Reaction products of benzenesulfonic acid, mono-C20-24 (even)-sec-alkyl derivs. para-, calcium salts

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
In this justification, the read-across (bridging) concept is applied, based on the chemical structure of the potential analogues, their toxicokinetic behaviour and other available (eco-)toxicological data.

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
C20-24 calcium sulfonate and Benzenesulfonic acid, mono-C16-24-alkyl derivs., calcium salts (CAS 70024-69-0) are members of a category of chemicals described as alkaryl sulfonates, which was established as part of the U.S. Environmental Protection Agency High Production Volume (HPV) Challenge Program. The substances of this category have a common functional group - the salt of aryl sulfonic acid. Furthermore, they all have a divalent alkaline earth metal, one or more linear and/or branched alkyl groups of variable chain length and branching characteristics or extended heterocyclic carbon system from the sulfonated benzene ring. Finally, they have common precursors and/or the likelihood of common breakdown products via physical and biological processes, resulting in structurally similar chemicals, and similar physicochemical properties, environmental fate, ecotoxicity and mammalian toxicity.
Concerning biodegradation only the physico-chemical properties of the respective counterion have to be evaluated. Since biodegradation is not applicable to dissociating metals in aqueous environment, only the benzenesulfonic acid cation undergoes biodegradation. It is believed to be metabolised by the same mechanisms by microorganisms and by other classes of living organisms. Therefore they are expected to follow the same pattern of biodegradation. For the detailed procedure of the read-across principle and justifications, please refer to the analogue approach justification depicted below and the separate Read-Across Statement (Chemservice S.A., 2017).

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source chemical: Benzenesulfonic acid, mono C16-24-alkyl derivs., calcium salts (CAS 70024-69-0, EC 274-263-7)
Target chemical: Reaction products of benzenesulfonic acid, mono-C20-24 (even)-sec-alkyl derivs. para-, calcium salts (C20-24 calcium sulfonate, CAS No none, EC No none)

3. ANALOGUE APPROACH JUSTIFICATION
C20-24 calcium sulfonate and Benzenesulfonic acid, mono C16-24-alkyl derivs., calcium salts are UVCB substances that are produced using similar manufacturing process and raw materials and are manufactured in mineral oil. They are members of a category of chemicals described as alkaryl sulfonates, which was established as part of the U.S. Environmental Protection Agency High Production Volume (HPV) Challenge Program. These substances are similar in that they have a common functional group, the salt of aryl sulfonic acid. TOXMATCH and OECD Toolbox QSAR structure similarity assessments using Tanimoto distance fingerprint, Hellinger distance atom environment, Euclidian distance and Dice calculations indicate that these substances are very similar. Likewise, they have similar physicochemical properties, similar environmental fate characteristics, and similar ecotoxicity and mammalian toxicity profiles. For example, these substances can dissociate only in the presence of strong acids such as in the stomach but are not expected to dissociate under environmental conditions. For further details on this, please refer to the separate Read-Across Statement (Chemservice S.A., 2017). The similar toxicity profiles indicate that they have a similar MOA. C20-24 calcium sulfonate and Benzenesulfonic acid, mono-C16-24-alkyl derivs., calcium salts (CAS 70024-69-0) are both not classified for environmental toxicity.
The similar findings (refer to data matrix outlined below and the separate Read-Across Statement) for both substances support the conclusion that similar molecules are expected to be formed from both substances, and in consequence, similar effects can be reasonably expected. Hence, the analogue may perfectly serve as read-across substance for the C20-24 calcium sulfonate and vice versa. So, based on the WOE of these data, the available data on CAS 70024-69-0 can be used to cover the systemic endpoints currently lacking for C20-24 calcium sulfonate and read across is scientifically justified, making further testing obsolete.

4. DATA MATRIX
There is mainly data available on the toxicological properties of the analogues CAS 61789-86-4 / its overbased version CAS 68783-96-0 and for CAS 70024-69-0 / its overbased version CAS 70024-71-4. Data on Reaction products of benzenesulfonic acid, mono-C20-24 (even)-sec-alkyl derivs. para-, calcium salts covers merely the physico chemical properties. Hence, the identification and discussion of common properties of the analogues and the C20-24 calcium sulfonate will be mainly based on this physicochemical data.
The available data for the following physico-chemical properties, which are relevant for absorption into living organisms, are very similar. The substances are rather huge molecules and have a similar molecular weight range, which triggers already similarities in their absorption/adsorption and desorption behaviour. Furthermore, the physico-chemical properties like their partition coefficient, water solubility and vapour pressure are similar. Regarding the application of these substances, the substances are usually solved in an inert mineral oil to enable handling. The C20-24 calcium sulfonate and all analogous substances are hydrolytically stable in the natural environment, as they do not contain hydrolysable groups. In addition, at least CAS 70024-69-0 and CAS 61789-86-4 are not readily biodegradable, and the available data suggests this to apply also for C20-24 calcium sulfonate. Taking into account the vast amount of data available for partition coefficient data on various calcium sulfonates it can be concluded that they do not have a significant potential for bioaccumulation in aquatic and terrestrial organisms. However, they are expected to be adsorbed to a significant extent to the sediment and soil and to be thereby not bioavailable, which was confirmed by the results of short-term toxicity tests to fish, daphnia and algae for CAS 70024-71-4; CAS 115733-09-0 and CAS 61789-64-4, in which the lowest LL50 was already > 100 mg/L WAF.
For the following toxicological endpoints there is data available derived from CAS 70024-69-0/ CAS 70024-71-4, Analogue of CAS 70024-69-0, CAS 115733-09-0, CAS 61789-86-4/ CAS 68783-96-0 and CAS 75975-85-8: Acute toxicity, Skin irritation / corrosion, Eye irritation /corrosion, Skin sensitization, Repeated dose toxicity, Genetic toxicity in vitro and in vivo and Toxicity to reproduction (fertility / developmental toxicity). Furthermore a rather extensive data package is available concerning the human sensitization potential of numerous analogous substances. For the acute oral toxicity, the values for all read across substances are very high, all LD50 values being above 2000 mg/kg (reaching in older tests up to greater than 20,000 mg/kg) and the values for the substances can be considered as similar within normal biological variations. The substances are also not toxic via the inhalation or the dermal route of exposure. Regarding Skin/Eye Irritation, the available data on CAS 70024-69-0 and CAS 61789-86-4 shows both substances to be not irritating to the skin or the eyes. The skin sensitization data in animals and humans (for CAS 75975-85-8; CAS 61789-86-4 and EC 939-141-6) evaluated in a weight-of-evidence approach indicates that low TBN calcium sulfonates (TBN < 300) are skin sensitizers with a specific concentration limit (SCL) of 10% and that high TBN calcium sulfonates (TBN ≥ 300) are not skin sensitizers. Last but not least, the available genetic toxicity data for Analogue of CAS 70024-69-0, CAS 61789-86-4 and its overbased version CAS 68783-96-0 prove all of these substances to be not mutagenic. The NOAELs derived for the endpoints Repeated dose toxicity (Analogue of CAS 70024-69-0 and CAS 61789-86-4) and Toxicity to reproduction (fertility / developmental toxicity for CAS 115733-09-0)) have been also found to be in a similar range.
For further details please refer to the separate Read-Across Statement (Chemservice S.A., 2017) and/or the robust study summaries of the respective studies in this IUCLID file.

Reason / purpose for cross-reference:

read-across source

Preliminary study:

Not applicable.

Test performance:

The positive controls were degraded by > 60 % within 28 days.

Parameter:

other: COD

Value:

8

Sampling time:

28 d

Results with reference substance:

Sodium benzoate 97 % after 28 days; aniline 61 % after 28 days.

Validity criteria fulfilled:

yes

Remarks:

Both the reference substances achieved greater or equal to 60% degradation, and therefore, the test was valid.

Interpretation of results:

other: Only limited biodegradation observed (8 %/28 d)

Conclusions:

The report describes a valid guideline study with GLP compliance. The calcium sulfonate read across substance is not readily biodegradable, achieving 8 % degradation over 28 days. The calcium sulfonate read across substance CAS 70024-69-0 is therefore considered to be persistent, but the small amount of biodegradation suggests the calcium sulfonate read across substance is not unduly toxic to sewage sludge. These results can be used to fulfill the information requirements for the chemical substance Reaction products of benzenesulfonic acid, mono-C20-24 (even)-sec-alkyl derivs. para-, calcium salts, due to the high structural similarity of these substances. For the detailed procedure of the read-across principle and justifications, please refer to the separate Read-Across Statement (Chemservice S.A., 2017).

Executive summary:

A 28 day aerobic ready biodegradability study, which was conducted according to OECD Guideline 301D was conducted using an initial Calcium sulfonate read across substance concentration of 2 mg/L ( Cas 70024 -69 -0). The effects of the test substance were assessed based on chemical oxygen demand (COD) measurements using activated sludge from a domestic wastewater plant as inoculum. No pre-adaption was performed. The COD was determined using the Hach semi-micro sample digestion methods followed by direct reading using a Hach DR/2 Spectrometer. Each vessel was incubated twice, the temperature was held constant at 20 +/- 1 °C. For evaluation, sodium benzoate and aniline were used as reference substances, which attained 97 % and 61 % degradation after the incubation period of 28 days, respectively. The experiment can be considered as valid. At the end of the exposure period, the test substance attained 8 % degradation. It can be concluded that the substance is not readily biodegradable.

These results can be used to fulfill the information requirements for the chemical substance Reaction products of benzenesulfonic acid, mono-C20-24 (even)-sec-alkyl derivs. para-, calcium salts, due to the high structural similarity of these substances. For the detailed procedure of the read-across principle and justifications, please refer to the separate Read-Across Statement (Chemservice S.A., 2017).

Description of key information

RA_CAS 70024-69-0, OECD 301D: 8 % degradation after 28 days (Douglas, 1989). Therefore, the read-across substance is not readily biodegradable.      

RA_CAS 61789-86-4, OECD 301F: 8.6 % degradation after 28 days (Sanitised, O. 1996). Therefore, the read-across substance is not readily biodegradable.

RA_CAS 68783-96-0, OECD 301B: 9.1 % degradation after 28 days (Sanitised, P., 1995). Therefore, the read-across substance is not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

Calcium sulfonate read-across substance (CAS 70024-69-0) attained 8 % degradation during the test duration of 28 days (OECD Guideline 301D, Douglas, 1989). With regard to the supporting studies, Sanitised, O. (1996) determined 8.6 % degradation after 28 days (OECD Guideline 301F) for the calcium sulfonate read-across substance (CAS 61789 -86 -4) while 9.1 % degradation was attained for the calcium sulfonate read-across substance (CAS 68783-96-0) after 28 days (OECD Guideline 301B, Sanitised, P., 1995).

Based on the results of this study, the calcium sulfonate target substance (Reaction products of benzenesulfonic acid, mono-C20-24 (even)-sec-alkyl derivs. para-, calcium salts) is not expected to be readily biodegradable.