Chemical exposure via inhalation of soil derived dust Modelling versus measurement
Chemical exposure via inhalation of soil derived dustModelling versus measurement
Outline
• The problem
• Assessing exposure via dust inhalation
– Modelling
– Measurement
• Conclusions
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The problem
• Dust inhalation is one of the modelled pathways in CLEA
• Exposure via dust inhalation is generally small relative to ingestion of soil + household dust– e.g. CLEA residential land-use, ADEdust = 0.3% ADEingest
• As a result, dust inhalation is only important when:– Inhalation toxicity >> oral toxicity; or
– Dust inhalation is the only active pathway
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Problem contaminants
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HCVoralug.kg-1.d-1
HCVinhalug.kg-1.d-1
Ratio (inhal/oral)
Assessment Criteria mg.kg-1
SGV or GAC
mg.kg-1
Basis
Oral Inhal
Arsenic 0.3 0.002 150 32 85 32 Oral
Cadmium 0.36 0.0014 257 11 185 10 Integrated
2-Chloro naphthalene
80 0.286 280 1300 22 22 Integrated
Benzo[a]pyrene 0.02 0.00007 286 1.5 2.9 1 Integrated
Copper 160 0.286 559 2660 10400 2330 IntegratedChromium (III) 150 0.1 1500 19500 3550 3000 Integrated
Nickel 12 0.006 2000 531 127 130 Inhal
Chromium (VI) 1 0.0001 10000 12.4 4.3 4.3 Inhal
Asbestos ? ?? >1000?
Dust important?
How do we assess dust exposure?
• Most dust > PM10 caught in trachea + ingested
• Particles in PM10 or PM2.5 range are able to reach lungs
• Smaller particles penetrate further, have longer residence times + therefore present greater risk
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10–150 um
1–10 um
<1 umExposure = Respiration
ratex [PM10] x
Conc. of contaminant on PM10
Measure or Model
Modelling
CLEA model
• Different equations for exposure (mg.d-1) for outdoor + indoor inhalation:
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=
241 out
inhsoutTV
PEFCIR
+
=
24..1 in
inhssinTVDLTFC
PEFCIR
PM10 outdoors arising from soil (0.425 ug.m-3, residential)
PM10 indoors (50 ug.m-3, residential)
Contaminant concentration in PM10 indoors
Inhalation of dust outdoors
• 1/PEF (i.e. PM10 from soils) calculated using Cowherd’s model + air dispersion model
• Jw = PM10 emission flux (g.m-2.s-1) estimated using Cowherd
• Jw = 1 x 10-6 g.m-2.s-1 for residential land-use
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wind
w
CQ
JPEF
=1
( ) )(..13
xFuuVJ
tw
−=
(1-V) = fraction of site with bare soilu = average windspeed at 10m heightut = threshold windspeed at 10m heightF(x) = empirical factor based on u:ut
0
500
1000
1500
2000
2500
3000
3500
4000
0.01 0.1 1 10
Q/C
win
dSite area (ha)
Belfast
London
Newcastle
Plymouth
Inhalation of dust outdoors
• Q/C = dispersion factor estimated using US EPA AERMOD PRIME
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• PM10 increases with increasing area
• Are predicted PM10 concsrealistic? Predicted PM10 for > 1 ha
bare earth site ≈ 40 ug.m-3
• Are predicted contam concsin air realistic? Predicted air conc of As using this PM10 & 20mg.kg-1 in soil = 0.8 ng.m-3
UK average air conc As for rural areas = 1 to 4 ng.m-3
• But note: uncertainties in Cowherd model are HUGE!
Inhalation of dust indoors
• What is indoor dust composed of?– Many things, e.g. soil particles, hair, skin,
fibres, pollen, dust mites, soot, ash, animal fur and dander, food, building components
– PM10 < 10% by mass of typical house dust collected in hoover bag?
– Composition is highly variable between houses
• Contaminants in house dust– Tracked back soil/dirt
– Outdoor air
– Internal sources
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Estimation of exposure – indoor dust inhalation
• Indoor air PM10 = dust loading factor (DL)– Range of values reported by Oomen + Litzen, 2004 = 12.6 to 157 ug.m-3
– Highest value occurred for a school
– WHO (1989) give range of 20 to 60 ug.m-3
– CLEA assumes 50 ug.m-3 for UK houses – is this reasonable?
• Concentration of contamination in PM10 = Cs x TF– TF = transport factor and should be contaminant specific
– Default value = 0.5, i.e. concentration of contaminant in PM10 = half the concentration in soil
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Transport factor
• Trowbridge & Burmaster (1997)– found reasonable correlation between
conservative tracer components in garden soil + indoor dust
– Mean TF = 0.43
• But, TF varies for many contaminants and can exceed 1 due to enrichment– E.g. Cu, Cd, Pb, Zn (Culbard et al, 1988,
Rasmussen et al, 2001, Oomen +Litzen, 2004)
– Pb can be up to 3?
– PAHs?12
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Al Ce Fe Hf K La Mn Na Sc Sm Th V
TF
Trowbridge PR, Burmaster DE 1997. A parametric distribution for the fraction of outdoor soil in indoor dust. J Soil Contam 6: 161–168
Pb in dustmg.kg-1
Pb in soilmg.kg-1
Rasmussen et al, 2001
Measurement
Research
• Preliminary research on dust exposure in UK:– Amateur research on my house in 2009
• Comparison of PAH concentrations in house dust + garden soil
• Measuring PM10 indoors
– Current research by Dr Chris Collins, University of Reading• Comparison of PAH concentrations in house dust + garden/allotment soils
• Measuring PM10 indoors
• Measuring PAH concentrations in suspended dust
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Measuring PM10
• Air pump with filter sent to lab for gravimetric analysis ( ≈ £10/sample)
• Infrared refractive sampling e.g. Casella DustPro monitor ( ≈ £2500)
• Laser photometry e.g. Turnkey Instruments Osiris ( ≈ £6000)
• Real-time gravimetric analysis e.g. Thermo Partisol 2025 (≈ £16000)
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Chemical analysis of suspended dust
• University of Reading using passive sampling technique developed by Abdallah & Harrad (2010)– Polyurethanefoam disk for assessing vapour phase PAHs
– Glass fibre filter for assessing particulate sorbed PAHs
16Abdallah, MAE & Harrad, S. 2010. Modification and Calibration of a Passive Air Sampler for Monitoring Vapor and Particulate Phase Brominated Flame Retardants in Indoor Air: Application to Car Interiors. Environ. Sci. Technol. Vol. 44, 3059–3065
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06:43 06:57 07:12 07:26 07:40 07:55 08:09 08:24 08:38 08:52 09:07
PM10
(mg/
m3)
10 sec average
5 min average
Hooveredfor 10 mins
PM10 indoors – my house – DustPro results
• PM10 indoors measured using Casella DustPro= 30 to 40 ug/m3
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PM10 indoors – my house – Osiris results
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Dus
t con
cent
ratio
n (u
g/m
3)
total
PM10
PM2.5
PM1Gone to bedGet up
Leave for school
Wife + youngest leave
Wife + kids gets back
• PM10 = 8 to 97 ug.m-3
• PM2.5 = 4 to 24 ug.m-3
• Average PM10 = 15 ug.m-3
• Average PM2.5 = 6 ug.m-3
Soil to dust transport factor – my house• What proportion of PM10 is likely to be from garden soil?
• 2 lines of evidence:– PAH analysis of dust from hoover bag vs soil analysis
0%
2%
4%
6%
8%
10%
12%
14%
16%
18%
20%
DS-1 HA1-1 HA1-2 HA1-3 HA2-1 HA3-1 HA4-1 HA5-1 HA6-1 HA7-1
% c
ontr
ibut
ion
to t
otal
PA
H
Naphthalene
Acenaphthylene
Acenaphthene
Fluorene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Benz(a)anthracene
Chrysene
Benzo(b)fluoranthene
Benzo(k)fluoranthene
Benzo(a)pyrene
Indeno(123cd)pyrene
Dibenzo(ah)anthracene
Benzo(ghi)perylene
• Average [BaP] in surface soil = 1.2 mg/kg
• [BaP] in dust = 1.0 mg/kg
• PAH profile in dust similar to garden soil
– SOM analysis of dust from hooverbag vs soil analysis
• Average SOM in surface soil = 13%
• SOM in dust = 32%
• If we assume that dust composed of soil (13% SOM) + skin/food (100% SOM), TF = 0.8 – higher than CLEA generic assumption!
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University of Reading study
• Sampled and analysed soils from garden + allotment (0.5 miles from house) for PAHs
• Sampled and analysed house dust from hoover bag for PAHs
• Indoor air PM10 monitoring using Osiris
• Passive suspended dust sampling for PAHs
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University of Reading results
• Very similar PAH profiles between garden soil, allotments soil + house dust
• Awaiting PM10 + passive sampler results
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0.40
0.60
0.80
1.00
1.20
1.40
1.60
Conc
entr
atio
n re
lati
ve to
BaP
Allotment
Garden
Dust
Conclusions• Dust inhalation indoors is a key pathway for BaP, Ni, Cr(VI) and
asbestos
• Key uncertainties:– PM10 – Highly variable – need long-term monitoring in occupied buildings to
determine
– Transport factor - Varies significantly from site to site + contaminant to contaminant
• Hoover bag analysis helps check on TF but may not be valid for respirable particles
• Further research required to ascertain if there is a correlation between concentrations in soil + respirable dust (especially for PAHs + asbestos)
• Why is HCVinhal << HCVoral for BaP, Ni + Cr(VI)?22