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

Part B, Section 7
7.5.2.3 Lowest Observed Effect Concentration Method. When the minimum data requirements
for the weight of evidence method cannot be met, the TEC is derived by extrapolating from the lowest
available, lowest observed effect concentration (LOEC) divided by an uncertainty factor (if needed). In
this method, the TEC is estimated to be somewhere below the lowest reported effect concentration (see
Figure 9). The TEC is calculated using the following equation.
TEC
= lowest LOEC/UF
where TEC = threshold effects concentration (mg/kg soil)
LOEC = lowest observed effect concentration (mg/kg soil)
UF = uncertainty factor (if needed)
A minimum of three studies reporting LOEC and NOEC endpoints must be considered. Requirements
also include at least one terrestrial plant and one soil invertebrate study.
If expert judgement determines that an UF is warranted, the following criteria should be used as a guide
for application to determine an UF between one and five:
• The LOEC is considered "biologically significant" and not just statistically different from controls, and
therefore extrapolation below this level of effect is required.
• The LOEC is taken from an acute lethal or sublethal study.
• Only the minimum number of studies (three) was available to select the lowest LOEC.
• Fewer than three taxonomic groups are represented when selecting the lowest LOEC.
An uncertainty factor greater than five for other levels of uncertainty (e.g., model error, intra-species
variation) is not recommended since a large measure of conservatism is already added by selecting the
species with the lowest available LOEC.
The TEC should now be compared with the microbial value to determine the SQG SC for agricultural and
residential/parkland land uses (see Appendix A).
7.5.2.4 Median Effects Method. Alternatively, if the minimum data requirements cannot be met for
the weight of evidence and LOEC methods, the TEC is derived by extrapolating from the lowest
available EC 50 or LC 50 datum using an uncertainty factor (UF). In this method, the TEC is estimated in
the region of predominantly no effects (see Figure 11). The TEC is calculated as follows:
TEC
= lowest EC 50 or LC 50 /UF
where TEC = threshold effects concentration (mg/kg soil)
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