Heavy Metals in Marine Mammals

Das et al 2003

&

O’Hara et al 2003

MM Context

• Long lived – ? bowheads >100y

• Predators

• Bioaccumulators

• Epizootics in relatively polluted regions such as Baltic, N. Sea and Med. Possibly associated with immunosuppression

Problems

• Complex inorganic and organic mixtures• Multiple stressors – foraging, reproducing, fasting,

moulting, migrating, predators, disease, habitat degradation.

• Limited experimental opportunity• Most samples from dead stranded animals• de Swart 1996 seal pcb/ immuno study did not examine

metal concentrations, only HAH’s.• Hard to distinguish natural from anthropogenic• Hg naturally high in Med, Cd in Arctic• Experiments mimic levels in wild?• Are high levels bio-available?

Metals

• Can be immunotoxic, although no clear indication in MM yet

• Essential: Zn, Cu, Cr, Ni, Se, Al• Non-essential Hg, Cd, Pb• Cr, Ni and Pb usually low in MM (few µg/g

dw)• Ringed seal stillbirth correlates with [Ni] in

air in Finland• Zn, Cu, Cd and Hg are bigger concerns

Das et al 2003

Arctic

• Higher in Greenland Arctic 15th century Inuit and seal hair than in N Sea today. Natural source. Same for porpoises. May reflect lack of organic binders in Arctic water.

• Hg, CD, Zn and Cu levels vary across Arctic with natural sediment levels.

• ? Exposed for millenia and well adapted

Routes

• Lungs

• Skin

• Placenta

• Milk

• Mouth

Diet

• Cephalopods concentrate Cd in viscera – Holsbeek saw high Cd in Sperm whale (Physeter) – see osteomalacia in humans – not seen in Pm

• Bivalves transfer Cd and Pb to walrus.• Dugongs – High Cd and Zn. ? Results

from low seagrass Cu augmenting intake• Minke whale: Hg Greenland >>>>Antarctic

(fish vs krill)

Organ distribution

• Hg – Liver > Kidney > Muscle

• Beluga slough 20% of Hg burden annually in skin

• Cd – Kidney

Hg

• Me-Hg most lipid soluble and toxic form, so [ΣHg] poor indicator of Hg toxicity. Se demthylates Hg and reduces intake. Ratio important

• Biomagnifies up chain from zooplankters• Easy placental transfer• Sensory and motor deficits, anorexia and

lethargy• Hg in Tt hepatic lipofuchsin• Hi Hg in N Sea Pp ? Assoc with incr. parasitism

Hg detoxification

• Hg/Se mutual antagonism• Hg is demthylated – see mercuric selenide in hepatic

macrophages – in Ziphius, striped dolphin, Tursiops and G mac also in lung assoc w C particles in latter 2 spp. – leads to high but non-toxic concentrations

Hg in Faroes G melas

• Faroese eat 1200-2900µg Hg/week• Health advisory – no viscera and meat & blubber

only once per week• High Se may protect human consumer, but

Weihe, Grandjean et al showed Hg associated cognitive deficits in human offspring

• Beluga – hepatic Hg levels high but may not be a major human diet item

Cd

• Kidney, lung, cardiovascular, hemopoietic • Carcinogenic, mutagenic, teratogenic• Osteomalacia ‘itai-itai’• Arctic ringed seals < 2000 µg/g dw (800 µg/g dw

induces renal damage in humans), but no effects documented in seals: implies efficient detoxification and tolerance to high levels

• High in baleen whales – no effects seen• Bowhead renal Cd levels of possible concern to

human subsistence consumers

Metalothioneins

• High cysteine content – mainly in liver and kidney

• High affinity for divalent cations such as Cu2+ and Zn2+ as well as Cd2+, Ag+, Hg2+ and Pb2+

• Lowest levels in stranded sperm whales - ? Cd tox part of the syndrome

Organotins• Higher in coastal water animals

• Higher in cetaceans than pinnipeds ( hair excretion)

• High in liver and hair of Steller’s sea lion

• TBT and DBT immunotoxic in vitro – Nakata et al 2002 – in Tt, Zc and humans

• Little loss to offspring from mothers – adult M and F levels compare – cf. HAH

Nakata et al 2002 Environmental Pollution Volume 120, Issue 2 , December 2002, Pages 245-253

Fig. 2. Proliferation response of peripheral blood mononuclear cells (PBMCs) in two bottlenose dolphins following the treatment with non-ortho coplanar PCB congeners and butyltins. #: P<0.01.

Fig. 5. Proliferation response of peripheral blood mononuclear cells (PBMCs) in bottlenose dolphins following the treatment with the mixture of butyltins and non-ortho coplanar PCB congeners and butyltins. #: P<0.01.

Elevated accumulation of tributyltin and its breakdown products in bottlenose dolphins (Tursiops truncatus) found stranded along the U.S. Atlantic and Gulf coasts

? Immunosupression enhanced morbillivirus die- offs

Kannan, et al 1997Environmental Science & Technology vol. 31, no. 1, pp. 296-301

Fluoride

• Fluoride concentration in fin whales higher than that normally occurring in any mammalian species, ranging from 4,340 to 18,570 ppm. – Significantly above the levels causing bony exostoses in sheep and cattle. Krill are high in Fl. Assume resistant – Landy et al 1991

Issues

• Many MM were over-exploited – some not recovering: vessel collision, gear entanglement, ? heavy metal impact, organic contaminants.

• Some species directly compete with commercial fisheries, others do not

• May have important community structure role as predators

• Do metals impact immune function?