Health hazards of ‘mosquito coil smoke’

Mosquitoes are the main vectors for most human diseases such as malaria, lymphatic filariasis (barawa) and dengue. Among these mosquito-borne diseases, dengue is one of the rapidly spreading mosquito-borne viral infections throughout tropical and sub-tropical regions of the world. In order to control these mosquito-borne diseases around the residential areas, many people adopt several methods. There are four major different types of mosquito control methods used worldwide; namely insecticides product aerosols, mosquito coil, liquid vaporizes and vaporizing units.

There is strong research evidence that the emission of formaldehyde from burning one coil can be as high as that released from burning 51 cigarettes as documented earlier

Mosquito coils are the preferred anti-mosquito product in low income countries since it is cheap and readily available. Burning of mosquito coil is a common indoor practices in many households in Asian, South Americn and African countries.  A large population of the developing countries including our country is still using mosquito coils daily in order to protect themselves from mosquito bites. However long-term exposure to this kind of chemical smoke will adversely effect our health. 

Thus I have selected this topic to discuss the possible health effects of prolong exposure to mosquito coil fume. 

Chemical composition and activity of mosquito coil
According to proximate analysis done in research studies, mosquito coils comprise an insecticides or repellent, organic filers capable of burning with smoking, binders and additives such as synergists, dyes and fungicides while the major active ingredients of the mosquito coil are pyrethrins and accounting for about 0.3–0.4% of coil mass which is effective against many genera of mosquitoes including Aedes, Anopheles and Mansonia. When a mosquito coil is burned, the insecticides evaporate with the smoke, which prevents the mosquitoes from entering the room. Pyrethrins are of low chronic toxicity to humans and low reproductive toxicity in animals.  However this burning practice eventually releases health damaging particulates and gaseous pollutants.

•  Effect of factors on toxicity
•  Type of substance that’s burnt
•  Burning intensity
•  Size of room or enclosed area
•  Ventilation rate in room 
•  Duration of exposure
•  Size of pollutant particle size
•  Composition of emission
•  Chemical composition of mosquito coil smoke

Mosquito smoke is a very complicated mixture of metallic vapors (lead, iron, zinc, cadmium and chromium); natural or synthetic insecticides such as pyrethrum, pyrethroids, organophosphates, carbamates;organic compounds including phenol, o-cresol, benzene, toluene, xylene; and coating the surfaces of the submicron particles.

Health effects of prolong exposure to mosquito coil smoke
Mosquito coils are often used overnight during sleeping time where elevated exposure may occur and epidemiological studies have shown that long-term exposure to mosquito coils can induce the vast range of health concerns.

Number of research studies indicate that the different pollutants that are released during the burning of mosquito coils such as volatile organic compounds, considerable levels of particulates with aerodynamic less than 2.5 micrometer in diametre and polycyclic aromatic hydrocarbons are highly induce the health issues in human. 

These small particles, metal fumes and vapours in mosquito coils may reach the alveolar region of lungs and researchers have discovered that the gas phase of mosquito coil smoke contains carbonyl compounds including formaldehyde and acetaldehyde that can produce strong irritating effects on the upper part of respiratory tract.

There is strong research evidence that the emission of formaldehyde from burning one coil can be as high as that released from burning 51 cigarettes as documented earlier. 

As mentioned in research studies, there is a significant association between mosquito coil usage and cough in children with or without cold and epidemiological studies shown that prolong exposure of mosquito coil smoke can induce the asthma and persistent wheeze in children. In addition to that, evidences of epidemiological and toxicological studies widely reported that lifetime cancer risk from exposure to mosquito coils can be alarming. 

Moreover, it was discovered that the release of pollutants particles from burning one mosquito coil is approximately the same as burning 75-137 cigarettes with a much wider implications to public health.

Furthermore, animal studies reported that decrease of growth rate of rats in mosquito coil smoke inhalation tests and reduction in body weight might well be due to the effects of the smoke which lowered the food consumption of rats. A prominent effect of coil smoke was to induce the increased secretion of epithelial glandular cells in the trachea. Dust particles which had settled on the airway wall were reported to stimulate the output of mucus by a local effect on epithelial secretory cells or by vagal nerve reflex. An increase in the rate of mucus secretion from the large airways is likely to accelerate the rate of removal of particles by the mucociliary escalator. However, the presence of a very thick mass of mucus secretion coagulated with pyknotic cells on the surface of the inflammatory respiratory epithelium obstructed the airflow of the respiratory system and also impaired the mucociliary clearance of the ciliated epithelial cells of the smoke-exposed rats. The clearance dysfunction may be a factor in the pathogenesis of chronic and acute lung disease. 

The increase of the levels of the serum enzymes such as LDH coincides with the morphological observations of the lung that the enzymes were released from the damaged tissues into the serum. LDH, a cytoplasmic enzyme and AP, a marker enzyme of lysosome, are commonly used as indicators for cell damage. The increase in liver enzymes (SGOT and SGPT) may indicate liver damage.

Conclusion
The present mosquito coil is a popular product which used to prevent mosquito bites during this dengue season due to it being inexpensive and readily available. However, long-term exposure to this smoke of mosquito coils may adversely effect our health especially the respiratory system since mosquito coil smoke contains toxic compounds. Therefore, the prolong use of mosquito coils is not an ideal solution to control mosquito in surrounding areas.

(The writer is a medical laboratory technologist at a private hospital and holds a MSc. Degree in Industrial and Environmental Chemistry from the University of Kelaniya and a BSc in Food Production and Technology Management and a degree from the Wayamba University of Sri Lanka)