So I’ve had a quick look at the BGS London Earth data for lead in top soil. The map provides a colour coded map based on the percentiles of the data:
Mean: 301 mg/kg
50th: 185 mg/kg
75th: 346 mg/kg
90th: 617 mg/kg
95th: 866 mg/kg
99th: 1,919 mg/kg
And Mean + 2xSD = 1,171 mg/kg.
The BGS report states that typical lead levels in the GLA area are five times higher than local countryside.
The G-Base local rural study provides:
Rural Mean: 50 mg/kg
Rural Mean+ 2xSD: 192 mg/kg
The Agency soil surveys also provide further data:
Rural Mean: 62 mg/kg
Rural Mean+ 2xSD: 232 mg/kg
Urban mean: 137 mg/kg
Urban Mean+ 2xSD: 307 mg/kg
Clive’s and Simon’s outputs from the IEUBK model indicate that 400 to 450 mg/kg gives a median blood lead (BL) of around the 5 ug/dl mark (which takes into account other non-soil sources), with Simon’s IEUBK model for 450 mg/kg giving c. 12% of kids with >10 ug/dl BL.
If the IEUBK model was realistic and 400 to 450 mg/kg soil gave rise to >10% of children with >10 ug/dl BL (including other non-soil inputs), then we would be seeing a large number of children in urban areas with very significant lead levels of > 10 ug/dl (as urban lead soil concentrations (BGS) are at mean 301 mg/kg and 95th percentile at 866 mg/kg).
So is there evidence of significant child BL > 10 ug/dl?
The UK BPSU study deals with reported cases of blood levels > 10 ug/dl in children aged up to 15. They had 22 cases reported to them last year, 8 of which were confirmed to meet the 'case definition' of the study. The BPSU report says: "Although the number of children reported to the study in the first ten months is lower than expected, it is greater than the number reported through existing surveillance systems”
The US NHANES study (tests 5,000 people each year) reported that the 97.5 BL percentile was c. 5 ug/dl.
The IEH 1998 R9 report (6,857 samples analysed, 6,517 adults (3,119 men, 3,398 women), 340 children (180 boys 160 girls)):
- No children had blood lead levels above 10 μg/dl.
- 5% of men and 1.1% of women had levels above 10 μg/dl.
- 0.17 % of adults had levels above 25 μg/dl
The IEH also has some other interesting data:
Blood Lead of Urban versus Rural areas. Small differences were observed in geometric mean levels between urban/rural area:
Male Urban: 3.8 ug/dl
Male Rural: 3.5 ug/dl
Female Urban: 2.6 ug/dl
Female Rural: 2.6 ug/dl
Now that is very interesting, as we know that urban soil have significantly higher lead levels than urban (BGS indicate around 5 times in London). But going from BGS mean rural of 50 mg/kg to BGS mean urban of 300 mg/kg (about 250 mg/kg more lead loading in urban soil), doesn’t raise mean female BL and only raises male mean BL by 0.3 ug/dl.
Very crudely, for an adult you could estimate that 450 mg/kg in soil gives rise to an increase of about 0.6 ug/dl BL. Be interested to know how that correlation fits with IEUBK.
I also seem to remember that the BGS data points to old urban top soil (i.e. exposed) having much higher lead than urban soils historically covered with hardstanding. The IEH data by age of property (presumably they were looking for correlation to lead in paint) is therefore interesting:
Pre 1945 house Male: 3.8 ug/dl
Post 1945 house Male: 3.4 ug/dl
Pre 1945 house Female: 2.8 ug/dl
Post 1945 house Female: 2.4 ug/dl
Although IEH said these differences were not statistically significant, older properties could be giving rise to an increase in BL about 0.4 ug/dl. So picking apart the BGS data by property age could therefore provide another possible insight to increase BL due to higher lead levels in gardens of older properties.
I would like to see the IEUBK predicted BLs (and corresponding percentage children > 5 ug/dl and >10 ug/dl) for the range of BGS urban soils concentrations. If the IEUBK predicts large number of children and adults with >5 ug/dl and >10 ug/dl BL from exposure to the range of lead in urban soils we know are there, yet all the blood data indicates that we are not seeing high levels of BL in children and relatively rare incidences in adults, then something is surely adrift with the parameters/algorithms of the IEUBK model.
Surely we need to be very careful we do not ‘create’ a problem of lead in soil (especially at a GAC level of around 400 mg/kg or less), when there may be little data to suggest that known high urban levels in soil are leading to elevated BL levels in adults & children.
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