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

Part B, Section 7
An uncertainty factor greater than five for other levels of uncertainty (e.g. intra-species variation,
extrapolation to field conditions) is not recommended since a large measure of conservatism is already
added by selecting the species with the lowest available LOAEL.
7.6.2 Determining Body Weight
The mean body weight for the species used to calculate the DTED is estimated and is required with the
DTED as well as soil and food ingestion rates (SIR and FIR) to evaluate the soil quality guideline for
ingestion (Section 7.6.7).
7.6.3 Determining the Rate of Soil Ingestion
Animals ingest soil principally as a result of soil adhering to forage. The ingestion rate of soil and forage
together is referred to as the dry matter intake rate (DMIR) (kg/bw/day). To estimate the rate of soil
ingested directly, the percentage of the DMIR attributed to soil ingestion must be isolated. In most soilbased
exposure studies, the proportion of soil ingested (PSI), is reported with the DMIR. Therefore,
an animal's soil ingestion rate (SIR) (kg/bw day) is calculated as a proportion of the DMIR according to
the following equation:
SIR = (DMIR • PSI)
where: SIR = the soil ingestion rate (kg dw soil/day)
DMIR = geometric mean of the available dry matter intake rates (kg/day)
PSI = geometric mean of available soil ingestion proportions reported with the
DMIR
It is assumed that the DMIR contains only dry matter as food or soil. If no DMIR data is available for
the species used in the DTED, employ the geometric mean DMIR for grazing herbivores in the
preceeding equation. A recent review of soil ingestion information comparing wildlife and livestock
species (M c Murter, 1993) reported that a small difference existed in the PSI among domestic grazing
herbivores or wildlife. Therefore, if no information is available on the PSI for the species used to
calculate the DTED, a default value of 0.083 shall be used for domestic livestock while a default value
of 0.077 will be used for wildlife species, in the preceeding equation (M c Murter, 1993).
7.6.4 Determining the Rate of Food Ingestion
Similar to the SIR, the food ingestion rate (FIR) by livestock and wildlife is expressed as a proportion of
the DMIR. Because the proportion of the DMIR for soil ingestion has already calculated, the FIR is
simply the remaining proportion of the DMIR attributed to food intake. The FIR should be calculated
using data from the species used in the DTED. The FIR is calculated as follows:
FIR = DMIR - SIR
68