1,1-difluoroethane

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.048 mg/L

Assessment factor:

1 000

PNEC freshwater (intermittent releases):

0.48 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.005 mg/L

Assessment factor:

10 000

STP

Hazard assessment conclusion:

no emission to STP expected

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.19 mg/kg sediment dw

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.019 mg/kg sediment dw

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.141 mg/kg soil dw

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Conclusion on classification

The substance is a gas under relevant environmental conditions with a vapor pressure of 514624 Pa at 25°C. Given the physical state of the substance and its physical-chemical properties reported in the dossier, there are no relevant pathways for entry of the substance into the aquatic environment. The substance does not meet the CLP criteria for acute classification which are based solely on the acute hazard of the substance. 

The chronic aquatic classification criteria under CLP recognize that potential for exposure mitigates the need for chronic aquatic classification, “i.e., Part 4. Environmental Hazards, 4.1.1.1 Definitions, (g) “chronic aquatic toxicity” means the intrinsic property of a substance to cause adverse effects to aquatic organisms during aquatic exposures which are determined in relation to the life-cycle of the organism.”

The inference from the underlined text above is that the importance of chronic classification is related to the potential for chronic environmental exposure and there must be a possibility of chronic exposure to make a chronic classification meaningful. Based on the physical form of the substance and its vapour pressure, it is unlikely that aquatic organisms in the ambient environment could be exposed to the substance for periods of time sufficient to cause chronic toxicity.

In the absence of chronic toxicity data for the substance, acute toxicity data and environmental fate data (degradability and bioaccumulation data) are considered for classification. In this situation, degradability is a surrogate indicating the potential for chronic, long-term exposure in the aquatic compartment. The observation that extraordinary measures must be taken in attempts to maintain even minimal test concentrations during acute aquatic testing of analog compounds also indicates the unlikely nature of aqueous exposures of the substance sufficient to cause chronic toxicity.

As a gas under relevant environmental conditions, the substance also has a very large vapour pressure and analogously a high Henry’s law constant. Although volatilization is not a “degradation” mechanism per se, it is a mechanism that for the substance in question limits potential for both acute and chronic exposure since it would quickly remove the substance from water.

The reported acute toxicity endpoint for the substance, an estimated 96-hour EC₅₀ based on biomass, was estimated using ECOSAR ver 1.0. An estimated growth rate 72-hour EC₅₀ (the typical endpoint based on the relevant OECD TG 201 acute exposure period and regulatory endpoint) would undoubtedly yield a larger (less toxic) EC₅₀ value since the biomass endpoint is always more sensitive (but less ecologically relevant) than the growth rate endpoint.

The role of ECOSAR for characterising the aquatic toxicity to algae was that of supporting information rather than a replacement value owing to the uncertainty in the point estimate. While, in general, halogenated alkanes were reasonably predicted and examples of chlorinated alkanes served to demonstrate the validity of the ECOSAR model, it was specifically noted in the QPRF that fluorinated alkanes were vastly overestimated in terms of their toxicity. Thus relying on the predicted EC₅₀ value alone would have resulted in an extremely conservative evaluation of aquatic toxicity to algae that was inconsistent with the two fluorinated analogues that had been identified with experimental data. Furthermore, the log Kow as estimated by KOWWIN that was used as input for the prediction in ECOSAR was also an overprediction of the log Kow. Experimental data that had been identified in the SRC database (as noted in the associated QPRFs) indicated that the measured log Kow was 0.75 rather than the 1.13 that had been estimated by KOWWIN v1.67. The variation in log Kow and how this can impact the aquatic profile was described in the QPRF to provide additional context for the interpretation of the estimated EC₅₀ value. Furthermore, since the time of original submission, the ECOSAR suite has evolved and, in particular, revisions have been made to the neutral organics algae model. If ECOSAR v1.1 were to be used to re-derive the same values, the estimated 96-hour biomass EC₅₀ (using the estimated log Kow of 1.13) would be 91.6 mg/L while using the empirical log Kow of 0.75 the 96-hour biomass EC₅₀ would be 168.3 mg/L. Thus it is evident that small changes in log Kow can result in significant changes in toxicity and the newer version of ECOSAR results in substantial differences in the predicted 96-hour biomass EC₅₀s. The version of ECOSAR v1.0 used for characterising algae toxicity was used in the absence of other tools at the time and gave rise to a highly conservative estimate for the substance that was not aligned with the expected values based on other fluorinated alkanes. Thus the scientific confidence in the use of this estimated value as the sole piece of evidence to characterise aquatic toxicity to algae was considered insufficient for use, whilst relying on the ECOSAR estimate as a piece of evidence in an overall approach of characterising toxicity was considered reasonable.

As a final point, the REACH document,Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7b: Endpoint Specific Guidance, November 2012; pp. 197-198, contains the following information that is pertinent to the classification of substances that are gases under environmental conditions.

“VOLATILISATION

Chemicals may be removed from some aquatic environments by volatilisation. In general these data do not represent degradation and are not used in classification. The reason is that the degree of volatilisation from the aquatic environment is highly dependent on the environmental conditions ofthe specific water body in question, such as the depth and the gas exchange coefficients (depending on wind speed and water flow). In general, therefore, the Henry's Law constant cannot be used for assessment of the degradation (here removal of a chemical from the water phase) in relation to aquatic hazard classification of substances.However, substances that are gases at ambient temperature may be exempted from this general recommendation.”

 

Based on the information above and exposure-based waiving of chronic aquatic and microbial respiration testing due to physical-chemical properties of the substance and the lack of exposure to relevant environmental compartments, and the not P and not vP classifications in the PBT assessment (i.e., indicating no long-term aquatic exposure potential), the registrant believes that the appropriate and scientifically defensible CLP Aquatic Chronic classification is “Not Classified”.