Why we need DDT

Forty years after the publication of Rachel Carson’s Silent Spring, there is still no evidence that DDT is hazardous to human health. But banning it is.

Dave Hallsworth

Topics Politics

Rachel Carson’s Silent Spring, the environmentalists’ bible, is 40 years old this year.

In 1936, Carson became the first woman biologist hired by the US Bureau of Fisheries, and later became its Head of Information Services. She left government service in 1952 to focus on writing. Silent Spring appeared in 1962; Carson died of breast cancer two years later.

Silent Spring claimed that the pesticide DDT (1) was a threat to wildlife, and also to human health. As Ronald Bailey, science correspondent for Reason magazine, points out: ‘Carson was…an effective populariser of the idea that children were especially vulnerable to the carcinogenic effects of synthetic chemicals.’ Carson declared that ‘a quarter of a century ago, cancer in children was considered a medical rarity. Today, more American schoolchildren die of cancer than any other disease’. To support this claim, she claimed that ‘12 percent of all deaths of children between the ages of one and 14 are caused by cancer’.

In reality, deaths from most other causes in children were steadily declining, while deaths from cancer remained fairly static. As Ronald Bailey’s figures show, in 1938, cancer killed 939 children under 14 in the USA, in a general population of 130million. In 1998, with a general population of 280million cancer killed 1700.

Carson wrote: ‘Dr [James] DeWitt’s now classic experiments [show] that exposure to DDT, even when doing no observable harm to the birds, may seriously affect reproduction. Quail, into whose diet DDT was introduced throughout the breeding season, survived and even produced normal numbers of fertile eggs. But few of the eggs hatched.’

In fact, DeWitt’s 1956 article in the Journal of Agriculture and Food Chemistry came to a very different conclusion. DeWitt reported no significant difference in egg hatching between birds fed DDT and birds not fed DDT. Carson also omitted to mention DeWitt’s report that DDT-fed pheasants hatched about 50 percent more eggs than ‘control’ pheasants. As to DDT causing cancer in humans, study after study reports no association between DDT exposure and cancer rates.

Dr Joel Bitman and his associates at the US Department of Agriculture published an article in Nature in 1969, which found that Japanese quail fed DDT produced eggs with thinner shells and lower calcium content. Further examination of Dr Bitman’s study revealed that the quails under experiment had been fed a diet with a calcium content of only 0.56 percent, whereas a normal quail diet consists of 2.7 percent calcium. Calcium deficiency is known to cause thin eggshells. After much criticism, Bitman repeated the test, this time with sufficient calcium levels, and the birds produced eggs without thinned shells.

Following years of feeding experiments, scientists at the Department of Poultry Science at Cornell University ‘found no tremors, no mortality, no thinning of eggshells and no interference with reproduction caused by levels of DDT which were as high as those reported to be present in most of the wild birds where “catastrophic” decreases in shell quality and reproduction have been claimed’ (2).

There are many causes of thinning eggshells, including season of the year, nutrition (in particular insufficient calcium, phosphorus, vitamin D, and manganese), temperature rise, type of soil, and breeding conditions (for example, sunlight and crowding). But then, environmentalists rarely let scientific evidence get in the way of their campaigns against DDT and other ‘modern evils’.

DDT became well known in Britain in the 1940s and 50s, via the newsreels of the day. We watched the liberation of the German concentration camps at the cinemas and saw our troops puffing DDT on to the freed inmates and their clothing. Those who claim DDT is a killer must never have seen such film clips. It is difficult to imagine people in a more compromised state of health than those liberated from the Nazi camps. DDT saved many survivors’ lives, by ridding them of disease-carrying lice – and there are no reports in the scientific literature of any adverse health effects from their being soaked.

Carson’s Silent Spring gave rise to the modern environmental movement. And DDT became the prime target of the growing anti-chemical and anti-pesticide campaigns during the 1960s. Reasoned scientific discussion and sound data on the favourable human health effects of DDT were brushed aside by greens, who repeated two allegations against DDT: (i) it is a carcinogen, and (ii) it endangers the environment, particularly for certain birds.

The bandwagon soon took over. In 1969, a study found a higher incidence of leukaemia and liver tumours in mice fed DDT than in non-exposed mice. But many scientists protested that the laboratory-animal studies flew in the face of epidemiology, pointing out that DDT had been used widely during the preceding 25 years with no increase in liver cancer in any of the populations among whom it had been sprayed.

When the World Health Organisation (WHO) investigated the 1969 mice study, it discovered that both cases and controls had developed a surprising number of tumours. Further investigation revealed that the foods fed to both mice groups were mouldy and contained aflatoxin, a carcinogen. When the tests were repeated using non-contaminated foods, neither group developed tumours.

Before long, environmentalists were blaming the decline in bird populations – for example, the osprey and the peregrine falcon – on DDT’s contamination of their environment. A number of states moved to ban DDT, and in 1970 the US Department of Agriculture announced a plan to phase out all but essential uses – even though the National Academy of Sciences declared in the same year that ‘in little more than two decades, DDT has prevented 500million human deaths due to malaria, that would otherwise have been inevitable’.

Here in the UK in 1969, a three-year government study noted that the decline of peregrine falcons in Britain had ended in 1966, even though DDT levels were as abundant as ever. The study concluded: ‘There is no close correlation between the decline in population of predatory birds, particularly the peregrine falcon and the sparrow hawk, and the use of DDT.’

As wrong as Carson was, the Environmental Protection Agency’s (EPA’s) conduct was worse. Anti-DDT activism led to hearings before an EPA administrative law judge in 1971. After seven months of hearing testimonies from all sides of the DDT debate, Judge Edmund Sweeney concluded: ‘DDT is not a carcinogenic hazard to man.… DDT is not a mutagenic or teratogenic hazard to man.… The use of DDT under the regulations involved here do not have a deleterious effect on freshwater fish, estuarine organisms, wild birds or other wildlife.’ But despite the ruling, then-EPA administrator William Ruckelshaus banned DDT.

However, Ruckelshaus never attended the hearings, did not read the transcript, and refused to release the materials used to make his decision. He even rebuffed a US Department of Agriculture effort to obtain those materials through the Freedom of Information Act, claiming they were just ‘internal memos’. Later, it was discovered that Ruckelshaus was a member of the activist group, the Environmental Defence Fund (EDF). Ruckelshaus asked for donations for EDF on stationery that read, ‘EDF’s scientists blew the whistle on DDT by showing it to be a cancer hazard, and three years later, when the dust had cleared, EDF had won’.

Much of the scientific community opposed the DDT ban, pointing out that there was no evidence that DDT was particularly harmful to human health. Yet the ban still took effect. Now, 30 years later, it is apparent that the banning of the domestic use of DDT led to its diminished production in the USA, meaning less availability of DDT for the developing world. The results have been disastrous: between one and two million people die from malaria every year. In South Africa, malaria cases increased by 1000 percent in the late 1990s alone – but dropped by 80 percent in Kwa Zulu Natal in 2000, the one province that still extensively used DDT.

According to the WHO, malathion, the cheapest alternative to DDT, costs more than twice as much as DDT and must be sprayed twice as often. Deltamethrin, another mosquito-fighting chemical, is three times as expensive, and the highly effective propoxur costs 23 times as much. For countries with minimal public health budgets, dependent on foreign aid, such substitutes are impractical.

Dr Charles Wurster, chief scientist for the Environmental Defence Fund, may have revealed how some environmentalists really feel about human beings when he was asked if people might die as a result of the DDT ban: ‘Probably…so what? People are the causes of all the problems; we have too many of them. We need to get rid of some of them, and this is as good a way as any.’ (3)

Read on:

Without DDT, malaria bites back, by Roger Bate

Greens vs. the World’s Poor, by Ronald Bailey, Reason magazine

Further readings:

At risk from the pesticide myth, Fox News, 28 July 2002 (on Junkscience)

Statistics on Malaria, The International Development Research Centre

The DDT ban turns 30 – Millions Dead of Malaria Because of Ban, More Deaths Likely, by Todd Seavey, American Council on Science and Health, June 2000

(1) DDT (dichlorodiphenyltrichoroethane) was first synthesized in 1877, but it was not until 1940 that a Swiss chemist discovered that it could be sprayed on walls and would cause any insect that touched it to die within the next six months, without any apparent toxicity to humans. Its effectiveness and persistence as well as costing only a few pennies a pound resulted in its use in anti-malarial efforts worldwide. It was introduced into widespread use during World War II, and became the single most important pesticide through the next two decades. The USA used it widely to prevent troops catching insect bourn diseases like typhus and malaria. After the war, DDT rapidly replaced the old, extremely poisonous, arsenic-based pesticides. The scientist who discovered the insecticidal properties of DDT, Dr Paul Muller, was awarded the 1948 Nobel Prize in Physiology and Medicine.

(2) ‘Effects of PCBs, DDT, and mercury compounds upon egg production, hatchability and shell quality in chickens and Japanese quail’, ML Scott, JR Zimmermann, S Marinsky, PA Mullenhoff, Poultry Science, 1975; 54:350-368

(3) Is the DDT ban intended to control global population?, Paul K Driessen

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Topics Politics


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