Ammonium sulphite

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

1.23 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.12 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

93 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

no exposure of sediment expected

Sediment (marine water)

Hazard assessment conclusion:

no exposure of sediment expected

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

no exposure of soil expected

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

 Derivation of freshwater PNEC_aquaticvalue using assessment factor method

 

The general principle of these methods is that the result from a laboratory test is divided by an appropriate assessment factor (ECHA, 2008). The sparser the available data, the higher is the assessment factor which is applied. PNECs are estimated by division of the lowest value for the toxicity with the relevant assessment factor. Results of long-term tests (expressed as EC₁₀ or NOEC for a sublethal parameter) are preferred to those of short-term tests (E(L)C₅₀), because such results give a more realistic picture of effects on the organisms during their entire life cycle.

 

In establishing the size of these assessment factors, a number of uncertainties have been addressed to extrapolate from single-species laboratory data to a multi-species ecosystem. These areas comprise:

 

• intra- and inter-laboratory variation of toxicity data;

• intra- and inter-species variations (biological variance);

• short-term to long-term toxicity extrapolation;

• laboratory data to field impact extrapolation.

 

The assessment factors recommended for the determination of the PNEC for the freshwater aquatic are shown in Table below.

 

Table: Assessment factors to derive a PNEC_aquatic

Available data	Assessment factor
At least one short-term L(E)C50 from each of three trophic levels (fish, invertebrates (preferred Daphnia) and algae)	1000
One long-term EC10 or NOEC (either fish or Daphnia)	100
Two long-term results (EC10, NOECs) from species representing two trophic levels (fish and/or Daphnia and/or algae)	50
Long-term results (EC10, NOECs) from at least three species (e.g., fish, Daphnia and algae) representing three trophic levels	10
Species sensitivity distribution (SSD) method	5-1(to be fully justified case by case)
Field data or model ecosystems	Reviewed on a case by case basis)

 

When only short-term toxicity data are available, an assessment factor of 1000 will be applied on the lowest E(L)C₅₀ of the relevant available toxicity data, irrespective of whether or not the species tested is a standard test organism. A lower assessment factor will be applied on the lowest EC₁₀ or NOEC derived in long-term tests with a relevant test organism. 

 

For some compounds, a large number of validated short-term E(L)C₅₀ values may be available. Therefore, it is proposed to calculate the geometric mean if more than one E(L)C₅₀ value is available for the same species and endpoint. Prior to calculating the geometric mean an analysis of test conditions must be carried out in order to find out why differences in response were present. 

 

The algal growth inhibition test of the base-set is, in principle, a multi-generation test. However, for the purposes of applying the appropriate assessment factors, the EC₅₀ is treated as a short-term toxicity value. The EC₁₀ or NOEC from this test may be used as an additional long term result when other long-term data are available. In general, an algal EC₁₀ or NOEC should not be used unsupported by long-term EC₁₀ or NOECs of species of other trophic levels. 

 

Microorganisms representing a further trophic level may only be used if non-adapted pure cultures were tested. The investigations with bacteria (e.g., growth tests) are regarded as short-term tests. Additionally, blue-green algae should be counted among the primary producers due to their autotrophic nutrition.

 

The assessment factors should be considered as general factors that under certain circumstances may be changed. In general, justification for changing the assessment factor could include one or more of the following:

-      evidence from structurally similar compounds (evidence established by read across from closely related compounds may demonstrate that a higher or lower factor may be appropriate);

-      knowledge of the mode of action including endocrine disrupting effects (Some substances, by virtue of their structure, may be known to act in a non-specific manner);

-      the availability of test data from a wide selection of species covering additional taxonomic groups other than those represented by the base-set species;

-      the availability of test data from a variety of species covering the taxonomic groups of the base- set species across at least three trophic levels. In such a case the assessment factors may only be lowered if these multiple data points are available for the most sensitive taxonomic group.

 

Since no large dataset from long-term tests for different taxonomic groups is available for sulfites/disulfites, no Species Sensitivity Distribution (SSD) can be developed and statistical extrapolation methods can thus not be used to derive the PNEC_aquatic. Instead, The PNEC_aquatic calculation will be conducted using assessment factors method.

An overview of the species-specific data is given below. All relevant effects data are expressed as mg SO₃^2-/L and mg S/L.

 

Table: Overview of most sensitive species-specific EC₁₀/NOEC-values for sulfite ion the freshwater environment

Species	Trophic level	NOEC/EC10 (mg SO3^2-/L)	Reference
Scenedesmus subspicatus	Algae	28	BASF, 1989
Daphnia magna	Crustacea (invert.)	≥8.41	BASF, 1990
Danio rerio	Fish	50.0	ECT, 2010

 

 

In this scenario an assessment factor (AF) of 10 should be used to calculate the PNEC_aquatic from the lowest value for the toxicity. This factor can be applied since three long-term results (e.g. NOECs) from species representing three trophic levels (algae, invertebrates, fish) are available. The lowest value for chronic toxicity was and unbounded NOEC of 8.41 mg SO₃^2-/L. Applying the AF of 10 results in a PNEC_aquatic of 0.84 mg SO₃^2-/L.Translating this value to (NH₄)₂SO₃ gives a PNEC_aquatic of 1.23 mg test substance/L.

As the lowest NOEC-value is an unbounded value (i.e., no effect was noted at the highest test concentration), this value can be considered as a worst-case estimate. Further refinement of the NOEC-value for daphnids could increase the PNEC_aquatic up to a maximum value of 2.8 mg SO₃^2-/L (i.e., an assessment factor of 10 on the algal 72h-EC₁₀ value), which is equivalent to 4.07 mg ammonium sulfite/L.

 

 

PNEC_sediment

 

Due to the expected oxidation of sulfite to sulfate under environmental conditions (worst-case half life of 77h), and its physicochemical properties which make adsorption to sediments unlikely, the derivation of a PNEC for the sediment compartment is not feasible/appropriate:

-      due to rapid oxidation of sulfite/disulfite substances, no relevant test design and toxicity data can be generated

-      due to the lack of a relevant adsorption coefficient for sulfites/disulfites to sediment, the equilibrium partitioning method for deriving a PNEC_sediment is not applicable

-      taking into account the industrial use, exposure pathways and environmental fate of sulite/disulfite substances, long-term exposure of sediment organisms to this substance can be excluded.

Consequently, there is no need to derive a PNEC_sediment for sulfite/disulfite compounds.

 

PNEC_terrestrial

 

Due to the expected oxidation of sulfite to sulfate under environmental conditions (worst-case half life of 77h), and its physicochemical properties which make adsorption to sediments unlikely, the derivation of a PNEC for the terrestrial compartment is not feasible/appropriate:

-      due to rapid oxidation of sulfite/disulfite substances, no relevant test design and toxicity data can be generated

-      due to the lack of a relevant adsorption coefficient for sulfites/disulfites to soil, the equilibrium partitioning method for deriving a PNEC_terrestrial is not applicable

-      taking into account the industrial use, exposure pathways and environmental fate of sulfite/disulfite substances, long-term exposure of sediment organisms to this substance can be excluded.

Consequently, there is no need to derive a PNEC_terrestrial for sulfite/disulfite compounds.

 

PNEC_STPderivation

 

The aim of the assessment for micro-organisms is the protection of the degradation and nitrification functions and process performance and efficiency of domestic and industrial STPs. A PNECmicro-organism can be derived in different ways based on the information at hand, and expert judgement of the weight of evidence.

 

For many substances, including a data-poor substances like sufites/disulfites, there are insufficient useful data for aquatic micro-organisms available for the application of the statistical extrapolation method for PNEC-derivation. In that case, the assessment factor methodology can be used on the extracted relevant/reliable test results. Two types of tests are considered relevant for deriving the PNEC_{micro-organism} in STPs: (1) tests with a mixed inoculum (e.g. activated sludge) for the endpoint respiration, and (2) a test with ciliated protozoa (preferablyTetrahymena) for the endpoint mortality.

 

In general, an AF of 10 is to be applied to the NOEC/EC₁₀ of a sludge respiration test, reflecting the lower sensitivity of this endpoint as compared to nitrification, as well as the short duration of the test. The corresponding AF is 100 when based on the EC₅₀. The PNEC_{micro-organism} is set equal to a NOEC (AF = 1) for a test performed with specific bacterial populations such as nitrifying bacteria, P. putida, ciliated protozoa, the Shk1 Assay. An EC₅₀from this test is divided by an AF of 10 to derive the PNEC_{micro-organism}. If no standard microbial inhibition test data are available, the PNEC_{micro-organism} can also be derived from available ready biodegradation tests. An assessment factor of 10 is applied to the test concentration at which no toxicity to the inoculum is observed. This approach can also be used for inherent biodegradability tests. From an activated sludge simulation study, a PNEC_{micro-organism} can be derived based on the PEC_{micro-organism} or PEC_influent, using an AF between 1 and 10 depending on the parameters monitored. The AF of 1 can be used in case there is no impact on nitrification and BOC/COD removal performance (NB: if sludge from an industrial STP was used for the test, the PNEC_{micro-organism} can not be used for the extrapolation to a domestic STP). No AF is needed to derive a PNEC_{micro-organism} based on good quality field data.

 

So, the rationale for the application of a higher assessment factor for the heterotrophic micro-organisms compared to the nitrifying bacteria, is that they are exposed to a higher concentration which relates more to the influent concentration. For the nitrifying bacteria the exposure concentration is more related to the effluent concentration since nitrification is the last treatment step in a STP.

 

 

A 3h-NOEC of 634 mg SO₃^2-/L (endpoint: respiration rate of activated sludge) has been put forward for the derivation of a PNEC_{micro-organism}. Application of an assessment factor of 10 results in a PNEC_{micro-organism} of 63.4 mg SO₃^2-/L. Translating this value to Na₂SO₃ gives a PNEC_{micro-organism} of 93 mg test substance/L

Conclusion on classification

Acute and chronic toxicity data were available for the three main aquatic trophic levels that are considered for classification purposes. Classification is based on the lowest acute and chronic value, referred to as the acute and chronic toxicity reference value (TRV).

The lowest acute effect concentration was observed for the alga S. subspicatus (72h-EC₅₀), and was 36.8 mg SO₃^2-/L. Translating this value to (NH₄)₂SO₃ results in an acute TRV of 53.4 mg/L for this substance.

A substance for which the acute TRV is situated between 10 and 100 mg/L, should be classified as Chronic 3, unless the chronic TRV is situated above 1 mg/L; in that case classification can be waived.

For sulfite/disulfite compounds, the lowest chronic value was a NOEC of >8.41 mg SO₃^2-/L for the invertebrate D. magna. Translating this value to (NH₄)₂SO₃ results in a chronic TRV of 12.2 mg/L for this substance, i.e., > 1 mg/L.

Consequently, there is no need to classify ammonium sulfite for the environment.