CHAPTER 13 . Endocrine-Disrupting Chemicals in Marine Environment
13.4
The Effects of Endocrine Disrupting Chemicals in Vertebrates
13.4.1
Fish
313
The fact that certain observed changes in fish (including intersex, production of the
female yolk precursor lipoprotein vitellogenin and abnormal testicular development
in both adult male and juvenile fish) could be related to substances present in sewage
and industrial effluent gave the first clear indications of an endocrine-disrupting
chemical problem (Purdom et al. 1994; Harries et al. 1993; Jobling and Sumpter 1993;
Sumpter and Jobling 1995; Jobling et al. 1996; Kime 1998; Vos et al. 2000). Such effects
have been linked to oestrogenic hormones from human waste and from alkylphenols
(Jobling et al. 1996). In the UK., a considerable number of studies have now also demonstrated a high prevalence (locally up to 100%) of intersex occurrence (Jobling et al.
1998). Table 13.4 provides some examples of the types of effects and associated contaminants in marine systems.
In the US., other effects have been observed, including delayed sexual development,
altered blood sex hormone profiles, impaired reproductive performance, and masculinization in fish exposed to effluents from kraft pulp mill effluents (Hester and
Harrison 1999). Tall oil, a major component of kraft mill effluent, contains 3% plant sterols, which are dominated by sitosterol and stigmastanol, but the link between this possible cause and the observed effects has not been established (Howell and Denton 1989),
though j3-sitosterol is known to be oestrogenically active (Phillips and Harrison 1999).
The endocrine system in fish has similar features to that of mammals (Fig. 13.1; Kime
1999), though there are a number of important ways in which reproductive physiology is different between mammalian and non-mammalian animals (Dawson 1998).
External stimuli such as seasonal changes in temperature or day length of the behaviour
of a potential mate are processed by the brain, leading to the release of gonadotrophin releasing hormone (GnRH) by the hypothalamus. GnRH induces the pituitary
gland to release gonadotrophin (GtH), which stimulates steroid synthesis in the gonads. Some fish are known to produce two gonadotrophins (GtH-l and GtH-2), which
are analogous to the follicle stimulating and luteinising hormones (FSH and LH) that
regulate the female cycle in mammals. In fish, GtH-l stimulates the ovary to produce
oestradiol, which in turn induces production of a yolk protein (vitellogenin) by the
liver. GtH -2 is most important prior to spawning when it stimulates ovarian synthesis
of a progestogen (17,20-j3-dihydroXY-4-pregnen-3-one; 17,20j3P), which induces maturation of the oocytes prior to ovulation. This progestogen may playa role in the maturation of sperm, but there is no known role for progesterone, which is a key mammalian hormone. A further difference between fish and mammals is that the main hormone produced by the testis is ll-ketotestosterone rather than testosterone. However,
both male and female fish produce testosterone, which may be involved in feedback
signals to the pituitary. Fish gonads have some of the same functions as mammalian
livers insofar as they are able to convert steroid hormones into metabolites that in some
fish species may act as pheromones.
The interrelationships between the processes shown in Fig. 13.1 indicate that disruption of a single part of the system can lead to a profound overall disturbance.
13.4
The Effects of Endocrine Disrupting Chemicals in Vertebrates
13.4.1
Fish
313
The fact that certain observed changes in fish (including intersex, production of the
female yolk precursor lipoprotein vitellogenin and abnormal testicular development
in both adult male and juvenile fish) could be related to substances present in sewage
and industrial effluent gave the first clear indications of an endocrine-disrupting
chemical problem (Purdom et al. 1994; Harries et al. 1993; Jobling and Sumpter 1993;
Sumpter and Jobling 1995; Jobling et al. 1996; Kime 1998; Vos et al. 2000). Such effects
have been linked to oestrogenic hormones from human waste and from alkylphenols
(Jobling et al. 1996). In the UK., a considerable number of studies have now also demonstrated a high prevalence (locally up to 100%) of intersex occurrence (Jobling et al.
1998). Table 13.4 provides some examples of the types of effects and associated contaminants in marine systems.
In the US., other effects have been observed, including delayed sexual development,
altered blood sex hormone profiles, impaired reproductive performance, and masculinization in fish exposed to effluents from kraft pulp mill effluents (Hester and
Harrison 1999). Tall oil, a major component of kraft mill effluent, contains 3% plant sterols, which are dominated by sitosterol and stigmastanol, but the link between this possible cause and the observed effects has not been established (Howell and Denton 1989),
though j3-sitosterol is known to be oestrogenically active (Phillips and Harrison 1999).
The endocrine system in fish has similar features to that of mammals (Fig. 13.1; Kime
1999), though there are a number of important ways in which reproductive physiology is different between mammalian and non-mammalian animals (Dawson 1998).
External stimuli such as seasonal changes in temperature or day length of the behaviour
of a potential mate are processed by the brain, leading to the release of gonadotrophin releasing hormone (GnRH) by the hypothalamus. GnRH induces the pituitary
gland to release gonadotrophin (GtH), which stimulates steroid synthesis in the gonads. Some fish are known to produce two gonadotrophins (GtH-l and GtH-2), which
are analogous to the follicle stimulating and luteinising hormones (FSH and LH) that
regulate the female cycle in mammals. In fish, GtH-l stimulates the ovary to produce
oestradiol, which in turn induces production of a yolk protein (vitellogenin) by the
liver. GtH -2 is most important prior to spawning when it stimulates ovarian synthesis
of a progestogen (17,20-j3-dihydroXY-4-pregnen-3-one; 17,20j3P), which induces maturation of the oocytes prior to ovulation. This progestogen may playa role in the maturation of sperm, but there is no known role for progesterone, which is a key mammalian hormone. A further difference between fish and mammals is that the main hormone produced by the testis is ll-ketotestosterone rather than testosterone. However,
both male and female fish produce testosterone, which may be involved in feedback
signals to the pituitary. Fish gonads have some of the same functions as mammalian
livers insofar as they are able to convert steroid hormones into metabolites that in some
fish species may act as pheromones.
The interrelationships between the processes shown in Fig. 13.1 indicate that disruption of a single part of the system can lead to a profound overall disturbance.