Why Soft Sounds Are Pleasurable

At the other extreme of physical pain, are soft, tactile impressions that are just above the threshold of perception. Imagine a gentle wind finding its way through body hair or the lightest of drizzles falling on one’s bare shoulders. The acoustic equivalent of such pleasures is the distant sound of rustling leaves. At about 10 decibels it has less than 10 times the intensity of the faintest audible sound. And it has only one of ten trillionths of the power per area of a sound wave that could cause pain. It seems that we have evolved not only to react to extreme stimuli that endanger us but also to be rewarded when the environment toys with the lower limits of our senses.

Although the above numbers are mathematically accurate—-they are based on the formula which equates decibels with 10 times the logarithmic ratio of a sound’s intensity to our threshold intensity of 10-12 watts/meter2—they exaggerate what our eardrums actually experience.


from hyperphysics.phy-astr.gsu.edu  Check link for neat demo idea using methane in pipe to visualise pressure variations.

Before delving further, just what is sound? When a leaf moves back and forth, or some other body vibrates, the oscillation causes a periodic disturbance of the surrounding air molecules. The movement in one direction causes molecules of the air (or other transmitting medium) to bunch up, increasing pressure in one region. As the object reverts to its original position, a region of less crowding among molecules occurs as well. Meanwhile, the crowded region transmits its kinetic energy to other particles of the medium, repeating the pattern of high and low densities as the pressure wave propagates away from its source.

As a result, what’s more appropriate in comparing sound-strength is the use of pressure amplitude, which is proportional to the square root of a sound’s intensity. For example if our slightly rustling leaves come in at 10 dB and a pneumatic sidewalk-breaker next to us is painfully wreaking havoc at 120 dB, first we figure out the intensity ratio from the exponential version of the decibel-log formula:

I2/I1 = 10 0.1(dB2 – dB1) =10 0.1(120 – 10) = 1011.

Then by taking the square root  of 1011, we obtain the pressure ratio— about 316 000. That’s still a huge factor for how much louder the pneumatic drill is in comparison to the distant sound of gently moving leaves.

A little more number-crunching can make us appreciate how wonderfully sensitive our ears are, at least when they are working well. The exact pressure amplitude(ΔPm) of a rustling sound can be calculated from:

ΔPm = √(2Iρv) ,

where I is the intensity, and ρ and v are the density and velocity of the medium. For air at room temperature the latter numbers are 1.2 kg per meter cubed and 343 m/s, and for a 10 dB-sound, I = 10-11 W/m². Thus ΔPm is  9.07 X 10-5 pascals. Comparing it to the atmospheric pressure of 101.3 kPa, we can actually detect a difference of 1 part in a billion, and it’s enough to give us pleasure! When you consider that it takes a few parts per million of psychotropic substances to buzz the brain, something that many marvel at, to me our acute sensitivity to sound seems more remarkable, while no drugs are necessary.


The History of DDT Through an Ellulian Lens

We rarely see the word technique used in the Ellullian sense of the word. Coined by Jacques Ellul in the 1950s when Technological Society was first published, technique refers to an ensemble of methods embedded in every field of human activity. These methods are rationally arrived at and seek efficiency. By such a definition, technique does not only include machines, robots and electronic technology but also economic systems, military and advertising strategies, human resources and management of government departments, corporations and research labs. In technique, spontaneity and tradition are replaced by a complex set of acts with the aim to achieve some kind of quantifiable goal. While technical progress grows irreversibly and exponentially, its far-reaching effects on the human psyche, physiology, culture and environment cannot all be foreseen. It’s through this lens that we’ll examine the history of the pesticide dichlorodiphenyltrichloroethane, abbreviated as DDT.

ddt-spray-beach.jpgIn order to encourage living scientists to continue their excellent work, Nobel Prizes are never awarded posthumously. The problem with that restriction is that a discovery’s full impact on its field and society is usually not immediately apparent. And unfortunately there is no minimum time that has to elapse between publication of the achievement and the granting of the award. One year before the Nobel committee committed its biggest blunder by awarding the 1949 Prize for Medicine for the lobotomy, the 1948 Prize for Medicine was awarded to Paul Müller “for his discovery of the high efficiency of DDT as a contact poison against several arthropods.” DDT had been first synthesized back in 1874 by Zeidler, but Müller found uses for the compound in the 1930s while searching for a contact poison against clothes moths and carpet beetles.  In his acceptance speech, Müller mentioned the heavy World War II outbreak of typhus in Naples in October 1943. Three months later, 1.3 million people were sprayed with DDT over a period of 3 weeks.


An Epidemic Typhus species, the type of louse that was killed by DDT.

The poison was not absorbed through human skin but killed body lice which were infected with the cause of typhus fever, Rickettsia prowazekii. The disease, which otherwise would have had about a 40% mortality rate, was brought under control. Hundreds of thousands of lives were saved.

Once technique was involved in war, with its tentacles spread over weaponry, strategy, propaganda and economics, the effects became devastating on an unprecedented scale.  Typhus was more likely to develop in an already poor area impacted by such a war. And often the only way to deal with problems exacerbated by technique is with more technique, which in this case was, again in Müller ‘s words, “an introduction by General Fox of DDT with total exclusion of the old, slow methods of treatment.”

After the war, DDT also became an effective way of fighting malaria by attacking their vector, the Anopheles mosquito. By 1967 endemic malaria was wiped out in Greece, Italy and in many subtropical Asian and Latin American countries. It should be pointed out that draining breeding grounds in those areas also played a key role in eradicating the disease. This wasn’t possible in tropical areas in Africa where, in addition, the necessary infrastructure for a spraying program was often lacking. Consequently only a few African countries participated. A couple of years later, it was learned that some mosquito populations were becoming resistant to DDT.

Insect resistance should not have come as a complete surprise. In accepting his prize almost twenty years earlier, Muller had stated:

Generally speaking the housefly is very susceptible to DDT; unfortunately some fairly resistant species of fly have lately been observed. 

It turns out that within any species being treated with any insecticide, there will always be a few individuals who escape death. These survivors are the ones who continue to reproduce, so they will leave behind more of the genes that made them less vulnerable. (Some recent evidence suggests that only a single gene may be required.) After many generations—and it doesn’t take very long; in a single year mosquitoes can go through 25 to 70 life cycles—a once-rare trait becomes the norm.


C14H9Cl5 : 1,1′-(2,2,2-trichloroethane-1,1-diyl)bis(4-chlorobenzene) aka dichlorodiphenyltrichloroethane aka DDT

That wasn’t the only issue with DDT.  It’s highly resistant to light and oxygen and to organisms’ mixed-function oxidase
enzymes (MFOs), which normally oxidize and break down fat-soluble toxic substances. Other enzymes can convert DDT to DDE by replacing a chlorine and a hydrogen from the middle of the DDT molecule with a double bond. But DDE is still toxic and is  even more resistant to the action of MFO enzymes. In other words we can consider DDT not to be biodegradable overall. Moreover DDT’s and DDE’s strong tendency to dissolve  in lipids(100 g/L for DDT at room temperature) and not in water (only 2μg/L for DDT) means that fat tissue can act as a sponge: an organism’s intake of DDT will exceed the amount excreted. This mechanism repeatedly increases concentration of the toxin as one organism eats another. The higher the organism is in the food chain, the more DDT it will have in its fat tissue. Populations of high trophic predators such as eagles and falcons were affected when DDT was used heavily as a pesticide. The accumulated poison in their tissue interfered with steroid metabolism. Affected birds became incapable of moving enough calcium into their eggshells.  As the thin shells cracked, their embryos were killed by the entry of bacteria. Along with unrelated pressures that had been placed on the birds, DDT led to their precipitous decline.

Although written in the 1950s Ellul’s Technological Society already mentioned DDT’s unforeseen effects on mammals—there was research revealing DDT’s impact on bones of newborn calves. I couldn’t find any later work that corroborated such a claim, but DDT is eliminated far more slowly in cattle than in humans. Without further input, the half life of DDT in humans is 69 days but 335 days in cattle based on lactation studies in 1965 by RC Laben. More recently (2011), adults with high serum concentrations of organochlorine pesticides such as DDT have been found to have lower vitamin D levels. Although DDT is not a category 1 carcinogen, it is classified as a probable carcinogen based on animal studies. And there are other serious health concerns to be considered. A few years ago, a Lancet review study of the health risks and benefits of DDT stated that indoor application of DDT could be effective in some settings of malaria-infested areas. But they also pointed out that through continuous spraying, mothers could carry a body burden of DDT, which raises the risk of preterm birth and early weaning. Other risks such as neurological effects could also affect mothers and workers receiving and applying the spray, respectively.

Organizations currently dedicated to abating malaria seem to be using a variety of strategies. Non-DDT alternatives have been used in eave tubes, which cause mosquitoes to get fooled into entering the tubes as they follow the CO2 trail coming from human inhabitants inside the homes. Along with better built houses, these have helped control malaria in Tanzania. Elsewhere this approach is being combined with sugar traps and sterilisation of male mosquitoes.


After the second world war, clothes sprays contained a 5% solution of DDT to kill moths. The same compound was included in moth balls.

What made DDT a serious problem was the scale of its application, a recurring theme when it comes to technique. First used as an insecticide in 1939, it eventually became one of the most ubiquitous pesticides on the planet from 1946 to 1972. It was used on cotton, fruits, potatoes and corn to kill worms, moths, beetles and borers, respectively. Aside from its use against life-threatening diseases such as malaria and typhus, it also served as an agent against far less serious pests such as moths in clothes and insects in museum specimens. With such overzealous applications it’s no surprise that by the mid 1960s human breast milk across the planet suddenly contained twice the maximum levels set by WHO (World Health Organization). These levels were equal to the concentrations needed to cause biochemical changes in rats. Soon after, Sweden issued a two-year moratorium of DDT. The eventual cancellation of DDT’s registration by the USA’s Environmental Protection Agency in 1972 was based on human health concerns, not directly on ecological grounds. From Public Health Reports:

Hayes, a witness for the state, declared DDT safe on the grounds that soldiers sprayed with it in the 1940s and prisoners who swallowed it in studies performed in the 1950s had suffered no adverse effects. Lawyers and witnesses for the petitioners dismantled Hayes’ testimony by focusing on the human health questions left unanswered by such studies: DDT’s long-term toxicity; its effects on the endocrine system and liver; and its effects on newborns, children, and women.

DDT also inspired the synthesis of similar organochlorine pesticides, most of which are fortunately banned today due their toxicity and environmental persistence. The worst of the bunch were the cyclodiene pesticides, which unlike DDT, were absorbed through the skin. Even at low doses these compounds induced convulsions. Meanwhile in a reasonable position, the World Health Organisation supports the ban on DDT in most countries while concluding:

that countries that are relying on DDT for disease vector control may need to continue such use until locally safe, effective, affordable and environmentally sound alternatives are available for a sustainable transition away from DDT.

Needless to say there are many influential people who disagree with Ellul’s analysis of technique. They find the concept too fuzzy and his tone excessively pessimistic. His dismissers include those who believe that DDT should never have been banned anywhere, even if the countries were malaria-free. Oddly some DDT-enthusiasts even villify Rachel Carson, author of Silent Spring, even though, as we mentioned previously, the decision to deregister DDT in the United States was not directly based on environmental concerns. Like Hayes, they are “couched in a political view that remained faithful to a vision of the U.S. as the superpower and global protector it became in the years after WWII.” While not acknowledging the existence of technique’s web, they also feel society does more harm than good by trying to stifle or regulate technology. (Ironically the regulating bureaucracies are part of Ellul-defined technique.) Ellul was not at the opposite end of the spectrum. He was apolitical and certainly never felt that we should get rid of technology; he realised that its abandonment would be suicide for our species. Instead he expressed the need to transcend it. How could that happen? If we remain scientific while letting more than just a trickle of ecological and spiritual sense flow through our beings, we will be on more benign and autonomous tracks.*

*The fact that the word “track” initially came to my mind in the singular, is one of so many reminders of how narrow our points of view can be when contemplating our futures. There was a time, not too long ago, when different civilisations coexisted, unaware of the others’ existence and travelling a variety of paths.

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