THEY ARE called POPs (Persistant Organic Pollutants) and, according to the United Nations Environment Programme, they are the nastiest chemicals on the planet. Some are extremely toxic - swallow the tiniest amount and you will die - and others don't seem toxic at all, which probably explains why we've been drenching our planet with them for years. They last for a very long time in our environment. And in quantities as small as parts per trillion, they can cause cancer as well as playing havoc with our ultra-sensitive reproductive, immune and central nervous systems.
They have become known as the 'dirty dozen' and, as part of the 1997 Montreal Treaty, the United Nations is trying to ratify a globally binding legislation that will ban their production forever. Global pressure groups have a much longer list of pesticides they want banned. Although the 'dirty dozen' are banned in Hong Kong, as they are in many other countries in the world, they are still in widespread used in the developing world, where many of the West's remaining stockpiles are being 'dumped'. POPs circulate globally through 'the grasshopper effect': POPs released in one part of the world can, though a repeated (and often seasonal) process of deposit, release, deposit, be transported to regions far away from their original source. Traces are found constantly in Hong Kong's ecosystem. In fact, because of their strength and resistance, they are ubiquitous across the globe.
CHLORDANE has been used on a wide range of crops, including vegetables, grains, potatoes, sugar cane, sugar beet, fruits, nuts, cotton and jute. It has also been used in the control of termites. It's highly insoluble in water but is soluble in fats - which means it accumulates in the fat of animals, as well as in marine sediments. It was strong and very persistent, which means it can travel long distances: Chlordane has been detected in Arctic air, water and organisms. Evidence suggests long-term exposure can cause cancer and effect immune-system responses in humans. Traces of it are found in food but exposure is more likely to be from residues in the air.
DDT was widely used in World War II to protect troops from malaria, typhus and other diseases. For the next 25 years, it was the most widely used chemical in agriculture and disease pest-control. It can take up to 100 years to disappear, which means its presence in our environment is ubiquitous. It's everywhere, and it finds its way into the fatty tissue of all living organisms. At first it seemed harmless - human volunteers who were given DDT for up to 21 months showed no immediate adverse effects - but it has since been discovered to have a wide range of effects on wildlife, including feminisation (turning males into females), suppression of the immune system and severe impacts on the reproductive process. It is classified as a carcinogen and its continuing presence in the environment has raised serious concerns regarding future effects on developing infants.
THE 'DRINS' (Aldrin, Dieldrin, Endrin) were widely used on corn, potatoes and rice, as well as cotton and grain. Symptoms are wide-ranging. Acute poisoning includes headaches, dizziness, nausea, vomiting, followed by muscle twitchings, myoclonic jerks and convulsions. Cronic effects in wildlife include spinal deformities, reproductive abnormalities, weight abnormalities and cancer. Recent research suggests they may have serious effects on human immune system responses. The 'Drins' accumulate in fat and, therefore, the primary sources of exposure are dairy products such as milk and butter as well as fatty meat.
POLYCHLORINATED DIBENZO (dioxins and furans) are by-products resulting from the production of other chemicals: dioxins mainly from pesticides, furans from PCBs. They can last for more than 10 years in soil. Exposure can cause fatigue, depression, personality changes, hepatitis, cancer and leukaemia. Most human exposure comes from eating meat or fish.
HEXACHLOROBENZENE (HCB) is a fungicide first introduced in 1945 for seed treatment. It can last in soil for more than 50 years, is insoluble in water and bioaccumulates in fat. Side-effects range from skin problems to acting as a possible human carcinogen. Tests on animals showed it seriously effects reproduction. It can travel a long way - it has been detected in Arctic air, water and organisms - and residues have been found in many different food types, including fish, seafood, dairy products and meat.