Workplace exposure to nanomaterials

ICOH, Cancun, Mexico, March 20th 2012

Workplace exposure to nanomaterials
Olivier Witschger

olivier.witschger@inrs.fr

Laboratoire de Métrologie des Aérosols
Département Métrologie des Polluants
Centre de Lorraine, Vandoeuvre-les-Nancy, France

Introduction

 First researches in toxicology on nanomaterials started in the late 80’s, while studies of
workplace related exposure were initiated in the late 90’s

 1st ISO guideline on inhalation exposure characterization and assessment in 2006
(TR/27628), 2nd in 2008 (TR/12885)

ICOH, Cancun, Mexico, March 20th 2012 2

Nanomaterials and potential sources of exposure

Nanomaterials

Nanoparticles (powder, liquid Materials incorporating
Nanostructured matérials
suspensions, aerosols) nanoparticles

free suspensed in the
matrix in the bulk

agglomerates, aggregates
on the surface
bounded on the
surface

 For each category a potential scenario of airborne particle release and exposure can be
defined


Aggregate (~ 3 µm) of nanoparticles (~20 nm)



 TEM images of airborne particles collected after aerosolization of nanopowders

30 nm 30 nm 30 nm

Fe3O4 SiO2 Al2O3

30 nm 30 nm 30 nm

Fe2O3 Al2O3- 80 ZrO2 MWCNT



 TEM images of a sanding particles with protuding CNTs

Cena and Peters, (2012) JOEH


Two sub-categories for nanomaterials

 Mass-produced:
 TiO2, BC, metal(n)-oxides (Al, Si, Zn, Fe…), CaCO3, rare
earth elements…
 Many industrial sectors make use of them in significant
quantities (paints and coatings, cosmetics, catalysts and
polymer composites etc.)

 Specialized:
 Pure metals, single- or multi-metal oxides,
 High aspect ratio nanoparticles (HARNs):
nanotubes, nanofibers
 Produced on a bench- or pilot-scale, in small quantities

 A great diversity of substances (and morphologies) applies to many
types of ENM


How to evaluate exposure for nanomaterials?

 Which parameters are relevant to evaluate health effects ?

Hazard

Exposure
X
Particle size range, Indice of exposure (metric)
Chemical composition, morphology etc.

 The determination of the most relevant parameter(s) for health-related sampling of aerosol
released is still a key issue
 It is needed for the development of concepts/techniques/methods for exposure
measurement
 An international agreement has to be found


Exposure criteria

 Particle size range and aerosol fraction


Exposure criteria (cond’t)

 Indices of exposure:
 On-going research to identify under which circumstances different exposure
metrics might be relevant.
 Surface: relevant but is not universally relevant, measurement issues
 Mass: relevance is questionable, offers continuity with historic and current
monitoring, sampling and quantification issues
 Number: has been associated with adverse response, relatively easy to
measure, “background aerosol” issue

 Until it has been agreed which are the most appropriate measurable quantities, it has been
recommended to provide full characterization of the nanoaerosols in workplaces (ISO TR
27628):
 This requires a large number of instruments
 There is not one method (strategy)
 This context contributes to the sparseness of published data


Possible “aerosol” measurement and sampling devices

mass Sss + weighing/wet analysis
Time integrated number Sss + TEM/SEM
surface Sss + weighing/BET/TEM
Size integrated
mass Oscillating microbalance
Time resolved number Particle Counters / Diffusion chargers

surface Diffusion Chargers

Cascade impactors
Time integrated
Diffusion batteries

Size resolved

Mobility Particle Sizers (SMPS & FMPS)
Time resolved
Electrical Low Pressure Impactor (ELPI)


Size selective samplers

 Today, few prototypes of personal samplers available developed

 Alternative approach: cascade impactors
 Numerous instruments (geometry, flowrates, stages, cut-off sizes, collection etc.)
 Static (high flowrate) or personal (low flowrate)
Sioutas Impactor
(9 Lpm)
MiniMOUDI
(2 Lpm)



Naneum., 2010
Non-conductive nylon nets

Combines: cyclone + diffusion battery + terminal filter
Operating flowrate: 5 Lpm
5 stages: 0.3-0.06-0.015-0.005-0.001 µm

Developed/validated within EU Project Nanodevice



 Nanoparticle Respiratory Deposition (NRD) personal sampler

Diffusion
Stage

Impaction
Stage
d50 = 300nm

Respirable
Cyclone
d50 = 4µm

Cena, Peters (2011) EST


Measurement strategy

Witschger et al.,(2012) HST



 This approach will require revision, based on more recent knowledge, leading ultimately
to a harmonized approach at international level.
Witschger et al.,(2012) HST



 Several issues:
 Background aerosol distinction (airborne nano-scale particles that originate
from multiple indoor and outdoor sources)
 Near field/far field approaches, (single) particle characterization
 Most of current instruments are not “personal”, produce real-time measurement
data


Field studies

 INRS conducts field studies in the objective of:

 helping companies/laboratories in their efforts to prevent risk of using
nanomaterials/nanoparticles,
 documenting knowledge on nanoaerosols in the workplaces,
 studying the performance of measuring instruments,
 developing and testing strategies for measuring exposures,
 defining and developing tools for data interpretation,
 defining and developing protocols for the characterization of nanoparticles &
nanopowders (particle size a liquid, nanodustiness, electron microscopy etc.).


Field studies / spatial mapping of aerosol characteristics

 Workshop manufacturing a medium of low density based on inorganic fibers (SiO2)

No activity Activity 1 Activity 2

ELPI data


Field studies / bagging pigment grade and nano‐TiO2

 Manufactured plant delivering ‘pigment grade’ and ‘nanostructured’ TiO2 powders.
 Conditioning in 25kg paper bags and 600kg plastic big bags
 Several releases are possible
 Very few published data

Hall 1 - Pigment grade. Hall 1 - Nano (A) Hall 2 - Nano (B)

Witschger et al., 2010



 Multifaceted strategy was based on:
 real-time concentrations (number, deposited surface-area) measurements,
 real-time and averaged size distributions measurements
 mass-based sampling (respirable aerosol fraction) at fixed positions.

 Background measurements were addressed for real-time instruments with activity/time
as variable (i.e. ‘near-field’ approach).



 Field measurements were completed by release experiments in the laboratory
(nanodustiness)
RDM 280 Filtered air suppl y
(TSI 3074B)
2 Lpm Compr essed
Air

HEPA
Brooks
filter

4.5 Lpm
HEPA 5851S
Cycl one filter
DC = 2.5 µm

5 Lpm
Room
Air
HEPA
filter

15000
Flow
splitter
Nanopowder
+ 1.5 Lpm CNC 5.403
Bronze beads

10 Lpm

ELPI 10000

IKA Vortex
Genius 3

INRS / Witschger / avril 2009



 Bagging operations release aerosols in the respirable size range for both pigment grade
TiO2 and nano-TiO2.
 Only the aerosols coming from nano-TiO2 bagging are made of nanostructured particles
with high specific surface area.
 The smallest nano-TiO2 objects that have been sampled from workplace atmosphere and
visualized by SEM were compact aggregates of ~100 nm.


Field studies / cleaning of a reactor containing nanoAg

 Academic research lab on coatings

 Lab-scale reactor (cold plasma-deposition)

 Thin films (~150 nm) containing silver
nanoparticles in a polymeric matrix (SiCxOyHz).

 Task: cleaning done manually every day using a
flexible abrasive (sandpaper-like "P")



 Average mass concentration over 2 operations

Sampler CI(Resp) RPM_A RPM_B RPM_D

CMCI(Resp)/CMX 1 261 2000 30000



 Average mass particle size over 2 operations

Mass Ag Fe Ni Cr
% < 250 nm 26 9 61 19 19
% < 1000 nm 36 25 73 28 28



1 µm 500 nm 100 nm

Red: Ag

Green: Fe, Ni, Cr

5 µm

SEM-EDS analysis

Perspectives

 Need for further research on the following:
 Robust methods for testing instruments/sampling devices, harmonization
 Performances of existing instruments/sampling devices, development of new
portable and relevant ones.
 Harmonized approach for measuring strategy (with different levels of
sophistication), data analysis reporting and storing has to be developed and a
international consensus found.
 Nanoparticle release studies under laboratory condition, harmonization
 Field studies for exposure situations found throughout the complete life cycle of
the nanoparticles & nanomaterials.

 Many questions remain to be addressed, and it is foreseen for the next 10+ years a
continuing extended research in the fields of nanomaterials/nanoparticles
characterization and exposure evaluation.


Workplace exposure to nanomaterials

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