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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