by Dr. Ivan Chang Yen and Dr. Carlyle Kalloo

Presented by Mr. D. Roopnarine

In Trinidad and Tobago, as in many other Caribbean countries, the control of mosquitoes involves the use of many insecticidal preparations, including aerosols, electrically heated vapor mats and mosquito coils. The latter, also referred to as mosquito destroyer, anti-mosquito, or mosquito incense coils, are very popular in many local households, due their low cost relative to aerosols and vapor mats, and their long-lasting action.

Many brands of these coils are manufactured locally and regionally, but several others are imported from far-eastern countries, notably China. The active ingredients in most of these coils are allethrin or bioallethrin, which are synthetic pyrethroids deemed safe for use in these products.

However in 1992 DDT-containing mosquito coils were imported into Trinidad and Tobago in improperly labeled packages. Such labels, which initially listed no active ingredients attracted the attention of the Trinidad and Tobago Bureau of Standards. Subsequent investigations by the Chemistry Food and Drugs Division of the Ministry of Health determined the coils to contain DDT.

The resulting investigation into the concentrations of DDT in various brands revealed that three brands, namely Cock, Double Rabbit and Lion, contained DDT. Concentrations of opN-DDT and ppN-DDT, collectively referred to as DDT ranged from 0.7 to as high as 8.8 % by weight. Investigations into the volatility of DDT from some of these mosquito coils showed that between 84 to 97% of the DDT vaporized during burning of the coils. In addition, approximately 16% of the DDT was converted to DDE during this process.

The widespread use of mosquito coils in many households, and particularly in rooms where persons requiring protection sit or sleep, exposes such persons to vapors containing DDT and DDE, the latter being produced from DDT during vaporization. The common use of DDT-containing coils in bedrooms with young children is of particular concern.

Once the severity of the situation was realized, increased monitoring of imported mosquito coils was undertaken. However the task of identifying the DDT- contaminated coils was made more difficult by the replacement of DDT by other chemicals in some shipments of mosquito coils. Nevertheless, any shipment of mosquito coils found to contain DDT were detained on port for reshipment, although a small quantity was buried in local landfills.

Negative Listing of chemicals including DDT through the Ministry of Trade and Industry in 1994 resulted in an effective end to imports of DDT-containing products. One brand of mosquito coils was eventually prohibited from entry into the country due to discrepancies between listed active ingredients and those actually found in the products.

It is conservatively estimated that over the period 1992 to 1994, about 3 tonnes of DDT were imported into Trinidad and Tobago in mosquito coils. The widespread local distribution and use of such coils is likely to have contaminated a large number of households, persons, and personal effects. The eventual entry of the DDT and its metabolites into the local environment is cause for concern, due to the persistence of such compounds in the environment and along food chains.

Research into the impacts of DDT and its metabolites from mosquito coils on exposed populations and the local environment is required. This concern is due to the tendency of DDT and its metabolites to accumulate in lipid tissues and along food chains, and to produce a range of adverse effects in animals.

The lack of consistent monitoring programs for persistent organic pollutants such as DDT and its metabolites in products imported into the Caribbean is likely to result in a recurrence of such incidents. The finding of DDT-containing coils in Jamaica at about the same time as the problem was being investigated in Trinidad, underscores the need for closer cooperation among countries likely to be affected by such products. It is necessary for such countries to provide the necessary resources to allow effective monitoring and control of hazardous and persistent chemicals.

On the other hand there is need for countries exporting such chemicals and products to observe the United Nations Environment Programme Guidelines on Prior Informed Consent, to allow importing countries to implement their own measures of protection.

Likewise education of the local public on the hazards of exposure to DDT, its metabolites and other persistent organic pollutants is necessary to avoid any recurrence of such episodes.

In many countries with tropical environments, the control of insect vectors and in particular mosquitoes has involved the use of insecticides including DDT (Cherritt 1971). The broad spectral activity of DDT against a range of insect pests, its low mammalian toxicity and resistance to degradation were major factors influencing its popularity and widespread use (Zweig 1964).

However, their persistence in the environment (Cooke and Stringer 1982) and bioaccumulation along food chains (Benvenue 1976) and the many reports of adverse effects of DDT and related organochlorine compounds on animals (Spindler 1983), eventually led to their use being discontinued in many countries (UN Consolidated List of Banned, Withdrawn or Severely Restricted by Governments 1987).

In Trinidad and Tobago, up to 1961, DDT was used widely by public health authorities for the control of malaria through its application against the disease vector, the Aedes aegypti mosquito. However less persistent and more selective insecticides including Malathion and Propoxur are now used.

Members of the public also make extensive use of insecticides for their own protection against mosquitoes. For example aerosols, electrically heated vapor mats (Figure 1b), or mosquito coils (Figure 1a) are used in almost every local household. The latter devices, also referred to as Mosquito Destroyer, Anti-Mosquito, or Mosquito Incense Coils, are very popular in the Caribbean, due to their low cost relative to aerosols and vapor mats, and their long-lasting action. The recent outbreak of Dengue and Dengue Haemorrhagic Fever, and the subsequent public health campaign in Trinidad and Tobago (Caribbean Epidemiology Center 1997) have resulted in increased use of such insecticidal devices in local households.

Mosquito coils are slow-burning devices which emit smoke containing one or more insecticides. Each coil burns for several hours and is used in close proximity to persons requiring protection against mosquitoes. Their use in sitting rooms and bedrooms is particularly prevalent. Consequently, during the burning of these coils, human exposure and inhalation of the vapors occur. The necessity for the insecticides used in mosquito coils to be of low mammalian toxicity is thus of paramount importance. This requirement, in addition to the need for the insecticide to be vaporized without significant decomposition have resulted in only a few insecticides being found suited for use in these devices. The synthetic pyrethroid allethrin (Sumitomo Pyrethroid World 1991, The Pesticide Manual 1994) is used extensively for this purpose.

In Trinidad and Tobago, several brands of mosquito coils containing allethrin are manufactured locally. In addition some are also imported from Asia (Table 1, Figure 2a), and in particular the Peoples Republic of China. In 1992, complaints were made to the Trinidad and Tobago Bureau of Standards by members of the public that boxes of imported mosquito coils offered for sale were improperly labeled, with no active ingredients being listed (Figure 2b). Subsequent investigations and analyses of the coils by the Chemistry Food and Drugs Division of the Ministry of Health revealed that several brands of mosquito coils did in fact contain DDT (Table 2). The concentrations of op=-DDT AND pp=-DDT, collectively referred to as DDT, ranged from 1.2 % by weight to as high 7.7%.

When the presence of DDT in the coils was first confirmed, the Pesticide and Toxic Chemicals Control Board (PTCCB), constituted under The Pesticide and Toxic Chemicals Act (1979) was the regulatory body responsible for the approval of importation of all toxic chemicals, including DDT, into Trinidad and Tobago. In addition Trinidad and Tobago was one of the countries observing the United Nations Environment Programme Guidelines on Prior Informed Consent (1987). Under this arrangement, prior notification by countries exporting chemicals restricted or banned in such countries must be made to the importing countries. Unfortunately, the country of origin of the DDT-containing coils, namely the Peoples Republic of China, was not a participant in this arrangement. It was therefore necessary to implement other measures to bring an end to the importation of the DDT-containing mosquito coils into this country.

Consequently, increased monitoring of mosquito coils imported into Trinidad and Tobago and suspected to contain DDT was undertaken prior to their release for distribution. Any shipments held in port and found to contain DDT were deemed to be prohibited items and subject to reshipment back to their suppliers. In a few cases, shipments were released to local warehouses for disposal in local landfills, since appropriate incineration facilities are not available locally for destruction of such materials. The task of identifying the DDT-containing coils was also made harder by the replacement of DDT in some shipments of imported brands by other chemicals.

In the meanwhile, Negative Listing of DDT and other chemicals was effected by an Order of Parliament (1994) and prohibited further imports of DDT in any form.

Nevertheless, by this time it was conservatively estimated that about 3 tonnes of DDT were imported into Trinidad and Tobago in mosquito coils. This estimate was based on the number of container loads of DDT-containing coils imported between 1992 to 1994 (Appendix I).

Significantly, similar DDT-containing coils were imported into Jamaica in 1995 (Pesticide News 1996) in spite of a ban on DDT, using improperly-labeled packages as was done in Trinidad and Tobago.

Investigations into the volatility of the DDT in some of these coils (Wahid 1996) revealed that between 84 to 97% of the DDT analogues vaporized during burning, with about 16% being converted to DDE (Table 2), which is highly persistent in the environment. In fact, DDE was one of the most commonly detected organochlorine pesticides in sediments and biota in the Caroni Swamp (Sampath 1982), and along food chains (Deonarine 1980).

This episode of importation and widespread distribution of DDT-containing mosquito coils has far-reaching implications for countries with limited land masses and resources to deal with such problems. For example, exposure to and inhalation of DDT and DDE by persons using such coils would have resulted in accumulation in those exposed, with possible adverse long-term effects (Bern 1992, Colborn et al 1993, Colborn and Smolen 1996). In addition, the contamination of clothing, furniture, walls and any other items capable of adsorbing DDT and its metabolites will continue to provide sources of exposure to those in contact with such sources. It is also likely that a significant number of DDT-containing coils are still in the possession of small-scale retailers and householders and may eventually be used.

Any leaching of DDT into the local environment may result in contamination of soils, local waterways, sediments and biota as has been observed previously (Sampath 1982, Deonarine 1980). Due to the small land mass of Trinidad and Tobago, such contamination will ultimately impact on the surrounding coastal waters, and particularly the Gulf of Paria, which is in contact with the eastern coast of Venezuela. It is conceivable that the large quantities of fish, crabs and shellfish caught for human consumption from the Gulf could eventually become contaminated by DDT and its metabolites.

It is clear that the task of controlling the importation and use of Persistent Organic Pollutants (POP) such as DDT in developing countries is expensive and difficult, especially when legislation governing such imports is weak and ineffective. This problem is compounded when support services, including the monitoring of imported products are inadequately funded to allow existing legislation to be effectively enforced.

It is therefore recommended that the following measures be undertaken to prevent a recurrence of the episode of importation of undesirable chemicals into Trinidad and Tobago:

A list of all chemical that are to be banned from entering Trinidad and Tobago should be prepared by the relevant authorities, subject to public comment, and approved in parliament at the earliest opportunity.

Monitoring of all hazardous or toxic chemicals, or items containing such chemicals entering Trinidad and Tobago should be undertaken. This should ensure compliance with the Pesticide and Toxic Chemicals Act (1979), the Negative List (1994), and any other legislation that may be enacted to control such imports.

A major weakness of this strategy has been a chronic lack of funding to support monitoring activities, which are at present limited to investigations of complaints and ad hoc monitoring. This weakness needs to be urgently addressed in order to provide effective consumer protection against undesirable and prohibited chemicals.

With reference to the episode of DDT-containing mosquito coils, further research is necessary to determine the extent of human and environmental contamination caused by the use of these coils. Collection and proper disposal of any unused DDT-containing coils should also be undertaken to prevent further contamination.

Education of the local population via regular updates in the local media on problems caused by undesirable hazardous and toxic chemicals, should be undertaken to allow citizens to better protect themselves against such hazards.

Black Hawk Mosquito Coil Allethrin Trinidad

Bug Off Mosquito Coil Allethrin Trinidad

Cock Crowing Mosquito Destroyer Allethrin China

Double Rabbit Mosquito

Incense Coil * Bioallethrin China

Fish Mosquito Destroyer Allethrin Barbados, Guyana

Flamingo Mosquito Coil Allethrin Trinidad

Golden Frog Anti-Mosquito Coil Allethrin China

Mokoto Mosquito Coil Allethrin Trinidad

Mosquitox Mosquito Coil Allethrin Indonesia

Peacock Mosquito Destroyer Allethrin Guyana

Serene Mosquito Coil Allethrin Trinidad

* This brand of mosquito coil was eventually prohibited from entry into Trinidad and Tobago, due to discrepancies between declarations of active ingredients and actual constituents found in the coils.