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

Appendix A
environment, to chemically reduce N 2 to ammonium. Cellular apparatus required to maintain these
conditions places a heavy energy demand on the cell that can be met only under favourable conditions
— including minimal contaminant stress. Conversely, nitrifiers maintain life on a very low energy budget
dictated by the small amount of energy available from oxidation of ammonium to nitrate. This low
energy yield limits growth rates and makes nitrifiers sensitive to stress conditions (Schmidt 1982).
For these reasons, nitrogen-fixers and nitrifiers are ecologically relevant, sensitive to a broad range of
stressors, and are functionally unique (i.e., when lost or damaged their functions cannot be overtaken by
related species). These properties, in turn, makes them good microbial indicators of soil quality.
Based on these findings, contaminant data from nitrification, nitrogen fixation, nitrogen mineralization,
decomposition and respiration studies are all potentially acceptable for checking against a single species
bioassay. Of these, nitrogen-fixation and nitrification data are preferred, but carbon cycling and nitrogen
mineralization measures may be used when the former are unavailable or insufficient.
3.0 Evaluation of Laboratory and Field Toxicological Data
In general, the guiding principles for selecting acceptable studies (described in Part B, Section 7.2) also
apply to the evaluation of laboratory and field toxicological data. While controlled, laboratory data are
preferred, field data may be used provided influential variables are measured and within acceptable
ranges. Acceptable data sources will include:
• a replicated and controlled statistical design,
• a known and reported exposure period, and
• analytical assessment of contaminant test concentrations.
Minimum toxicological data requirements also apply to soil nutrient and energy cycling process data (see
Part B, Section 7.3). Minimum requirements vary within the hierarchy of derivation methods described
in Section 4.0, Appendix A.
4.0 Deriving Soil Quality Guidelines
A tiered, or hierarchical approach to guideline derivation is presented that considers: land use, data
sources and derivation method. Four derivation methods {the weight of evidence, LOEC extrapolation,
and median effects methods (described in Part B, Section 7.5.1); and a modified LOEC method
applied to nitrogen and carbon cycling data} are used to perform the nutrient and energy cycling check.
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