Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:2:p9
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 2 (pt 9/15)
Character Range: 1274355–1277260

values to be used in assessing the importance of the various exposure pathways for organic contaminants
Henry's constant value  Classification
(cm3 air/cm3 solution)
 >2.5 x 10 -3           Highly volatile (H)
2.5 x 10-72.5 x 10 -5  Moderately volatile (M)
<2.5 x 10 -7            Not volatile (L)

2.3.1.3         Octanol-water partition
The octanolwater partition (Kow) is the ratio of the concentration of a contaminant that is dissolved in n-octanol to that dissolved in water at equilibrium and at a specified temperature. It is used as a surrogate to estimate the potential for contaminants to accumulate in tissue, both plant and animal (Connell 1989, Posthumus & Slooff 2001). The Kow values can often be so large that the values are usually expressed as the logarithm to base 10 (that is, log Kow). Contaminants with high log Kow values are more likely to accumulate in plants and soil invertebrates than contaminants with low Kow values (Connell 1989, Posthumus & Slooff 2001). If further magnification of these contaminants occurs in the food chain, the predators might experience toxicity while its prey does not. This effect is known as secondary poisoning.

Contaminants with log Kow values below 4 are not considered to biomagnify, while highly fat soluble, lipophilic contaminants with log Kow values equal to or greater than 4 are most likely to biomagnify. For most contaminants, it is expected that metabolism, excretion and degradation rates exceed the bioaccumulation rates at concentrations equivalent to the trigger values for protecting aquatic ecosystems (ANZECC & ARMCANZ 2000). Hence, only for contaminants with log Kow values equal to or greater than 4 should secondary poisoning be considered. This approach is also consistent with the starting point to consider biomagnification used in the Australian and New Zealand WQGs (ANZECC & ARMCANZ 2000).

For the purpose of this methodology, the log Kow values of contaminants are divided into two classes. These are:
    * low, log Kow <4: the contaminant has a low potential to biomagnify
    * high, log Kow ≥ 4: the contaminant has a high potential to biomagnify.

2.3.1.4         Overview of the main exposure pathways for organic contaminants
Table 4 below presents the various combinations of the three physicochemical properties of organic contaminants described above and the resulting two exposure routes that are considered the most important for deriving EILs and/or SQGs.

Slowly degrading contaminants (that is, t1/2 = slow, Table 2) with high log Kow values and low H will have biomagnification as the most important exposure pathway followed 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