Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:2:p10
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 2 (pt 10/15)
Character Range: 1276991–1280192

by direct toxicity. If, however, these slowly degrading, high log Kow contaminants have a high H, then direct toxicity will be the most important exposure pathway, followed by biomagnification.

For rapidly degrading contaminants (that is, t1/2 = fast), the metabolites of the contaminant might have a larger impact on the environment than the parent contaminant. Therefore, it is necessary to assess the toxicity of the parent contaminant and to separately assess the toxicity and exposure pathways of the metabolites, as these can be markedly different from the parent contaminant. It would be preferable for metabolites to have their own EIL and/or SQG values. However, in practice, the number of EILs and/or SQGs for metabolites will be very limited due to a lack of knowledge of their toxicity and environmental fate.
Table 4. The properties (half-life t½; logarithm of the octanolwater partition coefficient log KOW; Henry's gas law constant H) used to assess the importance of the various exposure pathways for organic contaminants and the corresponding two most important routes
t½a      Log Kowb   H b  Exposure routes to be considered

Primary  Secondary
S        H          LM  Biomagnification                  Direct toxicity
S        H          H    Direct toxicity                   Biomagnification
S        L          LM  Direct toxicity                   Metabolites
S        L          H    Direct toxicity                   Metabolites
M or F   H          LM  Direct toxicity                   Metabolites
M or F   H          H    Direct toxicity                   Metabolites
M or F   L          LM  Direct toxicity                   Metabolites
M or F   L          H    Direct toxicity                   Metabolites

a. S = slow, M = moderately fast, F = fast. b. H = high, M = medium, L = low

2.3.2         Exposure pathway assessment for inorganic contaminants

2.3.2.1         Biomagnification
There is no straightforward physicochemical property of inorganics that will predict their biomagnification potential, unlike organic contaminants. In the past, the bioconcentration, bioaccumulation and biomagnification factors (BCF, BAF and BMF respectively) have been used for this purpose, but this is not appropriate (Luoma & Rainbow 2008). Unless there is clear evidence that an inorganic element does not biomagnify, it should be considered to biomagnify and therefore secondary poisoning should be considered when deriving the EIL and/or SQG for that contaminant. A preliminary list of inorganic elements that do and do not biomagnify is given in Table 5 below.
Table 5. A preliminary list of inorganics known to biomagnify or known to not biomagnify based on information in the literature.
Biomagnification status  Inorganic contaminants
Known to biomagnify      Cd, Hg (especially methyl forms), Se
Known to not biomagnify  As, Cu, Fe, Mg,  Pb, Zn

Only three biomagnification classes for inorganics should be used: known biomagnifiers, known non-biomagnifiers, and unknown biomagnifiers (which are then treated as biomagnifiers pending further investigation).

     2.3.2.2         Henry's law constant
Henry's law constant (H) is a measure of the volatility of the