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Dealing with uncertainty in HHRA Living at home – too risky?

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Presentation on theme: "Dealing with uncertainty in HHRA Living at home – too risky?"— Presentation transcript:

1 Dealing with uncertainty in HHRA Living at home – too risky?

2 Outline Objectives Methodology Results Discussion of results Conclusions 2

3 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

4 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

5 Sampling strategy House Decking Grass Flower Beds Paving 5.3 m 7 m 5

6 Sampling strategy HA1 HA5 HA4HA3 HA2 HA6 HA7 (dup) Composite sample Samples analysed by ALcontrol Laboratories for PAHs and SOM DS1 + PM10 monitoring 6

7 Fieldwork Best practice sampling protocols followed Using suitably qualified and experienced field staff 7

8 Analytical results 8

9 GQRA Compared concentrations of PAHs with LQM/CIEH 2 nd 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? 9

10 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 10

11 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 contactinhalation of dustinhalation of vapours ADE ( -1.d -1 )6.80E-031.66E-034.54E-032.16E-052.93E-06 HCV ( -1.d -1 )2.00E-02 7.00E-05 ADE:HCV0.340.080.230.310.042 % Contribution to exposure52%13%35%0% % Contribution to risk34%8%23%31%4% Inhalation of dust important contributor to risk 11

12 CLEA parameters Soil and dust ingestion Exposure frequency Body weight Soil ingestion rate *HCV oral Dermal contact Exposure frequency Body weight Adherence factor Exposed skin area *Dermal absorption factor *Soil to dust transport factor Time indoors/outdoors *HCV oral Dust inhalation Exposure frequency Body weight PM 10 from soil outdoors (modelled) Time indoors/outdoors Daily respiration volume Dust loading factor *Soil to dust transport factor *HCV inhal * Contaminant specific 12

13 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

14 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) PM10 outdoor_soil = 0.425 ug/m3 Indoor dust loading (DL) = 50 ug/m3 Soil to dust transport factor (TF) = 0.5 Critical parameters 14

15 Indoor dust loading PM10 indoors = 30 to 40 ug/m 3 Further monitoring required to give average daily PM10 indoors CLEA generic DL = 50 ug/m 3 15

16 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 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! 16

17 Results of DQRA Exposure frequencies and gender made specific to my children Average (as opposed to upper 95 th %ile) dermal adherence factors used TF increased from 0.5 to 0.8 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 17

18 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 18

19 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 HCV oral 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 19

20 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 20

21 Acknowledgements Many thanks to

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