Chemical Pollution and Marine Mammals
- Marine mammal populations face an increasing barrage of stresses. These include noise and disturbance from
ship traffic and offshore development, competition with fisheries for food resources, and the impacts that
may be occuring with a changing climate and increased UV-B radiation. Some species have yet to recover from
prior commercial hunting, and many face the threats of oil spills, poisoning by planktonic toxins,
incidental capture in fishing nets, and infectious disease.
- Superimposed upon these stresses is the chemical contamination of their habitat. Every living marine mammal
is exposed to a suite of chemical pollutants via their food--many of which are persistent and readily
accumulate in body tissue. Furthermore, a portion of the pollutants which have accumulated in females are
transferred to their offspring during gestation and lactation, thus potentially affecting them during their most
sensitive periods of development.
- While it is well-documented that exposure to even low levels of various pollutants can have severe effects on
laboratory animals and on wildlife populations, it has been difficult to determine chemical impacts on marine
mammals. This is in large part due to ethical issues associated with wild animal experimentation and the
problems associated with studying and monitoring animals who spend much of their time underwater.
Overall, however, there is general scientific agreement that a number of health-related aspects are likely being
compromised in at least some marine mammal populations and that, ultimately, their survival and reproduction
are being affected. This conclusion is based on extrapolation from laboratory studies on terrestrial mammals,
the use of marine mammal cell cultures, and a growing amount of experimental and field research.
- Contaminants--notably PCBs and DDT--have for example been implicated in: the sterility, fatal intestinal
ulceration, sclerosis and other ailments in Baltic Sea seals; reduced immune system competence in Florida
bottlenose dolphins; the high incidence of disease, including cancer, in beluga whales of the St. Lawrence
River; premature pupping in California sea lions; and as a possible contributor to some of the recent seal
and dolphin disease and mass mortality events. Organotins (used in anti-fouling paints on boats) have been
suggested as a factor in the increased incidence of disease in California's sea otters as have organochlorines
(such as PCBs and DDT) in the decline of orca (killer whale) in the Puget Sound region.
- It is estimated that over 70,000 chemicals are currently in common use as industrial compounds, pesticides,
pharmaceuticals, food additives, and other purposes, and that this number is increasing by approximately
1,000 each year. Of particular concern to the health of marine mammal populations are the halogenated
hydrocarbons (HHCs) such as the PCBs, DDT, chlordane, dioxins and furans, and the chlorinated and
brominated diphenyl ethers. Other chemical groups of concern include trace metals such as mercury and cadmium, organometals such as tributyltin, polycyclic aromatic hydrocarbons (PAHs), and radionuclides. Those coastal
populations near intensive agriculture operations may be exposed to periodic pulses of carbamate and
organophosphate pesticides.
- There are a number of possible effects that contaminants can have on marine mammals. These include infertility
and reproductive failure, birth defects, cancer, behavioral change, immune and nervous system dysfunction,
damage to kidneys, liver and other organs, and alteration of hormone levels. The stress induced by chemical pollutants
may also combine with other stressors--natural or human-induced--thereby compounding the impacts and
making it increasingly difficult for an animal to cope with changing or deteriorating environmental conditions.
- There are many uncertainties over the current and potential future effects of pollutants on marine mammals
and their populations. The toxicity of the vast majority of chemicals now released into the environment is
very poorly known, and is even less so for the interactive effects of complex mixtures, the typical environmental
scenario. Little is known about the cumulative effects of contaminants in conjunction with the variety of
other stresses facing marine mammals, or on the effects of contaminant-induced foodweb changes. There are
large knowledge gaps concerning future trends in chemical production, on the biological and ecological effects
of "new generation" pesticides, and on the potential interactive effects between environmental pollution and
other components of global change. It is expected, however, that hitherto unrealised impacts will be uncovered
as scientific knowledge increases.
- Because of the continuing problems and the many unknowns associated with environmental pollutants there
have been an increasing number of calls for a management approach that is precautionary (i.e., that actively
attempts to prevent damage in the first place) rather than one that reacts only after public health and the
environment are threatened.
- The persistent organic pollutants, or POPs, are currently under the closest scrutiny because of their often
high toxicity, their ability to accumulate and biomagnify in the food chain--with the highest levels typically
found in high trophic level predators such as seals and dolphins--and their ability to resist overall degradation.
Most POPs are also semivolatile which has meant their global spread via the atmosphere.
- Though there are now an estimated 2,400 POPs with the potential to cause environmental problems, 12 – aldrin, chlordane, DDT, dieldrin, dioxins, endrin, furans, heptachlor, hexachlorobenzene, mirex, PCBs, and toxaphene – have been targeted by the Stockholm Convention on Persistent Organic Pollutants as requiring urgent international action for reduction in use and eventual elimination.
Dietz, R., Bossi, R., Riget, F.F., Sonne, C. and Born, E.W. 2008. Increasing perfluoroalkyl contaminants in east Greenland polar bears (Ursus maritimus): A new toxic threat to the Arctic bears. Environmental Science and Technology 42(7): 2701-2707.
Fair, P.A. et al. 2007. Polybrominated diphenyl ethers (PBDEs) in blubber of free-ranging bottlenose dolphins (Tursiops truncatus) from two southeast Atlantic estuarine areas. Archives of Environmental Contamination and Toxicology 53(3): 483-494.
Fossi, M.C., Casini, S. and Marsili, L. 2006. Endocrine disruptors in Mediterranean top marine predators. Environmental Science and Pollution Research 13(3): 204-207.
Hall, A.J. et al. 2006. The risk of infection from polychlorinated biphenyl exposure in the harbor porpoise (Phocoena phocoena): A case-control approach. Environmental Health Perspectives 114(5): 704-711.
Hickie, B.E., Ross, P.S., Macdonald, R.W. and Ford, J.K.B. 2007. Killer whales (Orcinus orca) face protracted health risks associated with lifetime exposure to PCBs. Environmental Science and Technology 41(18): 6613-6619
Jenssen, B.M. 2006. Endocrine-disrupting chemicals and climate change: A worst-case combination for arctic marine mammals and seabirds? Environmental Health Perspectives 114 (Suppl. 1): 76-80.
Kannan, K., Perrotta, E., Thomas, N.J. and Aldous, K.M. 2007. A comparative analysis of polybrominated diphenyl ethers and polychlorinated biphenyls in southern sea otters that died of infectious diseases and noninfectious causes. Archives of Environmental Contamination and Toxicology 53(2): 293-302.
Marine Mammal Commission. 1999. Marine Mammals and Persistent Ocean Contaminants: Proceedings of the Marine
Mammal Commission Workshop, Keystone, CO, 12-15 Oct., 1998. Marine Mammal Commission, Bethesda, MD:
150 pp. + vii.
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