This article was published in an Elsevier journal. The attached copy
is furnished to the author for non-commercial research and
education use, including for instruction at the author’s institution,
sharing with colleagues and providing to institution administration.
Other uses, including reproduction and distribution, or selling or
licensing copies, or posting to personal, institutional or third party
websites are prohibited.
In most cases authors are permitted to post their version of the
article (e.g. in Word or Tex form) to their personal website or
institutional repository. Authors requiring further information
regarding Elsevier’s archiving and manuscript policies are
encouraged to visit:
http://www.elsevier.com/copyright
Author's personal copy
Available online at www.sciencedirect.com
Science of the Total Environment 388 (2007) 300 – 315
www.elsevier.com/locate/scitotenv
Trace element concentrations in skin of free-ranging bottlenose
dolphins (Tursiops truncatus) from the southeast Atlantic coast
Hui-Chen W. Stavros a,⁎, Gregory D. Bossart b , Thomas C. Hulsey c , Patricia A. Fair a
a
National Oceanic and Atmospheric Administration, National Ocean Service, Center for Coastal Environmental Health & Biomolecular Research,
219 Fort Johnson Road, Charleston, South Carolina 29412, USA
b
Harbor Branch Oceanographic Institution, 5600 U.S. 1 North, Ft. Pierce, Florida 34946, USA
c
Medical University of South Carolina, 165 Ashley Avenue, PO Box 250566, Charleston, SC 29425, USA
Received 19 March 2007; received in revised form 12 July 2007; accepted 19 July 2007
Available online 31 August 2007
Abstract
Concentrations of trace elements (Al, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Sb, Se, Sn, Tl, U, V, Zn) and total mercury
(THg) were determined in skin samples collected from free-ranging bottlenose dolphin (Tursiops truncatus) populations. Dolphins
were captured in the estuarine waters of Charleston (CHS), South Carolina (n = 74) and the Indian River Lagoon (IRL), Florida
(n = 75) during 2003, 2004 and 2005. A subset of the skin tissue samples were used to determine methylmercury (MeHg) levels in
CHS (n = 17) and IRL (n = 8) bottlenose dolphins. Distributions of trace element concentrations by age (adult vs. juvenile), gender
(male vs. female) and study area (CHS vs. IRL) were examined. In general, higher elemental skin concentrations were found in
CHS adult males than those of IRL adult males, except for THg and MeHg. For CHS dolphins, adult females showed significantly
higher THg levels than juvenile females while higher Mn levels were found in juvenile females. For IRL dolphins, adult males
showed significantly higher As concentrations than that in juvenile males and females while higher Co and V levels were found in
juvenile males than adult males. Of all elements measured in this study, significantly higher levels of Fe, Se and Zn concentrations
in skin tissue of both dolphin populations were similar to other studies reported previously. Percentage of MeHg/THg in skin tissue
of CHS and IRL dolphin was about 72% and 73%, respectively. Dietary levels of trace elements may play an important role in
contributing to concentration differences for As, Co, Mn, Sb, Se, THg and Tl between CHS and IRL dolphins. Total Hg
concentrations were significantly correlated with the age of CHS dolphins, while an inverse relationship was detected for Cu, Mn,
Pb, U and Zn. The only significant correlation found between trace element concentration and IRL dolphins' age was Mn.
Geographic differences in several trace element concentrations (As, Co, Mn, Sb, Se, THg and Tl) in skin tissue may be potentially
useful to discriminate between dolphin populations and is a possibility that warrants further investigation.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Trace element; Methyl mercury; Skin; Free-ranging; Cetacean; Bottlenose dolphin; Tursiops truncatus
1. Introduction
⁎ Corresponding author. Tel.: +1 843 762 8539; fax: +1 843 762
8700.
E-mail address: huichen.stavros@noaa.gov (H.-C.W. Stavros).
0048-9697/$ - see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.scitotenv.2007.07.030
Trace element concentrations in the marine environment may be a result of natural and/or anthropogenic
sources (Law, 1996). Several toxic elements, such as Cd
and Hg, have been reported to accumulate through the
marine food chain in marine mammal tissues and organs
Author's personal copy
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
(Das et al., 2003; Yang et al., 2006). Marine mammals
may serve as a potential indicator of contaminants
because they occupy the top trophic level in the marine
food chain and have long life-spans and bioaccumulate
environmental contaminants. For a number of coastal
bottlenose dolphin (Tursiops truncatus) populations,
their high site fidelity supports the role of bottlenose
dolphin as sentinel species for monitoring spatial and
temporal contaminants trends (Fair and Becker, 2000;
Das et al., 2003; Wells et al., 2004; Bossart, 2006).
Bottlenose dolphins are the most common cetaceans in
the coastal waters of the southeastern U.S. and are found
throughout the temporal and tropic environments around
the world. During 1987 and 1988, an unusual mortality
event (UME) involving ∼ 740 bottlenose dolphins
occurred along the eastern coast of the U.S. with an
estimated 50% of the Mid-Atlantic coastal migratory
stock dying (Scott et al., 1988). The large scale mortality
of marine mammals raised concerns about the possible
impact of organic contaminants which may suppress
marine mammal immune systems and increase susceptibility to epizootic diseases (Ross et al., 1996; Ross, 2000).
Two other recent UMEs of bottlenose dolphins occurred
in Florida's Indian River Lagoon and panhandle during
2001 and 2004, respectively. The cause of the 2001
mortality is unknown while brevetoxins was identified as
cause of 2004 UME (MMC, 2001, 2005).
Several studies have been conducted on trace element
concentrations in the tissues of stranded bottlenose
dolphins along the U.S. southeast Atlantic coast and Gulf
of Mexico (Kuehl et al., 1994; Kuehl and Haebler, 1995;
Beck et al., 1997; Meador et al., 1999); French Atlantic
coast (Holsbeek et al., 1998); west Atlantic Ocean
(Carvalho et al., 2002); Mediterranean (Frodello and
Marchand, 2001; Roditi-Elasar et al., 2003) and Japan
(Endo et al., 2005). Generally, concentrations of Cr, Ni and
Pb were reported to be low in the liver of marine mammals,
rarely over a few μg/g dry weight (Das et al., 2003). Some
elements, such as Cd, Hg and Se liver concentrations were
found to increase with the length of bottlenose dolphins
from the South Carolina coast (Beck et al., 1997). Other
studies suggested that different concentrations of As
speciation chemical forms in higher trophic marine
animals may reflect the differences in metabolism of As
compounds among their prey (Kubota et al., 2002 and
2003). Samples collected from different geographic
locations are expected to have different trace element
concentrations as a result of various types and amounts of
dietary exposures (Das et al., 2003; O'Hara et al., 2003;
Booth and Zeller, 2005; Brookens et al., 2007).
Bottlenose dolphins usually consume a wide range
of prey species, such as sciaenids (i.e. drums, croakers,
301
and sea trout) or haemulids (i.e. grunts) available within
its geographic locations (Barros and Odell, 1990).
Feeding strategies could influence the trace element
concentrations found in dolphins. Stomach content
analysis has been the most common way to study
foraging ecology and prey species composition of
dolphins but previous studies have been restricted to
stranded animals (Barros and Wells, 1998; Walker et al.,
1999; Gannon and Waples, 2004) and may not represent
reliable indicators of diet in healthy feeding dolphins.
Barros and Odell (1995) reported that dolphins in the
Indian River Lagoon, FL compete directly or indirectly
with humans for similar fish resources (e.g. blue crab
fishery).
In the past decade, several studies have used nonlethal samples (i.e. blood, skin) to measure body
burdens of both organic and inorganic contaminants in
marine mammals (Fossi and Marsili 1997; Fossi et al.,
2004; Monaci et al., 1998; Yang et al., 2002; Wagemann
and Kozlowska, 2005). Skin collected via biopsy
techniques was found to provide the most useful sample
for assessing the ecotoxicological status in free-ranging
cetaceans because they can be used to measure
organochlorine exposure, mixed-function oxidase and
DNA damage (Fossi and Marsili, 1997; Fossi et al.,
2000). Concentrations of many trace elements (Ag, As,
Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V and Zn)
reported in skin tissue of marine mammals have been
limited to samples obtained from stranded carcasses
(Wagemann et al., 1996; Watanabe et al., 1996; Frodello
and Marchand, 2001; Carvalho et al., 2002; Kunito et
al., 2002; Shoham-Frider et al., 2002; Yang et al., 2002;
Roditi-Elasar et al., 2003; Fossi et al., 2004). However,
data on trace element concentrations obtained from
stranded animals may not be representative of values in
the wild population due to the degradation of these
samples; therefore, it is difficult to evaluate adverse
health impacts using stranded animals (Das et al., 2003;
O'Hara et al., 2003).
The objectives of this study were to determine
baseline trace element concentrations in skin tissue from
two free-ranging bottlenose dolphin populations and to
evaluate the potential relationship between element
levels and biological factors, such as age and gender.
Trace elements selected for analysis in this study were
based on their potential toxicity (e.g. As, Cd, THg, and
Pb) and biological functions (e.g. Cu and Zn). The
results in this study may provide information for further
comparison of trace element concentrations between
skin and internal organs in order to resolve the question
as to whether skin is suitable for predicting trace element
body burdens in dolphins.
Author's personal copy
302
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
2. Materials and methods
2.1. Sample collection
Skin samples were obtained from two free-ranging
bottlenose dolphin populations during capture–release
studies conducted at Charleston (CHS), South Carolina
and Indian River Lagoon (IRL), Florida during the
summers of 2003 to 2005 as part of Bottlenose Dolphin
Health and Risk Assessment (HERA) Project. This
project is a collaboration between the National Ocean
Service Center for Coastal Environmental Health and
Biomolecular Research in Charleston, South Carolina and
Harbor Branch Oceanographic Institution (HBOI) in Fort
Pierce, Florida. The CHS site (W 32°46′51″N, 79°55′33″
W, Fig. 1) includes the Charleston Harbor and portions
of the main channels and creeks of the Ashley River,
Cooper River, Wando River, and Stono River Estuary.
The IRL site (Fig. 2) extends from the north near Merritt
Island (80°47′46″W) to the south in the St. Lucie Inlet
(27°47′41″N). Dolphins were restrained using established
capture–release techniques (Hansen and Wells, 1996;
Fair et al., 2006). All animal capture and sampling
protocols were approved by the National Marine Fisheries
Permit No. 998-1678-01 and by the HBOI Institutional
Animal Care and Use Committee (IACUC). Dolphin ages
were determined by the examination of postnatal dentine
layers in an extracted tooth (Hohn et al., 1989). Pregnancy
was determined by ultrasound (SonoSite 180plus,
Bothell, WA). Additionally, samples of six prey species
(Cynoscion nebulosus, Micropogonias undulates, Scianops ocellatus, Leiostomus xanthurus, Mugil cephalus,
Lagodon rhomboid) were collected from the CHS site
in collaboration with the Inshore Fisheries Group and
SEAMAP (Southeast Area Monitoring and Assessment
Program) and the SCDNR (South Carolina Department of
Natural Resources) in 2002 and 2003. The selection of
prey species analyzed from the CHS site is based on
previous evidence indicating these species are potential
dolphin prey items (stomach content analyses in stranded
dolphins) and species available to sampling methods in
the CHS site as described by Recks (2004).
2.2. Sample preparation
A full-thickness skin and blubber wedge biopsy
sample was removed from a location ca 10 cm posterior
and 10 cm below the posterior insertion of the dorsal fin
using a pre-cleaned sterile scalpel and forceps (Fair et al.,
2006). The site then received a final methanol rinse. The
skin sample (epidermis and dermis) was immediately
subsection from the blubber (hypodermis), rinsed several
times with distilled water, placed in a pre-cleaned
Teflon® vial and immediately stored in a liquid nitrogen
vapor cooler. In the laboratory, samples were stored at
− 80 °C until processed. All skin samples were cleaned
with 18 MΩ Milli-Pore deionized water (Milli-Pore,
Billerica, MA) and dissected using a pre-cleaned (with
Fig. 1. Study site of the Charleston bottlenose dolphin health assessment.
Author's personal copy
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
303
Fig. 2. Study site of the Indian River Lagoon dolphin health assessment.
hexane and methanol) sterile scalpel to remove excess
blubber. Approximately 0.5 g of skin was dried for 12 h
at 80 °C. Sub-samples of ca 0.05 g dry skin were
prepared for total mercury analysis. Skin samples
(∼ 0.1 g) were digested in a Teflon digestion vessel
with ULTREXII ultrapure nitric acid (HNO3, J.T. Baker,
Phillipsburg, NJ) in a CEM MDS-2100 Microwave
(CEM Corporation, Matthews, NC) for 15 min at 66 W
power. After the first digestion, ULTREXII ultrapure
30% hydrogen peroxide (H2O2, J.T. Baker) was added
for an additional 10 min microwave digestion to
complete oxidation of organic matter. The final solution
was diluted with Milli-Pore deionized water for trace
element analyses. Approximately 2 g of homogenized
whole body prey species sample (n = 3 for each species)
was freeze-dried over night, and analyzed only for THg
in this study.
2.3. Chemical analyses
Concentrations of 20 trace elements (Al, As, Ba, Be,
Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Sb, Se, Sn, Tl, U, V,
Author's personal copy
304
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
Table 1
Biological data on free-ranging bottlenose dolphins from Charleston and Indian River Lagoon sampled in 2003, 2004 and 2005
CHS
Age
Juvenile male
a
Adult male
Juvenile female
Adult femalea
Pregnant female
Total a
a
6 ± 1.9
(3.5–9.0)
17 ± 5.8
(10.0–28.0)
4 ± 1.2
(2.5–6.0)
19 ± 6.7
(9.0–29.0)
20 ± 10.8
(8.0–33.0)
14 ± 8.0
(2.5–33.0)
IRL
n
9
36
14
11
4
74
Age
n
Total
7 ± 1.4
(4.5–9.0)
15 ± 4.0
(10.0–27.0)
5 ± 0.9
(3.5–6.0)
13 ± 5.2
(7.5–26.0)
7.0
19
7 ± 1.6
(3.5–9.0)
16 ± 5.1
(10.0–28.0)
4 ± 1.1
(2.5–6.0)
16 ± 6.6
(9.0–26.0)
18 ± 11.2
(7.0–33.0)
13 ± 6.9
(2.5–33.0)
11 ± 5.4
(3.5–27.0)
34
9
12
1
75
n
28
70
23
23
5
149
Indicates significant differences between CHS and IRL.
Zn) were screened and measured using Perkin Elmer
6100 inductively coupled plasma mass spectrometer
(ICP-MS, Wellesley, MA). Multiple-elements (45Sc,
72
Ge, 103Rh, 175 Lu) internal standards (High-Purity
Standards, Charleston, SC) were added to each sample
and calibration standard solutions. Total mercury (THg)
concentration was determined by Milestone direct
mercury analyzer (DMA-80, Shelton, CT). Certified
Reference Materials including 1566b (oyster tissue,
National Institute of Standards and Technology, USA),
TORT-2 (lobster hepatopancreas), DOLT-3 (dogfish
liver) and DORM2 (dogfish muscle, National Research
Council Canada) were used for quality assurance. All
plasticware was pre-cleaned with reagent grade HNO3
(69.0%–70.0%) and hydrochloric acid (HCl, 36.5%–
38.0%) to eliminate contamination. Due to the limited
amount of available skin for methylmercury (MeHg)
determination, only 25 skin samples (CHS = 17, IRL = 8)
were available for the determination of MeHg by coldvapor atomic fluorescence spectrometry and analyzed
by the Battelle Marine Sciences Laboratories at the
Pacific Northwest National Laboratory (Sequim, WI).
The analysis method of MeHg followed the EPA
method 1630 (EPA, 2001) and the standard reference
material DOLT-2 was used for quality assurance.
2.4. Statistical analyses
Concentrations of trace elements in this study are
presented on a μg/g dry weight (dw) basis. Descriptive
statistics for mean, standard deviation and range were
calculated using SAS (Version 9, SAS Institute Inc.,
Cary, NC) for each element concentration; only samples
having values greater than Method Detection Limit
(MDL) were included. Five different age and gender
groups were used in this study (Table 1). Dolphins b 7
and b 10 yr of age were classified as juvenile female and
male, respectively, while those ≥ 7 and ≥ 10 yr of age
were categorized as adult female (pregnant and nonpregnant) and male, respectively. Sample sizes for each
age and gender group varied due to non-detectable (nd)
and below MDL concentrations of some elements in this
study. Differences between means of two groups were
assessed by the Student's t-test. Differences between
means of three or more groups were assessed using
ANOVA. Because of the influence of the reproductive
status of element concentrations in adult females and
limited sample size of juvenile dolphins, only adult
males were included in the analysis of comparison of
trace elements concentrations between CHS and IRL.
Relationships between age and the concentration of each
element and MeHg were evaluated by Spearman rank
test and linear regression. Results were considered
significant when p ≤ 0.05.
3. Results
3.1. Trace element concentrations in skin
3.1.1. CHS dolphins
A total of 74 skin samples were collected from
CHS dolphins. The ranking of highest to lowest
element concentration found in skin was as follows:
Zn N Fe N Se N Al N As N Cu, THg N Co, Li, Cr, Mn, Sb N Pb,
Sn, Tl, V N U N Ba, Be, Ni N Cd, regardless of age or
gender (Table 2). All trace element concentrations
found in the skin of CHS dolphins were lower than
1 μg/g dw, with the exception of Al, As, Cu, Fe, THg,
Se and Zn. Trace elements Al, As, Cr, Cu, THg, Mn, Se,
U, V and Zn were detected in all skin samples from
Author's personal copy
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
CHS dolphins, while Be, Cd, Li and Sb were detected
in less than 50% of the samples. Significant differences
in skin concentrations of Cu, THg and Mn were found
between age and gender groups. Pregnant females
exhibited significantly higher (p = 0.026) Cu skin
concentrations than adult females. Significantly higher
THg skin concentration was found in adult females than
305
those of adult males and juvenile females. Juvenile
females showed significantly higher (p ≤ 0.01) Mn skin
levels than those in adult males and pregnant females.
In addition, significantly higher (p = 0.020) Mn skin
concentrations were found in juvenile males than those
in pregnant females. Skin THg concentrations significantly increased (p = 0.001) with age of CHS dolphins,
Table 2
Trace element concentrations (mean ± SD and range, μg/g dry weight) in skin tissue of bottlenose dolphins from Charleston, SC sampled in 2003,
2004 and 2005
Male
Al
As
Ba
Be
Cd
Co
Cr
Cu
Fe
Li
Mn
Ni
Pb
Sb
Se
Sn
THg
Tl
U
V
Zn
Female
Total
Juvenile
n
Adult
n
Juvenile
n
Adult
n
Pregnant
n
5.00 ± 1.72
(3.02–8.41)
1.80 ± 0.83
(1.09–3.78)
0.05 ± 0.03
(0.03–0.11)
0.06 ± 0.04
(0.02–0.12)
0.012 ± 0.002
(0.009–0.014)
0.59 ± 0.25
(0.25–0.92)
0.87 ± 0.48
(0.37–1.94)
1.63 ± 0.41
(1.22–2.35)
432 ± 607
(19–1438)
1.35 ± 1.70
(0.12–3.74)
0.77 ± 0.33
(0.25–1.22)
0.04 ± 0.02
(0.02–0.06)
0.40 ± 0.21
(0.049–0.64)
0.81 ± 0.19
(0.61–1.0)
24.0 ± 7.4
(13.4–36.3)
0.20 ± 0.29
(0.06–0.91)
1.6 ± 0.57
(0.73–2.4)
0.33 ± 0.18
(0.05–0.56)
0.29 ± 0.17
(0.08–0.57)
0.41 ± 0.40
(0.06–1.2)
748 ± 199
(410–1030)
9
11 ± 28
(0.96–157)
2.36 ± 0.76
(0.89–3.91)
0.16 ± 0.44
(0.02–2.1)
0.08 ± 0.05
(0.01–0.24)
0.011 ± 0.004
(0.005–0.016)
0.52 ± 0.27
(0.15–1.12)
0.94 ± 0.38
(0.36–2.19)
1.54 ± 0.29
(0.86–2.11)
129 ± 292
(14–1298)
0.49 ± 0.93
(0.07–3.61)
0.53 ± 0.34
(0.21–1.35)
0.06 ± 0.05
(0.01–0.19)
0.28 ± 0.27
(0.039–1.0)
0.84 ± 0.23
(0.50–1.1)
24.0 ± 7.7
(11.0–38.8)
0.44 ± 0.50
(0.03–1.6)
1.7 ± 1.0
(0.77–4.9)
0.24 ± 0.21
(0.04–0.68)
0.20 ± 0.18
(0.03–0.93)
0.37 ± 0.33
(0.07–1.3)
648 ± 262
(272–1588)
36
7.3 ± 14
(1.60–54)
2.16 ± 0.85
(0.84–4.16)
0.13 ± 0.22
(0.02–0.67)
0.06 ± 0.03
(0.03–0.10)
0.015 ± 0.006
(0.009–0.022)
0.73 ± 0.36
(0.36–1.58)
0.98 ± 0.40
(0.46–1.76)
1.74 ± 0.37
(1.03–2.42)
386 ± 471
(33–1080)
0.95 ± 1.26
(0.07–3.02)
0.84 ± 0.41
(0.29–1.90)
0.07 ± 0.08
(0.02–0.29)
0.48 ± 0.26
(0.2–1.0)
1.0 ± 0.41
(0.55–1.5)
25.6 ± 7.1
(16.3–43.9)
0.31 ± 0.34
(0.07–1.1)
1.2 ± 0.58
(0.65–2.9)
0.41 ± 0.23
(0.19–1.0)
0.32 ± 0.20
(0.04–0.67)
0.44 ± 0.35
(0.06–0.84)
752 ± 303
(401–1385)
14
2.3 ± 0.97
(1.19–4.11)
1.85 ± 0.81
(0.57–3.20)
0.05 ± 0.03
(0.02–0.11)
0.07
11
4
4
7
14 ± 19
(1.5–42)
2.26 ± 1.49
(1.12–4.39)
0.09
1
0.08
1
6
0.011
1
0.39 ± 0.05
(0.35–0.45)
0.86 ± 0.11
(0.75–1.00)
1.62 ± 0.16
(1.54–1.86)
33 ± 13
(21–52)
0.09
3
9
6
5
3
8
9
9
5
4
9
5
8
3
9
8
9
8
9
9
9
36
22
19
6
24
36
36
25
18
36
20
24
5
36
32
36
24
36
36
36
14
8
9
4
11
14
14
8
9
14
11
11
4
14
13
14
11
14
14
14
0.013 ± 0.004
(0.007–0.020)
0.71 ± 0.33
(0.32–1.38)
0.76 ± 0.31
(0.45–1.44)
1.31 ± 0.19
(0.93–1.64)
30 ± 7.2
(18–39)
0.08
0.72 ± 0.48
(0.24–1.63)
0.03 ± 0.01
(0.02–0.04)
0.37 ± 0.28
(0.06–0.86)
0.85 ± 0.30
(0.43–1.3)
24.7 ± 7.5
(13.1–35.1)
0.14 ± 0.16
(0.05–0.60)
2.1 ± 0.65
(1.4–3.3)
0.38 ± 0.28
(0.06–0.84)
0.25 ± 0.13
(0.04–0.51)
0.24 ± 0.20
(0.05–0.58)
717 ± 219
(441–1083)
11
10
11
11
6
1
11
7
10
1
4
4
4
1
0.31 ± 0.07
(0.25–0.40)
0.08
4
0.08 ± 0.02
(0.06–0.10)
3
1
6
11
11
11
10
11
11
11
22.1 ± 11.7
(13.4–38.7)
0.47 ± 0.72
(0.07–1.5)
2.4 ± 1.6
(1.0–4.7)
0.08 ± 0.02
(0.06–0.11)
0.13 ± 0.05
(0.05–0.17)
0.38 ± 0.18
(0.11–0.51)
598 ± 67
(543–678)
4
4
4
3
4
4
4
n
8.4 ± 21
(0.96–157)
2.17 ± 0.84
(0.57–4.39)
0.12 ± 0.33
(0.02–2.1)
0.07 ± 0.04
(0.01–0.24)
0.012 ± 0.004
(0.005–0.022)
0.60 ± 0.30
(0.15–1.58)
0.91 ± 0.38
(0.36–2.19)
1.6 ± 0.33
(0.86–2.42)
183 ± 358
(14–1438)
0.69 ± 1.12
(0.07–3.74)
0.63 ± 0.39
(0.21–1.90)
0.06 ± 0.05
(0.01–0.29)
0.34 ± 0.27
(0.04–1.0)
0.87 ± 0.23
(0.43–1.5)
24.3 ± 7.6
(11.0–43.9)
0.34 ± 0.43
(0.07–1.61)
1.7 ± 0.92
(0.65–4.9)
0.30 ± 0.23
(0.04–0.96)
0.23 ± 0.18
(0.03–0.93)
0.37 ± 0.32
(0.05–1.3)
687 ± 251
(272–1586)
74
74
44
35
20
56
74
74⁎a
48
33
74⁎c
44
56
18
74
68
74⁎b
56
74
74
74
⁎Significant difference among groups of CHS dolphins; aPregnant female N adult female; bAdult female N adult male, juvenile female; cJuvenile
male N adult male, pregnant female.
Author's personal copy
306
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
Fig. 3. Significant correlation of trace element concentrations and age of CHS dolphins.
while Cu, Mn, Pb, U and Zn levels were inversely
related (Fig. 3).
3.1.2. IRL dolphins
A total of 75 skin samples were collected from IRL
dolphins. The ranking of skin trace element concentrations from the highest to lowest was as follows:
Zn N Fe N Se N THg N Al N Cu N Cr, As N Mn, V N Co, Sn,
U N Pb, Sb N Tl, Li N Be, Ba, Ni N Cd, regardless of age
or gender (Table 3). The majority of trace element
concentrations in the skin of IRL dolphins were below
1 μg/g dw, with the exception of Al, Cr, Cu, Fe, THg, Se
and Zn. Concentrations of Al, Cu, THg, Mn, Pb, Se, Tl
and Zn in skin samples of IRL dolphins were all above
MDL, while Sb and Sn were detected in less than 50%
of samples. There were significant differences between
skin concentrations of As, Co and V and age and gender.
Significantly higher As concentrations were found in
skin of adult males compared to juvenile males and adult
females. Juvenile males exhibited higher (p = 0.040) Co
skin levels than those of adult males. Both juvenile
males and adult females showed significantly higher
(p ≤ 0.01) V skin concentrations than those in adult
males. In addition, significantly higher (p = 0.036) V
skin levels were found in adult females compared to
those in juvenile females. Skin Mn concentrations had a
significant (p = 0.049) inverse correlation with the age of
IRL dolphins (Fig. 4).
3.2. Comparison of trace element concentrations
between CHS and IRL (adult males)
In general, CHS dolphins exhibited significantly
higher trace element concentrations As, Co, Mn, Pb, Sb,
Se, and Tl than those in IRL, except for THg (Table 4).
No difference between CHS and IRL was found for skin
concentrations of Al, Ba, Be, Cd, Cr, Cu, Fe, Li, Ni, Sn,
U, V and Zn.
Author's personal copy
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
307
Table 3
Trace element concentrations (mean ± SD and range, μg/g dry weight) in skin tissue of bottlenose dolphins from Indian River Lagoon, FL sampled in
2003, 2004 and 2005
Male
Al
As
Ba
Be
Cd
Co
Cr
Cu
Fe
Li
Mn
Ni
Pb
Sb
Se
Sn
THg
Tl
U
V
Zn
Female
Total
Juvenile
n
Adult
n
Juvenile
n
Adult
n
Pregnant
n
3.36 ± 1.79
(1.08–7.25)
0.66 ± 0.25
(0.26–1.29)
0.05 ± 0.02
(0.02–0.09)
0.06 ± 0.03
(0.02–0.14)
0.011 ± 0.010
(0.003–0.037)
0.32 ± 0.20
(0.06–0.71)
0.98 ± 0.26
(0.64–1.58)
1.54 ± 0.29
(1.01–2.30)
98 ± 98
(32–307)
0.10 ± 0.05
(0.04–0.23)
0.46 ± 0.18
(0.21–0.96)
0.03 ± 0.02
(0.01–0.07)
0.17 ± 0.16
(0.04–0.65)
0.13 ± 0.05
(0.09–0.18)
17.9 ± 6.9
(7.2–31.6)
0.18 ± 0.14
(0.03–0.37)
6.5 ± 5.9
(0.33–20)
0.12 ± 0.10
(0.03–0.44)
0.24 ± 0.17
(0.07–0.75)
0.46 ± 0.18
(0.21–0.87)
605 ± 225
(426–1410)
19
3.37 ± 1.75
(1.02–7.40)
0.86 ± 0.29
(0.33–1.50)
0.06 ± 0.06
(0.01–0.30)
0.07 ± 0.04
(0.02–0.16)
0.010 ± 0.005
(0.003–0.017)
0.20 ± 0.07
(0.09–0.36)
0.78 ± 0.31
(0.08–1.23)
1.42 ± 0.30
(0.95–2.18)
104 ± 146
(24–565)
0.09 ± 0.06
(0.03–0.28)
0.38 ± 0.09
(0.24–0.61)
0.08 ± 0.13
(0.01–0.57)
0.11 ± 0.08
(0.03–0.30)
0.12 ± 0.05
(0.07–0.25)
16.7 ± 6.1
(2.4–28.4)
0.22 ± 0.25
(0.04–0.77)
6.4 ± 4.0
(0.33–15)
0.08 ± 0.05
(0.02–0.20)
0.16 ± 0.09
(0.05–0.34)
0.33 ± 0.11
(0.13–0.60)
583 ± 218
(305–1471)
34
2.26 ± 1.13
(0.77–4.25)
0.65 ± 0.18
(0.38–0.91)
0.04 ± 0.03
(0.01–0.10)
0.04 ± 0.02
(0.01–0.06)
0.006 ± 0.005
(0.003–0.015)
0.21 ± 0.12
(0.05–0.41)
1.02 ± 0.44
(0.31–1.71)
1.40 ± 0.33
(0.71–1.71)
48 ± 19
(23–76)
0.07 ± 0.02
(0.04–0.10)
0.41 ± 0.18
(0.21–0.72)
0.03 ± 0.01
(0.01–0.03)
0.13 ± 0.09
(0.03–0.26)
0.17 ± 0.10
(0.07–0.28)
17.7 ± 4.9
(10.7–26.4)
0.04 ± 0.01
(0.04–0.05)
9.3 ± 10.7
(1.2–31)
0.09 ± 0.05
(0.03–0.17)
0.16 ± 0.08
(0.05–0.29)
0.40 ± 0.15
(0.14–0.66)
632 ± 171
(431–955)
9
2.47 ± 1.00
(0.99–3.82)
0.70 ± 0.15
(0.49–0.90)
0.05 ± 0.03
(0.02–0.10)
0.05 ± 0.02
(0.02–0.08)
0.009 ± 0.007
(0.003–0.020)
0.24 ± 0.10
(0.05–0.39)
0.98 ± 0.30
(0.54–1.41)
1.30 ± 0.26
(0.91–1.6)
62 ± 46
(27–193)
0.08 ± 0.03
(0.04–0.13)
0.41 ± 0.11
(0.21–0.56)
0.03 ± 0.02
(0.02–0.08)
0.19 ± 0.12
(0.03–0.35)
0.10 ± 0.002
(0.101–0.103)
15.9 ± 5.9
(9.9–27.4)
0.14 ± 0.15
(0.03–0.31)
7.9 ± 6.4
(0.37–17)
0.12 ± 0.07
(0.03–0.24)
0.21 ± 0.11
(0.07–0.40)
0.45 ± 0.17
(0.17–0.74)
563 ± 185
(3345–1049)
12
3.78
1
12
0.91
1
16
15
15
13
16
16
19
14
16
19
11
19
3
19
5
19
19
16
16
19
29
26
18
16
29
29
34
29
28
34
17
34
15
34
10
34
34
30
29
34
9
7
7
5
9
9
9
7
8
9
5
9
4
9
2
9
9
9
9
9
9
10
9
9
0.43
1
12
0.60
1
12
1.52
1
32
1
8
11
12
0.44
1
6
12
0.04
1
2
12
13.9
1
3
0.19
1
12
5.9
1
12
0.03
1
11
12
0.37
1
12
509
1
n
3.10 ± 1.63
(0.77–7.40)
0.76 ± 0.26
(0.26–1.50)
0.05 ± 0.04
(0.01–0.30)
0.06 ± 0.03
(0.01–0.16)
0.010 ± 0.007
(0.003–0.037)
0.24 ± 0.13
(0.05–0.71)
0.89 ± 0.33
(0.08–1.71)
1.42 ± 0.30
(0.71–2.30)
87 ± 113
(23–565)
0.09 ± 0.05
(0.03–0.28)
0.41 ± 0.13
(0.21–0.96)
0.05 ± 0.09
(0.01–0.57)
0.14 ± 0.11
(0.03–0.65)
0.13 ± 0.06
(0.07–0.28)
17.0 ± 6.0
(2.4–31.6)
0.18 ± 0.20
(0.03–0.77)
7.0 ± 5.9
(0.33–31)
0.10 ± 0.07
(0.02–0.44)
0.19 ± 0.12
(0.05–0.75)
0.39 ± 0.15
(0.13–0.87)
590 ± 206
(305–1471)
75
67⁎a
57
50
43
67⁎b
67
75
62
63
75
39
75
24
75
21
75
75
66
67⁎c
75
⁎Significant difference among groups of IRL dolphins (p ≤ 0.05); aAdult male N juvenile male, adult female; bJuvenile male N adult male; cJuvenile
male, adult female N adult male.
3.3. Methylmecury (MeHg) levels in skin of bottlenose
dolphins
Concentrations of MeHg in 25 skin samples from CHS
and IRL dolphins are shown in Table 5. Significantly
higher (p b 0.001) MeHg levels were found in IRL
dolphins than those in CHS. A similar mean MeHg/
THg percentage was found in skin samples between CHS
(72%) and IRL (73%) dolphins. A significant positive
correlation was found between MeHg and THg concentrations in skin tissue of CHS (R2 = 0.88, p b 0.001) and
IRL (R2 = 0.0.84, p = 0.001) dolphins.
3.4. Total Hg concentrations in prey species collected
from CHS
Concentrations of THg in six prey species collected
from CHS in 2002 and 2003 are presented in Table 6.
Author's personal copy
308
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
Fig. 4. Significant correlation of Mn concentration and age of IRL
dolphins.
Highest THg levels were found in C. nebulosus
(mean = 0.095 μg/g wet weight, range = 0.052–
0.127 μg/g wet weight), while the lowest THg levels
were in M. cephalus (mean = 0.005 μg/g wet weight,
range = 0.004–0.005 μg/g wet weight).
marine mammals (Atwell et al., 1998; Das et al., 2003;
Dehn et al., 2006). In cetaceans, skin is reported to
accumulate some trace elements, such as Se and Zn,
because they lack hair or glands for excretion (Yang et al.,
2002). Turnover time and sloughing rate of skin tissue in
bottlenose dolphin has been estimated to be longer and
faster than in epidermal cells in humans (Hick et al.,
1985). This finding of epidermal cell kinetics may be used
to estimate trace element accumulation in skin tissue and
possibly be utilized to assess contaminant body burden in
marine mammals. A positive correlation of Hg concentrations between skin and liver of Dall's porpoises
(Phocoenoides dalli) suggested that skin can be used as
a surrogate tool for monitoring hepatic Hg concentrations
(Yang et al., 2002). Various biological and ecological
factors including geographic area, age, gender, diet, tissue
type, metabolic rate and temporal distribution may also
influence the potential accumulation of trace elements
(O'Hara et al., 2003). Our study is the first to report
several trace elements including Ba, Be, Li, Sb, Sn, Tl and
U levels in skin tissue of bottlenose dolphin populations.
4. Discussion
4.1. Hg and Se
Exposure pathways for the uptake of trace elements in
marine mammals may occur via the lung, skin, diet,
placental transfer and milk. However, many studies
suggest that diet is the major entry route of elements in
Mercury is one of the most toxic elements in marine
mammals because of its bioaccumulation and biomagnification through the marine food chains (Das et al., 2003).
Table 4
Statistical summary of the trace element concentrations in skin of different age and gender groups of CHS and IRL bottlenose dolphins
Juvenile male
Al
As
Ba
Be
Cd
Co
Cr
Cu
Fe
Li
Mn
Ni
Pb
Sb
Se
Sn
THg
Tl
U
V
Zn
CHS N IRL (p = 0.031)
CHS N IRL (p = 0.003)
n.s.
n.s.
n.s.
CHS N IRL (p = 0.009)
n.s.
n.s.
n.s.
n.s.
CHS N IRL (p = 0.022)
n.s.
CHS N IRL (p = 0.005)
CHS N IRL (p = 0.004)
CHS N IRL (p = 0.040)
n.s.
IRL N CHS (p = 0.002)
CHS N IRL (p = 0.001)
n.s.
n.s.
n.s.
Adult male
Juvenile female
Adult female
Total
n.s.
CHS N IRL (p b 0.001)
n.s.
n.s.
n.s.
CHS N IRL (p b 0.001)
n.s.
n.s.
n.s.
n.s.
CHS N IRL (p = 0.014)
n.s.
CHS N IRL (p = 0.008)
CHS N IRL (p = 0.002)
CHS N IRL (p b 0.001)
n.s.
IRL N CHS (p b 0.001)
CHS N IRL (p = 0.002)
n.s.
n.s.
n.s.
n.s.
CHS N IRL (p b 0.001)
n.s.
n.s.
CHS N IRL (p = 0.043)
CHS N IRL (p = 0.001)
n.s.
CHS N IRL (p = 0.034)
n.s.
n.s.
CHS N IRL (p = 0.0028)
n.s.
CHS N IRL (p = 0.001)
CHS N IRL (p = 0.008)
CHS N IRL (p = 0.009)
CHS N IRL (p = 0.015)
IRL N CHS (p = 0.009)
CHS N IRL (p = 0.001)
CHS N IRL (p = 0.018)
n.s.
n.s.
n.s.
CHS N IRL (p = 0.001)
n.s.
–
n.s.
CHS N IRL (p = 0.001)
n.s.
n.s.
n.s.
–
n.s.
n.s.
n.s.
CHS N IRL (p = 0.016)
CHS N IRL (p = 0.005)
n.s.
IRL N CHS (p = 0.010)
CHS N IRL (p = 0.017)
n.s.
IRL N CHS (p = 0.013)
n.s.
CHS N IRL (p = 0.033)
CHS N IRL (p b 0.001)
n.s.
n.s.
CHS N IRL (p = 0.030)
CHS N IRL (p b 0.001)
n.s.
CHS N IRL (p = 0.012)
n.s.
CHS N IRL (p = 0.004)
CHS N IRL (p b 0.001)
n.s.
CHS N IRL (p b 0.001)
CHS N IRL (p b 0.001)
CHS N IRL (p b 0.001)
CHS N IRL (p = 0.023)
IRL N CHS (p b 0.001)
CHS N IRL (p b 0.001)
n.s.
n.s.
CHS N IRL (p = 0.011)
n.s.: non significant;–: no data for comparison.
Author's personal copy
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
309
Table 5
Concentrations of methylmercury and total mercury (mean ± SD; μg/g wet weight) in skin samples of CHS and IRL dolphins
n
MeHg
Total mercury
MeHg/THg
R2⁎
p value⁎
CHS
17
0.84
0.001
Total
24
72% ± 13%
(43%–96%)
73% ± 16%
(56%–100%)
73% ± 14%
(43%–100%)
b0.001
8
0.495 ± 0.294
(0.195–1.445)
1.600 ± 0.850
(0.541–3.052)
0.848 ± 0.738
(0.195–3.052)
0.88
IRL
0.343 ± 0.178
(0.173–0.904)
1.172 ± 0.687
(0.581–2.650)
0.608 ± 0.561
(0.173–2.650)
0.92
b0.001
⁎R2 and p value were calculated by linear regression with MeHg as y-axis and THg as x-axis for CHS (n = 16) and IRL (n = 8).
Concentrations of THg in the internal organs and muscle
tissue of marine mammals in the U.S. National Monitoring Specimen Bank showed the greatest variability with
ranges of several orders of magnitude (Becker et al.,
1997). The only significant route reported for Hg intake in
captive dolphins is food (Nigro et al., 2002). Although the
mean age of CHS dolphins (14 yrs) was significantly
greater than those of IRL animals (11 yrs), mean THg
concentration in CHS dolphins were about five times
lower than those in IRL dolphins (Tables 2 and 3). For
adult males, mean THg level in CHS dolphins was
approximately four times lower than those in IRL
dolphins. This disparity suggests that these two populations likely consume prey with different THg body
burdens. Adams et al. (2003) reported that mean THg
concentrations (wet weight) in six fish species collected
from the IRL ranged from 3 to 12 times higher than those
determined in this study (Table 6). Atmospheric deposition is a significant source of Hg to aquatic environment.
Consistently higher wet deposition of mercury was
reported in Florida (Fulkerson and Nnadi, 2006), when
compared to South Carolina (NADP, 2004). Thus, it is
likely that dolphins in the IRL may be exposed to higher
dietary THg levels which contribute to the higher THg
levels in IRL dolphins.
Mercury is also known to accumulate in different
tissues and organs dependent upon the age or size of
marine mammals. Age is considered the most important
parameter for accumulation of Hg and Cd in the upper
level predators at the individual scale, while feeding
preference is probably the key factor controlling these
two elements at the population scale (Bustamante et al.,
2004; Lahaye et al., 2006). A positive relationship of
THg in skin with increasing ages was reported in Dall's
porpoises (Yang et al., 2002). Of the two populations in
this study, only the CHS dolphins exhibited a positive
relationship between THg in skin and age (Fig. 3). In
addition, adult CHS female dolphins exhibit higher THg
than juvenile females (Table 2). Both dolphin populations show high site-fidelity to these areas as documented by photo-identification studies in these two sites
(Zolman 2002; Mazzoil et al., 2005; Speakman et al.,
2006). The IRL site is an extensive ecosystem which
extends 250 km and dolphins were captured in both the
southern and northern ranges (Fig. 2). It may be possible
that different dietary exposures may exist within IRL
which could have obscured finding similar correlations
between THg and the dolphins' age. Further investigation on fatty acid and stable isotopes profiles of these
dolphins and their prey items in the foraging habitats
may assist in explaining the association of THg levels
and IRL dolphins' age.
A summary of trace element concentrations in skin
tissue of bottlenose dolphin from different geographic
locations is shown in Table 7. Data from Frodello and
Marchand (2001), Roditi-Elasar et al. (2003) and Bryan
(2006), which were originally presented on a wet weight
basis, have been converted to an approximate dry
Table 6
Concentrations of THg (μg/g wet weight) in fish species reported in the Charleston and Indian River Lagoon
CHS
IRL
Cynoscion
nebulosus
Micropogonias
undulates
Scianops
ocellatus
Leiostomus
xanthurus
Mugil
cephalus
Lagodon
rhomboid
(Spotted seatrout)
(Atlantic croaker)
(Red drum)
(Spot)
(Striped mullet)
(Pinfish)
0.095
(0.052–0.127)
0.47
(0.02–1.70)
0.019
(0.005–0.043)
0.06
(0.02–0.18)
0.033
(0.028–0.038)
0.37
(0.02–2.20)
0.023
(0.015–0.036)
0.12
(0.02–0.36)
0.005
(0.004–0.005)
0.06
(0.02–0.24)
0.034
(0.026–0.049)
0.34
(0.19–0.55)
Reference
This study
Adams et al.
(2003)
Author's personal copy
310
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
Table 7
Comparison of trace element concentrations (μg/g dry weight) in skin tissues and liver of bottlenose dolphins from different locations
Location
Tissue
West Atlantic a
Corsican coast b
Israel coast c
Sarasota, FL d
CHS, SC e
IRL, FL e
CHS, SC f
(n = 2)
(n = 7)
(n = 13)
(n = 40)
(n = 74)
(n = 75)
(n = 34)
Skin
Skin
Skin
Skin
Skin
Skin
Liver
0.59 ± 0.33
(0.13–1.15)
2.42 ± 1.36
(0.52–6.8)
1.05 ± 0.54
(0.45–2.92)
0.003 ± 0.003
(0.001–0.013)
3.6 ± 1.68
(1.0–7.3)
0.46 ± 0.32
(0.07–1.5)
2.0 ± 0.81
(1.2–4.4)
8.4 ± 21
(0.96–157)
2.2 ± 0.84
(0.57–4.4)
0.012 ± 0.004
(0.005–0.022)
0.60 ± 0.30
(0.15–1.6)
0.91 ± 0.38
(0.36–2.2)
1.6 ± 0.33
(0.86–2.4)
183 ± 358
(14–1438)
0.63 ± 0.39
(0.07–3.7)
0.06 ± 0.05
(0.01–0.29)
1.7 ± 0.92
(0.65–4.9)
0.34 ± 0.27
(0.04–1.0)
24 ± 7.6
(11–44)
590 ± 206
(305–1471)
3.1 ± 1.6
(0.77–7.4)
0.76 ± 0.26
(0.26–1.5)
0.010 ± 0.007
(0.003–0.037)
0.24 ± 0.13
(0.05–0.71)
0.89 ± 0.33
(0.08–1.7)
1.4 ± 0.70
(0.71–2.3)
87 ± 113
(23–565)
0.41 ± 0.13
(0.21–0.96)
0.05 ± 0.09
(0.01–0.57)
7.0 ± 5.9
(0.33–31)
0.14 ± 0.11
(0.03–0.65)
17 ± 6.0
(2.4–32)
687 ± 251
(272–1586)
Al
As
2.8 ± 1.7
(1.1–4.5)
Cd
Co
0.36
(0.13–0.66)
3.1 ± 1.0
(2.4–3.8)
Cr
Cu
Fe
Mn
Ni
Hg
Pb
Se
Zn
5.9 ± 1.0
(7.2–8.6)
40 ± 5.0
(38–41)
3.5 ± 0.2
(3.4–3.6)
2.1 ± 0.4
(1.8–2.4)
11.6 ± 4.5
(5.0–12.3)
5.2 ± 3.6
(2.6–7.7)
60 ± 9.0
(55–66)
180 ± 30
(80–222)
11.2
(2.3–18.5)
165 ± 139
(31–452)
0.18 ± 0.07
(0.09–0.45)
13.9 ± 9.9
(0.89–33)
10.6
(3.0–33)
1541
(280–3653)
1528 ± 2185
(12–8616)
7.0 ± 5.1
(1.2–21)
0.056 ± 0.076
(0.007–0.287)
18 ± 6.7
(6.6–32)
465 ± 139
(264–822)
0.95 ± 0.95
(b0.33–5.4)
0.173 ± 0.218
(b0.34–0.93)
37 ± 50
(4.0–268)
60 ± 94
(b1.7–498)
b0.34
32 ± 41
(0.6–160)
193 ± 174
(39–921)
Data are expressed as mean ± standard deviation with ranges given in parentheses.
a
Carvalho et al. (2002).
b
Frodello and Marchand (2001).
c
Roditi-Elasar et al. (2003).
d
Bryan (2006).
e
Present study.
f
Beck et al. (1997).
weight basis using the factor of 3.3 as determined in skin
tissue from this study. Trace element concentrations
reported in liver of stranded bottlenose dolphins (Beck
et al., 1997) have been converted to dry weight basis
using a factor of 3.4 as determined by Yang and
Miyazaki (2003). Total Hg levels found in skin samples
from CHS and IRL dolphins were within the ranges of
other reported studies (Table 7). Higher THg levels are
usually found in the liver tissue of marine mammals
compared to those found in skin tissue (Roditi-Elasar
et al., 2003; Yang et al., 2006).
Das et al. (2003) suggested that THg is not an
appropriate indicator for Hg toxic effects on marine
mammals because its organic compound (e.g. methylmercury, MeHg) is more toxic. The result of an in vitro
study of mercury-induced micronuclei frequency in skin
fibroblasts of beluga whales (Delphinapterus leucas)
were found at MeHg levels of 0.05 and 0.5 μg/ml which
are comparable to concentrations present in beluga
whales. These MeHg levels may be partly responsible
for the high incidence of cancer observed in this
population (Gauthier et al., 1998). In our study, MeHg
levels in skin tissue of IRL dolphins may also have
affected micronuclei frequency in skin fibroblasts since
the levels (1.17 μg/g dry weight) found were much
higher than those detected in beluga whales. Additional
research on MeHg exposure to dolphin skin cells may
provide information on the toxicity of MeHg contamination in bottlenose dolphin populations.
Wagemann et al. (1998) and Dehn et al. (2006)
reported a MeHg/THg ratio about 90% for skin tissue of
cetaceans and pinnipeds which is higher than those
found in skin tissue of bottlenose dolphins in the present
study (Table 5). Although significantly higher MeHg
Author's personal copy
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
skin levels were found in IRL dolphins, similar MeHg/
THg ratios were found between CHS and IRL dolphins.
Becker et al. (2000) determined that the highest
percentage of MeHg occurs at the low end of THg in
the liver of Alaska beluga whales. Their study suggested
that a threshold concentration of MeHg may exist in the
liver of Alaska beluga whales, above which MeHg no
longer accumulates in this organ. In our study (Table 5),
MeHg levels in CHS and IRL dolphins appeared to
increase with THg concentrations suggesting that either
a threshold concentration of MeHg in skin tissue has not
been reached or that a methylation mechanism may exist
in this tissue. Another study has suggested that that the
epidermis of cetaceans might be a significant route of
elimination of Hg compounds (Wagemann et al., 1996).
In addition, geographic location, species, tissue, and diet
differences may also contribute to the variations in
MeHg/THg ratio. Further investigations are needed to
identify mercuric selenide (HgSe) granules (tiemannite)
precipitation in the skin tissue as a byproduct of
demethylation of Hg (Nigro et al., 2002) and to
determine whether body burden concentrations of
MeHg found in these dolphin populations may potentially cause adverse health impacts.
Numerous studies have suggested that Se has an
important role in the detoxification of Hg via formation
of HgSe complex in the liver of marine mammals
(Becker et al., 1997; Ikemoto et al., 2004; Kunito et al.,
2004; Endo et al., 2006; Yang et al., 2006). It is possible
for Se to bioaccumulate and biomagnify in some aquatic
organisms. A positive correlation between Hg and Se in
the liver has been reported in many species of marine
mammals (Becker et al., 2000) but we did not find this
relationship in the skin samples measured in this study. A
possible reason may be the fact that there is a parallel
accumulation of Se and Hg in marine mammals observed
when Hg exceeds a certain level (50 μg/g ww) (Brunborg
et al., 2006). Selenium and THg concentrations measured in the skin of bottlenose dolphins were much lower
than values previously published in cetacean skin
(Monaci et al., 1998; Carvalho et al., 2002; Kunito
et al., 2002; Yang et al., 2006).
Concentrations of Se were the third highest element
found in both CHS and IRL dolphins, although these were
also lower than those reported elsewhere (Table 7).
Selenium levels in the skin of CHS dolphins (24 μg/g dw)
were similar with those reported for dolphin liver (Beck
et al., 1997). The high levels of Se in the skin were similar
to other studies (Kunito et al., 2002; Yang et al., 2002) and
imply that Se may provide protection for dolphins against
solar ultraviolet A (UVA) radiation effects. Significantly
higher Se levels were found in CHS dolphins compared to
311
IRL dolphins in all age and gender groups (Table 4). The
results suggested that diet may be a likely factor in
explaining the differences in Se between these two
populations and Se can be used as a tracer to separate these
dolphin populations. According to the data on tissue
concentrations determined by the Mussel Watch Program
of National Status & Trends during 1986 to 2004, higher
Se concentrations were found in South Carolina (range
from 1.5 to 3.1 μg/g dry weight) than those in Florida
(range from 1.9 to 3.8 μg/g dry weight, www8.nos.noaa.
gov/cit/nsandt/download/mw_monitoring.aspx).
4.2. Essential elements: Cr, Fe, Cu and Zn
Although Cr, Fe, Cu and Zn are essential elements,
excessive concentrations of these trace elements may
cause some toxic effects (e.g. neurological, hematological, immunological and developmental) in marine
mammals. Essential element concentrations are generally
characterized by a relatively narrow range within a species
indicating these elements are well regulated or have
relatively short biological half-lives (Becker et al., 1997).
The Cr concentration in liver tissue is usually less than
1.0 μg/g ww in marine mammals (Beck et al., 1997)
although very limited information exists for Cr in marine
mammals, especially in skin tissue (Bryan, 2006; Yang
et al., 2006), which is probably because Cr bioaccumulates poorly in mammalian tissue (Thompson, 1990). In
our study, Cr levels in skin tissue of dolphins were similar
to that reported in dolphin populations from Florida
(Table 7). No differences in Cr levels occurred between
adult male CHS and IRL dolphins, although there is a
highly contaminated Cr site located at Shipyard Creek,
North Charleston near the CHS area (Fulton et al., 2006).
It is possible that Cr may be effectively regulated or
perhaps the elevated Cr concentrations in CHS site were
in a chemical form unavailable for absorption through
ingestion in dolphins. Yang et al. (2002) suggested that Cr
in the skin of Dall's porpoises was probably not in the
hexavalent form, as this would cause dermatitis and
allergic skin reactions. Speciation of Cr is needed to
evaluate potential toxic effects in marine mammals.
Limited data is available for Fe in the skin tissue of
marine mammals (Carvalho et al., 2002; Roditi-Elasar
et al., 2003; Yang et al., 2006). Iron concentrations were
the second highest element in skin samples collected from
CHS and IRL dolphins. These levels were higher than
other reports in bottlenose dolphin skin (Table 7) but still
lower than that reported in liver of marine mammals (Beck
et al., 1997; Zhou et al., 2001; Carvalho et al., 2002). No
gender or age differences were found within and between
CHS and IRL dolphins for Fe. The element measured at
Author's personal copy
312
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
highest concentration in this study was Zn. Higher Fe and
Zn concentrations were also found in previous studies
(Table 7). It has been suggested that the liver is a target
organ for accumulation of Fe and Zn, while skin is a target
tissue for Se and Zn (Yang et al., 2006). Similar to Fe, no
gender or age differences were found in Zn skin
concentrations within and between CHS and IRL dolphins.
Copper has been discussed extensively in association
with Fe and Zn in marine mammals, especially its
relationship to metallothioneins (MT), a protein involving
essential element homeostasis (Das et al., 2006; Yang et al.,
2006). Significantly higher Cu concentrations were found
in pregnant CHS dolphins compared to non-pregnant
female dolphins (Table 2) suggesting that Cu may be
required for growth and development of the embryo (Eisler
1998). In humans, Cu and ceruloplasmin (a blue multicopper oxidase that contains N 65% of the copper found in
serum in vertebrate species) serum concentrations rise
significantly during the pregnancy resulting from an
increase in retention of dietary Cu by the pregnant mother
(McArdle, 1995; Uauy et al., 1998). However, more
samples from pregnant females will be needed to determine
Cu requirements for reproductive processes in dolphins.
Decreasing Cu and Zn concentrations with age were
found in CHS dolphins (Fig. 3) which is similar to other
studies that examined element concentrations in cetacean liver (Zhou et al., 2001). Another study suggested
that these higher Cu and Zn concentrations in juveniles
might relate to a biochemical requirement in newborns
or a very low excretion rate of these elements by the
fetus (Wagemann et al., 1988). Marine mammals usually
contain less than 44 μg/kg dry weight of Cu in tissue,
except for liver (Eisler, 1998). Higher Cu levels were
usually found in liver compared to skin tissue in the
dolphins (Roditi-Elasar et al., 2003; Yang et al., 2006).
In the present study, Cu concentrations in skin were
lower than values previously published for skin and
liver (Table 7). Similar to Fe and Zn, no gender difference was found for Cu between CHS and IRL
dolphins.
4.3. Other trace elements
Arsenic is a potentially toxic element for which there
is limited marine mammal data, especially in skin tissue
(Carvalho et al., 2002; Bryan, 2006). Similar to Hg, the
major route of As in marine mammals is thought to be
through the diet (Kubota et al., 2001). Finding
significantly higher As skin concentrations in IRL
adult male dolphins compared to juvenile males and
females was consistent with other skin (Carvalho et al.,
2002) and liver (Kubota et al., 2001) studies of marine
mammals. Hepatic As concentrations in cetacean liver
were generally found to be less than 1.0 μg/g wet weight
(Becker et al., 1997). Dolphins from CHS showed twice
the levels of As concentrations in the skin as those
reported in livers of dolphins stranded in South Carolina
(Table 7) although data were reported for a different
time period. Significantly higher As levels were found
in adult males from CHS than those from IRL dolphins
(Table 4) indicating that this element may also be used
as a potential tracer to separate these dolphin
populations.
The present study was the first report for several trace
elements (Ba, Be, Li, Sb, Sn, Tl, U) concentrations of
that have not often been measured in marine mammal
skin. The objective of this study was to compare
baseline data for trace elements in bottlenose dolphins at
the CHS and IRL sites for future monitoring purposes
and to compare these trace element concentrations to
other studies published for dolphin populations. Toxic
elements, such as Cd and Pb and other potential toxic
elements, such as Co, Ni and V, were also included in
this study, but their concentrations were much lower
than other reported studies of skin tissue (Table 7). Some
element levels measured were less than 1.0 μg/g (Ba,
Co, Li, Mn, Pb, Sb, Sn, Tl, U, V) or even 0.1 μg/g (Be,
Cd, Ni) dry weight, except for Al. Both CHS and IRL
dolphins had higher Al skin levels than those reported in
the skin of dolphins from Sarasota, FL (Table 7). These
concentration differences may be related to dietary Al
levels within their feeding locations. Very limited data is
available for Al concentrations in marine mammals.
Average hepatic Al concentrations in liver and kidney
tissues of cetaceans and pinnipedes ranged from
approximately 1.0 to 17 μg/g dry weight (Tilbury
et al., 2001; Bustamante et al., 2003). Significant
differences in concentrations of several trace elements
(Co, Mn, Sb and Tl) were found between CHS and IRL
adult male dolphins and these elements may be used as
potential tracers to discriminate these dolphin populations (Table 4). Skin concentrations were similar
between CHS and IRL dolphins for Ba, Be, Cr, Fe
and Ni, regardless of age or gender (Table 4).
In our study, Cd, Co, Mn, Ni and Pb concentrations
measured in skin tissue were generally lower than those
reported elsewhere for skin and liver tissues of
bottlenose dolphins (Table 7). Therefore, these elements
are not likely to have significant toxicological impacts
on the dolphin populations in this study. Geographic
location has been proposed to be an important determinant factor in trace element concentration differences
for skin tissue (Frodello and Marchand, 2001; Kunito
et al., 2002). Other studies use skin tissue to predict
Author's personal copy
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
several trace elements in internal organs or to discriminate between different populations (Monaci et al., 1998;
Kunito et al., 2002; Yang et al., 2002). However, both
prey availability and quantity as well as dolphin growth
rate in different population may also cause these
concentration disparities. For example, younger dolphins appear to have higher Mn level than older ones
(Figs. 3 and 4). Similar trends were also found for Pb and
U in CHS dolphins (Fig. 3). In adult males, higher
Mn, Co, Sb and Tl concentrations were found in the
skin tissue of CHS dolphins than that in IRL dolphins
(Table 4). Since very limited data of these trace element
concentrations in prey species exist in CHS and IRL
at the same temporal period, it is difficult to offer a
conclusive statement that geographic location is a contributing factor to these element concentration differences in the skin tissue of bottlenose dolphins.
5. Conclusion
The present study provides the largest trace element
data set for free-ranging bottlenose dolphins using
biopsied skin tissue. Trace element concentrations in
dolphin skin tissue reported herein were within the ranges
of other published studies. Skin was utilized as a nonlethal surrogate tissue for measuring trace elements and
based on different levels between CHS and IRL dolphins,
several elements (As, Co, Sb, Se, THg and Tl) may
possibly be used to discriminate these two dolphin
populations and probably other populations. Geographic
location appears to be a more important factor compared
to the biological parameters such as age and length of
dolphins when accounting for trace element concentration
differences in this study, especially for THg and MeHg.
Only skin accumulation of THg was found to positively
correlate with the age of CHS dolphins while other
elements such as Cu, Pb, Mn, U and Zn showed inverse
trends. Of all elements measured in this study, significantly higher levels of Fe, Se and Zn concentrations found
in skin tissue were consistent with levels reported in other
studies. Several of the trace elements (Ba, Be and U)
presented in this study are the first published data for
marine mammal skin. Additional research on element
concentrations, stable isotopes and fatty acid profiles in
prey species is needed to establish potential trophic
transfer pathways for the bottlenose dolphins. It will be
also interesting to broaden the scope of research on the
correlation of trace element concentrations between skin
and internal organs of stranded dolphins to evaluate using
epidermis-based prediction of trace element concentrations in these key tissues. Further examination of the
relationship between element concentrations and health
313
status (i.e. hematology and immunology), element
speciation and bioavailability will further our understanding on the role of trace elements and their potential
adverse impacts on these free-ranging bottlenose dolphins. It is important to assess trace element body burden
and their potential impacts on the health of bottlenose
dolphins to better inform the development of management
and conservation strategies in coastal ecosystems.
Acknowledgements
This study was conducted under National Marine
Fisheries Permit No. 998-1678, issued to Gregory
Bossart, V.M.D., Ph.D., of Harbor Branch Oceanographic Institution (HBOI) in March 2003. The authors
would like to thank the numerous researchers and
marine mammal specialists representing many institutions including NOAA and HBOI who participated in
the field study of dolphins at South Carolina and
Florida. We also would like to thank, Drs. Mike Fulton,
Ed Wirth and R.H. Defran and Mr. Wayne McFee for
reviewing this manuscript. We specially thank the
NOAA/NCCOS/CCEHBR Marine Ecotoxicology
Branch for providing analytical instrumentation. A
special thanks to Mr. Wayne McFee for conducting
analyses of dental enamel to estimate age of dolphin and
Mr. Jeff Adams for maps. This study was supported
through NOAA Fisheries Marine Mammal Health and
Stranding Response Program, NOAA/NCCOS/
CCEHBR and also the Florida Protect Wild Dolphins
License Plate Fund. This research was performed while
the author held a National Research Council Research
Associateship Award at NOAA/NCCOS/CCEHBR.
References
Adams DH, McMichael Jr RH, Henderson GE. Mercury levels in
marine and estuarine fishes of Florida 1989–2001. Florida marine
research institute technical report TR-9; 2003.
Atwell L, Hobson KA, Welch HE. Biomagnification and bioaccumulation of mercury in an arctic marine food web: insights from
stable nitrogen isotope analysis. Can J Fish Aquat Sci 1998;55:
1114–21.
Barros NB, Odell DK. Food habits of bottlenose dolphins in the
Southeastern United States. In: Leatherwood S, Reeves RR,
editors. The bottlenose dolphin. Academic Press; 1990. p. 309–28.
Barros NB, Odell DK. Bottlenose dolphin feeding and interactions
with fisheries in the Indian River Lagoon system, Florida. Bull Mar
Sci 1995;57:278–85.
Barros NB, Wells RS. Prey and feeding patterns of resident bottlenose
dolphin (Tursiops truncatus) in Sarasota Bay, Florida. 1998; 79:
1045–1049.
Beck KM, Fair PA, McFee W, Wolf D. Heavy metals concentrations in
livers of bottlenose dolphins stranded along the South Carolina
coast. Mar Pollut Bull 1997;34:734–9.
Author's personal copy
314
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
Becker PR, Mackey EA, Demiralp R, Schantz MM, Koster BJ, Wise
SA. Concentrations of chlorinated hydrocarbons and trace
elements in marine mammal tissues archived in the U.S. national
biomonitoring specimen bank. Chemosphere 1997;34:2067–98.
Becker PR, Krahn MM, Mackey EA, Demiralp R, Schantz MM,
Epstein MS, et al. Concentrations of polychlorinated biphenlys
(PCB's), chlorinated pesticides, and heavy metals and other
elements in tissues of Beluga whale, Delphinapterus leucas, from
Cook Inlet, Alaska. Mar Fish Rev 2000;62:81–98.
Booth S, Zeller D. Mercury, food webs, and marine mammals:
implications of diet and climate change for human health. Environ
Health Perspect 2005;113:521–6.
Bossart GD. Marine mammals as sentinel species for oceans and
human health. Oceanography 2006;19:44–7.
Brookens TJ, Harvey JT, O'Hara TM. Trace element concentrations in
the Pacific harbor seal (Phoca vitulina richardii) in central and
northern California. Sci Total Environ 2007;372:676–92.
Brunborg LA, Graff IE, Frøyland L, Julshamn K. Levels of nonessential elements in muscle from harp seal (Pagophilus
groenlandicus) and hooded seal (Cystophora cristata) caught in
the Greenland Sea. Sci Total Environ 2006;366:784–98.
Bryan CE. 2006. Non-lethal monitoring of trace elements in bottlenose
dolphin, Tursiops truncatus. Master thesis, College of Charleston,
Charleston, SC
Bustamante P, Garrigue C, Breau L, Caurant F, Dabin W, Greaves J, et al.
Trace elements in two odontocete species (Kogia breviceps and
Globicephala macrorhynchus) stranded in New Caledonia (South
Pacific). Environ Pollut 2003;124:263–71.
Bustamante P, Morales CF, Mikkelsen B, Dam M, Caurant F. Trace
element bioaccumulation in grey seals Halichoerus grypus from
the Faroe Island. Mar Ecol Prog Ser 2004;267:291–301.
Carvalho M, Pereira R, Brito J. Heavy metals in soft tissues of Tursiops truncates and Delphinus delphis from west Atlantic Ocean
by X-ray spectrometry. Sci Total Environ 2002;292:247–54.
Das K, Debacker V, Pillet S, Bouquegneau JM. Heavy metals in
marine mammals. In: Vos JG, Bossart GD, Fournier M, O'Shea TJ,
editors. Toxicology of marine mammals. Taylor and Francis; 2003.
p. 135–67.
Das K, De Groof A, Jauniaux T, Holsbeek L, Bouquegneau JM. Zn, Cu,
Cd and Hg binding to metallothioneins in harbour porpoise, Phocoena phocoena from the southern North Sea. BMC Ecol 2006;6:2.
Dehn LA, Follmann EH, Thomas DL, Sheffield GG, Rosa C, Duffy LK,
et al. Trophic relationships in an Arctic food web and implications
for trace metal transfer. Sci Total Environ 2006;362: 103–23.
Eisler R. Copper hazards to fish, wildlife and invertebrates: a synoptic
review. U.S. geological survey, biological resources division,
biological science report USGS/BRD/BSR 1997-0002; 1998.
Endo T, Haraguchi K, Hotta Y, Hisamichi Y, Lavery S, Dalebout ML,
et al. Total mercury, methyl mercury, and selenium levels in the red
meat of small cetaceans sold for human consumption in Japan.
Environ Sci Technol 2005;39:5703–8.
Endo T, Kimura O, Hisamichi Y, Minoshima Y, Haraguchi K,
Kakumoto C, et al. Distribution of total mercury, methyl mercury
and selenium in pod of killer whales (Orcinus orca) stranded in the
northern area of Japan: comparison of mature females with calves.
Environ Pollut 2006;144:145–50.
EPA Method 1630. Methyl mercury in water by distillation, aqueous
ethylation, purge and trap, and CVAVS. EPA-821-R-01-020.; 2001.
Fair PA, Becker PR. Review of stress in marine mammals. J Aquat
Ecosyst Stress Recovery 2000;7:335–54.
Fair PA, Adams JD, Zolman E, McCulloch SD, Goldstein JD,
Murdoch ME, et al. Protocols for conducting dolphin capture–
release health assessment studies. NOAA tech memo NOS
NCCOS 49; 2006.
Fossi MC, Marsili L. The use of non-destructive biomarkers in the
study of the marine mammals. Biomarkers 1997;2:205–16.
Fossi MC, Marsili L, Neri G, Casini S, Bearzi G, Politi E, et al. Skin
biopsy of Mediterranean cetaceans for investigation of interspecies
susceptibility to xenbiotic contaminants. Mar Environ Res 2000;50:
517–21.
Fossi MC, Marsili L, Lauriano G, Fortuna C, Canese S, Ancora S, et al.
Assessment of toxicological status of a SW Mediterranean
segment population of striped dolphin (Stenella coeruleoalba)
using skin biopsy. Mar Environ Res 2004;58:269–74.
Frodello JP, Marchand B. Cadmium, copper, lead and zinc in five
toothed whales species of the Mediterranean Sea. Int J Toxicol
2001;20:339–43.
Fulkerson M, Nnadi FN. Predicting mercury wet deposition in Florida:
a simple approach. Atmos Environ 2006;40:3962–8.
Fulton M, Key P, Wirth E, Leight AK, Daugomah J, Bearden D, et al.
An evaluation of contaminated estuarine sites using sediment
quality guidelines and ecological assessment methodologies.
Ecotoxicology 2006;15:573–81.
Gannon DP, Waples DM. Diets of coastal bottlenose dolphins from the
U.S. mid-Atlantic coast differ by habitat. Mar Mamm Sci 2004;20:
527–45.
Gauthier JM, Dubeau H, Rassart E. Mercury-induced micronuclei in
skin fibroblasts of Beluga whales. Environ Toxicol Chem 1998;17:
2487–93.
Hansen LJ, Wells RS. Bottlenose dolphin health assessment: field
report on sampling near Beaufort, North Carolina, during July
1995. NOAA Tech Memo NMFS-SEFSC-382, 1996.
Hick BD, St. Aubin DJ, Geraci JR, Brown WR. Epidermal growth in
the bottlenose dolphin, Tursiops truncatus. J Invest Dermatol
1985;85:60–93.
Holsbeek L, Siebert U, Joiris C. Heavy metals in dolphins stranded of
the French Atlantic coast. Sci Total Environ 1998;217:241–9.
Hohn AA, Scott MD, Wells RS, Sweeney J, Irvine AB. Groeth layers
in teeth from wild, known-age bottlenose dolphins. Mar Mamm
Sci 1989;5:315–42.
Ikemoto T, Kunito T, Tanaka H, Baba N, Miyazaki N, Tanabe S.
Detoxification mechanisms of heavy metals in marine mammals
and seabirds: Interaction of selenium with mercury, silver, copper,
zinc, and cadmium in liver. Arch Environ Contam Toxicol 2004;47:
402–13.
Kubota R, Kunito T, Tanabe S. Arsenic accumulation in the liver tissue
of marine mammals. Environ Pollut 2001;15:303–12.
Kubota R, Kunito T, Tanabe S. Chemical speciation of arsenic in the
livers of higher troophic marine animals. Mar Pollut Bull
2002;45:218–23.
Kubota R, Kunito T, Tanabe S. Occurrence of several arsenic
compounds in the livers of birds, cetaceans, pinnipeds, and sea
turtles. Environ Toxicol Chem 2003;22:1200–7.
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
1994;28:1245–53.
Kuehl DW, Haebler R. Organochlorine, organobromine, metal, and
selenium residues in bottlenose dolphins (Tursiops truncatus)
collected during an unusual mortality event in the Gulf of Mexico,
1990. Arch Environ Contam Toxicol 1995;28:494–9.
Kunito T, Watanabe I, Yasunaga G, Fujise Y, Tanabe S. Using trace
elements in skin to discriminate the populations of minke whales in
southern hemisphere. Mar Environ Res 2002;53:175–97.
Author's personal copy
H.-C.W. Stavros et al. / Science of the Total Environment 388 (2007) 300–315
Kunito T, Nakamura S, Ikemoto T, Anan Y, Kubota R, Tanabe S, et al.
Concentration and subcellular distribution of trace elements in
liver of small cetaceans incidentally caught along the Brazilian
coast. Mar Pollut Bull 2004;49:574–87.
Lahaye V, Bustamante P, Dabin W, Van Canneyt O, Dhermain F, Cesarini
C, et al. New insights from age determination on toxic element
accumulation in striped and bottlenose dolphins from Atlantic and
Mediterranean waters. Mar Pollut Bull 2006;52: 1219–30.
Law RJ. Metals in marine mammals. In: Beyer WN, Heinz GH,
Redmon-Norwood AW, editors. Environmental contaminants in
wildlife: interpreting tissue concentrations. CRC Press; 1996.
p. 357–76.
Mazzoil M, McCulloch SD, Defran RH. Observations on the site
fidelity of bottlenose dolphins (Tursiops truncatus) in the Indian
River Lagoon, Florida. Fla Sci 2005;68:217–27.
Marine mammal commission annual report to congress 2001.
Marine mammal commission annual report to congress 2005.
McArdle HJ. The metabolism of copper during pregnancy — a review.
Food Chem 1995;54:79–84.
Meador JP, Ernest D, Hohn AA, Tilbury K, Gorzelany J, Worthy G,
et al. Comparison of elements in bottlenose dolphins stranded on
the beaches of Texas and Florida in the Gulf of Mexico over a
one-year period. Arch Environ Contam Toxicol 1999;36:87–98.
Monaci F, Borrel A, Leonzio C, Marsili L, Calzada N. Trace metals in
striped dolphins (Stenella coeruleoalba) from the western
Mediterranean. Environ Pollut 1998;99:61–8.
NADP. MDN concentration and deposition maps. Illinois state water
survey, Champaign, IL; 2004. http://nadp.sws.uiuc.edu/mdn/maps/
2004/04MDNconc.pdf (accessed 27.06.2007).
Nigro M, Campana A, Lanzillota E, Ferrara R. Mercury exposure and
elimination in captive bottlenose dolphins. Mar Pollut Bull
2002;44:1071–5.
O'Hara TM, Woshner V, Bratton G. Inorganic pollutants in Arctic
marine mammals. In: Vos JG, Bossart GD, Fournier M, O'Shea TJ,
editors. Toxicology of marine mammals. Taylor and Francis; 2003.
p. 206–46.
Recks MA. An investigation into the use of blubber fatty acid profiles as a
means to determine dietary history of bottlenose dolphins (Tursiops
truncatus) in estuarine and nearshore coastal waters around
Charleston, South Carolina. MS Thesis, College of Charleston 2004.
Roditi-Elasar M, Kerem D, Hornung H, Kress N, Shoham-Frider E,
Goffman O, et al. Heavy metal levels in bottlenose and striped
dolphins off the Mediterranean coast of Israel. Mar Pollut Bull
2003;46:491–512.
Ross P, Swart RD, Addison R, Loveren HV, Vos J, Osterhaus A.
Contaminant-induced immunotoxicity in harbour seals: wildlife at
risk? Toxicology 1996;112:157–69.
Ross P. The role of immunotoxic environmental contaminants in
facilitating the emergence of infectious diseases in marine
mammals. Hum Ecol Risk Assess 2000;8:277–92.
Scott GP, Burn DM, Hansen LJ. The dolphin die-off: long-term effects
and recovery of the population. OCEANS '88. A partnership of
marine interests proceedings; 1988.
Shoham-Frider E, Amiel S, Roditi-Elasar M, Kress N. Risso's dolphin
(Grampus griseus) stranding on the coast of Israel (eastern
Mediterranean). Autopsy results and trace metal concentrations.
Sci Total Environ 2002;295:157–66.
Speakman T, Zolman E, Adams J, Defran RH, Laska D, Schwacke L,
et al. Temporal and spatial aspects of bottlenose dolphin occurrence
315
in coastal and estuarine waters near Charleston, South Carolina.
NOAA Tech Memo NOS NCCOS 37, 2006.
Thompson DR. Heavy metals in marine vertebrates. In: Furness RW,
Rainbow PS, editors. Heavy metal in the marine environment.
CRC Press; 1990. p. 143–82.
Tilbury K, Stein JE, Krone CA, Brownell Jr RL, Blokhin SA, Bolton
JL, et al. Chemical contaminants in juvenile grey whales
(Eschrichtius robustus) from a subsistence harvest in Arctic
feeding grounds. Chemosphere 2001;47:555–64.
Uauy R, Olivares M, Gonzalez M. Essentiality of copper in humans.
Am J Clin Nutr 1998;67:952S–9S.
Wagemann R, Stewart REA, Lockhart WL, Stewart BE, Povoledo M.
Trace metals and methyl mercury: associations and transfer in
harp seal (Phoca geoenlandica) mothers and their pups. 1988; 4:
339–355.
Wagemann R, Innes S, Richard PR. Overview and regional and
temporal differences of heavy metals in Arctic whales and
ringed seals in the Canadian Arctic. Sci Total Environ 1996;186:
41–66.
Wagemann R, Trebacz E, Boila G, Lockhart WL. Methylmercury and
total mercury in tissues of arctic marine mammals. Sci Total
Environ 1998;218:19–31.
Wagemann R, Kozlowska H. Mercury distribution in skin of the
beluga (Delphinapterus leucas) and narwhal (Monodon monoceros) from the Canadian Arctic and mercury burdens and
excretion by moulting. Sci Total Environ 2005;351–352:333–43.
Walker JL, Potter CW, Macko SA. The diets of modern and historic
bottlenose dolphin populations reflected through stable isotopes.
Mar Mamm Sci 1999;15:335–50.
Watanabe I, Ichihashi H, Tanabe S, Amano M, Miyazaki N, Petrov E,
et al. Trace element accumulation in Baikal seal (Phoca sibirica)
from the Lake Baikal. Environ Pollut 1996;94:169–79.
Wells RS, Rhinehart HL, Hansen LJ, Sweeny JC, Townsend FI, Stone R,
et al. Bottlenose dolphins as marine ecosystem sentinels: developing
a health monitoring system. Eco-Health 2004;1:246–54.
Yang J, Kunito T, Tanabe S, Amano M, Miyazaki N. Trace elements in
skin of Dall's porpoises (Phocoenoides dalli) from the northern
waters of Japan: an evaluation for utilization as non-lethal tracers.
Mar Pollut Bull 2002;45:230–6.
Yang J, Miyazaki N. Moisture content in Dall's porpoise (Phocoenoides
dalli) tissues: a reference base for conversion factors between dry and
wet weight trace element concentrations in cetaceans. Environ Pollut
2003;121:345–7.
Yang J, Miyazaki N, Kunito T, Tanabe S. Trace elements and butyltins
in a Dall's porpoises (Phocoenoides dalli) from the Sanriku coast
of Japan. Chemosphere 2006;63:449–57.
Zhou L, Salvador SM, Liu YP, Sequeira M. Heavy metals in the tissues
of common dolphins (Delphinus delphis) stranded on the
Portuguese coast. Sci Total Environ 2001;273:61–76.
Zolman ES. Residence patterns of bottlenose dolphins (Tursiops
truncatus) in the Stono River estuary, Charleston County, South
Carolina, USA. Mar Mamm Sci 2002;18:879–92.