DDT - The Resurrection of an Old Threat to Africa’s Wildlife
DDT - The Resurrection of an Old Threat to Africa’s Wildlife
The South African Minister of Health recently made it known that South Africa is about to resume the use of DDT for the control of mosquitoes, “because of the escalating number of human deaths in Africa due to malaria”. And she has urged other countries in Africa to do the same. The truth of the matter is that South Africa has never stopped using DDT for the control of mosquitoes!
So Africa must be told, once again, why the use of DDT – for ANY purpose – is not a good idea.
In the 1970s colonial Rhodesia used 1 000 tonnes of DDT a year, which carried over into the 1980s after Rhodesia became Zimbabwe. 400 tonnes were used for tsetse fly control, 300 tonnes to combat the maize-stalk borer; and 300 tonnes to kill mosquitoes in the country’s anti-malaria campaign. This rate of application was 96% the average annual application rate in the U.S. during the period 1956–1970. Rachel Carson’s book, Silent Spring, alerted America to the fact that DDT was killing end-of-food-chain birds, the songs of which could not be heard any more in the spring-time breeding season. It caused the banning of DDT in the United States.
In the 1970s and 1980s, Rhodesia/Zimbabwe was looking to initiate a green revolution and pro-DDT agriculture scientists, economists, government administrators and other influential people, advocated that DDT should be the pesticide of choice in this development. They said: “It has a reputation for low mammalian toxicity, is cheap, effective against a broad spectrum of crop pests, and requires no sophisticated equipment for its application. It is infinitely preferable than the more toxic to humans (but less harmful to the environment) organophosphates”.
In Africa, where rapid advancement is a major priority and where access to foreign currency is limited, the low cost of DDT and its short-term benefits are attractive. But are the costs to the environment – and to humanity - really worth it?
In America DDT caused serious declines in the country’s Bald Eagles, Ospreys, and Brown Pelicans. Even the ubiquitous American Robin suffered. The peregrine falcon was wiped out in the wild. Its was saved, on the brink of extinction, by a captive-breeding programme using birds surrendered for the purpose by America’s falconers. Arctic migrants were all seriously contaminated. It is highly likely, therefore, that a whole range of end-of-food-chain bird species would have become extinct in North America had DDT NOT been banned in 1970.
The pro-DDT lobby in Zimbabwe were told all this but they were unconcerned. “We have to have food in our bellies and shirts on our backs” they said. “And if the cost of that achievement is the loss of our fish eagles, of our peregrine falcons, and of other birds of prey that we never see anyway, then THAT must be the cost we are prepared to pay.”
We are now being told that the rate of human deaths to malaria in Africa has increased - and DDT has been prescribed to kill mosquitoes ALL OVER AFRICA! The old platitudes have been rung out. “The pesticide will be used ‘only’ on the outside walls of buildings under-the-eaves, and on the inside walls of houses where people sleep. These are places where DDT will have minimal impact on the environment“ – so the litany goes.
My experience is that, in Africa, when DDT is used ‘purely for malaria control’, once it is thus ‘available’, it is sold to peasant people in rural areas as a general agricultural pesticide - by the government operators who apply it. It is then used on the people’s vegetable crops and so finds its way into humans.
DDT has a ‘half-life’ of 26 years. This means if one kilogramme is applied today – anywhere – it will take 26 years to be reduced to half-a-kilogramme. But the half-kilogramme that is ‘lost’, at this stage, is not really lost at all. It has been degraded to what are called ‘metabolites’ which are just as environmentally harmful as DDT itself. This is why DDT is called a ‘persistent’ pesticide. It is also why it is so effective. One spraying, ONCE, on a solid surface will kill insects for months – even years.
DDT kills mosquitoes, tsetse flies and other insects because it is absorbed through the pads of their feet. It is absorbed through the skins of humans, too – such as when they lean up against sprayed bedroom walls. It is metabolised when people ingest it in their food and in their water. DDT is highly fat-soluble. It lodges in animal fats in an inert form – normally as a metabolite called DDE. When the ‘carrier’ loses weight DDE is excreted via his urine and faeces - as metabolites known as DDD and DDA. When it is released from fat into the blood stream it becomes a highly toxic nerve poison. In extreme cases human victims experience convulsions and persistent trembling, the causes of which are not easily determined. The symptoms, in fact, are not unlike those of malaria, but without the fever. So when DDT toxicity occurs together WITH malaria, nobody ever looks for the DDT connection.
Anyone with DDT contamination of their fat reserves WILL release DDT into their blood streams if they contract a disease that causes them to lose weight. Malaria is one such disease. Hepatitis, TB, pneumonia and HIV are others. Even injuries sustained in a motorcar accident can do the same thing.
When one considers the escalating rate of the HIV infection in Africa today a number of considerations beg examination. The first of these is the possibility that the apparent increase in malaria deaths may, in fact, not reflect an increase in malaria at all. It may equally reflect a general increase in HIV contamination of Africa’s populace and that the ultimate cause of HIV-infected patients’ deaths is more frequently, now, malaria.
It is well known that – to downplay the effect HIV/AIDS is having on their countries - many African government’s have instructed that when people die of AIDS only the ultimate cause of their deaths may be recorded – Pneumonia, TB, et cetera. Thus the proximate cause of death - HIV – is kept well hidden.
It would be tragic if this were the case and, as a result of a misrepresentation of the facts, the continent was broadly subjected to one of the most insidious environmental poisons ever created by man.
In the environment DDT (and DDT metabolites) is/are accumulated in the fat reserves of all animals in nature’s food chains. In the terrestrial environment, it goes from plants to caterpillars, from caterpillars to the birds that eat them, and then to the birds of prey that eat those birds.
When DDT washes off the plants or buildings where it has been applied, by rain, it enters the local river systems.
In the aquatic system DDT is absorbed by plant planktons, which are eaten by animal-planktons, which are eaten by aquatic insects, which are eaten by small fishes, which are then eaten by bigger fishes. And the bigger fishes are then eaten by fish-eating birds and mammals – including man.
All along the line DDT is passed on, and multiplies, from one organism to another. For example, IF plant-planktons in a river system each absorb just one tiny ‘particle’ of DDT we can say they are all contaminated with just one ‘part’. Then, when one animal-plankton eats 100 plant-planktons, it accumulates 100 parts of DDT. And IF one aquatic insect then eats 100 animal-planktons it will accumulate 10 000 parts of DDT. Then, if a small fish eats one hundred of those insects, it will accumulate 1 000 000 parts of DDT. This happens all along the food chain. Thus, it accumulates in very large concentrations in the fat reserves of the ultimate end-of-food-chain predators like Fish Eagles, Fishing Owls, cormorants and kingfishers – and man.
DDT contamination in birds causes infertility and eggshell thinning. Even when eggs are fertile the shells of the eggs become so fragile they are crushed by the incubating birds. One way of another, therefore, no eggs hatch and repeat breeding failures cause the ultimate and rapid extinction of susceptible species. The end-of-food-chain birds, therefore, are sensitive barometers that can tell us about the health of our environment.
If DDT is used as the pesticide of choice to kill malarial mosquitoes – especially if it is used on open water surfaces where mosquitoes breed (which is a possibility in unsophisticated Africa) – it will pose great dangers to Africa’s wildlife. And the resultant increase in human DDT contamination will exacerbate, rather than help, the rate of HIV/AIDS-related malaria deaths.
Results of studies conducted in the late 1970s and early 1980s in Zimbabwe were revealing. Eleven clutches of Fish Eagle eggs, collected between 1974 and 1979 exhibited an average contamination level of 37,8 p.p.m. (parts per million). Twenty-two clutches collected in 1980 recorded 70,1 p.p.m.. The highest was 390 p.p.m.. A further 15 clutches – collected from the upper reaches of Lake Kariba and the Zambesi River above the lake, in 1981 - had average residues amounting to 63,2 p.p.m..
Twenty percent of the shells of these Fish Eagle eggs were 20 % thinner than the shells of eggs collected before 1964 (before the DDT pollution era); and 71,5% were between 10% and 20% thinner. Only 8,5% showed no change.
There is no comparative data on Fish Eagles. But the congeneric American Bald Eagle showed signs of reproductive failure when DDT residue in their eggs exceeded 30 p.p.m., and when egg shell thinning exceeded 10%.
DDT residues from eggs collected from other raptors were also of interest. Peregrine Falcons – 95 p.p.m.; Lanner Falcons - 54 p.p.m.; Black Sparrowhawks – 315 p.p.m.; Pels Fishing Owl – 110 p.m.m.. The shells of Zimbabwe Peregrine Falcon eggs were declared to be the thinnest ever recorded by the Western Institute of Vertebrate Zoology, California.
Human contamination levels were the most illuminating. The analysis of random fat samples collected from a large number of cadavers of ordinary road accident victims showed the average human in Zimbabwe, in the early 1980s, carried residues between 10 and 70 p.p.m.. World Health Organisation figures from elsewhere in the world, at that time, showed that only four people had ever been recorded as carrying more than 20 p.p.m. – the highest ever recorded, up to that time, was 25 p.p.m.. A large sample of human breast milk had an average contamination level of 0,562 mg/L.. One individual had 0,807 mg./L.. The previous world record (West Germany) was 0,569 mg./L..
The South African Minister of Health’s recommendation that Africa, as a whole, should use DDT to combat what appears to be an increase in human deaths due to malaria, therefore, is alarming. Not only is it based on a flawed perception, it does not take into account ANY of the resultant environmental negative spin-offs. This is a matter that the environmental lobby needs to address with a high degree of expedition – because once this programme takes flight it will be very difficult to stop.