NOAA Technical Memorandum NMFS-NWFSC-135

Exposure to a Mixture

of Toxic Chemicals:

Implications for the Health of Endangered

Southern Resident Killer Whales

doi:10.7289/V5/TM-NWFSC-135

November 2016

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Northwest Fisheries Science Center
NOAA Technical Memorandum NMFS-NWFSC-135

Exposure to a Mixture

of Toxic Chemicals:

Implications for the Health of Endangered

Southern Resident Killer Whales

doi:10.7289/V5/TM-NWFSC-135

Teresa M. Mongillo, Gina M. Ylitalo,1 Linda D. Rhodes,1

Sandie M. O’Neill,1,2 Dawn P. Noren,3

 and M. Bradley Hanson3

National Marine Fisheries Service

West Coast Region

Protected Resources Division

7600 Sand Point Way Northeast

Seattle, Washington 98115

Northwest Fisheries Science Center

Environmental and Fisheries Science Division

2725 Montlake Boulevard East

Seattle, Washington 98112

Washington Department of Fish and Wildlife

600 Capitol Way North, MS 43150

Olympia, Washington 98501

Northwest Fisheries Science Center

Conservation Biology Division

2725 Montlake Boulevard East

Seattle, Washington 98112

November 2016

1

2

3

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Northwest Fisheries Science Center

https://www.nwfsc.noaa.gov/index.cfm
NOAA Technical Memorandum NMFS-NWFSC Series

The Northwest Fisheries Science Center of NOAA’s National 

Marine Fisheries Service uses the NOAA Technical Memorandum 

NMFS-NWFSC series to issue scientific and technical publications. 

Manuscripts have been peer-reviewed and edited. Publications in this 

series can be cited in the scientific and technical literature.

The Northwest Fisheries Science Center’s NOAA Technical 

Memorandum NMFS-NWFSC series continues the NMFS-F/NWC 

series established in 1970 by the Northwest and Alaska Fisheries 

Science Center, which subsequently was divided into the Northwest 

Fisheries Science Center and the Alaska Fisheries Science Center. The 

latter uses the NOAA Technical Memorandum NMFS-AFSC series.

NOAA Technical Memorandums NMFS-NWFSC

are available at the Northwest Fisheries Science Center

website, https://www.nwfsc.noaa.gov/index.cfm.

Mention throughout this document to trade names or commercial 

companies is for identification purposes only and does not imply 

endorsement by the National Marine Fisheries Service, NOAA.

Reference this document as follows:

Mongillo, T. M., G. M. Ylitalo, L. D. Rhodes, S. M. O’Neill, D. P. Noren, 

and M. B. Hanson. 2016. Exposure to a mixture of toxic chemicals: 

Implications for the health of endangered Southern Resident 

killer whales. U.S. Dept. Commer., NOAA Tech. Memo. NMFSNWFSC-135, 107 p. doi:10.7289/V5/TM-NWFSC-135

ii
Contents

List of Figures..............................................................................................................................................................iv

List of Tables.................................................................................................................................................................v

Executive Summary ..................................................................................................................................................vii

Acknowledgments......................................................................................................................................................ix

Introduction and Objectives...................................................................................................................................... 1

Contaminants of Concern..........................................................................................................................................3

Persistent Organic Pollutants (POPs)..................................................................................................................6

Polychlorinated Biphenyls (PCBs) ..................................................................................................................7

Polybrominated Diphenyl Ethers (PBDEs)....................................................................................................8

Dichlorodiphenyltrichloroethane (DDT and Metabolites) ....................................................................... 10

Other Toxic Chemicals of Concern ................................................................................................................... 12

Polycyclic Aromatic Hydrocarbons (PAHs) ................................................................................................ 12

Trace Elements................................................................................................................................................. 12

Geographic Distribution of Southern Resident Killer Whales............................................................................ 14

POPs in Southern Resident Killer Whale Prey...................................................................................................... 15

Factors Influencing Bioaccumulation in Whales..................................................................................................26

Influence of Geographic Distribution and Diet on POP Accumulation.......................................................26

Dynamics of POP Transfer from Mother to Offspring ...................................................................................27

Other Influential Factors Affecting POP Accumulation..................................................................................31

Potential Adverse Health Effects from POP Exposure......................................................................................... 33

Influence of Organic Contaminants on the Endocrine System...................................................................... 33

Thyroid Hormones.......................................................................................................................................... 33

Effects on Thyroid Hormones from Organic Contaminant Exposure .....................................................35

Sex Hormones..................................................................................................................................................36

Effects on Reproduction from Organic Contaminant Exposure ................................................................37

Influence of Organic Contaminants on the Nervous System ....................................................................38

Influence of Organic Contaminants on Immune Function and Disease Susceptibility..............................40

Immune System and Functional Testing Overview....................................................................................40

Effects on Immune Function of Organic Contaminant Exposure............................................................42

Disease Susceptibility......................................................................................................................................43

iii
The Development of Biomarkers for Toxicity........................................................................................................45

Interactive Effects......................................................................................................................................................48

PCBs and PBDEs..................................................................................................................................................48

PCBs, PBDEs, and Chlorinated Paraffins (CPs)...............................................................................................49

PCBs, PBDEs, and Methyl Mercury (MeHg)....................................................................................................50

(Anti)Estrogenic Compounds ............................................................................................................................50

Summary ...............................................................................................................................................................52

Implications for Southern Resident Killer Whales...............................................................................................53

Contaminated Prey and Nutritional Limitation...............................................................................................56

Endocrine Disruption and Sensitive Life Stages ..............................................................................................57

Immunotoxicity and Disease Susceptibility......................................................................................................59

Interactive Effects.................................................................................................................................................60

Data Needs and Future Directions..........................................................................................................................63

Persistent Pollutants in Killer Whales................................................................................................................63

Persistent Pollutant Exposure in Calves............................................................................................................64

Persistent Pollutants in Prey and Prey Availability ..........................................................................................66

Health Effects........................................................................................................................................................66

Conclusions................................................................................................................................................................69

References...................................................................................................................................................................70

Appendix A: Infectious Diseases Reported for Killer Whales.............................................................................95

References: Appendix A.......................................................................................................................................98

Appendix B: Noninfectious Diseases Reported for Killer Whales....................................................................100

References: Appendix B......................................................................................................................................101

Appendix C: Infectious Diseases of Sympatric Marine Mammals ................................................................... 102

References: Appendix C..................................................................................................................................... 105

iv
Figures

Figure 1. Chemical structure of PCBs.......................................................................................................................7

Figure 2. Chemical structure of PBDEs....................................................................................................................9

Figure 3. Chemical structure of DDT......................................................................................................................11

Figure 4. Primary components of the hypothalamic–pituitary–thyroid axis. The potential

mechanisms of action for PCBs and PBDEs on the hypothalamic–pituitary–thyroid axis............................34

Figure 5. Highly simplified diagram of the types, functions, and products of immune cells

involved in nonspecific and specific immunity.....................................................................................................40

Figure 6. Diagram showing the interaction between an aryl hydrocarbon receptor (AhR) and

a dioxin-like compound ...........................................................................................................................................46

Figure 7. Summed PCBs, PBDEs, and DDTs in the blubber of Southern Resident killer whales..................54

v
Tables

Table 1. Persistent pollutants that may pose a risk to Southern Resident killer whales..................................4

Table 2. Percent lipid and POP concentrations (ng/g wet weight) of adult and subadult

Pacific salmon sampled in terminal areas.............................................................................................................. 19

Table 3. Concentrations (±) of summed PCBs, PBDEs, and DDTs (lipid weight, ng/g)

measured in blubber collected from killer whales and other cetaceans from the North Pacific ....................23

Table 4. Contaminant transfer from delphinid and phocoenid females to calves during

gestation and/or lactation.........................................................................................................................................28

Table 5. Mixture content and interaction type, with corresponding health effect(s), from case studies.......48

Table 6. A list of some (anti)estrogenic PCB and PBDE congeners ................................................................... 51

Table A-1. Known or potential pathogens identified in killer whales. The method of

detection and whale origin are included ......................................................................................................96

Table C-1. Known and high-probability or putative pathogens affecting sympatric species

of cetaceans and pinnipeds .................................................................................................................................... 103

vi
Executive Summary

The distinct population segment (DPS) of Southern Resident killer whales (Orcinus orca) was 

listed as endangered under the Endangered Species Act (ESA) on 18 November 2005. The 

Southern Residents regularly occur in the inland waters of Washington and British Columbia 

during late spring, summer, and early fall. Less is known about their movements in the winter, 

but they occur in coastal waters from California to southeast Alaska. Many studies have indicated 

that they primarily consume Chinook salmon (Oncorhynchus tshawytscha). Several major threats 

were identified—both in the final determination to list the Southern Resident killer whale DPS as 

endangered, and in the Southern Resident killer whale recovery plan—one of which was exposure 

to high levels of organochlorine contaminants and increasing levels of emerging contaminants. 

The primary objectives of this Technical Memorandum are to review the contaminants that 

may pose a risk to the Southern Resident killer whales and to discuss the health implications of 

exposure to these contaminants. In this report, we focus on three persistent organic pollutants 

(POPs): polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and 

dichlorodiphenyltrichloroethane (DDT) and its metabolites. We focus on these three POPs 

because they are found at relatively high levels in the whales and may cause adverse health 

effects. We also describe what is currently known about the whales’ geographic distribution and 

diet, as well as contaminant levels measured in their prey. We review the factors that influence 

contaminant bioaccumulation and the development of biomarkers for exposure and toxicity. 

Lastly, we highlight data gaps and make recommendations for future studies. 

Adult killer whales are primarily exposed to POPs through the ingestion of prey. Based on 

the importance of Chinook salmon as prey, and their elevated POP levels compared to other 

salmonids, they are likely a significant source of contaminants to the Southern Residents. 

Various adverse health effects have been associated with exposures to PCBs, PBDEs, and DDTs 

in humans, laboratory animals, and wildlife. These POPs have the ability to cause endocrine 

disruption, reproductive disruption or failure, immunotoxicity, neurotoxicity, neurobehavioral 

disruption, and cancer. The average concentration of blubber summed PCBs (ΣPCBs) in male 

Southern Resident killer whales sampled between 2004 and 2013 was 45,000 ± 31,000 ng/g 

lw (lipid weight), which exceeds a health effects threshold in harbor seals (Phoca vitulina). 

Average blubber ΣPBDEs in sampled Southern Residents were 4,800 ± 3,500 ng/g lw, with most 

individuals exceeding the levels associated with altered thyroid hormone levels in post-weaned 

and juvenile gray seals (Halichoerus grypus). Although there has been no report in the literature 

on a marine mammal health effect threshold for DDTs, ΣDDTs levels in the blubber of Southern 

Residents were high, and ranged from 1,200 to 210,000 ng/g lw. 

The high levels of POPs in the Southern Residents have health implications that are influenced by 

interactions with other stressors, including the abundance of their prey. Reduced prey availability 

can cause a whale to draw on lipid reserves stored in its blubber, mobilizing POPs into circulation, 

where they have the potential to cause a toxic response. Therefore, nutritional stress from reduced 

Chinook salmon populations may act synergistically with high POP levels in Southern Residents 

and result in deleterious health effects.

vii
The potential for adverse health effects from POP exposure in an individual killer whale is 

also influenced by the timing of the exposure. For example, killer whale calves may be more 

susceptible to POP-induced endocrine disruption because they are exposed during critical stages 

of their development, when healthy growth and development rely on normal levels of hormones. 

The effects from exposure during this vulnerable life stage could include alterations to the 

individual’s metabolism, impeded growth and development, delayed or premature physical or 

sexual maturity, reduced future fecundity, or reduced perinatal survival. Contaminant exposure 

during neurodevelopment can also reduce learning or impair memory. With this reduced ability 

to learn, a killer whale’s capacity to successfully forage and interact with other pod members 

could be affected. 

High exposure at a young age can also compromise the immune system and increase disease 

susceptibility. For example, high POP exposure during nursing can cause a significant reduction 

in antibody response and create a greater predisposition for opportunistic or secondary 

infections. Because infectious diseases are a large source of morbidity and mortality in marine 

mammals, a compromised immune system bodes poorly for the overall health status, well-being, 

and anticipated life expectancy of individual killer whales. In the Appendices, we report and 

identify pathogens and infections for wild and public-display killer whales, noninfectious diseases 

for killer whales, and infectious diseases for sympatric marine mammals.

Health effects from exposure to PCBs, PBDEs, and DDTs should not be considered in isolation. 

Killer whales are exposed to a mixture of pollutants, some of which may interact synergistically 

and enhance toxicity, influencing the health of the Southern Residents. Although it is difficult 

to predict health effects from mixture interactions, it is important to predict the toxicity of such 

mixtures; disregarding the interactive effects may underestimate risk to an individual or to the 

population. Furthermore, we also stress the importance of establishing the impact on the health 

of killer whales of the transformed by-products, or metabolites, of the pollutants. The practice 

of examining only high doses of POPs may also underestimate the risk to the killer whales. 

Endocrine disruptors can produce non-linear dose–response effects and interact at lower doses 

than would occur with the isolated chemicals. Therefore, even low concentrations of persistent 

pollutants, when combined, have the potential to cause adverse effects in Southern Residents. 

Progress has been made in identifying potential effects from exposure to contaminants in other 

species. However, in order to draw meaningful conclusions about the health of killer whales, some 

uncertainties and data gaps still need to be addressed. In this report, we provide summaries of the 

projects currently in progress and recommendations for future work that can guide management 

actions to advance the recovery of Southern Resident killer whales. These recommendations 

include collecting better data on toxicant levels in the whales and their prey, examining the 

exposure of calves to toxicants, describing transfer dynamics, understanding the role of prey 

availability in the mobilization of toxicants, developing more biomarkers of exposure and toxicity, 

and conducting studies to assess health effects in the whales. We consider these recommendations 

an important step toward evaluating the current and future health of this endangered species.

viii
Acknowledgments

We would like to acknowledge the following people who reviewed this report and provided 

valuable feedback: Lynne Barre, Stephen Raverty, Pete Schroeder, Jessica Lundin, Chris Yates, 

and Alison Agness. We would also like to thank Tina Loucks-Jaret and Kailey Genther for their 

additional editorial reviews.

ix
Introduction and Objectives

Persistent organic pollutants (POPs) are a family of toxic chemicals that are lipophilic (i.e., fat 

soluble), resistant to environmental degradation, and can increase in concentration up the food 

chain (biomagnify). Because POPs are lipophilic, they are largely stored in fatty tissues in the 

body, such as marine mammal blubber, and can become mobilized during times of nutritional 

stress, illness, or during reproductive processes such as pregnancy or lactation. They are cleared 

from the body via several pathways, including metabolism (conversion to another product) 

and elimination via urine and feces or transplacental and/or lactational transfer. The ability 

for POPs to biomagnify means species that occupy positions at the top of the food chain can 

accumulate large amounts of these compounds throughout their lives and have body burdens that 

are several orders of magnitude greater than species that feed at lower trophic levels. At certain 

concentrations and mixtures, these pollutants have been associated with reproductive impairment 

(Reijnders 1986, Subramanian et al. 1987, Reddy et al. 2001, Schwacke et al. 2002), immunotoxicity 

(de Swart et al. 1996, Fonnum et al. 2006), endocrine disruption (de Boer et al. 2000, Legler 

and Brouwer 2003, Darnerud 2008, Legler 2008), neurotoxicity (Darnerud 2003, Viberg et al. 

2003, Viberg et al. 2006, Darnerud 2008), and cancer in humans and wildlife (Ylitalo et al. 2005, 

Bonefeld-Jørgensen et al. 2011). 

The distinct population segment (DPS) of Southern Resident killer whales (Orcinus orca) are 

long-lived, upper trophic-level predators that seasonally feed on prey that are in relatively close 

proximity to industrial discharge, urban drainage, and agricultural run-off areas where POPs 

can be highly concentrated. Consequently, they have high contaminant levels relative to other 

populations of killer whales. In 2001, the Committee on the Status of Endangered Wildlife in 

Canada (COSEWIC) categorized the Southern Residents as endangered. On 18 November 2005, 

the Southern Resident killer whales were listed as endangered under the U.S. Endangered Species 

Act (NMFS 2005) and a recovery plan was completed in 2008 (NMFS 2008). The Southern 

Resident killer whale population recently totaled fewer than 80 individuals in three distinct 

pods (J, K, and L). They consume a variety of fish species, but Chinook salmon (Oncorhynchus 

tshawytscha) are identified as their primary prey during spring, summer, and fall (Ford and Ellis 

2006, Hanson et al. 2010, Ford et al. 2016). 

Since the mid-1970s, the geographic range of Southern Residents has been determined primarily 

from opportunistic re-sightings of photo-identified individuals, and occasionally from strandings. 

In general, these pods have distinct summer/fall and winter/spring seasonal patterns. There is 

also seasonal variation between pods. While summer locations are well known (primarily inland 

and coastal waters of Washington and British Columbia), less is known about fall, winter, and 

spring. Passive autonomous acoustic recorders have recently provided more information on the 

seasonal occurrence of these pods along the West Coast of the United States (Hanson et al. 2013). 

In addition, satellite-linked tags were recently deployed in winter months on members of J, K, and 

L pods. Results were consistent with previous data, but provided much greater detail, showing J 

pod’s wide-ranging use of inland waters, and K and L pods’ extensive movements in U.S. coastal 

waters (NWFSC unpubl. data). 
Critical habitat was designated in 2006 and includes approximately 2,560 square miles of inland 

Washington waters in three specific areas: 1) the Summer Core Area in Haro Strait and the waters 

around the San Juan Islands, 2) Puget Sound, and 3) the Strait of Juan de Fuca (NMFS 2006). 

Water quality to support growth and development was identified as a feature of the critical 

habitat areas. In January 2014, NOAA Fisheries received a petition from the Center for Biological 

Diversity to revise the critical habitat designation based on new information about the whales’ 

habitat use along the coast and the consideration of in-water sound as an element of habitat. 

In February 2015, a 12-month finding was issued that identified next steps for collecting and 

analyzing data, and for developing a proposed rule to revise critical habitat, expected in 2017 (80 

FR 9682; 24 February 2015).

Several factors currently pose a risk to the Southern Residents, including exposure to high levels 

of organochlorine contaminants and increasing levels of emerging contaminants (e.g., brominated 

flame retardants); reduced prey availability, size, and quality; noise pollution and vessel activity; 

infectious disease; and oil spills (NMFS 2008). These factors most likely interact; for example, 

disease may be the ultimate result of chronic exposure to or increased levels of contaminants that 

can reduce resistance to pathogens in the marine environment.

The objectives of this Technical Memorandum are: 

•	 to review the contaminants that may pose a health risk to the Southern Resident killer whales;

•	 to describe what is currently known about the Southern Residents’ geographic distribution;

•	 to review the diet and the POP levels measured in the Southern Residents’ prey;

•	 to describe the factors that influence bioaccumulation and affect the variability of POP 

levels measured in Southern Resident killer whales and other marine mammals;

•	 to describe the potential adverse health effects of isolated POPs (PCBs, PBDEs, and DDTs);

•	 to review the development of biomarkers for exposure and toxicity;

•	 to describe the interactive effects of exposure to a mixture of POPs;

•	 to discuss the implications for the health of the Southern Residents from exposure to POPs; 

•	 to highlight data gaps and make recommendations for future studies.

2
Contaminants of Concern

In 2008, NMFS developed the Southern Resident killer whale recovery plan. In the plan, a 

number of environmental contaminants that may pose a health risk to killer whales were 

highlighted (Table 1). In this section, we provide background information on polychlorinated 

biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and dichlorodiphenyltrichloroethane (DDT) and its metabolites. Although levels of PCBs and DDTs have dramatically 

decreased in environmental samples since their production ban in the mid-1970s (Mearns 1988, 

Lieberg-Clark et al. 1995, Calambokidis et al. 2001, Rigét et al. 2010), these compounds continue 

to be found in substantial levels in marine biota around the world, including killer whales and 

other cetaceans from the eastern North Pacific (Ylitalo et al. 2001, Kajiwara et al. 2006, Krahn et 

al. 2007a, Kajiwara et al. 2008, Krahn et al. 2009, Ylitalo et al. 2009, Jepson et al. 2016). Levels of 

PBDEs were increasing almost exponentially in several marine species between the 1980s and 

early 2000s (Ikonomou et al. 2002, Lebeuf et al. 2004, Ross et al. 2013), causing a concern among 

scientists for many food webs. More recently, it appears that several species are experiencing 

declining or stabilizing PBDE concentrations (Elliott et al. 2005, Law et al. 2010, West et al. 2011, 

Ross et al. 2013), likely because of the decrease in production and use of certain PBDE technical 

mixtures. However, due to the presence of PBDEs in currently used products, they will continue 

to be delivered to the environment, contaminating the aquatic food web for many more years.

These three classes of POPs (PCBs, PBDEs, and DDTs) are the focus of this report, as they 

are found at relatively high levels in Southern Resident killer whales, their prey, and their 

environment. Adverse health effects may be exacerbated when combinations of these POPs 

are present in organisms. We also briefly discuss other toxic chemicals of concern, including 

polycyclic aromatic hydrocarbons (PAHs) and other trace elements that may pose a risk to the 

killer whales. Although there are several toxic chemicals of concern (e.g., dioxins, furans, personal 

care products, other endocrine disruptors, etc.), they are not discussed here as they are outside 

the scope of this Technical Memorandum. 

3
Table 1. Persistent pollutants that may pose a risk to Southern Resident killer whales.a

a Source: Updated from NMFS (2008).

Pollutant(s) Use and/or Source Persistent Bioaccumulative Risks

PCBs electrical transformer and capacitor fluid with yes yes reproductive 

(polychlorinated limited use in North America; enters environment skeletal abno

biphenyls) from runoff, spills, and incineration and immun

carcinogenicdisruption

PBDEs two of three product PBDEs banned in yes yes endocrine d

(polybrominated Europe; same two products withdrawn from thyroid func

diphenyl ethers) North American marketplace in 2005, one autoimmun

(deca-) product still used globally in electrical immunosupcomponents, backings of televisions and lung and necomputers, textiles and vehicle seats; ubiquitous in environment

DDT pesticide still used in some countries, currently yes yes reproductive 

(dichlorodiphenyl- banned in North America; persists in terrestrial immunosup

trichloroethane) runoff 30 years post-ban, enters atmosphere from thyroid effec

areas where still in use

dioxins, furans burning of salt-laden wood, municipal yes yes thymus and 

incinerators, residential wood and wood waste birth defectscombustion, runoff from sewage sludge, wood impairmenttreatment; by-product of chlorine bleaching, wood immunotoxproduct processing, and incomplete combustion; pulp and paper mills

PAHs fuel combustion, aluminum smelting, wood yes relatively low carcinogenic 

(polycyclic aromatic treatment, oil spills, metallurgical and coking potential; may dysfunction

hydrocarbons) plants, pulp and paper mills depend on neurotoxicit

molecular weight dysfunction

eggshell thin

PFOs stain, water, and oil repellent (until recently yes yes, in blood, liver, promotion o

(perfluorooctane included in Scotchgard), fire-fighting foam, fire kidney, and muscle

sulfonate) retardants, insecticides and refrigerants; ubiquitous 

in environment

4
Table 1 continued. Persistent pollutants that may pose a risk to Southern Resident killer whales.a

a Source: Updated from NMFS (2008).

Pollutant(s) Use and/or Source Persistent Bioaccumulative Risks

TBT, DBT antifoulant pesticide used on vessels yes yes unknown, b

(tributyltin, with hearing 

dibutyltin)

PCPs flame retardants, plasticizers, paints, sealants, and yes yes endocrine d

(polychlorinated additives in lubricating oils

paraffins)

PCNs ship insulation, electrical wires and capacitors, yes yes endocrine d

(polychlorinated engine oil additive, municipal waste incineration, 

naphthalenes) and chloralkali plants; contaminant in production 

of technical PCBs

APEs detergents, shampoos, paints, pesticides, plastics, moderate moderate endocrine d

(alkylphenol pulp and paper mills, textile industry; found in 

ethoxylates) sewage effluent and sediments

PCTs fire retardants, plasticizers, lubricants, inks and yes yes endocrine d

(polychlorinated sealants; enters environment in runoff reproductive 

terphenyls)

References: Primarily Grant and Ross (2002), but also Lindstrom et al. (1999), Hooper and McDonald (2000), Kannan et al(2003); Legler and Brouwer (2003), Van de Vijver et al. (2003), Rayne et al. (2004), Song et al. (2005), Ylitalo et al. (2005), DLegler (2008), Fernie et al. (2009), and Kodavanti et al. (2010).

5
Persistent Organic Pollutants (POPs)

POPs enter fresh and marine waters and sediments from numerous direct and indirect sources. 

For example, POPs can enter a local environment through poorly maintained hazardous 

waste sites, illegal dumping, leaks from electrical transformers, disposal of consumer products 

containing POPs, and burning of some wastes in municipal and industrial incinerators. Point 

source (or direct) pollution is pollution that is discharged directly into the marine environment 

from an identifiable source, such as an outfall from municipal and industrial wastewater 

treatment plants, or pulp and paper mills. In contrast, non-point source (or indirect) pollution 

does not have an identifiable source. Examples of non-point sources include surface runoff and 

atmospheric deposition. Oceans act as a repository for domestic and industrial wastes, and 

significant concentrations of POPs have been measured in ocean sediments and biota. Recently, 

a multiphase project was initiated by multiple agencies to assess toxic chemical loadings from 

point and non-point sources into the whales’ critical habitat. The 10 major pathways for pollution 

are from surface runoff, groundwater, rivers and streams, atmospheric deposition, wastewater, 

combined sewer overflows, oil spills, migrating biota such as salmon, inflow from the Pacific 

Ocean, and contaminated sediment (Hart Crowser, Inc. et al. 2007).

POPs are found throughout the world, regardless of where they were produced or used, because 

they can be transported through several pathways. They are typically concentrated near populated 

areas of high human activity and industrialization. The highest levels of these compounds have 

been measured in species from the Northern Hemisphere, specifically in industrialized Asia, 

North America, and Europe (Houde et al. 2005). The dispersion of POPs in the environment 

depends on the pollutant’s physicochemical properties, with long-range and global transport 

occurring via oceanic and riverine transport and atmospheric deposition (Iwata et al. 1993, 

Grant and Ross 2002, Houde et al. 2005). These physicochemical properties include persistence 

(measured by the environmental half-life), vapor pressure, water solubility, and bioaccumulation 

potential (expressed in terms of the octanol–water partitioning coefficient Kow; Grant and Ross 2002). 

Once the contaminants enter the marine environment, several factors influence the retention 

and flushing of these compounds in the local environment, including ocean circulation and the 

physical structure of the basin. For example, Puget Sound is a deep-water fjord with several sills 

that restrict mixing and inhibit both ocean inflow and the outflow of toxic chemicals. As a result, 

POPs that enter the Puget Sound basin have long residence times, resulting in an increase in 

contaminant exposure and bioaccumulation in local food webs. Additionally, many species are 

known to exhibit a high degree of residency within Puget Sound (e.g., there are several resident 

populations of fish in Puget Sound, including Pacific herring [Clupea pallasii] and Chinook 

salmon), resulting in more fish being exposed to more contaminants (West et al. 2008, O’Neill 

and West 2009). Thus, the Puget Sound ecosystem and food webs are especially susceptible 

to toxic input due to their proximity to urban areas and the combination of the hydrological 

isolation of Puget Sound and the biological isolation of its resident species (Collier et al. 2007, 

West et al. 2008, O’Neill and West 2009). 

6
Polychlorinated Biphenyls (PCBs)

PCBs are synthetic organic chemicals with 209 potential congeners, or forms. The chemical 

structure of PCBs consists of from one to ten chlorine or hydrogen atoms attached to biphenyl, 

a molecule composed of two benzene rings (Figure 1). PCB congeners are numbered according 

to the International Union of Pure and Applied Chemistry (IUPAC) system (i.e., a systematic 

method of naming organic chemical compounds). They were designed for chemical stability and 

were historically used for transformers and capacitors. The manufacture of PCBs was banned 

in the U.S. in 1979 with the recognition of their global distribution, persistence in nature, and 

potential for adverse health effects on wildlife and humans.

The number and position of chlorine atoms influence the volatility, persistence, aqueous 

solubility, bioaccumulation potential, and toxicity of the PCB congeners. For example, the 

more chlorinated PCB congeners tend to be more environmentally persistent and less volatile 

than the less chlorinated congeners (Grant and Ross 2002). In addition, the more chlorinated 

PCBs tend to have a higher bioaccumulation potential and resist metabolic degradation more 

than the less chlorinated PCBs that may readily metabolize (Grant and Ross 2002). The toxic 

endpoint of a PCB congener can depend on the planarity of the molecule or the position of the 

chlorine atoms (Silkworth and Grabstein 1982). The planar PCB congeners, such as those with 

non-ortho chlorine substitution, are structurally similar to dioxin. Dioxins are highly toxic and 

can cause reproductive impairment, disruption to the immune system, endocrine disruption, 

developmental problems, and also cause cancer (WHO 2010). Thus, the more acutely toxic PCB 

congeners are those that are more dioxin-like. However, further research is revealing that, though 

the non-dioxin-like PCB congeners—the ortho-substituted congeners—have different toxic 

endpoints, they are no less concerning. For example, researchers have reported that some of the 

non-dioxin-like PCBs can interfere with hormone-regulated processes (Bonefeld-Jørgensen et al. 

2001, Oh et al. 2007) and enhance developmental neurotoxicity (Fischer 2008) and cytotoxicity 

(Pellacani et al. 2014). In general, some PCBs persist in nature, bioaccumulate in upper trophic 

level species, resist metabolic degradation, and may cause adverse health effects in many species.

Figure 1. Chemical structure of PCBs. The numbers assigned to the carbon atoms indicate the potential 

positions of the chlorine atoms on the benzene rings. The meta-, ortho-, and para- labels describe the 

placement of the chlorine atoms.

7
Although many areas in the Pacific Northwest lack information on both historical and current 

levels of PCB contamination, there are some data that reveal regional PCB trends in sediment. 

Sediments in Washington and British Columbia have been routinely monitored for contaminant 

exposure since the early 1900s. These data indicate a trend in PCB contamination levels similar to 

the global production of PCBs. PCBs reached a peak in global production by 1970 (Breivik et al. 

2002). PCB trends in sediment in Puget Sound and the Strait of Georgia showed a steady increase 

in concentration beginning in 1930 that reached peak levels in the early 1960s (Lefkovitz et al. 

1997, Johannessen et al. 2008). The peak PCB levels in the sediment at that time were close to four 

times the levels of PCB sediment contamination in the 1990s (Lefkovitz et al. 1997). More recently, 

sediment cores from the Strait of Georgia indicate a declining trend in PCB concentrations 

(Johannessen et al. 2008). 

PCB data for some wildlife also indicate recent declines in concentrations. Since 1986, NOAA’s 

National Status and Trends Program has been monitoring PCBs and other contaminants in 

mussels and oysters around the U.S. coastline, including 17 sites within Washington State. Because 

these organisms are filter feeders, their tissue is considered an indicator for local water quality 

conditions. PCB concentrations in mussels in Puget Sound have been slowly declining; however, 

in general they remain above the national average (PSAMP 2007). Puget Sound harbor seals 

(Phoca vitulina) have also experienced declines in PCB concentrations beginning in the 1970s 

(Calambokidis et al. 1999). More recent data indicate that PCB concentrations in harbor seals 

have declined by 81% from 1986 to 2003 (Ross et al. 2013). Similar to the local declines of PCBs 

in both the sediment and wildlife, a global decline of PCB levels has been observed. For example, 

PCB levels in Swedish women’s breast milk were shown to decrease by 30% from 1972 to 1997 with 

a half-life of 14 years (Norén and Meironyté 2000). 

Not all species in Puget Sound, however, have experienced a decline in PCB levels. For instance, 

PCB concentrations in Pacific herring throughout Puget Sound remain high and have lacked a 

declining trend (West et al. 2011). PCB concentrations in English sole (Parophrys vetulus) from 

most urban locations have also lacked a declining trend and exceed harmful effects thresholds, 

indicating that PCBs are still a concern in Puget Sound (West et al. 2011).

Polybrominated Diphenyl Ethers (PBDEs)

PBDEs are another class of synthetic organic compounds with 209 possible congeners. The 

chemical structure consists of two phenyl rings connected by an ether bond with from one to 

ten bromine or hydrogen atoms attached (Figure 2). PBDEs are structurally similar to PCBs and 

have similar physicochemical properties. PBDE congeners are numbered according to the IUPAC 

system that was originally designed for PCBs. In general, several PBDEs are lipophilic, persistent 

in the environment, and accumulate in ocean sediments because of their high binding affinity to 

particles (de Wit 2002). The lighter PBDEs are highly bioaccumulative, more readily biomagnify 

in aquatic and terrestrial food webs, are more toxic than the heavier congeners, and present an 

increased risk to the health of marine mammals (Siddiqi et al. 2003, Ross et al. 2009). In contrast, 

the uptake of the larger congeners (e.g., BDE-209) is restricted by particle-binding (Ross et al. 

2009), although these heavier weighted congeners are still observed in upper trophic level species 

8
Figure 2. Chemical structure of PBDEs. The numbers assigned to the carbon atoms indicate the potential 

positions of the bromine atoms on the phenyl rings.

9

(e.g., harbor seals; Shaw et al. 2007). All of the PBDE homologue groups, or groups of congeners 

with the same number of bromine atoms, appear to be environmentally persistent (Ross et al. 

2009) and may be more persistent than PCBs (de Boer et al. 1998). 

PBDEs have been identified as a growing concern. They are ubiquitous, with increasing levels 

found in various matrices, including surface water, sewage sludge, sediment, air, and biota (Hale 

et al. 2003, Hites 2004). Since the 1960s, PBDEs have been used as additive flame retardants in 

many products, including electronics, textiles, and plastics. Additive flame retardants are mixed 

into products, which can cause them to leach more readily into the environment (de Boer et al. 

2000, de Wit 2002) than reactive flame retardants, which are covalently bound to their product 

and thus less likely to leach into the environment. PBDE production has three commercial 

mixtures (penta-, octa-, and deca-BDEs), and each mixture comprises a combination of PBDE 

congeners that have been used in a variety of products. For example, the main constituents of the 

penta-mixture include BDE-47, -99, and -100, and to a lesser degree congeners -153, -154, and -85 

(Hale et al. 2003). These congeners, as well as -209, are considered of particular importance and 

concern. Almost half of the production of the deca- and octa- forms, and over 95% of the pentaproducts, has occurred in North America (Hale et al. 2003, Hites 2004). As a result, PBDE levels 

in humans in the United States are from 10 to 100 times greater than elsewhere (Schecter et al. 2003). 

Because of health concerns, manufacturers in the United States voluntarily stopped producing the 

penta- and octa- mixtures by the end of 2004. In January 2006, the Washington State Department 

of Ecology (Ecology) and the Washington State Department of Health (Health) issued a Final 

PBDE Chemical Action Plan (Ecology and Health 2006), recommending that the Washington 

State Legislature prohibit the sale, manufacture, or distribution of new products containing pentaor octa-BDE in Washington State. In 2007, the Washington State Legislature adopted RCW 70.76; 

under this law, no person may manufacture, knowingly sell, offer for sale, distribute for sale, or 

distribute for use in this state nonedible products containing PBDEs, effective January 2008. 

The exemptions from this prohibition are described in RCW 70.76.020, and include products 

containing deca-BDE; the sale or distribution of any used vehicle or vehicle parts manufactured 

before January 2008; and equipment used primarily for military or federally funded space 

program applications, medical devices, and certain recycled materials. In 2010, Environment 
Canada and Health Canada published a Final Revised Risk Management Strategy for PBDEs 

that: 1) prohibits the use, sale, offer for sale, and import of all PBDEs; 2) prohibits PBDEs in 

products; 3) describes a commitment to a voluntary phase-out for deca-BDE; 4) monitors 

PBDEs in the Canadian environment, including landfills and at wastewater treatment plants; 

5) develops Federal Environmental Quality Guidelines; and 6) develops a strategy that includes 

continuing research and implementing risk-management activities. Effective January 2011, decaBDE was prohibited in televisions, computers, and furniture following the identification of safer 

alternatives. Deca-BDE (a commercial mixture of PBDEs that contains 97% of congener BDE209) now accounts for all PBDE production in North America, and is primarily used in textiles 

and added to various plastic polymers (Shaw and Kannan 2009). Consequently, the heavier PBDE 

congeners compose a major proportion of the total PBDEs found in the environment, and can 

become a source of the lighter, more persistent, and more toxic congeners (Johannessen et al. 

2008, Ross et al. 2009). 

Specific data are limited for PBDE levels in Washington State. The environmental levels of the 

less-brominated congeners appear to have surpassed PCBs in some areas in North America, 

including in air, water, sewage sludge, and sediment (Hale et al. 2003, Ross et al. 2009). Time 

trend studies indicate an increase of PBDEs in biota since the 1970s (de Wit 2002, Shaw and 

Kannan 2009). PBDE concentrations in harbor seals from Puget Sound increased exponentially, 

with a doubling time of 3.1 years, from 1984 to 2003, but appeared to drop in 2009 (Ross et al. 

2013). Pacific herring also appear to have PBDE levels that are declining or remaining stable, 

whereas English sole from urban basins showed no declining trend in PBDE concentrations 

(West et al. 2011). PBDEs in great blue heron (Ardea herodias) eggs from the Fraser River estuary 

and double-crested cormorant (Phalacrocorax auritus) eggs from the Strait of Georgia increased 

exponentially until the mid-1990s, followed by a brief decrease in concentrations (Elliott et al. 2005).

Dichlorodiphenyltrichloroethane (DDT and Metabolites)

DDTs have a ubiquitous distribution and are found in air, water, soil, and biota. DDTs are 

extremely persistent in nature, semi-volatile, highly stable, have low water solubility, biomagnify 

in the food chain, and are highly toxic to aquatic organisms. These organochlorines are produced 

by the reaction of chloral with chlorobenzene in the presence of a catalyst, sulfuric acid (Figure 3). 

DDTs have 14 carbon atoms, nine hydrogen atoms, and five chlorine atoms (Figure 3). DDE and 

DDD are the major metabolites of DDT, and are also highly persistent. In fact, p,p'-DDE is the 

most abundant DDT metabolite found in killer whale blubber, accounting for approximately 80% 

of the summed DDTs (ΣDDTs) measured between 1994 and 1999 in Alaska resident killer whales 

and 86% of the ΣDDTs in transient killer whales (Ylitalo et al. 2001).

DDT was first used as an insecticide in the late 1930s and during World War II on troops and 

civilians to control insects that transmit diseases such as malaria and typhus. After the war, the 

use of DDT increased to include controlling pests in commercial and agricultural areas, forests, 

homes, and gardens. By 1972, more than 675,000 tons of DDT had been applied domestically in 

the United States, with 1959 being the peak year for DDT use (40,000 tons; EPA 1972). 

10
Figure 3. Chemical structure of DDT. DDT contains 14 carbon atoms, nine hydrogen atoms, and five 

chlorine (Cl) atoms.

Reproductive dysfunction, as well as eggshell thinning, was linked to exposure to DDTs in 

various bird species (reviewed in Fry 1995). Because of its toxic effects on wildlife and laboratory 

animals and its potential health risks to humans, the United States and several other countries 

banned general usage of DDT in the 1970s. Production of this insecticide was stopped by 1985 

in the United States; its worldwide decrease in use, the development of alternative pesticides, 

public awareness of its potential toxicity to humans and wildlife, and insect resistance were all 

contributing factors. In 2001, the Stockholm Convention ratified that the use of DDT be restricted 

to controlling disease vectors under the guidance of the World Health Organization (Stockholm 

Convention 2001). Thus, this pesticide continues to be used in certain areas of the world (e.g., 

Africa) to control for malaria and other insect-borne diseases (Biscoe et al. 2005).

DDTs frequently co-occur in the marine environment with PCBs and other POPs. Many of these 

compounds possess certain chemical properties (e.g., stability, low flammability, lipophilicity) that 

not only made them effective pesticides and industrial compounds, but also make them highly 

persistent, bioaccumulative environmental contaminants. In Puget Sound, contemporary levels 

of DDTs in sediments and marine fish are generally lower than PCB concentrations (Brown et al. 

1998, Calambokidis et al. 2001, West et al. 2008). For example, Johnson et al. (2007) found that 

concentrations of ΣPCB measured in whole bodies of outmigrating juvenile Chinook salmon 

captured in Puget Sound were more than two times higher than the ΣDDT values. In contrast, 

contemporary levels of DDTs are higher than PCB concentrations in sediments and marine 

biota from central and southern California (Jarvis et al. 2007, Blasius and Goodmanlowe 2008, 

Kimbrough et al. 2008). These higher levels of DDTs in California (the “California signature”) are 

due to heavy agricultural use of this compound before its ban in the 1970s, as well as to the longterm significant discharges of DDTs from a manufacturing plant (Eganhouse et al. 2000, Bay et al. 

2003). Although bivalves in southern California had the highest ΣDDT concentrations compared 

to bivalves sampled elsewhere along the continental U.S., average concentrations are declining 

(Sericano et al. 2014).

11
Other Toxic Chemicals of Concern

Polycyclic Aromatic Hydrocarbons (PAHs)

There is a suite of toxicants, including polycyclic aromatic hydrocarbons (PAHs), that frequently 

occur in the marine environment and may affect Southern Resident killer whales. PAHs are 

a class of compounds that are derived primarily from petroleum products or the combustion 

of these products, and can enter the marine environment directly (e.g., oil spill) or indirectly 

(e.g., stormwater runoff, atmospheric deposition). Concerns have been raised over the effects 

of exposure to PAHs on marine organisms, both because of the worldwide use of fossil fuels 

(Geraci and St. Aubin 1990, Peterson et al. 2003) and the occurrence of oil spills in areas that 

support populations of marine life. Marine biota can take up PAHs present in the environment 

via a number of routes (e.g., dermal absorption, inhalation, consumption of contaminated prey 

or sediment; Meador et al. 1995). However, the persistence of these compounds in tissues and 

body fluids of exposed marine organisms varies depending upon the rates of uptake, metabolism, 

and elimination (Krahn and Stein 1998). Vertebrates, such as fish and marine mammals, quickly 

metabolize PAHs into more polar forms that are then excreted into urine or secreted into bile for 

rapid elimination via feces (Roubal et al. 1977, Krahn et al. 1984, Varanasi et al. 1989). However, 

some of the PAH intermediates formed during metabolism can be more toxic, and may pose a 

greater health risk than the parent PAHs (Varanasi et al. 1989). 

Exposure to PAHs in aquatic vertebrates, including the potential prey of Southern Residents, 

has been linked to developmental deformities, altered growth, adrenal dysfunction, 

immunosuppression, and hepatotoxicity (Heintz et al. 2000, Arkoosh et al. 2001, Incardona 

et al. 2004, Schwartz et al. 2004, Meador et al. 2006, Reynaud and Deschaux 2006, Carls and 

Meador 2009, Incardona et al. 2012). In marine mammals, studies examining the effects of oil 

exposure have demonstrated them to be both physiological (e.g., fouling of pelage or baleen) and 

toxicological (e.g., fetal distress and in utero pneumonia, conjunctivitis, increased plasma cortisol 

levels, neural damage, pulmonary emphysema, adrenal gland and lung lesions, gastric erosions 

and ulcers, and hepatocellular necrosis; Geraci and St. Aubin 1990, Spraker et al. 1994, O’Hara and 

O’Shea 2001, Venn-Watson et al. 2015, Colegrove et al. 2016). However, information on the effects 

of inhalation of PAHs by marine mammals is lacking.

Trace Elements

Unlike the persistent pollutants described above, trace elements (often referred to as metals) are 

naturally found in the environment. Some are essential to animals’ nutrition. Most metals, like 

persistent pollutants, settle to the ocean floor, where they can accumulate in sediment. Human 

activities can increase the concentrations, and metals can become toxic at certain exposure levels. 

Therefore, areas with high human activity can become hotspots of multiple toxic chemicals.

12
Marine mammal exposure to mercury, cadmium, and lead has been the focus of several studies 

due to the known toxicity of these metals to humans and other wildlife, with effects such as 

damage to the central nervous system, skeletal deformities, kidney lesions, and kidney or liver 

damage, as well as carcinogenic, mutagenic, and teratogenic effects (O’Shea 1999, Das et al. 2003). 

Although elevated mercury has been associated with immunosuppression in harbor seals (Das et 

al. 2008), little information is known about the toxic effects of heavy metals in marine mammals. 

The distribution or storage of heavy metals in marine mammals is dependent on the metal. In 

general, heavy metals are found in the liver, kidneys, muscles, and bones (O’Shea 1999, Reijnders 

and Aguilar 2002, Das et al. 2003). Concentrations and types of heavy metals measured in marine 

mammals are primarily influenced by the levels found in their prey and by their geographical 

range, as well as the age and sex of the individual. For example, marine mammals that feed on 

squid can be exposed to higher levels of cadmium, copper, and zinc, because squid have the 

ability to retain these elements (Reijnders and Aguilar 2002). Currently, there are few metals data 

available on Southern Resident killer whales (Anulacion et al. in prep.). Some metals may transfer 

from mother to offspring during gestation and lactation, although not to the same degree as the 

persistent organic pollutants. 

Some marine mammals (particularly from the northern arctic regions) appear to tolerate high 

levels of some metals, and are able to detoxify them through several processes. For example, 

cadmium and mercury can combine with selenium or metallothionein (MT, a protein molecule) 

to mitigate the toxic effects of exposure (Meador et al. 1999, Rooney 2007, Klaassen et al. 2009). 

These new complexes (mercury and selenium or cadmium and MT) in the liver or kidneys 

change the metals into non-toxic forms and mitigate their toxic effects (Klaassen et al. 2009). 

This detoxification mechanism appears to be species-specific. For example, unlike in sperm 

whales, that did not show an obvious relationship between mercury and selenium, pilot whales 

demonstrated a strong correlation between mercury and selenium, with an almost fourfold higher 

molar ratio than that found in the sperm whales (Nielsen et al. 2000).

13
Geographic Distribution of

Southern Resident Killer Whales

The summer range of Southern Residents has been fairly well defined based on numerous 

sightings over the past 34 years (Heimlich-Boran 1988, Hauser et al. 2007, Whale Museum 

unpubl. data). All three Southern Resident pods regularly occur in the waters of the Georgia 

Basin (the Strait of Georgia, Haro Strait, and the Strait of Juan de Fuca) during late spring, 

summer, and early fall (Heimlich-Boran 1988, McCluskey 2006, Hauser et al. 2007, Whale 

Museum unpubl. data). For the past few years, J pod has typically returned by May, and is usually 

not a regular visitor until June. Similarly, K and L pods return to the inland waters and are regular 

visitors in late June, although K pod has sometimes not been sighted in inland waters until July. 

With the exception of forays of a few days to the outer coast, all three pods generally remain in 

the Georgia Basin through October (Hanson and Emmons 2010, Whale Museum unpubl. data). 

During this summer and early fall period, their movements are concentrated primarily in Haro 

Strait and the southern Strait of Georgia (Heimlich-Boran 1988, Felleman et al. 1991, Hauser et 

al. 2007). During their forays to the outer coast, the whales typically travel along the southern 

coast of Vancouver Island and are occasionally sighted as far west as Tofino and Barkley Sound. 

Southern Resident killer whales clearly have a core summer range area that is spatially separate 

from Northern Resident killer whales, which predominantly frequent the waters of central and 

northern British Columbia. 

The range of Southern Residents throughout the rest of the year is not as well known. During 

the early fall, the movements of Southern Residents, particularly J pod, expand to include Puget 

Sound (Hanson and Emmons 2010, Whale Museum unpubl. data). By late fall, all three pods 

are seen less frequently in inland waters. These pods are typically observed to exit and enter 

through the Strait of Juan de Fuca, suggesting movements in the region of Vancouver Island and 

Washington State. In recent years, several sightings or acoustic detections of Southern Residents 

have been obtained off the Washington and Oregon coasts in the winter and spring (Hanson et 

al. 2010, Hanson et al. 2013, NWFSC unpubl. data). Although sightings on the outer coast are 

extremely limited, researchers have confirmed that K and L pods have traveled as far south as 

central California (NMFS 2008, Hanson et al. 2013) and as far north as southeast Alaska (one 

sighting occurred in Chatham Strait, AK; Hilborn et al. 2012). The limited range of the sightings/

acoustic detections of J pod in coastal waters, the lack of coincident occurrence during the K 

and L pod sightings, and the results from satellite tagging in 2012–2016 (NWFSC unpubl. data) 

indicate J pod’s limited occurrence along the outer coast and extensive occurrence in inland 

waters, particularly in the northern Georgia Strait. Because J pod spent very little time in coastal 

waters during tag deployments, we know less of its coastal distribution than we do for K and L 

pods. Indirect evidence of different ranges among the pods have also been gained from analyses 

of contaminant profiles of biopsy samples that show the “California signature” for K and L pods 

but not for J pod (Krahn et al. 2007a, Krahn et al. 2009). In addition, J pod has a much higher 

level of PBDEs, indicating consumption of prey that remain closer to urban settings (Krahn et al. 

2007a, Krahn et al. 2009). 

14
POPs in Southern Resident Killer Whale Prey

Marine mammals receive the majority of POPs from their diet. Adult Southern Resident killer 

whales primarily consume Pacific salmon, and therefore obtain the majority of their POPs from 

salmon. During the summer, resident killer whales in the Northeast Pacific Ocean frequent 

regions of high-relief topography along salmon migration routes, and early studies inferred 

salmon to be a primary prey item based on co-occurrence (Heimlich-Boran 1988). Anecdotal 

observations during subsequent studies indicated that salmon were common prey items for 

Southern Resident killer whales in the summer. Studies of stomach contents and surface 

predation event sampling indicated that Chinook salmon were a preferred prey item to both 

Northern and Southern Resident killer whales (Ford et al. 1998), although it was acknowledged 

that potential biases existed because of the small sample size and sampling only predation at 

the surface. Follow-up studies with increased sample sizes continued to indicate that Chinook 

salmon were a preferred prey item of resident killer whales (Ford and Ellis 2006). A more recent 

study with a much larger contemporary sample, as well as the genetic analysis of fecal samples, 

confirmed the importance of Chinook salmon in the summer diet (Hanson et al. 2010, Ford 

et al. 2016). Other Pacific salmon species and steelhead (Oncorhynchus mykiss) are sometimes 

consumed, but much less frequently than would be expected based on their abundance in coastal 

waters. Further data suggest that resident killer whales appear to be consuming older (i.e., 

larger) Chinook salmon (Ford and Ellis 2006, Hanson unpubl. data), indicating a high degree 

of selectivity (NWFSC unpubl. data). Additional genetic analyses from fish scales and tissues 

highlighted the seasonal importance of Fraser River Chinook salmon, particularly from the 

Upper and Middle Fraser, south Thompson, and Lower Fraser (Hanson et al. 2010). 

Relatively little is known about prey preferences in the other seasons, but the majority of 

the evidence suggests that salmon are consumed year round. Coho salmon (Oncorhynchus 

kisutch) contributed to over 40% of their diet in late summer (Ford et al. 2016). Chum salmon 

(Oncorhynchus keta), sockeye (Oncorhynchus nerka), and steelhead were also part of their diet, 

but in much smaller contributions (Ford et al. 2016). There are very limited direct observation 

data of prey preferences in the winter and spring; however, Southern Resident killer whales have 

been observed feeding on Chinook salmon off the coasts of California (Black et al. 2001) and 

Washington (Hanson et al. 2010). Moreover, the occurrence of Southern Resident killer whales 

off the Washington coast coincides with spring Chinook salmon returning to the Columbia River 

(Zamon et al. 2007). Prey and fecal samples recently collected in winter and early spring indicate 

a diet dominated by salmonids, particularly Chinook salmon, with the presence of some lingcod 

(Ophiodon elongatus) and Pacific halibut (Hippoglossus stenolepis; NWFSC unpubl. data). Stable 

isotope analysis, which shows that the whales are consistently consuming high trophic level prey 

(Krahn et al. 2007a, Krahn et al. 2009), provides additional evidence of salmon consumption. 

Bottom fish and squid (Ommastrephes spp.) have also been documented in the gut contents of 

stranded resident killer whales (Ford et al. 1998), and may potentially be important prey species 

in the winter diet of resident killer whales. Bottomfish known to be consumed include sablefish 

(Anoplopoma fimbria), English sole, and Dover sole (Microstomus pacificus). Boreopacific 

armhook squid (Gonatopsis borealis) were also identified in gut contents, but other large squid 

species (magister armhook squid [Berrytheuthis magister], boreal clubhook squid [Onychoteuthis 

15
borealijaponica], and neon flying squid [Ommastrephes bartramii]) may also be important prey 

items. Potential but undocumented prey species include abundant fish species with similar 

distributions to Southern Resident killer whales, such as chub mackerel (Scomber japonicus), 

Pacific hake (Merluccius productus), Pacific cod (Gadus macrocephalus) and Pacific herring. 

Various studies have measured low-to-moderate concentrations of POPs in many populations 

of free-ranging adult Pacific salmon, underscoring the widespread distribution of these 

contaminants in the aquatic environment (Table 2). Adult salmon accumulate the majority 

(>96%) of these POPs while feeding in the marine environment, rather than in their freshwater 

and estuarine habitats (Cullon et al. 2009, O’Neill and West 2009), as over 98% of their growth 

occurs while fish are feeding in salt water (Quinn 2005).

Overviews of PCB, PBDE, and DDT concentrations measured in Pacific salmon are presented 

in Table 2. The studies listed in Table 2 vary considerably in sampling design, tissue matrices 

analyzed, and analytical methods, and all of these factors can affect the reported POP 

concentrations. However, the pooled information contains sufficient data to provide general 

patterns of POP accumulation among fish species, and the larger geographic patterns within 

species. Reported POP values for Pacific salmon are limited to adults and sub-adults (i.e., those 

most applicable to the diet of the whales) sampled in terminal areas. Terminal areas include 

coastal marine waters and river mouths through which salmon migrate en route to their natal 

streams to spawn. Data are reported for salmon populations along the west coast of North 

America, from Alaska to California, to ensure adequate geographic coverage of the potential 

feeding ranges of Southern Residents.

Throughout their geographic range, the observed levels of POPs in adult Pacific salmon appear 

to be primarily determined by the marine distribution and the resulting geographic proximity 

of these fish to contaminated marine environments (and contaminated prey). Biological traits 

such as trophic status, lipid content, duration of exposure (life span and fish age), and speciesspecific metabolism and detoxification further exacerbate or mitigate the degree to which POPs 

accumulate in Pacific salmon. Species and populations of Pacific salmon vary considerably in 

their marine distribution and, depending on where they feed, can be differentially exposed to 

POPs. In general, salmon frequenting developed coastal marine waters are potentially more 

exposed to contaminants than those frequenting offshore waters, as coastal waters in areas with 

denser human populations tend to receive higher inputs from land-based sources of POPs. 

Remote and otherwise undeveloped offshore areas tend to be less contaminated; however, 

they can also receive some input of POPs via long-range atmospheric transport from more 

industrialized areas (Wania and Mackay 1996), or via bio-transport in the bodies of migrating 

animals (Blais et al. 2007). 

The marine distribution of salmon varies greatly among species and populations, but in 

general, Chinook salmon and coho salmon have a more coastal marine distribution (preferring 

the continental shelf and protected inland marine waters to offshore waters; reviewed by 

Quinn 2005). They are therefore more readily exposed to contaminants that are present in 

coastal waters than other Pacific salmon species. In contrast, sockeye salmon, pink salmon 

(Oncorhynchus gorbuscha), and chum salmon have a more offshore marine distribution in 

16
relatively uncontaminated marine waters. When sockeye salmon, pink salmon, and chum salmon 

enter the marine environment, they rapidly migrate northward and westward through coastal 

waters of North America and are found in the open waters of the North Pacific, Gulf of Alaska, 

and Bering Sea by the end of their first year at sea, where they reside until their return migration 

to their natal streams (Quinn 2005). Consequently, the amount of time they spend feeding 

in more contaminated coastal environments is limited, as is evident by their observed POP 

concentrations. Measured average concentrations of PCBs and PBDEs were highest for Chinook 

salmon, at 29 and 7.3 ng/g ww (wet weight), intermediate for coho salmon (14 and 0.2 ng/g ww), 

less for sockeye salmon (7.6 and 0.15 ng/g ww), and lowest for pink salmon and chum salmon (<3 

ng/g ww and <0.2 ng/g ww), as shown in Table 2. Similarly, average DDT values were elevated 

in Chinook salmon and coho salmon (15.7 and 18.1 ng/g ww), lower in sockeye salmon (8.6 ng/g 

ww), and lowest for pink salmon and chum salmon (<2 ng/g ww). 

Although Chinook salmon populations tend to be distributed along the coast, they can differ 

greatly in their marine distribution, even if they enter the ocean-proximate areas (Quinn and 

Myers 2004, Weitkamp 2010). Chinook salmon populations entering marine waters along the 

coast in California and Oregon encounter very different conditions than those in the Gulf of 

Alaska, and more northerly populations are more likely to migrate offshore than those farther 

south. In addition, Healey (1983) pointed out that Chinook salmon with a stream-type juvenile 

life history showed a greater tendency to use offshore waters than those with an ocean-type life 

history. A more recent analysis of Chinook salmon marine distribution confirmed this pattern, 

which was particularly evident in paired stream-type and ocean-type populations from the upper 

Columbia and Fraser rivers. Chinook salmon from coastal rivers, on the other hand, did not differ 

as much in marine distribution between the two life-history forms (Sharma and Quinn 2012). 

The importance of marine distribution as a factor affecting POP accumulation was particularly 

evident for Chinook salmon populations. Although Chinook salmon generally had higher 

concentrations of POPs than other Pacific salmon species, the levels varied considerably among 

populations, with those populations that feed in close proximity to land-based sources of 

contaminants having higher concentrations. The highest PCB and PBDE concentrations were 

observed in fish from Puget Sound (53 and 22.5 ng/g ww) and the Harrison River (47 and 17.7 

ng/g ww), a subset of the Fraser River Chinook salmon populations. While feeding in marine 

waters, these populations are primarily distributed within the urbanized waters of the Salish 

Sea and along the west coast of Vancouver Island (DFO 1999, Weitkamp 2010), with substantial 

proportions of the populations residing in the Salish Sea rather than migrating to the Pacific 

Ocean (O’Neill and West 2009, Chamberlin et al. 2011). Interestingly, other populations of 

Chinook salmon—originating from the developed Fraser River, but with a more northern 

distribution in the coastal waters of British Columbia and Alaska (DFO 1999)—had much lower 

PCB and PBDE concentrations (10 and 1.67 ng/g ww). Intermediate levels of PCBs (averages = 22 

and 14 ng/g ww) and PBDEs (averages = 3.53 and 2.56 ng/g ww) were measured in California and 

Oregon populations. Chinook salmon originating from California generally distribute northward 

in the coastal waters of California, whereas those originating from Oregon disperse both north, 

to the coastal waters of Washington and the west coast of Vancouver Island, and south, off the 

coast of California (Weitkamp 2010). Chinook salmon from the Central Valley of California 

have an adult marine distribution thought to be on the continental shelf. These Chinook salmon 

have higher ΣDDTs/ΣPCBs ratios than Chinook salmon from the Fraser River and Puget Sound, 

17
which have lower ΣDDTs/ΣPCBs ratios (O’Neill et al. 2006). The higher DDT concentrations that 

were measured in Chinook salmon originating from California (O’Neill et al. 2006) likely reflect 

the historically high inputs of DDTs there (Eganhouse et al. 2000). The Alaskan Chinook salmon 

populations distributed mostly along the remote waters of Alaska (Weitkamp 2010) had the lowest 

average PCB and PBDE levels (7.7 and 0.67 ng/g ww). 

Although elevated POPs in Pacific salmon are primarily driven by their marine distribution and 

general proximity to land-based sources of contaminants, their high lipid content and trophic 

status may also contribute to their contaminant concentrations. Lipophilic compounds like PCBs, 

PBDEs, and DDTs readily accumulate in adult Pacific salmon because of their relatively high 

fat content. Species and populations differ in their fat content, depending on their diet in salt 

water and the migratory pattern they undertake (Brett 1995, Quinn 2005), but overall, Chinook 

salmon and sockeye salmon have higher fat content (O’Neill et al. 2014). Assuming uniform 

environmental exposures to POPs, adult Chinook salmon and sockeye salmon returning to their 

natal streams would generally have higher associated POPs than coho salmon, pink salmon, 

and chum salmon because of their higher fat content. Such comparisons of POP levels among 

species and populations of Pacific salmon are best made with whole body measurements of POPs, 

which are less affected by changes in the lipid content of maturing salmon. The lipid content 

in the muscle tissue of adult salmon in marine waters decreases rapidly as they approach fresh 

water and reproductive maturity (Brett 1995, Ewald et al. 1998, Hendry and Berg 1999). During 

this reproductive phase, POPs are not metabolized with the fat, but rather are mobilized and 

redistributed to fattier tissues such as the gonads (Ewald et al. 1998, Kelly et al. 2007, Veldhoen 

et al. 2010). Although the POPs are redistributed into fattier tissues, they are not transformed or 

eliminated (deBruyn et al. 2004), such that whole body POP concentrations in Pacific salmon 

generally do not decline with reductions in fat content during maturation. 

Based on diet alone, POP levels would be highest for Chinook salmon, then coho salmon, 

followed by sockeye salmon, pink salmon, and chum salmon. Pacific salmon are trophic 

generalists that consume a mixture of fish and invertebrates while in marine waters. However, 

the proportion of fish in the diet is greatest for Chinook salmon, followed by coho salmon, then 

pink salmon and sockeye salmon, and least among chum salmon (Fresh et al. 1981, Peterson et 

al. 1982, Beacham 1986, Higgs et al. 1995), resulting in a higher trophic level for Chinook salmon 

(reviewed by Johnson and Schindler 2008) and potentially greater contaminant exposure. 

The interaction of lipid content and trophic status on POP accumulation is apparent when 

comparing Alaskan populations of Pacific salmon that generally are distributed in marine waters 

distant from land-based sources of contaminants. Average PCB and DDT levels are generally 

higher for Chinook salmon and sockeye salmon (PCB averages = 7.7 and 14.4 ng/g ww, and DDT 

averages = 13.0 and 10.4 ng/g ww, respectively) than for coho salmon, pink salmon, and chum 

salmon (PCB averages = 2.9, 2.2, and 2.7 ng/g ww, and DDT averages = 1.5, 1.2, and 1.9 ng/g ww, 

respectively). Similarly, average PBDE levels in Alaskan Chinook salmon are considerably higher 

than for other Alaskan salmon species.

18
Table 2. Percent lipid and POP concentrations (ng/g wet weight) of adult and subadult Pacific salmon sampled in terminal a

include coastal marine waters and river mouths through which fish migrate en route to their natal streams. NR = not re

Species Region Subregion Population

n

Tissue Analyzed

Lipids

(%) PCBs PBDE

Chinook 

salmon

Alaska unknown unknown 2 muscle, no skin NR 5.6 0.95 

Alaska Aleutian Islands unknown 3 muscle, skin 7.6 5.0 0.71 

Alaska SE Alaska/Gulf of 

Alaska/Bering Sea

unknown 35 muscle, no skin 9.7 11 0.53 

Alaska SE Alaska unknown 3 muscle, skin NR 8.0 0.50 

Alaska South Central River 10 muscle, no skin NR 9.1 NR 

Alaskan Chinook salmon average 8.7 7.7 0.67 

British Columbia BC North Coast Skeena 30 whole body NR 7.3 0.08 

British Columbia Fraser River Thompson 

6 muscle, no skin 10 9.1 NR 

British Columbia Fraser River 13 whole body NR 9.4 0.80 

British Columbia Fraser River Thompson 7 muscle, no skin 12 8.6 1.54 

British Columbia Fraser River Shuswap 2 muscle, no skin 3.0 9.8 NR 

British Columbia Fraser River Harrison

6 muscle, no skin 5.4 47 17.7 

Fraser River Chinook salmon average (excluding Harrison) 8.3 10 1.67 

British Columbia Chinook salmon average 7.6 15 4.87 

Washington Puget Sound Nooksack River 28 muscle, no skin 3.5 37 NR 

Washington Puget Sound Skagit River 29 muscle, no skin 4.8 40 NR Washington Puget Sound Duwamish River 65 muscle, no skin 7.3 56 NR Washington Puget Sound Nisqually River 20 muscle, no skin 3.8 41 NR 

Washington Puget Sound Deschutes River 34 muscle, no skin 1.7 59 NR 

Washington Puget Sound Puget Sound mixed 28 muscle, no skin 4.8 76 NR 

Washington Puget Sound Duwamish River 3 whole body 6.4 35 6.43 Washington Puget Sound Deschutes River

4 whole body 4.3 56 NR 

Washington Puget Sound Deschutes River 10 muscle, no skin 1.0 49 NR Washington Puget Sound Issaquah Creek 10 muscle, no skin 0.6 49 NR Washington Puget Sound Puget Sound mixed 36 whole body NR 43 18.9 

a Value estimated from figure. b Value estimated from reported lipid weight.

19
Table 2 continued. Percent lipid and POP concentrations (ng/g wet weight) of adult and subadult Pacific salmon sampled in 

Terminal areas include coastal marine waters and river mouths through which fish migrate en route to their natal stream

Species Region Subregion Population

n

Tissue Analyzed

Lipids

(%) PCBs PBDE

Chinook

salmon

Washington Puget Sound Puget Sound mixed 34 whole body NR 91 42.2 

Washington WA Coast Makah 10 muscle, no skin 1.5 19 NR 

Washington WA Coast Quinault 10 muscle, no skin 1.8 16 NR 

Puget Sound Chinook salmon average 3.8 53 22.5 Washington Coast Chinook salmon average 1.7 17 NR 

Washington Chinook salmon average 3.5 48 22.5 

Oregon unknown unknown 3 muscle, skin NR 10 2.10 

Oregon Columbia River unknown fall 17 whole body NR 18 3.69 

Oregon Columbia River unknown spring 20 whole body NR 33 9.77 

Oregon Columbia River mixed fall Chinook 15 muscle, skin 7.0 37 NR 

Oregon Columbia River mixed spring Chinook 24 muscle, skin 9.0 38 NR 

Oregon Columbia River fall Chinook

4 whole body 9.4 15 2.30 

Oregon Columbia River Clackamas River 3 muscle, skin 8.8 13 1.80 

Oregon Columbia River Clackamas River 3 muscle, no skin 6.1 10 1.50 

Oregon Chinook salmon average 8.1 22 3.53 

California Sacramento/

San Joaquin

unknown 29 whole body NR 14 2.56 

Chinook salmon average 5.6 29 6.22 

Sockeye 

salmon

Alaska unknown Alaska 2 muscle, no skin NR 3.6 0.21 

Alaska Aleutian Islands unknown 13 muscle, no skin 5.8 130 NR 

Alaska Kodiak unknown 3 muscle, skin NR 5.0 0.10 

Alaska Gulf of Alaska/

Bering Sea

unknown 24 muscle, no skin 8.2 13 0.22 

a Value estimated from figure.

20
Table 2 continued. Percent lipid and POP concentrations (ng/g wet weight) of adult and subadult Pacific salmon sampled in 

Terminal areas include coastal marine waters and river mouths through which fish migrate en route to their natal stream

Species Region Subregion Population

n

Tissue Analyzed

Lipids

(%) PCBs PBDE

Sockeye 

salmon

Alaska Gulf of Alaska/

Bering Sea

Copper River 97 muscle, no skin 5.5 37 NR 

Alaska SE Alaska unknown 3 muscle, skin NR 13.3 0.10 

Alaskan sockeye salmon average 6.5 14.4c 0.16 

British Columbia unknown unknown 3 muscle, skin NR 8.0 0.10 

British Columbia Fraser River Early Stuart 3 somad 16 13 NR British Columbia Fraser River Early Stuart 5 muscle, no skin 4.0 3.9 NR British Columbia Fraser River Early Stuart

6 muscle, no skin 5.0 6.9 NR 

British Columbia Fraser River Adams 5 muscle, no skin 8.8 7.7 NR British Columbia Fraser River Weaver Creek 3 muscle, no skin 1.4 6.8 NR 

British Columbia Fraser River Weaver Creek 2 muscle, no skin 1.1 3.6 NR British Columbia Fraser River Weaver Creek 2 muscle, no skin 1.5 5.3 NR British Columbia Fraser River Weaver Creek 1 muscle, no skin 1.1 4.0 NR British Columbia Fraser River Weaver 8 muscle, no skin 3.9 6.8 NR 

British Columbia West Coast VI Great Central Lake

6 muscle 6.1 1.7 NR 

British Columbia West Coast VI Great Central Lake 3 muscle 6.6 1.6 NR British Columbia West Coast VI Great Central Lake 2 muscle 1.0 1.5 NR British Columbia West Coast VI Great Central Lake 3 muscle 1.0 2.4 NR British Columbia sockeye salmon average 4.4 5.2 0.10 

Sockeye salmon average 4.8 7.6c 0.15 

Coho 

salmon

Alaska unknown unknown 2 muscle, no skin NR 1.6 0.32 

Alaska Kodiak unknown 3 muscle, skin NR 4.0 0.10 

Alaska SE Alaska/ 

Gulf of Alaska

unknown 14 muscle, no skin 2.9 2.0 0.19 

Alaska SE Alaska unknown 3 muscle, skin NR 4.0 0.10 

Alaskan coho salmon average 2.9 2.9 0.18 

a Value estimated from figure.b Value estimated from reported lipid weight.c Value excluded as an outlier.d Whole body minus gonads.

21
Table 2 continued. Percent lipid and POP concentrations (ng/g wet weight) of adult and subadult Pacific salmon sampled in 

Terminal areas include coastal marine waters and river mouths through which fish migrate en route to their natal stream

Species Region Subregion Population

n

Tissue Analyzed

Lipids

(%) PCBs PBDE

Coho 

salmon

British Columbia unknown unknown 3 muscle, skin NR 6.0 0.30 Washington Puget Sound unknown 32 muscle, no skin 3.1 35 NR 

Washington Puget Sound Puget Sound mixed 125 muscle, no skin 3.1 27 NR 

Washington Puget Sound Puget Sound mixed 266 muscle, no skin 3.3 NR NR 

Washington coho salmon average 3.2 31 NR Oregon Columbia River Umatilla River 3 muscle, skin 2.5 35 NR 

Coho salmon average 3.0 14 0.20 

Pink 

salmon

Alaska Kodiak unknown 3 muscle, skin NR 3.0 0.10 Alaska northern Alaska unknown 7 canned 6.3 2.6 NR 

Alaska SE Alaska/GOA unknown 12 muscle, no skin 3.5 1.3 0.22 

Alaska SE Alaska unknown 3 muscle, skin NR 2.0 0.10 Alaskan pink salmon average 4.9 2.2 0.14 British Columbia unknown unknown 3 muscle, skin NR 3.0 0.30 Pink salmon average 4.9 2.4 0.18 

Chum 

salmon

Alaska Kodiak unknown 3 muscle, skin NR 2.0 0.10 Alaska SE Alaska unknown 3 muscle, skin NR 3.0 0.10 Alaska Bering Sea unknown 18 muscle, no skin 4.8 3.2 0.16 

Alaskan chum salmon average 4.8 2.7 0.12 British Columbia unknown unknown 3 muscle, skin NR 2.0 0.20 Chum salmon average 4.8 2.6 0.14 

References: 1) Cullon et al. (2009), 2) deBruyn et al. (2004), 3) Hardell et al. (2010), 4) Hayward et al. (2007), 5) Hites et al. (2004b), 7) Kelly et al. (2007), 8) Missildine et al. (2005), 9) Montory et al. (2010), 10) O’Neill et al. (1998), 11) O’Neill et al. West (2009), 13) Rice and Moles (2006), 14) Shaw et al. (2008), 15) Shaw et al. (2006), 16) Stone (2006), 17) Veldhoen et al. 19) Ewald et al. (1998), 20) West et al. (2001), 21) ADEC (2011), 22) O’Hara et al. (2005)

a Value estimated from figure.

22
Table 3. Concentrations (±) of summed PCBs, PBDEs, and DDTs (lipid weight, ng/g) measured in blubber collected from ki

cetaceans from the North Pacific. NR = not recorded; LOQ = limit of quantification.

Species

Age, Sex-Class,

and/or Ecotype Collection Region

Collection 

Year(s)

n

Lipid Weight (ng/g)

ΣPCBs ΣPBDEs 

Bowhead whalea

(Balaena mysticetus)

NR Beaufort–Chukchi 

Sea, Alaska

1999–2000 25 540 ± 45 NR 

Fin whaleb

(Balaenoptera physalus)

Male

(unknown age)

Gulf of California 2004–2005 9 200 ± 30 NR 

Fin whaleb Female (unknown 

age)

Gulf of California 2004–2005 12 130 ± 25 NR 

Gray whalea

(Eschrichtius robustus)

Juvenile Russia 1994 17 1400 ± 130 NR 

Gray whaleb Unknown Neah Bay, WA 1996–1998 38 220 ± 42 NR 

Humpback whaleb Male

(unknown age)

Southern California 2004 5 800 ± 390 180 ± 56 

Humpback whaleb Male

(unknown age)

Northern California 2004 5 140 ± 60 55 ± 26 

Humpback whaleb Male

(unknown age)

Washington State 2004 10 560 ± 140 100 ± 29 

Humpback whaleb Male

(unknown age)

Southeast Alaska 2003–2004 10 430 ± 97 22 ± 6 

Humpback whaleb Male

(unknown age)

North Gulf of Alaska 2004 8 110 ± 86 <LOQ 

Humpback whaleb Male

(unknown age)

West Gulf of Alaska 2004 9 390 ± 180 8 

Humpback whaleb Male

(unknown age)

East Aleutian Islands 2004 10 200 ± 60 <LOQ 

Humpback whaleb Male

(unknown age)

Bering Sea 2004 10 160 ± 24 <LOQ 

Belugaa

(Delphinapterus leucas)

Mix Pt. Lay, AK 1999–2000 20 3300 ± 310 NR 

Belugaa Mix Cook Inlet, AK 2001–2002

4 1,700 ± 1,100 NR 

False killer whaleb

(Pseudorca crassidens)

Juvenile/Sub-adult Main Hawaiian 

Islands

2008 2 19,000 ± 7,100 2700 ± 350 

False killer whaleb Adult male Main Hawaiian 

Islands

2008 2 33,000 ± 0 1200 ± 580 6

a Blubber collected from subsistence-harvested animals.b Blubber collected from biopsied animals.

23
Table 3 continued. Concentrations (±) of summed PCBs, PBDEs, and DDTs (lipid weight, ng/g) measured in blubber collect

and other cetaceans from the North Pacific. NR = not recorded; LOQ = limit of quantification.

Species

Age, Sex-Class,

and/or Ecotype Collection Region

Collection 

Year(s)

n

Lipid Weight (ng/g)

ΣPCBs ΣPBDEs 

False killer whaleb Adult female Main Hawaiian 

Islands

2008 5 3,500 ± 4,200 420 ± 720 

Killer whalec Residents, Transients Puget Sound/British 

Columbia

1986–1989

6 22,000 NR 

Killer whaleb Adult male 

(Northern Residents)

Puget Sound/British Columbia

1993–1996 8 37,000 ± 6,100 200 ± 120 

(n = 13)

Killer whaleb Adult female 

(Northern Residents)

Puget Sound/British Columbia

1993–1996 9 9,300 ± 2,800 420 ± 680 

(n = 8)

Killer whaleb Adult male 

(Southern Residents)

Puget Sound/British Columbia

1993–1996

4 150,000 ± 33,000 940 ± 580 

(n = 5)

Killer whaleb Adult female 

(Southern Residents)

Puget Sound/British Columbia

1993–1996 2 55,000 ± 19,000 NR 

Killer whaleb Male (transients) Puget Sound/British 

Columbia

1993–1996 5 250,000 ± 55,000 1,000 ± 610 

(n = 6)

Killer whaleb Female (transients) Puget Sound/British 

Columbia

1993–1996 5 59,000 ± 21,000 890 ± 710 

(n = 6)

Killer whaleb Juvenile/Sub-adult 

(Southern Residents)

Puget Sound/British Columbia

2004–2007

4 44,000 ± 12,000 14,000 ± 2,400 5

Killer whaleb Adult male 

(Southern Residents)

Puget Sound/British Columbia

2004–2007 10 56,000 ± 46,000 3,600 ± 1,600 8

Killer whaleb Adult female 

(Southern Residents)

Puget Sound/British Columbia

2004–2007 7 37,000 ± 42,000 3,700 ± 2,800 3

Killer whaleb,c Juvenile/Sub-adult 

(Southern Residents)

Puget Sound/British Columbia

2008–2013 21 39,000 ± 19,000 5,300 ± 2,600 6

Killer whaleb Adult male 

(Southern Residents)

Puget Sound/British Columbia

2008–2013

4 40,000 ± 28,000 4,700 ± 3,000 

b Blubber collected from biopsied animals.c Blubber collected from stranded animals.

24
Table 3 continued. Concentrations (±) of summed PCBs, PBDEs, and DDTs (lipid weight, ng/g) measured in blubber collect

and other cetaceans from the North Pacific. NR = not recorded; LOQ = limit of quantification.

Species

Age, Sex-Class,

and/or Ecotype Collection Region

Collection 

Year(s)

n

Lipid Weight (ng/g)

ΣPCBs ΣPBDEs 

Killer whaleb Adult female 

(Southern Residents)

Puget Sound/British Columbia

2008–2013 22 30,000 ± 31,000 3,700 ± 3,200 4

Killer whalec Adult male Japan (Shiretoko 

Peninsula)

2005 1 57,000 270 

Killer whalec Calf Japan (Shiretoko 

Peninsula)

2005 3 50,000 ± 13,000 500 ± 36 1

Killer whalec Adult female Japan (Shiretoko 

Peninsula)

2005 5 31,000 ± 10,000 260 ± 72 6

Killer whaleb Mix (transients) Kenai Fjords/Prince 

William Sound, AK

1994–1999 64 230,000 ± 130,000 NR 3

Killer whaleb Mix (residents) Kenai Fjords/Prince 

William Sound, AK

1994–1999 13 14,000 ± 13,000 NR 1

Killer whaleb Adult male 

(residents)

Central Aleutian Islands, AK

2003–2004 3 15,000 ± 1,100 36 ± 32 

Killer whaleb Adult male 

(residents)

Eastern Aleutian Islands, AK

2003–2004 20 16,000 ± 4,900 50 ± 29 2

Killer whaleb Adult male 

(residents)

Gulf of Alaska 2003–2004 17 9,300 ± 5,200 120 ± 89 

Killer whaleb Adult male 

(transients)

Eastern Aleutian Islands, AK

2003–2004 15 120,000 ± 49,000 790 ± 590 2

Killer whaleb Adult male 

(transients)

West Coast (California)

2000–2001

4 630,000 ± 190,000 12,600 3

Killer whaleb Adult male 

(offshores)

Alaska 2003–2004

4 110,000 ± 22,000 3,300 ± 940 4

References: 1) Hoekstra et al. (2003), 2) Niño-Torres et al. (2010), 3) Tilbury et al. (2002), 4) Krahn et al. (2001), 5) Elfes et al. (2010), 6) K7) Ylitalo et al. (2009), 8) Jarman et al. (1996), 9) Ross et al. (2000), 10) Rayne et al. (2004), 11) Krahn et al. (2007a), 12) Krahn et al. (2009data, 14) Kajiwara et al. (2006), 15) Ylitalo et al. (2001), 16) Krahn et al. (2007b)b Blubber collected from biopsied animals.c Blubber collected from stranded animals.

25
Factors Influencing Bioaccumulation in Whales

Several chemical and biological factors are known to influence the bioaccumulation of lipophilic 

contaminants and the total body burdens in marine mammals. There can be large differences 

in concentrations among individuals within a population and between populations. Several 

studies have reported on the levels of POPs in killer whales and other marine mammals from the 

North Pacific (Table 3). These data come from both stranded animals (e.g., Calambokidis et al. 

1984, Jarman et al. 1996) and blubber biopsy samples of wild-ranging animals (details on biopsy 

techniques in Ylitalo et al. 2001, Ikonomou et al. 2007, Noren and Mocklin 2012). Relative to other 

marine mammal species, killer whales accumulate high levels of several POPs, predominantly 

ΣPCBs and p,p'-DDE, a major metabolite of DDT (Table 3). Below we review the primary factors 

influencing the bioaccumulation of POPs in whales.

Influence of Geographic Distribution and Diet

on POP Accumulation

As mentioned above, adult marine mammals receive the majority of POPs from their prey (e.g., 

de Swart et al. 1994); therefore, diet and trophic position are primary factors that influence 

accumulation. The effect of diet is significant for POPs that biomagnify up the food chain, and 

therefore top predators generally have higher levels than lower trophic-level species. For example, 

transient killer whales eat marine mammals, which are relatively high on the food chain. These 

transient killer whales have significantly higher ΣPCBs and ΣDDTs than resident killer whale 

communities that eat fish (Ross et al. 2000, Ylitalo et al. 2001), revealing the influence of diet and 

trophic position on contaminant concentrations. Diet and trophic position are thought to explain 

most of the variation of POP levels among species, and may contribute to the variation among 

populations of the same species or within a population if diet is age- or sex-specific (Aguilar et al. 1999). 

POPs in marine mammals can also vary based on geographic proximity to contaminated marine 

environments. Killer whales in Washington and British Columbia have notably higher POP levels 

than other North Pacific killer whales at similar trophic levels (Table 3), likely indicating a higher 

regional input of these contaminants. Krahn et al. (2008) compared patterns of POPs in Antarctic 

Type C killer whales to Alaska offshores, Alaska residents, Alaska and West Coast transients, and 

Eastern Tropical Pacific (ETP) killer whales. With the exception of hexachlorobenzene (HCB), 

Antarctic Type C killer whales had the lowest measured POPs of all the studied killer whale 

communities. These lower levels of POPs in Antarctic Type C killer whales were not unexpected 

considering the low potential of regional input.

POP levels in the blubber of humpback whales (Megaptera novaeangliae) from the eastern 

North Pacific were also recently measured to better understand the geographic distribution of 

contaminants (Elfes et al. 2010). Humpback whales serve as good bioindicators of contamination 

because they are seasonal feeders with strong site fidelity to feeding regions (Elfes et al. 2010). 

The researchers found that humpback whales that feed off California and Washington had higher 

26
concentrations of ΣPCBs, ΣPBDEs, and ΣDDTs than whales feeding in higher-latitude regions. 

ΣPBDEs were not detected in whales sampled in the northern Gulf of Alaska, eastern Aleutian 

Islands, or Bering Sea. ΣDDTs were exceptionally high in humpbacks that feed off California. 

Furthermore, whales that feed in southern California had six times the levels of ΣDDTs as whales 

that feed in northern California (Elfes et al. 2010). 

Dynamics of POP Transfer from Mother to Offspring

Marine mammals not only receive contaminants from the prey they consume; young marine 

mammals also receive contaminants from their mother, offloaded via transplacental transfer 

during gestation and via milk during lactation (e.g., Duinker and Hillebrand 1979, Donkin et 

al. 1981, Tanabe et al. 1982, Addison and Brodie 1987, Aguilar and Borrell 1994, Borrell et al. 

1995, Ridgway and Reddy 1995, Lee et al. 1996, Pomeroy et al. 1996, Ylitalo et al. 2001, Debier et 

al. 2003, Desforges et al. 2012). Indeed, the total contaminant load accumulated in a cetacean 

calf prior to consuming prey depends solely on the mother’s contaminant load. In addition, 

cetacean contaminant burdens are directly related to birth order; first-born young receive greater 

contaminant loads from their mothers than subsequent offspring (Ylitalo et al. 2001). 

Transfer rates of specific contaminants within each class tend to depend on molecular weight 

and degree of lipophilicity. Specifically, PCBs with higher molecular weights do not appear to 

transfer across the placenta (Salata et al. 1995) and are not easily mobilized from mother to 

offspring during gestation (Tanabe et al. 1981, Tanabe et al. 1982) or during lactation (Park et al. 

2010). In general, during gestation and lactation in both pinnipeds and delphinids, the most easily 

transferred organochlorines are HCH and HCB, followed by DDTs and then PCBs (Fukushima 

and Kawai 1981, Tanabe et al. 1982, Addison and Brodie 1987, Aguilar 1987, Borrell et al. 1995), as 

shown in Table 4.

Several biological factors also influence transfer rates during gestation and lactation. For example, 

Tanabe et al. (1982) proposed that transplacental transfer rates in delphinids depend on the ratio 

of the body weight of the fetus to that of the pregnant female. Although more data are needed 

to support this, the trend does seem to exist. Tanabe et al. (1982) estimated that a 25.5-year-old 

female striped dolphin (Stenella coeruleoalba) transferred 4.0% of her body burden of PCBs and 

4.7% of DDTs to her fetus, whose mass was 6.1% that of the female, during gestation. Borrell et 

al. (1995) estimated that the average transfer rate during gestation in long-finned pilot whales 

(Globicephala melas) for PCBs (~7%) and DDTs (~8%) was nearly double that reported by Tanabe 

et al. (1982) for striped dolphins. The ratio of fetus weight to mother weight (~9%) in long-finned 

pilot whales is also higher than that for striped dolphins (Borrell et al. 1995). Furthermore, a 

gestational transfer rate of 15% for organochlorine compounds was estimated for harbor porpoise 

(Phocoena phocoena), whose calves are approximately 17% the mass of females (Duinker and 

Hillebrand 1979). Offloaded amounts of contaminants also vary by individual female and are 

related to age and reproductive history. Specifically, transfer rates tend to decrease with a mother’s 

age, and are consequently much higher in primiparous females than in those that have already 

given birth (Aguilar and Borrell 1994, Borrell et al. 1995). For example, Fukushima and Kawai 

27
Table 4. Contaminant transfer from delphinid and phocoenid females to calves during gestation and/or lactation.

28

Contaminant Species

% Offload

(Gestation)

% Offload

(Lactation)

% Offload

(Total) 

ΣPCB Melon-headed whale 3.5%, 3.6% —— 89% Kaj

Beluga 11.4% Des

Bottlenose dolphin 3.7% ——

— Sa

Long-finned pilot whale (9-yr-old) 9.73%

(13-yr-old) 6.09%(30-yr-old) 4.14%

(9-yr-old) 99.9%

(13-yr-old) 95.5%(30-yr-old) 92.5%

— Bo

Striped dolphin (25.5-yr-old) 4.0%

—

— Ta

—

(25.5-yr-old) 4.0%

(17.5-yr-old) 92.6%(25.5-yr-old) 91.1%

— Ta

(values 

3.8% 88%

— Fukush

(assum

ΣPBDE Beluga 11.1%

—

— Des

Melon-headed whale 2.6%, 3.5%

— 85% Kaj

ΣDDT Bottlenose dolphin 5.1%

—

— Sa

Long-finned pilot whale (9-yr-old) 9.58%

(13-yr-old) 7.85%(30-yr-old) 6.95%

(9-yr-old) 67.6%

(13-yr-old) 80.7%

(30-yr-old) 100%

— Bo

Striped dolphin (ΣDDT) 4.7%

(p,p'-DDE) 5.4%

(p,p'-DDD) 6.6%

(p,p'-DDT) 3.0%

————

————

Ta

(25
Table 4 continued. Contaminant transfer from delphinid and phocoenid females to calves during gestation and/or lactation.

29

Contaminant Species

% Offload

(Gestation)

% Offload

(Lactation)

% Offload

(Total) 

ΣDDT Striped dolphin

—

(2.5-yr-old) 4.7%

(17.5-yr-old) 95.0%(25.5-yr-old) 94.6%

— Ta

(values 

4.2% 91%

— Fukush

(assum

TCPMOH Melon-headed whale 3.3%, 5.3%

— 84% 

TCPMe 0.55%, 1.2%

— 41%

HP-epox 2.7%, 3.5%

— 83%

ΣCHL 5.0%, 5.8%

— 89%

HCB 3.7%, 5.3%

— 76%

Striped dolphin (25.5-yr-old) 9.4%

—

— Ta

Striped dolphin

—

(25.5-yr-old) 9.4%

(17.5-yr-old) 98.1%(25.5-yr-old) 98.0%

— Ta

(values 

ΣHCH Melon-headed whale 5.6%, 6.0%

— 82% Kaj

ΣHCH

α-HCH

β-HCH

γ-HCH

Striped dolphin 8.9%

7.0%9.7%6.5%

————

————

Ta

(25

ΣBHC Striped dolphin

—

(25.5-yr-old) 8.9%

(17.5-yr-old) 94.9%(25.5-yr-old) 93.5%

— Ta

(values 

6.3% 72%

— Fukush

(assum

Nonspecific 

organochlorine 

compounds

Harbor porpoise 15%

—

— Duinker 
(1981) suggested that first-born dolphin calves receive a fourfold higher initial burden of PCBs 

and DDTs than subsequent calves, and that approximately 90% of this load is transferred through 

lactation. Cockcroft et al. (1989) also reported that first-born bottlenose dolphin (Tursiops 

truncatus) calves receive the majority of their mothers’ contaminant loads during lactation.

Regardless of maternal age (and presumably reproductive history), transfer rates during 

lactation are always much greater than during gestation (Fukushima and Kawai 1981, Tanabe et 

al. 1981, Tanabe et al. 1982, Borrell et al. 1995). Thus, lactation is the major elimination route of 

contaminants for female cetaceans. Currently, the quantity of contaminants typically offloaded 

from mother to calf in killer whales is unknown. However, PCBs and DDTs offload data are 

available for other delphinids. The ranges of transfer rates of PCBs and DDTs during gestation are 

3.7–9.73% and 4.2–9.58%, respectively, of a female’s total body load. During lactation, the ranges 

of transfer rates of PCBs and DDTs are 88–99.9% and 67.6–100%, respectively, of a female’s total 

body load (Table 4). 

Given the higher transfer rates during lactation, a large quantity of contaminants could be 

delivered to a suckling calf in a short amount of time. For example, Cockcroft et al. (1989) 

calculated that approximately 4% of a female bottlenose dolphin’s total body burden can be 

transferred to her calf during lactation daily; consequently, the mother’s full load would be 

transferred after approximately seven weeks of lactation. Interestingly, the one study (Aguilar 

and Borrell 1994) that estimated transfer rates for a mysticete (in this case, fin whales) found 

much lower total transfer rates for each reproductive cycle (gestation and lactation combined). 

Depending on the age of the female, transfer rates during each reproductive cycle ranged 

from 3–14% and 9–27% of a female’s total body load for PCBs and DDTs, respectively. The 

authors attributed the relatively low transfer rates to the shorter lactation duration of fin whales 

(approximately 7 months) compared to the longer lactation periods (18 months) of striped and 

bottlenose dolphins (Aguilar and Borrell 1994). PCBs and DDTs transfer rates of phocid seals 

that have relatively short lactation periods are near the range of those reported for fin whales 

(Kajiwara et al. 2008). Similar to delphinids, younger female fin whales offloaded a higher 

percentage of their body burden to their calves compared to older females that had reproduced 

more than once (Aguilar and Borrell 1994). These examples illustrate the importance of having a 

good understanding of the duration of lactation, in addition to individual females’ reproductive 

histories, when assessing contaminant transfer rates from female killer whales to their calves. 

Less is known about the transfer of PBDEs during gestation and lactation in cetaceans. However, 

it is reasonable to assume that the transfer rates of PCBs and PBDEs are comparable, because the 

chemical structures of these two classes of contaminants are similar. Recent studies have shown 

that maternal transfer of PBDEs during gestation and lactation occurs (Kajiwara et al. 2008, Park 

et al. 2010, Desforges et al. 2012) and that transfer rates of PCBs and PBDEs are comparable (Table 

4). For example, ΣPCB and ΣPBDE transfer patterns over the lactation period in bottlenose 

dolphins tend to be similar (D. Noren unpubl. data). Estimated placental transfer rates for two 

female melon-headed whales (Peponocephala electra) ranged from 3.5–3.6% and 2.6–3.5% for 

PCBs and PBDEs, respectively. The estimated transfer rates for gestation and lactation combined 

were 89% and 85% for PCBs and PBDEs, respectively (Kajiwara et al. 2008). Although transfer 

30
rates for killer whales have not been reported, recent studies have found that cetacean calves and 

young juveniles have blubber PBDE concentrations that are orders of magnitude greater than 

those of reproductive females (Krahn et al. 2007a, Haraguchi et al. 2009, Krahn et al. 2009, Ylitalo 

et al. 2009). Similar to the more highly chlorinated PCBs, the more highly brominated PBDE 

compounds are less transferable from delphinid and phocoenid females to their fetuses during 

gestation and to their calves during lactation (Kajiwara et al. 2008, Haraguchi et al. 2009, Park et 

al. 2010) because of their larger molecular size and higher lipophilicity. 

Other Influential Factors Affecting POP Accumulation

Age- and sex-related patterns of POP levels in marine mammals have been well cited in 

the literature. Persistent pollutants will accumulate in marine mammals when the input or 

exposure exceeds the ability of the individual to metabolize and excrete them. As a result of 

this bioaccumulation, concentrations can increase with the individual’s age (Ross et al. 2000, 

Ylitalo et al. 2008). However, this age-specific pattern is different in males and females. As 

mentioned above, reproductive females are able to offload their contaminants to their offspring 

via transplacental transfer and lactation. Therefore, reproductive females that have given birth 

to calves and nursed, or are pregnant, can have significantly lower POP levels than adult males 

of a similar age. For example, male and female resident killer whales have distinct age-related 

patterns of ΣPCB and ΣDDT accumulation. In males, these POPs continuously increase with age, 

allowing them to accumulate relatively high body burdens (Ross et al. 2000, Krahn et al. 2007a). 

In females, levels decline and remain low during reproductive years, and subsequently increase 

again in older females, likely reflecting reproductive senescence (Ross et al. 2000). 

Not all POP levels follow this general age- or sex-related pattern. For example, ΣPBDE 

concentrations in male Southern Residents and male and female transients sampled during the 

1990s did not differ, nor did these pollutants increase with age (Rayne et al. 2004). The difference 

in age-related patterns between the legacy PCBs and the PBDEs may be due in part to PBDEs 

being relatively new in the environment (Rayne et al. 2004, Mongillo et al. 2012). Thus, older 

individuals were not exposed when they were young and do not have a lifetime of accumulation. 

The difference may also be due to differences in metabolism and excretion of PBDEs among age 

classes. Adults may have a higher ability to metabolize these compounds than juveniles do. For 

example, the highest levels of PBDEs were measured in juveniles, not adults, in both Southern 

Residents and main Hawaiian Island false killer whales (Krahn et al. 2007a, Krahn et al. 2009, 

Ylitalo et al. 2009). 

Although cetaceans in general have a lower ability to metabolize certain lipophilic compounds 

than other mammals, killer whales may have some ability to metabolize some compounds 

(Wolkers et al. 2007). Unlike the ΣPCBs, ΣDDTs, and ΣPBDEs that have been measured at 

high concentrations in killer whales, other POPs, such as the polychlorinated dibenzodioxins 

and polychlorinated dibenzofurans (PCDDs and PCDFs), were low or undetectable in 

eastern North Pacific killer whales (Ross et al. 2000). Similarly, low POP concentrations of the 

hexachlorocyclohexanes α-HCH and γ-HCH in the blubber tissues of North Atlantic killer 

31
whales were also reported (McHugh et al. 2007). These patterns of high ΣPCBs and ΣDDTs 

and low dioxins, furans, and HCHs suggest the ability of these whales to either metabolize or 

regulate certain congeners, which plays a major role in the accumulation and retention of certain 

chemicals (Ross et al. 2000, McHugh et al. 2007). 

Wolkers et al. (2007) examined congener-specific metabolism and accumulation in killer whales 

from Norway, as well as the transfer of contaminants from their main prey, herring. They found 

that the more persistent PCB congeners and DDE can accumulate to some degree in killer whales, 

reflecting the whales’ inability to metabolize these compounds. Additionally, they suggested 

killer whales may have the ability to metabolize most PBDEs, but despite this, there are a few 

PBDE congeners that accumulate. Evidence of this is found in congener-specific contaminant 

profiles from different killer whale populations. For example, congener-specific PCB profiles are 

similar across killer whale ecotypes, with the more highly chlorinated congeners dominating, 

especially the ortho-substituted congeners -138 and -153 (Ross et al. 2000). Ylitalo et al. (2001) 

also found that PCB congeners -138 and -153 dominated in killer whale blubber. More specifically, 

PCB congeners -52, -101, -118, -138, -153, and -180 accounted for almost half of the ΣPCB 

concentrations in Southern Resident killer whale blubber (Ross et al. 2000). The more toxic nonortho-substituted congeners -77, -126, and -169 were not detected in the blubber of killer whales 

from Kenai Fjords/Prince William Sound, Alaska (Ylitalo et al. 2001). Similar PBDE congener 

profiles were also observed across killer whale populations. For example, Rayne et al. (2004) 

sampled transients, Northern Resident killer whales, and Southern Resident killer whales for 

PBDEs, and although the congener contribution varied among the killer whales, concentrations 

of PBDEs -47, -99, -100, -153, and -154 were higher than the other PBDE congeners (Rayne et al. 

2004), reflecting the killer whales’ inability to excrete these persistent congeners. 

Body composition and nutritive condition are additional factors that affect the dynamics of 

POP accumulation in marine mammals. Body size may also influence the accumulation pattern 

of pollutants; however, the effect is complex (Aguilar et al. 1999). Because POPs are generally 

lipophilic and accumulate in fatty tissues, species that have more fatty tissue will have a larger 

capacity for storing these pollutants. Approximately 70–95% of the total contaminant body load 

in whales is in the lipid-rich blubber (Aguilar et al. 1999, Yordy et al. 2010b). Blubber can serve 

as an energy store, and its contribution to body mass will depend on nutritive condition. The 

nutritive condition of an individual will affect both the volume and composition of the fat. When 

lipids are mobilized (e.g., because of seasonal fluctuations or reproductive status), the POPs 

can either remain in the blubber and become more concentrated, or become mobilized along 

with the lipids (Aguilar 1987, Krahn et al. 2002, Debier et al. 2006, Yordy et al. 2010c, Louis et al. 

2014). POPs may be selectively mobilized from the blubber when lipids are mobilized, based on 

their physicochemical properties (Yordy et al. 2010c). Once POPs enter the bloodstream, they 

may redistribute, leading to elevated tissue concentrations (Yordy et al. 2010c). During the early 

post-weaning fast in northern elephant seal (Mirounga angustirostris) pups, the fatty acids from 

the inner blubber layer are mobilized into circulation, whereas the rate of mobilization of POPs 

remains relatively low (Debier et al. 2006, Louis et al. 2014). During this early fasting period, POP 

concentrations are significantly higher in the inner blubber layer than the outer blubber layer. As 

the period of fasting progresses, POP concentrations increase in the pups’ serum (Debier et al. 

2006, Louis et al. 2014). Therefore, the effects of POPs may be compounded by stresses associated 

with nutritional limitation. 

32
Potential Adverse Health Effects

from POP Exposure

Various deleterious biological effects have been associated with exposures to PCBs, PBDEs, and 

DDTs in humans, laboratory animals, and wildlife. These pollutants have the ability to disrupt 

the endocrine system, nervous system, and immune system, and also cause cancer. In this section 

we discuss these adverse health effects from isolated POPs observed in wildlife and laboratory 

species, with a particular focus on PCBs and PBDEs in detail, and we include brief descriptions of 

the endocrine, nervous, and immune systems in marine mammals. 

Influence of Organic Contaminants on the

Endocrine System

Mammals have a sophisticated endocrine system that controls their physiological and metabolic 

processes. In general, the endocrine system consists of several endocrine glands that produce 

and regulate hormones, which play essential roles in several aspects of reproduction, neural 

development, and growth, in the regulation of metabolism, and in controlling heat loss. Some 

of the hormones produced in endocrine glands are released into the bloodstream, where they 

can travel to target cells, interact with hormone receptors, and activate a response (e.g., gene 

activation). The main parts of the endocrine system include the hypothalamus, pituitary gland, 

thyroid gland, adrenal glands, pineal gland, and the gonads (Figure 4). Below, we provide a 

general background on thyroid and sex hormones, followed by the health effects on these 

hormones that have been observed in wildlife and laboratory species as a result of exposure to 

organic contaminants.

Thyroid Hormones

The hypothalamus, located in the brain, links the nervous system with the endocrine system. 

The hypothalamus sends a thyroid releasing hormone (TRH) to the pituitary gland. This gland 

releases thyrotropin (TSH), which stimulates the production of thyroid hormones from the 

thyroid gland (Figure 4). Thyroid hormones, such as thyroxine (T4) and triiodothyronine (T3), 

are fat-soluble and are transported into circulation bound to the carrier protein complexes 

transthyretin (TTR) or T4-binding globulin (TBG). If they are not bound to a carrier protein, they 

are readily removed from the blood by the kidneys and liver. T4 is the most abundantly secreted 

hormone, but only a fraction of the total T4 enters target cells (i.e., cells that change their gene 

expression in response to the hormone). Once T4 is transported to a target cell, it is deiodinated 

to its biologically active form, T3, which then binds with nuclear receptors (NRs) that regulate the 

expression of certain genes (Figure 4). T3 is then released into circulation and recycled or excreted 

via the bile.

33
Figure 4. Primary components of the hypothalamic–pituitary–thyroid axis. The hypothalamus releases 

the thyroid releasing hormone (TRH), a hormone that stimulates the secretion of thyrotropin (TSH). 

TSH acts on the thyroid gland to stimulate iodide (I-

) uptake, and regulates the synthesis and release 

of thyroid hormones (T4

 and T3). T4 binds to transport proteins (TBG or TTR) and enters into 

circulation. Once the T4

 reaches a target cell, it is converted to T3, which binds to thyroid hormone 

receptors (TRs) and nuclear receptors (NRs) and activates transcription. T3

 is then excreted via bile or 

recycled. The potential mechanisms of action for PCBs and PBDEs on the hypothalamic–pituitary–

thyroid axis include: 1) inhibition of the synthesis of thyroid hormones by interfering with the TSH 

receptor; 2) binding to the transport protein; and/or 3) binding to the thyroid nuclear receptor and 

altering gene expression.

34
In pinnipeds, reported levels of circulating T4 have ranged from 4 to 190 μg/L, whereas T3

concentrations are much lower, ranging from 1.04 to 1.76 μg/L (see Gregory and Cyr 2003 and 

references within). There are several influential factors that affect TH concentrations in pinnipeds 

that may explain the variability observed. For example, thyroid hormone concentrations decrease 

with age or maturation in several pinnipeds (see Myers et al. 2006 and references within). Thyroid 

hormones have also been shown to vary by season in some marine mammals (e.g., harbor seals; 

Oki and Atkinson 2004), and have been associated in some pinnipeds with the annual molt (see 

Myers et al. 2006 and references within). 

In cetaceans, reported levels of circulating T4 have ranged from 5 to 190 μg/L, similarly to 

pinnipeds (Gregory and Cyr 2003). Thyroid hormones in cetaceans can also be influenced by 

several factors, including age, sex, diet (e.g., goitrogens), and season, and can vary by geographic 

region. For example, thyroid hormone levels were significantly higher in bottlenose dolphins 

from the coastal waters of South Carolina compared to those from Florida, which is likely 

attributed to coping with lower year-round temperatures (Fair et al. 2011). However, age had the 

most influence on TH concentrations, with decreasing concentrations measured with increasing 

age (Fair et al. 2011). A seasonal cycle in thyroid activity has also been described in belugas, where 

TH levels corresponded to the whales’ distinct seasonal use of warm river estuaries and cold 

ocean habitat (St. Aubin and Geraci 1989). In contrast, a seasonal cycle of THs was not apparent 

in Atlantic bottlenose dolphins, and sex had the most influence on TH concentrations with higher 

levels found in females (St. Aubin et al. 1996). Southern Resident killer whales that were sampled 

in late spring/early summer had higher fecal T3 levels than whales sampled in late fall/early winter 

(Ayres et al. 2012). The degree of influence these factors have on the endocrine system in marine 

mammals appears to be complex and species-specific, warranting further research. 

Effects on Thyroid Hormones from Organic

Contaminant Exposure

In addition to the influential factors described above, several contaminants are considered 

potential endocrine disruptors and can interfere with hormone signaling or activate signal 

pathways, acting as agonists or antagonists (i.e., enhancing or inhibiting the effect of hormones). 

In general, some endocrine disrupting chemicals (EDCs) are structurally similar to T4 and T3, and 

can affect the TH system through several potential mechanisms of action (Figure 4). For example, 

some EDCs may inhibit the synthesis of THs; modify the metabolism of THs; displace T4 and 

bind to TH receptors or transport proteins, reducing the transfer of retinol (vitamin A) and T4 to 

target organs; interfere with cellular uptake mechanisms; alter gene expression; and decrease the 

availability of progesterone (de Boer et al. 2000, Houde et al. 2005, Boas et al. 2006). Contaminant 

binding to a transport protein not only disrupts the transport of the hormones essential for 

brain development, but also facilitates transport of these compounds across the blood–brain and 

placental barriers (de Boer et al. 2000). EDCs may also be able to induce hepatic microsomal 

enzyme (e.g., uridine diphosphoglucuronosyltransferase, UDPGT) activity (these enzymes mediate 

extraction or clearance of these endogenous hormones), thereby increasing the excretion of T4. 

35
Several studies have reported reduced TH and vitamin A concentrations with high PCB 

concentrations in wildlife species (Brouwer et al. 1989, de Swart et al. 1996, Shaw et al. 1999, 

Jenssen et al. 2003, Fernie et al. 2005, Sørmo et al. 2005, Tabuchi et al. 2006, Letcher et al. 

2010, Schwacke et al. 2012). For example, PCBs were negatively correlated with total T4 and 

were positively correlated with TR-α (a thyroid hormone receptor) in free-ranging harbor seal 

pups from inland waters of Washington and British Columbia (Tabuchi et al. 2006). Similar 

to the free-ranging harbor seal pups from inland waters, preliminary results also revealed an 

association between reduced thyroid hormone levels in harbor seal pups from California with 

increasing levels of PCBs, and lower levels of PCBs were associated with a stronger immune 

response (Shaw et al. 1999). These studies suggest that harbor seals may be highly sensitive to 

contaminant-induced endocrine disruption. Correlations between contaminants, TH levels, 

and TR-α expression can also indicate an increased risk in thyroid hormone-dependent health 

effects, such as developmental abnormalities. For example, developmental disturbance, measured 

by fluctuating skull asymmetry in Baltic gray seals (Halichoerus grypus), was associated with a 

heavy pollution period (Zakharov and Yablokov 1990). Gray seals born in the 1960s experienced 

peak pollution levels in the environment and had higher levels of skull asymmetry compared 

to seals born prior to the peak in pollution (Zakharov and Yablokov 1990). Although the health 

status of ringed seals (Phoca hispida) from the polluted Baltic Sea has improved, they continue to 

experience thyroid disruption, changes in vitamin A, and changes in hepatic mRNA expressions 

(Routti et al. 2010). PCB-induced endocrine disruption has also been observed in cetaceans. For 

example, bottlenose dolphins off the Georgia coast have severely decreased TH levels that are 

significantly correlated with extreme concentrations of PCBs, and a high prevalence of anemia 

(26%) was observed (Schwacke et al. 2012). 

Several studies suggest that PBDEs are also potential endocrine disruptors (de Boer et al. 2000, 

Legler and Brouwer 2003, Darnerud 2008, Legler 2008). Similar to PCBs, PBDEs can interfere 

with the transport and metabolism of THs and disrupt the TH homeostasis. Because some PBDEs 

or their metabolites are structurally similar to T4, they can significantly reduce T4 concentrations 

in laboratory species (Zhou et al. 2001, Richardson et al. 2008). For example, a commercial PBDE 

mixture that contains tetra- and penta-forms (DE-71) caused serum T4 levels to be reduced in rat 

fetuses and offspring, and these levels did not recover until approximately 1 month later (Zhou et 

al. 2002). American kestrel (Falco sparverius) eggs and nestlings that were exposed to penta-BDE 

congeners also had lower plasma T4 and lower plasma retinol (Fernie et al. 2005; see review in 

Letcher et al. 2010). It may also be possible that a contaminant-induced reduction of T4 levels has 

the potential to alter hearing and communication in mammals (e.g., Crofton 2004).

Sex Hormones

Androgens, estrogens, and progestins are steroid hormones that are primarily synthesized in the 

adrenals, gonads, and placenta (see reviews in Gregory and Cyr 2003 and Atkinson et al. 2009). 

More specifically, testosterone is produced in the testes, estrogen and progesterone are produced 

in the ovaries, and all three can be produced in the adrenals. The hypothalamus produces 

and secretes gonadotropin releasing hormone (GnRH), which acts on the pituitary gland. 

36
The pituitary stimulates the synthesis and release of follicle stimulating hormone (FSH) and 

luteinizing hormone (LH). In females, FSH regulates the ovarian follicle and the production of 

estradiol, and LH triggers ovulation and ovarian production of estradiol. In males, FSH promotes 

spermatogenesis and LH stimulates secretion of testosterone. 

Sex steroids in marine mammals are consistently low in concentration prior to sexual maturity, 

followed by a fluctuation in concentration at the onset of sexual maturation (Atkinson et al. 

2009). In some male marine mammals, testosterone concentrations vary depending on the female 

breeding activity, but typically have peak concentrations prior to the breeding season (Atkinson 

et al. 2009 and references within). In captive male killer whales, mean serum testosterone 

concentrations at puberty and at sexual maturity were 0.7 ± 0.7 ng/mL and 6.0 ± 3.3 ng/mL, 

respectively (Robeck and Monfort 2006). However, unlike seasonally reproductive species that 

experience clear seasonal peaks in testosterone concentrations, captive male killer whales had 

“seasonal rhythms” in testosterone, but spermatogenesis was maintained throughout the year 

(Robeck and Monfort 2006). In male Southern Resident killer whales, fecal testosterone increased 

asymptotically with the onset of puberty, estimated at 11 to 12 years of age (Ayres 2011).

Progesterone is the primary hormone responsible for sustaining pregnancy in mammals. In 

fact, pregnancy detection has been successfully attempted by detecting progesterone and other 

reproductive steroids in several media, including serum or plasma, blubber, feces, saliva, milk, 

and ocular secretions (Rolland et al. 2005, Atkinson et al. 2009, Kellar et al. 2013, Trego et al. 2013, 

Wasser et al. in prep.). For example, serum progesterone levels were above 3 ng/mL in pregnant 

belugas and between 4.3 and 4.5 ng/mL in pregnant and ovulating minke whales (Balaenoptera 

acutorostrata; see Boyd et al. 1999 and references within). 

Effects on Reproduction from Organic Contaminant Exposure

Some contaminants can have endocrine-disrupting effects that mimic or alter reproductive 

processes. Consequently, sex-related hormone alteration and adverse reproductive effects have 

been associated with contaminant exposure in several studies. For example, high PCB loads have 

been associated with reproductive failure in several pinniped species. In one study, premature 

births were found to occur in California sea lions (Zalophus californianus) with higher levels 

of PCBs in the blubber and liver (Gilmartin et al. 1976). PCBs were also suggested as the main 

cause of the higher frequency of reproductive failures in harbor seals fed fish from the more 

polluted waters of the western part of the Wadden Sea than seals fed fish from the less polluted 

waters of the northeast Atlantic (Reijnders 1986). One possible explanation for the reproductive 

failure observed in the harbor seals is that 17β-estradiol levels were lower around the time 

of implantation, which may have impaired endometrial receptivity and prevented successful 

implantation (Reijnders 1986, Reijnders 2003). It was later suggested that the lower levels of 

estradiol were possibly from enzyme-induced metabolism by PCBs; however, further studies are 

needed to test this possibility (Reijnders 2003).

37
Contaminant-induced reproductive impairment (e.g., Subramanian et al. 1987) or failure (e.g., 

Schwacke et al. 2002) has also been suggested in cetaceans. Reproductive success in bottlenose 

dolphins, measured by the calf ’s survival, may be significantly reduced because of chronic 

exposure to PCBs (Schwacke et al. 2002), corroborating other studies that have measured 

maternal contaminant burdens and calf mortality rates (Reddy et al. 2001, Wells et al. 2005). 

However, other confounding factors, such as the mother’s age and maternal experience, may 

have influenced the reproductive success in some of these studies. Population growth rates may 

also be adversely affected by PCB contamination. For example, an individual-based model was 

used to estimate the effects of PCB accumulation rates on potential population growth rates in a 

bottlenose dolphin population (Hall et al. 2006b). Using a dose–response relationship based on 

maternal PCB burdens and first-year calf survival, the model results suggest that the current PCB 

accumulation rates may be depressing the population growth rate (Hall et al. 2006b). 

Sex determination at birth (or the sex ratio of a population) may have the potential to be affected 

by EDCs. Because EDCs can mimic reproductive hormones that are thought to influence 

sex determination processes, it has been suggested that populations with high burdens of 

these EDCs and poor body condition may exhibit an altered sex ratio toward either females 

or males. For example, the temperature of egg incubation determines the sex of some reptile 

hatchlings. However, turtle eggs exposed to PCB concentrations comparable to levels observed 

in human breast milk showed a significant reversal compared to what would be expected for the 

temperature in which they were reared (Bergeron et al. 1994). Similar results are shown for birds. 

For example, female glaucous gulls (Larus hyperboreus) with high organochlorine levels and in 

poor body condition had an unexpected skew toward male offspring (Erikstad et al. 2011). Skewed 

sex ratios are not isolated to wildlife, but are found in humans as well. For example, maternal 

exposure to PCB-contaminated fish from the Great Lakes appeared to skew the sex ratio toward 

females (Weisskopf et al. 2003). A statistically significant decline in male births was also observed 

in the Aamjiwnaang First Nation community in Ontario, Canada (Mackenzie et al. 2005). Though 

there is not a significant difference between time periods, in the 1970s, births in the Southern 

Resident killer whale population were biased toward females, whereas since 2000, the current 

population has been biased towards males (Ward et al. 2013). Currently, there is little information 

on maternal or paternal influences on the sex ratio in killer whales. However, recent studies have 

provided in vitro sperm characterization and characterized the sexual maturation of captive male 

killer whales (Robeck and Monfort 2006, Robeck et al. 2011), which may be useful in detecting 

the effects of EDCs on gamete quality. Although there are several biological and environmental 

factors that can affect or influence a population’s sex ratio, and little information is available 

for marine mammals, the potential for endocrine disruptors to influence the sex ratio warrants 

further assessment.

Influence of Organic Contaminants on the Nervous System

In mammals, the nervous system is divided into the central nervous system, formed by the brain 

and spinal cord, and the peripheral nervous system, which includes all the nervous tissues in the 

body (Pabst et al. 1999). The maturation and development of the central nervous system, also 

38
referred to as neurogenesis, has two main stages. The first stage consists of early embryonic brain 

development, and the second stage is referred to as the brain growth spurt (Fischer 2008, citing 

Davison and Dobbing 1968). 

The height of the brain growth spurt appears to be the most critical or sensitive period in 

mammals for developmental neurotoxicity due to contaminant exposure (e.g., Darnerud 2003, 

Viberg et al. 2003, Viberg et al. 2006, Darnerud 2008). For example, neonatal mice exposed 

to BDE-99 during a critical period of brain development (day 3 or 10) experienced impaired 

spontaneous behavior; however, mice exposed on day 19 did not experience the neurotoxic effect 

(Eriksson et al. 2002). In a separate study, neurobehavior in rats was examined subsequent to inutero exposure to BDE-99 (Kuriyama et al. 2005). Exposure during critical developmental phases 

caused hyperactivity in offspring. These studies indicate that adverse health effects from exposure 

to some PBDE congeners are not only dose-dependent and species-specific, but that the timing of 

exposure during gestation is a significant factor.

Developmental neurotoxicity is considered one of the greatest concerns for potential adverse 

health effects from exposure to PBDEs (Costa and Giordano 2007). More importantly stressed is 

the increased probability of the hydroxylated (OH-) PBDEs over their parent congeners causing 

developmental neurotoxicity (Dingemans et al. 2011). PBDE exposure can have continuing 

behavioral alterations (e.g., changes in spontaneous behavior such as locomotion, rearing, and 

total activity, hyperactivity, and decreased habituation) and cognitive impairment or reduced 

learning and memory in laboratory species (Eriksson et al. 2001, Viberg et al. 2003, Viberg et 

al. 2006, Costa and Giordano 2007, Johansson et al. 2008). Very few studies have investigated 

the neurobehavioral effects of PBDEs in humans; however, in one study, serum levels of PBDEs 

in adolescence were associated with reduced motor function (Kiciński et al. 2012). Several 

studies have also revealed effects of PBDEs on brain function and structure, cell viability, cell 

differentiation and migration, and neuronal signaling (Dingemans et al. 2011). The exposure 

effects on cell signaling and function have been reported at concentrations similar to, or higher 

than, PCB exposure effects (Costa and Giordano 2007). 

In many species, certain PCB congeners can cause neurological impairment (Porterfield 2000). 

In both laboratory animal and human studies, exposure to PCBs reduces motor activity, learning 

and memory, responsiveness, neuromuscular development, and sensory function (see Bowers et 

al. 2004 for citations). One potential mechanism of neurotoxicity is the disruption of the thyroid 

system (Porterfield 2000). Because the THs control the development of the central nervous 

system, abnormal TH levels during specific developmental periods could lead to significant 

neurological impairment. Hypothyroidism, a reduced production of THs, or hyperthyroidism, 

an increased production of THs, during development can have profound impacts. During 

brain development, the effects of PCBs on TH-dependent gene expression were found to be 

congener-specific (Roelens et al. 2005). Rats dosed orally with a PCB mixture from gestation 

day 1 to postnatal day 23 had increased mortality and reduced growth, thyroid function, and 

neurobehavioral development (Bowers et al. 2004).

39
Influence of Organic Contaminants on Immune 

Function and Disease Susceptibility

Immune System and Functional Testing Overview

The immune system of killer whales has been studied under the assumption that many of its 

cellular components are functionally similar to better-described mammalian systems such as 

mouse, harbor seal, or human. To provide a background, an extremely streamlined overview of 

the roles and interactions of mammalian immune cells is shown in Figure 5, one that covers only 

those aspects mentioned subsequently.

Immunity can be coarsely separated into non-specific (or innate) and specific (or acquired) 

immunity, operationally defined by whether the response is directed against a range of foreign 

molecules (or antigens) or a specific foreign antigen, respectively. Phagocytic cells, such as 

macrophages and neutrophils, are often early responders to the presence of foreign antigens. 

Phagocytes ingest and destroy pathogens using reactive oxygen species and respiratory burst 

chemistry, present antigens to B cells and T cells, and release molecules that stimulate the 

proliferation of other immune cells and signal for the recruitment of cells for further immune 

response (Figure 5). A second important cell type involved in non-specific immunity is the 

natural killer cells that contact and destroy infected cells by releasing cytotoxic molecules.

Figure 5. Highly simplified diagram of the types, functions, and products of immune cells involved in

nonspecific and specific immunity. Products that influence other immune cells are connected by

arrows. Diagram is not comprehensive for immune function observed or studied in marine mammals.

40
B cells are well-known components of specific immunity because of their role in conferring 

protection against specific pathogens through antibody production. Antibodies attach to foreign 

antigens, making them more susceptible to attack by non-cellular parts of the immune system 

(e.g., the complement system) or by non-specific immune cells such as phagocytes. Cytotoxic T 

cells operate similarly to natural killer cells, except that they target specific antigens or pathogens. 

Helper T cells are often considered the lynchpin of the specific immune response, because they 

not only identify specific foreign antigens but also release signaling molecules that direct further 

targeted immune response. 

Measuring the magnitude and speed of activity of these cellular components has been useful 

in assessing the competence of the immune system. The majority of these measurements are 

conducted on tissue that is removed from the organism and either placed into culture conditions 

(in vitro) or tested without using culture conditions (ex vivo). The function in the animal is 

inferred from these types of tests.

Immune function in whales and dolphins appears to have strong parallels to that observed in 

terrestrial mammals, particularly laboratory models (e.g., rodents) and humans. Components 

of both innate and acquired immunity have been identified, and assays to phenotype or test 

function have been developed for some of these components. Phagocytosis, respiratory burst 

(generation of reactive oxygen species), natural killer cell activity, and non-specific lymphocyte 

transformation are signature features of an innate immune response, and assays were adapted 

or modified for cetaceans as early as 1975 (Hrgovcic et al. 1975). Immune phagocytosis and 

respiratory burst are typically mediated by neutrophils and macrophages. Bottlenose dolphin 

neutrophils exhibit NADPH oxidase activity (Inoue et al. 2001), and sequence alignments of 

NADPH oxidase in neutrophils have significant homologies to ruminant molecules (Egawa 

et al. 2001). Functional markers of T cells, B cells, histiocytes, and macrophages have been 

identified through cross-reacting antibodies from humans, mice, cattle, and sheep, indicating 

that homologous immune subsets are present in whales and dolphins (Kumar and Cowan 1994, 

Shirai et al. 1998a, Shirai et al. 1998b, Beineke et al. 2001, Jaber et al. 2003a, Jaber et al. 2003b, 

Kawashima et al. 2004a, Kawashima et al. 2004b, Kawashima et al. 2004c, Komohara et al. 2006). 

Use of these and cetacean-specific antibodies directed to recognize lymphocyte and leukocyte 

subsets support the functional role of the markers by comparing healthy and diseased animals. 

For example, harbor porpoises suffering from suppurative lesions exhibited selective depletion of 

MHCII- cortical thymocytes, thymic medullary CD45R+ B cells, and splenic periarteriolar CD3+

lymphocytes (Beineke et al. 2007).

Cytokines are the primary soluble and membrane-associated signaling molecules of the immune 

system, and a spectrum of important and well-characterized cytokines have been isolated and 

sequenced (see Table 1 in Beineke et al. 2010). Sequence homologies to human and terrestrial 

mammalian cytokines typically occur within regions of biological activity, permitting an 

inference of function. However, better support for homologous activity is found in studies that 

demonstrate cross-species activity. For example, recombinant cetacean TNFα and IL-1β have been 

used to stimulate terrestrial mammalian cell lines (Inoue et al. 2001, Shoji et al. 2001). Conversely, 

cetacean NK cell activity can be potentiated with recombinant human IL-2 (de Guise et al. 1997).

41
Whole genome sequencing of the killer whale genome1

 (by the Baylor College of Medicine 

Human Genome Sequencing Center) and comparative analysis of killer whale genomes (Moura 

et al. 2014) are uncovering homologous immune genes that have been characterized in model 

organisms, such as mice. Genes encoding proteins ranging from non-specific (e.g., complement, 

C-reactive protein) to specific immune functions (e.g., interleukin-12 and granulocyte–

macrophage colony stimulating factor 2) have been identified. Furthermore, gene orthologs 

for surface molecules involved in mediating cell adhesion associated with inflammation, such 

as e-, l-, and p-selectins,

2

 as well as other cell surface molecules that modulate host response 

(e.g., integrins), have been identified. The homology with well-characterized mammalian genes 

suggests that killer whale immune function is likely to follow known mechanisms of immunity.

1 http://www.ncbi.nlm.nih.gov/bioproject/167475

2 http://www.ncbi.nlm.nih.gov/gene/?term=orcinus+orca+AND+selectin

42

Effects on Immune Function of Organic Contaminant 

Exposure

Several POPs have well-documented effects on the immune system in experimental animals 

ranging from mice to primates (e.g., Thomas and Hinsdill 1978, Thomas and Hinsdill 1980, Safe 

et al. 1989, Dahlman et al. 1994). Dioxin-like POPs are particularly effective at immunotoxicity 

across a range of species, e.g., affecting the formation of reactive oxygen species (ROS) in 

neutrophils (Fonnum et al. 2006) or reducing mitogen-stimulated lymphocyte proliferation (de 

Swart et al. 1996). Effects can also be exerted indirectly by modulating immune function, such as 

reducing transfer of maternal antibodies to offspring (Lyche et al. 2006). 

In vitro and ex vivo studies are often used to provide insights into potential effects on cellular 

functions of the immune system. In vitro experiments are typically conducted by exposure 

of immune cells to contaminants in a culture dish, and ex vivo experiments utilize immune 

cells isolated from animals with varying levels of tissue contaminants. Exposure of harbor seal 

peripheral blood leucocytes (PBLs) to PCBs can induce a reduction in phagocytic activity and 

respiratory burst, suggesting possible suppression of a non-specific immune response (Hammond 

et al. 2005). Similarly, exposure of PBLs from harbor seals to three different PBDE congeners 

resulted in reduced phagocytic activity and efficiency and a decrease in intracellular thiol, but a 

slight increase in ROS, a measure of respiratory burst (Frouin et al. 2010). Real-world exposures 

are usually mixtures of congeners, and even within the reduced complexity environment of 

in vitro exposures, non-specific and specific cellular responses vary with mixture (Levin et al. 

2007), emphasizing that immunotoxicity can have both elevating as well as suppressive effects 

on immune function. A seminal feeding study demonstrated significant immunomodulation 

of immune responses in harbor seals fed herring that had either high or low concentrations of 

PCBs and DDTs. Natural killer cell cytotoxicity and mitogen-stimulated lymphoproliferation 

were reduced for seals fed highly contaminated herring for 93 weeks, implying a lowered ability to 

contain viral infections (de Swart et al. 1994). Furthermore, the specific proliferative responses to 

immunizing antigens and delayed type hypersensitivity were also reduced, particularly during the 

latter half of the exposure period, indicating that more complex interactions among immune cell 
types were also impaired (de Swart et al. 1995). Interestingly, B cell responses such as LPS-induced 

proliferation and antigen-specific antibody production were not affected, and total white blood 

cell counts and the percentage of granulocytes in the peripheral circulation were increased (de 

Swart et al. 1994, de Swart et al. 1995).

Microscopy and hematology are time-honored techniques for assessing immune potential, 

and histological examinations can reveal integrated impacts of an immunocompromised state. 

In harbor porpoise that were either by-caught or stranded and had high levels of PCBs and 

PBDEs, severe lymphoid depletion in the thymus and spleen were observed (Beineke et al. 2005). 

The thymus, a primary lymphoid organ, is the source of T cells, while the spleen, a secondary 

lymphoid organ, is a site where activated T and B cells are localized to advance an immune 

response. Lymphoid depletion in the thymus was associated with elevated PCB levels, whereas 

depletion in the spleen was associated with increased PBDEs. Lymphoid depletion may also be 

associated with persistent stress and malnutrition, as well as bacterial and viral infections. A 

hematology survey of harbor seal in San Francisco Bay identified a positive correlation between 

total peripheral leucocytes and concentrations of PCBs, DDE, and PBDEs, but a negative 

correlation between total red cell counts and concentrations of PBDEs, indicating a potential for 

anemia with exposure (Neale et al. 2005). 

Disease Susceptibility

Killer whales have been diagnosed with a spectrum of infectious and non-infectious diseases 

(Appendix A and Appendix B), and these animals are exposed to a large array of pathogens in 

the aquatic environment. Some pathogens and pollutagens (anthropogenic pathogens, chemicals, 

and molecules) are derived from terrestrial sources, some are inherent to marine waters, some are 

commensals or compose part of the normal microbial flora of the animals, and some are found 

in humans and sympatric marine mammals (Appendix C). The preponderance of data indicates 

that POPs exert an immunomodulatory effect on cetaceans and pinnipeds proportional to their 

concentration in tissues. The effects of PBDEs and DDTs are considered less severe than those of PCBs. 

A common approach to assessing the association between contaminants and disease susceptibility 

has been to compare tissue contamination levels to morbidity, to the degree of inflammation 

(host response), or to infection (e.g., Isobe et al. 2011). Furthermore, chronic disease or infection 

can lead to emaciation, which may mobilize contaminants, increase exposure, and exacerbate 

a disease condition. Although nematode infections in stranded harbor porpoises between 1989 

and 2002 in the United Kingdom were positively correlated with blubber PCB levels, the authors 

noted that controlling factors, such as age, gender, and cause of death, were not included in 

the analysis (Bull et al. 2006). A wide geographic comparison of POP concentrations by cause 

of death (infectious vs. non-infectious) found significantly higher levels of PCBs and PBDEs 

in harbor porpoise that died from infections (Pierce et al. 2008). This association was not 

observed for the bottlenose dolphin, and the authors suggested that the low number of dolphins 

that died from infections (12 of 716) severely reduced the power of the comparison. An ad hoc 

analysis of the relationship between PCB concentrations in the blubber of harbor porpoises 

and cause of death (physical trauma, infectious disease) found higher levels of contaminants 

43
among animals that died from infectious disease, even when controlled for gender (Jepson et al. 

2005). In contrast, a study of California sea otter (Enhydra lutris) that classified cause of death into 

four categories (infectious disease, emaciation, trauma, and other) failed to identify a convincing 

association between infectious disease and concentrations of industrial POPs (PCBs and PBDEs) 

in the liver (Kannan et al. 2007). Unfortunately, it is not possible with these studies to determine 

whether the observations are species-specific or caused by particular combinations of POP congeners.

The occurrence of neoplasms, or tumors, associated with exposure to POPs may represent a 

combination of mutagenic effects with immunotoxicity, immunosuppression, and sustained 

exposure, because of the resistance of POPs to degradation or excretion. The longer time required 

for neoplastic development makes it difficult to define a mechanistic relationship. However, tumor 

induction in laboratory mice exposed to DDT over their lifetime, as well as in mice exposed 

to DDT for 15–30 weeks, demonstrates the neoplastic potential of POPs (Turusov et al. 2002). 

California sea lion with herpesvirus-induced metastatic carcinoma had higher levels of blubber 

PCBs than animals without carcinoma, even when controlling for blubber thickness (Ylitalo et al. 

2005). Similarly, St. Lawrence belugas had much higher PCB concentrations than Arctic belugas 

and had a higher occurrence of tumors and lesions, and some evidence of immunosuppression 

(Béland et al. 1993, Martineau et al. 1994). Even among humans, a significant risk of breast cancer 

associated with serum POP levels can be detected among certain populations through case–

control study methods (Bonefeld-Jørgensen et al. 2011), suggesting that POPs may contribute to 

carcinogenesis in multiple ways.

44
The Development of Biomarkers for Toxicity

Biomarkers can potentially signal whether a population is at risk from contaminant exposure. 

They are generally classified as biomarkers of exposure or biomarkers of effects. Biomarkers of 

exposure do not give an indication of a toxicological effect, but can provide early evidence of 

exposure in an individual (e.g., BPMO induction in marine mammal skin biopsies; Fossi et al. 

1999). More biomarkers need to be developed and validated for marine mammals, but there are 

several potential biomarkers that have been investigated and proposed, including induction of 

the cytochrome P4501A enzyme system, plasma TH and vitamin A levels, immune responses, 

morphologic lesions, and assessment of DNA damage. The interpretation of these biomarkers’ 

responses to contaminant exposure is challenging, however, because of the numerous factors that 

can influence the endocrine, nervous, and immune systems. Furthermore, there is still a large 

gap between observing a biomarker response and understanding how this response affects the 

animal or population (O’Hara and Becker 2003). Here we provide a few examples of proposed 

biomarkers of exposure and biomarkers of effects for marine mammals.

The cytochrome P4501A enzyme system is the primary biochemical pathway for metabolizing 

contaminants and is an established biomarker for environmental pollution levels. The induction 

of this system has been used for dioxin-like congeners (Ross and Birnbaum 2003, Angell et al. 

2004). The dioxin-like congeners are toxic, and can interact with the aryl hydrocarbon receptor 

(AhR) and stimulate the synthesis of cytochrome P450 (CYP450). In general, a dioxin-like 

molecule enters the cell and can bind to the AhR (Figure 6). The AhR-contaminant complex 

migrates into the nucleus and alters gene expression. This then leads to the transcription of 

mRNAs that induce forms of CYP450. Inducing these enzymes can lead to the metabolism 

of these dioxin-like congeners and the formation of more toxic metabolites (Darnerud 2008). 

Thus, the AhR is a key regulator of the cellular response to contaminant exposure. After these 

compounds are chemically transformed by hepatic biotransformation processes, the more 

hydrophilic metabolites circulate in the blood of marine mammals and are more readily excreted 

from the body (Houde et al. 2005).

The induction of cytochrome P4501A can occur within hours of exposure to contaminants, and will 

decrease when metabolism or excretion of the contaminant occurs (Angell et al. 2004). Therefore, 

the levels of P4501A are an early contaminant-induced biological response (Angell et al. 2004). 

However, the identification of other potential influential factors of P4501A levels, such as the species, 

sex, age, diet, migration, reproductive status, and sampling location along the body, is essential to 

properly interpreting P4501A expression (Angell et al. 2004). In a previous study, van den Brink et 

al. (2000) proposed that the pattern of PCB congeners in the blood was a potentially nondestructive 

biomarker, linking the induction of cytochrome P450 activity to PCB exposure.

Other biomarkers for contaminant-associated toxic effects include measurements of circulating 

vitamin A in the peripheral blood, the expression of the vitamin A receptor RARα, and levels of 

circulating THs. Vitamin A is essential for growth, development, immunity, and reproduction. 

Ingested vitamin A is primarily stored in the liver and then transported to other tissues by 

the retinol binding protein (RBP) along with the transport protein TTR. In general, these two 

45
Figure 6. Diagram showing the interaction between an aryl hydrocarbon receptor (AhR) and a dioxin-like 

compound. The dioxin-like compound (PCB-169) enters the cell and binds with AhR. The inducer–

receptor complex translocates to the nucleus, where the transcription of specific mRNA occurs. The 

result is the induction of enzymes (cytochrome P4501A).

46

proteins maintain a constant concentration of circulating vitamin A. Although there is strict 

regulation of vitamin A in the body, some PCB and PBDE congeners can interfere with its 

transport, metabolism, and storage, ultimately reducing circulating vitamin A levels (Rolland 

2000, Hallgren et al. 2001, Mos et al. 2007). Several studies have also shown that PCBs and 

PBDEs can reduce T4

 levels, although PCBs may have a stronger effect on reducing T4 levels than 

PBDEs (e.g., see Hallgren and Darnerud 2002). The interpretation of the reduction in vitamin 

A and thyroid hormone levels and increased levels of POPs must include a consideration of the 

confounding factors, such as season, sex, age, and life history. For example, Simms et al. (2000) 

found that age and lactation status may interfere with interpreting the effects of PCBs on circulatory 

vitamin A levels in harbor seals. In contrast to other studies, PCBs and vitamin A were positively 

associated in non-nursing harbor seal pups, and this association was attributed to vitamin A stores 

from the liver becoming mobilized following contaminant exposure (Simms et al. 2000).

It was previously thought that corpora albicans, or ovarian scars, in some cetaceans accumulate 

with age and can provide individual lifetime reproductive histories (Perrin and Donovan 1984). 

Thus, with an index of reproductive history, one may assess the effects of contaminants on 

reproductive output. This assumption is not without controversy. Dabin et al. (2008) examined 

age, reproductive history, and ovarian scars in a relatively large sample (n = 187) of short-beaked 

common dolphins (Delphinus delphis). They found that the numbers of scars present in ovaries 
did not increase with age after sexual maturity. Thus, counting ovarian scars to reconstruct 

reproductive histories may have limited potential in this species, and the authors suggest that 

the validity of this assumption for other cetaceans should be reassessed as well (Dabin et al. 

2008). More recently, Murphy et al. (2010) investigated this question (whether ovarian scars 

accumulate and are persistent), and also investigated the potential to use these scars as an index of 

reproductive activity in female common dolphins and the harbor porpoise from the eastern North 

Atlantic. They found that the number of scars in porpoise ovaries was significantly related to age 

up to around five years (soon after sexual maturity); in common dolphins, the number of scars 

increased until around age 12 (sexual maturity). Furthermore, Murphy et al. (2010) investigated 

POP effects on the reproductive activity in both species using ovarian scars as an index of 

reproductive activity. Higher PCB concentrations in harbor porpoises tended to be associated 

with low numbers of ovarian scars (Murphy et al. 2010). Common dolphins had PCB levels above 

a threshold level (17 μg/g lw [lipid weight]) for adverse health effects in marine mammals (Kannan 

et al. 2000); however, ovulation, conception, or implantation were not inhibited (Murphy et al. 

2010). The highest PCB burdens in the dolphins were found in mature females (non-lactating and 

non-pregnant), who had the highest number of ovarian scars. These conflicting results warrant 

more research on the potential to use ovarian scars in certain species as an index of reproductive 

history and an assessment of the effects of contaminants on reproductive output. 

Direct measurement of the immune responses can offer informative biomarkers for POP 

immunotoxicity (de Guise et al. 2003). Cellular measures of immune function, such as 

phagocytic capability and induction of lymphocyte proliferation in vitro, readily detect certain 

POP-associated impairments of immune function (Levin et al. 2005, Schwacke et al. 2012). The 

advent of molecular techniques to measure gene expression at the level of the RNA transcript 

allows assessment of immune signaling molecules, such as IL2, IL10, and interferonγ (Beineke 

et al. 2010). However, to make an appropriate interpretation, these results should be interpreted 

with an understanding of contaminant loads and patterns associated with gender, age, and/or 

physiological status, such as pregnancy or lactation (Frouin et al. 2010). Because these molecules 

are components of a complex suite of changes, no single molecule or cellular response can 

serve as an immune biomarker of POP exposure. Furthermore, factors such as chronic stress or 

nutritional deficiencies can also induce changes in immune function. 

Several recent studies have described gene expression and DNA damage as useful biomarkers of 

toxicity. Buckman et al. (2011) observed a positive correlation between ΣPCB concentrations in 

killer whale blubber and the expression of five gene targets: AhR, thyroid receptor α, estrogen 

receptor α, interleukin 10, and metallothionein 1. Their results strongly suggest that PCBs 

influence mRNA abundance or expression for these five genes (Buckman et al. 2011), and that 

these gene targets are likely potential biomarkers of toxicity. El-Zein et al. (2006) compared levels 

of DNA damage and apoptosis in California sea lion and human lymphocytes in response to two 

different toxicants, and found the comet assay to be a useful biomarker of contaminant-related 

effects. Fossi et al. (2010) analyzed a combination of several molecular biomarkers (CYP1A1 

and CYP2B) and levels of gene expression (qRT-PCR of HSP70, ERα, AHR, and E2F-1) with 

contaminants (PCBs, PBDEs, DDTs, and PAHs) in two fin whale populations. Their “multi-trial 

diagnostic tool” revealed that fin whales from the Mediterranean Sea (Pelagos Sanctuary) have 

a higher toxicological stress than fin whales from the Gulf of California (Sea of Cortez, Mexico), 

providing further support for the usefulness of these biomarkers. 

47
Interactive Effects

Killer whales are exposed to a mixture of contaminants, and the interactions of these 

contaminants have the potential to be additive, synergistic, or antagonistic. The effect of an 

additive interaction of two or more chemicals equals the sum of the effects of the isolated 

chemicals. The effect of a synergistic interaction is greater than the sum of the effects of the 

individual chemicals, whereas the effect of an antagonistic interaction is less than the sum of the 

effects of the chemicals separately. Only recently have studies examined the interactive effects of 

mixtures containing POPs (some examples are provided in Table 5), and we provide a brief review 

of some of these studies below.

PCBs and PBDEs

Some PCB and PBDE congeners can interact and enhance developmental neurobehavioral 

defects in laboratory species. For example, Eriksson et al. (2006) found that combined low doses 

of the congeners PCB-52 and BDE-99 interacted in neonatal mice and enhanced developmental 

neurobehavioral defects when the exposure occurred during the critical brain growth 

development. Although it is not certain that the effects were synergistic, the authors suggest that 

the effects of the interaction were more than just additive. The developmental neurotoxic effects 

of these two congeners included deviations in spontaneous behavior (i.e., locomotion, rearing, 

and activity) and habituation capability (defined as a decrease in spontaneous behavior over the 

trial period because of the diminishing novelty of the test chamber), and indicated a progression 

towards brain dysfunction. In addition, the habituation significantly deteriorated with advancing 

age in the mice exposed to the mixture, as well as in mice exposed to a higher dose of PCB-52. 

Developmental neurotoxic effects in the mice that received the combined low dose of PCB-52 and 

Table 5. Mixture content and interaction type, with corresponding health effect(s), from case studies.

Mixture Interaction Type Health Effect(s) Reference(s)

PCB-52 + BDE-99 additive and/or synergistic enhanced neurobehavioral 

defects

Eriksson et al. (2006)

PCB-153 + BDE-47 additive and/or synergistic enhanced developmental 

neurotoxicity and 

cytogenotoxicity

Gao et al. (2009),

He et al. (2009),

He et al. (2010)

PCB mixture + BDE-47 

+ CPs

additive and/or synergistic TH disruption, induced 

enzyme activity

Hallgren and Darnerud 

(2002)

PCB-126 + MeHg additive enhanced developmental 

neurotoxicity

Fischer (2008)

PCB-153 + MeHg additive and/or synergistic enhanced developmental 

neurotoxicity

Fischer et al. (2008a), 

Fischer (2008)

BDE-99 + MeHg additive and/or synergistic enhanced developmental 

neurotoxicity

Fischer et al. (2008b), 

Fischer (2008)

PCB + PBDE additive reduced T4 levels Miller et al. (2012)

BDE-47 or BDE-99 +

PCB-126 or PCB-153

additive, synergistic, and/or 

antagonistic

cytotoxicity Pellacani et al. (2014)

48
BDE-99 were significantly more pronounced than in mice that received a five-fold higher dose 

of PCB-52 alone. Moreover, no significant change in spontaneous behavior was observed in mice 

that were exposed only to the same low dose of PCB-52 or BDE-99, indicating that toxicity occurs 

at a lower dose when these two congeners are combined.

PCB and PBDE congeners can also interact and induce protein and mRNA expression and reduce 

learning and memory in laboratory species. For example, He et al. (2009) examined the learning 

and memory of 2-month-old rats neonatally exposed to a single dose of either a mixture of PCB153 and BDE-47 or of each congener individually. The results suggest that rats co-exposed to both 

congeners performed significantly worse on a learning and memory test than rats exposed to 

BDE-47 alone. BDE-47 induced neurotoxic effects by affecting the learning and memory in a dosedependent manner. In contrast, both additive and synergistic reactions were observed in inducing 

protein and mRNA expression in female and male rats. Lastly, several alterations were observed in 

the neuronal ultrastructure in rats exposed to the high dose of BDE-47 and the mixtures containing 

both congeners. Therefore, the results suggest that the mechanism of action was via damaging the 

neurons of the hippocampus (the hippocampus has been associated with memory and learning). 

These same congeners (PCB-153 and BDE-47), which can induce protein and mRNA expression 

and reduce learning and memory in rats, have also been observed to enhance neurotoxicity and 

cytogenotoxicity in human neuroblastoma cells in vitro (Gao et al. 2009, He et al. 2010). He et al. 

(2010) found that at both the lower nontoxic concentrations and the higher toxic concentrations, 

PCB-153 enhanced the cytotoxicity of BDE-47. The enhanced cytogenotoxicity was evident by 

enhanced DNA and chromosome damage, significant inhibition of cell division, and DNA–protein 

crosslink (DPC) formation. There was a greater increase of DNA and chromosomal damage in coexposures than from the single congener alone. Their results indicate that the effect of the mixture is 

more than simply additive at specific concentrations. PCB-153 and BDE-47 alone did not significantly 

inhibit cell survival; however, cell viability was significantly inhibited when co-exposure occurred. 

Pellacani et al. (2014) investigated the cytotoxic effects of the combined exposure of either BDE47 or BDE-99 and PCB-126 (a dioxin-like congener) or PCB-153 (a non-dioxin-like congener). 

The non-dioxin-like congener (PCB-153) interacted synergistically with both PBDE congeners. 

Interestingly, the lowest dose of PCB-153 and the highest dose of BDE-47 had an antagonistic effect. 

The interaction between BDE-47 and the dioxin-like congener (PCB-126) was additive; however, 

synergistic effects were observed at the higher concentration of BDE-47. The interactions between 

BDE-99 and PCB-126 were complex, with antagonistic, additive, and synergistic interactions all 

observed. These results suggest that the nature of the interactions is related to the structure of the 

PCB molecule, and that the types of interactions vary depending on the concentrations.

PCBs, PBDEs, and Chlorinated Paraffins (CPs)

In another study, Hallgren and Darnerud (2002) examined the effects of exposure to BDE47, a PCB mixture (Aroclor 1254), and a chlorinated paraffin (CP; Witaclor 171P) on thyroid 

hormones in seven-week-old female rats. Free T4 was considered to be the most sensitive 

parameter to indicate irregularity in thyroid hormone status. Aroclor and the highest dose of 

49
BDE-47 significantly reduced free T4

 levels when administered alone, whereas all mixture groups 

significantly reduced free T4 levels. In fact, BDE-47 + Witaclor showed a clear synergistic effect on 

free T4 levels. The additive effects to T4 levels were generally seen in all scenarios. The induction 

of enzyme (EROD, MROD, and PROD) activity was also determined. These enzymes transform 

the parent PCBs and PBDEs into their metabolites, which can affect the levels of circulating T4. 

EROD activity is a marker for CYP 1A1 activity (mediated via AhR). Therefore, BDE-47 (a nonplanar molecule) was not expected to induce such activity. However, BDE-47 + Witaclor had a 

synergistic effect on EROD activity. The induction of EROD can increase the contaminant’s effect, 

further enhancing the production of metabolites that bind to TTR, thereby decreasing plasma 

T4 levels. Hallgren and Darnerud (2002) found that decreases in T4 levels are primarily due to 

disruption in the serum transport caused by the binding of the self-induced PCB and PBDE 

metabolites to TTR. The most pronounced effect of reduced TTR binding was from the BDE-47 

+ Aroclor group, followed by the BDE-47 + Witaclor group. As a consequence of the synergistic 

effects observed on T4 levels and EROD activity, the investigators emphasized the importance of 

including interactive effects in risk assessment. The thyroid glands were also examined following 

exposure to the combined mixture of all three contaminants, or the mixture containing BDE-47 

and Aroclor, and showed highly active glands (control groups showed low-activity glands).

PCBs, PBDEs, and Methyl Mercury (MeHg)

Fischer (2008) investigated the neurotoxic effects of PCBs, PBDEs, and methyl mercury (MeHg) 

on neonatal mice co-exposed during the period of rapid growth and development of the brain, or 

the brain growth spurt. Co-exposure to PCBs (both the ortho-substituted non-dioxin-like PCB153 and the coplanar dioxin-like PCB-126) and MeHg enhanced developmental neurotoxicity, 

manifested as defective spontaneous behavior, reduced habituation, learning and memory 

dysfunction, and alterations in the cholinergic system. Additionally, the neonatal mice coexposed to PCB-126 and MeHg demonstrated changes in spontaneous behavior that increased 

over time. Synergistic interactions were observed for PCB-52 + BDE-99, PCB-153 + MeHg, and 

BDE-99 + MeHg, whereas the co-exposure of the more toxic PCB-126 and MeHg appeared to 

have an additive effect. Co-exposure to PCB-126 or BDE-99 (same molar dose) and MeHg also 

reduced nicotinic receptor density in the cerebral cortex and hippocampus, respectively. Most 

importantly, the observed mixture effects often occurred at low doses, where the individual 

congeners alone at similar low doses did not cause an effect.

(Anti)Estrogenic Compounds

An estrogenic compound can mimic a hormone, bind to the receptor, and activate a hormonelike response, whereas an antiestrogenic compound acts as an antagonist, potentially binding 

to a receptor and blocking natural hormones from activating a hormone-like response (O’Shea 

1999). There appears to be a wide range of (anti)estrogenic compounds (Table 6). The majority 

of the PBDE congeners, and two of the three PBDE metabolites tested for their (anti)estrogenic 

activities, showed estrogenic activity (Meerts et al. 2001). The T2- and T3-like metabolites showed 

the highest estrogenic activity of all the PBDE compounds tested, whereas the T4-like metabolite 

50
showed no estrogenic effect. In contrast, PCBs have been reported to include both antiestrogenic 

and estrogenic responses (Buchanan et al. 2000, Bonefeld-Jørgensen et al. 2001, Buchanan et al. 

2002, Oenga et al. 2004, Plíšková et al. 2005, Oh et al. 2007). 

Exposure to a mixture of contaminants containing contrasting toxicities (e.g., a mixture of estrogenic 

and antiestrogenic compounds) may mediate the effects of these contaminants. For example, the 

antiestrogenic compounds PCB-138 and -180 reduced the proliferative effects of the estrogenic 

compounds 4,4'-DDE and trans-nonachlor, when mixed together (Yordy et al. 2010a). In fact, the 

combination of the antiestrogenic congener PCB-138 with the estrogenic mixture 4,4'-DDE and 

trans-nonachlor reduced the estrogenic response (i.e., reduced the proliferative effect), whereas the 

combination of PCB-180 and the estrogenic mixture resulted in a mixture that was no longer estrogenic.

Table 6. A list of some (anti)estrogenic PCB and PBDE congeners. 

PCB- Estrogenic Antiestrogenic Reference(s)a PBDE- Estrogenic Antiestrogenic Reference(s)a

28 X 3 28 X 6

44 X 1, 5 30 X 6

49 X 1, 5 32 X 6

52 X 1, 3, 4, 5 47 X 6

66 X X 1, 3, 5 51 X 6

74 X X 1, 3, 5 71 X 6

77 X 1, 5 75 X 6

95 X 5 85 X 6

99 X 1, 3 99 X 6

101 X 1, 5 100 X 6

105 X X 1, 3, 5 119 X 6

110 X 5 153 X 6

118 X 1, 4, 5 166 X 6

128 X 1, 5 190 X 6

138 X 1, 2, 3, 4, 5

141 X 5

153 X 1, 2, 3, 4, 5

156 X 5

167 X 5

170 X 1, 3, 5

174 X 5

177 X 5

180 X 1, 2, 3, 4, 5

187 X X 1, 3, 5

194 X 3

199 X 3

201 X 5

203 X 1, 3 a References: 1) Wolff et al. (1997), 2) Bonefeld-Jørgensen et al. (2001), 3) Plíšková et al. (2005), 4) Oh et al. (2007),

5) Yordy et al. (2010a), 6) Meerts et al. (2001).

51
Summary

In summary, certain mixtures can have interactive effects and enhance toxicity, including 

enhancing developmental neurobehavioral defects, inducing protein and mRNA expression, 

reducing learning and memory, and enhancing neurotoxicity and cytogenotoxicity. If co-exposure 

to a mixture occurs during the sensitive brain growth development, individuals can be more 

susceptible to toxic effects. Of particular importance is that enhanced toxicity can sometimes 

occur at lower doses once chemicals are combined, including at concentrations that would be 

nontoxic for the isolated chemicals. Interestingly, interactive effects in these case studies were 

additive, synergistic, and/or antagonistic. It appears that the molecular structure of the PCB 

congener may influence the type of interaction in some cases, and warrants further research. 

Lastly, mixtures can contain contrasting toxicities that may help mediate the effects, but make it 

extremely difficult to predict the effects of mixtures on killer whales. 

52
Implications for Southern Resident Killer Whales

Southern Resident killer whales carry relatively high POP concentrations in their blubber (Ross 

et al. 2000; Krahn et al. 2007a, Krahn et al. 2009, NWFSC unpubl. data). POP concentrations 

in Southern Residents are mostly dependent on regional inputs, the distribution of prey items, 

and the primary foraging area of the whales, which differ between the pods. Here we discuss the 

three primary POPs (PCBs, PBDEs, and DDTs) that have been analyzed from biopsy samples of 

Southern Resident killer whales (Figure 7).

The majority of Southern Resident killer whales that have been sampled for biopsy have blubber 

ΣPCB concentrations that exceed 17,000 ng/g lw (lipid weight), a health effects threshold in 

harbor seals. However, PCB exposure may have declined over the most recent decades (Ross et 

al. 2000, Krahn et al. 2007a, Krahn et al. 2009). Ross et al. (2000) biopsied male killer whales 

between 1993 and 1996 and reported an average ΣPCBs of 146,000 ng/g lw (± 32,700). Krahn et al. 

(2007a) reported an average ΣPCBs in male killer whales biopsied in 2004–2006 of 66,000 ng/g 

lw (± 26,000). The apparent reduction in concentration may be due to several factors, including 

a reduced exposure to PCBs. Krahn et al. (2007a) also suggest it may be due to a difference in 

methodologies between these two studies (e.g., Ross et al. [2000] summed 136 PCB congeners, 

whereas Krahn et al. [2007a] summed only 45 congeners). The reduced average blubber ΣPCBs in 

male killer whales may also be due to the influence of age; the male killer whales biopsied in the 

more recent study were on average 10 years younger than the whales in the earlier study. Using 

the same methodology as Krahn et al. (2007a), the Northwest Fisheries Science Center found an 

average blubber ΣPCBs concentration of 45,000 ± 31,000 ng/g lw in male killer whales sampled 

between 2004 and 2013.

Although there is an apparent decrease in average PCBs in male Southern Residents, these killer 

whales carry substantially higher PCB body burdens than the Alaska residents (Krahn et al. 

2007b) and Northern Residents (Ross et al. 2000). In fact, some calves have ΣPCB concentrations 

in blubber that exceed the total PCBs health effects threshold for seals by factors of 2–3.6 (Krahn 

et al. 2009). Transient killer whales from Alaska (n = 15) and California (n = 4) have even higher 

blubber PCB concentrations—120,000 ± 49,000 and 630,000 ± 190,000 ng/g lw, respectively—

more than double the values derived from Southern Resident killer whales (Krahn et al. 2007b). 

PBDEs are also found in relatively high levels in Southern Resident killer whales (Figure 7). Most 

sampled individuals in the Southern Resident population had higher ΣPBDE concentrations than 

levels associated with altered thyroid hormone levels in post-weaned and juvenile gray seals (Hall 

et al. 2003, Krahn et al. 2007a, Krahn et al. 2009, NWFSC unpubl. data). In fact, one juvenile killer 

whale had 10 times higher ΣPBDE blubber concentrations than those associated with endocrine 

disruption in gray seals (Hall et al. 2003, Krahn et al. 2007a). This may not necessarily reflect a 

unique anomaly, because all of the young juvenile Southern Residents biopsied to date have the 

highest PBDE concentrations measured in this population (Krahn et al. 2007a, Krahn et al. 2009, 

NWFSC unpubl. data). This observation may be due to their small body size and high exposure 

from nursing, but it also may be related to their reduced capacity to metabolize these pollutants.

53
Figure 7. Summed PCBs, PBDEs, and DDTs in the blubber of Southern Resident killer whales. Charts were generated using 

(2007a), Krahn et al. (2009), and NWFSC unpubl. data. The squares are maturing adult males 13 years and older. The styears and older. The black circles are juveniles and sub-adult whales. The dashed line represents the adverse health effecmarine mammals.

54
Average ΣPBDE concentrations in the blubber of Southern Residents sampled between 2004 

and 2013 was 4,800 ± 3,500 ng/g lw. A higher mean ΣPBDE value (7,600 ± 4,200 ng/g lw) was 

measured in J pod than the mean levels determined for K (5,000 ± 4,100 ng/g lw) or L (3,500 

± 2,000 ng/g lw) pods, indicating that J pod likely consumes prey that remains closer to urban 

settings, a primary source of PBDEs (Krahn et al. 2007a, Krahn et al. 2009, NWFSC unpubl. 

data). These average levels are higher than those found in other resident populations, as well 

as levels observed in Alaska transients (Krahn et al. 2007b). According to Rayne et al. (2004), 

between 1993 and 1996, average ΣPBDE concentrations in the blubber were approximately similar 

in male Southern Resident killer whales (942 ± 582 ng/g lw) and male transient killer whales 

from the northeastern Pacific Ocean (1,015 ± 605 ng/g lw). Although transients forage at a higher 

trophic level than Southern Residents, the proportion of time transients spend foraging on prey 

that remain closer to urban settings (i.e., Puget Sound) is relatively less than the time J pod spends 

foraging in urban waters. However, one West Coast transient killer whale sampled off California 

had substantially higher ΣPBDE blubber levels (12,600 ng/g lw), similar to levels measured in 

juvenile Southern Residents (Krahn et al. 2007b, Krahn et al. 2009).

PBDE concentrations in the Southern Residents have likely increased exponentially, with a 

doubling time between 3 and 4 years (Mongillo et al. 2012). However, based on other species 

that have experienced declining PBDE levels (Elliott et al. 2005, Law et al. 2010, West et al. 2011, 

Ross et al. 2013), and because of the decrease in production and use of certain PBDE technical 

mixtures, this increase of PBDEs in Southern Residents is expected to slow, and we anticipate 

declining tissue levels in the future. Continued sampling and analysis is essential to validate the 

assumption that accumulation of PBDEs will slow in the future.

Mean ΣDDT levels in the blubber of J, K, and L pods vary from 37,000 ± 39,000 ng/g lw, 72,000 ± 

64,000 ng/g lw, and 61,000 ± 51,000 ng/g lw, respectively. They also range from 1,200 ng/g lw in a 

J pod individual to 210,000 ng/g lw in an L pod individual (Krahn et al. 2007a, Krahn et al. 2009, 

NWFSC unpubl. data). In fact, juvenile killer whales in K pod had more than double the levels of 

ΣDDTs than did individuals in J pod (Krahn et al. 2009). These higher ΣDDT levels in K and L 

pod members are likely because of the higher regional input of DDTs in California (Eganhouse et 

al. 2000, Bay et al. 2003) and the observation that both K and L pods travel to forage on prey (i.e., 

Chinook salmon) that originate in the Central Valley and remain primarily on the continental 

shelf south of Cape Blanco during their adult life stage (Krahn et al. 2009). In contrast, J pod has 

not yet been observed in California waters and is more frequently observed in the inland waters 

of Washington and British Columbia (Hauser et al. 2007). Because both K and L pods travel to 

forage on prey in California, their ΣDDTs/ΣPCBs ratios did not significantly differ from each 

other, but were significantly higher than those observed for J pod (Krahn et al. 2007a, Krahn et 

al. 2009, NWFSC unpubl. data). Therefore, the higher regional input of ΣDDTs from California 

is reflected in the higher contaminant ratios in K and L pod members. Like the pattern found 

for PCBs, ΣDDT body burdens in Southern Resident killer whales are substantially higher than 

other resident killer whale populations and significantly lower than the transient or offshore 

populations (Krahn et al. 2007b). 

55
In summary, although there is a potential trend toward declining blubber PCB concentrations 

in Southern Resident killer whales, the absolute values are still very high and probably harmful. 

PBDE concentrations in the blubber of Southern Resident killer whales have not yet shown the 

declining trend observed in other marine mammal species. Due to reductions in the production 

and use of PBDEs, tissue concentrations are anticipated to decrease in the future. DDT 

concentrations appear to be a signature of foraging in California waters. Tissue concentrations 

remain high in Southern Resident killer whales and other marine mammals that feed near 

California. The high levels of PCBs, PBDEs, and DDTs in Southern Resident killer whales 

have health implications that are influenced by interactions with other stressors, including the 

abundance of Chinook salmon, the vulnerability of certain life stages, and the interactive effects 

of contaminant mixtures. While we do not discuss health implications to transient killer whales, 

which generally have higher POP levels than resident killer whales, we would expect these 

stressors (abundance of prey, vulnerability of certain life stages, and interactive effects of POPs) to 

have similar effects on transient killer whale health. Although there are limited data to indicate if 

the Southern Resident or transient killer whales are experiencing adverse health effects from high 

POP exposure, the high levels of PCBs, PBDEs, and DDTs in these killer whales are a significant 

concern. Below we discuss the implications for the health of Southern Resident killer whales from 

exposure to these POPs.

Contaminated Prey and Nutritional Limitation

Based on contaminant levels in Pacific salmon throughout their geographic range and the 

contribution of Chinook salmon to the summer diet of killer whales, these fish are likely an 

important source of contaminants to Southern Residents. The elevated POP levels in Chinook 

salmon, particularly in populations from Puget Sound and Harrison Lake (Fraser River), have 

implications for the viability of Southern Resident killer whales that feed upon them. Based on 

modeled PCB values for whales, Hickie et al. (2007) concluded that a diet at the tissue residue 

guideline of 50 ng/g to protect human health, which is similar to the average concentration in 

Chinook salmon from Puget Sound and Harrison Lake (Fraser River), would place over 95% of 

the killer whale population above the PCB effects threshold for immunosuppression found in 

harbor seals (17,000 ng/g lw, Ross et al. 1996).

The levels of POPs in Chinook salmon populations may also be high enough to negatively impact 

the health of the fish and, indirectly, the whales’ food supply. Approximately 22% of maturing and 

sub-adult Chinook salmon samples collected from Puget Sound had PCB concentrations above 

an effects threshold identified for salmonids (O’Neill and West 2009), which could potentially 

affect their abundance. Previous studies have demonstrated that juvenile Chinook salmon from 

more polluted waters in Puget Sound have an increased risk of immunosuppression and are more 

susceptible to disease than Chinook salmon in less polluted areas (Varanasi et al. 1993a, Arkoosh et 

al. 1998), linking elevated contaminant levels with reduced health and survival (Arkoosh and Collier 2002).

Abundance of Chinook salmon along the west coast of North America has been correlated with 

survival and fecundity of resident killer whales (Ford et al. 2005, Ward et al. 2009, Ford et al. 

2010, Ward et al. 2013, Vélez-Espino et al. 2014b). In the 1990s, concurrent declines occurred 

56
in both the Southern Resident killer whales and Chinook salmon, suggesting the potential for 

nutritional stress in the whales (Ford et al. 2005, Ford et al. 2010). Food availability is strongly 

associated with lipid content in individual marine mammals (Aguilar 1987). When lipids in the 

blubber are mobilized because of nutritional limitation, the contaminants can become mobilized 

into circulation (Aguilar 1987, Krahn et al. 2002, Debier et al. 2006, Louis et al. 2014), where they 

have the ability to induce a toxic response. Thus, nutritional stress from reduced Chinook salmon 

populations may act synergistically with high contaminant burdens in Southern Resident killer 

whales and result in higher mortality rates, reduced fecundity, or other contaminant-induced 

adverse health effects.

Unlike with Southern Residents that have experienced population declines, the West Coast 

transient killer whale population, which ranges from California to southeastern Alaska (Allen 

and Angliss 2014), appears to have grown rapidly from the mid-1970s to the mid-1990s, likely due 

to increased survival and fecundity as well as increased immigration of animals to the study area 

(DFO 2009). Their primary prey, harbor seals, also experienced rapid growth during this time 

(DFO 2009). Since 2008, transient killer whale mortality has been low and recruitment has been 

high (Towers et al. 2012). Transient killer whales have substantially higher contaminant burdens 

(Ross et al. 2000), but they do not appear to be experiencing nutritional stress or adverse health 

effects. The extent of influence that nutritional stress has on POP exposure and adverse health 

effects is currently unknown. 

Endocrine Disruption and Sensitive Life Stages

Certain life stages are particularly vulnerable to endocrine disruption, such as thyroid hormone 

disruption. For example, because PCBs and PBDEs can transfer across the placenta and blood–

brain barriers, the fetus (including the fetal brain) can be exposed to relatively high contaminant 

loads (Meerts et al. 2000). This influx of toxicants at such a young age is troubling because the 

growth and development of an individual are highly dependent on normal levels of thyroid 

hormones (Boas et al. 2006). Contaminants may disrupt normal hormone function (e.g., Hall et 

al. 2003) and thereby interfere with these developmental processes (Eriksson et al. 2002, Eriksson 

et al. 2006). The metabolism of a younger whale may also not be fully developed, hampering 

biotransformation and elimination of these pollutants. As a result, killer whale calves may be 

intrinsically more susceptible to contaminant-induced endocrine disruption because they are 

exposed to relatively high contaminant concentration levels, their capacity to eliminate these 

contaminants is reduced, and exposure occurs during critical stages of their development. 

Endocrine disruption is difficult to observe in free-ranging killer whales, and the implications 

for individual and population health are unclear. Based on extrapolation from laboratory animal 

and human studies, the effects could include alterations to a calf’s metabolism or growth and 

development. Altering these processes could affect the amount of prey required to meet energetic 

demands and also impair an animal’s ability to metabolize other toxic chemicals. As a consequence, 

this may lead to further accumulation and intensify the sublethal and lethal effects of pollutants.

57
It has been well documented in the literature that exposure to endocrine disrupting chemicals 

during sensitive periods of gestation and development can impact an individual’s reproductive 

health (see Fowler et al. 2012 for a review). Impacts may include delayed or premature physical or 

sexual maturity, reduced fecundity, or lack of reproductive success. However, killer whales have 

long life spans with variable recruitment, making it difficult to detect, assess, or interpret small 

changes in life history traits. A recent examination of the life history parameters and reproductive 

patterns in female resident killer whales from southern Alaska revealed that the mean age of 

first reproduction was 13 years (Matkin et al. 2014). In Northern and Southern Resident killer 

whales, the mean age at first reproduction is 14 to 15 years of age (Olesiuk et al. 2005), where “age 

at first reproduction” is defined by having conceived and produced a viable calf. Male resident 

killer whales in all three communities typically reach sexual maturity around 12 years of age and 

reach physical maturity by age 18 (Olesiuk et al. 2005, Matkin et al. 2014). Recently, Ward et al. 

(2009, 2013) estimated a regional difference in fecundity between the Southern Residents and 

the Northern Residents, and found that Southern Residents have lower production. Although 

the Southern Residents’ and Northern Residents’ geographic ranges overlap to some degree and 

both populations consume salmon as a primary prey species, regional differences appear to have 

translated to lower calving rates in the Southern Resident population. Vélez-Espino et al. (2014a) 

also found significantly lower fecundity and survival of viable calves in the Southern Resident 

population compared to the Northern Resident population. It is unclear as to why a disparity 

in fecundity and calf survival exists between these two populations, or why the age at maturity 

differs between the three resident communities. It is notable that the Northern Residents have 

significantly lower levels of some POPs that affect reproductive performance than the Southern 

Residents. Further, Alaska residents sampled off the Aleutian Islands have lower POP levels than 

Northern Residents (Table 3).

Exposure to endocrine disrupters at a young age may also affect fetal and perinatal survival. 

However, it is unknown if POP exposure in the Southern Resident population has caused an 

increase in neonatal or calf mortality. Because of the seasonality of the births, calf mortality is often 

missed, and estimated calving intervals are likely minimum estimates of calf production. In resident 

killer whales, calving intervals range from 2–14 years and significantly increase with advancing 

age (Olesiuk et al. 2005, Matkin et al. 2014). For example, in Alaska residents, the average calving 

interval for a 20-year-old was estimated at 4.3 years, whereas by age 40, the estimated average 

calving interval was 6.5 years (Matkin et al. 2014). An increase in the calving interval may indicate 

the onset of senescence, calf mortality, or another form of reproductive failure. In an early study, 

Olesiuk et al. (1990) calculated that viable calving intervals were marginally (but significantly) 

different between the more contaminated Southern Resident population (mean of 5.86 years) and 

the less contaminated Northern Resident population (mean of 5.02 years). Subsequently, Olesiuk et 

al. (2005) further refined the calving interval in the Northern Resident population during periods of 

population growth (mean of 4.88 years) and during periods of stability or no growth (mean calving 

interval of 5.53 years). Although the calving intervals vary and are only estimates, a reduction in the 

production of viable calves may indicate a reduction in fecundity or pregnancy rates that can impact 

the status and growth of the population.

Endocrine disruption may also lead to sex hormone alterations, which can sometimes result in 

permanent reproductive impairment. Altering sex steroids in males and females may result in 

premature births, reduced pregnancy rates, or generally reduced or abrogated fertility in females. 

58
As with other mammalian species (e.g., Hany et al. 1999, Kuriyama et al. 2005), male killer whales 

exposed to contaminants may exhibit reductions in sperm and spermatid counts, testicular 

weights, and circulating testosterone levels. Any reduction in fecundity in Southern Residents 

will only further reduce the population size and recruitment rate. This potential to affect the 

population growth of a restricted population highlights the severity of the issue. 

Contaminant exposure during critical periods of neurodevelopment can also cause significant 

changes in behavior and cognitive impairment in several species (e.g., Eriksson et al. 2001, Viberg 

et al. 2003, Viberg et al. 2006, Costa and Giordano 2007, Johansson et al. 2008). Reduced motor 

and brain function have been associated with exposure to endocrine disruptors in laboratory 

species (e.g., Dingemans et al. 2011, Kiciński et al. 2012), and, based on extrapolation to killer 

whales, such exposure could have significant impacts on behavior and survival. For example, 

killer whales rely to some degree on memory for foraging success. Reduced learning or impaired 

memory may affect their ability to find and capture prey and interact with other pod members. As 

killer whale calves mature, they likely develop their call repertoires through learning from closely 

associated individuals (see references within NMFS 2008). Because killer whales are in highly 

stable social groups, learning and remembering complex vocalizations are necessary for the wellbeing of the individuals and the group. 

Immunotoxicity and Disease Susceptibility

Although there are few studies of the effects of POPs at the parturition and perinatal stages, the 

impacts of exposure are important. Northern fur seal (Callorhinus ursinus) pups that ingest POPs 

through nursing displayed a significant reduction in antibody response with higher contaminant 

exposure levels, indicating a greater predisposition for opportunistic or secondary infections 

(Beckmen et al. 2003). A comparison of in vitro peripheral blood immune function between 

seal pups residing in more (Baltic Sea) or less (Atlantic Ocean) polluted locations found a strong 

negative correlation between levels of blubber PCBs and mitogen-induced lymphoproliferation 

(Sørmo et al. 2009); a similar effect was observed in adult seals (de Swart et al. 1994, de Swart et 

al. 1995). This type of immune compromise in neonates bodes poorly for the overall health status 

and well-being of animals, and for their anticipated life expectancies.

Infectious diseases are a major source of morbidity and mortality for marine mammals of all 

ages. Between 2000 and 2006, 36.6% of marine mammal stranding mortalities in Cape Cod, 

Massachusetts were attributed to infectious disease (Bogomolni et al. 2010). From 1992 to 

2001 along the central California coast, infectious diseases were the primary cause of death 

for 34.2% (437 of 1,277) of the live stranded northern elephant seals and 30.6% (288 of 940) 

of the live stranded harbor seals (Colegrove et al. 2005). Clearly, infectious diseases are a 

substantial contributor to marine mammal morbidity and mortality. For killer whales, pathogen 

exposure may occur through ingestion of pathogens, vectors, or intermediate host species; via 

inhalation of aerosolized pathogens; or by aspiration of the sea surface microlayer. Many of 

these recognized etiologic agents (Appendices A through C) are found exclusively within the 

marine environment or are terrestrially sourced. In many stranded killer whales, commensal 

flora appear to overwhelm or take advantage of compromised immune or inflammatory systems, 

59
resulting in a proximate cause of death of septicemia or bacteremia.3

 For Southern Resident killer 

whales in particular, adverse health effects from contaminant exposure may be exacerbated by 

prey reduction and increased environmental pathogen contamination, culminating in increased 

susceptibility, morbidity, and mortality from multiple stressors (Sih et al. 2004).

At present, the range of pathogens or infectious diseases reported for killer whales is relatively 

small compared to more abundant, related, or sympatric odontocetes. The lack of defined 

pathogens may be due to reduced availability of live animals (wild or captive) and carcasses 

for diagnostic examination. Only 4–5% and 10% of dead Southern and Northern residents, 

respectively, have been available for necropsy, and from 1980–2004, few complete necropsies 

were performed. Nonetheless, researchers have made efforts to catalog and assess the threat 

of infectious diseases (Van Bressem et al. 1999, Gaydos et al. 2004), and a necropsy manual 

specifically for killer whales has been compiled, including tests for disease pathogens (Raverty 

et al. 2014). Appendix A presents pathogens and infections reported for wild and public display 

killer whales that were identified by culture, molecular screening, histopathology, or antibody 

detection. In some cases, infection was not necessarily associated with inflammation, but was 

suggestive of asymptomatic carriers (Brucella and Salmonella; Raverty et al. 2004 and Colegrove 

et al. 2010, respectively).

Interactive Effects

The pharmacodynamic and pharmacokinetic characteristics (i.e., what the contaminants do to the 

body and what the body does to contaminants, respectively) of PCBs and PBDEs can be speciesspecific, and influence the sensitivity in a species to toxic exposure. Thus, caution must be used 

when extrapolating risks between species (Schwacke et al. 2002). However, it is likely that killer 

whales are susceptible to synergistic effects of these two persistent pollutants, likely potentiating 

in vivo toxic health effects of individual contaminants.

Based on available evidence to date, killer whales assimilate multiple contaminants from prey and 

the environment, which likely interact and may enhance toxic effects. Historically, single class 

compound interactions appear to have been characterized, and only in more recent years have 

studies examined the health impacts of exposure to POP mixtures. Killer whales are exposed to 

a variety of chemicals, some of which may interact synergistically and cause enhanced toxicity in 

the whales. It is difficult to predict health effects in these whales from these mixture interactions, 

but disregarding mixture effects may underestimate risk to an individual or to the population. 

For chemicals that likely interact additively (e.g., dioxin-like PCBs), the most accepted approach 

to determine the toxicity has been to use toxic equivalency factors (TEFs), which assume an 

additive effect and a common mechanism of action. The toxicity of dioxin-like PCBs is reported 

in relation to toxic equivalency quotients (TEQs) using TEFs. Calculations of the TEFs of specific 

PCB congeners are based on the biological response of the congener relative to the biological 

response to dioxin. In other words, the ability of PCBs to induce dioxin-like responses is 

3

 Raverty, S. 2014. Pers. commun. Ministry of Agriculture and Lands, Animal Health Center, Abbotsford, BC, Canada.

60
expressed as a ratio. The TEQ of a mixture, considered to reflect the potential toxic impact more 

accurately, is calculated by the sum of the PCB congener concentrations in a mixture multiplied 

by their TEFs (O’Shea 1999). Silva et al. (2002) found this approach to be useful in determining 

the mixture effects of xenoestrogens when the mixture components had similar modes of action 

and similar concentration–response curves. However, this approach does not estimate the 

potential toxic impact from exposure to non-dioxin-like congeners. Non-dioxin-like chemicals 

may not act as AhR agonists in the way dioxin-like congeners do, and therefore may result in 

non-additive effects (i.e., synergistic or antagonistic). Thus, the TEQ approach, which adequately 

predicts effects for some chemicals, is likely the incorrect approach to use for mixtures containing 

both dioxin-like and non-dioxin-like chemicals.

Unlike the dioxin-like congeners that are more readily excreted, there is a selective retention 

of the non-dioxin-like congeners in marine mammals, likely because of a reduced capacity to 

metabolize some of these chemicals. For example, the non-planar congener, PCB-153, is not 

eliminated as efficiently as the dioxin-like congeners and is thus one of the most abundant 

congeners in both humans and wildlife. For this reason, it has often been used as a marker for 

total PCB burden (Fischer 2008). In general, the lower chlorinated PCBs and lower brominated 

PBDEs are less resistant to chemical biotransformation than the higher chlorinated or brominated 

congeners. However, metabolism appears to be enhanced at higher contaminant loads, and the 

ability of the individual to eliminate some contaminants from the body can improve with age 

(Aguilar 1987). Because the transformed by-product, or metabolite, may be more biologically 

active or more toxic than the parent compound (O’Shea 1999), it is important not only to 

adequately predict the toxicity of mixtures of the parent congeners, but also to establish the role of 

these metabolites on the health of killer whales.

The practice of examining only high doses of contaminants, especially endocrine disruptors, 

may also underestimate the risk to the killer whales. Endocrine disruptors have been shown to 

produce non-monotonic (or non-linear) dose–response effects. For example, Yordy et al. (2010a) 

observed a non-monotonic dose–response relationship for an estrogenic mixture containing 

biologically relevant concentrations of trans-nonachlor and 4,4'-DDE. At lower concentrations, 

the estrogenic response of the mixture in the absence of estradiol was additive; however, at 

higher concentrations, the estrogenic response was less than additive. Furthermore, the response 

was eliminated at the highest concentration (Yordy et al. 2010a). The non-monotonic dose–

response relationship is not uncommon in the literature (see Vandenberg et al. 2012). Indeed, in a 

separate study, cell proliferation was observed when cells were treated with 17β-estradiol and low 

concentrations of PCB congeners -138, -153, and -180, whereas inhibited cell growth was observed 

at high concentrations of these PCB congeners (Bonefeld-Jørgensen et al. 2001). 

Some contaminants can also interact at doses below the no-observed-effect concentrations 

(NOECs) and yet produce significant effects (Silva et al. 2002). For example, Crofton et al. (2005) 

tested the hypothesis that a mixture of thyroid hormone-disrupting chemicals has additive dose–

response effects in female rats. The chemicals tested were dioxin, furan, and 11 PCB congeners. 

They found a significant departure from additivity. At the three higher doses, total T4 was 

reduced more than predicted by the additive dose–response curve (i.e., the additivity model 

underestimates the observed toxic effects of the mixture). Thus, they demonstrated that the 

61
effects from a mixture consisting of thyroid hormone disrupters can be additive at low doses and 

synergistic at high doses, and, more importantly, the highest mixture dose levels were at or below 

the NOECs of the chemicals. Therefore, even low concentrations of persistent pollutants, when 

combined together, may have the potential to cause adverse effects in the Southern Resident killer 

whales. The available data suggest that the health effects of persistent pollutants, such as PCBs, 

PBDEs, and DDTs, should not be considered in isolation, a critical point for risk assessment.

62
Data Needs and Future Directions

This report provides the most current knowledge about PCBs, PBDEs, and DDTs in Southern 

Resident killer whales and the implications for the whales’ health from pollutant exposure. 

Although progress has been made in identifying potential effects from exposure to toxicants, 

there are uncertainties and data gaps that will need to be addressed in order to draw meaningful 

conclusions about the health of the killer whales. The past decade of research has shown that 

some of the most important threats facing the whales, such as high contaminant body burdens, 

cannot be addressed without a long-term commitment. The threat of contaminants is challenging, 

particularly considering that these long-lived whales remain contaminated by persistent 

pollutants that were banned decades ago. In this section, we describe the current data needs 

and recommend future directions. Although this discussion of data gaps is not exhaustive, we 

consider it to be an important first step.

Persistent Pollutants in Killer Whales

Researchers have measured PCBs, PBDEs, and DDTs in the blubber and scat of the majority 

of individuals in the Southern Resident killer whale population (Ross et al. 2000, Rayne et al. 

2004, Krahn et al. 2007a, Krahn et al. 2009, Lundin et al. 2015, NWFSC unpubl. data). However, 

continued efforts to assess status and trends to understand the long-term health implications 

for these whales are necessary. In addition to the persistent pollutants that we focused on in 

this report, there are other toxic chemicals of concern on which future research should focus its 

efforts. For example, although PAH exposure has been documented previously in various species 

of marine mammals (Krahn et al. 1993, Holsbeek et al. 1999, Marsili et al. 2001, Leung et al. 2005, 

Goldstein et al. 2009, Fair et al. 2010, Moon et al. 2011), few PAH exposure data are available for 

cetaceans and pinnipeds from the Pacific Northwest. In general, relatively low concentrations 

(<100 ng/g ww) of these compounds have been measured in marine mammal tissues (e.g., 

blubber, liver, muscle), except in certain visibly oiled harbor seals and stranded cetaceans 

collected in Prince William Sound, Alaska, after the 1989 Exxon Valdez oil spill (Varanasi et al. 

1993b, Frost et al. 1994), and in Indo-Pacific humpback dolphins (Sousa chinensis) from south 

China waters (Leung et al. 2005). Data on baseline exposure levels of parent and alkylated 

PAHs (e.g., in liver and/or feces) or PAH metabolites in other matrices (e.g., bile and/or feces) 

of Southern Resident killer whales are lacking, but are needed to determine if changes in PAH 

levels and/or patterns occur over time, and if these exposure levels are associated with biological 

effects. For example, in the aftermath of an oil spill in the region, baseline levels of PAHs could be 

compared to those measured in the tissues/fluids of Southern Resident killer whales post-spill to 

determine if increased PAH exposure had occurred.

Like the data on PAHs, baseline data on contemporary concentrations of toxic trace elements 

in the tissues of Southern Resident killer whales are scarce. The toxic non-essential elements 

most likely to pose a health risk to cetaceans are mercury, lead, and cadmium. Tissues of a few 

Southern Residents have been analyzed for trace metals (Wiles 2004). Levels of total mercury in 

skin biopsy samples of approximately 20 Southern Resident killer whales have been determined 

63
(Anulacion et al. in prep.), but it is unknown how these concentrations compare to those of 

other tissues and any biological effects associated with skin biopsy levels. A previous review on 

the potential effects of toxic metals on killer whales from Washington State indicates that these 

compounds may pose a greater threat to their prey than to the whales (Wiles 2004).

In 2013, the Environmental Protection Agency, in coordination with NMFS, hosted a series 

of technical working groups aimed at discussing PBDEs in Puget Sound and their effects on 

Southern Resident killer whales. The group, consisting of scientists from federal and state 

governments, as well as from universities in the United States and Canada, provided their 

recommendations and highlighted data gaps and uncertainties (Gockel and Mongillo 2013). 

Although their focus was specifically on PBDEs, their recommendations apply to persistent 

pollutants in Southern Residents in general. Here we list the projects currently in progress, 

provide our recommendations for future work, and highlight some of the recommendations 

derived from the PBDE working groups:

•	 Collect baseline measurements for PAH and PAH metabolite levels.

•	 Measure levels of metals, including mercury, in the skin of Southern Resident killer whales.

•	 Combine multiple sources of data on individual killer whales in a common database, to 

allow for the development of individual health profiles.

•	 Continue to collect blubber and fecal samples from Southern Residents, to measure 

contaminant levels in combination with health indices (including hormone levels and 

immune response indices).

•	 Estimate the proportion of toxicants in fecal samples that is attributable to the whales’ 

prey, and the proportion attributable to the whales’ body burden.

•	 Evaluate the whales’ health and nutritional status, and describe how these change both 

seasonally and between years.

•	 Create an integrated database of analyzed and archived samples.

•	 Archive tissues from stranded killer whale samples with the National Tissue Bank.

•	 Describe the congener-specific profiles of killer whales and their prey, to help reveal which 

compounds are more readily metabolized by the whales and therefore excreted, and which 

compounds more readily bioaccumulate and are therefore a greater health threat to the whales.

Persistent Pollutant Exposure in Calves

Some estimates of organochlorine transfer from cetacean mothers to calves have been made. 

Most of these studies have estimated POP transfer during gestation (e.g., Duinker and Hillebrand 

1979, Tanabe et al. 1981, Tanabe et al. 1982, Aguilar and Borrell 1994, Borrell et al. 1995, Salata et al. 

1995), while only a few have estimated transfer during lactation (e.g., Fukushima and Kawai 1981, 

Tanabe et al. 1981, Aguilar and Borrell 1994, Borrell et al. 1995). Studies that have attempted to 

quantify POP transfer during both gestation and lactation (e.g., Aguilar and Borrell 1994, Borrell 

et al. 1995) are rare. A wide variety of methods have been utilized, and more often than not, 

64
studies rely on samples collected from deceased individuals and incorporate several assumptions 

to estimate transfer rates (e.g., Duinker and Hillebrand 1979, Fukushima and Kawai 1981, Tanabe 

et al. 1981, Tanabe et al. 1982, Cockcroft et al. 1989, Aguilar and Borrell 1994, Borrell et al. 1995, 

Kajiwara et al. 2008). Consequently, estimates are highly variable and may not be accurate.

Direct quantification of POP transfer during both gestation and lactation is necessary to 

adequately assess the risk of exposure for neonatal cetaceans. Furthermore, a description of 

contaminant transfer dynamics is also needed, to assess the risk of exposure for the reproductive 

females. However, to date, only two studies conducted on pinnipeds have directly quantified 

the dynamics of PCB transfer from mothers to pups or to the fetus, by sampling blubber, milk, 

and blood from live animals at several intervals over the lactation period and last trimester 

of pregnancy (e.g., Debier et al. 2003, Greig et al. 2007). Both cetaceans and pinnipeds have 

a blubber layer that serves as the energy source for milk production—and as a reservoir for 

POPs—yet their life history patterns and behavior during lactation differ substantially (e.g., 

most female pinnipeds undergo a fasting period during lactation, whereas delphinid females 

do not). Thus, contaminant transfer dynamics during lactation may differ between delphinids 

and pinnipeds. Results from the few studies that have investigated POP levels in live delphinids 

support this hypothesis. For example, Ridgway and Reddy (1995) reported that PCB and DDT 

levels in milk from captive bottlenose dolphins decreased over the course of lactation (>600 

days), in contrast to the pattern observed over the 20-day lactation period of gray seals (Debier 

et al. 2003). Preliminary results from a study on PCB, PBDE, and DDT transfer from female 

bottlenose dolphins to their calves during lactation (>400 days) also suggest that POP levels in 

milk tend to decrease over the course of lactation, while levels in calf serum increase (Noren et 

al. unpubl. data). Although some data on contaminant transfer during lactation in live delphinids 

exist, additional studies are needed to better understand the dynamics of contaminant transfer in 

cetaceans. Such studies could:

•	 Collect blubber and/or blood samples from captive females at several intervals before and 

during pregnancy and from their calves (or stillborn calves) soon after birth, to quantify 

contaminant transfer and describe transfer dynamics in cetaceans during gestation.

•	 Collect milk samples (from captive mothers) and blubber and/or blood samples (from 

both captive mothers and calves) soon after birth and at several intervals during the 

nursing period, to quantify contaminant transfer and describe transfer dynamics in 

cetaceans during lactation.

•	 Examine neonatal exposure and subsequent effects on the developing immune system (de 

Guise et al. 2003).

•	 Establish and identify the POP levels in circulation at which health effects occur in killer 

whales, to help assess risk to both calves and pregnant or lactating females.

65
Persistent Pollutants in Prey and Prey Availability

Persistent pollutants and prey limitation are also important threats facing killer whales, but 

cannot be addressed without a long-term commitment. Recovery of threatened and endangered 

salmon, for example, is a monumental task in itself and is expected to take many years. Chemical 

tracer information can be used to infer the foraging habitats of salmon and their potential overlap 

with the Southern Residents. Historically, the Harrison population was the most abundant of 

all the Fraser Chinook salmon populations, but in recent years there have been lower returns 

(Henderson and Graham 1998). The Harrison population is believed to have a more localized 

marine distribution near the urbanized inland waters of Washington and British Columbia, and 

thus is anticipated to have higher contaminant concentrations relative to other Fraser Chinook 

salmon populations. Samples of Harrison Chinook salmon have been collected, but the tissues 

have not yet been analyzed. Additional information on the fat content and length of the fish 

(O’Neill et al. 2014) can also be used to calculate whether these fish or other fish populations 

represent a significant source of energy and lipophilic contaminants to the whales. Here we 

provide a list of projects currently in progress, and our recommendations for future research:

•	 Collect data on stable isotopes and POPs from spring-run Chinook salmon populations, 

especially those from the Columbia River.

•	 Collect data on POPs, stable isotopes, and lipids from additional Fraser River Chinook 

salmon populations, particularly the Harrison population.

•	 Collect stable isotope and POP data on other marine fish species, especially halibut, 

steelhead, and lingcod, from various populations along the west coast of North America, 

in order to help elucidate whether these species are significant prey to Southern Residents 

in the winter months.

•	 Continue to establish and identify the levels at which health effects occur in Chinook salmon.

•	 Reestablish monitoring efforts, to measure persistent pollutants in Chinook salmon from 

the outer coast and from the inland waters.

•	 Extend contaminants monitoring efforts to other fish, such as herring.

Health Effects

A major barrier to assessing health risks caused by POP exposure is poor information on dose–

response relationships and genetic variability within populations of concern. However, there have 

been attempts to identify quantitative values that may be applied in risk assessment. For example, 

based on studies measuring tissue concentrations and effects of exposure to PCBs in harbor seal, 

European otter (Lutra lutra), and mink (Neovison vison), Kannan et al. (2000) determined the 

suggested threshold values for physiological effects in marine mammals for liver and blood (8.7 

μg/g lw) and blubber (17 μg/g lw). POP levels in the blubber of Southern Resident killer whales 

frequently exceed this estimated effects threshold, particularly in males and juveniles (Krahn et al. 

2007a, Krahn et al. 2009). A reconstruction of PCB histories for Northern and Southern Resident 

killer whale prey and concentrations in whale tissues was used to formulate cumulative population 

projections for body burdens (Hickie et al. 2007). Based on a comparison of those projections 

against the effects threshold of 17 μg/g lw, 96% of the Southern Resident population may continue 

66
to bear burdens that exceed that threshold until 2020, and under a slower environmental turnover 

scenario, 5% of the population could still exceed the threshold by 2089 (Hickie et al. 2007). A risk 

assessment of PCB effects on reproductive success in three populations of bottlenose dolphins 

used gender- and age-matched measurements to derive a dose–response function. The median 

effective concentration (EC50) was calculated to be 33 μg/g lw for liver or blubber, and an 

approximate benchmark dose (an increasingly employed alternative to the no-observed-adverseeffect level, or NOAEL) was determined to be 14.8 μg/g lw (Schwacke et al. 2002). While this risk 

assessment was aimed at reproduction, not immune function, the proximity of the benchmark 

dose to the earlier physiologic threshold estimate suggests these values are physiologically 

relevant. To date, no risk assessment of infectious disease mortality associated with contaminant 

levels in tissues has been conducted for killer whales. A case–control risk study of harbor porpoise 

found a 2% increased risk of mortality because of infectious disease for each 1 mg/kg lw rise in 

blubber PCBs, with a doubling of risk occurring at 45 mg/kg lw (Hall et al. 2006a).

Although predictive models based on laboratory organisms are often applied to wild animals, 

extrapolation of these models to marine mammals can be incorrect (Mori et al. 2008). Support for 

an epidemiologic role for organic contaminants in marine mammal diseases has relied primarily 

on association or correlation patterns, rather than mechanistic data (Ross 2002). For example, the 

impact of tissue PCB and DDT contaminants was inferred in a comparison of two epizootics of 

morbillivirus in Mediterranean striped dolphin, where the earlier, more virulent epizootic occurred 

among animals with tenfold higher tissue concentrations of contaminants than the later, lessvirulent outbreak (Castrillon et al. 2010). The increased levels of PCBs were hypothesized to have 

suppressed the immune system, increasing susceptibility to infection and ultimately leading to 

mortality (Aguilar and Borrell 1994). However, it remains unclear if the suppressed immune system 

was a direct effect from PCB exposure or if other indirect processes contributed to mortality.

Currently, the effects of chronic exposure to PCBs, PBDEs, and DDTs on Southern Resident 

killer whales are unknown. During times of lipid mobilization (e.g., nutritional stress, migration, 

pregnancy, or nursing), these pollutants enter into circulation and have the potential to cause 

deleterious health effects. However, the extent of pollutant mobilization is unclear, and the 

consequences from these spurts of exposure due to lipid mobilization are not known. The PCB, 

PBDE, and DDT levels that will cause deleterious health effects in the Southern Resident killer 

whales are also unknown, and threshold levels of health effects in other species may not be 

directly applicable to the killer whales. To date, threshold levels have been observed in other 

species for single contaminants, and these can inform killer whale analyses, but how threshold 

levels may change when interaction occurs in a mixture is unknown.

An emerging aspect of health assessment is the recognition that the commensal microbial 

community (the “microbiome”) of animals represents a significant effector and indicator of 

changes in physiology, with the greatest attention on gut microbiomes. Analysis of bacterial 

DNA from fecal material characterizes the gastrointestinal microbial community structure, 

which can reflect changes in metabolic state and health (e.g., Kinross et al. 2011). Although fecal 

material from Southern Residents is already analyzed for hormones, prey sources, and individual 

animal identification, microbiome analysis has not been performed. Additionally, microbiomes 

associated with Southern Residents can be assessed for the presence of antibiotic resistance genes 

67
as a measure of exposure to human influences (e.g., Penders et al. 2013), including wastewater 

treatment effluent and stormwater runoff. An evaluation of respiratory microbiota of Southern 

Residents found resistance to widely used veterinary and human antibiotics in more than half of 

the tested isolates, and multi-drug resistance was common (Schroeder et al. 2010, Raverty et al. in 

prep.). The expansion of clinically significant genes for antibiotic resistance is widely recognized 

as a signal of anthropogenic impact, and is considered a negative indicator of environmental 

quality (e.g., Perry and Wright 2013). Here we provide our recommendations for future research 

to fill identified data gaps:

•	 Conduct a risk assessment of infectious disease morbidity and mortality associated with 

contaminant levels in tissues for killer whales.

•	 Perform microbiome analyses complementary to the other health measures (e.g., from 

scat collection).

•	 Conduct other noninvasive sampling, such as the collection of exhaled breath spray and 

shed mucus, for pathogen and microbiome analyses.

•	 Assess for the presence of antibiotic resistance genes in tissues and microbiomes.

•	 Correlate health measurements and reproductive endpoints to contaminant levels (in 

blubber and blood), and develop other biomarkers of exposure and toxicity.

68
Conclusions

Southern Resident killer whales frequent marine waterways where relatively high levels of PCBs, 

PBDEs, and DDTs are found. Adverse effects from exposure to these persistent pollutants are 

known to impact reproduction, immune function, and neurodevelopment, and to disrupt the 

endocrine system, in multiple mammalian species. Exposure to a mixture of these contaminants 

can heighten these detrimental biological effects and may hinder recovery of the Southern 

Resident killer whale population. Understanding the factors that affect whales’ health will help 

identify and prioritize the most important threats, understand how those threats may interact, 

and begin planning what we can do to reduce their impacts. We have provided recommendations 

to address some of the data gaps and guide management actions to advance the recovery of 

Southern Resident killer whales. Currently, new technologies are being developed to better 

understand disease threats, assess individual body condition and health of individuals, and gain 

a better understanding of the health effects of carrying large contaminant burdens. Ultimately, 

long-term monitoring, reducing exposure, and determining the risks posed by PCBs, PBDEs, and 

DDTs in the killer whales are essential for the effective protection of this endangered species.

69
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94
Appendix A:

Infectious Diseases Reported for Killer Whales

In addition to those caused by specific, known pathogens, infectious diseases not attributable 

to identified or specific agents have been commonly cited for captive animals. For example, 

pneumonia, abscesses, and septicemia are frequently observed without identification of specific 

etiologic agents (e.g., see Ridgway 1979, Greenwood and Taylor 1985, and this list of deceased

killer whales4). Although environmental conditions for captive animals differ considerably, 

clinical observations demonstrate the potential for killer whales to be hosts to a multitude 

of infectious and opportunistic agents, including many that also have been recovered from 

sympatric marine mammals and humans.

Infectious disease epidemics have not yet been observed among wild killer whales. Mass 

strandings of killer whales appear to be related more to entrapment by physical conditions (e.g., 

ice or outgoing tide) or deliberate hunting activity than to diseases (e.g., Uni et al. 2005, Lopez 

and Lopez 1985), although the possible contribution of algal toxins, seismic effects, sonar, climate 

change, or other underlying factors cannot be discounted. Network theory modeling predicts 

that the transient killer whales of the northeast Pacific are highly vulnerable to an infectious 

disease epidemic, based on population size, close social structure, and high degree of behavioral 

interaction within social groups (Guimaraes et al. 2007). The Southern Resident killer whale 

population is much smaller than the model population, has a narrower geographic distribution, 

and probably exhibits a similar highly interactive social network, suggesting that it is also at high 

risk for infectious disease outbreaks.

4 http://www.angelfire.com/nb/orca/dead.html

95
Table A-1. Known or potential pathogens identified in killer whales. The method of detection and whale 

origin are included. KEY: EM = electron microscopy; Antibodies = pathogen-reactive antibodies; 

Culture = in vitro culture; PCR = pathogen-specific polymerase chain reaction; Microscopy = 

histology or whole mount microscopy.

Pathogens

Method(s)

of Detection

Wild or 

Captive Reference(s)

Viruses

Cetacean pox-like virus 

(Orthopoxvirus)

EM Wild Van Bressem et al. (1999)

Cutaneous papillomavirus EM Captive Bossart et al. (1996),

Bossart et al. (2002)

Hepatitis B-like virus Antibodies Captive Bossart et al. (1990)

Influenza (suspected) Symptoms Captive Ridgway (1979)

Morbillivirus Antibodies Wild (live 

capture)

S. Raverty (pers. commun.)a

West Nile virus Microarray, 

RTPCR, 

immunohistology

Captive St. Leger et al. (2011)

Bacteria

Aeromonas sp. Culture Wild Schroeder et al. (2010)

Brucella spp. Antibodies, 

culture, PCR

Wild Jepson et al. (1997),

Raverty et al. (2004)

Burkholderia pseudomallei Culture Captive Hicks et al. (2000)

Burkholderia sp. Culture Wild Schroeder et al. (2010)

Clostridium perfringens Culture Wild Schroeder et al. (2010)

Corynebacterium ulcerans Culture Wild Seto et al. (2008)

Edwardsiella tarda Culture Wild Colegrove et al. (2010)

Erysipelothrix rhusiopathiae Culture Wild, captive Bossart and Eimstad (1988)

Kocuria sp. Culture Wild Schroeder et al. (2010)

Mycoplasma spp. (Mollicutes) PCR Wild Schroeder et al. (2010)

Nocardia farcinica, N. asteroids, 

N. otitidiscaviarum

Culture and/or 

PCR

Captive Sweeney and Ridgway (1975), 

Lamere et al. (2009) 

Pseudomonas aeruginosa Culture Captive, wild 

capture and 

introduction

S. Raverty (pers. commun.)a

Pseudomonas sp. Culture Wild Schroeder et al. (2010)

Rothia dentocariosa Culture Wild Schroeder et al. (2010)

Salmonella enterica serovar 

Heidelberg

Culture Wild Schroeder et al. (2010)

Salmonella enterica serovar 

Newport

Culture Wild Colegrove et al. (2010) 

Staphylococcus aureus Culture Wild Power and Murphy (2002)

Staphylococcus capitis Culture Wild Schroeder et al. (2010)

Staphylococcus cohnii cohnii Culture Wild Schroeder et al. (2010)

Staphylococcus epidermidis Culture Wild Schroeder et al. (2010)

Staphylococcus lugdunensis Culture Wild Schroeder et al. (2010)

Staphylococcus sp. Culture Wild Schroeder et al. (2010)

Staphylococcus warneri Culture Wild Schroeder et al. (2010)

Stenotrophomonas sp. Culture Wild Schroeder et al. (2010) a Raverty, S. 2014. Pers. commun. Ministry of Agriculture and Lands, Animal Health Center, Abbotsford, BC, Canada.

96
Table A-1 continued. Known or potential pathogens identified in killer whales. The method of detection 

and whale origin are included. KEY: EM = electron microscopy; Antibodies = pathogen-reactive 

antibodies; Culture = in vitro culture; PCR = pathogen-specific polymerase chain reaction; 

Microscopy = histology or whole mount microscopy.

Pathogens

Method(s)

of Detection

Wild or 

Captive Reference(s)

Bacteria

Streptococcus sp., alpha-hemolytic Culture Wild Schroeder et al. (2010)

Streptococcus sp., beta-hemolytic Culture Captive Greenwood and Taylor (1985)

Vibrio alginolyticus Culture Wild Schroeder et al. (2010)

Fungi

Alternaria sp. Culture Wild Schroeder et al. (2010)

Aspergillus fumigatus Culture Captive Reidarson et al. (1999) 

Candida albicans Culture Captive Sweeney and Ridgway (1975), 

Ridgway (1979),

Greenwood and Taylor (1985)

Cladosporidium sp. Culture Wild Schroeder et al. (2010)

Cunninhamella bertholletiae Culture Captive Abdo et al. (2012)

Phoma sp. Culture Wild Schroeder et al. (2010)

Saksenaea vasiformis Captive Reidarson et al. (1999),

Robeck and Dalton (2002) 

Parasites: Acanthocephala

Bolbosoma niponicum Unknown Unknown Heptner et al.(1976)

Bolbosoma physeteris Microscopy Wild Gibson et al. (1998)

Parasites: Cestoda

Diphyllobothrium polyrugosum Microscopy Wild Gibson et al. (1998)

Trigonocotyle spasskyi Unknown Unknown Daily and Brownell (1972)

Parasites: Nematoda

Anisakis simplex Microscopy Wild Gibson et al. (1998)

Anisakis pacificus Unknown Unknown Heptner et al. (1976) 

Parasites: Protozoa

Kyaroikeu cetarius Microscopy Unknown Sniezek et al. (1995) 

Neospora caninum Antibodies Wild Omata et al. (2006)

Sarcosystis sp. PCR Wild Gibson et al. (2011),

S. Raverty (pers. commun.)a

Toxoplasma gondii Antibodies, PCR Wild, captive Murata et al. (2004),

Gibson et al. (2011)

Parasites: Trematoda

Campula sp. Microscopy Wild Gibson et al. (1998)

Fasciola skrjabini Unknown Unknown Daily and Brownell (1972)

Leucasiella subtilla Unknown Unknown Heptner et al. (1976)

Oschmarinella albamarina Microscopy Wild Gibson et al. (1998)

a Raverty, S. 2014. Pers. commun. Ministry of Agriculture and Lands, Animal Health Center, Abbotsford, BC, Canada.

97
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99
Appendix B:

Noninfectious Diseases Reported

for Killer Whales

There has been one reported observation of an apparent genetic disease, Chediak-Higashi 

syndrome, an autosomal recessive trait (Ridgway 1979). This syndrome presents with a loss 

of cutaneous pigmentation, and has been reported to occur in at least six divergent species, 

including humans. Notably, affected individuals are prone to recurrent infections and low platelet 

counts. The whale reported by Ridgway (1979) died more than 2 years after capture, but the 

proximal cause of death was not cited.

Systemic changes that are not clearly attributable to infection have been reported in killer whales. 

For example, extensive atherosclerotic change with thrombi in the aorta and carotid artery was 

reported without an associated infection or etiologic agent (Roberts et al. 1965). This condition 

is commonly observed in beluga and other deep diving cetaceans, and may be an adaptive 

physiologic response, rather than a pathology.

Because killer whales are relatively long-lived, neoplasms are likely to occur, but few have been 

observed. A diagnosis of Hodgkin’s disease in a captive whale was based on cytologic criteria, 

and whether the disease was fatal is unknown (Yonezawa et al. 1989). Reported skin papillomas 

are likely to have a viral origin, although this has not always been confirmed (Geraci et al. 1987, 

Bossart et al. 1996). Genital papillomas have also been observed (Greenwood et al. 1974), but 

whether the lesions were likely to interfere with reproductive activity or fecundity was not noted.

Recently, an endogenous gammaretroviral provirus was cloned from the killer whale genome, 

which was the first retrovirus isolated from a cetacean (Lamere et al. 2009). Although some 

members of this genus are oncogenic (e.g., murine leukemia virus, feline leukemia virus), many 

are found in multiple host species without associated pathology. The lack of evidence of viral 

RNA suggested the killer whale provirus was not disease-causing (Lamere et al. 2009). 

100
References: Appendix B

Bossart, G. D., C. Cray, J. L. Solorazano, S. J. Decker, L. H. Cornell, and N. H. Altman. 1996. Cutaneous 

papillomaviral-like papillomatosis in a killer whale (Orcinus orca). Mar. Mamm. Sci. 12:274–281.

Geraci, J. R., N. C. Palmer, and D. J. St. Aubin. 1987. Tumors in cetaceans: Analysis and new findings. Can. 

J. Fish. Aquat. Sci. 44:1289–1300.

Greenwood, A. G., R. J. Harrison, and H. W. Whitting. 1974. Functional and pathological aspects of the 

skin of marine mammals. In R. J. Harrison (ed.), Functional anatomy of marine mammals, vol. 2, pp. 

73–110. Academic Press, London, U.K.

Lamere, S. A., J. A. St. Leger, M. D. Schrenzel, S. J. Anthony, B. A. Rideout, and D. R. Salomon. 2009. 

Molecular characterization of a novel gammaretrovirus in killer whales (Orcinus orca). J. Virol. 

83:12956–12967.

Ridgway, S. H. 1979. Reported causes of death of captive killer whales (Orcinus orca). J. Wildl. Dis. 15:99–104.

Roberts, J. C., R. C. Boice, R. L. Brownell, Jr., and D. H. Brown. 1965. Spontaneous atherosclerosis in Pacific 

toothed and baleen whales. In J. C. Roberts and R. Strauss (eds.), Comparative atherosclerosis, pp. 

151–155. Harper & Row, New York.

Yonezawa, M., H. Nakamine, T. Tanaka, and T. Miyaji. 1989. Hodgkin’s disease in a killer whale (Orcinus 

orca). J. Comp. Pathol. 100:203–207.

101
Appendix C:

Infectious Diseases of

Sympatric Marine Mammals

Identification of emerging infectious diseases among marine mammals is expanding with more 

focused research on nearshore and stressed populations, a heightened awareness of factors that 

may contribute to epidemics (Van Bressem et al. 2009), and the advancement of diagnostic tools. 

Sympatric marine mammals are potential reservoirs and vectors for infectious agents that have not 

yet been isolated from killer whales. Table C-1 presents a listing of known and high-probability or 

putative pathogens of sympatric cetaceans and pinnipeds, and the target tissues for infection.

Notably, many of these listed agents can infect divergent vertebrate hosts, including humans, 

birds, invertebrates, and terrestrial animals. Stormwater runoff and effluents from urban or 

agricultural activities are recognized sources of these and other pathogens that can infect marine 

mammals, resulting in increased concentrations in marine receiving waters (Arnone and Walling 

2007). For example, Conrad et al. (2005) show that the source of toxoplasmosis and sarcocystosis, 

a significant source of morbidity and mortality for sea otter along the California coast, is 

most likely freshwater runoff carrying oocysts shed by terrestrial animals, particularly felids 

(toxoplasmosis) and opossums (sarcocystosis). Pathogens capable of infecting multispecies hosts, 

such as T. gondii, are a particular threat for endangered populations.

In the Pacific Northwest, the appearance of Cryptococcus neoformans gattii (now Cryptococcus gattii) 

in free-ranging harbor porpoise, Dall’s porpoise (Phocoenoides dalli), and a solitary Pacific whitesided dolphin (Lagenorhynchus obliquidens) as part of a multispecies (including humans; Upton et 

al. 2007), large-scale marine and terrestrial outbreak of cryptococcosis (Stephen et al. 2002), has 

stimulated concern about the extent and prognosis for this emerging disease (MacDougall et al. 

2007). For humans, both immunocompromised and immunocompetent individuals have developed 

disease (Datta et al. 2009), underscoring the inherent virulence of this pathogen.

102
Table C-1. Known and high-probability or putative pathogens affecting sympatric species of cetaceans and 

pinnipeds. The target tissues for infection are indicated by an x. Target tissues included as Other are 

the liver, lymph nodes, kidney, and placenta.

Pathogens

Target Tissues Host 

Speciesa Enteric Skin Lung Neural Other Reference(s)

Viruses

Influenza A virus x x x Ph Danner et al. (1998) 

Morbillivirus

(cetacean, phocine)

x x x x x Pv Duignan et al. (1995) 

Norovirus/Calicivirus x Cu, Ej, 

Er, Ma, 

Ta, Zc

Smith et al. (1998)

Rotavirus x Zc S. Raverty (pers. commun.)b

Bacteria

Brucella spp. x Pv Godfroid et al. (2005), 

Lambourn et al. (2006)

Campylobacter jejuni x Ma Stoddard et al. (2008)

Clostridium difficile x Pv Raverty et al. (2005)

Clostridium perfringens x x Tt Buck et al. (1987) 

Coxiella burnetii Ej, Pv Kersh et al. (2010),

Lapointe et al. (1999)

Edwardsiella tarda Pd, Pp Raverty et al. (2005)

Escherichia coli x x x x x Pv Raverty et al. (2005)

Klebsiella pneumoniae x Zc Jang et al. (2010) 

Leptospira interrogans,

L. kirschneri

x x Ma, Zc Cameron et al. (2008), 

Lloyd-Smith et al. (2007), 

Raverty et al. (2005)

Pasteurella hemolytica x Pv Steiger et al. (1989)

Plesiomonas shigelloides x Pp, Zc Jagger et al. (2000) 

Pseudomonas spp. x x Pv Steiger et al. (1989), 

Raverty et al. (2005)

Salmonella spp. x x Ma, Pv, 

Zc

Gilmartin et al. (1979), 

Thornton et al. (1998), 

Stoddard et al. (2008)

Staphylococcus aureus x Ta Palmer et al. (1991)

Staphylococcus spp. x Pp, Zc Siebert et al. (2002),

Fravel and Evans (2008) 

Streptococcus spp. x x El, Pv Steiger et al. (1989),

Imai et al. (2009)

Vibrio spp. x Pd, Pv, 

Tt

Schroeder et al. (1985), 

Buck and Spotte (1986), 

Fujioka et al. (1988), 

Raverty et al. (2005)

a Host species are abbreviated as follows: Bm, Balaena mysticetus (bowhead whale); Cu, Callorhinus ursinus (Northern fur seal); Dl, 

Delphinapterus leucas (beluga whale); Ej, Eumetopias jubatus (Stellar sea lion); El, Enhydra lutris (sea otter); Er, Eschrichtius robustus

(gray whale); Kb, Kogia breviceps (pygmy sperm whale); Lo, Lagenorhynchus obliquidens (Pacific white-sided dolphin); Ma, Mirounga 

angustirostris (Northern elephant seal); Or, Odobenus rosmarus (walrus); Pd, Phocoenoides dalli (Dall’s porpoise); Ph, Phoca hispida

(ringed seal); Pp, Phocoena phocoena (harbour porpoise); Pv, Phoca vitulina (harbor seal); Ta, Tursiops aduncus (Indo-Pacific 

bottlenose dolphin); Tt, Tursiops truncatus (common bottlenose dolphin); Zc, Zalophus californianus (California sea lion). b

 Raverty, S. 2014. Pers. commun. Ministry of Agriculture and Lands, Animal Health Center, Abbotsford, BC, Canada.

103
Table C-1 continued. Known and high-probability or putative pathogens affecting sympatric species of 

cetaceans and pinnipeds. The target tissues for infection are indicated by an x. Target tissues included 

as Other are the liver, lymph nodes, kidney, and placenta.

Pathogens

Target Tissues Host 

Speciesa Enteric Skin Lung Neural Other Reference(s)

Protozoa

Cryptosporidium spp. x Bm, Dl, 

Ph, Zc

Deng et al. (2000), 

Hughes-Hanks et al. (2005)

Giardia spp. x Bm, Dl, 

Ph, Zc

Deng et al. (2000), 

Hughes-Hanks et al. (2005)

Neospora canium,

N. canium-like

x x El S. Raverty (pers. commun.)b

Sarcocystis spp.,

S. canis,

S. neurona

x x Ej, El, 

Pv

Lapointe et al. (1998), 

Miller et al. (2001),

Dubey et al. (2003a), 

Dubey et al. (2003b)

Toxoplasma gondii x Ej, El, 

Or, Ph, 

Pv, Tt

Miller et al. (2001),

Dubey et al. (2003b)

Fungi

Blastomyces dermatitidis x Tt Cates et al. (1986)

Coccidioides immitis x El, Zc Cornell et al. (1979), 

Fauquier et al. (1996) 

Cryptococcus gattii x Lo, Pd, 

Pp

Miller et al. (2002), 

Stephen et al. (2002)

Fusarium spp. x Kb, Pv Frasca et al. (1996) 

Sporothrix spp. x x x Lo Migaki et al. (1978) a Host species are abbreviated as follows: Bm, Balaena mysticetus (bowhead whale); Cu, Callorhinus ursinus (Northern fur seal); Dl, 

Delphinapterus leucas (beluga whale); Ej, Eumetopias jubatus (Stellar sea lion); El, Enhydra lutris (sea otter); Er, Eschrichtius robustus

(gray whale); Kb, Kogia breviceps (pygmy sperm whale); Lo, Lagenorhynchus obliquidens (Pacific white-sided dolphin); Ma, Mirounga 

angustirostris (Northern elephant seal); Or, Odobenus rosmarus (walrus); Pd, Phocoenoides dalli (Dall’s porpoise); Ph, Phoca hispida

(ringed seal); Pp, Phocoena phocoena (harbour porpoise); Pv, Phoca vitulina (harbor seal); Ta, Tursiops aduncus (Indo-Pacific 

bottlenose dolphin); Tt, Tursiops truncatus (common bottlenose dolphin); Zc, Zalophus californianus (California sea lion). b

 Raverty, S. 2014. Pers. commun. Ministry of Agriculture and Lands, Animal Health Center, Abbotsford, BC, Canada.

104
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Recent NOAA Technical Memorandums

published by the

Northwest Fisheries Science Center

NOAA Technical Memorandum NMFS-NWFSC134 Leonard, J. 2016. Washington and Oregon charter vessel survey: Methodology and results. 

U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-134, 22 p. doi:10.7289/V5/TMNWFSC-134.

133 Duffield, D., J. K. Gaydos, S. Raverty, K. Wilkinson, B. Norberg, L. Barre, M. B. Hanson, 

P. Foreman, A. Traxler, D. Lambourn, J. Huggins, J. Calambokidis, T. McKlveen, S.

Dennison, and H. Brubaker. 2016. Wild animal mortality investigation: Southern Resident

killer whale L-112 final report. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-133,

122 p. doi:10.7289/V5/TM-NWFSC-133.

132 Anderson, L. E., and M. Plummer. 2016. Puget Sound recreational shellfishing survey: 

Methodology and results. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-132, 38 p. 

doi:10.7289/V5/TM-NWFSC-132.

131 Waples, R. S. 2016. Small investments with big payoffs: A decade of the Internal Grants 

Program at the Northwest Fisheries Science Center. U.S. Dept. Commer., NOAA Tech. Memo. 

NMFS-NWFSC-131, 80 p. doi:10.7289/V5/TM-NWFSC-131.

130 Puget Sound Recovery Implementation Technical Team. 2015. Puget Sound Chinook 

salmon recovery: A framework for the development of monitoring and adaptive management 

plans. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-130, 146 p. NTIS number 

PB2016-100691. doi:10.7289/V5/TM-NWFSC-130.

129 Hard, J. J., J. M. Myers, E. J. Connor, R. A. Hayman, R. G. Kope, G. Lucchetti, A. R. 

Marshall, G. R. Pess, and B. E. Thompson. 2015. Viability criteria for steelhead within the 

Puget Sound distinct population segment. U.S. Dept. Commer., NOAA Tech. Memo. NMFSNWFSC-129, 332 p. NTIS number PB2015-105188. doi:10.7289/V5/TM-NWFSC-129.

128 Myers, J. M., J. J. Hard, E. J. Connor, R. A. Hayman, R. G. Kope, G. Lucchetti, A. R. 

Marshall, G. R. Pess, and B. E. Thompson. 2015. Identifying historical populations of 

steelhead within the Puget Sound distinct population segment. U.S. Dept. Commer., NOAA 

Tech. Memo. NMFS-NWFSC-128, 155 p. NTIS number PB2015-103741. doi:10.7289/V5/TMNWFSC-128.

127 Roni, P., G. R. Pess, T. J. Beechie, and K. M. Hanson. 2014. Fish–habitat relationships 

and the effectiveness of habitat restoration. U.S. Dept. Commer., NOAA Tech. Memo. NMFSNWFSC-127, 154 p. NTIS number PB2014-108836.

126 Russell, S., and M. S. Ruff. 2014. The U.S. whale watching industry of Greater Puget 

Sound: A description and baseline analysis. U.S. Dept. Commer., NOAA Tech. Memo. NMFSNWFSC-126, 171 p. NTIS number PB2014-105939.

NOAA Technical Memorandums NMFS-NWFSC are available at the

Northwest Fisheries Science Center website, https://www.nwfsc.noaa.gov/index.cfm.