National Institutefor Public Healthand the Environment The bioaccessibility and relative

bioavailability of lead from soils for fasted and fed conditionsDerivation of the “average physiological state”

correction factorWerner Hagens and Agnes Oomen

National Institutefor Public Healthand the Environment

Lead contamination in the Netherlands

several sources

(historic) use

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Exposure to lead via soil

- Contamination of lead in soils of old cities due to historical use and misuse

- Contact human-soil is relevant: Potential risk

- Especially children are at risk• Hand-to-mouth contact• Lead absorption is better (associated with calcium)• Toxic effects (neurobehavioral functioning, intelligence)

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Exposure to contaminant in a matrix

Ingestion of matrix + contaminant

Fb = Fraction released from matrix = bioaccessible fraction

Fa = Fraction of Fb absorbed by small intestine

Fh = Fraction of Fa passing liver without being metabolised

F = Fraction reaching systemic circulation = bioavailable fraction

F = Fb x Fa x Fh

In vitro digestion model

Oral bioavailabilityExternal exposure

small intestineportal vein

liver

mouth

oesophagus, stomach, small intestine

systemic circulation

Internal exposureF

FhFh

Fb

Fa

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• Bioavailability of lead from soil ≠

bioavailability dietary lead• Aim is to obtain a value for the relative bioavailability

• Where FMPR represents the bioavailability of lead in the matrix that was used in the studies for deduction of the Maximum Permissible Risk (MPR)

• MPR-studies based on dietary lead in which it was indicated that bioavailability of lead was about 40% (children)

Further information: ⇒ RIVM-report 711701042 (http://www.rivm.nl/en/)

b,soil a,soil h,soilsoil

MPR b,MPR a,MPR h,MPR

F F FFRelative F=F F F F

× ×=

× ×

Relative bioavailability

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Implementation of relative bioavailability in risk assessment

Risk assessment needs relative oral bioavailability as input (Rel F)

sA ID C FD IW

R e l× ×=

With:

•DI: uptake via ingestion (mg contaminant×kg-1×d-1)

•AID: daily intake soil/house dust via ingestion (kg×d-1)

•W: body weight (kg)

•Rel F: relative oral bioavailability factor (-)

•Cs : Concentration contaminant in soil/house dust (mg contaminant×kg-1)

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FED versus FASTED physiological state

• Lead is better absorbed in fasted conditions (Fa )• Bioaccessibility of lead from soil is higher for fasted

conditions (Fb )• In risk assessment, fasted state results in more

conservative relative bioavailability values (Rel F)

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Fed-Fasted physiological state in Dutch risk assessment

The choice of the physiological state (fed, fasted or average fed/fasted) influences bioaccessibility from lead

Dutch policy encourage an “average physiological state” condition

Rational:• A child will not always ingest soil when he/she is fasted or fed• Average conditions would be more realistic (not worst-case)

Derive an “average physiological state” correction factor- In vitro bioaccessibility for fasted conditions can be used to derive

Fb,average conditions- Reduction in time and costs - More realistic

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The Correction Factor for the Average Physiological State (CFAPS )

• α

= Fb soil, Fasted / Fb soil, Fed- α

= ratio bioaccessibility fasted/fed from soils- Fb soil, Fed = Bioaccessibility of lead from soil as estimated for fed conditions- Fb soil, Fasted = Bioaccessibility of lead from soil as estimated for fasted

conditions

• CFAPS = (1 + α)/2 - CFAPS = Correction Factor “Average Physiological State”- α

= ratio bioaccessibility fasted/fed from soils

• Fb soil, APS = Fb soil, Fasted x CFAPS

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From bioaccessibility to relative bioavailability factor for “average” physiological conditions

Fill in:• Fa, soil = 0.8 • Fh, soil = 1 (no lead metabolism)• Fb, soil = value from in vitro digestion model• FMPR = 0.4

• Rel FAverage physiological state = 2 x Fb soil, fasted x CFAPS

b,soil a,soil h,soilsoil

MPR b,MPR a,MPR h,MPR

F F FFRelative F=F F F F

× ×=

× ×

b,soil a,soil b,soil b,soil

b,MPR a,MPR

F F F 0.8 FRelative F=

F F 0.4 0.5× ×

= =×

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The current use of CFAPS

Up till now, fasted and fed conditions were tested for only 11 soils

A conservative percentile (P80) was chosen by Dutch policy makers to ensure safe application of the correction factor.

soil number breakfast spaghetti1 1.00 0.462 0.73 0.333 no data * no data *4 0.59 0.215 0.52 0.156 0.51 0.547 0.50 0.54 P50 0.56 0.7818 0.71 0.85 P60 0.59 0.7979 0.60 0.67 P70 0.66 0.832

10 0.70 0.65 P80 0.71 0.85511 0.58 0.34 P90 0.74 0.87112 0.36 0.74 P95 0.85 0.923

Percentile

Ratio fed/fasted conditions

α

"Average physiological state" correction factor

CFAPS

Bioaccessibility ratio for fed/fasted conditions

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Current use of bioavailability in Human risk assessment in the Netherlands (Lead)

• TDI (Tolerable daily intake) of lead in humans is 3.6 µg Pb/kg body weight/day (based on 40% bioavailability in MPR study)

• Intervention value for lead in soil should be 301 mg/kg for scenario “living with garden” in the Netherlands

But….. Dutch intervention value for lead is currently 530 mg soil

Because:1- assumption of daily ingestion of 100 mg soil (in stead of 150 mg)2- intervention value correction factor (see next sheet!)

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Current intervention value correction factor

Intervention value correction factor = 0.74• P80 for relative bioavailability of lead in tested soils (all

soils till 2007) (=Rel F soil,fasted )• P80 for difference between fasted and average state

in gastrointestinal tract (=CFAPS )

The current intervention value correction factor• P80 Rel Ffasted x P80 CFAPS = 0.87 x 0.855 = 0.74

The decision which percentile level is chosen in risk assessment is made by policy makers, depending on the level of certainty that is desired

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Objective of this study

• Derive an “average physiological state” correction factor (CFAPS )• To estimate the bioaccessibility of lead for “average physiological state”

conditions based on the bioaccessibility determined for fasted conditions. • To make risk assessment more realistic.

• Previously, the “average physiological state” correction factor (CFAPS ) was derived from fasted and fed data obtained with the in vitro digestion model for 22 samples (11 separate soils with 2 different food types).

• By order of the Ministry of Housing, Spatial Planning and Environment (VROM), this correction factor is now further substantiated by investigation of 45 additional soils

• With this study, the CFAPS can be determined more reliable, as the number of soils used for the calculation is increased.

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Materials and Methods• 45 Dutch city soils (+ reference soil MS2711)• RIVM in vitro digestion model

• Fed (solid-to fluid ratio of 1:1063, 0.04 gram soil)- Baby food

• Fasted (solid-to fluid ratio of 1:958, 0.06 gram soil)

Calculation of CFAPS based on- Previous 11 soil (spaghetti and breakfast)- Additional 45 soils (baby food)- Statistical analysis

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In vitro determination of bioaccessibility

saliva gastric juice

duodenal juicebile

5 minpH ± 1.5

pH ±

2.5

pH ± 6.0

pH ±

6.5

soil

2 h 2 hpH ± 6.5

pH ±

6.8

empty tube

Ingestion Mouth Stomach SmallIntestine

Fasted

Fed

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In vitro determination of bioaccessibility

chyme

+

pellet (destruction)

Analysisby ICP-MS

Centrifuge

Pellet (destruction)

pellet

chyme

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Results

Dataset*Avarage

StdvNumber of data

Percentile

P50 0.56 0.781 0.62 0.809P60 0.59 0.797 0.66 0.828P70 0.66 0.832 0.72 0.859P80 0.71** 0.855** 0.84 0.922P90 0.74 0.871 0.92 0.961P95 0.85 0.923 0.97 0.984

22 70

Ratio fed/fasted (α)

"Average physiological state"

correction factor (CFAPS)

Ratio fed/fasted (α)

"Average physiological state"

correction factor (CFAPS)

Current provisional dataset (2006), used in risk assessment

Newly proposed dataset (2008), used in risk assessment

0.20

II + III0.55

I + II + III0.640.23

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Discussion• The new dataset (70 sample) results in a smaller difference between

the bioaccessibility of lead from soils for fasted and fed conditions.

• As a consequence, the ratio fasted-fed (α) and its derived “average physiological state” correction factor (CFAPS ) are higher for the given percentiles compared to the current dataset (based on 11 soils).

- As the current data set is based on 11 soils only, a conservative P80 value of CFAPS (=0.855) was chosen for the scientific foundation of the intervention value of lead in soil.

- Based on the new dataset (70 samples), the P80 value of CFAPS, NEW will become 0.922.

• The new dataset (70 samples) results in a better foundation of the CFAPS : a lower percentile could be chosen by policy makers (P50- P80), resulting in a CFAPS of 0.81-0.92, depending on the level of conservatism that is desired.

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Acknowledgement

• Johannes Lijzen• Peter Kootstra• Menno Duits• Gerard Boom• Nikolaj Walraven (Geoconnect)

National Institutefor Public Healthand the Environment

QuestionsQuestions??

Agnes.OomenAgnes.Oomen@@rivm.nlrivm.nl