DDT

Synonyms and Trade Names (partial list): Agritan, Anofex, Arkotine, Azotox, Bosan Supra, Bovidermol, Chlorophenothan, Chloropenothane, Clorophenotoxum, Citox, Clofenotane, Dedelo, Deoval, Detox, Detoxan, Dibovan, Dicophane, Didigam, Didimac, Dodat, Dykol, Estonate, Genitox, Gesafid, Gesapon, Gesarex, Gesarol, Guesapon, Gyron, Havero-extra, Ivotan, Ixodex, Kopsol, Mutoxin, Neocid, Parachlorocidum, Pentachlorin, Pentech, PPzeidan, Rudseam, Santobane, Zeidane, Zerdane.
Appearance: Odourless to slightly fragrant colourless crystals or white powder.

Overview

DDT was widely used during the Second World War to protect the troops and civilians from the spread of malaria, typhus and other vector borne diseases. After the war, DDT was widely used on a variety of agricultural crops and for the control of disease vectors as well. It is still being produced and used for vector control. Growing concern about adverse environmental effects, especially on wild birds, led to severe restrictions and bans in many developed countries in the early 1970s. The largest agricultural use of DDT has been on cotton which accounted for more than 80% of USA use before its ban there in 1972. DDT is still used to control mosquito vectors of malaria in numerous countries.

DDT is highly insoluble in water and is soluble in most organic solvents. It is semi-volatile and can be expected to partition into the atmosphere as a result. Its presence is ubiquitous in the environment and residues have even been detected in the Arctic. It is lipophilic and partitions readily into the fat of all living organisms and has been demonstrated to bioconcentrate and biomagnify. The breakdown products of DDT, 1,1-dichloro-2,2-bis (4-chlorophenyl)ethane (DDD or TDE) and 1,1-dichloro-2,2bis (4-chlorophenyl) ethylene) (DDE), are also present virtually everywhere in the environment and are more persistent than the parent compound.

The use of DDT has been banned in 34 countries and severely restricted in 34 other countries. The countries that have banned DDT include Argentina, Australia, Bulgaria, Canada, Colombia,Cyprus, Ethiopia, Finland, Hong Kong, Japan, Lebanon, Mozambique, Norway, Switzerland, and the USA. Countries that have severely restricted its use include Belize, Ecuador, the EU, India, Israel, Kenya, Mexico, Panama, and Thailand.

Usage in South East Asia

 

Used or Found in Country?

Years of Usage

Regulatory Controls

Cambodia

Yes

1950-92 – present?

Banned in 1992

Lao PDR

Yes

1953 -1992
Present?

Banned in 1992

Malaysia

Yes

Until 1999

Banned in 1999

Thailand

Yes

1940

Banned in 1983
(for health in 2003)

Indonesia

   

Banned

Philippines

   

Restricted

Viet Nam

   

Banned in 1992

(table references)

Potential Effects on Humans

DDT has been widely used in large numbers of people who were sprayed directly in programs to combat typhus and in tropical countries to combat malaria. Dermal exposure to DDT has not been associated with illness or irritation in a number of studies. Studies involving human volunteers who ingested DDT for up to 21 months did not result in any observed adverse effects. A non-significant increase in mortality from liver and biliary cancer and a significant increase in mortality from cerebrovascular disease has been observed in workers involved in the production of DDT. There is some evidence to suggest that DDT may be suppressive to the immune system, possibly by depressing humoral immune responses. Perinatal administration of weakly estrogenic pesticides such as DDT produces estrogen-like alterations of reproductive development, and there is also limited data that suggest a possible association between organochlorines, such as DDT and its metabolite DDE, and the risks of breast cancer.

Potential Effects on Plants and Animals

DDT is not acutely toxic to laboratory animals, with acute oral LD50 values in the range of 100 mg/kg body weight for rats to 1,770 mg/kg for rabbits. In a six generation reproduction study in mice, no effect on fertility, gestation, viability, lactation or survival were observed at a dietary level of 25 ppm. A level of 100 ppm produced a slight reduction in lactation and survival in some generations, but not all, and the effect was not progressive. A level of 250 ppm produced clear adverse reproductive effects. In both these and other studies, no evidence of teratogenicity has been observed.

IARC has concluded that while there is inadequate evidence for the carcinogenicity of DDT in humans, there is sufficient evidence in experimental animals. IARC has classified DDT as a possible human carcinogen (Group 2B).

DDT is highly toxic to fish, with 96-hour LC50 values in the range of 0.4 µg/L in shrimp to 42 µg/L in rainbow trout. It also affects fish behaviour. Atlantic salmon exposed to DDT as eggs experienced impaired balance and delayed appearance of normal behaviour patterns. DDT also affects temperature selection in fish.

DDT is acutely toxic to birds with acute oral LD50 values in the range of 595 mg/kg body weight in quail to 1,334 mg/kg in pheasant, however it is best known for its adverse effects on reproduction, especially DDE, which causes egg shell thinning in birds with associated significant adverse impact on reproductive success. There is considerable variation in the sensitivity of bird species to this effect, with birds of prey being the most susceptible and showing extensive egg shell thinning in the wild. American kestrels were fed day old cockerels injected with DDE. Residues of DDE in the eggs correlated closely with the dietary DDE concentration and there was a linear relationship between degree of egg shell thinning and the logarithm of the DDE residue in the egg. Data collected in the field has confirmed this trend. DDT (in conjunction with other halogenated aromatic hydrocarbons) has been linked with feminization and altered sex-ratios of Western Gull populations off the coast of southern California, and Herring Gull populations in the Great Lakes.

Bioconcentration

DDT and related compounds are very persistent in the environment and as much as 50% can remain in the soil 10-15 years after application. This persistence, combined with a high partition coefficient (log KOW = 4.89-6.91) provides the necessary conditions for DDT to bioconcentrate in organisms. Bioconcentration factors of 154,100 and 51,335 have been recorded for fathead minnows and rainbow trout, respectively. It has been suggested that higher accumulations of DDT at higher trophic levels in aquatic systems results from a tendency for organisms to accumulate more DDT directly from the water, rather than by biomagnification. The chemical properties of DDT (low water solubility, high stability and semi-volatility) favour its long range transport and DDT and its metabolites have been detected in Arctic air, water and organisms. DDT has also been detected in virtually all organochlorine monitoring programs and is generally believed to be ubiquitous throughout the global environment.

Accumulation Studies

DDT and its metabolites have been detected in food from all over the world and this route is likely the greatest source of exposure for the general population. DDE was the second most frequently found residue (21%) in a recent survey of domestic animal fats and eggs in Ontario, Canada, with a maximum residue of 0.410 mg/kg. Residues in domestic animals, however, have declined steadily over the past 20 years. In a survey of Spanish meat and meat products, 83% of lamb samples tested contained at least one of the DDT metabolites investigated, with a mean level of 25 ppb. An average of 76.25 ppb p,p'-DDE was detected in fish samples from Egypt. DDT was the most common organochlorine detected in foodstuffs in Vietnam with mean residue concentrations of 3.2 and 2.0 µg/gm fat in meat and fish, respectively. The estimated daily intake of DDT and its metabolites in Vietnam was 19 µg/person/day. Average residues detected in meat and fish in India were 1.0 and 1.1 µg/g fat respectively, with an estimated daily intake of 48 µg/person/day for DDT and its metabolites.

DDT has also been detected in human breast milk. In a general survey of 16 separate compounds in the breast milk of lactating mothers in four remote villages in Papua, New Guinea, DDT was detected in 100% of samples (41), and was one of only two organochlorines detected. DDT has also been detected in the breast milk of Egyptian women, with an average total DDT detected of 57.59 ppb and an estimated daily intake of total DDT for breast feeding infants of 6.90 µg/kg body weight /day. While lower than the acceptable daily intake of 20.0 µg/kg body weight recommended by the Joing FAO/WHO Meeting on Pesticide Residues (JMPR), its continuing presence raises serious concerns regarding potential effects on developing infants.

 


Adapted from Persistent Organic Pollutants: Information on POPs, their alternatives and alternative approaches (United Nations Environmental Programme (UNEP) 1995).

50 year old DDT found in a Hospital in Tunisia
Source: FAO
Hatfield Consultants The World Bank funded by the Canadian POPs Trust Fund through the      
Canadian International Development Agency
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