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The bombshell of 1962

The unquestioning complacency and acceptance of the scientific progress offered by the chemical and agricultural industries was shattered in 1962 by the highly detailed and well-documented book by Rachel Carson called Silent Spring (the reprint of 2012 is still powerful reading!). In it, she highlighted the technological downsides of many of the practices that were then current. She began with applications of insecticides and herbicides that were being used indiscriminately. Her first example was DDT, which indeed is a very effective pesticide—it was initially used to attempt to reduce mosquito populations, and hence malaria. Even today malaria kills around one million people per year, so clearly this is a significant disease. In the enthusiasm to suppress malaria, however, the highly negative side effects of DDT in other types of usage were ignored.

The chemical industries were geared up for mass production as part of the wartime efforts, so inevitably they were seeking new mass-market applications, including agriculture. Consequently, vast quantities of pesticides were being manufactured and applied, not just by specific crop spraying, but by aerial sprays from low-flying planes. This style of technology was rapid, but totally random, as it covered far more area than was intended or needed. The USA alone used in excess of 300,000 tons of pesticides, just in 1962. To Carson, and to most modern critics, the very obvious downside of this crude approach is that the pesticides not only killed pests, but also every other creature that came into contact with the chemicals. Doses were high and poorly controlled. Further, the pesticides often were retained for a considerable time, not only in the plants and the soil, but also in the creatures that ingested them from the spraying or by eating contaminated products.

The real mistake was that such crude chemical attacks caused the death not just of specific pests, but all the insects and other wildlife that had been helping to maintain a natural balance. Once destroyed, the process was irreversible. It was also an ineffective method as, without natural predators, the creatures that fed on the crops (nominally pests) could re-establish themselves very rapidly without predators. This is a fairly obvious blunder, because insect life cycles are far shorter than those of birds or small mammals that would normally have been maintaining a natural equilibrium among various species.

Carson cited numerous examples of data that showed, even where the sprayed concentrations were well below parts per million, that many chemicals accumulate in the bodies of animals: subsequent analyses of corpses included organs with values of many thousand parts per million. This is a thousand-fold concentration enhancement as a result of biological reactions, so this totally invalidates testing at the levels that were being applied. Indeed, this style of problem is just as serious today. The results of contamination were death or sterility for many animals, and extinction of various species. All such data were discredited by the agrichemical companies as pure coincidence. They also organized a campaign to discredit Carson’s entire work.

Fortunately (perhaps an odd choice of word), people who were using the sprays, or received high doses, were also taken ill or died. Human deaths then opened a way to gain attention for the general public and commence impartial studies and analyses of the effects of the pesticides and herbicides. At the time, in 1962, there was far less understanding that many chemicals can play a catalytic role in biochemistry, and that, once ingested, they could react to produce damage and diseases that would never have appeared in trials on plants for which they were initially intended.

Trials on the toxicity of pesticides on humans were of course never attempted, although they would have revealed a wide range of effects, from temporary to permanent disability or death. There should have been a greater awareness of the dangers, as even then some other species showed extreme sensitivity; for example, young shrimps were killed by insecticide concentrations below one part per billion. From the shrimp perspective, this is a volume of insecticide of one cubic centimetre (i.e. baby shrimp size) diluted into an Olympic-size swimming pool. Note that current analytical techniques can often do one hundred times better than this, so in the future, far more of these problems will be identified.

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