Hazard Assessment and Contaminated Sites - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 563

Metabolite A contaminant that is the product of biochemical alteration of the
parent contaminant in an organism.
Model A mathematical representation of a biological system intended to mimic
the behaviour of the real system, allowing descriptions from empirical data and
predictions about untested states of the system.
NOAEL The No-Observed-Adverse-Effect Level is the highest dose of a contam-
inant at which no toxic (i.e., adverse) effects are observed (WHO 1990 ). It may also
be worded in more detail thus: The NOAEL is defined as the highest exposure at
which there is no statistically- or biologically-significant increase in the frequency
of an adverse effect when compared to a control group (National Academy of
Sciences/National Research Council 1994). The definition of NOEL is equivalent,
but with the removal of the term, “adverse”. Often, the difficult issue in the use of the
terms NOEL or NOAEL is in deciding whether a contaminant-related effect noted
in a particular study is necessarily an “adverse” effect. Alterations of morphology,
functional capacity, growth, development or life span of the target organism may be
detected which are judged not to be adverse.
Nongenotoxic carcinogen A contaminant which induces tumours via a mecha-
nism which does not involve direct damage to DNA (IEH 1999 ).
Physiologically-based pharmacokinetics (PBPK) Modelling the dose or degree
of exposure to a contaminant at a target tissue, cell or receptor, by integration of
pharmacokinetic data with anatomical, physiological and biochemical data (IEH
1999 ).
NOEL The “No-Observed-Effect Level” or “No-Observable-Effect Level”
(NOEL) is the highest dose of a contaminant administered to a group of experi-
mental animals at which there is an absence of observable effects on morphology,
functional capacity, growth, development or life span, which are observed or mea-
sured at higher dose levels used in the study. Thus, dosing animals at the NOEL
should not produce any biologically significant differences between the group of
chemically exposed animals and an unexposed control group of animals maintained
under identical conditions. The NOEL is expressed in milligrams of contaminant
per kilogram of body weight per day (mg/kg bw /day) or, in a feeding study, in ppm
in food (converted to mg/kg bw of contaminant intake by measured or estimated
food intake over the period of the study) The NOEL has been simply defined as
the highest dose of a contaminant which causes no changes distinguishable from
those observed in normal (control) animals (WHO 1990 ).
PTWI Provisional Tolerable Weekly Intake. The tolerable intake of a contaminant
expressed as a weekly amount. The termwas established by WHO ( 1972 ) for several
heavy metals which “are able to accumulate within the body at a rate and to an extent
determined by the level of intake and by the contaminant form of the heavy metal
present in food.” (WHO 1989 )
Public Health The science and art of preventing disease, prolonging life and
promoting health through organised efforts of society.