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EC number: 235-804-2
CAS number: 12767-90-7
Setting the PNECadd soil.
1. Sources of ecotoxicological data
In the EU risk assessment on zinc, an extensive analysis was made of the
available terrestrial toxicity data, available at that time (ECB 2008).
The data were carefully scrutinised for quality and relevancy by the
Rapporteur and member states. In the present exercise, all data that
were considered useful for deriving the PNEC soil in the risk
assessment, are used. In addition, an update of the terrestrial toxicity
data that became available after the closure of the EU RA, has been
made. Based on this update, the PNEC derivation for Zn in soils has been
revised. This PNEC derivation is now based on the data and
bioavailability models presented in the Risk Assessment Report (RAR) for
Zn under the existing substances regulation, the comments of the SCHER
on this RAR and new reliable data not yet included in the RAR.
All toxicity data judged reliable and relevant in the RAR for Zn are
included (171 NOEC or EC10 values). On March 2 2010, an additional
literature search was performed covering the scientific literature since
2000 for new reliable toxicity data for Zn on terrestrial organisms
(plants, invertebrates and micro-organisms). This new data search
resulted in 43 new NOEC or EC10 values.
2. Selection of ecotoxicological data
The toxicity data on invertebrates and plants are from single-species
tests that study common ecotoxicological parameters such as survival,
growth and/or reproduction. The toxicity data on micro-organisms are
from tests in which microbe-mediated soil processes, such as C- and N-
mineralisation were studied. These microbial toxicity tests are multiple
species tests because these microbe-mediated processes reflect the
action of many species in soil microbial communities.
The toxicity data on terrestrial organisms are from ecotoxicity tests
that study relevant ecotoxicological parameters such as survival,
growth, reproduction, litter breakdown, abundance. Relevant endpoints
for soil micro-organisms focused on functional parameters (such as
respiration, nitrification, mineralisation) and microbial growth, but
also enzymatic processes are considered relevant.
Relevancy of the test media
Only data from observations in natural and artificial (OECD) soil media
have been used in this report, tests performed in substrates that were
judged as not representative for soils (e.g. nutrient solution, agar,
pure quartz sand and farmyard manure) were not included in this effects
The data used in the effect assessment should be based on organisms and
exposure conditions relevant for Europe. Excluding all data derived in
non-EU soils would, however, considerably reduce the amount of data to
be used. Therefore, also data based on soils collected outside Europe
have been used when the soil properties were within the representative
range for Europe.
What comprises “chronic exposure” is a function of the life cycle of the
test organisms. A priori fixed exposure durations are therefore not
relevant. The duration should be related to the typical life cycle and
should ideally encompass the entire life cycle or, for longer-lived
species the most sensitive life stage. Retained exposure durations
should also be related to recommendations from standard ecotoxicity
(e.g. ISO, OECD, ASTM) protocols.
Typically chronic test duration for the higher plants are within the
range of 4 (e.g. the barley root elongation test based on ISO 11269-1
(1995)) and 21 days (e.g. the tomato shoot yield test based on ISO
11269-2 (1995)). OECD n° 208 (plant seedling emergence and growth test,
1984) recommended a test duration of at least 14 days after emergence of
the seedlings. For soil invertebrates, assessing the chronic effects of
substances on sub-lethal endpoints such as reproduction on oligochaetes
has a typical exposure duration of 3 to 6 weeks for the standard
organism Enchytraeus albidus (OECD, 2000; ISO 16387). For another
standard species Folsomia candida survival and reproduction is
typically assessed after 28 days of exposure (ISO 11267, 1999). Reported
test duration using soil micro-organisms vary largely but standard tests
last 28 days for carbon transformation (OECD n° 216) and for nitrogen
transformation (OECD n° 217).
Type of test
Both standard test organisms and non-standard species can be used in the
framework of a risk assessment. In general, toxicity data generated from
standardized tests, as prescribed by organizations such as OECD and
USEPA will need less scrutiny than non-standardized test data, which
will require a more thorough check on their compliance with reliability
criteria before being used. GLP and non-GLP tests can be used provided
that the latter fulfil the stipulated requirements.
Because effect concentrations are statistically derived values,
information concerning the statistics should be used as a criterion for
data selection. If no methodology is reported or if values are
‘visually’ derived, the data were considered unreliable. Effect levels
derived from toxicity tests using only 1 test concentration always
results in unbounded and therefore unreliable data. Therefore, only the
results from toxicity tests using 1 control and at least 2 Zn
concentrations were retained.
Tests that do not comply with the above-mentioned stipulations are rated
as not reliable and are not recommended for use in the risk assessment
3. Derivation of EC10/NOEC values
According to the REACH Guidance on information requirements and chemical
safety assessment (Chapter R.10.2.2.1), there is a preference to use
EC10 values as calculated from the concentration-effect relationship,
for derivation of the Predicted No Effect Concentration (PNEC). In some
cases no reliable EC10 can be derived because e.g. no significant
dose-response curve can be fitted or the EC10 is outside the
concentration range tested. When in these cases a bounded NOEC value can
be derived, this NOEC value will be used instead of the EC10 for PNEC
derivation. No unbounded NOEC (i.e. no effect at highest dose tested) or
LOEC (i.e. significant effect at lowest dose tested) values or EC10
values extrapolated outside the concentration range tested are used for
derivation of the PNEC.
4. Toxicity data
In accordance to the EU RA, all toxicity data are expressed as added Zn
concentration in soil, based on either the nominal dose added or on
measured, background corrected soil Zn concentrations.
For plants, in total 45 individual high quality NOEC or EC10 values are
selected for the PNEC derivation, representing 18 different species.
NOEC or EC10 values vary from 32 mg Zn/kg dw for Trifolium pratense and
Vicia sativa (Van der Hoeven and Henzen, 1994) to 5855 mg Zn/kg
dw for Triticum aestivum (Warne et al., 2008a).
Information on soil properties allowing bioavailability correction for
plants (eCEC and pH) is only available for 31 NOEC or EC10 values,
representing 9 different plant species and including the same minimum
and maximum values as the total dataset for plants.
In total 61 individual high quality NOEC or EC10 values for reproduction
of terrestrial invertebrates are selected for the PNEC derivation.
Twenty-four NOEC/EC10 values are available for toxicity of Zn to
reproduction of terrestrial arthropods, representing 2 different species
and ranging between 14.6 and 1000 mg Zn/kg dw (both for Folsomia
candida; Lock and Janssen, 2001c and Lock et al., 2003). The
other 37 NOEC or EC10 values cover 6 different worm species and vary
from 35.7 mg Zn/kg for Enchytraeus albidus (Lock and Janssen,
2001c) to 1634 mg Zn/kg dw for Lumbricus terrestris (Spurgeon et
For all 61 reliable toxicity thresholds, the information on soil
properties allowing bioavailability correction for plants (eCEC) is
For microbial assays, in total 108 individual high quality NOEC/EC10’s
are selected for the PNEC derivation. These values represent 4 nitrogen
transformation processes, 5 carbon transformation processes and 8
enzymatic processes and range from 17 mg Zn/kg dw for respiration (Chang
and Broadbent, 1981 and Lighthart et al., 1983) to 2623 mg Zn/kg dw for
phosphatase (Doelman and Haanstra, 1989).
Information on the background Zn concentration, allowing correction for
differences in bioavailability among soils, is only available for 76
NOEC or EC10 values, representing 13 microbial processes (4 for N cycle,
5 for C cycle and 4 enzymatic processes). The total range in NOEC/EC10
values for the dataset with results for background Zn concentration is
the same as for the total dataset for micro-organisms.
5. Calculation of the HC5-50
The available ecotoxicity database for the effect of Zn to soil
organisms is large. Therefore, the use of the statistical extrapolation
method is –as specified by the Guidance document on information
requirements and chemical safety assessment Chapter R.10.3.1.3–
preferred for PNEC derivation rather than the use of an assessment
factor on the lowest NOEC. The PNEC will be based on the 50% confidence
value of the 5th percentile value (HC5-50) and an additional assessment
factor taking into account the uncertainty on the HC5-50 (thus PNEC =
5.1. Generic, non-normalised HC5-50
The non-normalised terrestrial HC5-50 was derived based on either all
individual reliable NOEC/EC10 values or the species mean NOEC/EC10
values for the most sensitive endpoint. The generic PNEC was derived
from using all data. For comparison, distributions where only the data
that could be normalised for bioavailability, were also made.
It must be stressed that, considering the important influence of soil
properties on bioavailability and toxicity of zinc in soils, the
non-normalised HC5-50 is less ecologically relevant compared to the
HC5-50 values taking into account correction for bioavailability (both
ageing and effect of variation in soil properties). The cumulative
frequency distribution (SSD) of the non-normalised species mean NOEC
values for Zn is presented in the CSR.
Using statistical extrapolation and the log-normal distribution results
in a HC5-50 of 35.6 mg Zn/kg based on all individual NOEC/EC10 data and
a HC5-50 of 33.7 mg Zn/kg when using all individual NOEC/EC10 data with
information on soil properties allowing correction for bioavailability
among soils (Table 1). Based on the Anderson-Darling goodness-of-fit
statistics, the log-normal distribution is accepted for all
distributions based on both all individual reliable observations and the
species/process mean values.
Table 1:Generic HC5 and HC5-50 (with 5% and 95% confidence
interval) values for toxicity of Zn to the terrestrial environment based
on a log-normal distribution of non-normalised NOEC/EC10addedvalues.
All individual NOEC/EC10 values
Species/process mean values
Data allowing bioavailability correction
Using a species/process mean approach for non-normalised data yields
higher HC5-50 values compared to SSD based on all individual values:
51.3 and 35.8 mg Zn/kg for the total dataset or the data with
information on soil properties allowing correction for bioavailability
among soils, respectively. Averaging (geomean) all the results available
for one species/process avoids over-representation of commonly tested
species or processes, e.g.Eisenia fetida (29 data) or
nitrification (20 data). This species/process mean approach is preferred
for data corrected for the differences in soil properties when the
intra-species variation can be considered as the main source of
variation among data for a given species/process. However, this is not
the case for the generic approach (non-normalised data) where variation
between toxicity data for a certain species or process is also caused by
differences in bioavailability among soils.
Table 2:Generic species/process mean values.
Glutamic acid mineralization
Vigna mungo L.
Trigonella poenum graceum
Maize residue mineralization
There is no clear distinction among the three trophic levels (plants,
invertebrates and micro-organisms) in their sensitivity to Zn in soil
(Table 2). Both individual and species/process mean toxicity data for
the various plant and invertebrates species and microbial processes
strongly overlap (see CSR for figures). Therefore, all data are pooled
together into one species sensitivity distribution for the derivation of
the PNEC value. In this respect, it is also noted that the EU Scientific
Committee for Health and Environmental Risks (SCHER) also recommended to
merge the different data sets obtained on plants, arthropods, and
microbial functions, respectively (SCHER 2007).
For 46 NOEC or EC10 values, no information is available on soil
properties allowing correction for differences in bioavailability among
soils (CEC and pH for plants and background Zn concentration for
microbial processes). The toxicity data with information on these soil
properties available cover 30 species/processes compared to a total of
43 for the total dataset. Toxicity data for 9 plant species and 4
microbial processes (all enzymatic processes) do not have information on
the soil properties required. The reduced dataset however still covers
the same extreme values (both minimum and maximum) as the total dataset
(Table 2). The HC5-50 values as calculated from a log-normal
distribution are consistently lower for the reduced dataset compared to
the total dataset (both based on all individual values as based on
species/process mean values, Table 1). It can therefore be concluded
that the dataset with information on soil properties is both
representative for the total dataset and conservative for the assessment
of toxicity of Zn to terrestrial organisms.
6. PNECadd soil
Based on an extensive uncertainty analysis (CSR), and in particular the
availability of normalisation models (CSR), a large toxicity database
covering a representative range in plant and invertebrate species,
microbial processes and soil conditions, and an extensive field
validation, it can be concluded that the available database and models
allow for the derivation of an HC5-50 that is protective for the
terrestrial environment by statistical extrapolation.
3 types of PNECadd soil can be considered:
- The generic PNECadd based on the entire ecotoxicity
database is 35.6 mg Zn/kg.
-The generic PNECadd
can (in accordance with the EU risk assessment) be
multiplied with a default “lab-to-field” correction factor of 3 for
taking into account differences of zinc bioavailability after ageing
(generic PNECadd including ageing= 107mg/kg
-If information on soil type and soil conditions is available, a
soil-specific PNECaddedcan be calculated, by applying a
further correction for bioavailability. A tool is available for this.
For illustration, some examples were developed in the present analysis
resulting in PNECaddedvalues for soil types representative
for the EU conditions between approx. 30 and 300mg Zn/kg.
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