Rachel Carson’s Silent Spring – Part 3

Following on from part 1 and part 2 in a series of summarised points about pesticide use presented in Rachel Carson’s book, Silent Spring. For some practical advice on smart biological controls in your garden to reduce pesticide use, check out Daphne’s Dandelions.

Beyond the dreams of the Borgias

The build up of chemicals due to recurrent exposure can have disastrous cumulative effects on individuals’ health. While many pesticides are labelled as safe, they often cannot account for the effects of multiple uses, or the effect of the interaction with other chemicals, or indeed the concentrations that can be achieved when combined with the use of neighbours and the wider community. Many of the tests are conducted in highly artificial lab conditions on rats whose diets are carefully controlled – very unlike the human diet.

Some farmers have been known to use pesticides that exceed the amount legally allowable on many foods, and there is often little protection afforded to the consumer in this regard.

Government departments that test foods are often underfunded and understaffed so that only a very small percentage of food sold is actually tested [additional comment: this appears to be the case in New Zealand as well]. When it is found to be dangerous, often nothing is done to warn the public or recall the product from the shelves, due to local and national laws that limit the powers of the related agencies. In cases where products have been withdrawn, it is after the fact and the damage has already been done.

A brilliant quote to summarise: “to establish tolerances is to authorize contamination of public food supplies with poisonous chemicals in order that the farmer and processor may enjoy the benefit of cheaper production – then to penalize the consumer by taxing him to maintain a policing agency to make certain that he shall not get a legal dose. But to do the policing job properly would cost money beyond any legislator’s courage to appropriate, given the present volume and toxicity of agricultural chemicals. So in the end the luckless consumer pays his taxes but gets his poisons regardless.” (p. 183, 2002 edition)

The human price

While some chemicals are known to be safe for humans, sometimes this is due to an enzyme in the body which may lessen its harm. However, if this enzyme is disabled due to contact with other chemicals, then the body’s defense is severely compromised. Since, in day to day life, humans come into contact with a wide range of chemicals, the risks of some chemicals that have been established as “safe” may be heightened from prolonged exposure to a range of chemicals (not necessarily other pesticides even, but food additives or natural substances), whose interactions cannot always be predicted.

The ability to directly point to any one chemical as the cause of particular symptoms is compromised by varying responses of individuals to such chemicals.

One in every four

It is becoming clearer that cancer can be caused by various environmental factors. While Carson does not try to prove that DDT based pesticides directly cause cancer in all individuals, she notes that, based on the knowledge of cells and what causes cancerous cells, and the knowledge of the effects of DDT pesticides, their use should be extremely limited given the potential cause-and-effect relationship. Cleverly, she addresses a question many may ask: why not just look to cures for cancer? She cites Dr Hueper, a cancer researcher who has also had much experience with patients. While treatment is obviously necessary, prevention can be far more effective and cause far less damage to individual health in the first place.

Nature fights back

While some chemical attacks can be effective on the target insect, often this paves the way for other pests to invade as the natural checks and balances of the new pest have been upset by chemical spraying. Sometimes the new pests or species resistant to the chemicals that have flourished in the absence of other insects can be dangerous not just to plants, but to humans and livestock.

While biological controls offer effective and low-cost alternatives to chemical spraying, they are incredibly rare. This is often because large chemical companies support research in Universities on pesticides, but not biological controls. This creates a wealth of attractive scholarships and staff positions. Biological control studies on the other hand are often underfunded, thus salaries are often low and positions few. Many of the leading entomologists on the other hand have had their entire research repertoire sponsored by the chemical industry.

While chemical sprays are not altogether ineffective, optimal results are actually achieved when they are applied sparingly and at the appropriate time, as they do not upset the natural predators and other checks on a pest. Chemical companies often have little motive to inform farmers of this fact.

The rumblings of an avalanche

Pest resistance is becoming an increasing problem, because unlike humans, insects can become resistant to a chemical in the period of two months to several years. Carson illustrates the problem with a few alarming statistics: “Before 1945 only a dozen species were known to have developed resistance to any of the pre-DDT insecticides…resistance began a meteoric rise that reached the alarming level of 137 species in 1960.” The problem of resistance was especially acute with vector (disease carriers) control programmes. Additional note: The problem is analagous to bacterial resistance through the excessive and unnecessary use of antibiotics for humans and animals, and anti-bacterial cleaners. In New Zealand, antibiotic resistant bacteria was a virtually nonexistent problem in 1999, but in 2008 an estimated 5000 cases were evident, according to the Institute of Environmental Science & Research. Read the full NZ Herald article for more, or google “superbugs”.

While DDT is still used in controlling disease-carrying pests (vectors), Carson argues that their use often exacerbates the problem by simply giving way to resistant strands, and notes several areas in which this is becoming an issue: mosquitoes carrying malaria, bacteria carrying houseflies, and body lice. Often vector populations actually increased after being treated with DDT pesticides, and one wonders why they are still used to control mosquitoes in the developing world today.

Due to the fast development of resistance to chemical pesticides, their use is not only futile but economically inefficient. Acquiring stockpiles of the latest miracle pesticide carries the very real risk of it being useless in a very short amount of time, yet great investment can be required for those relying on its properties.

The other road

In this chapter Carson describes an array of biological controls that could be used, and have been used with great success under certain conditions, with fewer ecological and sometimes economic, costs. What she stresses is that each is a biological approach that is “based on an understanding of the living organisms they seek to control, and of the whole fabric of life to which these organisms belong.”

The controls she mentions include:

The breeding and releasing of sterilized male insects, which was successfully used to control the screw-worm fly.

The introduction of a disease, bacterial or viral, to the target species’ environment, such as the bacillus thuringienis which causes fatal septicemia in the larvae of the flour moth. Damage to crops is far less than chemical sprays as the insects have less time to develop, and the diseases are often species specific so they don’t harm other living creatures, or if they do, it is much smaller in number.

The introduction of predatory or parasitic animals that attack or consume the target pest, as was used to control the gypsy moth, Japanese beetle, scales and mealy bugs. This method is used in many planted European forests, where they go so far as to build homes for woodpeckers.

Using or manufacturing the secretions of insects, such as the manufacture of a fake pheromone (sex hormone) to confuse male insects and prevent them from finding mates. This has been used in some cases such as the gypsy moths. Sometimes attractants are used in combination with poisons, but instead of spraying the whole lot over vast areas of land, the chemicals are administered to pieces of fiberboard, which are then scattered on the affected area. These pieces are unlikely to be eaten by other wildlife, and the residues are quickly dissipated, thus not contaminating soil or water.

The use of sound, such as the playing of female mosquito noises at a charged grid that zaps mosquitoes on contact. Repellant noises are also a potential avenue of research.

A quote which summarises the key messages in Carson’s book well:

“Through all these new, imaginative, and creative approaches to the problem of sharing our earth with other creatures there runs a constant theme, the awareness that we are dealing with life – with living populations and all their pressures and counter-pressures, their surges and recessions. Only by taking account of such life forces and by cautiously seeking to guide them into channels favorable to ourselves can we hope to achieve a reasonable accommodation between the insect hordes and ourselves. The current vogue for poisons has failed utterly to take into account these most fundamental considerations.”


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