Paracelsus said that the dosage determines whether a substance is toxic. The controversial story about chrysotile in the fibro cement roof sheets is an example.

The agent of health risk and its dosage

Nearly 500 years ago, the Swiss physicist and chemist – Paracelsus presented the basic principle of toxicology: “Everything is toxic and nothing is non-toxic. It is the dose that determines whether a substance is toxic”. It means that the toxicity of a substance depends on many different factors, including the exposure dose, the method of exposure and exposure time.

In April 2017, a 16-year-old student in South Carolina, USA died in the classroom because of drinking a large bottle of Mountain Dew, a cup of latte coffee, and a can of energy drink two hours before. A research published in the Journal of the American Heart Association in 2017 showed that energy drinks have a serious health risk as only one can also cause blood pressure and ECG changes significantly.

Controversial story about chrysotile

Chrysotile fiber is wetted before going to the production.

Despite being used for the production of AC roof sheets more than 50 years in Vietnam, chrysotile is considered as a carcinogen. Anti-chrysotile organizations claim that chrysotile is a substance classified as Group I of the list of carcinogens by IARC. This is a group of 120 different substances such as lead metal, mercury and common agents like solar radiation, cigarettes, vehicle emissions, bacon, dried fish, wood dust, etc.

Chrysotile is an important input for the production of AC roof sheets, so the prohibition of importing and using the fiber will make a variety of factories face the potential risk of closure, thousands of workers loss their jobs.

With 60-year practical experiences of using and many scientific studies with no case of chrysotile-related cancer, experts believe that it is not necessary to ban chrysotile as this type of fiber can be used safely. Industrial fibers or silicon dust are potentially dangerous to human health; however, there are three determinants including size, exposure dose and durability in the body. In 2014, according to researches, the US Environmental Protection Agency (EPA) set the non-carcinogenic safety level of chrysotile to be 9 × 10-5 fibers/cc or 9 fibers/m3.

Asbestos is the common name for groups of mineral fibers in which brown and blue fibers are banned all over the world. Due to the straight, rough, needle-like structure, they can cause mesothelioma tumors. On the contrary, the group of white fibers is twisted, soft and porous. Researches have shown that they are excreted from the lungs after 3-14 days. Therefore, it is the only type of mineral fiber still being used in more than 130 countries and territories such as the US, Russia, China, India and ASEAN countries.

In the past, asbestos was used indiscriminately under unsanitary working conditions for industrial races. In Japan, before 1975, the fact that a large amount of asbestos including both brown and blue fibers was directly sprayed on ceilings, walls and structural iron frames in buildings caused thousands of cancers in countries.

Australia is a notable example with the second highest number of mesothelioma deaths in the world. Green fibers were mined in Australia from the 1930s to 1966. The country used brown fibers until the mid-1980s as well.

The asbestos industry of American has developed since 1858, and all types of asbestos were banned in 1989. However, the US Supreme Court canceled the ban on chrysotile because there was no evidence of the harmful effects of chrysotile in 1991. Eventually, this fiber is still an irreplaceable material in many products, especially in the industries of automotive, aerospace and defense.

Currently, there are 38,000 people working in the industry of exploiting and producing products of chrysotile in the Russian territory. Chrysotile is used domestically and exported to 30 countries around the world. There are two mines for the exploitation of chrysotile in Russia consisting of the mine in Asbest town (Sverdlov province) and the other in Yasniy town (Orenburg province). These are all 100-year-old chrysotile mines. The industry has driven the economy development for the cities. According to the confirmation of the chief physician of Yasniy Town to the Vietnam delegation in 2017, no worker or local resident has suffered from chrysotile-related cancer in the past 70 years because of the short distance of around 10 km between the Orenburg mine and residential area.

Houses made of fiber cement products in Orenburg, Russia.

Each country has its own regulations for the control of fiber concentration and labor safety. The maximum concentration of the US is 0.1 fiber/ml in a shift, the requirement of India is 1.0 fiber/ml and that of Russia is 2.0 fibers/ml. Vietnam applies the maximum concentration similar to that of the US of 0.1 fiber/ml. The regulations in other ASEAN countries vary from one country to another. The Philippines’ is 2.0 fibers/ml; Indonesia’s is 1.0 fiber/ml; Thailand’s is 5.0 fibers/ml. There is no doubt that the regulation of fiber concentration in the workplace of Vietnam is equivalent to the US standard and more stringent than many countries in the region and around the world.

Conclusion

In practice, AC roof sheet products contain a very small amount of 8 – 10 percent of chrysotile, the remaining 90 percent is cement. According to Assoc. Prof. Dr. Luong Duc Long – Former Director of Vietnam Institute for Building Materials, Ministry of Construction, chrysotile fibers have hollow structure so cement-like binder will fill these fibers. This creates a very cohesive, sustainable, coherent and difficult to destroy and disperse into the environment.