Bengaluru, Sep 22 : Cigarette butts (CBs) thrown into garbage as trash can be turned into a valuable resource for killing mosquitoes that cause malaria, a new study by an international team, including from India, has revealed.
This novel method for pest control -- using CBs for the synthesis of silver nanostructures -- has been reported by the international of scientists in the latest issue of the journal Environmental Science and Pollution Research.
Besides nicotine -- a known poison -- CBs contain a mixture of toxic substances including heavy metals, Kadarkarai Murugan, lead author and Vice Chancellor of Thiruvalluvar University at Vellore, told this correspondent in an email.
The researchers report experiments with water extracts of CBs collected from the campus of the Bharathiar University in Coimbatore, another participating institution from India.
Scientists from Italy, Saudi Arabia, Taiwan and Malaysia also participated in the study, during which they used the CB extract as a source to synthesise silver nanoparticles.
According to their report, "A single treatment with CB extracts and silver nanostructures -- synthesised using the extract -- significantly reduced egg hatchability of 'Anopheles stephensi', the mosquito species that spreads the 'P. falciparum' malaria parasite."
Low doses of the silver nanostructures also inhibited the growth of a soil bacteria (Bacillus subtilis), the organism (Klebsiella pneumoniae) that causes pneumonia and "Salmonella typhi", that causes typhoid, says the report.
Normally, the larvae of malaria mosquitoes in water are eaten by their predators -- small crustaceans called M. aspericornis -- and thus naturally get eliminated before they become adult mosquitoes.
According to the researchers, who evaluated the impact of their nanomaterial in an aquatic environment, the predation efficiency of these useful crustaceans was not affected by the introduction of CB-synthesised nanoparticles.
Smoke toxicity experiments conducted against adult mosquitoes showed that "CB-based coils led to mortality comparable to the standard pesticide permethrin", the report says.
CBs are one of the most ubiquitous forms of garbage with an estimated environmental burden of 4.5 trillion butts discarded annually.
"Overall, the present research would suggest that an abundant hazardous waste, such as cigarette butts, can be turned into an important resource for nanosynthesis of novel insecticides highly effective against young instars and adults of the A. stephensi chloroquin resistant P. falciparum malaria parasite and microbial pathogens," says the report.
Considering the growing threat of drug-resistant P. falciparum strains, the CB synthesized nanomaterial "can be considered for the development of an alternative" approach for treating and controlling chloroquin resistant malaria parasites.
Payyalore Rajagopalan, former director of the Vector Control Research Centre in Pondicherry, said that nicotine is a known mosquito killer. "But the authors have done a lot of work and it needs to be encouraged," he told this correspondent in an email.
(K.S. Jayaraman is a senior journalist who specialises in writing on scientific issues. He can be contacted at [email protected])
