Toxicology Why are wood chips carcinogenic?

Pollutants in prefabricated timber frame houses - Part 1

Occurrence and evaluation in houses from the 1970s and 1980s: Thousands of prefabricated houses were built in the 1970s and 1980s. These objects have been brokered for years. Due to the increasing awareness of indoor pollutants and the growing desire for a “healthy” home, the inquiries about the appraisal of such objects are also increasing.

The objects in question were created by larger, nationwide companies as well as local carpenters. What the house types have in common is the timber frame construction: a frame structure made of pesticide-treated frame wood, clad in different ways from the outside and inside - at that time required by law as part of preventive wood protection - was created in some cases with a high degree of prefabrication and installed on the construction site. The figure below shows a typical construction of such an exterior wall. The compartments were filled with mineral wool. The room-side paneling was done either with chipboard of various types or with plasterboard. In some cases, vapor retarders in the form of foils were also used. In this context, however, component openings in external walls are always surprising, because where a vapor barrier was provided in the construction drawing, there is actually none on the object. Basically, it can be stated that the execution of the air seal on the inside, i.e. on the warm side of the outer wall construction, does not correspond to today's standard. It can generally be assumed that there are defects in the air seal.

Pesticides in prefabricated houses

The essential and relevant pollutants in prefabricated houses are the pesticides, i.e. the so-called wood preservatives. In older prefabricated houses, at least eight different pesticides are usually examined in order to obtain a general overview of the indoor air pollution. These non-volatile pollutants often find their way into the room air from the timber frame. In most cases, increased levels of potentially carcinogenic lindane are measured in the air we breathe.

Due to their high vapor pressure, these substances are only released very slowly from the primarily treated components into the room air and are therefore still relevant decades after the building has been constructed.

Lindane is a halogenated hydrocarbon, a colorless, almost odorless powder and a widely used contact insecticide. Lindane is one of the hormone-active substances that are also known as "endocrine disruptors". In the human body, the substance has a hormone-like and bioaccumulative effect, i.e. it remains persistent in the body and accumulates when it comes into contact with the substance or when it is absorbed via the food chain.

Lindane was often used as a wood preservative in conjunction with pentachlorophenol (PCP) or dichlorodiphenyltrichloroethane (DDT). It was used in wood and building protection against wood-destroying insects.

This can lead to indoor air pollution in buildings (especially prefabricated houses) with appropriately treated materials, mainly from the 60s to 80s. Lindane mainly has a damaging effect on nerves and the liver. In addition, there may be abnormal sensations on the skin, headaches, dizziness and / or changes in the blood count and liver functions. Since 2015, lindane has been classified as carcinogenic in humans (group 1) by the WHO. In order to be able to comprehensively assess a possible health risk, the level of concentration and the period of exposure also play a role in the intensity of the use of the room.

Overall, a distinction is made between the pollution of the indoor air and the pollution of the components or house dust. However, there is currently no such guide value for lindane as is the case for pentachlorophenol (PCP). The guideline values ​​for PCP are therefore also used for lindane: “Since the threshold values ​​of the PCP guideline are 0.1 and 1 μg / m3 lie in a similar area (ARGE-BAU 1996), it seems possible and, from a practical point of view, quite reasonable to follow this system for indoor pollution with lindane ”[2].

Chlorine anisoles

The chlorine anisoles represent a secondary phenomenon, whereby this umbrella term also includes the chloronaphthalenes. Chlorine anisoles arise from the microbial activity of existing chlorophenols (e.g. pentachlorophenol - PCP) and are compounds that were previously known to the public mainly as the cause of the cork note in wine. Chlorine anisoles are essentially responsible for the musty and musty, slightly sweet smell that is typical and very common in prefabricated houses, and which sometimes sticks to clothing. According to the current state of knowledge, there is no toxicologically justified health hazard, but one can certainly speak of “social toxicity”, since the musty, moldy smell that arises when the chlorine anisoles are released into the air is e.g. B. in clothing and people who “smell of mold” are often avoided. The similarity of the odor to the typical mold odor often creates an uncertainty as to whether the building is not infected with mold. Thus, the presence of chlorine anisoles can also indicate microbial contamination of the building fabric. In prefabricated houses, the insulation level can be affected.


The “classic” among the pollutants, the carcinogenic formaldehyde, must also be included in the examination of prefabricated houses.

Essentially, formaldehyde is released from the chipboard in prefabricated houses. Objects that are planked on the room side with gypsum material panels often have lower indoor air concentrations. In order to achieve a corresponding analytical security, at least two measuring points are to be provided for single-storey objects.

Formaldehyde is one of the most well-known indoor pollutants and of all aldehydes has the greatest technical importance. Formaldehyde has a disinfecting, germicidal and preservative effect, which is why it, among other things. is used to manufacture chipboard, adhesives, varnishes, paints, wood preservatives and much more. It is released into the room air through emissions from such products. In June 2014 the EU Commission published a new classification of formaldehyde [3]. This states that formaldehyde is classified as carcinogenic 1B and mutagenic 2 in the EU. Category 1B substances are likely to be carcinogenic in humans.

There is sufficient evidence from long-term animal experiments. Formaldehyde may also be able to cause heritable mutations in germ cells. However, the information available from suitable animal experiments is not sufficient for classification in Category 1. In 2016, the guideline value of the Federal Environment Agency was set to 0.1 mg / m3 (corresponding to 100 μg / m3) fixed [4].

Carboxylic acids

Although the analysis of indoor air in older prefabricated houses has been carried out for many years and there is extensive experience with wood preservatives and chlorine anisoles as well as formaldehyde, new knowledge is currently being gained about indoor air pollution in such objects. The main concern here is the irritation and unpleasant smell caused by lower carboxylic acids such as formic and acetic acid. “Acetic acid is a typical breakdown product from wood and is therefore also known as so-called wood acid.

It is possible that the emission of acetic acid is significantly more involved in the occurrence of irritation of the mucous membranes than previously assumed. A significant occurrence of acetic acid concerns prefabricated houses - older models and interestingly also newer prefabricated houses - but also other interiors and is mainly due to emissions from pressboard or MDF panels. The determination of formic and acetic acid as wood acids should therefore not be omitted from any expert assessment. In the event of fire, high concentrations of acetic acid can also occur as a corrosive substance in the room air. "[5]

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With regard to possible health consequences, the fibers z. B. from asbestos or artificial mineral fiber insulation (KMF). Asbestos can be found on many objects as large-format cladding on the facade. In normal use, these claddings have no relevance for indoor air, as they are firmly bound asbestos products. This pollutant load must be taken into account when working on the facade, such as B. the installation of ventilation systems or an energetic upgrade of the facade. Here, increased costs are to be expected due to the legally prescribed professional dismantling and disposal by appropriately qualified specialist companies.

Artificial mineral fibers were used for thermal insulation of the outer walls and the top floor ceiling. In principle, what has been said about asbestos applies here.


Mold exposure must also be taken into account when assessing and evaluating such objects. Due to the above-mentioned structural deficiencies in the area of ​​the air seal, moist, warm room air regularly enters the structure. There it mainly condenses in the colder seasons and thus offers ideal growth conditions for mold when viewed over the years. Exposure to the air we breathe should be carried out by examining both cultivable and non-cultivable molds in the form of a total spore test.

Depending on the reason for the examinations and the subject matter of the contract, the examination of the microbially generated highly volatile organic substances (MVOC) is recommended. “Population-based studies have adequately shown that people exposed to mold indoors are at increased risk of a variety of respiratory diseases, including developing asthma, respiratory infections, symptoms such as coughing, wheezing, and shortness of breath. In addition, asthma symptoms may worsen in people who already have asthma if they are in damp and mold-infested rooms. "[6]

Sources and literature:
[1] - Prefabricated house directory, No. 100: The Streif house. Bauverlag GmbH 1967
[2] - Bavarian State Office for Health and Food Safety: Evaluation of increased lindane concentrations in indoor air,
[3] - European Commission: Regulation (EU) No. 605/2014 of June 5, 2014 amending Regulation (EC) No. 1272/2008 of the European Parliament and of the Council on the classification, labeling and packaging of substances and mixtures for the purpose of inserting hazard and safety notices and for the purpose of adapting to technical and scientific progress
[4] - Federal Environment Agency: Guideline values ​​for formaldehyde in indoor air: Bundesgesundheitsblatt 2016.59: 1040-1044, Springer Verlag, 2016
[5] - ARGUK Umweltlabor GmbH: Formic and acetic acid in the room air as a trigger for irritation of the mucous membranes. Circular, January 2015
[6] - Federal Environment Agency: Guidelines for the prevention, recording and remediation of mold infestation in buildings (mold guide), Federal Environment Agency, 2017

Find out more from the specialist magazine WOHNUNG + GESUNDHEIT No. 166

Pollutants, mold, pests Keywords: Building biology measurement technology, prefabricated houses, indoor air measurement, pollutant measurement