Age-specific Exposure Assessment for Children Johan Bierkens, Christa Cornelis, Mirja Van Holderbeke, Rudi Torfs 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 2- FUN (Full-chain and UNcertainty Approaches for Assessing Health Risks in FUture ENvironmental Scenarios; Contract n°: ) 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: It is a collection of statistics and references on exposure factors for Europe. The ExpoFacts Sourcebook covers 30 European countries compiled during 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. 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. 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. [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. RESULTS AND DISCUSSION 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 US- EPA 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.