Tiered aggregate exposure assessment - when to launch

Criteria for using “simple” versus aggregate exposure assessment
John Cherrie for the TAGS Group

Summary…
Some definitions
When not to do an aggregate exposure assessment
Knowing why you want to do the assessment
Criteria for deciding what type of assessment is needed
Aggregating routes
Aggregating pathways
An example – pesticide
7/6/10
2
TAGS workshop

Talking the same language - definitions
Exposure scenario - a set of circumstances through which someone may become exposed to the substance of interest
Sources, pathways and exposure routes
outdoor motor vehicle > outdoor air > breathing zone > inhalation
Exposure, intake and uptake
7/6/10
3
TAGS workshop

Criteria…
When should we launch an aggregate exposure assessment?
or
When is it appropriate to just do a simple exposure assessment?
7/6/10
4
TAGS workshop

Aims and objectives…
Define the population at risk
Set out the exposure scenario
Specify the toxicological / health effects of interest for each route of exposure
Risk assessment, ranking routes, ranking pathways?
Note: aggregating across routes more problematic than across sources / pathways
7/6/10
5
TAGS workshop

General scheme…
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6
TAGS workshop
Define the purpose of the exposure assessment
Purpose to distinguish between pathways/routes?
Y
AEA
N
Ignoring the magnitude of exposure, is there a basis for aggregation across routes?
Screening of relative magnitude of routes: is one route more important than others?
N
Y
N
Y
N
Can we subdivide the population to simplify the
assessment?
Ignoring the magnitude of exposure, is there a basis for aggregation across sources/ pathways?
Screening of relative magnitude of different sources/pathways: is one more important than others?
N
Y
Y
N
Y
SEA

Specific issues…
Subdividing the population:
Consumers, workers, people only exposed from the environmental pollution (i.e. on exposure)
Age, gender, socioeconomic status etc (i.e. on susceptibility)
Considering the health effects
More than one route must be linked to the same systemic effects
If these systemic effects are a result of acute exposure, then exposure by more than one route must happen at the same time, or within the same (short) time window
7/6/10
7
TAGS workshop

Account for magnitude of exposure…
Exposure “negligible” or not by route?
What do we mean by negligible and
How do you “assess” exposure
Should this also include an assessment of intake?
Does the susceptibility of the sub-population need to be taken into account in assessing when a route can be considered negligible?
7/6/10
8
TAGS workshop

Conceptual models…
7/6/10
9

7/6/10
10

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11

An example: Pesticide X
Purpose: risk assessment for British population
Food contaminated > ingestion
Use of a consumer product (Y) containing
Only concerned with chronic exposure
Xis non volatile and is not taken up through the skin so ingestion is the only possible route
Not necessary to aggregate over routes
7/6/10
12
TAGS workshop

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TAGS workshop
13
Y
AEA
N
N
Y
N
Y
N
assessment?
N
Y
Y
N
Y
SEA

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14

Pathways for X
contaminated food > ingestion
use of product Y > skin contamination layer > ingestion
use of product Y > surfaces > ingestion
use of product Y > surfaces > skin contamination layer > ingestion
use of product Y > surfaces > clothing > skin contamination layer > ingestion
use of product Y > clothing > skin contamination layer > ingestion
7/6/10
15
TAGS workshop

A Simple Exposure Assessment?
Two scenarios for exposure to chemical X
For consumers who use the product the presence of trace amounts of chemical in food would make a negligible contribution to their aggregate exposure
Simplify the approach into two SEAs
one for consumers who use product Y
one for the remainder of the population
It is therefore not necessary to conduct an AEA in this case.
7/6/10
16
TAGS workshop

An example revisited : Pesticide X
Purpose: risk assessment for British population
Food contaminated > ingestion
Use of a consumer product (Y) containing
Only concerned with chronic exposure
X is non volatile
X is taken up through the skin and by ingestion
Ignoring the magnitude of exposure aggregation across routes may be necessary
7/6/10
TAGS workshop
17

7/6/10
TAGS workshop
18
Y
AEA
N
N
Y
N
Y
N
assessment?
N
Y
Y
N
Y
SEA

Tiered aggregate exposure assessment - when to launch

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