Also worth noting that lead is one of a small number of metals capable of crossing the blood brain barrier (hence it's neurotoxicity) it tends to complex with enzyme within the brain containing with sulphur as part of the structure which are active within the metabolic cycles which are essential to cell function. This once lead is in the brain it tends to stay there and continue to exert a toxic effect.
Blood levels may therefore not always be a good indicate of the impact on the brain. Also lead mobility can vary widely dependant on chemical form and other factors such as pH. It is important to note that lead is very potent as a bio-accumulator and its impacts are similar to and to an extent caused by the same factors (complexing with and disrupting the function of key enzymes involved in cell metabolism) as cadmium and mercury and therefore that the 450mg/kg level may therefore have been a considerable overestimate. Also IQ impacts etc unlike more other toxicological impacts may not have been so obvious and are only now being measured and correlated against lead exposure.
Brad Balmer, BSc(Hons), MRSc
Associate Director, Land & Development
ATKINS
75 years of design, engineering and project management excellence
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-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Gareth Rees
Sent: 19 February 2014 17:01
To: [log in to unmask]
Subject: Re: calculating lead screening level using JECFA 2010 findings
Just because blood lead of 10µg/dl is not being exceeded doesn’t mean lead isn’t a problem
For starters it assums a threshold effect which is now known not to be the case
toxicological studies are finding IQ effects at lower blood lead levels in children
in 2012 the USA-CDC announce their blood lead level reference value to 5µg/dl
COT (2008). COT statement on the 2006 UK total diet study of metals and other elements (http://cot.food.gov.uk/pdfs/cotstatementtds200808.pdf) found that blood lead in children in developed countries averages at ~3µg/dL
WHO 2000a. Safety evaluation of certain food additives and contaminants, prepared by the fifty-third meeting of the Joint FAO/WHO Expert Committee on Food Additives. WHO, Geneva says 1 μg Pb/kg bw/day oral assumed to increase B‐Pb by 1 μg/dL With those figures it wouldn't take much exposure to increase a childs intake to a level that will increase blood lead to an unacceptable level
March 2010 – EFSA Expert Panel on Contaminants in the Food Chain (CONTAM) published Scientific Opinion of Lead in Food derived a BMDL10 of 1.2 μg/dL (i.e. lower 95% confidence limit of the benchmark dose B‐Pb level associated with a 1 point IQ loss) with a Corresponding dietary intake of 0.5 μg/kg bw/day I wouldn’t personally be happy telling someone that its ok for their child to lose 1 IQ point
Thanks
Gareth Rees Mgeol (HONS) FGS
Contaminated Land Officer
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Please Note I only work for Harborough District Council on Thursdays Fridays and alternate Wednesdays
-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]] On Behalf Of Chris Dainton
Sent: 19 February 2014 16:16
To: [log in to unmask]
Subject: Re: calculating lead screening level using JECFA 2010 findings
Lead is an unusual (unique?) soil contaminant where intake is correlated to a clinical test that is very widely measured.
If soil lead was a 'real' problem (e.g. at levels >40 mg/kg or >c. 200/300 mg/kg), then given the high urban background and the known MDI inputs we'd be seeing high urban BL in children.
Where's the evidence base for this - blood lead has fallen dramatically after lead in fuels was removed.
http://www.who.int/ceh/publications/leadguidance.pdf
Page 37 of document
Average US BL on 2000 = 2 ug/dl
PHE monitor cases > 10 ug/dl:
http://www.hpa.org.uk/chemicals/slic
http://www.rcpch.ac.uk/system/files/protected/page/BPSU%20Annual%20Report%202013%20highres.pdf
... 22 valid reports since 2010, potentially only 58 cases of >10 ug/dl since 2010.
USA uses 5 ug/dl.
DIET TO BLOOD
JEFCA estimated that there would be 0.052 to 0.16 ug/dl of lead in blood for every 1 ug/day dietary intake for infants.
DIETARY INTAKE
Lets say adult Dietary intake is 57 ug/day, plus say an additional allowance of 1.7 ug/day via inhalation. Corrected for average AC1-6 (66%), this is 38 ug/day.
This gives a predicted ball park background blood lead level of between 2 and 6 ug/dl.
For the following Cases we'll ignore dusts inhalation pathways.
CASE-1
So using the JEFCA TDI of 0.3 ug/bw-kg/day for 13.13 kg AC1-6 = 8.4 ug/day
This gives a predicted blood lead level of between 0.44 and 1.34 ug/dl.
Firstly, lets imagine that the 'safe' (8.4 ug/day intake) soil level is 40 mg/kg (ignoring MDI) based on a CLEA approach.
Secondly, lets say we have 450 mg/kg to 810 mg/kg of lead in urban soils (11x to 20x the safe level of 40 mg/kg) [Old SGV and BGS NBC]
That should mean that we see the following increase in blood levels in urban children from this exposure to these soils:
At 450 mg/kg: 4.8 to 15 ug/dl
At 810 mg/kg: 8.7 to 27 ug/dl
Taking into account MDI, we would expect to see many urban children to have blood levels in the range of 7 to 33 ug/dl.
CASE-2
Using the TOX-6 oral TDI equivalent of 3.6 ug/bw-kg/day for 13.13 kg AC1-6 = 48 ug/day
This gives a predicted blood lead level of between 2.5 and 8 ug/dl.
Firstly, lets imagine that the 'safe' (48 ug/day intake) soil level is 250 mg/kg (ish, ignoring MDI) based on a CLEA approach.
Secondly, lets say we have 450 mg/kg to 810 mg/kg of lead in urban soils (1.8x to 3.2x the safe level of 250 mg/kg).
That should mean that we see the following increase in blood levels in urban children from this exposure to these soils:
At 450 mg/kg: 4.5 to 14 ug/dl
At 810 mg/kg: 8 to 25 ug/dl
Taking into account MDI, we would expect to see many urban children to have blood levels in the range of 6.5 to 31 ug/dl.
CASE-3
Using the TOX-6 and a blood level approach of old SGV (to give 450 mg/kg). Oral TDI equivalent of 3.6 ug/bw-kg/day for 13.13 kg AC1-6 = 48 ug/day
This gives a predicted blood lead level of between 2.5 and 8 ug/dl (10 ug/dl used to be acceptable),
Again, lets imagine that the 'safe' (48 ug/day intake) soil level is 450 mg/kg.
Again, lets say we have 450 mg/kg to 810 mg/kg of lead in urban soils (1.x to 1.8x the safe level of 450 mg/kg).
That should mean that we see the following increase in blood levels in urban children from this exposure to these soils:
At 450 mg/kg: 2.5 to 8 ug/dl
At 810 mg/kg: 4.5 to 14 ug/dl
Taking into account MDI, we would expect to see many urban children to have blood levels in the range of 4.5 to 20 ug/dl.
SO THAT'S INTERESTING!
So are we seeing anywhere near these BL levels predicted by CASE 1 & 2 in significant numbers of urban children ? Of course not.
Which means our approach to calculating the 'safe' soil level in CASE 1 and CASE 2 (from either JEFCA or TOX-6 data) is completely floored (given the Tox science if well founded).
Looking at Case 3 - although the range of potential increases in blood level somehow feels more realistic, the blood model still looks like it is over predicting the resultant BL for the range of urban lean numbers we know we have (e.g. 1,100 mg/kg average in many London Boroughs.
I say stick with good old 450 mg/kg. It has served us well and, to me, provides a balanced/reasonable way to deals with 'higher' lead concentrations in urban soils.
PLEASE DON'T QUOTE OR USE THESE 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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