|Surprisingly, animals in the Arctic can be subject to very high levels of pollution – one reason being the fact that air and water currents carry contaminants from the south. Many aquatic animals, particularly species with a lot of fat, accumulate these bioaccumulating contaminants in their bodies at much higher levels than in the surrounding water.
Polar bears, through their diet of seals, can absorb very high levels of contaminants. A comparison of polar bears from Svalbard in the Norwegian Arctic with those in less polluted areas in the Canadian Arctic found extreme concentrations of PCBs in older male bears from Svalbard. Females have lower levels because they pass the toxic chemicals on to their young through their fat-rich milk. PCBs reduce the ability of the immune system of Svalbard bears to combat common infections such as influenza, reo and herpes viruses. This poses a particular threat to these long-living, slowly reproducing animals which have few offspring. Bears with higher PCB contamination also produce lower levels of the male sex hormone testosterone. Other research into Svalbard bears found four of 269 females to be masculinised.
Levels of newer-generation chemicals such as brominated flame-retardants and artificial musks are also rising in the Arctic. The toxic properties of these flame retardant chemicals are similar to PCBs and if the current trend of growing global production is not broken, levels will surpass those of PCBs within the next 50 years. Although no direct link between these chemicals and adverse effects on polar bears has yet been established, the wildlife and people of the Arctic may face a new PCB-like problem from chemicals that can disrupt thyroid hormone function, affect the immune system, disrupt brain development and affect coordination, learning abilities and memory.
North Sea and Baltic seals
| In the 1970s, common seals in the Wadden Sea (the east coast of the North Sea) produced few pups and the population went into decline. The animals were heavily polluted with PCBs. Seals fed on contaminated Wadden Sea herring had only half the breeding success of those feeding on less contaminated North Atlantic herring.
Embryos failed to attach to the womb, and while this phenomenon can be associated with low levels of the female hormone, PCBs are known to stimulate the production of enzymes that break down that hormone. The seals’ immune system was also affected, and this combination is believed to have contributed to the mass deaths of common seals in the North Sea and Baltic caused by the distemper virus in the late 1980s. Those areas where the seals were most exposed to pollution, such as the Wadden Sea, suffered the highest death rates.
Few now doubt that the decline of Baltic ringed and grey seals was the result of pollution. Effects observed were spontaneous abortions and deformed wombs, and 70% of ringed seals and 30% of grey seals had problems reproducing. An analysis of PCB and DDT levels in grey seals between 1969 and 1997 implicated PCBs as the leading cause of reproductive failure. The grey seals also suffered an impaired immune system, associated with high PCB and DDT levels, hyperactivity of hormonal glands, bone degeneration, intestinal ulcers, claw malformations, arthritis, cancer of the womb and skin-thinning. Now, modern-use chemicals such as brominated flame retardants have also been found in marine life. In the North Sea, for example, contaminated species include the white beaked dolphin, bottle-nosed dolphin, harbour porpoise and harbour seal. The threat of man-made chemical contamination is far from over and new problems may emerge.
Otters and mink
|The otter declined widely throughout western Europe between the 1960s and 1980s. Research led to the conclusion that this was due to PCB contamination. A study of recent increases in Swedish otter populations, correlated with falling PCB levels, supports this conclusion.
Widespread declines of Great Lakes mink, Canadian otter and other species have also been recorded in North America and western Europe. PCBs and dioxins are suspected, and studies of farmed and laboratory mink provide supporting evidence.
Subtle effects on the reproductive organs of otters have also been noted in those from polluted areas. Organ weights were compared between otters that had died in the Lower Columbia River and those from other geographical areas. Baculums (penis bones) and testicles of young males were shorter or smaller than in animals of the same age class from non-polluted areas.
Persistent organic pollutants and indicators of otter health: other factors at play? highlights serious concerns for the health of otters in the UK.
Otters are one of our best loved species and research indicates that they may not be in the best of reproductive health. This raises the question as to whether modern chemicals, particularly endocrine disrupting chemicals (EDCs - hormone disruptors), could be to blame.
CHEM Trust’s report: Effects of Pollutants on the Reproductive Health of Male Vertebrate Wildlife - Males Under Threat by Gwynne Lyons.
This report shows that male fish, amphibians, reptiles, birds and mammals have been harmed by chemicals in the environment. Widespread feminisation of male vertebrate wildlife is highlighted. These findings add to mounting worries about the role of hormone-disrupting or so-called ‘gender-bending' chemicals in the environment, and the implications for human health.