Questions that have always intrigued you about the world will appear in this, your section,
and be answered by other readers. Please address your answers and questions to ‘Curiosities’.
Just how dangerous is DDT? If it is as dangerous as some people suggest, why is it still being used in countries like Namibia? What is behind this strategy?
DDT passes through all links of the food chain, beginning as a dusting over crops and ending in milk and butter. Residues of DDT are little affected by washing. It is an organochlorine compound which, although discredited, remains in our environment as it accumulates in the body fat of fish, animals and ultimately humans, causing cancers and other health problems. It is now banned in many countries but still makes profit for the chemicals industry peddling it in the Third World. Of interest may be an information sheet entitled WHO Murdered Africa from Nemesis, 1 Quarry Bank Road, Chesterfield S41 OHH, England.
Dubai, United Arab Emirates
There is no straightforward answer. DDT has a very bad public image, which may be both deserved – and exaggerated. It is a persistent insecticide, which hangs around in the environment for a long time and has the ability to build up in food chains. Just how persistent depends on temperature, sunlight intensity or rainfall.
In terms of wildlife, it can be classified as dangerous. It’s toxic to fish and a range of invertebrates, can interfere with oestrogen production in fish and may have effects on hormonal balance and fertility in other animals as well.
Its use in agriculture in the US and Europe led to population decline in birds of prey – but populations recovered a decade after use stopped. It also led to imbalances in the populations of insects, causing severe pest outbreaks.
Even used very carefully in Zimbabwe to control tsetse flies, it harmed woodland birds, lizards and birds of prey. (See RJ Douthwaite & CCD Tingle, DDT in the Tropics: The impact on wildlife in Zimbabwe of ground-spraying for tsetse fly control, 1994, Natural Resources Institute ISBN 0 85954 364 1. Available from CAB International, Wallingford, Oxon OX10 8DE, UK)
However, toxicity to humans is actually rather low. A single, oral dose of 10 mg/kg is sufficient to cause illness in some but not all people. The WHO classes it as ‘moderately hazardous’. Young babies whose mother’s milk contains high levels of DDT have slower reactions. Interference with thyroid activity has also been shown, with resulting disturbance of steroid hormone metabolism.
DDT is still used because it’s cheap and effective at killing insects. In the absence of alternatives and where its use saves lives – as in malaria control – governments in developing countries may have little choice but to use it. DDT is a prime case for caution and each instance should be looked at carefully before application is approved. To assess any potential environmental and health impacts in Namibia I would need to know what it is used for, in what quantities and whereabouts. If you wish to pursue this further, please write to me at the address below and I shall be happy to look into it for you.
Dr Colin CD Tingle
Environmental Sciences Department,
NRI, Central Avenue, Chatham Maritime,
Kent ME44TB, UK.
Tel: 1634 883205 (direct line).
e-mail: [email protected]
1, 9 Refit at Louvre no picnic – potential 11, 30 (8,8)
6 Badger rest to get the dirt! (5)
10 Right headwear, with ice particles forming, for Alpine romance (7)
11 Natal unaffected? (7)
12 The gallery is what the modern-day professional is all about (5)
13 Part of Russia sat about in rumpled plaid (9)
14 Back snail at Indianapolis – home of the Nationals (8)
16 Bite back-biter (4)
20 Antediluvian type using craft to avoid 11, 30? (4)
21 Sacrifice Tamil move – preparing to omit Vishnu’s initial influence (8)
24 Bloomer after a laboratory association with mineral (9)
25 Does rotating action force the king to remove hat? (5)
27 It immunizes hundreds in eastern Virginia in the van (7)
28 Guy turns up in rumpled suit – a potential 11, 30 (7)
29 Sovereign city of Belgium (5)
30 Ruin princess’s 24 plant (8)
2 So laid back, with alias coming from Japan (5)
3 Broad-minded Roman, perhaps (8)
4 Muses about bed – one is on dope (8)
5 Dane gets fish back into the Community review (6)
6 Jog up to former wife and squeeze! (6)
7 Hope country plays Turin aria (9)
8 The Spanish in heaven – no heart to show classic beauty (5)
9 See 1
15 Barrage to prevent potential 11, 30? (9)
17 Press argument to reciprocate aid (3,5)
18 Steamier parts of the Gulf! (8)
19 Explores below bluff the lie of the land (8)
22 Ugandan despot encased in iron – a human 30 (6)
23 Lend an ear to a non-alcohol aim ...(6)
24 ...block ear piece ! (5)
26 Move (following 6 across) peaceful Christian right away from potential 11, 30 (5)
1, 9 It happened to Mount Saint Helens in 1980 (8,8)
6, 26 Violent movement of tectonic plates (10)
10 A Romance dialect or a geological epoch – or referring to an Alpine province conquered by Augustus (7)
11, 30 Catastrophe, factor of physical geography (7,8)
12 Important art gallery of Madrid (5)
13 Autonomous republic of Russia, capital Kazan (9)
14 Citizens of a Mediterranean country, unified in 1870 (8)
16 Flying insect, member of the Culicidae – mosquito family (4)
20 Old Testament father of Shem, Ham and Japheth (4)
21 Sacrifice or offer for sacrifice (8)
24 Fine form of gypsum, ranked 2 in Moh's Scale of Hardness (9)
25 Small brimless hat or cap (5)
27 Injected preparation intended to provide antibody reaction and, hence, immunity to disease (7)
28 Tidal wave (7)
29 City of south-east Belgium (5)
30 See 11
2 Japan's oldest city, on Honshu island (5)
3 The Western Christian Church (8)
4 Poison which turns brown when exposed to the air (8)
5 Anglicized spelling of the King of England, 1016-35 (6)
6 Blackmail (6)
7 Fictitious country of South-East Europe created by Anthony Hope (9)
8 Wife of Menelaus, abducted by Paris (5)
9 See 1
15 Mass movement of ice and snow – from the French verb 'to swallow' (9)
17 Catch-all term adopted for TV and newspapers (3,5)
18 Domains of Muslim rulers (8)
19 Lines on a map joining points of equal altitude (8)
22 Extreme scarcity, particularly of food and water (6)
23 Escort or turn up (6)
24 Smithy's block (5)
26 See 6 across
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