Environmental Engineering Reference
In-Depth Information
table 12.2
Defi nitions for Human and Ecological Risk Assessment
Acceptable daily intake (ADI):
The amount of a food additive that could be consumed daily for an entire life span
without appreciable risk. Often determined by measuring the highest dose of the substance that has no effect on
experimental animals, then dividing by a safety factor of 100. Substances that are not given an ADI are regarded as having
no adverse effect at any level of intake. Set by the U.S. Food and Drug Administration Offi ce of Food Additive Safety.
Benchmark dose:
The lower confi dence limit on a dose that produces an effect in some percent (10% or less) of the
animals in a laboratory study.
Bioindicator:
Species used as an indicator of overall exposure or effects of a stressor, such as mercury.
Biomarker:
Indicators of internal dose or effect; can include alterations in enzyme activity disturbances to cell structure
or function. Biomarkers are most useful when they are specifi c to a contaminant and quantifi able.
Biomonitoring:
Periodic and regular measurement of contaminant levels in bioindicator species or of biomarkers of
exposure or effects.
Ecological screening quotient (ESQ):
A quotient used to assess risk in which protective assumptions are used. Generally,
the numerator is the reasonable worst-case concentration at the point of exposure and the denominator is the no-
adverse-effects-based toxicity reference value.
Hazard quotient (HQ):
Chemical-specifi c HQ risk characterization is used in both HRAs and ERAs, It is a ratio of an
exposure estimate to a toxicity reference value or benchmark. An HQ less than or equal to a value of 1 indicates that
adverse impacts to human and ecologic receptors are considered unlikely.
Lowest observable adverse effects level (LOAEL):
The lowest level tested in animals studies that resulted in an adverse
effect. A threshold is presumed to exist between the NOAEL and LOAEL.
Minimal risk level (MRL):
Health guidance values developed by Agency for Toxic Substances and Disease Registry
(CDC-ATSDR) in its Toxicological Profi les. “An MRL is an estimate of the daily human exposure to a hazardous substance
that is likely to be without appreciable risk of adverse noncancer health effects over a specifi ed duration of exposure.”
Long-term MRLs assumes a lifetime exposure. “Conceptually equivalent” to the EPA RfD, the FDA ADI, and the WHO
PTWI. The uncertainty values convey the impression of a margin of safety that may be real or illusory.
No observable adverse effect level (NOAEL):
The highest level of a toxicant that appears to cause no adverse effect in
animal studies. Whether a NOAEL is detected depends on the dosages chosen for a study.
No observable effect level (NOEL):
The level of a toxicant that appears to cause no effect of any kind in animal studies;
not usually used in risk assessment.
Provisional tolerable weekly intake (PTWI):
Set by the United Nations Food and Agriculture Organization and World
Health Organization through its, FAO/WHO Joint Expert Committee on Food Additives (JECFA).
Reference dose (RfD):
The daily dose that a human can be exposed to every day (usually for a 50-year life span) without
experiencing an adverse effect. Established by the Environmental Protection Agency based on cancer and noncancer end
points.
Screening level:
Level of a contaminant, such as mercury, that is known to produce adverse effects in humans or
ecologic receptors.
Total maximum daily load (TMDL):
A calculation of the maximum amount of a pollutant that a body of water can
receive and still meet water-quality standards.
SOURCE
: Compiled from Bartell et al., 1992; Peakall, 1992; Tardiff and Goldstein, 1992; Sorensen et al., 2004; Burger, 2006; Gochfeld and Burger, 2007.
note: For additional defi nitions, see USEPA (2010).
higher-tier risk evaluations require receptor-specifi c toxicol-
ogy. These values can apply specifi cally to humans or to a
given species of animal (Clark et al., 1999; Hays et al., 2007).
More specifi cally, a benchmark dose is the lower confi dence
limit on a dose that produces an effect in some percent of
animal trials (Table 12.2). It thus relies on animal models for
extrapolation to humans (and sometimes to other animals).
It assumes that some level of illness in humans is tolerable.
