Tuesday March 5, 2013
Chemical exposure contributes to decline of wildlife population
By TAN CHENG LI
Chemical exposure plays a role in the deterioration of wildlife health.
WILDLIFE species and populations are on the decline worldwide – and it is not just due to over-exploitation or loss of habitat. Chemical contamination is also at play here.
Long-term monitoring as well as laboratory studies have shown that chemicals known to interfere with the function of the human body’s endocrine system, do the same in wildlife.
The evidence shows that exposure to endocrine disrupting chemicals (EDCs) can affect behaviour, fecundity, growth and disease resistance in wildlife.
A recently released report, State of the Science of Endocrine Disrupting Chemicals 2012, by the United Nations Environment Programme (UNEP) and the World Health Organisation warns of the health risks posed by EDCs, which can be found in a wide range of products, including many everyday items.
“Given our understanding of EDCs and their effects on the reproductive system, it is extremely likely that declines in the numbers of some wildlife populations (raptors, seals and snails) were because of the effects of endocrine disrupting chemicals on these species,” says the report, developed by a global team of experts grouped under the Inter-Organisation Programme for the Sound Management of Chemicals (IOMC, a multi-UN-agency body established in 1995).
Human and wildlife health depends on a well-functioning endocrine system to regulate the release of certain hormones that are essential for functions such as metabolism, growth and development. EDCs can alter the functions of this hormonal system, leading to adverse effects on human and wildlife health.
Some EDCs occur naturally – in metals such as lead, cadmium and methymercury and in chemical elements such as arsenic.
Synthetic EDCs can be found in a large variety of materials and goods, including pesticides, packaging materials, pharmaceuticals (contraceptive, hormone therapies, lipid regulators, beta-blockers, anti-depressants), flame retardants (used in mattresses, sofas and textiles), electronics, plastic additives, personal care products, household cleaners and construction materials.
EDCs also enter the environment through industrial and urban discharges, agricultural run-off and the burning of coal and wood.
EDCs are found in wildlife worldwide. The current body burdens of pollutants such as polychlorinated biphenyls (PCB), organochlorine pesticides and methylmercury in some fish-eating birds and marine mammal populations are at levels known to cause effects on breeding and on the immune system. Some of these populations are threatened or endangered.
For instance, perfluorooctane sulfonate (PFOS, used in stain repellents, surface coating agents and fire-fighting foams) has been detected in the liver of marine mammals, the highest being in harbour porpoise and seal in Europe, finless porpoise in Japan, and Indo-Pacific dolphin in the Far East.
Killer whales and harbour seals in British Columbia, Canada, have high levels of PCBs and moderate levels of polybrominated diphenyl ethers (PBDEs, used as flame retardants in textiles, electronics and electric appliances).
Wildlife across the globe have displayed EDC-related reproductive effects:
> In the 1970s and 1980s, seals in the heavily polluted Baltic Sea had very high rates of female reproductive pathologies (uterine fibroids) and reproductive failure, which correlated with PCB contamination. Thanks to declines in PCB pollution, these effects are uncommon today.
> Disturbances of the normal functioning of the thyroid and of bone health have been traced to high levels of persistent organic pollutants in grey seals.
> In rivers receiving sewage effluent, fish have been found with reduced fecundity, altered sexual organs and reproduction problems. In male fish, increased levels of the female egg yolk proteins and the occurrence of eggs in the testes have been observed. These effects are triggered by synthetic and natural hormones as well as active ingredients in pharmaceuticals that are excreted by humans and end up in sewerage.
> In many harbours worldwide, molluscs are showing imposex (having both male and female genitalia), a phenomenon linked to exposure to the anti-fouling compound tributyltin (TBT), that is found in paints used on ships. The sexual abnormalities have caused reproductive failures and in the 1970s, many populations of molluscs, including the commercially important oyster, collapsed in areas with high TBT use. Imposex of marine snails has also been reported in Malaysia, with female rock snails off the coast of Selangor found to have sperm ducts.
> In Dutch and Belgian colonies of common tern, eggs with higher concentrations of persistent organic pollutants took longer to hatch, and the chicks were smaller in size.
The mechanisms underlying the effects and the outcomes of chemical exposures in wildlife are often similar to those in humans.
As such, parallels can be drawn between the two.
The effects of EDCs on animals might result in devastating effects on wildlife populations over the long term. This is hard to prove until the declines in populations are evident, at which point it may be too late to save these species.
So, it is crucial that known EDCs be phased out of commerce as experience has shown that as levels of EDCs decline, wildlife populations have shown recovery. For example, numbers of birds and molluscs are increasing in regions where their exposure to chemicals (such as the pesticide DDT and the anti-foulant TBT) have been reduced.