Transcript Johan Bierkens, Christa Cornelis, Mirja Van Holderbeke

Age-specific Exposure Assessment for Children
Johan Bierkens, Christa Cornelis, Mirja Van Holderbeke, Rudi Torfs
[email protected]
INTRODUCTION
Recognition has grown that children are not
just “little adults” but that they are a group
within the population who have unique
exposures and special vulnerabilities to
some/many environmental toxicants.
Children are behaviourally and
physiologically different from adults. Young
children play close to the ground and come
into contact with soil and with dust on indoor
surfaces and carpets. Exposure to
chemicals in breast milk affects infants and
young children. Also, children may differ
from adults because they have
proportionally higher breathing rates,
relative surface area, and food intake
requirements by which exposure may be
increased. Differences in absorption,
metabolism, storage, and excretion may
result in higher biologically-effective doses
to target tissues. Within the context of the
EU funded Integrated Research Project 2FUN (Full-chain and UNcertainty
Approaches for Assessing Health Risks in
FUture ENvironmental Scenarios; Contract
n°: 036976) specific exposure pathways
for children have been reviewed and
associated exposure factors have been
derived.
The single most important source that has
been consulted is the Exposure Factors
Sourcebook for Europe (ExpoFacts:
http://cem.jrc.it/expofacts/). It is a collection
of statistics and references on exposure
factors for Europe. The ExpoFacts
Sourcebook covers 30 European countries
compiled during 2003-2006. The data
represented in the database are what has
been published in official statistics, survey
reports etc. Apart from this information also
recent scientific papers, and reports
available to the authors have been
consulted. In particular, the results from two
previously published studies by Vito on the
parameterisation of an adapted version of
the human exposure model Vlier-Humaan
[1] and on soil ingestion [2] have been
integrated.
RESULTS AND DISCUSSION
METHODOLOGY
In order to establish a comprehensive
database with exposure factors relevant to
children’s exposure including - whenever
possible - their associated probability
density function (PDF), an initial overview
of data sources with relevant exposure
factors has been compiled. The nature,
format, comprehensiveness and
applicability of the available data and
existing gaps in the dataset have been
inventoried. In the first instance, focus has
been on public available databases.
However, when no data could be readily
retrieved from these databases, an attempt
has been made to obtain additional
information from published results in
scientific papers, abstracts and reports.
Exposure factors related to the child’s
physiology
As far as exposure factors related to the
physiology of children is concerned, data
have been gathered on body weight, body
length, skin surface area and the surface
area of specific body parts. On body length
and body weight extensive data bases exist
for a large number of European countries.
Therefore age specific values for both
parameters and attached PDF could be
calculated. On skin surface area no specific
EU data were available. Until these data
become available it is proposed to use U.S.
EPA data. The confidence rating assigned
by U.S. EPA to these values is medium. The
same holds for the area of specific body
parts. The areas, expressed as a
percentage of total body surface, from U.S.
EPA are proposed.
Exposure factors related to the child’s
time activity patterns
On time activity patterns quite some
information exists for different EU countries.
However, while for some countries the focus
is on children, other countries provide data
on the general public at large. Moreover, the
applied age bins between countries are
inconsistent and do not cover the entire
childhood. Therefore, for some time activity
patterns it might be considered to use USEPA data. In conclusion, for the moment
being there is a clear lack of adequate
information on effective time-activity
patterns for children of different age. There
are also insufficient data to distinguishing
between the overall population and
participants which is required for certain
activities such as sports and other
recreational activities, and mode of
transport.
Exposure factors related to the child’s
dietary and behavioural characteristics
Soil ingestion through mouthing contributes
to a large extent to children’s exposure.
Therefore, several lines of evidence have
been brought together, in order to propose
soil ingestion values for children < 6 years.
More research is required in order to be
able to differentiate between different age
groups. Apart from ingestion values other
receptor contact rates such as soil
adherence to the skin, hand-to-mouth
frequency, and efficacy of hand-to-mouth
transfer have been parameterised. To all of
them considerable uncertainty is attached
so that further research is recommended.
Finally, the results from food consumption
surveys in several European countries have
been compared. However, the comparison
of different food consumption inventories
was severely hampered because these
surveys show large differences in respect to
study design, the age bins that apply and
the total life span that is covered. As such,
derivation of age related generic intake
values for all different food categories was
shown to be impossible.
[1] Cornelis, C., J. Provoost, P. Seuntjens, M. Van Holderbeke, I. Joris, A. Colles, K. De Ridder, F. Lefebre, G. Cosemans, J. Maes, B. De Raeymaeckers, J. Bakker, J. Lijzen, J. Bakker (2008)
Herziening Vlier-Humaan F-Risk, Vito rapport 2008/IMS/R/033. Mol, Belgium.(In Dutch). [2] Van Holderbeke, M., C. Cornelis, J. Bierkens, R. Torfs (2007) Review of the soil ingestion pathway in human
exposure assessment. Study in support of the BeNeKempen project – Subgroup on harmonization of the human health risk assessment methodology.
CONCLUSIONS
A review has been made of specific exposure pathways for children and exposure factors for many of these pathways are
proposed so as to be able to integrate them in exposure assessment and perform a separate risk assessment for children.
For some exposure factors more research is required to generate parameter values with high confidence level attached to
them.