your head on a block-part 2a decisions dr naomi earl associate director head of human health risk...

Your head on a block-Part 2A decisionsDr Naomi EarlAssociate DirectorHead of Human Health Risk AssessmentLand QualityAtkins Limited

0044 121 483 5530

[email protected]

23 September 2009 Your head on a block-Part 2A decisions

The Part 2A decision

• Is the condition for “significant possibility of significant harm” to human health being met on site by one or more pollutant linkages

• “If the amount of the pollutant in the pollutant linkage in question…which a human being might take in….would represent an unacceptable intake…assessed on the basis of relevant information on the toxicological properties of that pollutant” (Table B, Chapter A Annex 3)


What does “unacceptable” mean?• In the absence of overarching national guidance, depends on local authority

opinion

Contaminated land officer/Environmental health officer? CLO/EHO’s line manager? Councillors? Lawyers? All of the above?

All of these groups comprise individuals with different levels of knowledge and attitudes to risk


Risks of getting it “wrong”

• Too precautionary• Sets local precedent which may result in high proportion of local area being

“contaminated”• Potential for blight• Out of step with neighbouring authorities• Potential for legal challenge• ?Site may not be priority for funding?

• Insufficiently precautionary –harder to prove but• Out of step with neighbouring authorities• Local pressure groups• (Risk of significant harm?)


Some key aspects to consider

• Evidence for level of intake

• Toxicology

• Scope for refining Conceptual Site Model

May help to consider what approach you might take to some of these in advance of any site investigation


Evidence for level of intake “Lies, damned lies and statistics”

• New CIEH guidance-make sure you use the correct test!Upper confidence level-”How confident can I be that a representative site concentration lies below assessment criterion?”Lower confidence level “How confident can I be that representative site concentration lies above assessment criterion”

• Does exotic distribution derived from statistical tool mask two different populations?

• Care how you “mix and match” targeted and non-targeted results


Evidence for level of intake –statistics don’t tell the whole story

• No substitute for “eyeballing” data up front• Do there appear to be two populations visually, even if statistics say not?

• e.g. when a “zone” covers a large area, with more than one property lying within a hotspot• May “dilute” genuine hotspot• Hotspot may raise mean of whole zone so more properties considered than should be

May need to be prepared to reconsider initial zoning depending on results of investigation


Evidence for level of intake – how certain do you want/need to be?• Unexplained solitary high concentrations

Initial Scenario

Confidence in laboratory data and precise recording of visual and olfactory indicators critical


Is it like this one?….

…or like this one?

Consider further SI to answer…

Consider including contingency to go back to certain percentage properties?


Toxicology-the underlying basis

Complex and province of experts but some basic questions to consider:

• What is effect that Health Criteria Value based on?• Would it meet criteria for “significant harm”?

• Is there a consensus between various expert organisations?

• Do you understand uncertainty factors used-(what for, how many) ?


Toxicology-mean daily intakes

• Calculated or 50% rule?

• Dietary intake based on:• mean estimates in food or upper bound estimates?• mean consumption rates or higher level consumers?

• Water intake based on:• mean drinking water levels?• maximum measured drinking water levels?• drinking water standards?

• Air intake based on:• national data?• urban data?• mean estimates or upper estimates?• old dataset, recent dataset or combined dataset?


Is there scope to refine the CSM?

• Which pathways driving risks for contaminants of concern?• What are key uncertainties in these pathways?• Can these uncertainties be reduced by collection of more

data• Vapour sampling if vapour pathway risk driver?• Bioaccessibility data if soil ingestion risk driver?• Site specific plant uptake factor?• Further information about form contaminant is in?


Other Factors

• What would you personally consider a significant margin of exceedance of your SSAC and does it depend on the substance (and do your colleagues agree)?

• What decisions have been made by the local contaminated land group?

• Do you want to take background concentrations of local soils into account?

• Comparison of local air quality to estimated air concentrations from soil contamination?

your head on a block-part 2a decisions dr naomi earl associate director head of human health risk...

Documents

site investigationyour

riskyour head

comyour head

level of intaketoxicologyscope

nontargeted resultsyour

lower confidence level

upper confidence level

conceptual site modelmay