Environmental Health Perspectives Volume
103, Supplement 4, May 1995
[Citation
in PubMed] [Related
Articles]
Decreased Lymphocyte Responses in Free-ranging Bottlenose Dolphins (Tursiops
truncatus) Are Associated with Increased Concentrations of PCBs and
DDT in Peripheral Blood
Garet P. Lahvis,1 Randall S. Wells,2 Douglas
W. Kuehl,3 Jennifer L. Stewart,4 Howard L. Rhinehart,5
and Charles S. Via6
1Department of Microbiology and Immunology, University of
Maryland School of Medicine, Baltimore, Maryland; 2Chicago Zoological
Society, Sarasota, Florida; 3U.S. Environmental Protection Agency,
Environmental Research Laboratory, Duluth, Minnesota; 4Johns
Hopkins School of Hygiene and Public Health, Baltimore, Maryland; 5Dolphin
Biology Research Institute, Sarasota, Florida; 6University of
Maryland School of Medicine and Research Service, Baltimore Veterans Administration
Medical Center, Baltimore, Maryland
Abstract
Since 1987, large-scale mortalities of dolphins have been reported along
the Atlantic coast of North America, in the Gulf of Mexico, and in the Mediterranean
Sea. Autopsied bottlenose dolphins, Tursiops truncatus, which were
collected from the large-scale mortality along the Atlantic coast in 1987
to 1988, exhibited opportunistic infections indicative of immune dysfunction.
Further, these animals had high levels of chlorinated hydrocarbons, such
as PCBs and DDT, that can suppress immune functions. The purpose of this
study was to determine whether there is a relationship between chemical
contaminant exposure and immune response in free-ranging dolphins. In June
of 1991, peripheral blood was obtained from members of a bottlenose dolphin
population that resides along the west coast of Florida. Peripheral blood
lymphocyte responses to Concanavalin A (Con A) and phytohemagglutinin (PHA)
were determined in vitro and compared by regression analysis with
contaminant concentrations in whole blood from a small subset of these animals
(n=5). These data indicate that a reduced immune response in these
bottlenose dolphins was correlated with increasing whole blood concentrations
of several contaminants. Specifically, inverse correlations were found between
Con A-induced lymphocyte proliferation and tetrachlorinated to octachlorinated
biphenyls (r2 values ranged from 0.70 to 0.87). Con A-induced
lymphocyte responses also correlated inversely with p,p' DDT (r2
values of 0.73 and 0.79); o,p' - DDE (r2 values
of 0.93 and 0.96); and p,p' - DDE (r2 values of
0.73 and 0.81). -- Environ Health Perspect 103(Suppl 4):00-00 (1995)
Key words: dolphin, Tursiops truncatus, marine, strandings,
immune response, lymphocyte, contaminant, polychlorinated hydrocarbons,
PCB (polychlorinated biphenyl), DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane)
This paper was presented at the Conference on Environmentally
Induced Alterations in Development: A Focus on Wildlife held 10-12 December
1993 in Racine, Wisconsin.
The dolphin capture and release project was conducted
by the Dolphin Biology Research Institute and was supported by Earthwatch,
the National Science Foundation, and the Chicago Zoological Society. Chemical
analyses were supported by the U.S. Environmental Protection Agency, Office
of Research and Development, Office of Environmental Processes and Effects
Research. Immunology was also supported by the Office of Environmental
Processes and Effects Research, as well as by the generous contributions
of the American Oceans Campaign and the Whale and Dolphin Conservation
Society. We deeply appreciate Andy Palmer, Michael Slimak, Theo Colborn,
Forrest Townsend, Dave Casper, Jay Sweeney, Blair Irvine, Michael Scott,
Andy Read, Peter Tyack, Sue Hofmann, Kim Urian, and Christine Berini.
Address correspondence to Dr. Garet P. Lahvis, Department
of Microbiology and Immunology, University of Maryland School of Medicine,
Bressler Research Building, Rm. 13-009, 655 West Baltimore Street, Baltimore,
MD 21201. Telephone (410) 706-7114. Fax (410) 706-2129.
Introduction
Since 1987, there have been several large-scale dolphin mortalities.
Between the midsummer of 1987 and the spring of 1988, over 740 bottlenose
dolphins (Tursiops truncatus) were stranded along the Atlantic coast
of North America from New Jersey to central Florida (1). This single
epizootic may have depleted the coastal migratory stock by as much as 53%,
and population recovery may require as many as 100 years to return to pre-1987
population levels (1). In 1990 and again in 1992, there were two
additional incidents of high or unusual mortality of bottlenose dolphins
in the Gulf of Mexico (2). There has also been extensive mortality
among striped dolphins (Stenella coeruleoalba) in the Mediterranean
Sea (3-6). These incidents of high mortality have initiated scientific
studies to determine their cause(s).
There are several commonalities among these large-scale mortalities.
Geraci (7) described Atlantic coast stranded dolphins with epidermal
lesions, possibly due to viral infection; dermal lesions presumed to be
caused by bacteria, fungi or protozoans; and septicemia, a systemic bacterial
infection. The bacteria identified included Edwardsiella spp.,
Streptococcus spp., Vibrio spp., Pseudomonas spp.,
Klebsiella spp., Acinetobacter spp., Bacillus spp., and
Staphylococcus spp., with Vibrio spp. representing 52% of
the total isolates. Bacteria were isolated from the liver, spleen, lung,
lymph nodes, blood, urine, blubber, abdominal fluid, kidney, and brain.
Similar bacterial isolates were obtained from other stranded cetaceans along
the Atlantic and Gulf coasts (8). Geraci concluded that these infections
indicated that stranded dolphins were immunologically suppressed and were
therefore less capable of surviving infectious diseases. Similarly, there
was evidence of immunosuppression among the members of the striped dolphin
population that were stranded along the coasts of the Mediterranean Sea
(5). Lesions attributable to opportunistic fungi and bacteria in
the oral cavity, brain, and lungs, and opportunistic parasitic infection
of the lymph nodes, lungs, and brain were also reported in these animals
(5). Immunosuppression was also inferred from studies of stranded
beluga whales (Delphinapterus leucas) of the St. Lawrence Estuary
(9).
One of the initial hypotheses to explain the cause of the 1987 to 1988
large-scale mortality of bottlenose dolphins was exposure to a natural algal
neurotoxin, brevetoxin, that is produced by the marine dinoflagellate Ptychodiscus
brevis. It is known that a large algal bloom, or red tide, of this species
occurred during the summer of 1987 (7,10). It was therefore suggested
that migrating dolphins ingested brevetoxin-contaminated fish and that neurotoxicity
initiated a suppression of the immune system that resulted in opportunistic
bacterial infection. In support of this hypothesis, it was found that 8
of 17 animals sampled from the mid-Atlantic coast die-off contained detectable
concentrations of brevetoxin. However, it is equally important to note that
brevetoxins could not be identified in the remaining nine dead dolphins.
An independent study of the available data concluded that evidence for this
hypothesis was circumstantial and that other explanations were also possible
(10). Further, there does not appear to be evidence supporting a
role for brevetoxins in the large-scale mortalities in the Gulf of Mexico
or in the Mediterranean Sea.
A second hypothesis to explain the deaths of Atlantic bottlenose dolphins
is that immune suppression occurred as a result of morbillivirus infection.
Marine mammals from mortality events have been found with morbillivirus
infections and rotaviruses, such as morbillivirus, can be immunosuppressive
(11). Two common porpoises (Phocoena phocoena), for example,
that were found dead on the coast of Northern Ireland were infected with
morbillivirus (12). Morbillivirus infection was also identified in
striped dolphins (Stenella coeruleoalba) collected from the Mediterranean
Sea in 1990. Among necropsied striped dolphins, the morbillivirus antigen
was closely associated with microscopic lesions and was found in lymph nodes
where there was also extensive lymphoid cell depletion (5). Recently,
morbilliviral antigen was also identified in preserved dolphin samples from
the 1987 to 1988 mortality event (13) and from a stranded bottlenose
dolphin in the Gulf of Mexico (14).
However, although it is clear that morbillivirus infection can result
in immunosuppression, the question remains: why were the dolphins susceptible
to the morbillivirus infection initially? In the Mediterranean mortality
event, morbillivirus infection was probably not the initial cause of the
large-scale mortality because it rapidly invades lymph nodes and causes
death within weeks (3); yet the increased prevalence of ectoparasites
in the diseased animals (relative to healthy animals studied earlier) indicated
that the immunosuppression may have begun a few months before the beginning
of the epizootic (3,4). Thus the increased prevalence of parasites
indicated that the dolphins may have been immunologically suppressed long
before the morbillivirus infection. However, morbillivirus infection may
have caused enhanced impairment of immune system function during later stages
of bacterial, viral, and parasitic infection in each mortality event.
A third hypothesis was that chronic exposure to immunosuppressive pollutants,
such as polychlorinated biphenyls (PCBs) and 1,1,1-trichloro-2,2-bis(p-chlorophenyl)
ethane (p,p´-DDT), could have facilitated the development of
viral, bacterial, and parasitic infections. Bottlenose dolphins stranded
along the mid-Atlantic coast exhibited PCB and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene
(p-p´-DDE, a metabolite of p,p´-DDT) concentrations
in blubber, which were among the highest reported for cetaceans (7).
Subsequent coplanar PCB analysis of dolphin tissues collected during the
1987 to 1988 large-scale mortality event indicated higher 2,3,7,8-tetrachlorodibenzo-p-dioxin
(TCDD) toxic equivalent concentrations (15) of PCBs in blubber of
bottlenose dolphins than either common (Delphinus delphis) or white-sided
(Lagenorhynchus acutus) dolphins (16). Further, stranded Mediterranean
striped dolphins examined in 1990 carried PCB levels that were higher (mean
concentration 778 ppm lipid basis) than the levels found in healthy free-ranging
animals (mean concentration 282 ppm lipid basis) (4). Isomer-specific
analysis of PCBs and further DDT analysis also showed higher levels of these
contaminants than in the blubber of unaffected striped dolphins (6).
High levels of PCBs and DDE have also been found in stranded white-beaked
dolphins (Lagenorhynchus albirostris) and pilot whales (Globicephala
melaena) from the coast of Newfoundland, Canada (17), and stranded
beluga whales (Delphinapterus lucas) of the St. Lawrence Estuary
(18,19).
Based upon the above observations, it is possible that anthropogenic
chemical contaminants such as PCBs and DDTs initially cause immunosuppression,
rendering dolphins susceptible to opportunistic bacterial, viral, and parasitic
infection. Debilitating viruses such as morbillivirus may result in further
immunosuppression and death. The purpose of the present study was to determine
if a relationship exists between chemical contaminant exposure and immune
suppression in dolphins. Because it is not feasible to dose individual dolphins
with candidate toxicants and measure the immune response to known infectious
agents, such as the pathogens identified in natural populations, this study
used an indirect approach to determine if there is a relationship between
pollutant levels and immune response. Specifically, we have correlated the
levels of PCBs and p,p´-DDT; p,p´-DDE; and o,p´-DDE
in whole blood from free-ranging dolphins with the degree of their peripheral
blood lymphocyte responses in vitro.
Materials and Methods
Sampling
Peripheral blood was obtained from 15 males of a resident community of
T. truncatus along the central west coast of Florida, near Sarasota
(27°N 82°W) (20,21) in June 1991. Dolphins were encircled
with a seine net in shallow water, maneuvered into a sling, and sampled,
measured, and examined aboard a small vessel, and then released. Peripheral
blood (50 ml) for lymphocyte proliferation studies was drawn from the plexus
of blood vessels in the tail fluke through a 20 gauge butterfly needle via
vacutainer vacuum into sodium heparin vacutainers. Collected blood was stored
at 24 to 26°C until the end of the day and shipped via overnight freight
packaged without ice for next day analysis. Blood intended for chemical
residue analysis was drawn with a teflon syringe and stored at -20°C
until analysis. Additional blood samples were drawn for chemistry and hematology
as part of an ongoing health assessment study.
Lymphocyte Proliferation
Lymphocyte proliferation assays were conducted as described previously
(22), using modifications of existing methods (23-25). Briefly,
aliquots of blood (10 ml) were diluted 1:4 in phosphate-buffered saline
(PBS) and layered over 10 ml ficoll. After centrifugation (200g for
20 min), cells were harvested from the interface and resuspended in culture
medium containing RPMI 1640, 10% fetal calf serum, 100 U penicillin/streptomycin,
1% glutamine, 1% nonessential amino acids, 1% pyruvate, and 0.05% 2-mercaptoethanol.
Cells were cultured at 37°C in 6 to 8% CO2 from 1 to 8 days
in 96-well flat-bottom microtiter tissue culture plates (4 x 105
cells/well) and were either unstimulated or stimulated with the mitogens
Concanavalin A (Con A) or phytohemagglutinin (PHA) at the concentrations
indicated. Following an overnight pulse of 9 hr with 3H-thymidine
(1.0 µC), cells were harvested and thymidine uptake was measured by
liquid-scintillation counting. Results were expressed as mean counts per
min (cpm) for three replicate wells. Standard errors were typically less
than 15% and have been omitted. We have observed that in vitro lymphocyte
responses are altered by storage of samples for greater than 48 hr prior
to analysis and by changes in fetal calf serum lots (unpublished observations).
For these reasons, lymphocyte separation was initiated within approximately
24 hr of obtaining the sample, and the same batch of fetal calf serum was
used for all tests. Because the time to peak proliferation can vary among
dolphins, proliferative responses were assayed daily for between 1 and 8
days of culture, and the maximal proliferation value for each individual
dolphin in response to a given mitogen concentration was determined.
Chemical Analysis
Samples were analyzed for polychlorinated dibenzo-p-dioxins, polychlorinated
dibenzofurans, PCBs, pesticides, and other chlorinated compounds using established
protocols (26-29). Briefly, each sample of peripheral blood (10 ml)
was treated with methanol to lyse cells, dried with anhydrous sodium sulfate,
and fortified with internal standards. Samples were soxhlet extracted overnight
with 400 ml of solvent (1:1 v:v hexane/methylene chloride) and reduced in
volume with a Kuderna-Danish apparatus to 1 ml. Analytes were isolated from
the extracted lipid by chromatography on silica gel and carbon on silica
gel. Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans
(PCDFs), and coplanar PCBs were quantified using high resolution gas chromatography/high
resolution mass spectroscopy (HRGC/HRMS) (Finnigan-MAT model 8230). Pesticides
and total PCBs were quantified using HRGC/low resolution mass spectrometry
(LRMS) (Finnigan-MAT model 4500). High and low resolution GCs were fitted
with temperature programmed 30m DB-5 fused silica columns. Quantification
and quality assurance/quality control were conducted as previously described
(28,29).
Results
Lymphocytes were isolated from peripheral blood of 15 dolphins and cultured
in the presence of Con A or PHA. In this study, lymphocyte proliferation
was consistently strongest when concentrations of Con A were 0.5 and 0.13
µg/ml and concentrations of PHA were 2.0 and 0.5 µg/ml (data
not shown). Table 1 shows the peak proliferative responses of all 15 male
dolphins. Dolphin FB 156 exhibited the lowest responses to Con A at both
concentrations and exhibited nearly the lowest responses to PHA. Similarly,
dolphin FB 24 showed the highest response to both mitogens.
Based upon these data, five males were selected for chemical residue
analysis. High cost precluded residue analysis for all male dolphins, so
5 of the 15 dolphins were selected for contaminant analysis. Individual
samples which were either relatively low or high with regards to mitogen
stimulation were analyzed for pollutant residues. PCBs; p,p´-DDT;
o,p´-DDE; and p,p´-DDE were found in most individuals
(Table 2). Hexachlorinated PCBs represented the greatest fraction of total
PCBs, though pentachlorinated and heptachlorinated PCBs also contributed
substantially to total peripheral blood PCB levels. p,p´-DDE
levels were more than 10-fold higher than p,p´-DDT levels,
and at least two orders of magnitude greater than blood levels of o,p´-DDE
levels.
Linear regression analysis was used to determine the relationship between
peripheral blood contaminant concentration and lymphoproliferative responses
to mitogens. Figures 1A and B illustrate respectively the
inverse correlation between lymphocyte proliferative responses to Con A
and pentachlorinated (r2=0.87) and hexachlorinated (r2=0.84)
PCB levels. Figures 2A and B show a similar inverse correlation
between lymphocyte responses to Con A and peripheral blood p,p´-DDT
(r2=0.79) and p,p´-DDE concentrations (r2=0.81).
In one of the five animals, o,p´-DDT was not detected. For
linear regression analysis, we have arbitrarily assigned this individual
a value for p,p´-DDT of one half of the
detection limit.
A |
B |
Figure 1. Correlation
of maximal mitogen responses and PCB concentrations. Maximal in vitro
proliferative responses (Con A 0.13 µg/ml) and whole blood pentachlorinated
(A) and hexachlorinated (B) biphenyl concentrations were analyzed
by linear regression for five dolphins. Squares represent individual dolphins.
Levels of PCB (ng/g) in whole blood are indicated on the x axis. Proliferation
is reflected by 3H-thymidine incorporation and measured by liquid
scintillation counting. Counts per minute (cpm)/1000 are indicated on the
y axis.
A |
B |
Figure 2. Correlation
of maximal mitogen responses and DDT concentrations. Maximal in vitro
proliferative responses (Con A 0.5 µg/ml) and whole blood p,p´-DDT
(A) and p,p´-DDE (B) concentrations were analyzed
by linear regression for five dolphins. Squares represent individual dolphins.
Axes are the same as in Figure 1. The concentration of p,p´-DDT
for dolphin FB 164 was below the detection level and was assigned a value
of 0.5 times this level for the purposes of regression analysis.
Proliferative responses correlated inversely with contaminant levels
of several PCB congeners, p,p´-DDT; o,p´-DDE;
and p,p´-DDE. R2 values for the correlation
between Con A- and PHA-induced lymphoproliferation, and the concentration
of DDT and DDT metabolites and total trichlorobiphenyl to decachlorobiphenyl
congeners are presented in Table 3. Inverse correlations (r2
values greater than 0.75) were often observed between total trichlorobiphenyl
to heptachlorobiphenyl congeners and Con A-induced lymphoproliferative responses.
Inverse correlations were also observed between DDT and DDT metabolites
and Con A-induced lymphocyte responses. Weak correlations, or lack of correlations
(r2 values less than 0.60), were often exhibited between
blood contaminant levels and PHA-induced lymphocyte responses and may be
accounted for by the single depressed response of FB164 to PHA.
Discussion
In an effort to test the hypothesis that polyhalogenated environmental
chemical contaminants suppress the immune system of dolphins, thereby causing
susceptibility to infection and mortality, we have studied contaminant concentrations
in blood and lymphocyte proliferation responses to mitogens for a small
set of male bottlenose dolphins. These data indicate that in bottlenose
dolphins a reduced in vitro immune response is associated with increasing
levels of PCBs and DDT in peripheral blood. The small sample size in this
study (n=5) and the lack of control (uncontaminated) dolphins from
which we can determine the normal range of immune responses, precludes drawing
extensive conclusions. However, these data are consistent with the results
of other studies which show that PCBs and DDT can suppress immune responses.
Abundant evidence generated from controlled animal studies indicates
that PCBs and DDT suppress immune responses. PCB-induced immunosuppression
has been documented in mice (29-32), rats (33), guinea pigs
(34), ducks (35), monkeys (36-38), and possibly in
humans (39). Exposure to PCBs can result in reduced relative spleen
(31,32,40) and thymus (40) size, decreased T cell-dependent
antibody-forming cell (AFC) formation (31,32), lower T cell-dependent
antibody titer (32,36,39), depressed cytotoxic T lymphocyte (CTL)
response (40), and reduced delayed-type hypersensitivity (39).
Further, PCB exposure can reduce lymphocyte proliferation responses to phytohemagglutinin
(33,38) and can alter natural killer (NK) cell activity (33).
Experimental studies with rodents have shown that DDT exposure can result
in decreased spleen/body ratio (41-43) and decreased lymphocyte response
to lipopolysaccharide (LPS) (44). Further, T cell-dependent (43)
and T cell-independent (42,44,45) B cell responses can be depressed
by exposure to DDT. Thus, it is biologically plausible that immune suppression
of bottlenose dolphins can result from PCB and/or DDT exposure.
Exposure to PCBs can render animals more susceptible to viral and bacterial
infection. Mallard ducklings (Anas platyrhynchos) that were exposed
to PCBs exhibited higher mortality than unexposed ducklings after challenge
with duck hepatitis virus (35). Similarly, PCB exposure can increase
mouse susceptibility to malaria (Plasmodium bergei) infection (27),
to Salmonella spp. (29,36), and to both ectromelia virus and
Herpes simplex virus infection (30). Again, this suggests the possibility
that the dolphins that were stranded and showed mortality-associated infectious
diseases may have become more susceptible to a virus, such as morbillivirus,
as a result of exposure to these compounds.
Environmentally relevant concentrations of PCBs have also been shown
to impair immunity of harbor seals (Phoca vitulina), which have experienced
large-scale mortality events (due, in part, to the morbillivirus-related
distemper virus) in Europe since 1988. A recent study shows that harbor
seals exhibited depressed immune responses if fed contaminated fish from
the Baltic Sea rather than cleaner fish from the Atlantic Ocean (46).
While the data presented here are preliminary, they are consistent with
other studies that have found high levels of pollutants in dolphins, with
laboratory findings demonstrating the effects of PCBs and DDT on the immune
system, and with data showing that environmentally relevant levels of PCBs
in fish can cause immunosuppression in other marine mammals. Future work
must be conducted to determine whether a larger sample size can also support
the correlations found in this study and, if so, if specific pollutants
are responsible for the decreased lymphocyte proliferation response.
REFERENCES
1. Scott GP, Burn DM, Hansen LJ. The dolphin dieoff: long-term
effects and recovery of the population. In: Proceedings of the Oceans 88
Conference, 31 October-2 November 1988, Baltimore, MD. Vol 3:819-823.
2. Bossart G, Busbee D, Lahvis G, Worthy GAJ. Research
perspectives for dolphin mortalities in North America. Report No. EPA/600/R-93/217.
Cincinnati:Center for Environmental Research Information, 1993.
3. Aguilar A, Raga JA. Mortandad de delfines en el Mediterraneo.
Politica Cientifica 25:51-54 (1990).
4. Aguilar A, Raga JA. The striped dolphin epizootic in
the Mediterranean Sea. Ambio 22:524-528 (1993).
5. Domingo M, Visa J, Pumarola M, Marco AJ, Ferrer L, Rabanal
R, Kennedy S. Pathologic and immunocytochemical studies of morbillivirus
infection in striped dolphins (Stenella coeruleoalba). Vet Pathol
29:1-10 (1992).
6. Kannan K, Tanabe S, Borrell A, Aguilar A, Focardi S,
Tatsukawa R. Isomer-specific analysis and toxic evaluation of polychlorinated
biphenyls in striped dolphins affected by an epizootic in the western Mediterranean
Sea. Arch Environ Contam Toxicol 25:227-233, (1993).
7. Geraci JR. Clinical investigation of the 1987-88 mass
mortality of bottlenose dolphins along the U.S. central and south Atlantic
coast. Final Report to the National Marine Fisheries Service and U.S. Navy,
Office of Naval Research and Marine Mammal Commission. Guelph, Ontario:Ontario
Veterinary College, University of Guelph, 1989.
8. Buck JD, Overstrom NA, Patton GW, Anderson HF, Gorzelany
JF. Bacteria associated with stranded cetaceans from the northeast USA and
southwest Florida Gulf coasts. Dis Aquat Org 10:147-152 (1991).
9. Martineau D, Legace A, Beland P, Higgins R, Armstrong
D, Shugart LR. Pathology of stranded beluga whales (Delphinapterus leucas)
from the St. Lawrence Estuary, Quebec, Canada. J Comp Pathol 98:287-311
(1988).
10. Anderson DM, White AW. Toxic dinoflagellates and marine
mammal mortalities. 89-3 (CRC-89-6). Woods Hole, MA: Woods Hole Oceanographic
Institution, 1989.
11. Kapikian AZ, Chanock RM. Rotaviruses. In: Fields Virology,
Vol. 2 (Fields BN, Knipe DM, eds). New York:Raven Press, 1990;1353-1404.
12. Kennedy S, Smyth JA, Cush PF, McCullough SJ, Allan
GM. Viral distemper now found in porpoises. Nature 336:21 (1988).
13. Lipscomb TP, Schulman FY, Moffett D, Kennedy S. Morbilliviral
disease in Atlantic bottlenose dolphins (Tursiops truncatus) from
1987-88 epizootic. J Wildl Dis 30:567-571 (1994).
14. Lipscomb TP, Kennedy S, Moffett D, Ford BK. Morbilliviral
disease in an Atlantic bottlenose dolphin (Tursiops truncatus) from
the Gulf of Mexico. J Wildl Dis 30:572-576 (1994).
15. Safe S. Development, validation, and limitation of
toxic equivalency factors. Chemosphere 25:61-64 (1992).
16. Kuehl DW, Haebler R, Potter C. Coplanar PCB and metal
residues in dolphins from the U.S. Atlantic coast including Atlantic bottlenose
obtained during the 1987/1988 mass mortality. Chemosphere 28:1245-1253 (1994).
17. Muir DCG, Wagemann R, Grift NP, Norstrom RJ, Simon
M, Lien J. Organochlorine chemical and heavy metal contaminants in white-beaked
dolphins (Lagenorhynchus albirostris) and pilot whales (Globicephala
melaena) from the coast of Newfoundland, Canada. Arch Environ Contam
Toxicol 17:613-629 (1988).
18. Masse R, Martineau D, Tremblay L, Beland P. Concentration
and chromatographic profile of DDT metabolites and polychlorinated biphenyl
(PCB) residues in stranded beluga whales (Delphinapterus leucas)
from the St. Lawrence Estuary, Canada. Arch Environ Contam Toxicol 15:567-579
(1986).
19. Martineau D, Beland P, Desjardins C, Lagace A. Levels
of oranochlorine chemicals in tissues of beluga whales (Delphinapterus
leucas) from the St. Lawrence Estuary, Quebec, Canada. Arch Environ
Contam Toxicol 16:137-147 (1987).
20. Scott MD, Wells RS, Irvine AB. A long-term study of
bottlenose dolphins on the west coast of Florida. In: The Bottlenose Dolphin
(Leatherwood S, Reeves RR, eds). San Diego:Acedemic Press, 1990;235-244.
21. Wells RS. The role of long-term study in understanding
the social structure of a bottlenose dolphin community. In: Dolphin Societies:
Discoveries and Puzzles (Pryer K, Norris KS, eds). Berkeley, CA:University
of California Press, 1991;199-225.
22. Lahvis GP, Wells RS, Casper D, Via CS. In vitro
lymphocyte response of bottlenose dolphins (Tursiops truncatus):
mitogen-induced proliferation. Mar Environ Res 35:115-119 (1993).
23. Mumford DM, Stockman GD, Barsales PB, Whitman T, Wilbur
JR. Lymphocyte transformation studies of sea mammal blood. Experientia 31:498-500
(1975).
24. Colgrove GS. Stimulation of lymphocytes from a dolphin
(Tursiops truncatus) by phytomitogens. Am J Vet Res 39:141-144 (1978).
25. Romano TA, Ridgeway SH, Quaranta V. MHC Class II molecules
and immunoglobulins on peripheral blood lymphocytes of the bottlenosed dolphin,
Tursiops truncatus. J Exp Zool 263:96-104 (1992).
26. Kuehl DW, Butterworth RC, Libal J, Marquis P. An isotope
dilution high resolution gas chromatographic-high resolution mass spectrometric
method for the determination of coplanar polychlorinated biphenyls: application
to fish and marine
mammals. Chemosphere 22:849-858 (1991).
27. U.S. Environmental Protection Agency. Analytical procedures
and quality assurance plan for the determination of xenobiotic chemical
contaminants in fish. Report No. 600/3-90/022. Cincinnati:Center for Environmental
Research Information, 1990.
28. U.S. Environmental Protection Agency. Analytical procedures
and quality assurance plan for the determination of PCDD/PCDF in fish. Report
No 600/3-90/023. Cincinnati: Center for Environmental Research Information,
1990.
29. Loose LD, Silkworth JB, Pittman KA, Benitz KF, Muellar
W. Impaired hot resistance to endotoxin and malaria in polychlorinated biphenyl-
and hexachlorobenzene-treated mice. Infect Immun 20:30-35 (1978).
30. Imanishi J, Nomura H, Matsubara M, Kita M, Won S-J,
Mizutani T, Kishida T. Effect of polychlorinated biphenyl on viral infections
in mice. Infect Immun 29:275-277 (1980).
31. Silkworth JB, Grabstein EM. Polychlorinated biphenyl
immunotoxicity: dependence on isomer planarity and the Ah gene complex.
Toxicol Appl Pharmacol 65:109-115 (1982).
32. Silkworth JB, Antrim L, Kaminsky LS. Correlations between
polychlorinated biphenyl immunotoxicity, the aromatic hydrocarbon locus,
and liver microsomal enzyme induction in C57Bl/6 and DBA/2 mice. Toxicol
Appl Pharmacol 75:156-165 (1984).
33. Smialowicz RJ, Andrews JE, Riddle MM, Rodgers RR, Luebke
RW, Copeland CB. Evaluation of the immunotoxicity of low level PCB exposure
in the rat. Toxicology 56:197-211 (1989).
34. Vos JG, Roij T de. Immunosuppressive activity of a
polychlorinated biphenyl preparation on the humoral response of guinea pigs.
Toxicol Appl Pharmacol 21:549-555 (1972).
35. Friend M, Trainer DO. Polychlorinated biphenyl: interaction
with duck hepatitis virus. Science 170:1314-1316 (1970).
36. Thomas PT, Hinsdill RD. Effect of polychlorinated biphenyls
on the immune responses of rhesus monkeys and mice. Toxicol Appl Pharmacol
44:41-51 (1978).
37. Tryphonas H, Luster MI, White KL Jr, Naylor PH, Erdos
MR, Burleson GR, Germolec D, Hodgen M, Hayward S, Arnold DL. Effects of
PCB (Aroclor 1254) nonspecific immune parameters in rhesus (Macaca mulata)
monkeys. Int J Immunopharmacol 13:639-648 (1991).
38. Tryphonas H, Luster MI, Schiffman G, Dawson LL, Hodgen
M, Germolec D, Hayward S, Bryce F, Loo JCK, Mandy F, Arnold DL. Effect of
chronic exposure of PCB (Aroclor 1254) on specific and nonspecific immune
parameters in the rhesus (Macaca mulata) monkey. Fundam Appl Toxicol
16:773-786 (1991).
39. Chang K-J, Hsieh K-H, Tang S-Y, Tung T-C, Lee T-P.
Immunologic evaluation of patients with polychlorinated biphenyl poisoning:
evaluation of delayed-type skin hypersensitive response and its relation
to clinical studies. J Toxicol Environ Health 9:217-223 (1982).
40. Kerkvliet NI, Baecher-Steppan L, Smith BB, Youngberg
JA, Henderson MC, Buhler DR. Role of the Ah locus in suppression of cytotoxic
T lymphocyte activity by halogenated aromatic hydrocarbons (PCBs and TCDD):
structure-activity relationships and effects in C57Bl/6 mice congenic at
the Ah locus. Fundam Appl Toxicol 14:532-541 (1990).
41. Wassermann M, Wassermann D, Girshon Z, Zellermayer
L. Effects of organochlorine insecticides on body defense systems. Ann NY
Acad Sci 260:393-401 (1969).
42. Banerjee BD, Ramachandran M, Hussain QZ. Sub-chronic
effect of DDT on humoral immune response in mice. Bull Environ Contam Toxicol
37:433-440 (1986).
43. Banerjee BD. Effects of subchronic DDT exposure on
humoral immune response to a thymus-indepedent antigen (bacterial lipopolysaccharide)
in mice. Bull Environ Contam Toxicol 39:822-826 (1987).
44. Rehana T, Rao PR. Effect of DDT on the immune system
in Swiss albino mice during adult and perinatal exposure: humoral responses.
Bull Environ Contam Toxicol 39:822-826 (1992).
45. Banerjee BD. Subchronic effect of DDT on humoral and
cell-mediated immune responses in albino rats. Bull Environ Contam Toxicol
39:827-834 (1987).
46. Swart RL, Ross PS, Vedder LJ, Timmerman HH, Helsterkamp
S, Van Loveren H, Vos JG, Reijnders PJH, Osterhaus ADME. Impairment of immune
function in harbor seals (Phoca vitulina) feeding on fish from polluted
waters. Ambio 23:155-159 (1994).
[
Table
of Contents] [
Citation
in PubMed] [
Related
Articles]
Last Update: September 23, 1998
