technical guidance documents - Institute for Health and Consumer ...

EFFECTS ASSESSMENT
ecotoxicological tests for hazard assessment of chemicals for the soil compartment is not
currently available.
Reference can be made to Section 6.3.4 and an OECD project in which a testing strategy for
terrestrial ecosystems is being developed (Léon and Van Gestel, 1994). In summary, the
assessment factors proposed in Table 20 must be regarded as indicative. As more information on
the sensitivity of soil organisms becomes available these factors may have to be revised.
Table 20 Assessment factors for derivation of PNECsoil
Information available Assessment factor
L(E)C50 short-term toxicity test(s) (e.g. plants, earthworms, or microorganisms) 1000
NOEC for one long-term toxicity test (e.g. plants) 100
NOEC for additional long-term toxicity tests of two trophic levels 50
NOEC for additional long-term toxicity tests for three species of three trophic levels 10
Species sensitivity distribution (SSD method)
118
5 – 1, to be fully justified on a case-by-case
basis (cf. main text)
Field data/data of model ecosystems case-by-case
A PNECsoil is calculated on the basis of the lowest determined effect concentration. If results
from short-term tests with a producer, a consumer and/or a decomposer are available, the result
is divided by a factor of 1000 to calculate the PNECsoil. If only one terrestrial test result is
available (earthworms or plants), the risk assessment should be performed both of this test result
and on the basis of the outcome of the aquatic toxicity data to provide an indication of the risk.
As a matter of precaution, the larger PECsoil/PNECsoil ratio determines which further actions
should be taken in the framework of the further testing strategy. If additional soil test results are
available the assessment factors given in Table 20 should be applied.
3.6.2.3 Calculation of PNEC using statistical extrapolation techniques
Calculation of a PNECsoil using statistical extrapolation techniques can be considered when
sufficient data are available (see Section 3.3.1.2. for minumum requirements). For comparable
data on the same end-point and species, by default the geometric mean should be used as the
input value for the calculation of the species sensitivity distribution. When results are available
from tests using different soils and it is likely that the soil characteristics have influence on the
results, the effect data should be normalised before further processing. If not possible, the lowest
NOEC per end-point and species should be used. Data on microbial mediated processes and
single species tests should be considered separately due to fundamental differences between
these tests (functional vs. structural test, multi-species vs. single species, adapted indigenous
microbe community vs. laboratory test species, variability of test design and different endpoints,
etc.). The results should be compared and evaluated on a case-by-case basis in deciding on a
final PNEC for the soil compartment.
The approach of statistical extrapolation is still under debate and needs further validation.