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ASBESTIFORM MINERALS ASSOCIATED WITH CHRYSOTILE FROM THE
WESTERN ALPS (PIEDMONT - ITALY): CHEMICAL CHARACTERISTICS
AND POSSIBLE RELATED TOXICITY
Antonella Astolfì, Bice Fubini, Elio Giamello
and Marco Volante
Dipartimento di Chimica Inorganica, Chimica Fisica
e Chimica dei Materiali
Università di Torino
Via Pietro Giuria 7
10125 Torino, Italy
Elena Belluso and Giovanni Ferraris
Dipartimento di Scienze della Terra
- Sezione di Mineralogia e Cristallografia
Università di Torino
Via Valperga Caluso 37
10125 Torino, Italy
ABSTRACT
Two new asbestiform minerals, balangeroite (Balangero, Italy) and carlosturanite
(Val Varaita, Italy), have been investigated from the standpoint of their potential toxicity.
Their characteristics have been compared with chrysotile and antigorite with which they
are always associated. EPR spectra of the minerals revealed the presence of paramagnet-
ic ions, including Fe3+ and Mnt*, in different crystal configurations. The presence of
Fe2+ was shown by the enhancement of the Fe3+ signals after grinding in air. Baiange-
roite is the richer in both Fe2+ and Fe3+ which are in magnetic interaction with each
other, unlike antigorite, in which only isolated and weakly interactive ions are present.
Profound modifications of the structures are found upon standing in solutions rnimicking
the biological environment. This suggests that these minerals may interact in a number of
ways ln vivo. Taking into account both their form and chernical composition they rnay be
Mechailsms in Fibre Ctcbngenisís
Edited by R.C. Brown el a/., Plenum press, New york 1991 269
regarded as potentially carcinogenic colnponents of fibrous minerals extracted from the
Piedmont mines.
INTRODUCTION
Two new asbestiform silicate rninerals have recently been found in serpentinite
rocks frorn the Western Alps (Piedmont, Itaiy): balangeroite at Balangero (Cornpagnoni er
at.,1983) and carlosturanite in Val Varaita (Compagnoní et al., 1985; Mellini et al.,
1985). A subsequent systematic field exploration of the Piedmont Western Alps resulted
in the discovery of two new localities for balangeroite and twenty-one for carlosturanite
(Belluso & Ferraris, in press). Carlosturanite has also been reported from Taberg
(Sweden) by Mellini and Zussman (1986).
Both ninerals occur as brown centimetric fìbres, macroscopically very similar to
long-fibre chrysotile with which they have always been mistaken. The fibres consist of
bundles of single fibres which are randomly distributed around the fibre axis (Fig. 1).
Single fibres (Fig. 2) have cross-sections of a few hundred Àngstróms and are usually
intergrown with chrysotile and other fibrous minerals at submicroscopic level. The new
minerals are clearly distinguishable by their chemical and physical properties.
Balangeroite
Balangeroite occurs as brown, rigid and brittle xyloid fibres. Apart from the other
physical properties reported by Compagnoni and coworkers (1983), the best way to iden-
tify balangeroite is by diffraction; e.g., its XRD powder pattern exhibits strong reflections
for d,,n, at 9.59, 6.71, 3.37 8, 3.27 8 and 2.7 14 L.
Balangeroite is rnonoclinic with a strong pseudo-orthorhornbic symmetry (Ferraris
et at.,1987) and its crystal structure can be described as an octahedral fiarnework with
channels occupied by a chain of silicate tetrahedra (Fig. 3a). In the unit cell there are four
formula units with the ideal composition:
Mrr03(OH)20(Si4o1')2
where M (octahedral) is Mg, Fe(II) and Fe(IIl) (major cations); Mn, Al; Ca' Cr, Ti
(traces).
Carlosturanite
The macroscopic characteristics of carlosturanite are sirnilar to those of balange-
roite. The brown colour is slightly lighter although sarnples from Taberg (Mellini &
Zussman, 1986) are green. Also carlosturanite can only be reliably identified by diffrac-
tion. The XRD powder pattent of carlosturanite is, however, siurilar to that of chrysotile
and so care must be taken to record the low angle reflection with dn*, of 18.02 A. Other
strong reflections have dn*, at 7. 11 ,3.595,3.391 ,2.562 L'
Carlosturanite is rnonoclinic (Mellini et al., 1985) and its crystal structure pre-
serves the octahedral sheet of serpentine, while in the tetrahedral sheet rows of [Si2O7]6-
groups are substituted by rows of [(OH)u.HrO]6- groups (Fig. 3b). In the unit cell there
are two formula units with the ideal fortnula:
MrrTrrOr8(OH)34.HrO
270
where M (octahedral) : Mg (major cation), Fe, Ti, Mn with traces of cr and ca; T
(tetrahedral) : Si (mainly) and A1. carlosturanite can be regarded as a Si-poor and H,o-
rich serpentine.
Both fibrous minerals contain paramagnetic ions in low oxidation states (e.g.
Mn(II), Fe(II)) which upon contact with air or in a biological medium may give rise to
active oxygen species. Their toxicity to hurnans is unknown as their association with
chrysotile and antigorite (another serpentine) inhibits the assessment of the individual
toxicity of each rock component. No in vivo or in vitro studies have been performed so
far. Several epidemiological studies have been carried out on the workers from the Ba-
langero mine(Rubino et al. l979a,b; Berrino etat. 1983; pioratto et al.,inpress), which
revealed asbestosis and an excess of laryngeal cancer and pleural mesothelioma. An inves-
tigation of the non-occupationally exposed population of the village is underway.
In order to investigate the possible role of each individual fibre in the overall
toxicity of the mineral dust, the chemical properties of balangeroite, chrysotile, carlostu-
ranite and antigorite have been compared. The various fibres extracted from the rocks
have been characterised by XRD, electron microscopy and chemical analysis in order to
check their purity.
The present paper reports some preliminary results showing the presence and
localisation within the fibres of paramagnetic ions detected by Electron Paramagnetic
Resonance (EPR). Taking into account the proposal that iron is implicated in asbestos
related toxicity (Mossman et al. , 1988; Pezerat et al. , 1989) , much care has been devoted
to the detection of Fe2+ and Fe3+ ions in different crystal configurations. Both these ions
may play a role in the production of active oxygen species, via redox cycles. Fe2* at the
surface partially reduces oxygen to O; initiating a redox chain and yielding OH. in aqueous
rnedia (Zalma et al., lg87). The feiric ion rnay also be active in oH. production, but
requires the presence of Hro, and, in some cases, a reducing agent such as ascorbate
(Kennedy et a.1., 1989).
To evaluate any reaction which may occur upon inhalation of the fibres, small
amounts were incubated at37 'C in the dark in phosphate buffered saline (PBS). Since
the fate of an inhaled particle may involve phagocytosis by alveolar macrophages, saline
media containing Hro, and clo-, to mimic the environment within the rnacrophage, were
also used. The solids were then re-examined by EPR to detect rnodifications due either to
redox reactions or to the release of components into the media.
MATERIALS AND METHODS
Balangeroite was collected from the Ponte del Diavolo (Lanzo-Torino); carlostu-
ranite from Colle Sampeyre (Cuneo); the two chrysotile samples from Alpe Praiet and
Punta Sbaron (Lemie-Torino) and antigorite from the Rio Milanese (Sampeyre-cuneo).
A long preliminary preparation of the rock specimens was necessary before analy-
sis of the minerals because of their asbestiform morphology and natural association with
other minerals. Srnall bundles of fibres 'were separated from the matrix rock with the aid
of tweezers and then the bundles were freed frorn impurities with the aid of the optical
microscope. Separated fibres were powdered as finely as possible in acetone suspension
to avoid loss, mixed with Vaseline oil and spread on the specimen support grid. Finally,
the samples were submitted to X-ray diffraction for identification.
27 1
F-lLP'-.t
50 um
t+l
Figure 1" Scanning electron microscope (SEM) imrtges of bundles of single
fìbres of balangeroite (a) and carlosturanite (b).
Powder X-ray diffraction and chernical analysis of the samples was carried out
using:
- a Nonius Guinier-Lenné carnera for powder XRD with CuK." radiation.
- an ARL SEMQ microprobe.
- a cambridge 5-360 sEM wirh EDS 860-500 Link Sysrem.
- a Philips 400T electron microscope with EDAX 707.
272
b
roooÀ soooÀ
Figure 2. Transmission electron microscope (TEM) images of single fibres of balangeroite (a)
and carlosturanite (b).
Electron Paramagnetic Resonance spectra were recordedatTl K on a Varian E
109 using the appropriate celis. All spectra are shown with the magnetic field increasing
from left to right and at the same scale: a corresponding scale for the g values is also
given, together with the amplification used during recording. The EPR spectra of the
minerals was recorded before and after grinding to determine the presence and abundance
of paramagnetic ions and to study the development of the Fe3 + spectra arising through
oxidation of Fe2+ exposed to the air during grinding.
In order to provide evidence for their possible modification in vivo the fibres were
kept for 15 days in the dark at37 'C in the following solutions: i) Dulbecco and Vogt
PBS; ii) PBS plus HzO2Q.5%); iii) PBS plus NaCIO (0.02 M). The solids were rhen
washed, vacuurll dried and transferred into the EPR cell.
RESULTS
Characteristics of the EPR spectra of the new fibrous minerals. Comparison with
UICC standards.
The EPR spectra of balangeroite, carlosturanite, chrysotile and antigorite are
shown in Fig. 4-7. To distinguish the characteristic features of the minerals from those of
occasional contaminants spectra from at least two separate samples were examined. No
significant variations were found between different samples of each mineral with the
exception of chrysotile. In this mineral remarkable differences in the intensities of the
spectral lines were found. Figure 6 shows two chrysotile spectra, samples A and B, of
rock froln two different locations: sample A was associated with calcite. The main feature
of the spectra in Fig. 4-7 is the very intense broad band given by both balangeroite and
carlosturanite which contrasts with the lower intensity bands of chrysotile and antigorite
273
Oy
F*
oT
vl*
Figure 3. a) Projection along the z axis (fibre axis) of the crystal structure of balangeroite
ref'erred to a pseudo-orthorhombic cell. Chains of silicate tetrahedra (large dots) lie within the
channels defìnetl by Mg-octaheclra (small clots) gathered in groups of three and fbur rows running
along the fibre axis. b) Pro.iection along the z axis of the crystal structure of carlosturanite.
The fibre axis is parallel to the y axis. A brucite octahedral sheet is coupled with a phyllosilicate
tetraheclral sheet where [010] rows of silicate tetrahedra are substituted with hydroxyl anions
(small filled circles) and water molecules (large fìlled circles).
which are resolved into well defined different components. The sextet of lines centred at
E : 2 in the spectra of antigorite and chrysotile A are due to dispersed Mn2+ ions. We
assune, on the basis of chemical composition, that all other resonances are due to Fe3+
centres isolated or in magnetic interaction with other paramagnetic ions of the same or
different krnd.
The spectrum of UICC crocidolite (Fig. 5c) closeiy resembles those of balange-
roite (Fig. 4a,b) and carlosturanite (Fig. 5a,b) each consisting of a broad intense signal.
Spectra of integrai fibres show fine structure superimposed on the broad band which is
lost on grinding. Chrysotile and antigorite have spectra (Fig. 6a and 7a) similar to that of
274
.I
BALANGEROI TE
INTEGRAL
FI BRES
emp 40
BROI(EN
FIBRES
arnp 63
FINELY
DIVIDED
FI BR ES
amp40
GROU N D
FI BRES
emp 40
108 6200 G
Figure 4. EPR spectra of balangeroite af'ter progressive fragmentation of the fibres"
UICC chrysotile (Fubini et al. , 1991, this volume). The spectrum of UICC chrysotile has
a broad band superirnposed on singie lines. This band is less intense in chrysotile B and
absent from antigorite and chrysotile A. The intensity of this broad component increases
when the spectrum is recorded at room temperature, which may be indicative of interionic
magnetic interactions involving ferric iron (Friebele et at. 1971\.
The effect of grinding
Samples which remain as long fibres afier extraction from the rocks are modified
on grinding because fresh surfaces are brought into contact with the air when oxidation of
newly exposed ions may occur. The spectra of balangeroite after progressive comminu-
275
H
20
CARLOSTURAN ITE
INTEGRAL
FIBRES
amplooo
GROUND
F I BRES
amp2@
tut b2.O H2@G
CROC I DOLI TE
amp 60
^tlrl l+
e :oeO a 2.O H 2OOG
Figure 5. EPR spectra of carlosturanite fibres before (spectrum a) and after
grinding (spectrum a') and of UICC crocidolite.
tion and then grinding is shown in Fig' 4 . lncreasing fragmentation causes disappearance
of the low field spectral bands and a shift of the whole spectrum towards a lower field'
Grinding changes both linewidth and position of the band with displacement of the cen-
troid to lower field. The spectrum of carlosturanite (Fig. 5a and b) shows an increase in
intensity and a shiti to lower field after grinding and the disappearance of the lines super-
imposeà on the broad signal from the starting material. With chrysotile A and antigorite
grinding produces a small signal centred at g : 2 superimposed on the sextet of lines'
itr" rp".tiu* of chrysotile B, in contrast, is considerably changed by grinding, probably
because the mineral contains more iron ions.
276
CHRYSOTILE A@
GROUND
FIBRES
PHYS
SALINE
PHYS. SALINE
i H2o2
PIIYS. SALIN
+ Na CiO
q ìII I *__
- 1086 4
+rt
H 2CJ]G
1086 4 2A
+H
H 2OOG
2A
Figure 6. BPR spectra of chrysotile A and B. Spectrum a: integral fìbres; spectrum
b; kept in phosphate buffered saline @BS); spectrum c: kept in pBS with added Hror;
spectrum d: kept in pBS with added NaClO.
Evidence of paramagnetic ions in various configurations
The EPR signals shown in Figs. 4 and 5 are very broad and asymmetric. This
structure can be due to various phenomena. There can be mutual magnetic interactions
between similar ions (Fe3+-Fe3+) or dissimilar ions (Fe3+-Fez*, rlnz*y; ttr" possiute
presence of a magnetically ordered (or partially ordered) lattice; additional ,t on! dirtor-
tions of the crystal electric field felt by paramagnetic ions, e.g. those at surfaces. In
balangeroite and carlosturanite the number of different octahedral sites for Fe3+ or other
cations is at least 21 and 11 per unit cell respectively. Each site will give a slightly
277
CHRYSOTILE B
different contribution to the overall spectrum: assignment of bands is clearly not easy in
such cases. The similarity of the spectra of the two new fibrous minerals with that of
crocidolite, whose spectrum is rnainly ascribed to the simultaneous presence of iron in the
two oxidation states in relatively high concentration, suggests the presence of
similar arrangements in the hbres under study'
The spectra of crysotile A, with only three independent sites, and antigorite, are
similar. Each consists of a relatively narrow signal at g: 4.3 and a sextet of lines cen-
tred near E:2. A similar spectrum has been reported for one sample of Canadian
chrysotile (Sharrock, 1982). The signal at E : 4.3 is characteristic of ferric ions in a
tetrahedral or slightly distorted octahedral field. In the former case it is attributed to an
iron ion substituting for silicon in the silicate tetrahedra, in the latter to an iron ion substi-
tuting for ,r,ugn"riu* in the brucite layer. It is well known that the ratio between these
two conhgurations varies from one mineral to another. The sextet of lines is due to
ANT IGORITE
FIBRES
FI BRES
+ H2O2
108 62.o
Figure ?. EPR spectra of antigorite" Details as in Figure 6.
278
H 2OOG
amp 4OO
P HYS
BALANGEROI TE
amp 20
S. SALI N E
sAL.+ H2 02
SAL.+ NiaC lO
.--.>
H 2OOG
Figure 8. EPR spectra of balangeroite kept in various solutions. Spectrurn a,: start-
ing material; other fèatures as in Figure 6"
manganese substituting for magnesium in the brucite layer; the relatively small linewidth
indicates that the manganese is well dispersed in the lattice at a concentration below I %.
The absence of broad bands in the spectra of Chrysotile A and antigorite shows that these
minerals are poorer in iron than chrysotile B. This confirms the large variation in the
amounts of iron substituting for magnesium from one chrysotile to another"
The effect of immersion in aqueous solutions: mimicking the biological enyironment
The spectra from fibres left standing at3i "c for two weeks in pBS (b), pBS with
added with hydrogen peroxide (c), or PBS with added hypochlorite (d) are compared with
those of the starting materials in Fig. 6-9. The spectrum of balangeroite is a broad signai
due to magnetic interactions between the various paramagnetic ions. After immersion the
overall features are still the same, but variations in shape, symmetry and the g value of
the centroid indicate that some ions have undergone chemical modification. In physiologi-
cal solutions balangeroite undergoes a slow fragmentation, the resulting material
279
20
CARLOSTU RAN I TE
SALI N E
SALr HrO,
SALTNaCIO
108 6 4
+
H 2OOG
Figure 9" EPR spectra of carlosturanite kept in various solutions. Features as in Figure 8.
consisting of much smaller fibrils and appearing as a brownish powdery material. Irach-
ing with hydrochloric acid completely eliminates the brown colour and leaves a still
fibrous white material which contains no iron. XRD shows that the original structure is
preserved.
Carlosturanite (Fig. 9) is profoundly changed by immersion. A constant depletion
of iron ions occurs in PBS: the broad signal in the spectrum decays but several new lines
appear with an overall decrease in intensity. In contrast the presence of HrO, produces an
increase in signal intensity. Most spectral features are changed: two new bands appear at
B : l0 and g :4.2, both characteristic of Fe3+ in distorted octahedral positions. These
resonance lines are also visible in the sample treated with NaCIO but are less intense and
the overall intensity is less than that of the starting material. No visible changes were
detected in the shape of the fibres.
280
2.o
Chrysotile A (Fig. 6A b,c,d) is virtually unchanged by the saline solutions where-
as chrysotile B (Fig. 68 b ,c ,d) undergoes profound modification. Some spectral features
of the starting material, before-grinding, reappear after standing in the saline solution,
indicating a solubilisation of Fe3+ brought to the surface by grinding. Differences in the
spectral features in Fig. 6c and d indicate that different redox reactions have occurred in
the two cases. The presence of iron therefore imparts a particular reactivity to the
mineral.
Antigorite (Fig.7) is little affected by immersion in the various solutions. No
significant variations in the overall intensity of the spectra were found and no broad bands
appeared indicating an extreme dilution of all the paramagnetic ions. The most remarka-
ble feature of the spectra are the bands at g = 6 and g = 10 characteristic of isolated
Fe3+ which only show up with the HrO, solution, indicating some oxidation of Fe(II) to
Fe(II!.
DISCUSSION
The role of iron in asbestos toxicity
The main hypothesis of this research is that the chemical functionalities implicat-
ed in asbestos toxicity have to be sought in the chemistry of iron and its involvement in
the production of active oxygen species (AOS). This is in agreement with what has recent-
ly been proposed (Mossman et at. 1988, pezerat et al. 19g9, zalma et al. l9g7). we
have looked for the presence of Fe(II) or other ions in a low oxidation slate and examined
their oxidation in different media. Besides the well known Fenton reaction which occurs
in presence of Hro, various other reactions may be envisaged in which iron produces
AOS directly from atmospheric oxygen (Pezerat et al. 1989).It has recently been shown
that the initiation of lipid peroxidation by Fe2+ and HrO, is mediated by an oxidant which
requires both Fe2+ and Fe3+ (Minotti & Aust, 19g7;.-rairs of these two ions may be
present at the surface of some asbestos minerals and there is the possibility that similar
reactions could also occur at the solid liquid interphase. We will therefore focus our
interest on the presence of Fe2+. Fe2+ does not give an EpR spectrum under our experi-
mental conditions. However, we can show evidence for the presence of this ion either
through its interaction with Fe3+ (broad band) or by the enhancement of the signal due to
Fe3+ ions produced by oxidation of Fe2+. Although no biological data are available, we
also consider that Mn2+ can act as a possible redox site.
New asbestiform minerals: balangeroite and carlosturanite.
The chemical formulae of the two new minerals show that they contain relatively
large amounts of Fe2+, Fe3+ and Mn2+. For this to affect their toxicity, however, re:
quires that those ions exist at, or can be brought to, the surface of the solid where the
redox reaction involving AOS will occur in a biological medium.
Our results show:
i) the presence of relatively large amounts of Fe2+ and Fe3+, sirnilar to those found
in crocidolite;
ii) that changes occur on grinding which indicate that oxidation is taking place at the
newly formed surfaces;
iit a decrease in EPR signal intensity and other spectral changes after immersion in a
281
physiological solution which partially mimícs the macrophage environment (HrO,
or ClO-). These changes imply that redox reactions occur at the mineral surface
and there is substantial leaching of metal ions into the rnedia. The relevance of
both these findings to the potential reactivity of these minerals in vivo is obvious.
Chrysotile and antigorite from the Western Alps
The chrysotile specimens examined differed in their iron content. Iron substitutes
for magnesium in the matrix and marked differences in the composition of rock samples
is found. The samples also underwent modification in physiological soiutions. Antigorite -
whose toxicity has never been reported to our knowledge - behaves in physiological solu-
tions in a similar manner to chrysotile A. No significant changes could be measured in
PBS and only minor ones in oxidising solutions. The two main features of the spectrum,
those due tO isolated Fe3+ and Mnt*, are unchanged. These ions, therefore, must be
away from the surface and unable to react with molecules in biological media.
Effect of HrO, and CIO-
The àsslgnment of each spectral component to a defined ion in its crystallographic
environment is required for the interpretation of the chemical reactions brought about
independently by H"O, and NaClO. It is noteworthy that the two oxidants act in different
ways. Hydrogen peroxide carries out redox reactions at various sites and creates new
surface arrangements of ions, whereas CIO-, which suppresses part of the spectra, proba-
bly oxidises and assists solubilisation of sr.rrface ions. Since both H,O, and ClO- are
present within the macrophage, the effects of both these species will have to be taken into
account in any discussion of mineral toxicity.
CONCLUSIONS
Chrysotile asbestos from the Western Alps contains two recentiy described fibrous
silicates: balangeroite and carlosturanite. A preliminary examination of this asbestos
suggests a potential toxicity for these fibres ln vivobut not for the other associated miner-
al - antigorite. Balangeroite has an EPR spectrum very similar to crocidolite and has a
higher iron content, both Fe(II) and Fe(III), than carlosturanite. Considering its associa-
tion with chrysotile in the Balangero mine it may well be that the excess of cancer in
workers at this mine should be related to its presence. The use of EPR spectra to illustrate
the modifications that occur when the minerals are kept in physiological solutions, mim-
icking the biological environment of the inhaled fibre, turns out to be an effective tool for
assessing their reactivity. The changes, both in the ìntensity and in the relevant lines of
the spectra, monitors the release of ions into the mediurn and the formation of new poten-
tially active sites on the mineral surface.
ACKNOWLEDGEMENTS
We would like to dedicate this paper about minerals from Balangero to the
memory of Dr. Primo Levi, chernist and novelist, who worked as an analyst in the mine
during hard times and reported on it in the short novel "Nickel" in his book "The Periodic
Table", Shocken Books, New York, 1984.
282
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