3rd Meeting of the
UK Natural Dust and Health Network
Final Workshop
29 July 2008
Institute of Hazard & Risk Research, Durham University, UK
Attended by:
Claire Horwell (Durham), Peter Baxter (Cambridge), Ken Donaldson (Edinburgh)
Apologies from:
Ed Derbyshire (Royal Holloway, University of London)
This meeting is to discuss the outcomes of the Plenary Workshop held in March 2008 in
Cambridge. The points below are a synthesis of the discussion:
 What is our definition of Natural Mineral Particles (NMPs)? We answered this
question with the following definition:
Natural mineral particles are produced and released by natural processes.
(distinguishes them from anthropogenic quarrying/mining).
We need to produce a table to describe different types of NMPs: e.g. crustal particles,
volcanic (including altered volcanic deposits eg. Turkey & Biancavilla), desert dusts,
combustion particles at ambient temperature (e.g. forest fires – fires are a natural process of
mineral production), sea salt.
 Is there a different paradigm for formation of NMPs compared with anthropogenic
quarrying/mining?
The mode of generation of particles may affect their toxicity e.g. grinding, blasting, eruption,
glaciation. This needs to be considered. We need new paradigms and metrics depending on
the mode of formation and toxic components – currently all metrics are based on
anthropogenic factors. A new metric should be based as closely as possible on the
Biologically Effective Dose (BED) which needs to be determined. How can we screen the
dusts without animal experiments? Oxidative capacity is the closest metric to the BED at the
moment. However, we have a problem: Currently, for volcanic ash, we do not see a
correlation between surface reactivity (Fenton chemistry by EPR) and oxidative capacity
(Frank Kelly’s experiments). There should be a clear link and we do not currently know why
volcanic ash shows high reactivity but no oxidative capacity. This needs addressing.
 Natural nanoparticles – there may be an additional risk from nano-particles which is
currently unknown. Horwell addressing this through PhD project in 2009.
 Mixed dust fibrosis – a disease specifically related to dusts of heterogeneous
mineralogical composition. The nodules in the lung are observed to be stellate lesions with
less collagen than a typical silicotic nodule. Spread out rather than concentrically formed.
(Ref: ‘Pathology of occupational lung disease’ by A. Churg & FHY Green (editors), Regnery
Publishing, 1998, pp497). We should not expect classic silicosis from our mixed dusts
particularly because the dust needs > 10 % crystalline silica for silicosis to occur. As a general
exposure we expect occupational exposure to be higher than natural exposure. Depends on
dose, dust, susceptibility and exposure. Inflammation may be a better start point. Clear link
between oxidative stress and inflammation. Need to make diagram showing process of
toxicity – Ken has one that we can adapt.
 Exposure studies
o Overload exposure - happens in rat studies but not in humans because only
coal mine exposures come close to these levels but need a lifetime of high
exposures and in today’s civilised society, workers are not exposed to those
levels. Failed clearance can occur, however, which is a type of overload.
o Coarse fraction exposure – There is currently a disparity between
epidemiology and toxicology knowledge with regards to the coarse (PM2.510) fraction – epidemiology says the coarse fraction is non-toxic whereas
toxicologists believe that it is toxic. We need good exposure levels for the
coarse fraction. We should review existing studies and recommend and plan
more studies:
o Plan of studies – 24 hour monitoring – check John Cherrie’s comment on new
monitors. Dust trak etc. are mass related. P-trak (Ultrafine Particle Counter
made by TSI) measures particle number right down to nano. Doesn’t give
numbers per fraction but if numbers go up, dominated by smaller fractions.
 Indoor biomass burning - exposures are far greater than outdoor exposures. Do see effect
of PM10 on smokers independently of cigarette smoke disease. May be because exposure to
smoke is not 24 hrs/day.
 Haemolysis – An easy, basic toxicological test to determine red blood cell (erythrocyte)
death from particles – should be added to our protocol for ash analysis.
 Protocols for dust analysis – We already have a protocol for volcanic ash analysis which
can be adapted (particularly for fibrous dusts) for other natural dusts.
 Endotoxins – are potent inflammogens but are not integrated into schemes for harmful
effects of particles. However, because we are interested in natural particles perhaps we need
to take note of them. We can measure endotoxins on particles.
 Volcanic particles as a model for PM10 - We don’t think now that we can use volcanic
particles as a model for other NMP, mainly because we still don’t understand the toxicity of
volcanic particles.
 Plan for a critical literature review paper: We need to review and to recommend more
epidemiology and exposure studies. We will ask NERC if we can use excess money from the
grant to do the literature review and pay page charges (Environmental Health Perspectives?)
Names in italics are potential authors of each section.
o Introduction – Peter Baxter et al.
 What are NMPs?
 Why are we concerned?
 Take examples e.g. Ladakh.
 Paradigms used for PM10 and asbestos, silica may not apply to NMPs.
 We need to change paradigm – needs to be contextualised to particles
of concern – show these particles in a table.
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o
o
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People now asking public health questions which weren’t asked before,
e.g. Montserrat – use volcanic ash story as exemplar – people out there
who need answers
 Information so far in exposure, toxicology, epidemiology:
Case studies of dust types:
 Desert dust (e.g. Ladakh, China) – Ed Derbyshire
 Volcanic ash – Peter Baxter, Clive Oppenheimer, Claire Horwell,
Pierre Delmelle?
 Nanoparticles – Claire Horwell & Ken Donaldson
 Biomass burning/haze - Ross Anderson
 Endotoxins and micro-organisms - ?
Competing morbidities and mortalities – Anthony Seaton
 Other risks (e.g. indoor burning)
Toxicology, BED and metrics. – Ken Donaldson
Exposure – John Cherrie
Discussion - controversial areas - ?
To be written during late 2008/ early 2009 with aim to publish by the end of 2009.