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

Part C, Section 5
these data are available. The exposure term is the ratio of the defined exposure period for each land
use to the maximum exposure period (24 hours/day x 365 days/year).
5.2 Preliminary Soil Guidelines Derivation for Non-threshold Substances
If the chemical is identified as a non-threshold substance by Health Canada, then the SEQCCS will
develop a guideline employing a critical risk specific dose (RSD) based on an incremental risk from soil
exposure of 10 -6 . The use of other critical risk levels can easily be accommodated at a site-specific
objective level. The preliminary human health soil guideline is established as follows:
where,
PSQG HH = RSD × BW + BSC
[(AF I × IR) + (AF D × DR) + (AF S × SR)] × ET
PSQG HH = preliminary human health-based soil quality guideline (mg/kg)
RSD = risk specific dose (mg/kg⋅day)
BW = body weight (kg)
BSC = background soil concentration (mg/kg)
AFI = absorption factor for gut (unitless)
AF D = absorption factor for lung (unitless)
AF S = absorption factor for skin (unitless)
IR = soil ingestion rate (kg/day)
DR = soil inhalation rate (kg/day)
SR = soil dermal contact rate (kg/day)
ET = exposure term (unitless)
The adult is the receptor when considering lifetime cancer risk. Absorption factors may be required
when the critical toxicity study used in developing the cancer slope factor has used an absorbed dose
rather than an administered dose. Absorption factors may also be required when the critical toxicity
study employed a different medium in developing the cancer slope factor than that under investigation.
Then soil ingestion, dermal contact, and inhalation rates are multiplied by corresponding absorption
factors (AF), when these data are available. For non-threshold substances, the exposure term for all
land uses (including commercial and industrial) is one since the exposure period (i.e., 10 hours/day, 5
days/week, 48 weeks/year for 30 to 40 years over a lifetime) exceeds the likely latency period for most
carcinogens.
5.3 Indirect Soil Contaminant Exposure
5.3.1 General
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