Gaseous Pollutant Emissions and Mosquito Susceptibility from the Use of Mosquito Coils in the Indoor Environment

Malaria remains a challenge in sub-Saharan Africa and continues to be the primary cause of morbidity and mortality in Ghana. The use of mosquito coil is one of the ways people prevent themselves from mosquito bites. Burning these mosquito coils indoor produces smoke that can control mosquitoes effectively. This exercise is presently used not only in Africa but also in many households in Asia and South America. However, the smoke generated may contain pollutants of great health concern. Efficacy and emission studies of five different commercial mosquito coils containing esbiothrin, dimefluthrin, d-allethrin and meperfluthrin were performed in three different experimental rooms under ventilated and poorly ventilated conditions in the Department of TAB, KNUST, Kumasi. All mortality tests were performed on 3-6 days old (sucrose fed) reared female Anopheles mosquitoes. Aeroqual Gas Monitor (S500) was used to determine the level of pollutants emitted from mosquito coil smoke (CO, TVOC, NO2 and SO2) and environmental factors like temperature and relative humidity. Ventilation rates were determined using a single-compartment mass balance model. Mortality studies under poorly ventilated conditions were higher in all the three experimental rooms than under ventilated conditions. Statistically, there was a significant difference (p < 0.05) between the mortalities of mosquitoes under ventilated and poorly ventilated conditions. Mosquito coils containing esbiothrin recorded the highest insecticidal activity. There was statistically no significant difference (p > 0.05) between mortalities of the five tested coils under ventilated conditions but under the poorly ventilated conditions, there was a significant difference (p < 0.05) between the mortalities of MC 1 (esbiothrin) and MC 2 (dimefluthrin). Efficacy was found to decrease with an increase in room size from 8.5 m3 to 19 m3 and then to 34 m3 however there was no statistical difference between the mortalities recorded in 8.5 m3 and 19 m3 room as well as 19 m3 and 34 m3 room. The results also showed that active ingredients of the coils played a key role in the efficacy of the mosquito coils. Pollutant concentrations resulting from burning mosquito coils especially under poorly ventilated conditions could substantially exceed health-based air quality standards or guidelines. Pollutant concentrations decreased as ventilation rates increased in the experimental rooms. The pollutant concentrations recorded under ventilated conditions were lower than concentrations under poorly ventilated conditions. The result of this study did not show any clearly defined trend of decreasing pollutant levels with increasing room sizes. The findings from this study suggest that individuals sleeping in rooms with lit mosquito coils may be exposed to some undesirable levels of pollutants emitted from the coils. If it becomes necessary to use mosquito coil, the coil should first be burned in a closed indoor environment to achieve maximum insecticidal effect, following which the rooms should be well aerated prior to sleeping in them.

Source: KNUST