We do not accept use of the old SGV, particularly where the land use scenario involves use/access by children under 4 years old.
This is due to increasing evidence that a very small increase in blood lead level can lead to significant adverse impact on neurological development.
Questions we have had to consider previously:
How much lead is in a child's fist of soil?
What would be the resultant increase in blood lead level if this were ingested by a young child?
Ruth
Ruth Willcox
Environmental Protection Officer
Environmental Services
Plymouth City Council
Civic Centre
Plymouth
PL1 2AA
T +441752304154
E [log in to unmask]
www.plymouth.gov.uk
-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Chris Dainton
Sent: 19 February 2014 12:19
To: [log in to unmask]
Subject: Re: calculating lead screening level using JECFA 2010 findings
Hello Gareth
As no one else wants to reply openly!
Firstly, don't go down this route in the real world - it ends in QRA madness (and that's not from the lead). But it's good to do the calcs.
The soil ingestion pathway alone (at TDI of 0.3 ug/kg-bw/day) will give a 'GAC' of 20 mg/kg (by contrast Oral TDI via Tox -6 gives 243 mg/kg for soil ingestion alone using same MDI).
If you ignore oral MDI, then soil ingestion pathway becomes 40 mg/kg (50% rule is invoked for the 20 mg/kg 'GAC' effectively making the TDI 0.15 ug/kg-bw/day!).
The MDI also makes a mockery of the 0.3 ug/kg-bw/day TDI as background oral intake by BW for average female AC1-6 is 2.3 ug/kg-bw/day (average BW is 13.3 kg).
For plant uptake you could adopt default 5/0.5/0.5/0.5/0.5 factors and let the model sort it.
At kd = 3,000 the veg consumption pathway alone would give 508 mg/kg (Dutch RIVM kd = 36,000 would give pathway output of c. 6,100 mg/kg)
Dermal indoors comes in at 41 mg/kg using default approach (the oral and dermal indoors pathways (both using Oral TDI) essentially drive the 'GAC')
All the pathways conspire (taking into account MDI) to give a lead 'GAC' of 13 mg/kg (by my quick calcs...).
Ignoring all MDI gives an upper bound of 26 mg/kg (50% rule invoked at 13 mg/kg)
The best you'll get using CLEA (at the moment, C4SL approach aside) and the TDI of 0.3 ug/kg-bw/day will be between 20 and 40 mg/kg as you are rate limited by the soil ingestion pathway (soil ingestion rate) and the adopted MDI.
Most other CLEA approaches I've seen/tried come in the range of 180 to 300 mg/kg.
And given the BGS Urban NBC is 810 mg/kg.....
And most LA seem to be happy to accept the old SGV of 450 mg/kg as a reasonable compromise.
PLEASE DON'T QUOTE OR USE THESE CLEA OUTPUTS - THEY ARE QUICK ROUGH CALCS JUST FOR ILLUSTRATION!
Kind regards
Chris Dainton
Peak Environmental Solutions Limited
www.peakenvironmentalsolutions.com
uk.linkedin.com/in/chrisdainton
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