For a long time now, scientists have known of the dangers posed by Persistent Organic Pollutants (or POPs). In 1944 traces of DDT were found in human fat and by 1951 scientists were able to detect traces of this contaminant in the milk of breast feeding mothers. In the early 1950s naturalists were noting the thinning of eggshells that lead to a crash in the bird populations. However, it was only when Rachel Carson wrote her book "Silent Spring" that what had become an accademic concern became more widely known. In this book she described the devastating effects of persistent pesticides on wildlife and warned of the so-far overlooked human health problems which might occur with exposure.
Following the banning or restricting of certain POP chemicals, levels of contamination have declined in many industrialised countries. However, not enough has been done to avert this threat, and unless more is done, soon, we will have a full scale disaster on our hands the like of which we have never known.
What are POPs?
Living things are composed of organic compounds which contain hydrogen and carbon. These organic compounds are virtually indestuctible. The persistent organic pollutants we are talking about are manmade organic compounds.
All persistent organic pollutants have three major qualities:
- They are persistent that is that they do not break down through the actions of sunlight and water.
- They are toxic. In other words they have a detrimental effect on living things.
- They are bioaccumulative which means that they build up in living fatty tissues in the bodies of humans and animals.
Twelve types of chemicals have been named as POPs. These are: DDT, Aldrin,Dieldrin, Endrin, Chlordane, Heptachlor, Hexachlorlbenzene, Mirex, Toxaphene, Polychlorinated Biphenyls, Dioxin and Furans.
Most of these chemicals are found in organochlorine pesticides, brominate flame retardants or vinyls. Others are released as a biproduct of processing. For instance PVC is a prime source of dioxin both in its production and its use. The burning of PVC in incinerators or the burying of it in landfill sites will also release dioxins.
Why are POPs so much trouble to manage?
- They are an accumulated poison that does not dispers naturally.
- They are a global pollutant which is now found in every part of the world, no matter how remote, and within the bodies of every living creature.
- They build up in living fatty tissues and are transferred from prey to predator up the food chain. This means that the higher the predator is in the food chain, the higher burden of contaminates he/she receives.
