Physiological and Genetic Responses to Environmental Stress
171
likely because these turtles are at a higher trophic level and thus more subject to
bioaccumulation. Species-, gender-, or age-specific physiological differences clearly
will play a role in the effects and accumulation of various chemicals; the “offloading”
of pollutants to eggs, for example, is clearly not an option for male sea turtles as it
is for the females. Unfortunately, most of such differences even in basic physiology
are unknown (Milton et al., in press).
6.3.2.2 Effects
6.3.2.2.1 Toxicity
The toxicity of heavy metals and organopesticides is well established in other
vertebrate groups (mammals and fish), with wide-ranging effects on the neurological,
immunological, and reproductive systems. Although no long-term investigations in
sea turtles have been reported, one might expect similar deleterious consequences.
For many compounds with potentially toxic effects, there are little or no data
for sea turtles. Hexachlorobenzene (HCB), for example, is one of the most toxic
and most persistent of the chlorobenzene compounds, which as a highly volatile
compound is able to travel long distances in the atmosphere. No data on HCB,
dioxin, or furan levels have been reported for sea turtle tissues or eggs. There is
only one report of hexachlorocyclohexane and few for dieldrin, even though dieldrin
is one of the most commonly detected and easily analyzed pesticides reported in
marine biota (Pugh and Becker, 2001).
Although acutely toxic levels of xenochemicals have not been reported in sea
turtles, even trace amounts may be of concern because of potential sublethal effects
on health and normal physiology. Because of the difficulty of working with endangered animals, however, data are lacking on the normal physiology, immunology,
and population biology of sea turtles, and it is difficult to determine chronic effects
of pollutants. Such difficulties are compounded by the nature of the pollutants as
well. For example, comparisons between studies on the harmful effects of organochlorines such as PCBs are difficult because of between-study variations in
identification and quantification of congeners. Not all PCB congeners are metabolized at the same rate, and some are more toxic than others (Kannan et al., 1989).
Despite these limitations, studies on other species indicate cause for concern. High
organochlorines (such as PCBs and DDE) have been associated with uterine deformities and decreased pup production in seals (Baker, 1989; Reijnders, 1980);
embryotoxicity and effects on the hypothalamus–pituitary–adrenal axis in herring
gulls ( Larus argentatus ) (Fox et al., 1991; Lorenzen et al., 1999); decreased levels
of circulating thyroid hormone and lesions of the thyroid gland in seals and rats
(Byrne et al., 1987; Collins et al., 1977; Schumacher et al., 1993); decreased activity
levels, feeding rates, and whole body corticosterone levels in tadpoles of the
northern leopard frog ( Rana pipiens ) (Glennemeler and Denver, 2001); and
decreased immune responsiveness in chicks (Andersson et al., 1991), rats (Smialowicz et al., 1989), primates (Tryphonas et al., 1989), mice (Thomas and Hinsdill,
1978), and beluga whales (De Guise et al., 1998). Beluga whales living in the highly
contaminated St. Lawrence Seaway also have increased incidence of neoplasias
(De Guise et al., 1995); PCBs apparently act as a tumor promoter as well as an
1123 book.book Page 171 Monday, November 11, 2002 11:11 AM
171
likely because these turtles are at a higher trophic level and thus more subject to
bioaccumulation. Species-, gender-, or age-specific physiological differences clearly
will play a role in the effects and accumulation of various chemicals; the “offloading”
of pollutants to eggs, for example, is clearly not an option for male sea turtles as it
is for the females. Unfortunately, most of such differences even in basic physiology
are unknown (Milton et al., in press).
6.3.2.2 Effects
6.3.2.2.1 Toxicity
The toxicity of heavy metals and organopesticides is well established in other
vertebrate groups (mammals and fish), with wide-ranging effects on the neurological,
immunological, and reproductive systems. Although no long-term investigations in
sea turtles have been reported, one might expect similar deleterious consequences.
For many compounds with potentially toxic effects, there are little or no data
for sea turtles. Hexachlorobenzene (HCB), for example, is one of the most toxic
and most persistent of the chlorobenzene compounds, which as a highly volatile
compound is able to travel long distances in the atmosphere. No data on HCB,
dioxin, or furan levels have been reported for sea turtle tissues or eggs. There is
only one report of hexachlorocyclohexane and few for dieldrin, even though dieldrin
is one of the most commonly detected and easily analyzed pesticides reported in
marine biota (Pugh and Becker, 2001).
Although acutely toxic levels of xenochemicals have not been reported in sea
turtles, even trace amounts may be of concern because of potential sublethal effects
on health and normal physiology. Because of the difficulty of working with endangered animals, however, data are lacking on the normal physiology, immunology,
and population biology of sea turtles, and it is difficult to determine chronic effects
of pollutants. Such difficulties are compounded by the nature of the pollutants as
well. For example, comparisons between studies on the harmful effects of organochlorines such as PCBs are difficult because of between-study variations in
identification and quantification of congeners. Not all PCB congeners are metabolized at the same rate, and some are more toxic than others (Kannan et al., 1989).
Despite these limitations, studies on other species indicate cause for concern. High
organochlorines (such as PCBs and DDE) have been associated with uterine deformities and decreased pup production in seals (Baker, 1989; Reijnders, 1980);
embryotoxicity and effects on the hypothalamus–pituitary–adrenal axis in herring
gulls ( Larus argentatus ) (Fox et al., 1991; Lorenzen et al., 1999); decreased levels
of circulating thyroid hormone and lesions of the thyroid gland in seals and rats
(Byrne et al., 1987; Collins et al., 1977; Schumacher et al., 1993); decreased activity
levels, feeding rates, and whole body corticosterone levels in tadpoles of the
northern leopard frog ( Rana pipiens ) (Glennemeler and Denver, 2001); and
decreased immune responsiveness in chicks (Andersson et al., 1991), rats (Smialowicz et al., 1989), primates (Tryphonas et al., 1989), mice (Thomas and Hinsdill,
1978), and beluga whales (De Guise et al., 1998). Beluga whales living in the highly
contaminated St. Lawrence Seaway also have increased incidence of neoplasias
(De Guise et al., 1995); PCBs apparently act as a tumor promoter as well as an
1123 book.book Page 171 Monday, November 11, 2002 11:11 AM