318
M. R. Preston
taminants, particularly chlorinated ones. A recently discovered phenomenon is that
in some cases (e.g. chlordane and aHCH), bioaccumulation in polar bears, seals and
cetaceans is enantioselective, and enantiomer ratios are important variables for sample
groupings and for class separation of malelfemale seals and fat/liver tissues (Minh et al.
2000; Wiberg et al. 2000). The consequences of this observation are likely to be profound, and further research will clearly be necessary.
The distribution of contaminants in high latitudes is not uniform, and several researchers have reported temporal and geographical trends (see e.g. Norstrom et al.
1998; Muir and Norstrom 2000; Muir et al. 1999, 2000). The main source of these contaminants to polar bears is probably their food and in particular ringed seals (Phoca
hispida) and harp seals (Phoca groenlandica) (Kleivane et al. 2000). Very high concentrations of PCBs have been reported in the literature in other top predators such
as glaucus gulls (Henriksen et al. 2000). However, whilst there is growing evidence that
immunotoxic effects such as changes in immunoglobulin levels are arising as a result,
there is no evidence that there is a relationship between organochlorine concentrations and fertility (Bernhoft et al. 1997, 2000). Neverilieless, of considerable concern is
ilie observation made by Wiig et al. (1998) iliat 4 of 269 animals examined exhibited female hermaphroditism. 'I\vo possible explanations for iliis phenomenon are (i) excessive
androgen excretion by the moilier (possibly as a result of a tumour) and (ii) that there
is endocrine disruption as a result of the presence of environmental pollutants.
Polar bears are thought to be particularly vulnerable to contaminant exposure,
because iliey undergo one of the most extreme fasts known for any mammal (Polischuk
et al. 1995). As organochlorine (and other lipophilic contaminants) are very largely
stored in body fat, it is not surprising that contaminant concentration in both adipose
tissue and milk increase as the fast progresses (Polischuk et al. 1995). The transfer of
contaminants to cubs therefore also increases as the fast continues.
A second group of marine mammals that have been studied extensively are seals.
Declines in populations of seals notably in the Baltic and North Sea areas have been
evident over many years. As far back as 1976 Helle et al. (1976a,b) reported correlations between pathological changes in seals and PCB concentrations. A number of
diseases have been linked to organochlorine contaminants, but the mechanisms are
incompletely understood, and Vos et al. (2000) observed that it is conceivable iliat the
disease syndrome is caused by several classes of persistent organohalogens and several independent mechanisms of action. It is also possible that the problems lie at least
in part with metabolic or degradation products of the original compounds. For example, MeSOz-DDE apparently has a role in the etiology of adrenocortical hyperplasia in Baltic seals (Brandt et al.1992). Significant cytochrome P450-catalysed irreversible binding of MeSOz-DDE has also been observed in seals (Lund 1994). Vos et al.
(2000) and Van Loveren et al. (2000) have concluded that both reproduction and immune functions in Baltic grey and ringed seals and Wadden Sea harbour seals are
impaired by PCBs in the food chain. Damage to reproductive systems has led to population declines, and impairment of immune function has probably contributed to mass
mortalities due to morbillivirus infections.
Experimental evidence relating to mammals such as dolphins suggests that there
is the potential for damage as a result of exposure to contaminants (Wilson et al.1999).
However, in the wild such conclusions are hard to validate because of the natural variability. So, for example, Wilson et al. (op. cit.) determined that there were no links be-
M. R. Preston
taminants, particularly chlorinated ones. A recently discovered phenomenon is that
in some cases (e.g. chlordane and aHCH), bioaccumulation in polar bears, seals and
cetaceans is enantioselective, and enantiomer ratios are important variables for sample
groupings and for class separation of malelfemale seals and fat/liver tissues (Minh et al.
2000; Wiberg et al. 2000). The consequences of this observation are likely to be profound, and further research will clearly be necessary.
The distribution of contaminants in high latitudes is not uniform, and several researchers have reported temporal and geographical trends (see e.g. Norstrom et al.
1998; Muir and Norstrom 2000; Muir et al. 1999, 2000). The main source of these contaminants to polar bears is probably their food and in particular ringed seals (Phoca
hispida) and harp seals (Phoca groenlandica) (Kleivane et al. 2000). Very high concentrations of PCBs have been reported in the literature in other top predators such
as glaucus gulls (Henriksen et al. 2000). However, whilst there is growing evidence that
immunotoxic effects such as changes in immunoglobulin levels are arising as a result,
there is no evidence that there is a relationship between organochlorine concentrations and fertility (Bernhoft et al. 1997, 2000). Neverilieless, of considerable concern is
ilie observation made by Wiig et al. (1998) iliat 4 of 269 animals examined exhibited female hermaphroditism. 'I\vo possible explanations for iliis phenomenon are (i) excessive
androgen excretion by the moilier (possibly as a result of a tumour) and (ii) that there
is endocrine disruption as a result of the presence of environmental pollutants.
Polar bears are thought to be particularly vulnerable to contaminant exposure,
because iliey undergo one of the most extreme fasts known for any mammal (Polischuk
et al. 1995). As organochlorine (and other lipophilic contaminants) are very largely
stored in body fat, it is not surprising that contaminant concentration in both adipose
tissue and milk increase as the fast progresses (Polischuk et al. 1995). The transfer of
contaminants to cubs therefore also increases as the fast continues.
A second group of marine mammals that have been studied extensively are seals.
Declines in populations of seals notably in the Baltic and North Sea areas have been
evident over many years. As far back as 1976 Helle et al. (1976a,b) reported correlations between pathological changes in seals and PCB concentrations. A number of
diseases have been linked to organochlorine contaminants, but the mechanisms are
incompletely understood, and Vos et al. (2000) observed that it is conceivable iliat the
disease syndrome is caused by several classes of persistent organohalogens and several independent mechanisms of action. It is also possible that the problems lie at least
in part with metabolic or degradation products of the original compounds. For example, MeSOz-DDE apparently has a role in the etiology of adrenocortical hyperplasia in Baltic seals (Brandt et al.1992). Significant cytochrome P450-catalysed irreversible binding of MeSOz-DDE has also been observed in seals (Lund 1994). Vos et al.
(2000) and Van Loveren et al. (2000) have concluded that both reproduction and immune functions in Baltic grey and ringed seals and Wadden Sea harbour seals are
impaired by PCBs in the food chain. Damage to reproductive systems has led to population declines, and impairment of immune function has probably contributed to mass
mortalities due to morbillivirus infections.
Experimental evidence relating to mammals such as dolphins suggests that there
is the potential for damage as a result of exposure to contaminants (Wilson et al.1999).
However, in the wild such conclusions are hard to validate because of the natural variability. So, for example, Wilson et al. (op. cit.) determined that there were no links be-