An analysis of the need for an additional uncertainty factor for infants and children

Uncertainty factors have been used for over 40 years to establish safe inta kes of threshold toxicants. Tenfold factors are used to allow for species d ifferences and for human variability, with extra factors for database inade quacies. The proposal to introduce an additional 10-fold factor for pestici des when exposure of infants and children is anticipated implies either age -related differences between species or differences within humans which exc eed those present in adults. Alternatively, the extra factor could be relat ed to deficiencies of current testing methods or concerns over irreversibil ity in developing organ systems. Available data do not provide a scientific rationale for the extra factor due to inadequacy of inter- and intraspecie s uncertainty factors. Justification for the factor therefore must relate t o the adequacy and sensitivity of current methods or concern about irrevers ible effects in the developing organism. (C) 2000 Academic Press.