Dealing with uncertainty in HHRALiving at home – too risky?

Outline

• Objectives

• Methodology

• Results

• Discussion of results

• Conclusions

2

Objectives• Part IIA style investigation of a residential property in Bristol• Objectives:

– Understand the risks posed to residents from contaminants in soil (specifically PAHs)– Determine whether those risks pose significant possibility of significant harm– Assess the need for further assessment to more accurately assess risk– Assess the need for risk mitigation

3

Property• Terraced house built c.1900 on greenfield site• Located adjacent to a park• Small, mostly hard covered front garden

• Small (5 x 7 m) rear garden with some parts used for growing vegetables

4

Sampling strategy

House

DeckingGrass

Flower Beds

Paving

5.3

m

7 m

5

Sampling strategy

HA1HA5

HA4HA3

HA2

HA6HA7 (dup)

Composite sample

• Samples analysed by ALcontrol Laboratories for PAHs and SOM

DS1 + PM10 monitoring

6

Fieldwork

• Best practice sampling protocols followed

• Using suitably qualified and experienced field staff

7

Analytical results

0

1000

2000

3000

4000

5000

6000

DS-1 HA1-1 HA1-2 HA1-3 HA2-1 HA3-1 HA4-1 HA5-1 HA6-1 HA7-1

Soil

Conc

entr

ation

(ug/

kg)

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

8

GQRA• Compared concentrations of PAHs with LQM/CIEH 2nd

edition GAC for residential land-use• Concentrations of PAHs < GAC with exception of BaP

• Mean concentration of BaP in surface soil samples = 1.2 mg/kg

• So now what?0

500

1000

1500

2000

2500

3000

3500

DS-1 HA1-1 HA1-2 HA1-3 HA2-1 HA3-1 HA4-1 HA5-1 HA6-1 HA7-1

Soil

Conc

entr

ation

(ug/

kg) Benzo(a)pyrene

Residential GAC - BaP

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DQRA• Exceedence of GAC means further assessment required• DQRA moves from the use of GAC based on generic assumptions to SSAC based on site specific assumptions• Uncertainty analysis is also an important element of DQRA• Identify site specific adjustments that will produce a more realistic estimation of risks:

– Changes to conceptual model?– Changes to models used?– Changes to input parameters?– Use of statistics?

• Changes to input parameters - focus on principle risk driving pathways

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Pathway contributions• Pathway contributions to total exposure and risk for

generic residential scenario (0 to 6 yr female child)direct soil ingestion

consumption of homegrown

produce

dermal contact inhalation of dust inhalation of vapours

ADE (ug.kg-1.d-1) 6.80E-03 1.66E-03 4.54E-03 2.16E-05 2.93E-06

HCV (ug.kg-1.d-1) 2.00E-02 2.00E-02 2.00E-02 7.00E-05 7.00E-05

ADE:HCV 0.34 0.08 0.23 0.31 0.042% Contribution to

exposure 52% 13% 35% 0% 0%% Contribution to

risk 34% 8% 23% 31% 4%

Inhalation of dust important contributor to risk

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CLEA parametersSoil and dust ingestion

Exposure frequency

Body weight

Soil ingestion rate

*HCVoral

Dermal contact

Exposure frequency

Body weight

Adherence factor

Exposed skin area

*Dermal absorption factor

*Soil to dust transport factor

Time indoors/outdoors

*HCVoral

Dust inhalation

Exposure frequency

Body weight

PM10 from soil outdoors (modelled)

Time indoors/outdoors

Daily respiration volume

Dust loading factor

*Soil to dust transport factor

*HCVinhal

* Contaminant specific

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Exposure via soil/dust ingestion• Generic assumptions:

– Child eats average of 100 mg soil per day 365 days per year– Female child of average body weight

• Site specific assumptions– I have two boys, no girls yet– Big one is skinny, little one is not– Both eat soil indoors and out– Do they eat 36.5 grams soil per year?– Does it all come from garden?

13

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

12:54 12:54 12:55 12:56 12:56 12:57 12:58 12:59 12:59 13:00

Tota

l dus

t (m

g/m

3)Rufus dropped probe on carpet

Back garden

Front garden

Back garden

Exposure via dust inhalation• Generic assumptions:

– Soil derived PM10 indoors >> soil derived PM10 outdoors– Indoor PM10 from soil = outdoor PM10 derived from soil + (DL x TF)

• PM10outdoor_soil = 0.425 ug/m3

• Indoor dust loading (DL) = 50 ug/m3• Soil to dust transport factor (TF) = 0.5 Critical parameters

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0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

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 averageHooveredfor 10 mins

Indoor dust loading

• PM10 indoors = 30 to 40 ug/m3

• Further monitoring required to give average daily PM10 indoors

• CLEA generic DL = 50 ug/m3

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Soil to dust transport factor• 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

% co

ntri

butio

n to

tota

l 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 hoover bag 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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Results of DQRA• Exposure frequencies and gender made specific to my children• Average (as opposed to upper 95th %ile) dermal adherence factors

used• TF increased from 0.5 to 0.8

0

500

1000

1500

2000

2500

3000

3500

Soil

Conc

entr

ation

(ug/

kg)

Benzo(a)pyreneSSAC - BaP

• SSAC for BaP = 1.28 mg/kg• [BaP] in surface soil = 0.65 to 1.6

mg/kg• Average [BaP] in surface soil = 1.2

mg/kg• UCL 95 [BaP] = 1.57 mg/kg

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Discussion of results• DQRA shows that best (most realistic) estimate of ADE:HCV ratio for my children = 0.92• ADE:HCV ratio < 1 indicate minimal or negligible risk• However, there is uncertainty in the 0.92 number

– Uncertainties in representative exposure concentration, soil ingestion rate etc, mean that actual ADE:HCV ratio could differ from 0.92

• May be more meaningful to say that ADE:HCV ratio is likely to be somewhere between 0.5 to 1.5

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Discussion of results• Even if ADE:HCV ratio = 1.5 – is this a problem?• Dust inhalation biggest contributor to risk

(57%)• How does dust inhalation pathway

compare to background inhalation exposure?• Exposure to BaP via inhalation of soil

derived dust = 20% of background exposure to BaP via inhalation (assuming average UK urban air conc of BaP of 0.21 ng/m3)

• Thus remediation of garden soil will not cause significant reduction in overall inhalation risk

• Soil/dust ingestion contributes 40% of risk

• HCVoral for BaP based on WHO drinking water standard which is based on dose-response data for forestomach tumours in mice.

• High degree of uncertainty in trying to extrapolate the dose-response to humans

• WHO DWS incorporates safety factors to account for this uncertainty and ensure that DWS is protective

• As a result of these safety factors an ADE:HCV ratio of 1.5 is unlikely to constitute SPOSH

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Conclusions• Risk assessment is meaningless without consideration of uncertainties• Generic parameters in CLEA model appear a reasonable basis for Part IIA assessments but:

– site specific adjustments should be made where possible– uncertainties should be recognised and made transparent in risk assessment report

• This amateur research work has identified a need for further research:– Exposure from inhalation of indoor dust– Soil and dust ingestion rates

• Further guidance required on:– Significance of exceedence in the context of uncertainties involved in derivation of HCV

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Acknowledgements• Many thanks to

www.firthconsultants.co.uk