DDT in Food
1. Dichlorodiphenytrichloroethane (DDT) is an organochlorine insecticide with a broad spectrum of activities such as the control of pest in forest and on agricultural crops, household pests, vector-borne diseases like malaria, typhus, etc.
2. DDT is ubiquitous in the environment. It may enter the environment via its production, transport, application and disposal. DDT can also be migrated to places where DDT has been greatly restricted via long-range transboundary movement. While low levels of DDT in food might be unavoidable, due to its high persistence and lipohilicity, DDT and its metabolites tend to accumulate in fatty tissues of living organisms, and have a tendency to become more concentrated at high levels in the food chain.
3. Because of its possible adverse effects on the environment and human health, the use of DDT has been banned in many countries and later designated as a persistent organic pollutant with restricted use under the Stockholm Convention by the United Nations in 2001.
4. There have been studies indicating that levels of DDT in breast milk samples of Hong Kong mothers were high when compared with those obtained from mothers of other countries. Therefore, there are concerns on the public health implications of exposure to DDT in the population in Hong Kong.
5. Since diet is considered to be the major route of DDT exposure for the general population, the Food and Environmental Hygiene Department (FEHD) undertook a study to investigate the level of exposure to DDT via food in people in Hong Kong.
Toxicity of DDT
1. The target organ for acute effects is the nervous system. It has been reported that a single oral dose of 10 mg/kg body weight (bw) DDT produced illness in some individuals and that 16 mg/kg bw or greater led to convulsions.
2. The Joint Food Agricultural Organization / World Health Organization Meeting on Pesticide Residues (JMPR) in 2000 considered that DDT was no longer used in agricultural practice but might be present in food commodities as a contaminant because of its persistence in the environment.
3. The JMPR in 2000 established a provisional tolerable daily intake (PTDI) of 0.01 mg/kg bw for DDT and its associated compounds. PTDI is an estimate of the amount of a contaminant that can be ingested over a lifetime without appreciable risk. An intake above the PTDI does not automatically mean that health is at risk. Transient excursion above the PTDI would have no health consequences provided that the average intake over long period is not exceeded as the emphasis of PTDI is a lifetime exposure. As peaks of acute dietary intake above the PTDI were not likely to occur, an acute reference dose* was not allocated.
4. DDT could impair reproduction and/or development in a number of animal species. However, available data, though few, on reproductive effects did not support such correlation in humans. DDT was also reported to cause liver damage in experimental animals.
5. DDT is not genotoxic. The International Agency for Research on Cancer (IARC) of WHO has evaluated DDT and its associated compounds. IARC considered that there is sufficient evidence in experimental animals but inadequate evidence in humans for the carcinogenicity of DDT and its associated compounds, and classified them as Group 2B agents, i.e., possibly carcinogenic to humans.
1. FEHD had conducted a study on the dietary exposure to DDT of secondary school students. Results indicated that dietary exposures to DDT for average and high consumers of the secondary school students in Hong Kong were 0.00015 and 0.00029 mg/kg bw/day respectively. Both exposure levels fell well below the PTDI of 0.01mg/kg bw established by the JMPR. It could be concluded that both the average and high consumers of the secondary school students were unlikely to experience major toxicological effects of DDT.
2. The food group "seafood", particularly fish and oyster, was identified as the main dietary source of DDT.
3. Moreover, the study finds that dietary exposure to DDT of secondary school students in Hong Kong is relatively high when compared with dietary exposure studies conducted in other countries such as Australia, Canada, Japan, the United Kingdom and the USA. This might explain other research findings that levels of DDT in breast milk of Hong Kong mothers are higher than the levels in other countries.
Advice to the Trade
1. To observe good agricultural and manufacturing practices to minimise DDT contaminations in food.
2. To source food supplies from reliable suppliers.
Advice to the Public
1. To maintain a balanced diet so as to avoid excessive exposure to DDT from a small range of food items, particularly fatty foods of animal origin.
2. To consume fish and fish products (though found to be one of the main dietary sources of DDT) in moderation as they are good sources of high-quality protein and low in saturated fat.
Risk Assessment Section
Centre for Food Safety
* Acute reference dose refers to an estimate of the amount of a substance in food and/or drinking water, normally expressed on a body weight basis, that can be ingested in a period of 24 hour or less without appreciate health risk to the consumer on the basis of all known facts at the time of the evaluation.