170
The Biology of Sea Turtles, Vol. II
the specific contaminant. Manufactured chemicals released into the environment
may act as endocrine-disrupting contaminants, affect tumor growth, depress immune
function, or be acutely or chronically toxic. Two of the most significant groups of
chemical stressors are the heavy metals and organopesticides.
6.3.2.1 Bioaccumulation
6.3.2.1.1 Heavy Metals
Despite the high toxicity of some compounds such as methylmercury, there is a
relative paucity of data either for contaminated animals or for normal ranges (of
trace elements) in tissues (for a review, see Pugh and Becker, 2001). In general,
concentrations of heavy metals and trace elements appear to be lower in sea turtle
tissues (by as much as one to two orders of magnitude) than values reported for
marine birds and mammals, which may be a function of differences in their metabolic rates. Studies on liver concentrations of mercury indicate a correlation
between diet and mercury accumulation, such as occurs in piscivorous marine
mammals and seabirds, with mercury levels higher in the omnivorous loggerhead
(Sakai, 1995; Storelli et al., 1998a; 1998b; Godley et al., 1999) than in herbivorous
green and jellyfish-eating leatherback turtles (Godley et al., 1999; Davenport et al.,
1990). Day et al. (2002) reported higher levels of mercury in loggerhead turtles
residing near river mouths than those from farther away. One must be wary, however,
of making assumptions based solely on trophic levels: Saeki et al. (2000) reported
the surprising finding that arsenic levels were higher in hawksbill turtles (which
consume primarily sponges) than in algae- and mollusk-eating green and loggerhead
turtles. Changes in heavy metal accumulation with age (size) within a species have
also been reported. For example, Sakai et al. (2000) found higher levels of copper
in the livers of small green turtles than in larger ones; liver cadmium was also
negatively correlated with size. They hypothesized a difference based on diet (i.e.,
life history stage), because cadmium levels are higher in the zooplankton diet of
juvenile greens than in seagrasses. No data on heavy metal burdens are available
for Kemp’s or olive ridley turtles.
6.3.2.1.2 Pesticides
Reported levels of PCBs and other organic contaminants in sea turtle tissues are
also generally an order of magnitude lower than those found in marine mammals
(Becker et al., 1997). In particular, total dichlorodiphenyltrichloroethane (DDT)
tissue concentrations in sea turtles are at the lowest end of the range reported for
marine mammals and seabirds (Pugh and Becker, 2001). However, PCB contamination in sea turtles is widespread. One frequently detected congener, PCB 153, has
been reported in the tissues of loggerheads and Kemp’s ridleys along the East Coast
of the U.S., in loggerheads and green turtles from the Mediterranean Sea, and in
leatherbacks from the United Kingdom (Lake, 1994; Rybitski et al., 1995; Mckenzie
et al., 1999). PCBs 153 and 138 were the dominant congeners detected in Hawaiian
green turtle liver and adipose tissues, with detectable amounts of the more toxic
congeners PCB 77, PCB 126, and PCB 169 (Miao et al., 2001). In these studies,
levels were higher in loggerhead and Kemp’s ridley turtles than in greens, most
1123 book.book Page 170 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
the specific contaminant. Manufactured chemicals released into the environment
may act as endocrine-disrupting contaminants, affect tumor growth, depress immune
function, or be acutely or chronically toxic. Two of the most significant groups of
chemical stressors are the heavy metals and organopesticides.
6.3.2.1 Bioaccumulation
6.3.2.1.1 Heavy Metals
Despite the high toxicity of some compounds such as methylmercury, there is a
relative paucity of data either for contaminated animals or for normal ranges (of
trace elements) in tissues (for a review, see Pugh and Becker, 2001). In general,
concentrations of heavy metals and trace elements appear to be lower in sea turtle
tissues (by as much as one to two orders of magnitude) than values reported for
marine birds and mammals, which may be a function of differences in their metabolic rates. Studies on liver concentrations of mercury indicate a correlation
between diet and mercury accumulation, such as occurs in piscivorous marine
mammals and seabirds, with mercury levels higher in the omnivorous loggerhead
(Sakai, 1995; Storelli et al., 1998a; 1998b; Godley et al., 1999) than in herbivorous
green and jellyfish-eating leatherback turtles (Godley et al., 1999; Davenport et al.,
1990). Day et al. (2002) reported higher levels of mercury in loggerhead turtles
residing near river mouths than those from farther away. One must be wary, however,
of making assumptions based solely on trophic levels: Saeki et al. (2000) reported
the surprising finding that arsenic levels were higher in hawksbill turtles (which
consume primarily sponges) than in algae- and mollusk-eating green and loggerhead
turtles. Changes in heavy metal accumulation with age (size) within a species have
also been reported. For example, Sakai et al. (2000) found higher levels of copper
in the livers of small green turtles than in larger ones; liver cadmium was also
negatively correlated with size. They hypothesized a difference based on diet (i.e.,
life history stage), because cadmium levels are higher in the zooplankton diet of
juvenile greens than in seagrasses. No data on heavy metal burdens are available
for Kemp’s or olive ridley turtles.
6.3.2.1.2 Pesticides
Reported levels of PCBs and other organic contaminants in sea turtle tissues are
also generally an order of magnitude lower than those found in marine mammals
(Becker et al., 1997). In particular, total dichlorodiphenyltrichloroethane (DDT)
tissue concentrations in sea turtles are at the lowest end of the range reported for
marine mammals and seabirds (Pugh and Becker, 2001). However, PCB contamination in sea turtles is widespread. One frequently detected congener, PCB 153, has
been reported in the tissues of loggerheads and Kemp’s ridleys along the East Coast
of the U.S., in loggerheads and green turtles from the Mediterranean Sea, and in
leatherbacks from the United Kingdom (Lake, 1994; Rybitski et al., 1995; Mckenzie
et al., 1999). PCBs 153 and 138 were the dominant congeners detected in Hawaiian
green turtle liver and adipose tissues, with detectable amounts of the more toxic
congeners PCB 77, PCB 126, and PCB 169 (Miao et al., 2001). In these studies,
levels were higher in loggerhead and Kemp’s ridley turtles than in greens, most
1123 book.book Page 170 Monday, November 11, 2002 11:11 AM