CHARACTERIZATION AND BIOLOGICAL ACTIVITY OF QUARTZ EXTRACTED FROM BENTONITE

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CHARACTERIZATION AND BIOLOGICAL ACTIVITY OF
QUARTZ EXTRACTED FROM BENTONITE

• ASTM Symposium
• Silica Sampling and Analysis
• Salt Lake City, UT April 23, 2004
• W. Miles, G. Tomaino, W. Moll, S. Ampian, R.
  Hamilton. Creutzenburg, G. Oberdörster and H.
  Muhle

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IARC 1997(paraphrased)

• QUARTZ CAUSES CANCER EXCEPT WHEN IT DOESNT
• (illustrates a good example of the need to better
  understand the human toxicology of minerals)

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HYPOTHESIS

• The surface characteristics of airborne,
  respirable size quartz particles are the
  principal factors controlling their biological
  activity

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FOR QUARTZSurface Age Defines Characteristics

• Recently broken (seconds - days) active
  surfaces
• Aged (days - centuries) hydroxylated and/or
  hydrocarbon contaminated surfaces
• Geologically ancient (gtcenturies) occluded
  surfaces

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QUARTZ TOXICOLOGY

• FACT The standard for toxicology assessment is
  in vivo animal testing
• PROBLEM Historically, all in vivo testing is
  with newly crushed quartz
• PREFERABLE In vivo testing with respirable size
  quartz particles obtained without crushing or
  altering the surface HOW?

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SOLUTION

• Sodium bentonite
• Matrix smaller than 1 µm
• Easily dispersible in water
• Separable through exhaustive settling and
  centrifugation
• 1-10 µm isolate can contain 65 quartz for
  unambiguous toxicological results (termed quartz
  isolate)

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TEST STRATEGY

• Compare in vivo biological activity of quartz
  isolate with a crushed quartz, with suitable
  controls
• Thoroughly characterize quartz samples and
  controls

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MATERIALS

• Uncrushed quartz quartz isolate
• Positive control (crushed quartz DQ12lt5µm)
• Negative control titanium dioxide (rutile)
• Clay montmorillonite
• Carrier saline

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MINERALOGY OF QUARTZ ISOLATE

• QUARTZ 65
• MONTMORILLONITE 29
• ANALCIME 2
• CALCITE lt1
• AMORPHOUS SILICA 3

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MINERALOGY OF DQ12

• SiO2 content 99.39
• QUARTZ 87
• OTHER SiO2 13
• amorphous silica?
• opal?
• superfine quartz?
• poorly crystalline quartz?

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DQ12lt5µm
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QUARTZ ISOLATE
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PROPERTY Montmorillonite TiO2

• SA (BET) m2/g 6.4 1.9
• SA (EGME) m2/g 480 21.7
• Particle size µm lt1 0.9
• Quartz, 0.03 0.0

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TOXICOLOGY

• Johnston, Carl J., Kevin E. Driscoll, et al.
  (2000) Pulmonary chemokine and mutagenic
  responses in rats after subchronic inhalation of
  amorphous and crystalline silica, Toxicological
  Sciences, 56, 405-413.

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TOXOLOGY PROTOCOL

• Male Wistar rats, 330g
• Intratracheal instillation of particles in
  saline, 15.2 mg/kg (11.7 for DQ12)
• Bronchoalveolar lavage (BAL) after 3 and 28
  days, second study after 90 days
• Histopathological examination after 28 days,
  second study after 90 days

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ENDPOINTS (BAL)

• Total cell count
• Differential cell count
• Macrophages, neutrophils, lymphocytes,
  eosinophils, epithelial cells

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ENDPOINTS (BAL)

• Biochemical parameters
• Lactic dehydrogenase (LDH) cytosolic marker
  enzyme, increased permeability of membranes, cell
  damage and lysis
• ß-glucuronidase, total protein measure of
  phagocytic activity of macrophages, lysis of
  macrophages

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ENDPOINTS

• Lung wet weight marker of transduction, damage
  of epithelial cells
• Histopathology after 28 days and after 90 days
• Scoring of inflammation and fibrosis of all five
  lung lobes

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BAL RESULTS3day/28 day

• Quartz isolate DQ12
• Total protein ()/ /
• Total cell number /() /
• PMN / /
• Lung weights /- /

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HISTOPATHOLOGY28 days

• Quartz isolate DQ12
• Inflammation
• Interstitial ()
• fibrosis
• Alveolar
• lipoproteinosis

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BAL RESULTS3day/28 day

• Montmorillonite TiO2
• Total protein /()
• Total cell number /()
• PMN /
• Lung weights /

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HISTOPATHOLOGY28 days

• Montmorillonite TiO2
• Inflammation () ()
• Interstitial
• fibrosis
• Alveolar lipoproteinosis

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CONCLUSIONS

• Significantly lower quantitative and qualitative
  inflammatory effects of quartz isolate vs. DQ12
• BAL moderate effects vs. high acute and
  persisting effects
• Inflammation/interstitial fibrosis slight vs.
  moderate effect
• Alveolar lipoproteinosis not observed vs.
  moderate effect

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CONCLUSIONS

• A detailed physico-chemical and toxicological
  characterization of quartz-containing particles
  is absolutely necessary for a valid toxicological
  assessment.
• All quartz does not elicit the same biological
  response