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EC number: 231-793-3
CAS number: 7733-02-0
A quality-screened database on the toxicity
of zinc towards freshwater and marine sediment-dwelling organisms has
been compiled from the Zn RAR (2008) and updated with newly retrieved
literature data (search 1995-2021). Evaluation of the study quality
followed the Klimisch scoring system, and only the toxicity data that
received a Klimisch score of 1 or 2 were considered relevant for the
derivation of the Predicted No Effect Concentration (PNEC) . Chronic
NOEC/EC10 values based on measured Zn concentrations for ecologically
relevant endpoints for risk assessment purposes (i.e. survival, growth
or reproduction) were retained. The available database of chronic
freshwater sediment toxicity tests for zinc provides information on
seven different species (single-species exposures) and two long-term
field colonization studies.
Chronic toxicity test results for the
freshwater compartment are available for the following sediment-dwelling
organisms representing different feeding habits and life strategies i.e.
the amphipods Hyalella azteca and Gammarus pulex, the
oligochaetes Tubifex tubifex and Lumbriculus variegatus,
the insect Chironomus dilutus, Epheron virgo and Hexagenia.
For the marine compartment an additional test result is available
for the amphipod Melita plumulosa .
Since several data for different taxonomic
groups are available, the ‘PNEC sediment’ was calculated using a
statistical extrapolation method, and a species sensitivity distribution
curve (SSD) was constructed both on the freshwater data set and on the
pooled freshwater/marine dataset. The PNEC sediment was derived from
the median Hazardous Concentration (5th percentile) of the SSD. As zinc
toxicity in sediments is mitigated by the presence of Acid Volatile
Sulfides (AVS) and organic carbon (OC), only the chronic toxicity data
obtained under conditions of low OC concentrations and low-to-median AVS
concentrations in the sediment were used (i.e maximizing bioava. Further
analysis showed that there is no need for applying an additional
assessment factor on the derived HC5-50 value due to the conservative
nature of the assessment. Consequently, the PNEC is set at the level of
the median HC5 value, which is considered as protective for EU
freshwater ecosystems resulting in a PNEC sediment of 146.9 mg/kg dry
wt. for the freshwater compartment and PNEC sediment of 162.2 mg/kg dry
wt. for the marine sediment compartment.
In the the overview is given of all chronic
values that are available. The underlined values have finally been used
and used as input values for the SSD for deriving the 5th
percentile as a basis for the derivation of the PNEC sediment. Please
note that data were not aggregated if several EC10/NOEC values were
available because not all tested sediments were worst case sediments.
The hexagenia datapoint was omitted from the analysis because
the sediment was not a realistic worst case sediment leaving 6 EC10/NOEC
values for six species. Including this data point would result in a
higher HC5 value (results not shown). This example highlights again that
only data obtained under the most conservative sediment conditions, were
used for the SSD.
Table 1: Summary of chronic values (those
underlined and in bold) that were used as input values for the SSD for
deriving the 5th percentile values as a basis for the PNEC freshwater
Only one EC10 value for the marine amphipod Melita
plumulosa was deemed appropriate to be included (Table 2).
Table 2: Species EC-10 values (total Zn) for
the most sensitive endpoint for all sediment dwelling organisms
If the long term marine and freshwater
sediments effect data are pooled a sediment effects dataset of seven EC10/NOEC
values for seven different species is available for zinc for the
sediment compartment (Table 3).
Table 3: Species EC10-NOEC values
(total Zn) for the most sensitive endpoint for all sediment dwelling
organisms (marine and freshwater data pooled; only those underlined and
in bold were used in the SSD)
more information, see the background document on environmental risk
assessment of zinc in sediment, attached to section 13 of IUCLID.
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