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

Section 5
Preliminary Guidelines Derivation
The exposure assumptions used in calculating the preliminary soil quality guidelines (PSQG HH ) for each
land use were described in Sections 4.3.2 to 4.3.5. Details of the equations and numerical procedures
used to calculate the preliminary soil quality guidelines are provided in Sections 5.1 and 5.2.
In principle, for threshold contaminants, the total exposure from direct soil pathways should not exceed
typical background soil exposures by more than 20% of the residual tolerable daily intake (RTDI). If
the chemical is identified as a non-threshold substance by Health Canada, then the SEQCCS will
develop a criterion employing a risk specific dose (RSD) based on an incremental risk from soil
exposure of 10 -6 .
5.1 Preliminary Soil Guidelines Derivation for Threshold Substances
The preliminary human health soil guideline (PSQG HH ) is calculated using the following equation:
where,
PSQG HH = ( TDI - EDI ) × SF × BW + [BSC]
[(AF I × IR) + (AF D × DR) + (AF S × SR)] × ET
100
PSQG HH = preliminary human health-based soil quality guideline (mg/kg)
TDI = tolerable daily intake (mg/kg bw⋅day)
ED = estimated daily intake (multimedia exposure assessment)
(mg/kg⋅day)
SF = soil allocation factor (unitless)
BW = body weight (kg)
BSC = background soil concentration (mg/kg)
AF I = 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 soil inhalation rate is defined as the amount of respirable soil particles inhaled in a day. The soil
dermal contact rate is the amount of soil contacting the skin in a day. The soil ingestion rate refers to the
amount of soil ingested on a daily basis. Absorption factors may be required where the critical toxicity
study used in developing the NO(A)EL employed an absorbed dose rather than an administered dose,
or where the critical toxicity study has employed a different medium than that under investigation. Then
soil ingestion, dermal contact, and inhalation rates are multiplied by corresponding absorption factors
(AF), when