Registration Dossier

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
0.021 µg/L
Assessment factor:
1 000
Extrapolation method:
assessment factor
PNEC freshwater (intermittent releases):
0.2 µg/L

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
0.021 µg/L
Assessment factor:
1 000
Extrapolation method:
assessment factor

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
0.01 mg/L
Assessment factor:
1 000
Extrapolation method:
assessment factor

Sediment (freshwater)

Hazard assessment conclusion:
no data available: testing technically not feasible

Sediment (marine water)

Hazard assessment conclusion:
no data available: testing technically not feasible

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
no data available: testing technically not feasible

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

Chorine dioxide

A complete set of freshwater acute studies are available for chlorine dioxide. As no chronic data are available a standard assessment factor of 1000 is placed on the lowest EC50 of 0.02 mg/L in freshwater fish.

For the marine PNEC, further acute studies on marine organisms are available supporting the conclusion that the toxicity to freshwater and marine fish is the same and that other marine Phyla, such as Echinoderms or macrophytes, do not appear to be more sensitive to chlorine dioxide than freshwater organisms and therefore the supplementary factor of 10 placed on marine organisms has been waived. The assessment factor is therefore 1000 placed on the lowest LC50 of 0.02 mg/L in freshwater fish.

No further studies are available to determine PNECs on sediment or soil experimentally.

Due to the ephemeral nature of the substance, no chlorine dioxide is expected to be present outside of the wastewater treatment plants. Chlorine dioxide is known to degrade extremely rapidly to chlorite and chlorate and ultimately to chloride. For this reason, key ecotoxicological data on chlorite and chlorate have been included as full robust summaries in the dossier such that their respective environmental risks can be considered in this CSR.

Chlorite

For chlorite, short term data are available for fish daphnids and algae. Further data are also available on marine organisms. The most sensitive species is Daphnia magna with a 48 h EC50 of 0.063 mg/L. Algae are less sensitive with an ErC50 of greater than or equal to 0.15 mg/L depending on the species and the least sensitive species tested is fish with toxicity values of >55 mg/L in all species tested, freshwater and marine. Due to the large difference in sensitivity between species, and the low log Kow of chlorite such that bioaccumulation is not expected, a long term fish study is not considered necessary as part of a chronic dataset to provide the PNEC for chlorite.

Chronic data for PNEC derivation for chlorite

The lowest endpoint value obtained and used to calculate the PNEC aquatic for freshwater is a chronic NOEC of 0.015 mg/L based on reproductive output, parental body weight and length. An assessment factor of 10 is applied to this value to provide a PNEC of 0.0015 mg/L. Several marine acute data are available on marine Phyla such as molluscs as well as on marine fish, crustaceans and algae and no endpoint values were found to be lower than those for the acute daphnid study. For this reason, the supplementary factor of 10 normally applied to obtain a PNECmarine has been waived and the PNECmarine is taken as 0.0015 mg/L.

PNEC sediment and soil have not been determined for this substance as chlorite is both an inorganic chemical, for which a log Kow determination is not normally considered necessary and also experimental evidence has shown that it is rapidly (seconds to minutes) abiotically degraded on contact with a host of substances including organic matter and any reducing agents (e.g. ferric compounds) readily available in the sediment and soil.

Chlorate

Multiple acute studies are available on chlorate. Chlorate is not acutely toxic to Freshwater or marine fish, invertebrates at concentrations up to 1000 mg/L. For algae toxicity no effects were found above 100 mg/L in any Guideline study on unicellular algae. While some effects have been found under certain experimental conditions, this has been due to the nitrate concentration used in the test medium as nitrate is a competitive inhibitor for chlorate and its presence greatly reduces chlorate toxicity. Marine Guideline studies using standard marine media do not find higher toxicity of chlorate to marine unicellular algae than freshwater species.

Chronic data for PNEC derivation of chlorate

Chronic data exist for fish invertebrates and algae. For fish and algae, no effects were found up to the maximum concentration tested of 500 mg/L (as sodium chlorate). However, a NOEC concentration of 10 mg/L based on frond growth, biomass and growth rate was found in a 7-day study on Lemna minor considered as long term. This study has been used to derive the PNEC aquatic for chlorate. An assessment factor of 10 has been added to this NOEC in order to derive a PNEC of 1 mg/L (as sodium chlorate). As several guideline marine studies on molluscs as well as fish, crustacean and algae are available, the supplementary factor of 10 to cover uncertainty of extrapolation from freshwater to the marine environment has been waived to derive a PNEC marine of 1 mg/L (as sodium chlorate).

In this case, and despite the fact that chlorate is an inorganic substance, it is expected to be less ephemeral in the aquatic environment with measured half-lives in the order of days to weeks. Moreover, a log Kow has been determined experimentally for the salt, sodium chlorate and this has been used to derive PEC value in the Chemical safety report. In the absence of sediment studies it is possible to derive a Freshwater and Marine PNEC sediment.

The PNEC sediment for both freshwater and marine compartments is 3.6 mg/kg dwt.The PNEC soil is taken as 3.3 mg/kg dwt and the PNEC STP as 100 based on a 3h Activated Sludge Respiration Inhibition EC50 study which found no effects at 1000 mg/L, the highest concentration tested.

Conclusion

While several PNECs can be determined from existing data, their relevance for risk assessment purposes needs to be examined. Chlorine dioxide will not be present at any concentration in the environment and a PNEC for this substance is not relevant for risk assessment;

Chlorite, a degradation product of chlorine dioxide, may be present for short periods of time but degrades within minutes in the aquatic compartment and will not be found in sediment or soil. Relevant PNECs are therefore restricted to 1.5 µg/L for both freshwater and marine aquatic compartments;

Chlorate, a degradation product of chlorine dioxide and chlorite, may be found in all compartments although concentrations in sediment and soil are expected to be relatively low due to its low log Kow and rapid degradation under less aerobic conditions. PNECS based on experimental data are available for STP (100 mg/L), freshwater (1 mg/L), marine water (1 mg/L) and soil organisms (3.3 mg/L). PNECs derived from the Partition equilibrium method are available for marine and freshwater sediment (3.6 mg/L).

Conclusion on classification

Chlorine dioxide is highly toxic to aquatic organisms with an EC50<1 mg/L but degrades within minutes when placed in contact with environmental media. Moreover, it has a log Kow < 4. This is consistent with the harmonised classification as Acute 1 but not as chronic according to CLP criteria.

Based on the M factor of 10, aqueous solutions as registered, i.e. maximum 2% will NOT require any classification for aquatic environment.