We often come across fibrous materials in everyday life.
These fibres are either natural ones like cellulose, hemp and
asbestos, or artificial ones like polyester or viscose (see
Figure 1).
The artificial kind comprise crystalline fibres such as
carbon fibre and silicon carbide, but also amorphous fibres
like glass or rock wool. Glass-like fibres are commonly used as
insulating wool or as an additive in construction materials to
enhance stability, toughness and durability.
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Mineral wool, is a common insulating
material and construction additive, via
Flickr
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As such, mineral wools are a significant end market for
companies that mine and refine the elements that go into these
products.
Modern artificial mineral fibres are considered ecologically
safe and perform well against environmental and health
standards.
According to European Union (EU) guideline 97/69/EG, these
fibres are defined as "artificially produced glass-like
(silicate) fibres with a content of alkaline or earth-alkaline
mineral oxides (Na2O + K2O + CaO + MgO + BaO) above 18%
(w/w)".
In 1998, the German Association of Mineral Wool (GGM) was
founded under the umbrella of the German Institute for Quality
Assurance (RAL), thus creating a voluntary internal and
external mechanism for quality control.
To obtain the RAL quality label, and thereby evidence that
mineral fibres do not contain any harmful ingredients,
producers need to prove, among other things, that their
products pass an intratracheal test or score appropriately on
an index of carcinogenicity and pass an intratracheal test,
short-term inhalation test or long-term inhalation
test.
Alternatively, an intraperitoneal test needs to be passed to
earn RAL certification.
Mineral fibres that were produced in Germany until 1995 and
sold until 2000 were widely used in buildings and have
similarities to asbestos fibres, raising concerns over their
safety.
Mineral wool particles (length <250µm, diameter
<3µm) are potentially harmful if they enter the lungs.
The World Health Organization defines mineral wools as critical
substances if the length exceeds 5µm, the diameter is
smaller than 3µm and the ratio of length to diameter is
more than three.
German safety standards for mineral
wool
In 1994, Germany’s Committee for Hazardous
Substances defined a classification for artificial mineral
fibres, which not only guides on length and diameter but also
the persistence of the fibres in the human body. The faster the
fibres dissolve in the lungs, the lower the risk of them
causing serious health problems.
The bio-solubility of fibres describes the capacity of any
organism to damage and repel the fibre from the body. This is
done with the help of macrophages and lung surfactant (pH 7.4)
which chemically attack the fibres before macrophages remove
them.
Since 1994, a formula has been used to determine the index
of carcinogenicity (IC) to evaluate the persistence of the
fibres in the body (see Figure 2).
Some producers of mineral wool felt that the IC did not
sufficiently describe the bio-solubility of mineral fibre and,
in 1995, it was proved that the index gave incorrect
information on the bio-solubility of modern rock wool. In
contrast to other types of mineral fibre, the aluminium oxide
in modern rock wool served to enhance their bio-solubility,
rather than reduce it.
Consequently, this IC was not included in the 1997 EU
guideline defining artificial mineral wool. Around 1997, a
collaboration between Germany’s Fraunhofer
Institute for Toxicology and Aerosol Research, the Fraunhofer
Institute for Silicate Reaearch and various German mineral wool
producers and associations helped to develop modern artificial
mineral fibres with more positive environmental and health
aspects.
The bio-solubility of modern mineral fibres is determined by
the length-to-diameter ratio of the fibres, as well as by their
persistence in the human body.
It is therefore vital that the sanitary evaluation of
mineral fibres obtains correct and reliable chemical analyses,
both during production processes and during recycling or
dismantling of buildings.
Fibres are evaluated in accordance with the criteria of the
German Ordinance on Hazardous Substances set by the German
Association of Mineral Wool (Annex II, No. 5).
There are four institutes approved by the German Association
of Mineral Wool which analyse artificial mineral fibres,
including the IGR Institute for Glass and Raw Material
Technology GmbH, based in Gottingen (see box).
The IGR has developed a comprehensive auditing process,
which is based on duplicate determination of all
parameters.
For example, mineral wool element oxides are analysed with
two separate ICP-OES instruments against an IGR-produced and
matrix-adjusted internal standard.
Elements with higher concentrations, like sodium, potassium,
calcium and magnesium are analysed with radial plasma
observation, whereas elements with lower concentrations, like
cadmium, lead and chromium, are analysed with the more
sensitive axial plasma observation.
In addition to the fibre sample designated for testing, IGR
always analyses another mineral fibre sample with the same
matrix as a reference.
Equipment for mineral wool sampling
Prior to reliable analysis, mineral wool fibres must be
homogenised in a laboratory mill. This is an important step
during which there is a risk of preparation mistakes.
For example, only a few milligrams of sample are required
for elemental analysis by ICP-OES, but this small amount needs
to represent the complete initial sample.
Depending on the part of the original sample from which the
sub-sample is taken, its composition may vary. Reproducible
sample homogenisation prior to analysis is a premise for
reliable results.
Accuracy of the analysis depends on the choice of mill and
grinding tool material (agate or zirconium oxide are examples
of materials commonly used) but also on parameters like speed
or frequency. Agate tools, for example, increase the
concentration of silicon dioxide (SiO2) due to abrasion. The
German Association of Mineral Wool stipulates sample
preparation of fibres with agate tools.
The quantity of the sample is also relevant – too
little sample material in the jar leads to increased wear,
resulting in more abrasion and dilution of the sample. This may
falsify the values obtained by subsequent analysis.
At a time when consumer groups and governments are
increasingly conscious of toxicity risks of everyday materials
and with an ever-growing precedent for legal action against
manufacturers of products found to be harmful, accurate
analysis of mineral wools is becoming increasingly crucial.
Leading engineering and biotechnology groups, academic
institutions and industry bodies are among those leading the
charge to ensure than manufacturers and consumers have
confidence in the products they sell and buy.
As well as being vital for safety, the role performed by
these bodies is important to protect the producers of
minerals that go into making the wools used in everyday
applications worldwide.
References
Bundesinstitut fur Bau- Stadt und Raumordnung:
Kunstliche Mineralfaserdammstoffe BBSR-Berichte KOMPAKT,
1/2011.
Mai, Anna: Unter Dach und Fach, Test Dachdammstoffe, in
Oko-Test 10/2009, S. 140–148.
Amtsblatt der Europaischen Gemeinschaften: Richtlinie
97/69/EB der KommiL 343/10, 13.12.97.
Gutegemeinschaft Mineralwolle e.V.:Gesundheitliche
Bewertung von Mineralwollen an Hand der Bioloslichkeit,
2015
Gutegemeinschaft Mineralwolle e.V.: Die Güte- und
Prüfbestimmungen, April 2013
Pott, F./Freidrichs, K H: Tumoren der Ratte nach
i.p.-Injektion faserförmiger Stäube, in
Naturwissenschaften 59, S. 318, 1972.
Bayerisches Landesamt fur Umwelt: UmweltWissen,
Künstliche Mineralfasern, 2008.
Bundesanstalt für Arbeitsschutz und Arbeitsmedizin:
905-anorganische-fasern, Januar 2002
GGM Gütegemeinschaft Mineralwolle e.V.:
Aktualisierung des Merkblatts, "Bewertung von
Mineralwolle-Dämmstoffen im Zusammenhang mit Abbruch-,
Sanierungs-, lnstandhaltungs- und Instandsetzungsarbeiten", Mai
2016
Laborpraxis: Kleine Partikel – großer
Effekt: Planeten-Kugelmuhlen erlauben die Herstellung von
Nanopartikeln; April 2011
*This is an edited version of a paper authored by Dirk
Diederich, of the IGR Institut für Glas- und
Rohstofftechnologie GmbH; Dr Tanja Butt, of Retsch GmbH; Jorg
Reipke, of Thermo Fisher Scientific GmbH.