Formaldehyde removal myth: Be careful of those who say "formaldehyde can be removed completely"

Formaldehyde is an indispensable part of modern industry and affects human life in all aspects. However, because formaldehyde is harmful to health, there are often news reports about diseases caused by excessive formaldehyde, which makes many people afraid of "formaldehyde". This has given rise to the formaldehyde detection and formaldehyde removal industries. Is formaldehyde detection reliable? How to effectively remove formaldehyde? In the world of "all kinds of formaldehyde", let us learn to live in harmony with it.

Written by Li Cunpu

What do you think of when you hear the word formaldehyde? Respiratory diseases, skin problems, damage to health, and even cancer are probably the first reactions of many readers when they hear formaldehyde.

Formaldehyde is harmful, but it is something we cannot live without.

1. The world of aldehydes

Formaldehyde has surrounded human society since ancient times. The burning of wood, the eruption of volcanoes, the oxidation of organic matter by ozone, and the frying and deep-frying of delicious food all produce formaldehyde. With the development of modern industry, new resin materials, disinfectants, adhesives and preservatives that have greatly improved people's quality of life all require the use of formaldehyde; coupled with the large amount of formaldehyde produced by ubiquitous smokers and car exhaust, we actually live in a "world of formaldehyde" where formaldehyde is everywhere.

Figure 1. Many chemical reactions in nature produce formaldehyde. Humans have long been creating formaldehyde pollution by burning wood.

In recent years, excessive formaldehyde in enclosed spaces such as indoors and in cars has become a hot topic of public concern. Concerns about the harm of formaldehyde to health have spawned a series of formaldehyde detection and formaldehyde removal industries, as well as various "zero formaldehyde" products. As a chemist, the most common daily consultation I receive is about how to eliminate indoor formaldehyde. In order to avoid frequent harassment, I think it's time to formally introduce formaldehyde to everyone.

2. Sources, identification and hazards of formaldehyde

(1) Sources of formaldehyde: All are sources

Formaldehyde is the simplest aldehyde substance, with the molecular formula HCHO. Due to its symmetrical structure, other groups can be grafted on both sides of the only carbon atom of formaldehyde, gradually growing into polymer materials. These polymer materials are used as adhesives to produce density boards, particle boards, multi-layer boards (also called multi-layer solid wood) and other boards, which are made into cabinets, bookshelves and other furniture and enter thousands of households, becoming a necessity for modern families. Therefore, the formaldehyde that is not fully polymerized in the board and the decomposition of the adhesive in the board will slowly release the formaldehyde, and the release cycle may run through the entire life cycle of the furniture.

Since formaldehyde is the simplest aldehyde, all volatile organic compounds may produce formaldehyde during the degradation process: such as automobile exhaust, fuel combustion, cooking (especially frying), oxidation of detergents and disinfectants, etc.; what is often unexpected is that smoking will continue to produce formaldehyde.

Figure 2. Formaldehyde is the simplest aldehyde

In addition, like many animals, the human body produces formaldehyde. Formaldehyde is produced as part of the metabolism of each cell, so there is 2-3 mg/L of formaldehyde in the human blood[1]. Inhaled formaldehyde does not significantly change the formaldehyde concentration in the blood.

(2) Identification of formaldehyde: It can be measured, but it is basically inaccurate

According to the national recommended standard GB/T 16127-1995 “Sanitary Standard for Formaldehyde in Indoor Air”, the maximum allowable concentration of formaldehyde in indoor air is 0.08 mg/m3[2]. The World Health Organization recommends that exposure to formaldehyde concentrations below 0.1 mg/m3 will not cause (Prevent) lung function damage, lung cancer, leukemia, etc.[3], so indoor formaldehyde concentrations that meet national standards will theoretically not affect the health of residents. However, according to literature reports, at least at the beginning of this century, the problem of excessive formaldehyde concentrations in urban areas in my country was still quite serious. The average formaldehyde concentration in newly renovated houses from 1999 to 2006 was 0.236 mg/m3, about twice the national standard[4]; the median indoor formaldehyde concentration reported in 2017 from 2002 to 2015 was 0.125 mg/m3[5]. There are many instruments, test strips, or professional teams on the market that can test indoor formaldehyde concentrations. It is clear that it is not easy to detect formaldehyde concentration, whether by electrochemical or chemical methods. Accurate trace quantitative detection equipment generally costs hundreds of thousands of yuan, that is, unless it is a particularly professional device, the test results of formaldehyde test equipment/test paper purchased by yourself have no strong reference value.

So how do you identify formaldehyde? Formaldehyde itself is colorless and odorless, and only has a certain pungent smell at high concentrations (0.3 mg/m3, which varies depending on the sensitivity of the nose). Therefore, the "decoration smell" we smell when we enter a newly renovated house or a new car is probably not the smell of formaldehyde, but the smell of other volatile organic compounds (VOCs). Compared with the smell, the irritation of formaldehyde to the eyes is easier to detect. When there is no obvious smell in the newly renovated house, but you blink more frequently or suddenly cry, in addition to the possibility that someone is secretly thinking of you, excessive formaldehyde concentration may also be one of the reasons. Of course, the above subjective judgment is easily affected by psychological effects.

(3) Harm of formaldehyde: It is harmful, but not completely harmful

There is no doubt that formaldehyde is harmful to the human body. However, due to various reasons, the health hazards of formaldehyde may be exaggerated in the public domain, and many accusations against formaldehyde are unfair. Formaldehyde is very active and easily reduced. When inhaled or swallowed (yes, we eat a lot of formaldehyde with food every day), it is converted into formic acid/formate, and then excreted as carbon dioxide, which is also the main metabolite of formaldehyde in the body. When excessive formaldehyde accumulates (often only occurs in specific workplaces) and exceeds the processing capacity of enzymes, formaldehyde may cause DNA-protein cross-linking, thereby modifying DNA and protein and losing activity, that is, producing various symptoms or potential cancer. Therefore, formaldehyde is listed as a Class 1 carcinogen by the International Agency for Research on Cancer (IARC) under the World Health Organization (WHO).

At the same time, reports such as "newly renovated houses cause people to suffer from pneumonia and leukemia" appear every once in a while and then spread in the media, causing people to worry too much about formaldehyde. It should be made clear that most scientific studies have shown that there is no clear link between living in newly renovated houses or school buildings and the occurrence of cancer [3, 7, 8], so we don't need to worry too much.

According to a large number of literature reports, formaldehyde generally causes obvious sensory irritation (blinking crazily, respiratory discomfort, etc.) only when the formaldehyde concentration is higher than 1 mg/m3 (about 10 times the national standard) [6]; while formaldehyde concentrations below 0.38 mg/m3 (about 4 times the national standard) will not cause sensory irritation. Even for children, there is no clear evidence that newly renovated classrooms are more likely to cause respiratory discomfort than old classrooms [8].

The link between formaldehyde and cancer is also far from being established. Long-term exposure to a formaldehyde environment of 7.5 mg/m3 (about 100 times the national standard concentration) may cause squamous cell carcinoma, while there is no evidence that formaldehyde concentrations below 1.25 mg/m3 (about 13 times the national standard concentration) are associated with nasopharyngeal cancer [3]. Both of the above concentrations are far higher than the national standard, so there is basically no need to worry in daily indoor life.

When we hear about concepts such as "formaldehyde-free boards" and "formaldehyde-free paints", we should realize that the so-called 0 formaldehyde is often based on national standards, and the formaldehyde content tested is lower than a certain index (similar to the operation of sugar-free beverages); and even if there is no formaldehyde, it does not mean that there are no other harmful substances in these products. When we pay attention to indoor air quality, it should be a systematic project, not just formaldehyde. According to the "WHO guidelines for indoor air quality: selected pollutants" issued by the World Health Organization, formaldehyde ranks third among the 9 important indoor pollutants (respectively: benzene, carbon monoxide, formaldehyde, naphthalene, nitrogen dioxide, polycyclic aromatic hydrocarbons, radon, trichloroethylene, and tetrachloroethylene, see the table below for specific sources and hazards), many of which may be the real culprits of human cancer.

Figure 3. In addition to formaldehyde, the board may also contain other harmful substances

Sources and hazards of major indoor pollutants released by WHO, compiled from "WHO guidelines for indoor air quality: selected pollutants"

3. How to “eliminate” formaldehyde?

But formaldehyde is harmful to the human body after all and should be eliminated.

The following suggestions can be provided to readers who are concerned about formaldehyde:

(1) There are four principles for removing formaldehyde: high temperature, high humidity, long time, and more ventilation. Formaldehyde is a volatile organic compound. The volatilization of formaldehyde in furniture such as cabinets and desks and in wooden floors will become more intense as the temperature rises. Therefore, a high temperature environment is conducive to the rapid removal of formaldehyde. In addition, formaldehyde is extremely soluble in water and easily reacts with water to form formaldehyde hydrates, or further combines with water to form geminal dimethanol (CH2(OH)2). Although pure geminal dimethanol was just produced last year [9], most of the formaldehyde in water or high humidity environments will be converted into geminal dimethanol and discharged with the wind. Generally speaking, the formaldehyde in qualified boards will be basically evaporated within a few months. Therefore, for a newly renovated house with furniture placed in it, it is recommended to leave it for at least one summer before moving in, provided that the room is well ventilated, and during the placement process, use methods such as spraying water and placing water basins to ensure high humidity in the room.

Figure 4. Although pure geminal dimethanol is difficult to synthesize, formaldehyde is largely converted into geminal dimethanol with lower energy when combined with water [9]

The decomposition of glue in boards and floors or the release of unreacted formaldehyde is long-lasting and slow, so the so-called formaldehyde removal team can only ensure that the indoor formaldehyde concentration meets the standard after treatment, and cannot truly and permanently remove indoor formaldehyde. For the same reason, products such as activated carbon and diatom mud that remove formaldehyde by adsorption have almost no effect. Because formaldehyde is often released slowly indoors, the adsorption material cannot adsorb formaldehyde after being fully absorbed, and instead becomes a source of slow release of formaldehyde. The above four principles are reasonable and economical solutions.

(2) In addition to the above four principles, as discussed above, formaldehyde comes from a wide range of sources and is not only released by wooden furniture. Imitation porcelain tableware, toilet seats, etc. are also often made of resin materials containing formaldehyde. Therefore, when cooking indoors, using detergents, adhesives, disinfectants, air fresheners and other daily necessities containing formaldehyde or other volatile organic compounds, attention should be paid to ventilation.

It is worth mentioning that since the above products will produce formaldehyde or other harmful substances, it is not recommended to store them in large quantities indoors. In addition, eat less barbecued and fried foods, as these foods are likely to contain high concentrations of formaldehyde.

Figure 5. Both melamine tableware and urea-formaldehyde resin toilet seats require formaldehyde to make

(3) Pay attention to odors in enclosed spaces. If there is an odor in the room or car, it may not be the smell of formaldehyde, but it is very likely that the concentration of other harmful substances is too high. The above four principles are also effective for other harmful indoor pollutants, especially volatile organic compounds. It is recommended to ventilate more and avoid long-term stay of sensitive people.

(4) Use ozone disinfection with caution. Ozone is a relatively environmentally friendly disinfectant, but it is not very suitable for use in a home environment. On the one hand, ozone itself is toxic to a certain extent. On the other hand, ozone can cause organic materials such as resins in the room to decompose and produce harmful substances such as formaldehyde, resulting in secondary pollution. If ozone disinfection is used, please be sure to ventilate the room thoroughly after disinfection.

(5) Smoking is harmful to health, so please do not smoke indoors. In addition to damaging your own health, secondhand smoke contains a large amount of harmful substances including formaldehyde. If there are smokers in your home who are accustomed to smoking indoors, you can give up all the above-mentioned methods of removing formaldehyde: just like a person who is bleeding heavily and insists on killing a mosquito that is sucking blood from his body, there is no point in removing it.

In short, we live in a world full of formaldehyde, but formaldehyde is not scary. What may be scary is the heart of those who tell you that "formaldehyde can definitely be removed".

References

[1] Formaldehyde (CH2O) Concentrations in the Blood of Humans and Fischer-344 Rats Exposed to CH2O Under Controlled Conditions. doi.org/10.1080/15298668591394275

[2] Hygienic standards for formaldehyde in indoor air. http://std.samr.gov.cn/gb/search/gbDetailed?id=71F772D7AAAAD3A7E05397BE0A0AB82A

[3] WHO guidelines for indoor air quality: selected pollutants. https://www.who.int/publications/i/item/9789289002134

[4] Formaldehyde in China: Production, consumption, exposure levels, and health effects. doi.org/10.1016/j.envint.2009.06.002

[5] Indoor formaldehyde concentrations in urban China: Preliminary study of some important influencing factors. 10.1016/j.scitotenv.2017.02.187

[6] A recommended occupational exposure limit for formaldehyde based on irritation. Journal of Toxicology and Environmental Health. 1997 Feb;50(3):217-263. PMID: 9055874.

[7] Formaldehyde and cancer: a critical review. doi.org/10.1007/BF00378361

[8] Asthmatic Symptoms among Pupils in Relation to Winter Indoor and Outdoor Air Pollution in Schools in Taiyuan, China. dor.org/10.1289/ehp.10576

[9] Synthesis of methanediol [CH2(OH)2]: The simplest geminal diol. PNAS2022 Vol. 119 No. 1 e21119381. doi.org/10.1073/pnas.2111938119

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