Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p14
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 14/21)
Character Range: 1381336–1384514

is not available, then CCME (1991) and the US EPA (1986) use a generic ACR. CCME (1991) uses an ACR of 2 or 10 depending on the environmental persistence of the contaminant, while the modified (OECD 1995) and unmodified US EPA (1986) methods use one generic ACR of 10.

However, an acute-to-chronic extrapolation is not used in soil guideline value derivation. An acute-to-chronic extrapolation should only be used for short-term contact exposure studies. Such tests are a very short-term acute toxicity test performed on direct dermal contact using earthworms, which might not represent exposure in soils accurately. The test will very likely give toxicity values that are an underestimation of chronic exposure toxicity data.

Most AF methods used in most jurisdictions have minimum data requirements. When these are not met then an interspecies extrapolation is used. This is used because there is increased uncertainty in deriving guideline values from such a small sample size.
Table 18. The assessment factors, types and magnitudes of the extrapolations used in the modified US EPA and CCME methods
Available toxicity data        Type of extrapolation                                      Modified US EPA methoda  CCME methodb
Chronic NOEC (for the US EPA)  Field-to-laboratory                                        10                       10
or LOEC (for CCME)
Acute LC50 or EC50             Field-to-laboratory and acute-to-chronic                   100                      ACR or
                                                                                          (10 x 10)                20 or 100c
Acute LC50 or EC50 for one     Field-to-laboratory and acute-to-chronic and interspecies  1000                     ACR or
or two species                                                                            (10 x 10 x 10)           20 or 100d

a It is assumed toxicity data is available for at least an algae, a crustacean and a fish (OECD 1992).
b Assumes that toxicity data is available for at least three species of fish, of which two must be chronic; two invertebrates, one of which should be planktonic; and a freshwater vascular plant or algae (CCME 1991).
c An AF of 50 is used for non-persistent contaminants while 100 is used for persistent contaminants when no ACR is available.
d Where data is not sufficient to meet the requirements set in b, then interim WQGs are derived (CCME, 1991).

3.2.3.1         Criticisms
Criticisms of the AF approach revolve around the scientific validity of AFs, the magnitude of the AFs, and whether or not the method is consistent with a risk framework and the principle of ecologically sustainable development. Many scientists and organisations have acknowledged the arbitrary nature of AFs, that they have no theoretical scientific basis and are purely empirical (Hart 1974; Nicholson 1984; Kooijmand 1987; Okkerman et al. 1991; OECD 1992; Schudoma 1994; Rand et al. 1995; OECD 1995; Warne 1998). Goldberg (1975) asserted that using AFs was tantamount to admitting that information essential for risk assessments was lacking.

Nicholson (1984) considered that:
'There is little scientific basis for application