Bone Pb by K-XRF in young children vs older

people

Toronto Bone Pb StudyA laboratory was established in St Joseph’s Health Centrel, Toronto by staff from McMaster University, Health Canada and St Joseph’s Health Centrel.

The laboratory housed a bone lead measurement system and facilities for obtaining blood under clean conditions.

The laboratory was on site from September 2009 until March 2011

Bone Pb XRF is a measure of long term lead exposure

Pb XRF Measurement DescriptionMeasurement is performed in a backscatter geometry using 109Cd. The measurement took 22 minutes per bone.

50mm x 20 mm

HpGe Crystal

109-Cd Source

Sample

System is designed to be in backscatter geometry

in tungsten collimator

The radiation dose is extremely low, much less than a dental x-ray

109Cd K XRF spectrum

63.00 68.40 73.80 79.20 84.60 90.00(Thousands)

Energy (eV)

10

100

1000

10000

100000

400000

Pb alpha peaks

Pb beta peaks

Elastic PeakScatter

Compton

Peak

Toronto Bone Pb Study

The goal of the study was to recruit 273 subjects who each had tibia and calcaneus bone Pb XRF measurements, a venous blood sample drawn, and answered a questionnaire.

The venous blood sample was split into two fractions: one was to be sent for whole blood analysis; one was processed to permit serum testing.

The time available for each individual appointment was 1 hour.

Toronto Bone Pb Study

263 men women and children aged 1 – 82 were recruited into the study under a convenience sampling strategy.

Difficulties were determined in recruiting girls under age 10. Anecdotal evidence from the nurse recruiter was that young girls expressed concerns about blood sampling and refused to volunteer.

Toronto Bone Pb Study

An attempt was made to measure the tibia and calcaneus of every volunteer for a period of 22 minutes each.

A measurement was made for every person, but it was found that some bone measurements of very young children had to be foreshortened.

Only one volunteer refused a blood lead measurement at time of testing.

BLOOD LEAD VERSUS AGE Average blood lead level = 1.29 μg dl-1Pattern is similar to NHANES data

TIBIA VERSUS AGE Average tibia content per age decile

CALCANEUS VERSUS AGE Average calcaneus content per age decile

Bone Pb levels 20 years apart

In the 1990s, a series of bone lead measurements of environmentally exposed subjects were performed in Hamilton, Ontario. This allows for the comparison of data from this Health Canada funded study to be made to an urban Ontario group from 20 years earlier.  

Bone Pb levels 20 years apartRoy et al published a relationship of tibia versus age for men and women aged 6 to 81. A similar analysis was performed, therefore, for this study, of tibia lead content versus age in men and women aged 6 to 83.

In this study, for this comparison group, a significant relationship, as determined by linear regression, between tibia content and age was found (p < 0.001 for the slope of the regression line).

TIBIA VERSUS AGE Individual tibia lead content increases with age

Bone Pb levels 20 years apartFor men and women combined, the slope of tibia v age, in this study was 0.11 ± 0.02For men and women, the slope of tibia v age, in Roy et al., was 0.24 ± 0.03 

The slope of the relationship as measured between 2009 and 2011 is 46 ±10 % of that determined in the early 1990s.

Cumulative lead exposure, that is, the sum of lead exposure over a several year period, in Southern Ontario is approximately half of what it was two decades ago.

CURRENT BLOOD PB VERSUS CALCANEUS PB

The relationship means that some proportion of current blood lead is being driven by historical exposure

Endogenous ExposureCurrent blood Pb = 0.040 (± 0.008) * current calcaneus Pb + 1.17 (± 0.11). Lead is being returned to blood from bone and so the level in blood is related to the level in bone.

For this group of women, the average calcaneus Pb value is 7.34 μg Pb per g bone mineral. On average, for the group, the contribution to current blood lead level from bone is estimated to be 0.29 μgdl-1.

Endogenous exposure is accounting for approximately 20% of current blood lead levels, or alternatively, the data suggest that exogenous exposure from water, soil, dust etc, is accounting for approximately 80% of current blood lead levels in women of an average age of 44.