Environmental Engineering Reference
In-Depth Information
Some of the TVs were derived by applying a factor of 10 to the lowest of at least three
acceptable multiple species tests. To derive moderate reliability TVs, when only acute
data for more than five species are available, a factor of 10 is applied before applying
the ACR. No justification for choosing a factor of 10 is given. Low reliability TVs are
derived by applying factors that range from 20 to 1000; larger factors are applied
when data sets are smaller or contain more acute than chronic data.
The Danish methodology utilizes the EU AFs for its AF method (Samsoe-
Petersen and Pedersen 1995); however, if the SSD method (that of Wagner and
Løkke 1991) is used, application of default ACRs to derive NOECs is not
allowed.
The South African methodology (Roux et al. 1996) follows that of the USEPA
(1985) very closely, except that the FAV is divided by one of several safety factors
(rather than 2) to derive the AEV. The FCV is calculated as in the USEPA guidance
(1985), but again, safety factors ranging from 1 to 1000 are applied to derive the
CEV. If no chronic data and no ACRs are available, a CEV is derived by multiplying
the FAV or the FPV by 1000. The FPV is the lowest result from a 96 hr algae test
or from a chronic test with a vascular plant.
AF, safety factor, application factor, ACR, and margin of safety are all terms that
refer to a value that is used as a multiplier for experimentally determined toxicity
values; the values described by these terms are all designed to account for the
uncertainty of using that experimentally derived number to predict real-world
outcomes. Chapman et al. (1998) reviewed the use of safety factors in ecological
risk assessment. They point out that, despite a lack of supporting data, standardized
factors of 0.1, 0.05, and 0.01 are used throughout the world in various regulatory
programs (often expressed inversely, i.e., 10, 20, and 100, for use as divisors). They
also note that safety factors are applied as policy to assure protection, rather than
being based on empirical science.
According to Irmer et al. (1995), factors used in derivation of German water
quality criteria were based on internationally accepted practices until 1992, when
political motivations limited factors to a total value of 0.01. The factor of 0.1 is
applied to extrapolate from lab, single-species tests, to field conditions; and a further
factor of 0.1 may be applied to protect against various uncertainties. Yet an addi-
tional acute-to-chronic factor of 0.1 may be applied, when chronic data are not
available. Irmer et al. (1995) argue that limiting the total applied safety factor to
0.01 results in weak water quality targets, because ACRs as high as 1000 are not
uncommon.
Factors used in preliminary effect assessment, in the Netherlands, are derived
from two sources. First, is the TGD for derivation of the PNEC (ECB 2003).
Second, is a USEPA (1984b) document cited by Van De Meent et al. (1990). A
more recent version of the same USEPA procedure is now available (Nabholz
1991). The TGD (ECB 2003) factors address the uncertainty associated with intra-
and interlaboratory variation in toxicity data, intra- and interspecies variations,
short- to long-term toxicity extrapolation and laboratory to field extrapolation
(which includes mixture effects). For each of these extrapolations, a factor (divisor)
of between 1 and 10 is applied, and if multiple extrapolations are required, then the
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