland case study. J. Environ. Eng.-ASCE 126:313–320. 

Eisler, R. 1998. Copper hazards to fish, wildlife, and invertebrates: A synoptic review. U.S. Geological 

Survey, Biological Resources Division, Biological science report USGS/BRD/BSR-1997-0002. 

EPA (U.S. Environmental Protection Agency). 1995. The use of the benchmark dose approach in health 

risk assessment. EPA/630/R-694/007. Office of Research and Development, Washington, DC. 

EPA (U.S. Environmental Protection Agency). 2002. National recommended water quality criteria. 

EPA-822-R-02-047. Environmental Protection Agency, Washington, DC. 

21
EPA (U.S. Environmental Protection Agency). 2005. Ecological risk assessment for re-registration 

copper-containing pesticides (Case#0636 copper sulfate, Case#0649 Group II copper compounds, 

Case#4029 copper salts, and Case#4025 copper and oxides (Cuprous oxide)). Screening level 

risk assessment. Environmental Protection Agency, Office of Pesticide Programs, Washington, 

DC. 

EPA (U.S. Environmental Protection Agency). 2007. Aquatic life ambient freshwater quality criteria - 

copper, 2007 revision. EPA-822-R-07-001. Environmental Protection Agency, Office of Water, 

Office of Science and Technology, Washington, DC. 

Evans, R. E., and T. J. Hara. 1985. The characteristics of the electro-olfactogram (EOG): Its loss and 

recovery following olfactory nerve section in rainbow trout (Salmo gairdneri). Brain Res. 

330:65–75. 

Farag, A. M., C. J. Boese, D. F. Woodward, and H. L. Bergman. 1994. Physiological changes and tissue 

metal accumulations of rainbow trout exposed to foodborne and waterborne metals. Environ. 

Toxicol. Chem. 13:2021–2030. 

Farag, A. M., D. Skaar, D. A. Nimick, E. MacConnell, and C. Hogstrand. 2003. Characterizing aquatic 

health using salmonid mortality, physiology, and biomass estimates in streams with elevated 

concentrations of arsenic, cadmium, copper, lead, and zinc in the Boulder River watershed, 

Montana. Trans. Am. Fish. Soc. 132:450–467. 

Folmar, L. C. 1976. Overt avoidance reaction of rainbow trout fry to nine herbicides. Bull. Environ. 

Contam. Toxicol. 15:509–514. 

Forget, J., J. Pavillon, B. Beliaeff, and G. Bocquene. 1999. Joint action of pollutant combinations 

(Pesticides and metals) on survival (LC50 values) and acetylcholinesterase activity of Tigriopus 

Brevicornis (Coperpoda, Harpacticoida). Environ. Toxicol. Chem. 18:912–918. 

Giattina, J. D., R. R. Garton, and D. G. Stevens. 1982. The avoidance of copper and nickel by rainbow 

trout as monitored by a computer-based aquisition system. Trans. Am. Fish. Soc. 111:491–504. 

Good, J. C. 1993. Roof runoff as a diffuse source of metals and aquatic toxicity in storm water. Water 

Sci. Technol. 28:317–321. 

Hansen, J. A., J. C. A. Marr, J. Lipton, D. Cacela, and H. L. Bergman. 1999a. Differences in 

neurobehavioral responses of Chinook salmon (Oncorhynchus tshawytscha) and rainbow trout 

(Oncorhynchus mykiss) exposed to copper and cobalt: Behavioral avoidance. Environ. Toxicol. 

Chem. 18:1972–1978. 

Hansen, J. A., J. D. Rose, R. A. Jenkins, K. G. Gerow, and H. L. Bergman. 1999b. Chinook salmon 

(Oncorhynchus tshawytscha) and rainbow trout (Oncorhynchus mykiss) exposed to copper: 

Neurophysiological and histological effects on the olfactory system. Environ. Toxicol. Chem. 

18:1979–1991. 

Hartwell, S. I., D. S. Cherry, and J. J. Cairns. 1987. Field validation of avoidance of elevated metals by 

fathead minnows (Pimephales promelas) following in situ acclimation. Environ. Toxicol. Chem. 

6:189–200. 

Korver, R. M., and J. B. Sprague. 1989. Zinc avoidance by fathead minnows: Computerized tracking 

and greater ecological significance. Can. J. Fish. Aquat. Sci. 46:494–502. 

22
Kruzynski, G. M., and I. K. Birtwell. 1994. A predation bioassay to quantify the ecological significance 

of sublethal responses of juvenile Chinook salmon (Oncoryhynchus tshawytscha) to the 

antisapstain fungicide TCMTB. Can. J. Fish. Aquat. Sci. 51:1780–1790. 

Leland, H. V., and J. L. Carter. 1985. Effects of copper on production of periphyton, nitrogen-fixation 

and processing of leaf litter in a Sierra-Nevada, California, stream. Freshw. Biol. 15:155–173. 

Leland, H. V., S. V. Fend, T. L. Dudley, and J. L. Carter. 1989. Effects of copper on species 

composition of benthic insects in a Sierra-Nevada, California, stream. Freshw. Biol. 21:163–179. 

Linbo, A. O., C. M. Stehr, J. P. Incardona, and N. L. Scholz. 2006. Dissolved copper triggers cell death 

in the peripheral mechanosensory system of larval fish. Environ. Toxicol. Chem. 25:597–603. 

Lorz, H. W., and B. P. McPherson. 1976. Effects of copper or zinc in freshwater on the adaptation to sea 

water and ATPase activity, and the effects of copper on migratory disposition of the coho salmon 

(Oncorhynchus kisutch). J. Fish. Res. Board Can. 33:2023–2030. 

Lorz, H. W., and B. P. McPherson. 1977. Effects of copper and zinc on smoltification of coho salmon. 

EPA 600/3-77-032. Oregon Department of Fish and Wildlife and U.S. EPA Environmental 

Research Laboratory, Corvallis, OR. 

Lorz, H. W., R. H. Williams, and C. A. Futish. 1978. Effects of several metals on smolting of coho 

salmon. EPA 600/3-78-090. Oregon Department of Fish and Wildlife and U.S. EPA 

Environmental Research Laboratory, Corvallis, OR. 

Marr, J. C. A., J. Lipton, D. Cacela, M. G. Barron, D. J. Beltman, C. Cors, K. LeJune, A. S. Maest, T. L. 

Podrabsky, H. L. Bergman, J. A. Hansen, J. S. Meyer, and R. K. MacRae. 1995. Fisheries 

toxicity injury studies, Blackbird Mine site, Idaho. Contract 50-DGNC-1-00007, task order 

50084. Prepared by RCG/Hagler Bailly and the University of Wyoming for NOAA, Boulder, 

CO, and Laramie, WY. 

Marr, J. C. A., J. Lipton, D. Cacela, J. A. Hansen, H. L. Bergman, J. S. Meyer, and C. Hogstrand. 1996. 

Relationship between copper exposure duration, tissue copper concentration, and rainbow trout 

growth. Aquat. Toxicol. 36:17–30. 

Marr, J. C. A., J. Lipton, D. Cacela, J. A. Hansen, J. S. Meyer, and H. L. Bergman. 1999. Bioavailability 

and acute toxicity of copper to rainbow trout (Oncorhynchus mykiss) in the presence of organic 

acids simulating natural dissolved organic carbon. Can. J. Fish. Aquat. Sci. 56:1471–1483. 

McIntyre, J. K., D. H. Baldwin, J. P. Meador, and N. L. Scholz. In press. Chemosensory deprivation in 

juvenile coho salmon exposed to dissolved copper under varying water chemistry conditions. 

Environ. Sci. Technol. 

McKim, J. M. 1985. Early life stage toxicity tests. In G. M. Rand and S. R. Petrocelli (eds.), 

Fundamentals of aquatic toxicology: Methods and applications, p. 58–95. Hemisphere 

Publishing, New York. 

McKim, J. M., and D. A. Benoit. 1971. Effects of long-term exposure to copper on survival, growth, and 

reproduction of brook trout (Salvelinus fontinalis). J. Fish. Res. Board Can. 28:655–662. 

McPherson, T. D., R. S. Mirza, and G. G. Pyle. 2004. Responses of wild fishes to alarm chemicals in 

pristine and metal-contaminated lakes. Can. J. Zool. 82:604–700. 

Mebane, C. A. 1994. Blackbird Mine preliminary natural resource survey. NOAA, Hazardous Material 

Assessment and Response Division, Seattle, WA. 

23
Mebane, C. A. 2000. Evaluation of proposed new point source discharges to a special resource water and 

mixing zone determinations: Thompson Creek Mine, upper Salmon River subbasin, Idaho. Idaho 

Department of Environmental Quality, Boise, ID. 

Meyer, J. S. 2005. Toxicity of dietborne metals to aquatic organisms. Society of Environmental 

Toxicology and Chemistry, Pensacola, FL. 

Moran, D. T., J. C. Rowley, G. R. Aiken, and B. W. Jafek. 1992. Ultrastructural neurobiology of the 

olfactory mucosa of the brown trout, Salmo trutta. Microscopy Res. Tech. 23:28–48 

Mudge, J. E., T.E. Northstrom, G.S. Jeane, W. Davis, and J. L. Hickam. 1993. Effect of varying 

environmental conditions on the toxicity of copper to salmon. In J. W. Gorsuch, F. J. Dwyer, C. 

G. Ingersoll, and T. W. La Point, (eds.), Environmental toxicology and risk assessment, ASTM 

STP 1216, p. 19–33. American Society for Testing and Materials, Philadelphia, PA. 

Niyogi, S., and C. M. Wood. 2004. Biotic ligand model, a flexible tool for developing site-specific water 

quality guidelines for metal. Environ. Sci. Technol. 38:6177–6192. 

Norwood, W. P., U. Borgmann, D. G. Dixon, and A. Wallace. 2003. Effects of metal mixtures on 

aquatic biota: A review of observations and methods. Hum. Ecol. Risk Assess. 9:795–811. 

Playle, R. C. 2004. Using multiple metal-gill binding models and the toxic unit concept to help reconcile 

multiple-metal toxicity results. Aquat. Toxicol. 67:359–370. 

Sandahl, J. F., D. H. Baldwin, J. J. Jenkins, and N. L. Scholz. 2004. Odor-evoked field potentials as 

indicators of sublethal neurotoxicity in juvenile coho salmon (Oncorhynchus kisutch) exposed to 

copper, chlorpyrifos, or esfenvalerate. Can. J. Fish. Aquat. Sci. 61:404–413. 

Sandahl, J. F., D. H. Baldwin, J. J. Jenkins, and N. L. Scholz. 2007. A sensory system at the interface 

between urban storm water runoff and salmon survival. Environ. Sci. Technol. 41:2998–3004. 

Sandahl, J. F., and J. J. Jenkins. 2002. Pacific steelhead (Oncorhynchus mykiss) exposed to chlorpyrifos: 

Benchmark concentration estimates for acetylcholinesterase inhibition. Environ. Toxicol. Chem. 

21:2452–2458. 

Sandahl, J. F., G. Miyasaka, N. Koide, and H. Ueda. 2006. Olfactory inhibition and recovery in chum 

salmon (Oncorhynchus keta) following copper exposure. Can. J. Fish. Aquat. Sci. 63:1840–1847. 

Sansalone, J. J., and S. G. Buchberger. 1997. Partitioning and first flush of metals in urban roadway 

storm water. J. Environ. Monit. 123:134–143. 

Saucier, D., L. Astic, and P. Rioux. 1991. The effects of early chronic exposure to sublethal copper on 

the olfactory discrimination of rainbow trout, Oncorhynchus mykiss. Environ. Biol. Fishes 

30:345–351. 

Saunders, R. L., and J. B. Sprague. 1967. Effects of copper-zinc mining pollution on a spawning 

migration of Atlantic salmon. Water Res. 1:419–432. 

Scherer, E., and R. E. McNoil. 1998. Preference-avoidance responses of lake whitefish (Coregonus 

clupeaformis) to competing gradients of light and copper, lead, and zinc. Water Res. 32:494–

502. 

Schreck, C. B., and H. W. Lorz. 1978. Stress response of coho salmon (Oncorhynchus kisutch) elicited 

by cadmium and copper and potential use of cortisol as an indicator of stress. J. Fish. Res. Board 

Can. 35:1124–1129. 

24
Scott, J. W., and P. E. Scott-Johnson. 2002. The electroolfactogram: A review of its history and uses. 

Microscopy Res. Tech. 58:152–160. 

Seim, W. K., L. R. Curtis, S. W. Glenn, and G. A. Chapman. 1984. Growth and survival of developing 

steelhead trout (Salmo gairdneri) continuously or intermittently exposed to copper. Can. J. Fish. 

Aquat. Sci. 41:433–438. 

Smith, E. H., and H. C. Bailey. 1990. Preference/avoidance testing of waste discharges on anadromous 

fish. Environ. Toxicol. Chem. 9:77–86. 

Soller, J., J. Stephenson, K. Olivieri, J. Downing, and A. W. Olivieri. 2005. Evaluation of seasonal scale 

first flush pollutant loading and implications for urban runoff management. J. Environ. Manag. 

76:309–318. 

Sorensen, E. M. B. 1991. Chapter VII: Copper. In E. M. B. Sorensen (ed.), Metal poisoning in fish, p. 

235–284. CRC Press, Boca Raton, FL. 

Sprague, J., P. Elson, and R. Saunders. 1965. Sublethal copper-zinc pollution in a salmon river—A field 

and laboratory study. Int. J. Air Water Pollut. 9:531–543. 

Stephan, C. E., D. I. Mount, J. A. Hansen, J. H. Gentile, G. A. Chapman, and W. A. Brungs. 1985. 

Guidelines for deriving numerical national water quality criteria for the protection of aquatic 

organisms and their uses. National Technical Information Service, Springfield, VA. 

Stevens, D. G. 1977. Survival and immune response of coho salmon exposed to copper. EPA 600/3-77-

031. U.S. EPA Environmental Research Laboratory, Corvallis, OR. 

Sutterlin, A., and R. Gray. 1973. Chemical basis for homing of Atlantic salmon (Salmo salar) to a 

hatchery. J. Fish. Res. Board Can. 30:985–989. 

Thomas, P. R., and G. R. Greene. 1993. Rainwater quality from different roof catchments. Water Sci. 

Technol. 28:291–299. 

USGS (U.S. Geological Survey). No date. National Water Information System databases. Online at 

http://waterdata.usgs.gov/nwis [accessed 27 September 2007]. 

Waiwood, K. G., and F. W. H. Beamish. 1978a. The effect of copper, hardness, and pH on the growth of 

rainbow trout, Salmo gairdneri. J. Fish Biol. 13:591–598. 

Waiwood, K. G., and F. W. H. Beamish. 1978b. Effects of copper, pH, and hardness on the critical 

swimming performance of rainbow trout (Salmo gairdneri). Water Res. 12:611–619. 

Wheeler, A. P., P. L. Angermeier, and A. E. Rosenberger. 2005. Impacts of new highways and 

subsequent landscape urbanization on stream habitat and biota. Rev. Fish. Sci. 13:141–164. 

Winberg, S., R. Bjerselius, E. Baatrup, and K. B. Doving. 1992. The effect of Cu(II) on the electroolfactogram (EOG) of the Atlantic salmon (Salmo salar L.) in artificial freshwater of varying 

inorganic carbon concentrations. Ecotoxicol. Environ. Saf. 24:167–178. 

25
26
Appendix A: 

Other Salmonid Sensory Effects of dCu 

In this appendix, results are highlighted from several studies that we thought were 

particularly relevant, including comparing the concentrations that have caused sensory effects to 

concentrations causing lethality or growth reductions in field and laboratory experiments. As 

such, the following review is not an exhaustive summary of copper’s adverse effects to 

anadromous salmonids. We emphasize studies that were conducted in waters with low alkalinity 

and hardness (<50 mg/L as calcium carbonate), and if reported, low concentrations of dissolved 

organic material. These conditions were emphasized since we believe these are the most 

relevant water quality conditions for an area of particular concern to us—freshwater habitats 

used by juvenile salmonids in the Pacific Northwest and California.

Migratory Disruption 

Laboratory and field experiments with salmonids have shown avoidance of low 

concentrations of copper, disruption of downstream migration by juvenile salmonids, loss of 

homing ability, and loss of avoidance response to even acutely lethal concentrations of copper 

following long-term habituation to low level copper exposure. Saucier et al. (1991) examined 

the impact of a long-term sublethal copper exposure (22 μg/L, 37–41 weeks in duration) on the 

olfactory discrimination performance in rainbow trout (Oncorhynchus mykiss). When controls 

were given a choice between their own rearing water or other waters, they significantly preferred 

their own rearing water, whereas both copper-exposed groups showed no preference. They 

concluded that their results demonstrate that a long-term sublethal exposure to copper, as it 

commonly occurs under “natural” conditions, may result in olfactory dysfunction with potential 

impacts on fish survival and reproduction. 

Field studies have reported that copper impairs both upstream spawning migration of 

salmonids and downstream outmigration of juveniles. Avoidance of copper in the wild has been 

demonstrated to delay upstream passage of Atlantic salmon (Salmo salar) moving past coppercontaminated reaches of the river to their upstream spawning grounds, cause unnatural 

downstream movement by adults away from the spawning grounds, and increase straying from 

their contaminated home stream into uncontaminated tributaries. Avoidance thresholds in the 

wild of 0.35 to 0.43 toxic units were about seven times higher than laboratory avoidance 

thresholds (0.05 toxic units), perhaps because the laboratory tests used juvenile fish rather than 

more motivated spawning adults. For this study 1.0 toxic unit was defined as an incipient lethal 

level (ILL, essentially a time independent LC50), of 48 μg/L in soft water (Sprague et al. 1965, 

Saunders and Sprague 1967). Studies of home water selection with returning adult salmon 

showed that addition of 44 μg/L copper to their home water reduced the selection of their home 

stream by 90% (Sutterlin and Gray 1973). Releases of about 20 μg/L from a mine drainage into 

a salmon spawning river resulted in 10–22% repulsion of ascending salmon during four 

consecutive years compared to 1–2% prior to mining (Sutterlin and Gray 1973). The upstream 

27
spawning migration of Chinook salmon (O. tshawytscha) in Panther Creek, Idaho, may have 

been interrupted during the 1980s and early 1990s when the fish encountered dCu concentrations 

of 10–25 μg/L. In Panther Creek, the majority of spawning habitat and historical locations of 

Chinook salmon spawning were high in the watershed, upstream of copper discharges. 

However, Chinook salmon were only observed spawning below the first major diluting tributary, 

a point above which copper concentrations averaged about 10–25 μg/L during the times of the 

spawning observations (Mebane 1994, 2000). 

Sublethal copper exposure has been shown to interfere with the downstream migration to 

the ocean of yearling coho salmon (O. kisutch). Lorz and McPherson (1976, 1977) and Lorz et 

al. (1978) evaluated the effects of copper exposure on salmon smolts’ downstream migration 

success in a series of 14 field experiments. Lorz and McPherson (1976, 1977) exposed yearling 

coho salmon for six to 165 days to nominal copper concentrations varying from 0–30 μg/L. 

They then marked and released the fish during the normal coho salmon migration period and 

monitored downstream migration success. The fish were released simultaneously, allowing for 

evaluation of both copper exposure concentrations and exposure duration on migration success. 

All dCu exposures resulted in reduction of migration compared with unexposed control fish. 

Migration success decreased with both increasing copper concentrations and increased exposure 

time for each respective concentration. Exposure to 30 μg/L dCu for as little as 72 hours caused 

a considerable reduction in migration (≈60%) compared to control fish. The reductions in 

migration following short-term exposures to dCu are illustrated in Figure A-1. Following 

exposure to 30 μg/L dCu, 80% of coho did not reach the migratory point in 49 days. These 

concentrations (5-20 μg/L) were one-tenth to one-third the 96-hour LC50 for the same stock of 

juvenile coho salmon in the same water. Lorz et al. (1978) further tested downstream migration 

with yearling coho salmon previously exposed to copper, cadmium, copper-cadmium mixtures, 

zinc, and copper-zinc mixtures. Copper concentrations in all tests were held at 10 μg/L. In all 

cases, the copper exposed fish again had poorer migratory success than did controls. The other 

metals did not show the dose-dependent result found for copper. These studies suggest that 

exposure to copper concentrations at levels found in streams subject to nonpoint copper pollution 

may impair downstream migration, a result of direct and indirect effects to salmon smolts, 

including reproductive success. 

Laboratory Avoidance Studies 

Studies have shown that salmonids can detect and avoid copper at low concentrations 

when tested in troughs or streams that allow them to choose between concentration gradients. To 

our knowledge, the lowest copper concentration reported to cause avoidance in laboratory 

conditions was 0.1 μg/L (Folmar 1976). However, these results may have low applicability to 

ambient conditions because copper exposure concentrations were not analytically verified. 

Avoidance thresholds of 2 μg/L copper have been reported for Atlantic salmon (Salmo salar), 

concentrations that are less than one-tenth of acute LC50 values (Saunders and Sprague 1967). 

Giattina et al. (1982) reported that rainbow trout appeared to detect copper concentrations down 

to 1.4–2.7 μg/L, because declines in residence time started to occur at these lower 

concentrations. However, the responses were only statistically significant at 4.4 to 6.4 μg/L 

depending on whether fish were exposed to a gradually increasing or abruptly increasing 

concentration gradient respectively. At exposure to extremely high dCu levels, for example, 

28
0

20

40

60

80

100

05

10154550

Downstream migration (%)

Days post release

0 μg/L 5 μg/L 10 μg/L 20 μg/L 30 μg/L

Figure A-1. Reduction in downstream migration of yearling coho salmon following 6 days of exposure to 

copper at various concentrations. (Redrawn from Lorz and McPherson 1977, their Figure 19.) 

330–390 μg/L, trout showed diminished avoidance and sometimes attraction to acutely lethal 

concentrations (Giattina et al. 1982, Hansen et al. 1999a, Chapman unpubl. data). 

Chapman (unpubl. data) reported that long-term sublethal copper exposures had impaired 

the avoidance performance of salmonids. Steelhead (O. mykiss), acclimated to low copper levels 

by surviving about 3 months early life stage toxicity testing, subsequently failed to avoid much 

higher, acutely lethal concentrations. Following about 3 month continuous exposure to 9 μg/L 

copper (from fertilization to about 1 month after swim up) the copper-acclimated fish and control 

fish with no previous copper exposure were exposed to a range of copper concentrations from 

10 to 80 μg/L in avoidance-preference testing. The tests used the same counter flow avoidancepreference test chambers described by Giattina et al. (1982). The acclimated steelhead failed to 

avoid even the highest copper concentrations while most of the unexposed fish avoided all 

concentrations. 

Hansen et al. (1999a) and Marr et al. (1995) conducted a variety of behavioral and other 

toxicity studies with Chinook salmon and rainbow trout exposed to copper. In these studies they 

used well water that was diluted with deionized water and spiked with copper to obtain a 

hardness, alkalinity, and pH that simulated those in Panther Creek, a mine-affected stream in 

Idaho. The avoidance response of the Chinook salmon was statistically significant for 0.8 and 

2.8–22.5 μg/L copper but was not significant for a 1.6 μg/L copper treatment. Since the 

avoidance responses (percent time spent in test water) were similar between the 0.8, 1.6, and 3 

μg/L treatments, but the 1.6 μg/L treatment had fewer replicates than the other treatments (10 vs. 

20), the lack of statistical significance for the 1.6 μg/L treatment was probably an artifact of the 

29
different sample sizes rather than a true lack of response. Rainbow trout consistently avoided 

copper at concentrations of 1.6 μg/L and above. To simulate avoidance responses that might 

result on exposing fish to background levels of copper, Hansen et al. (1999a) acclimated both 

Chinook salmon and rainbow trout to 2 μg/L copper for 25 days, and repeated the avoidance 

experiments. They observed that the avoidance response of Chinook salmon was greatly 

dampened such that no copper treatments resulted in statistically significant responses. In 

contrast, the avoidance response of rainbow trout was unaffected by the acclimation. This 

dramatic difference between Chinook salmon and rainbow trout avoidance was so unexpected 

that Hansen et al. (1999a) ran a second set of experiments that yielded the same results. 

Background dCu concentrations (<4 μg/L) are commonly observed in natural waterways, yet 

Chinook salmon failed to avoid any higher dCu concentrations following an acclimation to a 

nominal 2 μg dCu/L. Importantly, if Chinook salmon will not avoid any dCu concentrations 

following acclimation to low dCu concentrations, the behavioral defense against chronic and 

acute exposures to dCu is lost, and high mortality or chronic physiological effects are probable if 

subsequent higher levels of dCu exposure occur. Unlike Chinook salmon, dCu-acclimated 

rainbow trout preferred clean water and avoided higher dCu concentrations. Other differences 

between Chinook salmon and rainbow trout avoidance responses to copper were that addition of 

4 and 8 mg/L dissolved organic carbon (DOC) did not appreciably affect the avoidance response 

of Chinook salmon to copper, nor did altering pH across a range of 6.5 to 8.5. In contrast, the 

addition of DOC (4 and 8 mg/L) did reduce the avoidance response of rainbow trout to copper. 

Although variable, avoidance responses of rainbow trout were slightly stronger at pH 7.5 and 8.5 

than at 6.5 (Marr et al. 1995). 

A further repeated finding from these laboratory avoidance tests was that although 

rainbow trout, steelhead, and Chinook salmon avoided low concentrations of dCu, they were 

apparently intoxicated and sometimes attracted to very high concentrations (Giattina et al. 1982, 

Hansen et al. 1999a, Chapman unpubl. data). The direct relevance of laboratory avoidance 

studies to the behaviors of fish in the wild is debatable since in natural waters fish likely select 

and move among habitats based on myriad reasons such as access to prey, shelter from predators, 

shade, velocity, temperature, and interactions with other fish. In contrast, laboratory 

preference/avoidance tests are commonly conducted under simple, highly artificial conditions to 

eliminate or minimize confounding variables other than the water characteristic of interest. 

Laboratory tests may overestimate the actual protection this behavior provides fish in 

heterogeneous, natural environments (Hartwell et al. 1987, Korver and Sprague 1989, Scherer 

and McNoil 1998). 

However, at least one study suggested that experimental avoidance responses observed 

with salmonids are relevant to fish behaviors in the wild. From 1980 to 1982, sublethal levels of 

a contaminant (fluoride) from an aluminum mill at the John Day Dam on the Columbia River 

were associated with a significant delay in salmon passage and decreased survival (Damkaer and 

Dey 1989). Salmon took an average of 36 hours to pass up the fish ladder at the Bonneville and 

McNary dams compared to 157 hours delay at the John Day Dam. Greater than 50% mortality 

occurred between the Bonneville and McNary dams (above and below the John Day dam), 

compared to about 2% mortality associated with the other dams. Damkaer and Dey (1989) 

introduced similar levels of the contaminant in streamside test flumes alongside a salmon 

spawning stream (Big Beef Creek, Washington). Significant numbers of adult Chinook salmon 

failed to move out of their holding area and continue upstream; those that did move upstream 

30
chose the noncontaminated side of the flume. By adjusting the dose, Damkaer and Dey (1989) 

predicted a threshold detection limit for avoidance by salmon. The mill subsequently reduced its 

release of the contaminant to below these experimental threshold levels, which did not show a 

response in the streamside tests. Afterwards, fish passage delays and salmon mortality between 

the dams decreased to 28 hours and <5%, respectively (Damkaer and Dey 1989). This study 

suggested that the delay due to avoidance of a chemical affected the spawning success of 

migrating adult salmonids. These results are also consistent with the field studies of salmon 

migration in copper-contaminated streams and from laboratory avoidance/preference testing. 

Experimental avoidance/preference testing thus appears to be relevant to fish behavior in nature. 

Other Adverse Effects 

The focus of this literature synthesis is sensory effects of copper on juvenile salmonids. 

However, other adverse effects of copper to salmonids reported in the literature include 

weakened immune function and disease resistance, increased susceptibility to stress, liver 

damage, reduced growth, impaired swimming performance, weakened eggshells, and direct 

mortality (McKim and Benoit 1971, Stevens 1977, Schreck and Lorz 1978, Waiwood and 

Beamish 1978a, 1978b, Chapman 1982, Farag et al. 1994, Marr et al. 1996, Farag et al. 2003). 

While a comprehensive review of other adverse effects of copper on fish is beyond the scope of 

this synthesis, we discuss several studies of interest below. 

Stevens (1977) reported that preexposure to sublethal levels of dCu interfered with the 

immune response and reduced the disease resistance in yearling coho salmon. Juvenile coho 

salmon were vaccinated with the bacterial pathogen Vibrio anguillarum prior to copper exposure 

to investigate the effects of copper upon the immune response and survival. Following copper 

exposure (9.6–40 μg/L), surviving juveniles were challenged under natural conditions to V. 

anguillarum, the causative agent of vibriosis in fish. Vibriosis is a disease commonly found in 

wild and captive fish from marine environments and has caused deaths of coho and Chinook 

salmon. Coho salmon were exposed to constant concentrations of dCu for about one month at 

levels that covered the range from no effect to causing 100% mortality, 9.6–40 μg/L. The 

antibody titer level against V. anguillarum was significantly reduced in fish exposed to 13.9 μg/L 

of dCu when compared to that developed in control fish. The survivors of the dCu bioassays 

were then exposed in saltwater holding ponds for an additional 24 days to the V. anguillarum

pathogen. The unvaccinated, non-dCu exposed control fish had 100% mortality and the 

vaccinated, non-dCu exposed fish had the lowest mortality. The vaccinated, dCu-exposed fish 

had increasing mortality corresponding to the lower antibody titer levels which in turn 

corresponded to the increasing dCu exposure levels. Therefore, dCu exposure can significantly 

reduce a fish's immune function and disease resistance at concentrations as low as 13.9 μg/L 

following 30 days of exposure (Stevens 1977). 

Schreck and Lorz (1978) studied the effects of copper exposure to stress resistance in 

yearling coho salmon. Fish that were exposed for 7 days to 15 μg/L dCu and unexposed control 

fish were subjected to severe handling and confinement stress. Copper-exposed fish survived 

this additional stress for a median of 12–15 hours while control fish experienced no mortality at 

36 hours. Schreck and Lorz (1978) concluded that exposure to copper placed a sublethal stress 

on the fish which made them more vulnerable to handling and saltwater adaptation. Further, 

31
they hypothesized that dCu exposure may make salmonids more vulnerable to secondary stresses 

such as disease and pursuit by predators. 

Exposure of brook trout (Salvelinus fontinalis) eggs to 17.4 μg dCu/L for 90 days 

resulted in weakened chorions (eggshells) and embryo deformities. After hatching, poor yolk 

utilization and reduced growth were demonstrated. These overall weakened conditions may 

reduce survival chances in the wild (McKim and Benoit 1971, McKim 1985). Copper 

accumulation in the liver of rainbow trout caused degeneration of liver hepatocytes, which 

resulted in reduced ability to metabolize food, reduced growth, or eventual death (Leland and 

Carter 1985, Farag et al. 1994, Meyer 2005). Waiwood and Beamish (1978a), Chapman (1982), 

Seim et al. (1984), McKim and Benoit (1971), and Marr (1996) have also observed reduced 

growth of salmonids in response to chronic copper exposures as low as 1.9 μg/L. Waiwood and 

Beamish (1978b) reported that rainbow trout exposed to copper levels had reduced swimming 

performance (10, 15, 20, 30 μg/L dCu) and reduced oxygen consumption (25, 40 μg/L dCu) 

apparently due to gill damage and decreased efficiency of gas exchange. 

In sum, there is a large body of literature showing that behavior of salmonids and other 

fishes can be disrupted at concentrations of dCu that are only slightly elevated above background 

concentrations. Further, dCu stress has been shown to increase the cost of maintenance to fish 

and to limit oxygen consumption and food metabolism. Reduced growth may result in increased 

susceptibility to predation, and impaired swimming ability may result in reduced escape reaction 

and prey hunting, with a possible consequence of reduced survival at the population level. We 

summarize selected examples of effect concentrations reported with copper for several different 

types of effects in Table 1 of this technical memorandum. In general, typical copper exposures 

probably do not kill juvenile salmonids directly until concentrations greater than about 10 times 

that of sensory thresholds, and then only if the concentrations are sustained for at least several 

hours. In selecting these examples, we sought to list representative effects and concentrations 

rather than extreme values that could be gleaned from the literature. However, the selected 

examples do not constitute an exhaustive review of the effects of copper to fish; more general 

reviews of effects of copper to fish and other aquatic organisms are available elsewhere (Leland 

and Carter 1985, Sorensen 1991, Eisler 1998, USEPA 2007). 

32
Appendix B: Supplementary Bibliography 

Copper Sources 

Good, J. C. 1993. Roof runoff as a diffuse source of metals and aquatic toxicity in storm water. Water 

Sci. Technol. 28:317–322. 

Thomas, P. R., and G. R. Greene. 1993. Rainwater quality from different roof catchments. Water Sci. 

Technol. 28:291–297. 

Benchmark Concentration/Dose 

Crump, K. S. 1995. Calculation of benchmark doses from continuous data. Risk Anal. 15:79–89. 

Sandahl, J. F., and J. J. Jenkins. 2002. Pacific steelhead (Oncorhynchus mykiss) exposed to chlorpyrifos: 

Benchmark concentration estimates for acetylcholinesterase inhibition. Environ. Toxicol. Chem. 

21:2452–2458. 

Slikker, W., K. S. Crump, M. E. Andersen, and D. Bellinger. 1996. Biologically based, quantitative risk 

assessment of neurotoxicants. Fundam. Appl. Toxicol. 29:18–30. 

U.S. Environmental Protection Agency. 1995. The use of the benchmark dose approach in health risk 

assessment. EPA 630/R-94/007. EPA Office of Research and Development, Washington, DC. 

Copper and Neurobiology 

Baldwin, D. H., J. F. Sandahl, J. S Labenia, and N. L. Scholz. 2003. Sublethal effects of copper on coho 

salmon: Impacts on nonoverlapping receptor pathways in the peripheral olfactory nervous system. 

Environ. Toxicol. Chem. 22:2266–2274. 

Baldwin, D. H., and N. L. Scholz. 2005. The electro-olfactogram: An in vivo measure of peripheral 

olfactory function and sublethal neurotoxicity in fish. In G. K. Ostrander (ed.), Techniques in 

aquatic toxicology, Volume 2, p. 257–276. CRC Press, Boca Raton, FL. 

Bettini, S., F. Ciani, and V. Franceschini. 2006. Recovery of the olfactory receptor neurons in the 

African Tilapia mariae following exposure to low copper level. Aquat. Toxicol. 76:321–328 

Beyers, D. W., and M. S. Farmer. 2001. Effects of copper on olfaction of Colorado pikeminnow. 

Environ. Toxicol. Chem. 20:907–912. 

Bjerselius, R, S. Winberg, Y. Winberg, and K. Zeipel. 1993. Ca2+ protects olfactory receptor function 

against acute copper (II) toxicity in Atlantic salmon. Aquat. Toxicol. 25:125–138. 

Carreau, N. D., and G. G. Pyle. 2005. Effect of copper exposure during embryonic development on 

chemosensory function of juvenile fathead minnows (Pimephales promelas). Ecotoxicol. 

Environ. Saf. 61:1–6. 

33
Chai, M., and X. Chen. 1999. Inhibition of Cd2+, Hg2+ and Pb2+ on EOG responses of Tilapia sp. Journal 

of Fishery Sciences of China/Zhongguo Shuichan Kexue Beijing 6:89–92. 

Chai, M., and Z. Huang. 1996. Effect of Ca2+ on the EOG of Tilapia sp. and exploration of detoxifying 

feasibility. Journal of Xiamen University Natural Science/Xiamen Daxue Xuebao Xiamen 

35:941–946. 

Chai, M., and L. Pan. 1996. Effects of heavy metal (Cu2+, Zn2+) on the EOG response of fish (Tilapia

sp.). Journal of Xiamen University Natural Science/Xiamen Daxue Xuebao Xiamen 35:94–99. 

Goldstein, J. N., D. F. Woodward, and A. M. Farag. 1999. Movements of adult Chinook salmon during 

spawning migration in a metals-contaminated system, Coeur d’Alene River, Idaho. Trans. Am. 

Fish. Soc. 128:121–129. 

Hansen, J. A., J. C. A. Marr, J. Lipton, D. Cacela, and H. L. Bergman. 1999. Differences in 

neurobehavioral responses of Chinook salmon (Oncorhynchus tshawytscha) and rainbow trout 

(Oncorhynchus mykiss) exposed to copper and cobalt: Behavioral avoidance. Environ. Toxicol. 

Chem. 18:1972–1978. 

Hansen, J. A., J. D. Rose, R. A. Jenkins, K. G. Gerow, and H. L. Bergman. 1999. Chinook salmon 

(Oncorhynchus tshawytscha) and rainbow trout (Oncorhynchus mykiss) exposed to copper: 

Neurophysiological and histological effects on the olfactory system. Environ. Toxicol. Chem. 

18:1979–1991. 

Hara, T. J., Y. M. C. Law, and S. Macdonald. 1976. Effects of mercury and copper on the olfactory 

response in rainbow trout. J. Fish. Res. Board Can. 33:1568–1573. 

Hernández, P. P., V. Moreno, F. A. Olivari, and M. L. Allende. 2006. Sublethal concentrations of 

waterborne copper are toxic to lateral line neuromasts in zebrafish (Danio rerio). Hear. Res. 

213:1–10. 

Julliard, A. K., D. Saucier, and L. Astic. 1993. Effects of chronic low-level copper exposure on 

ultrastructure of the olfactory system in rainbow trout (Oncorhynchus mykiss). Histol. 

Histopathol. 8:655–672. 

Julliard, A. K., D. Saucier, and L. Astic. 1995. Metal X-ray microanalysis in the olfactory system of 

rainbow trout exposed to low level of copper. Biol. Cell 83:77–86. 

Julliard, A. K., D. Saucier, and L. Astic. 1996. Time-course of apoptosis in the olfactory epithelium of 

rainbow trout exposed to a low copper level. Tissue Cell 28:367–377. 

Kasumyan, A. O. 2001. Effects of chemical pollutants on foraging behavior and sensitivity of fish to 

food stimuli. J. Ichthyol. 41:76–87. 

Kasumyan, A. O., and A. M. H. Morsi. 1998. Effect of heavy metals on the feeding activity and taste 

behavior responses of carp Cyprinus carpio: 1. Copper, cadmium, zinc, and lead. J. Ichthyol. 

38:393–409. 

Klima, K. E., and F. M. Applehans. 1990. Copper exposure and the degeneration of olfactory receptors 

in rainbow trout (Oncorhynchus mykiss). Chem. Speciat. Bioavailab. 2:149–154. 

Linbo, A. O., C. M. Stehr, J. P. Incardona, and N. L. Scholz. 2006. Dissolved copper triggers cell death 

in the peripheral mechanosensory system of larval fish. Environ. Toxicol. Chem. 25:597–603. 

34
Little, E. E., R. D. Archeski, B. A. Flerov, and V. I. Kozlovskaya. 1990. Behavioral indicators of 

sublethal toxicity in rainbow trout. Arch. Environ. Contam. Toxicol. 19:380–385. 

Little, E. E., and S. E. Finger. 1990. Swimming behavior as an indicator of sublethal toxicity in fish. 

Environ. Toxicol. Chem. 9:13–19. 

McPherson, T. D., R. S. Mirza, and G. G. Pyle. 2004. Responses of wild fishes to alarm chemicals in 

pristine and metal-contaminated lakes. Can. J. Zool. 82:694–700. 

Moran, D. T., J. C. Rowley, and G. Aiken. 1986. Trout olfactory receptors degenerate in response to 

waterborne ions: A potential bioassay for environmental neurotoxicology? Chem. Senses 11:642. 

Moran, D. T., J. C. Rowley, G. R. Aiken, and B. W. Jafek. 1992. Ultrastructural neurobiology of the 

olfactory mucosa of the brown trout, Salmo trutta. Microscopy Res. Tech. 23:28–48. 

Rehnberg, B., and C. B. Schreck. 1986. Acute metal toxicology of olfaction in coho salmon: Behavior, 

receptors, and odor-metal complexation. Bull. Environ. Contam. Toxicol. 36:579–586. 

Sandahl, J. F., D. H. Baldwin, J. J. Jenkins, and N. L. Scholz. 2007. A sensory system at the interface 

between urban stormwater runoff and salmon survival. Environ. Sci. Technol. 41:2998–3004. 

Sandahl, J. F., D. H. Baldwin, J. J. Jenkins, and N. L. Scholz. 2004. Odor-evoked field potentials as 

indicators of sublethal neurotoxicity in juvenile coho salmon (Oncorynchus kisutch) exposed to 

copper, chlorpyrifos, or esfenvalerate. Can. J. Fish. Aquat. Sci. 61:404–413. 

Saucier, D., and L. Astic. 1995. Morphofunctional alterations in the olfactory system of rainbow trout 

(Oncorhynchus mykiss) and possible acclimation in response to long-lasting exposure to low 

copper levels. Comp. Biochem. Physiol. A Physiol. 112:273–284. 

Saucier, D., L. Astic, and P. Rioux. 1991. The effects of early chronic exposure to sublethal copper on 

the olfactory discrimination of rainbow trout, Oncorhynchus mykiss. Environ. Biol. Fishes 

30:345–351. 

Saunders, R. L., and J. B. Sprague. 1967. Effects of copper-zinc mining pollution on a spawning 

migration of Atlantic salmon. Water Res. 1:419–432 

Starcevic, S. L., and B. S. Zielinski. 1997. Neuroprotective effects of glutathione on rainbow trout 

olfactory receptor neurons during exposure to copper sulfate. Comp. Biochem. Physiol. C 

117C:211–219. 

Tjalve, H., and J. Henriksson. 1999. Uptake of metals in the brain via olfactory pathways. 

Neurotoxicology 20:181–195. 

Weis, J. S., and P. Weis. 1996. The effects of using wood treated with chromated copper arsenate in 

shallow-water environments: A review. Estuaries 19:306–310. 

Winberg, S., R. Bjerselius, E. Baatrup, and K. B. Døving. 1992. The effect of copper (II) on the electroolfactogram (EOG) of the Atlantic salmon (Salmo salar L.) in artificial freshwater of varying 

inorganic carbon concentrations. Ecotoxicol. Environ. Saf. 24:167–178. 

Reviews 

Brown, G. E. 2003. Learning about danger: Chemical alarm cues and local risk assessment in pre fishes. 

Fish Fish. 4:227–234. 

35
Døving, K. B. 1991. Assessment of animal behaviour as a method to indicate environmental toxicity. 

Comp. Biochem. Physiol. C 100:247–252. 

Eisler, R. 1998. Copper hazards to fish, wildlife, and invertebrates: A synoptic review. Report No. 

USGS/BRD/BSR--1998-0002. U.S. Geological Survey, Biological Resources Division. 

Halpern, B. P. 1982. Environmental factors affecting chemoreceptors: An overview. Environ. Health 

Perspect. 44:101–105. 

Hara, T. J. 1972. Electrical responses of the olfactory bulb of Pacific salmon Oncorhynchus nerka and 

Oncorhynchus kisutch. J. Fish. Res. Board Can. 29:1351–1355. 

Hara, T. J. 1992. Mechanisms of olfaction. In T. J. Hara (ed.), Fish chemoreception, p. 150–170. 

Chapman & Hall, London. 

Kats, L. B., and L. M. Dill. 1998. The scent of death: Chemosensory assessment of predation risk by 

prey animals. Ecoscience 5:361–394. 

Klaprat, D. A., R. E. Evans, and T. J. Hara. 1992. Environmental contaminants and chemoreception in 

fishes. In T. J. Hara (ed.), Fish chemoreception, p 321–342. Chapman & Hall, London. 

Scott, J. W., and P. E. Scott-Johnson. 2002. The electroolfactogram: A review of its history and uses. 

Microscopy Res. Tech. 58:152–160. 

Scott, G. R., and K. A. Sloman. 2004. The effects of environmental pollutants on complex fish 

behaviour: Integrating behavioural and physiological indicators of toxicity. Aquat. Toxicol. 

68:369–392. 

Shumway, C. A. 1999. A neglected science: Applying behavior to aquatic conservation. Environ. Biol. 

Fishes 55:183–201. 

Smith, R. J. F. 1992. Alarm signals in fishes. Rev. Fish Biol. Fish. 2:33–63. 

Sorensen, E. M. B. 1991. Chapter VII: Copper. In E. M. B. Sorensen (ed.), Metal poisoning in fish, p. 

235–284. CRC Press, Boca Raton, FL. 

Sutterlin, A. M. 1974. Pollutants and the chemical senses of aquatic animals—perspective and review. 

Chem. Senses Flavor 1:167–178. 

Studies with Other Metals 

Baatrup, E. 1991. Structural and functional effects of heavy metals on the nervous system, including 

sense organs, of fish. Comp. Biochem. Physiol. C 100:253–257. 

Baatrup, E., and K. B. Døving. 1990. Histochemical demonstration of mercury in the olfactory system of 

salmon (Salmo salar L.) following treatments with dietary methylmercuric chloride and dissolved 

mercuric chloride. Ecotoxicol. Environ. Saf. 20:277–289. 

Baatrup, E., K. B. Døving, and S. Winberg. 1990. Differential effects of mercurial compounds on the 

electroolfactogram (EOG) of salmon (Salmo salar L.). Ecotoxicol. Environ. Saf. 20:269–276. 

Baker, C. F., and J. C. Montgomery. 2001. Sensory deficits induced by cadmium in banded kokopu, 

Galaxias fasciatus, juveniles. Environ. Biol. Fishes 62:455–464. 

36
Beauvais, S. L., S. B. Jones, J. T. Parris, S. K. Brewer, and E. E. Little. 2001. Cholinergic and 

behavioral neurotoxicity of carbaryl and cadmium to larval rainbow trout (Oncorhynchus mykiss). 

Ecotoxicol. Environ. Saf. 49:84–90. 

Chakrabarti, P., M. Ghosal, and D. K. Mandal. 1994. Microanatomical and histopathological sequels of 

cadmium intoxication on the olfactory epithelium of the fish Mystus vittatus (Bloch). Environ. 

Ecol. 12:540–544. 

Hernadi, L. 1993. Fine structural characterization of the olfactory epithelium and its response to divalent 

cations Cd2+ in the fish Alburnus alburnus (Teleostei, Cyprinidae): A scanning and transmission 

electron microscopic study. Neurobiology 1:11–31. 

Scott, G. R., K. A. Sloman, C. Rouleau, and C. M. Wood. 2003. Cadmium disrupts behavioural and 

physiological responses to alarm substance in juvenile rainbow trout (Oncorhynchus mykiss). J. 

Exp. Biol. 206:1779–1790. 

Selected Behavioral Studies 

Berejikian, B. A., R. J. Smith, E. P. Tezak, S. L. Schroder, and C. M. Knudsen. 1999. Paired chemical 

alarm signals and complex hatchery rearing habitats affect predator behavior and survival of 

Chinook salmon (Oncorhynchus tshawytscha) juveniles. Can. J. Fish. Aquat. Sci. 56:830–838. 

Brown, G. E., J. C. Adrian Jr., T. Patton, and D. P. Chivers. 2001. Fathead minnows learn to recognize 

predator odor when exposed to concentrations of artificial alarm pheromone below their 

behavioral-response threshold. Can. J. Zool. 79:2239–2245. 

Brown, G. E., and R. J. Smith. 1997. Conspecific skin extracts elicit antipredator responses in juvenile 

rainbow trout (Oncorhynchus mykiss). Can. J. Zool. 75:1916–1922. 

Døving, K. B., H. Westerberg, and P. B. Johnsen. 1985. Role of olfaction in the behavioral and neuronal 

responses of Atlantic salmon, Salmo salar, to hydrographic stratification. Can. J. Fish. Aquat. 

Sci. 42:1658–1667. 

Hatfield, C. T., and J. M. Anderson. 1972. Effects of two pesticides on the vulnerability of Atlantic 

salmon (Salmo salar) parr to brook trout (Salvenius fontinalis) predation. J. Fish. Res. Board 

Can. 29:27–29. 

Hatfield, C. T., and P. H. Johansen. 1972. Effects of four insecticides on the ability of Atlantic salmon 

parr (Salmo salar) to learn and retain a simple conditioned response. J. Fish. Res. Board Can. 

29:315–321. 

Hiroven, H., E. Ranta, J. Piironen, A. Laurila, and N. Peuhkuri. 2000. Behavioural responses of naive 

Artic charr young to chemical cues from salmonid and nonsalmonid fish. Oikos 88:191–199. 

Kruzynski, G. M., and I. K. Birtwell. 1994. A predation bioassay to quantify the ecological significance 

of sublethal responses of juvenile Chinook salmon (Oncoryhynchus tshawytscha) to the 

antisapstain fungicide TCMTB. Can. J. Fish. Aquat. Sci. 51:1780–1790. 

McLennan, D. A., and M. J. Ryan. 1997. Responses to conspecific and heterospecific olfactory cues in 

the swordtail Xiphophorus cortezi. Anim. Behav. 54:1077–1088. 

Mirza, R. S., and D. P. Chivers. 2001. Chemical alarm signals enhance survival of brook charr 

(Salvelinus fontinalis) during encounters with predatory chain pickerel (Esox niger). Ethology 

107:989–1005. 

37
Poulin, R., D. Marcogliese, and J. McLaughlin. 1999. Skin-penetrating parasites and the release of alarm 

substances in juvenile rainbow trout. J. Fish Biol. 55:47–53. 

Wisby, W. J., and A. D. Hasler. 1954. Effect of occlusion on migrating silver salmon (Oncorhynchus 

kisutch). J. Fish. Res. Board Can. 11:472–478. 

Recovery of Olfactory Epithelium after Damage 

Evans, R. E., and T. J. Hara. 1985. The characteristics of the electro-olfactogram (EOG): its loss and 

recovery following olfactory nerve section in rainbow trout (Salmo gairdneri). Brain Res. 

330:65–75. 

Zielinski, B. S., and T. J. Hara. 1992. Ciliated and microvillar receptor cells degenerate and then 

differentiate in the olfactory epithelium of rainbow trout following olfactory nerve section. 

Microscopy Res. Tech. 23:22–27. 

Additional Endpoints 

Ali, A., S. M. Al-Ogaily, N. A. Al-Asgah, and J. Gropp. 2003. Effect of sublethal concentrations of 

copper on the growth performance of Oreochromis niloticus. J. Appl. Ichthyol. 19:183–188. 

Beaumont, M. W., P. J. Butler, and E. W. Taylor. 2003. Exposure of brown trout Salmo trutta to a 

sublethal concentration of copper in soft acidic water: Effects upon gas exchange and ammonia 

accumulation. J. Exp. Biol. 206:153–162. 

Bielmyer, G. K., D. Gatlin, J. J. Isely, J. Tomasso, and S. J. Klaine. 2005. Responses of hybrid striped 

bass to waterborne and dietary copper in freshwater and saltwater. Comp. Biochem. Physiol. C 

Toxicol. Pharmacol. 140:131–137. 

Brix, K. V., D. K. DeForest, and W. J. Adams. 2001. Assessing acute and chronic copper risks to 

freshwater aquatic life using species sensitivity distributions for different taxonomic groups. 

Environ. Toxicol. Chem. 20:1846–1856. 

Buckley, J. T., M. Roch, J. A. McCarter, C. A. Rendell, and A. T. Matheson. 1982. Chronic exposure of 

coho salmon to sublethal concentrations of copper. 1. Effect on growth, on accumulation and 

distribution of copper, and on copper tolerance. Comp. Biochem. Physiol. C Pharmacol. Toxicol. 

Endocrinol. 72:15–19. 

Campbell, H. A., R. D. Handy, and D. W. Sims. 2002. Increased metabolic cost of swimming and 

consequent alterations to circadian activity in rainbow trout (Oncorhynchus mykiss) exposed to 

dietary copper. Can. J. Fish. Aquat. Sci. 59:768–777. 

Campbell, H. A., R. D. Handy, and D. W. Sims. 2005. Shifts in a fish’s resource holding power during a 

contact paired interaction: The influence of a copper-contaminated diet in rainbow trout. Physiol. 

Biochem. Zool. 78:706–714. 

Darwish, A. M., D. L. Straus, and B. R. Griffin. 2005. Histologic evaluation of the safety of copper 

sulfate to channel catfish. N. Am. J. Aquacult. 67:122–128. 

De Boeck, G., A. Vlaeminck, and R. Blust. 1997. Effects of sublethal copper exposure on copper 

accumulation, food consumption, growth, energy stores, and nucleic acid content in common 

carp. Arch. Environ. Contam. Toxicol. 33:415–422. 

38
Diamond, J., M. Bowersox, H. Latimer, C. Barbour, J. Bearr, and J. Butcher. 2005. Effects of pulsed 

contaminant exposures on early life stages of the fathead minnow. Arch. Environ. Contam. 

Toxicol. 49:511–519. 

Furuta, T., N. Iwata, K. Kikuchi, and K. Namba. 2005. Effects of copper on survival and growth of 

larval false clown anemonefish Amphiprion ocellaris. Fish. Sci. 71:884–888. 

Galvez, F., and C. M. Wood. 2002. The mechanisms and costs of physiological and toxicological 

acclimation to waterborne silver in juvenile rainbow trout (Oncorhynchus mykiss). J. Comp. 

Physiol. B Biochem. Syst. Environ. Physiol. 172:587–597. 

Hansen, J. A., J. Lipton, P. G. Welsh, D. Cacela, and B. MacConnell. 2004. Reduced growth of rainbow 

trout (Oncorhynchus mykiss) fed a live invertebrate diet pre-exposed to metal-contaminated 

sediments. Environ. Toxicol. Chem. 23:1902–1911. 

Hansen, J. A., J. Lipton, P. G. Welsh, J. Morris, D. Cacela, and M. J. Suedkamp. 2002. Relationship 

between exposure duration, tissue residues, growth, and mortality in rainbow trout 

(Oncorhynchus mykiss) juveniles subchronically exposed to copper. Aquat. Toxicol. 58:175–188. 

Hansen, J. A., P. G. Welsh, J. Lipton, and D. Cacela. 2002. Effects of copper exposure on growth and 

survival of juvenile bull trout. Trans. Am. Fish. Soc. 131:690–697. 

Lorz, H. W., and B. P. McPherson. 1976. Effects of copper or zinc in freshwater on adaptation to 

seawater and Atpase activity, and effects of copper on migratory disposition of coho salmon 

(Oncorhynchus kisutch). J. Fish. Res. Board Can. 33:2023–2030. 

Marr, J. C. A., J. Lipton, D. Cacela, J. A. Hansen, H. L. Bergman, J. S. Meyer, and C. Hogstrand. 1996. 

Relationship between copper exposure duration, tissue copper concentration, and rainbow trout 

growth. Aquat. Toxicol. 36:17–30. 

Rajotte, J. W., and P. Couture. 2002. Effects of environmental metal contamination on the condition, 

swimming performance, and tissue metabolic capacities of wild yellow perch (Perca flavescens). 

Can. J. Fish. Aquat. Sci. 59:1296–1304. 

Roch, M., and J. A. McCarter. 1984. Metallothionein induction, growth, and survival of Chinook salmon 

exposed to zinc, copper, and cadmium. Bull. Environ. Contam. Toxicol. 32:478–485. 

Sloman, K. A., D. W. Baker, C. G. Ho, D. G. McDonald, and C. M. Wood. 2003. The effects of trace 

metal exposure on agonistic encounters in juvenile rainbow trout, Oncorhynchus mykiss. Aquat. 

Toxicol. 63:187–196. 

Sloman, K. A., D. W. Baker, C. M. Wood, and G. McDonald. 2002. Social interactions affect 

physiological consequences of sublethal copper exposure in rainbow trout, Oncorhynchus mykiss. 

Environ. Toxicol. Chem. 21:1255–1263. 

Sloman, K. A., T. P. Morgan, D. G. McDonald, and C. M. Wood. 2003. Socially induced changes in 

sodium regulation affect the uptake of waterborne copper and silver in the rainbow trout, 

Oncorhynchus mykiss. Comp. Biochem. Physiol. C Toxicol. Pharmacol. 135:393–403. 

39

Most NOAA Technical Memorandums NMFS-NWFSC are available online at the

Northwest Fisheries Science Center web site (http://www.nwfsc.noaa.gov)

NOAA Technical Memorandum NMFS-NWFSC82 Helser, T.E., I.J. Stewart, C.E. Whitmire, and B.H. Horness. 2007. Model-based estimates of abundance 

for 11 species from the NMFS slope surveys. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC82, 145 p. NTIS number pending.

81 Hard, J.J., J.M. Myers, M.J. Ford, R.G. Cope, G.R. Pess, R.S. Waples, G.A. Winans, B.A. Berejikian, 

F.W. Waknitz, P.B. Adams. P.A. Bisson, D.E. Campton, and R.R. Reisenbichler. 2007. Status review of 

Puget Sound steelhead (Oncorhynchus mykiss). U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC81, 117 p. NTIS number PB2008-100451.

80 Berntson, E.A., P.S. Levin, and P.C. Moran (editors). 2007. Conservation of North Pacific rockfishes: 

Ecological genetics and stock structure. Proceedings of the workshop, March 2-3, 2004, Seattle, Washington. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-80, 80 p. NTIS number PB2007-111137.

79 Lawson, P.W., E.P. Bjorkstedt, M.W. Chilcote, C.W. Huntington, J.S. Mills, K.M.S. Moore, T.E.

 Nickelson, G.H. Reeves, H.A. Stout, T.C. Wainwright, and L.A. Weitkamp. 2007. Identification of 

 historical populations of coho salmon (Oncorhynchus kisutch) in the Oregon coast evolutionarily significant 

 unit. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-79, 129 p. NTIS number PB2007-111607.

78 Ruckelshaus, M.H., K.P. Currens, W.H. Graeber, R.R. Fuerstenberg, K. Rawson, N.J. Sands, and J.B. 

Scott. 2006. Independent populations of Chinook salmon in Puget Sound. U.S. Dept. Commer., NOAA 

Tech. Memo. NMFS-NWFSC-78, 125 p. NTIS number PB2007-104920.

77 Sloan, C.A., D.W. Brown, G.M. Ylitalo, J. Buzitis, D.P. Herman, D.G. Burrows, G. Yanagida, R.W. 

Pearce, J.L. Bolton, R.H. Boyer, and M.M. Krahn. 2006. Quality assurance plan for analyses of environmental samples for polycyclic aromatic compounds, persistent organic pollutants, fatty acids, stable isotope ratios, 

lipid classes, and metabolites of polycyclic aromatic compounds. U.S. Dept. Commer., NOAA Tech. Memo. 

NMFS-NWFSC-77, 30 p. NTIS number PB2007-104919.

76 Gustafson R.G., J. Drake, M.J. Ford, J.M. Myers, E.E. Holmes, and R.S. Waples. 2006. Status review 

of Cherry Point Pacific herring (Clupea pallasii) and updated status review of the Georgia Basin Pacific 

herring distinct population segment under the Endangered Species Act. U.S. Dept. Commer., NOAA Tech. 

Memo. NMFS-NWFSC-76, 182 p. NTIS number PB2007-104918.

75 Keller, A.A., B.H. Horness, V.J. Tuttle, J.R. Wallace, V.H. Simon, E.L. Fruh, K.L. Bosley, and D.J.

 Kamikawa. 2006. The 2002 U.S. West Coast upper continental slope trawl survey of groundfish resources

 off Washington, Oregon, and California: Estimates of distribution, abundance, and length composition. 

U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-75, 189 p. NTIS PB2006-111432.

Recent NOAA Technical Memorandums

published by the

Northwest Fisheries Science Center