INSTITUTE OF OCCUPATIONAL MEDICINE www.iom-world.sg

Hazards of asbestos and their identification

Prof. Rob AitkenManaging Director IOM Singapore

Asbestos forum23 January 2014

About IOM

• Multidisciplinary research, consultancy, training in occupational and environmental health, hygiene, risk

• Exposure, toxicology, epidemiology, risk management, particles, fibre, chemicals, human factors

• Clients – Governments, industry, academia

• Independent and impartial, charitable status

• Mission – “For the benefit of those at work and in the community”

• 140 staff, Edinburgh HQ, international activity

• Since 2012

IOM Singapore, 30 Raffles Place,

#17-08 Chevron House, Singapore 048622

www.iom-world.sg

IOM’s work in asbestos

• Research and development• Animal studies and toxicology to understand the mechanisms of

disease• Development of measurement methods

• Walton Becket graticule for fibre counting• World Health Organisation (WHO) PCOM method and counting

rules• Developed and ran regular Interlaboratory Counting Exchanges

(RICE) /AFRICA• Asbestos in soils

• Consulting and services• Asbestos surveys and management• Measurement and analysis

• Asbestos in air• Bulk asbestos• Asbestos in soils • Fully accredited analytical laboratory

• Exposure reconstruction and risk quantification• Expert witness testimony in litigation cases in the US and UK

Asbestos types

Serpentines Amphiboles

Asbestos

type

Chrysotile (white) Crocidolite (blue), Amosite (brown),

Tremolite, Anthophyllite & Actinolite

Crystal

structure

Coiled sheets Double chains held together by

cations

Appearance Softer, wavy Sharper, splinters

Si

O

OO

Si

O

OO

Si

O

OOSi Si

Si

O

OO

Si

O

OOSi

O

O

Si

O

OSi

O

Mg

OH

oo

oo o ooo o

ooo

Naturally occurring mineral fibres

Uses

• Cement piping and sheeting

• Roofing

• Thermal and electrical insulation

• Textiles

• Flooring

• Gaskets and jointing

• Friction materials

• Acoustical damping

• Coatings

• Plastics

• Paper

• Others (wine & cigarette filters)

Global consumption

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Asb

esto

s c

on

su

mp

tio

n(1

000 m

etr

ic t

on

nes)

Total worldwide

Asia

Africa

Americas

Europe

Australia

Source: USGS

Diseases

• Asbestosis (1930’s), lung cancer, mesothelioma (1960’s)

• Laryngeal cancer, ovarian cancer, (parenchymal fibrosis) and pleural plaques

• Limited evidence for colorectal, pharyngeal and stomach cancers

• Apparent synergistic effect for lung cancer when smoking and asbestos exposures present together

• Risks of disease relates to the levels of exposure and the toxicity of the material

Determinants of disease

• Fibre characteristics: Chemical composition and dimensions

• Amphiboles more hazardous than chrysotile towards mesothelioma induction but potency differences unclear in regards to lung cancer

• Longer/thinner fibres can reach respirable regions of lung where they can persist for many years

• Magnitude of exposure: Concentration, duration, frequency

• Time since exposure – latency period can be 40 years for mesothelioma

Thin

Small aerodynamic diameter

enables deposition beyond the

ciliated airways

Long

Cannot be completely

enclosed by a macrophages

producing frustrated

phagocytosis

Longer than 15-20µm

Bio-persistent

Retains its long

term shape over

long-term

residence in the

lungs

High Aspect represents an attribute conveying enhanced toxicity to a particle due to the physical hindrance of

normal clearance from the deep lung and interaction with cells

Fibre Paradigm

Craig Poland, IOM

Exposure scenarios

Magnitude of exposure: Concentration, duration, and frequency

Exposure is predominantly occupational:

• Mining of asbestos or asbestos-contaminated minerals• Milling• Manufacture or use asbestos-containing products• Brake repair and maintenance• Building maintenance, renovation or demolition • Asbestos abatement

• Take home exposure e.g. home cleaning of work clothes

Global burden of asbestos –related disease (ARD)

• 100,000 ARD deaths annually attributable to occupational exposure

• 43,000 deaths from mesothelioma in 2000

• ARD incidence only peaking now in countries that banned or restricted use in the 1970’s

• 125 million still exposed in the workplace

Archives of environmental & occupational health 65.3 (2010): 121-126

Mesothelioma in the UK

Approximately 1% of all men in the UK aged 45 will eventually

die from this disease.

Where have Singaporeans been exposed?

• Asbestos cement factory which closed in 1984

• Shipyards and large construction sites

• Operators of heavy machinery

• Auto repair shops

• Singapore banned the import of raw asbestos and the use of asbestos in buildings in 1989

• Current exposures mostly during maintenance, renovation and demolition of buildings constructed before the ban

Sampling and analysis

• Analysis by fibre counting

• WHO Counting rules reflect the hazard

• Fibres are harmful because…

• they are thin (d < 3m)

• they are long (l > 5m) and

• because of their shape(l/d > 3)

• and because they persist in the lung

Analysis methods

Method Determines

airborne

concentration

Identifies

type

Min

resolution

Polarized light microscope No Yes ~ 1 to 2 um

Phase contrast microscope Yes No ~ 0.25 um

Scanning electron microscope* Yes Yes ~ 0.03 um

Transmission electron microscope* Yes Yes ~ 0.001 um

X-ray diffraction No Yes n/a

* With energy dispersive x-ray system

PCM 400x SEM 400x SEM 10,000x

Concluding remarks

• Asbestos remains a very real problem

• Exposure to even low levels can cause fatal disease

• The current risks are mainly to those involved in the maintenance, renovation and repair of buildings

• Great care and effort must be taken to identify the presence of asbestos and minimise (to zero) any exposures

• The new revisions support this effort

Acknowledgements

Co-authors: Midori Courtice (IOM Singapore)John Cherrie (IOM)

Other contributions:Michael Riediker, Zephan Chan (IOM Singapore)Craig Poland (IOM)

IOM Singapore30 Raffles Place, #17-08 Chevron

HouseSingapore

www.iom-world.sg

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