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

Part C, Section 2
This philosophy is consistent with the CCME philosophy to encourage remediation to the lowest
reasonable levels. To derive numerical, generic environmental quality guidelines for soil, the
Subcommittee has adopted the position that contaminated site related risks arising from human exposure
to non-threshold agents should be at least remediated to levels within the range of 10 -4 to 10- 7 . The
guidelines derived in this protocol reflect a level of risk of 10 -6 for incremental risk from soil.
2.1.1 Guidelines for Classification of Carcinogenicity and of Mutagenicity in Germ Cells
Chemicals are classified into six categories on the basis of the following guidelines outlined by Health
Canada (1994).
Group I:
Group II:
Group III:
Group IV:
Group V:
Group VI:
Carcinogenic to Humans/Human Germ Cell Mutagens
Probably Carcinogenic to Humans/Probable Human Germ Cell Mutagens
Possibly Carcinogenic to Human/Possible Human Germ Cell Mutagen
Unlikely to be Carcinogenic to Humans/Unlikely to be Human Germ Cell Mutagen
Probably Not Carcinogenic to Humans/Probably Not a Human Germ Cell Mutagen
Unclassifiable with Respect to Carcinogenicity in Humans/Unclassifiable with Respect to
Germ Cell Mutagenicity in Humans
Health Canada considers those substances classified into Groups I and II as carcinogens having no
threshold dose for effects. The risks from chemicals in groups III to VI are assessed on toxicological
data relating to effects where some threshold is assumed to exist, and below which no risk exists.
2.2 Threshold Contaminants
The approach to the assessment of substances classified in Groups III to VI, based on the above
guidelines, is that adopted for "threshold toxicants" described in this section. However, for at least one
of these categories (Group VI), adopting this approach is due to the lack of reliable data on
carcinogenicity/mutagenicity, rather than certain knowledge that the substance is not carcinogenic.
Though this may appear to be less than conservative, tolerable daily intakes for compounds in this group
are developed using large uncertainty factors to account for inadequacies in the database.
Where possible, a dose (or concentration) of a chemical substance that does not produce any (adverse)
effect [i.e., "no-observed-(adverse)-effect-level" (NO(A)EL)] for the critical endpoint is identified,
usually from toxicological studies involving experimental animals, but sometimes from epidemiological
studies of human populations. If a value for the NO(A)EL cannot be ascertained, a lowest-observed-
(adverse)-effect-level (LO(A)EL) is used. The nature and severity of the critical effect (and to some
76