Protocol for the Derivation of Environmental and Human ... - CCME

Appendix F
A. Data Collection: Data on concentrations in air, water, soil, food, consumer products are
combined with information on the rate of contact with air, water, and food to estimate exposure.
Alternately, data on the concentrations in human tissues (i.e., hair, blood, urine, fat) can be
combined with pharmacokinetic data to predict exposure rates. When no residue data is available
because concentrations in the medium are below detection limit, the current detection limit will
estimate the concentration in that medium. This would constitute a maximum value.
B. Determination of Intake: Receptors are classified into five groups based on age (i.e., newborn
to 6 months, 7 months to 4 years, 5 to 11 years, 12 to 19 years, 20 years plus). In this document,
the term child describes any individual up to 11 years of age. For each particular receptor group,
quantities of air breathed, or water, food, and soils ingested, and surface area of exposed skin are
required to convert a concentration in a contaminated medium (such as air or food) to a dose.
Some basic assumptions routinely made about Canadians in risk assessments can be found in the
CCME working document "Review and Evaluation of Receptor Characteristics for Multimedia
Assessments". Figures for daily food consumption patterns in Canada by age group are available
within the Health Protection Branch. Once data on the level of contamination are known for these
foods, it is then possible to estimate the daily dose that these age classes might experience.
C. Determination of Retention and Absorption: It is often assumed that 100% of the dose
ingested, inhaled or applied to the skin is bioavailable. However, where possible, more precise
data on actual retention and absorption is used to make the assessments as accurate as possible.
D. Identification of Sensitive Receptors: It is important to attempt to identify individuals
(receptors) who may be at greater risk from exposure to a substance or at greater risk due to
increased sensitivity to toxic effects. For example, the fetus and newborn are at greater risk to
mercury and lead due to the sensitivity of the developing neurological system.
Often, data do not exist to permit the precise quantification of exposure. However, it may be known or
suspected that the substance is present in the environment and some indication of exposure and risk is
needed. In these cases, it is common to use predictive models to estimate levels in environmental
media. Environmental fate and partitioning models have been developed to predict relative
concentrations in water, soil, air and foods. These models rely on regression equations or other
mathematical relationships which can predict environmental partitioning from simple chemical
characteristics such as water solubility, octanol/water partition coefficients, Henry's Law Constant, and
organic carbon partition coefficient. Rates of physical, chemical and biological degradability can also be
predicted by some models.
Different models have been developed for different purposes. Environmental partitioning models are
based on the assumption of chemical equilibrium between all media. However, deterministic models are
required if one wants to predict the concentration of a substance at some specified distance from a point
source of contamination. These models exist to assess chemicals released from incinerator stacks and
from spills into soil or groundwater.
In foods, simple bioaccumulation or biomagnification factors were established for many chemicals.
These will give a simplistic indication of the likelihood that a chemical will build up in fish, game or
domestic animals and the approximate ratio of concentrations in the food to that in the environment. For
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