Comparison of Risk Assessment for Radioactive and Chemical Contaminants

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Comparison of Risk Assessment for Radioactive and
Chemical Contaminants

• Similarities, Differences and Scope for
  Comparison
• BRMF/SAFESPUR Workshop,
• 30 September 2008
• Dr James Wilson, Quintessa, Ltd.

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Structure of this Presentation

• Exposure and Response
• Pathways, mechanisms and responses
• Comparison of criteria for the protection of
  human health for radionuclides and
  non-radioactive contaminants in soil
• Comparison of exposure assessment tools for
  radiological and non-radiological soil
  contamination
• An example of rad vs non-rad contamination
  assessment

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Exposure Pathways

• Similarities
• Low concentrations
• Intake (ingestion, inhalation)
• Differences
• Irradiation at distance
• Hypersensitisation

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Exposure-Response Radionuclides

• Most evidence from A-bombs
• Same mechanism for all radionuclides
• Direct ionisation or free radicals
• Depends on intensity, duration, organs
• Deterministic threshold
• Stochastic non-threshold
• Important uncertainties remain
• Progression from damage to cancer
• Response at low dose rates
• Extrapolation from animals

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Exposure-ResponseChemicals

• Observations are key (animal experiments, human
  epidemiology, occupational exposures)
• Threshold and non-threshold effects
• Uncertainties include
• Extrapolation from animal experiments
• Exposure route extrapolation and bio-availability
• Inter and intra-species variability

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Dose Criteria Radionuclides

• Recommendations of ICRP
• Dose proportional to absorbed energy
• Weightings type of radiation, organ
• Risk proportional to dose (lt thresholds)
• Standards and Criteria (IAEA, Euratom)
• Risks and thresholds
• Can be compared with natural background
• Independent of particular radionuclides
• UK legislation reflects ICRP recommendations

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Radiation Dose Criteria for Contaminated Land

• HPA (2006) Annual dose approaching 10 mSv
  justifies intervention (considers ICRP
  recommendations)
• HPA health criteria for determination 3 mSv
  yr-1 (to protect from non-threshold effects,
  lifetime cancer risk of 1/100)
• - or annual equivalent dose to lens of eye gt 15
  mSv or annual equivalent dose to skin gt 50 mSv
• Dose criteria apply to incremental dose from
  contamination (i.e. total dose background),
  average UK background dose is 2.2 mSv yr-1
  therefore additional dose of 3 mSv yr-1 is
  increase between 2 and 3 times UK annual average.

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Health Criteria Values for Chemicals- threshold
effects

• Defra/Environment Agency CLR Toxicological
  reports
• Assess international and other national guidance
  (e.g. WHO)
• HCV Tolerable Daily Soil Intake (TDSI)
• TDI (from all sources) identified from NOAELs (or
  LOAELs) often from animal experiments -
  multiplied by uncertainty factor(s) e.g. 10 for
  interspecies and 10 for intra-species variation
• Mean Daily Intake (MDI) set by considering other
  (non-soil) routes of exposure
• TDSI TDI - MDI
• Old approach If MDI gt 80 TDI, then TDSI 20
  TDI.
• New approach If MDI lt 50 TDI, then TDSI
  TDI-MDI
• If MDI TDI, TDSI 50 TDI

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Setting a LOAEL from animal data
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Health Criteria Values for Chemicals- non
threshold effects

• HCV Index Dose (ID)
• ID is daily intake that represents a very low to
  negligible risk to human health (i.e. set to be
  protective)
• Provision that all exposures (inc. soil) should
  be ALARP, therefore intakes from sources other
  than soil not included
• In UK not directly based on a fixed level of risk
  (issue of animal to human extrapolation for
  quantitative risk assessment)
• Excess lifetime cancer risks generally 1/10 000
  to 1/ 100 000 depending on substance and
  exposure route
• Possible future use of Benchmark Dose (BMD) data?

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Soil Assessment Criteria Chemicals

• Soil Guideline Values / Site Specific Assessment
  Criteria
• SGVs are concentrations of contaminant in soil
  such that Health Criteria Values should not be
  exceeded (based on CLEA exposure model
  assumptions)
• Generic non-statutory guidance
• Difficulties reported by Local Authorities in use
  of SGVs for determination under Part IIA of the
  EPA (1990), and uncertainty in how great HCV has
  to be exceeded to represent significant
  possibility of significant harm
• triggered Way Forward consultation (Defra)

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Non-threshold riskChemical vs. Radiation

• Chemicals
• Index Dose not set at specific risk - excess
  lifetime cancer risks generally range from 1/10
  000 to 1 000 000
  (ID oral for As 1/1000)
• UK Expert Medical Committee (CoC) does not
  endorse quantitative cancer risk models based on
  high-dose animal data
• Non-soil intakes not considered (ALARP principle
  assumed to have been applied to all sources of
  exposure)
• Radiation
• UK effective dose criteria set at 3 mSv yr-1
  (lifetime fatal cancer risk of 1/100)
• Background doses were considered in setting
  effective dose

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CLEA Approach

• CLEA UK (now in redevelopment) and RCLEA
• Tiered approach
• Contaminant-specific guideline values
• Produces soil concentrations SGVs/RSGVs, or Site
  Specific Assessment Criteria (SSACs)
• Generic land-use scenarios residential both with
  and without plant uptake, allotments,
  commerical/industrial
• Critical receptors

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Differences between CLEA UK and RCLEA

• CLEA SGVs are contaminant specific, RCLEA allows
  additive effective dose to be calculated
• CLEA UK had 18 age groups, RCLEA has 3 (infant,
  adult, child)
• RCLEA has 2 additional exposure pathways (1)
  whole body external irradiation from
  contamination at a distance (2) irradiation of
  skin from direct contact with contaminated
  material
• Adsorption through skin not applicable in RCLEA
  (tritium exposure should be considered
  separately)
• RCLEA has only 1 soil type due to uncertainties
  in solidliquid Kd values
• Volatilisation is excluded from RCLEA
  considered insignificant for historic
  contamination

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Similarities, Differences

• Exposure-response
• Threshold and non-threshold effects
• Intake pathways/other pathways
• Dependence on contaminant
• Standards
• Epidemiological/toxicological studies
• Protection from threshold effects
• Dependence on contaminant/pathway
• Regulatory approach to non-threshold risks
• Assessments
• Exposure pathways and groups

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Common Basis for Comparison?

• Only intended to be an illustration
• Hypothetical site
• Radionuclides assessed using RCLEA
• Non-radionuclides assessed using CLEA UK (beta)

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Rads vs Non-rads Example

• Substances include H-3, Co-60, Sr-90, Ra-226,
  As, Cd.
• Ingestion, inhalation, ext. irradiation, dermal
• SSAC values for residential land use (with plant
  uptake and female infant receptor

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Example SSAC Values
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Example risk comparison

• Arsenic oral intake is 2.6 times oral Index Dose
  (ID oral 0.3 µg/kgbw/day
  lifetime risk of developing skin cancer 1/1000,
  assuming 1 mortality rate of those who develop
  skin cancer, risk of death 1/10 000)
• Cadium oral intake is 3.1 times TDSI
• (TDSI 0.77 µg/kg bw/day set to protect
  against kidney damage, based on studies of
  proteinuria in humans)
• Total effective radiation dose is 1.2 times
  criteria dose (3 mSv yr-1 lifetime fatal
  cancer risk of 1/100)

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Conclusions

• Comparisons of risk can be made
• Differences in risk assessment approaches are
  significant (especially with regard to
  availability of toxicological data and regulatory
  approaches for using cancer risk models)

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References

• Defra/Environment Agency. (2002) Contaminants in
  soil collation of toxicological data and intake
  values for humans (CLR 9).
• HPA (2006) Dose criteria for the designation of
  radioactively contaminated land. Report RCE-2.
• Defra/Environment Agency. (2002) The Contaminated
  Land Exposure Assessment (CLEA) model technical
  basis and algorithms (CLR 10).
• Defra (2005) CLAN briefing note 2/05 Soil
  Guideline Values and the Determination of Land as
  Contaminated Land under Part IIA.
• Defra (2007) The radioactively contaminated land
  exposure assessment methodology - technical
  report (CLR 14)