The metabolites of indoor molds move with water vapour in the air

Microbes and their metabolites, such as microbitoxins, are a major factor in indoor air problems

Studies have shown that microbes produce toxins as vesicles, i.e., as fat-soluble toxic exudates. Almost all vesicles are hydrophobic, which means that they stick to the water-air interface, and travel through the building with the humidity.

For example, the liquid contained in vesicles, excreted by indoor molds, is up to a thousand times more toxic than the spores of the same mold species.

Toxicity is caused, in addition to moisture damage, by the biocides in building materials, active ingredients in detergents and cleaning agents, as well as the nanoparticles, caused by transport, containing cell-damaging substances. Even a single cellular toxicity test reveals the existence of a potential indoor air problem.

The cause is not always the moisture damage in the structure, but at its simplest, for example, residues of cleaning agents on surfaces and in indoor air. Excluding such pollutants from indoor air is simple and economically viable. It is not always necessary to demolish the building. The determination of indoor air toxicity is part of the comprehensive assessment of indoor climate problems. This missing piece complements the methods currently in use.

Wet and impermeable construction, as well as the use of biocides, causes increased microbial toxicity in the structures

Detergents containing biocides are in themselves harmful to cells, and using them increases microbial toxicity in the building. Dry building with natural materials means that biocides do not need  to be used. Products containing no biocides can be chosen for cleaning. This will improve both indoor air quality and health. When determining clean indoor air, it is advisable to make measurements with human cell culture like in medical research.

Honorary Doctor of Engineering (Aalto University), PhD in Organic Chemistry, Emerita Prof. in Microbiology (University of Helsinki), Mirja Salkinoja-Salonen (born 1940), has stated that more research is needed on the toxins in the indoor air, as health problems seem to correlate with the toxicity of the indoor sample. According to her, “measuring the toxicity of water condensed from indoor air vapour could be one way to assess the health effects of the indoor air.”

More research is needed to fill in the gaps that currently exist in understanding cases of indoor air -related diseases.  Attempts have been made to clarify this connection with current methods, but without success.

Professor Mirja Salkinoja-Salonen

Indoor air has been studied for thirty years, but no cause has been found for why it makes people ill. In her book Diagnostic Tools for Building Pathology, Professor Mirja Salkinoja-Salonen sheds light on what it is in Finnish buildings that makes people ill.

Science will not progress without the passion to solve the problem

The prevailing perception is that there are only gaseous and particulate pollutants in indoor air. Various methods have been used to collect these contaminants. Previous studies have hypothesized that toxins move with mold spores. However, the toxicity of indoor air was revealed in connection with Johanna Salo’s diploma thesis in 2014, when a toxin-producing mold was cultivated from material samples of a damaged building, and it formed toxic vesicles in the culture dish. These droplets proved to be toxic still as 1,000-10,000-fold dilutions for all cell species used.

Most of the toxic metabolites produced by microbes have a molar mass of 300-2000 g/mol, i.e., they are non-volatile. In addition, they are mainly fat-soluble, are transferred primarily by water vapour, and the relative humidity of the air promotes their aerosolization. In Salo’s thesis, samples of indoor water vapour were collected on a cold steel plate surface, and the toxicity of the condensed water was tested with living cells. The result of this research changes the prevailing perception of the states of indoor air pollutants.

In Finland indoor humidity has been blamed for the formation of mold growth. But in fact the detrimentality of indoor air humidity seems to be that water vapour transports mold toxins and harmful chemicals in indoor air. After this study, the toxicity of indoor water vapour has been researched in Finland.

Scientific studies by the research group

The research team in Aalto University has repeated the existence and toxicity of the vesicles produced by these molds. Their study showed that the strain of Penicillium expansum growing on gypsum boards produced toxic droplets, i.e., vesicles, that were transported into the air.  In cell tests they were more than a hundred times more toxic than the strains of Aspregillus, Chaetomium, Stachybotrys, and Paecilomyces genuses that were isolated from indoor spaces. In 2018, the same research team published an article showing that molds of the genus Trichoderma, isolated from spaces that have indoor air problems, produced toxic droplets. These Trichoderma also grew on gypsum board.

Another group of researchers from Aalto University and Helsinki University has shown that some substances that are known to be harmful, and whose own vapour pressure is negligible, are carried quite quickly into the humid indoor air. Microbial toxins and antimicrobial substances of cleaning and remediation products, and neutral and cationic tensides, also called surfactants are transferred from surfaces into the air.

Indoor air pollutants

The pollutants in indoor air come in three different forms: particles (solid matter), gases and liquids. The study of liquid pollutants has become possible because of Johanna Salo’s diploma thesis and the development of the Aattela Measurement Method that is used to find out the overall toxicity of a building.

Liquid pollutants in indoor air are, e.g., toxins produced by molds, products of microbial metabolism, biocides in materials, active ingredients in detergents, and nanoparticles produced by traffic. These pollutants must be collected from the water vapour contained in the indoor air. Toxic metabolites excreted by molds into the indoor air are much more harmful than dust containing molds.

Lungs do not have any protective mechanism against toxins, so they are absorbed directly into the lung tissue. Our environment contains bacteria, molds and fungi, and their metabolites. Most of them are useful and harmless, but some of the metabolites are toxic, damaging or killing cells, which results in various symptoms.

The recent trend to kill microbes is an incomprehensible measure that leads to indoor air problems.

Biocides are substances that are added into the most common building materials to damage and kill organisms. They destroy ordinary microbes. Strong, toxin-producing microbes remain because they tolerate biocides and/or these biocides feed these alternative oxidase types of microbes.

Microbial transformation capacity

The ability of microbes to transform is effective, so killing them with man-made synthetic substances is not going to work. At the same time, we put our own cells in danger as substances enter our bodies with the air we breathe.

Wet and impermeable construction, as well as the use of biocides, leads to increased microbial toxicity in the structures. Detergents containing biocides are harmful to cells and their use in cleaning increases indoor air toxicity. By dry building and using as much natural materials as possible, the use of biocides can be abandoned. Products that do not contain biocides can be chosen for cleaning.

Surfactants (molar mass 234–1,562 g / mol) are used to reduce the surface tension of water. Surfactants are used, e.g., in washing and cleaning agents, shampoos, and paints. They are also added to concrete and gypsum to speed up drying. Also these substances are transported to the breathing air.

When we want to improve indoor air quality, we must abandon the use of synthetic chemicals and biocides because they are meant to destroy microbes. Microbes are everywhere and they are essential to man and nature. The triggering factor for harmful growth arises from the excess moisture in the structure, which allows moisture damage to occur. That, of course, needs to be fixed.