Team:CIEI-BJ/Background
Mosquito is probably one of the most obnoxious living organisms that have ever existed on earth. These buzzing creatures are always flying around, stinging every being on which they can be fed with blood. Everyone must have been the victim of these tiny, annoying ‘bombers’ at least once. However, even with that diminutive figure, mosquito can bring troubles far worse than being bitten.
Among all species of mosquitoes, those that have evolved the life cycle interfering humans are responsible for transmitting harmful infections within the settlements. The saliva of mosquitoes is where the danger hides. Saliva mainly serves as circumventing the physical responses of the preys. Through continuously stinging among different individuals, the saliva of mosquitoes that have contacted with the blood may contain pathogens of various kinds of diseases.
As a mosquito-borne infectious disease, malaria is widely spread within tropical and subtropical regions where the combination of moisture and heat provides ideal environment for reproduction of mosquitoes. Malaria causes symptoms typically include fever, feeling tired, vomiting and headaches, results deaths in severe cases.[3]
One trouble brought by mosquitoes is the horrific Zika virus. It spreads mainly in Africa, South America and Southeast Asia, among which Brazil suffers the most tremendous outbreak. Symptoms of Zika are desperately various, including microcephaly, red eye, headache and so on.
This disease is difficult to be told apart from other illnesses, especially in early stages, since the symptoms include fever, headaches, and chills. The condition will be accompanied with liver and kidney problems during late period. Currently, nearly a billion people live in an area of the world where the disease is common.[5]
To prevent the devastating disaster brought by mosquitoes, people have come up with several basic methods to restrain the spread of pathogens. The first is to prevent the mosquitoes from entering human colonies. The second is to directly eliminate the mosquitoes either by poisonous medicines or physical ways including beat and electric shocks. The third method utilizes chemicals to disturb the mosquitoes. Mosquitoes mainly identify the hosts by detecting the CO2 released or by the amino acids that form the odor from animals or humans. Therefore, when the substance can produce smell that mosquitoes dislike, or can leak molecules that block the receptors of mosquitoes, the mosquitoes can be successfully repelled.[7]
To identify the effectiveness of current mosquito repellent products, we looked up for existing researches as well as surveyed by ourselves on people’s opinions.
Fig 1 Purpose of using anti-mosquito products
Q9 Your Age/ Q4 The Main purpose of using mosquito repellents (Multiple Choice)
Avoid the mosquito borne diseases（e.g malaria）
Among the people aged 16 or older who polled , only 39% of them claimed that they are aware of the danger of mosquito-borne disease.
Here are several types of mosquito repellent products that we’ve surveyed on:
Mosquito net has been an orthodox tool to repel mosquitoes. However, there are still several constraints upon it. For instance, its portability is frustrating. Consequently, it only contributes to protect human from sleep disturbance caused by mosquitoes.
Burdick lamp seems to be effective as the ultra violet light attracts mosquitoes, while the fact is that carbon dioxide released by humans tempt mosquitoes better. Therefore when putting one person and one Burdick lamp into the same room, mosquitoes will simply ignore the lamp and pounce on the person, sucking as many drops of blood as they can.[8]
Safety of these products worth suspicion. According to quality research, harmful substances were checked out in 37.14% of samples, seven samples contained insectifuge ester, five samples contained toluene, one sample contained benzene, toluene, xylene.[9]
A mosquito repelling incense made from a dried paste of pyrethrum powder, usually made into a spiral. A mosquito-repellent smoke can be produced through burning. Being aware of the potential for developing fire hazards, consumers have to be careful with using mosquito coils. Some studies highlight concerns when mosquito coils are used in closed rooms. Coils sold in China and Malaysia were found to produce as much smoke PM 2.5 as 75-137 burning cigarettes and formaldehyde emission levels in line with 51 burning cigarettes. [10] Moreover, smoke produced from coil combustion may cause sensory irritation of respiratory system.
Citronella oil enjoys a widespread reputation of repelling mosquitoes. Unfortunately, one of its ingredients, methyl eugenol, has been proved that it can cause great irritation to our skin. Concerning its doubtful safety, Canadian Ministry of Health bans citronella oil.
The most common repellent for mosquitoes in China must be Floral water. But this doesn’t mean that it is the safest. 75% of floral water is literally alcohol, which is combustible. In consequence, we mustn’t go into kitchen and have to keep ourselves away from cigarettes after applying floral water to our skin. Furthermore, if we overuse Floral water, it will harm our body for the ingredient DEET or BAAPE is actually poisonous.
| Types of Mosquito Repellent Product | Advantages | Disadvantages |
|---|---|---|
| Mosquito Net | Effective in protection | Lack Portability |
| Burdick Lamp | Can attract mosquitoes | Less efficient in killing mosquitoes |
| Mosquito Repellent Bracelet | Convenient with no pungent odor | Has no actual impact on repelling mosquitoes |
| Mosquito Coil | Valid in eliminating mosquitoes | Might cause fire hazards, produce irritating smoke |
| Citronellol Oil | Good reputation for mosquito repelling | Irritation to skin, is banned in some countries |
| Floral Water | Nice odor with some effects | Combustible, poisonous when being overused |
Fig. 2 Comments on effectiveness of products
Towards the current mosquito repellent products, only about half of the participators feel satisfied.
Fig. 3 Worry towards mosquito repellent product
Most participators have considered the negative effect of anti-mosquito products on humans, this means that potential consumers care about whether the product is poisonous.
Only when a repellent is suitable for the majority can it be good and widespread. To elaborate, not only healthy adults can use it, but infants, children, the old, pregnant women, the disabled and many others who are vulnerable can also use it.
To be a good mosquito repellent, efficacy is a consequential standard that should always be regarded. An ideal repellent ought to repel or even kill a large amount of mosquitoes. In this case, repellents like floral water whose DEET or BAAPE is little don’t really reach our demands.
Being portable is very important. If it is too heavy or too big for us to carry around, how can it protect us from those voracious mosquitoes which seem to never have enough blood?
It is better for producing procedures of repellents to be as simple as possible. If the process is too complicated, the cost will rise as well. Plus, an ideal repellent has to be environmental-friendly, which means no pollutants should be emitted during manufacturing or after being used.
Last but not least, it is of necessity of repellents production to have high productivity. With much of the reactants turning into products, the company can reduce the waste of raw materials as well as successfully cutting down the budget.
Considering all the challenges we mentioned above, lots of improvements can be made. Therefore, our team utilized citronellol as the main substance for repellents.
Citronellol is a natural substance extracted from Cymbopogon. It acts as an effective mosquito repellent which has already been applied to some products. Citronellol releases a natural odor smells like roses, which makes it a common ingredient of perfume and spices. The United States FDA considers citronellol as generally safe (GRAS) for food use, which ensures its safety.[11]
People have been researching for better methods of synthesizing citronellol for decades. Here we list some typical pathways.
Fig.4 process of Geraniol Hydrogenation
The main source of geraniol is palmarosa oil, which is a high cost raw material, making the production less economical beneficial.
Fig.5 process of 1-Menthone Method
Designed by Tatsuya and Yoshiro in 1974, this method requires nine steps. In this way, too many steps limit the industrialized production of citronellol.
Although the principles of using pre-existed substances are clear and simple, these raw materials are only abundant in typical locations due to differentiated geological characteristics, plus the radical group that can be reduced in the molecule will influence the selective reduction in hydrogenation.
Fig.6 process of Citral Hydrogenation
Currently, Citral is catalyzed by Raney nickel under the condition of 100℃ and (136398) kPa, together with the alcoholic environment to undergo hydrogenation thus producing citronellol. This method requires heavy metal as the catalysts and requires restrained reaction circumstances, thus making the process of production complicated.
In conclusion, the widening gap between the increasing threat from mosquitoes and the unsatisfying development of anti-mosquito products reveals the urgent demand of an innocuous substance that effectively repels mosquitoes, and can be applied to mass production in low cost.
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[2]African Safari Travel Blog » Blog Archive» Facts you may not know about mosquitoes. Safari.co.uk (2011-07-05). Retrieved on 2013-04-01.
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[4]GBD 2015 Disease and Injury Incidence and Prevalence, Collaborators. (8 October 2016)."Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990-2015: a systematic analysis for the Global Burden of Disease Study2015.".Lancet.388(10053):1545-1602.
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[7] Shuihua Diao (2015) “Microcapsules Preparation of Citronella Extracts and Mosquito Repellent Finishing of Nylon Knitted Fabrics"
[8]CCTV News (2014) "UV Light of the Burdick Lamp Can't Kill Mosquitoes, Is that True?".
[9] Huang Dai, January (2017) “Product Quality and Safety Research of Anti-mosquito Stickers and Wristbands’.
[10] Liu Weili, Zhang, Junfeng; Hashim Jamal H, Jalaludin Juliana, Hashim Zailina, Goldstein Bernard D.(September 2003). "Mosquito Coil Emissions and Health Implications" (PDF). Environmental Health Perspectives. 111 (12): 1454–1460.
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[12] Lihong Xu. (May 2003) “Dihydromyrcene Synthesize Citronellol”.
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[18] Ning Tian.(May 2015)“Fermentation Technology for Biosynthesis of Geraniol using Engineered Escherichia coli”.
[19] Zhang LI et al. “The Study on Application of Bicistronic Vector in Transgenic Zebrafish Based on 2A Peptide”. 1000-7083(2015)03-0338-07.
[20] YING xiangxian et al. “Optimization of Asymmetric Reduction of Citral for the Synthesis of Citronellol using Old Yellow Enzyme and Formate Dehydrogenase”. 1674-2214(2016)02-0070-05
