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

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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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n (u

g/m

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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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entr

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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