Written by Dickson Yip (HKU Master of Toxicology)
In the last article we discussed some of the most common disinfectants available in the market. After that, I received some enquiries from my friends asking about the newly emerged disinfectants whether they work as they claimed. As a person with science background, I will not recommend any products if they cannot provide enough evidence to consumers.
1. Chlorine dioxide
Chlorine dioxide shares the same working principle with bleach. They oxidize biomolecules from bacteria and viruses in order to eliminate them. However, the method of applying chlorine dioxide may worth a discussion.
On the image below, it states that chlorine dioxide solution can be applied to humidifier and release in form of aerosols to every corner of the room. This is very dangerous as chlorine dioxide is highly oxidizing (corrosive) – similar to the bleach. It will corrode metal surfaces and fabrics and if inhaled, it will corrode human body cells as well, possessing cytotoxicity. That’s the reason why I won’t recommend the use of chlorine dioxide under poor ventilated area, but normal use like a bleach to clean floors or non-metal surfaces are fine.
2. Photocatalyst
The main component of photocatalyst is titanium dioxide. It is mainly used to decompose volatile organic compounds like formaldehyde. Its principle is to break down water molecules in air to reactive oxygen species (OH．) under UV light. In theory it can decompose proteins and nucleic acids on bacteria and viruses as well, however that hasn’t enough proof on that yet, especially on viruses. Titanium dioxide exists in form of ultra-fine particles (10 um or less), if inhaled can accumulate in the lungs causing cytotoxicity. Titanium dioxide is classified as “possibly carcinogenic to humans” by WHO, so extra care is necessary when using photocatalyst.
3. Products that claim to have prolonged effect
要證實一樣消毒產品有沒有效其實已經不容易。因為實際效用已經會受使用環境影響，例如溫度，濕度，物件表面，細菌/病毒數種類和數量等等。如果還要證明產品的持續性，幾乎是不可能。要是有產品聲稱已有實驗實明，也只是代表產品在密封、控制的條件下對某種細菌有作用，絕不能代表日常情況。退一萬步說假設這些產品都是長時間有效，他們又如何證明人類長時間接觸這物質是不會影響健康？既然這些產品有很多東西都無法證實，倒不如腳踏實地勤洗手勤清潔罷了。
Source: HKTV Mall, WHO
