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EC number: 231-901-9
CAS number: 7778-39-4
The lowest reliable chronic data in the
saltwater database are for the marine diatom Skeletonema costatum,
with LOECs of 13 µg/l for As (V) (it was not possible to derive a NOEC
or an LC10 from the data reported in the study references). This study
was based on measured exposure concentrations in a static system and was
regarded as suitable for PNEC derivation. In addition, data for the
macroalga Fucus serratus indicate a growth and mortality related
NOEC of 20 µg/l As(V) . This datapoint was generated in a flow-through
study with measured exposure concentrations and is reliable for PNEC
Reliable chronic effects values for marine
invertebrates are much higher than those reported for algae. However,
there is one 48-hour test on sea urchin embryo development that may be
considered as an early life stage (ELS) test rather than anacute test;
this reported a LOEC of 11 µg l -1 As(V) for development of embryos of
the sea urchin Strongylocentrosus purpuratus. On the basis of the data
reported, it was possible to derive an EC10 of 6 µg/l and an EC50 of 15
µg/l. This study was based on nominal concentrations, but was regarded
as valid for PNEC derivation because in
studies where nominal concentrations of
arsenic have been compared with measured concentrations they have been
found to be almost identical .
Only limited fish data were available.
For some acute effects, the lowest reported
values are in the same range as the lowest chronic data, i.e. the
120-hour EC50 for the alga Skeletonema costatum of 9 µg/l As(V) and the
96-hour LC50 of the crustacean Tigriopus brevicornis of 11 µg/l As(V).
Following the given in the TGD for marine
risk assessment, this situation (in which the lowest acute effect values
are as low as the lowest chronic values) requires the use of an
assessment factor of 1,000 on the lowest acute value. However, as it is
not possible to gain access to the background documentation for the
Skeletonema acute EC50 of 9 µg/l in the original reference, the validity
of this test result is not
assignable. The other references have been
evaluated and are considered reliable.
Based on the other data, the saltwater acute
to chronic ratios for arsenic appear to be low, suggesting that only a
small assessment factor would be required to extrapolate from an effects
concentration to a no-effect concentration. In addition, long-term NOECs
for more than three marine species representing three trophic levels
(i.e. algae, crustaceans, echinoderms and molluscs) plus acute data for
a further marine
group (annelids) are available.
Consequently, it is recommended that the PNEC add,saltwater_lt is based
on the lowest available EC10 of 6 µg/l reported by Garman et al. and an
assessment factor of 10:
PNEC add,saltwater_lt = 6 µg/l /AF (10) =
0.6 µg/l arsenic (dissolved)
Long-term PNEC for saltwaters
Similar toxicities (expressed as LOECs) are
seen in studies with the marine diatom, Skeletonema costatum, for
As(III) and As(V) (10 and 13 µg/l , respectively). Although most
invertebrates are less sensitive, embryo development in the sea urchin
Strongylocentrosus purpuratus was impaired after 48-hour exposure to
As(V). This gave rise to a LOEC of 11 µg/l, but it was not possible to
estimate a NOEC from this study. Subsequent re-analysis of the study
data gave an EC50 of 15 µg/l and an EC10 (considered equivalent to a
NOEC) of 6 µg/l. Given the availability
of data for other trophic levels, an assessment factor of 10 applied to
this EC10 is recommended, leading to a PNEC saltwater_long-term of 0.6
µg/l arsenic (dissolved).
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