Environmental equilibrium and chemicals – impossible or not?
I have taken several examples from Rachel Carson’s book Silent spring. One of the examples deals with an attempt in the 1950s to save the forests from pests such as the spruce budworm by a large-scale spraying program of insecticides. These were such massive operations that their logic is difficult to understand today. According to Carson DDT ended up in the forest creeks and killed small insects, but then the young salmon and trout which depend on these insects for food died from hunger. Not only the fish in forest creeks died, also forest birds in parks were killed, many of them after eating large amounts of insects, caterpillars and earthworms poisoned with the organochlorine pesticides. However, since the insects recovered more rapidly than birds after this onslaught, there were nowhere near enough birds to keep insect numbers in check, and so the authorities ordered an ever more massive spraying operation.
Horror of vacuum
It is not only birds and insects. There is a complex and fierce competition in nature for limited resources, indeed it can be looked as a war of everybody against everybody else. If empty space is found in one niche, it results in a boom of reproduction and a rush to utilise any unused resources. The worst outcome may well be that the most harmful organism may be the most successful, and from the human perspective, the situation has gone from bad to worse.
Antibiotics, the poisons of microbes
Competition is not only between animals, it is also between microbes. If we destroy the microbes of our gut by using antibiotics we may soon be seriously ill with a superinfection. The numbers of a microbe which are normally well controlled, such as Pseudomonas bacterium or Candida fungus, may explode before the normal gut flora recovers after an antibiotic treatment. In such a case, a microbial species which exists normally as a minority in a mixed microbial population may cause a life-threatening intestinal infection. Therefore two important principles are followed in the treatment of infectious diseases. Firstly, one should not treat just to be on safe side. There must be a clear indication for the use of antibiotics, e.g. flu is not a reasonable indication for using antibiotics. Secondly one should use as selective an antibiotic substance as possible, one that affects only the microbe in question in that particular infection.
A typical example is tonsillitis caused by A-type Streptococcus. It is treated with penicillin, an antibiotic effective against gram positive bacteria, and not with an antibiotic which is non-selectively killing very many types of bacteria. Tetracyclines and similar broad-spectrum antibiotics which destroy many gram negative bacteria of the gut tend to cause superinfections that may be worse than the original infection.
This should not be interpreted to mean that severe diseases should not be treated by potent and life-saving antibiotic drugs. The message also is not that insecticides should never be used. The guiding principle emphasized in all pharmacology teaching is that one should treat only after concluding by using professional skills that the benefit is greater than the risks. Physicians call this a proper indication of treatment. For antibiotic treatment, this indication is bacterial, not a viral infection. Therefore one should never buy over-the-counter antibiotics in less developed countries for self-treatment of infections. In the same way, the use of pesticides should always be left in hands of trained people. The aim is always that the operations are as limited as possible, that they are only used when a clear benefit can be expected, and that there is no attempt to destroy everything, because that will be clearly more harmful than beneficial.
When the principles of ecological competition were not yet understood, there was an assumption of the more the better. One could imagine that no insects would be beneficial for crops, just as in the beginning of the antibiotic treatment one thought that no bacteria could be beneficial to health. Both ideas show clearly that the initial enthusiasm led to misdirected ideas when taking into consideration only one aspect and not the entire ecological consequences. Later, it has become clear that properly directed and sensible use of carefully selected pesticides has only a minimal impact on the ecological balance.
There are large variations between countries in the use of pesticides. In some countries only half a kilogram of pesticides are used for every hectare of crop field whereas in other countries, fifteen kilograms are utilized. This may reflect different conditions, but it also depends on different cultures and attitudes. Indiscriminate use of pesticides just as promiscuous use of drugs is a great problem, and much educational work has to be done to change the traditions of how things have always been done, to improve safety and to increase trust among consumers.
Persistence is a problem
DDT and other chlorinated pesticides are a special problem because of their persistence. The most toxic among these agents such as dieldrin, aldrin, and endrin have been banned for good reasons in most countries for a long time. With respect to the relatively non-toxic DDT, there is no point of trying to achieve a complete ban, but instead one should strive for a limited, strictly controlled use in the most crucial indications similarly to the proper use of drugs with side effects. An important use of DDT is malaria control. A good way of preventing access of malaria-carrying mosquitoes into dwellings is by using malaria nets impregnated by DDT. These are much more efficient than plain netting alone. This kind of use causes no ecological harm.
In fact also Rachel Carson recommended careful and well controlled use of less toxic pesticides, linked with better research, rather than a total ban on their use. She was an environmental expert, and many of her recommendations are still valid. In health aspects she was a layman, and her theoretical considerations were often off-key. She also did not seem to understand the crucial meaning of dose, failing to appreciate the difference between a low and a large dose. This sometimes creates problems, when the readers believe indiscriminately both her valid and her outdated and ill-advised opinions without proper critical analysis.
Remarkable progress has been made in understanding the rules by which pesticides can be used and how they should not be used. As a consequence, the worst environmental problems of today are not caused by pesticides or other very toxic chemicals, our most important threat is unsustainable consumption as well as inappropriate land use that fragments and destroys the ecological habitat in such a way than in the long run it will be catastrophic both to nature and to ourselves.
To be able to live in harmony with our environment without destroying nature and our own future, the human being has to understand the basic principles of nature. In this way, opportunities can be exploited in a safe and sustainable manner, respecting the other species inhabiting this globe.
Notes and references
- Bacteria are divided to gram-positive bacteria stained blue in so called Gram-staining, and gram negative bacteria stained red. The difference is based on different cell wall structures of these microbes.
- See the chapter "What is the wisdom in “It’s the dose that determines that a thing is not a poison”?"
One level up: How to protect our common environment?