Environmental Engineering Reference
In-Depth Information
or more flow-through tests, in which toxicant concentrations were measured, but if
no such data are available, then data from static or static-renewal tests with nominal
toxicant concentrations are used. The same procedure applies to chronic data.
Chronic values are calculated from the geometric means of NOEC and LOEC values
(i.e., MATC values), or from a value derived by regression analysis (with no indica-
tion of whether to use an EC 5 , EC 10 , EC 25 , or other EC x value). The South African
guidelines follow the USEPA procedure for data reduction (Roux et al. 1996), but
specify that only chronic MATCs are to be used for criteria derivation.
The Dutch methodology offers very clear instructions regarding preliminary
data processing (RIVM 2001). For a given substance, if several study results are
available for one species for the same endpoint, then the geometric mean of
these values is used. If study data are available for one species, but have multiple
endpoints, then the values for the most sensitive endpoint are used. If data are avail-
able for multiple life stages of one species, then data from the most sensitive life
stage are used. All acceptable chronic toxicity data are converted into NOEC
values, as follows (RIVM 2001):
- The highest reported concentration not statistically different from the control
(p < 0.05) is the NOEC.
- The highest concentration showing 10% effect, or less is considered the NOEC
if statistical evaluation is not possible.
- A reported LOEC is converted to an NOEC by use of factors (factors may be
adjusted if justified by data):
- NOEC = LOEC/2 for cases where: 10% effect <LOEC <20% effect.
- NOEC = EC 10 for cases where: LOEC ≥20% effect and dose-response relation-
ship is available.
- NOEC = LOEC/3 for cases where: 20% <LOEC <50% effect.
- NOEC = LOEC/10 for cases where: 50≤ LOEC ≤80% effect.
- NOEC is reported as ≥ [highest observed no-effect concentration] if none of the
treatment groups was significantly different from the control; these values are
not used in statistical extrapolation methods.
- “Toxic Threshold” values, as defined by Bringmann and Kühn (1977) are
regarded as NOECs.
- For a MATC expressed as a range of values, the NOEC is the lower value; for
MATC expressed as a single value, the NOEC = MATC/2.
- NOEC values expressed as total concentrations in water are converted to dis-
solved concentrations, if the K p and concentration of particulate matter are known.
Further data processing is required by the Dutch methodology (RIVM 2001) if
toxicity data for a particular toxicant appear to be bimodally distributed; in this
case, statistical analysis must be performed to determine if the apparent differences
are significant. This requirement would apply to differences between, for example,
freshwater and saltwater species. If the differences are not significant, then the data
are combined for criteria derivation. If the differences are significant, then separate
criteria must be developed.
Search WWH ::




Custom Search