Children-specific assessment factor

Concern has been raised that infants and children are at higher risk than adults from exposure to environmental chemicals. The question of an extra assessment factor in the hazard and risk assessment for chemicals of concern for children has therefore been raised and the rationale for such a children-specific assessment factor has been discussed. 

In conclusion, the traditional assessment factors (interspecies, intraspecies, subchronic-to-chronic, LOAEL-to-NOAEL, and database-deficiency) are considered to cover the concerns and uncertainties for children adequately, i.e., no children-specific assessment factor is needed when setting tolerable intakes. However, it is recommended to perform children-specific risk assessments for chemical substances in products and foods intended for children, based on specific exposure assessments for children. 

The US-EPA Child Specific Exposure Factors Handbook (US-EPA 2006), first published in 2002, consolidates all children s exposure factors data into one document. The document provides a summary of the available and up-to-date statistical data on various factors assessing children s exposures. These factors include drinking water consumption soil ingestion inhalation rates dermal factors including skin area and soil adherence factors consumption of fruits, vegetables, fish, meats, dairy products, homegrown foods, and breast milk activity patterns body weight consumer products and life expectancy. 

US-EPA. 2006. Child Specific Exposure Factors Handbook 2006 (External Review Draft). Washington, DC National Center for Environmental Assessment. Office of Research and Development. Presently undergoing update (In press), http //cfpub.epa.gov/ncea/cfm/recordisplay.cfm7deid = 56747 US-EPA. 2007a. EPA/OPPT Exposure Assessment Tools and Models website, http //www.epa. gov/opptintr/ exposure /pub s/opptexpo. htm... 

Guidelines for exposure assessment (USEPA, 1992a OECD, 1999 IPCS, 2000) and a handbook of child-specific exposure factors (USEPA, 2002a) have been published. Both list a number of references that are applicable to the quantitative estimate of exposure. Generally, the methods used for the quantitative estimate of exposure are not different for children and adults. The magnitude of exposure is a product of the exposure concentration as a function of... 

USEPA (2002a) Child-specific exposure factors handbook (interim report). Washington, DC, United States Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment (EPA-600-P-00-002B). 

U.S. Environmental Protection Agency, 2008. Child-Specific Exposure Factors Handbook. Report No. EPA/600/R-06A196F. National Center for Enviromnental Assessment, Washington, DC. 

Environmental Assessment (NCEA) within the EPA s Office of Research and Development (ORD), this document supplements the 1997 Exposure Factors Handbook with child-specific data on exposure activities and other parameters for assessing exposure to contaminants in the environment. 

In the case of noncarcinogenic substances, there exists a threshold this is an exposure with a dose below which there would not be adverse effect on the population that is exposed. This is the reference dose (RfD), and it is defined as the daily exposure of a human population without appreciable effects during a lifetime. The RfD value is calculated by dividing the no observed effect level (NOEL) by uncertainty factors. When NOEL is unknown, the lowest observed effect level (LOEL) is used. NOEL and LOEL are usually obtained in animal studies. The main uncertainty factor, usually tenfold, used to calculate the RfD are the following the variations in interspecies (from animal test to human), presence of sensitive individuals (child and old people), extrapolation from subchronic to chronic, and the use of LOEL instead of NOEL. Noncancer risk is assessed through the comparison of the dose exposed calculated in the exposure assessment and the RfD. The quotient between both, called in some studies as hazard quotient, is commonly calculated (Eq. 2). According to this equation, population with quotient >1 will be at risk to develop some specific effect related to the contaminant of concern. 

The concept that infants and children may be a sensitive subgroup relates to their relative immaturity compared to adults. Children, as well as the unborn child, have in some cases appeared to be uniquely vulnerable to toxic effects of chemicals because periods of rapid growth and development render them more susceptible to some specific toxic effects when compared to adults. In addition to such toxicodynamic factors, differences in toxicokinetics may contribute to an increased susceptibility during these periods. It should be noted, however, that during the developmental and maturational periods the susceptibility to exposure to xenobiotics in children may be higher, equal, or even lower than in adults. Except for a few specific substances, not very much is known about whether and why the response to a substance may differ between age groups. It should also be borne in mind that, in terms of risk assessment, children are not simply small adults, but rather a unique population (Nielsen et al. 2001). 

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